As the next step, heating at 200° - 500 °C for minimum 3 hours in inert atmosphere is needed to diminish surface roughness, stress, microcracks or other type defects caused by the production process of aluminum sheet. At elevated temperature the metal recovers and recrystallization process takes place [7a].

To find out what current parameters should be used for the polishing process, one should run polarization curves and mark out plateau where current density will change very little and the polishing process should be stable.

As it can be seen above, the resulting surface after the polishing process is characterized by much less surface defects and roughness, is more shiny, shows better reflection and better tribological properties. Removing technological origin microstructures guarantees better self-organization of pores at the Al surface.

Anodization process is anodic oxidation of the electrode material. In case of anodic alumina oxide, the initially continuous surface of Al plate becomes structured and has a unique ordered porous structure. The order of pores and their quality can be tuned by the process condition and current parameters. The effects of the conditions changes on the matrix structural parameters are depicted in Fig. 4.

Fig. 4. Examples of porous alumina oxide surface topography and pores cross section.

Electrochemical Methods in Nanomaterials Preparation 267

The temperature of anodization electrolyte should be lower than room temperature to avoid too fast alumina dissolution process. Low temperature also prevents local overheating of the Al plate, which can cause cracking and pill of the alumina layer. Such unwanted effect is

Anodization potential influences not only pores size but also their ordering. However, applying to a large value of potential can effect in surface degradation, which is shown in

At first stage, Al surface is covered by flat barrier oxide layer which is conducting very little (1010 ~ 1012Ωcm) [10]. At the next stage, this layer becomes more and more rough and corrugated, which results in local increasing of the current density, which therefore causes the increase of temperature and dissolving of the oxide layer also locally. In such a way, the pores are created. Prolongation of anodization process influences the diameter of obtained

The matrix prepared in such a way is not yet ready to use because at the surface the barrier oxide layer is present. This layer contains impurity from the solution and should be dissolved in one of the following solutions: mixture of 6% H3PO4 and 1,8% H2C2O4, 5% solution of H3PO4, mixture of 1M H2SO4 and 2M H3PO4, solution of HgCl2 (saturated) [11].

Two kinds of deposition processes can be considered with controlled potential or current. Current controlling demands two electrode system with voltmeter and ampere-meter

Controlling of the potential adjusted to a stable value is performed in three electrode setups, where, besides working and reference, a counter electrode is needed. This electrode should be chosen in such a way that it has a significant surface so that the current obtained

Fig. 6. a) effect of too high temperature of solution; b) effect of too high anodization

(a) (b)

To illustrate the effect of this process, please look at the last row of Fig. 4. Finally, a perfect ordered porous alumina layer is obtained (see Fig.7).

pores, a distance between them and their ordering.

**3. Deposition of the materials**

presented in Fig. 6 a.

Fig. 6 b.

potential.

devices.

The images of the pores presented above prove that in large range pores diameter and distance between them can be tuned by process and current parameters. The obtained example cross section image of that presents that the template pores are rather even and well defined.

During anodization process two parallel reactions are taking place:

$$Al \to Al^{3+} + 3e^- \tag{6}$$

$$
\frac{3}{2}H\_2O \to 3H^+ + \frac{3}{2}O^{2-} \tag{7}
$$

Formed ions Al3+ and O2- migrate to the interface metal/oxide and form Al2O3.

Fig. 5. Schematic sketch of: processes proceed at the electrode surface (a), alumina oxide quality (b).

Parallel to the reaction mentioned above, dissolution of the oxide takes place according to the scheme (8):

$$
\frac{1}{2}Al\_2O\_3 + 3H^+ \to Al^{3+} + \frac{3}{2}H\_2O\tag{8}
$$

This shows that both processes creation and dissolution of the oxide run at the same time, and to obtain needed porous oxide layer, the first one should dominate over the second one, respectively. The best ratio between the both processes is 7:3 [9].

The images of the pores presented above prove that in large range pores diameter and distance between them can be tuned by process and current parameters. The obtained example cross

3 3 3 2 2

2

3 *Al Al e* 3 (6)

*HO H O* (7)

section image of that presents that the template pores are rather even and well defined.

2

Formed ions Al3+ and O2- migrate to the interface metal/oxide and form Al2O3.

(a) (b)

respectively. The best ratio between the both processes is 7:3 [9].

Fig. 5. Schematic sketch of: processes proceed at the electrode surface (a), alumina oxide

Parallel to the reaction mentioned above, dissolution of the oxide takes place according to

This shows that both processes creation and dissolution of the oxide run at the same time, and to obtain needed porous oxide layer, the first one should dominate over the second one,

3 2 3 2 1 3 3 2 2

*Al O H Al H O* (8)

During anodization process two parallel reactions are taking place:

metal layer (7):

quality (b).

the scheme (8):

The temperature of anodization electrolyte should be lower than room temperature to avoid too fast alumina dissolution process. Low temperature also prevents local overheating of the Al plate, which can cause cracking and pill of the alumina layer. Such unwanted effect is presented in Fig. 6 a.

Anodization potential influences not only pores size but also their ordering. However, applying to a large value of potential can effect in surface degradation, which is shown in Fig. 6 b.

Fig. 6. a) effect of too high temperature of solution; b) effect of too high anodization potential.

At first stage, Al surface is covered by flat barrier oxide layer which is conducting very little (1010 ~ 1012Ωcm) [10]. At the next stage, this layer becomes more and more rough and corrugated, which results in local increasing of the current density, which therefore causes the increase of temperature and dissolving of the oxide layer also locally. In such a way, the pores are created. Prolongation of anodization process influences the diameter of obtained pores, a distance between them and their ordering.

The matrix prepared in such a way is not yet ready to use because at the surface the barrier oxide layer is present. This layer contains impurity from the solution and should be dissolved in one of the following solutions: mixture of 6% H3PO4 and 1,8% H2C2O4, 5% solution of H3PO4, mixture of 1M H2SO4 and 2M H3PO4, solution of HgCl2 (saturated) [11]. To illustrate the effect of this process, please look at the last row of Fig. 4.

Finally, a perfect ordered porous alumina layer is obtained (see Fig.7).

## **3. Deposition of the materials**

Two kinds of deposition processes can be considered with controlled potential or current. Current controlling demands two electrode system with voltmeter and ampere-meter devices.

Controlling of the potential adjusted to a stable value is performed in three electrode setups, where, besides working and reference, a counter electrode is needed. This electrode should be chosen in such a way that it has a significant surface so that the current obtained

Electrochemical Methods in Nanomaterials Preparation 269

Theoretically, this potential should increase by the value (*EA – Ec*), where *EA* – anode

In reality, decomposition potential between two electrodes is higher compared to the

( ) *U E E IR A C*

Overpotential is present due to deviation of electrodes potential from equilibrium value during current flow. The reasons why such phenomenon is present are the following: to slow ion diffusion from solution to electrodes, to slow velocity of redox reactions, delay in crystallization processes and electrode surface, too big difference of ions concentration in electrolyte. The value of overpotential depends on: a type of electrode, electrode surface

Electrolysis process is a few stage process: (i) ion transportation in electrolyte from one electrode to the opposite one; (ii) chemical reaction with electrical charge transfer at the interface electrode/solution; (iii) other type of surface reactions – adsorption, desorption,

Faraday law defines dependence between current flow through solution and amount of material reduced at the electrodes. The first law – mass of material deposited at electrodes is proportional to the amount of current flow through electrolyte, which is described by the

potential, *Ec* – cathode potential, which is needed to obtain current *I* and resistivity.

*U SEM IR r* (10)

*m kQ kIt* (12)

(11)

Fig. 8. Drawing of potential changes during electrodeposition process.

Decomposition potential can be described in the following way (12):

Where: *SEM* – electromotive force of cell, *I -* current, *R -* resistance

theoretical one by the value of overpotential *η* [12]:

quality, current density, and temperature of electrolyte.

where: *m* – mass of material reduced at electrode; *k* – electrochemical equivalent

crystallization.

equation [13]:

*Q* – charge *I* – current *t* – time

Fig. 7. AFM images of final matrixes: a) oxalic acid, b) phosphoric acid.

in the electrolysis process is not changing its potential. This electrode is applied to the working electrode's constant current, which stabilizes constant potential in the reference electrode. A potential value of the electrode is controlled by potentiostat.

Accelerating current mode demands a two electrode device, where working and reference electrodes can be made from the same material.

Constant current deposition can be carried out without adjusting other current parameters before the deposition process. In case of deposition with the controlled potential, its value should be calculated from the equations described below to assure large enough process efficiency. It is also possible to run voltoamperometric or chronoamperometric curves and on its ground a characteristic value of the deposition process is established. Such specific potential has to be calculated for every type of electrolyte and electrodes.

Electrodeposition is a method by which ions from the solution are deposited at the surface of the cathode (working electrode). This process can run parallel to electrolysis, and deposited material can form a continuous layer, wires or tubes when prestructured matrixes are used. The amount of the deposited material, thickness of the layer or wires length depend on the deposition time matrix structure.

Electrolysis is a number of processes taking place in electrolyte and at electrode interfaces while electrical current is applied from external sources. In electrolysis the change from electrical energy to chemical potential takes place. The most important reactions proceed at the interfaces electrode metal/solution. When the electrode is dissolved and in oxide form is present in the solution, this electrode we call anode. The opposite electrode – cathode, is one where ions are reduced and metallic surface is formed. During the electrolysis process, large gradients of ions concentrations are observed. The reactions taking place at the electrodes are described in the following form [12]:

$$\begin{aligned} \text{C(-)}: \text{Ox}\_A + z\_A e &\to \text{Re} \, d\_A\\ A(+): \text{Re} \, d\_B &\to \text{Ox}\_B + z\_B e \end{aligned} \tag{9}$$

In a two electrode system, both electrodes are connected to a proper potential source. Current starts to increase when the value of decomposition potential *Ur* is exceeded (Fig. 8). After that, the value of potential electrolysis can be used in a practical application.

in the electrolysis process is not changing its potential. This electrode is applied to the working electrode's constant current, which stabilizes constant potential in the reference

Accelerating current mode demands a two electrode device, where working and reference

Constant current deposition can be carried out without adjusting other current parameters before the deposition process. In case of deposition with the controlled potential, its value should be calculated from the equations described below to assure large enough process efficiency. It is also possible to run voltoamperometric or chronoamperometric curves and on its ground a characteristic value of the deposition process is established. Such specific

Electrodeposition is a method by which ions from the solution are deposited at the surface of the cathode (working electrode). This process can run parallel to electrolysis, and deposited material can form a continuous layer, wires or tubes when prestructured matrixes are used. The amount of the deposited material, thickness of the layer or wires length

Electrolysis is a number of processes taking place in electrolyte and at electrode interfaces while electrical current is applied from external sources. In electrolysis the change from electrical energy to chemical potential takes place. The most important reactions proceed at the interfaces electrode metal/solution. When the electrode is dissolved and in oxide form is present in the solution, this electrode we call anode. The opposite electrode – cathode, is one where ions are reduced and metallic surface is formed. During the electrolysis process, large gradients of ions concentrations are observed. The reactions taking place at the electrodes

( ): Re

In a two electrode system, both electrodes are connected to a proper potential source. Current starts to increase when the value of decomposition potential *Ur* is exceeded (Fig. 8).

*C Ox z e d A d Ox z e*

*A A A B BB*

(9)

( ) : Re

After that, the value of potential electrolysis can be used in a practical application.

 (a) (b) Fig. 7. AFM images of final matrixes: a) oxalic acid, b) phosphoric acid.

electrodes can be made from the same material.

depend on the deposition time matrix structure.

are described in the following form [12]:

electrode. A potential value of the electrode is controlled by potentiostat.

potential has to be calculated for every type of electrolyte and electrodes.

Fig. 8. Drawing of potential changes during electrodeposition process.

Decomposition potential can be described in the following way (12):

$$
\mathcal{L}I\_r = \mathcal{S}EM + IR \tag{10}
$$

Where: *SEM* – electromotive force of cell, *I -* current, *R -* resistance

Theoretically, this potential should increase by the value (*EA – Ec*), where *EA* – anode potential, *Ec* – cathode potential, which is needed to obtain current *I* and resistivity.

In reality, decomposition potential between two electrodes is higher compared to the theoretical one by the value of overpotential *η* [12]:

$$\mathcal{U} = (E\_A - E\_\mathbb{C}) + IR + \eta \tag{11}$$

Overpotential is present due to deviation of electrodes potential from equilibrium value during current flow. The reasons why such phenomenon is present are the following: to slow ion diffusion from solution to electrodes, to slow velocity of redox reactions, delay in crystallization processes and electrode surface, too big difference of ions concentration in electrolyte. The value of overpotential depends on: a type of electrode, electrode surface quality, current density, and temperature of electrolyte.

Electrolysis process is a few stage process: (i) ion transportation in electrolyte from one electrode to the opposite one; (ii) chemical reaction with electrical charge transfer at the interface electrode/solution; (iii) other type of surface reactions – adsorption, desorption, crystallization.

Faraday law defines dependence between current flow through solution and amount of material reduced at the electrodes. The first law – mass of material deposited at electrodes is proportional to the amount of current flow through electrolyte, which is described by the equation [13]:

$$
\hbar m = k \cdot \mathbb{Q} = k \cdot I \cdot \mathbf{t} \tag{12}
$$

where: *m* – mass of material reduced at electrode;

*k* – electrochemical equivalent *Q* – charge *I* – current *t* – time

Electrochemical Methods in Nanomaterials Preparation 271

concentration of electrolyte, pH of electrolyte, temperature, presence of surfactants, matrix properties, etc., has significant influence on the quality of deposited material. For each

Current density is a ratio between total current value and electrode surface. This is probably the most important parameter defining quality of deposited material. For low current density, its value coarse surface can be obtained because the speed of nucleation centers creation is much lower compared to crystal growth of the existing seeds. For high current density, quite often a decrease of ions concentration close to the deposited surface is observed, or hydrogen evolution takes place and the obtained layers become noncontinuous, spongy and porous. To avoid non-equal current density in deposition process, a parallel arrangement of electrodes in the centre of vessels should be assured. In case of nanowires, deposition proper current density should be well matched to protect hydroxide and cracks or discontinuous inclusion of the wire creation. This avoids too fast degradation of the wires during fabrication processes and assures good electrical conductivity [12].

pH variation also influences surface morphology heavily. Low pH causes hydrogen evolution, which penetrates the layer, and deposited material becomes harder, and it introduces a lot of stress to the layer. pH also influences magnetic properties of deposited material. Because of that, electrodeposition process should be conducted at a stable value of pH, any variation can be compensated by the addition of alkaline or acidic media [12].

Electrolyte concentration – increase of electrolyte concentration, effects in continuously grown and well attached layers. Growth speed in-plane dominates growth out-of-plane, which avoids high roughness [12]. Higher ion concentration allows to work with higher current density without the risk of hydrogen evolution. A very similar effect is observed in case of solution stirring because it eliminates the concentration of gradients in the solution. Temperature – its increase, influences two opposite phenomena. First of all, it helps in diffusion process, which prevents rough and spongy layer growth even for high current density. On the other hand, it increases the speed of crystal growth and causes the presence of bigger crystals and hydrogen evolution. At lower temperatures, the first scenario dominates and better quality layers are obtained compared to higher temperatures. Moderate heating of electrolyte influences positively on the quality of deposited layers but

The presence of surfactants in electrolyte decreases surface tension at the electrode surface and influences the release of hydrogen from the electrode surface, which is produced in hydrogen evolution process [12]. The addition of surface active substances and their adsorption at crystal surfaces stops the growth of existing agglomerates and affects nucleation of new ones. Such modification of the process helps to fabricate layers build up from small crystalline material. Very alike phenomenon is observed in case of complex ions. Extremely important parameter which governs good quality of obtained films is used matrix, which often influences and modifies a crystal structure at least in the first layers of

In aqueous solution of metal *M0* salts *Mz+* ions are present. Placing two electrodes connected

too large temperature elevation gives rather bad quality surfaces [12].

with current source into it originates the following process [13]:

deposited material.

material a range of parameters giving best quality surface can be assigned.

The second Faraday law – mass of different substances deposited at electrodes during flow of equal charge is proportional to its electrochemical equivalent according to the equation [14]:

$$\frac{m}{Q} = \frac{1}{F} \cdot \frac{M}{m} \quad \text{or} \quad F = \frac{Q}{m} \cdot \frac{M}{m} \tag{13}$$

where: *F* –Faraday constant (96 500 C) *M* – molar mass *n* – number of electrons in the process

Before each deposition process it is preferable to run voltamperometric or chronovoltamperometric curves to optimize current parameters of the process. Voltamperometric dependence is current function of potential which changes in a way shown in Fig. 9 (a). Intensity of peak and at the same time current value can be calculated according to Randles – Sevčik equation [15]. In cyclic curve two peaks can be observed: cathodic reduction and anodic oxidation of the ions Fig. 9 (b). To obtain deposition with reasonable effect, deposition should be conducted in a range of cathodic reduction peak.

Fig. 9. (a) Typical voltamperomertic curve I=f(E), (b) typical cyclic voltoamperometric curve.

In addition to these two methods, chronoamperometric dependence *I=f(t)* should be done, where the value of current is monitored as a function of potential. Such measurement gives us additional qualitative and quantitative information about electrolyte composition, speed of electrode processes and chemical reaction taking place at the electrodes and in electrolyte. These curves inform about electrode deposition process [15]. Chronoamperometric curves should be registered at potential exceeding overpotential value. By collecting these curves for few potential values best deposition condition can be determined.

Current parameters for each particular deposition process should be estimated for each electrochemical cell and electrolyte.

Electrochemically deposited material has in most cases a crystalline structure but the quality of the obtained layers can be different due to the various speed of crystal growth and crystal seeds creation. Modification of few parameters such as: current density, type and

The second Faraday law – mass of different substances deposited at electrodes during flow of equal charge is proportional to its electrochemical equivalent according to the equation

Before each deposition process it is preferable to run voltamperometric or chronovoltamperometric curves to optimize current parameters of the process. Voltamperometric dependence is current function of potential which changes in a way shown in Fig. 9 (a). Intensity of peak and at the same time current value can be calculated according to Randles – Sevčik equation [15]. In cyclic curve two peaks can be observed: cathodic reduction and anodic oxidation of the ions Fig. 9 (b). To obtain deposition with reasonable effect, deposition should be conducted in a range of cathodic reduction peak.

Fig. 9. (a) Typical voltamperomertic curve I=f(E), (b) typical cyclic voltoamperometric curve.

In addition to these two methods, chronoamperometric dependence *I=f(t)* should be done, where the value of current is monitored as a function of potential. Such measurement gives us additional qualitative and quantitative information about electrolyte composition, speed of electrode processes and chemical reaction taking place at the electrodes and in electrolyte. These curves inform about electrode deposition process [15]. Chronoamperometric curves should be registered at potential exceeding overpotential value. By collecting these curves

Current parameters for each particular deposition process should be estimated for each

Electrochemically deposited material has in most cases a crystalline structure but the quality of the obtained layers can be different due to the various speed of crystal growth and crystal seeds creation. Modification of few parameters such as: current density, type and

(a) (b)

for few potential values best deposition condition can be determined.

electrochemical cell and electrolyte.

*Q M F*

*m n* (13)

*m M* 1 *Q Fn* or

[14]:

where: *F* –Faraday constant (96 500 C) *M* – molar mass

*n* – number of electrons in the process

concentration of electrolyte, pH of electrolyte, temperature, presence of surfactants, matrix properties, etc., has significant influence on the quality of deposited material. For each material a range of parameters giving best quality surface can be assigned.

Current density is a ratio between total current value and electrode surface. This is probably the most important parameter defining quality of deposited material. For low current density, its value coarse surface can be obtained because the speed of nucleation centers creation is much lower compared to crystal growth of the existing seeds. For high current density, quite often a decrease of ions concentration close to the deposited surface is observed, or hydrogen evolution takes place and the obtained layers become noncontinuous, spongy and porous. To avoid non-equal current density in deposition process, a parallel arrangement of electrodes in the centre of vessels should be assured. In case of nanowires, deposition proper current density should be well matched to protect hydroxide and cracks or discontinuous inclusion of the wire creation. This avoids too fast degradation of the wires during fabrication processes and assures good electrical conductivity [12].

pH variation also influences surface morphology heavily. Low pH causes hydrogen evolution, which penetrates the layer, and deposited material becomes harder, and it introduces a lot of stress to the layer. pH also influences magnetic properties of deposited material. Because of that, electrodeposition process should be conducted at a stable value of pH, any variation can be compensated by the addition of alkaline or acidic media [12].

Electrolyte concentration – increase of electrolyte concentration, effects in continuously grown and well attached layers. Growth speed in-plane dominates growth out-of-plane, which avoids high roughness [12]. Higher ion concentration allows to work with higher current density without the risk of hydrogen evolution. A very similar effect is observed in case of solution stirring because it eliminates the concentration of gradients in the solution.

Temperature – its increase, influences two opposite phenomena. First of all, it helps in diffusion process, which prevents rough and spongy layer growth even for high current density. On the other hand, it increases the speed of crystal growth and causes the presence of bigger crystals and hydrogen evolution. At lower temperatures, the first scenario dominates and better quality layers are obtained compared to higher temperatures. Moderate heating of electrolyte influences positively on the quality of deposited layers but too large temperature elevation gives rather bad quality surfaces [12].

The presence of surfactants in electrolyte decreases surface tension at the electrode surface and influences the release of hydrogen from the electrode surface, which is produced in hydrogen evolution process [12]. The addition of surface active substances and their adsorption at crystal surfaces stops the growth of existing agglomerates and affects nucleation of new ones. Such modification of the process helps to fabricate layers build up from small crystalline material. Very alike phenomenon is observed in case of complex ions.

Extremely important parameter which governs good quality of obtained films is used matrix, which often influences and modifies a crystal structure at least in the first layers of deposited material.

In aqueous solution of metal *M0* salts *Mz+* ions are present. Placing two electrodes connected with current source into it originates the following process [13]:

Electrochemical Methods in Nanomaterials Preparation 273

Next, the collection of ad-atoms in agglomerates nucleates crystallization seeds of a new phase, which grows upwards. Such a scenario is very profitable because the whole pore can

Using the above phenomena, Cu, Ni, Co and Fe were deposited to the porous AAO matrix characterized by a different pores diameter [7]. As it was already mentioned, the deposition conditions influence strongly the quality and length of the obtained nanowires. Such structures as nanowires and nanotubes can be obtained via constant current deposition (DC) method when well distributed nanowires standing perpendicularly to the surface plane are relatively easily obtained. The acceleration current method (AC) in most cases (for long enough time of deposition) ends up with long wires which are randomly oriented at the

AC platting is often performed in a two electrode cell where working electrode is AAO plate and reference electrode Pt plate or wire. The example of the electrolyte composition used in the process was: 120 g/l NiSO 4 + 40 g/l H3BO3, electrolyte: 50 g/l CoSO4·7H2O + 25 g/l H3BO3 + 20 g/l glycerin, 0.9 mol/l FeSO4 7H2O, 0.15 mol/l FeCl2 4H2O and 0.43 mol/l NH4Cl for Ni, Co, Fe AC deposition at current condition 20V, 16V and 10V, respectively. DC deposition required a three electrode cell and besides, two already mentioned counter

Effective platting is only in this case when deposition dominates dissolution process.

A choice of deposition mode depends on the needs and effectiveness of deposition processes. In DC mode, whole time while current is on deposition process takes place. AC plating combines deposition and dissolution processes which are running after each other. Firstly, the material is deposited and in the opposite current phase this layer is dissolved.

The principles mentioned above should be modified and few additional phenomena must be considered. In general, kinetic parameters of deposition process are quite complex and depend on many parameters, which can be seen in the following equations (15-20). There are still many unknown points in deposition process which demand big effort of scientists and consume much time to be resolved. In many cases the proper and most accurate values describing the observed processes are obtained by different models. In case of porous membranes, one possible model is developed by Osterle called Space-Charge model [16]. There are modifications of this and some points are improved. In general, there are few

(a) (b)

Fig. 12. Different quality of obtained wires by (a) DC and (b) AC modes

be used as a template for wire growth and no stuffing of the pore takes place.

surface due to strong magnetic interaction between them.

electrodes as Ag wire is present [2].

$$M\_{aq}^{z+} + ze^- = M^0 \tag{14}$$

The mechanism of layer deposition is quite complex and is illustrated in Fig. 10. Metal ions are covered by hydration shell, which helps in easier diffusion, convection and migration processes. These phenomena cause transport of hydrated ions in cathode direction. Close to cathode party dehydration process takes place and released ion can be placed in a crystal structure of a growing layer.

Fig. 10. Schematic drawing of the process taking place close to electrode.

In case of metal ions, deposition at electrode surface (other metal) incorporation of its into layer is not an immediate process after landing at the surface because of energetic differentiation between the sites (Fig.11). Normally, atoms migrate at the electrode surface until free defects sites with lowest energy meet.

Elecrodeposition process can be divided into two main steps: (i) seeds nucleation (when *z Maq* ion approaches the surface, loose solvation shell and its charge is reduced by charge transfer. In such a way, neutral ad-atom *M0* is formed (Fig.11). Ad-atom can migrate at the surface as long as preferred site will be reached. Most energetically favorite site is hole, next node, dislocation and least flat surface.

Fig. 11. Drawing of the atoms location in deposition process

These principles define electrodeposition of the material in prestructured or porous matrixes (e.g. anodic alumina oxide), where at first atoms are deposited at the bottom of the pores.

*z* 0 *M ze M aq*

The mechanism of layer deposition is quite complex and is illustrated in Fig. 10. Metal ions are covered by hydration shell, which helps in easier diffusion, convection and migration processes. These phenomena cause transport of hydrated ions in cathode direction. Close to cathode party dehydration process takes place and released ion can be placed in a crystal

Fig. 10. Schematic drawing of the process taking place close to electrode.

until free defects sites with lowest energy meet.

Fig. 11. Drawing of the atoms location in deposition process

node, dislocation and least flat surface.

*z Maq*

In case of metal ions, deposition at electrode surface (other metal) incorporation of its into layer is not an immediate process after landing at the surface because of energetic differentiation between the sites (Fig.11). Normally, atoms migrate at the electrode surface

Elecrodeposition process can be divided into two main steps: (i) seeds nucleation (when

These principles define electrodeposition of the material in prestructured or porous matrixes (e.g. anodic alumina oxide), where at first atoms are deposited at the bottom of the pores.

 ion approaches the surface, loose solvation shell and its charge is reduced by charge transfer. In such a way, neutral ad-atom *M0* is formed (Fig.11). Ad-atom can migrate at the surface as long as preferred site will be reached. Most energetically favorite site is hole, next

structure of a growing layer.

(14)

Next, the collection of ad-atoms in agglomerates nucleates crystallization seeds of a new phase, which grows upwards. Such a scenario is very profitable because the whole pore can be used as a template for wire growth and no stuffing of the pore takes place.

Using the above phenomena, Cu, Ni, Co and Fe were deposited to the porous AAO matrix characterized by a different pores diameter [7]. As it was already mentioned, the deposition conditions influence strongly the quality and length of the obtained nanowires. Such structures as nanowires and nanotubes can be obtained via constant current deposition (DC) method when well distributed nanowires standing perpendicularly to the surface plane are relatively easily obtained. The acceleration current method (AC) in most cases (for long enough time of deposition) ends up with long wires which are randomly oriented at the surface due to strong magnetic interaction between them.

AC platting is often performed in a two electrode cell where working electrode is AAO plate and reference electrode Pt plate or wire. The example of the electrolyte composition used in the process was: 120 g/l NiSO 4 + 40 g/l H3BO3, electrolyte: 50 g/l CoSO4·7H2O + 25 g/l H3BO3 + 20 g/l glycerin, 0.9 mol/l FeSO4 7H2O, 0.15 mol/l FeCl2 4H2O and 0.43 mol/l NH4Cl for Ni, Co, Fe AC deposition at current condition 20V, 16V and 10V, respectively. DC deposition required a three electrode cell and besides, two already mentioned counter electrodes as Ag wire is present [2].

Fig. 12. Different quality of obtained wires by (a) DC and (b) AC modes

A choice of deposition mode depends on the needs and effectiveness of deposition processes. In DC mode, whole time while current is on deposition process takes place. AC plating combines deposition and dissolution processes which are running after each other. Firstly, the material is deposited and in the opposite current phase this layer is dissolved. Effective platting is only in this case when deposition dominates dissolution process.

The principles mentioned above should be modified and few additional phenomena must be considered. In general, kinetic parameters of deposition process are quite complex and depend on many parameters, which can be seen in the following equations (15-20). There are still many unknown points in deposition process which demand big effort of scientists and consume much time to be resolved. In many cases the proper and most accurate values describing the observed processes are obtained by different models. In case of porous membranes, one possible model is developed by Osterle called Space-Charge model [16]. There are modifications of this and some points are improved. In general, there are few

Electrochemical Methods in Nanomaterials Preparation 275

The movement of the ions in cylindrical tubes which are characterized by small radius is impeded in proximity of the pore wall. This fact decreases ionic diffusivity, which can be

Pore fluid conductivity of the capillary tube (cp) can be calculated by dividing the fluid

*p* 2 *K C*

In principle, pore conductivity and the electrical potential gradient should increase with the

Apart from that, simplified assumptions (small Debye length, small surface charge density, constant surface charge and surface potential) can be used to describe electrokinetic phenomena to derive phenomenological coefficients. Simplified equations can also be based

The characteristic parameters of electrical double layer such as electrical potential and profile of ion concentration are often modified by dielectric saturation effects, which, on the other hand, depend on the strength of electric field, and this derives from the interaction between fixed charges at, e.g., pore wall and the mobile ions present in electrolyte [18].

Even if a theoretical approach to electrodeposition can be done in many ways, quite often experimental results are difficult to understand because quite many parameters can vary at the same time and the variation of one of them in other order leads to completely opposite results. This is a huge problem for scientists and makes nanomaterials become very ardent

Not only single element wires are interesting but even more promising are these which are fabricated from more than one element. Such elements can be distributed in wire body in few manners: i) alloy-like composition, ii) layered structures, iii) core-shell structures (see

 (a) (b) (c) (d) (e) Fig. 13. Examples of possible structure modification of electrodeposited nanowires (a) single

Where: *Ri* – ion specific hydrodynamic retardation factor.

conductivity coefficient K by cross-section area (a2) of the pore [17].

*D RD i ii* (21)

*a* (22)

described as *Di* :

increase of ion concentration.

only on terms of forces and fluxes.

**4. Variation of deposited materials**

but also extremely difficult topic to study.

phase, (b) alloy like, (c) layered, (d) core-shell, (e) tubes.

Fig. 13).

equations which can be considered for the explanation of the problem and few equations must be fulfilled to understand the deposition phenomena [17]. The Nernst-Planck equation – which describes molar flux density (*J*) present in the tube:

$$\mathbf{J} = -D\nabla \mathbf{C} - \mathbf{K}Z \mathbf{C}Q \nabla \phi + \mathbf{C}u \tag{15}$$

Where: *D* – diffusion coefficient (diffusivity), *C* – ion concentration, *K* - mobility *Z* – valence of the ion, *Q* – , *Φ* – electrical potential, *u* – fluid velocity

The Einstein-relation which combines dependence between mobility and diffusivity of ions [17]:

$$K = \frac{D}{RT} \tag{16}$$

The Navier-Stokes equation – describing the fluid flow in a cylindrical tube [17]:

$$-\nabla p - F\sum\_{i=1}^{2} ZC\nabla \phi + \iota \nabla^2 \iota = 0\tag{17}$$

Where: *p* – hydrostatic pressure,

*F* - Faraday constant

The Poisson-Boltzmann equation – which takes into account a relation between charge density and electrical potential in cylindrical coordinates [17]:

$$\frac{\varepsilon\_0}{r} \frac{\partial}{\partial r} \left( \varepsilon r \frac{\partial \rho}{\partial r} \right) = \sum\_{i=1} Z F c^b \exp \left[ -\frac{Z F \rho(r)}{RT} - \frac{A F}{e RT} \left( \frac{1}{\varepsilon} - \frac{1}{\varepsilon\_p} \right) \right] \tag{18}$$

Where: *e* – electric charge, *r* – hydrated radius, ε – permittivity of free space, *A* – hydration constant, ε – dielectric constant.

Surface charge density – fraction of the total number of surface sites per unit area that are unbounded/charged [17]:

$$
\sigma\_s = \mathcal{e}\left(\left[A H\_2^{2+}\right]\_s - \left[A^-\right]\_s\right) \tag{19}
$$

Where: *\_A-* - fixed charges, *s* –surface quantity, *H+* - mobile ions,

Finite size ion effects for strongly hydrated electrolytes which consider the case of dissociated ions and full penetration in case of binary electrolytes [17]:

$$\frac{m}{m^b} \left( \frac{N - n^b}{N - n} \right) = \exp\left[ -\frac{z}{RT} \frac{F\Psi(r)}{RT} - \frac{A}{eRT} \left( \frac{1}{\varepsilon} - \frac{1}{\varepsilon\_b} \right) \right] \tag{20}$$

Where: *n* – number of density of ions near the charged wall, *nb* - number of density of ions in the bulk, N – total number of vacant sites (N=1/*v* here *v* is the volume of the hydrated ion)

equations which can be considered for the explanation of the problem and few equations must be fulfilled to understand the deposition phenomena [17]. The Nernst-Planck equation

*J D C KZCQ Cu*

Where: *D* – diffusion coefficient (diffusivity), *C* – ion concentration, *K* - mobility *Z* – valence

The Einstein-relation which combines dependence between mobility and diffusivity of ions

*D K*

*p F ZC u u*

The Poisson-Boltzmann equation – which takes into account a relation between charge

exp *b*

*ZF r AF r ZFc rr r RT eRT*

Where: *e* – electric charge, *r* – hydrated radius, ε – permittivity of free space, *A* – hydration

Surface charge density – fraction of the total number of surface sites per unit area that are

Finite size ion effects for strongly hydrated electrolytes which consider the case of

Where: *n* – number of density of ions near the charged wall, *nb* - number of density of ions in the bulk, N – total number of vacant sites (N=1/*v* here *v* is the volume of the hydrated

*n N n zF r AF n N n RT eRT*

 2 *s* 2 *s s*

() 1 1 exp

The Navier-Stokes equation – describing the fluid flow in a cylindrical tube [17]:

2

1

*i*

 0 1

dissociated ions and full penetration in case of binary electrolytes [17]:

*b*

*b*

Where: *\_A-* - fixed charges, *s* –surface quantity, *H+* - mobile ions,

2

*i p*

0

(17)

1 1

(18)

*e AH A* (19)

*b*

(20)

(15)

*RT* (16)

– which describes molar flux density (*J*) present in the tube:

of the ion, *Q* – , *Φ* – electrical potential, *u* – fluid velocity

density and electrical potential in cylindrical coordinates [17]:

Where: *p* – hydrostatic pressure,

constant, ε – dielectric constant.

unbounded/charged [17]:

ion)

*F* - Faraday constant

[17]:

The movement of the ions in cylindrical tubes which are characterized by small radius is impeded in proximity of the pore wall. This fact decreases ionic diffusivity, which can be described as *Di* :

$$D\_i = \mathcal{R}\_i D\_i \tag{21}$$

Where: *Ri* – ion specific hydrodynamic retardation factor.

Pore fluid conductivity of the capillary tube (cp) can be calculated by dividing the fluid conductivity coefficient K by cross-section area (a2) of the pore [17].

$$C\_p = \frac{K}{\pi a^2} \tag{22}$$

In principle, pore conductivity and the electrical potential gradient should increase with the increase of ion concentration.

Apart from that, simplified assumptions (small Debye length, small surface charge density, constant surface charge and surface potential) can be used to describe electrokinetic phenomena to derive phenomenological coefficients. Simplified equations can also be based only on terms of forces and fluxes.

The characteristic parameters of electrical double layer such as electrical potential and profile of ion concentration are often modified by dielectric saturation effects, which, on the other hand, depend on the strength of electric field, and this derives from the interaction between fixed charges at, e.g., pore wall and the mobile ions present in electrolyte [18].

## **4. Variation of deposited materials**

Even if a theoretical approach to electrodeposition can be done in many ways, quite often experimental results are difficult to understand because quite many parameters can vary at the same time and the variation of one of them in other order leads to completely opposite results. This is a huge problem for scientists and makes nanomaterials become very ardent but also extremely difficult topic to study.

Not only single element wires are interesting but even more promising are these which are fabricated from more than one element. Such elements can be distributed in wire body in few manners: i) alloy-like composition, ii) layered structures, iii) core-shell structures (see Fig. 13).

Fig. 13. Examples of possible structure modification of electrodeposited nanowires (a) single phase, (b) alloy like, (c) layered, (d) core-shell, (e) tubes.

Electrochemical Methods in Nanomaterials Preparation 277

Wires obtained in matrixes can be released by dissolving the alumina layer by such solutions as: 0,52 M H3PO4 or 1 M NaOH. Dissolution of matrix can be performed up to the stage when only a part of or until the whole template is removed from the plate surface. It

An interesting type of composites were these which had elongated nanostructures as nanowires or nanotubes in the structure. A special type of these are the nanostructures which are made of pure metal or metal oxide. Many of them have magnetic and at the same time conducting properties or selectively only one of them. This causes that the elements or whole composite materials can be easily manipulated by external magnetic field, which extends their application possibility. A special kind of nanocomposites are bionanocompisites, where the structure is constructed in such a way that bimolecule is already attached to the composite or can be caught by free active bonding. All non organic elements can be connected with biomolecules directly or via linkage chemistry (see Fig.

Fig. 15. Examples of biomolecule attachment to composite (a) via linkage chemistry,

Variation of the nanowires composition causes that properties of a particular composite can be modified in such a way that enhance needed one and weakened useless. Modification of the wires composition also influences affinity to certain linkage chemistry, which

Nanomaterials with high aspect ratio are particularly interesting due to the possibility of combining easily two kinds of totally different species. It allows to modify them by linkage chemistry, which is sensitive to various molecules. The array of nanowires can be used as chip for catching specific chemical materials. In external magnetic field manipulation of

Deposition of core-shell nanowires is particularly interesting when prevention from oxidation process is expected. This is particularly important when any modification of

depends on the particular application of fabricated nanowires [22].

**5. Composite preparation**

15.).

(b) directly.

determines a particular application.

**6. Possible application of described materials**

separate wires to construct long chains is possible to obtain.

Depending on the application, one of these are more interesting compared to other one. The application of noble metal wires such as Ag, Au, Pt and Cu are interesting in bioapplication but they are almost of no use in electronic devices or sensor application. On the other hand, Co and Ni oxides are often interesting to use in electronic and sensing industry and rather no application in biotechnology can be found. For example, if one considers modification of the wire surface by a compound which is active only with metal oxides, the surface of the wire should be covered intently by such. At the same time, affinity to thiols and amine groups will show wires which posses layered structure of Ag and Fe. Such structures require modification of electrodeposition process to obey both material deposition conditions (Fig. 14).

Among elongated structures nanotubes are placed and they also have quite a large variety of possible applications. Variation of the inert structure of nanomaterials allows to estimate the best composition which obeys the best productivity of surface functionalization processes.

Fig. 14. TEM images of electrodeposited nanowires and nanotubes

Effectiveness of deposition process strongly depends on elements which are deposited. This problem can be faced when deposition of elements such as Co, Ni and Fe in AAO matrix is compared. On the one hand , the diffusion of the ions is almost the same because we use the same type of the matrix and the radius of the ions is very alike. This suggests that the value will rather be the same for the considered elements and the same matrix. However, the difference in a growing rate of the two compared cases is observed. This uneven process can be due to dissimilar crystal growth modes in the pores. The evolution of H2 can also be not the same and it can sustain each element differently. When the surface is smoother, there are fewer nucleation centers and the atoms are worse adsorbed on the surface. On the other hand, the quality of the wires is much better compared to one which possesses a large number of the nucleation centers [19, 20].

Electrodeposition can also be performed in non-aqueous solution, which is valuable especially for very expensive or rare elements. Such deposition process can be done in, for example, acetone electrolyte by AC platting method, where one electrode (working) is matrix at which a layer should be deposited, and the second electrode from which the element is released (dissolved). [21]

Wires obtained in matrixes can be released by dissolving the alumina layer by such solutions as: 0,52 M H3PO4 or 1 M NaOH. Dissolution of matrix can be performed up to the stage when only a part of or until the whole template is removed from the plate surface. It depends on the particular application of fabricated nanowires [22].

## **5. Composite preparation**

276 Recent Trend in Electrochemical Science and Technology

Depending on the application, one of these are more interesting compared to other one. The application of noble metal wires such as Ag, Au, Pt and Cu are interesting in bioapplication but they are almost of no use in electronic devices or sensor application. On the other hand, Co and Ni oxides are often interesting to use in electronic and sensing industry and rather no application in biotechnology can be found. For example, if one considers modification of the wire surface by a compound which is active only with metal oxides, the surface of the wire should be covered intently by such. At the same time, affinity to thiols and amine groups will show wires which posses layered structure of Ag and Fe. Such structures require modification of electrodeposition process to obey both material deposition

Among elongated structures nanotubes are placed and they also have quite a large variety of possible applications. Variation of the inert structure of nanomaterials allows to estimate the best composition which obeys the best productivity of surface functionalization

wires tubes

Effectiveness of deposition process strongly depends on elements which are deposited. This problem can be faced when deposition of elements such as Co, Ni and Fe in AAO matrix is compared. On the one hand , the diffusion of the ions is almost the same because we use the same type of the matrix and the radius of the ions is very alike. This suggests that the value will rather be the same for the considered elements and the same matrix. However, the difference in a growing rate of the two compared cases is observed. This uneven process can be due to dissimilar crystal growth modes in the pores. The evolution of H2 can also be not the same and it can sustain each element differently. When the surface is smoother, there are fewer nucleation centers and the atoms are worse adsorbed on the surface. On the other hand, the quality of the wires is much better compared to one which possesses a large

Electrodeposition can also be performed in non-aqueous solution, which is valuable especially for very expensive or rare elements. Such deposition process can be done in, for example, acetone electrolyte by AC platting method, where one electrode (working) is matrix at which a layer should be deposited, and the second electrode from which the

Fig. 14. TEM images of electrodeposited nanowires and nanotubes

number of the nucleation centers [19, 20].

element is released (dissolved). [21]

conditions (Fig. 14).

processes.

An interesting type of composites were these which had elongated nanostructures as nanowires or nanotubes in the structure. A special type of these are the nanostructures which are made of pure metal or metal oxide. Many of them have magnetic and at the same time conducting properties or selectively only one of them. This causes that the elements or whole composite materials can be easily manipulated by external magnetic field, which extends their application possibility. A special kind of nanocomposites are bionanocompisites, where the structure is constructed in such a way that bimolecule is already attached to the composite or can be caught by free active bonding. All non organic elements can be connected with biomolecules directly or via linkage chemistry (see Fig. 15.).

Fig. 15. Examples of biomolecule attachment to composite (a) via linkage chemistry, (b) directly.

Variation of the nanowires composition causes that properties of a particular composite can be modified in such a way that enhance needed one and weakened useless. Modification of the wires composition also influences affinity to certain linkage chemistry, which determines a particular application.

## **6. Possible application of described materials**

Nanomaterials with high aspect ratio are particularly interesting due to the possibility of combining easily two kinds of totally different species. It allows to modify them by linkage chemistry, which is sensitive to various molecules. The array of nanowires can be used as chip for catching specific chemical materials. In external magnetic field manipulation of separate wires to construct long chains is possible to obtain.

Deposition of core-shell nanowires is particularly interesting when prevention from oxidation process is expected. This is particularly important when any modification of

Electrochemical Methods in Nanomaterials Preparation 279

[9] F. Li, L. Zhang, R. M. Metzger "On the growth of highly ordered pores in anodized

[10] B. Vanderlinden, H.Terryn, J. Vereecken "Investigation of anodic aluminum-oxide

[11] Ch.-G.Wu, H.L.lin, N.-L.Shan ''Magnetic nanowires via template electrodeposition'',

[12] W. Szczepaniak "Metody instrumentalne w analizie chemicznej" Wydawnictwo

[13] A. Cygański: "Metody elektroanalityczne" Wydawnictwo Naukowo-Techniczne

[14] J. Garaj: Fizyczne i fizykochemiczne metody analizay; Wydawnictwo Naukowo-

[15] Herman N.A., Kalestyoski A., Widomski L. "Fizyka dla kandydatów na wyższe

[16] R.J Gross and J.F Osterle, Membrane transport characteristics of ultrafine capillaries. J.

[17] S. Basu, M.M. Sharma, J. Memb.Scien. 124 (1997) 77, F. Wang, S. Arai, M. Endo,

[18] M. A. V. Devanathan and B. V. Tilak, The Structure of the Electrical Double Layer at the

[19] C.L. Chiena, L. Sun, M. Tanase, L.A. Bauer, A. Hultgren, et al. *Electrodeposited magnetic*

[20] M.S. Dresselhausa, Y.M. Lin, O. Rabin, M.R. Black, G. Dresselhaus. *Nanowires.* January

[21] *B. Kalska-Szostko, E. Orzechowska, W. Olszewski*. Electrochemical deposition of Fe

nanowires from nonaquaeous solution submitted for publication

Magnetism and Magnetic Materials 249 (2002) 146–155

naukowe PWN W-wa 2005, "Poradnik galwanotechnika". Praca zbiorowa. Wyd. II

uczelnie I studentów", wyd. PWN, Warszawa 1995, P. M. S. Monk, R. J. Mortimer and D. R. Rosseinsky, Electrochromism and Electrochromic Devices, Cambridge

Electr. Comm. 7 (2005) 674, A. Vicenzo, P.L. Cavalloti, Electr. Acta 49 (2004) 4079, M. Motoyama, Y. Fukunaka, T. Sakka, Y.H. Ogata, Electr. Acta 53 (2007)

*nanowires: arrays, field-induced assembly, and surface functionalization.* Journal of

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poprawione, WN-Tech. W-wa 1985

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metal-solution interface 1965

Techniczne Warszawa 1981

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2, 2003

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aluminum oxide", Chem. Mater. 1998, 10, 2470-2480, A.P.Li, F. Müller, A. Birner, K.Nielch, U.Gösele "Hexagonal pore arrays with a 50-420 nm interpore distance formed by self-organization in anodic alumina" J. Appl. Phys., vol.84,(1998) p

layers by electrochemical impedance spectroscopy", J. Apll. Electrochem., vol. 20,

J.Solid State Electrochem. 2006, 10,198-202; S.inoue, S.-Z.Chu, K. Wada, D.Li ''New roots to formation of nanostructures on glass surface through anodic oxidation of sputtered aluminum'' Science and Technology of Advanced Materials 4, 2003, 269-276; Y.Sui, B.Z.Cui, L.Martinez, et all.''Pore structure, barrier layer topography and matrix alumina structure of porous anodic alumina film'', Thin Solid Films 406 :1-2, 2002, 64-69; S.Lazarouk, S.Stanovski, et all.''Porous alumina as low-ε insulator for multilevel mettalization'',

magnetic core is critical and application due to oxidation process is limited. Controlling of the oxide layer opens a new field in fabrication and application of electrochemically obtained nanowires.

Elongated and differentiated particles combine possible immobilization at differently active parts of particle various active particles. This opens a quite broad field of application in biology and medicine.

The possibilities in constructing new nanomaterials is huge. There is an enormous number of structures which are described in the literature. However, there is also a gigantic number of unknown structures and a lot of hard work must be performed to define and describe their properties.

## **7. Acknowledgement**

I would like to thank all my students and co-workers for contribution to this work. This work was partly supported by Polish National Grant No. N N204 246435.

## **8. References**

magnetic core is critical and application due to oxidation process is limited. Controlling of the oxide layer opens a new field in fabrication and application of electrochemically

Elongated and differentiated particles combine possible immobilization at differently active parts of particle various active particles. This opens a quite broad field of application in

The possibilities in constructing new nanomaterials is huge. There is an enormous number of structures which are described in the literature. However, there is also a gigantic number of unknown structures and a lot of hard work must be performed to define and describe

I would like to thank all my students and co-workers for contribution to this work. This

[1] P. G. Romero, C. Sanchez, Functional Hybrid Materials, (wiley, Weinheim, 2003) p 86; Y.

[2] B. Kalska-Szostko, E. Brancewicz, W. Olszewski, K. Szymański, P. Mazalski, J, Sveklo,

[3] B. Kalska-Szostko, E. Brancewicz, W. Olszewski, K. Szymański, P. Mazalski, J, Sveklo,

Orzechowska, P. Mazalski, T. Wojciechowski, Mater. Sci. For. 674 (2011) 231 [4] G.D. Sułka " Wysokouporządkowane nanostruktury na anodyzowanym aluminium"

[5] P. Tomassi "Ochrona aluminium przed korozją" Instytut Mechaniki Precyzyjnej, W-wa

[6] J. Choi "Fabrication of monodomain porous alumina using nanoimprint lithography and

[7] a) B. Kalska, E. Orzechowska Mater. Chem. Phys (2011), Curr. Apel. Phys. (2011); b) H.

[8] A.P.Li, F. Müller, A. Birner, K.Nielch, U.Gösele "Hexagonal pore arrays with a 50-420 nm

Wu, J. Xiang, C. Yang, W. Lu, M.C. Liber, Nature 430 (2004) 61; B. H. Kim, J.H. Jung, S.H Hong, J. Joo, A.L Epstein, K. Mizoguchi, J.W. Kim, H.J. Choi, Macromolecules 35 (2002) 1419; W.U. Huynh, J.J.Dittmer, A.P. Alivisatos, Science

Solid State. Phenom. 151 (2009) 190; B. Kalska-Szostko, E. Brancewicz, E.

its applications" Mathematisch-Naturwissenchaftlich-Technischen Fakultät der

Adelkhani, S. Nasoodi, A. H. Jafari "A study of the Morphology and Optical Properties of Electropolished Aluminum in the Vis-IR region" Int. J. Electrochem.

interpore distance formed by self-organization in anodic alumina", J. Appl. Phys.,

work was partly supported by Polish National Grant No. N N204 246435.

Instytut Chemii Fizycznej, Uniwersytet Jagielloński

Martin-Luther-Universität Halle-Wittenberg 2004

obtained nanowires.

biology and medicine.

**7. Acknowledgement**

295 (2002) 2425;

Sci., 4 (2009) 238 – 246.

vol.84, p 6023, 1998

2006

Acta Phys. Pol. A 115 (2009) 542

their properties.

**8. References**

**13**

*México*

**Novel Electroless Metal Deposition -**

*S.C., Parque Tecnológico Querétaro-Sanfandila,*

José de Jesús Pérez Bueno1,\* and Maria Luisa Mendoza López2 *1Centro de Investigación y Desarrollo Tecnológico en Electroquímica,*

**Oxidation on Mn – MnxOy for Water Remediation**

*2Instituto Tecnológico de Querétaro, Av. Tecnológico s/n Esq. M. Escobedo Col. Centro*

Water pollution not only increases in amount every year but it increases in higher toxic contaminants. Humanity has acquired, with harsh and tragic experience, a consciousness of care for the environment. New laws and norms throughout the world prove this. The quest for new processes, as an alternative to those already in use, has been testing many different

A conventional procedure for the removal of metal ions is chemical precipitation of hydroxides by adjusting the pH (Zouboulis et al., 2002). During the last decade, zero-valent iron has been used for the removal of metals such as zinc and mercury (Dries et al., 2005; Oh

The electroless metal deposition has been used in many industries especially due to polymers metallization. Electroless is comprised into three different procedures;

The cementation process offers the possibility of removing contaminants from water considering its standard electrode potential according to the electromotive series without an external current. Ions of a relatively nobler element are reduced using electrons in exchange for a less nobler metal that gets oxidized. Usually, this process occurs over the entire surface, which concludes by blocking the deposition. This through that limits the applications of the

The cementation process has been used for the removal of gold, e.g., using magnesium. The deposition rate of gold is directly proportional to its initial concentration and time (Kuntyi et

Electroless metal deposition has been used for the synthesis of self-assembling silicon nanowires. In this case, it was assumed that the simultaneous growth of metal dendrites, accompanied with the etching of the silicon wafer, was important for the formation of 1D

The quantity of oxide formed on the cementating surface depends on pH, the quantity of the cementation agent and the stir variation. The reactivity of Fe0 depends on the porosity of the

et al., 2007; Noubactep, 2010). This procedure is part of the electroless deposition.

**1. Introduction**

process.

al., 2007).

nanostructures (Peng, 2003).

physical and chemical procedures.

autocatalytic, cementation and galvanic deposition.

[22] A. Jagminas, R. Juškėnas, I. Gailiūtė, G. Statkutė, R. Tomašiūnas "Electrochemical synthesis and optical characterization of copper selenide nanowires arrays within the alumina pores" Journal of Crystal Growth 294(2006) 343-348

## **Novel Electroless Metal Deposition - Oxidation on Mn – MnxOy for Water Remediation**

José de Jesús Pérez Bueno1,\* and Maria Luisa Mendoza López2 *1Centro de Investigación y Desarrollo Tecnológico en Electroquímica, S.C., Parque Tecnológico Querétaro-Sanfandila, 2Instituto Tecnológico de Querétaro, Av. Tecnológico s/n Esq. M. Escobedo Col. Centro México*

## **1. Introduction**

280 Recent Trend in Electrochemical Science and Technology

[22] A. Jagminas, R. Juškėnas, I. Gailiūtė, G. Statkutė, R. Tomašiūnas "Electrochemical

the alumina pores" Journal of Crystal Growth 294(2006) 343-348

synthesis and optical characterization of copper selenide nanowires arrays within

Water pollution not only increases in amount every year but it increases in higher toxic contaminants. Humanity has acquired, with harsh and tragic experience, a consciousness of care for the environment. New laws and norms throughout the world prove this. The quest for new processes, as an alternative to those already in use, has been testing many different physical and chemical procedures.

A conventional procedure for the removal of metal ions is chemical precipitation of hydroxides by adjusting the pH (Zouboulis et al., 2002). During the last decade, zero-valent iron has been used for the removal of metals such as zinc and mercury (Dries et al., 2005; Oh et al., 2007; Noubactep, 2010). This procedure is part of the electroless deposition.

The electroless metal deposition has been used in many industries especially due to polymers metallization. Electroless is comprised into three different procedures; autocatalytic, cementation and galvanic deposition.

The cementation process offers the possibility of removing contaminants from water considering its standard electrode potential according to the electromotive series without an external current. Ions of a relatively nobler element are reduced using electrons in exchange for a less nobler metal that gets oxidized. Usually, this process occurs over the entire surface, which concludes by blocking the deposition. This through that limits the applications of the process.

The cementation process has been used for the removal of gold, e.g., using magnesium. The deposition rate of gold is directly proportional to its initial concentration and time (Kuntyi et al., 2007).

Electroless metal deposition has been used for the synthesis of self-assembling silicon nanowires. In this case, it was assumed that the simultaneous growth of metal dendrites, accompanied with the etching of the silicon wafer, was important for the formation of 1D nanostructures (Peng, 2003).

The quantity of oxide formed on the cementating surface depends on pH, the quantity of the cementation agent and the stir variation. The reactivity of Fe0 depends on the porosity of the

Novel Electroless Metal Deposition - Oxidation on Mn – MnxOy for Water Remediation 283

other hand, the surfaces of the manganese chips were usually constituted by alternating the areas of oxide and metal. The predominance of any of them depends on the preparation of the surface. The proposed sequence in the process, considers this nature of metal – oxide surface as anode – cathode, respectively. Micro-electrochemical cell requires favourable ΔG, standard electrode potential, and electric conductivity in order to initiate and continue with

Each element deposition possesses particular characteristics but then also share similarities. The deposition structures vary among each element from soft dendritic branches of silver to compact layers of aluminium or columnar grains of lead. The similarities can lead to these conditions required for deposition, such as: a) electrical conductivity between active deposition sites and the substrate, b) a higher rate of deposition than the rate of dissolution,

In the case of lead, there was no visible bubble formations associated with water electrolysis. In the case of silver, there were bubble formations and their liberation caused the lost of electrical contact between metal substrate and the active deposition sites, which particularly favoured the soft structure. In the case of aluminium, with a very low standard electrode potential, there were prolific formations of bubbles but the layers deposition prevents any

The process of electroless deposition of lead ions, from aqueous solution on the system

Electrolytically refined manganese chips, covered with oxide (Figure 1a) or polished (Figure 1b), were either used to illustrate deposition and for comparison. Pieces of manganese metal covered with a layer of manganese oxide, formed naturally under normal environmental conditions (amorphous MnO2), and pieces free of rust were immersed separately in aqueous solutions with 100 ppm of lead during 24 h and one week. The oxide layer of the piece of Mn was removed by using a SiC No. 400 grit. The solutions were kept at room temperature (25 °C) without agitation. At the end of those periods, both samples were removed from the lead solutions, which were then filtered and stored for later analysis. The substrates with

The following analysis corresponds to deposits from solutions containing around 100ppm of lead, which depends on the surface preparation (metallic manganese or manganese oxide)

The Figs. 2a-b show the deposit covertures after 24 h of immersion in a 100ppm lead solution of a flat Mn chip covered with oxide (Fig. 2a) and a polished Mn (Fig. 2b). These tests were conducted at room temperature (25 °C) without stirring. It was evident, during the tests, that the polished surface had a delay of around half an hour, allowing for the formation of manganese oxide clusters, which posteriorly contribute in starting deposition. Finally, there was a thicker deposit on the manganese oxide surface. The waviness in Fig 2b

c) a diffusion of ions on the active sites of deposition.

**3.1 Lead ions transformed into oxides by Electroless deposition**

or the deposition period (middle and long term; 24 h and one week).

corresponded to original formations of the electrolytic Mn chip.

manganese metal - manganese oxide, is described in this section.

the deposition.

significant effect.

deposits were analyzed by SEM.

oxides formed, the water salinity and the nature of the contaminant. A generation of thicker oxides was identified as being beneficial for the removal of contaminants and their potential reaction products can progressively be trapped in the matrix and remain very stable (Noubactep, 2010).

The removal of metallic ions in aqueous solution by zero-valent iron has been studied in research papers during the last decade (Noubactep, 2009). This route is fundamentally a cementation electroless process. It has been identified as having a synergic effect between adsorption, co-precipitation and the reduction of the contaminant on Fe0/H2O. Those studies associate metal removal through a combination of adsorption and co-precipitation onto iron corrosion products and reduction by using Fe0, FeII or H2/H.

This work considers the remediation of water by using electroless going through the formation of oxides immediately after the reduction of the metallic specie on the active surface. A high porosity of the deposited oxide may result, but not necessarily, fundamental in the process of forming the deposit.

## **2. Methodology**

This work used standard ions solutions for water remediation evaluation because of the influence of manganese-manganese oxide. Silver nitrate, aluminum nitrate and lead nitrate (JT Baker) were used for the 1000ppm, 500ppm, and 100ppm solutions in deionizer water.

The crystallinity of manganese-manganese oxide substrates (Alfa Aesar, 99%) and that of deposits were characterized by X-ray diffraction (D8 Advance, Bruker AXS). The deposits weights were obtained by weight differences between the deposit-substrate and the substrate.

The pieces of manganese-manganese oxide used as substrates, with weight and area previously measured, were immersed in 50mL of a standard ion solution. The substrates had two different surfaces, one of them flat and the other irregular; for this study, the depositions were always on the flat surfaces.

When each test concluded, the solution was removed carefully with a pipette from the flask were the test were conducted, leaving the deposit-substrate samples untouched. The depositsubstrate samples were dried at room temperatures. The weight of the deposits was determined by weight difference between the deposit-substrate sample and the original substrate.

The characterizations of morphology and microanalysis of deposits and substrate were performed in a scanning electron microscopy (SEM, JEOL model JSM-5400LV) coupled to a microanalysis (EDS, Kevex-TermoNORAN).

The absorbance and reflectance studies of deposits were determined by Ocean Optics –USB 2000 spectrometer with a coupled integrating sphere in the range of 190 and 850nm.

The profiles of the deposits were analyzed by Veeco profiler, model Dektak 8, for obtaining the surfaces roughness.

## **3. Results and discussion**

Manganese dioxide adsorbs ions of metals in a solution. Also, it undertakes the role of a cathode, which accepts electrons, and which consequently acts as an oxidizing agent. On the

oxides formed, the water salinity and the nature of the contaminant. A generation of thicker oxides was identified as being beneficial for the removal of contaminants and their potential reaction products can progressively be trapped in the matrix and remain very stable

The removal of metallic ions in aqueous solution by zero-valent iron has been studied in research papers during the last decade (Noubactep, 2009). This route is fundamentally a cementation electroless process. It has been identified as having a synergic effect between adsorption, co-precipitation and the reduction of the contaminant on Fe0/H2O. Those studies associate metal removal through a combination of adsorption and co-precipitation

This work considers the remediation of water by using electroless going through the formation of oxides immediately after the reduction of the metallic specie on the active surface. A high porosity of the deposited oxide may result, but not necessarily, fundamental

This work used standard ions solutions for water remediation evaluation because of the influence of manganese-manganese oxide. Silver nitrate, aluminum nitrate and lead nitrate (JT Baker) were used for the 1000ppm, 500ppm, and 100ppm solutions in deionizer water. The crystallinity of manganese-manganese oxide substrates (Alfa Aesar, 99%) and that of deposits were characterized by X-ray diffraction (D8 Advance, Bruker AXS). The deposits weights were obtained by weight differences between the deposit-substrate and the substrate. The pieces of manganese-manganese oxide used as substrates, with weight and area previously measured, were immersed in 50mL of a standard ion solution. The substrates had two different surfaces, one of them flat and the other irregular; for this study, the

When each test concluded, the solution was removed carefully with a pipette from the flask were the test were conducted, leaving the deposit-substrate samples untouched. The depositsubstrate samples were dried at room temperatures. The weight of the deposits was determined

The characterizations of morphology and microanalysis of deposits and substrate were performed in a scanning electron microscopy (SEM, JEOL model JSM-5400LV) coupled to a

The absorbance and reflectance studies of deposits were determined by Ocean Optics –USB

The profiles of the deposits were analyzed by Veeco profiler, model Dektak 8, for obtaining

Manganese dioxide adsorbs ions of metals in a solution. Also, it undertakes the role of a cathode, which accepts electrons, and which consequently acts as an oxidizing agent. On the

by weight difference between the deposit-substrate sample and the original substrate.

2000 spectrometer with a coupled integrating sphere in the range of 190 and 850nm.

onto iron corrosion products and reduction by using Fe0, FeII or H2/H.

(Noubactep, 2010).

**2. Methodology**

in the process of forming the deposit.

depositions were always on the flat surfaces.

microanalysis (EDS, Kevex-TermoNORAN).

the surfaces roughness.

**3. Results and discussion**

other hand, the surfaces of the manganese chips were usually constituted by alternating the areas of oxide and metal. The predominance of any of them depends on the preparation of the surface. The proposed sequence in the process, considers this nature of metal – oxide surface as anode – cathode, respectively. Micro-electrochemical cell requires favourable ΔG, standard electrode potential, and electric conductivity in order to initiate and continue with the deposition.

Each element deposition possesses particular characteristics but then also share similarities. The deposition structures vary among each element from soft dendritic branches of silver to compact layers of aluminium or columnar grains of lead. The similarities can lead to these conditions required for deposition, such as: a) electrical conductivity between active deposition sites and the substrate, b) a higher rate of deposition than the rate of dissolution, c) a diffusion of ions on the active sites of deposition.

In the case of lead, there was no visible bubble formations associated with water electrolysis. In the case of silver, there were bubble formations and their liberation caused the lost of electrical contact between metal substrate and the active deposition sites, which particularly favoured the soft structure. In the case of aluminium, with a very low standard electrode potential, there were prolific formations of bubbles but the layers deposition prevents any significant effect.

## **3.1 Lead ions transformed into oxides by Electroless deposition**

The process of electroless deposition of lead ions, from aqueous solution on the system manganese metal - manganese oxide, is described in this section.

Electrolytically refined manganese chips, covered with oxide (Figure 1a) or polished (Figure 1b), were either used to illustrate deposition and for comparison. Pieces of manganese metal covered with a layer of manganese oxide, formed naturally under normal environmental conditions (amorphous MnO2), and pieces free of rust were immersed separately in aqueous solutions with 100 ppm of lead during 24 h and one week. The oxide layer of the piece of Mn was removed by using a SiC No. 400 grit. The solutions were kept at room temperature (25 °C) without agitation. At the end of those periods, both samples were removed from the lead solutions, which were then filtered and stored for later analysis. The substrates with deposits were analyzed by SEM.

The following analysis corresponds to deposits from solutions containing around 100ppm of lead, which depends on the surface preparation (metallic manganese or manganese oxide) or the deposition period (middle and long term; 24 h and one week).

The Figs. 2a-b show the deposit covertures after 24 h of immersion in a 100ppm lead solution of a flat Mn chip covered with oxide (Fig. 2a) and a polished Mn (Fig. 2b). These tests were conducted at room temperature (25 °C) without stirring. It was evident, during the tests, that the polished surface had a delay of around half an hour, allowing for the formation of manganese oxide clusters, which posteriorly contribute in starting deposition. Finally, there was a thicker deposit on the manganese oxide surface. The waviness in Fig 2b corresponded to original formations of the electrolytic Mn chip.

Novel Electroless Metal Deposition - Oxidation on Mn – MnxOy for Water Remediation 285

(a)

(b)

The Mn pieces showed uniform covertures on the surface with the deposits (Fig. 3a), on which there was profuse growth. Fig. 3b shows a magnification, which resulted notorious for having frequent growths of hexagonal platelets. Along with a basis of columnar growth, there were regular hexagons with some dots on their sides. Moreover, Fig. 3b has the

Fig. 2. **a**. SEM image, using 80X, from a flat Mn chip covered with oxide immersed in a 100ppm lead solution during 24 h.; **b.** SEM image, using 80X, from a polished Mn chip

immersed in a 100ppm lead solution during 24 h.

peculiarity of hexagonal growths on the edge of other hexagons.

(b)

Fig. 1**. a.** SEM image using 79X of an oxide layer formed naturally on the surface of a Mn chip; **b.** SEM image using 79X on the surface of a polished Mn chip.

(a)

(b)

Fig. 1**. a.** SEM image using 79X of an oxide layer formed naturally on the surface of a Mn

chip; **b.** SEM image using 79X on the surface of a polished Mn chip.

(a)

(b)

Fig. 2. **a**. SEM image, using 80X, from a flat Mn chip covered with oxide immersed in a 100ppm lead solution during 24 h.; **b.** SEM image, using 80X, from a polished Mn chip immersed in a 100ppm lead solution during 24 h.

The Mn pieces showed uniform covertures on the surface with the deposits (Fig. 3a), on which there was profuse growth. Fig. 3b shows a magnification, which resulted notorious for having frequent growths of hexagonal platelets. Along with a basis of columnar growth, there were regular hexagons with some dots on their sides. Moreover, Fig. 3b has the peculiarity of hexagonal growths on the edge of other hexagons.

Novel Electroless Metal Deposition - Oxidation on Mn – MnxOy for Water Remediation 287

When analyzing the surface near the edge of the substrate, shown in Fig. 4, there were columnar formations made of numerous granules that resembled dendrites. Those growths covered the whole surface with heights that could be visible to the naked eye. The growing rate diminishes with time. This is not only due to a decrease in lead ions concentration but mainly because electrical resistivity was increasing due to lead oxide and the increasing number of grain frontiers. This characteristic of grain pillaring was frequently observed in

Fig. 4. SEM image, using 5077X, of dendrites stacked near an edge of the polished Mn chip.

In the non polished Mn piece, a uniform deposit was observed, on which, hexagonal lamellar formations were also present and had very symmetric profiles (Fig. 5). In the image, rod-like formations appear to be located at the center and at the left inferior corner, which were made of irregular packed granules. The rod-like formations were similar to those shown in Fig. 4 and had multiple granules which were formed concurrently through

The effect of tunneling electrons, used for imaging in the SEM, was repeatedly observed in several of the thin hexagonal platelets at Fig 5. The image shows their thickness and size were not closely associated. The electrons tunneling through hexagonal formations having

EDX analyses were conducted in both samples, polished (Fig. 6a) or covered by manganese oxide (Fig. 6b). The identified elements were: lead, manganese, oxygen and carbon. The percentages of these elements in the deposit are presented, only in an illustrative form, in

lead oxide deposits.

nucleation and growth.

Table 1.

translucent effect allow seeing an inner surface.

(a)

(b)

Fig. 3**. a.** SEM image, using 79X, from a flat Mn chip covered with oxide immersed in a 100ppm lead solution during one week; **b.** SEM image, using 1269X, from a flat Mn chip covered with oxide immersed in a 100ppm lead solution during one week.

(a)

(b)

Fig. 3**. a.** SEM image, using 79X, from a flat Mn chip covered with oxide immersed in a 100ppm lead solution during one week; **b.** SEM image, using 1269X, from a flat Mn chip

covered with oxide immersed in a 100ppm lead solution during one week.

When analyzing the surface near the edge of the substrate, shown in Fig. 4, there were columnar formations made of numerous granules that resembled dendrites. Those growths covered the whole surface with heights that could be visible to the naked eye. The growing rate diminishes with time. This is not only due to a decrease in lead ions concentration but mainly because electrical resistivity was increasing due to lead oxide and the increasing number of grain frontiers. This characteristic of grain pillaring was frequently observed in lead oxide deposits.

Fig. 4. SEM image, using 5077X, of dendrites stacked near an edge of the polished Mn chip.

In the non polished Mn piece, a uniform deposit was observed, on which, hexagonal lamellar formations were also present and had very symmetric profiles (Fig. 5). In the image, rod-like formations appear to be located at the center and at the left inferior corner, which were made of irregular packed granules. The rod-like formations were similar to those shown in Fig. 4 and had multiple granules which were formed concurrently through nucleation and growth.

The effect of tunneling electrons, used for imaging in the SEM, was repeatedly observed in several of the thin hexagonal platelets at Fig 5. The image shows their thickness and size were not closely associated. The electrons tunneling through hexagonal formations having translucent effect allow seeing an inner surface.

EDX analyses were conducted in both samples, polished (Fig. 6a) or covered by manganese oxide (Fig. 6b). The identified elements were: lead, manganese, oxygen and carbon. The percentages of these elements in the deposit are presented, only in an illustrative form, in Table 1.

Novel Electroless Metal Deposition - Oxidation on Mn – MnxOy for Water Remediation 289

**b)**

**d)**

Fig. 6. EDX analysis conducted on surface: a) initially covered by manganese oxide and b) polished Mn; both during 24 h. c) Initially covered by manganese oxide and d) polished Mn;

**c)**

**a)**

Table 2 presents the lead removal of samples showed after a week in contact with the solution at room temperature (25 ° C) and without agitation. ICP analysis was conducted on the solutions after the tests. There were greater depositions on Mn pieces covered by oxide than in polished Mn pieces during both periods. Also, the total lead removal after a week

The deposition was influenced by both, time and surface preparation. Nonetheless, there were other principal variables in the process: Pb concentration, the area of deposition, and the temperature. The lead deposit structure was then strong enough to apply a flow or stirring to the solution during tests. Also, this may increase the deposition rate causing a

X-ray diffraction analyses were conducted in order to identify the crystal composition of the deposits. The diffractograms of these samples identify a crystalline content of Pb5O8 (Fig. 7). In order to observe the lead concentration influence on the structure of the deposits a 500 ppm of lead solution was used for deposits. In this series of tests, the deposition process was conducted three times, without changing the solution, but only substituting the Mn plate. Fig. 8 shows this sequence. Also, only one half of the Mn pieces were polished and subsequently

both during one week.

reached ninety percent.

time reduction or a rise in the lead removed percentage.

Fig. 5. SEM image at 669X from polished Mn chip immersed in the Pb solution. There were thin hexagonal formations, some of which allow transmission of the electrons from the microscope beam making them look translucent.

The EDX analysis was semi-quantitative, consequently, it is considered here illustrative of chemical composition of the deposit. The exposure to air may considerably change those compositions and change the surface appearance as manganese oxides tend to form. Considering the information from both samples, there was a close relationship between lead and oxygen content. The condition of the analyzed surfaces, there were lead oxides with manganese that eventually tended to be oxidized in the air. In other conducted experiments, lead manganese oxides tend to form (PbxMnyOz).

Table 1. Semi-quantitative EDX percentages of elements on the surfaces: a) initially covered by manganese oxide and b) polished Mn; both during 24 h. c) Initially covered by manganese oxide and d) polished Mn; both during one week.

Fig. 5. SEM image at 669X from polished Mn chip immersed in the Pb solution. There were thin hexagonal formations, some of which allow transmission of the electrons from the

The EDX analysis was semi-quantitative, consequently, it is considered here illustrative of chemical composition of the deposit. The exposure to air may considerably change those compositions and change the surface appearance as manganese oxides tend to form. Considering the information from both samples, there was a close relationship between lead and oxygen content. The condition of the analyzed surfaces, there were lead oxides with manganese that eventually tended to be oxidized in the air. In other conducted experiments,

> **Sample b (%)**

Lead 52.44 39.35 37.95 1.41 Manganese 15.64 42.54 36.34 64.64 Oxygen 24.04 14.62 21.59 1.41 Carbon 7.88 3.5 4.12 4.95 Table 1. Semi-quantitative EDX percentages of elements on the surfaces: a) initially covered

by manganese oxide and b) polished Mn; both during 24 h. c) Initially covered by

**Sample c (%)**

**Sample d (%)**

microscope beam making them look translucent.

lead manganese oxides tend to form (PbxMnyOz).

**Element Sample a**

**(%)**

manganese oxide and d) polished Mn; both during one week.

Fig. 6. EDX analysis conducted on surface: a) initially covered by manganese oxide and b) polished Mn; both during 24 h. c) Initially covered by manganese oxide and d) polished Mn; both during one week.

Table 2 presents the lead removal of samples showed after a week in contact with the solution at room temperature (25 ° C) and without agitation. ICP analysis was conducted on the solutions after the tests. There were greater depositions on Mn pieces covered by oxide than in polished Mn pieces during both periods. Also, the total lead removal after a week reached ninety percent.

The deposition was influenced by both, time and surface preparation. Nonetheless, there were other principal variables in the process: Pb concentration, the area of deposition, and the temperature. The lead deposit structure was then strong enough to apply a flow or stirring to the solution during tests. Also, this may increase the deposition rate causing a time reduction or a rise in the lead removed percentage.

X-ray diffraction analyses were conducted in order to identify the crystal composition of the deposits. The diffractograms of these samples identify a crystalline content of Pb5O8 (Fig. 7).

In order to observe the lead concentration influence on the structure of the deposits a 500 ppm of lead solution was used for deposits. In this series of tests, the deposition process was conducted three times, without changing the solution, but only substituting the Mn plate. Fig. 8 shows this sequence. Also, only one half of the Mn pieces were polished and subsequently

Novel Electroless Metal Deposition - Oxidation on Mn – MnxOy for Water Remediation 291

(a)

(b)

(a)

layer without a prominent accumulation on its surface (Fig. 8C). Only in the third sample there was evidence of difference between the half polished area and the oxide covered

Fig. 8. a) Picture of sample A, b) picture of sample B, c) picture of sample C.

surface, which appeared as a dark area on the right hand side.

immersed in the lead solution. The immersion time for samples A and B was 24h, but sample C remained for 64h, since the formation of a deposit was not evident initially.

Table 2. Removal of Pb by Mn pieces after 24 h and one week in contact with the solution, analyzed by ICP.

Fig. 7. X-ray diffraction of a lead deposit.

Fig. 8A shows the image corresponding to the first immersed plate into the 500 ppm lead solution A), after drying in air. The deposit was very visible and it was apparently formed by accumulations of dendrites. Under similar conditions, a second Mn plate immersed into the solution showed a still visible deposit, with thin columnar-dendritic growths and thickness (Fig. 8B). Finally, sample C showed that the deposit was present as a homogeneous

immersed in the lead solution. The immersion time for samples A and B was 24h, but sample

**Pb content after test (ppm)**

Polished Mn 125 118.45 5.24 0.58 69.73

Polished Mn 125 19.15 84.68 0.40 267.84

 **lead deposit without line base**

 **Pb3O4 Pb PbO Pb5O8**

**10 20 30 40 50 60 70 80**

**2**

Fig. 8A shows the image corresponding to the first immersed plate into the 500 ppm lead solution A), after drying in air. The deposit was very visible and it was apparently formed by accumulations of dendrites. Under similar conditions, a second Mn plate immersed into the solution showed a still visible deposit, with thin columnar-dendritic growths and thickness (Fig. 8B). Finally, sample C showed that the deposit was present as a homogeneous

Table 2. Removal of Pb by Mn pieces after 24 h and one week in contact with the solution,

**Pb removal (%)**

125 115.44 7.65 0.55 92.01

125 10.82 91.344 0.31 368.96

**Area (cm2) Pb removal**

**(ppmPb/cm2)**

C remained for 64h, since the formation of a deposit was not evident initially.

**content (ppm)**

**Time Sample Pb initial**

Surface covered by manganese oxide

Surface of

Surface covered by manganese oxide

Surface of

**0**

Fig. 7. X-ray diffraction of a lead deposit.

**50**

**100**

**150**

**200**

**Intensity (u.a.)**

**250**

**300**

**350**

24 h

1 week

analyzed by ICP.

(b)

(a)

Fig. 8. a) Picture of sample A, b) picture of sample B, c) picture of sample C.

layer without a prominent accumulation on its surface (Fig. 8C). Only in the third sample there was evidence of difference between the half polished area and the oxide covered surface, which appeared as a dark area on the right hand side.

Novel Electroless Metal Deposition - Oxidation on Mn – MnxOy for Water Remediation 293

Fig. 10. Image from a lead deposition in an edge of a manganese plate with a semi-dendritic

There were some factors limiting the extent of growth, such as the reduction in Pb ions concentration in solution and electric contact with the substrate. Since there were such limitations, the initial lead concentration can be reduced by increasing the area, increasing

column constituted by grain nucleations and leaves-like forms on top.

the time of contact or by successive stages of deposition.

These pieces were analyzed by X-ray diffraction, which identified a predominance of Pb5O8 along with small signals indicating the presence of Pb and PbO (Fig. 9).

Fig. 9. Difractogram of Mn samples with deposition from a 500 ppm lead solution. A) First plate, B) second plate, C) third plate.

The kinetics of deposition of lead on manganese depends on the Pb ion concentration in solution. High concentration promotes a fast deposition and growing in a dendritic structure. The intermediate deposition rate combines semi-dendritic columns with grain nucleations. Slow deposition rates propitiate nucleations with spherical shaped grains. Nevertheless, some cases were observed with different deposition configurations.

Usually, lead deposition in the edges of a manganese substrate tended to generate the combined form of deposition. Fig 10 presents such projections from an edge of a manganese piece. It possessed a semi-dendritic column formed by grain nucleations. In this infrequent case, it was coronated by forms in a leaves-like shape.

Figure 11 shows the surface of a manganese substrate cover with a lead-based deposit after its immersion was prolonged during a month in a lead containing aqueous solution. Figure 12 shows the element EDS mapping indicating the chemical composition on surface of the lead-based deposit. The manganese covering predominantly the surface (top right). The mapping of Pb (bottom left) and O (bottom right) were more sensible to features on the surface topography. The top coverage presented an intricate needle formation. This kind of deposit covered the exposed surface of the substrate. In this case, the prolonged aging of the deposit permitted those formations as a middle point between those factors that allow the deposit and those that limited its extent.

These pieces were analyzed by X-ray diffraction, which identified a predominance of Pb5O8

 **sample 1 sample 2 sample 3 Pb5O8 PbO Pb Pb3O4**

**10 20 30 40 50 60 70 80 90**

**2**

Fig. 9. Difractogram of Mn samples with deposition from a 500 ppm lead solution. A) First

The kinetics of deposition of lead on manganese depends on the Pb ion concentration in solution. High concentration promotes a fast deposition and growing in a dendritic structure. The intermediate deposition rate combines semi-dendritic columns with grain nucleations. Slow deposition rates propitiate nucleations with spherical shaped grains.

Usually, lead deposition in the edges of a manganese substrate tended to generate the combined form of deposition. Fig 10 presents such projections from an edge of a manganese piece. It possessed a semi-dendritic column formed by grain nucleations. In this infrequent

Figure 11 shows the surface of a manganese substrate cover with a lead-based deposit after its immersion was prolonged during a month in a lead containing aqueous solution. Figure 12 shows the element EDS mapping indicating the chemical composition on surface of the lead-based deposit. The manganese covering predominantly the surface (top right). The mapping of Pb (bottom left) and O (bottom right) were more sensible to features on the surface topography. The top coverage presented an intricate needle formation. This kind of deposit covered the exposed surface of the substrate. In this case, the prolonged aging of the deposit permitted those formations as a middle point between those factors that allow the

Nevertheless, some cases were observed with different deposition configurations.

along with small signals indicating the presence of Pb and PbO (Fig. 9).

**0**

plate, B) second plate, C) third plate.

case, it was coronated by forms in a leaves-like shape.

deposit and those that limited its extent.

**1000**

**2000**

**3000**

**Intensity (a.u)**

**4000**

**5000**

**6000**

Fig. 10. Image from a lead deposition in an edge of a manganese plate with a semi-dendritic column constituted by grain nucleations and leaves-like forms on top.

There were some factors limiting the extent of growth, such as the reduction in Pb ions concentration in solution and electric contact with the substrate. Since there were such limitations, the initial lead concentration can be reduced by increasing the area, increasing the time of contact or by successive stages of deposition.

Novel Electroless Metal Deposition - Oxidation on Mn – MnxOy for Water Remediation 295

 Fig. 12. EDS mapping indicating the chemical composition on surface of the lead-based deposit shown in Fig. 11. The manganese covering predominantly the surface (top right),

The second step was the preparation of an aqueous solution with a silver content of 500 ppm. As in the previous case, one half of a manganese plate was polished and the other one

On this occasion, as soon as the piece came into contact with the solution, the metallic part was covered with a black homogeneous deposit. Meanwhile, in the other half of the piece that still had its oxide layer a broad white spot appeared. The Mn piece was covered with a deposit of gray moss-like colour in less than a minute, which turned dark after three minutes. Five minutes after initializing the test, it was obvious that at the edges of the piece the appearance of deposit was silvery and in the form of dendrites. Throughout the whole

In the case of water containing silver there were some features that differed to lead and other metals. The deposit's rate of formation is by far much faster, with a very long extent of growth, more dendritic and, hence, openly structured with small volumetric density. On the other hand, the only identified crystalline formation was metallic silver. There are two main causes for this behaviour, the standard electrode potential for silver and its electrical conductivity. The first one is related to a favourable ∆G for deposition. The second one allows the electrons transmission from the active reduction sites to the substrate. Also, under normal environmental conditions due to their electronegativity, silver patina is

which also contains Pb (bottom left) and O (bottom right).

left with manganese oxide.

surface, the piece was acquiring this colour.

formed by silver sulfide rather than silver oxides.

Fig. 11. SEM image of a manganese substrate covered with an intricate needle formation of a lead-based deposit after its immersion was prolonged during a month in a lead containing aqueous solution.

## **3.2 Electroless deposition from an aqueous solution containing Silver ions**

The first step was the preparation of an aqueous solution with a silver content of 100 ppm. One half of a manganese plate was polished (grit 400), on its superior flat area, exposing a portion of the bare metal. The other half of the plaque was left with its manganese oxide which was naturally formed in air. The fundamental assumption was that there were microdomains on the surface acting as anodes and cathodes. The purpose of this test was to discern the role that each area may play as predominantly anodic or cathodic. Both areas had oxide and metallic regions, but initializing the test in each area clearly predominated one of them.

The polished area began to be covered by a dark homogeneous layer immediately after immersion. The dendritic deposition became perceptible to the naked eye after four minutes of contact with the solution of Ag. The deposit spread to the entire surface and edges of the Mn piece after twenty minutes. The deposits initial colour was dark gray, but after seven hours, the deposit colour changed to a silvery metallic lustre. Posterior observations through a microscopy made it evident that those dendritic deposits began immediately after immersion of the Mn plate. That deposit was studied by X-ray diffraction. However, the corresponding difractogram only revealed the presence of metallic silver and it did not show any crystalline form of oxides.

Fig. 11. SEM image of a manganese substrate covered with an intricate needle formation of a lead-based deposit after its immersion was prolonged during a month in a lead containing

The first step was the preparation of an aqueous solution with a silver content of 100 ppm. One half of a manganese plate was polished (grit 400), on its superior flat area, exposing a portion of the bare metal. The other half of the plaque was left with its manganese oxide which was naturally formed in air. The fundamental assumption was that there were microdomains on the surface acting as anodes and cathodes. The purpose of this test was to discern the role that each area may play as predominantly anodic or cathodic. Both areas had oxide and metallic regions, but initializing the test in each area clearly predominated

The polished area began to be covered by a dark homogeneous layer immediately after immersion. The dendritic deposition became perceptible to the naked eye after four minutes of contact with the solution of Ag. The deposit spread to the entire surface and edges of the Mn piece after twenty minutes. The deposits initial colour was dark gray, but after seven hours, the deposit colour changed to a silvery metallic lustre. Posterior observations through a microscopy made it evident that those dendritic deposits began immediately after immersion of the Mn plate. That deposit was studied by X-ray diffraction. However, the corresponding difractogram only revealed the presence of metallic silver and it did not

**3.2 Electroless deposition from an aqueous solution containing Silver ions**

aqueous solution.

one of them.

show any crystalline form of oxides.

Fig. 12. EDS mapping indicating the chemical composition on surface of the lead-based deposit shown in Fig. 11. The manganese covering predominantly the surface (top right), which also contains Pb (bottom left) and O (bottom right).

The second step was the preparation of an aqueous solution with a silver content of 500 ppm. As in the previous case, one half of a manganese plate was polished and the other one left with manganese oxide.

On this occasion, as soon as the piece came into contact with the solution, the metallic part was covered with a black homogeneous deposit. Meanwhile, in the other half of the piece that still had its oxide layer a broad white spot appeared. The Mn piece was covered with a deposit of gray moss-like colour in less than a minute, which turned dark after three minutes. Five minutes after initializing the test, it was obvious that at the edges of the piece the appearance of deposit was silvery and in the form of dendrites. Throughout the whole surface, the piece was acquiring this colour.

In the case of water containing silver there were some features that differed to lead and other metals. The deposit's rate of formation is by far much faster, with a very long extent of growth, more dendritic and, hence, openly structured with small volumetric density. On the other hand, the only identified crystalline formation was metallic silver. There are two main causes for this behaviour, the standard electrode potential for silver and its electrical conductivity. The first one is related to a favourable ∆G for deposition. The second one allows the electrons transmission from the active reduction sites to the substrate. Also, under normal environmental conditions due to their electronegativity, silver patina is formed by silver sulfide rather than silver oxides.

Novel Electroless Metal Deposition - Oxidation on Mn – MnxOy for Water Remediation 297

covering the bottom of the container. Its size surpassed the original Mn piece, even reaching inches away from the substrate and was several millimeters thick. At some point, this layer reached its maximum extent but it is of low density with an algae-like formation and, with

Fig. 13 shows the sequence of images of silver growth using two manganese pieces. The dendrites on the border of the pieces grew faster. The white appearance was due to the formation of shiny silver needles (Fig 13C). The deposition ended when bubbles, formed underneath, breaking the electrical contact between the active reduction sites and the metallic substrate. In Fig. 13F, the black spots, over the silver growths of the right piece,

The third stage was directly associated with bubble formation, which in turn may depend on the thickness of the first layer. A first thick dendritic formation may subsequently promote a rapid bubble generation. On the other hand, a first thin dendritic formation fosters the growth of crystals of silver, which started as needle-like formations but then grow in dendritic shapes. Higher concentrations may cause a short first stage, which indeed may reduce the probability of bubble formation and a corresponding abrupt interruption of the deposition. The silver ions concentration in the solution plays an important role in the kinetics of forming deposits. High concentrations and overpotentials propitiate such

When considering the whole silver deposition process, the growth was in dendritic form, and there were different dendrite types in each stage. Upon removal of the deposition from the solution, there were two forms, an algae-like mass and long single silvery needles (some

Fig. 14. Another silver dendritic growth with needle-like formation. The black spots on top

As in the case of the previous section with lead, the dendritic growths were bigger at the borders of the Mn pieces. Also, exposing the deposits to air over the Mn piece leads to a manganese oxide coverage (Mn3O4). This not happened when the Mn piece was removed. In any circumstance, the silvery needles with single monocrystals appearance remained

time, it increased its density and stiffness.

were the apertures made by the bubbles ejection.

dendritic configurations (Herlach, 2004).

were holes left by the bubbles ejection.

millimeters long).

unchanged.

The process of silver deposit growth showed three stages. In the first, the deposit began with a dark appearance that later changed to clearer as dark gray. In the second, it continued generating an algae or moss-like structure consisting of dendritic formations. Subsequently, the silver crystals grew into a lustrous white metallic colour in the form of dendrites with long needle-shaped branches. Those formations were projected from the sponge-like formation with extensions of around seven millimeters.

Finally, the previous stages were covered by a dendritic growth with a dark and closely packed cauliflower-like formation. This formation was extended beyond the Mn piece

Fig. 13. Sequence of silver deposits growth on the system manganese-manganese oxide. The white appearance was a highly crystalline form of needle-dendritic silver. The dark appearance was dendritic silver.

The process of silver deposit growth showed three stages. In the first, the deposit began with a dark appearance that later changed to clearer as dark gray. In the second, it continued generating an algae or moss-like structure consisting of dendritic formations. Subsequently, the silver crystals grew into a lustrous white metallic colour in the form of dendrites with long needle-shaped branches. Those formations were projected from the

Finally, the previous stages were covered by a dendritic growth with a dark and closely packed cauliflower-like formation. This formation was extended beyond the Mn piece

**C)**

**A)**

**B)**

**D)**

**F)**

Fig. 13. Sequence of silver deposits growth on the system manganese-manganese oxide. The

white appearance was a highly crystalline form of needle-dendritic silver. The dark

**E)**

appearance was dendritic silver.

sponge-like formation with extensions of around seven millimeters.

covering the bottom of the container. Its size surpassed the original Mn piece, even reaching inches away from the substrate and was several millimeters thick. At some point, this layer reached its maximum extent but it is of low density with an algae-like formation and, with time, it increased its density and stiffness.

Fig. 13 shows the sequence of images of silver growth using two manganese pieces. The dendrites on the border of the pieces grew faster. The white appearance was due to the formation of shiny silver needles (Fig 13C). The deposition ended when bubbles, formed underneath, breaking the electrical contact between the active reduction sites and the metallic substrate. In Fig. 13F, the black spots, over the silver growths of the right piece, were the apertures made by the bubbles ejection.

The third stage was directly associated with bubble formation, which in turn may depend on the thickness of the first layer. A first thick dendritic formation may subsequently promote a rapid bubble generation. On the other hand, a first thin dendritic formation fosters the growth of crystals of silver, which started as needle-like formations but then grow in dendritic shapes. Higher concentrations may cause a short first stage, which indeed may reduce the probability of bubble formation and a corresponding abrupt interruption of the deposition. The silver ions concentration in the solution plays an important role in the kinetics of forming deposits. High concentrations and overpotentials propitiate such dendritic configurations (Herlach, 2004).

When considering the whole silver deposition process, the growth was in dendritic form, and there were different dendrite types in each stage. Upon removal of the deposition from the solution, there were two forms, an algae-like mass and long single silvery needles (some millimeters long).

Fig. 14. Another silver dendritic growth with needle-like formation. The black spots on top were holes left by the bubbles ejection.

As in the case of the previous section with lead, the dendritic growths were bigger at the borders of the Mn pieces. Also, exposing the deposits to air over the Mn piece leads to a manganese oxide coverage (Mn3O4). This not happened when the Mn piece was removed. In any circumstance, the silvery needles with single monocrystals appearance remained unchanged.

Novel Electroless Metal Deposition - Oxidation on Mn – MnxOy for Water Remediation 299

The electroless deposition process using manganese-manganese oxide usually stops by removing the metallic substrate. As mentioned previously, and similarly to the case of lead, by the exposure of deposits to air that remained on the substrate got a Mn3O4 coverage (Fig. 16 – inserted picture). Fig. 16 shows the diffractograms of a sample with and without the Mn substrate. The coverage of the deposits by a manganese oxide changes the shiny silver finish to a brownish colour, which happened in a matter of minutes. The reason for this change was not associated to a reaction of the silver with environmental sulfur, which usually

On the other hand, if the silver deposit lost contact with the manganese substrate, a manganese oxide layer was not formed. This behaviour seems related to a Mn migration to the outer surface, which was interrupted. These are explained by redox reactions that require the transfer of electrons between the surface where oxidation takes place and the cathode, where deposits grew. Figures 13 and 14 show the deposited material corresponding to the three stages of the deposit, where highlighted the prominent needles and the foamy material generated in the third stage. A simply water cleaning allowed appreciate the state of the

From those tests, we can infer that Mn metal parts with its oxide may result with the

In the study of a manganese-manganese oxide surface, immersed into an aluminum ion solution, a distinctive dense deposit, nearly continuous and homogeneous, was obtained. In this case, the deposit did not present dendritic formations and a high number of bubbles were formed on the surface. The proposed explanation refers to the potential difference between the areas acting as anodes and cathodes, which had favourable results the potential

The kinetic was fast using a solution with 500 ppm of aluminum. It was possible to observe a deposit and bubbles few seconds after immersion. However, the deposition rate decreased faster possibly attributed to two facts: a) the bubbles covering the surface (each measuring up to 2mm in diameter) and b) a thick and viscous layer of hydroxides forming above the surface. In order to permit deposited layer growth, some physical methods were used such as: a) magnetic stirring, b) ultrasound, or c) direct friction with other surface. Those methods were effective to displace both, the bubbles and the hydroxides. This procedure was

The deposited layer became perceptible through colour changes on the surface. The substrate acquired a lustrous golden metallic tonality, which appeared homogeneously and was perceptive to the naked eye and cameras without amplification. This effect was attributed to the interference of the light reflecting on the surface due to the thickness of the layer and its refraction index. Subsequently, as the layer became thicker, the surface took a lustrous metallic

The deposit from an aluminum containing solution did not show dependence on the initial surface condition, regardless of starting with a polished or oxide surface. Also, it differed from silver and lead susceptibility to a cover of manganese oxide. The final cleaned surface

potential for water remediation as well as for recovering some precious metals.

water electrolysis forming hydrogen and oxygen on the substrate.

contrary to the requirements in the previous case for silver deposition.

remained unchanged when exposed to air for long periods.

**3.3 Electroless deposition from an aqueous solution containing Aluminum ions**

constitutes the dark patina (Ag2S).

white tone.

manganese surface with few firmly attached material.

Figure 15 shows the status achieved by the growth of silver deposit on manganese when it is allowed to continue for several weeks without external disturbance. The same manganese piece, with a clean surface, can restart the process even in the same solution whether starting with 100 ppm or 1000 ppm. The latter contains enough silver ions to repeat the procedure several times. In the case of those silver growths, the substrate easily lost contact with the depositions. An easy cleaning of the surface made the Mn piece available for a new deposition.

Fig. 15. Two silver deposits, after a month, on Mn pieces located at the center of the formation.

Fig. 16. Diffractograms of the bare silver deposit and on the Mn piece.

Figure 15 shows the status achieved by the growth of silver deposit on manganese when it is allowed to continue for several weeks without external disturbance. The same manganese piece, with a clean surface, can restart the process even in the same solution whether starting with 100 ppm or 1000 ppm. The latter contains enough silver ions to repeat the procedure several times. In the case of those silver growths, the substrate easily lost contact with the depositions. An easy cleaning of the surface made the Mn piece available for a new

 **susbtrate-deposit in air**

 **deposit without substrate**

 **Ag Mn3O4**

**20 30 40 50 60 70 80 90**

**2**

Fig. 16. Diffractograms of the bare silver deposit and on the Mn piece.

Fig. 15. Two silver deposits, after a month, on Mn pieces located at the center of the

deposition.

formation.

**0**

**500**

**1000**

**1500**

**Intensity (u.a.)**

**2000**

**2500**

**3000**

The electroless deposition process using manganese-manganese oxide usually stops by removing the metallic substrate. As mentioned previously, and similarly to the case of lead, by the exposure of deposits to air that remained on the substrate got a Mn3O4 coverage (Fig. 16 – inserted picture). Fig. 16 shows the diffractograms of a sample with and without the Mn substrate. The coverage of the deposits by a manganese oxide changes the shiny silver finish to a brownish colour, which happened in a matter of minutes. The reason for this change was not associated to a reaction of the silver with environmental sulfur, which usually constitutes the dark patina (Ag2S).

On the other hand, if the silver deposit lost contact with the manganese substrate, a manganese oxide layer was not formed. This behaviour seems related to a Mn migration to the outer surface, which was interrupted. These are explained by redox reactions that require the transfer of electrons between the surface where oxidation takes place and the cathode, where deposits grew. Figures 13 and 14 show the deposited material corresponding to the three stages of the deposit, where highlighted the prominent needles and the foamy material generated in the third stage. A simply water cleaning allowed appreciate the state of the manganese surface with few firmly attached material.

From those tests, we can infer that Mn metal parts with its oxide may result with the potential for water remediation as well as for recovering some precious metals.

## **3.3 Electroless deposition from an aqueous solution containing Aluminum ions**

In the study of a manganese-manganese oxide surface, immersed into an aluminum ion solution, a distinctive dense deposit, nearly continuous and homogeneous, was obtained. In this case, the deposit did not present dendritic formations and a high number of bubbles were formed on the surface. The proposed explanation refers to the potential difference between the areas acting as anodes and cathodes, which had favourable results the potential water electrolysis forming hydrogen and oxygen on the substrate.

The kinetic was fast using a solution with 500 ppm of aluminum. It was possible to observe a deposit and bubbles few seconds after immersion. However, the deposition rate decreased faster possibly attributed to two facts: a) the bubbles covering the surface (each measuring up to 2mm in diameter) and b) a thick and viscous layer of hydroxides forming above the surface. In order to permit deposited layer growth, some physical methods were used such as: a) magnetic stirring, b) ultrasound, or c) direct friction with other surface. Those methods were effective to displace both, the bubbles and the hydroxides. This procedure was contrary to the requirements in the previous case for silver deposition.

The deposited layer became perceptible through colour changes on the surface. The substrate acquired a lustrous golden metallic tonality, which appeared homogeneously and was perceptive to the naked eye and cameras without amplification. This effect was attributed to the interference of the light reflecting on the surface due to the thickness of the layer and its refraction index. Subsequently, as the layer became thicker, the surface took a lustrous metallic white tone.

The deposit from an aluminum containing solution did not show dependence on the initial surface condition, regardless of starting with a polished or oxide surface. Also, it differed from silver and lead susceptibility to a cover of manganese oxide. The final cleaned surface remained unchanged when exposed to air for long periods.

Novel Electroless Metal Deposition - Oxidation on Mn – MnxOy for Water Remediation 301

The x-ray diffraction analysis of deposits, from an aluminum containing aqueous solution, did not allow the identification of the metallic aluminum phase. Fig. 17 shows a diffractogram that identifies only the manganese metallic substrate and, in some cases as this one, Mn3O4. Presumably, the X-ray diffraction was not able to identify the aluminum

The Fig. 18 shows the deposition from a solution containing aluminum on manganese substrate at different time during the process. It is possible to observe the bubbles forming

Fig. 19 shows a SEM micrograph of the Aluminum deposit using 1000X (the scale bar indicate 25m). The first notorious characteristic of this kind of deposits is a flat surface devoid of dendritic growths. An EDS microanalysis shows Mn, O and Al on surface. The signals for Aluminum and oxygen were very weak. The semi-quantitative calculus was: Oxygen 1.71wt% (5.6 atom%), Aluminium 0.42 (0.82 atom%) and Manganese 97.87 wt% (93.58 atom%). This can be attribute to a thin layer of Aluminum deposit, as in the case of the difractogram. The composition distribution maps on surface corresponding to Al, O, and

Mn, respectively. There was a small distribution of Aluminum detected on surface.

Fig. 19. SEM micrograph of the Aluminum deposit using 1000X (the scale bar indicate 25m). Also, EDS microanalysis shows Mn, O and Al on surface. In the second line, the composition distribution maps on surface corresponding to Al, O, and Mn, respectively.

The Figure 20a shows the absorbance and reflectance spectra for a deposit from an aluminum solution on a manganese-manganese oxide substrate. The spectrum of the substrate is presented in order to compare the effect of the aluminum deposit on the absorbance and

due to the small thickness of the layer.

on the substrate with a metallic deposit appearance.

Fig. 17. Difractogram of aluminum deposit on manganese substrate.

Fig. 18. Aluminum deposits on manganese at different times in the process. The white metallic finishing remained unchanged with exposition to air.

 **Mn3O4 Mn**

 **Mn - Al lustrous**

 **Mn - Al golden**

**20 30 40 50 60 70 80 90**

**2**

Fig. 18. Aluminum deposits on manganese at different times in the process. The white

metallic finishing remained unchanged with exposition to air.

Fig. 17. Difractogram of aluminum deposit on manganese substrate.

**0**

**500**

**1000**

**1500**

**Intensity (u.a.)**

**2000**

**2500**

**3000**

The x-ray diffraction analysis of deposits, from an aluminum containing aqueous solution, did not allow the identification of the metallic aluminum phase. Fig. 17 shows a diffractogram that identifies only the manganese metallic substrate and, in some cases as this one, Mn3O4. Presumably, the X-ray diffraction was not able to identify the aluminum due to the small thickness of the layer.

The Fig. 18 shows the deposition from a solution containing aluminum on manganese substrate at different time during the process. It is possible to observe the bubbles forming on the substrate with a metallic deposit appearance.

Fig. 19 shows a SEM micrograph of the Aluminum deposit using 1000X (the scale bar indicate 25m). The first notorious characteristic of this kind of deposits is a flat surface devoid of dendritic growths. An EDS microanalysis shows Mn, O and Al on surface. The signals for Aluminum and oxygen were very weak. The semi-quantitative calculus was: Oxygen 1.71wt% (5.6 atom%), Aluminium 0.42 (0.82 atom%) and Manganese 97.87 wt% (93.58 atom%). This can be attribute to a thin layer of Aluminum deposit, as in the case of the difractogram. The composition distribution maps on surface corresponding to Al, O, and Mn, respectively. There was a small distribution of Aluminum detected on surface.

Fig. 19. SEM micrograph of the Aluminum deposit using 1000X (the scale bar indicate 25m). Also, EDS microanalysis shows Mn, O and Al on surface. In the second line, the composition distribution maps on surface corresponding to Al, O, and Mn, respectively.

The Figure 20a shows the absorbance and reflectance spectra for a deposit from an aluminum solution on a manganese-manganese oxide substrate. The spectrum of the substrate is presented in order to compare the effect of the aluminum deposit on the absorbance and

Novel Electroless Metal Deposition - Oxidation on Mn – MnxOy for Water Remediation 303

Using Figure 20 and Table 3, it is possible to evaluate the obtained deposit finishing. It was possible to observe a bigger difference comparing the deposit and a manganese-manganese oxide substrate, which had a dark brown color. On the other hand, the bright deposit

The aluminum deposits on manganese- manganese oxide have a high reflectance. The

The images in Figure 21 were acquired by a video camera integrated to the profilometry apparatus, in the magnification range up to 70. A white LED was used as an illumination

**CIE L\*** 99.5 98.4 76.2 44 97 **CIE a\*** -0.5 3 5.5 9.5 4.5 **CIE b\*** -0.4 18.1 22.9 20.6 17.2 **dominant (nm)** 583.0 580.6 589.3 595.0 589.2 **purity** 0.014 0.231 0.352 0.478 0.226

**Golden deposit**

**Dark brawn Mn3O4**

**A) B)**

**C) D)**

**Mn polished**

obtained was brighter than the deposit on the polished manganese.

**Deposit**

Table 3. Colour parameters for the five samples represented in Figure 16B.

Fig. 21. Images of aluminum deposit on manganese-manganese oxide. A) and B) corresponds to a deposit on mangense-manganese oxide as susbtrate at 70 and 700x, respectively; C) and D) corresponds to a deposit on manganese with an ititially polished

surface at 70 and 700x, respectively.

profilometry analyses allowed quantify the surface roughness.

 **Aluminum Al bright**

reflectance. In black, associated with the left **y** axis, the reflectance is shown. Correspondingly, associated with the right **y** axis, the absorbance is shown. The band presented in the reflectance spectrum for the bright aluminum deposit corresponds to the lamp used for illumination. Despite having used of an integration sphere in contact with the sample surface, the sample maintains a difference in reflectance in relationship to the reference that causes a lamp spectrum replication. Additionally, in Figure 20b, it is possible to quantify the surface appearance with the chromaticity diagrams.