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<sup>\*</sup> Corresponding Author

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[19] Marple VA, Rubow KL, Behm, SM (1991) A microorifice uniform deposit impactor (MOUDI): Description, calibration and use. Aerosol Science and Technology 14: 434-

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[22] Burtscher H (1992) Measurement and characteristics of combustion aerosols with special consideration of photoelectric charging and charging by flame ions. Journal of

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[24] Keshtkar H, Ashbaugh LL (2007) Size distribution of polycyclic aromatic hydrocarbon particulate emission factors from agricultural burning. Atmospheric Environment 41:

[25] Phuleria HC, Sheesley RJ, Schauer JJ, Fine PM, Sioutas C (2007) Roadside measurements of size-segregated particulate organic compounds near gasoline and diesel-dominated

[26] Kamens RM, Guo Z, Fulcher JN, Bell DA (1988) Influence of humidity, sunlight, and temperature on the daytime decay of polycyclic aromatic hydrocarbons on atmospheric

[27] Lungren DA, Paulus HJ (1975) The mass distribution of large atmospheric particles.

[28] Pierce RC, Katz M (1975) Dependency of polynuclear aromatic hydrocarbon content on size distribution of atmospheric aerosols. Environmental Science and Technology 9:

[29] Venkataraman C, Lyons JM, Friendlander SK (1994) Size distributions of polycyclic aromatic hydrocarbons and elemental carbon. 1. Sampling, measurement methods, and

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[31] Wiest F, Fiorentina HD (1975) Suggestions for a realistic definition of an air quality index relative to hydrocareonaceous matter associated with airborne particles.

[32] Garivait H, Polprasert C, Yoshizumi K, Reutergardh LB (1999) Airborne polycyclic aromatic hydrocarbons (PAH) in Bangkok urban air I. Characterization and

[33] Miguel AH, Kirchstetter TW, Harley RA (1998) On-road emissions of particulate polycyclic aromatic hydrocarbons and black carbon from gasoline and diesel vehicles.

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[6] Panther B, Hooper M, Limpaseni W, Hooper B (1996) Polycyclic aromatic hydrocarbon as environmental contaminants: Some results from Bangkok. The third international symposium of ETERNET-APR: Conservation of the hydrospheric environment.

[7] Venkataraman C, Thomas S, Kulkarni P (1999) Size distributions of polycylic aromatic hydrocarbons – Gas/particle partitioning to urban aerosols. Journal of Aerosol Science

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[9] European Environment Agency (2004) Air pollution in Europe 1990-2000. Topic report. [10] Panther B, Hooper MA, Tapper NJ (1999) A comparison of air particulate matter and associated polycyclic aromatic hydrocarbons in some tropical and temperate urban

[11] Garivait H, Polprasert C, Yoshizumi K, Reutergardh LB (2001) Airborne polycyclic aromatic hydrocarbons (PAH) in Bangkok urban air: Part II. Level and distribution.

[12] Chetwittayachan T, Shimazaki D, Yamamoto K (2002) A comparison of temporal variation of particle-bound polycyclic aromatic hydrocarbons (pPAHs) concentration in different urban environments: Tokyo, Japan, and Bangkok, Thailand. Atmospheric

[13] Boonyatumanond R, Murakami M, Wattayakorn G, Togo A, Takada H (2007) Sources of polycyclic aromatic hydrocarbons (PAHs) in street dust in a tropical Asian megacity,

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**Chapter 3**

© 2012 Srivastava et al., licensee InTech. This is an open access chapter distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

© 2012 Srivastava et al., licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

**Aerosol Characteristics**

**over the Indo-Gangetic Basin:**

A.K. Srivastava, Sagnik Dey and S.N. Tripathi

Additional information is available at the end of the chapter

understanding of their role in the Earth's radiation budget.

http://dx.doi.org/10.5772/48314

Indo-Gangetic Basin (IGB) region.

**1. Introduction**

**Implications to Regional Climate**

The climatic and environmental effects of atmospheric aerosols are the critical issues in global science community because aerosols, derived from variety of natural and man-made (or anthropogenic) emission sources, are well known to affect the air quality, human health and radiation budget [1]. While comparing the third and fourth assessment report of the Intergovernmental Panel on Climate Change (IPCC) as shown in Figure 1, the level of scientific understanding for the role of green house gases (GHGs) in projected temperature changes is higher relative to that of aerosols [2,3]. This is because of inadequate measurements of aerosols, their microphysical and optical properties and poor

Aerosols influence the Earth's climate directly by scattering and absorbing the solar and terrestrial radiations and indirectly by modifying the cloud macro- and micro-physical properties [4]. The direct and indirect effects of atmospheric aerosols are shown in the schematics in Figure 2a and 2b, respectively. Varity of aerosols present in the atmosphere from natural and anthropogenic emission sources can influence our Earth's atmosphere directly by absorbing/scattering the incoming solar radiations (Figure 2a). It can also absorb and re-radiated the outgoing radiations emitted from the Earth. On the other hand, aerosols indirectly affect the climate system by acting as cloud condensation nuclei (CCN) and ice nuclei (IN) and thereby modify the cloud properties and their impacts depending upon the environment like polluted or un-polluted regions (Figure 2b). In a recent study, reported in [5], they have investigated the indirect aerosol effect during the successive contrasting monsoon seasons over Indian subcontinent. However, a different study reported in [6] was carried out to investigate the intensity and the spatial extent of the indirect effect over the

[35] Hoshiko T, Nakajima F, Prueksasit T, Yamamoto K (2012): 4. Health risk of exposure to vehicular emissions in wind-stagnant street canyons, In: "Ventilating cities -Air-flow criteria for healthy and comfortable urban living-" (Eds.: Kato S and Hiyama K), pp.59- 95, Springer


Clay Hybrid Membranes in Wastewater Treatment

*Tanushree Choudhury*

## **Abstract**

Most of NF membranes which are developed recently are composite membranes, whose support layer is covered with an active layer. Among different ceramic support materials that are currently used as support layer, α-alumina supports are integral part of the membrane which is made of artificial materials like alumina and thus adds to the high price of the membrane. This draws our attention in making low cost support material of natural clay which aims to be an excellent membrane support as it possesses high mechanical strength, high permeability, narrow pore size distribution and low manufacturing cost. Titania as active layer for ceramic membrane is preferred over Al2O3 membranes. One of the problems encountered when photocatalysts are immobilized on support is the detachment of the micro particles from the support for high flow rates of liquid effluent. This can be overcome by using Montmorillonite clay as support material as it is a great binder.

**Keywords:** pillared clay, Titania, photocatalysis, dye removal, wastewater treatment, regeneration

## **1. Introduction**

Wastewater encompasses potential contaminants from toxic wastes to natural organic matter and minerals that augurs for a definite treatment and reuse method so as to make water available for the ever increasing population. Some of the typical methods include adsorption, electrocoagulation, sedimentation, chemical oxidation and biological digestion. Each of these processes has its own advantages and disadvantages. Thus the search is on to find effective nanomaterials/technology for the remediation/purification of contaminated water [1–9]. Though titania is an important solid acid photocatalyst, the use of titania pillared clay membranes for wastewater treatment finds less mention in the literature. As a consequence, catalyst screening and design are imperative for efficient wastewater treatment [10]. The integration between catalysis and membrane is a very relevant area to mention for the development of a sustainable novel water treatment technology [11].

Titania as an active layer for ceramic membrane is preferred to Al2O3 membranes because of the following reasons such as (a) no neurological toxicity (b) high chemical stability in organic solvents and caustic soda (c) high material purity (d) small crystallite size (e) high surface area and porosity (f) narrow pore size distribution (g) low cost of crystalline anatase form and (h) extreme photostability and (i) extremely amphoteric character [12–14]. Moreover if the TiO2 material (active layer) is immobilized onto porous support (clay), the photocatalytic membrane

reactor renders immense advantage due to the multiple functions ranging from decomposition of organic pollutants to self antibiofouling action [15].

## **2. National and international status of the work**

Membrane separation processes have attracted the attention of researchers of late due to its manifold advantages such as cost effectiveness, ease in material recovery, and environmental impact reduction as compared to other separation techniques [16]. The performance of such a system can be further enhanced by the incorporation of nanomaterials and nanotechnology. Composite materials of polymers and ceramics can be used to synthesize membranes with increased permeability, selectivity, and resistance to fouling. Nanofiltration membranes are thus finding applications in wastewater treatment processes too.

Nanofiltration membranes are widely classified into i) organic polymeric membranes and ii) inorganic polymeric membranes. Polymers such as polysulfone, cellulose acetate, polyamide, etc. are commercially used to make polymeric nanofiltration membranes. Conventionally cellulose membranes are used in ultrafiltration and reverse osmosis membrane process. The performance of cellulose acetate membranes can be improved by blending it with appropriate polymers in view of the fact that polymers in view of the fact polymer blends have provided an efficient way to fulfill new requirements for material property. Cellulose acetate/sulfonated Polyethyl ether ketone blend ultrafiltration membranes have been used for separating Cr (III) ions [17].

Phenol is a potential human carcinogen and is of considerable health concern, even at low concentration. A. Bodalo et al. studied the behavior of different nanofiltartion membranes of polyamide thin film composite membranes to remove phenol in wastewater in different operating conditions [18]. It has been observed that the concentration of As in drinking water can be considerable reduced by nanofiltration and reverse osmosis techniques. Literature finds mention of these methods in abundance, but they are not cost effective.

Membrane based separation separation techniques have been widely employed in different countries for treating a wide variety of industrial effluents. The effectiveness of nanofiltration membrane processes in water and wastewater treatment has now become one of the most reliable standard techniques to obtain good drinking water. Harisha et al. investigated the feasibility of arsenic removal from simulated arsenic contaminated water by an indigenously built nanofiltration plant with commercial thin film composite membrane of polyamide [19]. The potential use of nano filtration polyamide membrane for removing Co and Pb ions from wastewater was investigated by Saliha et al. [20]. Polyaniline because of its high degree of solvent resistance is employed to be used as an ultrafiltration membrane by Jinwen Wang et al. [21].

Cr, a typical example of class of pollutant, is generated in aircraft maintenance, electroplating, dye, textile and leather industries. Cr is highly toxic and traditional techniques for Cr removal include adsorption, precipitation, and extraction using aliquat 336 solvents. The membranes used for Cr separation are mostly organic polymer (for example cellulose acetate, polyaniline, etc). The major drawback is that the chemical stability of conventional polymeric membranes is limited with respect to corrosive media like strong acids and organic solvents. Therefore research focuses on ceramic nanofiltration membranes, though only few studies exist on use of ceramic membranes for Cr removal. A novel separation scheme for the removal of As and Cr from water based on adsorption and ultrafiltration processes using porous ceramic membranes has been proposed by A. E. Pagana et al. [22]. In recent years, great advances were made regarding the development of non-silicate ceramic

#### *Clay Hybrid Membranes in Wastewater Treatment DOI: http://dx.doi.org/10.5772/intechopen.99075*

membranes as these membranes have a high selectivity against small macro molecules, drugs, hormones and antibodies. ZrO2/TiO2 microporous ceramic membranes were developed by U. Aust et al. for gas separation applications [23].

Ceramic nanofiltration membranes can be used to separate solvents from multivalent ions and small organic molecules. Promising membrane materials for separation of highly charged molecules are Nafion, Nafion/silica hybrid membranes, supported γ-alumina membranes and mesostructured silica layers supported on porous α-alumina. Sandwich type ceramic composite membranes with NF characteristics became available having pore size in the range 0.5–2 nm which can be used efficiently for large ion recovery. Chowdhury. S et al. studied the transport and retention properties of potentially suitable membranes for recovery of highly charged large polyoxomethylate (POM) catalyst molecules from aqueous solution [24].

Wastewater in petrochemical industry is currently treated by activated sludge process with pretreatment of oil/water separation. Tightening efficient regulation and increasing need for reuse of treated water have generated interest in the treatment of petrochemical wastewater by membrane bio-reactor process [25]. Ceramic membranes under micro, ultra and nanofiltration conditions have proven to be economically attractive for the removal of oil from oil produced water [26]. Of all ceramic NF membranes in literature, sol–gel derived γ-Al2O3 membranes have emerged as perhaps the most intensively studied inorganic membrane system, because of their unique surface charge characteristics. γ-Al2O3 membranes may acquire either a positive or negative charge due to their amphoteric behavior of their surface sites (-OH groups). This allows controlling the sign and charge of the membrane through pH of the solution [27]. Majority of the reported γ-Al2O3 membranes were derived from the expensive Al alkoxides that makes them very costly. Hence, research should be focused on the development of an alternative cost effective membrane material.

Clay minerals find potential application as a choice for membrane support material due to its low cost, environmentally benign, good rheological, barrier, adsorption, and binding properties. Though not much work has been done in this regard, development of clay based membrane material would usher in a new technological advancement in the field of Clay Science.

Utilization of clay minerals is now of growing interest. Unmodified and modified UF zeolite clay composite membranes (pore size of the order 10–30 nm) have been used for the separation of Cr by A. Shukla and A. Kumar [28]. Low cost γ-Al2O3 composite membrane on clay support has been prepared by Abhijit et.al for the separation of electrolytes from its aqueous solutions [29]. Removal of phenol and o-cresol from water by a combined process of clay adsorption and ultrafiltration was investigated by Liu. S. Hsia et al. [30]. Low cost γ-Al2O3 clay composite membrane on a clay support has been prepared using local available cheap clays by Abhijit et al. for the separation of Bovine Serum albumin [31].

However, membrane fouling is still a critical problem of NF plants, which results in flux decline with operating time. TiO2 has received much attention because of its important role in various applications such as photocatalysts, oxygen sensors, antimicrobial coatings, pigments etc. Among them, the photocatalytic properties to decompose organic compounds can be used in filtration membranes which possibly overcome fouling phenomenon [32]. Zhang. H et al. prepared TiO2/Al2O3 composite membranes with photocatalytic ability by sol–gel technique which has the multifunction of separation and photocatalysis simultaneously [33].

Going by the literature, there are many reports about the preparation of TiO2 composite membranes, especially using Al2O3 as support, but work needs to be done using clay as support material. Development of such low cost membranes shall offer to remove heavy metal ions from industrial wastewater and thus provide a sustainable solution.

## **2.1 Methods of preparation**

## *2.1.1 Preparation of titania pillared clay membranes*

Scientific description of the process **Figure 1**:

Preparation of asymmetric membranes: The development of such a configuration includes shaping of an appropriate support material and formation of mesoporous interlayers with a cut off value less than 1000 Da.

Preparation of flat disk support: Montmorillonite (Mt) was fabricated into flat disks of 25 mm diameter and 2 mm thickness, and was sintered at 600°C in a temperature controlled muffle furnace with a heating and cooling rate of 2°C/min with a hold time of 30 minutes. Mechanical hardness of such membranes was analyzed using Micro vickor, Shimadzu, Model No HMVG20S (load range of 10 g to 2 kg) in Mechanical Workshop in VIT Chennai. It was found to be 26.4 Hv.

Preparation of interlayer Titania sol by colloidal sol–gel process: The precursor for the colloidal sol–gel process was Ti (IV) isopropoxide, common titanium based organometallic compound, purchased from Avra chemicals, India, and was

#### **Figure 1.**

*The flat disk TiPILC membranes prepared at pH 2 and pH 3.5 and sintered at 300°C can be used for filtration of organic contaminants, over a wide range of pH (1–11), with a MW less than 1000 Da. The direct beneficiaries include textile industries (to remove coloring agents), food and pharmaceutical industries (small organic molecules), and wastewater recycling.*

#### *Clay Hybrid Membranes in Wastewater Treatment DOI: http://dx.doi.org/10.5772/intechopen.99075*

hydrolysed by adding excess water. The sol was then stirred at room temperature for 3 hrs after which it was peptized by the addition of glacial acetic acid (99%, Sigma Aldrich, USA) to attain pH 2 and pH 3.5 respectively.

Preparation of interlayer binary (Titania and clay) sol: 0.1 g of Mt. (Montmorillonite K10 with CEC of 80–100 meq/g, Himedia) was dispersed in 10 mL deionized water and was kept for stirring for 3 hrs. 0.1 wt% of cetyl trimethyl ammonium bromide (CTAB, Himedia) solution was added to the clay sol as an organic modifier. The resulting clay sol was then added dropwise to titania sol prepared at pH 2 and pH 3.5 respectively and was stirred overnight for complete intercalation of Ti4+ ions into the interlayer spaces of Mt. [34].

Preparation of TiPILC membranes: The interlayer sols thus prepared were immobilized on the flat disk supports by a dip coater with a withdrawal rate of 25 mm/sec. 5 wt% of binder carboxymethyl cellulose (CMC, Avra chemicals, India) was added to the sol as pore directing agent. After uniform coating, the membranes were dried at room temperature and then in air oven at 40°C for few hours. They were then sintered in programmable temperature controlled muffle furnace at 300°C, 500°C, 600°C, which was ramped at a heating/cooling rate of 2°C/min and was kept for hold time of 1 hour. The excess drained from supports were poured onto petri dishes, dried in oven and sintered at same temperatures as above for characterization by Fourier Transform-Infra Red Spectrocopy (FT-IR), X-Ray Diffraction (XRD), Brunnauer Emmett Teller specific surface area (BET), Zeta Potential analysis and Scanning Electron Microscope (SEM).

Number of samples prepared: 24 (12 supported membranes and 12 unsupported ones).

Nomenclature (Supported Membranes).

S1, S6, S10 - Membranes with TiO2 interlayer at pH 2 sintered at 300°C, 500°C, and 600°C.

S2, S5, S11 - Membranes with binary interlayer of TiO2 and clay at pH 2 sintered at 300°C, 500°C, and 600°C respectively.

S3, S4, S12 - Membranes with TiO2 interlayer at pH 3.5 sintered at 300°C, 500°C, and 600°C respectively.

S8, S9, S13 - Membranes with binary interlayer of TiO2 and clay at pH 3.5 sintered at 300°C, 500°C, and 600°C respectively.

Unsupported Membranes.

PS1, PS6, PS10 - Powder membrane materials with TiO2 interlayer at pH 2 sintered at 300°C, 500°C, and 600°C respectively.

PS2, PS5, PS11 - Powder membrane materials with TiO2 and clay binary interlayer at pH 2 sintered at 300°C, 500°C, and 600°C respectively.

PS3, PS4, PS12 - Powder membrane materials with TiO2 interlayer at pH 3.5 sintered at 300°C, 500°C, and 600°C respectively.

PS8, PS9, PS13 - Powder membrane materials with binary interlayer of TiO2 and clay at pH 3.5 sintered at 300°C, 500°C, and 600°C respectively.

#### *2.1.2 Instrumentation*

XRD was done using Bruker AXS D8 advance powder diffractometer equipped with Cu-Kα generator (λ= 1.5405600 A°). The generator tension was 35 kV. IR was done on Thermo Nicolet Avatar 370 in the spectral range of 4000–400 cm−1. Zeta potential was measured using Horiba Scientific Nano Partica Nano Particle Analyzer SZ-100. SEM of cross section of membranes was taken using High Resolution Hitachi S-4800 Scanning Electron Microscope. BET surface area of samples was characterized by Nova 1000 Quantachrome Instrument by N2 sorption at 77.35 K. The concentration of the permeate samples from filtration experiment

was measured using Thermoscientific UV–Vis Spectrophotometer in the visible range of 200–800 nm. The membrane filtration unit consisted of a cylindrical chamber with a membrane adapter connected to a pressure gauge of 2 Pa and a peristaltic pump Model No RH-P120 VS [34].

**Figure 2.** *(a) And (b) FT-IR spectra of unsupported membrane materials at pH 2 and pH 3.5 respectively.*

**Figure 3.** *(a) And (b) XRD diffractograms of unsupported membrane materials at pH 2 and pH 3.5 respectively.*

**Figure 4.**

*(a) And (b) zeta potential values of unsupported membrane materials prepared at a) pH 2 and b) pH 3.5 respectively.*

*Clay Hybrid Membranes in Wastewater Treatment DOI: http://dx.doi.org/10.5772/intechopen.99075*

*2.1.3 Characterization*

FT-IR (**Figure 2**) XRD (**Figure 3**) Zeta potential analysis (**Figure 4**) Pore size distribution (**Figure 5**) SEM (**Figures 6** and **7**) **Figures 2**–**7**

**Figure 5.**

*(a) And (b) pore size distribution curves of TiO2 interlayer and binary interlayer of TiO2 and clay respectively.*

#### **Figure 6.**

*(a) To (d) SEM of membranes S1, S2, S3, and S8 sintered at 300°C respectively. (e) To (h) SEM of membranes S6, S5, S4, and S9 sintered at 500°C respectively. (i) To (l) SEM of membranes S10, S11, S12, and S13 sintered at 600°C respectively.*

**Figure 7.** *SEM of asymmetric membrane showing the interlayer of thickness 5.2* μ*m on the support.*

## **3. Result and discussion**

Temperature affects the pore size distribution pattern as can be clearly seen from **Figure 5(a)** and **(b)**. It can be clearly observed that a narrow pore size distribution is observed at a sintering temperature 300°C for membrane materials with interlayer of TiO2 and binary interlayer of TiO2 and clay. Addition of clay to TiO2 alters its pore size distribution facilitating removal of organic dye molecules. XRD diffractograms show the presence of single phase of anatase TiO2 at temperature 300°C. As the temperature increases to 500°C and 600°C, the anatase phase is the major crystal type which is very efficient for photocatalytic degradation of organic pollutants. FT-IR spectra show the presence of strong bands at 3399.03 cm−1 and 1621.55 cm−1 due to bonded –OH stretching and bending vibrations of water, thus indicating the formation of anatase phase. Characteristic bands at 1049.31 cm−1 and 523.68 cm−1 which correspond to Si-O-Si stretch and Si-O stretch respectively are lost completely, indicating complete intercalation of Ti4+ ions into the interlayer space resulting in formation of a delaminated and homogeneous TiPILC material [34]. **Figure 4** shows the results for the zeta potential of powder suspensions of membrane materials and model TiO2 obtained from measurements of the electrophoretic mobility in an aqueous medium. Zeta potential values obtained for membrane materials at pH 2 and sintered at a lower temperature show more negative value as the number of hydroxyl groups in the anatase phase is higher than that of rutile obtained at higher sintering temperature.

## **3.1 Determination of membrane cut off through filtration with methylene blue (MB) dye**

30 ppm of 30 mL MB (Sigma Aldrich, USA) dye solution was prepared. Filtration test was carried by using a peristaltic pump and a cylindrical membrane adapter fitted with a pressure gauge. An average flux rate of 70–110 L/m2 /h was obtained at a constant pressure of 1.2–1.7 Pa. Permeates from the separation experiments were collected and their concentrations were measured by Uv–vis spectrophotometer using the equation:

$$\text{\textbullet \text{\textbullet Removal}} = \left(\text{C}\_0 - \text{C}\_r \; / \text{C}\_0\right) \times \mathbf{100} \tag{1}$$

As can be seen from **Figures 8**–**10** which correspond to percentage removal of MB dyes by membranes sintered at 300°C, 500°C, and 600°C respectively in 3 cycles of filtration, around ~100% removal is achieved. This retention can be explained by high polarity of compounds which causes interactions with the charged membrane.

**Figure 8.** *% removal of MB dye by membranes sintered at 300°C.*

**Figure 9.** *% removal of MB dye by membranes sintered at 500°C.*

**Figure 10.**

*% removal of MB dye by membranes sintered at 600°C.*

Thus the feed solution pH can be considered one of the most important parameters influencing hydrophobicity, the adsorption, and the chemical separation of dissociable organic compounds as well as the membrane surface charge during the experiment.

#### **3.2 Static corrosion test**

The corrosion test was performed by dipping the membranes in 50 mL of four different pH solutions i. e pH 1, pH 3, pH 11, and pH 13 for 24 hours followed by drying in oven at 100°C for 4 hours. These membranes were then studied for MB dye rejection test. Corrosion measurements as that of **Figures 11** and **12** indicate that membranes prepared at pH 2 are most stable in mild aqueous media (pH 3–11) as compared to those prepared at pH 3.5.

Thus in aqueous media with a lower/higher pH, the membrane configuration composed of anatase at pH 2 with a MW cut off <1000 Da on Mt. support is preferred.

#### **Figure 11.**

*% removal of MB dye by membranes prepared at pH 2 after corrosion.*

**Figure 12.** *% removal of MB dye by membranes prepared at pH 3.5 after corrosion.*

## **4. Conclusion and outlook**

Titania pillared clay membranes are amphoteric membranes, whose surface charge depends on the pH of the solution. It is a hybrid membrane reactor which integrates the functions of both separations with photocatalysis. These hybrid membranes are characterized by their asymmetric configuration, i. e a top layer of titania in nanometer range immobilized on a porous ceramic support. The separation depends on the thickness of the top layer deposited on the base membrane. The pore size, and the microstructure of the membranes can be governed by choosing the right solvent, suitable pH, temperature of the reaction and peptization during the sol–gel process that governs the key to fine separation. Sintering temperature is a function of the porosity developed in the membranes. TiPILC membranes sintered at 300°C yielded only anatase phase with a narrow pore size distribution for effective separation of organic contaminants. It has been observed during the treatment of such membranes with synthetic dyes such as Methylene Blue (MB), a thin cake is adsorbed on the surface which decreases the flux rate with time thus resulting in the loss of efficiency of the membrane. Titania immobilized on clay support not only increases the hydrophilicity and the flux rate, but also helps in self-cleaning mechanism of the membrane for prolonged use.

Development of field membrane out of that developed in the laboratory is desired for complete utilization. The developed membranes can also be used for removal of heavy metal ions from wastewater followed by their recovery from the membranes would yield the maximum benefit. The product developed can best treat textile effluent from dye industry with concentration in the range of 50 ppm.

*Clay and Clay Minerals*

## **Author details**

Tanushree Choudhury VIT Chennai, Chennai, India

\*Address all correspondence to<EMAIL_ADDRESS>
© 2021 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

*Clay Hybrid Membranes in Wastewater Treatment DOI: http://dx.doi.org/10.5772/intechopen.99075*

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[11] Rios. G. M et al. Membrane technologies at the service of sustainable development through process intensification. In: Centi. G, Trifiro. F, Perathoner. S, Cavani. F, editors. Sustainable industrial processes, Wiley; 2009. p. 257-278

[12] Hong Wang. Y et al. Titania membrane preparation with chemical stability for very harsh environmental applications. J. Membr. Sci, 2006; 280: 261-269.

[13] Molinari. R et al. Study on a photocatalytic membrane reactor for water purification. Catal Today, 2000; 55: 71-78.

[14] Chin. S., Chiang. K., Fane. A. G. The stability of polymeric membranes in a TiO2 photocatalysis process. J. Membr. Sci, 2006; 275: 202-211.

[15] Choi. H., Statathos. E., Diaonysiour. D. D. Photocatalytic TiO2 films and membranes for the development of efficient wastewater treatment and reuse systems. Desalination, 2007; 202: 199-206.

[16] Tarabara. V. V. Multifunctional Nanomaterial Enabled Membranes for water Treatment. In: Nanotechnology Applications: Solutions for Clean Water. Diallo M, Duncan J, Savage N, Sustich R, Street A; 2009. p. 59-75.

[17] Nagendran. A et al. Toxic metal ion separation by cellulose acetate/ sulfonated poly (ether imide) blend membranes: Effect of Polymer Compositions and additive. Journal of Hazardous Materials, 2008; 155: 477-485.

[18] Bodalo. A et al. Nanofiltration membranes to reduce phenol concentration in wastewater. Desalination, 2009; 245: 680-686.

[19] Harisha. R. S. Arsenic removal from drinking water using thin film composite NF membrane. Desalination, 2010; 252: 75-80.

[20] Bouranene. S et al. Influence of operating conditions on the rejection of Co and Pb ions in aqueous solutions by a NF polyamide membrane. J. Membr. Sci, 2008; 325: 150-157

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## *Edited by Gustavo Morari Do Nascimento*

New two-dimensional materials based on clays and clay minerals are attracting attention for their outstanding properties that make them useful as hosts or supporting matrixes in applications such as pharmaceuticals, tissue engineering, environmental remediation, biosensors, filtration, wound dressings, drug delivery, and more. This book is a comprehensive overview of clay science and technology, focusing on synthesis, characterization, simulation, and applications. Chapters cover such topics as polymer–clay nanocomposites, the structure and properties of different clays, the use of clays for environmental remediation, and much more.

Published in London, UK © 2021 IntechOpen © kazmulka / iStock

Clay and Clay Minerals

Clay and Clay Minerals

*Edited by Gustavo Morari Do Nascimento*


*2.1. Participants*

Eighteen students (9 male) of the University of Lübeck participated. This sample size was well in the range of our previous studies using this task where consistent behavioral and ERP effects had been obtained. Informed written consent was obtained and 7 € per hour were paid. All participants reported normal or corrected-to-normal vision, normal color vision, and no history of neurological disorders. Four of those 18 participants turned out to be unable to identify T2 reliably above chance, with mean identification rates markedly below 20%, and were excluded from analysis. The remaining 14 participants (7 males) were aged 20 to 29 years (M = 25, SD = 2.7). One was left-handed (laterality score −100), the others were right-handed, with a mean score of +94 (SD 9) in the Edinburgh Handedness Inventory [27].

#### *2.2. Stimuli and Apparatus*

The task is illustrated in Figure 1. Two simultaneous sequences of black capital letters of the Latin alphabet were rapidly (9/s) presented left and right from fixation. The 17" screen had a white background (120 cd/m2) and was driven with 100 Hz at about 1.2 m from participants' faces. Letters were 8.5 mm wide and 11 mm high (0.5◦ × 0.6◦ visual angle) with their inner edges 10 mm from fixation (0.6◦). Fixation was marked by a small red cross (0.1◦ × 0.1◦) at screen center. In each trial, two targets had to be identified. The first target (T1) was a red letter (24 cd/m2; D, F, G, J, K, or L). The second target (T2) was a blue digit (18 cd/m2; 1, 2, 3, 4, 5, 6, 7, 8, or 9). Background stimuli consisted of all other letters in black (standard), or in blue (color lures) or of the digits 1–9 in black (digit lures). Presentation® software, version 14.5, was used for experimental control (Neurobehavioral Systems Inc., Berkeley, CA, USA).


**4. Huge electrocaloric effect in LB ferroelectric polymer thin films**

Recently, the huge electrocaloric effect (ECE) resulting from changes in the entropy and temperature of a material under an applied electric field has attracted the attention of re‐ searchers to ferroelectric materials [11,12]. The ECE occurs in both ferroelectric and paraelectric phases and is found to be larger in the paraelectric phase just above the ferroelectric–para‐ electric phase transition [13].

In a working cycle-based ECE, the working material contacts the load and absorbs entropy from it. Then the material is isolated from the load and an electric field is applied. With an increase in the electric field, the polarization and temperature of the working material increase under adiabatic condition. The material is then placed in thermal contact with the heat sink and transfers the entropy absorbed from the load to the heat sink. Then the material is isolated from the heat sink. As the applied field is reduced, the temperature of the material decreases under 350MVm−1

**Films**

back to the temperature of the cooling load. Thus, the larger the ECE of the working material, the better the efficiency of cooling. the material decreases back to the temperature of the cooling load. Thus, the larger the ECE of the working material, the better the efficiency of cooling.

the material is isolated from the heat sink. As the applied field is reduced, the temperature of

We present a detailed investigation of the ECE of P(VDF-TrFE) and P(VDF-TrFE-CFE) films grown by the LB technique on technologically desirable aluminized flexible polyimide substrates. Our results clearly show a large ECE, as the variations of adiabatic temperature ∆*T* of P(VDF-TrFE) films (at 390 K under 300 MVm−1) and P(VDF-TrFE-CFE) films (at 350 K under 350MVm−1) are 21 K (shown in Fig. 5). We present a detailed investigation of the ECE of P(VDF-TrFE) and P(VDF-TrFE-CFE) films grown by the LB technique on technologically desirable aluminized flexible polyimide substrates. Our results clearly show a large ECE, as the variations of adiabatic temperature *T* of P(VDF-TrFE) films (at 390 K under 300 MVm−1 ) and P(VDF-TrFE-CFE) films (at 350 K

) are 21 K (shown in Fig. 5).

Figure 5. Polarizations from *P*-*E* loops and adiabatic temperature change *T* versus temperature in different electric fields for (a) P(VDF-TrFE) films and(b) P(VDF-TrFE-CFE) **Figure 5.** Polarizations from *P*-*E* loops and adiabatic temperature change ∆*T* versus temperature in different electric fields for (a) P(VDF-TrFE) films and(b) P(VDF-TrFE-CFE) films

films Especially for P(VDF-TrFE-CFE) terpolymer films, the peak of *T* is close to room temperature. Considering their practical availability, ferroelectric PVDF-based polymers are potentially applicable for refrigeration by ECE. Professor J. F. Scott has pointed out that Especially for P(VDF-TrFE-CFE) terpolymer films, the peak of ∆*T* is close to room temperature. Considering their practical availability, ferroelectric PVDF-based polymers are potentially applicable for refrigeration by ECE. Professor J. F. Scott has pointed out that PVDF-based polymers are the most promising commercial material due to their large temperature cooling per volt and to their scalability in size and shape [14].

PVDF-based polymers are the most promising commercial material due to their large

### temperature cooling per volt and to their scalability in size and shape [14]. **
Ferroelectric-Like Phase Transition in P(VDF-TrFE-CFE) Terpolymer Ultrathin 5. Ferroelectric-like phase transition in P(VDF-TrFE-CFE) terpolymer ultrathin films**

P(VDF-TrFE-CFE) terpolymer has attracted considerable attention for its fruitful properties and related potential application. Investigations have shown that the all-trans (*TTTT*)polar conformations have been converted into shorter all-trans conformations or polar nanodomains by the induced defect modifications [15]. Further studies verify that there coexist various molecular conformations in the terpolymer, such as trans-gauche (*TGTG)*, and less polar *TTTG* conformations, and the *TTTG* is the dominant one responsible for the relaxor nature. Klein et al. found that the crystallization conditions can also impact the P(VDF-TrFE-CFE) terpolymer has attracted considerable attention for its fruitful properties and related potential application. Investigations have shown that the all-trans (*TTTT*) polar conformations have been converted into shorter all-trans conformations or polar nanodomains by the induced defect modifications [15]. Further studies verify that there coexist various molecular conformations in the terpolymer, such as trans-gauche (*TGTG)*, and less polar *TTTG* conformations, and the *TTTG* is the dominant one responsible for the relaxor nature. Klein et al. found that the crystallization conditions can also impact the microstructures and the ferroelectric properties [16]. We have observed that the electric fields can change the length of the conformation.

The temperature dependence of the complex permittivity for the terpolymer films measured at 1 kHz in the heating process is shown in Fig. 6. For the film with 10 nm, the temperature of permittivity maximum *Tm* is at 308 K, which is consistent with the bulk terpolymer or thick films. Note that *Tm* increases with the decreasing thickness, and it is up to 360 K for the film with one transferred layer, which is even higher than the Curie temperature *T*c of the copoly‐ mers with the same composition.

back to the temperature of the cooling load. Thus, the larger the ECE of the working material,

of the working material, the better the efficiency of cooling.

*T* of P(VDF-TrFE) films (at 390 K under 300 MVm−1

fields for (a) P(VDF-TrFE) films and(b) P(VDF-TrFE-CFE) films

per volt and to their scalability in size and shape [14].

) are 21 K (shown in Fig. 5).

the material is isolated from the heat sink. As the applied field is reduced, the temperature of the material decreases back to the temperature of the cooling load. Thus, the larger the ECE

We present a detailed investigation of the ECE of P(VDF-TrFE) and P(VDF-TrFE-CFE) films grown by the LB technique on technologically desirable aluminized flexible polyimide substrates. Our results clearly show a large ECE, as the variations of adiabatic temperature

Figure 5. Polarizations from *P*-*E* loops and adiabatic temperature change *T* versus temperature in different electric fields for (a) P(VDF-TrFE) films and(b) P(VDF-TrFE-CFE)

**Figure 5.** Polarizations from *P*-*E* loops and adiabatic temperature change ∆*T* versus temperature in different electric

Especially for P(VDF-TrFE-CFE) terpolymer films, the peak of ∆*T* is close to room temperature. Considering their practical availability, ferroelectric PVDF-based polymers are potentially applicable for refrigeration by ECE. Professor J. F. Scott has pointed out that PVDF-based polymers are the most promising commercial material due to their large temperature cooling

Especially for P(VDF-TrFE-CFE) terpolymer films, the peak of *T* is close to room temperature. Considering their practical availability, ferroelectric PVDF-based polymers are potentially applicable for refrigeration by ECE. Professor J. F. Scott has pointed out that PVDF-based polymers are the most promising commercial material due to their large

**
Ferroelectric-Like Phase Transition in P(VDF-TrFE-CFE) Terpolymer Ultrathin**

P(VDF-TrFE-CFE) terpolymer has attracted considerable attention for its fruitful properties and related potential application. Investigations have shown that the all-trans (*TTTT*)polar conformations have been converted into shorter all-trans conformations or polar nanodomains by the induced defect modifications [15]. Further studies verify that there coexist various molecular conformations in the terpolymer, such as trans-gauche (*TGTG)*, and less polar *TTTG* conformations, and the *TTTG* is the dominant one responsible for the relaxor nature. Klein et al. found that the crystallization conditions can also impact the

temperature cooling per volt and to their scalability in size and shape [14].

**5. Ferroelectric-like phase transition in P(VDF-TrFE-CFE) terpolymer**

P(VDF-TrFE-CFE) terpolymer has attracted considerable attention for its fruitful properties and related potential application. Investigations have shown that the all-trans (*TTTT*) polar conformations have been converted into shorter all-trans conformations or polar nanodomains by the induced defect modifications [15]. Further studies verify that there coexist various molecular conformations in the terpolymer, such as trans-gauche (*TGTG)*, and less polar *TTTG* conformations, and the *TTTG* is the dominant one responsible for the relaxor nature. Klein et al. found that the crystallization conditions can also impact the microstructures and the ferroelectric properties [16]. We have observed that the electric fields can change the

) and P(VDF-TrFE-CFE) films (at 350 K

We present a detailed investigation of the ECE of P(VDF-TrFE) and P(VDF-TrFE-CFE) films grown by the LB technique on technologically desirable aluminized flexible polyimide substrates. Our results clearly show a large ECE, as the variations of adiabatic temperature ∆*T* of P(VDF-TrFE) films (at 390 K under 300 MVm−1) and P(VDF-TrFE-CFE) films (at 350 K under

the better the efficiency of cooling.

156 Ferroelectric Materials – Synthesis and Characterization

350MVm−1) are 21 K (shown in Fig. 5).

under 350MVm−1

films

**Films**

**ultrathin films**

length of the conformation.

**Figure 6.** The dielectric constant of different thickness terpolymer films as a function of temperature of at 1 k Hz

The coercive voltage is 1.2 V, which is also in accord with the polarization versus electric field (*P*-*E)* loop and *C*-*V* curve. In addition, the temperature dependence of the *C*-*V* curves for the terpolymer film with one monolayer is measured and shown in Fig. 7. The butterfly-shape feature disappears as the temperature is higher than 360 K, indicating a transition from ferroelectric-like to paraelectric phase. This is in accord with the temperature dependence of the capacitance.

A hypothesis can be deduced from the above results that all-trans-like molecular conforma‐ tions form in the ultrathin terpolymer films. As mentioned earlier, the dominant conformation in P(VDF-TrFE-CFE) terpolymer is the less polar *TTTG* conformation. It has been reported that the polar phase or ferroelectric-like phase can be induced by controlling the kinetic factors of the annealing process of terpolymer because the crystal structure is determined by both thermodynamics and kinetics. As it is known, the large PVDF dipoles can induce mirror charges on conducting substrates, thus forming an extrinsic vertical electric field on the substrate [17]. Here, it is considered that the terpolymer dipoles are also large enough to induce mirror charges on the conducting Al electrodes, which then can lead to a vertical electric field. Under such high vertical electric field, the less polar conformations are converted into higher polar conformations.

**Figure 7.** The temperature dependence of *C*-*V* curve at 10 kHz for one transferred layer terpolymer film. (a) 300 K, (b) 340 K, (c) 360 K, and (d) 375 K

The ferroelectric-like phase transition is observed in the P(VDF-TrFE-CFE) terpolymer films as the thickness is lower than 3 nm. The ferroelectric-like features are considered to result from the induced electric field due to the mirror charges in the electrodes.