The results on mechanical properties showed the increase in the tensile strength (TS) and elastic modulus (EM) of such nanocomposite films can be attributed to the high rigidity and aspect ratio of the nanoclay as well as the high affinity between the chitosan and the bentonite. On the other hand, the CS/BNT nanocomposites have shown significant decrease in elongation at break (EB). This reduction can be attributed to the restricted mobility of macromolecular chains. In **Figure 14**, effect of BNT addition is being illustrated for the diluted systems (CS nanocomposites). The ductile response of the CS films is maintained after the addition of BNT with strength and a relative lower decrease in the elongation at break. The systems with 3 wt%

+

as expected for a biopolymer with high water retention capability [38, 39].

**glycerol (CSG), and chitosan/glycerol/bentonite (CSGBNT) films**

chains due to the strong electrostatic interactions between the NH2

and the formation of hydrogen bonding after the addition of glycerol.

BNT presented the lowest enhancement in all mechanical properties.

interactions and thus their reinforcing ability.

tion may be expected when – NH3

(CS). This fact may be related to the –NH3

+ vibra-

+

57

groups interact electrostatically with the negatively

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groups that do not interact electrostatically with

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and NH3

+

groups. The CSG

**Figure 11.** Images of antimicrobial films casted from solutions containing modified chitosan (2% w/w) and essential oils (0.05% w/w) added as pure rosemary essential oil.

1390 cm−1 was given to (N–H stretching or C–N bond stretching vibrations, amide III vibration). The peak at 1116.93 cm−1 corresponds to the symmetric stretching of C–O–C groups. The absorption peaks in the range 900–1200 cm−1 are due to the antisymmetric C–O stretching of saccharide structure of chitosan.

As can be seen in **Figure 12**, the FTIR spectrum of BNT shows a peak at 1010 cm−1 that belongs to Si-O-Si linkage. In addition, the characteristic absorption peaks are found at around 3670 cm−1 (stretching vibration of Al-OH and OH), at 3465 cm−1 (stretching vibration of O-H and H-O-H groups), at 1638 cm−1 (H-O-H bending vibration), at 933 cm−1 (Al-Al-OH bending frequency), and at 509 cm−1 (bending vibration of Si-O).

**Figure 12.** FTIR spectrum of: Chitosan film (FCSBNT0%), Chitosan/BNT films respectively (FCSBNT3%) and (FCSBNT5%).

The FTIR was also used to study the polymer/clay interaction, since a shift in the NH3 + vibration may be expected when – NH3 + groups interact electrostatically with the negatively charged sites of the clay [35]. Nevertheless, this shift is higher for CSBNT nanocomposite film with the lowest amounts of CS, while the chitosan/clay films with the highest amounts of biopolymer show a frequency value that trends to that observed in the films of pure chitosan (CS). This fact may be related to the –NH3 + groups that do not interact electrostatically with the clay substrate. The spectrum of CBNT nanocomposite film (**Figure 12**) shows a characteristic band at 3462.78 cm−1 attributed to hydrogen bonding formation due to the functional groups of CS (O-H and N-H groups) and BN (O-H groups) [36, 37]. The intensity of the NH3 + band also increases for higher amounts of intercalated chitosan. The secondary amide band at 1645 cm−1 of chitosan is overlapped with the HOH bending vibration band at 1628 cm−1 of the water molecules associated to the chitosan/clay films, which are present as in the starting clay, as expected for a biopolymer with high water retention capability [38, 39].

#### **3.3. Tensile measurements of chitosan (CS), chitosan/bentonite (CSBNT), chitosan/ glycerol (CSG), and chitosan/glycerol/bentonite (CSGBNT) films**

1390 cm−1 was given to (N–H stretching or C–N bond stretching vibrations, amide III vibration). The peak at 1116.93 cm−1 corresponds to the symmetric stretching of C–O–C groups. The absorption peaks in the range 900–1200 cm−1 are due to the antisymmetric C–O stretching of

**Figure 11.** Images of antimicrobial films casted from solutions containing modified chitosan (2% w/w) and essential oils

As can be seen in **Figure 12**, the FTIR spectrum of BNT shows a peak at 1010 cm−1 that belongs to Si-O-Si linkage. In addition, the characteristic absorption peaks are found at around 3670 cm−1 (stretching vibration of Al-OH and OH), at 3465 cm−1 (stretching vibration of O-H and H-O-H groups), at 1638 cm−1 (H-O-H bending vibration), at 933 cm−1 (Al-Al-OH bending

**Figure 12.** FTIR spectrum of: Chitosan film (FCSBNT0%), Chitosan/BNT films respectively (FCSBNT3%) and (FCSBNT5%).

saccharide structure of chitosan.

(0.05% w/w) added as pure rosemary essential oil.

56 Chitin-Chitosan - Myriad Functionalities in Science and Technology

frequency), and at 509 cm−1 (bending vibration of Si-O).

The stress-strain curves of the tested specimens are being presented in **Figure 13**, while the average values along with the standard deviation of Young's modulus, tensile strength and elongation at break of the films on the stress-strain behavior of the chitosan and chitosan/ glycerol films, respectively [40], are shown in **Figure 14**. The higher strength obtained in the case of the CS films can be attributed to more efficient stress transfer between the adjacent chains due to the strong electrostatic interactions between the NH2 and NH3 + groups. The CSG specimen presents almost double strength (at yield and break) and elongation at break. Due to the lower acidity of the diluted films, a weaker hydrogen bond network was established between the amino groups and the glycerol chains. On the other hand, the extensive deformation strengthening in undiluted systems (CSG) suggests the creation of a long-range order and the formation of hydrogen bonding after the addition of glycerol.

The effect of BNT addition on the tensile response of the chitosan and chitosan/glycerol films is being depicted. The stress–strain curves of BNT composite films prepared from the 1 w/v% chitosan solution is being presented. The addition of BNT results in a pronounced enhancement of the stiffness and a dramatic decrease in the elongation at break of all clay-added systems. Further addition of BNT leads in intercalated structures which limited the polymer-clay interactions and thus their reinforcing ability.

The results on mechanical properties showed the increase in the tensile strength (TS) and elastic modulus (EM) of such nanocomposite films can be attributed to the high rigidity and aspect ratio of the nanoclay as well as the high affinity between the chitosan and the bentonite. On the other hand, the CS/BNT nanocomposites have shown significant decrease in elongation at break (EB). This reduction can be attributed to the restricted mobility of macromolecular chains.

In **Figure 14**, effect of BNT addition is being illustrated for the diluted systems (CS nanocomposites). The ductile response of the CS films is maintained after the addition of BNT with strength and a relative lower decrease in the elongation at break. The systems with 3 wt% BNT presented the lowest enhancement in all mechanical properties.

**3.4. Thermal stability analysis**

the second step.

with increasing clay.

**3.5. XRD analysis**

The thermal stability of the chitosan (CS) and its nanocomposites has been investigated by TGA under nitrogen (**Figure 15**). There are two steps of degradation. The first range (50–200°C) is associated with the loss of water, whereas the second range at 270°C corresponds to the deacetylation and degradation of chitosan, and the third step, in the temperature range 450–550°C, can be associated with the oxidative degradation of the carbonaceous residue formed during

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The nano-dispersed clay in the chitosan matrix exhibits a significant delay in weight loss. The nanocomposite forms char with a multilayered carbonaceous-silicate structure, which may keep its multilayered structure in the polymer matrix. This high-performance carbonaceous-silicate char builds up on the surface during burning, thus insulating the underlying material and slowing the escape of the volatile products generated during decomposition. The decomposition temperature CS/BNT nanocomposites show higher thermal stability than those of the pure CS. The thermal stability of the nanocomposites increases systematically

For nanocomposites containing glycerol, a further degradation step at T≈250°C is observed, related to the loss of unbound glycerol, as indicated in **Figure 16**. Furthermore, it can also be observed that the presence of glycerol plasticizer increases of about 20°C the degradation

The XRD patterns of chitosan and chitosan-based nanocomposite films in the range of 5–30° are shown in (**Figure 17**). The basal plane of BNT shows a reflection peak at about 2θ = 8.8°. After incorporating BNT within CS, with CS/BNT, the basal plane of BNT at 2θ = 8.8° disappears, substituted by a new weakened broad peak at around 2θ = 12.8°–13.0° (CSBNT3%,

CSBNT5%). It is suggested that the BNT form intercalated and flocculated structures.

**Figure 15.** Thermal properties of: Chitosan (FCSBNT0%) and Chitosan/Bentonite films (FCSBNT3%), (FCSBNT5%).

temperature for the third step, irrespective of the presence or not of the clay.

**Figure 13.** Stress-strain curves of chitosan film (FCSBNT0%), chitosan/BNT films (FCSBNT3%), (FCSBNT5%), respectively.

**Figures 13** and **14** present the combined effect of glycerol and BNT on the tensile response of the CS-based nanocomposites. The first observation is that the addition of BNT results in a direct reduction of the strength of the chitosan/glycerol. A completely different stress–strain behavior is being obtained after the addition of BNT in diluted chitosan/glycerol systems (**Figure 14**). The CS/glycerol-based nanocomposites behave like hyperelastic materials rather than like ductile polymers. It is assumed that more water and glycerol are distributed in the chitosan network, inducing a very obvious plasticization effect. The extent of hydrated chitosan crystals was confirmed from the intensities of the XRD patterns. It is very interesting to note that although the mechanical properties of the unreinforced chitosan are comparable before and after the application of the reflux processing, reflux resulted in a fourfold increase of the stiffness and strength of the nanocomposite films.

**Figure 14.** Mechanical properties of chitosan/BNT particles films. Chitosan film (FCSBNT0%), chitosan/BNT films (FCSBNT3%), (FCSBNT5%), respectively, and chitosan/glycerol film (FCSGBNT0%), chitosan/glycerol/BNT films (FCSGBNT3%), (FCSGBNT5%), respectively.

#### **3.4. Thermal stability analysis**

The thermal stability of the chitosan (CS) and its nanocomposites has been investigated by TGA under nitrogen (**Figure 15**). There are two steps of degradation. The first range (50–200°C) is associated with the loss of water, whereas the second range at 270°C corresponds to the deacetylation and degradation of chitosan, and the third step, in the temperature range 450–550°C, can be associated with the oxidative degradation of the carbonaceous residue formed during the second step.

The nano-dispersed clay in the chitosan matrix exhibits a significant delay in weight loss. The nanocomposite forms char with a multilayered carbonaceous-silicate structure, which may keep its multilayered structure in the polymer matrix. This high-performance carbonaceous-silicate char builds up on the surface during burning, thus insulating the underlying material and slowing the escape of the volatile products generated during decomposition. The decomposition temperature CS/BNT nanocomposites show higher thermal stability than those of the pure CS. The thermal stability of the nanocomposites increases systematically with increasing clay.

For nanocomposites containing glycerol, a further degradation step at T≈250°C is observed, related to the loss of unbound glycerol, as indicated in **Figure 16**. Furthermore, it can also be observed that the presence of glycerol plasticizer increases of about 20°C the degradation temperature for the third step, irrespective of the presence or not of the clay.

#### **3.5. XRD analysis**

**Figures 13** and **14** present the combined effect of glycerol and BNT on the tensile response of the CS-based nanocomposites. The first observation is that the addition of BNT results in a direct reduction of the strength of the chitosan/glycerol. A completely different stress–strain behavior is being obtained after the addition of BNT in diluted chitosan/glycerol systems (**Figure 14**). The CS/glycerol-based nanocomposites behave like hyperelastic materials rather than like ductile polymers. It is assumed that more water and glycerol are distributed in the chitosan network, inducing a very obvious plasticization effect. The extent of hydrated chitosan crystals was confirmed from the intensities of the XRD patterns. It is very interesting to note that although the mechanical properties of the unreinforced chitosan are comparable before and after the application of the reflux processing, reflux resulted in a fourfold increase

**Figure 13.** Stress-strain curves of chitosan film (FCSBNT0%), chitosan/BNT films (FCSBNT3%), (FCSBNT5%),

**Figure 14.** Mechanical properties of chitosan/BNT particles films. Chitosan film (FCSBNT0%), chitosan/BNT films (FCSBNT3%), (FCSBNT5%), respectively, and chitosan/glycerol film (FCSGBNT0%), chitosan/glycerol/BNT films

of the stiffness and strength of the nanocomposite films.

58 Chitin-Chitosan - Myriad Functionalities in Science and Technology

respectively.

(FCSGBNT3%), (FCSGBNT5%), respectively.

The XRD patterns of chitosan and chitosan-based nanocomposite films in the range of 5–30° are shown in (**Figure 17**). The basal plane of BNT shows a reflection peak at about 2θ = 8.8°. After incorporating BNT within CS, with CS/BNT, the basal plane of BNT at 2θ = 8.8° disappears, substituted by a new weakened broad peak at around 2θ = 12.8°–13.0° (CSBNT3%, CSBNT5%). It is suggested that the BNT form intercalated and flocculated structures.

**Figure 15.** Thermal properties of: Chitosan (FCSBNT0%) and Chitosan/Bentonite films (FCSBNT3%), (FCSBNT5%).

On the base of XRD patterns, it is suggested that the BNT forms intercalated and exfoliated structures at higher CS content (CSBNT5%), while decreasing the CS content (CSBNT3%), clay layers (BNT) form intercalated and flocculated structures. According to [23], the formation of flocculated structure in CS/clay nanocomposites can be due to the hydroxylated edgeedge interactions of the clay layers. Since one chitosan unit possesses one amino and two hydroxyl functional groups, these groups can form hydrogen bonds with the clay hydroxyl edge groups. This strong interaction is believed to be the main driving force for the assembly

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The XRD patterns of chitosan/glycerol films obtained from 30 w/v% solutions are shown in **Figure 18**. The addition of glycerol results in a pronounced peak at 12.5°. Because of the hydrophilic and polycationic nature of chitosan in acidic media, this biopolymer has good miscibility which is attributed to the interaction of glycerol molecules with chitosan

**Figure 18.** XRD patterns of: Chitosan (CS), Bentonite (BNT), Chitosan/Glycerol (FCSG) and Chitosan/Glycerol/Bentonite

films (FCSGBNT3%) and (FCSGBNT5%).

of BNT in the CS matrix to form flocculated structures.

**Figure 16.** Thermal properties of: Chitosan/Glycerol (FCSG), Chitosan/Glycerol (FCSGBNT0%) and Chitosan/Glycerol/ Bentonite (FCSGBNT3%) and (FCSGBNT5%) films.

**Figure 17.** XRD patterns of: Chitosan (CS), Bentonite (BNT) and Chitosan/Bentonite films (FCSBNT3%) and (FCSBNT5%).

On the base of XRD patterns, it is suggested that the BNT forms intercalated and exfoliated structures at higher CS content (CSBNT5%), while decreasing the CS content (CSBNT3%), clay layers (BNT) form intercalated and flocculated structures. According to [23], the formation of flocculated structure in CS/clay nanocomposites can be due to the hydroxylated edgeedge interactions of the clay layers. Since one chitosan unit possesses one amino and two hydroxyl functional groups, these groups can form hydrogen bonds with the clay hydroxyl edge groups. This strong interaction is believed to be the main driving force for the assembly of BNT in the CS matrix to form flocculated structures.

The XRD patterns of chitosan/glycerol films obtained from 30 w/v% solutions are shown in **Figure 18**. The addition of glycerol results in a pronounced peak at 12.5°. Because of the hydrophilic and polycationic nature of chitosan in acidic media, this biopolymer has good miscibility which is attributed to the interaction of glycerol molecules with chitosan

**Figure 18.** XRD patterns of: Chitosan (CS), Bentonite (BNT), Chitosan/Glycerol (FCSG) and Chitosan/Glycerol/Bentonite films (FCSGBNT3%) and (FCSGBNT5%).

**Figure 17.** XRD patterns of: Chitosan (CS), Bentonite (BNT) and Chitosan/Bentonite films (FCSBNT3%) and (FCSBNT5%).

**Figure 16.** Thermal properties of: Chitosan/Glycerol (FCSG), Chitosan/Glycerol (FCSGBNT0%) and Chitosan/Glycerol/

Bentonite (FCSGBNT3%) and (FCSGBNT5%) films.

60 Chitin-Chitosan - Myriad Functionalities in Science and Technology

macromolecules. Glycerol favors the chains mobility and thus the chitosan crystallization process in the early stage of the post-processing aging the effect of glycerol addition. The XRD patterns of chitosan/glycerol/BNT films obtained from chitosan solution are shown in **Figure 18**. The combined addition of glycerol and clays resulted in great enhancement of the chitosan crystallinity of the nanocomposite films prepared with 1 w/v% chitosan solution. This indicates that the presence of clay facilitates the distribution of glycerol within the chitosan matrix and the interaction of glycerol molecules with chitosan macromolecules. The combined addition of glycerol and clay had an opposite effect in films obtained from low content chitosan solution leading to decrease of the XRD peaks intensities. In addition a new peak at 18.2° appeared in XRD patterns of all obtained films. This diffraction peak is characteristic for chitosan films prepared using acetic acid solution as solvent.

The addition of glycerol favors the opening of the clay galleries resulting in intercalated nanocomposites in comparison to samples without glycerol.

Chitosan/Na-BNT nanocomposites exhibit an intercalated or intercalated/orientated structure of clays. In particular, the X-ray diffraction results show that in film without glycerol, the BNT stacks lay with their platelet surface parallel to the casting surface. The presence of glycerol, on the other hand, enhances the chitosan intercalation in the silicate galleries and hinders the flocculation process, leaving the BNT stacks randomly orientated in the space.

#### **3.6. SEM and MET images of chitosan, oxidized chitosan, and bionanocomposite materials**

The SEM images of chitosan and oxidized chitosan at high vacuum and at different magnifications are shown in **Figure 19**, showing that there is no change of elongated and fibrous network of chitosan, but on the surface of oxidized chitosan, we can see a slight degradation of some leaves.

#### *3.6.1. FEGSEM analysis*

We present in this study the microstructural characterization results obtained on the chitosan/ Na-BNT nanocomposites too. The dispersion and the exfoliation of the clay were observed at field emission gun scanning electron microscope (FEGSEM) and transmission electron microscopy (TEM).

At higher magnification, small clay particles similar in size to those observed in the CSBNT

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Transmission electron microscopy (TEM) images indicated that the silicate layers were dispersed in the chitosan matrix. The results of the TEM observation of the chitosan/BNT 3% sample show that small particles of clay from less than 100 nanometers to a few hundred nanometers are observed at low magnification which is consistent with the FEGSEM observa-

Depending on the level of the clay particles, the leaflets are sometimes well aligned (**Figure 22**) and sometimes of more unstructured appearance (**Figure 23**). This unstructured aspect of the

3% sample are regularly observed with chitosan/BNT 5% as shown in **Figure 21**.

**Figure 19.** SEM images of (a & b) chitosan and (c & d) oxidized chitosan at different magnifications.

tions. Larger aggregates of clay are also observed but more rarely.

*3.6.2. TEM analysis*

The results of the observation of the microtome block of chitosan/bentonite (CSBNT3%) and (CSBNT5%) samples are presented in **Figure 20**.

At low magnification, the CSBNT 3% powders were observed, and clusters were found grouped into in the epoxy more matte and dark appearance (**Figure 20a**). Decohesion between the epoxy and the sample powders is visible in greater or lesser proportion, probably due to preparation and cutting. At higher magnification, small clay particles of a few hundred nanometers are observed, which are relatively well dispersed in the polysaccharide (**Figure 20b**). However, a large clay aggregate of about 10 microns was also observed (**Figure 20c** and **d**).

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**Figure 19.** SEM images of (a & b) chitosan and (c & d) oxidized chitosan at different magnifications.

At higher magnification, small clay particles similar in size to those observed in the CSBNT 3% sample are regularly observed with chitosan/BNT 5% as shown in **Figure 21**.

#### *3.6.2. TEM analysis*

macromolecules. Glycerol favors the chains mobility and thus the chitosan crystallization process in the early stage of the post-processing aging the effect of glycerol addition. The XRD patterns of chitosan/glycerol/BNT films obtained from chitosan solution are shown in **Figure 18**. The combined addition of glycerol and clays resulted in great enhancement of the chitosan crystallinity of the nanocomposite films prepared with 1 w/v% chitosan solution. This indicates that the presence of clay facilitates the distribution of glycerol within the chitosan matrix and the interaction of glycerol molecules with chitosan macromolecules. The combined addition of glycerol and clay had an opposite effect in films obtained from low content chitosan solution leading to decrease of the XRD peaks intensities. In addition a new peak at 18.2° appeared in XRD patterns of all obtained films. This diffraction peak is

The addition of glycerol favors the opening of the clay galleries resulting in intercalated nano-

Chitosan/Na-BNT nanocomposites exhibit an intercalated or intercalated/orientated structure of clays. In particular, the X-ray diffraction results show that in film without glycerol, the BNT stacks lay with their platelet surface parallel to the casting surface. The presence of glycerol, on the other hand, enhances the chitosan intercalation in the silicate galleries and hinders the

The SEM images of chitosan and oxidized chitosan at high vacuum and at different magnifications are shown in **Figure 19**, showing that there is no change of elongated and fibrous network of chitosan, but on the surface of oxidized chitosan, we can see a slight degradation

We present in this study the microstructural characterization results obtained on the chitosan/ Na-BNT nanocomposites too. The dispersion and the exfoliation of the clay were observed at field emission gun scanning electron microscope (FEGSEM) and transmission electron

The results of the observation of the microtome block of chitosan/bentonite (CSBNT3%) and

At low magnification, the CSBNT 3% powders were observed, and clusters were found grouped into in the epoxy more matte and dark appearance (**Figure 20a**). Decohesion between the epoxy and the sample powders is visible in greater or lesser proportion, probably due to preparation and cutting. At higher magnification, small clay particles of a few hundred nanometers are observed, which are relatively well dispersed in the polysaccharide (**Figure 20b**). However, a large clay aggregate of about 10 microns was also observed

characteristic for chitosan films prepared using acetic acid solution as solvent.

flocculation process, leaving the BNT stacks randomly orientated in the space.

**3.6. SEM and MET images of chitosan, oxidized chitosan, and bionanocomposite**

composites in comparison to samples without glycerol.

62 Chitin-Chitosan - Myriad Functionalities in Science and Technology

**materials**

of some leaves.

*3.6.1. FEGSEM analysis*

microscopy (TEM).

(**Figure 20c** and **d**).

(CSBNT5%) samples are presented in **Figure 20**.

Transmission electron microscopy (TEM) images indicated that the silicate layers were dispersed in the chitosan matrix. The results of the TEM observation of the chitosan/BNT 3% sample show that small particles of clay from less than 100 nanometers to a few hundred nanometers are observed at low magnification which is consistent with the FEGSEM observations. Larger aggregates of clay are also observed but more rarely.

Depending on the level of the clay particles, the leaflets are sometimes well aligned (**Figure 22**) and sometimes of more unstructured appearance (**Figure 23**). This unstructured aspect of the

**Figure 20.** Images of FEGSEM of chitosan/BNT 3%.

clay sheets may be a sign of a more advanced level of intercalation. There are also some isolated single or double leaflets around other clay particles (**Figure 23**), which is a clear sign of exfoliation.

As expected, the concentration of clay in the polysaccharide affects the dispersion of the clay. The higher the concentration, the poorer the dispersion is obtained which is the effect of the greater aggregation of the clay. A good but not always uniform dispersion is observed in chitosan/BNT 3% and 5%. Similarly, the concentration of clay also appears to affect the level

of intercalation/exfoliation. Based on MET observations, signs of exfoliation (the presence of isolated single or double clay leaflets and more unstructured appearance of the leaflets in the

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Natural biopolymer-based biodegradable packaging materials are a new generation of polymers emerging on the packaging market, and driven by the perception that biodegradable plastics are "environmentally friendly," their use is predicted to increase chitosan, a natural material that has interesting antimicrobial and film-forming activities. Its application in films can contribute to food preservation and shelf-life extension. In this study, various films were successfully prepared

particles) are visible in samples of lower clay concentration less than 10%.

**4. Conclusion**

**Figure 22.** Images TEM of chitosan/BNT 3% (x 500K).

**Figure 23.** Images TEM of chitosan/BNT 3% (x 600K).

**Figure 21.** Image of FEGSEM of chitosan/BNT 5%.

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**Figure 22.** Images TEM of chitosan/BNT 3% (x 500K).

**Figure 23.** Images TEM of chitosan/BNT 3% (x 600K).

of intercalation/exfoliation. Based on MET observations, signs of exfoliation (the presence of isolated single or double clay leaflets and more unstructured appearance of the leaflets in the particles) are visible in samples of lower clay concentration less than 10%.

#### **4. Conclusion**

clay sheets may be a sign of a more advanced level of intercalation. There are also some isolated single or double leaflets around other clay particles (**Figure 23**), which is a clear sign of exfoliation. As expected, the concentration of clay in the polysaccharide affects the dispersion of the clay. The higher the concentration, the poorer the dispersion is obtained which is the effect of the greater aggregation of the clay. A good but not always uniform dispersion is observed in chitosan/BNT 3% and 5%. Similarly, the concentration of clay also appears to affect the level

**Figure 20.** Images of FEGSEM of chitosan/BNT 3%.

64 Chitin-Chitosan - Myriad Functionalities in Science and Technology

**Figure 21.** Image of FEGSEM of chitosan/BNT 5%.

Natural biopolymer-based biodegradable packaging materials are a new generation of polymers emerging on the packaging market, and driven by the perception that biodegradable plastics are "environmentally friendly," their use is predicted to increase chitosan, a natural material that has interesting antimicrobial and film-forming activities. Its application in films can contribute to food preservation and shelf-life extension. In this study, various films were successfully prepared by the solution casting technique and characterized with particular regard to structural, thermal, and mechanical properties. Films of chitosan/bentonite, chitosan/glycerol/bentonite, and chitosan/glycerol/bentonite/essential oil nanocomposites were prepared with purified bentonite (BNT), and according to the process used, they might be less expensive than other packaging materials.

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Exfoliated chitosan/clay nanocomposites of varying clay contents have been successfully prepared with or without the presence of glycerol (plasticizer) and oxidized chitosan (crosslinker). This approach represents a new route to prepare high-performance nanocomposite materials. The oxidized chitosan could partially react with the amine groups on chitosan; as a result, high mechanical properties can be obtained. The Na-BNT layers are exfoliated by chitosan chains and disorderly dispersed in the chitosan matrix, as confirmed by XRD and TEM characterization. The incorporation of a small amount of clay into the chitosan matrix results in obvious enhancement in the thermal properties of chitosan. The chitosan/clay nanocomposites retain good mechanical properties. Once the clay is exfoliated and efficiently dispersed into the chitosan matrix, the storage modulus and tensile property of the chitosan/clay nanocomposites are significantly improved with respect to that of neat chitosan.

#### **Acknowledgements**

This work would not have been possible without the great support of Julian Zhu, a polymer chemist professor at Montreal University, Department of chemistry, Quebec, Canada. This work was supported by the Francophone University Association (AUF).

#### **Author details**

Asmae Laaraibi1 \*, Fatiha Moughaoui1 , Fouad Damiri1 , Amine Ouakit1 , Imane Charhouf1 , Souad Hamdouch1 , Abdelhafid Jaafari2 , Abdelmjid Abourriche1 , Noureddine Knouzi1 , Ahmed Bennamara1 and Mohammed Berrada1

\*Address all correspondence to<EMAIL_ADDRESS>
1 Department of Chemistry, Laboratory of Biomolecules and Organic Synthesis (BIOSYNTHO), Faculty of Sciences Ben M'Sik, University Hassan II of Casablanca, Morocco

2 Department of Chemistry, Laboratory of Applied Chemistry and environment, Faculty of Sciences and Technologies, University Hassan I of Settat, Morocco

#### **References**

[1] Martinho G, Balaia N, Pires A. The portuguese plastic carrier bag tax: the effects on consumers' behavior. Waste Management. 2017;**61**:3-12

[2] Tan W, Zhang Y, Szeto Y, Liao L. A novel method to prepare chitosan/montmorillonite nanocomposites in the presence of hydroxy-aluminum oligomeric cations. Journal of Computer Science and Technology. 2008;**68**:2917-2921

by the solution casting technique and characterized with particular regard to structural, thermal, and mechanical properties. Films of chitosan/bentonite, chitosan/glycerol/bentonite, and chitosan/glycerol/bentonite/essential oil nanocomposites were prepared with purified bentonite (BNT), and according to the process used, they might be less expensive than other packaging

Exfoliated chitosan/clay nanocomposites of varying clay contents have been successfully prepared with or without the presence of glycerol (plasticizer) and oxidized chitosan (crosslinker). This approach represents a new route to prepare high-performance nanocomposite materials. The oxidized chitosan could partially react with the amine groups on chitosan; as a result, high mechanical properties can be obtained. The Na-BNT layers are exfoliated by chitosan chains and disorderly dispersed in the chitosan matrix, as confirmed by XRD and TEM characterization. The incorporation of a small amount of clay into the chitosan matrix results in obvious enhancement in the thermal properties of chitosan. The chitosan/clay nanocomposites retain good mechanical properties. Once the clay is exfoliated and efficiently dispersed into the chitosan matrix, the storage modulus and tensile property of the chitosan/clay

This work would not have been possible without the great support of Julian Zhu, a polymer chemist professor at Montreal University, Department of chemistry, Quebec, Canada. This

, Fouad Damiri1

(BIOSYNTHO), Faculty of Sciences Ben M'Sik, University Hassan II of Casablanca, Morocco 2 Department of Chemistry, Laboratory of Applied Chemistry and environment, Faculty of

[1] Martinho G, Balaia N, Pires A. The portuguese plastic carrier bag tax: the effects on con-

, Abdelmjid Abourriche1

, Amine Ouakit1

, Imane Charhouf1

, Noureddine Knouzi1

,

,

nanocomposites are significantly improved with respect to that of neat chitosan.

work was supported by the Francophone University Association (AUF).

\*, Fatiha Moughaoui1

66 Chitin-Chitosan - Myriad Functionalities in Science and Technology

, Abdelhafid Jaafari2

\*Address all correspondence to<EMAIL_ADDRESS>
and Mohammed Berrada1

Sciences and Technologies, University Hassan I of Settat, Morocco

sumers' behavior. Waste Management. 2017;**61**:3-12

1 Department of Chemistry, Laboratory of Biomolecules and Organic Synthesis

materials.

**Acknowledgements**

**Author details**

Asmae Laaraibi1

**References**

Souad Hamdouch1

Ahmed Bennamara1

[16] Holzer L, Münch B, Rizzi M, Wep R, Marschall P, Graule T. 3D-microstructure analysis of hydrated bentonite with cryo-stabilized pore water. Journal Applied Clay Science. 2010;**47**:330-342

[31] Karbowiak T, Hervet H, Léger L, Champion D, Debeaufort F, Voiley A. Effect of plasticizers (water and glycerol) on the diffusion of a small molecule in iota-carrageenan biopoly-

Chitosan-Clay Based (CS-NaBNT) Biodegradable Nanocomposite Films for Potential Utility…

http://dx.doi.org/10.5772/intechopen.76498

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[33] Charhouf I, Bennamara A, Abourriche A, Chenite A, Zhu J, Berradae M. Characterization of a dialdehyde chitosan generated by periodate oxidation. International Journal of

[34] Bilia AR, Guccione C, Isacchi B, Righeschi C, Firenzuoli F, Bergonzi MC. Essential oils loaded in nanosystems: a developing strategy for a successful therapeutic approach. Evidence-based Complementary and Alternative Medicine. 2014;**2014**:651593.

[35] Wang L, Wang A. Adsorption characteristics of congo red onto the chitosan/montmoril-

[36] Paluszkiewicz C, Stodolak E, Hasik M, Blazewicz M. FT-IR study of montmorillonite–chitosan nanocomposite materials. Spectrochimica Acta Part A: Molecular and

[37] Tan W, Zhang Y, Szeto Y, Liao L. A novel method to prepare chitosan/montmorillonite nanocomposites in the presence of hydroxy-aluminum oligomeric cations. Journal of Computer

[38] Darder M, Colilla M, Ruiz-Hitzky E. Chitosan-clay nanocomposites: application as. 500

[39] Han Y, Lee SH, Choi KH, Park I. Preparation and characterization of chitosan–clay nanocomposites with antimicrobial activity. Journal of Physics and Chemistry of Solids. 2010;**71**:

[40] Laaraibi A, Charhouf I, Bennamara A, Abourriche A, Berrada M. Berrada. Valorization of marine wastes in a preserving film based on chitosan for food applications. Journal of

lonite nanocomposite. Journal of Hazardous Materials. 2007;**147**:979-985

electrochemical sensors. Journal Appl Clay Science. 2005;**28**:199-208

Materials and Environmental Science. 2015;**6**(12):3511-3516

Sciences: Basic and Applied Research (IJSBAR). 2014;**16**(2):336-348

mer films for edible coating application. Biomacromolecules. 2006;**7**(6):2011-2019 [32] Kristo E, Biliaderis CG. Water sorption and thermo-mechanical properties of water/ sorbitol-plasticized composite biopolymer films: caseinate-pullulan bilayers and

blends. Food Hydrocolloids. 2006;**20**(7):1057-1071

Biomolecular Spectroscopy. 2004;**79**:784-788

Science and Technology. 2008;**68**:2917-2921

DOI: 10.1155/2014/651593

464-467

[31] Karbowiak T, Hervet H, Léger L, Champion D, Debeaufort F, Voiley A. Effect of plasticizers (water and glycerol) on the diffusion of a small molecule in iota-carrageenan biopolymer films for edible coating application. Biomacromolecules. 2006;**7**(6):2011-2019

[16] Holzer L, Münch B, Rizzi M, Wep R, Marschall P, Graule T. 3D-microstructure analysis of hydrated bentonite with cryo-stabilized pore water. Journal Applied Clay Science.

[17] Li Q, Yue QY, Sun H, Su Y, Gao Y. Comparative study on the properties, mechanisms and process designs for the adsorption of non-ionic or anionic dyes onto cationic-polymer/

[18] Utracki L. Clay-containing polymeric nanocomposites. Shrewsbury: Rapra Technology

[19] Wei J, Zhu R, Zhu J. Simultaneous sorption of crystal violet and 2-naphthol to bentonite

[20] Nguyen QT, Baird DG. An improved technique for exfoliating and dispersing nanoclay particles into polymer matrices using supercritical carbon dioxide. Polymer.

[21] Pillai SK, Ray S. Chitosan-based nanocomposites.Journal of Natural Polymers. 2012:33-68 [22] DeLeo C, Augusto C, do Carmo Goncalves PM, Velankar S. Preparation and characterization of clay nanocomposites of plasticized starch and polypropylene polymer

[23] Charhouf I. Thesis titled Synthesis and characterization of hydrogel of Chitosan for medical applications. Hassan II University of Casablanca, Faculty of Science Ben M'Sik;

[24] Lavertu M, Xia Z, Serreqi AN, Berrada M, Rodrigues A, Wang D, Buschmann MD, Ajay Gupta. A validated 1H NMR method for the determination of the degree of deacetylation of chitosan. Journal of Pharmaceutical and Biomedical Analysis. 2003;**32**:1149-1158 [25] Sedighi H, Irannajad M, Gharabaghi M, Amirkabir. Silica impurities removal on bentonite sample for nanoclay production. Journal of Science & Research (Civil & Environmental

[26] Charhouf I, Bennamara A, Abourriche A, Berrada M. Characterization of chitosan and fabrication of chitosan hydrogels matrices for biomedical applications. MATEC Web of

[27] Standard Test Method for Tensile Properties of Thin Plastic Sheeting, Annual Book of

[28] ASTM D882 published on June 2002, originally published as D 882-46 T. and Last previ-

[29] Cheng LH, Karim AA, Seow CC. Effects of water-glycerol and water-sorbitol interactions on the physical properties of konjac glucomannan films. Journal of Food Science.

[30] Cuq B, Gontard N, Cuq J, Guilbert S. Selected functional properties of fish myofibrillar protein-based films as affected by hydrophilic plasticizers. Journal of Agricultural and

bentonite. Journal of Environmental Management. 2010;**91**:1601-1611

with different CECs. Journal of Hazardous Materials. 2013;**166**:195-199

blends. Journal of Polymers and the Environment. 2011;**19**:689-697

Engineering) (AJSR – CEE), Summer. 2013;**45**(1):11-13

Conferences 5. 2013;**04030**. DOI: 10.1051/matecconf/20130504030

ASTM Standards. Current edition approved April 10, 2002

March 2006;**71**(2). DOI: 10.1111/j.1365-2621.2006.tb08898.x

Ltd; Polymer International. May 2005;**54**:860

68 Chitin-Chitosan - Myriad Functionalities in Science and Technology

2010;**47**:330-342

2007;**48**:6923-6933

10 January 2015

ous edition is D 882-01

Food Chemistry. 1997;**45**(3):622-626

**Chapter 4**

**Provisional chapter**

**A Review of Chitosan-Based Materials for the Removal**

**A Review of Chitosan-Based Materials for the Removal**

DOI: 10.5772/intechopen.76540

**of Organic Pollution from Water and Bioaugmentation**

Chitin is a natural polymer extracted mostly from shrimp or crab shells and is the Earth's second most abundant polysaccharide. After a simple deacetylation procedure, chitin is converted into chitosan that consists in a polysaccharide structure of deacetylated-β-glucosamine. Chitosan has been largely employed in wastewater treatment the removal of colloids through coagulation-flocculation processes. Different chitosan based materials have been produced and tested in the removal of inorganic pollutants such as toxic metals and metalloids, nutrients, dyes, micropollutants and hydrocarbons. Sorbents such as magnetic-activated carbon chitosan have been successfully tested in the removal of antibiotics (ciprofloxacin, erythromycin and amoxicillin) from water. Raw chitosan and ZnO nanoparticles entrapped in chitosan have demonstrated an excellent potential for the removal of the insecticide permethrin from aqueous effluents. Chitin and chitosan in flake and powder form have also demonstrated a promising effectiveness in the removal of oil spilled in seawater. Superhydrophobic and superoleophilic sponges modified by thioles have been also prepared from chitosan and used for the removal of oil spills. Chitosan hydrogels have been tested as well as entrapment matrices for the immobilization of hydrocarbon-degrading biomass for oil spills. Strains such as *R. corynebacteriorides* (QBTo), *Bacillus subtilis* LAMI008 and *B. pumilus* have been successfully immobilized and employed in hydrocarbon degradation processes. In this book chapter, the use of chitosan and chitosan-based materials in the removal of organic pollutants from

**Keywords:** chitin, chitosan, adsorption, organic pollutants, sorbents, oil spill pollution,

**of Organic Pollution from Water and Bioaugmentation**

© 2016 The Author(s). Licensee InTech. 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.

© 2018 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.

Carlos Escudero-Oñate and Elena Martínez-Francés

Carlos Escudero-Oñate and Elena Martínez-Francés

Additional information is available at the end of the chapter

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/intechopen.76540

**Abstract**

water is reviewed.

bioaugmentation, water treatment

#### **A Review of Chitosan-Based Materials for the Removal of Organic Pollution from Water and Bioaugmentation A Review of Chitosan-Based Materials for the Removal of Organic Pollution from Water and Bioaugmentation**

DOI: 10.5772/intechopen.76540

Carlos Escudero-Oñate and Elena Martínez-Francés Carlos Escudero-Oñate and Elena Martínez-Francés

Additional information is available at the end of the chapter Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/intechopen.76540

#### **Abstract**

Chitin is a natural polymer extracted mostly from shrimp or crab shells and is the Earth's second most abundant polysaccharide. After a simple deacetylation procedure, chitin is converted into chitosan that consists in a polysaccharide structure of deacetylated-β-glucosamine. Chitosan has been largely employed in wastewater treatment the removal of colloids through coagulation-flocculation processes. Different chitosan based materials have been produced and tested in the removal of inorganic pollutants such as toxic metals and metalloids, nutrients, dyes, micropollutants and hydrocarbons. Sorbents such as magnetic-activated carbon chitosan have been successfully tested in the removal of antibiotics (ciprofloxacin, erythromycin and amoxicillin) from water. Raw chitosan and ZnO nanoparticles entrapped in chitosan have demonstrated an excellent potential for the removal of the insecticide permethrin from aqueous effluents. Chitin and chitosan in flake and powder form have also demonstrated a promising effectiveness in the removal of oil spilled in seawater. Superhydrophobic and superoleophilic sponges modified by thioles have been also prepared from chitosan and used for the removal of oil spills. Chitosan hydrogels have been tested as well as entrapment matrices for the immobilization of hydrocarbon-degrading biomass for oil spills. Strains such as *R. corynebacteriorides* (QBTo), *Bacillus subtilis* LAMI008 and *B. pumilus* have been successfully immobilized and employed in hydrocarbon degradation processes. In this book chapter, the use of chitosan and chitosan-based materials in the removal of organic pollutants from water is reviewed.

**Keywords:** chitin, chitosan, adsorption, organic pollutants, sorbents, oil spill pollution, bioaugmentation, water treatment

© 2016 The Author(s). Licensee InTech. 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. © 2018 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.

#### **1. Introduction**

Chitin is a natural polysaccharide and the second most abundant biopolymer on Earth after cellulose [1]. This biopolymer consists of units of β-(1–4)-N-acetyl-D-glucosamine and is the main component of the exoskeleton of arthropods and crustaceans but also can be found in relevant amount in the cell walls of fungi. Chitin is a structural biopolymer whose role is analogous to that of collagen in the higher animals and cellulose in terrestrial plants [2]. In a similar way, plants produce cellulose in their cell walls, and insects and crustaceans synthetize chitin and accumulate it in their shells. Chitin may be regarded as cellulose with hydroxyl at position C2 replaced by an acetamide group (-CONH2 ). This similarity partly explains some analogies occurring in chitin and cellulose, such as low solubility and low chemical reactivity [3]. Chitin is found in three polymeric forms, α-, β- and γ-chitin, usually found in shrimp and crab shells, squid pen and stomach cuticles of cephalopod, respectively. From the three aforementioned forms of the biopolymer, α-chitin is the most abundant and stable form. α-, β- and γ-chitin correspond to antiparallel, parallel and alternated arrangements of polymer chains, respectively. A hydrogen bond between the acetamide group on the C2 carbons and the secondary alcoholic hydroxyl groups on the C3 carbon is linked through a water molecule with the primary alcoholic hydroxyl groups on a C6 carbon. As a result of this configuration, chitin possesses a strong crystalline structure, which explains the high chemical and solvent stability of the biopolymer. Due to its crystalline structure, chitin exhibits remarkable differences from cellulose in the solubility and reactivity despite of the relatively similar chemical structure [3].

The production of chitin uses basic raw materials of the cuticles of various crustaceans, principally crabs and shrimps. In regular fishery wastes, the biopolymer chitin is associated with proteins, minerals, lipids and pigments [4]. All these substances are considered impurities, and they all have to be quantitatively removed to achieve the required purity of the chitin. The chitin is normally extracted from the carapaces from crustaceans treating the crushed material with acid to achieve complete dissolution of the calcium carbonate structure. After this process, the material is submitted to an alkaline extraction to achieve the solubilization of the proteins. In a later purification step, the material obtained from the deproteinization process follows a decolorization step to remove residues of pigments to yield an almost colorless product [5]. Partial deacetylation of chitin leads to the formation of the polymer chitosan, consisting of units poly(D-glucosamine). A scheme of the production of chitosan from waste crustacean shells following chemical and biological approaches is presented in **Figure 1**.

Chitosan is insoluble in water, alkali and organic solvents but soluble in most solutions of organic acids when the pH of the solution is lower than 6. Acetic and formic are two of the most widely used acids employed to solubilize chitosan. Some dilute inorganic acids such

**Figure 1.** Production of chitin and chitosan using chemical and biological methods (adapted from Jo and co-authors [6]).

), hydrochloric acid (HCl), perchloric acid (HClO4

Chitosan exhibits a unique set of properties that makes this polymer a great candidate for the development of water treatment processes. Among them, the most relevant are its high biodegradability, low toxicity, low price and natural availability. The weaknesses exhibited by

) can also be used to prepare chitosan solutions but only after prolonged stirring and warming [7]. At low pH chitosan remains as a polycationic species, due to protonation of the

A Review of Chitosan-Based Materials for the Removal of Organic Pollution from Water and…

http://dx.doi.org/10.5772/intechopen.76540

73

) and phosphoric acid

as nitric acid (HNO3

amino group according to **Figure 3** [8].

(H3 PO4

When the degree of deacetylation of chitin reaches about 50%, the material obtained starts becoming soluble in aqueous acidic media and is called chitosan [5]. The degree of deacetylation is indicative of the amount of amino groups (-NH2 ) along the chitosan chain and refers to the degree of removal of acetyl groups (-COCH3 ) from the amido moieties. The degree of deacetylation and the degree of polymerization (DP), which in turn decides molecular weight of polymer, are two important parameters dictating the use of chitosans for various applications [1]. A scheme of the deacetylation reaction that converts raw chitin into chitosan is presented in **Figure 2**.

**1. Introduction**

structure [3].

presented in **Figure 1**.

presented in **Figure 2**.

position C2 replaced by an acetamide group (-CONH2

72 Chitin-Chitosan - Myriad Functionalities in Science and Technology

lation is indicative of the amount of amino groups (-NH2

to the degree of removal of acetyl groups (-COCH3

Chitin is a natural polysaccharide and the second most abundant biopolymer on Earth after cellulose [1]. This biopolymer consists of units of β-(1–4)-N-acetyl-D-glucosamine and is the main component of the exoskeleton of arthropods and crustaceans but also can be found in relevant amount in the cell walls of fungi. Chitin is a structural biopolymer whose role is analogous to that of collagen in the higher animals and cellulose in terrestrial plants [2]. In a similar way, plants produce cellulose in their cell walls, and insects and crustaceans synthetize chitin and accumulate it in their shells. Chitin may be regarded as cellulose with hydroxyl at

analogies occurring in chitin and cellulose, such as low solubility and low chemical reactivity [3]. Chitin is found in three polymeric forms, α-, β- and γ-chitin, usually found in shrimp and crab shells, squid pen and stomach cuticles of cephalopod, respectively. From the three aforementioned forms of the biopolymer, α-chitin is the most abundant and stable form. α-, β- and γ-chitin correspond to antiparallel, parallel and alternated arrangements of polymer chains, respectively. A hydrogen bond between the acetamide group on the C2 carbons and the secondary alcoholic hydroxyl groups on the C3 carbon is linked through a water molecule with the primary alcoholic hydroxyl groups on a C6 carbon. As a result of this configuration, chitin possesses a strong crystalline structure, which explains the high chemical and solvent stability of the biopolymer. Due to its crystalline structure, chitin exhibits remarkable differences from cellulose in the solubility and reactivity despite of the relatively similar chemical

The production of chitin uses basic raw materials of the cuticles of various crustaceans, principally crabs and shrimps. In regular fishery wastes, the biopolymer chitin is associated with proteins, minerals, lipids and pigments [4]. All these substances are considered impurities, and they all have to be quantitatively removed to achieve the required purity of the chitin. The chitin is normally extracted from the carapaces from crustaceans treating the crushed material with acid to achieve complete dissolution of the calcium carbonate structure. After this process, the material is submitted to an alkaline extraction to achieve the solubilization of the proteins. In a later purification step, the material obtained from the deproteinization process follows a decolorization step to remove residues of pigments to yield an almost colorless product [5]. Partial deacetylation of chitin leads to the formation of the polymer chitosan, consisting of units poly(D-glucosamine). A scheme of the production of chitosan from waste crustacean shells following chemical and biological approaches is

When the degree of deacetylation of chitin reaches about 50%, the material obtained starts becoming soluble in aqueous acidic media and is called chitosan [5]. The degree of deacety-

deacetylation and the degree of polymerization (DP), which in turn decides molecular weight of polymer, are two important parameters dictating the use of chitosans for various applications [1]. A scheme of the deacetylation reaction that converts raw chitin into chitosan is

). This similarity partly explains some

) along the chitosan chain and refers

) from the amido moieties. The degree of

**Figure 1.** Production of chitin and chitosan using chemical and biological methods (adapted from Jo and co-authors [6]).

Chitosan is insoluble in water, alkali and organic solvents but soluble in most solutions of organic acids when the pH of the solution is lower than 6. Acetic and formic are two of the most widely used acids employed to solubilize chitosan. Some dilute inorganic acids such as nitric acid (HNO3 ), hydrochloric acid (HCl), perchloric acid (HClO4 ) and phosphoric acid (H3 PO4 ) can also be used to prepare chitosan solutions but only after prolonged stirring and warming [7]. At low pH chitosan remains as a polycationic species, due to protonation of the amino group according to **Figure 3** [8].

Chitosan exhibits a unique set of properties that makes this polymer a great candidate for the development of water treatment processes. Among them, the most relevant are its high biodegradability, low toxicity, low price and natural availability. The weaknesses exhibited by

the functional properties of chitosan while improving the mechanical strength, cross-linking might be found. Several reagents such as glyoxal, glutaraldehyde and epichlorohydrin have

A Review of Chitosan-Based Materials for the Removal of Organic Pollution from Water and…

Chitosan has revealed a large potential in the detoxification of polluted effluents. This biopolymer on itself and chitosan-based materials have not only shown a high capacity to remove a variety of toxic metals such as Cu(II) [24–27], Pb(II) [28, 29], Cr(VI) [30, 31], As(V) [32], Mo(VI) [33] and Hg(II) [34] but also have demonstrated a large potential to remove other concerning

the abatement of inorganic pollution from water, this biopolymer has been also explored as sorbent against organic pollution. In the next sections, we review the use of raw chitosan and chitosan-based materials in the removal of micropollutants and in the abatement of hydrocar-

In recent years, chitosan-based composites using metals [37], metal oxides [38] and bimetals [39] have been receiving a large attention as alternative sorbents in water treatment processes. These kinds of materials have been chosen primarily due to their high adsorption capability [40]. Arayne and co-workers in 2011 studied the potential of raw chitosan beads and chitosan beads modified with ZnO nanoparticles (Cs/ZnO NPs) to remove permethrin, an insecticide largely employed in agriculture [41]. Through this study, the authors demonstrated that chitosan beads have an excellent adsorption performance and that the removal efficiency from a 0.1 ppm solution of permethrin increased from 49% when using chitosan beads to 99% when using Cs/ZnO NPs. Despite chitosan demonstrated a high capacity on itself to remove permethrin, including Cs/ZnO NPs in the matrix of the biopolymer, provided a large enhancement that leads to the almost total removal of this pollutant [42]. Saifuddin and co-authors, also in 2011, reported the use of a composite system based on cross-linked chitosan-silver nanoparticles (Cs-Ag NPs) to remove the pesticide atrazine (a very persistant herbicide of the triazine class) [43]. In their study, the kinetics of removal of the pesticide by the developed sorbent was evaluated. The authors reported an equilibrium time at about 65 min for 1, 5, 10, 20 and 25 ppm of atrazine. During their experiments, the authors detected a remarkable increase in the reduction of the pesticide content in water when increasing the sorbent dose. At the dosage of 2.0 g/L of Cs-AgNPs composite, 98% of the initial concentration of atrazine (from 1 ppm solution) was removed [43]. Danalıoğlu and co-authors, in a recent study, developed and tested a novel adsorbent based on a composite magnetic-activated carbon/chitosan system (MACC) for the removal of three widely employed antibiotics: ciprofloxacin, erythromycin and amoxicillin [44]. In their study, MACC nanocomposite demonstrated a good adsorption performance towards the targeted antibiotics [44]. Herein, the initial concentrations of antibiotics tested were 15, 60 and 60 ppm for ciprofloxacin, erythromycin and amoxicillin, respectively. To the initial antibiotic solution,

− , NO2 −

and PO4

−3) [35, 36]. In addition to

http://dx.doi.org/10.5772/intechopen.76540

75

been employed to reinforce the structure of chitosan by cross-linking [19, 21–23].

**2. Chitosan-based systems for the removal of organic pollutants**

inorganic species from water such as nutrients (NO3

**2.1. Chitosan-based materials for the removal of organic pollutants**

bon pollution associated to oil spills.

**Figure 2.** Chemical structure of (a) chitin and (b) chitosan.

this biopolymer however derive from its low acid stability, poor mechanical properties, low thermal stability, resistance to mass transfer, low porosity and surface areas [9, 10]. In order to overcome the drawbacks exhibited by chitosan, a large amount of effort has been devoted to the development of physicochemical modification methods to include different types of functionalization in the polymer. Chemical modifications such as oligomerization, alkylation, acylation, quaternization, hydroxyalkylation, carboxyalkylation, thiolation, sulfation, phosphorylation, enzymatic modifications and graft copolymerization have been carried out, allowing obtaining modified properties for specific end used applications in a large variety of fields [1]. Following physical and chemical methods, researchers have managed to produce a variety of forms of chitosan such as gel beads, membranes, film, fibers, porous frameworks, powders, sponges, hollow fibres and nanoparticles [11–20]. Some chemical modifications have been found capable of enhancing its flexibility and chemical stability and lower its susceptibility to acidic media. Among the most widely employed modifications that contribute modulation of

**Figure 3.** Protonation and deprotonation equilibrium of chitosan.

the functional properties of chitosan while improving the mechanical strength, cross-linking might be found. Several reagents such as glyoxal, glutaraldehyde and epichlorohydrin have been employed to reinforce the structure of chitosan by cross-linking [19, 21–23].

#### **2. Chitosan-based systems for the removal of organic pollutants**

Chitosan has revealed a large potential in the detoxification of polluted effluents. This biopolymer on itself and chitosan-based materials have not only shown a high capacity to remove a variety of toxic metals such as Cu(II) [24–27], Pb(II) [28, 29], Cr(VI) [30, 31], As(V) [32], Mo(VI) [33] and Hg(II) [34] but also have demonstrated a large potential to remove other concerning inorganic species from water such as nutrients (NO3 − , NO2 − and PO4 −3) [35, 36]. In addition to the abatement of inorganic pollution from water, this biopolymer has been also explored as sorbent against organic pollution. In the next sections, we review the use of raw chitosan and chitosan-based materials in the removal of micropollutants and in the abatement of hydrocarbon pollution associated to oil spills.

#### **2.1. Chitosan-based materials for the removal of organic pollutants**

this biopolymer however derive from its low acid stability, poor mechanical properties, low thermal stability, resistance to mass transfer, low porosity and surface areas [9, 10]. In order to overcome the drawbacks exhibited by chitosan, a large amount of effort has been devoted to the development of physicochemical modification methods to include different types of functionalization in the polymer. Chemical modifications such as oligomerization, alkylation, acylation, quaternization, hydroxyalkylation, carboxyalkylation, thiolation, sulfation, phosphorylation, enzymatic modifications and graft copolymerization have been carried out, allowing obtaining modified properties for specific end used applications in a large variety of fields [1]. Following physical and chemical methods, researchers have managed to produce a variety of forms of chitosan such as gel beads, membranes, film, fibers, porous frameworks, powders, sponges, hollow fibres and nanoparticles [11–20]. Some chemical modifications have been found capable of enhancing its flexibility and chemical stability and lower its susceptibility to acidic media. Among the most widely employed modifications that contribute modulation of

**Figure 2.** Chemical structure of (a) chitin and (b) chitosan.

74 Chitin-Chitosan - Myriad Functionalities in Science and Technology

**Figure 3.** Protonation and deprotonation equilibrium of chitosan.

In recent years, chitosan-based composites using metals [37], metal oxides [38] and bimetals [39] have been receiving a large attention as alternative sorbents in water treatment processes. These kinds of materials have been chosen primarily due to their high adsorption capability [40]. Arayne and co-workers in 2011 studied the potential of raw chitosan beads and chitosan beads modified with ZnO nanoparticles (Cs/ZnO NPs) to remove permethrin, an insecticide largely employed in agriculture [41]. Through this study, the authors demonstrated that chitosan beads have an excellent adsorption performance and that the removal efficiency from a 0.1 ppm solution of permethrin increased from 49% when using chitosan beads to 99% when using Cs/ZnO NPs. Despite chitosan demonstrated a high capacity on itself to remove permethrin, including Cs/ZnO NPs in the matrix of the biopolymer, provided a large enhancement that leads to the almost total removal of this pollutant [42]. Saifuddin and co-authors, also in 2011, reported the use of a composite system based on cross-linked chitosan-silver nanoparticles (Cs-Ag NPs) to remove the pesticide atrazine (a very persistant herbicide of the triazine class) [43]. In their study, the kinetics of removal of the pesticide by the developed sorbent was evaluated. The authors reported an equilibrium time at about 65 min for 1, 5, 10, 20 and 25 ppm of atrazine. During their experiments, the authors detected a remarkable increase in the reduction of the pesticide content in water when increasing the sorbent dose. At the dosage of 2.0 g/L of Cs-AgNPs composite, 98% of the initial concentration of atrazine (from 1 ppm solution) was removed [43].

Danalıoğlu and co-authors, in a recent study, developed and tested a novel adsorbent based on a composite magnetic-activated carbon/chitosan system (MACC) for the removal of three widely employed antibiotics: ciprofloxacin, erythromycin and amoxicillin [44]. In their study, MACC nanocomposite demonstrated a good adsorption performance towards the targeted antibiotics [44]. Herein, the initial concentrations of antibiotics tested were 15, 60 and 60 ppm for ciprofloxacin, erythromycin and amoxicillin, respectively. To the initial antibiotic solution, 1 mg of MACC adsorbent was added. As a result, adsorption took place rapidly during the first 30 min, and then the adsorption rate slowed down to reach the equilibrium at about 120 min. The authors performed a set of equilibrium experiments and, by means of the Langmuir isotherm model, managed to calculate the maximum sorption capacity of the material for the different antibiotics (90.01 mg/g for ciprofloxacin, 178.57 mg/g for erythromycin and 526.31 mg/g for amoxicillin [44]). Danalıoğlu et al. also compared the adsorption capacity of MACC for ciprofloxacin to that reported for magnetic alginate-Fe3 O4 hydrogel fiber and graphene oxide/calcium alginate [44]. Magnetic alginate-Fe3 O4 hydrogel presented an adsorption capacity for ciprofloxacin ranging from 153 to 555 μg/g [45], and graphene oxide/calcium alginate varied from 18.45 to 39.06 mg/g [46].

Different kinds of adsorbents have been explored for the removal of oil droplets from oil-inwater emulsions. For instance, activated carbon, biopolymers, organoclays, sawdust, vermiculite, walnut shell and resins have been tested for this purpose [53–58]. Biopolymer-supported materials have demonstrated being an efficient adsorbent for the removal of several contaminants from aquatic ecosystems. However, some of them have exhibited limitations when facing the scenario of oil removal. Chitosan has demonstrated being one of the most efficient biopolymers for the removal of oil droplets from water. The polymer, in addition to its oil sorption capacity, exhibits a unique structure that is very prone to chemical functionalization, allowing a large versatility in the production of novel sorptive materials with oil-enhanced selectivity and capacity. In addition to this, chitosan has a good biodegradability, biocompat-

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77

Barros and co-workers [61] investigated the adsorption capacity of chitin flakes, chitin and chitosan powder, chitosan flakes and chitosan solution towards crude oil spilled in seawater. In their study, 5 L of seawater were placed in a plastic container, and 7 g of petroleum were added to it. After 30 min, 50 mL of a 0.5% chitosan solution was sprayed over the oil spill. The results showed that, although chitosan flakes had a better adsorption capacity for oil (0.379 ± 0.030 g oil/g adsorbent) compared to the others, the biopolymer sank after adsorbing the oil. Such a characteristic offered a clear hinder in practical applications. On the other hand, chitosan solution, despite presenting lower adsorption capacity (0.013 ± 0.001 g oil/g adsorbent), did not present the low buoyancy drawback [61]. Elanchezhiyan and colleagues [62] investigated the recovery of oil from oil-in-water emulsion using chitosan/ magnesium-aluminum layered double hydroxide hybrid composite (CS-LDHCs) obtained by a single co-precipitation method. CS-LDHC adsorbent was dispersed in 20 mL of deionized water solution containing 4% of oil and the effect of contact time in the oil removal by the CS-LDHCs and the layered double hydroxide hybrid (LDH) was investigated [62]. This was done by varying the contact time from 10 to 120 min at room temperature. Both adsorbents, CS-LDHCs and LDH, reached maximum oil removal saturation at 90 min, and, thus, the authors set 90 min as contact time for both adsorbents in further experiments. The researchers reported an oil removal capacity of 78% for CS-LDHCs, while for the LDH was found to be 30%. Since CS-LDHCs showed a much higher oil adsorption capacity, further studies were performed just targeting this material [62]. The effect of pH was also investigated in their study in the range from 3 to 11. This was done because normally the change in pH of oil-in-water emulsions cause emulsion breaking, which means that demulsification takes place [59, 63]. After their pH study, the authors demonstrated that the adsorption

Elanchezhiyan and co-workers also studied the effect of contact time on the removal of oil from oil-in-water emulsion using zirconium-chitosan composites (Zr-CS-HC) in timecourse experiments at room temperature [59]. The study of the effect of sorbent dosage of Zr-CS-HC indicated that a maximum oil removal percentage of 79% was achieved when exposing 400 mg of sorbent to 25 mL of polluted solution [59]. The authors determined that the maximum oil uptake on chitosan was reached after 4 h contact time. In their study, the authors demonstrated that Zr-CS-HC had a higher removal efficiency compared to chitosan and provided an explanation based on the higher number of vacant sites on the surface of

ibility, eco-friendliness and low cost [59, 60].

of oil was enhanced in acidic medium (pH 3.0) [62].

Zr-CS-HC [59].

In addition to the studies described above, other researchers have reported the removal of phenol and o-chlorophenol using chitosan beads modified with sodium alginate and calcium chloride [47]. These authors reported that such a modification improved the stability of the obtained material as well as the sorption capacity of the beads. The maximum sorption capacity for phenol reported by the authors in this study was 108.69 mg/g, while for o-chlorophenol was 97.08 mg/g. Lie and colleagues investigated the use of raw chitosan, chitosan chemically modified with salicylaldehyde (CS-SA), β-cyclodextrin (CS-CD) and a cross-linked β-cyclodextrin polymer (EPI-CD) in the removal of phenol, p-nitrophenol and p-chlorophenol from aqueous solution [48]. In their study, it was observed that the adsorption capacity of unmodified chitosan for phenol was remarkably lower than that observed for the modified biopolymer. While the chitosan modified by CS-CA was able to achieve a capacity of 8.50, 20.49 and 44.92 mg/g for phenol, p-chlorophenol and p-nitrophenol, respectively, the raw, unmodified chitosan was only able to barely remove about 2 mg/g of the substances. On the other hand, the sorption capacity of chitosan chemically modified by CS-CD was 34.93, 179.73 and 20.562 mg/g for phenol, p-chlorophenol and p-nitrophenol. The last modification by EPI-CD led to the sorption capacities of 131.50 mg/g (phenol), 74.25 mg/g (p-chlorophenol) and 41.11 mg/g (p-nitrophenol) [49].

The removal of phthalate esters (PAEs) [50] by molybdate-impregnated chitosan beads (MICB) in an aqueous solution has also been reported by Chen and co-workers in 2007. The experiments performed by the authors indicated that all PAEs studied were adsorbed by MICB; however, diheptyl phthalate (DHpP) was most efficiently removed, achieving capacity values of 3.01 mg/g and a removal value of 92.5% [51].

#### **2.2. Chitosan-based materials for the removal of oil pollution from water**

Among the different types of organic pollution affecting water bodies, a specially concerning type nowadays is the oil pollution. While catastrophic spills such as the Exxon Valdez oil spill in the coast of Alaska (1989) or the BP Deepwater Horizon oil spill in the Gulf of Mexico (2010) caused a very important harm and gathered a large amount of public attention, most of the oil spills are less extraordinary [52]. It is estimated that about 9 million barrels of oil are released globally into the oceans every year. Of this amount, however, more than half come from natural seepage from the ocean floor, and human consumption activities represent the second largest source of oil released into the oceans (about 35%) [52]. Eco-friendly and sustainable approaches to remove oil pollution from water are therefore required to avoid the environmental threat and hazards associated to it.

Different kinds of adsorbents have been explored for the removal of oil droplets from oil-inwater emulsions. For instance, activated carbon, biopolymers, organoclays, sawdust, vermiculite, walnut shell and resins have been tested for this purpose [53–58]. Biopolymer-supported materials have demonstrated being an efficient adsorbent for the removal of several contaminants from aquatic ecosystems. However, some of them have exhibited limitations when facing the scenario of oil removal. Chitosan has demonstrated being one of the most efficient biopolymers for the removal of oil droplets from water. The polymer, in addition to its oil sorption capacity, exhibits a unique structure that is very prone to chemical functionalization, allowing a large versatility in the production of novel sorptive materials with oil-enhanced selectivity and capacity. In addition to this, chitosan has a good biodegradability, biocompatibility, eco-friendliness and low cost [59, 60].

1 mg of MACC adsorbent was added. As a result, adsorption took place rapidly during the first 30 min, and then the adsorption rate slowed down to reach the equilibrium at about 120 min. The authors performed a set of equilibrium experiments and, by means of the Langmuir isotherm model, managed to calculate the maximum sorption capacity of the material for the different antibiotics (90.01 mg/g for ciprofloxacin, 178.57 mg/g for erythromycin and 526.31 mg/g for amoxicillin [44]). Danalıoğlu et al. also compared the adsorption capacity

tion capacity for ciprofloxacin ranging from 153 to 555 μg/g [45], and graphene oxide/calcium

In addition to the studies described above, other researchers have reported the removal of phenol and o-chlorophenol using chitosan beads modified with sodium alginate and calcium chloride [47]. These authors reported that such a modification improved the stability of the obtained material as well as the sorption capacity of the beads. The maximum sorption capacity for phenol reported by the authors in this study was 108.69 mg/g, while for o-chlorophenol was 97.08 mg/g. Lie and colleagues investigated the use of raw chitosan, chitosan chemically modified with salicylaldehyde (CS-SA), β-cyclodextrin (CS-CD) and a cross-linked β-cyclodextrin polymer (EPI-CD) in the removal of phenol, p-nitrophenol and p-chlorophenol from aqueous solution [48]. In their study, it was observed that the adsorption capacity of unmodified chitosan for phenol was remarkably lower than that observed for the modified biopolymer. While the chitosan modified by CS-CA was able to achieve a capacity of 8.50, 20.49 and 44.92 mg/g for phenol, p-chlorophenol and p-nitrophenol, respectively, the raw, unmodified chitosan was only able to barely remove about 2 mg/g of the substances. On the other hand, the sorption capacity of chitosan chemically modified by CS-CD was 34.93, 179.73 and 20.562 mg/g for phenol, p-chlorophenol and p-nitrophenol. The last modification by EPI-CD led to the sorption capacities of 131.50 mg/g (phenol), 74.25 mg/g (p-chlorophenol) and 41.11 mg/g (p-nitrophenol) [49].

The removal of phthalate esters (PAEs) [50] by molybdate-impregnated chitosan beads (MICB) in an aqueous solution has also been reported by Chen and co-workers in 2007. The experiments performed by the authors indicated that all PAEs studied were adsorbed by MICB; however, diheptyl phthalate (DHpP) was most efficiently removed, achieving capacity values

Among the different types of organic pollution affecting water bodies, a specially concerning type nowadays is the oil pollution. While catastrophic spills such as the Exxon Valdez oil spill in the coast of Alaska (1989) or the BP Deepwater Horizon oil spill in the Gulf of Mexico (2010) caused a very important harm and gathered a large amount of public attention, most of the oil spills are less extraordinary [52]. It is estimated that about 9 million barrels of oil are released globally into the oceans every year. Of this amount, however, more than half come from natural seepage from the ocean floor, and human consumption activities represent the second largest source of oil released into the oceans (about 35%) [52]. Eco-friendly and sustainable approaches to remove oil pollution from water are therefore required to avoid the

**2.2. Chitosan-based materials for the removal of oil pollution from water**

O4

hydrogel presented an adsorp-

O4

hydrogel fiber and

of MACC for ciprofloxacin to that reported for magnetic alginate-Fe3

graphene oxide/calcium alginate [44]. Magnetic alginate-Fe3

alginate varied from 18.45 to 39.06 mg/g [46].

76 Chitin-Chitosan - Myriad Functionalities in Science and Technology

of 3.01 mg/g and a removal value of 92.5% [51].

environmental threat and hazards associated to it.

Barros and co-workers [61] investigated the adsorption capacity of chitin flakes, chitin and chitosan powder, chitosan flakes and chitosan solution towards crude oil spilled in seawater. In their study, 5 L of seawater were placed in a plastic container, and 7 g of petroleum were added to it. After 30 min, 50 mL of a 0.5% chitosan solution was sprayed over the oil spill. The results showed that, although chitosan flakes had a better adsorption capacity for oil (0.379 ± 0.030 g oil/g adsorbent) compared to the others, the biopolymer sank after adsorbing the oil. Such a characteristic offered a clear hinder in practical applications. On the other hand, chitosan solution, despite presenting lower adsorption capacity (0.013 ± 0.001 g oil/g adsorbent), did not present the low buoyancy drawback [61]. Elanchezhiyan and colleagues [62] investigated the recovery of oil from oil-in-water emulsion using chitosan/ magnesium-aluminum layered double hydroxide hybrid composite (CS-LDHCs) obtained by a single co-precipitation method. CS-LDHC adsorbent was dispersed in 20 mL of deionized water solution containing 4% of oil and the effect of contact time in the oil removal by the CS-LDHCs and the layered double hydroxide hybrid (LDH) was investigated [62]. This was done by varying the contact time from 10 to 120 min at room temperature. Both adsorbents, CS-LDHCs and LDH, reached maximum oil removal saturation at 90 min, and, thus, the authors set 90 min as contact time for both adsorbents in further experiments. The researchers reported an oil removal capacity of 78% for CS-LDHCs, while for the LDH was found to be 30%. Since CS-LDHCs showed a much higher oil adsorption capacity, further studies were performed just targeting this material [62]. The effect of pH was also investigated in their study in the range from 3 to 11. This was done because normally the change in pH of oil-in-water emulsions cause emulsion breaking, which means that demulsification takes place [59, 63]. After their pH study, the authors demonstrated that the adsorption of oil was enhanced in acidic medium (pH 3.0) [62].

Elanchezhiyan and co-workers also studied the effect of contact time on the removal of oil from oil-in-water emulsion using zirconium-chitosan composites (Zr-CS-HC) in timecourse experiments at room temperature [59]. The study of the effect of sorbent dosage of Zr-CS-HC indicated that a maximum oil removal percentage of 79% was achieved when exposing 400 mg of sorbent to 25 mL of polluted solution [59]. The authors determined that the maximum oil uptake on chitosan was reached after 4 h contact time. In their study, the authors demonstrated that Zr-CS-HC had a higher removal efficiency compared to chitosan and provided an explanation based on the higher number of vacant sites on the surface of Zr-CS-HC [59].

Grem and co-authors reported that chitosan microspheres produced by ionic gelation of chitosan with sodium tripolyphosphate (STP) were able to separate 90% of the oil from produced water containing 200 ppm oil suspension using packed columns [64].

membrane had equilibrium swelling of 217 g/g and CM10 of 162 g/g and concluded that the best membrane was CM10 due to its excellent sorption capacity and fast removal kinetics [68].

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Among the different clean-up actions and materials employed as a first response against oil spills, the use of booms, skimmers, absorbent materials, controlled burning and vacuum and centrifuges might be found. These techniques cannot however achieve a complete clean-up of the polluted area, and their implementation should be done short after the oil spill occurs [69]. In the last years, the use of bioremediation-based techniques has largely attracted the attention of researchers and industrial stakeholders. The use of microorganisms for these decontamination purposes is considered as an effective and environmentally friendly treatment for, i.e., shorelines contaminated as a result of marine oil spills. Most of the compounds present in crude oil and refined products are prone to biodegradation and therefore might be removed from the environment through consumption by microbes [69]. There are mostly two complementary approaches: bioaugmentation and biostimulation. While the first approach involves addition of oil-degrading bacteria to the polluted system, the second approach intends to support the growth of the indigenous hydrocarbon degraders present in the system by the addition of nutrients and/or other growth-limiting substances [69, 70]. A scheme of a biodegradation is presented in **Figure 4**. The most rapid and complete degradation of the majority of organic pollutants is brought about under aerobic conditions. Such a process is normally initiated through an intracellular oxidative attack and the activation of the organic molecule through incorporation of oxygen in a reaction catalyzed by oxygenases and peroxidases [71]. A com-

**2.3. Chitosan-based materials containing immobilized bacteria for the removal of**

plete oxidation of the target hydrocarbon would lead to the production of CO2

both bioaugmentation- and biostimulation-based decontamination processes.

generation of different series of structures corresponding to different transformation products should however not be disregarded when this kind of bioremediation techniques is explored. In order to improve the performance of the degradation of oil-related pollutants, some researchers have proposed strategies that involve the use of biomass in immobilized systems. One of the preferred entrapment systems for these purposes has been chitosan. In addition to the natural trend of chitosan to absorb oil, chitosan hydrogels have excellent water permeability and mass transfer properties (allowing the required access of the biomass to the nutrients they require). In addition to the aforementioned benefits, chitosan contributes to providing shelter to the valuable biomass while helping preserving the integrity of the culture. The use of microorganisms entrapped in chitosan gel matrices is therefore expected to have a very positive impact in

Dellagnezze and co-workers studied a bacterial consortium composed of four metagenomic clones and *Bacillus subtilis* strain CBMAI 707 (all derived from petroleum reservoirs) entrapped in chitosan beads towards hydrocarbon degradation capacity [72]. Experiments were carried out in mesocosm scale (3000 L) with seawater artificially polluted with crude oil. The compounds present in the oil that were the target of the biodegradation studies were benzo (a) pyrene (C20H12), benzo (a) anthracene (C18H12) and benzo (K) fluoranthene (C20H12) [73–75]. The degradation of hydrocarbons was evaluated in two different treatments: bioaugmentation and control. The authors performed time-course experiments, following the system at days 0, 5, 10, 20 and 30. The researchers demonstrated that degradation ratios increased abruptly from

and water. The

**oil pollution**

In another very recent study, Doshi and colleagues [65] studied amphiphilic sodium salt of oleoyl carboxymethyl chitosan (NaO-CMCS) for the removal of oil from a simulated oil spill. Marine diesel was chosen as oil phase for the emulsion studies [65], and in their study, both deionized water and seawater were used to simulate oil-in-water (o/w) emulsions (1:1 v/v). The o/w creamy emulsions were prepared with different dosages of NaO-CMCS (0.5–5 g/L), and a calcium chloride dihydrate solution (0.1%) was also added to that mixture. From the results obtained, the authors concluded that about 75–85 and 19–49% of oil was recovered from the emulsified oil using deionized water and seawater, respectively [65]. The recovery of oil from the polluted aqueous phase was 76% in the case of deionized water containing a 0.5 g/L concentration of NaO-CMCS and 20% from seawater with a 2 g/L dose of NaO-CMCS. It was therefore concluded that this chitosan derivative was an effective material for the removal of oil from spills from polluted seawater [65].

Ummadisingu and co-workers [66] prepared chitosan from seafood industry waste and tested the purified material for the removal of oil from aqueous solutions. The authors explored the effect of contact time, pH, initial concentration and mass of adsorbent. They reported that the sorption equilibrium of oil on chitosan was reached after only 6 min of contact time, and the maximum capacity of chitosan to adsorb oil from oil–water solution was found to be 17.96 g/g of adsorbent [66].

Su and colleagues [67] have recently reported the preparation of a superhydrophobic and superoleophilic chitosan sponge using a freeze-drying method with the assistance of a crosslinking process employing tripolyphosphate/citral followed by octadecanethiol modification. In their paper, the authors describe a procedure that allowed getting a three-dimensional porous structure with large pore volume and good compressive properties. The obtained sponge was able to effectively absorb oil, reaching an absorptive capacity up to 60 times its own weight. The material was able to selectively absorb the emulsified oils in water and achieve continuous oil–water separation. The authors reported an oil–water separation efficiency up to 99% and claimed that the sponge still maintained a highly absorptive capacity after being reused for many cycles while having a good biodegradability.

Bibi and co-workers [68] investigated the adsorption capacity of carbon nanotubes (CNTs) mixed with chitosan (Cs)/poly(vinyl alcohol) (PVA) and cross-linked with silane. In their experimental setup, naphthalene was selected as polycyclic aromatic hydrocarbon (PAH) model, and its removal was studied with two membranes, CM10 and CW with and without CNTs, respectively [68]. A standard solution of 3 mg/L of naphthalene was prepared, and 30 mg of membranes were placed in 40 ml naphthalene-containing solution. The removal percentage of naphthalene with the CW membrane during the first 5 min reported by the authors was 10% and after 150 min 93%. For the CM10 membrane, more than 50% of naphthalene was removed during the first 5 min and 97% after 150 min. These results showed that CM10 membrane had good sorption capacity for naphthalene and that the sorption process took place fast [68]. The correlation between CNT content of the membrane and the removed amount of the naphthalene was 0.16 mg of naphthalene/1 mg CNTs. The authors reported that CW membrane had equilibrium swelling of 217 g/g and CM10 of 162 g/g and concluded that the best membrane was CM10 due to its excellent sorption capacity and fast removal kinetics [68].

#### **2.3. Chitosan-based materials containing immobilized bacteria for the removal of oil pollution**

Grem and co-authors reported that chitosan microspheres produced by ionic gelation of chitosan with sodium tripolyphosphate (STP) were able to separate 90% of the oil from produced

In another very recent study, Doshi and colleagues [65] studied amphiphilic sodium salt of oleoyl carboxymethyl chitosan (NaO-CMCS) for the removal of oil from a simulated oil spill. Marine diesel was chosen as oil phase for the emulsion studies [65], and in their study, both deionized water and seawater were used to simulate oil-in-water (o/w) emulsions (1:1 v/v). The o/w creamy emulsions were prepared with different dosages of NaO-CMCS (0.5–5 g/L), and a calcium chloride dihydrate solution (0.1%) was also added to that mixture. From the results obtained, the authors concluded that about 75–85 and 19–49% of oil was recovered from the emulsified oil using deionized water and seawater, respectively [65]. The recovery of oil from the polluted aqueous phase was 76% in the case of deionized water containing a 0.5 g/L concentration of NaO-CMCS and 20% from seawater with a 2 g/L dose of NaO-CMCS. It was therefore concluded that this chitosan derivative was an effective

Ummadisingu and co-workers [66] prepared chitosan from seafood industry waste and tested the purified material for the removal of oil from aqueous solutions. The authors explored the effect of contact time, pH, initial concentration and mass of adsorbent. They reported that the sorption equilibrium of oil on chitosan was reached after only 6 min of contact time, and the maximum capacity of chitosan to adsorb oil from oil–water solution was

Su and colleagues [67] have recently reported the preparation of a superhydrophobic and superoleophilic chitosan sponge using a freeze-drying method with the assistance of a crosslinking process employing tripolyphosphate/citral followed by octadecanethiol modification. In their paper, the authors describe a procedure that allowed getting a three-dimensional porous structure with large pore volume and good compressive properties. The obtained sponge was able to effectively absorb oil, reaching an absorptive capacity up to 60 times its own weight. The material was able to selectively absorb the emulsified oils in water and achieve continuous oil–water separation. The authors reported an oil–water separation efficiency up to 99% and claimed that the sponge still maintained a highly absorptive capacity

Bibi and co-workers [68] investigated the adsorption capacity of carbon nanotubes (CNTs) mixed with chitosan (Cs)/poly(vinyl alcohol) (PVA) and cross-linked with silane. In their experimental setup, naphthalene was selected as polycyclic aromatic hydrocarbon (PAH) model, and its removal was studied with two membranes, CM10 and CW with and without CNTs, respectively [68]. A standard solution of 3 mg/L of naphthalene was prepared, and 30 mg of membranes were placed in 40 ml naphthalene-containing solution. The removal percentage of naphthalene with the CW membrane during the first 5 min reported by the authors was 10% and after 150 min 93%. For the CM10 membrane, more than 50% of naphthalene was removed during the first 5 min and 97% after 150 min. These results showed that CM10 membrane had good sorption capacity for naphthalene and that the sorption process took place fast [68]. The correlation between CNT content of the membrane and the removed amount of the naphthalene was 0.16 mg of naphthalene/1 mg CNTs. The authors reported that CW

water containing 200 ppm oil suspension using packed columns [64].

78 Chitin-Chitosan - Myriad Functionalities in Science and Technology

material for the removal of oil from spills from polluted seawater [65].

after being reused for many cycles while having a good biodegradability.

found to be 17.96 g/g of adsorbent [66].

Among the different clean-up actions and materials employed as a first response against oil spills, the use of booms, skimmers, absorbent materials, controlled burning and vacuum and centrifuges might be found. These techniques cannot however achieve a complete clean-up of the polluted area, and their implementation should be done short after the oil spill occurs [69]. In the last years, the use of bioremediation-based techniques has largely attracted the attention of researchers and industrial stakeholders. The use of microorganisms for these decontamination purposes is considered as an effective and environmentally friendly treatment for, i.e., shorelines contaminated as a result of marine oil spills. Most of the compounds present in crude oil and refined products are prone to biodegradation and therefore might be removed from the environment through consumption by microbes [69]. There are mostly two complementary approaches: bioaugmentation and biostimulation. While the first approach involves addition of oil-degrading bacteria to the polluted system, the second approach intends to support the growth of the indigenous hydrocarbon degraders present in the system by the addition of nutrients and/or other growth-limiting substances [69, 70]. A scheme of a biodegradation is presented in **Figure 4**. The most rapid and complete degradation of the majority of organic pollutants is brought about under aerobic conditions. Such a process is normally initiated through an intracellular oxidative attack and the activation of the organic molecule through incorporation of oxygen in a reaction catalyzed by oxygenases and peroxidases [71]. A complete oxidation of the target hydrocarbon would lead to the production of CO2 and water. The generation of different series of structures corresponding to different transformation products should however not be disregarded when this kind of bioremediation techniques is explored.

In order to improve the performance of the degradation of oil-related pollutants, some researchers have proposed strategies that involve the use of biomass in immobilized systems. One of the preferred entrapment systems for these purposes has been chitosan. In addition to the natural trend of chitosan to absorb oil, chitosan hydrogels have excellent water permeability and mass transfer properties (allowing the required access of the biomass to the nutrients they require). In addition to the aforementioned benefits, chitosan contributes to providing shelter to the valuable biomass while helping preserving the integrity of the culture. The use of microorganisms entrapped in chitosan gel matrices is therefore expected to have a very positive impact in both bioaugmentation- and biostimulation-based decontamination processes.

Dellagnezze and co-workers studied a bacterial consortium composed of four metagenomic clones and *Bacillus subtilis* strain CBMAI 707 (all derived from petroleum reservoirs) entrapped in chitosan beads towards hydrocarbon degradation capacity [72]. Experiments were carried out in mesocosm scale (3000 L) with seawater artificially polluted with crude oil. The compounds present in the oil that were the target of the biodegradation studies were benzo (a) pyrene (C20H12), benzo (a) anthracene (C18H12) and benzo (K) fluoranthene (C20H12) [73–75]. The degradation of hydrocarbons was evaluated in two different treatments: bioaugmentation and control. The authors performed time-course experiments, following the system at days 0, 5, 10, 20 and 30. The researchers demonstrated that degradation ratios increased abruptly from

bacterial strain. The authors performed biodegradation tests in a crude oil-polluted seawater microcosms [77]. For this purpose, three different microcosm situations were tested. In the microcosms inoculated with QBTo immobilized onto chitosan, 60% of hydrocarbons in the hexane extracts were removed compared with the control microcosms sample and the seawater microcosms. In the control microcosms, QBTo could not produce a significant reduction in the hydrocarbon concentrations [77]. In the seawater microcosms, QBTo was inoculated without a carrier, and a decrease of 30% of hexane extract was obtained. The degradation of hydrocarbons in the microcosms with the strain QBTo immobilized onto chitosan was higher than that obtained in the microcosms without the carrier. The explanation to this improvement is due to the enhancement of the strain survival, since the carrier material and the biofilm

A Review of Chitosan-Based Materials for the Removal of Organic Pollution from Water and…

Costa and co-authors [78] investigated the potential of the bacterial strain *B. pumilus* entrapped in chitosan in the degradation of hexadecane. The biodegradation assays were performed with free-living and immobilized bacterial cells with 1% hexadecane (v/v). In addition to this, 5 mL of an adjusted culture with 109 CFU/mL were used in free-living cell assays [78]. For the immobilized assays with bacterial cells, 5 g of chitosan beads containing the selected strain were used, and the biodegradation was studied at 0, 48, 96 and 144 h. The biodegradation results indicated that after 48 h, the free-living cells removed 81.83% of the hydrocarbon, while the culture of immobilized cell was able to remove only 38.12%. The authors provided an explanation to this based on the fact that in the assays performed

ments performed with immobilized cells. The authors pointed out that during the immobilization process there was an important loss of cells. Cell counting performed by the authors during the biodegradation experiments showed that the immobilized biomass grew progressively and removed 84.53% of hexadecane after 96 h. These results, obtained in a larger time span, where similar to the 86.28% removed in assays performed with nonimmobilized, free-living cells. Moreover, the authors found that the biomass concentration inside the beads was similar to that observed in the free-living cultures at 144 h and also

Chitosan offers a large potential in the development of sorbent materials for abatement of organic pollution from water. The biopolymer can be used in many different applications on its raw form or included in the preparation of a large variety of materials such as hydrogel beads, nanoparticles, films, membranes and meshes. Among the different scenarios of severe organic pollution, the pollution caused by hydrocarbon spills into water bodies deserves a special mention. Chitosan and materials based on this polymer have demonstrated an enormous potential to efficiently remove hydrocarbons from contaminated water. In addition to the aforementioned, the potential offered by chitosan to develop biological remediation systems deserves a special mention. The excellent biocompatibility of this polymer makes possible development of oil remediation biosystems based on bacteria

times more biomass than in the experi-

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81

structure that the cells developed on it exert a protective effect [77].

with free-living cells, there was approximately 104

removed hexadecane efficiently [78].

**3. Conclusions**

entrapped into chitosan.

**Figure 4.** Oil biodegradation scheme under aerobic conditions.

the 5th to the 10th day and then just slightly increased until the end of the experiment. The system remained closed during the first 5 days to allow the acclimation of the bacteria to both treatments, and during this period, the authors did not observe significant biodegradation rates [72]. More than 90% of hydrocarbons' degradation was produced by the 10th day in both treatments. Similar to the 10th day, in day 20 most of the hydrocarbons were totally degraded. After 30 days from the beginning of the assays, the degradation percentages in the bioaugmentation treatment were higher than those observed in the control treatment. For instance, 35% of benzo (k) fluoranthene was degraded in the control treatment, 70% was degraded in the bioaugmentation treatment, and benzo (a) pyrene was almost completely degraded (99%). Likewise, benzo (a) anthracene showed higher degradation percentage, reaching 85% in the bioaugmented series compared to a 68% observed in the control [72].

Sar and Rosenberg [76] studied the biodegradation of n-hexadecane and its biosurfactant recovery. For this purpose, spores of *Bacillus subtilis* LAMI008 were entrapped in 3 mm chitosan beads and cross-linked with 0.3% glutaraldehyde [76]. The authors performed biodegradation assays in 50 mL of mineral medium containing 1% n-hexane (v/v) supplemented with 1% glucose (w/v) and inoculated with 10% of spore suspension (v/v) or with 10% of spore-entrapped chitosan beads (w/v). Both cultures were adjusted to 107 CFU/mL [76]. The biodegradation of n-hexadecane by *Bacillus subtilis* LAMI008 entrapped in chitosan beads was compared with that by free cells under similar conditions, and almost 100% of 1% n-hexadecane was degraded within 48 h in both assays.

In another study Gentili and co-authors [77] examined the potential of chitosan flakes as carrier material for the immobilization of *R. corynebacteriorides* (QBTo), a hydrocarbon-degrading bacterial strain. The authors performed biodegradation tests in a crude oil-polluted seawater microcosms [77]. For this purpose, three different microcosm situations were tested. In the microcosms inoculated with QBTo immobilized onto chitosan, 60% of hydrocarbons in the hexane extracts were removed compared with the control microcosms sample and the seawater microcosms. In the control microcosms, QBTo could not produce a significant reduction in the hydrocarbon concentrations [77]. In the seawater microcosms, QBTo was inoculated without a carrier, and a decrease of 30% of hexane extract was obtained. The degradation of hydrocarbons in the microcosms with the strain QBTo immobilized onto chitosan was higher than that obtained in the microcosms without the carrier. The explanation to this improvement is due to the enhancement of the strain survival, since the carrier material and the biofilm structure that the cells developed on it exert a protective effect [77].

Costa and co-authors [78] investigated the potential of the bacterial strain *B. pumilus* entrapped in chitosan in the degradation of hexadecane. The biodegradation assays were performed with free-living and immobilized bacterial cells with 1% hexadecane (v/v). In addition to this, 5 mL of an adjusted culture with 109 CFU/mL were used in free-living cell assays [78]. For the immobilized assays with bacterial cells, 5 g of chitosan beads containing the selected strain were used, and the biodegradation was studied at 0, 48, 96 and 144 h. The biodegradation results indicated that after 48 h, the free-living cells removed 81.83% of the hydrocarbon, while the culture of immobilized cell was able to remove only 38.12%. The authors provided an explanation to this based on the fact that in the assays performed with free-living cells, there was approximately 104 times more biomass than in the experiments performed with immobilized cells. The authors pointed out that during the immobilization process there was an important loss of cells. Cell counting performed by the authors during the biodegradation experiments showed that the immobilized biomass grew progressively and removed 84.53% of hexadecane after 96 h. These results, obtained in a larger time span, where similar to the 86.28% removed in assays performed with nonimmobilized, free-living cells. Moreover, the authors found that the biomass concentration inside the beads was similar to that observed in the free-living cultures at 144 h and also removed hexadecane efficiently [78].

#### **3. Conclusions**

the 5th to the 10th day and then just slightly increased until the end of the experiment. The system remained closed during the first 5 days to allow the acclimation of the bacteria to both treatments, and during this period, the authors did not observe significant biodegradation rates [72]. More than 90% of hydrocarbons' degradation was produced by the 10th day in both treatments. Similar to the 10th day, in day 20 most of the hydrocarbons were totally degraded. After 30 days from the beginning of the assays, the degradation percentages in the bioaugmentation treatment were higher than those observed in the control treatment. For instance, 35% of benzo (k) fluoranthene was degraded in the control treatment, 70% was degraded in the bioaugmentation treatment, and benzo (a) pyrene was almost completely degraded (99%). Likewise, benzo (a) anthracene showed higher degradation percentage, reaching 85% in the

Sar and Rosenberg [76] studied the biodegradation of n-hexadecane and its biosurfactant recovery. For this purpose, spores of *Bacillus subtilis* LAMI008 were entrapped in 3 mm chitosan beads and cross-linked with 0.3% glutaraldehyde [76]. The authors performed biodegradation assays in 50 mL of mineral medium containing 1% n-hexane (v/v) supplemented with 1% glucose (w/v) and inoculated with 10% of spore suspension (v/v) or with 10% of spore-entrapped chitosan beads (w/v). Both cultures were adjusted to 107 CFU/mL [76]. The biodegradation of n-hexadecane by *Bacillus subtilis* LAMI008 entrapped in chitosan beads was compared with that by free cells under similar conditions, and almost 100% of 1% n-hexadecane was degraded

In another study Gentili and co-authors [77] examined the potential of chitosan flakes as carrier material for the immobilization of *R. corynebacteriorides* (QBTo), a hydrocarbon-degrading

bioaugmented series compared to a 68% observed in the control [72].

**Figure 4.** Oil biodegradation scheme under aerobic conditions.

80 Chitin-Chitosan - Myriad Functionalities in Science and Technology

within 48 h in both assays.

Chitosan offers a large potential in the development of sorbent materials for abatement of organic pollution from water. The biopolymer can be used in many different applications on its raw form or included in the preparation of a large variety of materials such as hydrogel beads, nanoparticles, films, membranes and meshes. Among the different scenarios of severe organic pollution, the pollution caused by hydrocarbon spills into water bodies deserves a special mention. Chitosan and materials based on this polymer have demonstrated an enormous potential to efficiently remove hydrocarbons from contaminated water. In addition to the aforementioned, the potential offered by chitosan to develop biological remediation systems deserves a special mention. The excellent biocompatibility of this polymer makes possible development of oil remediation biosystems based on bacteria entrapped into chitosan.

#### **Conflict of interest**

The authors certify that they have no conflict of interest.

#### **Author details**

Carlos Escudero-Oñate\* and Elena Martínez-Francés

\*Address all correspondence to<EMAIL_ADDRESS>
Norwegian Institute for Water Research (NIVA), Oslo, Norway

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