**4. Functionalised polysaccharide adsorbents for the efficient removal of organic dye in aqueous solution**

The polysaccharide surface modification can improve their physicochemical properties and mechanical characteristics [26]. This strategy has also been reported to avoid leaching of organic substances and improve the adsorption potential of the nanoengineered adsorbent. The polysaccharide surface modification can be accomplished through graft copolymerisation and/or incorporation of specific nanoscale inorganic particles. Deposition of inorganic nanoparticles such as SiO2, Fe3O4, TiO2, and carbon nanotube onto polymeric supports has been reported to enhance their chemical, mechanical and thermal stabilities [36, 37].

#### **4.1 Polysaccharide functionalised by graft copolymerisation**

Graft copolymerisation of vinyl monomers onto polysaccharides is a wellreported and versatile technique that allows for the increased potential applicability of biopolymers. This procedure usually involves the attachment of a vinyl monomer to the polysaccharide backbone. In general, the vinyl monomer will undergo polymerisation in the presence of polysaccharide chains to generate a copolymeric network. The vinyl monomers that are frequently reported for the modification of gum-based polysaccharides involve the acrylamide (AAm), methyl methacrylate (MAA), acrylic acid (AA), *N*-vinyl imidazole (VI), and acrylonitrile (AN). The synthesis of polysaccharide graft copolymers is achieved by amending the biopolymer molecules *via* formation of branches of synthetic polymers. This can be accomplished through "grafting onto" or "grafting from" methodology [38]. The "grafting from" process entails the development of polymer chains from initiating sites

*Novel Nanomaterials*

**300**

**Figure 2.**

**Table 1.**

*The molecular structure of xanthan gum (XG) and* kappa*-carrageenan (*k*C) polysaccharides.*

**Name Composition Sources**

Fruit, nuts, grains, and

Deacetylation of chitin

vegetables

Shrimp shell

Algae, Bacteria

crops

Guar seed

Marine algae

Cereal grains, tuber

*Xanthomonas* bacteria

Cellulose Anhydroglucose units linked by the *β*-(1 → 4) glycosidic

2-acetamido-2-deoxy-D-glucose

Alginate *β*-(1 → 4)-Linked D-mannuronic acid and *α*- (1 → 4)-linked L-guluronic acid

branch linkages

Xanthan gum (1 → 4)-Attached D-glucose

residues

*Polysaccharides used as adsorbents for wastewater treatment.*

Chitosan Copolymer of *N*-glucosamine and *N*-acetylglucosamine

Starch (1 → 4)-Attached *α*-D-glucopyranosyl units with α-(1 → 6)

Guar gum Glycosidically *β*-(1 → 4)-linked D-mannose subunits and

Carrageenan D-galactose and 3,6-anhydrogalactose connected by

*α*-(1 → 3)- and *β*-(1 → 4)-glycosidic linkages

glycosidically (1 → 6)-linked D-galactose subunits

D-mannosyl, D-glucuronyl acid, O-acetyl and pyruvyl

bonds

units

Chitin Glycosidically *β*-(1 → 4)-linked

bacterial fermentation of carbohydrate source. This biopolymer is recovered through precipitation in ethanol, isopropyl alcohol or *tert*-butanol [31]. It is a high molecular weight polysaccharide, which provides suspension, thickness, and stabilisation of the combined material. The negative charge of XG biopolymer is mainly ascribed to the presence of carboxylic acid group within its backbone, thereby indicating its affinity for cationic species. XG main chain is made of

Xanthan gum (XG) is an anionic polymer obtained by *Xanthmonous campestris*

repeating cellulosic units with side chains involving an α-D-mannose with an acetyl group, a β-D-glucuronic residues and a terminal β-D mannose bearing the pyruvate substituent [32]. The physicochemical characteristics of XG include higher stability onto the polysaccharide framework. In the "grafting onto" method, on the other hand, the pre-formed polymer bearing a reactive end-functionality interacts with the functional groups that are located on the polysaccharide backbone. However, the latter presents inherent shortcomings, including the crowding of chains at the polysaccharide surface and a limited number of attachments [39].

Many techniques have been employed for the attachment of monomers onto polysaccharide surface, and these involve free radical graft copolymerisation, living radical polymerisation, and ionic polymerisation. Grafting using free radical approach requires an initiator (chemicals, photoirradiation, plasma ions or gamma rays exposure) to generate a free radical on the polysaccharide backbone. In ionic polymerisation technique, on the other hand, the chemical initiator generates cationic or anionic active centers which participate in the grafting process. Nevertheless, more than 60% of all the reported polymers are still synthesised by free radical polymerisation method. It is worth noting that the solubility, wettability, glass transition temperature, and elasticity of polysaccharides are tailored through grafting with synthetic monomer. For example, grafting of chitosan with vinyl monomer *N*-acryloylglycine in the presence of 2,2-dimethoxy-2-phenyl acetophenone initiator was reported to yield a material with relatively decreased solubility and wettability profiles [40]. The polysaccharide affinity to water limits its adsorption property owing to competitive phenomenon between the water molecules and pollutants in the aquatic milieu. Characterisation of the graft copolymerised polysaccharides can be ascertained using FTIR spectra analysis. Data obtained from this technique indicate the formation of covalent bonds. Considering the involvement of hydroxyl groups during graft copolymerisation, a shift and change in intensity of the band corresponding to O–H vibration can be evidenced.

In a recent study by our research team, the surface-modified XG polysaccharide obtained through grafting with acrylamide and acrylic acid monomers to afford XG grafted poly(AAm/AA) [XG-g-P(AAm/AA)], was used as an adsorbent for the removal of rhodamine B and methylene blue (MB) in aqueous solution. The UV irradiation method in the presence of benzophenone as initiator was employed to effect the attachment of monomers. UV irradiation approach is of interest because of its mild reaction conditions and less adverse effect to change bulk properties [41]. Moreover, lower radiation energy may be applied for the modification to proceed. The structural change from XG to XG-g-P(AAm/AA) was elucidated using FTIR spectroscopy (**Figure 3**).

The spectra of pristine XG showed absorption bands at 3263, 2915, 1712, 1653, 1416 and 1019 cm−1 attributed to O–H stretching vibration, C–H stretching vibration, C–O stretching, O–H bending, the symmetrical stretching of –CCO– group of glucuronic acid and C–O–C of the ether group, respectively [42, 43]. The formation of XG-g-P(AAm/AA) was evidenced with the change in intensity of the band around 3263 cm−1, the strong vibrational bands at 1593, and the shift of band at 1416 cm−1. After dye adsorption, the FTIR spectrum of loaded XG-g-P(AAm/ AA) was characterised by a shift in absorption bands, indicating a dye–adsorbent interaction. However, the peak of 2895 cm−1 attributed to C–H stretching did not experience a significant shift, suggesting that the dye adsorption took place through electrostatic and hydrogen-bonding interactions with the XG-g-P(AAm/AA) polysaccharide (**Figure 4**). Electrostatic interactions presumably occur between the nucleophilic functional groups (–COO<sup>−</sup> ) and the positively charged centres of the organic dye molecules (S and N). Also, hydrogen-bonding interactions are expected to take place between the hydroxyl groups of XG and aromatic π-electrons and/or nitrogen lone pair of electrons of the dye molecules.

The adsorption kinetics investigation for the removal of rhodamine B and methylene blue dyes in synthetic solutions using our prepared XG-g-P(AAm/AA)

**303**

solution (500 mg/l, pH 7).

**Figure 3.**

lowered efficiency [46].

*aureus* and *Escherichiacoli* [45].

*FTIR spectra of XG and XG-g-P(AAm/AA).*

*Nanoengineered Polysaccharide-Based Adsorbents as Green Alternatives for Dye Removal…*

material demonstrated that the procedure followed a pseudo-second-order model. On the other hand, the isothermal study indicated multilayer adsorption behaviour. In a different study, Elella et al. reported the synthesis of XG-g-poly(*N*-vinyl imidazole) copolymers using *N,N′*-methylene bisacrylamide as cross-linker [44]. This modified XG polysaccharide was obtained by a free radical technique using potassium persulfate initiator and then evaluated as an adsorbent for the removal of crystal violet dye from synthetic water samples. The maximum dye uptake onto this cross-linked grafted XG (0.04 g) was determined to be 625 mg/g in 50 ml crystal violet dye

Interestingly, the analogous XG-g-poly(*N*-vinyl imidazole) derivatives without linker have also been found to exhibit antibacterial activity against *Staphyloccus* 

**4.2 Polysaccharide functionalised by incorporation of inorganic nanoparticles**

Incorporation of inorganic NPs with the higher surface area has also been described as a fascinating strategy for improved adsorption procedure. This results from a strong synergistic outcome between the organic polysaccharide matrixes and embedded inorganic NPs. This methodology also affects the modification in mechanical properties of the hybrid adsorbent. Moreover, the polysaccharide moiety is anticipated to stabilise the nanoparticles and prevent aggregation. Metal oxide nanoparticles having desirable attributes as adsorbents often suffer tendency to agglomerate in aqueous solution due to their higher surface energy, leading to

XG grafted polyacrylamide XG-g-PAAm incorporated with nanosilica (SiO2 NPs), for example, was obtained *in situ* through hydrolysis and condensation of

*DOI: http://dx.doi.org/10.5772/intechopen.94883*

*Nanoengineered Polysaccharide-Based Adsorbents as Green Alternatives for Dye Removal… DOI: http://dx.doi.org/10.5772/intechopen.94883*

**Figure 3.** *FTIR spectra of XG and XG-g-P(AAm/AA).*

*Novel Nanomaterials*

onto the polysaccharide framework. In the "grafting onto" method, on the other hand, the pre-formed polymer bearing a reactive end-functionality interacts with the functional groups that are located on the polysaccharide backbone. However, the latter presents inherent shortcomings, including the crowding of chains at the

Many techniques have been employed for the attachment of monomers onto polysaccharide surface, and these involve free radical graft copolymerisation, living radical polymerisation, and ionic polymerisation. Grafting using free radical approach requires an initiator (chemicals, photoirradiation, plasma ions or gamma rays exposure) to generate a free radical on the polysaccharide backbone. In ionic polymerisation technique, on the other hand, the chemical initiator generates cationic or anionic active centers which participate in the grafting process. Nevertheless, more than 60% of all the reported polymers are still synthesised by free radical polymerisation method. It is worth noting that the solubility, wettability, glass transition temperature, and elasticity of polysaccharides are tailored through grafting with synthetic monomer. For example, grafting of chitosan with vinyl monomer *N*-acryloylglycine in the presence of 2,2-dimethoxy-2-phenyl acetophenone initiator was reported to yield a material with relatively decreased solubility and wettability profiles [40]. The polysaccharide affinity to water limits its adsorption property owing to competitive phenomenon between the water molecules and pollutants in the aquatic milieu. Characterisation of the graft copolymerised polysaccharides can be ascertained using FTIR spectra analysis. Data obtained from this technique indicate the formation of covalent bonds. Considering the involvement of hydroxyl groups during graft copolymerisation, a shift and change in intensity of the band corresponding to O–H vibration can be evidenced. In a recent study by our research team, the surface-modified XG polysaccharide obtained through grafting with acrylamide and acrylic acid monomers to afford XG grafted poly(AAm/AA) [XG-g-P(AAm/AA)], was used as an adsorbent for the removal of rhodamine B and methylene blue (MB) in aqueous solution. The UV irradiation method in the presence of benzophenone as initiator was employed to effect the attachment of monomers. UV irradiation approach is of interest because of its mild reaction conditions and less adverse effect to change bulk properties [41]. Moreover, lower radiation energy may be applied for the modification to proceed. The structural change from XG to XG-g-P(AAm/AA) was elucidated using FTIR

The spectra of pristine XG showed absorption bands at 3263, 2915, 1712, 1653, 1416 and 1019 cm−1 attributed to O–H stretching vibration, C–H stretching vibration, C–O stretching, O–H bending, the symmetrical stretching of –CCO– group of glucuronic acid and C–O–C of the ether group, respectively [42, 43]. The formation of XG-g-P(AAm/AA) was evidenced with the change in intensity of the band around 3263 cm−1, the strong vibrational bands at 1593, and the shift of band at 1416 cm−1. After dye adsorption, the FTIR spectrum of loaded XG-g-P(AAm/ AA) was characterised by a shift in absorption bands, indicating a dye–adsorbent interaction. However, the peak of 2895 cm−1 attributed to C–H stretching did not experience a significant shift, suggesting that the dye adsorption took place through electrostatic and hydrogen-bonding interactions with the XG-g-P(AAm/AA) polysaccharide (**Figure 4**). Electrostatic interactions presumably occur between the

organic dye molecules (S and N). Also, hydrogen-bonding interactions are expected to take place between the hydroxyl groups of XG and aromatic π-electrons and/or

The adsorption kinetics investigation for the removal of rhodamine B and methylene blue dyes in synthetic solutions using our prepared XG-g-P(AAm/AA)

) and the positively charged centres of the

polysaccharide surface and a limited number of attachments [39].

**302**

spectroscopy (**Figure 3**).

nucleophilic functional groups (–COO<sup>−</sup>

nitrogen lone pair of electrons of the dye molecules.

material demonstrated that the procedure followed a pseudo-second-order model. On the other hand, the isothermal study indicated multilayer adsorption behaviour. In a different study, Elella et al. reported the synthesis of XG-g-poly(*N*-vinyl imidazole) copolymers using *N,N′*-methylene bisacrylamide as cross-linker [44]. This modified XG polysaccharide was obtained by a free radical technique using potassium persulfate initiator and then evaluated as an adsorbent for the removal of crystal violet dye from synthetic water samples. The maximum dye uptake onto this cross-linked grafted XG (0.04 g) was determined to be 625 mg/g in 50 ml crystal violet dye solution (500 mg/l, pH 7).

Interestingly, the analogous XG-g-poly(*N*-vinyl imidazole) derivatives without linker have also been found to exhibit antibacterial activity against *Staphyloccus aureus* and *Escherichiacoli* [45].

#### **4.2 Polysaccharide functionalised by incorporation of inorganic nanoparticles**

Incorporation of inorganic NPs with the higher surface area has also been described as a fascinating strategy for improved adsorption procedure. This results from a strong synergistic outcome between the organic polysaccharide matrixes and embedded inorganic NPs. This methodology also affects the modification in mechanical properties of the hybrid adsorbent. Moreover, the polysaccharide moiety is anticipated to stabilise the nanoparticles and prevent aggregation. Metal oxide nanoparticles having desirable attributes as adsorbents often suffer tendency to agglomerate in aqueous solution due to their higher surface energy, leading to lowered efficiency [46].

XG grafted polyacrylamide XG-g-PAAm incorporated with nanosilica (SiO2 NPs), for example, was obtained *in situ* through hydrolysis and condensation of

#### **Figure 4.**

*The mechanism for dye adsorption onto XG-g-P(AAm/AA).*

tetraethylorthosilicate [Si(OC2H5)4] in the presence of ammonia at the copolymer surface [10]. This synthetic approach exploits the occurrence of hydrophilic groups on the polysaccharide backbone to control the hydrolysis, condensation and nucleation growth of metal oxide nanoparticles [47]. The functionalised SiO2 NPs@XG-g-PAAm composite was described as a highly improved adsorbent for the removal of anionic Congo red dye in aqueous solution. Grafting of polyacrylamide chain on XG was accomplished *via* free radical polymerisation technique in the presence of potassium persulphate initiator. The branched XG gum matrix acted as a template for the formation, growth, and stabilisation of SiO2 NPs through hydrogen bonding interaction between the –OH bonded surface group of SiO2 NPs with oxygen atom of the polysaccharide –COOH surface group [48].

Decoration of XG-g-P(AAm/AA) with SiO2 NPs (diameters range 2–7 nm) was also reported by Ghorai and coworkers [34]. These authors subjected the XG-g-PAAm material to hydrolysis in the presence of NaOH to generate the graft copolymer of XG [XG-g-P(AAm/AA)] (**Figure 5**). Subsequently, functionalisation of the later with SiO2 NPs was achieved *in situ* through hydrolysis and condensation of silica sol–gel Si(OC2H5)4 precursor (**Figure 6**). The resultant nanocomposite was employed as an adsorbent for the removal of cationic dyes in the aqueous milieu. The adsorbent exhibited good adsorption efficiency of 497.5 mg/g and 378.8 mg/g towards MB at pH 8 (adsorbent dose: 0.03 g/25 mL solution, contact time: 20 min, and temperature: 50°C) and methyl violet at pH 9 (adsorbent dose: 0.04 g/25 mL solution, contact time: 15 min, and temperature: 40°C), respectively.

*k*C modified with carbon nanotubes (10–20 nm diameter), and Fe3O4 (10–25 nm) was also synthesised following polymer grafting on the surface of multiwall carbon

**305**

238 m2

**Figure 6.**

**Figure 5.**

MOH2 +

and K+

and MO−

blue R = N(CH3)

arise from the Coulombic interaction between MOH2

*Hydrolysis of Si(OC2H5)4 and condensation of the silicic acid intermediate.*

*Fabrication of SiO2 NPs@XG-g-P(AAm/AA) composite and TEM image.*

−

tively charged (e.g. methyl orange R–SO3

+

/*k*-carrageenan–SO3

easily with an external magnet.

*Nanoengineered Polysaccharide-Based Adsorbents as Green Alternatives for Dye Removal…*

nanotubes and suspension in a solution of iron precursors Fe(III)/Fe(II) under nitrogen atmosphere [49]. The Brunauer–Emmett–Teller (BET) technique indicated an increase in specific surface area after attachment of carbon nanotubes (SBET:

/g) and deposition of magnetic Fe3O4 nanoparticles (SBET: 55 m2

occurrence of this metal oxide was evidenced by transmission electron microscopy (TEM) pictures analysis. Magnetism is an exclusive physical property that has been demonstrated to ease the water treatment procedure in adsorption technique. This property allows for the removal of spent adsorbent from the aqueous solution by a simple application of a magnet. The prepared magnetic *k*C-carbon nanotubes-Fe3O4 composite exhibited high adsorption toward MB dye in aqueous solution. The maximum dye uptake onto 0.4 g/L of this biofunctional nanocomposite was determined to be 1.24 × 10−4 mol/g−1 at pH 6.5. In aqueous solution, the adsorption potential of metal oxide (MOH) is regulated by the pH-dependent formation of complex ions

−

dispersing nanoparticles into gelatin environment and limiting their agglomeration. This technique has been reported to afford bio-related materials with better thermal stability and mechanical properties [53]. The magnetic behaviour of this cationic dye adsorbent was assessed with the vibrating sample magnetometer (VSM) standard method. The hysteresis loop revealed an S-shape with an estimated value of saturation magnetisation 3.4 emu/g, suggesting that the spent adsorbent can be removed

et al. described the modification of *k*C with polyvinyl alcohol (PVA) and Fe3O4 nanoparticles [52]. This nanocomposite was engineered using the *in-situ* chemical co-precipitation of Fe(II) and Fe(III) salts in the presence of PVA and ionic *k*C biopolymer under basic condition (**Figure 7**). Cross-linking of the occurring Fe3O4 nanoparticles and polymer matrixes was achieved by the freezing–thawing technique

[12, 50, 51]. Therefore, dye adsorption onto metal oxide surfaces

) centers, respectively. In a cognate investigation, Mahdavinia

+

interaction. Freezing–thawing plays a crucial role in

and MO−

) and positively charged (e.g. methylene

/g). The

, and the nega-

*DOI: http://dx.doi.org/10.5772/intechopen.94883*

*Nanoengineered Polysaccharide-Based Adsorbents as Green Alternatives for Dye Removal… DOI: http://dx.doi.org/10.5772/intechopen.94883*

**Figure 5.**

*Novel Nanomaterials*

tetraethylorthosilicate [Si(OC2H5)4] in the presence of ammonia at the copolymer surface [10]. This synthetic approach exploits the occurrence of hydrophilic groups on the polysaccharide backbone to control the hydrolysis, condensation and nucleation growth of metal oxide nanoparticles [47]. The functionalised SiO2 NPs@XG-g-PAAm composite was described as a highly improved adsorbent for the removal of anionic Congo red dye in aqueous solution. Grafting of polyacrylamide chain on XG was accomplished *via* free radical polymerisation technique in the presence of potassium persulphate initiator. The branched XG gum matrix acted as a template for the formation, growth, and stabilisation of SiO2 NPs through hydrogen bonding interaction between the –OH bonded surface group of SiO2 NPs with

Decoration of XG-g-P(AAm/AA) with SiO2 NPs (diameters range 2–7 nm) was also reported by Ghorai and coworkers [34]. These authors subjected the XG-g-PAAm material to hydrolysis in the presence of NaOH to generate the graft copolymer of XG [XG-g-P(AAm/AA)] (**Figure 5**). Subsequently, functionalisation of the later with SiO2 NPs was achieved *in situ* through hydrolysis and condensation of silica sol–gel Si(OC2H5)4 precursor (**Figure 6**). The resultant nanocomposite was employed as an adsorbent for the removal of cationic dyes in the aqueous milieu. The adsorbent exhibited good adsorption efficiency of 497.5 mg/g and 378.8 mg/g towards MB at pH 8 (adsorbent dose: 0.03 g/25 mL solution, contact time: 20 min, and temperature: 50°C) and methyl violet at pH 9 (adsorbent dose: 0.04 g/25 mL

*k*C modified with carbon nanotubes (10–20 nm diameter), and Fe3O4 (10–25 nm) was also synthesised following polymer grafting on the surface of multiwall carbon

oxygen atom of the polysaccharide –COOH surface group [48].

*The mechanism for dye adsorption onto XG-g-P(AAm/AA).*

solution, contact time: 15 min, and temperature: 40°C), respectively.

**304**

**Figure 4.**

*Fabrication of SiO2 NPs@XG-g-P(AAm/AA) composite and TEM image.*

#### **Figure 6.**

*Hydrolysis of Si(OC2H5)4 and condensation of the silicic acid intermediate.*

nanotubes and suspension in a solution of iron precursors Fe(III)/Fe(II) under nitrogen atmosphere [49]. The Brunauer–Emmett–Teller (BET) technique indicated an increase in specific surface area after attachment of carbon nanotubes (SBET: 238 m2 /g) and deposition of magnetic Fe3O4 nanoparticles (SBET: 55 m2 /g). The occurrence of this metal oxide was evidenced by transmission electron microscopy (TEM) pictures analysis. Magnetism is an exclusive physical property that has been demonstrated to ease the water treatment procedure in adsorption technique. This property allows for the removal of spent adsorbent from the aqueous solution by a simple application of a magnet. The prepared magnetic *k*C-carbon nanotubes-Fe3O4 composite exhibited high adsorption toward MB dye in aqueous solution. The maximum dye uptake onto 0.4 g/L of this biofunctional nanocomposite was determined to be 1.24 × 10−4 mol/g−1 at pH 6.5. In aqueous solution, the adsorption potential of metal oxide (MOH) is regulated by the pH-dependent formation of complex ions MOH2 + and MO− [12, 50, 51]. Therefore, dye adsorption onto metal oxide surfaces arise from the Coulombic interaction between MOH2 + and MO− , and the negatively charged (e.g. methyl orange R–SO3 − ) and positively charged (e.g. methylene blue R = N(CH3) + ) centers, respectively. In a cognate investigation, Mahdavinia et al. described the modification of *k*C with polyvinyl alcohol (PVA) and Fe3O4 nanoparticles [52]. This nanocomposite was engineered using the *in-situ* chemical co-precipitation of Fe(II) and Fe(III) salts in the presence of PVA and ionic *k*C biopolymer under basic condition (**Figure 7**). Cross-linking of the occurring Fe3O4 nanoparticles and polymer matrixes was achieved by the freezing–thawing technique and K+ /*k*-carrageenan–SO3 − interaction. Freezing–thawing plays a crucial role in dispersing nanoparticles into gelatin environment and limiting their agglomeration. This technique has been reported to afford bio-related materials with better thermal stability and mechanical properties [53]. The magnetic behaviour of this cationic dye adsorbent was assessed with the vibrating sample magnetometer (VSM) standard method. The hysteresis loop revealed an S-shape with an estimated value of saturation magnetisation 3.4 emu/g, suggesting that the spent adsorbent can be removed easily with an external magnet.

**Figure 7.**

*Fabrication of magnetic* k*C/PVA nanocomposite as an adsorbent for cationic dye removal in aqueous solution.*

#### **Figure 8.**

*Experimental setup for electrospinning of TiO2 nanoparticles in polysaccharide solution.*

FTIR, X-ray photoelectron spectroscopy (XPS) spectra analysis and assessment of the pH at the point of zero charge (pHpzc) can be used to clarify the adsorption mechanism at the surface of metal oxide in aqueous milieu,. Thus, this additional interaction is anticipated to improve the adsorption capacity of polysaccharide adsorbents functionalised with metal oxides. The –OH groups of polysaccharides are highly reactive in encouraging polycondensation, or in interacting with cations or hydroxylated cations, capable of undergoing nucleation and growth processes. Polysaccharide matrix also provides a cavity that is capable of immobilising the developing inorganic entities and controlling their growth. Furthermore, carbon nanotubes ability to abstract organic dyes from wastewater has been reported to take place through π–π stacking, hydrogen bonding, hydrophobic, Coulombic, and/or van der Waals interactions [54–56]. The occurrence of defects and active centers, and the morphology of the carbon nanotubes play a key role in their dye adsorption capability. The carbon nanotubes are rolled-up graphene or graphitic sheets of single-layer carbon atoms. These are π-conjugative structures possessing a hydrophobic surface. The dynamic mechanical investigation of polymer adsorbents and their inorganic particle-functionalised derivatives has uncovered relatively better properties of the latter through restriction of the mobility of polymer macromolecular chains [57].

Cai and coworkers also described the cellulose nanofibers (average diameter 237–443 nm) modified with TiO2 nanoparticles as a precursor for the synthesis of

**307**

solution.

**5. Conclusion**

impressive adsorption capacities.

*Nanoengineered Polysaccharide-Based Adsorbents as Green Alternatives for Dye Removal…*

the excitation of TiO2 valence band electrons and formation of •

therm, with the maximum capacity of 666 mg/g.

These species are responsible for the degradation of organic pollutants in aqueous

Composite hydrogel of NH2–silica functionalised TiO2 NPs@*k*C-g-PAA was developed by Pourjavadi et al. for the removal of malachite green (MG) in synthetic water samples [61]. The functionalised TiO2 NPs were synthesised by the hydrolysis of TiCl4 at 90°C in the presence of HNO3 followed by the treatment of hydrated TiO2 NPs with 3-aminopropyltriethoxysilane. Graft copolymerisation of *k*C with AA monomer in the presence of ammonium persulfate initiator, methylenebisacrylamide as a crosslinking agent, and the pre-synthesised NH2–silica functionalised TiO2 NPs yielded an adsorbent with impressive potential for the removal of cationic dye. MG adsorption onto NH2–silica functionalised TiO2 NPs@*k*C-g-PAA hydrogel followed the pseudo-second-order rate model, and best fitted the Langmuir iso-

Herein, we present a well-elaborated discussion on the developed polysaccharide-based materials for the removal of highly toxic organic dyes from contaminated water using adsorption procedure. Naturally occurring, non-toxic, and biodegradable xanthan gum and kappa-carrageenan matrixes were used as representatives for effective dye remediation owing to their surface charged functionalities that serve as active binding sites. The polysaccharide surface modification through graft copolymerisation with monomers and/or incorporation of nano-sized inorganic particles having high surface areas like metal oxides and carbon nanotubes has been found to yield composites with improved mechanical stability and

OH/O2

•− radicals.

composite hydrogels [58]. Graft copolymerisation of these nanofibers using AAm, AA, and N,N′-methylene bisacrylamide in the presence of ammonium persulfate afforded the polysaccharide-based hydrogels with good MB dye adsorption capacity. The nanofibers material was fabricated through electrospinning of cellulose acetate solution containing TiO2 nanoparticles of average diameter 25 nm, followed by deacetylation under basic condition. The voltage power and flow rate applied in this investigation were 20 kV and 1 mL/h, respectively. Electrospinning is a versatile and efficient method for the fabrication of nanofibers. This technique utilises high voltage to charge the surface of a polymer solution and initiates the ejection of fluid jets through a small hole (**Figure 8**). Solidification of these thin jets yields nanofibers. The size of nanofibers obtained using this procedure depends on parameters like solution physical properties, voltage, hydrostatic pressure, size of a hole, and distance hole-collector [59]. The light-driven catalytic activity of TiO2 has also been described to improve the MB removal performance of TiO2-containing cellulose nanofibers. TiO2, also known as titania, is a low-cost and environmentally benign oxide that has gained commercial success in beauty, cosmetic, and personal care applications. Moreover, interest in TiO2 nanoparticles for the degradation of organic pollutants in wastewater has been tremendous since the early report by Frank and Bard [60]. This is attributed to their unique electronic structure, impressive UV-light absorption properties, prolonged excited-state lifetimes and enhanced charge transport features. The high-energy photons emitted by UV-light initiates

*DOI: http://dx.doi.org/10.5772/intechopen.94883*

*Nanoengineered Polysaccharide-Based Adsorbents as Green Alternatives for Dye Removal… DOI: http://dx.doi.org/10.5772/intechopen.94883*

composite hydrogels [58]. Graft copolymerisation of these nanofibers using AAm, AA, and N,N′-methylene bisacrylamide in the presence of ammonium persulfate afforded the polysaccharide-based hydrogels with good MB dye adsorption capacity. The nanofibers material was fabricated through electrospinning of cellulose acetate solution containing TiO2 nanoparticles of average diameter 25 nm, followed by deacetylation under basic condition. The voltage power and flow rate applied in this investigation were 20 kV and 1 mL/h, respectively. Electrospinning is a versatile and efficient method for the fabrication of nanofibers. This technique utilises high voltage to charge the surface of a polymer solution and initiates the ejection of fluid jets through a small hole (**Figure 8**). Solidification of these thin jets yields nanofibers. The size of nanofibers obtained using this procedure depends on parameters like solution physical properties, voltage, hydrostatic pressure, size of a hole, and distance hole-collector [59]. The light-driven catalytic activity of TiO2 has also been described to improve the MB removal performance of TiO2-containing cellulose nanofibers. TiO2, also known as titania, is a low-cost and environmentally benign oxide that has gained commercial success in beauty, cosmetic, and personal care applications. Moreover, interest in TiO2 nanoparticles for the degradation of organic pollutants in wastewater has been tremendous since the early report by Frank and Bard [60]. This is attributed to their unique electronic structure, impressive UV-light absorption properties, prolonged excited-state lifetimes and enhanced charge transport features. The high-energy photons emitted by UV-light initiates the excitation of TiO2 valence band electrons and formation of • OH/O2 •− radicals. These species are responsible for the degradation of organic pollutants in aqueous solution.

Composite hydrogel of NH2–silica functionalised TiO2 NPs@*k*C-g-PAA was developed by Pourjavadi et al. for the removal of malachite green (MG) in synthetic water samples [61]. The functionalised TiO2 NPs were synthesised by the hydrolysis of TiCl4 at 90°C in the presence of HNO3 followed by the treatment of hydrated TiO2 NPs with 3-aminopropyltriethoxysilane. Graft copolymerisation of *k*C with AA monomer in the presence of ammonium persulfate initiator, methylenebisacrylamide as a crosslinking agent, and the pre-synthesised NH2–silica functionalised TiO2 NPs yielded an adsorbent with impressive potential for the removal of cationic dye. MG adsorption onto NH2–silica functionalised TiO2 NPs@*k*C-g-PAA hydrogel followed the pseudo-second-order rate model, and best fitted the Langmuir isotherm, with the maximum capacity of 666 mg/g.

## **5. Conclusion**

*Novel Nanomaterials*

**Figure 7.**

**Figure 8.**

**306**

FTIR, X-ray photoelectron spectroscopy (XPS) spectra analysis and assessment of the pH at the point of zero charge (pHpzc) can be used to clarify the adsorption mechanism at the surface of metal oxide in aqueous milieu,. Thus, this additional interaction is anticipated to improve the adsorption capacity of polysaccharide adsorbents functionalised with metal oxides. The –OH groups of polysaccharides are highly reactive in encouraging polycondensation, or in interacting with cations or hydroxylated cations, capable of undergoing nucleation and growth processes. Polysaccharide matrix also provides a cavity that is capable of immobilising the developing inorganic entities and controlling their growth. Furthermore, carbon nanotubes ability to abstract organic dyes from wastewater has been reported to take place through π–π stacking, hydrogen bonding, hydrophobic, Coulombic, and/or van der Waals interactions [54–56]. The occurrence of defects and active centers, and the morphology of the carbon nanotubes play a key role in their dye adsorption capability. The carbon nanotubes are rolled-up graphene or graphitic sheets of single-layer carbon atoms. These are π-conjugative structures possessing a hydrophobic surface. The dynamic mechanical investigation of polymer adsorbents and their inorganic particle-functionalised derivatives has uncovered relatively better properties of the latter through restriction of the mobility of polymer macromolecular chains [57]. Cai and coworkers also described the cellulose nanofibers (average diameter 237–443 nm) modified with TiO2 nanoparticles as a precursor for the synthesis of

*Experimental setup for electrospinning of TiO2 nanoparticles in polysaccharide solution.*

*Fabrication of magnetic* k*C/PVA nanocomposite as an adsorbent for cationic dye removal in aqueous solution.*

Herein, we present a well-elaborated discussion on the developed polysaccharide-based materials for the removal of highly toxic organic dyes from contaminated water using adsorption procedure. Naturally occurring, non-toxic, and biodegradable xanthan gum and kappa-carrageenan matrixes were used as representatives for effective dye remediation owing to their surface charged functionalities that serve as active binding sites. The polysaccharide surface modification through graft copolymerisation with monomers and/or incorporation of nano-sized inorganic particles having high surface areas like metal oxides and carbon nanotubes has been found to yield composites with improved mechanical stability and impressive adsorption capacities.
