# Chitosan Nanocomposite Coatings for Food, Paints, and Water Treatment Applications
## 4 Applications of Chitosan-Based Nanocomposites  
### Water Purification  
The use of synthetic dyes is increasing day-by-day for industrial applications, particularly in the textile industry, which leads to severe water pollution because of their discharge into water bodies without suitable treatments. Over 10,000 different colorants (dyes and pigments) are used in textile industries and over \(7\times 10^{5}\) tons of synthetic dyes are annually produced worldwide [102; 103]. Most of the synthetic dyestuffs are discharged into the ecosystem without appropriate treatments, which has triggered global environmental problems [103]. Removal of dyes from water bodies is challenging because of their inert nature and existence in low concentrations. Chitosan has received attention in water purification as it is an inexpensive biopolymer and also due to the presence of a large number of reactive amino (-NH\({}_{2}\)) and hydroxyl (-OH) groups. Adsorption of acid dyes with chitosan and modified chitosan occurs because of the electrostatic interaction between negatively charged dye ions and the protonated amino groups [104]. [PERSON] et al. demonstrated that the removal of dyes from alkaline effluent involves chelating interactions rather than electrostatic interactions [105]. The removal of dye from wastewater using nanocomposites of chitosan has been achieved using several processes, such as physical adsorption, ion-exchange, hydrogen bonds, hydrophobic attractions, and chemical bonding. Chitosan-based composite fibres (MNPs/ZnPc-CS) and pellets of zinc photocatalysts (ZnPc)-supported metallic and bimetallic nanoparticles have been synthesized by [PERSON] et al. for metal ions uptake [106]. The MNPs/ZnPc-CS fibres were used as dip-catalysts for the reduction of nitrophenols and azo dyes like methyl orange (MO) and cargo red (CR). The results showed that the developed composites exhibited excellent catalytic efficiency and recyclability in the reduction of these dyes. Recent studies conducted by many researchers on the removal of dyes from wastewater using chitosan-based nanocomposites are summarized in Table 2. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Chitosan-Based** & **Dye/Metal** & **pH** & **Removal Process** & **References** \\ \hline CS/AgNPs & Methyl orange & 3–11 & \begin{tabular}{c} Photocatalytic \\ decolourization \\ \end{tabular} & [107] \\ \hline CS/AuNPs & 4-nitropenol & No data & Catalytic reduction & [108] \\ \hline CS/TiO\({}_{2}\) & Rhodamine-B, Congo red & 3–11 & \begin{tabular}{c} Photocatalytic degradation \\ under visible light \\ irradiation \\ \end{tabular} & [109] \\ \hline CS/Polyaniline/CdS & Reactive Blue-19 & 6 & Adsorption & [110] \\ \hline CS/PVA/ZnO & Acid Black-1 & No data & Adsorption & [111] \\ \hline CS/SiO\({}_{2}\)/CNT & \begin{tabular}{c} Direct Blue-71, Reactive \\ Blue-19 \\ \end{tabular} & 0–12 & Adsorption & [112] \\ \hline CS/lignin/titania & Brilliant Black & No data & Adsorption & [113] \\ \hline CS/Bio-silica & Acid Red 88 & 1–12 & Adsorption & [114] \\ \hline CS/Palladium & 4-Nitrophenol & No data & Catalytic hydrogenation & [115] \\ \hline CS/SnO\({}_{2}\) & \
\begin{tabular}{c} Methyl orange, \\ Rhodamine-B \\ \end{tabular} & No data & Photocatalytic degradation & [116] \\ \hline CS/Ag\({}_{3}\)PO\({}_{4}\)/CdS & Methyl orange & 3–8 &
\begin{tabular}{c} Photocatalytic \\ decolourization \\ \end{tabular} & [117] \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Chitosan-based nanocomposites for removal of dyes from wastewater. [PERSON] et al. fabricated three low-cost polypyrrole-based composites, i.e., polypyrrole-chitosan -lignosulfonate (PPY-CS-LS), polypyrrole-chitosan (PPY-CS), and polypyrrole-lignosulfonate (PPY-LS) via polymerization (in-situ) of pyrrole monomers with chitosan (CS) and/or lignosulfonate (LS) as dispersants in order to improve the dye adsorption capacity of polypyrrole [123].