# Chitosan Nanocomposite Coatings for Food, Paints, and Water Treatment Applications
## 4 Applications of Chitosan-Based Nanocomposites
### Antifouling Paints and Coatings  
Marine biofouling is the undesirable growth of organisms on submerged surfaces [124]. Any submerged, clean, and unprotected substrata will be quickly colonized by microorganisms (bacteria, diatoms, and unicellular eukaryotes) and later by larvae of invertebrates and spores of algae [125; 126]. Biofouling has huge economic impacts in maritime industries [127]. Biofouling significantly increases vessel drag, fuel consumption, clogs membranes and pipes, and also interfere with the stability of sensors attached to the vessels. Worldwide, countries spend billions of US dollars in order to manage and prevent this problem [128]. Currently, antifouling paints utilize toxic biocides that pollute the environment [127]. Thus, new low-cost and non-toxic antifouling paints are urgently needed. Chitosan has been proposed as a promising antifouling agent due to its antimicrobial properties [129] (Table 3). Plastic substrates coated with 2.5% chitosan significantly reduced the settlement of bryozoon _Bugula neritiua_ compared to untreated substrates. Chitosan mixed with a non-toxic paint base and applied to plastic substrates were found to protect the substrates from bacterial fouling over one week of laboratory experiments [130]. Chitosan incorporated into a silicon-polyurethane marine paint was exposed to biofouling for over two months in cold seawater [129]. Experiments demonstrated a short-term antibacterial action of chitosan, while no anti-algal action was observed. In contrast, chitosan paints significantly reduced densities of micro-fouling on the surface of a sea glider exposed to periodical oscillations of environmental conditions in the Sea of Oman. Moreover, it was found that \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Chitosan-Based** & **Dye/Metal** & **pH** & **Removal Process** & **References** \\ \hline CS/zirconium & Reactive Blue-21, Reactive & & & \\ tungstate & Red-141, Rhodamine-6G and & & No data & Photocatalytic degradation & [118] \\  & binary mixture; RB+RR, & & & \\  & RR+RH, RB + RH & & & \\ \hline CS/SnO\({}_{2}\) & & & & \\ intercalated & Methylene blue Reactive & & & \\ polyaniline (PANI) & & yellow-15 & & \\ \hline CS/TiO\({}_{2}\) fibers & Methyl orange, Congo red & & & \\ supported & (CR), Methylene blue, & & & \\ zero-valent metal & Acridine orange, & & & \\ nanoparticles (like & 4-nitrophenol, & & \\ Cu\({}^{0}\), Co\({}^{0}\), Ag\({}^{0}\) and Ni\({}^{0}\)) & 2-nitrophenol, 3-nitrophenol, & & & \\ \hline CS coated cotton & & & & \\ cloth supported & & blue,4-nitrophenol, & & \\ zero-valent metal & & Rhodamine-B & & \\ nanoparticles & & & & \\ \hline CS/MoO\({}_{3}\)/TiO\({}_{2}\) & Methyl orange & No data & Photocatalytic degradation & \\  & & & & under solar light & [122] \\ \hline \hline \end{tabular}
\end{table} 
Table 2: _Cont._the structure of microbial communities formed on chitosan paints were similar to unprotected surfaces and were totally different from what is found on surfaces coated with copper-based antifouling paints, suggesting that chitosan-based coatings have minimal negative impact on marine communities [131]. Few researchers have combined chitosan with nanoparticles in order to increase antifouling properties and stability of coatings (Table 3). Chitosan-ZnO hybrid coatings were found to inhibit bacterial and diatom fouling more efficiently than chitosan coatings alone [86]. In another study, nanocomposite films of chitosan mixed with silver nanoparticles were found to be effective against _E. coli_ and _Bacillus_ bacteria and thus it was proposed that these \"green\" films can be used as packaging materials [132]. Nitric oxide (NO)-releasing chitosan coatings were found to exhibit dose-dependent behaviour for the degradation of biofilms of _Pseudomonas aeruginosa_[133]. The effect of NO-chitosan coating was better than chitosan alone, suggesting synergistic action of chitosan and NO.