## 4 Chitosan as Catalytic Support
### Chitosan-Containing Composite Biocatalysts
[214] reported the synthesis of a biocatalyst usingco-encapsulation of LAC and a natural redox mediator soybean meal extract (SBE) on Ca-modified CS-alginate beads (CA-Ca-SBE-LAC). SA was dissolved in SBE solution and then mixed with certain amount of LAC. Then, an alginate-SBE-LAC mixture was slowly dripped into CS-CaCl\({}_{2}\) solution in acetic acid. The obtained CA-Ca-SBE-LAC beads were hardened at room temperature for 6 h and applied for degradation of phenanthrene. A high degradation efficiency of 94.4% was achieved for 0.5 ppm phenanthrene aqueous solution for 20 min, which was 20-30% higher than that of free LAC. The CA-Ca-SBE-LAC maintained high catalytic activities over a wide range of pH values (from 4 up to 9) and remained stable during 10 cyclic runs (the degradation efficiency of phenanthrene was 83.1%) and after 50 days of storage at 4 \({}^{\circ}\)C (the degradation efficiency of phenanthrene was 92%). The contributions of the free radical pathway and nonradical pathway to phenanthrene were 12.5% and 87.5%, respectively, and achieved the maximum double synergy of the mediator and LAC. Metal oxide NPs can benefit not only fromthe activity of inorganic catalysts, but also biocatalysts. [PERSON] et al. [215] synthesized crosslinked CS/ZnO nanocomposite, which was additionally improved by Fe\({}_{2}\)O\({}_{3}\) NPs. ZnO NPs were suspended in CS acidic solution followed by mixing different concentrations of Fe\({}_{2}\)O\({}_{3}\) NPs. A CS/ZnO/Fe\({}_{2}\)O\({}_{3}\) nanocomposite was washed with distilled water and dried at 80 \({}^{\circ}\)C. No shaping, crosslinking or activation of CS/ZnO/Fe\({}_{2}\)O\({}_{3}\) was carried out. The immobilization of catalase was provided by adsorption at room temperature overnight. The CS/ZnO/Fe\({}_{2}\)O\({}_{3}\) achieved an immobilization yield of 84.32%. After 10 repeated cycles, the remaining immobilized catalase activity was 45%. After 60 days of storage at 4 \({}^{\circ}\)C, the remaining activity of the immobilized enzyme was found to be 47%. Maximum activity immobilized catalase was 19.92 umol/mL, which is nearly double compared to the free enzyme (10.45 umol/mL). [PERSON] et al. [216] developed ahybrid support using calcium ion as a linking agent that coordinated the silanol and hydroxyl groups of CS. Silica was treated with Ca(NO\({}_{3}\))\({}_{2}\) and added to the CS solution. Then, the aqueous phase was removed with evaporation under vacuum, while the solid phase was treated with methanol and KOH. The obtained SiO\({}_{2}\)-Ca-CS (Figure 32) was used to immobilize LAC, which was preliminarily oxidized with periodate (see also Ref. [187]). SiO\({}_{2}\)-Ca-CS-LACwas then packed in a column and used in a flow system for phenol removal. Seven different phenolic compounds (catechol, 4-methylcatechol, tyrosol, phenol, caffe acid, vanillic acid, syringe acid, \(p\)-coumaric acid) were oxidized in a continuous mode for 21 h. The SiO\({}_{2}\)-Ca-CS-LAC for allowed 90% of the phenols' removal, showed good storage stability (70% of activity in 70 days) and good reusability (90-50% of catalytic activity at the 4 th reuse depending on the CS type). The best performance was obtained with the low molecular weight CS (50-190 kDa) at pH = 5 and with a flow rate of 0.7 mL/min. In addition, when all the phenols were together, a general increase inthe phenols' removal was obtained in contraststowhen they were alone [216]. [PERSON] et al. [217] synthesized a biocatalyst based on \(\beta\)-galactosidase physically adsorbed on PANI-CS or PANI-CS-Ag nanocomposites. PANI-CS was prepared by using the copolymerization technique, according to which CS was added to aniline solution at 0-5 \({}^{\circ}\)C, and then ammonium persulfate (APS) was added (typical conditions for PANI synthesis via oxidative polymerization of aniline). Ag NPs were obtained separately and added to the CS-containing aniline solution prior PANI synthesis. The resulting PANI-CS and PANI-CS-Ag nanocomposites were used for deposition of \(\beta\)-galactosidase.