## 5 Conclusions  
CS provides a number of opportunities for the production of environmentally friendly adsorbents and catalytic supports due to the existence of functional groups andthe ability to form different shapes (fibers, membranes, beads, NPs, etc.). For adsorption purposes, the general trend is the use of crosslinking agents (preferably covalent crosslinking) and grafting of functional groups, resulting in a noticeable increase in thenumber of adsorption sites. However, this approach (CS modification) is rarely used in catalysis, especially inthe development of biocatalysts, since the high adsorption ability of CS with respect to both inorganic and organic components may have a negative influence on the biocatalysts' efficiency. Thus, in the case of biocatalysts, CS can be used as a surface modifier of solid supports in an amount of less than 1 wt.%. This also contributes to the maximum availability of active centers of the immobilized enzymes. At the same time, in the case of metal-catalyzed catalytic reactions, the high adsorption ability of CS can be used for the development of catalytic systems, in which the inorganic part entrapped by CS is a catalytically active phase while organic adsorbate is the subject of catalytic transformation. Thus, modified (grafted), CS-based materials are promising catalytic supports. In the composition of catalytic supports, crosslinking agents are typically not used, as well as certain shaping at a macro-level of the resulting catalytic materials. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Enzyme** & **Support** & **Shape** & \begin{tabular}{c} **Conslinking** \\ **Agent** \\ \end{tabular} & \begin{tabular}{c} **Additional Activating** \\ **Agent** \\ \end{tabular} & \
\begin{tabular}{c} **Recycling** \\ **Stability** \\ \end{tabular} &
\begin{tabular}{c} **Storage** \\ **Stability** \\ \end{tabular} & **Ref.** \\ \hline \multirow{3}{*}{Inlines} & CS & Beads & TPP & GA & 78.2\% of activity & Not indicated & [177] \\ \cline{2-8}  & CS/Fe\({}_{0}\)O\({}_{4}\) & NPs & no & EDAC/NHS & 50\% of activity & Not indicated & [120] \\ \hline \multirow{3}{*}{INU} & CS8 & Beads & no & GA & 45\% of activity & Not indicated & [192] \\ \cline{2-8}  & CS & & & & & & \\ \cline{2-8}  & CS & Beads & GA & GA & 50\% of activity & 50\% of activity & 50\% of activity & [181] \\ \cline{2-8}  & CS & Beads & GA & GA & 22\% of activity & 60\% of activity & [182] \\ \cline{2-8}  & CS & Beads & TP & & & & & \\ \cline{2-8}  & CS & Beads & GA & GA & 10\%-activity & [183] \\ \cline{2-8}  & CS & Beads & TP & No & Not indicated & 100\%-activity & [193] \\ \hline \hline \end{tabular}
\end{table} 
Table 2: _Cont._The use of CS in biocatalytic processes is based primarily on its excellent gel-forming ability and the presence of amino groups available for interactions in its composition. Thanks to gelation, it is possible to synthesize various stable forms of solid supports for the immobilization of enzymes. Amino groups of CS are used for the covalent crosslinking of enzymes via activating agents due to the formation of Schiff's bases (GA) or amide bonds (carbodiimides), as well as the crosslinking of CS itself in order to form particles of a certain shape. The combination of these properties allows for the achievement of high activity and the operational stability of synthesized biocatalytic systems. CS is most widely used for the immobilization of oxidoreductase (peroxidases, LACs and GOxs) and hydrolases (e.g., LIPs). Magnetically separable catalysts/biocatalysts obviously have the advantage of easy separation from the reaction mixture, but most of these catalysts have the limitation of sensitivity to low pH. Thus, the further improvement of magnetically separable CS-based composites is a promising area of research. Conceptualization, L.Z.N., B.B.T. and V.G.M. ; methodology, L.Z.N. ; software, L.Z.N. ; validation, V.G.M. ; formal analysis, B.B.T. ; investigation, P.E.I. and P.Y.S. ; resources, L.Z.N. ; data curation, P.E.I. and P.Y.S. ; writing--original draft preparation, L.Z.N. and B.B.T.