Insight into the adsorption mechanism between chitosan and kaolinite surface by density functional theory calculation

The interaction between chitosan and kaolinite has an important influence on the performance of their composites, the adsorption mechanism of chitosan onto kaolinite surface was investigated by density functional theory (DFT) calculation. The results show that the adsorption energies of chitosan have significant difference on different kaolinite surfaces, but has few difference at different sites on the same kaolinite surface. Chitosan structural unit can interact stablely with kaolinite (001) surface through two strong hydrogen bonds and two moderately strong hydrgeon bonds, and the hydrgeon bond formed between the N atom of chitosan and H atom of hydroxyl group is the strongest. However, the interaction between chitosan and kaolinite(001¯) surface is through two weak hydrogen bonds between the H(N-H, O-H) atoms on chitosan and O atoms on kaolinite(001¯) surface. The structural difference between kaolinite (001) and (001¯) surface is the main reason for the obvious difference in their interaction with chitosan.