Adsorption of chitosan combined with nicotinamide-modified eupatorium adenophorum biochar to Sb3+: Application of DFT calculation.

The pollution and harm of Sb3+ to aquatic systems is a global problem, so Sb3+ removal from the water environment to make sure environment safety and human beings wellbeing is of urgency. This study explored the effect of chitosan combined with nicotinamide-modified eupatorium adenophorum biochar (CEBC) on adsorbing Sb3+ through batch adsorption experiments. The experiments indicated CEBC's maximum adsorption capacity to Sb3+ is 170.15 mg·g-1. Meanwhile, the capacity of the original biochar (EBC) is only 9.97 mg·g-1. Compared with EBC, CEBC contains more functional groups, such as CO, -OH and -NH2. In addition, the pseudo-second-order kinetic model and the Langmuir model are fit to describe the kinetics and isotherms of adsorption of CEBC to Sb3+, which suggests that the adsorption of CEBC to Sb3+ is dominated by monolayer chemisorption. Density functional theory (DFT) calculations confirmed that the chelation between -NH2 and Sb3+ is of significance in the adsorption process of CEBC. DFT calculations also found that the newly added -OH and CO in EBC have a synergistic enhancement effect on the absorption of Sb3+. The mechanism of CEBC absorbing Sb3+ includes electrostatic interactions, pore filling, Л-Л interactions, hydrogen bonding, functional group complexation, chelation, and oxidation. CEBC has an excellent anti-interference ability for inorganic anions (NO3-, SO42- and Cl-) and can also use the coexisting HA to improve its adsorption performance. In addition, CEBC has better mitigation of Sb3+ on the performance of Sb3+ about its secondary release and good reproducibility, which indicates that CEBC is a viable Sb3+ adsorbent.