Amino/MnO2 combined modified biochar for enhancing Pb2+ and Cd2+ removal and mechanisms from aqueous solution

Heavy metals from aqueous solutions tend to pose toxicity to the environment, hence it is urgent to treat this pollution. Current studies have exhibited the adsorption capacity of original biochar for Pb2+ and Cd2+ in water, while effective methods were lacking to enhance its adsorption capacity and alleviate competitive adsorption. In this study, MnO2 and amino group combined modification was proposed to improve the Pb2+ and Cd2+ adsorption capacity of rice straw-derived biochar (MNBC) in water. The adsorption performances and mechanisms of MNBC were obtained from batch experiments, several characterizations, and DFT calculation. The results found that modified methods rose the variety of functional groups variety and improved the pore structure of biochar. Maximum removal rates for Pb2+ and Cd2+ were 96.18 % and 64.26 % and still reached 87.6 % and 54.4 % after four cycles in single Pb2+ or Cd2+ system. Cation exchange as well as electrostatic attraction might the main adsorption mechanism in the Pb2+ and Cd2+ adsorption process. In binary system, theoretical calculation exhibited that electron cloud neared Pb was more possible to transfer with adsorbent than that of Cd, which was accordance to the results of competitive adsorption. The p orbital of O atom in MnO2 and N orbital atom in amino groups could hybridize with d orbital of Cd and Pb, which effectively reduced the effect of competitive adsorption. Overall, this study proved removal prospect of MNBC for Pb2+ and Cd2+ and its highly efficient and stable in application.