Study on the adsorption performance of manganese dioxide loaded modified biochar composite materials for cadmium ions (Ⅱ) in solution

Abstract

The manganese dioxide loaded peanut shell activated carbon composite material (MnO₂-AC) was prepared by coprecipitation method using peanut shell and natural graphite as raw materials. The response surface methodology (RSM) was used to screen the optimal preparation condition for AC (carbon alkali ratio 2:3, time 5h, temperature 700℃) and the preparation process has been optimized. MnO₂-AC was synthesized by loading AC and MnO₂ under the optimal preparation condition.The adsorption effect of Cd²⁺ in aqueous solution was compared, and the effects of pH value and ion strength on Cd²⁺ adsorption were investigated. The adsorption kinetics and isothermal adsorption characteristics were analyzed. The results showed that the surface of modified MnO₂-AC exhibits spherical aggregates with rougher surfaces, more micropores, and larger specific surface area. In comparison to BC and AC, MnO₂-AC possessed more surface adsorption sites and oxygen-containing functional groups. Kinetic adsorption studies have shown that the maximum adsorption capacity of MnO₂-AC (138.14mg·g^− 1) for Cd²⁺ has significantly increased, which is 3.06 and 1.15 times higher than that of BC (45.16mg·g^− 1) and AC (119.21mg·g^− 1), respectively. The adsorption capacity has increased by 205.9% and 15.8%, respectively. At the same time, the adsorption capacity of MnO₂-AC for Cd²⁺ remained as high as 60.96mg·g^− 1 after 6 adsorption desorption cycles, with an increase of 217.83% and 32.15% compared to the adsorption capacity of BC (19.18mg·g^− 1) and AC (46.13mg·g^− 1) after 6 adsorption desorption cycles, respectively, proving that MnO₂-AC has good reusability. MnO₂-AC loaded modification has significant adsorption effects on heavy metal ions, and has good application potential.