Understanding of manganese-sulfur functionalized biochar: Bridging effect enhanced specific passivation of lead in soil

Widespread contamination of soils by neurotoxic lead ions (Pb) posed a serious risk to food security, but efficient treatment in soil remained a challenge. For the adsorption of Pb, DFT calculations were firstly performed to predict the synergistic effect of sulfhydryl-hydroxyl groups as well as the ability of sulfur ions to strengthen Pb-OH bonding. Consequently, Mn-S functionalized coffee ground biochar (MSBC) was then synthesized utilizing precipitation and impregnation methods. In the soil experiment, the removal efficiency of Pb reached 82.92%, exceeding the previous research results. In addition, it successfully restored the polluted farmland near the mining area and increased the plant height of Swiss chard by 186.23%. Subsequently, synergistic effect of sulfhydryl-hydroxyl groups was confirmed by XPS, FT-IR, and DFT calculations. Furthermore, the factors affecting the structural stability of O-Pb-S were discussed by regression analysis. These reflected that MSBC can enhance the removal efficiency of Pb in soil by mitigating the competition of impurity ions to adsorption sites. These findings may provide new insights into the development of the specific passivation materials for other heavy metals.