Insight into the mechanism and effect of the Gleditsia sinensis peel-derived biochar/FexOy composites as an effective and recyclable absorbent for wastewater

Gleditsia sinensis is a major crop for the extraction of triterpenoid saponins, which peel waste is rich in oxygenated functional groups and considered an ideal raw material of modified biochar. In this work, iron oxide/biochar composites were prepared using Gleditsia sinensis peel as raw material and iron oxide. The adsorption capacity of the modified Gleditsia sinensis biochar was significantly enhanced with the highest adsorption rate of 89.5% for methylene blue (MB), while the highest adsorption removal rate for Cr (VI) was close to 70%. The possible adsorption mechanism was investigated by quantitative computational methods combined with density functional theory (DFT) and adsorption thermodynamic and adsorption kinetic studies. The adsorption process of pollutants by biochar is consistent with the Freundlich isotherm model and the quasi-secondary kinetic model, performed spontaneously and absorbs heat. This study prepared a recyclable biomass-based adsorbent, which provides a new option for the high-value utilization of forest residues.