3D magnetic nanocomposite modified with molybdenum disulfide: preparation and application in aqueous Cr(vi) remediation.

Hexavalent chromium (Cr(vi)) poses severe environmental risks due to its high toxicity, persistence, and bioaccumulation. Adsorption technology is recognized as one of the core strategies for Cr(vi) remediation, but the development of low-cost, high-efficiency biochar-based adsorbents remains an urgent demand. In this work, 3D Molybdenum disulfide Magnetic Biochar (3DMMB) was successfully fabricated via a combination of calcination pyrolysis and hydrothermal methods, using traditional Chinese medicine residues (CMR) as the biomass feedstock and iron-based sludge (IS) as an alternative to conventional iron sources. Solution pH was found to exert a significant influence on Cr(vi) removal, with an acidic environment being favorable for Cr(vi) adsorption. Kinetic and isothermal analyses revealed that the adsorption process fits well with the pseudo-second-order kinetic model and Langmuir isotherm model, confirming that the adsorption is an endothermic and spontaneous monolayer process, dominated by chemical adsorption as the rate-limiting step, with a maximum adsorption capacity of 83.33 mg g-1. The potential adsorption mechanisms mainly involve physical adsorption, electrostatic interaction, chemical reduction, and complexation. Notably, 3DMMB exhibits excellent recyclability and regeneration performance, retaining 89.55% of its initial adsorption capacity after six cycles of desorption and regeneration. This study provides a novel and cost-effective approach for the preparation of waste-derived functional adsorbents and realizes selective and efficient purification of Cr(vi)-contaminated wastewater through sulfur-based grafting modification.