Synergistic removal of Cr(VI) by a xanthan-grafted hydrochar supported manganese sulfide composite: Mechanistic insights

Background The development of high-performance and recyclable composite is of great significance for the efficient removal of hexavalent chromium (Cr(VI)). Methods Herein, a xanthan gum (XG) modified manganese sulfide (MnS)/soy sauce residue hydrochar (SRH) composite (XG/MnS@SRH) was fabricated by integrating 5 wt% XG, MnS, and nitrogen-enriched SRH. The structural features, Cr(VI) removal performance, cycling behavior, ionic tolerance, and removal mechanism were systematically elucidated through scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), batch removal, regeneration, and coexisting-ion experiments. Significant Findings The incorporation of XG introduced abundant –COOH and –OH groups and promoted the structural integration of MnS with the SRH matrix. Benefiting from the synergistic contribution of XG-derived functional groups, nitrogen-doped carbon sites, and MnS, XG/MnS@SRH1 exhibited a remarkable Cr(VI) removal capacity of 486.18 mg/g at 298 K. The removal process was well described by the pseudo-second-order kinetic model and Langmuir isotherm. XG/MnS@SRH1 retained >60.0% of its initial Cr(VI) removal performance after five adsorption-regeneration cycles and exhibited favorable tolerance toward coexisting ions. Electrostatic attraction, Cr(VI) reduction, and surface complexation collectively governed Cr(VI) removal.