Hexavalent chromium (Cr(VI)) is one of the most rigorously regulated contaminants frequently detected in surface and groundwater. Magnetic iron sulfides are naturally abundant, environmentally friendly materials ideal for the removal of Cr(VI) from contaminated water, but the high-spin states of Fe(III) ions limits their adsorption affinity. Herein, we develop a heteroatom-doping approach to boost the Cr(VI) removal efficacy of greigite. Compared to pristine greigite, cobalt doping significantly enhances the capability of greigite to adsorption Cr(VI) by decreasing electron occupancy in the e