Nitrogen sites induce homogeneous dispersion of iron species on biochar for enhanced hydrogen sulfide removal in a low-temperature anaerobic environment.

Hydrogen sulfide (H2S) removal under dry, anaerobic, and low-temperature conditions remains challenging due to limited active-site accessibility and rapid pore blockage in conventional adsorbents. This study addresses these limitations by developing a nitrogen-rich biochar-supported iron composite derived from spent coffee grounds. Nitrogen-rich biochar features a hierarchical pore structure, a high specific surface area (1,919.5 m2 g-1), and abundant nitrogen sites that facilitate Fe-N coordination, enabling uniform dispersion of iron species. The iron-based nitrogen-rich biochar (Fe30/NrB) effectively removes H2S under dry, anaerobic, and low-temperature (120 °C) conditions, achieving a sulfur capacity of 126.1 mg g-1. Furthermore, the spent H2S adsorbent shows promising potential for heavy metal purification in water, enabling the reuse of spent adsorbents. This work converts waste coffee grounds into a dual-functional material, enabling synergistic treatment of toxic H2S gas and aqueous heavy metals while promoting resource circularity in environmental remediation.