Phosphorylated Zerovalent Iron Boosts Active Hydrogen Species Generation from Water Dissociation for Superior Hg(II) Reduction

Mercury (Hg) is a toxic metal of great concern, and its reduction from Hg(II) to Hg(0) is crucial to prevent its mobilization and transformation to even more hazardous methylmercury. Fe° could reduce Hg(II), but the role of active hydrogen species (*H) remains unexplored. Herein, we prepared the phosphate-modified zero-valent iron by ball milling (P-ZVI bm ) and investigated its Hg(II) reduction and immobilization capacity compared with the ZVI bm counterpart. P-ZVI bm rapidly adsorbed and reduced Hg(II) from water at a rate 22 times faster than ZVI bm , with *H accounting for 36% of Hg(II) reduction. A greatly higher proportion of negative surface electrostatic potential on P-ZVI bm (50.38%) than ZVI bm (37.61%) facilitated the adsorption of Hg(II) cation. H 2 O adsorption on P-ZVI bm was more favorable, as demonstrated by the in situ ATR-FTIR spectra, H 2 O TPD-mass spectra, and the substantially lower adsorption energy (-0.78 eV) than ZVI bm (-0.17 eV). The energy span of H 2 O dissociation to *H also decreased from 2.80 eV on ZVI bm to 1.99 eV on P-ZVI bm . Moreover, *H adsorption energy on P-ZVI bm (1.70 eV) was lower than on ZVI bm (-1.20 eV), thereby inhibiting consumption of *H by H 2 evolution. P-ZVI bm demonstrated remarkable efficacy in removing Hg(II), Cu(II), Ni(II), Cd(II), and Pb(II) from electroplating and mining wastewater. These results highlight P-ZVI bm as a promising material for Hg(II) and other heavy metal remediation and underscore the essential role of *H in the enhanced Hg(II) reduction.