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-ZVIbm) and investigated its Hg(II) reduction and immobilization capacity compared with the ZVIbm counterpart. P-ZVIbm rapidly adsorbed and reduced Hg(II) from water at a rate 22 times faster than ZVIbm, with *H accounting for 36 % of Hg(II) reduction. A greatly higher proportion of negative surface electrostatic potential on P-ZVIbm (50.38 %) than ZVIbm (37.61 %) facilitated the adsorption of Hg(II) cation. H2O adsorption on P-ZVIbm was more favorable, as demonstrated by the in situ ATR-FTIR spectra, H2O TPD-mass spectra, and the substantially lower adsorption energy (-0.78 eV) than ZVIbm (-0.17 eV). The energy span of H2O dissociation to *H also decreased from 2.80 eV on ZVIbm to 1.99 eV on P-ZVIbm. Moreover, *H adsorption energy on P-ZVIbm (1.70 eV) was lower than on ZVIbm (-1.20 eV), thereby inhibiting consumption of *H by H2 evolution. P-ZVIbm 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-ZVIbm 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.