Enhanced retention of surface-adsorbed atomic hydrogen through sulfidation of nano zerovalent iron for water decontamination

Sulfide-modified nano zerovalent iron (S-nZVI) has garnered considerable attention in water decontamination due to its exceptional reactivity. However, there is still limited knowledge regarding the importance of different atomic hydrogen species (i.e., absorbed H* and adsorbed H*) in S-nZVI-mediated reductions, as well as the role of sulfur in regulating the catalytic performance. Therefore, we systematically characterized H* during the re-action of S-nZVI by the cyclic voltammetry (CV) analysis and electron paramagnetic resonance (EPR) spec-troscopy, whereas nZVI and palladized nZVI (Pd-nZVI) were used as the reference. H* originating from the reduction of H2O molecules would recombine to H2 or be absorbed into the Fe crystal lattices forming inert absorbed H* (H*abs) on nZVI. In contrast, S-nZVI significantly boosted the accumulation of relatively reactive surface-adsorbed H* (H*ads). Consequently, S-nZVI exhibited the promoted degradation of diatrizoate (DTA), a kind of H*ads-sensitive contaminant. The increased solvent kinetic isotope effect (SKIE) value for DTA degradation by S-nZVI demonstrated that the reduction of H2O into H*ads played a significant role in the reaction. Raman spectroscopy and 1H nuclear magnetic resonance (1H NMR) further offered compelling evidence that S-nZVI preferred to stabilize H*ads by forming S-H*ads bonds on the surficial S sites, leading to the shift in the relative abundance of H*abs and H*ads. This study provides direct evidence for the identification of H* species in the S-nZVI system, and elucidates the fundamental mechanism of the enhanced H*ads retention resulting from the sulfidation of nZVI, inspiring the future optimization of S-nZVI for accelerating the reductive degradation of contaminants.

Automated summary

S-nZVI enhances the degradation of contaminants by adsorbing and stabilizing reactive surface hydrogen species (H*ads). The presence of sulfur plays a role in regulating the catalytic performance.