Unveiling the kinetics and mechanism of sulfide-modified zero-valent iron activated hydrogen peroxide for phenol degradation

Abstract

In this study, sulfide-modified zero-valent iron (S-ZVI) synthesized by a two-step process with optimal S/Fe ratio of 0.056 was used to activate hydrogen peroxide (H2O2) to degrade phenol, and the kinetics and reaction mechanism of phenol degradation were investigated under different conditions. Phenol degradation kinetics in S-ZVI/H2O2 system was characterized by an initial lag phase followed by a rapid reaction period, which was accurately described by Logistic regression model, deviating from conventional pseudo-first-order and pseudo-second-order models. Over 80 % of phenol degradation occurred via liquid-phase reactions, predominantly driven by hydroxyl radicals (•OH). The consumption of H2O2 and the removal of total organic carbon (TOC) were both significantly correlated with the total dissolved iron content, underscoring the importance of iron dissolution. The S-ZVI/H2O2 system outperformed other activated H2O2 systems, with a 41.71 %, 35.89 %, and 44.02 % increase in H2O2 utilization efficiency for TOC removal compared to FeSO4, ZVI, and ZVI(H+), respectively. Sulfide-modification of ZVI significantly promoted the sustained release of dissolved iron with a higher proportion of Fe2+, which was identified as a key factor in enhancing H2O2 utilization efficiency. Our findings provide new insight into a better description of the pollutant removal kinetics process in the S-ZVI/H2O2 system and the synergistic effects between S-ZVI and H2O2 for organic pollutant degradation.