Pyrite/H2O2/hydroxylamine system for efficient decolorization of rhodamine B

Influence of natural cellulose on hydroxyl radical generation by abiotic oxidation of pyrite under acidic conditions

Natural cellulose is one of the most important substances coexisting on the surface of pyrite. Oxidation of pyrite produces hydroxyl radicals (•OH). In this study, a pyrite-cellulose binary system was constructed with natural cellulose to investigate the effect of cellulose on the mechanism of •OH generation via oxidation of pyrite, and the mechanism for abiotic oxidative •OH production by pyrite under the influence of cellulose was investigated with oxidation and quenching experiments and characterization techniques. It was demonstrated that cellulose was chemisorbed onto the pyrite surface and some of the Fe(II) on the pyrite surface was masked, thus inhibiting the reaction between pyrite and O2 and decreasing the •OH production level from 33.54 to 22.48 μM under oxic conditions. In addition, the cellulose caused SS bond breakage, resulting in defects on the pyrite surface, which oxidized H2O to produce •OH in anoxic conditions. Therefore, under anoxic conditions, cellulose promoted the production of •OH and increased the •OH content from 11.85 to 14.78 μM. In addition to •OH, pyrite oxidation also produced SO42-. The amount of SO42- produced by a single pyrite crystal was less than that produced in the pyrite-cellulose system in all cases, and the amount produced under oxic conditions was approximately 10 times greater than that produced under anoxic conditions. More sulfate production indicated more sulfur intermediates during the reaction, such as S2O32-, which may decompose to produce S0 or Sn2- adsorbed on pyrite and decrease the amount of •OH produced. During the oxidation of pyrite by H2O2, cellulose competed with pyrite to react with H2O2, which inhibited the reaction between pyrite and H2O2 and decreased •OH production. Therefore, natural cellulose influenced the abiotic oxidation of pyrite to produce •OH.

Hydroxylamine promoted hydroxyl radical production and organic contaminants degradation in oxygenation of pyrite

The heterogeneous Fenton-like process using pyrite (FeS₂) is increasingly recognized as a promising advanced oxidation process for removal of organic contaminants. However, the slow regeneration of Fe(II) limits the generation of reactive oxygen species for environment implication. To overcome this drawback, hydroxylamine was applied to enhance the reactivity of FeS₂ to degrade organic contaminants under oxic conditions. Results showed that hydroxylamine facilitated the regeneration of Fe(II) on FeS₂ surface to promote reactive oxygen species generation, thereby efficiently degrading different organic contaminants. The underlying mechanism was further elucidated that the presence of hydroxylamine enhanced electron transfer from FeS₂ to O₂ to produce superoxide radicals (O₂^•-), hydrogen peroxide (H₂O₂) and hydroxyl radical (HO^•) via Fenton-like pathways, which induced the rapid degradation of organic contaminants (e.g., sulfamethoxazole (SMX)). The reactivity of FeS₂ for organic contaminant degradation changed negligibly after seven cycles in the presence of hydroxylamine. The effects of pH and inorganic anions on SMX degradation were also clarified in details. The finding of this study would provide a novel strategy to enhance the contaminants degradation by FeS₂-based advanced oxidation technologies for environmental remediation.

Sulfite activation by oxidized pyrite for dye degradation assisted by oxygen

Fe(iii) on the surface of pyrite, instead of Fe(ii), acted as the active site of sulfite activation.