Metal Sulfides as Excellent Co-catalysts for H<inf>2</inf>O<inf>2</inf> Decomposition in Advanced Oxidation Processes

Abstract

Advanced oxidation processes (AOPs) are widely proposed for treating persistent pollutants by the ⋅OH radicals generated from H2O2 decomposition. However, their broad applications in practical settings have been hampered by the low efficiency of H2O2 decomposition. Here, we report that metal sulfides (MoS2, WS2, Cr2S3, CoS2, PbS, or ZnS) can serve as excellent co-catalysts to greatly increase the efficiency of H2O2 decomposition and significantly decrease the required dosage of H2O2 and Fe2+ in AOPs. Unsaturated S atoms on the surface of metal sulfides can capture protons to form H2S and expose metallic active sites with reductive properties to accelerate the rate-limiting step of Fe3+/Fe2+ conversion. The efficiency of AOPs involving co-catalysts can be further enhanced by visible-light illumination thanks to the sensitization of organic pollutants. This discovery is expected to drive great advances in the use of AOPs for large-scale practical applications such as environmental remediation. Metal ions such as Fe2+ and Cu2+ have been used previously to enhance the efficiency of H2O2 decomposition in advanced oxidation processes (AOPs). However, this does not reduce the cost to an acceptable level because large doses of H2O2 (30–6,000 mmol/L) and Fe2+ (18–410 mmol/L) are required. This large amount of Fe2+ also causes sludge formation and catalyst poisoning. We report that metal sulfides (MoS2, etc.) can serve as co-catalysts to maximize the decomposition efficiency of H2O2 up to 75.2% so that minimal concentrations of H2O2 (0.4 mmol/L) and Fe2+ (0.07 mmol/L) are necessary for standard water treatment. We found that unsaturated S atoms on the surface of metal sulfides can capture protons to form H2S and expose reductive metallic active sites to greatly accelerate Fe3+/Fe2+ conversion. Our discovery represents a breakthrough in the field of AOPs and will greatly push it toward practical utility for environmental applications. Metal sulfides such as MoS2 can serve as co-catalysts to greatly promote the overall efficiency of Fe2+-catalyzed advanced oxidation processes (AOPs). Unsaturated S atoms on the surface of metal sulfides can capture protons from the solution to form H2S and at the same time expose reductive metallic active sites to greatly accelerate the rate-limiting step of Fe3+/Fe2+ conversion. The significantly enhanced efficiency of H2O2 decomposition makes the AOPs viable for practical applications in the remediation of organic pollutants.