Metal Sulfides as Excellent Co-catalysts for H₂O₂ Decomposition in Advanced Oxidation Processes

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.