Co-Catalytic Effect of Molybdenum Disulfide on Fenton Reaction for the Degradation of Acid Orange 7 Dye: Reaction Mechanism, Performance Optimization, and Toxicity Evaluation

Fenton reaction is extensively used in wastewater treatment to produce •OH, which can be used to remove organic pollutants excellently. However, the greatest issue of the process is the low efficiency of Fe2+/Fe3+ conversion cycle and hydrogen peroxide (H2O2) decomposition rate (<30%). In this study, molybdenum disulfide (MoS2) was used as a co-catalyst in Fenton system to accelerate the oxidation of acid orange 7 (AO7) dye. The enhanced removal efficiency was attributed to that the unsaturated S atoms on the surface of MoS2 could capture the protons in solutions and turn into H2S, exposing the active sites with reducibility and accelerating the conversion of Fe2+/Fe3+. A high degradation rate of 98% was obtained in 30 min under the optimal conditions of AO7 concentration 100 mg/L, MoS2 6 g/L, FeSO4·7H2O 50 mg/L, H2O2 concentration 1.5 mmol/L, and pH 3.5. Furthermore, the degradation pathway and mechanism of AO7 were thoroughly discussed. The toxicity of the intermediates during the degradation progress slightly increased initially, which then decreased to nontoxicity. MoS2 can keep stable, which can maintain high AO7 removal efficiency even after being reused for seven times. Moreover, the obtained results provide a theoretical basis and guidance for the application of inorganic co-catalyst in practical wastewater remediation applications.