High efficiency of energy recovery from formaldehyde wastewater over CoS2@MoS2 heterostructure: Enhanced electronic transfer and mechanism

Recently, the simultaneous recovery of hydrogen energy via purification of formaldehyde (FA) wastewater has been recognized as a promising and environmentally beneficial method. In this study, a novel bis-transition metal disulfide heterojunction material CoS2@MoS2 was prepared by a hydrothermal method for peroxymonosulfate (PMS) activation towards formaldehyde wastewater treatment and synchronous hydrogen evolution. Interestingly, CoS2@MoS2 exhibited high performance on formaldehyde-degrading and hydrogen evolution (k = 12.65 μmol/min), outperforming CoS2 (k = 4.13 μmol/min) and MoS2 (k = 3.28 μmol/min) by 3 and 4 times, respectively. Besides, the impacts of catalyst dosage, PMS dosage, NaOH dosage, FA concentration, and reaction temperature on the system's hydrogen generation performance were thoroughly examined. Moreover, anions (Cl−, NO3− and HCO3−) in aqueous solution were also examined for their impact on hydrogen evolution. Through radical quenching experiments, the superoxide radical (O2−) was identified to be the main reactive oxygen species (ROS), while sulfate radical (SO4−) played a minor role and hydroxyl radical (OH) effect can be ignored in the CoS2@MoS2/PMS system. The heterostructure of CoS2@MoS2 enhanced the conductivity, promoted the activated decomposition of PMS as tested by linear sweep voltammetry (LSV), electrochemical impedance spectroscopy (EIS) and Tafel slope analysis. Additionally, after four cycles, the composite still presented good hydrogen evolution rate. This study furnishes a new method for constructing catalysts with highly efficient towards in-situ FA wastewater purification and clean energy development.