Enhanced activation of peroxymonosulfate by bimetallic spinel sulfides CoNi2S4 for organic dye degradation

The activation of peroxymonosulfate (PMS) with bimetallic spinel sulfides to degrade refractory organic pollutants is a promising method. In this work, a one-step hydrothermal method was used to synthesize high catalytic activity CoNi2S4. Catalyst CoNi2S4 was characterized by X-ray photoelectron spectroscopy (XPS), energy dispersive spectroscopy (EDS), X-ray diffractometer (XRD), Fourier transform infrared spectroscopy (FT-IR) and field-emission scanning electron microscopy (SEM). Subsequently, CoNi2S4 was applied to activate PMS for Rhodamine B (RhB) degradation. After 50 mins of catalytic reaction, the removal rate of RhB (20 mg/L) reached 99.1% and the removal rate of COD reached 60.0% in the CoNi2S4 (150 mg/L) + PMS (150 mg/L) system at room temperature of 20 ℃. The experiment results showed that the CoNi2S4 had preeminent catalytic activity. The singlet oxygen (1O2) and sulfate radical (SO4•−) were proved to perform critical roles in the catalytic degradation process by electron paramagnetic resonance (EPR) analysis and quenching experiment. Meantime, the potential catalytic mechanism of PMS activation by CoNi2S4 was proposed mainly in two aspects: one is that S22- and S2- species promote the Co3+/Co2+ and Ni3+/Ni2+ cycles on CoNi2S4 surface, and the other is that there is the synergistic effect of Co-Ni cycles for PMS activation by CoNi2S4. Recycling tests showed that the degradation efficiency of RhB was stable, indicating that CoNi2S4 had good recyclability. Because of its outstanding catalytic activity, easy preparation, and reusability, the CoNi2S4 catalyst has broad application prospects in the field of controlling water pollution.