Mechanism study of CoS2/Fe(III)/peroxymonosulfate catalysis system: The vital role of sulfur vacancies

Peroxymonosulfate (PMS) activation methods have attractive advantages in advanced oxidation process (AOPs) due to their powerful ability of directly or indirectly generating various reactive oxygen species (ROS). Herein, trace amount of Fe(III) ions were added into the commercial-CoS2/PMS system to improve the CoS2/PMS decomposition for organics removal. The organics removal efficiency could reach >90% towards methylene blue (MB), diclofenac sodium (DCF), sulfamethoxazole (SMX) and bisphenol A (BPA) in the CoS2/Fe(III)/PMS system, with the kinetic apparent rate constant kobs of 0.141, 0.206, 0.247 and 0.091 min-1, respectively. The synergistic effect between Fe(III) ions and sulfur-vacancies on CoS2 for PMS degradation were revealed for the first time in cobalt sulfides/PMS system. Quenching experiments and ESR analysis proved that 1O2 was the major ROS and was produced mainly by the hydrolysis of SO5•-. Besides, the high degradation efficiency was obtained by the contribution of SO4•- and •OH. Electron spin-resonance spectroscopy (ESR), cyclic voltammetry (CV) and Raman spectrum data revealed that the addition of Fe(III) ions could optimize the intensity of sulfur vacancies on the CoS2 surface, which hindered the PMS reduction ability of Co(II), but accelerated the PMS oxidation to form 1O2. The degradation path of MB was analyzed by liquid chromatograph-mass spectrometer (LC-MS). The mechanism studies speculated that the sulfur vacancies of CoS2 provided the binding sites for Fe(III) ions with Co(II), which facilitated the PMS activation by Co(III).