Activation of peroxymonosulfate by a novel waxberry-like C@CoS2 composite for the removal of organic pollutants

In this work, a novel waxberry-like C@CoS2 composite was fabricated by a two-step hydrothermal method and used for peroxymonosulfate (PMS) activation. The unique morphology was beneficial to provide a large number of active sites. The C@CoS2 composite exhibited high performance on phenol degradation with the kinetic constant of 0.2795 min(-1), which was 6-7 times that of simple CoS2 (0.0421 min(-1)) under the optimal conditions of C@CoS2 composite dose 0.3 g/L, PMS concentration 2.5 mM, 30 degrees C and initial pH=7. The Cl- and NO3- had a slight inhibition on phenol degradation, while the HCO3- had a quick boost on phenol degradation. After five cycles, the phenol removal rate could still reach 90 % in the C@CoS2/PMS system. The sulfate radical (SO4 center dot-) and singlet oxygen (O-1(2)) were identified to be the main active oxygen species (ROS) by radical quenching experiments and the electron paramagnetic resonance (EPR) measurements. The results of electrochemical impedance spectroscopy (EIS) indicated that the carbon spheres enhanced the conductivity of the composite, thus accelerating the electrons transport from Co(II) to PMS, and the X-ray photoelectron spectroscopy (XPS) results proved that the S species in the CoS2 promoted the conversion cycle of Co(III)/Co(II) by donating electrons, resulting in the rapid PMS activation. This work is expected to provide a new strategy for establishing cobalt-based catalysts with high performance in the field of SO4 center dot--based advanced oxidation processes (AOPs).