Activation of Peroxymonosulfate by a ${\mathrm{CoAl}}_2{\mathrm{O}}_4/{\mathrm{Co}}_2{\mathrm{O}}_3@\gamma \text{-}{\mathrm{Al}}_2{\mathrm{O}}_3$ Catalyst for Efficient Phenol Degradation in Water

Activation of peroxymonosulfate (PMS) by catalysts for water treatment is very important for the sulfate radicals-based advanced oxidation technology. Constructing affordable and recyclable transition metal catalysts with high efficiency is highly desirable, but still challenging. In this study, a novel ${\mathrm{CoAl}}_2{\mathrm{O}}_4/{\mathrm{Co}}_2{\mathrm{O}}_3@\gamma {\text{-}\mathrm{Al}}_2{\mathrm{O}}_3$ catalyst for the activation of PMS was prepared with an excessive impregnation method, and its performance on the catalytic degradation of phenol in water was investigated. The composition and structure of the catalyst were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and ${\mathrm{N}}_2$ adsorption-desorption experiments. It was found that the catalyst could greatly promote the phenol mineralization in water as the total organic carbon removal increased from 4.27% to 57.64% after 60 min of reaction. The presence of ${\mathrm{Cl}}^{-}$ inhibited the catalytic degradation of phenol in water at low concentrations, but promoted the catalytic degradation at high concentrations. However, ${\mathrm{HCO}}_3^{-}$ and ${\mathrm{CO}}_3^{2-}$ revealed inhibitory effects on the catalytic degradation because they could scavenge free radicals in the system. Based on the electron spin resonance technique and the quenching experiments, ${{}^1\mathrm{O}}_2$ and ${\mathrm{SO}}_4^{-}·$ were identified to be the primary reactive species for the catalytic degradation. The ${\mathrm{CoAl}}_2{\mathrm{O}}_4/{\mathrm{Co}}_2{\mathrm{O}}_3@\gamma {\text{-}\mathrm{Al}}_2{\mathrm{O}}_3$ could be easily recovered and reused. The toxicity evaluation verified that the toxicity of the treated water was greatly decreased after the catalytic degradation. Therefore, the ${\mathrm{CoAl}}_2{\mathrm{O}}_4/{\mathrm{Co}}_2{\mathrm{O}}_3@\gamma {\text{-}\mathrm{Al}}_2{\mathrm{O}}_3$ prepared in this study could be an effective catalyst for the catalytic degradation of phenol in water by activating PMS.