Photoelectrocatalytic oxidation of phenol by UV-assisted electrogenerated Ce(IV) in aqueous solution

A UV (UV-C, 254 nm)-assisted Ce(IV) mediated electrochemical oxidation (MEO) system is developed to treat phenol-containing water. For comparison, an individual Ce(IV)-MEO system without UV and a UV photocatalytic oxidation system without applying an electrical current are also evaluated. The operation conditions of electrical current, nitric acid concentration, stirring speed, and electrode area ratio of anode to cathode for Ce(IV) electrogeneration are optimized in terms of percent yield of Ce(IV) and energy consumption. According to the kinetic model of the Ce(IV)/Ce(III) redox reaction, the forward rate constant of Ce(III) oxidation is twice as high as that of the reverse reaction. For the wastewater treatment, Ce(IV)-MEO and photocatalytic oxidation systems both show good capability for degrading phenol in an acidic environment rather than the direct electrochemical oxidation (DEO) system. Importantly, the UV-assisted MEO system exhibits excellent removal efficiency (RE) of phenol (up to 98%) in only 40 min because of the synergistic effect of the electrocatalytic and photocatalytic systems, which individually exhibit REs of <80%. Moreover, phenol degradation in the photoelectrocatalytic oxidation system follows pseudo-first order kinetics with a rate constant of 0.083 min⁻¹.