Cathode-mediated electrochemical conversion of phenol to benzoquinone in wastewater: High yield rate and low energy consumption

Selective conversion of organic pollutants in wastewater into value-added chemicals is a promising strategy for sustainable water management. Electrochemical processes offer attractive features of precise control over reaction pathway to achieve desired products, however, the traditional anode-mediated processes still face challenges of over-oxidation by the inevitably formed of hydroxyl radical (HO^•). Herein, we proposed a new cathode-mediated approach for selective conversion of phenol to p-benzoquinone (p-BQ) through peroxymonosulfate (PMS) activation. A core-shell layered mesoporous spherical iron-based carbon catalyst (denoted Fe/C-MS) was rationally designed to initiate the reactions, where the first shell layer composed of mesoporous carbon provided a confined environment to enrich PMS and phenols, and the electronic configuration of encapsulated Fe species favored the formation of high-valent ion-oxo species (Fe^IV=O) during PMS activation. Notably, the electrochemical process with Fe/C-MS and PMS (denoted Fe/C-MS-E/PMS) achieved a high yield of p-BQ at 80.2 % and a selectivity of 93.7 % within 5 min, resulting in an ultra-low energy consumption (0.07 KWh/mol phenol). The p-BQ production rate reached an impressive value of 1002.5 %/h, 30-500 times higher than the traditional chemical and anodic oxidation methods. The applicability of this cathode-mediated process was further validated by its successful treatment of real coking wastewater, underscoring the potential as a sustainable strategy for selective conversion of phenol to desired products with high yield and low energy consumption. All the findings available in this study drive us to image that the long-neglected cathode-mediated process, if rationally designed, may serve as an attractive strategy for more sustainable resource recovery during wastewater treatment.