Reactive species conversion into 1O2 promotes substantial inhibition of chlorinated byproduct formation during electrooxidation of phenols in Cl laden wastewater

作者：Zheng, Wenxiao; Chen, Yingkai; Fu, Hengyi; Yan, Zhang; Lei, Zhenchao; Duan, Weijian; Feng, Chunhua^*

来源：Water Research, 2022, 225: 119143.

DOI：10.1016/j.watres.2022.119143

• Electrochemical oxidation
• Chlorinated byproducts
• Reactive oxygen species
• Reactive chlorine species
• Degradation of phenols
• Halide wastewater treatment

The generation of chlorinated byproducts during the electrochemical oxidation (EO) of Cl(-)laden wastewater is a significant concern. We aim to propose a concept of converting reactive species (e.g., reactive chlorines and HO circle resulting from electrolysis) into O-1(2) via the addition of H2O2, which substantially alleviates chlorinated organic formation. When phenol was used as a model organic compound, the results showed that the H2O2-involving EO system outperformed the H2O2-absent system in terms of higher rate constants (5.95 x 10(-2) min(-1) vs. 2.97 x 10(-2) min(-1)) and a much lower accumulation of total organic chlorinated products (1.42 mg L-1 vs. 8.18 mg L-1) during a 60 min operation. The rate constants of disappearance of a variety of phenolic compounds were positively correlated with the Hammett constants (sigma), suggesting that the reactive species preferred oxidizing phenols with electron-rich groups. After the identification of O-1(2) that was abundant in the bulk solution with the use of electron paramagnetic resonance and computational kinetic simulation, the routes of O-1(2) generation were revealed. Despite the consensus as to the contribution of reaction between H2O2 and ClO to O-1(2) formation, we conclude that the predominant pathway is through H2O2 reaction with electrogenerated HO circle or chlorine radicals (Cl-circle and Cl-2 (circle-)) to produce O-2(circle-), followed by self-combination. Density functional theory calculations theoretically showed the difficulty in forming chlorinated byproducts for the O-1(2)-initiated phenol oxidation in the presence of Cl, which, by contrast, easily occurred for the Cl-circle-or HO circle-initiated phenol reaction. The experiments run with real coking wastewater containing high-concentration phenols further demonstrated the superiority of the H(2)O(2)involving EO system. The findings imply that this unique method for treating Cl- -laden organic wastewater is expected to be widely adopted for generalizing EO technology for environmental applications.