Contribution of cathodic hydroxyl radical generation to the enhancement of electro-oxidation process for water decontamination

The degradation of organic pollutants in water by electro-oxidation (EO) process is a very active research topic, but it has been pre-eminently focused on the development of anodes with enhanced electrocatalytic ability to produce center dot OH at their surface. Conversely, the degradation pathways that may arise from the potential center dot OH production at the cathode surface are often disregarded. This work discusses the contribution of center dot OH, formed at a Ti, graphite, stainless steel or Pt cathode from the reduction of O-2 or H2O2, to phenol oxidation in 0.5 mol dm(-3) H2SO4 medium. The center dot OH production in the cathodic compartment of a divided cell was assessed from coumarin oxidation monitored via UV/Vis spectroscopy and HPLC with a fluorescence detector, salicylic acid oxidation evaluated by HPLC with a photodiode array detector and electron paramagnetic resonance. It was demonstrated that the production depended on the cathode nature, decreasing as: Pt > graphite >> stainless steel > Ti. It was concluded that a two-electron reaction converted O-2 to H2O2, which was monoelectronically reduced to center dot OH. The results reveal the importance of cathode selection in water treatment by EO. (c) 2019 Elsevier Ltd. All rights reserved.