Kinetics of ultrasound-enhanced electrochemical oxidation of diuron on boron-doped diamond electrodes

Abstract

Freshwater polluted with herbicides is an environmental problem of concern due to the high toxicity and non-biodegradability of these compounds. This work analyses for the first time the degradation and mineralization of diuron (N-(3,4-dichlorophenyl)-N,N-dimethyl-urea), considered priority substance by the European Commission, by electrochemical oxidation (EO) at a boron-doped diamond anode enhanced by low frequency (20 kHz) ultrasound (US). A synergistic analysis was initially performed to evaluate the relative contribution of individual oxidation technologies to the global abatement and mineralization rates of diuron observed under sonoelectrochemical (US–EO) treatment. Under the operation conditions, j = 60 mA cm −2, ν US = 20 kHz, pH = 12, T = 10 °C and 8 h of experimental running, results demonstrated improvements on the mineralization kinetics of diuron closely to 43% when ultrasounds are coupled to the electrochemical treatment. The process efficiency was evaluated through the analysis of the mineralization rate as a good indicator of the formation of organic metabolites which may have higher toxic effects than parent diuron. The mineralization kinetics of diuron degradation by US–EO have been experimentally and theoretically analysed working with 20–30 mg L −1 of diuron, initial pH values between 2 and 12 and temperatures between 10 °C and 40 °C. The encouraging results showed that alkaline pH favours the mineralization rate obtaining reductions of the total organic carbon higher than the 92% after 6 h of degradation. The temperature in the range between 10 °C and 40 °C has a weak impact on the kinetics of the sonoelectrochemical mineralization of diuron.