Sonoelectrocatalytic decomposition of methylene blue using Ti/Ta2O5–SnO2 electrodes

•The annual worldwide production of dyes is estimated to be 7×105tonnes.•Complete sonoelectrocatalytic MB degradation was achieved after 45min.•The COD reduction of 85.4% and 38.4% TOC reduction was achieved after 2h. Sonoelectrochemical decomposition of organic compounds is a developing technique among advanced oxidation processes (AOPs). It has the advantage over sonication alone that it increases the efficiency of the process in terms of a more rapid decrease in chemical oxygen demand (COD) and in total organic carbon (TOC) and accelerates electrochemical oxidation which normally requires a lengthy period of time to achieve significant mineralisation. Moreover the use of an electrocatalytic electrode in the process further accelerates the oxidation reaction rates. The aim of this study was to improve the decomposition efficiency of methylene blue (MB) dye by sonoelectrochemical decomposition using environmentally friendly and cost-effective Ti/Ta2O5–SnO2 electrodes. Decolourisation was used to assess the initial stages of decomposition and COD together with TOC was used as a measure of total degradation. The effect of a range of sonication frequencies 20, 40, 380, 850, 1000 and 1176kHz at different powers on the decolourisation efficiency of MB is reported. Frequencies of 850 and 380kHz and the use of higher powers were found more effective towards dye decolourisation. The time for complete MB degradation was reduced from 180min using electrolysis and from 90min while carrying out sonolysis to 45min when conducting a combined sonoelectrocatalytic experiments. The COD reduction of 85.4% was achieved after 2h of combined sonication and electrolysis which is a slightly higher than after a single electrolysis (78.9%) and twice that of sonolysis (40.4%). A dramatic improvement of mineralisation values were observed within 2h of sonoelectrocatalytic MB degradation. The TOC removal efficiency increased by a factor of 10.7 comparing to sonication alone and by a factor of 1.5 comparing to the electrolytic process. The energy consumption (kWh/m3) required for the complete degradation of MB was evaluated.