Sonoelectrochemical degradation of formic acid using Ti/Ta₂O₅-SnO₂ electrodes

Advanced oxidation processes (AOPs) are modern methods using highly reactive hydroxyl radicals for the oxidation of persistent organic (sometimes inorganic) compounds in aqueous phase. Among AOPs, sonoelectrochemical degradation is a technique employing electrochemistry and ultrasound as the main source of energy without the need for additional chemicals for the process. The annual production of formic acid (FA) is around 800,000 tons and is a constituent in wastewaters from tannery, chemical, pharmaceutical, dyeing industries etc. Thus far sonoelectrochemical methods have never been applied to FA decomposition. The aim of this paper is to investigate the sonoelectrochemical decomposition of FA, optimize the sonochemical and electrochemical parameters involved in FA degradation and compare the results with other existing AOPs. Sonoelectrochemical degradation of FA was found to be either comparable or better than other AOPs in terms of time and degradation efficiency. The highest 97% mineralization of FA was obtained using 1176 kHz ultrasonic irradiation combined with 20 mA electrolysis in 120 min. The fastest FA degradation kinetics with a rate constant of 0.0374 min^− 1 were generated at 381 kHz at 20 mA at an ultrasonic power of 0.02 W/cm³.