Cyclic volatile methylsiloxanes (cVMSs) are widely used in industrial processes and consumer products, which have been reported to be potentially toxic to human health due to their persistence and bioaccumulation. In this study, a novel photo-catalytic zinc oxide (ZnO)-coated aluminum (ZnO@Al) anode was prepared by a facile hydrothermal epitaxial process for the purpose of degrading cVMSs in practical wastewater. Morphological data and compositional analysis showed a compact coating layer that had the characteristic peaks of ZnO. To optimize the degradation process, central composite design combined with response surface methodology was applied to acquire the optimum parameters of cVMSs removal, and results indicated the cVMSs removal efficiency was approximately 63.3% at the conditions of current density = 17.3 mA/cm2, initial pH of electrolyte = 7.8, plate distance = 18 mm, UV intensity = 90 W, and reaction time = 80 min. Furthermore, the photo-electrocatalytic degradation of cVMSs obeys the pseudo-first order kinetic reaction, and the anode exhibited high durability as the attenuation of cVMSs removal efficiency was <6% after four times reuse. It was also observed that with the application period of the anode was extended, the electroflocculation reaction gradually occurred. The FT-IR of the generated flocs and the total ion gas chromatograms mass spectrometer analysis unraveled the methyl groups in Si-CH3 could be easily attacked by hydroxyl radicals to form the intermediates of monohydroxy substituted products (m/z = 298, 372, and 446) and eventually short-chain carboxylic acids, alkyl radical and silicate. The effective removal of cVMSs by photo-electrocatalytic process using ZnO@Al anode provide significant implication in treatment of practical wastewater.
Keywords: Methyl siloxanes; Photo-electrocatalysis; RSM; ZnO.
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