Towards wastewater treatment: Photo-assisted electrochemical degradation of 2-nitrophenol and orange II dye at a tungsten trioxide-exfoliated graphite composite electrode

The degradation of organics in water treatment by electrochemical and photo-assisted electrochemical processes was carried out using a photoanode consisting of tungsten trioxide (WO₃) and exfoliated graphite (EG). The WO₃-EG nanocomposite was characterised using voltammetry, X-ray diffractometry, Raman and FTIR spectroscopy, and scanning electron microscopy connected to energy dispersive X-ray spectrometry. The applicability of the WO₃-EG as photoanode material was investigated by the degradation of 2-nitrophenol and orange II dye as model organic pollutants in a 0.1 M Na₂SO₄solution, using a 10 mA cm⁻²current density. The removal efficiencies and the extent of mineralisation of the dye and 2-nitrophenol were monitored using a UV–Visible spectrophotometer and a TOC analyser respectively. The results showed that the WO₃-EG nanocomposite electrode gave a higher removal efficiency (82% for 2-nitrophenol and 95% for orange II dye) and a higher degree of mineralisation (69% for 2-nitrophenol and 67% for orange II dye) in comparison to the EG electrode. Furthermore, efforts were made to evaluate the degradation intermediates which indicated the formation of carboxylic acids that were further degraded by hydroxyl radicals.