Photoelectrochemical oxidation of p-nitrophenol on an expanded graphite–TiO2 electrode

Abstract

In the quest for more efficient photoanodes in the photoelectrochemical oxidation processes for organic pollutant degradation and mineralisation in water treatment, we present the synthesis, characterisation and photoelectrochemical application of expanded graphite–TiO₂ composite (EG–TiO₂) prepared using the sol–gel method with organically modified silicate. The Brunauer–Emmett–Teller surface area analyser, ultraviolet–visible diffuse reflectance, scanning electron microscopy, energy dispersive spectroscopy, X-ray diffractometry, Raman spectrometry and X-ray photoelectron spectroscopy were employed for the characterisation of the composites. The applicability of the EG–TiO₂ as photoanode material was investigated by the photoelectrochemical degradation of p-nitrophenol as a target pollutant in a 0.1 M Na₂SO₄ (pH 7) solution at a current density of 5 mA cm⁻². After optimising the TiO₂ loading, initial p-nitrophenol concentration, pH and current density, a removal efficiency of 62% with an apparent kinetic rate constant of 10.4 × 10⁻³ min⁻¹ was obtained for the photoelectrochemical process as compared to electrochemical oxidation and photolysis, where removal efficiencies of 6% and 24% were obtained respectively after 90 min. Furthermore, the EG–TiO₂ electrode was able to withstand high current density due to its high stability. The EG–TiO₂ electrode was also used to degrade 0.3 × 10⁻⁴ M methylene blue and 0.1 × 10⁻⁴ M Eosin Yellowish, leading to 94% and 47% removal efficiency within 120 reaction time. This confirms the suitability of the EG–TiO₂ electrode to degrade other organic pollutants.