Enhanced visible light-induced photoelectrocatalytic degradation of phenol by carbon nanotube-doped TiO2 electrodes

We used a modified sol–gel method to prepare titanium dioxide and multi-walled carbon nanotube (CNT) composites that we subsequently deposited onto indium tin oxide (ITO) conductive glass plates. We characterized these CNT-doped TiO2 (CNT–TiO2) films using X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and diffuse reflectance UV–vis spectroscopy. The photoelectrocatalytic (PEC) activity of the composites was evaluated through their ability to mediate the degradation of phenol. XRD measurements indicated that the TiO2 component existed solely in the anatase phase and that the crystallinity of the CNTs was low. XPS indicated that carbon atoms could substitute for both oxygen and titanium atoms in the TiO2 lattice to form Ti–C and Ti–O–C structures, which were responsible for the extra photoabsorption and PEC activity under illumination with visible light, in addition to those provided by the CNTs and carbonaceous and Ti3+ species. An interphase interaction between TiO2 and the CNTs elevated the photoabsorbance of the composites in the visible light region. A sample of TiO2 doped with 10% CNTs and calcined at 400 °C exhibited the highest photocurrent and PEC efficiency. We systematically investigated the effects of several parameters of the PEC process, including the applied potential and pH, on the phenol conversion.