Tungsten and nitrogen co-doped TiO2 electrode sensitized with Fe–chlorophyllin for visible light photoelectrocatalysis

► N and W co-doped TiO2 were prepared via sol-hydrothermal method. ► The band gap energy of TiO2 has been narrowed due to W/N co-doping. ► W/N–TiO2 electrode sensitized with Fe–chl showed high PEC activities. Sol-hydrothermal method was used to fabricate tungsten (W) and nitrogen (N) co-doped titanium oxide (TiO2) nanoparticles. The nanoparticles were sensitized with a natural dye, sodium–iron–chlorophyllin (Fe–chl). The W and N co-doped TiO2 nanoparticles were analyzed using X-ray diffraction (XRD), filed scanning electron microscopy (FSEM), X-ray photoelectron spectroscopy (XPS) and high resolution transmission electron microscopy (HRTEM). This catalyst was sensitized with different concentrations of Fe–chl to prepare a photoelectrochemical electrode that was characterized by electrochemistry analysis and UV–visible diffuse reflectance spectra. The photoelectrocatalytic (PEC) degradation of methyl orange (MO) under visible light illumination on the obtained electrodes was investigated. The conduction and valence bands of TiO2 were respectively modified with W and N. The 3d orbit of W lowered the conduction band level of TiO2 and the 2p orbit of N shifts the valence band level of TiO2 upward. This condition, along with the excitation of the TiO2 electrode to electron–hole that was induced by porphyrin in Fe–chl under visible illumination, resulted in the high PEC activity of the W/N–TiO2–Fe–chl electrode. The highest degradation (64.3%) and CODCr removal (48.2%) efficiencies of MO on W/N–TiO2–Fe–chl-2mM under visible light illumination for 4h were obtained by applying bias potential +1.5V.