Photoelectrochemical degradation of azo dye over pulsed laser deposited nitrogen-doped TiO2 thin film

We investigated the synergetic effect of electrochemical and photocatalytic oxidation in photoelectrochemical (PEC) process for the degradation of hazardous organic compounds exemplified by methyl orange, an azo dye. Nitrogen doped TiO2 thin film (NTTF) synthesized by the pulsed laser deposition (PLD) method, was used as the working anode. The crystalline, optical properties, surface morphology, and structure of the NTTF were characterized by XRD, UV–vis absorbance edges, SEM, and XPS. Results showed that the NTTF was dominated by anatase phase after sintered at 600 °C with significant visible light response at 595 nm. XPS analyses indicated nitrogen doping was mainly responsible for reducing the band gap as evidence of 3% N doping into the structure via the linkage of TiON and NTiO bond. SEM images illustrated the nitrogen-doped TiO2 nanoparticles being attached firmly and spread evenly over the ITO glass surface, which is beneficial for PEC applications. The degradation efficiency of MO by photoelectrochemical, photocatalytic, electrochemical and photolysis methods were compared in terms of pseudo-first-order reaction rate. PEC was the most efficient in degrading MO at a bias potential of 2.0 V (vs. SCE) under light at a wavelength of 325 nm, which was consistent with results of IPCE (%) measurements. The synergetic effect was quantified at current/bias potential of 0.07 mA/0.3 V and 0.6 mA/2.0 V, respectively. Results demonstrated that the bias potential could separate photogenerated holes and electrons effectively and enhance the electrochemical-oxidation of MO. The mechanistic aspects of MO degradation by the PEC process were discussed.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Nitrogen was successfully doped into TiO2 structure using PLD method. ► Nitrogen doping extended the band gap of TiO2 from 400 to 595 nm. ► NTTF had peak IPCE (λ) of 26.77% under 2 V bias potential 325 nm light. ► Two-chamber PEC system improves photocatalytic oxidation of methyl orange.