Tungsten-doped TiO/reduced Graphene Oxide nano-composite photocatalyst for degradation of phenol: A system to reduce surface and bulk electron-hole recombination.

Recombination of photogenerated charges is the main factor affecting the photocatalytic activity of TiO. Here, we report a combined strategy of suppressing both the bulk as well as the surface recombination processes by doping TiO with tungsten and forming a nanocomposite with reduced graphene oxide (rGO), respectively. Sol-gel method was used to dope and optimize the concentration of W in TiO powder. UV-Vis, XPS, PL and time resolved PL spectra along with DFT calculations indicate that W in TiO lattice creates an impurity level just below the conduction band of TiO to act as a trapping site of electrons, which causes to improve the lifetime of the photo-generated charges. Maximum reduction in the PL intensity and the improvement in charge carrier lifetime was observed for TiO doped with 1 at.% W (1W-TiO), which also displayed the highest photo-activity for the degradation of p-nitro phenol pollutant in water. Tuning of rGO/TiO ratio (weight) disclosed that the highest activity can be achieved with the composite formed by taking equal amounts of TiO and rGO (1:1), in which the strong interaction between TiO and rGO causes an effective charge transfer via bonds formed near the interface as indicated by XPS. Both these optimized concentrations were utilized to form the composite rGO/1W-TiO, which showed the highest activity in photo-degradation of p-nitro phenol (87%) as compared to rGO/TiO (42%), 1W-TiO (62%) and pure TiO (29%) in 180 min. XPS and PL results revealed that in the present nanocomposite, tungsten species traps the excited electron to reduce the interband recombination in the bulk, while the interaction between TiO and rGO creates a channel for fast transfer of excited electrons towards the latter before being recombined on the surface defect sites.