Optimization of N doping in TiO nanotubes for the enhanced solar light mediated photocatalytic H production and dye degradation.

Herein, we report the optimization of nitrogen (N) doping in TiO nanotubes to achieve the enhanced photocatalytic efficiencies in degradation of dye and H gas evolution under solar light exposure. TiO nanotubes have been produced via hydrothermal process and N doping has been tuned by varying the concentration of urea, being the source for N, by solid-state dispersion process. The structural analysis using XRD showed the characteristic occupancy of N into the structure of TiO and the XPS studies showed the existence of Ti-N-Ti network in the N-doped TiO nanotubes. The obtained TEM images showed the formation of 1D tube-like structure of TiO. Diffuse reflectance UV-Vis absorption spectra demonstrated that the N-doped TiO nanotubes can efficiently absorb the photons of UV-Vis light of the solar light. The optimized N-doped TiO nanotubes (TiO nanotubes vs urea @ 1:1 ratio) showed the highest degradation efficiency over methyl orange dye (∼91% in 90 min) and showed the highest rate of H evolution (∼19,848 μmol h.g) under solar light irradiation. Further, the recyclability studies indicated the excellent stability of the photocatalyst for the durable use in both the photocatalytic processes. The observed efficiency was ascribed to the optimized doping of N-atoms into the lattices of TiO, which enhanced the optical properties by forming new energy levels of N atoms near the valence band maximum of TiO, thereby increased the overall charge separation and recombination resistance in the system. The improved reusability of photocatalyst is attributed to the doping-induced structural stability in N-doped TiO. From the observed results, it has been recognized that the established strategy could be promising for synthesizing N-doped TiO nanotubes with favorable structural, optical and photocatalytic properties towards dye degradation and hydrogen production applications.