Facile synthesis of N-doped biphasic TiO2 nanoparticles with enhanced visible light-driven photocatalytic performance

Undoped and N-doped TiO2 anatase/brookite mixed-phase nanoparticles were synthesized via a facile sol-gel method using urea as a nitrogen source. Surprisingly, nitrogen played a dual role in doping and controlling the anatase and brookite phases in the nanoparticles. The as-synthesized photocatalysts were characterized by powder X-ray diffraction (PXRD), Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET) analysis and UV-vis diffuse reflectance spectroscopy (DRS). PXRD results revealed that TiO2 nanoparticles consisted of a mixture of anatase and brookite crystalline phases where the anatase phase increased with increasing urea concentration (1-60 wt. %), and the pure anatase phase was found at a urea concentration of >= 15 wt. %. N-doped anatase/brookite mixed-phase (brookite similar to 20 wt. %) nanoparticles exhibited superior photocatalytic activity over others in degrading rhodamine-B (RhB) under simulated visible light irradiation, and its photocatalytic performance was comparable to that of Degussa P25. The enhanced photodegradation activity was credited to biphasic composition, narrower bandgap energy, and stronger light absorption in the visible region.