Effect of nitrogen doping on anatase-rutile phase transformation of TiO2

► N-TiO2 nanoparticles were prepared by hydrolysis of TiCl4 and urea. ► The phase transformation temperature of anatase to rutile was found to be increased by N-doping. ► The mechanism for the transformation temperature increase was summarized as the effects of the similar structure of titanium nitride and anatase, the crystal aberration and the retained crystal growth induced by N-doping. ► N-doped TiO2 showed much higher visible light photocatalytic activity in comparison with P25. The higher photocatalytic efficiency could be attributed to the synergetic effect of N-doping and appropriate crystallinity of anatase phase TiO2.