Formation of crystalline TiO2−xNx and its photocatalytic activity

Amorphous precursors to nitrogen-doped TiO2 (NTP) and pure TiO2 (ATP) powders were synthesized by hydrolytic synthesis and sol–gel method (SGM), respectively. Corresponding crystalline phases were obtained by thermally induced transformation of these amorphous powders. From FT-IR and XPS data, it was concluded that a complex containing titanium and ammonia was formed in the precipitate stage while calcination drove weakly adsorbed ammonium species off the surface, decomposed ammonia bound on surface of precipitated powder and led to substitution of nitrogen atom into the lattice of TiO2 during the crystallization. The activation energies required for grain growth in amorphous TiO2−xNx and TiO2 samples were determined to be 1.6 and 1.7 kJ/mol, respectively. Those required for the phase transformation from amorphous to crystalline TiO2−xNx and TiO2 were determined to be 129 and 142 kJ/mol, respectively. A relatively low temperature was required for the phase transformation in NTP sample than in ATP sample. The fabricated N-doped TiO2 photocatalyst absorbed the visible light showing two absorption edges; one in UV range due to titanium oxide as the main edge and the other due to nitrogen doping as a small shoulder. TiO2−xNx photocatalyst demonstrated its photoactivity for photocurrent generation and decomposition of 2-propanol (IPA) under visible light irradiation (image).