Preparation of Red TiO₂ with Excellent Visible Light Absorption from Industrial TiOSO₄ Solution for Photocatalytic Degradation of Dyes

At present, it is still difficult to significantly reduce the bandgap of TiO₂ to promote its visible light absorption. Herein, we first synthesized sulfur-doped TiO₂ from industrial TiOSO₄ and then successfully synthesized red TiO₂ nanoparticles by calcination with the N source melamine. Theoretical calculations show that predoped S could markedly decrease the formation energy and substitution energy of N-doped TiO₂, especially in high N/Ti ratios. The red TiO₂ nanoparticles have a low bandgap (2.10 eV) and exhibit remarkable visible light absorption capacity. Electron paramagnetic resonance measurements show that the red TiO₂ has abundant oxygen vacancies and Ti³⁺. The synergetic effect of Ti³⁺, oxygen vacancies, and nonmetallic element doping leads to the bandgap of TiO₂ significantly being reduced. In addition, the red TiO₂ exhibits great photocatalytic activity in the visible light degradation of rhodamine B (Rh.B) and methylene blue (MB). This study provides a new idea for the preparation of TiO₂ with high visible light absorption.