Fluorine‐Free Synthesis of Well‐Dispersed Hollow TiO 2 Spheres via Ostwald Ripening: Process, Mechanism, and Photocatalytic Performance

Well‐dispersed hollow TiO 2 spheres were synthesized via Ostwald ripening through a fluorine‐free solvothermal process in a n‐ PrOH / H 2 O mixed solvent. Several commonly used acids, such as HNO 3 , HCl , and H 2 SO 4 , were found to be effective as the ripening‐directing agent to replace the highly corrosive HF , and the hollow TiO 2 sphere size could be modulated by varying the reactant concentrations. The effects of the solvents and reactants were explored in details, which demonstrated that four important criteria existed in this fluorine‐free process to create well‐dispersed hollow TiO 2 spheres, including the utilization of n‐ PrOH / H 2 O mixed solvent, certain degree of acidity, coexistence of different acids, and the existence of SO 4 2− in the reaction solution. After calcination for a better crystallization, these hollow TiO 2 spheres were composed of pure anatase phase, and had a good photocatalytic degradation performance on RhB under UV illumination.