Topochemical synthesis of mesoporous TiO ₂ co-doped with nitrogen and fluorine for improved photocatalytic O ₂ evolution under visible light

Mesoporous rutile TiO₂ photocatalysts co-doped with N and F were synthesized via a topotactic ammonolysis approach using mesostructured TiO₂ as a precursor. The co-substitution of N and F into the rutile lattice led to substantial modulation of the Ti electronic structure and to extension of visible-light absorption, accompanied by local distortion of TiO₆ octahedra. Systematic characterization revealed that the balance between dopant incorporation and structural integrity of the mesoporous framework played a decisive role in determining photocatalytic performance for half-cell O₂ evolution. Although higher-temperature ammonolysis promoted N incorporation and enhanced visible-light absorption, it also compromised the mesostructure, reducing the overall activity. The highest O₂ evolution rate under visible-light irradiation was achieved with the sample prepared under optimal conditions that maintained both phase-pure rutile and mesoporosity. These results highlight the importance of controlling both chemical doping and structural features when designing high-performance non-metal-doped oxide photocatalysts for solar-driven water oxidation.