TiO2/SiO2 dopant-free nanophotocatalysts for highly efficient photocatalytic water splitting: Challenging traditional TiO2-based systems

Abstract

Three preparation methods of mesoporous silica nanosupports were investigated for H2 production: molecular imprinting, surface functionalization, and hybrid framework. The effect of the surface nature of SiO2 on the growth and distribution of TiO2 actives sites, as well as on photocatalytic reactions, was also explored. TiO2 and TiCl4 were used as precursors for the catalytic centers, and the results were compared to each other. The molecular imprinting created on the SiO2 support improved the exposure of catalytic species and changed the electronic properties, resulting in a narrow energy bandgap (Eg, 2.85-2.94 eV). A deep discussion of the textural, morphological, optical, spectral, electronic, surface fractal, and crystal structure characteristics of the TiO2/SiO2 metal-free nanocatalyst performance for water splitting is presented. The dopant-free nanocatalysts stand out for the small amount of TiO2 (0.0778–0.1747% wt. Ti/SiO2) used in their preparation and for their high catalytic activity for H2 photoproduction. A surprising performance was achieved by the SiTi1200 sample, 140.22 mmol H2.g−1, mainly due to the specific surface area, the surface fractal structure, and the band gap energy. This performance was much higher than that of commercial P25 and other TiO2 materials, which are more complex catalytic systems reported in the literature. The study shows that easily synthesized TiO2/SiO2 nanosystems with tunable main characteristics may overcome the existing limitations for water splitting by TiO2-based photocatalysts, allowing new opportunities for other catalytic applications.