Size-Dependent Mie’s Scattering Effect on TiO₂ Spheres for the Superior Photoactivity of H₂ Evolution

A novel strategy of coupling Mie’s scattering effect into the light-absorption region of TiO 2 was developed to enhance the photocatalytic performance of H 2 evolution over TiO 2 spheres. The TiO 2 spheres with different diameters (330–750 nm) were controllably fabricated via adopting different sized polymer poly(methyl methacrylate) (PMMA) templates. The UV–visible absorption and reflectance spectra were employed for studying the absorption and scattering properties of these TiO 2 spheres. It was found that the scattering resonant peaks that indicate the strongly efficient scattering in different wavelength regions were largely dependent on the sizes of the TiO 2 spheres. The scattering resonant peaks have been detected around 366, 400, and 440 nm for the TiO 2 spheres with diameters of 380, 450, and 600 nm, respectively. Moreover, the photocatalytic efficiency of the H 2 evolution was found to be dependent on the size of the TiO 2 spheres. Among them, the TiO 2 spheres with a diameter of 380 nm exhibited the highest photocatalytic activity (313 μmol/(h·m 2 )), about 5 times and 3 times of that of 330 and 450 nm sized TiO 2 spheres, respectively. The highest activity observed on 380 nm sized TiO 2 may be attributed to its optimized diameter, which can result in a highly efficient scattering effect in the light-absorption region of TiO 2 (λ < 387 nm).