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 TiO2 was developed to enhance the photocatalytic performance of H-2 evolution over TiO2 spheres. The TiO2 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 TiO2 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 TiO2 spheres. The scattering resonant peaks have been detected around 366, 400, and 440 nm for the TiO2 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 TiO2 spheres. Among them, the TiO2 spheres with a diameter of 380 nm exhibited the highest photocatalytic activity (313 mu mol/(h.m(2))), about 5 times and 3 times of that of 330 and 450 nm sized TiO2 spheres, respectively. The highest activity observed on 380 nm sized TiO2 may be attributed to its optimized diameter, which can result in a highly efficient scattering effect in the light-absorption region of TiO2 (lambda < 387 nm).