Hydrogen production versus photocatalyst dimension under concentrated solar light: A case over titanium dioxide

Revealing the trend of hydrogen production and corresponding photocatalyst behavior under different light intensities is of significance for the targeted synthesis of photocatalyst of certain morphology, which is crucial for efficient photocatalytic reaction under real solar energy, considering that in real cases solar concentration is often employed and the intensities of the solar light is always changing. To this end, the evolution of physicochemical properties of nanoparticle slurry and their hydrogen production under concentrated solar light irradiation over TiO₂ of different dimensions have been systematically explored, i.e., nanosphere, nanorod, and nanosheet. Interestingly, monotonously enhanced hydrogen production activities versus increasing light intensity up to 11 suns (1 sun = 1 kW·m⁻²) were observed for nanorods and nanosheets. However, hydrogen production exhibited an initial rapid increase and then an obvious falling tendency for nanospheres once the light intensity beyond 8 suns. It was revealed that nanospheres slurry with higher thermal conductivity and lower viscosity under higher light intensity resulted in heavier particle agglomeration due to the stronger collision tendency among particles, hence, decreased light absorption and lowered reaction temperature. Consequently, fewer photo-induced charge carriers and slower reaction kinetics resulted in the falling tendency of hydrogen production under high light intensities over nanosphere TiO₂. It is believed that this work could provide a useful guidance for the targeted synthesis of photocatalyst of certain morphology, which is crucial for efficient photocatalytic reaction under real concentrated solar energy.