Selective photoredox activity on specific facet-dominated TiO2 mesocrystal superstructures incubated with directed nanocrystals

Abstract

The photocatalytic performance of nanocrystalline TiO2 is crucially influenced by specific facet-induced adsorption and charge separation. Herein, different morphologies of anatase TiO2 mesocrystal superstructures with directed nanocrystal assembly were controllably synthesized by introducing NH4F as an orientation-directing agent. The ratio of the basal and lateral external surfaces of mesocrystals was tuned from 1.1 to 5.8 by increasing the amount of NH4F, along with that of {001} and {101} facets of incubated TiO2 nanocrystals from 0.56 to 0.76. With increasing the ratios, the mesocrystal superstructures exhibited higher photo-oxidation activities in the degradation of 4-chlorophenol (by 1.7 times) and lower activities in Cr6+ reduction (by 0.47 times) and H2 generation (by 0.32 times). The H2 production from dye-sensitized TiO2 mesocrystal using eosin Y (pH 10) and Ruthenizer 470 (pH 3) are further identify the dominant facets in photocatalysis. It was confirmed that the mesocrystal superstructures with higher ratio of {001}/{101} are more effectively (by 6 times) adsorbed the dye sensitizers under acidic conditions and enhanced charge separation by efficient electron migration through the incubated nanocrystal network and crystal-facet-specific modification of the Pt cocatalyst. The synergetic crystal-facet engineering between mesocrystals and incubated nanocrystals will significantly improve the efficiencies and selectivities of semiconductor photocatalysts.