Synthesis of hierarchically porous metal oxides and Au/TiO2 nanohybrids for photodegradation of organic dye and catalytic reduction of 4-nitrophenol

Abstract

Hierarchically porous metal oxide materials including titanium dioxide (TiO2), ferric oxide (Fe2O3), zinc oxide (ZnO), and ceria (CeO2) were prepared on a large scale by an improved sol-gel method assisted with evaporation-induced surfactant self-assembly. Hierarchical metal oxide networks with well-defined macroporous windows and mesoporous walls were obtained after the surfactant molecules were removed by calcination. The factors influencing the morphology, pore structure and size of these porous metal oxides were studied. Moreover, this method can also be used for one-pot synthesis of hierarchical nanohybrids loaded with noble-metal nanoparticles. The synthesis and catalytic properties of Au/TiO2 nanohybrids with different Au loading (2, 5, and 10 wt.%) were typically demonstrated. Benefiting from the uniform dispersion of Au nanoparticles, the Au/TiO2 nanohybrids show favorable catalytic activity in both the photooxidation of rhodamine B (RhB) under visible light and the catalytic reduction of 4-nitrophenol with sodium borohydride to 4-aminophenol. The photooxidation mechanism of RhB in aqueous solution over Au/TiO2 nanohybrid was verified experimentally. This work provides a general method for the scalable preparation of diverse hierarchically porous metal oxides and noble-metal/oxide nanohybrids, which are expected to have more applications in catalysis and energy conversion.