Hierarchical porous TiO2 single crystals templated from partly glassified polystyrene.

Hierarchical macro-mesoporous anatase TiO2 single crystal is one-pot synthesized in an EtOH-H2O system using polystyrene (PS) as the single porogen both for macropore and mesopore and TiF4 as the titanium precursor. The key to the simultaneous growth of single crystal and the introduction of hierarchical pores is the assembly of PS and titania at the glassification temperature of PS (100 °C). During the hydrolytic polymerization of TiF4, PS is encapsulated inside titania and gradually glassified. The interference from elastic PS on the oriental growth of TiO2 crystallite is thus minimized and the final removal of PS through calcination leaves interconnected macropore and mesopore inside the single crystal. According to XPS, EPR and fluorescence analyses, abundant oxygen vacancies are formed on the hierarchical porous single crystal, which presents extraordinary photocatalytic activity and stability in degrading organic pollutants under simulated sunlight irradiation using Rhodamine B as the model. The improved photocatalytic activity is a synergistic effect of improved separation of charge carrier and facilitated interfacial charge transfer benefitting from highly accessible porous single crystal structure.