Heterojunctions between amorphous and crystalline niobium oxide with enhanced photoactivity for selective aerobic oxidation of benzylamine to imine under visible light

Abstract

The formation of heterojunctions between two crystals with different band gap structures, acting as a tunnel for the unidirectional transfer of photogenerated charges, is an efficient strategy to enhance the photocatalytic performance of semiconductor photocatalysts. Considering that surface complex photocatalysts also exhibit charge separation and recombination processes, the heterojunctions may also promote the visible-light-response photoactivity of any surface complex catalysts by influencing the transfer of photogenerated electrons. Herein, Nb₂O₅ microfibers, with a high surface area of interfaces between an amorphous phase and a crystalline phase, were designed and synthesised by the calcination of hydrogen-form niobate while controlling the crystallisation. The photoactivity of these microfibres towards selective aerobic oxidation reactions was investigated. As predicted, the Nb₂O₅ microfibres containing heterojunctions exhibited the highest photoactivity. This could be due to the band gap difference between the amorphous phase and the crystalline phase that allows electron transfer unidirectionally, which decreased the recombination rate and improved the efficiency.