Layer-by-Layer Self-Assembly Construction of Highly Ordered Metal-TiO2 Nanotube Arrays Heterostructures (M/TNTs, M = Au, Ag, Pt) with Tunable Catalytic Activities

We have developed a facile and easily accessible layer-by-layer (LBL) self-assembly route to synthesize hierarchically ordered M/TNTs (M = Au, Ag, Pt) heterostructures. These integrated heterostructures show remarkably enhanced photoactivity and outstanding photostability; photoelectrochemical exploitations substantiated the contribution role of metal NPs acting as "electron reservoir" in prolonging the lifetime of photogenerated electron-hole charge carriers. In addition, these well-defined self-assembled hybrid systems can also be used as a promising catalyst for recycled selective catalytic reduction of 4-nitrophenol toward 4-aminophenol. The integration of high photoactivity and efficient catalytic reduction properties of the heterostructures lies crucially on the LBL self-assembly-induced monodispersivity of metal NPs on the framework of TNTs, and, particularly, the intimate interfacial contact between metal NPs and TNTs substrate arising from the pronounced electrostatic attractive interaction afforded by polyelectrolytes multilayering. Our results show that the design and utilization of highly ordered metal/1-D semiconductor hybrid nanostructures based on the facile LBL self-assembly strategy can find diverse catalytic applications.