Interfacial band alignment for photocatalytic charge separation in TiO2 nanotube arrays coated with CuPt nanoparticles

摘要

n-Type anatase-phase one-dimensional TiO2 nanostructure arrays coated with nanoparticles of Cu or CuPt have emerged as high performance photocatalysts for both photooxidation and photoreduction. The properties of the catalyst-promoter interface are recognized to be critical to this high performance but are largely unknown. Using X-ray and ultraviolet photoelectron spectroscopies (XPS/UPS), we probed the electronic properties of the CuPt\u2013TiO2 interface in transparent TiO2 nanotube arrays (TTNTAs) coated with photodeposited CuPt nanoparticles (CuPt\u2013TTNTA hybrids) as well as those coated with sputtered CuPt (Sput-CuPt\u2013TTNTA hybrids). XPS and UPS spectra provided the evidence of a Schottky barrier with a band-bending of 0.49\u20130.67 eV at the CuPt\u2013TiO2 interface in CuPt\u2013TTNTA hybrids due to which photoexcited electrons are expected to be retained in the TiO2 while photoexcited holes will be collected by the CuPt nanoparticles. For Sput-CuPt\u2013TTNTA hybrids, no such band-bending was observed. These results point to the importance of the metal nanoparticle preparation technique on interfacial band-alignments and challenge the conventional understanding of the promoting action of noble metal nanoparticles on TiO2 photocatalysts as sinks for photoexcited electrons.