Single-crystal TiO2 nanorods assembly for efficient and stable cocatalyst-free photocatalytic hydrogen evolution

Abstract

TiO2 with abundant surface oxygen vacancies is notoriously difficult to stabilize upon photochemical oxidation, which in turn limits its photocatalytic application. To address this limitation, the gray fries cake-like TiO2 assembly composed of single-crystal TiO2 nanorods by in-situ carbon adherence was fabricated via hydrogenation of protonic titanate nanosheets (PTN) under normal pressure. During the hydrogenation process, the residual butyl alcohol adsorbed on PTN from tetrabutyl titanate hydrolysis can be in-situ converted into carbon in company with the formation of oxygen vacancies (O-vacancies) on TiO2. The carbon layer and O-vacancies are able to induce the growth of single-crystal TiO2 nanorods and their assembly to form the fries cake-like structure. Moreover, the carbon layer can not only offer a favorable reduction environment to generate rich O-vacancies on TiO2, but also efficiently improve these O-vacancies and TiO2 nanorods’ stability during catalytic reaction. O-vacancies/carbon layer can serve as electron trap active sites which can capture and transfer electrons to improve the separation of electron-hole pairs. As a consequence, in the absence of any co-catalysts, a high efficiency of hydrogen evolution was achieved for the TiO2 assembly with 69.7 μmol h−1 (quantum efficiency ∼2.3% at 420 nm) under solar light irradiation. After laying six months, our TiO2 assembly still exhibited high photocatalytic performance, which is superior to previous TiO2-based photocatalyst. The results indicate that the photocatalytic activity of TiO2 assembly can be enhanced by stabilizing the surface rich oxygen vacancies with carbon coating.