Creation of oxygen vacancies to activate lanthanum-doped bismuth titanate nanosheets for efficient synchronous photocatalytic removal of Cr(VI) and methyl orange

Abstract

Bi3.25La0.75Ti3O12 (BLTO) nanosheets were synthesized via a simple hydrothermal process, followed by an economically facile vacuum-deoxidized treatment to fabricate Bi3.25La0.75Ti3O12-x (BLTO12-x) nanosheets with abundant surface oxygen vacancies. Relative ratio of surface and bulk oxygen vacancy, as evidenced with positron annihilation lifetime and X-ray photoelectron spectra, was controllable via adjusting vacuum-deoxidized temperature and time. Photocatalytic performance of the pristine and deoxidized nanosheets for synchronous photocatalytic removal of Cr(VI) and methyl orange (MO) were thoroughly investigated. Control experimental results show that the photocatalytic activities of the BLTO12-x nanosheets significantly relied on vacuum-deoxidized temperature and time. The optimal deoxidized nanosheets as activated at 330 °C for 3 h, which has the largest relative concentration of surface oxygen vacancy, shows highest activity under visible light irradiation. Moreover, the synergetic effect for synchronous enhanced photocatalytic degradation of Cr(VI) and MO were observed over all BLTO12-x nanosheets. The detailed synergistic reduction−oxidation removal mechanism is proposed. The surface oxygen vacancy led to rise of valence band maximum, which is responsible for both widening of valence band and decreasing of band gap. The former enhances separation efficiency of photoinduced e−/h + pairs, and the latter extends photoresponse range into visible light region. As a result, compared with pristine BLTO, the visible-light catalytic activity of deoxidization-activated BLTO12-x was significantly enhanced. The vacuum-deoxidized strategy proposed in this work can introduce oxygen vacancy into the matrix of catalyst, which provides an effective way to design and prepare high-efficiency oxides based photocatalyst.