Upgrading photocatalytic hydrogen evolution in Ba–Sr–Ta–O perovskite-type layered structures

Photocatalytic hydrogen evolution from water is investigated in Ba–Sr–Ta–O layered compounds possessing two different crystal structures: Sr2Ta2O7 (S.G. Cmcm, a (110) type layered pervoskite), and BaSrTa2O7 (S.G. Immm, a (100) type layered perovskite). High purity samples of BaSrTa2O7 and Sr2Ta2O7 are successfully prepared by solid state reaction. Hydrogen production under UV irradiation is 26% larger in BaSrTa2O7 (15.2 mmol g−1) than in Sr2Ta2O7 (11.4 mmol g−1). The band gaps determined by diffuse reflectance spectroscopy (DRS) are 4 eV and 4.6 eV for BaSrTa2O7 and Sr2Ta2O7, respectively. Density Functional Theory (DFT) calculations provide insights into the crystal and electronic structures of Sr2Ta2O7, BaSrTa2O7, and their derived series Sr2-xBaxTa2O7 (0 ≤ x ≤ 1). It is found that independently of the Sr/Ba content, the BaSrTa2O7-derived series show a ∼0.6 eV lower band gap and a wider conduction band than the Sr2Ta2O7-derived series. DFT results indicate that the enhanced hydrogen production of BaSrTa2O7 is related to particular features of its crystal structure which favor Ta–Ta interactions.