Electron Transfer Reduction by Hydrogen Creates Porosity in Tantalate Crystals and Produce Multifunctionality

Abstract

Contrary to partially substituted systems, WO3 molecular sieves that exclusively comprise a d0 transition metal ion and do not possess template ions in the cavity are a new class of materials for photocatalysis owing to their framework structure. Because WO3 thermodynamically lacks proton-reduction capability, exploring diverse synthetic approaches of other materials is desirable for facilitating utilization as H2 evolution and water splitting systems. Herein, we report an efficient approach for the protonation of Ag2Ta4O11 to afford H2Ta4O11 for application as a H2 molecular sieve. Hydrogen reduction of Ag2Ta4O11 at 300 °C and post-treatment using HNO3 afforded H2Ta4O11. Characterizations of H2Ta4O11, coupled with density functional theory (DFT) calculations, reveal that the intrinsic structure of Ag2Ta4O11 is maintained. Moreover, H+ is generated from H2 oxidation and forms OH, and the orientation of OH is parallel to that of the ab plane. Desorption and adsorption of H2 within H2Ta4O11 were achieved by heating H2Ta4O11 to above 90 °C. This is attributed to positive thermal expansion, as confirmed by high-temperature X-ray diffraction. H2Ta4O11 is an active heterogeneous photocatalyst for the half-reactions of water splitting. Moreover, deuteration experiments of H2Ta4O11 in D2O suggest its capability as a H2–D2 conversion catalyst. Furthermore, H2Ta4O11 functions as an active synthetic precursor for new tantalate materials, the direct synthesis of which is challenging.