Photophysical and Photocatalytic Properties of <scp> <scp>Zn</scp> ₃ <scp>M</scp> ₂ <scp>O</scp> ₈ </scp> (M = <scp> <scp>Nb</scp> </scp> , <scp> <scp>Ta</scp> </scp> )

Abstract

The Zn 3 M 2 O 8 (M = Nb , Ta ) compounds with layered crystal structures were prepared by a conventional solid‐state reaction method, and their electronic‐band structures, optical properties, and photocatalytic activities were investigated. The prepared compounds were characterized by X ‐ray diffraction ( XRD ), scanning electron microscopy ( SEM ), UV –Vis diffuse reflectance, and Mott–Schottky measurement. The UV–V is diffuse reflectance spectra revealed Zn 3 Nb 2 O 8 and Zn 3 Ta 2 O 8 exhibited band gaps of 4.1 and 4.5 eV, respectively. From the electronic‐band‐structure calculations using DFT method, it was found that the valence band in both compounds was constructed by the hybridization of Zn 3 d and O 2 p orbitals, whereas the conduction band was consisted of Nb 4 d ( Zn 3 Nb 2 O 8 ) and Ta 5 d ( Zn 3 Ta 2 O 8 ) orbitals. The photocatalytic activity of both compounds was examined by the measurement of the H 2 production rate in an aqueous methanol solution under UV light irradiation. The Zn 3 Ta 2 O 8 with a larger band gap exhibited higher activity than Zn 3 Nb 2 O 8 , which was attributed to its higher reduction potential resulting from the difference of its electronic‐band configuration.