Enhanced photocatalytic reduction of hexavalent chromium ions over Zn-bearing in CuZn hydroxy double salts: Insight into the structural investigation using extended X-ray absorption fine structure

CuZn hydroxy double salts (CuZn-HDS) are often used as adsorbent and Fenton-like catalysts. In this work, we report the photocatalytic activity of CuZn-HDS for Cr(VI) reduction. In detail, CuZn-HDS with different Cu/Zn ratios were prepared as photocatalysts through the metal oxide-assisted hydrothermal method. The CuZn-HDS samples were characterized and applied for photocatalytic reduction of Cr(VI), which is a toxic inorganic pollutant in the wastewater. The CuZn-HDS which has the Cu/Zn ratio of about 4 (CuZn-HDS-4) showed the heist photocatalytic Cr(VI) reduction activity more than other samples, especially for copper hydroxy salts (Cu-HS) which have no Zn in the structure. Thus, the Zn-bearing in CuZn hydroxy double can improve the photocatalytic activity for Cr(VI) reduction compared with Cu-HS. The increase in the Cr(VI) reduction activity of the optimized CuZn-HDS-4 was attributed to the excellent separation and transportation of photogenerated electron-holes pairs, as proven by the photoluminescence, photocurrent density, and electrochemical impedance spectroscopy results. Moreover, the atomic structure of the synthesized CuZn-HDS was elucidated by an extended X-ray absorption fine structure technique, which is the first time to report the CuZn-HDS structure. Based on the optical properties, and activity test, a photocatalytic reduction of Cr(VI) over a CuZn-HDS was proposed. Thus, the CuZn-HDS can be employed as a potential photocatalyst for the detoxification of Cr(VI) in wastewater.