Development of Mn doped ZnAl₂O₄ via hydrothermal method as photocatalyst for Cr(VI) reduction under visible light

A hydrothermal method was employed to synthesise zinc aluminate oxides doped with manganese, with the aim of enhancing the photocatalytic reduction of hexavalent chromium to trivalent chromium. The optical, textural, microscopic, and structural features of the materials were assessed by a range of analytical techniques. These results revealed that incorporation of Mn dopant into the ZnAl₂O₄ (ZAO) reduced to band gap of ZAO and MD-ZAO are 3.56 and 2.79 eV, respectively. The best photoreduction efficiency was found with manganese-doped ZnAl₂O₄ (MD-ZAO) is 86.39 % than ZAO (69.38 %) after 120 min. The surface area study displays the 21.43 and 38.65 m² g⁻¹ for ZAO and MD-ZAO, respectively. When surface area of a nanomaterial is increased, a greater percentage of the material in contact with Cr ion, which increases the photocatalytic activity. A large interfacial area and pore volume aids in development of photoinduced electrons (e⁻) as well as hole pairs. The impedance study indicates the lower Rct value of ZAO and MD-ZAO are 0.45 Ω and 0.7 Ω, respectively. The finding indicates that Mn doped ZnAl₂O₄ work as excellent photocatalyst for photoreduction of hexavalent of Cr. The doped material can also act as potential catalyst in different future electrochemical and photocatalytic study.