Synthesis, structural, and opto-electrochemical properties of cobalt aluminate type spinel and its use with ZnO for Cr(VI) photoreduction.

The discovery of the occurrence of inorganic pollutants in surface waters is identified in the system assessment quality. The most harmful elements are pesticides, persistent organic pollutants, pharmaceuticals, personal care products, and heavy metals are still dangerous to the environment due to their general uses. Chromate has the largest concentration compared to the other metals in the wastewater industries. This work evaluates the application of the spinel p-CoAl2O4 as a photocatalyst prepared by the nitrate synthesis process to reduce Cr(VI), a hazardous metal for the environment. The photocatalyst was characterized using thermal analysis (TG), X-ray diffraction, UV-diffuse reflectance spectroscopy, scanning electron microscopy, fluorescent X-ray, Fourier transform infrared spectroscopy, electrical conductivity, and photoelectrochemically. The results showed that the efficiency of optimum reduction of Cr(Vl) to Cr(IIl) photoreduction is more effective (77%) for pH = 3.6 than that at high pH values up to 8 (7%). Moreover, the effect of the hetero-system CoAl2O4/ZnO on photocatalytic efficiency was investigated. The photocatalytic activity increases up to 99% with 1 g L-1, a total catalyst dosage over the hetero-system CoAl2O4/ZnO at a ratio of 75%/25%. This data is better relative to CoAl2O4 or ZnO alone. The Cr(VI) photoreduction activity improvement was caused by the best separation and the photogeneration of electron-hole on the CoAl2O4/ZnO surfaces. Finally, the Lagergren pseudo-first-order and the Langmuir-Hinshelwood models fit well the experimental kinetics.