Effect of annealing on physicochemical and photocatalytic activity of Cu5% loading on ZnO synthesized by sol–gel method

In this study, mesoporous Zn0.95Cu0.05O was prepared using a simple sol-gel method in the presence of tartaric acid as catalyst. The obtained powders were annealed under air in the range of TC: 250–550 °C for Zn0.95Cu0.05O. The ratio of Cu:Zn obtained from energy dispersive X-ray (EDX) (4.8 %) is in good agreement with the desired experimental result. The X-ray diffraction analysis indicated that the wurtzite structure was maintained for all samples and copper was successfully doped into ZnO at low TC. However, the formation of monoclinic CuO was observed at higher TC. For Zn0.95Cu0.05O, the crystallite size increased with the annealing temperature from 15.86 to 24.24 nm. The isotherms obtained were type IV with a hysteresis type H3, confirming the mesoporous behavior of the catalysts. The surface area was in the range of 35.1 to 8.66 m2/g. All the prepared catalysts mainly showed two emission regions: a sharp peak in the ultraviolet region and another broad peak in the visible region. The photocatalytic activity was achieved by the degradation of 300 mg/L malachite green (MG) aqueous solution under UV irradiation. The findings showed that the increased annealing of Cu5% doped ZnO with CuO on the surface resulted in highly improved photocatalytic activity.