Effect of annealing on physicochemical and photocatalytic activity of Cu_5% loading on ZnO synthesized by sol–gel method

In this study, mesoporous Zn_0.95Cu_0.05O 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 T_C: 250–550 °C for Zn_0.95Cu_0.05O. 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 T_C. However, the formation of monoclinic CuO was observed at higher T_C. For Zn_0.95Cu_0.05O, 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 Cu_5% doped ZnO with CuO on the surface resulted in highly improved photocatalytic activity.