*2.2. Fabrication of CuO*/*ZnO*

The mechanochemical combustion method was used to prepare CuO/ZnO. In agitate mortar, 2.195 g of zinc oxalate dihydrate and 2.521 g of acetic acid were taken. Then, the mixture was ground for 10 min to produce Zn(CH3COO)2·2H2O and (COOH)2·2H2O paste. In the above paste, Cu(CH3COO)2 was added as a source of Cu, and then the grinding process was continued for the next 10 min to produce a precursor of zinc oxalate−copper oxalate. The precursor powders were calcined at 500 ◦C for 3 h in the presence of air atmosphere to obtain the CuO/ZnO composite [28]. For comparison, un-doped ZnO was prepared from the zinc oxalate and acetic acid paste.
