*2.1. Chemicals*

The samples were synthesized using zinc acetate dihydrate (Zn(CH3COO)2·2H2O), oxalic acid dihydrate (COOH)2·2H2O), and copper acetate (Cu(CH3COO)2). Methylene blue (C16H18ClN3S) was employed in the photodegradation experiment. Three scavengers were selected: Ascorbic acid (C6H8O6), 2−propanol (CH3)2CHOH), and *di*−ammonium oxalate monohydrate (NH4)2C2O4·H2O). All of the analytical grade chemicals were used without any purification.
