Fig. 8.

Reaction kinetics of first-order for MO dye removal under the illumination of UV light; (Experimental condition: dose of photocatalyst: 0.060–0.210 g of ZnO, Cu/ZnO, Ni/ZnO, and Cu/Ni/ZnO, pH: 8.7, initial MO dye conc.: 10 mg L⁻¹).