*3.7. Role of Reactive Species*

The scavengers of *di*–ammonium oxalate monohydrate (AO), 2–propanol, and ascorbic acid (AA) were used to identify the reactive species for MB photodegradation. The three scavengers' effect on the MB photodegradation with CuO/ZnO is displayed in Figure 7. From the results (Figure 7), it was observed that with the addition of 2–propanol, AO, and AA as a scavenger, photocatalytic degradation dropped from 66% (without scavenger) to 23% (•O2 <sup>−</sup>), 13% (•OH), and 53% (h+) for 1h, while the photocatalytic activity significantly decreased from 88% (without scavenger) to 29% (•O2 −), 37% (•OH), and 79% (h+) for 2 h irradiation, respectively. It can be surmised that the important roles played for the photodegradation of MB were by •O2 <sup>−</sup> and •OH radicals, while a minor role was played by the h<sup>+</sup> radical in the degradation process under sunlight [38].

**Figure 7.** Effects of scavengers on the photodegradation of MB with CuO/ZnO using sunlight.
