2.2.3. Effect of Catalyst Loading

The reactions were carried out by varying the quantity of catalyst (ranging from 10 to 50 mgs). The decomposition of SDB increased from 68% to 89% with the increase in the quantity of the nanocatalysts from 10 to 40 mg/15 mL and dropped to 87% for 50 mg catalyst loading. The initial enhancement in SDB decolorization might be due to an excess availability of active sites, as the amount of catalyst increases [97]. However, a further increase in the catalyst amount leads to an increase in the turbidity and reduces the light penetration depth, thus, the quantity of the photoactive suspension decreases [98,99]. Figure 13 shows that the nanocatalysts amount of 40 mg/15 mL is optimum for maximal SDB removal. Therefore, the remaining experiments were carried out with 40 mg of catalyst loading.

**Figure 13.** Effect of variation of the amount of Mn2+:ZnS Qds catalyst on the sonophotocatalytic degradation of SDB under optimum conditions (15 mL of SDB 70 ppm, pH 6, 75 min irradiation, 40 kHz).
