The effect of MgO nanoparticles dosage (0.2e1.4 g/L) on the
photocatalytic degradation of AR73 was investigated at initial pH of
5 and the reaction time of 30 min. According to the results, the
removal of AR73 was improved as the catalyst dosage increased up
to the dosage of 0.8 g/L, but no significant increasewas observed for
further concentrations (Fig. 4b). The total COD and AR73 removal
efficiencies for MgO nanoparticles dosage of 0.8 g/L were 77%
(±0.94) and 99.5% (±0.24), respectively. The enhanced AR73
removal, along with increasing the photocatalyst dosage, is due to
the increased surface area, producing more active sites for the
photocatalytic reaction and the efficient adsorption of UVA by the
catalyst. This leads to the generation of more OH for the photocatalytic
degradation of the target pollutant (Kordouli et al., 2015).
However, as shown in Fig. 4b, the total COD removal did not
improved beyond the photocatalyst dosage of 0.8 g/L and even
decreased in dosage of 1.4 g/L. Increasing the photocatalyst dosage
over an optimum value leads to the aggregation of photocatalyst
particles in the solution, deactivating surface active sites responsible
for the generation of OH (Affam and Chaudhuri, 2013;
Khataee et al., 2015). Therefore, photocatlyst dosage of 0.8 g/L
was selected for the study on the real wastewater samples.