*4.2.3. Effect of the process conditions*

The dye photodegradation of dye by TiO2 -AgNP under UV light is controlled by the level of Ag in photocatalysts and irradiation light. Also, the effectiveness of the dye photodegradation is affected by operating conditions such as photocatalyst dose, initial concentration, contact time and solution pH.

## *4.2.3.1. The effect of the photocatalyst dose*

The dye photodegradation increases with the increase in the photocatalyst dose. The effectiveness of the photodegradation reduces when the photocatalyst dose is further increased [66–68, 81]. The maximum photodegradation is obtained by using 1 g photocatalyst/100 mL [68, 74, 81]. In other work, the use of 0.6 g photocatalyst/L is also reported [67]. Such data can be explained based on the number of active sites available for photocatalytic reactions. More active sites of the photocatalyst are available when the dose of the photocatalyst increases. However, the use of a large number of photocatalysts may cause agglomeration of the material to produce big particle size. The large particle size gives small surface area, which decreases the number of active sites on the surface [36, 38]. Another reason for the decrease in the degradation can be attributed to the increase in the turbidity of suspension due to more suspended photocatalyst solids. The light scattering by the catalyst particles leads to the blockage of photon absorption. Moreover, less OH radicals can be created [1, 2].
