*3.4. Quantum Dot Based Catalytic Experiments*

After characterization, the synthesized Qds were used in the sonophotocatalytic degradation experiments of SDB dye. A 100-ppm stock solution of SDB was prepared for the studies. In order to optimize the amount of catalyst, various concentrations of dye solutions were prepared, then the desired pH value was adjusted initially, and the appropriate amount of Qds catalyst was added to each suspension. The mixtures were stirred for 20 min in the dark before irradiation/ultrasound to ascertain an adsorption– desorption state of equilibrium. Then the sonicator and/or lamp were connected and the reaction started.

The solutions were irradiated by adopting a UV-C (λ = 254 nm) light mounted above as the driving energy source, as shown in Figure S5. A distance of 12 cm between the light source and the solution was set for overall degradation experiments. An ultrasonic bath (40 kHz, 120 W) was used as the ultrasound source for the sonocatalytic and sonophotocatalytic experiments. The sonicator water was continuously replaced by circulation, in order to maintain the desired temperature (29 ± 1 ◦C, unless otherwise mentioned). The reactor position in the ultrasonic bath was the same.

The experimental conditions employed for photocatalysis, sonocatalysis and sonophotocatalysis were similar. After certain time intervals, sample aliquots were removed, centrifuged and analyzed for the remaining dye by recording the absorbance in spectrophotometer. The absorbance decrease (at λmax = 560 nm) for SDB samples after irradiation and/or sonication for a certain time showed the decolorization rate, that is, efficiency of decolorization of SDB, and therefore sonophotocatalytic activity of Qds.
