Comparative studies of Rhodamine B decolorization in the combined process Na2S2O8/visible light/ultrasound

In this study, the possibility of rhodamine B (RhB) decomposition in the presence of ultrasound (US) and sodium persulfate (Na2S2O8) activated by visible light (Vis) was investigated. A combination of these processes (Na2S2O8/Vis/US) were examined. As a part of this study, the optimal dose of Na2S2O8, glucose dose, reaction time, and RhB concentration were selected. In addition, radical scavenger test was conducted. Under optimal conditions (RhB concentration = 10.0 mg dm–3; pH = 6.0; reaction time: 60.0 min; Na2S2O8 dose = 20.0 mM; glucose dose = 200.0 mM; US power: 60 W; US frequency: 40 kHz; temperature: 295 K), RhB decomposition in the Na2S2O8/Vis/US process was set to 85%. Under the same conditions, the RhB decomposition in the US, Na2S2O8, Na2S2O8/Vis and Na2S2O8/US processes was 17%, 29%, 49% and 67%, respectively. The determined parameters of the pseudo- first-order reaction showed the advantage of the dynamics of the Na2S2O8/Vis/US process over the US, Na2S2O8, Na2S2O8/Vis and Na2S2O8/US processes. The mathematically calculated half-life (t/2) for the combined process was 2.1 min, while half-life values for the US, Na2S2O8, Na2S2O8/Vis and Na2S2O8/US processes are 25.5, 15.9, 7.8 and 4.6 min, respectively. Hydroxyl radicals were mainly responsible for the decolorization of rhodamine B. The conducted studies showed that the activation of sodium persulfate in the combined process of sodium persulfate-visible light-ultrasound is an interesting alternative for the purification of solutions containing rhodamine B with variable dye concentrations (up to 20 mg dm–3).