The degradation kinetics and mechanisms of Rhodamine B (RhB) dye by • OH and SO 4 •- based advanced oxidation processes were investigated. The • OH and SO 4 •- radicals were generated by UV photolysis of hydrogen peroxide and persulfate (i.e., UV/H 2 O 2 and UV/PS), respectively. The effects of initial solution pH, RhB concentration, oxidant dosage, Fe 2+ concentration, and water matrices were examined. The results showed that the degradation of RhB followed pseudo-first-order kinetics in both processes, with the UV/H 2 O 2 process exhibiting better performance than that of the UV/PS process. Acidic conditions were favorable to the degradation of RhB in both systems. Increasing the oxidant dosage or decreasing the contaminant concentration could enhance the degradation of RhB. Photo-Fenton-like processes accelerated the performance when Fe 2+ was added into both systems. The removal efficiency of RhB was inhibited upon the addition of humic substances. The addition of Cl − displayed no significant effect and promoted RhB degradation in UV/H 2 O 2 and UV/PS systems, respectively. The presence of NO 3 − promoted RhB degradation, while H 2 PO 4 − and C 2 O 4 2− showed an inhibitory effect on both UV/H 2 O 2 and UV/PS processes. Radical scavenging tests revealed the dominant role of SO 4 •- radicals in the UV/PS system. Furthermore, the evolution of low molecular weight organic acids and NH 4 + during the degradation of RhB in these two processes were compared. Both UV/H 2 O 2 and UV/PS systems led to similar formation trends of NH 4 + and some ring-opening products (e.g., formic acid , acetic acid, and oxalic acid), suggesting some analogies in the decay pathways of RhB by • OH and SO 4 •- -induced oxidation processes .
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Ding et al. (2020) studied this question.