Hydroxyl and sulfate radical-based oxidation of RhB dye in UV/H2O2 and UV/persulfate systems: Kinetics, mechanisms, and comparison

Abstract:

The degradation kinetics and mechanisms of Rhodamine B (RhB) dye by ^•OH and SO<inf>4</inf>^•- based advanced oxidation processes were investigated. The ^•OH and SO<inf>4</inf>^•- radicals were generated by UV photolysis of hydrogen peroxide and persulfate (i.e., UV/H<inf>2</inf>O<inf>2</inf> and UV/PS), respectively. The effects of initial solution pH, RhB concentration, oxidant dosage, Fe²⁺ 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<inf>2</inf>O<inf>2</inf> 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 Fe²⁺ 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<inf>2</inf>O<inf>2</inf> and UV/PS systems, respectively. The presence of NO<inf>3</inf>⁻ promoted RhB degradation, while H<inf>2</inf>PO<inf>4</inf>⁻ and C<inf>2</inf>O<inf>4</inf>²⁻ showed an inhibitory effect on both UV/H<inf>2</inf>O<inf>2</inf> and UV/PS processes. Radical scavenging tests revealed the dominant role of SO<inf>4</inf>^•- radicals in the UV/PS system. Furthermore, the evolution of low molecular weight organic acids and NH<inf>4</inf>⁺ during the degradation of RhB in these two processes were compared. Both UV/H<inf>2</inf>O<inf>2</inf> and UV/PS systems led to similar formation trends of NH<inf>4</inf>⁺ 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<inf>4</inf>^•--induced oxidation processes.

Año de publicación:

2020

Keywords:

• UV/H O 2 2
• UV/PS
• Rhodamine B
• Hydroxyl radical
• Sulfate radical
• UV/H2O2

Fuente:

scopus

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