UV/PMS降解水中罗丹明B的动力学及反应机理

采用紫外(UV)活化过硫酸氢钾(PMS)产生强氧化性硫酸根自由基(SO_4~·-)降解人工染料罗丹明B(RhB).考察了溶液初始p H、氧化剂剂量、RhB初始浓度、天然有机物(NOM)、Fe~(2+)浓度、自由基淬灭剂(甲醇和叔丁醇)及水体中常见阴离子对降解效果的影响,并探测反应体系中生成的无机阳离子及小分子有机酸的种类和浓度.结果表明,降解反应遵循准一级反应动力学,其降解速率受到溶液初始pH的显著影响,当溶液酸性越强或碱性越强时,RhB的降解效果越好,且酸性条件下降解效果优于碱性条件.同时,加大氧化剂剂量及降低底物浓度也会对RhB的降解起促进作用.体系中投加过渡金属Fe~(2+)可显著促进RhB的降解效果,当Fe~(2+)与PMS的浓度比为1∶1时,降解效果最佳.水体中的NO_3~-对RhB的降解有着显著的促进作用,而H_2PO_4~-、C_2O_4~(2-)、Cl~-和NOM则对RhB的降解有抑制作用.采用离子色谱分析了UV/PMS体系降解RhB所产生的NH_4~+,以及甲酸、乳酸、乙酸和草酸,推测RhB在UV/PMS体系中的降解主要是通过共轭结构的破坏、N-位脱乙基并伴有苯环结构的破坏进行的.综合分析表明,UV/PMS工艺可有效运用于罗丹明B污染水体的修复处理过程.

Degradation of Rhodamine B in aqueous solution by UV/PMS system: Kinetics and reaction mechanism

In this study, UV/PMS (peroxymonosulfate) was employed to generate the powerful oxidizing SO₄^·- radicals for the degradation of the synthetic dyes Rhodamine B(RhB) in aqueous in aqueous solution. The effect of experimental parameters such as initial solution pH, oxidant concentration, RhB initial concentration, natural organic matter (NOM), Fe²⁺concentration, free radical quenching agents such as methanol and tert-butyl alcohol, and common anions in water on Rhodamine B degradation were investigated. And the evolution of inorganic cations and small molecule organic acids during the reaction was monitored by IC. The results showed that degradation reaction is in accordance with the pseudo first-order reaction kinetics. The initial solution pH had a significant effect on RhB degradation. RhB showed good degradation under both acidic and alkaline conditions and it had better degradation in acidic condition than in alkaline condition. The increase in oxidant concentration and the decrease in initial RhB concentration will contribute to the degradation of RhB. The addition of transition heavy metal Fe²⁺in the system could significantly accelerate RhB degradation and when themolarratio of Fe²⁺ and PMS was 1:1, the RhB degradation performance was the best.NO₃^- had a positive effect on the degradation of RhB, while H₂PO₄^-, C₂O₄^2-, Cl^-and humic acid could inhibit the degradation of RhB. Furthermore, inorganic cation NH₄⁺ was identified as the end products. Besides, small molecular organic acids such as formic acid, lactic acid, acetic acid and oxalic acid were identified during the degradation process. It was deduced that the degradation of RhB in UV/PMS system mainly occurs via the destruction of the conjugated structure, N-de-ethylation and simultaneously with the open of benzene ring. The result suggested that UV/PMS is a promising alternative as a possible application for treatment of water polluted by Rhodamine B.