ABSTRACT

Amino acid cysteine has been used as reducing mediator with the aim of improving dye degradation by homogeneous Fenton processes (Fe²⁺/H₂O₂ and Fe³⁺/H₂O₂). Through its known Fe³⁺-reducing activity, this amino acid can enhance the production of reactive oxygen species as HO^• (hydroxyl radical) and its pro-oxidant properties have been verified while decolorizing diverse dyes in the present work. Its presence enhanced decolorization of Methyl Orange, Phenol Red, Safranin T, Rhodamine B, Reactive Black 5 and Reactive Yellow 2, mainly in reactions initially containing Fe³⁺ as a catalyst (Fe³⁺-reactions). E.g. Fe³⁺/H₂O₂ and Fe³⁺/H₂O₂/cysteine systems decolorized 27% and 44% of Phenol Red after 60 min, respectively. A kinetic modeling analysis has revealed that 1st-order and mainly 2nd-order kinetic models were well fitted to both Fe²⁺- and Fe³⁺-reactions data. Improvements in reaction rate constants have been observed by adding cysteine. In experiments performed at varied temperatures, it was found a decrease in activation energy (Ea) due to cysteine addition while decolorizing Safranin T: Ea decreased from 104.6 to 88.9 kJ mol⁻¹ for Fe³⁺-reactions and from 81.0 to 52.2 kJ mol⁻¹ for Fe²⁺-reactions. Therefore, it was found that cysteine decreases the energy barrier so as to improve Fenton-based decolorization reactions.

摘要

氨基酸半胱氨酸已被用作还原介质，目的是通过均相 Fenton 过程（Fe ²⁺ /H ₂ O ₂和 Fe ³⁺ /H ₂ O ₂）改善染料降解。通过其已知的Fe ³⁺还原活性，该氨基酸可以增强活性氧物质如HO ^•（羟基自由基）的产生，并且在目前的工作中已经证实了它的促氧化特性同时对多种染料进行脱色。它的存在增强了甲基橙、酚红、番红 T、罗丹明 B、活性黑 5 和活性黄 2 的脱色，主要在最初含有 Fe ³⁺作为催化剂的反应中（Fe ³⁺-反应）。例如，Fe ³⁺ /H ₂ O ₂和 Fe ³⁺ /H ₂ O ₂ /半胱氨酸系统分别在 60 分钟后使 27% 和 44% 的酚红脱色。动力学建模分析表明，一级和主要二级动力学模型很好地拟合了 Fe ²⁺ - 和 Fe ³⁺ -反应数据。通过添加半胱氨酸观察到反应速率常数的改善。在不同温度下进行的实验中，发现在脱色番红 T 时添加半胱氨酸导致活化能 ( Ea ) 降低：对于 Fe ， Ea从 104.6 降低到 88.9 kJ mol ^-13+ -反应和从 81.0 到 52.2 kJ mol ^-1对于 Fe ²⁺ -反应。因此，发现半胱氨酸降低能垒从而改善基于芬顿的脱色反应。