紫外活化甲酸产二氧化碳阴离子自由基还原Cr (VI)的研究

研究高效还原技术是去除废水中Cr（VI）的有效手段，本研究提出了一种新颖有前景的基于紫外（UV）活化甲酸（HCOOH）产还原性二氧化碳阴离子自由基（CO₂^?；-）去除Cr（VI）的方法.通过对比UV、HCOOH、UV/HCOOH三种体系对Cr（VI）还原效率和电子自旋共振（EPR）对体系中自由基的检测研究了其活化原理和还原机制.结果表明UV能显著活化HCOOH产生CO₂^?-（α_H=19.08G，α_N=15.86G，g=2.0036）.此外，试验考察了主要影响因素对Cr（VI）去除效果的影响，包括初始Cr（VI）浓度、甲酸投加量、初始pH值、反应温度、有机污染物以及水中常见阴离子.结果显示当甲酸浓度为40mmol/L，Cr（VI）初始浓度为10mg/L，反应时间在60min内，UV/HCOOH体系对Cr（VI）的去除率能达到100%.在酸性条件下（pH≤3.5）能显著促进Cr（VI）的还原，且Cr（VI）去除效率随着初始HCOOH浓度和反应温度升高而增加.进一步研究表明，该体系下NO₃^-对Cr（VI）的还原有着显著的促进作用，而Cl^-、HCO₃^-和对硝基苯酚（pNP）则有抑制作用.不同温度下Cr（VI）去除率与时间关系的拟合结果表明，当反应时间t³；40min，UV/HCOOH体系去除Cr（VI）过程遵循准一级反应动力学，根据不同温度下对应的反应速率常数k，结合阿伦尼乌斯方程，计算求得准一级反应的活化能为15.9kJ/mol.

Reduction performance of Cr(VI) by carbon dioxide anion radical based on UV-activated formic acid

It is well recognized that the development of highly efficient reduction is an effective way to remove Cr(VI) from wastewater. Herein, a novel carbon dioxide anion radical (CO₂^?-) production induced by UV-activated formic acid system is expected to offer a promising technology for removal of Cr(VI). In the present study, the activation and reduction mechanism have been investigated by comparing the reduction efficiency of the three reduction systems (UV、HCOOH、UV/HCOOH) and detection of electron paramagnetic resonance (EPR), which suggested that UV can significantly activate HCOOH producing CO₂^?-(α_H=19.08G,α_N=15.86G, g=2.0036). Moreover, the main influencing factors, including initial Cr(VI) concentration, dosage of formic acid, initial pH, reaction temperature, organic containments and common anions were also discussed, the results showed that percent Cr(VI) removal of 100% was obtained in 60min when the initial concentration of formic acid and Cr(VI) was 40mmol/L and 10mg/L, respectively. It was further revealed that percent Cr(VI) removal efficiency increased with the increase of formic acid concentration and reaction temperature, and appeared to be an acid-pH-favoured condition(pH£3.5). NO₃^- could remarkably promote the reduction of Cr(VI), while Cl^-, HCO₃^- and p-nitrophenol showed an inhibitory effects. From the fitting results of the removal kinetics data at different temperatures, it is clearly exhibited that the reduction of Cr(VI) by the UV/HCOOH system followed the pseudo-first order reaction kinetics after 40min. Arrhenius activation energy E_a were calculated as 15.9kJ/mol according to the rate constants k at different temperatures.