聚乙二醇光催化还原Cr(VI)的特性与机理研究

Chromium and its compounds are widely used in many industries and a large quantity of Cr(VI)-containing wastewater are released into environment．Chromium，especially hexavalent chromium[Cr(VI)] has posed great threat on environmental safety and human health．The reduction of quite toxic Cr(VI) into less toxic trivalent chromium [Cr(III)] is the key for the detoxification of chromium．The photoreduction,which is considered as an efficient and economical pollution control technology, has been caused great concern.The existing literatures on photoreduction of Cr(VI)commonly employed semiconductors such as TiO2, which has the disadvantages of low quantum efficiency and low utilization of solar energy. In the study, poly(ethylene glycol) (PEG), which is a cheap,easy available and environment friendly polymer, is firstly used as a photoreductant for Cr(VI). The parameters including light source,light intensity,solution acidity,temperature, reducing atmosphere, PEG amount, Cr（VI） initial concentration and associated metal ions on the photoreduction of Cr（VI） is investigated, changes of physicochemical properties of PEG during the photoreduction are unveiled, the mechanism of photoreduction of Cr(VI) by PEG is explained and the related kinetics is analyzed for the sake of exploring the technic data and laying a theoretical base for the application of the feasible Cr(VI) photoreductant-PEG.

铬及其化合物在工业中被广泛应用，导致大量含铬废水产生，对环境造成严重污染。在铬污染治理中，将毒性极强的Cr(VI)还原为毒性较小的Cr(III)是减少铬污染危害的关键。光催化还原法作为一项高效、经济的治理Cr(VI)污染的技术受到了国内外的普遍关注，已有文献报道光催化还原Cr(VI)多使用TiO2等半导体材料，存在量子效率低、太阳能利用低的缺点。本项目使用一种价廉易得、绿色环保的聚合物—聚乙二醇（PEG）做光催化还原剂将Cr(VI)转化为Cr(III)，系统研究光源、光强、溶液酸度、温度、还原气氛、PEG用量、Cr(VI)离子初始浓度及共存金属离子等因素对PEG光催化还原Cr(VI)效率的影响，揭示PEG在反应过程中的理化性质变化，阐释PEG光催化还原Cr(VI)的机理，并分析PEG光催化还原Cr(VI)过程动力学，为Cr(VI)的潜在的光催化还原剂—PEG的应用探索技术参数和奠定理论基础。

铬及其化合物在工业中被广泛应用，导致大量含铬废水产生，对环境造成严重污染。在铬污染治理中，将毒性极强的Cr(VI)还原为毒性较小的Cr(III)是减少铬污染危害的关键。以一种价廉易得、绿色环保的聚合物—聚乙二醇（PEG）做光催化还原剂将Cr(VI)转化为Cr(III)，系统研究了不同因素对PEG光催化还原Cr(VI)效率的影响并分析了PEG光催化还原Cr(VI)过程动力学，Cr(VI)还原速率随着光照强度的增大而增大，光照强度大时，单位时间能吸收更多数量的光量子，从而发生更多的光还原反应。Cr(VI)更容易在高酸度溶液中被还原，高的氢离子浓度能够促进PEG的质子化与产生更多的HCrO4-形态的Cr(VI)，进而为Cr(VI)－PEG缔合物形成创造便利条件；高的酸度还可以引起Cr(VI)/Cr(III)电极电势增大。由于小分子量的PEG链段短，从而灵活性更大，与Cr(VI)结合几率亦更大，且相同质量浓度时，分子量小的PEG溶液所含的PEG分子数要多于分子量大的PEG溶液所含有的PEG分子数，相应地含有更多的给电子端羟基，所以，小分子量的PEG对Cr(VI)的还原性能更强。Cr(VI)的还原率随着PEG用量的增大而增大，随着初始Cr(VI)浓度增大而减小。揭示了PEG在反应过程中的理化性质变化，阐释了PEG光催化还原Cr(VI)的机理，指出Cr(VI)－PEG缔合物的形成和两电子转移是Cr(VI)光还原反应的两个缺一不可的特征，为Cr(VI)的潜在的光催化还原剂—PEG的应用探索了技术参数和奠定了理论基础。