College of Environmental Science and Engineering, Zhongkai University of Agriculture and Engineering, Guangzhou 510025, PR China; College of Agriculture, Guangdong Ocean University, Zhanjiang 524088, PR China.
College of Environmental Science and Engineering, Zhongkai University of Agriculture and Engineering, Guangzhou 510025, PR China.
Ecotoxicol Environ Saf. 2019 Apr 30;171:594-599. doi: 10.1016/j.ecoenv.2019.01.024. Epub 2019 Jan 15.
The surface catalysis of goethite on the Cr(VI) reduction by tartaric acid was examined together with its adsorption characteristics towards the two reactants. The results showed the adsorption of tartaric acid by goethite was favorable at low pH and adsorption isotherm could be properly described by Langmuir model. The adsorption kinetic curves for both reactants obeyed the pseudo second-order rate model (R >0.99). The FTIR spectrum suggested the formation of bidentate binuclear surface complexes between tartaric acid and goethite. At pH 4.50, the reduction percentage of 0.1 mM Cr(VI) by 1.0 mM tartaric acid alone was about 12% after 72 h, while which was increased to 100% in the presence of goethite within 24 h. Kinetic results revealed the Cr(VI) reduction only occurred between the adsorbed tartaric acid and the aqueous Cr(VI) since the Cr(VI) adsorption was completely inhibited under the examined conditions. Meanwhile, the catalysis of aqueous Fe(III) released from the goethite surfaces was excluded due to its low concentration (<5 μM). With the initial concentration of tartaric acid decreased to 0.1 mM, Cr(VI) reduction could be completed within 4 h, confirmed by the XPS result that only Cr(III) species existed on the goethite surfaces. In this case, electron transfer was suggested to occur directly between the two adsorbed reactants or goethite was believed to serve as an ideal channel to allow electron excited from the adsorbed tartaric acid to transfer to the adsorbed Cr(VI). The findings above were helpful for us to understand the Cr(VI) reduction by organic compounds in soils with rich contents of Fe-oxides.
针铁矿对酒石酸还原 Cr(VI)的表面催化作用及其对两种反应物的吸附特性进行了研究。结果表明，在低 pH 值下，酒石酸在针铁矿上的吸附是有利的，吸附等温线可以用 Langmuir 模型很好地描述。两种反应物的吸附动力学曲线均符合准二级速率模型（R>0.99）。FTIR 光谱表明，酒石酸与针铁矿之间形成了双齿双核表面配合物。在 pH 4.50 下，单独存在 1.0 mM 酒石酸时，0.1 mM Cr(VI)的还原率在 72 h 后约为 12%，而在有针铁矿存在时，24 h 内还原率增加到 100%。动力学结果表明，Cr(VI)的还原仅发生在吸附的酒石酸和水溶液中的 Cr(VI)之间，因为在考察条件下，Cr(VI)的吸附完全受到抑制。同时，由于浓度较低（<5 μM），从针铁矿表面释放的水合 Fe(III)的催化作用被排除在外。随着初始酒石酸浓度降低至 0.1 mM，Cr(VI)还原可在 4 h 内完成，XPS 结果表明，针铁矿表面仅存在 Cr(III)物种，这一结果得到了证实。在这种情况下，电子转移被认为直接发生在两个吸附的反应物之间，或者针铁矿被认为是允许从吸附的酒石酸中激发的电子转移到吸附的 Cr(VI)的理想通道。上述发现有助于我们理解富含铁氧化物的土壤中有机化合物还原 Cr(VI)的过程。
