鞣酸纳米铁去除六价铬的反应动力学研究

Kinetics Investigation on Removal of Hexavalent Chromium by Tannic Acid Stabilized Nanoscale Zero-valent Iron

通过添加不同剂量的鞣酸来制备鞣酸与铁离子摩尔比例分别为0.012 5、0.025 0、0.050 0、0.100 0、0.200 0的鞣酸纳米铁(TA-nZVI),通过TEM、UV-Vis、XRD、GT方法来分析不同比例TA-nZVI的形貌、粒径、成分、热稳定性。TA-nZVI是一种特殊的团簇结构,粒径主要分布在40~70nm之间,比表面积可高达180.1 m^(2)·g^(-1),具有极高的反应活性,对Cr(Ⅵ)去除率在30 min内均可达到100%。TA-nZVI还原去除Cr(Ⅵ)的实验结果表明:不同鞣酸与铁离子摩尔比例条件下制备的纳米铁与Cr(Ⅵ)的反应均符合一级动力学,相同条件下,TA-nZVI的表观速率常数可达到Bare-nZVI的1 119倍,表面积归一化速率常数可达到Bare-nZVI的70.64倍。因此,TA-nZVI对Cr(Ⅵ)的高效去除不仅与其具有的巨大比表面积有关,而且也与其单位体积表面积内的Fe0的活性有关。

Tannic acid stabilized nanoscale zero-valent iron(TA-nZVI)with molar ratios of tannic acid and nanoscale zero-valent iron of 0.0125,0.0250,0.0500,0.1000 and 0.2000 was prepared by adding different doses of tannic acid.TEM,UV-Vis,XRD,GT methods were used to analyze the morphology,particle size,composition,and thermal stability of TA-nZVI in different proportions.TA-nZVI is a special cluster structure with size of distributing between 40~70 nm,whose specific surface area can be as high as 180.1 m^(2)·g^(-1).So TA-nZVI has extremely high reactivity,and the removal rate of Cr(Ⅵ)can reach 100%within 30 min.The reduction of Cr(Ⅵ)by TA-nZVI synthesized in different conditions fits the pseudo first-order model quite well.Under the same conditions,the apparent rate constant and surface area normalized rate constant of TA-nZVI are 1119 times and 70.64 times higher than that of Bare-nZVI,respectively.Therefore,the efficient removal of Cr(Ⅵ)by TA-nZVI is related to its huge specific surface area and its Feoactivity per unit volume surface area.