Zhang Yu, Yang Min, Dou Xiao-Min, He Hong, Wang Dong-Sheng
State Key Laboratory of Environmental Aquatic Chemistry, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Post Office Box 2871, Beijing 100085, China.
Environ Sci Technol. 2005 Sep 15;39(18):7246-53. doi: 10.1021/es050775d.
An Fe-Ce bimetal adsorbent was investigated with X-ray powder diffraction (XRD), transmission electron micrograph (TEM), Fourier transform infrared spectra (FTIR), and X-ray photoelectron spectroscopy (XPS) methods for a better understanding of the effect of surface properties on arsenate (As(V)) adsorption. In the adsorption test, the bimetal oxide adsorbent showed a significantly higher As(V) adsorption capacity than the referenced Ce and Fe oxides (CeO2 and Fe3O4) prepared by the same procedure and some other arsenate adsorbents reported recently. XRD measurement of the adsorbent demonstrated that the phase of magnetite (Fe3O4) disappears gradually with the increasing dosage of Ce4+ ions until reaching a molar ratio of Ce4+ to Fe3+ and Fe2+ of 0.08:0.2:0.1 (Fe-CeO8 refers to the adsorbent prepared at this ratio), and the phase of CeO2 begins to appear following a further increase of the Ce dose. Combined with the results of TEM observation, it was assumed that a solid solution of Fe-Ce is formed following the disappearance of the magnetite phase. Occurrence of a characteristic surface hydroxyl group (MOH, metal surface hydroxyl, 1126 cm(-1)), which showed the highest band intensity in the solid solution state, was confirmed on the bimetal oxide adsorbent by FTIR. Quantificational calculation from the XPS narrow scan results of O(1s) spectra also indicated that the formation of the bimetal Fe-CeO8 was composed of more hydroxyl (30.8%) than was the formation of CeO2 and Fe3O4 (12.6% and 19.6%). The results of adsorption tests on Fe-CeO8 at differentAs(V) concentrations indicated that both the integral area of the As-O band at 836 cm(-1) and the As(V) adsorption capacity increased almost linearly with the decrease of the integral area of M-OH bands at 1126 cm(-1), proving that the adsorption of As(V) by Fe-CeO8 is mainly realized through the mechanism of quantitative ligand exchange. The atomic ratio of Fe on Fe-CeOB decreased from 20.1% to 7.7% with the increase of the As atom ratio from 0 to 16% after As(V) adsorption, suggesting that As(V) adsorption might be realized through the replacement of the M-OH group of Fe (Fe-OH) with arsenate. The well splitting of three v3 bands at As-O band (836 cm(-1)) of FTIR and the hydroxyl ratio (1.7) of Fe-CeO8 calculated from the XPS results suggested that the diprotonated monodentate complex (SOAsO(OH)2) is possibly dominant on the surface of Fe-CeO8.
采用X射线粉末衍射（XRD）、透射电子显微镜（TEM）、傅里叶变换红外光谱（FTIR）和X射线光电子能谱（XPS）等方法对一种铁铈双金属吸附剂进行了研究，以更好地理解表面性质对砷酸盐（As(V)）吸附的影响。在吸附试验中，该双金属氧化物吸附剂对As(V)的吸附容量明显高于通过相同程序制备的参考Ce和Fe氧化物（CeO2和Fe3O4）以及最近报道的其他一些砷酸盐吸附剂。对吸附剂的XRD测量表明，随着Ce4+离子用量的增加，磁铁矿（Fe3O4）相逐渐消失，直至Ce4+与Fe3+和Fe2+的摩尔比达到0.08:0.2:0.1（Fe-CeO8指以此比例制备的吸附剂），随着Ce剂量的进一步增加，CeO2相开始出现。结合TEM观察结果，推测在磁铁矿相消失后形成了Fe-Ce固溶体。通过FTIR在双金属氧化物吸附剂上证实了特征表面羟基（MOH，金属表面羟基，1126 cm(-1)）的存在，该羟基在固溶体状态下显示出最高的谱带强度。从O(1s)光谱的XPS窄扫描结果进行的定量计算还表明，双金属Fe-CeO8的形成中羟基含量（30.8%）比CeO2和Fe3O4的形成中羟基含量（12.6%和19.6%）更多。对不同As(V)浓度下Fe-CeO8的吸附试验结果表明，836 cm(-1)处As-O带的积分面积和As(V)吸附容量几乎都随着1126 cm(-1)处M-OH带积分面积的减小而呈线性增加，证明Fe-CeO8对As(V)的吸附主要通过定量配体交换机制实现。As(V)吸附后，随着As原子比从0增加到16%，Fe-CeOB上Fe的原子比从20.1%降至7.7%，这表明As(V)吸附可能是通过砷酸盐取代Fe的M-OH基团（Fe-OH）来实现的。FTIR在As-O带（836 cm(-1)）处三个v3带的良好分裂以及根据XPS结果计算的Fe-CeO8的羟基比（1.7）表明，双质子化单齿络合物（SOAsO(OH)2）可能在Fe-CeO8表面占主导地位。
