Division of Chemical Engineering, Luleå University of Technology, SE-97187, Luleå, Sweden.
J Colloid Interface Sci. 2010 Nov 15;351(2):523-31. doi: 10.1016/j.jcis.2010.07.064. Epub 2010 Aug 2.
In the present study, in situ ATR-FTIR spectroscopy was used for the first time to study the competitive adsorption of phosphate and arsenate on ferrihydrite. Deuterium oxide was used as solvent to facilitate the interpretations of recorded infrared spectra. It was found that arsenate and phosphate adsorbed more strongly at lower pD-values, showing similarities in the adsorption behavior as a function of pD. However, arsenate complexes were found to be more strongly adsorbed than phosphate complexes in the pD range studied. About five times higher concentration of phosphate in solution was needed to reduce the absorbance due to pre-adsorbed arsenate to the same relative level as for pre-adsorbed phosphate, which was desorbed using a solution containing equal (molar) concentrations in arsenate and phosphate. At pD 4, two phosphate complexes were adsorbed on the iron oxide, one deuterated and one de-deuterated. When phosphate was pre-adsorbed and arsenate subsequently added to the system, the deuterated phosphate complex desorbed rapidly while the de-deuterated phosphate complex was quite stable. At pD 8.5, only the de-deuterated phosphate complex was adsorbed on the iron oxide. Moreover, the arsenate adsorbed was also predominantly de-deuterated as opposite to the arsenate adsorbed at pD 4. During the substitution experiments the configuration of these complexes on the iron oxide surface did not change. To the best of our knowledge, this is the first time this difference in stability of the different phosphate complexes is reported and shows the power of employing in situ spectroscopy for this kind of studies.
在本研究中，首次使用原位衰减全反射傅里叶变换红外光谱（ATR-FTIR）研究了磷酸盐和砷酸盐在水铁矿上的竞争吸附。使用重水作为溶剂，以方便解释记录的红外光谱。结果发现，砷酸盐和磷酸盐在较低的 pD 值下吸附更强，表明它们在 pD 作为函数的吸附行为相似。然而，在所研究的 pD 范围内，砷酸盐配合物的吸附强度比磷酸盐配合物强。溶液中需要高出五倍的磷酸盐浓度才能将预吸附的砷酸盐的吸光度降低到与预吸附的磷酸盐相同的相对水平，而使用含有等摩尔浓度的砷酸盐和磷酸盐的溶液可以将预吸附的磷酸盐解吸。在 pD 4 时，有两个磷酸盐配合物吸附在氧化铁上，一个氘代，一个去氘代。当磷酸盐被预吸附，然后向体系中添加砷酸盐时，氘代磷酸盐配合物迅速解吸，而去氘代磷酸盐配合物则非常稳定。在 pD 8.5 时，只有去氘代磷酸盐配合物吸附在氧化铁上。此外，吸附的砷酸盐也主要是去氘代的，与在 pD 4 时吸附的砷酸盐相反。在取代实验中，这些配合物在氧化铁表面的构型没有改变。据我们所知，这是首次报道不同磷酸盐配合物稳定性的这种差异，并展示了原位光谱学在这类研究中的应用优势。
