Oleate Adsorption at an Apatite Surface Studied by Ex-Situ FTIR Internal Reflection Spectroscopy
Oleate Adsorption at an Apatite Surface Studied by Ex-Situ FTIR Internal Reflection Spectroscopy
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DOI：
10.1006/jcis.1998.5466
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发表时间：
1998-06
期刊：
影响因子：
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通讯作者：
Yongqiang Lu;J. Drelich;Jan D. Miller
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文献类型：
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作者：
Yongqiang Lu;J. Drelich;Jan D. Miller
摘要采用非原位傅里叶变换红外内反射光谱（FTIR/IRS）研究了油酸在磷灰石表面的吸附。吸附等温线已被确定使用磷灰石内反射元件（IRE），它已被发现，pH值有显着的影响，由磷灰石的油酸吸附。在pH 8.0和20°C下，油酸盐吸附密度随着平衡油酸盐浓度从5 × 10− 6增加到1 × 10− 3 M而单调增加。这些结果与pH 9.5和20°C下的结果形成鲜明对比，在后一种情况下，吸附密度仅限于对应于大约单层覆盖的密度。油酸盐吸附磷灰石相比，油酸盐吸附萤石和方解石和不同的吸附行为在这三种矿物表面是由于在表面钙位的密度和这些矿物的溶解度的差异的差异。在pH 8.0和20°C下的光谱结果表明，磷灰石表面的主要吸附物种是油酸，这可以通过在约1710 cm− 1处出现强IR吸收峰来表示，对于从5 × 10− 6至1 × 10− 3 M的整个油酸盐浓度范围进行了研究。另一方面，在pH 9.5，20°C和低表面覆盖度下，油酸盐似乎被化学吸附，如在1554 cm− 1处的峰和在较高温度下增加的吸附密度所示。在对应于单层覆盖的上方，通过在1575和1540 cm−1处的双峰表明二油酸钙盐的表面沉淀。在pH 9.5和升高的温度（65°C）下，油酸盐的化学吸附和二油酸钙在磷灰石表面的表面沉淀都得到增强。这些FTIR/IRS光谱与漫反射技术获得的光谱进行了比较，并讨论了光谱之间的差异。最后，接触角已被测量在磷灰石IRE表面，它已被证明，无论是吸附物种的量和性质的影响表面的疏水状态。
Abstract Oleate adsorption at an apatite surface was investigated by ex-situ Fourier transform infrared internal reflection spectroscopy (FTIR/IRS). Adsorption isotherms have been determined using an apatite internal reflection element (IRE) and it has been found that pH has a significant influence on oleate adsorption by apatite. At pH 8.0 and 20°C, oleate adsorption density increases monotonically as equilibrium oleate concentration increases from 5 × 10−6to 1 × 10−3M. These results are in contrast to the results at pH 9.5 and 20°C in which case the adsorption density is limited to that corresponding to approximately monolayer coverage. Oleate adsorption by apatite was compared to oleate adsorption by fluorite and calcite and the different adsorption behavior at these three mineral surfaces is attributed to the differences in the densities of surface calcium sites and to the differences in the solubilities of these minerals. The spectral results at pH 8.0 and 20°C, suggest that the dominant adsorbed species at the apatite surface is oleic acid as indicated by the appearance of a strong IR absorbance peak at about 1710 cm−1for the whole oleate concentration range investigated from 5 × 10−6to 1 × 10−3M. On the other hand at pH 9.5, 20°C, and low surface coverage, it appears that oleate is chemisorbed as indicated by a peak at 1554 cm−1and an increased adsoption density at higher temperatures. Above what corresponds to monolayer coverage, surface precipitation of calcium dioleate salt is suggested by the doublet at 1575 and 1540 cm−1. At pH 9.5 and elevated temperature, 65°C, both chemisorption of oleate and surface precipitation of calcium dioleate at the apatite surface are enhanced. These FTIR/IRS spectra are compared with those obtained by the diffuse reflection technique, and the difference between the spectra are discussed. Finally, contact angles have been measured at the apatite IRE surface and it has been demonstrated that both the amount and the nature of the adsorbed species influence the hydrophobic state of the surface.