Ion specificity of the zeta potential of α-alumina, and of the adsorption of p-hydroxybenzoate at the α-alumina-water interface
Ion specificity of the zeta potential of α-alumina, and of the adsorption of p-hydroxybenzoate at the α-alumina-water interface
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DOI：
10.1016/j.jcis.2009.12.048
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发表时间：
2010-04-15
影响因子：
9.9
通讯作者：
Mahiuddin, Sekh
中科院分区：
文献类型：
--
作者：
Das, Manash R.;Borah, Jayanta M.;Mahiuddin, Sekh
研究了无机阴离子（NO3、I-、Br-、Cl-、SO 42-和S2 O32-）和二价阳离子（Ca 2+和Mg 2+）对水性介质中α-氧化铝的zeta电位和等电点的影响。即使在盐浓度低至5 × 10（-4）M时，阴离子的作用也具有高度的离子特异性。这一出乎意料的发现与最近的报告[Bostrom et al.，J. Chem.Phys.128（2008）135104]。这也与早期的理论预测[B.W. Ninham，V.V. Yaminsky，Langmuir 13（1997）2097]。结果与经典的Hofmeister级数一致，除了NO3-的情况。二价阴离子（SO 42-和S2 O32-）降低了α-氧化铝在水介质中的zeta电位的大小，更准确地说; S2 O3在研究的pH范围内产生了大的负zeta电位（类似于-12至-47 mV），而没有α-氧化铝的等电点（IEP）。然而，在这方面，SO_4 ~（2-）使α-Al_2O_3的zeta电位有不同程度的降低（在实验酸性和碱性pH标度的两端，最大值与25 mV相似），IEP轻微偏移Ca 2+和Mg 2+产生的α-氧化铝的ζ电位大致等于纯α-氧化铝的ζ电位，但略高于Na+的ζ电位在IEP的两侧。我们已经进一步表明，相同的离子特异性或等效的竞争性离子效应与对羟基苯甲酸到α-氧化铝表面上的吸附密度一起发生。对羟基苯甲酸盐在α-氧化铝表面上的吸附密度的阴离子（具有共同的阳离子）顺序遵循Hofmeister系列顺序：S_2 O_（32）- <SO_4（2-）< Cl- >Br- > l（-）> NO_3-。二价阳离子（Ca 2+和Mg 2+）对对羟基苯甲酸酯在α-氧化铝表面上的吸附表现出大致相当的效果。利用对羟基苯甲酸酯吸附后的DRIFT谱中v（as）（-COO-）和v（s）（-COO-）的频移和其他特征峰，我们证明了在5 × 10（-4）M NaCl（aq）存在下，对羟基苯甲酸酯在pH 5和6时在α-氧化铝表面上形成外球络合物，在pH 7、8和9时形成内球络合物。(C)2009 Elsevier Inc. All rights reserved.
The influence of inorganic anions (NO3, I-, Br-, Cl-, SO42-, and S2O32-) and of divalent canons (Ca2+ and Mg2+) on the zeta potential and on the isoelectric point of a-alumina in aqueous medium has been studied. The effect of the anions is highly ion specific even at salt concentrations as low as 5 x 10(-4) M. This unexpected finding is in line with a recent report [Bostrom et al., J. Chem. Phys. 128 (2008) 135104]. It is also in agreement with an earlier theoretical prediction [B.W. Ninham, V.V. Yaminsky, Langmuir 13 (1997) 2097]. The results are consistent with the classical Hofmeister series, except for the case of NO3-. Divalent anions (SO42- and S2O32-) decrease the magnitude of the zeta potential of alpha-alumina in aqueous medium, more precisely; S2O3 produced large negative zeta potential (similar to-12 to -47 mV) within the pH range of the study without the isoelectric point (IEP) of alpha-alumina. However, the SO42- decreased the zeta potential of alpha-alumina of different magnitudes (maximum similar to 25 mV at both ends of the experimental acidic and basic pH scale) with a minor shift of the IEP (similar to 0.5 unit) toward lower pH. Ca2+ and Mg2+ produce zeta potentials of alpha-alumina roughly equal to that of neat alpha-alumina but slightly higher than that of Na+ at both sides of the IEP. We have shown further that the same ion specificity or equivalently competitive ion effects occur with the adsorption density of p-hydroxybenz oate onto alpha-alumina surfaces. The sequence of anions (with common cation) for the adsorption density of p-hydroxybenzoate on the alpha-alumina surfaces follows the Hofmeister series sequence: S2O32- < SO4(2-) < Cl- > Br- > l(-) > NO3-. The divalent cations (Ca2+ and Mg2+) exhibit a roughly equivalent effect on the adsorption of p-hydroxybenzoate onto a-alumina surfaces. Using the frequency shifts of v(as)(-COO-) and v(s)(-COO-) in the DRIFT spectra of p-hydroxybenzoate after adsorption and other characteristic peaks, we have demonstrated that p-hydroxybenzoate forms outer-sphere complexes onto alpha-alumina surfaces at pH 5 and 6 and inner-sphere complexes at pH 7, 8, and 9 in the presence of 5 x 10(-4) M NaCl(aq). (C) 2009 Elsevier Inc. All rights reserved.