The role of metal ion-ligand interactions during divalent metal ion adsorption.
The role of metal ion-ligand interactions during divalent metal ion adsorption.
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DOI：
10.1016/j.jcis.2015.04.056
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发表时间：
2015-09
影响因子：
9.9
通讯作者：
Daniel S. Eldridge;R. Crawford;I. Harding
中科院分区：
文献类型：
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作者：
Daniel S. Eldridge;R. Crawford;I. Harding
本文研究了Fe_2O_3、石英SiO_2和三种不同的两性聚苯乙烯胶乳（含胺和羧基）对七种二价金属离子（Ca（II）、Cd（II）、Cu（II）、Mg（II）、Ni（II）、Pb（II）、Zn（II））的吸附。对于金属氧化物，在从溶液中除去50%的金属时的pH（pH 50）和金属离子的第一水解常数（pK 1）之间观察到高度相关性。对于聚苯乙烯胶乳，与pK 1相反，在pH 50和pKc（描述金属-羧基亲和力的平衡常数）之间观察到高得多的相关性。这些观察结果提供了金属对溶液中特定配体的亲和力与该金属离子对作为吸附表面的一部分存在的相同配体的亲和力之间存在强关系的证据。降低乳胶表面羧基含量可提高两性乳胶表面的等电点。对于所有7种金属离子，对于任何给定的pH值，这导致吸附大幅降低。我们认为，这可能部分是由于羧基含量减少，但主要是由于存在不太有利的静电条件。这反过来表明，静电在金属离子吸附到两性胶乳表面上起控制作用，并且除了金属离子的性质之外，还控制吸附发生时的pH。
A suite of seven different divalent metal ions (Ca(II), Cd(II), Cu(II), Mg(II), Ni(II), Pb(II), Zn(II)) was adsorbed from solution onto two Fe2O3samples, quartz SiO2and three different amphoteric polystyrene latices (containing amine and carboxyl functional groups). For the metal oxides, a high correlation was observed between the pH at which 50% of the metal was removed from solution (pH50) and the first hydrolysis constant for the metal ion (pK1). For the polystyrene latices, a much higher correlation was observed between the pH50and pKc(equilibrium constant describing metal-carboxyl affinity) as opposed to pK1. These observations provide evidence of a strong relationship that exists between a metal’s affinity for a particular ligand in solution and for that metal ion’s affinity for the same ligand present as part of an adsorbing surface. The isoelectric point of the amphoteric latex surface can be increased by decreasing the carboxyl content of the latex surface. For all 7 metal ions, this resulted in a substantial decrease, for any given pH, in adsorption. We suggest that this may be partly due to the decreased carboxyl content, but is dominantly attributable to the presence of less favorable electrostatic conditions. This, in turn, demonstrates that electrostatics play a controlling role in metal ion adsorption onto amphoteric latex surfaces and, in addition to the nature of the metal ion, also controls the pH at which adsorption takes place.