Experimental anion affinities for the air/water interface
Experimental anion affinities for the air/water interface
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DOI：
10.1021/jp066197k
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发表时间：
2006-12-28
影响因子：
3.3
通讯作者：
Colussi, A. J.
中科院分区：
文献类型：
--
作者：
Cheng, Jie;Vecitis, Chad D.;Colussi, A. J.
用电喷雾电离质谱法测定了水溶液（Br- + NO3- + I- + SCN- + BF4- + ClO4-）气相界面的阴离子亲和力γ (-)(X)。从裂变纳米液滴表面喷射出的离子组成表明，γ (-)(X)随阴离子半径呈指数增加（减少），a(X)(-)(脱水自由能，(d)G(X)(-))，并选择性地响应表面活性剂的存在。BF4-是这组阴离子中最不水合和极化的阴离子，具有最大的γ (-)(X)值之一。非离子型表面活性剂降低γ (-)(I)和γ (-)(SCN)，增加γ (4-)（BF）。十六烷基三甲基铵显著增强较小阴离子的γ (-)(X)。当本体溶液的pH值从8.2降至3.0时，观察到类似但较弱的效果。十二烷基硫酸盐对γ (-)(X)的影响可以忽略不计。考虑到(i)普遍的多体电动力学相互作用将逐渐稳定界面层，因为它的介电常数相对于体溶液的介电常数下降；（ii）水的介电常数随着这些阴离子浓度的增加而均匀降低，我们推断观察到的Hofmeister相关性ln γ (-)(X)与- (d)G(X)（-）成正比，与最少水合离子对干燥器界面层介电常数的最佳抑制一致。界面离子-离子相互作用可以显著影响环境水介质中的γ (-)(X)。
Anion affinities, gamma(-)(X), for the aerial interface of aqueous (Br- + NO3- + I- + SCN- + BF4- + ClO4-) solutions are determined by electrospray ionization mass spectrometry. The composition of the ions ejected from the surface of fissioning nanodroplets shows that gamma(-)(X) increase (decrease) exponentially with anionic radii, a(X)(-)(dehydration free energies, (d)G(X)(-)), and selectively respond to the presence of surfactants. BF4-, the least hydrated and polarizable anion of the set, has one of the largest gamma(-)(X) values. Non-ionic surfactants decrease gamma(-)(I) and gamma(-)(SCN) but increase gamma(4-)(BF). Cetyltrimethyl ammonium markedly enhances the gamma(-)(X) of smaller anions. A similar but weaker effect is observed upon lowering the pH of the bulk solutions from 8.2 to 3.0. Dodecyl sulfate has a negligible effect on gamma(-)(X). Considering that (i) universal many-body electrodynamic interactions will progressively stabilize the interfacial layer as its dielectric permittivity falls relative to that of the bulk solution and (ii) water permittivity is uniformly depressed by increasing concentrations of these anions, we infer that the observed Hofmeister correlation, ln gamma(-)(X) proportional to - (d)G(X)(-), is consistent with the optimal depression of the permittivity of the drier interfacial layer by the least hydrated ions. Interfacial ion-ion interactions can significantly influence gamma(-)(X) in environmental aqueous media.