Yu Weiyan, Du Na, Gu Yongtao, Yan Jingen, Hou Wanguo
Key Laboratory of Colloid and Interface Chemistry (Ministry of Education), Shandong University, Jinan 250100, P.R. China.
Gudong Petroleum Production Factory, Shengli Oilfield of Sinopec, Dongying 257237, P.R. China.
Langmuir. 2020 Jun 16;36(23):6557-6568. doi: 10.1021/acs.langmuir.0c01089. Epub 2020 Jun 7.
The surface charge properties and aggregation behavior of positively charged Mg-Al-NO layered double hydroxide (LDH) single-layer nanosheets dispersed in water were investigated in the presence of K salts with different mono-, di-, and trivalent anions, using electrophoresis and dynamic light scattering techniques. An increase in the salt concentration can significantly decrease the effective surface charge density (σ) of LDHs, leading to the aggregation of nanosheets. The critical coagulation concentration (CCC) or ionic strength (CCIS) of salts for nanosheets significantly decreases with an increase in the valence of anions. Specific ion effects, with a partially reverse Hofmeister series, are observed. On the basis of the Stern model and the DLVO theory, the relationship of CCC with σ and the ionic valences of salts () is theoretically analyzed, which can accurately describe the dependence of CCC on the σ and but cannot explain the origin of specific ion effects. To explore the origin of specific ion effects, a correlation between CCIS and the specific adsorption energy () of anions within the Stern layer is developed. Especially, an empirical relationship of with the characteristic physical parameters of anions is proposed. Our model can accurately predict the CCISs of at least monovalent anions and divalent anions (CO and SO), demonstrating that the specific ion effects observed can be attributed to the differences in ionic size, polarizability, and hydration free energy (or the formation capacity of anion-cation pairs) of different anions. This work not only deepens the understanding of specific ion effects on the colloidal stability but also provides useful information for the potential applications of LDH single-layer nanosheets.
采用电泳和动态光散射技术，研究了分散于水中的带正电的Mg-Al-NO层状双氢氧化物（LDH）单层纳米片在含有不同一价、二价和三价阴离子的钾盐存在下的表面电荷性质和聚集行为。盐浓度的增加会显著降低LDH的有效表面电荷密度（σ），导致纳米片聚集。纳米片的盐临界聚沉浓度（CCC）或离子强度（CCIS）随着阴离子价数的增加而显著降低。观察到具有部分反向霍夫迈斯特序列的特定离子效应。基于斯特恩模型和DLVO理论，从理论上分析了CCC与σ和盐的离子价数（）之间的关系，该关系可以准确描述CCC对σ和的依赖性，但无法解释特定离子效应的起源。为了探究特定离子效应的起源，建立了CCIS与斯特恩层内阴离子的特定吸附能（）之间的相关性。特别是，提出了与阴离子特征物理参数的经验关系。我们的模型可以准确预测至少一价阴离子和二价阴离子（CO和SO）的CCIS，表明观察到的特定离子效应可归因于不同阴离子在离子大小、极化率和水化自由能（或阴离子-阳离子对的形成能力）方面的差异。这项工作不仅加深了对特定离子效应影响胶体稳定性的理解，还为LDH单层纳米片的潜在应用提供了有用信息。
