• Rui Tian

      Articles written in Journal of Chemical Sciences

    • Observation of the Unusual Aggregation Kinetics of Colloidal Minerals in Acidic Solutions

      Rui Tian Gang Yang Xinmin Liu Chengzhi Huang Xiaodan Gao Hang Li

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      Hofmeister (Specific ion) effects have been considered as important to chemical science as Mendel’s work was to genetics. In this work, the aggregation kinetics of montmorillonite colloids in H+, Ag+, NH$^+_4$, K+ and Na+ solutions were measured in situ, detecting the unusual kinetics and ion specificity for H+. Activation energies that can quantitatively estimate the underlying specific ion effects change in the order of H+ < Ag+ < NH$^+_4$ < K+ < Na+. Meanwhile, it was found that although the aggregation of montmorillonite colloids with lower particle densities results in higher activation energies, Hofmeister series will not be affected. It was sufficiently testified that interaction energies of colloidal particles with adsorbed ions show fine correlation with activation energies for colloidal aggregation, and larger interaction energy corresponds to lower activation energy. An attempt was made to quantitatively estimate the ion specificity for H+, and it was substantialized that the unusual ion specificity of H+ is caused by steric effect.

    • Impact of electric field on Hofmeister effects in aggregation of negatively charged colloidal minerals

      Ying Tang Hang Li Hualing Zhu Rui Tian Xiaodan Gao

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      In this study, the aggregation kinetics of negatively charged colloidal minerals in Na+, K+, NH+4 , Mg2+, Ca2+ and Cu2+ solutions were measured and Hofmeister effects therein were estimated through total average aggregation (TAA) rates and critical coagulation concentration (CCC). Hofmeister effects of TAA rates increased exponentially with the increase in electric field strength, which cannot be explained by the classical theories (i.e., ionic size, hydration and dispersion forces), indicating strong electric field at colloidal surface was an indispensable factor in studying Hofmeister effects. Meanwhile, Hofmeister series of CCC values Na+ > K+ > NH+4 > Mg2+ > Ca2+ > Cu2+ show fine correlation with the polarization of various cations, implying that onic polarization in strong electric field would be responsible for Hofmeister effects in aggregation of colloidal minerals, and the deduction was confirmed by the calculated results of electrostatic interactions between colloidal minerals.

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