Acta Phys. -Chim. Sin. ›› 2014, Vol. 30 ›› Issue (12): 2272-2282.doi: 10.3866/PKU.WHXB201410231

• ELECTROCHEMISTRY AND NEW ENERGY • Previous Articles     Next Articles

Quantitative Characterization of Specific Ion Effects Using an Effective Charge Number Based on the Gouy-Chapman Model

GAO Xiao-Dan, LI Hang, TIAN Rui, LIU Xin-Min, ZHU Hua-Ling   

  1. Chongqing Key Laboratory of Soil Multi-scale Interfacial Process, College of Resources and Environment, Southwest University, Chongqing 400715, P. R. China
  • Received:2014-07-22 Revised:2014-10-22 Published:2014-11-27
  • Contact: LI Hang E-mail:lihangswu@163.com
  • Supported by:

    The project was supported by the National Natural Science Foundation of China (41371249, 41101223) and Scientific and Technological Innovation Foundation of Southwest University for Graduates, China (ky2011009).

Abstract:

Specific ion effects have been observed in a wide range of phenomena at solid-liquid interfaces. Recent studies have indicated that the origin of these effects in some relatively low-electrolyte-concentration systems is the ion polarization in the strong electric field near the interface, rather than dispersion forces, classical induction forces, ionic size, or hydration effects. These effects cause the counterions near the interface to become strongly polarized (with a polarization that is nearly ten thousands times stronger than classical polarization). This strong polarization causes that the Coulomb force exerted by the polarized ions near the interface is far greater than the force generated by the ionic charge, which is reflected in the fact that the effective charge number of polarized ions is much larger than their original charge number. We therefore used the effective charge number of strongly polarized cations to quantitatively characterize the strength of specific ion effects in colloid systems. In this study, we observed the strong, specific ion effects of Na+, K+, Ca2+, and Cu2+ in the montmorillonite-humic acid composite aggregation process. Furthermore, we established a method to calculate the effective charge number of polarized cations based on the critical coagulation concentration (CCC) measured using dynamic light scattering. We successfully obtained the effective charge number of polarized ions. The experimental effective charge numbers for Na+, K+, Ca2+, and Cu2+ were ZNa(effective)=1.46, ZK(effective)=1.86, ZCa(effective)=3.92, ZCu(effective)=6.48, respectively. These results showed that the non-classical polarization greatly enhanced the effective charge number of ions, greatly enhancing the Coulomb force exerted by the ions; and that the more electronic layers the ions had and the stronger the ionic polarization, the more the effective charge of ions increased.

Key words: Hofmeister effect, Dynamic light scattering, Aggregation kinetics, Effective charge coefficient, Electric field, Non-classical polarization effect

MSC2000: 

  • O646