The effect of cation and anion species on the transition and adsorption behaviors of thermosensitive sulfobetaine gel-based adsorbent

This study was conducted to examine the ion absorption behavior of zwitterionic sulfobetaine type N,N-dimethyl(acrylamidopropyl) ammonium propane sulfonate (DMAAPS) gels. In addition, it also examines the effect of salt solution concentration and ionic strength on the poly(DMAAPS) transition behavior in different salt solutions. The adsorption behavior of the gel in nitrate, chloride and sulfate solutions was found to be a strong function of the valence. The number of ions adsorbed onto the DMAAPS gel increases in line with the increase of cations valences, with the order of adsorption being Zn²⁺ > Ni²⁺ > Na⁺, K⁺. The level of ion adsorption onto the DMAAPS gel in various salt solutions with common cations of Na⁺, K⁺ and Zn²⁺ shows a tendency in the order of NO₃^- > Cl^- > SO4^2-. Comparing the effect of the anion and cation of the same charge on the number of ions adsorbed, the anion species effect is greater than that of the cation species at all concentrations. At first, the transition temperature of the poly(DMAAPS) within the salt solution increases. However, it then decreases when the ions adsorbed onto the DMAAPS gel increase and reach a maximum level. On the other hand, the level depends on the species and ion concentration. Therefore, it can be concluded that the maximum level of ions adsorbed can be simply ascertained by determining the transition temperature.