Effect of polyelectrolyte structure on perchlorate adsorption performance by functionalized montmorillonite

Polyelectrolyte (with different unit structure or molecular weight) modified montmorillonite (PMt) was synthesized for perchlorate (ClO₄^-) removal. It was found polyelectrolytes were successfully loaded on montmorillonite (Mt), and the surface potential of most PMt changed from negative to positive. Polyelectrolyte desorption on Mt was < 10 % after 48 h. Poly(diallyldimethylammonium chloride) species modified montmorillonite (PDDA_x-Mt) showed excellent adsorption performance for ClO₄^- with maximum adsorption amount over 2.78 mmol/g and equilibrium time within 10 min. The adsorption performance of PMt toward ClO₄^- followed this order: PDDA_x-Mt > CH-Mt > PAM-Mt > PQ28-Mt. Moreover, PDDA_x-Mt and CH-Mt showed a superior adsorption selectivity to ClO- 4 among competitive oxyanions in the quaternary-adsorbate system (ClO₄^- > PO₄^3- > SO₄^2- > NO₃^–). The enhanced ClO- 4 adsorption could be mainly attributed to the presence of anion exchange sites (−R₄N⁺-Cl⁻ or –NH₃⁺-Cl⁻) provided by PDDA or CH, followed by electrostatic gravitation and weak hydrogen bonding interaction. Density functional theory (DFT) calculation revealed that ClO₄^- adsorbed on PMt is a process of electrons transferring from O atoms in ClO₄^- to H atoms on C in PDDA⁺ or N in CH⁺, PAM⁺ and PQ28⁺. The preparation method of PMt is simple with excellent adsorption performance and selectivity toward ClO₄^-, suggesting promising applications in anion wastewater treatment.