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 (ClO- 4) 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 (PDDAx-Mt) showed excellent adsorption performance for ClO- 4 with maximum adsorption amount over 2.78 mmol/g and equilibrium time within 10 min. The adsorption performance of PMt toward ClO- 4 followed this order: PDDAx-Mt > CH-Mt > PAM-Mt > PQ28-Mt. Moreover, PDDAx-Mt and CH-Mt showed a superior adsorption selectivity to ClO- 4 among competitive oxyanions in the quaternary-adsorbate system (ClO- 4 > PO3- 4 > SO2- 4 > NO– 3). 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 ClO- 4 adsorbed on PMt is a process of electrons transferring from O atoms in ClO- 4 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 ClO- 4, suggesting promising applications in anion wastewater treatment.