Interplay of clay mineral structures and PDDA functionalization in enhancing perchlorate adsorption for water treatment

Background

Clay minerals are considered highly effective adsorbents for eliminating pollutants from aqueous solutions. However, it is not clear how the structural differences in clay layers impact their adsorption properties, especially in relation to anion capture when modified with polyelectrolytes.

Methods

This research explored the potential and effectiveness of perchlorate adsorption using montmorillonite (Mt), sepiolite (Se), and kaolinite (Kn) that were modified with poly (diallyl dimethylammonium chloride) (PDDA), each possessing distinct interlayer configurations.

Significant findings

The results demonstrated that the adsorption kinetics of PDDA on montmorillonite and kaolinite were significantly quicker than on sepiolite, which can be attributed to the porous characteristics of sepiolite. XRD and FTIR analyses indicated that PDDA bonded between the layers of Mt via hydrogen bonding in a monolayer configuration, leading to expanded interlayer spacing and enhanced surface hydrophobicity. In contrast, PDDA primarily attached to the surfaces of Se and Kn through electrostatic forces. Moreover, the perchlorate adsorption capacity of Mt, Se, and Kn significantly increased upon PDDA functionalization. The strong alignment with the Pseudo-second-order model indicated that the adsorption of perchlorate onto PDDA-Mt, PDDA-Se, and PDDA-Kn is mainly governed by chemisorption processes. When comparing PDDA-Se and PDDA-Kn, it was indicated a reduction in both the adsorption capacity and regeneration rate of PDDA-Mt, the reduction was not significant enough to affect its cost-effectiveness and reusability. This research highlights the critical need to understand the interactions between pollutants and adsorbents in order to enhance the development of polymer-clay mineral composites for water purification.