Removal of GenX by APTES functionalized diepoxyoctane cross-linked chitosan beads

Abstract

Perfluoro-2-propoxypropanoic acid ammonium salt, commonly known as GenX, is a persistent, bioaccumulative, and toxic synthetic organofluorine compound utilized in producing various products. It has become a concern due to its extensive presence in the aquatic environment and its resistance to conventional water treatment methods. This study achieved effective adsorption of GenX by employing chitosan (CS) modified adsorbent. Cross-linked and aminated CS beads were synthesized using 1,2:7,8-diepoxyoctane (DEO) and 3-aminopropyl triethoxysilane (APTES). The prepared CS-DEO-APTES adsorbent exhibited an adsorption capacity of 825.9 mg/g, which was 2.26 times higher than that of CS beads (364.6 mg/g), attributed to its higher content of amino groups. Additionally, the CS-DEO-APTES adsorbent demonstrated excellent stability under acidic conditions (optimal pH= 4) due to the cross-linking process. Kinetic data, following a pseudo-second-order rate and isothermal data, fitting well with the Langmuir model, indicated that the interactions between GenX and CS-DEO-APTES were chemisorptive, with a nearly uniform distribution of adsorption sites. GenX-saturated beads were successfully regenerated for at least 6 cycles using a 1 % w/v aqueous NaCl and methanol solution (30:70 % v/v). Density functional theory (DFT) calculations suggested that electrostatic interactions primarily influence the adsorption of GenX. These results highlight the effectiveness of the CS-DEO-APTES adsorbent as a viable option for removing GenX from aqueous solutions.