Adsorption behavior of solids incorporated in alginate hydrogel beads using herbicides 2,4-D and paraquat as test molecules

Abstract

This study investigates the behavior of adsorbent solids within three-dimensional networks of biopolymers. Two chemically different herbicides, 2,4-D and paraquat (PQ) were employed as test molecules. Alginate (ALG) hydrogels in bead form were synthesized, incorporating activated carbon (PSCA) and montmorillonite clay (MMT) simultaneously and in varying proportions, resulting in multicomponent beads. The Langmuir isotherm parameters, KL (L mmol− 1) and qmax (mmol g− 1), in the adsorption of herbicides on beads with an increasing amount of montmorillonite (MMT) were as follows: For PQ, KL values were 10.709, 61.951, 162.33, 223.27, and qmax values were 0.0711, 0.1484, 0.2135, 0.2497. For 2,4-D, KL values were 13.360, 8.3234, 7.4126, 5.4308, andqmax values were 0.9529, 0.7096, 0.6534, 0.5881. The values clearly demonstrates that, even when solids are mixed in the hydrogel network, their reactive sites remain exposed, interacting with molecules to which they have greater affinity. Adsorption was also investigated on identical materials using binary mixtures of herbicides, revealing trends similar to those observed for individual solutions. Moreover, it was demonstrated that the adsorption capacity of multicomponent beads is equivalent to that achieved by proportionally mixing beads synthesized exclusively with clay or activated carbon. This suggests the tangible possibility of creating ondemand adsorbents by synthesizing distinct hydrogels, each incorporating a specific solid. Subsequently, dry­ing, storing, and mixing them based on the target contaminant for retention are feasible. Finally, a column waspacked with a proportional mixture of beads and successfully retained PQ and 2,4-D using a flow-through system.