Transport mechanisms of herbicides in nanocomposite hydrogels under pH and ionic strength gradients
The use of biodegradable hydrogels for the removal or controlled release of agrochemicals is a promising approach that has been widely investigated. This study aims to investigate the effect of chitosan (CH) and zeolite on polymerization solution viscosity, thermal properties, and sorption and desorption properties of the herbicides paraquat (PQ) and difenzoquat methylsulfate (DFZ), in different pH and ionic strength, using poly(methacrylic acid)-co-polyacrylamide (PMAA-co-PAAm) as polymeric matrices. The results indicated that the presence of polysaccharide CH and zeolite increased the thermal stability and viscosity of the polymerization solution. From kinetic studies, it was possible to observe that zeolite-based nanocomposites had slower adsorption of DFZ (k2 = 0.026 g/mg.h) when compared to PQ (k2 = 0.054 g/mg.h) pesticides. However, slower adsorption led to a more controlled release, whereas a broader pH range improved herbicide retention in these nanocomposites. Another important factor was the influence of Ca2+ and Al3+ ions on the release behavior, releasing almost all the herbicide contained in the hydrogels, except for the nanocomposites, which released 87.3% of the sorbed PQ. These results indicate that the performance of these materials is influenced by both the application environment and the molecular structure of the compound. In this way, these nanocomposites demonstrate high efficiency in removing unwanted chemicals from water, aligning their application primarily with environmental remediation and wastewater treatment systems to mitigate pesticide pollution.