A pyridinium-functionalized chitosan derivative as ecofriendly carrier for efficient adsorption and controlled release of 2,4-dichlorophenoxyacetic acid sodium.

Herbicides with wide use and low efficiency in agriculture severely threaten the environment. However, employing adsorbents and controlled-release formulations (CRFs) can alleviate these environmental risks. Herein, a pyridinium-functionalized chitosan derivative (PFCS) was prepared successfully and characterized by various techniques. The abundant cationic pyridinium groups enable PFCS to strongly adsorb a typical anionic herbicide, 2,4-dichlorophenoxyacetic acid sodium (2,4-D Na), across a broad pH range of 4 to 10. The adsorption kinetics follow the pseudo-second-order model, and the adsorption isotherms align with the Langmuir equation. The adsorption capacity can exceed 618.03 mg·g. Batch assays and further characterization reveal the mechanism of PFCS adsorbing 2,4-D Na anions mainly involves electrostatic attraction, anion exchange and other forces (e.g., π-π stacking and H bonding). Notably, PFCS loaded with 2,4-D Na (2,4-D@PFCS) demonstrates a significant sustained-release behavior, responding to changes in environmental pH and ion strength. The release rate was more influenced by ion strength than pH, and the release process adhered to a first-order kinetic model, primarily driven by ion exchange. Additionally, the 2,4-D@PFCS CRF has shown high biological efficacy on rapeseed. This work demonstrates the PFCS can effectively adsorb and control the release of anionic herbicides, minimizing their adverse impact on aquatic ecosystems.