Protonated pentaethylenehexamine-functionalized hydrochar for adsorption of anionic pharmaceuticals and controlled-release of pesticides

The inappropriate use and discharge of pesticides and pharmaceuticals pose a serious threat to ecosystems, which can be effectively mitigated with environmentally friendly hydrochar. Here, a protonated pentaethylenehexamine-functionalized hydrochar (PEHA-HC) was successfully synthesized through preparation of glycidyl ester-functionalized hydrochar, amination grafting with PEHA, and protonation. The performance of PEHA-HC in removing two anionic pharmaceuticals, 2,4-dichlorophenoxyacetate (2,4-D Na) and diclofenac sodium (DS), was systematically investigated. The rich protonated amino groups on the surface endow PEHA-HC with a positive charge and a high point of zero charge, enabling efficient adsorption of these chemicals across a broad pH range, with the largest adsorption capacities exceeding 417.78 and 679.43 mg·g −1 , respectively. The adsorption kinetics followed the pseudo-second-order model, while the adsorption isotherms conformed to the Langmuir equation. The primary mechanisms for adsorption of these anions by PEHA-HC were electrostatic attraction and anion exchange. Furthermore, PEHA-HC was explored as a stimuli-responsive carrier for controlled pesticide delivery. The release behavior of the 2,4-D@PEHA-HC formulation was highly sensitive to environmental pH and ionic strength. Release profiles were well expressed with the Ritger-Peppas model (release exponent n  = 0.37–0.65), implying a combined diffusion-erosion mechanism or Fickian diffusion. Notably, 2,4-D@PEHA-HC demonstrated high biological efficacy for rapeseed. Thus, PEHA-HC functions not only as a high-capacity adsorbent for removing anionic pharmaceuticals from aqueous but also as an intelligent carrier for constructing environmentally responsive controlled-release pesticide formulations. These dual functionalities highlight its potential in reducing pharmaceutical pollution in aquatic systems while improving agrochemical utilization efficiency.