Efficient removal of sodium diclofenac and sodium 2,4-dichlorophenoxyacetate from aqueous solution using a poly(imidazolium)-grafted hydrochar

The efficient removal of emerging anionic organic pollutants, particularly pharmaceuticals and herbicides such as sodium diclofenac (DCF-Na) and sodium 2,4-dichlorophenoxyacetate (2,4- D -Na), from aqueous environments remains a significant challenge. Although hydrochar is a sustainable and low-cost adsorbent, its intrinsic negative surface limits its affinity for anionic contaminants. To overcome this, a novel mesoporous poly(imidazolium)-grafted hydrochar (PIHC) was synthesized via a one-pot in situ quaternization polymerization by directly grafting 1,3,5-tris(1H-imidazol-1-yl)benzene and 1,3,5-tris(bromomethyl)benzene onto bamboo hydrochar. The impact of aqueous pH, adsorbing temperature, ionic strength and contact time on the removal of DCF-Na and 2,4- D -Na by PIHC was systematically investigated. The resulting PIHC exhibited rapid and efficient adsorption, removing 52 % of DCF-Na (C 0 = 400 mg·L −1 ) and 88 % of 2,4- D -Na (C 0 = 100 mg·L −1 ) within 5 min. The adsorption kinetic and isotherm data fitted well with the pseudo-second-order kinetic model and the Langmuir model, indicating that the adsorption was dominated by monolayer chemical adsorption. Thermodynamic test uncovered a spontaneous and endothermic adsorption, with the spontaneity mainly driven by entropy. The high performance is attributed to the synergistic effects of the mesoporous structure and high positive charge density, enabling multiple mechanisms including electrostatic attraction, ion exchange, and π-π interactions. This work provides a versatile molecular design strategy for developing high-performance, imidazolium-grafted hydrochar for pharmaceutical and herbicide remediation.