Biomass-based efficient and eco-friendly adsorbent for chloridazon and its metabolites

• Hierarchical porous carbon from coffee waste has a specific surface area of 1100 m 2 ·g −1 area. • In 20 min this carbon adsorbs 448 mg·g −1 of chloridazon—markedly higher than that of commercial activated carbon. • X-ray photoelectron spectroscopy reveals that hydrogen bonding and π–π stacking drive adsorption. Chloridazon, a widely applied herbicide in European sugar beet farming, and its degradation products (desphenyl-chloridazon and methyl-desphenyl-chloridazon) are frequently found in surface waters, raising environmental and health concerns. Among the available treatment methods, adsorption stands out as an efficient and economical option, making the search for low-cost, high-performance sorbents essential. In this study, waste coffee grounds were converted into hierarchical porous carbon (HPC) with a specific surface area of about 900 m 2 ·g −1 and further activated using CO 2 at 800 °C to yield an enhanced material (aHPC) with a surface area near 1100 m 2 ·g −1 . Both adsorbents reached equilibrium within 20 minutes, with aHPC exhibiting notably higher uptake—448 mg·g −1 (chloridazon), 281 mg·g −1 (desphenyl-chloridazon), as well as 294 mg·g −1 (methyl-desphenyl-chloridazon)—surpassing commercial activated carbon and other reported adsorbents. This outstanding performance is attributed to the hierarchical porous structure which at the same time allows for optimal water transport through the adsorbent and facilitates contact of the target molecules with the walls in the micro- and mesopores. Isotherm analysis favoured the Freundlich model, the kinetics followed a pseudo-second order law and thermodynamic measurements indicated the process to be exothermic in nature. X-ray photoelectron spectroscopy analysis identified hydrogen bonds and π–π interactions as driving forces for contaminant binding.