Abstract

This study presents the development of iron oxide/activated hydrochar composites from brewer’s spent grain (BSG) to remove 2-chlorophenol (2-CP) from water via adsorption and Fenton oxidation. Two synthesis methods were employed: (1) incipient wetness impregnation via hydrothermal carbonization (FeOHC) and (2) chemical coprecipitation of iron oxide onto the hydrochar surface (FeOHC-C). Characterization revealed mesoporous structures with surface areas ranging from 44 to 66 m² g?¹ and magnetite (Fe?O?) as the predominant iron oxide phase. Adsorption studies demonstrated equilibrium capacities of 24.63 mg g?¹ for FeOHC and 18.70 mg g?¹ for FeOHC-C, with adsorption kinetics best described by the Elovich model and equilibrium behavior fitting the Sips isotherm, suggesting a heterogeneous monolayer adsorption process. Thermodynamic analysis confirmed that adsorption was spontaneous and exothermic, primarily driven by physical interactions, including hydrogen bonding, ?–? interactions, and electrostatic attraction. Fenton oxidation experiments revealed that 2-CP degradation was most efficient under acidic to neutral conditions (pH 3.0–6.0), diminishing drastically at alkaline conditions. The fact that good results were obtained at neutral pH demonstrates its practical applicability. Reusability tests confirmed the long-term stability of the materials, with FeOHC-C maintaining sustained catalytic performance over multiple cycles. These findings highlight the dual functionality of composites as efficient adsorbents and self-regenerating catalysts, offering a promising and scalable solution for the remediation of chlorinated organic pollutants in water. © The Author(s) 2025.