Synthesis of iron oxide/activated hydrochar composite from residual brewery biomass for remediation of water contaminated with chlorophenol

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 (Fe₃O₄) 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, π-π 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.