Thermo-kinetic characterization and performance evaluation of Fe3O4@activated carbon for gas-phase PAH adsorption

Abstract

Acenaphthene (ACE), a pervasive ambient air pollutant, constitutes considerable health threats even at low concentrations. Although carbonaceous materials are commonly utilized for ACE remediation, their efficiency is still debated with experiments showing their effects under different conditions. The mechanisms explaining these seemingly contradictory observations are not fully understood, limiting the development of adsorbents with stable and predictable performance under varying thermos-hygrometric conditions. To address this gap, we synthesized a material featuring a tailored morphology, mesoporous architecture, and rich surface functionalization, and we carried out an extensive characterization using SEM, BET, FTIR, VSM, and XRD techniques to quantify structural, thermal, and magnetic properties. The Fe3O4 nanoparticles-functionalized activated carbon (BG-AC@NPs) demonstrated a high gas-phase ACE removal efficiency of 99.7% under controlled adsorption conditions, and the equilibrium was stabilized within 40 min, with a maximum adsorption capacity (BG-AC@NPs) of 378.3 mg/g. Adsorption kinetics were precisely fitted through the use of a pseudo-second-order (PSO) model, which gave an R-2 coefficient higher than 0.940. Moreover, the Langmuir model provided a good representation of the adsorption isotherms and the R-2 value is > 0.988, indicating the occurrence of monolayer adsorption. Thermodynamic analysis indicated a positive Delta H degrees (51.354 kJ/mol) and Delta S degrees (0.024 J/mol K), together with a negative Delta G degrees, it verifies the spontaneous, endothermic nature of adsorption with enhanced randomness. Notably, BG-AC@NPs retained over 80% efficiency after multiple regeneration cycles. This study advances gas-phase adsorption systems by integrating material design and thermal-kinetic measurement strategies. Furthermore, it highlights how solid-gas clustering phenomena at pore inlets influence adsorption kinetics even at optimum levels, guiding the optimization of pore structure and surface chemistry for high-performance PAHs capture.