Iron nanoparticles-chitosan/reduced graphene oxide (mCS@rGO) beads as a multifunctional material for the adsorption and degradation of phenol from aqueous media

A magnetic multifunctional material (mCS@rGO) was developed and used to remove phenol from water through adsorption and Fenton-based degradation processes. The adsorption performance of the mCS@rGO beads towards phenol was evaluated through kinetic, equilibrium, and thermodynamic analyses. An adsorption capacity of 50.1 mg/g and a removal rate of 55 % were obtained. The kinetic data showed that multiple adsorption mechanisms and rate-limiting steps may be involved. The equilibrium data were most accurately described by the Sips isothermal model. Thermodynamic parameters indicated that the process is spontaneous and endothermic. The beads were also used as catalysts in Fenton-type processes. The influence of process variables on degradation performance was assessed through a factorial design, which revealed that the optimal conditions were an H₂O₂:phenol molar ratio of 25:1, a catalyst dosage of 1.5 g/L, and a solution pH of 4.95. Then, a heterogeneous Fenton-type process, a heterogeneous sono-Fenton-type process, and a combination of adsorption and oxidation processes were evaluated, yielding removals of 63 %, 83 %, and 91 %, respectively. The best performance, observed for the adsorption/heterogeneous sono-Fenton-type system, confirmed the synergistic effect of the combined techniques. Characterization analyses revealed no significant changes in the composition of mCS@rGO after the processes. Phenol removal was suggested to occur in two sequential stages: adsorption onto the beads via hydrogen bonding and π–π interactions, followed by oxidative reactions.