Preparation and Characterization of a Novel Porous Magnetic Chitosan-g-RMF Bead for Phenolic Compound Adsorption

Many industries such as pharmaceuticals, dye manufacturing, fungi and pest control, petroleum refineries etc. generate a huge amount of effluents containing phenolic compounds. These Phenolic compounds have been known to exhibit toxic effects on both humans and aquatic biota. Also, consumption of potable water containing these phenolic compounds can have undesired effects on human health since they are suspected to be carcinogenic and can cause liver damage even at very low concentrations. Hence, it is essential to properly treat industrial waste containing phenols before discharge into the environment. In this study, we proposed a simple hydrothermal method to synthesize a magnetic mesoporous resin (m-RMF) and magnetic porous resin grafted onto chitosan beads (R-g-Ch) and applied it for removal of two phenolic compounds (4- Chloro phenol and phenol) via adsorption. The as-synthesized adsorbents; m-RMF and R-g-Ch were characterized using Fourier Transfer Infrared (FT-IR), scanning electronic microscopy (SEM), vibrating sample magnetometer (VSM), X-ray diffraction (XRD), thermogravimetric (TG) and derivative thermogravimetric (DTG) analysis. Batch adsorption studies were conducted under varying conditions of contact time, temperature, dosage, pH etc. to optimize the experimental conditions required for the optimum removal of phenol and 4-CP. Experimental data were then analyzed using pseudo-first order, pseudo-second order and intra-particle diffusion models. In addition, two commonly used adsorption equilibrium isotherms i.e. the Freundlich and Langmuir isotherm models were utilized to analyze the equilibrium isotherms for the adsorption of both phenolic compounds. The collected results indicate that the adsorption process fitted the Langmuir isotherm model well in both cases which implies monolayer adsorption. The maximum adsorption capacity of R-g-Ch was found to be 180.9 mg/g and 95.5 mg/g for phenol and 4-CP while that of m-RMF was 2.49 and 1.5 mmol/g respectively. Equilibrium uptake of both phenols increased with an increase in initial concentration while the adsorption was found to be highly pH dependent with maximum removal obtained in the alkaline pH. The kinetics of the adsorption process was well explained by the pseudo-second-order kinetic model. Thermodynamic parameters (Gibbs free energy ΔG° at 298K, -14.37 and -14.29 kJ mol-1, enthalpy ΔH°, -23.29 and -15.54 kJ mol-1, and entropy ΔS°, -29.9 and -4.2 J mol-1 K-1 for phenol and 4-chlorophenol respectively) were also calculated. The overall adsorption process was irreversible, spontaneous, exothermic and feasible within the range of 298.15–318K. These results suggest that both the R-g-Ch porous beads and m-RMF could be used as efficient adsorbents for remediation of waste water containing phenols and 4-CP. Keywords: Phenol, 4-Chlorophenol, Chitosan, Melamine, Resorcinol