Preparation and characterization of novel phenolic acid (hydroxybenzoic and hydroxycinnamic acid derivatives) grafted chitosan microspheres with enhanced adsorption properties for Fe(II)

The adsorption behaviors of Fe(II) on novel adsorbents, phenolic acid grafted chitosan microspheres were investigated. The chemical structures of phenolic acid grafted chitosans were characterized by Fourier transform infrared spectrometer, nuclear magnetic resonance and X-ray diffraction. Results showed that the graft copolymerization occurred at amino groups (C2), hydroxyl groups (C3 and C6) of chitosan and carboxyl groups of phenolic acids with remarkable decrease in crystallinity. Scanning electronic microscope observation showed the diameters of all microspheres were within the range of 800-1000 μm. The surface morphology of chitosan microspheres was greatly changed after functionalization with phenolic acids. The adsorption experiments indicated the maximum adsorption capacity occurred at pH 5.0 and 50 °C. Thermodynamic analysis revealed the endothermic nature of the adsorption process. Kinetics data were better fitted by pseudo-second-order kinetic model and intraparticle diffusion model, indicating the intraparticle diffusion and chemisorption process. Langmuir isotherm was demonstrated as the best fitting model to describe the equilibrium adsorption. Moreover, the adsorption capacity of adsorbents decreased in the order of PA-g-chitosan > HA-g-chitosan > chitosan > GA-g-chitosan > CA-g-chitosan > VA-g-chitosan microspheres. The maximum Fe(II) adsorption capacity, based on Langmuir isotherm, was 125 mg g−1 for PA-g-chitosan microspheres.