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

•Phenolic acids were successfully grafted onto chitosan by a redox system.•Amide and ester linkages formed between phenolic acids and chitosan.•Phenolic acids grafted chitosan microspheres had different surface morphologies.•Adsorption capacity of chitosan microspheres was enhanced by grafting PA and HA.•Adsorption process was endothermic, monolayer and chemisorption in nature. 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 800–1000μm. 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 125mgg−1 for PA-g-chitosan microspheres.