Enhanced adsorption of fluoride by cerium immobilized cross-linked chitosan composite

Abstract

In this present study, a bio-adsorbent based on cerium immobilized cross-linked chitosan (CTS-Ce) composite was prepared and employed for the removal of fluoride from water. This bio-absorbent was characterized by fourier transform infrared spectroscopy (FTIR), Brunauer-Emmett-Teller (BET), energy-dispersive X-ray spectroscopy (EDS), scanning electron microscopy (SEM), elemental mapping images (EMI) and X-ray photoelectron spectroscopy (XPS) analyses. Adsorption properties for fluoride removal were systematically investigated, including pH (2–11), initial fluoride concentrations (5.0–100mg/L), contact time, temperature (10–40°C) and co-existing ions. Besides, kinetics, isotherms, thermodynamics and regeneration were also studied to evaluate the fluoride adsorption performance on this adsorbent. Results showed the experimental data followed Langmuir isotherm and pseudo-second order kinetic model. The adsorption process was controlled by intra-particle diffusion and the maximum adsorption capacity calculated by Langmuir isotherm was 153mg/g at 20°C (close to experimental qe value 149mg/g), which was higher than the raw chitosan (13.2mg/g) and most of the reported adsorbents. The adsorption mechanisms for fluoride removal were (i) the electrostatic attraction among −NH3+ and Ce3+/4+ with F− ions, (ii) the ligand exchange between NO3− and F− and (iii) the formation of CTS-Ce-F complexation. This novel composite can be easily regenerated with NaOH solution while maintaining 78% removal efficiency after 3 cycles. It was believed that this composite had great potential to remove fluoride from contaminated water.