(528f) Metal Ion Adsorption by Chitosan Nanoparticles and Alginate Gel Microparticles for Water Purification Applications

Chitosan and alginate are both low-cost natural materials used for the removal of metal ions from aqueous solutions. In this research, three different concentrations of chitosan gel nanoparticles were synthesized by ionic cross-linking with sodium tripolyphosphate and characterized by zeta-sizing and TEM.  The equilibrium adsorption capability and adsorption kinetics of Cu²⁺ from copper sulfate solution on to chitosan gel nanoparticles, calcium-alginate gel microbeads and alginate-chitosan combination particles at fixed pH have been explored in batch system.

Results show that the equilibrium adsorption properties of chitosan nanoparticles have similar trends to those of alginate microbeads, and the adsorption capacity varies with the synthesis concentration of chitosan nanoparticles. The Langmuir isotherm fits the low concentration region well for both chitosan nanoparticles and alginate microbeads and correlation coefficients were determined. Alginate-chitosan combination particles were found to have intermediate maximum adsorption capacity and Langmuir adsorption equilibrium constants similar to those of alginate microbeads in low concentration copper sulfate solutions. The adsorption capabilities of combination particles can be predicted by the weight ratio of calcium-alginate gel microbeads and chitosan gel nanoparticles.

In kinetics experiments, it was observed that as the adsorption process proceeded, a rapid uptake occurred first and was followed by a slow increase approaching equilibrium for both chitosan nanoparticles and calcium-alginate gel microbeads. Calcium-alginate gel microbeads need a longer time to reach equilibrium than chitosan nanoparticles, likely due to the significant difference in particle size. The adsorption kinetics also vary with the initial concentration of copper sulfate solution. The results will aid the design of  fixed-bed columns for continuous adsorption, which are extensively used in industry.