Preparation And Adsorption Properties Of Selective Polysaccharide Biosorbent

Chitosan, a natural amino-polysaccharide, has excellent adsorption properties due to the presence of high amounts of amino and hydroxyl groups in its molecule. However, the application of chitosan as biosorbent is limited by its low adsorption selectivity and degradability in acid media. To solve this problem, we prepared Pb(II) ion imprinted crosslinked chitosan beads(Pb(II)-ICB) and EGCG imprinted crosslinked chitosan beads(E-ICCB) using imprinting technology and crosslinking reaction, and their adsorption properties were extensively studied in this work.Firstly, we prepared Pb(II)-ICB and studied its physico-chemical properties and adsorption performance. The optimum conditions for Pb(II)-ICB preparation were as follows: NaOH concentration of 2 mol/L, beads forming time of 10 h, mole ratio of EGDE: CTS of 2:1, crosslinking time of 12 h, Pb(II) concentration of 50 mmol/L, imprinting time of 10 h. Pb(II)-ICB had more cavities and lower crystallinity and thermal stability than non-imprinted crosslinked chitosan beads(NICB), which facilitate the adsorption performance. The adsorption kinetics of Pb(II) ions onto Pb(II)-ICB is well described by the pseudo-second-order kinetics model, indicating that chemisorption is the rate limiting step in the adsorption process. The adsorption isotherm well fits the Langmuir model, which means that adsorption process is monolayer adsorption. Thermodynamic results indicate that the adsorption process is spontaneous and endothermic. Pb(II)-ICB exhibited higher adsorption capacity than NICB, and the maximum adsorption capacity of Pb(II) ions onto Pb-ICB reached 177.62 mg/g. Pb(II)-ICB showed better selectivity to Pb(II) ions in binary system than NICB.Secondly, E-ICCB was prepared and physico-chemical and adsorption properties of E-ICCB were studied. The optimal preparation conditions were as follows: EGCG imprinting concentration of 291 mol/L, concentration for porogen of 0.53 mg/m L, mole ratio of EGDE: CTS of 2:1. Compared with non-imprinted crosslinked chitosan beads(N-ICCB), E-ICCB showed more cavities and lower crystallinity and thermal stability. The adsorption kinetic data well fit the pseudo-second-order kinetics model, and the adsorption isotherm closely follows the Langmuir model. The adsorption process is spontaneous and endothermic. E-ICCB showed higher adsorption capacity than N-ICCB, with a maximum adsorption capacity of 135.50 mg/g. Additionally, E-ICCB showed better selectivity to EGCG moleculars in binary system than N-ICCB.Pb(II)-ICB and E-ICCB showed high adsorption capacities, proper selectivity to target molecules/ions and good reusability, implying their potential as effective and selective biosorbents.