An effective and selective ion-imprinted biosorbent was prepared from chitosan, using Pb(II) ions as templates and ethylene glycol diglycidyl ether as the crosslinker. The resultant Pb(II)-imprinted chitosan beads (Pb-ICB) were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, X-ray diffraction, and thermogravimetric analysis. The adsorption property and selectivity of Pb-ICB were evaluated for the adsorption of Pb(II). The results showed that Pb-ICB had more cavities, but lower crystallinity and thermal stability than non-imprinted chitosan beads (NICB). Much higher adsorption capacity in the single metal system and better selectivity in the binary metal system for the adsorption Pb(II) were achieved with Pb-ICB than NICB. The maximum adsorption capacity of Pb (II) on Pb-ICB reached 177.62 mg/g. The kinetic and isothermal analyzes showed that the adsorption process of Pb(II) onto Pb-ICB well-fitted pseudo-second-order kinetic and Langmuir isotherm models. The thermodynamic analysis revealed that the adsorption of Pb(II) onto Pb-ICB was a spontaneous and endothermic process. Furthermore, Pb-ICB showed good reusability within five cycles of adsorption-desorption.
In this study, the cross-linked chitosan-polyphosphateepichlorohydrin (CCPE) beads were prepared by cross-linking chitosan with both polyphosphate and epichlorohydrin and used as bioadsorbent for the removal of Pb(II) and Cu(II) ions from aqueous solutions. The effects of the dosage of CCPE beads, solution pH, initial metal ion concentration, contact time, and temperature were investigated. Then, three important factors were selected to optimize the removal processes by the orthogonal test. The results show that CCPE beads can effectively remove the Pb(II) and Cu(II) ions from aqueous solutions, and the maximum percentage removals for Pb(II) and Cu(II) ions are 99.7% and 91.2%, respectively. The data show also that the removal processes for both Pb(II) and Cu(II) ions fit best the pseudo-second order kinetic model. Moreover, the decrease of the adsorption ability of CCPE beads is less than 10% after reuse for 9 times, which suggests that CCPE beads have good reusability.
The (2)-epigallocatechin gallate (EGCG) imprinted chitosan beads (EICBs) were fabricated for the effective and selective separation of EGCG. The EGCG molecules interacted with the amino groups of chitosan in the imprinting process, resulting in a highly porous structure of EICBs and more adsorption sites. Consequently, EICBs exhibited better adsorption performance than nonimprinted chitosan beads. The maximum adsorption capacity of EGCG onto EICBs reached 135.50 mg/g at 313 K. The imprinting factor of EICBs was 4.22, indicating that EICBs possess good recognition ability and selectivity for EGCG. After five cycles of reuse, only a slight decrease (7.77%) in the adsorption capacity was observed, demonstrating the satisfactory reusability of EICBs. Furthermore, the adsorption of EGCG onto EICBs is deduced to be the monolayer adsorption on an energetically homogeneous surface; the hydrogen bonding between EGCG and EICBs is the main driving force for the adsorption. Our studies suggest that EICBs have a great potential for the effective and selective separation of EGCG.
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