Molecularly Imprinted Adsorbents for The Removal of Iodine Isotopes from Nuclear Wastewater

Abstract

Chitosan biopolymer was chosen as an efficient candidate for the synthesis of molecularly imprinted adsorbents for the selective removal of iodine isotopes from nuclear wastewater. The chitosan’s abundance, biodegradability, low cost, and ease of modification made it a good candidate to produce an eco-friendly bio-adsorbent. In this study, iodide ions have been investigated due to their similarity to the iodine isotopes and their suitability to the available laboratory measurements. Thus, the novel iodide-imprinted chitosan beads are synthesized using the phase-inversion method. Iodide-imprinted chitosan beads were successfully produced and tested which achieved a maximum adsorption capacity of 0.65 mmol/g and an adsorption efficiency of 39 %, compared to the non-imprinted native chitosan beads which achieved a maximum adsorption capacity of 0.27 mmol/g and an adsorption efficiency of 16 % only at pH 7. The prepared iodide-imprinted beads were modified via cross-linking with Epichlorohydrin and grafting with SiO2 nanoparticles, which boosted the adsorption capacities to 0.72 mmol/g and 0.91 mmol/g for each of the cross-linked iodide-imprinted chitosan beads and the SiO2 grafted and cross-linked iodide imprinted chitosan beads, respectively, achieving the following corresponding adsorption efficiencies of 43% and 54% at pH 7. Batch adsorption experiments were conducted, which achieved a best fit with the pseudo-second-order model and Weber and Morris intraparticle model, which suggest an intraparticle pore diffusion adsorption mechanism, with the involvement of the physical electrostatic interactions with the cationic chitosan surface. Kinetic data were collected for the batch adsorption experiments, which has shown a best fit with the Freundlich model that describes multilayer heterogeneous diffusion. The molecular, thermal, and morphological characterizations of the ion-imprinted beads have proven the stability molecular structure of the chitosan polymer in the synthesized beads and the correct removal of the templates and the thermal stability of the synthesized iodide-imprinted chitosan beads through Fourier-Transform Infrared Spectrometry, Thermal Gravimetric Analysis, and X-ray Diffraction analysis. The morphological analysis of scanning electron microscopy has proven the emergence of new pores on the ion-imprinted chitosan surface compared to the non-imprinted chitosan native beads. Different factors such as the adsorbent dosage, speed of stirring, pH of the adsorbate, and the co-existing ions have affected the adsorption capacity of the beads, where the maximum adsorption capacity of 1.16 mmol/g was achieved at pH 5 via iodide-imprinted cross-linked chitosan beads grafted with SiO2. The chitosan has shown good recyclability and reusability of the beads several times.

Date of Award	Apr 2023
Original language	American English
Supervisor	Ali Alhammadi (Supervisor)