Mechanistic studies of uranyl interaction with functionalized mesoporous chitosan-superparamagnetic nanocomposites for selective sorption: Characterization and sorption performance

Abstract

Herein, two hybrid magnetic-chitosan nanocomposite core-shell were synthesized via subsequently heterogeneous nucleation immobilized with alanine/serine functionality for enhanced uranyl ions (UO 2 2+ ) sorption. The physiochemical characteristics of nanocomposites were determined by CHN, FTIR, XRD, BET, pHzpc, TEM, TGA, XPS and VSM studies. The synthesized mesoporous alanine (Ala) and serine (Ser) nanocomposites were found: superparamagnetic with saturation magnetization ( M S : 26.54 and 23.05 emu g -1 for Ala and Ser, respectively), large surface-to-volume ratio for Ser (61.1 m 2 g -1 to 0.41 cm 3 g -1 ), compared to Ala (60.4 m 2 g −1 to 0.36 cm 3 g −1 ), and amine content for Ala and Ser was (2.69 and 2.58 mmol N g -1 with density of ⁓13.42 and ⁓12.73 nm 2- , respectively. The sorption characteristics of uranyl ions were thoroughly examined and compared. At the optimal pH range of 3.5-5.0, Ala and Ser nanocomposites show maximum sorption capacities of 0.498 and 0.609 mmol U/g, respectively in sulfate medium, as well 0.583 and 0.742 mmol U/g in nitrate medium. The Langmuir model suits the sorption process well, and the pseudo-second-order rate equation (PSORE) enables single-layer chemical reactions. Small-size particles afford rapid sorption ⁓50 minutes with half-sorption-time (t 0.5 ) 3.9 and 4.2 min for Ser and Ala nanocomposite, respectively. The sorption is spontaneous, exothermic and regulated by entropy change. The sorption efficiency in various medium types can be arranged according to sorption capacity as follows: nitrate > chlorides >> sulphate medium. According to spectroscopic analyses (FTIR and XPS), the sorption sites are N/O functional groups, which adsorbed UO 2 2+ by anion-exchange, electrostatic attraction and chelation mechanisms. Elution and regeneration are successfully accomplished with using acidified urea solution achieving ⁓92%. Finally, both sorbents were tested and compared for the selectivity of UO 2 2+ from multicomponent simulated waste containing uranyl species. Both sorbents showed high sorption capacity, excellent selectivity, and good recyclability and reusability over multiples sorption cycles. • Alanine and serine efficiently functionalized the magnetic-chitosan nanocomposite core-shell, which were extensively characterized and tested for uranium sorption. • Sorbents have a high sorption capacity, great selectivity, and strong recyclability and reusability through numerous sorption cycles. • Nanocomposites show a high affinity for U(VI) and great selectivity from acidic simulated nuclear effluent. • Interaction mechanisms of nanocomposites with uranyl ions have been elucidated.