Removal of Uranium from Aqueous Solution and Simulated Seawater Using a Mixed Matrix Membrane Fabricated by Cyclophosphazene and Triazine-Based Inorganic–Organic Hybrid Material

Abstract

The efficient removal of uranium ions from aqueous and simulated seawater is reported by using a mixed matrix membrane (MMM-2) fabricated by cyclophosphazene and triazine-based inorganic−organic hybrid material (CTHM-2) as the adsorbent. CTHM-2 with a specific surface area of 76 m 2 g −1 was synthesized within 60 min by microwave-assisted polycondensation reaction. In batch mode adsorption, the concentration of uranium has been decreased from 5 ppm to <15 ppb (permissible limit of uranium by the World Health Organization) within 120 min at pH of 6 and 298 K. However, a maximum adsorption capacity of 580 mg g −1 is estimated with 500 ppm of the initial concentration. The isotherm and kinetic studies indicate that it could fit well with the Freundlich isotherm and pseudo-second order kinetics. The negative ΔG and ΔH values indicate the spontaneous and exothermic adsorption processes, respectively. When the MMM-2 was used to treat 5 L of 5 ppm U(VI) solution, with a water flux of 8.1 L m −2 h −1 and 2 bar transmembrane pressure, it provides safe drinkable water (<15 ppb) for 300 min. Additionally, the CTHM-2 and MMM-2 could be further used to remove uranium ions from the simulated seawater with adsorption capacities of 53 and 167 mg g −1 , respectively.

Fabrication of a Mixed Matrix Membrane Using Nitrogen-Enriched Nanoporous Polytriazine for Removal of Pb2+ from Aqueous Solution

“…The decrease in randomness during the adsorption process is shown by a negative value of Δ S . Based on several reports, the negative Δ H value shows the exothermic nature of adsorption. − Furthermore, the Δ G values represent the degree of spontaneity of the adsorption process, which, as determined by the aforementioned eq S16, at 298, 308, 318, 328, and 338 K are −1.8, −12.5, −12.2, −11.6 and −9.8 kJ mol –1 , respectively.…”

“…Regression analysis is a widely used method for linear and nonlinear methods to obtain the adsorption and kinetic model using MATLAB software. For adsorption isotherm studies, two pronounced methods, i.e., Langmuir and Freundlich, are used. − Linear and nonlinear fittings are applied to the experimental data (Figures a and S6) for the estimation of the corresponding parameters. − The equations representing both Langmuir and Freundlich isotherms for linear and nonlinear fitting are given in eqs S6–S9. The linear and nonlinear versions of the isotherms were fitted to the experimental data using linear and nonlinear regression techniques.…”

“…The linear and nonlinear pseudo-first-order and pseudo-second-order kinetic models were used to study the adsorption kinetics (Figures b and S7). − The equations represent both the models with linear and nonlinear forms represented in eqs S10–S13. Linear and nonlinear regression analysis was employed in both pseudo-first-order and pseudo-second-order kinetic models on the experimental parameters, which indicates that the pseudo-first-order nonlinear fitting outperforms pseudo-second-order linear and nonlinear fitting (Table S4).…”

“…In this direction, several methods for removing contaminants from aqueous solution have been documented, including coagulation, adsorption, ion exchange, membrane filtration, precipitation, and flocculation. − Among them, adsorption and membrane filtration methods are frequently utilized not only for Pb 2+ removal but also for overall water treatment . However, for large-scale applications, membrane filtration technology is considered a more pronounced method.…”

“…Consequently, the synthesis of a heteroatom-enriched material and its utilization for the selective removal of not only Pb 2+ but also other metal ions from an aqueous solution is an important prototype. In the same direction, our research group has developed the heteroatom-enriched (N, S, P) nanoporous material CTHM for the selective and effective removal of Hg 2+ and uranium ions from water bodies. , Another material, viz., nitrogen-enriched nanoporous material (NENP), with a maximum adsorption capacity of 580 mg g –1 and a very high nitrogen content (52 wt %), has been used as an adsorbent for the effective removal of uranium ions from aqueous solution as well as simulated seawater conditions . Because of the high nitrogen content of NENP, it has been used to test its adsorption behavior for the removal of Pb 2+ ions as well.…”