Tunable Swelling Behaviors of Temperature-Responsive UO22+-Imprinted Polymeric Hydrogel Tailored for Highly Selective Uranium Extraction

The ion imprinting technique was applied in this work to prepare a thermosensitive biomass-based polymeric hydrogel, termed UITB, which exhibits unique temperature-dependent swelling behavior: it shrinks at high temperatures but swells at low temperatures. The reversible swelling property enables the UITB polymer gel to capture and release UO22+ ions by adjusting the temperature within a moderate range of 20°C–45°C. A high adsorption selectivity of UITB for the target UO22+ ions was observed in the presence of decoy metal ions. Rinsing with pure water for the elution of the absorbed UO22+ greatly extends the lifetime of the polymer gel. Subsequently, various thermodynamic models were used to theoretically study the adsorption equilibrium and kinetics of UITB. A monolayer adsorption was identified, with the adsorption dynamics being controlled by both the diffusion process and electron transfer. To explore the molecular mechanism of UO22+ adsorption at the microscale level, atomistic molecular dynamics simulations were performed to investigate the adsorption behavior of UO22+ in two computationally modeled hydrogel network units of different pore sizes. Analysis of the energies showed that the negative intermolecular ELE+EGB energy is responsible for the adsorption and desorption of UO22+ on the polymer gel, while the positive intermolecular VDW energy indicates that the UO22+ ions are prevented from being absorbed anywhere except within the cavities. Finally, testing of the application revealed that our UITB polymer gel demonstrates effective adsorption capabilities for UO22+ in natural seawater, highlighting its potential for practical use.