Conformational control via grafting density modulation boosts uranium extraction from seawater

Adsorbents with same grafting ratio but varied chain densities were obtained. • Different grafting densities yield distinct conformations and uptake abilities. • High-density, short-chain materials show better salt tolerance; • High-density adsorbent reaches 9.6 mg/g in seawater-twice that of low-density one. Polymers with distinct chain conformations exhibit pronounced performance differences across various applications, and the grafting density as a critical parameter that governs both chain conformation and the overall performance of polymeric materials. However, existing seawater uranium extraction materials rely exclusively on grafting ratio as the sole criterion for functionalization, but neglecting the critical role of grafting density, resulting in insufficiently extended chain conformations and limited accessibility of adsorption sites, which ultimately constrains uranium extraction efficiency. Herein, a series of materials with identical degrees of functionalization but varying grafting densities and chain lengths of the polymers were obtained, and their uranium adsorption behavior were systematically investigated. In aqueous systems, the adsorption capacities of these adsorbents are comparable. However, in saline environments (including simulated, U-spiked and natural seawater) the adsorbent with high grafting density and short chains architecture exhibits the highest uranium adsorption performances. To gain deeper insight into the underlying mechanisms, the conformational behaviors of polymer chains were monitored by Quartz Crystal Microbalance with Dissipation (QCM-D). The results reveal that high grafting density and short chains display a significantly stronger anti-polyelectrolyte effect compared to that low grafting density and long chains. Consequently, the high grafting density and short of polymer chain adsorbent demonstrates superior resistance to salt-shrinkage and achieves higher uranium extraction capacity (9.6 mg/g) in natural seawater, substantially outperforming the low grafting density long chain (4.9 mg/g). This study provides critical design principles for developing polymeric adsorbents tailored for high-salinity environment applications, such as uranium extraction from seawater.