Salinity-gradient-driven charge separation for enhanced photocatalytic uranium reduction from seawater

Seawater harbors vast uranium reserves essential for the long-term sustainability of nuclear energy, yet its ultra-trace concentration and complex ionic matrix make efficient extraction a persistent challenge. Photocatalysis offers a green route to uranium recovery, but its practical deployment is hindered by rapid charge recombination and reliance on sacrificial agents or external bias. Here, we introduce an osmotic-energy-coupled photoelectrochemical platform that directly converts a natural salinity gradient into a driving force for charge separation, enabling reagent-free uranium (VI) reduction from seawater. The designed heterostructure combines a p-type hole transport layer with uranyl-selective nano-pockets, and its integration with a cation-selective membrane allows the harvested osmotic energy to suppress electron–hole recombination. This coupling boosted uranium extraction efficiency by over 400% at natural seawater concentrations, demonstrating strong applicability in ultra-trace environments. This work offers a sustainable pathway for metal recovery from dilute and complex aqueous systems. An osmotic-energy-coupled photoelectrochemical system is developed for enhanced uranium extraction from seawater. A salinity gradient across a cation-selective membrane generates spontaneous electron flow, promoting charge separation and suppressing electron–hole recombination in the NiO@UiO-66-3C4N photocathode. This coupling enhances U(VI) photoreduction without sacrificial agents or external bias, increasing uranium extraction efficiency by over 400% at natural seawater concentrations. The strategy provides a sustainable approach to utilizing naturally available salinity-gradient energy for uranium recovery.