3D-Porous Carbon Nitride Through Proton Regulation and Photocatalytic Synergy for Efficient Uranium Extraction From Seawater

Extracting uranium from seawater is crucial for tapping oceanic resources vital to future energy supply. This study synthesized a novel nitrogen vacancy carbon nitride (NCN) grafted polyethyleneimine (PEI) composite material (NCNP). Experiments and molecular dynamics simulations reveal that NCNP effectively hinders the diffusion of uranyl ions (UO₂²⁺) to the NCN surface, thereby inhibiting electron transfer reactions. This is primarily achieved by the PEI layer, which repels UO₂²⁺ and prevents its direct contact with the NCN surface. Water-soluble O₂ can still diffuse to the NCN surface for reduction reactions, ensuring the reduction performance of NCNP. The introduction of PEI enhances the proton affinity of the material. Under acidic conditions, protons (H⁺) bind with PEI, reducing competition between protons and uranyl ions for adsorption on the NCN surface. Under alkaline conditions, protons detach from PEI, facilitating H₂O₂ generation and promoting uranium extraction. This dynamic proton regulation allows NCNP to perform effectively under varying pH conditions. Experimental results show that NCNP achieves a uranium extraction capacity of 498.7 mg g⁻¹ in uranium-spiked simulated seawater, which is significantly higher than that of unmodified carbon nitride (CN), which is one of the highest performances for simulating seawater uranium extraction.