Efficient Photocatalytic Reduction of U(VI) by a Heterostructured NiAl-LDH/Phosphorus-Modified g-C₃N₄: Performance and Mechanism

The contamination of water by soluble hexavalent uranium (U(VI)) requires the development of highly active and stable treatment materials. This study presents a rational design for a heterostructured photocatalyst by coupling phosphorus-modified graphitic carbon nitride (PCN) with NiAl-layered double hydroxide (NiAl-LDH). The structural theory was that P-doping would tailor the optoelectronic properties of g-C₃N₄, while integration with NiAl-LDH would establish a synergistic system for concurrent adsorption and photoreduction. As anticipated, the P modification inhibited crystal growth and improved charge separation in g-C₃N₄, elevating its U(VI) reduction rate by 3.67-fold. The NiAl-LDH component provided a high-specific-surface-area substrate for pollutant enrichment. The resulting optimal NiAl-LDH/PCN composite formed a Type-II heterojunction, which directed efficient charge transfer between the two phases. Under simulated sunlight, the composite achieved high removal efficiencies of 96.0% for U(VI) and 95.2% for Cr(VI). The performance stems from a synergy where NiAl-LDH concentrates target ions at the interface, and PCN furnishes photogenerated electrons via facilitated charge transfer, thereby accelerating the photoreduction kinetics. The material also demonstrated robust reusability and effectiveness in treating actual wastewater, highlighting its strong potential for practical heavy-metal-ion remediation.