Engineering fast sodium-ion transport channels in a NASICON phosphate for targeted U(VI) removal from radioactive wastewater

The advancement of nuclear energy inevitably generates substantial volumes of radioactive uranium-containing wastewater. Therefore, developing materials capable of efficiently capturing uranium from wastewater is imperative for environmental remediation and the secondary utilization of uranium resources. In this study, a NASICON-type phosphate adsorbent, Na 4 MnAl(PO 4 ) 3 (NMAP), featuring an R -32 space group structure, was synthesized via a sol–gel method coupled with high-temperature solid-state sintering. Its unique spatial configuration effectively broadens ion transport channels and establishes rapid Na + diffusion pathways essential for uranium adsorption. Experimental results demonstrate that NMAP exhibits superior selectivity and high efficiency in uranium removal. At pH 3.0, NMAP exhibited rapid adsorption kinetics (reaching equilibrium within approximately 120 min) and a remarkable maximum adsorption capacity of 670.19 mg/g. Furthermore, density functional theory (DFT) calculations explicitly reveal that the framework phosphate groups and sodium vacancies provide highly favorable binding sites for uranyl ions, perfectly corroborating the multi-spectroscopic findings. Moreover, the material maintained exceptional selectivity ( K d > 10 5 mL/g) even in the presence of complex water matrices (e.g., industrial wastewater and lake water) and high concentrations of competing ions, while retaining robust stability and reusability over five consecutive adsorption–desorption cycles. Detailed characterization elucidated the important roles of ion exchange, surface redox reactions mediated by Mn species, coordination with P O and M–O groups, and electrostatic attraction in the uranium adsorption process. Owing to its facile synthesis, rapid kinetics, high selectivity, and strong environmental adaptability, NMAP presents a promising and cost-effective solution for the advanced treatment of radioactive uranium-containing wastewater and the recovery of uranium resources.