Optimization of Zn/Al cationic ratio in Zn-Al-LDH for efficient U(VI) adsorption
Nikita Ivanov, О. О. Шичалин, Alexander L. Trigub, V. L. Rastorguev, N. A. Nekrasova, Viktoriya Provatorova, E. A. Gnilyak, A. Zaikova, V.B. Rinchinova, А. О. Лембиков, T. L. Simonenko, A. N. Fedorets, V. Yu. Mayorov, V. V. Korochentsev, I. Yu. Buravlev, Е. К. Папынов
Abstract
The critical need for effective uranium separation from complex aqueous solutions remains a central challenge in materials science today. Layered double hydroxides (LDHs) have emerged as promising uranium-absorbing materials. This study examines how different zinc-to-aluminum ratios (3,1, 2:1, and 1:1) affect both the structure and uranium(VI) absorption properties of Zn-Al LDHs. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), low-temperature N 2 adsorption, and Zn K-edge extended X-ray adsorption fine structure (EXAFS) analyses revealed that while the crystal structure of the materials remained consistent, significant changes occurred in their porous and microstructures. EXAFS spectroscopy near the U L3-edge demonstrated that the dominant mechanism for U(VI) adsorption at pH 4.0 is inner-sphere complexation, involving negatively charged uranyl carbonate and hydroxyl complexes. Increasing the degree of Al substitution for Zn led to a logical enhancement in sorption capacity, reaching a maximum value of 47.2 mg/g at the optimal Zn/Al ratio of 2/1. Further increase in the substitution degree resulted in a shift towards a mesoporous structure, accompanied by a decrease in specific surface area and sorption capacity. Our findings demonstrate the potential of Zn-Al LDHs for U(VI) removal and provide a fundamental basis for future research aimed at developing more effective materials for the remediation of wastewater contaminated with hazardous radionuclides .