Uranyl Polyoxotungstate Cluster for Visible-Light-Driven Heterogeneous C-H Selective Fluorination

The selective fluorination of C-H bonds at room temperature using heterogeneous visible-light catalysts is both interesting and challenging. Herein, we present the heterogeneous sandwich-type structure uranyl-polyoxotungstate cluster Na17{Na@[(SbW9O33)2(UO2)6(PO3OH)6]}·46H2O (denoted as U6P6) to regulate the selective fluorination of the C-H bond under visible light and room temperature. This is the first report in which uranyl participates in the fluorination reaction in the form of an insoluble substance. U6P6 is capable of the effective selective fluorination of cycloalkanes and the recyclability of the photocatalyst due to the synergistic effect of multiple uranyl (UO2)2+ and the insolubility of organic reagents of polyoxotungstate. In situ electron paramagnetic resonance spectroscopy captured the generation of cycloalkane radicals during the photoreaction, confirming the mechanism of direct hydrogen atom transfer.

High-Performance Material for the Effective Removal of Uranyl Ion from Solution: Computationally Supported Experimental Studies

Adsorption is a widely used method for pollution removal and for the recovery of valuable species. In recent years, the use of metal-organic compounds among the adsorbents used in adsorption studies has increased. In this study, the performance of the water-insoluble Fe complex as a metal organic framework (MOF-Fe-Ta) of water-soluble tannic acid, which is not used as an adsorbent in uranium recovery and removal, was investigated. For the characterization of the new synthesized material, Fourier transform infrared, scanning electron microscopy, and X-ray diffraction analyses were performed. The changes in the adsorption process based on various parameters were investigated and discussed. The point of zero charges value of the adsorbent was found as 5.52. It was noticed that the adsorption increases as the pH increases. Analyzing the effect of concentration on adsorption, we determined which model explained the adsorption better. The monolayer capacity of the adsorbent determined in light of the Langmuir model was reported as 0.347 mol kg^-1. The Freundlich constant, namely the β value obtained in the Freundlich model, which is a measure of surface heterogeneity, was found to be 0.434, and the E_DR value, which was found from the Dubinin-Raduskevich model and accepted as a measure of adsorption energy, was 10.3 kJ mol^-1. The adsorption was kinetically explained by the pseudo-second-order model and the adsorption rate constant was reported as 0.15 mol^-1 kg min^-1. The effect of temperature on adsorption was studied; it was emphasized that adsorption was energy consuming, that is, endothermic and ΔH was found as 7.56 kJ mol^-1. The entropy of adsorption was positive as 69.3 J mol^-1 K^-1. As expected, the Gibbs energy of adsorption was negative (-13.1 kJ mol^-1 at 25 °C), so adsorption was considered as a spontaneous process. Additionally, the power and mechanism of the interaction between studied adsorbent and adsorbate are explained through density functional theory computations. Computationally obtained data supported the experimental studies.

Rational Construction of Porous Metal-Organic Frameworks for Uranium(VI) Extraction: The Strong Periodic Tendency with a Metal Node

Although metal-organic frameworks (MOFs) have been reported as important porous materials for the potential utility in metal ion separation, coordinating the functionality, structure, and component of MOFs remains a great challenge. Herein, a series of anionic rare earth MOFs (RE-MOFs) were synthesized via a solvothermal template reaction and for the first time explored for uranium(VI) capture from an acidic medium. The unusually high extraction capacity of UO₂²⁺ (e.g., 538 mg U per g of Y-MOF) was achieved through ion-exchange with the concomitant release of Me₂NH₂⁺, during which the uranium(VI) extraction in the series of isostructural RE-MOFs was found to be highly sensitive to the ionic radii of the metal nodes. That is, the uranium(VI) adsorption capacities continuously increased as the ionic radii decreased. In-depth mechanism insight was obtained from molecular dynamics simulations, suggesting that both the accessible pore volume of the MOFs and hydrogen-bonding interactions contribute to the strong periodic tendency of uranium(VI) extraction.

Single crystal structure and photocatalytic behavior of grafted uranyl on the Zr-node of a pyrene-based metal–organic framework

The zirconium MOF NU-1000 was post-synthetically modified through solvothermal deposition to include the uranyl ion and characterized via single-crystal X-ray diffraction; photo-oxidation was also performed.