Efficient removal of radionuclides U(VI) by rod-like metal organic framework (MOF-5) nanomaterials

As the radionuclide 235U(VI) is inevitably released into the natural environment, the potential toxicity and irreversibility impact on the natural environment has become one of the most forefront pollution problems in nuclear energy utilization. A recent study revealed that a rod-like metal-organic framework (MOF-5) nanomaterial was used as a high-efficiency adsorbent for sorption of U(VI), indicating that MOF-5 can be used as a candidate for rapid and efficient removal of radionuclides in practical applications material.

The paper was reported in Science Bulletin (2018, 63(13): 831-839), entitled "Synthesis of novel rod-like metal-organic framework (MOF-5) nanomaterial for efficient removal of U(VI): batch experiments and spectroscopy study" by Xiang-Ke Wang and Shu-Jun Yu from North China Electric Power University. The authors synthesized a rod-like metal-organic framework (MOF-5) nanomaterial by solvothermal method and used for effective sorption of U(VI) in aqueous solution. The batch experimental results showed that the dominant interaction mechanism was inner-sphere surface complexation and electrostatic interaction. The maximum sorption capacity of U(VI) on MOF-5 was 237.0 mg/g at pH = 5.0 and T = 298 K, and the sorption equilibrium was reached within 5 min. The thermodynamic parameters indicated that the removal of U(VI) on MOF-5 was a spontaneous and endothermic process. Additionally, the FT-IR and XPS analyses implied that the high sorption capacity of U(VI) on MOF-5 was mainly attributed to its abundant oxygen-containing functional groups (i.e., C-O and C=O).

Metal-organic frameworks (MOFs) are a class of crystalline porous materials consisting of metal nodes (i.e., metal ions or clusters) and organic linkers connected via coordination bonds. It is well established that MOFs are one of the most widely investigated materials of the 21st century owing to their structural tailorability, controlled porosity, and high crystallinity. Widely used metal ions for the construction of MOFs include Fe(III), Cu(II), Ca(II), Al(III), Mg(II), Zn(II), Cd(II), Co(II), Zr(IV), Ln(III), and Ti(III), which can adopt various coordination geometries, such as trigonal bipyramidal, pyramidal, square, tetrahedral and octahedral. A commonly used strategy for preparing MOFs can be divided into two categories: (I) direct non-aqueous or aqueous synthesis and (II) mixed non-aqueous or aqueous synthesis. Widely used synthesis methods include solvothermal, hydrothermal, mechano-chemical, layer-by-layer growth, ultrasonic, electrochemical, microwave and high-throughput synthesis.

Since the discovery of MOFs in 1995, they have been applied in the fields of sorption, gas storage, separation, catalysis, sensing, and biomedicine. Recently, many kinds of MOF-based materials (e.g. SCU-100 and UiO-66-AO) have been successfully synthesized and shown rapid U(VI) removal (within 10 min) than other contaminants. Until now, about twenty MOF materials have been applied to sequester U(VI). However, few articles have addressed the study of MOF-5 material for U(VI) removal, especially the interaction mechanism.

In this study, a solvothermal method was successfully used to synthesize a MOF-5 sample and to remove U(VI) from radioactive wastewater. The morphologies and microstructures of MOF-5 were characterized by SEM, TEM, FT-IR, XRD and XPS. The batch experiments were performed as a function of contact time, U(VI) concentration, temperature, pH and ionic strength. Furthermore, the interaction mechanism between U(VI) and MOF-5 was evaluated from the experimental results and spectroscopy characterization. This paper highlighted the application of MOF-5 as a superior candidate for U(VI) enrichment, which provided a new material for removing radionuclides from aqueous solutions and alleviating the environmental pollution pressure.

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This work was supported by National Key Research and Development Program of China (2017YFA0207002), the National Natural Science Foundation of China (21577032, 21607042), the Fundamental Research Funds for the Central Universities (2018ZD11, 2018MS114, 2016MS02), and the Jiangsu Provincial Key Laboratory of Radiation Medicine and Protection and the Priority Academic Program Development of Jiangsu Higher Education Institutions.

See the article: Yihan Wu, Hongwei Pang, WenYao, Xiangxue Wang, Shujun Yu, Zhimin Yu, Xiangke Wang. Synthesis of rod-like metal-organic framework (MOF-5) nanomaterial for efficient removal of U(VI): batch experiments and spectroscopy study. Science Bulletin, 2018, 63(13): 831-839

https://www.sciencedirect.com/science/article/pii/S2095927318302433

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