Recent progress in high-performance environmental impacts of the removal of radionuclides from wastewater based on metal-organic frameworks: a review

Abstract

The nuclear industry is rapidly developing and the effective management of nuclear waste and monitoring the nuclear fuel cycle are crucial. The presence of various radionuclides such as uranium (U), europium (Eu), technetium (Tc), iodine (I), thorium (Th), cesium (Cs), and strontium (Sr) in the environment is a major concern, and the development of materials with high adsorption capacity and selectivity is essential for their effective removal. Metal-organic frameworks (MOFs) have recently emerged as promising materials for removing radioactive elements from water resources due to their unique properties such as tunable pore size, high surface area, and chemical structure. This review provides an extensive analysis of the potential of MOFs as adsorbents for purifying various radionuclides rather than using different techniques such as precipitation, filtration, ion exchange, electrolysis, solvent extraction, and flotation. This review discusses various MOF fabrication methods, focusing on minimizing environmental impacts when using organic solvents and solvent-free methods, and covers the mechanism of MOF adsorption towards radionuclides, including macroscopic and microscopic views. It also examines the effectiveness of MOFs in removing radionuclides from wastewater, their behavior on exposure to high radiation, and their renewability and reusability. We conclude by emphasizing the need for further research to optimize the performance of MOFs and expand their use in real-world applications. Overall, this review provides valuable insights into the potential of MOFs as efficient and durable materials for removing radioactive elements from water resources, addressing a critical issue in the nuclear industry.

Fig. 1. (a) A model of MOF fabrication. (b) Different MOF structures.

Fig. 2. Techniques for the removal of toxic and radioactive elements.

Fig. 3. (a) An illustration of the preparation of MIL-125/Ag/g-C₃N₄ [adapted from ref. with permission from Elsevier B.V., copyright 2016]. (b) Schematic illustration of the synthesis of AgCl–Ag/g-C₃N₄ [adapted from ref. with permission from Elsevier B.V., copyright 2019]. (c) High efficient release of hydrogen from formic acid using AgPd/g-C₃N₄ [adapted from ref. with permission from Elsevier B.V., copyright 2017]. (d) Silver melamine-based MOF structure in the presence of acetic acid [adapted from ref. with permission from Elsevier Inc., copyright 2019].

Fig. 4. (a) A strontium terephthalate MOF structure [adapted from ref. with permission from WILEY-VCH Verlag, copyright 2013]. (b) NiCo-MOF using 4,4′-biphenyldicarboxylic acid [adapted from ref. with permission from Elsevier Inc, copyright 2019]. (c) Zn-MOFs based on 1,4-naphthalenedicarboxylic acid [adapted from ref. with permission from Elsevier Inc, copyright 2019]. (d) Four MOFs using oxalic acid as a linker [adapted from ref. with permission from Royal Society of Chemistry, copyright 2013].

Fig. 5. (a) Adipic acid-Cu MOF [adapted from ref. with permission from Elsevier B.V., copyright 2012], (b) Ca, Sr, Mg and Ba ions MOFs with anthraquinone-2,6-disulfonate [adapted from ref. with permission from American Chemical Society, copyright 2011], (c) structure of UiO-67 showing a single octahedral cage [adapted from ref. with permission from The Royal Society of Chemistry, copyright 2013], (d) structure of UiO-66 [adapted from ref. with permission from American Chemical Society, copyright 2017].

Fig. 6. (a) Ferric oxide ZIF-8 composite synthesis and removal mechanism [adapted from ref. with permission from Elsevier B.V., copyright 2019]. (b) The synthetic route for UiO-66-AO: (i) CuCN, N-methyl pyrrolidone, microwaved at 170 °C for 20 min; (ii) NH₂OH·HCl, CH₃CH₂OH, refluxing for 24 h [adapted from ref. with permission from American Chemical Society, copyright 2017]. (c) Schematic of the capture of UO₂²⁺ ions in the one-dimensional channels of MOF-76 [adapted from ref. with permission from The Royal Society of Chemistry, copyright 2013]. (d) Schematic sorption properties of UiO-66, UiO-66-COOH, and UiO-66-(COOH)₂ [adapted from ref. with permission from Elsevier Inc, copyright 2019].

Fig. 7. (a) Single-crystal to single-crystal, the controlled uptake and release of iodine, and electrical conductivity [adapted from ref. with permission from American Chemical Society, copyright 2010]. (b) Zeolitic imidazolate framework-8 structure and its captured molecular iodine (I₂) [adapted from ref. with permission from the American Chemical Society, copyright 2011]. (c) The selective uptake of radioactive strontium-90 ions [adapted from ref. with permission from Elsevier Inc, copyright 2019].

Fig. 8. A roadmap figure from the authors' viewpoint of the future of MOFs materials for the adsorption, removal, and separation of radionuclides and toxic metals from contaminated water sources.