Application of zirconium aspartic acid metal-organic framework (MIP-202(Zr)) for high efficient ruthenium adsorption from aqueous solutions

The zirconium metal - organic framework MIP-202(Zr), based on L-aspartic acid, was prepared by hydrothermal method and used for study of ruthenium adsorption from aqueous solutions. The obtained material was characterized by X-ray diffraction (XRD), infra red spectroscopy (IR), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The batch adsorption experiment was performed for determination of adsorption equilibrium, kinetics and thermodynamics parameters to Ru(III) from aqueous solution on MIP-202(Zr). The data of ruthenium sorption onto MIP-202(Zr) were fitted and analyzed by the Langmuir, Freundlich and Temkin equilibrium isotherm models, while the Langumir adsorption isotherm models fit the best. Kinetic data were analyzed by four kinetic models, and ruthenium sorption on MIP202(Zr) can be describes the best by intra particle diffusion (Weber Morris). Analysis of thermodynamic properties of ruthenium ions sorption onto MIP-202(Zr) shows that the sorption process has a spontaneous and endothermic nature and is energetically beneficial.

Modeling separation of lanthanides via heterogeneous ligand binding

Individual lanthanide elements have physical/electronic/magnetic properties that make each useful for specific applications. Several of the lanthanides cations (Ln3+) naturally occur together in the same ores. They are notoriously difficult to separate from each other due to their chemical similarity. Predicting the Ln3+ differential binding energies (ΔΔE) or free energies (ΔΔG) at different binding sites, which are key figures of merit for separation applications, will help design of materials with lanthanide selectivity. We apply ab initio molecular dynamics (AIMD) simulations and density functional theory (DFT) to calculate ΔΔG for Ln3+ coordinated to ligands in water and embedded in metal-organic frameworks (MOFs), and ΔΔE for Ln3+ bonded to functionalized silica surfaces, thus circumventing the need for the computational costly absolute binding (free) energies ΔG and ΔE. Perturbative AIMD simulations of water-inundated simulation cells are applied to examine the selectivity of ligands towards adjacent Ln3+ in the periodic table. Static DFT calculations with a full Ln3+ first coordination shell, while less rigorous, show that all ligands examined with net negative charges are more selective towards the heavier lanthanides than a charge-neutral coordination shell made up of water molecules. Amine groups are predicted to be poor ligands for lanthanide-binding. We also address cooperative ion binding, i.e., using different ligands in concert to enhance lanthanide selectivity.

Adsorbents for the Uranium Capture from Seawater for a Clean Energy Source and Environmental Safety: A Review

On the global level, uranium is considered the main nuclear energy source, and its removal from terrestrial ores is enough to last until the end of the current century. Therefore, a major focus is attracted toward the capture of uranium from a sustainable source (seawater). Uranium recovery from seawater has been reported over the last few decades, and recently many efforts have been devoted to the preparation of such adsorbents with higher selectivity and adsorption capacity. The purpose of this review is to report the advancement in adsorbent preparation and modification of porous materials. It also discusses challenges such as adsorbent selectivity, low uranium concentration in seawater, contact time, biofouling, and the solution to the problems necessary to ensure a better adsorption performance of the adsorbent.

Efficient and selective capture of thorium ions by a covalent organic framework

The selective separation of thorium from rare earth elements and uranium is a critical part of the development and application of thorium nuclear energy in the future. To better understand the role of different N sites on the selective capture of Th(IV), we design an ionic COF named Py-TFImI-25 COF and its deionization analog named Py-TFIm-25 COF, both of which exhibit record-high separation factors ranging from 102 to 105. Py-TFIm-25 COF exhibits a significantly higher Th(IV) uptake capacity and adsorption rate than Py-TFImI-25 COF, which also outperforms the majority of previously reported adsorbents. The selective capture of Py-TFImI-25 COF and Py-TFIm-25 COF on thorium is via Th-N coordination interaction. The prioritization of Th(IV) binding at different N sites and the mechanism of selective coordination are then investigated. This work provides an in-depth insight into the relationship between structure and performance, which can provide positive feedback on the design of novel adsorbents for this field.

Ion solvation as a predictor of lanthanide adsorption structures and energetics in alumina nanopores

Adsorption reactions at solid-water interfaces define elemental fate and transport and enable contaminant clean-up, water purification, and chemical separations. For nanoparticles and nanopores, nanoconfinement may lead to unexpected and hard-to-predict products and energetics of adsorption, compared to analogous unconfined surfaces. Here we use X-ray absorption fine structure spectroscopy and operando flow microcalorimetry to determine nanoconfinement effects on the energetics and local coordination environment of trivalent lanthanides adsorbed on Al2O3 surfaces. We show that the nanoconfinement effects on adsorption become more pronounced as the hydration free energy, ΔGhydr, of a lanthanide decreases. Neodymium (Nd3+) has the least exothermic ΔGhydr (-3336 kJ·mol-1) and forms mostly outer-sphere complexes on unconfined Al2O3 surfaces but shifts to inner-sphere complexes within the 4 nm Al2O3 pores. Lutetium (Lu3+) has the most exothermic ΔGhydr (-3589 kJ·mol-1) and forms inner-sphere adsorption complexes regardless of whether Al2O3 surfaces are nanoconfined. Importantly, the energetics of adsorption is exothermic in nanopores only, and becomes endothermic with increasing surface coverage. Changes to the energetics and products of adsorption in nanopores are ion-specific, even within chemically similar trivalent lanthanide series, and can be predicted by considering the hydration energies of adsorbing ions.

A rationale for the rapid extraction of ultra-low-level uranyl ions in simulated bioassays regulated by Mn-dopants over magnetic nanoparticles

Although the sorption of uranyl ions and other heavy metal ions over magnetic nanoparticles is well reported, the parameters governing the sorption process over the magnetic nanoparticles have not been clearly enumerated. However, to increase the efficiency of the sorption over the surface of these magnetic nanoparticles, it is essential to understand the different structural parameters that are involved in the sorption process. The sorption of uranyl ions and other competitive ions in simulated urine samples at different pH was effectively accomplished over magnetic nanoparticles of Fe₃O₄ (MNPs) and Mn-doped Fe₃O₄ (Mn-MNPs). The MNPs and Mn-MNPs were synthesized using an easily modified co-precipitation method and were thoroughly characterised using several techniques, such as XRD, HRTEM, SEM, zeta potential, and XPS. The substitutional doping of Mn (1 to 5 at%) in the Fe₃O₄ lattice (Mn-MNPs) showed better sorption ability as compared to that of MNPs. The sorption properties of these nanoparticles were mainly correlated with the different structural parameters to understand the roles of surface charge and different morphological parameters. The interaction centres over the surface of MNPs with the uranyl ions were designated and the effects of ionic interactions with uranyl ions for these sites were calculated. Extensive XPS, ab initio calculations and zeta potential studies have provided deep insights into the different aspects that play key roles in the sorption process. These materials showed one of the best K_d values (∼3 × 10⁶ cm³) in a neutral medium with very low t_1/2 values (∼0.9 min). The fast sorption kinetics (very low t_1/2) makes them amongst the best sorption materials for uranyl ions and optimal for the quantification of ultra-low-level uranyl ions in simulated bioassays.

γ-Resistant Microporous CAU-1 MOF for Selective Remediation of Thorium

A simple solvothermal method was used to synthesize a metal-organic framework (MOF) with an Al metal entity, viz., CAU-1 NH₂. The synthesized MOF was characterized using different techniques like X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetric analysis, scanning electron microscopy (SEM), field emission SEM (FE-SEM), transmission electron microscopy, small-angle X-ray scattering, positron annihilation lifetime spectroscopy, and X-ray photoelectron spectroscopy. The radiation stability was evaluated by irradiating the material up to a cumulative dose of 2 MGy using ⁶⁰Co for the first time. The studies showed a remarkable gamma irradiation stability of the material up to 1 MGy. The porosity and surface area of the synthesized MOF were determined by Brunauer-Emmett-Teller, which showed a high specific surface area of 550 m²/g. The pH dependence study of Th uptake from an aqueous solution was performed from pH 2-8, followed by adsorption isotherm and adsorption kinetics studies. These results revealed that the Langmuir and pseudo-second-order kinetic models can be well adapted for understanding the Th uptake and kinetics, respectively. The synthesized MOF exhibited an ∼404 mg/g thorium adsorption capacity. Selectivity studies of adsorption of Th w.r.t. to U and different metal ions such as Cu, Co, Ni, and Fe showed that Th gets adsorbed preferentially as compared to other metal ions. In addition, the MOF could be used multiple times without much deterioration.

Not Just Another Methanation Catalyst: Depleted Uranium Meets Nickel for a High-Performing Process Under Autothermal Regime

Ni-based catalysts prepared through impregnation of depleted uranium oxides (DU) have successfully been employed as highly efficient, selective, and durable systems for CO₂ hydrogenation to substituted natural gas (SNG; CH₄ ) under an autothermal regime. The thermo-physical properties of DU and the unique electronic structure of f-block metal-oxides combined with a nickel active phase, generated an ideal catalytic assembly for turning waste energy back into useful energy for catalysis. In particular, Ni/UO_x stood out for the capacity of DU matrix to control the extra heat (hot-spots) generated at its surface by the highly exothermic methanation process. At odds with the benchmark Ni/γ-Al₂ O₃ catalyst, the double action played by DU as a "thermal mass" and "dopant" for the nickel active phase unveiled the unique performance of Ni/UO_x composites as CO₂ methanation catalysts. The ability of the weakly radioactive ceramic (UO_x ) to harvest waste heat for more useful purposes was demonstrated in practice within a rare example of a highly effective and long-term methanation operated under autothermal regime (i. e., without any external heating source). This finding is an unprecedented example that allows a real step-forward in the intensification of "low-temperature" methanation with an effective reduction of energy wastes. At the same time, the proposed catalytic technology can be regarded as an original approach to recycle and bring to a second life a less-severe nuclear by-product (DU), providing a valuable alternative to its more costly long-term storage or controlled disposal.

Metal-Organic Framework-Based Materials for Adsorption and Detection of Uranium(VI) from Aqueous Solution

The steady supply of uranium resources and the reduction or elimination of the ecological and human health hazards of wastewater containing uranium make the recovery and detection of uranium in water greatly important. Thus, the development of effective adsorbents and sensors has received growing attention. Metal-organic frameworks (MOFs) possessing fascinating characteristics such as high surface area, high porosity, adjustable pore size, and luminescence have been widely used for either uranium adsorption or sensing. Now pertinent research has transited slowly into simultaneous uranium adsorption and detection. In this review, the progress on the research of MOF-based materials used for both adsorption and detection of uranium in water is first summarized. The adsorption mechanisms between uranium species in aqueous solution and MOF-based materials are elaborated by macroscopic batch experiments combined with microscopic spectral technology. Moreover, the application of MOF-based materials as uranium sensors is focused on their typical structures, sensing mechanisms, and the representative examples. Furthermore, the bifunctional MOF-based materials used for simultaneous detection and adsorption of U(VI) from aqueous solution are introduced. Finally, we also discuss the challenges and perspectives of MOF-based materials for uranium adsorption and detection to provide a useful inspiration and significant reference for further developing better adsorbents and sensors for uranium containment and detection.

High Sorption and Selective Extraction of Actinides from Aqueous Solutions

The selective elimination of long-lived radioactive actinides from complicated solutions is crucial for pollution management of the environment. Knowledge about the species, structures and interaction mechanism of actinides at solid–water interfaces is helpful to understand and to evaluate physicochemical behavior in the natural environment. In this review, we summarize recent works about the sorption and interaction mechanism of actinides (using U, Np, Pu, Cm and Am as representative actinides) on natural clay minerals and man-made nanomaterials. The species and microstructures of actinides on solid particles were investigated by advanced spectroscopy techniques and computational theoretical calculations. The reduction and solidification of actinides on solid particles is the most effective way to immobilize actinides in the natural environment. The contents of this review may be helpful in evaluating the migration of actinides in near-field nuclear waste repositories and the mobilization properties of radionuclides in the environment.

High-performance removal of radionuclides by porous organic frameworks from the aquatic environment: A review

Dealing with unwanted nuclear waste is still a serious issue from the point of view of humans and the environment because of its harmful and dangerous effects. Recently, porous organic frameworks (POFs) have gained an increasing concern as effective materials in the removal of various types of hazardous metal ions, especially radioactive metal ions. POFs are a unique class that included covalent organic frameworks (COFs) and metal-organic frameworks (MOFs) with strong covalent bonds, large surface area, high adsorption capacity, tunable porosity, and a porous structure with more efficient than conventional adsorbents. This review highlights the recent developments of POFs for the rapid elimination of radionuclide. The unique characteristics, adsorption properties, and interaction mechanisms between radioactive metal ions and the POF-based materials are summarized. Also, prospects for enhancing the performance of POFs to capture radioactive metal ions are discussed.

Metal-organic frameworks as superior porous adsorbents for radionuclide sequestration: Current status and perspectives

Efficient separation of hazardous radionuclides from radioactive waste remains a challenge to the global acceptance of nuclear power due to complex nature of the waste, high radiotoxicities and presence of large number of interfering elements. Sorption of radioactive elements from liquid phase, gas phase or their solid particulates on various synthetic organic, inorganic or biological sorbents is looked as one of the options for their remediation. In this context, highly porous materials, termed as metal-organic frameworks (MOFs), have shown promise for efficient capturing of various types of radioactive elements. Major advantages that have been advocated for the application of MOFs in radionuclide sorption are their excellent chemical stability, and their large surface area due to abundant functional groups, and porosity. In this review, recent developments on the application of MOFs for radionuclide sequestration are briefly discussed. Focus has been devoted to address the separation of few crucial radioactive elements such as Th, U, Tc, Re, Se, Sr and Cs from aqueous solutions, which are important for liquid radioactive waste management. Apart from these radioactive metal ions, removal of radionuclide bearing gases such as I₂, Xe, and Kr are also discussed. Aspects related to the interaction of MOFs with the radionuclides are also discussed. Finally, a perspective for comprehensive investigation of MOFs for their applications in radioactive waste management has been outlined.

Post synthetically modified IRMOF-3 for efficient recovery and selective sensing of U(vi) from aqueous medium

A simple and efficient route to develop various novel functionalized MOF materials for rapid and excellent recovery of U(vi) from aqueous medium, along with selective sensing has been demonstrated in the present study. In this connection, a set of four distinct post synthetically modified (PSM) iso-reticular metal organic frameworks were synthesized from IRMOF-3 namely, IRMOF-PC (2-pyridine carboxaldehyde), IRMOF-GA (glutaric anhydride), IRMOF-SMA (sulfamic acid), and IRMOF-DPC (diphenylphosphonic chloride) for the recovery and sensing of U(vi) from aqueous medium. The MOFs were characterized by Fourier transform infrared spectroscopy (FTIR), powder XRD, BET surface area analysis, thermogravimetric analysis (TGA), NMR (13C, 1H and 31P), Scanning Electron Microscopy (SEM), and energy dispersive X-ray spectroscopy (EDX). Among all MOFs, post synthetically modified IRMOF-SMA showed enhanced thermal stability of about 420 °C. The MOFs were investigated for U(vi) sorption studies using a batch technique. All the MOFs exhibit excellent sorption capacity towards U(vi) (>90%) and maximum uptake was observed at pH 6. Sorption capacity of MOFs have the following order; IRMOF-3-DPC (300 mg U g-1) > IRMOF-SMA (292 mg U g-1) > IRMOF-PC (289 mg U g-1) > IRMOF-GA (280 mg U g-1) > IRMOF-3 (273 mg U g-1). IRMOF-DPC shows rapid sorption of uranium within 5 min with excellent uptake of U(vi) (>99%). The desorption of U(vi) was examined with different eluents and 0.01 M HNO3 was found to be most effective. The fluorescence sensing studies of U(vi) via IRMOF-3 and its PSM MOFs revealed high sensitivity and selectivity towards U(vi) over other competing rare earth metal ions (La3+, Ce4+, Sm3+, Nd3+, Gd3+, and Eu3+), wherein IRMOF-GA displayed an impressive detection limit of 0.36 mg L-1 for U(vi).

Grafting functional groups in metal–organic frameworks for U(vi) sorption from aqueous solutions

Recent highlights of the organic groups-functionalized MOFs for uranium extraction from aqueous solution are discussed.

Selective Th(iv) capture from a new metal–organic framework with O− groups

New MOF adsorbent with functional N⁺–O⁻ groups was designed. The material shows fast adsorption of Th(iv) and high removal efficiency, and is selective over La(iii), Sm(iii), Ho(iii), Cd(ii), Pb(ii) and K(i) ions.

Removal of U(VI) from aqueous solution using phosphate functionalized bacterial cellulose as efficient adsorbent

In this study, phosphate functionalized bacterial cellulose with micro-fibrous structure was prepared, characterized and applied for U(VI) adsorption. The successful grafting of phosphoric functional groups was proved by the FTIR spectra and EDS analysis (P~4.15 wt%), and the porous structure was confirmed by SEM and BET analyses. Furthermore, the effect of initial pH, contact time, initial concentration, and temperature were studied. The as-prepared adsorbent showed a high adsorption capacity at wide pH range (4.0–8.0) and its maximum adsorption capacity was calculated to be 50.65 mg/g. This endothermic adsorption process conformed to the pseudo second-order kinetic model and the Elovich kinetic models and the Langmuir isothermal models. According to the FTIR and XPS analysis, an adsorption mechanism was tentatively proposed, mainly due to the interaction between U(VI) and phosphoric groups.

A robust and water-stable two-fold interpenetrated metal–organic framework containing both rigid tetrapodal carboxylate and rigid bifunctional nitrogen linkers exhibiting selective CO2 capture

A robust and water-stable two-fold interpenetrated metal–organic framework containing both rigid tetrapodal carboxylate and rigid bifunctional nitrogen linkers exhibiting selective CO₂ capture is reported.

MIL-101(Cr) metal–organic framework functionalized with tetraethylenepentamine for potential removal of Uranium (VI) from waste water

The metal–organic frameworks material functionalized by grafting amino group of tetraethylenepentamine on the coordinative unsaturated Cr (III) centers is described. The obtained tetraethylenepentamine-functionalized adsorbents with different mass ratios of tetraethylenepentamine have been characterized by scanning electron microscopy, Fourier-transform infrared, X-ray powder diffraction, and N2 adsorption and desorption isotherms. Significantly, MIL-101-tetraethylenepentamine 60% exhibited high adsorption capacity (350 mg/g) for removal of uranium (VI) from water at pH 4.5. At uranium concentration <20 mg/L, the isothermal plot was best represented by Freundlich model. At U(VI) concentration approximately >30 mg/L, the isotherm was best described by Langmuir model.

Metal-organic framework-based materials: superior adsorbents for the capture of toxic and radioactive metal ions

Highly efficient removal of metal ion pollutants, such as toxic and nuclear waste-related metal ions, remains a serious task from the biological and environmental standpoint because of their harmful effects on human health and the environment. Recently, highly porous metal-organic frameworks (MOFs), with excellent chemical stability and abundant functional groups, have represented a new addition to the area of capturing various types of hazardous metal ion pollutants. This review focuses on recent progress in reported MOFs and MOF-based composites as superior adsorbents for the efficient removal of toxic and nuclear waste-related metal ions. Aspects related to the interaction mechanisms between metal ions and MOF-based materials are systematically summarized, including macroscopic batch experiments, microscopic spectroscopy analysis, and theoretical calculations. The adsorption properties of various MOF-based materials are assessed and compared with those of other widely used adsorbents. Finally, we propose our personal insights into future research opportunities and challenges in the hope of stimulating more researchers to engage in this new field of MOF-based materials for environmental pollution management.

The Hydrolytic Stability and Degradation Mechanism of a Hierarchically Porous Metal Alkylphosphonate Framework

To aid the design of a hierarchically porous unconventional metal-phosphonate framework (HP-UMPF) for practical radioanalytical separation, a systematic investigation of the hydrolytic stability of bulk phase against acidic corrosion has been carried out for an archetypical HP-UMPF. Bulk dissolution results suggest that aqueous acidity has a more paramount effect on incongruent leaching than the temperature, and the kinetic stability reaches equilibrium by way of an accumulation of a partial leached species on the corrosion conduits. A variation of particle morphology, hierarchical porosity and backbone composition upon corrosion reveals that they are hydrolytically resilient without suffering any great degradation of porous texture, although large aggregates crack into sporadic fractures while the nucleophilic attack of inorganic layers cause the leaching of tin and phosphorus. The remaining selectivity of these HP-UMPFs is dictated by a balance between the elimination of free phosphonate and the exposure of confined phosphonates, thus allowing a real-time tailor of radionuclide sequestration. Moreover, a plausible degradation mechanism has been proposed for the triple progressive dissolution of three-level hierarchical porous structures to elucidate resultant reactivity. These HP-UMPFs are compared with benchmark metal-organic frameworks (MOFs) to obtain a rough grading of hydrolytic stability and two feasible approaches are suggested for enhancing their hydrolytic stability that are intended for real-life separation protocols.