Li-Yong Yuan

Introduction of amino groups into acid-resistant MOFs for enhanced U(VI) sorption

Metal–organic frameworks (MOFs) have recently been receiving increasing attention in various scientific fields, including nuclear industry, due to their unique properties. In this work, the acid-resistant chromium-based MOF, MIL-101, and its amino derivatives were prepared to explore their potential usage in separation, removal and/or recovery of radionuclides from aqueous solutions. The synthesized MIL-101-NH2, MIL-101-ED (ED = Ethanediamine), and MIL-101-DETA (DETA = Diethylenetriamine) were characterized by X-ray diffraction spectrometry (XRD), infrared spectrometry (IR), N2 adsorption–desorption measurements, scanning electron microscopy (SEM) and thermogravimetric analysis (TGA), which confirm the successful modification of amino groups and the preservation of porous structures. The sorption performances of these materials toward U(VI) from an aqueous solution were investigated in detail. It was found that all the amine-grafted MOFs were highly efficient in capturing U(VI) compared to raw MIL-101. The sorption capacity of these MOFs for U(VI) sorption follows the order of MIL-101-DETA > MIL-101-ED > MIL-101-NH2 > MIL-101, in which MIL-101-DETA possesses the highest sorption capacity of 350 mg g−1 at pH ∼5.5. Moreover, the sorbed U(VI) can be easily desorbed by lowering the pH (pH ≤ 3.0), and the prepared materials also display a desirable selectivity toward U(VI) in a solution containing a range of competing ions. Based on the FTIR and EXAFS characterizations, the sorption mode of U(VI) onto MOFs is fully discussed. This work promises to provide a facile approach for developing acid-resistant MOFs toward a highly efficient and selective extraction of radionuclides from aqueous solutions.

MOF-76: from a luminescent probe to highly efficient U(VI) sorption material.

MOF-76 exhibits not only high sensitivity for the detection of U(vi), but also high adsorption capacity of 298 mg g(-1) at a low pH value of ∼3.0. Furthermore, the high selectivity for uranium adsorption over a series of competing metal ions is also illustrated.

High performance of phosphonate-functionalized mesoporous silica for U(VI) sorption from aqueous solution

The renaissance of nuclear energy promotes increasing basic research on the separation and enrichment of nuclear fuel associated radionuclides. Herein, we report the first study for developing mesoporous silica functionalized with phosphonate (NP10) as a sorbent for U(VI) sorption from aqueous solution. The mesoporous silica was synthesized by co-condensation of diethylphosphatoethyltriethoxysilane (DPTS) and tetraethoxysilane (TEOS), using cationic surfactant cetyltrimethylammonium bromide (CTAB) as the template. The synthesized silica nanoparticles were observed to possess a mesoporous structure with a uniform pore diameter of 2.7 nm, and to have good stability and high efficiency for U(VI) sorption from aqueous solution. A maximum sorption capacity of 303 mg g(-1) and fast equilibrium time of 30 min were achieved under near neutral conditions at room temperature. The adsorbed U(VI) can be easily desorbed by using 0.1 mol L(-1) HNO(3), and the reclaimed mesoporous silica can be reused with no decrease of sorption capacity. In addition, the preconcentration of U(VI) from a 100 mL aqueous solution using the functionalized mesoporous silica was also studied. The preconcentration factor was found to be as high as 100, suggesting the vast opportunities of this kind of mesoporous silica for the solid-phase extraction and enrichment of U(VI).

Efficient removal of uranium from aqueous solution by zero-valent iron nanoparticle and its graphene composite

Zero-valent iron nanoparticle (ZVI-np) and its graphene composites were prepared and applied in the removal of uranium under anoxic conditions. It was found that solutions containing 24 ppm U(VI) could be completely cleaned up by ZVI-nps, regardless of the presence of NaHCO3, humic acid, mimic groundwater constituents or the change of solution pH from 5 to 9, manifesting the promising potential of this reactive material in permeable reactive barrier (PRB) to remediate uranium-contaminated groundwater. In the measurement of maximum sorption capacity, removal efficiency of uranium kept at 100% until C0(U) = 643 ppm, and the saturation sorption of 8173 mg U/g ZVI-nps was achieved at C0(U) = 714 ppm. In addition, reaction mechanisms were clarified based on the results of SEM, XRD, XANES, and chemical leaching in (NH4)2CO3 solution. Partially reductive precipitation of U(VI) as U3O7 was prevalent when sufficient iron was available; nevertheless, hydrolysis precipitation of U(VI) on surface would be predominant as iron got insufficient, characterized by releases of Fe(2+) ions. The dissolution of Fe(0) cores was assigned to be the driving force of continuous formation of U(VI) (hydr)oxide. The incorporation of graphene supporting matrix was found to facilitate faster removal rate and higher U(VI) reduction ratio, thus benefitting the long-term immobilization of uranium in geochemical environment.

Mesoporous silica SBA-15 functionalized with phosphonate and amino groups for uranium uptake

Mesoporous silicas have a very attractive ability of sorption and enrichment of metal ions due to their huge surface area and facile functionalization by organic ligands. In this work, phosphonate-amino bifunctionalized mesoporous silica SBA-15 (PA-SBA-15) as U(VI) sorbent was fabricated through post-grafting method. The obtained mesoporous silica was characterized by SEM, XRD, NMR and nitrogen sorption/desorption experiments, which revealed the existence of ordered mesoporous structure with uniform pore diameter and large surface area. The adsorptivity of PA-SBA-15 for U(VI) from aqueous solution was investigated using batch sorption technique under different experimental conditions. The preliminary results show that the U(VI) sorption by PA-SBA-15 is very quick with equilibrium time of less than 1 h, and the U(VI) uptake is as large as 373 mg/g at pH 5.5 under 95 °C. The sorption isotherm has been successfully modeled by the Langmuir isotherm, suggesting a monolayer homogeneous sorption of U(VI) in PA-SBA-15. The sorption is pH-dependent due to the pH-dependent charge of sorbent in the aqueous solution. The thermodynamics research shows that the sorption is a feasible and endothermic process. Based on these results, PA-SBA-15 could be a promising solid phase sorbent for highly-efficient removal of U(VI) ions from waste water and enrichment of U(VI) from a solution at a very low level.

Introduction of bifunctional groups into mesoporous silica for enhancing uptake of thorium(IV) from aqueous solution.

The potential industrial application of thorium (Th), as well as the environmental and human healthy problems caused by thorium, promotes the development of reliable methods for the separation and removal of Th(IV) from environmental and geological samples. Herein, the phosphonate-amino bifunctionalized mesoporous silica (PAMS) was fabricated by a one-step self-assembly approach for enhancing Th(IV) uptake from aqueous solution. The synthesized sorbent was found to possess ordered mesoporous structures with uniform pore diameter and large surface area, characterized by SEM, XRD, and N2 sorption/desorption measurements. The enhancement of Th(IV) uptake by PAMS was achieved by coupling of an access mechanism to a complexation mechanism, and the sorption can be optimized by adjusting the coverage of the functional groups in the PAMS sorbent. The systemic study on Th(IV) sorption/desorption by using one coverage of PAMS (PAMS12) shows that the Th(IV) sorption by PAMS is fast with equilibrium time of less than 1 h, and the sorption capacity is more than 160 mg/g at a relatively low pH. The sorption isotherm has been successfully modeled by the Langmuir isotherm and D-R isotherm, which reveals a monolayer homogeneous chemisorption of Th(IV) in PAMS. The Th(IV) sorption by PAMS is pH dependent but ionic strength independent. In addition, the sorbed Th(IV) can be completely desorbed using 0.2 mol/L or more concentrated nitric acid solution. The sorption test performed in the solution containing a range of competing metal ions suggests that the PAMS sorbent has a desirable selectivity for Th(IV) ions.

Exploring Actinide Materials Through Synchrotron Radiation Techniques

Synchrotron radiation (SR) based techniques have been utilized with increasing frequency in the past decade to explore the brilliant and challenging sciences of actinide-based materials. This trend is partially driven by the basic needs for multi-scale actinide speciation and bonding information and also the realistic needs for nuclear energy research. In this review, recent research progresses on actinide related materials by means of various SR techniques were selectively highlighted and summarized, with the emphasis on X-ray absorption spectroscopy, X-ray diffraction and scattering spectroscopy, which are powerful tools to characterize actinide materials. In addition, advanced SR techniques for exploring future advanced nuclear fuel cycles dealing with actinides are illustrated as well.

Loading Actinides in Multilayered Structures for Nuclear Waste Treatment: The First Case Study of Uranium Capture with Vanadium Carbide MXene

Efficient nuclear waste treatment and environmental management are important hurdles that need to be overcome if nuclear energy is to become more widely used. Herein, we demonstrate the first case of using two-dimensional (2D) multilayered V2CTx nanosheets prepared by HF etching of V2AlC to remove actinides from aqueous solutions. The V2CTx material is found to be a highly efficient uranium (U(VI)) sorbent, evidenced by a high uptake capacity of 174 mg g(-1), fast sorption kinetics, and desirable selectivity. Fitting of the sorption isotherm indicated that the sorption followed a heterogeneous adsorption model, most probably due to the presence of heterogeneous adsorption sites. Density functional theory calculations, in combination with X-ray absorption fine structure characterizations, suggest that the uranyl ions prefer to coordinate with hydroxyl groups bonded to the V-sites of the nanosheets via forming bidentate inner-sphere complexes.

Interactions between Th(IV) and graphene oxide: experimental and density functional theoretical investigations

Graphene oxide (GO) has been receiving increasing research efforts in recent years because of its wide applications in various scientific fields. In this work the sorption of Th(IV) onto graphene oxide (GO) was studied using a batch method under ambient conditions. The sorption kinetics were found to be fast and fitted the pseudo-second-order model very well, with an equilibrium time of about 10 min. The sorption is strongly dependent on the solution pH but independent of the ionic strength of the solution. The maximum sorption capacity of as high as 214.6 mg g−1 can be achieved at pH 2.60 ± 0.05, and Th(IV) can be desorbed readily from the GO with 1.0 M HNO3. The thermodynamic investigations revealed that the sorption of Th(IV) on the GO was an endothermic and spontaneous process. The Scanning Electron Microscopy (SEM) results indicated obvious surface morphology changes of the GO induced by Th(IV) sorption. Furthermore, the interaction mechanism of Th(IV) and the GO was investigated by infrared (IR) spectroscopy and extended X-ray absorption fine structure (EXAFS) spectroscopy combined with density functional theory (DFT) calculations. The results of EXAFS indicated that Th(IV) was bonded to ∼8 or 9 oxygen atoms and the average bond length of Th–O was estimated to be ∼2.45 A in the first coordination shell. The DFT calculations further confirm the rationality of experimental and the EXAFS results. This work demonstrates the tremendous potential opportunities offered by GO in pre-concentration and removal of thorium and other tetravalent actinides for the recovery and remediation of the environment.

Nanomaterials and nanotechnologies in nuclear energy chemistry

Abstract With the rapid growth of human demands for nuclear energy and in response to the challenges of nuclear energy development, the world’s major nuclear countries have started research and development work on advanced nuclear energy systems in which new materials and new technologies are considered to play important roles. Nanomaterials and nanotechnologies, which have gained extensive attention in recent years, have shown a wide range of application potentials in future nuclear energy system. In this review, the basic research progress in nanomaterials and nanotechnologies for advanced nuclear fuel fabrication, spent nuclear fuel reprocessing, nuclear waste disposal and nuclear environmental remediation is selectively highlighted, with the emphasis on Chinese research achievements. In addition, the challenges and opportunities of nanomaterials and nanotechnologies in future advanced nuclear energy system are also discussed.