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The direct detection method possesses the ability of both content detection of uranyl ions and structural analysis of uranyl compounds in nmol level, while the indirect detection method can detect the uranyl ions as low as fmol level.

In this paper, two kinds of composites constructed by UO3 nanoflakes (which is UO3·yNH3·xH2O, precisely) and different graphene oxide (GO) nanosheets (homemade GO, GO-h, and commercial GO, GO-c) were prepared via solution chemical reaction. The two kinds of GO share similar morphology and possess the same species of functional groups. Nevertheless, GO-h possesses higher oxidization degree and thus could adsorb more uranyl ions, and the corresponding composite shows a much more regular shape: UO3 nanoflakes and GO nanosheets cross each other, which would help overcome the disadvantage of graphene aggregation. As a result, homemade reduced graphene oxide (RGO-h) sheets inside the final UO2 pellets (named as UO2/GO-h) could construct a well-bulit thermally conductive network to enhance its thermal conductivity. However, similar RGO-c network cannot be observed in the UO2/GO-c pellest originated from GO-c. Therefore, only the thermal conductivity of UO2/GO-h pellet acquires a dramatic increase, 37.30% relative to UO2 pellet at 1200 °C, showing that UO2/GO-h possesses great potential for the development of novel UO2-based ATF fuels.

In this study, a novel UO2/SiC nanocomposite pellet was constructed via in-situ hydrothermal synthesis and SPS. Such method could avoid the problem of traditional mechanical mixing that could obtained the molecular level mixing during a chemical process. Using such method, SiC was dispersed uniformly in the UO2 matrix. Its thermal conductivity is significantly higher than those of UO2 pellet fabricated using hydro-thermally prepared powder and traditional UO2 pellets at both working temperature (400 °C) and near-accident temperature (1000 °C). The thermal conductivity of UO2/SiC nanocomposite pellet increased 23.7 % over traditional UO2 and 48.9 % over UO2 pellet fabricated using hydro-thermally prepared powder at 400 °C. It also increased 33.6 % over traditional UO2 and 74.8 % over UO2 pellet fabricated using hydro-thermally prepared powder at 1000 °C. These advantages are expected to maintain high thermal conductivity of fuels, enhance heat transferring efficiency of reactors, and minimize risks of pellet failure in the entire fuel life cycle.

Charge-transfer (CT) is an important enhancement mechanism in the field of surface-enhanced Raman scattering (SERS) that typically increases the Raman intensity of molecules by as much as 10-100 times. Herein, a low-cost Ag2O aggregates substrate was prepared via a facile chemical precipitation method, and the calculated CT-based enhancement factor of the uranyl ions adsorbed on it reached as high as 105, a metal-comparable value. The efficient photoinduced CT process from the valence band of Ag2O to the LUMO of uranyl ions under appropriate excitation sources resulted in the repulsion of the axial oxygen atoms of the O U O bond, which enhanced its polarizability, creating a more intense Raman mode. To the best of our knowledge, this study firstly reports such a strong photoinduced CT enhancement of uranyl ions, with concentrations of 10−8 mol L−1 or lower being detected using this Ag2O substrate. Most importantly, this research has shown that the photoinduced CT enhancement also contributes to the SERS of uranyl ions on pure Ag substrates which have often been ascribed to the electromagnetic enhancement in previous studies. In addition, Ag2O can be used to selectively detect uranyl ions without interference from many other molecules or ions because of the energy matching rule of the photoinduced CT process, which was readily available for uranyl detection in the environmental aqueous solution.

Three (3,4)-connected uranyl-organic frameworks (UOFs) with pto and tbo topologies were synthesized. The UOF with a pto net possesses a 2-fold interpenetrating network and exhibits 2D interconnected channels. The UOF with a tbo net is constructed from two types of ultralarge nanocages. All these compounds can efficiently remove large cationic dye crystal violet (CV) through a cation exchange mechanism.

In this article, a novel method to synthesize graphene quantum dots was developed via thermal treatment of crude graphite oxide (GO) in a dry and alkaline condition to cut the crude GO sheets into small graphene quantum dots (named as aGQDs). The aGQDs are nano-scale reduced graphene oxide pieces with the sizes around 5–10 nm. The aGQDs could disperse in water for their richment of oxygen-containing groups. The fluorescence properties were carefully investigated. The aGQDS aqueous solution shows a bright yellow-green fluorescence under the UV illumination. Besides, the uranyl ions show a strong fluorescence quenching effect on the a aGQD aqueous solution even at a low concentration (~10−7 M) compared with other common ions in natural water-body, which makes that these aGQDs could be applied as a chemosensor for detection of uranyl ions with good sensitivity and selectivity., Analytical chemistry; Environmental science; Materials science; Graphene dots; Uranyl; Detection; Fluorescence quenching

In this study, a novel signal-increase electrochemiluminescence (ECL) biosensor has been developed for the detection of glucose based on graphene quantum dot/glucose oxidase (GQD/GO x ) on Ti foil. The proposed GQD with excellent ECL ability is synthesized through a green one-step strategy by the electrochemical reduction of graphene oxide quantum dot. Upon the addition of glucose, GO x can catalytically oxidize glucose and the direct electron transfer between the redox centre of GO x and the modified electrode also has been realized, which results in the bio-generated H 2 O 2 for ECL signal increase in GQD and realizes the direct ECL detection of glucose. The signal-increase ECL biosensor enables glucose detection with high sensitivity reaching 5 × 10 −6 mol l −1 in a wide linear range from 5 × 10 −6 to 1.5 × 10 −3 mol l −1 . Additionally, the fabrication process of such GQD-based ECL biosensor is also suitable to other biologically produced H 2 O 2 system, suggesting the possible applications in the sensitive detection of other biologically important targets (e.g. small molecules, protein, DNA and so on).

Figure S1 A) CVs of the electrolysis of 1.0 mg mL−1 GOQD at a scan rate of 50 mV s−1; B) CVs of Ti foil after GOQD electrolysis in 0.067 M pH~7 PBS.;Figure S2 FTIR spectra of GQD and GOQD.;Figure S3 Raman spectra of GQD and GOQD.;Figure S4 XPS spectra of (A) GOQD and (B) GQD.;Figure S5 Photoluminescence spectra of GOQD/Ti foil, GQD/Ti foil and the supernatant after centrifugation of the GQD/Ti foil.

SERS has been used for rapid and trace analysis of uranyl compounds due to its fast response and high sensitivity. However, the difficulties in preparing stable and reusable SERS substrate as well as quantitative detection severely restrict its practical application prospects. Herein, HfO2-wrapped slanted Ag nanorods array was used as SERS substrate for sensitive analysis of trace uranyl compounds for the first time. The proposed substrate with uniform surface roughness and well-distributed Ag nanorods showed excellent spectral reproducibility, while the ultrathin HfO2 film fully covering Ag nanorods effectively improved the substrate stability and contributed to its cyclic utilization. Besides, quantitative detection of trace uranyl ions was achieved by using this substrate with an ultra-low detection limit of 8.33 ppb. Most importantly, SERS spectra of varied uranyl hydroxides at different pH values together with in situ SERS spectrum of U O 2 ( C O 3 ) 3 4 − were recorded on this substrate, building the correspondence between SERS band position of O U O(ν1) and uranyl species. Thus, SERS technique based on this substrate could be a promising method for both concentration detection of uranyl ions and structure identification of some uranyl compounds in trace level, indicating high potential application prospects in the environmental monitoring.

The solid reaction of lithium hydride and lithium hydroxide in lithium hydride pellet is first directly observed at normal ambient condition after 4 years storage. Layer-by-layer XPS results show that LiOH hydrolysis layer quickly forms on the LiH surface, LiOH reacts with bulk LiH to form Li2O and H2. Due to the great H2 outgassing after long time conservation, bubbling problem actually exists during the practical long-time preserving period. Using CO2 as pre-treatment gas during the LiH sample preparation process is a feasible way to prevent LiH sample from bubbling after long storage period. Moreover, Li2CO3 shows possible delay effect on the solid reaction of LiOH with LiH in this work, thus preserving LiH sample in CO2 containing atmosphere might also be an prospective way to protect the sample from further corrosion.

Graphite flakes (GFs) were introduced into UO2 via spark plasma sintering to improve its thermal conductivity (TC). The effect of GFs on the sintering behavior and TC of GFs/UO2 was systematically investigated. GFs/UO2 composites exhibited a highly oriented structure; thus, the radial TC was significantly higher than the axial TC. GFs/UO2 was crack-free below a sintering temperature of 1673 K. At higher temperatures, some cracks were formed owing to the reaction at the interface. Accordingly, the radial TC of GFs/UO2 reached its peak value at 1673 K. The radial TC presented a nearly linear relationship with the GF fraction. The radial TC of GFs/UO2 composites was averagely improved by 340% from 298 to 1273 K with 15 vol.% GFs addition. The radial TC continuously increased with the diameter of the GFs. In contrast, the volume fraction and diameter of the GFs had a relatively inconspicuous effect on the axial TC. This was attributed to the thermal resistance of the interface and deflection of GFs from the radial direction.

A flexible adhesive tape decorated with SERS-active silver nanorods (AgNRs) in the form of an array nanostructure is described. The tape was constructed by transferring the AgNRs nanostructures from silicon to the transparent tape by a “paste & peel off” procedure. The transparent, sticky, and flexible properties of commercial tapes allow almost any SERS-inactive irregular surface to be detected in-situ by pasting the SERS tape onto the position to be analyzed. Three examples for an analytical application are presented, viz. determination of (a) tetramethylthiuram disulfide and thiabendazole (two pesticides), (b) colorants in the gel of a writing pen, and (c) the fluorophore Rhodamine B. The tetramethylthiuram disulfide on apple surface was rapidly detected with a LOD of 28.8 ng·cm−2. The AgNRs effectively quenched the fluorescence of the matrix and fluorophores, this enabling the colorants and Rhodamine B to be identified. The results demonstrated that the SERS tape can be used for versatile in-situ detection. Conceivably, it may find applications in food analysis, non-invasive identification, environmental monitoring, and in other areas of daily life.

In order to increase the radial thermal conductivity (TC) of UO2 pellets, highly-oriented graphite flakes (GFs) were first introduced to UO2 pellets by spark plasma sintering. The radial TC of GFs/UO2 agreed well with Hatta-Taya model, which was closely related to the well-bonded interface and highly-oriented structure. Compared with UO2, the radial TC of GFs/UO2 was greatly improved by about 200 % within a wide temperature range, higher than all the other reported value until now. Such enhancement in TC would significantly improve the safety of UO2 fuel pellets.

U3O8, the most stable state of uranium oxides, is a key intermediate compound for pyroprocessing of used nuclear fuel. However, compared to UO2, the electro-deoxidation mechanism of U3O8 is still cursory due to the complicated U-O intermediate phases. In this paper, the electro-deoxidation processes of U3O8 were investigated via diverse methods. A molybdenum metallic cavity electrode loaded with U3O8 powder was adopted to investigate the electrochemical behavior via cyclic voltammetry and square wave voltammetry. Sintered U3O8 pellets were used as cathodes to obtain electrolytic products with varying applied voltages or duration time. The composition and microstructure of electrolytic products were characterized by Raman spectroscopy, X-ray diffraction, scanning electron microscope and energy dispersive spectrometer. Based on above analysis results, electro-reduction processes of porous U3O8 pellets were proposed. First, U3O8 undergoes a rapid transition to U4O9 (U4O9-y). Then, the intermediate compound was gradually reduced to UO2 from the outer layer to the center of the bulk due to the limited migration rate of O2−. Before the transformation completed, metallic U generated on the surface of the bulk through direct electro-deoxidation and Li metal thermal reduction. With the increase of porosity and the propagation of metal-oxide-electrolyte three-phase interline, the U3O8 pellet was finally reduced to metallic U bulk.

To precisely determine uranium in aqueous solution, we combined the synthesis of gold nanoparticles (AuNPs) with stripping voltammetry to develop a new electrochemical detection method with high sensitivity toward uranyl ions on account of its enrichment by deposition and determination by stripping. The uranyl was reduced and deposited on the surface of the electrode followed up with a stripping process catalyzed by AuNPs to determine the concentration of uranyl ions. The experimental parameters, such as pH, deposition potential and time were optimized. Under optimal conditions, the stripping voltammetry response of the modified electrode to uranyl shows a linear relationship with the concentration from 2.4 μg L−1 to 48 μg L−1 and 48 μg L−1 to 480 μg L−1, respectively. The AuNPs based electrode could be used to determine the concentration of uranyl ion in a few minutes with a detection limit of 0.3 μg L−1. The reproducibility and reliability of the electrode were also evaluated with good results. Finally, the proposed procedure was successfully applied to the determination of uranyl ions in natural water. This method is potentially applicable for the on-site environmental analysis.

In this paper, g-C3N4/GR hybrid has been prepared by a novel one-step electrochemical reduction technology for the first time. GR not only serves as immobilization platform for g-C3N4, but also significantly enhances the electrochemiluminescence (ECL) signal of g-C3N4 (∼4.7 times); additionally, the ECL signal can be further enhanced in the presence of the self-produced coreactant from oxygen reduction. Moreover, due to the quenching effect of pentachlorophenol (PCP) on the ECL signal of g-C3N4/GR, an advanced ECL sensor based on g-C3N4/GR has been fabricated for the ultrasensitive and rapid detection of PCP with unprecedented sensitivity reaching 1.0 × 10−11 mol L−1 in a wide linear range from 1.0 × 10−11 to 1.0 × 10−7 mol L−1, and the possible ECL detection mechanism has been proposed in detail. The practicability of the sensing platform in real water sample shows ideal recovery rates. Moreover, we also find that the one-step electrodeposition technology might be a good and viable way to make the bulk g-C3N4 thinner. Our experiments display the powerful utility of GR to g-C3N4 ECL studies and will emerge eximious applications in analytical communities and environmental monitoring.

We report on the facile, reliable fabrication of novel magnetic cucurbit[6]uril/graphene oxide (CB[6]/GO/Fe3O4) composite by using an in-situ co-precipitation method, for which the formation process and possible formation mechanism were also investigated. Moreover, the composite was used as an adsorbent for the removal of uranium(VI) from aqueous solution. Herein, GO nanosheets were chosen as a substrate to immobilize CB[6] and Fe3O4. During the co-precipitation of Fe3O4 nanoparticles on surface of GO nanosheets, CB[6] molecules was fixed through hydrogen bonding simultaneously. The as-prepared composite exhibited a high efficiency of magnetic separability, competitive adsorption performance and acceptable reusability and stability for U(VI) removal, indicating a potential application in uranium-bearing wastewater treatment.

This study aims to understand the complexation of U(VI) with oxydiacetic acid (ODA), iminodiacetic acid (IDA) and thiodiacetic acid (TDA) through density functional theory (DFT) calculations. The structures, complexation stabilities and bonding nature were investigated for U(VI)/XDA complexes (XDA is short for the three ligands). The calculations have proved that tridentate structures are more favorable than terminal bidentate ones for all stoichiometries, and steric hindrance is a factor that cannot be ignored especially for 1:2 complexes. The binding stabilities of the ligands and relative binding groups are in the sequences IDA > ODA ≫ TDA and CO > OH− ≫ H2O > X (Oether, N and S), respectively. All of the coordination bonds exhibit typically ionic character. The coordination bonds are mainly contributed by the interactions of U 5f-orbital and O(C)/X p-orbitals. The strength of all coordination bonds follows the order U–O(C) > U–N > U–O(H2) ≈ U–Oether > U–S. U–S interaction was solidly confirmed by MO and AIM analysis, which is found for U(VI)/TDA complexes for the first time. U–X bonds play an important role in U(VI)/XDA coordination.

Persistent organic pollutants (POPs) are key pollutants due to their persistence, refractory biodegradation, high toxicity and bioaccumulation in the food chain. This review (with 93 refs.) covers the progress made in the past decades in the application of carbonaceous materials for electrochemical detection of POPs as listed in the Stockholm Convention. Following an introduction into the field, typical carbonaceous materials for use in electrodes are discussed, with subsection on carbon nanotubes, graphene, reduced graphene oxide, graphitic carbon nitride and carbon dots. This is followed by a section on application of carbonaceous materials in electrochemical detection, with subsections on the use of carbon nanotubes, of (doped-) graphene, of reduced graphene oxide, of graphitic carbon nitride, and of carbon dots. The review concludes with conclusions and future perspectives. The detection mechanisms of POPs are also discussed. Graphical abstract Advanced carbonaceous materials for the electrochemical determination of persistent organic pollutants.

Here for the first time, we present a novel electrochemiluminescence (ECL) sensor based on graphitic carbon nitride/graphene oxide (g-C3N4/GO) hybrid for the ultrasensitive detection of Cu(2+), which is a common pollutant in environmental system. The g-C3N4/GO shows stable ECL signal in the presence of the self-produced coreactant from oxygen reduction, and the ECL signal could be effectively quenched by Cu(2+), the possible ECL detection mechanism has been proposed in detail. GO can not only significantly enhance the cathodic ECL signal of g-C3N4 (∼3.8 times), but also serve as immobilization platform for g-C3N4. After optimization of experimental conditions, the proposed protocol can offer an ultrasensitive, highly selective and recyclable method for the detection of Cu(2+) with a low detection limit of 1.0 × 10(-11) M and a wide linear range from 1.0 × 10(-11) to 1.0 × 10(-7) M. Moreover, the practicability of the ECL sensor in real wastewater samples is also tested, showing that the proposed ECL sensor could be a promising alternative method for the emergency and routine monitoring of Cu(2+) in real sample.

A facile surface-enhanced Raman scattering (SERS) substrate based on the self-assembly of silver nanoparticles on the modified silicon wafer was obtained, and for the first time, an advanced SERS analysis method basing on this as-prepared substrate was established for high sensitive and rapid detection of uranyl ions. Due to the weakened bond strength of OUO resulting from two kinds of adsorption of uranyl species ("strong" and "weak" adsorption) on the substrate, the ν1 symmetric stretch vibration frequency of OUO shifted from 871cm-1 (normal Raman) to 720cm-1 and 826cm-1 (SERS) along with significant Raman enhancement. Effects of the hydrolysis of uranyl ions on SERS were also investigated, and the SERS band at ~826cm-1 was first used to approximately define the constitution of uranyl species at trace quantity level. Besides, the SERS intensity was proportional to the variable concentrations of uranyl nitrate ranging from 10-7 to 10-3molL-1 with an excellent linear relation (R2=0.998), and the detection limit was ~10-7molL-1. Furthermore, the related SERS approach involves low-cost substrate fabrication, rapid and trace analysis simultaneously, and shows great potential applications for the field assays of uranyl ions in the nuclear fuel cycle and environmental monitoring.

Some important thermal properties of both PuO2 and α-Pu2O3 have been investigated by atomic simulation between 298 K and 1500 K using BMH empirical potential and shell potential, including thermal expansion coefficient, entropy, heat capacity and enthalpy. The BMH empirical potential of Pu–O bond in α-Pu2O3 was fitted by GULP program. The calculated values are in good agreement with the experimental data for PuO2, shows that the parameters we selected are appropriate. But especially for α-Pu2O3, these thermal properties were too difficult to be truly measured in experiments because of its radio-toxicity and the high chemical activity. So we could not evaluate our calculated results accurately.

We perform first-principles calculations of electronic structure and optical properties for UO2 and PuO2 based on the density functional theory using the generalized gradient approximation (GGA)+\emph{U} scheme. The main features in orbital-resolved partial density of states for occupied \emph{f} and \emph{p} orbitals, unoccupied \emph{d} orbitals, and related gaps are well reproduced compared to experimental observations. Based on the satisfactory ground-state electronic structure calculations, the dynamical dielectric function and related optical spectra, i.e., the reflectivity, adsorption coefficient, energy-loss, and refractive index spectrum, are obtained. These results are consistent well with the attainable experiments., Comment: 6 pages, 4 figures

Uranium dioxide films were deposited on Si (1 1 1) substrates by dc magnetron sputtering method at different sputtering parameters. The structure, morphology and chemical state of the films were studied by field emission scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy and atomic force microscopy. Influences of film thickness on the microstructure and optical properties were investigated. Experimental results show that the film crystallites are preferentially oriented with the (1 1 1) planes. The average grain size increases with increasing film thickness. AFM images show that the root mean square roughness of the films is between 1.2 nm and 2.1 nm. Optical constants (refractive index, extinction coefficient) of the films in the wavelength range of 350–1000 nm are obtained by ellipsometric spectroscopy. The result shows that the refractive index decreases with the increasing film thickness, while extinction coefficient increases with the film thickness.