Search

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).

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.

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.