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Photostability of oxygen-sensitive core-shell nanofibers
摘要： Core-shell electrospun nanofibers constitute a vehicle enabling novel uses for phosphorescent oxygen-sensitive molecules. In this work, we investigate compositional parameters and other factors governing fiber design appropriate to long-term sensor applications. These nanofibers contain an oxygen-sensitive palladium (II) porphyrin species within a polysulfone core; an outer polycaprolactone shell protects the core from the surrounding environment. The presence of a core-shell architecture was confirmed using advanced time-of-flight secondary ion mass spectrometry (ToF-SIMS). Although these sensors exhibit excellent photostability in the short-term, long-term exposures (up to 1,000 hr) are shown to detrimentally impact performance via photobleaching phenomenon. We also investigated higher porphyrin concentrations to determine whether the resulting sensors are predisposed to photobleaching. High porphyrin loadings (up to 10 wt%) could be successfully incorporated into the core. While increased probe content should logically enhance emission intensity, we sought to investigate the balance between a stronger signal and the potential for decreased photostability. The resulting behavior is rationalized by (1) establishing the spacing associated with a ‘perfect’ molecular dispersion and (2) invoking five distinct populations of porphyrin agglomeration. Populations that are not molecularly dispersed experience varying degrees of agglomeration-catalyzed photobleaching. The photobleaching rate increases with the extent of agglomeration and, therefore, the initial porphyrin content. Although it is demonstrated that low porphyrin loadings exhibit improved photobleaching resistance, the initial brightness is inadequate. In contrast, enhanced brightness via increased porphyrin content also leads to diminishing returns due to the apparent emergence of a self-quenched population. For a given application, selection of an appropriate porphyrin concentration is critical to achieving a compromise between initial brightness and photobleaching resistance. Detector sensitivity and anticipated duration of use must be considered when weighing the relative benefits of these attributes and selecting a specific porphyrin content.
关键词： Core-shell electrospinning,electrospun nanofiber,agglomeration,porphyrin,oxygen sensing
更新于2025-09-09 09:28:46
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Effect of thickness of Cr layer on Ag cocatalyst surface for highly selective photocatalytic conversion of CO <sub/>2</sub> by H <sub/>2</sub> O
摘要： In this study, we developed a Ag–Cr core–shell-structured (Ag@Cr) cocatalyst that modified the surface of the Ga2O3 photocatalyst. Compared to results provided by modifications with Ag cocatalysts and M–Cr dual cocatalysts (M = Au, Cu, Pd, and Pt), this change significantly improved the formation rate of CO and selectivity toward CO evolution in the photocatalytic conversion of CO2 by the electron donor H2O. As a result of this modification, the Cr(OH)3?xH2O shell changed to Cr(OH)x(CO3)y during the photocatalytic conversion. Furthermore, the thickness of the Cr(OH)3?xH2O shell was found to influence the photocatalytic performance. More specifically, Cr(OH)3?xH2O shells that were too thick or too thin were not beneficial to the CO evolution and suppression of H2 evolution. Notably, the highest photocatalytic activity (525.3 μmol h?1), selectivity toward CO evolution (85.2 %), and turnover number of CO to Ag (167) was achieved over 0.25 mol% (Ag@Cr)/Ga2O3. In addition to Ga2O3, the Ag@Cr cocatalyst modification strategy can also be applied to other photocatalyst materials such as NaTaO3, ZnGa2O4, and ZnGa2O4/Ga2O3 for the highly effective photocatalytic conversion of CO2 to CO when using H2O as an electron donor.
关键词： carbon dioxide,chromium hydroxide,Photocatalysis,core–shell structure,Ag cocatalyst
更新于2025-09-09 09:28:46
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Characterization and Photocatalytic Performance of Potassium-Doped Titanium Oxide Nanostructures Prepared via Wet Corrosion of Titanium Microspheres
摘要： Potassium doped titanium oxide (KTiOx) nanowires were prepared by the wet corrosion process (WCP) and their photocatalytic effects were systematically characterized. For the synthesis of KTiOx, the potassium hydroxide concentration of the WCP was varied in order to obtain nanostructures with different surface area and surface charge. Structural and crystalline properties of KTiOx were studied by means of X-ray diffraction, scanning and transmission electron microscopy. Chemical composition was determined by X-ray fluorescence and energy-dispersive X-ray analysis. Photocatalytic performance was investigated as a function of the surface area, pH, and crystalline structures by studying the degradation of methylene blue, cardiogreen, and azorubine red dyes upon UV irradiation. The negatively charged crystalline KTiOx nanostructures with high surface area showed significantly higher photocatalytic degradation compared to their TiOx counterpart. They also showed high efficiency for recovery and re-use. Annealing KTiOx nanostructures improved structural properties leading to well-ordered layered structures and improved photocatalysis. However, annealing at temperatures higher than 600 °C yielded formation of rutile grains at the surface of nanowires, significantly affecting the photocatalytic performance. We believe that KTiOx nanostructures produced by WCP are very promising for photocatalysis, especially due to their high photocatalytic efficiency as well as their potential for re-use and durability.
关键词： Titanium Core Shell,KTiOx,Wet Corrosion Process,Photocatalysis,Nanostructures
更新于2025-09-09 09:28:46
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Probing Energy Migration through Precise Control of Interfacial Energy Transfer in Nanostructure
摘要： A novel mechanistic strategy for probing the energy migration through constructing the interfacial energy transfer (IET) in a core–shell–shell nanostructure is reported. In this design, the trilayer nanostructure is composed of a sensitizing core, a migratory interlayer, and a detective shell layer that interact with each other only by IET and the latter two shell layers are nonresponsive to the incident irradiation. This model is well applied in investigating the energy migration over the Tb, Gd, and Yb sublattices, and the results show that the Gd sublattice holds the best energy migratory performance. Moreover, the finding of energy migration over the Yb sublattice enables the 808 nm excited long-lived upconversion of Tb3+ and Eu3+, which exhibits unique time-gating performance for information security. The results provide a facile and powerful nanosized model for an in-depth understanding of the fundamentals involving lanthanide interactions, which will further help excite new chances for the frontier applications of lanthanide-based luminescent materials.
关键词： mechanistic study,core–shell–shell nanostructure,energy migration,interfacial energy transfer
更新于2025-09-04 15:30:14
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Resonant Plasmon-Enhanced Upconversion in Monolayers of Core-Shell Nanocrystals: Role of Shell Thickness
摘要： The upconversion luminescence (UCL) of colloidal lanthanide-doped upconversion nanocrystals (UCNCs) can be improved either by precise encapsulation of the surface by optically inert shells around the core, by an alteration of the nearby environment via metal nanoparticles, or by a combination of both. Considering their potential importance in crystalline silicon photovoltaics,the present study investigates both effects for two-dimensional arrangements of UCNCs. Using excitation light of 1500 nm wavelength, we study the variation in the upconversion luminescence from an Er3+-doped NaYF4 core as a function of the thickness of a NaLuF4 shell in colloidal solutions as well as in spin-cast-assisted self-assembled monolayers of UCNCs. The observed UCL yields and decay times of Er3+ ions of the UCNCs increase with increasing shell thickness in both cases, and nearly no variation in decay times is observed in the transition of the UCNCs from solution to film configurations. The luminescence efficiency of the UCNC monolayers is further enhanced by electron-beam-lithographic-designed Au-nanodiscs deposited either on top or buried within of the monolayer. It is observed that the improvement by the nanocrystal shells is greater than that of the Au-nanodiscs.
关键词： shell thickness,core-shell nanocystals,monolayer,upconversion,Plasmon enhancement
更新于2025-09-04 15:30:14
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Dumbbell to Core–Shell Structure Transformation of Ni–Au Nanoparticle Driven by External Stimuli
摘要： Conversion of CO2 gas to CO fuels is one of the most promising solutions for the increasing threat of global warming and energy crisis. The efficient catalyst Ni–Au dumbbell converting CO2 into CO at elevated temperatures has high CO product selectivity; however, the accompanied atomic diffusion and subsequent surface reconstruction affect the catalytic efficiency of chemical reaction. Atomic scale characterization of structural evolution of the catalyst, which is essential to correlate the functional mechanism to active catalyst surfaces, is yet to be studied. Here, in situ transmission electron microscopy experiments and atomistic simulations are performed to characterize the structural evolution of Ni–Au dumbbell nanoparticles under two different external stimuli. In the condition of high temperature and vacuum, the Ni–Au nanostructure reveals a clear shape reconstruction from the initial dumbbell to core–shell-like, which is induced by capillary force to minimize free surface energy of the system. The shape transformation involves two stages of processes, initial fast Au diffusion followed by slow source-controlled diffusion. At ambient temperature, the combination of CO2 and electron flux surprisingly induces analogous structural transformation of Ni–Au nanostructure, where the associated chemical reaction and CO absorption stimulate the Au migration on Ni surface. Such surface reconstruction can be widely present in catalytic reactions in different environmental conditions, and the results herein demonstrate the detailed processes of Ni–Au structure evolution, which provide important insights for understanding the catalyst performance.
关键词： core–shell,in situ TEM,catalyst,Ni–Au,gas cell
更新于2025-09-04 15:30:14
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Fabrication of Silver-coated Gold Nanoparticles to Simultaneously Detect Multi-class Insecticide Residues in Peach with SERS Technique
摘要： Fast sampling and multicomponent detections are important in the analysis of pesticide residues detection. In this work, surface-enhanced Raman scattering (SERS) method based on silver-coated gold nanoparticles (Au@Ag NPs) was used to simultaneously detect multi-class pesticide residues such as thiacloprid (carbamate), profenofos (organophosphate) and oxamyl (neonicotinoid) in standard solution and peach fruit. The Au@Ag NPs with 26 nm Au core size and 6 nm Ag shell thickness exhibited significant Raman enhancement, especially by the creation of hot spots through NPs aggregation induced by the connection between Au@Ag NPs and target molecules. The findings demonstrated that the characteristic wavenumber of the pesticides (thiacloprid, profenofos, and oxamyl) could be precisely identified using the SERS method. Compared with earlier studies, the current approach was rapid, inexpensive and without lengthy sample pretreatment. Moreover, the results revealed that the limit of detection (LOD) was 0.1 mg/kg for thiacloprid obtained in the peach extract with determination coefficient (R2) of 0.986. Additionally, LOD for both profenofos and oxamyl was 0.01 mg/kg with a determination coefficient (R2) of 0.985 and 0.988, respectively. Good recovery percentage (78.6 to 162.0 %) showed the high SERS activity with better accuracy for the detection of the thiacloprid, profenofos, and oxamyl in peach. The results of this study could offer a promising SERS platform for simultaneous detection of other contaminants such as thiacloprid, profenofos and oxamyl in multifaceted food matrices.
关键词： oxamyl,substrate,fruit,SERS,thiacloprid,simultaneous detection,profenofos,core-shell nanoparticles
更新于2025-09-04 15:30:14
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Controllable coating polypyrrole on silicon carbide nanowires as a core-shell nanostructure: a facile method to enhance attenuation characteristics against electromagnetic radiation
摘要： Continuous polypyrrole (PPy) shells were coated on silicon carbide (SiC) nanowires to form core-shell nanostructures and the thicknesses of the shells were efficiently tuned through controlling the rate of polymerization. Compared with the composites loaded with pure SiC nanowires, the values of ε′ and ε′′ for the composites loaded with PPy@SiC nanowires were strengthened remarkably along with the increased thickness of the shells. The electromagnetic absorption (EA) bandwidth lower than ?10 and ?20 dB can be monitored in the area of 3.67-18.00 and 4.13-18.00 GHz, when 5 wt% of PPy@SiC nanowires were loaded in the composite. Meanwhile, the effective EA bandwidth can reach 6.88 GHz and the strongest reflection loss is ?58.6 dB.
关键词： dielectric properties,polypyrrole,silicon carbide nanowires,core-shell nanostructures,electromagnetic absorption
更新于2025-09-04 15:30:14
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Ag@Fe <sub/>3</sub> O <sub/>4</sub> Core–Shell Surface-Enhanced Raman Scattering Probe for Trace Arsenate Detection
摘要： Developing an effective and reliable method for trace arsenic (As) detection is a prerequisite for improving the safety of drinking water. In this paper, we designed and prepared Ag@Fe3O4 core–shell nanoparticles (NPs), which were then used as Surface-Enhanced Raman Scattering (SERS) probe for trace arsenate (As(V)) detection. The Ag@Fe3O4 core–shell NPs were prepared by in situ growth of Fe3O4 NPs on the surface of AgNPs, which can effectively combine the strong adsorption ability of Fe3O4 nanoshells to As(V) with high SERS activity of Ag nanocores to decrease the detection limit. By use of Ag@Fe3O4 core–shell NPs for As(V) detection, the detection limit can be as low as 10 (cid:2)g/L, and a good linear relationship between the SERS intensity of As(V) and their concentrations in the range from 10 to 500 (cid:2)g/L was achieved. Furthermore, Ag@Fe3O4 core–shell NPs could be regenerated through desorption of As(V) from Fe3O4 nanoshells in NaOH solution, and then used for recyclic SERS detection. Therefore, it has been demonstrated for the ?rst time that multifunctional Ag@Fe3O4 core–shell SERS probe could be applied to realize the highly sensitive and reversible detection of As(V).
关键词： Drinking Water,Core–Shell,Fe3O4,Heavy Metals,Trace Detection
更新于2025-09-04 15:30:14
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[IEEE 2018 XXIIIrd International Seminar/Workshop on Direct and Inverse Problems of Electromagnetic and Acoustic Wave Theory (DIPED) - Tbilisi, Georgia (2018.9.24-2018.9.27)] 2018 XXIIIrd International Seminar/Workshop on Direct and Inverse Problems of Electromagnetic and Acoustic Wave Theory (DIPED) - Magnetometry and NMR Study of Carbon Nanopowders Doped with Cobalt Nanoclusters and Self-assembly of their Polymer Nanocomposites under Magnetic Field
摘要： The RF resonant magnetometry and NMR studies were carried out on carbon nanoparticles doped with magnetic cobalt clusters, which were synthesized by a technology combining of the hydrocarbon vapor pyrolysis and the chemical vapor deposition (CVD) process in a horizontal continuous reactor. The RF resonant magnetometry data show that the obtained carbon cobalt nanopowders are superparamagnetic at room temperatures and ferromagnetic at liquid nitrogen temperatures. The NMR study with the excitation by additional magnetic video-pulses of nanopowders obtained by using different hydrocarbons pyrolysis made it possible a fast assessment of their magnetic phase and hardness properties. The simple non-contact RF resonant magnetometry study of self-assembling processes in carbon cobalt polymer composite films synthesized using these nanopowders was made also.
关键词： magnetic nanoclusters,carbon nanopowder,core-shell structure,self-assembly,NMR,cobalt
更新于2025-09-04 15:30:14