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1.
We report the results of investigation of the interaction of silver with presynthesized ZnS nanoparticles (NPs) that was stabilized
by cetyl trimethyl ammonium bromide (CTAB). The photoluminescence properties of ZnS NPs were followed in the presence of Ag + ions, Ag NPs and by the synthesis of Ag@ZnS core-shell nanoparticles. We observed that CTAB stabilized ZnS NPs emitted broadly
in the region from 350–450 nm, when excited by 309 nm light. In the presence of Ag + ions the emission peak intensity up to 400 nm was reduced, while two new and stronger peaks at 430 nm and 550 nm appeared.
Similar results were obtained when Ag NPs solution was added to ZnS solution. However, when Ag@ZnS NPs were synthesized, the
emission in the 350–450 nm region was much weaker in comparison to that at 540 nm, which itself appeared at a wavelength shorter
than that of Ag + ion added ZnS NPs. The observations have been explained by the presence of interstitial sulfur and Zn 2+, especially near the surface of the nanocrystals and their interaction with various forms of silver. In addition, our observations
suggest that Ag + ions diffuse into the lattice of the preformed ZnS NPs just like the formation of Ag + doped ZnS NPs and thus changes the emission characteristics. We also have pursued similar experiments with addition of Mn 2+ ions to ZnS and observed similar results of emission characteristics of Mn 2+ doped ZnS NPs. We expect that results would stimulate further research interests in the development of fluoremetric metal
ion sensors based on interaction with quantum dots. 相似文献
2.
Metallic silver (Ag) and its ability to combat infection have been known since ancient history. In the wake of nanotechnology advancement, silver's efficacy to fight broad spectrum bacterial infections is further improved in the form of Ag nanoparticles (NPs). Recent studies have ascribed the broad spectrum antimicrobial properties of Ag NPs to dissociation of Ag* ions from the NPs, which may not be entirely applicable when the size of Ag NPs decreases to the sub-2 nm range [denoted Ag nanoclusters (NCs)]. In this paper we report that ultrasmall glutathione (GSH)-protected Ag^+-rich NCs (Ag^+-R NCs for short, with a predominance of Ag+ species in the NCs) have much higher antimicrobial activities towards both gram-negative and gram-positive bacteria than the reference NC, GSH-Ag^+-R NCs. They have the same size and surface ligand, but with different oxidation states of the core silver. This interesting finding suggests that the undissociated Ag^+-R NCs armed with abundant Ag^+ ions on the surface are highly active in bacterial killing, which was not observed in the system of their larger counterpart, Ag NPs. 相似文献
3.
3-Thiopropionic acid (TPA) capped ZnS:Cu nanocrystals have been successfully synthesized by simple aqueous method. Powder
X-ray diffraction (XRD) studies revealed the particle size to be 4·2 nm. Surface characterization of the nanocrystals by FTIR
spectroscopy has been done and the structure for surface bound TPA based on spectral analysis was proposed. The optical studies
were done using UV-VIS spectroscopy and particle size and diameter polydispersity index (DPI) were calculated. Photoluminescence
(PL) spectrum reveals emission related to the transition from conduction band of ZnS to t
2 level of Cu 2 + . Electron microscopy was also done by scanning electron microscopy (SEM). 相似文献
4.
Ag/Ag 2S-ZnO nanocomposites were prepared via a simple hydrothermal process followed by a plasmonic Ag + reduction through a photo-deposition method. Ag 2S was introduced to narrow the overall composite bandgap and activate the surface plasmon resonance (SPR) effect of the Ag + cation present. The physicochemical properties of the as-synthesised catalysts were characterised by X-ray diffraction (XRD), scanning and transmission electron microscopies (SEM and TEM), Brunauer-Emmett-Teller (BET) analysis. Fourier-transform infrared spectroscopy (FTIR), Ultraviolet diffuse reflectance spectroscopy (UV–vis DRS), photoluminescence emission spectra (PL) and X-ray photoelectron spectroscopy (XPS) was conducted to investigate the photo-absorption and emission spectra of the nanocomposites. The degradation efficiency of all the synthesised catalysts (ZnO, Ag 2S, Ag/ZnO and Ag 2S/ZnO) prior to the final product, Ag/Ag 2S/ZnO was tested and compared. Results showed that the ternary Ag/Ag2S/ZnO achieved a 98 % phenol removal compared to 50 %, 11 %, 64 % and 93 % for ZnO, Ag2S, Ag/ZnO and binary Ag2S/ZnO, respectively. The degradation kinetics followed the Langmuir-Hinshelwood model, which typically describes heterogeneous photocatalytic surface reactions. The linear fits had R 2 values higher than 0.97, which confirms the degree of accuracy or statistical fitness to the kinetic model. Degradation scavenger test confirmed the holes (h +) as the main inhibitor and identified the superoxide O 2?¯ radical as the main active specie responsible for the degradation. Total organic carbon analysis using the ternary Ag/Ag 2S-ZnO catalyst only achieved a 74% phenol mineralization after 24 h of photocatalysis. Recyclability tests showed good phenol removal stability of Ag/Ag 2S-ZnO at 41 % after five recycle runs. Hence, a synergistic degradation mechanism responsible for the efficient photo-degradation performance was proposed. 相似文献
5.
Ag + chemisorption by R-phycoerythrin in an aqueous solution is shown to lead to the formation of silver nanoparticles, without the need for a reductant of Ag +. According to electron-microscopic results, most of the nanoparticles are elongated, (3 ± 0.5) × (6 ± 2) nm in dimensions. Also present are cubic Ag crystallites 22.5 nm in size (standard deviation of ±5.9 nm) and aggregates 53 × 48 nm in dimensions (standard deviation of ±8.8 × 8 nm). The absorption spectrum of the Ag nanoparticles in R-phycoerythrin is typical of small nanoparticles. Their fluorescence spectrum shows peaks of individual nanoparticles (450 nm) and fractal aggregates (630 and 670 nm). The fluorescence intensity of the Ag nanoparticles and their aggregates is an order of magnitude higher in comparison with other matrices. 相似文献
6.
The native cysteine (Cys)‐Ag 3 cluster hydrogel is approved for the first time by both experimental and theoretical studies. From the detailed molecular structure and energy information, three factors are found to ensure the self‐assembly of Cys and Ag 3, and result in the hydrogel. First, the Ag–S bonds make Cys and Ag 3 form Cys‐Ag 3‐Cys monomer. Second, intermolecular hydrogen bonds between carboxyl groups of adjacent monomer push them self‐assembled. Third, more monomer precisely self‐assemble to produce the –[Cys‐Ag 3‐Cys] n multimer, e.g., a single molecular chain with the left‐handed helix conformation, via a benign thermodynamic process. These multimers entangle together to form micro‐network to trap water and produce hydorgel in situ. The hydrogen bonds of hydrogel are sensitive to thermal and proton stimuli, and the hydrogel presents lysosome targeting properties via fluorescent imaging with biocompatibility. 相似文献
7.
The thermal effect on silver in ion-exchanged glasses was investigated in situ by X-ray photoelectron spectroscopy (XPS) in an ultra-high vacuum environment. Each XPS signal of Ag 3d 3/2 and 3d 5/2 consists of two components, the metallic state (Ag 0) and the oxidized state (Ag +), resolved after curve fitting. The toward-surface diffusion of silver was observed by monitoring the changes in concentration on the surface during sample annealing between 20 and 450°C. Judging from the variations in line shape and binding energy and from the enhancement of surface silver under annealing, both metallic and oxidized silver are accumulated on the surface. By applying the diffusion theory in a semi-infinite system to the experimental data, the thermal activation energy of the oxidized silver in ion-exchanged glass, 0.16 eV, was estimated. The activation energy of metallic Ag precipitated during heating, 0.23 eV, was estimated as well. 相似文献
8.
Surface properties of Ag nanoparticles may not be perturbed when they are filled with the relatively cheap Cu. To better understand how Ag can be coated on Cu, growth of the Cu and Ag bimetal during the temperature-programmed carbonisation (TPC) of Ag +- and Cu 2+-β-cyclodextrin (CD) complexes having the Cu/Ag ratios of 0.5, 1 and 2 was studied by in situ synchrotron small angle X-ray scattering (SAXS) spectroscopy. The SAXS spectra provide the detailed structural changes corresponding to the growth of Ag and Cu nanoparticles as the Ag +- and Cu 2+-CD complexes are carbonised at the temperature range of 363–513 K. It seems that Cu having a relatively high surface free energy is enriched in the core of the cherry-like Cu@Ag bimetal nanoparticles. The Cu@Ag bimetals are encapsulated in the carbon-shell formed from carbon unconsumed in the oxidation of CD during TPC. A rapid growth of the bimetal nanoparticles occurs at 393–423 K. As Ag + and Cu 2+ are reduced during the CD oxidation, the Ag nanospheres are filled with Cu, and eventually encapsulated in the carbon-shell. Note that the carbon-shell coated on Cu@Ag can be removed by steam reforming at 573 K. 相似文献
9.
Hierarchically flowerlike Ag microstructure with uniform silver nanosheets as building blocks has been facilely prepared on a composite film surface via in situ reduction of Ag + by a polyaniline component. The morphology of the as-prepared Ag microstructure is determined by the reaction duration, not the concentration of Ag + in the reaction process. The complex geometry, rough surface, and interlaced nanosheets of the hierarchical Ag microstructure create interstitial sites and thus result in enhanced Raman signals. 相似文献
10.
Recently, Bi‐doped Cs 2Ag 0.6Na 0.4InCl 6 lead‐free double perovskites demonstrating efficient warm‐white emission have been reported. To enable the solution processing and enrich the application fields of this promising material, here a colloidal synthesis of Cs 2Ag 1?xNa xIn 1?yBi yCl 6 nanocrystals is further developed. Different from its bulk states, the emission color temperatures of the nanocrystal can be tuned from 9759.7 to 4429.2 K by Na + and Bi 3+ incorporation. Furthermore, the newly developed nanocrystals can break the wavefunction symmetry of the self‐trapped excitons by partial replacement of Ag + ions with Na + ions and consequently allow radiative recombination. Assisted with Bi 3+ ions doping and ligand passivation, the photoluminescence quantum yield of the Cs 2Ag 0.17Na 0.83In 0.88Bi 0.12Cl 6 nanocrystals is further promoted to 64%, which is the highest value for lead‐free perovskite nanocrystals at present. The new colloidal nanocrystals with tunable color temperature and efficient photoluminescence are expected to greatly advance the research progress of lead‐free perovskites in single‐emitter‐based white emitting materials and devices. 相似文献
11.
TiO 2 nanotubes were fabricated by a hydrothermal method. Silver nanoparticles with diameters around 3–5 nm were loaded onto the
surface of TiO 2 nanotubes via a deposition approach followed by a photochemical reduction process under ultraviolet irradiation. Transmission
electron microscopy (TEM), N 2 adsorption measurements, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, UV-vis diffuse
reflectance spectroscopy (UV-vis), and fluorescence spectroscopy (FL) were applied to characterize the as-prepared Ag/TiO 2 nanotube composites. The photocatalytic activity of the as-prepared materials was investigated by photodegrading of methyl
orange. The results showed that silver particles were in zero oxidation state and highly dispersed on the surface of TiO 2 nanotubes when the concentration of Ag + was low. The presence of metallic silver can help the electron-hole separation by attracting photoelectrons. The Ag/TiO 2 nanotube composites with a suitable amount of silver showed a further improvement on the photocatalytic activity for degradation
of methyl orange in water. 相似文献
12.
Developing dental restorations with enhanced antibacterial properties has been a constant quest for materials scientists. The aim of this study was to synthesize silver doped calcium phosphate particles and use them to improve antibacterial properties of conventional glass ionomer cement. The Ag doped monetite (Ag-DCPA) and hydroxyapatite (Ag-HA) were synthesized by precipitation method and characterized using X-ray diffraction, scanning electron microscope and X-ray fluorescence spectroscopy. The antibacterial properties of the cements aged for 1 day and 7 days were evaluated by direct contact measurement using staphylococcus epidermis Xen 43. Ion concentrations (F ? and Ag +) and pH were measured to correlate to the results of the antibacterial study. The compressive strength of the cements was evaluated with a crosshead speed of 1?mm/min. The glass ionomer cements containing silver doped hydroxyapatite or monetite showed improved antibacterial properties. Addition of silver doped hydroxyapatite or monetite did not change the pH and ion release of F ?. Concentration of Ag + was under the detection limit (0.001?mg/L) for all samples. Silver doped hydroxyapatite or monetite had no effect on the compressive strength of glass ionomer cement. 相似文献
13.
Ion implantation is an effective method for changing surface properties and inducing various functionalities. However, a high vacuum is generally necessary for ion implantation, which limits the range of applications. Here, we describe a palm‐sized Ag+ ion emission gun produced using a solid electrolyte. AgI–Ag2O–B2O3 glass, known as a super‐ion‐conducting glass, has a Ag+ ion conductivity higher than 5 × 10?3 S cm?1 at room temperature. In addition, the melted glass has suitable viscous flow, and a sharp glass‐fiber emitter with a pyramid‐like apex can be obtained. Ag+ ion emission is observed from the tip of the glass fiber at accelerating voltages corresponding to electric fields above 20 kV cm?1, even at room temperature in a non‐vacuum atmosphere. Ag nanoparticles of size 50–350 nm are precipitated on a Si target substrate. Other glass components such as boron and iodine are not detected. Electrochemical quartz crystal microbalance (EQCM) measurements show that the mass of Ag nanoparticles estimated from the emission current using Faraday's law of electrolysis is in good agreement with that estimated from the QCM frequency shift. 相似文献
14.
Ag 2S quantum dots (QDs) are well‐known near‐infrared fluorophores and have attracted great interest in biomedical labeling and imaging in the past years. However, their photoluminescence efficiency is hard to compete with Cd‐, Pb‐based QDs. The high Ag + mobility in Ag 2S crystal, which causes plenty of cation deficiency and crystal defects, may be responsible mainly for the low photoluminescence quantum yield (PLQY) of Ag 2S QDs. Herein, a cation‐doping strategy is presented via introducing a certain dosage of transition metal Pb 2+ ions into Ag 2S nanocrystals to mitigate this intrinsic shortcoming. The Pb‐doped Ag 2S QDs (designated as Pb:Ag 2S QDs) present a renovated crystal structure and significantly enhanced optical performance. Moreover, by simply adjusting the levels of Pb doping in the doped nanocrystals, Pb:Ag 2S QDs with bright emission (PLQY up to 30.2%) from 975 to 1242 nm can be prepared without altering the ultrasmall particle size (≈2.7–2.8 nm). Evidently, this cation‐doping strategy facilitates both the renovation of crystal structure of Ag 2S QDs and modulation of their optical properties. 相似文献
15.
ZnS:Cl − nanoparticles with strong blue emission have been synthesized successfully by a solid-state reaction at low temperature. The dependence of photoluminescence (PL) properties of ZnS:Cl − nanoparticles on the Cl − contents was researched, and the influences of the annealing ambience and using polyvinyl alcohol (PVA) during the synthesis on the PL of ZnS:Cl − (Cl/Zn = 0.35) nanoparticles were discussed. X-ray power diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and ultraviolet-visible spectroscopy were used to characterize their structure, chemical state, diameter, surface states, and PL properties. The results showed that ZnS:Cl − nanoparticles had a cubic blende crystal structure and an average crystallite size of 17.40–19.16 nm. The most intensity blue emission peaking at about 425 nm was obtained when Cl/Zn = 0.35 under 330 nm excitation at room temperature. The emission intensity of ZnS:Cl − (Cl/Zn = 0.35) was increased 3-fold than that of ZnS. The results showed that the PL of ZnS:Cl − (Cl/Zn = 0.35) nanoparticles was enhanced after annealing or using PVA during the synthesis, and annealing in vacuum had a stronger effect in improving the luminescence properties of ZnS nanoparticles than in air. This work suggests that it is an effective method to improve the PL intensity of ZnS nanocrystals by doping with Cl − in ZnS. 相似文献
16.
Photoluminescence (PL) properties of silver (Ag) and dysprosium (Dy) codoped zeolites were investigated. It was found that PL from the 4F 9/2– 6H 13/2 transition of Dy 3+ ions at 575 nm is more than 50 times enhanced by the presence of Ag + ions under ultraviolet excitation. The excitation wavelength dependence of the PL intensity coincided well with the absorption spectra of Ag + ions, indicating that Dy 3+ ions are excited by the energy transfer from Ag + ions. In addition, by carefully optimizing annealing condition and Dy and Ag concentration, white light was realized due to the combination of blue emission of Ag + ions, yellow emission of Dy 3+ ions and red emission of Ag clusters. 相似文献
17.
Photoluminescence and X-ray photoelectron spectroscopy studies of Mn 2+ doped ZnS nanocrystals in inorganic-organic hybrid coatings prepared by a sol-gel process are presented. A 25-fold enhancement of photoluminescence was observed after UV irradiation for 6 h in an ambient atmosphere. X-ray photoelectron spectroscopy results indicate a chemical shift of binding energy from ZnS to ZnSO 4 after UV irradiation. X-ray diffraction results show a decrease of ZnS nanocrystal size during UV irradiation. The cause of these phenomena was discussed based on a photochemical reaction on ZnS nanocrystal surface. 相似文献
18.
An in situ optical microspectroscopy investigation of the growth and oxidation of silver nanoparticles (NPs) embedded in SiO 2 thin films deposited on soda-lime glass has been conducted in real time during thermal processing in air. Variation of Ag NP size is followed by fitting of surface plasmon resonance (SPR) with spectra calculated by Mie theory, and analysed concurrently with the time evolution of SPR peak intensity. The NP transformations appeared to be temperature and time dependent. Silver NPs were indicated to grow at relatively high temperatures (e.g. 600 °C) due to Ostwald ripening, followed by a plateau and a gradual decrease in size resulting in SPR vanishing due to oxidation. The three phases were well separated in time. Oxidation appeared dominant at lower temperatures (e.g. 400 °C) as indicated by a continuous decrease in Ag particle size. The product of Ag NP oxidation was revealed by photoluminescence spectroscopy as single Ag + ions. Furthermore, the data indicated that: (i) Ag + ions are formed during heat treatment under an Ag/Ag + redox equilibrium; (ii) the ions diffuse from the SiO 2 matrix towards the soda-lime substrate where they stabilize; and (iii) the continuous removal of these ions from the matrix is necessary in order for the equilibrium to be displaced towards oxidation. 相似文献
19.
CeO2 nanoparticles doped with different types of Pr, Y, W and CaF2 are prepared via a facile one-pot combustion method. Their crystallinity, particle size and absorption spectrum are investigated by X-ray diffraction (XRD), grading analysis and ultraviolet–visible spectroscopy (UV–Vis) absorption spectrum. Among the doped samples, W-doped CeO2 (Ce0.9W0.1O2) is selected out, which exhibits obvious red-shift of the absorption band as compared with the undoped CeO2, achieving good match between the ceria absorption peak and the industrial 365 nm light source. Consequently, under the 365 nm exposure, the W-doped CeO2 show more efficient reduction ability for Ag+ to Ag. The results indicate that W-doped CeO2 is a very promising photosensitizer for photosensitive glass ceramics under industrial 365 nm light exposure, which can better absorb photons under UV light and then reduce Ag+ to elemental Ag. 相似文献
20.
A simple method of synthesizing hybrid silver–polyacrylic acid–poly(N-vinylpyrrolidone) (Ag–PAA–PVP) nanogels was demonstrated through in situ reducing Ag + inside PAA–PVP nanogels, which were formed by polymerization of acrylic acid in the PVP solution. Due to the ion exchange between Ag + and acid protons of PAA, stable Ag + clusters were formed inside the PAA–PVP nanogels, and hybrid nanogels were obtained by reducing Ag + by ascorbic acid. Transmission electronic microscopic (TEM) images clearly showed the existence of silver nanoparticles inside the Ag–PAA–PVP nanogels. These hybrid nanogels showed typical surface plasma resonance absorption peak around 420 nm, and the size of the silver nanoparticles inside the Ag–PAA–PVP nanogels could be controlled from 9.5 ± 1.6 nm to 1.9 ± 0.4 nm by increasing the feeding amount of Ag +. In addition, these hybrid nanogels showed photoluminescent properties in fluorescent spectra. Considering the pH sensitive property of these hybrid nanogels, they will have potential application in drug delivery and biomedical imaging systems. 相似文献
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