Surface Of Ag Nanoparticles Research Articles

Effect of Silver Nanoparticles on the Microstructure, Non-Isothermal Crystallization Behavior and Antibacterial Activity of Polyoxymethylene.

Silver (Ag) nanoparticles were synthesized by a facile route in the presence of oleic acid and n-propylamine. It was shown that the average primary size of the as-synthesized Ag nanoparticles was approximately 10 nm and the surface of as-synthesized Ag nanoparticles was capped with monolayer surfactants with the content of 19.6%. Based on as-synthesized Ag nanoparticles, polyoxymethylene (POM)/Ag nanocomposites were prepared. The influence of Ag nanoparticles on non-isothermal crystallization behavior of POM was investigated by differential scanning calorimetry (DSC). The Jeziorny, Jeziorny-modified Avrami, Ozawa, Liu and Mo, Ziabicki and Kissinger models were applied to analyze the non-isothermal melt crystallization data of POM/Ag nanocomposites. Results of half time (t1/2), crystallization rate parameter (CRP), crystallization rate function (K(T)), kinetic parameter (F(T)), the kinetic crystallizability at unit cooling rate (GZ) and the crystallization activation energy (∆E) were determined. Small amounts of Ag nanoparticles dispersed into POM matrix were shown to act as heterogeneous nuclei, which could enhance the crystallization rate of POM, increase the number of POM spherulites and reduce POM spherulites size. However, the higher loading of Ag nanoparticles were easily aggregated, which restrained POM crystallization to some degree. Furthermore, the POM/Ag nanocomposites showed robust antibacterial activity against Escherichia coli and Staphylococcus aureus.

Silver nanoparticles enhanced luminescence and stability of CsPbBr3 perovskite quantum dots in borosilicate glass

AbstractSeries of silver nanoparticles (NPs) embedded CsPbBr3 quantum dots (QDs) glass was synthesized via the melt‐quench method. Ag NPs and CsPbBr3 QDs coexist in the TEM image of the Ag‐doped glass sample. Photoluminescence (PL) spectra show that the 0.1 molar ratio Ag2O‐doped sample had a PL intensity 2.37 times than the undoped sample. This increase is generated by localized surface plasmon resonance coupling between the Ag NPs and CsPbBr3 QDs. Excessive Ag doping weakens the PL intensity due to spectral self‐absorption of the Ag NP surface plasmon resonance (SPR). Self‐adsorption of SPR is detrimental to luminescence properties because it increases the amount of photogenerated charge carriers, which proceed through nonradiative relaxation pathways. In addition, stability results of Ag NP‐doped‐CsPbBr3 QD glass show that they have excellent stability. This study on Ag NP‐doped‐CsPbBr3 QD glass provides a new idea for the future development of perovskite QD optoelectronic devices.

Control of the neuromorphic learning behavior based on the aggregation of thiol-protected Ag-Ag2S core–shell nanoparticles

The neuromorphic learning switching behavior was investigated in electric devices that were constructed based on the aggregation of thiol-stabilized Ag/Ag2S core–shell nanoparticles (NPs). The NPs were synthesized using the two-phase modified Brust–Schiffrin procedure and exhibited Ag–S and Ag–S–R bonding states at the surfaces of Ag NPs. The memristive behavior of such a device at room temperature under ambient pressure, which can be used to emulate the functions of biological synapses with long and short memories, is achieved. The importance of the Ag2S and the thiol layer at the surface of Ag NPs for the demonstration of learning behavior, such as the potentiation and depression of synapses in the human brain is explained.

Highly-Conductive, Transparent Ga-Doped ZnO Nanoneedles for Improving the Efficiencies of GaN Light-Emitting Diode and Si Solar Cell

The growths of transparent, highly-conductive Ga-doped ZnO (GaZnO) nanoneedles (NNs) on the tops of GaN-based light-emitting diodes (LEDs) and Si solar cells for enhancing light extraction and reducing surface reflection, respectively, and hence increasing their efficiencies are demonstrated. The GaZnO NNs are grown based on the vapor-liquid-solid process by using surface Ag nanoparticles (NPs) as growth catalyst. In the application to LED, the residual Ag NPs can induce the surface plasmon (SP) coupling effect for increasing the LED emission efficiency. By combining the SP coupling effect, the light extraction effects of the GaZnO NNs and simultaneously deposited GaZnO thin film, and the current spreading effect of the thin film, the LED output intensity can be increased by 100%. In the solar cell application, the SP resonance of the residual Ag NPs can also enhance sunlight harvest and hence the energy conversion efficiency. By combining the effects of the residual Ag NPs, the GaZnO thin film, and the GaZnO NNs, the energy conversion efficiency of a Si solar cell can increase from 9.65 to 12.30%, corresponding to a relative enhancement of 27.5%.

Liquid-Phase Hydrogenation of Internal and Terminal Alkynes on Pd–Ag/Al2O3 Catalyst

The structure and catalytic properties of a bimetallic Pd–Ag/α-Al2O3 catalyst are studied in the liquid-phase hydrogenation of substituted internal and terminal alkynes using diphenylacetylene, phenylacetylene, 1-phenyl-1-propyne, and 1-phenyl-1-butyne as sample alkynes. IR spectroscopy of adsorbed CO, X‑ray diffraction (XRD), and electron microscopy were used to show that the active sites on the Pd–Ag nanoparticle surface are Pd1 sites. The synthesized Pd–Ag/α-Al2O3 catalyst shows a much higher selectivity in the hydrogenation of internal symmetric and asymmetric alkynes compared to the monometallic Pd/α‑Al2O3 sample. Also, it was found in the hydrogenation of diphenylacetylene and 1-phenyl-1-propyne on Pd–Ag/α-Al2O3 that the rate of the stage of desired olefin hydrogenation substantially decreases, which favors the kinetic control of the process.

Enhanced luminescence properties of Eu3+-doped high silica glass by Ag nanoparticles

Eu3+ and Ag nanoparticles (Ag-NPs) doped high silica glass (HSG) was synthesized by absorbing and sintering porous glass. The effect of localized surface plasmon resonance (LSPR) of Ag-NPs on absorbance, luminescence properties and decay curves was investigated. The results indicate that Ag-NPs are effectively doped into HSG. The surface plasmon coupling can be formed between the Eu3+ ions and the Ag-NPs surface because the broad absorption band of Ag-NPs overlaps with the excitation peaks of Eu3+. The profiles of the excitation and emission spectra were not affected by Ag-NPs. By optimizing the Ag concentration, the emission intensity and quantum yield (QY) of HSG-Eu3+-0.1%Ag are significantly higher than those of HSG-Eu3+. Plasmon-enhanced luminescence can occur through enhancement of local electromagnetic field and radiative decay rate.

Spectroelectrochemical Investigation of the Interaction of Adenine with Pyridoxine at Physiological pH

Spectroelectrochemical techniques were used to probe the interaction of adenine with pyridoxine at pH 7.0. Analysis of UV-visible absorption of the adenine-pyridoxine complex at 260 nm using the Lineweaver–Burk double reciprocal plot produced a linear graph indicating a 1 : 1 mode of interaction between the compounds and a binding constant of 29.1. Change in the background current and broadening of adenine and pyridoxine cyclic voltammetry (CV) oxidation peaks at 1.0 V and 0.8 V, respectively, compared to the CV of the individual compounds is indicative of an interaction. The Raman shift of the coupled –C(11)H2-OH bending and in-plane N(7)-H mode at 1235 cm−1 to 1215 cm−1 of pyridoxine and the shift to the lower wavenumber of the adenine –N(10)H2 rocking band from 942 to 906 cm−1 confirm that the adenine exocyclic amino group and its purine nitrogen atom N(7) interacts with pyridoxine O(12) via the formation of hydrogen bonds. Strong enhancement of surface-enhanced Raman spectroscopy (SERS) bands pertaining to adenine and the bathochromic shift of the normal Raman band due to the adenine ring breathing mode observed at 722 cm−1 in the spectrum of adenine, to 732 cm−1 in the SERS spectrum of aqueous adenine-pyridoxine indicates that the complex adsorbs onto the Ag nanoparticle surface with the adenine portion possessing a perpendicular orientation.

Novel Preparation of Reduced Graphene Oxide-Silver Complex using an Electrical Spark Discharge Method.

This study used an electrical discharge machine (EDM) to perform an electrical spark discharge method (ESDM), which is a new approach for reducing graphene oxide (GO) at normal temperature and pressure, without using chemical substances. A silver (Ag) electrode generates high temperature and high energy during gap discharge. Ag atoms and Ag nanoparticles (AgNP) are suspended in GO, and ionization generates charged Ag+ ions in the Ag plasma with a strong reducing property, thereby carrying O away from GO. A large flake-like structure of GO was simultaneously pyrolyzed to a small flake-like structure of reduced graphene oxide (rGO). When Ag was used as an electrode, GO was reduced to rGO and the exfoliated AgNP surface was coated with rGO, thus forming an rGOAg complex. Consequently, suspensibility and dispersion were enhanced.

Selectively encapsulating Ag nanoparticles on the surface of two-dimensional graphene for surface-enhanced Raman scattering

Abstract For preparation of surface-enhanced Raman scattering (SERS) substrate with high stability, reproducibility, and sensitivity performances, graphene/Ag nanoparticles were chosen to make further improvement by introducing molecularly imprinted polymer (MIP) film to protect Ag nanoparticles. The thickness of the resulting ultra-thin MIP layer is 2 nm on the surface of Ag nanoparticles. The preparation of two-dimensional/core-shell structure SERS substrate (G/Ag@MIP) possesses high SERS activity toward the probe of bovine serum albumin (BSA) target molecule, which exhibits a 10 −12 M detection limit. The G/Ag@MIP shows good selectivity and recycle rate in the detecting process. These results show that the hybrid material as a SERS sensor is potential for medical diagnosis in life sciences.

Photochemical Synthesis of Composite Noble Metal Nanoparticles for Fuel Cell Catalysts

Direct methanol fuel cell is an ideal way for energy use because of its low noise, simple structure, rich fuel source, low price, easy storage and transportation. However, in the commercial application, it is necessary to overcome high catalyst cost and short life. The work used photochemical reduction and seed crystal growth to reduce PtII and PdII on the surface of Ag nanoparticles to form Ag@Pt-Pd core-shell composite nanoparticles with particle size of about 5∼10 nm. The results showed that the synthesized composite nanoparticles have good electrocatalytic activity, with good research and application in the electrode catalysts of fuel cells.

Observing Transient Bipolar Electrochemical Coupling on Single Nanoparticles Translocating through a Nanopore.

We report the observation of transient bipolar electrochemical coupling on freely moving 40 nm silver nanoparticles. The use of an asymmetric nanoelectrochemical environment at the nanopore orifice, for example, an acid inside the pipette and halide ions in the bulk, enabled us to observe unusually large current blockages of single Ag nanoparticles. We attribute these current blockages to the formation of H2 nanobubbles on the surface of Ag nanoparticles due to the coupled faradaic reactions, in which the reduction of protons and water is coupled to the oxidation of Ag and water under potentials higher than 1 V. The appearance of large current blockages was strongly dependent on the applied voltage and the choice of anions in the bulk solution. The correlation between large current blockages with the oxidation of Ag nanoparticles and their nanopore translocation was further supported by simultaneous fluorescence and electric recordings. This study demonstrates that transient bipolar electrochemistry can take place on small metal nanoparticles below 50 nm when they pass through nanopores where the electric field is highly localized. The use of a nanopore and the resistive-pulse sensing method to study transient bipolar electrochemistry of nanoparticles may be extended to future studies in ultrafast electrochemistry, nanocatalyst screening, and gas nucleation on nanoparticles.

Synthesis of Ag3Sn Submicrometer Particles via an Adapted Polyol Process in View of Their Use As Die-Attach Material in Power Modules

Intermetallic Ag3Sn was synthesized in the form of submicrometer particles through an adapted two-step polyol process. The precursor salts were tin (II) chloride (SnCl2) and silver nitrate (AgNO3), while the polyol used was ethylene glycol (EG). Sodium hydroxide (NaOH) and sodium borohydride (NaBH4) were selected as alkaline and reducing agents, respectively, and polyvinylpyrrolidone (PVP) was used to prevent the particles from coalescing. In the first step, Ag nanoparticles were obtained when silver nitrate and PVP, dissolved in polyol, were heated at 160°C. The as-obtained Ag nanoparticles served as seeds for the nucleation and growth of the Sn species obtained in the second step. In this second step, the SnCl2 salt, combined with NaOH and NaBH4 as a strong reducing agent, was added to the polyol solution. Stannous ions, which were likely adsorbed at the Ag nanoparticle surface, were reduced to tin metal using the strong reducing power of NaBH4. Then, the Sn atoms diffused inside the Ag nanoparticles producing Ag3Sn submicrometer particles with diameter in the range of 100–200 nm. The submicrometer size of the Ag3Sn particles, as well as its high melting point at approximately 485°C makes this compound a good candidate for a lead-free die-attach material in power module devices.

Facile fabrication of Ag–Bi2GeO5 microflowers and the high photodegradable performance on RhB

In this work, a simple template-free one-pot solvothermal method was used to prepare hierarchical microflowers from Ag-modified Bi2GeO5 nanosheets. To characterize the phases and morphologies of the products, powder X-ray diffraction (XRD), scanning electron microscopy (SEM), UV–Vis diffuse reflectance spectroscopy (DRS), X-ray photoelectron spectroscopy (XPS) and Brunauer–Emmett–Teller (BET) surface area measurements were used. The characterization results showed the deposition of some spherical metal Ag particles ranging from 10 to 20 nm in size on the Bi2GeO5 nanosheets surface and the nanosheets-assembly of hierarchical microflowers with macroporous structures. Based on the Ag nanoparticles surface plasmonic resonance (SPR) and the hierarchical microflowers structure of Bi2GeO5, the Ag-modified Bi2GeO5 self-assembly microflowers exhibited excellent UV-light absorption. Photodegradable tests indicated that the decolorization rate of RhB with Ag-modified Bi2GeO5 (RN = 0.1) microflowers was nearly 100% within 25 min, which was 1.5 times higher compared to that of unmodified Bi2GeO5 microflowers. Additionally, the photocatalytic performance stability tests demonstrated that the Ag-modified Bi2GeO5 hierarchical microflowers has excellent chemical stability. Investigations into the main oxidative species indicate that the main active species of Ag-modified Bi2GeO5 in RhB photodegradation are the superoxide radical ( $${\text{O}}_{2}^{ \cdot - }$$ ), and the ·OH and h+ are also partially involved in the photocatalytic process. Finally, a possible photocatalytic mechanism for RhB photo-degradation onto Ag-modified Bi2GeO5 microflowers was proposed.

2D-porphrinic covalent organic framework-based aptasensor with enhanced photoelectrochemical response for the detection of C-reactive protein

In this study, a novel photoelectrochemical (PEC) aptasensor based on two-dimensional (2D) porphyrinic covalent organic frameworks (p-COFs) for the label-free detection of C-reactive protein (CRP) is presented. The obtained p-COFs possess high conductivity and an improved stability due to strong and rigid covalent linkages. The introduction of p-COFs hinder the recombination of electrons and holes, decreasing their band gap (Eg), thereby which improved the photocurrent conversion efficiency. Compared with pure porphyrin, p-COFs exhibited enhanced photocurrent intensity. An amplified photocurrent conversion efficiency and enhanced photocurrent results from H2O2, which act as active molecules and electron donors. As an unprecedented application of COFs in PEC bioanalysis, the detection of CRP with a PEC aptasensor is presented. The assembly of a CRP aptamer on the surface of Ag nanoparticles hinders the electron transfer, resulting in the decrease of the photocurrent response. This PEC aptasensor exhibits good analytical performances such as a rapid response, high stability, wide linear range and excellent selectivity, making COFs promising candidates for PEC bioanalysis.

Silver nanoparticles stabilized with a silicon nanocrystal shell and their antimicrobial activity.

The antimicrobial activity of a hybrid nanoparticle (NP) composed of a silver (Ag) NP core decorated with silicon (Si) nanocrystals (NCs) on the exterior (Ag/Si NPs) is evaluated. The shell of Si NCs effectively protects the surface of Ag NPs, thus the particles are more stable in water and in air compared to conventional organic-capped Ag NPs. The bacterial growth kinetic analysis reveals that the Si NC shell does not suppress the release of Ag ions from the Ag NP surface due probably to the porous structure. For the antimicrobial coating application, a thin film of the hybrid Ag/Si NPs is produced by drop coating the solution on a cover glass. Thanks to the Si NC shell, agglomeration of Ag NPs in the film is prevented and the film shows a very similar optical absorption spectrum to that of the solution. The film exhibits a larger zone of inhibition in an agar diffusion assay of Escherichia coli compared to a film produced from organic-capped Ag NPs.

Photocatalytic oxidation of aromatic alcohols over silver supported on cobalt oxide nanostructured catalyst

In this paper, we report an in-situ synthesis of silver supported on cobalt oxide (Ag/Co3O4) nanoparticles (NPs) and studied the catalytic activity of this material as an eco-friendly, simple, recyclable and efficient catalyst for one-pot photocatalytic oxidation of aromatic alcohols. Ag nanoparticles with the sizes of 2–5 nm supported on spherical Co3O4 with the radius between 40 and 60 nm were synthesized by homogeneous chemical precipitation followed by hydrothermal heating. The as-synthesized catalyst was thoroughly characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), elemental mapping, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA) and N2 adsorption-desorption isotherm (BET) analysis. It was observed that the catalysts with 1 wt% of silver loading shows high activity and selectivity toward the target aldehyde product. The effects of different reaction parameters such as reaction time, oxidant and solvent were investigated and studied in detail. The synergistic effect between the surface Ag NPs and Co3O4 nanospheres plays a vital role toward very high catalytic activity.

Chemical Requirement for Extracting Energetic Charge Carriers from Plasmonic Metal Nanoparticles to Perform Electron-Transfer Reactions.

Performing electron-transfer reactions on metal nanoparticles requires separation of charge carriers at the nanoparticle and their transfer to the reacting molecules. Inducing these reactions using light is challenging due to the exceedingly short lifetimes of energetic charge carriers formed in metal nanoparticles under light illumination. The results described here show that certain conditions must be met to drive these electron-transfer reactions on plasmonic nanoparticles. One critical requirement is that the process of electronic excitation takes place at the nanoparticle/molecule interface. This is accomplished by high plasmonic electric fields at the surface of plasmonic nanoparticles. Furthermore, it is also evident from our study that the electron (or hole)-donating capacity of the hole (or electron) scavengers needs to be high enough to allow for the extraction of holes (or electrons) from the nanoparticle/molecule complex, therefore completing the catalytic cycle. We discuss these findings through a case study of the conversion of methylene blue (MB) into a reduced MB ion radical on the surface of plasmonic Ag and Ag-Pt core-shell nanoparticles. To directly monitor the reduction reaction of MB on the nanoparticle surfaces, we have used time-dependent in situ surface-enhanced Raman scattering measurement, which also informs us about the underlying mechanistic details of plasmon-driven charge transfer.

A Surface Mediated Supramolecular Chiral Phenomenon for Recognition of l- and d-Cysteine.

Chiral recognition is of fundamental importance in chemistry and life sciences and the principle of chiral recognition is instructive in chiral separation and enantioselective catalysis. Non-chiral Ag nanoparticles (NPs) conjugated with chiral cysteine (Cys) molecules demonstrate strong circular dichroism (CD) responses in the UV range. The optical activities of the l-/d-Cys capped Ag NPs are associated with the formation of order arrangements of chiral molecules on the surface of Ag NPs, which are promoted by the electrostatic attraction and hydrogen bonding interaction. The intensity of the chiroptical response is related to the total surface area of Ag NPs in the colloidal solution. The anisotropy factor on the order of 10−2 is acquired for Ag NPs with the size varying from ~2.4 to ~4.5 nm. We demonstrate a simple and effective method for the fabrication of a quantitative chiral sensing platform, in which mesoporous silica coated Ag nanoparticles (Ag@mSiO2) were used as chiral probes for recognition and quantification of Cys enantiomers.

Quantitation of cobalt in Chinese tea by surface‐enhanced Raman spectroscopy in combination with the spectral shape deformation quantitative theory

AbstractA surface‐enhanced Raman spectroscopy (SERS) method for the quantification of Co2+ in Chinese tea was developed in this contribution. SERS‐enhancing substrates with a high selectivity for Co2+ were prepared by attaching 2‐(bis (pyridin‐2‐ylmethyl)amino)ethane‐1‐thiol onto the surfaces of Ag nanoparticles. A calibration model based on the spectral shape deformation quantitative theory was derived to address the poor reproducibility problem in SERS assays due to the practical impossibility in controlling the number and distribution of “hot spots” on or close to the surface of enhancing substrates. The proposed SERS platform was applied to the quantification of Co2+ in Chinese tea samples and achieved quite satisfactory quantitative results. The average relative deviation between the quantitative results of the proposed SERS platform and those of inductively coupled plasma mass spectrometry was about 6.0%. It is therefore reasonable to expect that the proposed SERS platform can be a competitive alternative for the quantification of Co2+ in food samples.

Green synthesis of biocompatible trypsin-conjugated Ag nanocomposite with antibacterial activity

In this work, water-soluble Ag nanoparticles were prepared in aqueous solution by using trypsin as reducing and capping agent. The protein-assisted synthetic strategy eliminates the need of intermediate protecting and linking agents compared with organometallic approach, which is simple, effect, less energy consuming, and closer to the requirements of green chemistry. The morphology, size and antibacterial activity properties could be controlled by varying experimental conditions. The results of FT-IR and SDS-PAGE analysis indicated that trypsin molecules could control the nucleation and growth of nanocrystals through chemical interaction between Ag and functional groups of trypsin. The binding of trypsin on the surface of Ag nanoparticles significantly reduced nano-toxicity through capping effect. The trypsin-conjugated Ag nanoparticles exhibited strong antibacterial activity toward both Gram-positive and Gram-negative bacteria due to small size and specific morphologies. Compared with traditional antibacterial materials, the water-solubility and biocompatibility make the products more suitable for the application in biological and medical science.