Silver Nanoplates Research Articles

Monitoring the Shape Evolution of Silver Nanoplates: A Marker Study

Out of the frame: A marker study using gold frames was designed to reveal that silver nanoplates undergo a shape transition during their seeded growth from triangular to circular to hexagonal plates before ultimately returning to triangular structures with an orientation 180° relative to that of the original triangular seeds (see picture, the original gold triangular frame is visible at the center of the silver nanoplate).

Synthesis of crystalline silver nanoplates and their application for detection of nitrite in foods

The high-yield crystalline silver nanoplates were synthesized by mixing para-phenylenediamine (PPD) and silver nitrate with the addition of an appropriate amount of formic acid at low temperature. X-ray diffraction measurements show that the silver samples are pure face-centered cubic (fcc) phase with a preferred orientation of (1 1 1) direction. The silver nanoplates modified electrode (AgNP/GC) exhibits an excellent electrocatalytic activity toward the oxidation of nitrite ( NO 2 - ) . The corresponding linear range and detection limit are estimated to be from 1 × 10 −5 M to 1 × 10 −3 M ( r = 0.999) and 1.2 × 10 −6 M, respectively, at a signal-to-noise ratio of 3. It was successfully applied to the determination of nitrite in some food samples and the results were consistent with those obtained with the standard spectrometer procedure.

Seed-mediated Plasmon-driven Regrowth of Silver Nanodecahedrons (NDs)

We report the synthesis of silver nanodecahedrons (NDs) for extending the localized surface plasmon resonance (LSPR) of silver nanostructures from blue to green-orange (~590 nm), which will enable much wider application opportunities using common laser light sources. In our photo-assisted method, we use a light-emitting-diode (LED) to control regrowth of silver ND from precursor seeds. Highly uniform silver NDs are synthesized when the LED emission peak coincides with the LSPR peak of the seeds. A two-step process involving precursor self-transformation into silver nanoprisms and nanoplates, and subsequent photo-activated regrowth of silver NDs has been proposed. Surface-enhanced Raman scattering of silver NDs in different sizes has been studied, and the average enhancement factor for each size is estimated to be in the order of ~106.

Preparation of Silver Nanoplates and Application in PCB Ink-Jet

Compared with traditional etch processing, inkjet technology has the features of simpler workmanship, less resources-utilizing, lower cost and environmentally friendly adaptation, which is sure to be another innovation of printed circuit board(PCB) technology. In this paper, size and shape controlled silver nanoparticles have been synthesized，which was used as conductive medium in ink-jet inks. Then it was printed into conductive lines on epoxy resin by a drop-on-demand inkjet printer. PVP was used as a polymeric stabilizer providing both electrostatic and steric stabilization. Ag2C2O4 was used to prepared spherical nano-silver. In the preparation of flake-like silver powders, the fully inorganic phase system contains AgNO3 as a silver precursor, DMF as a as a media dissolving silver salt, and PVP as a reducing reagent. The morphologies and structures of the nanoparticles were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). It was shown that the sample is silver with cubic asymmetry from the pattern of XRD. TEM images indicated that the size of spherical nano-particles was no more than 20 nm. But the small triangular nanoplates, with rather narrow size distribution, were in the range from 20nm up to 60 nm in edge length. The electrical conductivity was also measured by the four-probe tested method after calcined on the substrates. It was shown that the conductivity was 25S/cm when adding the spherical powders and the nano-silver ink has been successfully designed for inkjet printing.

A Systematic Study of the Synthesis of Silver Nanoplates: Is Citrate a “Magic” Reagent?

In this work we have carried out systematic studies and identified the critical role of hydrogen peroxide instead of the generally believed citrate in the well-known chemical reduction route to silver nanoplates. This improved understanding allows us to develop consistently reproducible processes for the synthesis of nanoplates with high efficiency and yields. By harnessing the oxidative power of H(2)O(2), various silver sources including silver salts and metallic silver can be directly converted to nanoplates with the assistance of an appropriate capping ligand, thus significantly enhancing the reproducibility of the synthesis. Contrary to the previous conclusion that citrate is the key component, we have determined that the group of ligands with selective adhesion to Ag (111) facets can be expanded to many di- and tricarboxylate compounds whose two nearest carboxylate groups are separated by two or three carbon atoms. We have also found that the widely used secondary ligand polyvinylpyrrolidone can be replaced by many hydroxyl group-containing compounds or even removed entirely while still producing nanoplates of excellent uniformity and stability. In addition to the general understanding of NaBH(4) as a reducing agent, it has also been found to act as a capping agent to stabilize the silver nanoparticles, prolong the initiation time required for nanoplate nucleation, and contribute to the control of the thickness as well as the aspect ratio of silver nanoplates. The improved insight into the specific roles of the reaction components and significantly enhanced reproducibility are expected to help elucidate the formation mechanism of this interesting nanostructure.

Synthesis of silver nanodiscs and triangular nanoplates in PVP matrix: Photophysical study and simulation of UV–vis extinction spectra using DDA method

Circular nanodiscs and truncated triangular shaped silver nanoplates have been synthesized through a seeding growth approach in polyvinyl pyrrolidone (PVP) matrix at room temperature. Seeds are prepared on reduction of silver nitrate (AgNO 3) by sodium borohydride (NaBH 4) and methyl cellulose (MC) is being used as encapsulating matrix. Colored silver sols are obtained as variable amounts of seeds are added to the growth solution containing silver nitrate, polyvinyl pyrrolidone (PVP) and ascorbic acid. Silver nanostructures are characterized using UV–vis spectroscopic and transmission electron microscopic (TEM) study. TEM studies reveal that particles are mostly circular disc and truncated triangular plate like as different amount of seeds are used in the growth solution. Simulation of UV–vis extinction spectra using discrete dipole approximation (DDA) method nicely explains the observed localized surface Plasmon resonance (LSPR) band of spherical and circular disc like silver nanoparticle.

Cadmium Sulfide Silver Nanoplate Hybrid Structure: Synthesis and Fluorescence Enhancement

Semiconductor–noble metal hybrid nanostructures are of current interest in the development of bioimaging agents. To enhance photoluminescence of cadmium sulfide nanoparticles via surface plasmon mode coupling, cadmium sulfide conjugated silver nanoplates (denoted as CdS-Ag NP) have been prepared by a forward–reverse cation exchange method. The morphology, crystallinity, and atomic composition of the CdS-Ag NP have been investigated by energy dispersive X-ray spectroscopy and high-resolution transmission electron spectroscopy, and the CdS-Ag NP can be described as Cd2+-rich CdS nanoparticles covalently bonded to the surfactant of Ag nanoplates. Photoluminescence enhancement of CdS measured is attributed to the matching between the emission bands of cadmium sulfide and the tailor-made localized surface plasmons resonance bands provided by the Ag NP. Application of the CdS-Ag NP in cell imaging has also been demonstrated.

Green, effective chemical route for the synthesis of silver nanoplates in tannic acid aqueous solution

Silver nanoplates, with average size tunable from 50 to 500 nm, have been synthesized via a simple room-temperature tannic acid (TA) solution-phase chemical reduction method. The synthesis was a seedless process in which tannic acid was used as a reducing as well as a capping agent, and did not need any other surfactant or capping agent to direct the anisotropic growth of the silver nanoparticles. The morphology of silver nanoplates has been confirmed by transmission electron microscopy, the growth process of nanoplates has been studied by UV/vis spectroscopy. Control experiments have been explored for a more thorough understanding of the growth mechanism. It was found that both the concentrations of TA and the pH of solution were the key elements to control the morphology silver nanoplates. The optical in-plane dipole plasmon resonance bands of these silver plates could be tuned from 520 to 1100 nm.

Self-Assembly of Large-Scale and Ultrathin Silver Nanoplate Films with Tunable Plasmon Resonance Properties

We describe a rapid, simple, room-temperature technique for the production of large-scale metallic thin films with tunable plasmonic properties assembled from size-selected silver nanoplates (SNPs). We outline the properties of a series of ultrathin monolayer metallic films (8-20 nm) self-assembled on glass substrates in which the localized surface plasmon resonance can be tuned over a range from 500 to 800 nm. It is found that the resonance peaks of the films are strongly dependent on the size of the nanoplates and the refractive index of the surrounding dielectric. It is also shown that the bandwidth and the resonance peak of the plasmon resonance spectrum of the metallic films can be engineered by simply controlling aggregation of the SNP. A three-dimensional finite element method was used to investigate the plasmon resonance properties for individual SNPs in different dielectrics and plasmon coupling in SNP aggregates. A 5-17 times enhancement of scattering from these SNP films has been observed experimentally. Our experimental results, together with numerical simulations, indicate that this self-assembly method shows great promise in the production of nanoscale metallic films with enormous electric-field enhancements at visible and near-infrared wavelengths. These may be utilized in biochemical sensing, solar photovoltaic, and optical processing applications.

Modulating absorption band of triangular silver nanoplates in aqueous solvent and on substrates using tannin as reducing agent

Triangular silver nanoplates in aqueous solvent and on the surface of quartz substrate have been synthesized by seed-mediated growth approach in the presence of tannin. It was found that both the amount of tannin and the small triangular silver nanoplate seeds added to the growth solution are the key factors to modulation absorption band of triangular silver nanoplates. The optical in-plane dipole surface plasmon resonance (SPR) bands of these Ag nanoplates can be tuned from 608 nm to 980 nm via tannin deoxidization method. The formation mechanism of triangular silver nanoplates was proposed. The tannin deoxidization method realizes a convenient modulation of the absorption band of Ag nanostructures within the visible near-infrared (IR) region both in aqueous solvent and on substrates under mild conditions.

Triangular Au-Ag framework nanostructures prepared by multi-stage replacement and their spectral properties

Triangular Au-Ag framework nanostructures (TFN) were synthesized via a multi-step galvanic replacement reaction (MGRR) of single-crystalline triangular silver nanoplates in a chlorauric acid (HAuCl 4) solution at room temperature. The morphological, compositional, and crystal structural changes involved with reaction steps were analyzed by using transmission electron microscopy(TEM), energy-dispersive X-ray spectrometry (EDX), and X-ray diffraction. TEM combined with EDX and selected area electron diffraction confirmed the replacement of Ag with Au. The in-plane dipolar surface plasmon resonance (SPR) absorption band of the Ag nanoplates locating initially at around 700 nm gradually redshifted to 1 100 nm via a multi-stage replacement manner after 7 stages. The adding amount of HAuCl 4 per stage influenced the average redshift value per stage, thus enabled a fine tuning of the in-plane dipolar band. A proposed formation mechanism of the original Ag nanoplates developing pores while growing Au nanoparticles covering this underlying structure at more reaction steps was confirmed by exploiting surface-enhanced Raman scattering (SERS).

Crystal growth of different morphologies (nanospheres, nanoribbons and nanoplates) of silver nanoparticles

Silver nanoribbons and nanoplates have been synthesized by the classical silver-mirror reaction by changing the reaction conditions at room temperature. It was found that the reaction time and [ammonia] were an important factor for the growth of nanoparticles having different morphologies. Silver nanoplates and nanoribbons can be achieved in high yield by adjusting the reaction time and ammonia content, respectively. The formation rate of silver nanoparticles was investigated by UV–visible spectroscopy. Transmission electron microscopy (TEM) and selected areas electron diffraction (SAED) have been employed to characterize the resulting nanoplates and nanoribbons. Ostwald ripening process was observed which caused fusion among growing small spheres silver nanoparticles leads to the formation of nanoribbons at lower [ammonia].

Facile fabrication of silver nanoplates via a solvothermal method

This paper describes a simple solvothermal route to synthesize silver nanoplates by reduction of silver nitrate (AgNO3) with N,N-dimethylformamide. In this approach, ferric chloride (FeCl3) servers as the controlling agent, enabling the control over the concentration of free Ag+ ions in the solution. As the concentration of FeCl3 added to the reaction was increased, the morphologies of silver nanostructures evolved from triangular silver nanoplates to hexagonal silver nanoplates. The structures of these nanoplates were characterized by X-ray diffraction, electron microscopy and electron diffraction. A possible mechanism is proposed to interpret the shape-controlled synthesis of silver nanostructures. Finally, our results suggest that this method provides a convenient way to prepare silver nanostructures with different morphologies.

High-yield, size-controlled synthesis of silver nanoplates and their applications as methanol-tolerant electrocatalysts in oxygen reduction reaction

A novel method for the synthesis of as-prepared Ag nanoplates in high yield and the control of their dimensions has been developed. In this method, hexadecyltrimethyl ammonium ions (CTA +) are used as a trace additive in a seed solution for blocking the seed surface to govern the growth direction on nanoplate in the growth pathway, leading to a high-yield production of the Ag nanoplates with mixed morphologies, mainly triangular nanoplates and nanodisks. The spectra of the obtained nanoplate solution showed a high-intensity peak attributed to the in-plane dipole resonance and a low-intensity peak at 400 nm. By decreasing the amount of CTA +, the mean edge length of triangular nanoplates could be changed from ∼78.7 nm–∼124.8 nm. The in-plane dipole resonance peak corresponding to change in the mean edge length shifted from 630 nm to 785 nm, respectively. The mean edge length of triangular nanoplates could also be controlled from 70 nm to 148 nm by decreasing the CTA +-adsorbed seed amount. To investigate the practical feasibility of application of the proposed method, the prepared nanoplates were used as a methanol-tolerant electrocatalyst in an oxygen reduction reaction (ORR). An analysis conducted using a rotating ring-disk electrode showed that these nanoplates have high activity towards the ORR and that the electron transfer numbers ( n) were 3.85, 3.83, 3.81, and 2.94 for 70 nm, 124 nm, 148 nm nanoplates, and macroscopic Ag electrode, respectively. If the present of methanol, the corresponding n values of 3.82, 3.81, 3.78, and 2.30 were detected. Despite working in the methanol-tolerant solution, the prepared Ag nanoplates still exhibited high electroactivity and their ORR proceeded via an approaching 4-electron pathway.

Isothermal crystallization of polyethylene oxide/silver nanoplate composites

AbstractThis research was accomplished to investigate the kinetics of isothermal crystallization of polyethylene oxide (PEO)/silver nanoplate composites. It was obtained that the spherulites increased in size and numbers with time for the composites with various particle loadings. Additionally, the spherulite growth rate of composites decreased with an increase in the crystallization temperature and increased with the addition of nanoplates. The spherulite growth rate was further analyzed by the theory developed by Lauritzen and Hoffman. The product of the lateral surface free energy (σ) and the end surface free energy (σe) decreased with an increase in the content of nanoplates. We proposed the possible crystallization mechanisms of these PEO/nanoplate composites according to the change of σ and σe with the presence of nanoplates. A controlled experiment showed a minor change in PEO crystallization with the presence of a surfactant C16TAB. This implied that the unique size and shape of nanoplates plays a key role on hindering the primary nucleation of PEO and increasing the spherulite growth rate. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Non‐isothermal crystallization of poly(ethylene oxide)/silver nanoplate composites

AbstractThe non‐isothermal crystallization of poly(ethylene oxide) (PEO)/silver nanoplate composites was studied using differential scanning calorimetry. The non‐isothermal crystallization was analyzed by combining the Avrami and Ozawa equations. It was found that the Avrami exponent for neat PEO ranges from 2.51 to 2.53, whereas it ranges from 2.54 to 3.16 for its composites, indicating that the spherical crystal morphology does not change with the addition of nanoplates. However, the rate determination of crystal growth transfers from diffusion to nucleation. The crystallization half‐time showed an increase with the addition of silver nanoplates in PEO, indicating that the overall crystallization rate of PEO decreases with the addition of nanoplates. However, the nucleation activity is larger than unity in the composites and the value increases with an increase in the nanoplate content. This behavior implies that the nanoplates act as anti‐nucleating agents to hinder nucleation. Copyright © 2011 Society of Chemical Industry

Polyol synthesis of silver nanoplates: The crystal growth mechanism based on a rivalrous adsorption

A polyol reducing approach has been applied to synthesize silver nanoplates with an average thickness of 50 nm and edge length of 3 μm in the presence of poly (vinylpyrrolidone) (PVP) and HNO 3. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscropy (TEM), and electron diffraction are used to characterize these silver nanoplates. Findings indicate that the nanoplates are single crystals and with their basal plane as (1 1 1) lattice plane. On the basis of the results from thermogravimetric analysis (TG), Fourier transform infrared spectroscopy (FT-IR) and Raman spectroscopy, a crystal growth mechanism based on the rivalrous adsorption between PVP and CN − ions on the surface of silver nanoplates is supposed to explain the crystal anisotropic growth.

Silver nanoplates and nanowires by a simple chemical reduction method

This paper describes a simple preparation of single-crystalline Ag-nanoparticles including plates, and wires in water by truncated triangular particles for the first time during the reduction of [Ag(NH₃)₂]⁺ complex with glucose at room temperature. Silver particles were characterized by means of the conventional transmission electron microscopy (TEM) and UV-VIS spectroscopy. Cetyltrimethylammonium bromide, CTAB, plays a number of roles during the redox process by solubilizing the reactants, controlling the nucleation and/or growth of nanoparticles, stabilizing the thus-prepared Ag-nanoparticles and minimizing the formation of Ag₂O, AgCl, and AgBr precipitates. It was found that the rate constant and absorbance of silver nanoparticles were sigmoidal to the concentration of silver nitrate.

Synthesis of silver/SiO 2/Eu:Lu 2O 3 core–shell nanoparticles and their polymer nanocomposites

We report a core–shell approach that combines silver nanoparticles as the metal core component with Eu:Lu 2O 3 as the phosphor shell component. The core–shell design contains an optically transparent SiO 2 intermediate layer that separates the metallic nanoparticle core and the phosphor shell. The thickness of the SiO 2 layer is in the nanometer range and can be tuned, so as to provide for different interactions between the core and shell. To demonstrate the versatility of the design, spherical silver nanoparticles or wavelength-tunable plasmonic silver nanoplates are used as the core component. In addition, a nanocomposite phosphor was fabricated by embedding the core–shell nanoparticles into a transparent polymeric matrix. The core–shell metal-phosphor design presented here serves as framework for the fabrication of inexpensive nanocomposite scintillator.

Direct printing of silver nanoparticles by an agarose stamp on planar and patternedsubstrates

In this study, we have used an agarose stamp to conduct direct printing of silver nanoparticles,nanowires and nanoplates on both planar and structured substrates. Nanoparticle solutioncould be first coated on an agarose stamp, and then transferred to a planar substrate.Micro-patterns comprising metal nanoparticles could be printed on planar substrates withoutthe formation of residual layers. Thus a three-dimensional metal microstructure could beeasily fabricated. The patterning of electrodes by printing Ag nanowires directly onTiO2 was also demonstrated to fabricate resistive random access memory (RRAM) devices byall-solution-processing methods. By using a flat agarose stamp, the patterns printed on themicrostructured substrates were quite different from those on the nanostructuredsubstrates. On the microstructured substrates, direct printing could print silvernanoparticles onto the protrusion surface, and could print silver layers as thickas several microns, useful for high conductivity electrodes. On the substrateswith nanostructures such as photonic crystals or nano-gratings, direct printingcould transfer nanoparticles into the grooves or cavities only due to the contactof the agarose stamp with the groove or concavity surface. A new approach tofabricate metal wire grid polarizers was further demonstrated. A nanoporousagarose stamp has a good potential for printing using nanoparticle suspension.