Ag Nanosheets Research Articles

Self‐seeding synthesis of silver nanosheets with binary reduction in poly(vinylpyrrolidone)–sodium dodecyl sulphate aggregation microreactor

Silver (Ag) nanosheets were synthesised through a facile self-seeding strategy with binary reduction in the poly(vinylpyrrolidone) (PVP)–sodium dodecyl sulphate (SDS) aggregation microreactor, in which the size and morphology of Ag nanoparticles were able to be regulated by concentration or pH dependence. In this approach, PVP and SDS built the microreactor together and served as a synthesis template; a trace of sodium borohydride (NaBH4) was employed to rapidly trigger the competitive formation of small Ag seeds, while PVP was responsible for the subsequent reduction and slow crystal growth. The size and morphology of the nanosheets could be gently regulated with the concentrations of PVP or SDS and the pH of the reaction solution; while the dramatic variance of size and morphology was primarily induced by NaBH4 concentration. Free PVP monomers with lower concentration induced irregular particles, while the lower concentration of NaBH4 led to the formation of small and regular nanosheets. Both particle size and morphology could be regulated with SDS concentration dependence if the SDS concentration was higher than the critical aggregation concentration. Higher SDS concentrations favoured smaller particle sizes and nanosheet formation. Two-dimensional planar Ag nanostructures were generated at pH 9–10, where [Ag(NH3)2]+ existed at a stable complex ionisation state.

Investigation of the synthesis, SERS performance and application in glucose sensing of hierarchical 3D silver nanostructures

In this paper, the synthesis, SERS performance and application in glucose sensing of hierarchical 3D Ag nanostructures (NSs) are reported. Large-scale Ag jujube-like architectures were produced via the galvanic reaction process in a mixed solution of trisodium citrate (TSC) and AgNO3 on Cu nanoparticles disproportioned from Cu2O membranes. X-ray diffraction, scanning electron microscopy, atomic force microscopy, high resolution transmission electron microscopy, and Raman spectroscopy have been utilized to characterize the as-prepared samples. It was found that the defects existed in the Ag crystals may play a significant role in the morphological formation of the building units of the self-assemblies. In addition, the optimum ratio of the Ag+ concentration to the TSC addition amount for preparing the desired Ag nanojujubes (NJs) was determined by studying the effects of the Ag+ concentration and the TSC addition on the morphology of the final products. The formation mechanism of the hierarchical 3D AgNJs was then discussed. Furthermore, in terms of sensitivity, reproducibility and stability, jujube-like hierarchical architectures constituted of Ag nanosheets with highly-roughened surfaces were proved to be promising for surface-enhanced Raman scattering (SERS) applications, which were further demonstrated in comparison with other AgNSs. It is also worth pointing out that jujube-like hierarchical Ag architectures performed well in glucose detection, which would have great potential in the biological and medical fields.

Seed-mediated approach for the size-controlled synthesis of flower-like Ag mesostructures

Flower-like Ag mesostructures with the sizes in the range of 200nm to 700nm have been synthesized via a simple seed-mediated approach. The size-tunable synthesis can be easily attained by adjusting the concentration of Ag seeds. The obtained Ag mesostructures are assembled by primary Ag nanosheets, which exhibit a flower-like architecture. None of surfactant was involved during the synthesis process, and thus, these Ag mesostructures hold the chemically clean surfaces. Compare to the previous approach for flower-like Ag mesostructures, the present method is not only simple and reliable, but also exhibits the advantages both in green procedure and size controllable. These flower-like Ag mesostructures reveal large surface area and can serve as highly efficient catalysis for the NaBH4 reduction of p-nitrophenol to p-aminophenol.

Fabrication of silver nanosheets on quartz glass substrates through electroless plating approach

Silver nanosheets (NSs) have been synthesized by an electroless plating approach using a complexation mechanism of triethanolamine (TEA) and Ag+ to reduce the oxidation–reduction potential difference and slow down the deposition speed of Ag on quartz glass substrates. The synthesized Ag NSs with 500 nm in edge length and 30 nm in thickness stand on the substrates and are dispersed uniformly. The formation mechanism of Ag NSs is proposed. The formation of Ag NSs is attributed to the molar ratio of AgNO3 to TEA, the concentration of AgNO3 and the influence of reaction temperature. This study is important in vertical immobilization Ag NSs on solid substrates, which could provide substrates for catalysis or surface-enhanced Raman scattering.

One-step large-scale synthesis of micrometer-sized silver nanosheets by a template-free electrochemical method

We have synthesized micrometer-sized Ag nanosheets via a facile, one-step, template-free electrochemical deposition in an ultra-dilute silver nitrate aqueous electrolyte. The nanosheet growth was revealed to occur in three stages: (1) formation of polygonal Ag nuclei on a substrate, (2) growth of {112}-faceted nanowire from the nuclei, and (3) anisotropic growth of (111)-planar nanosheets, approximately 20 to 50 nm in thickness and 10 μm in width, in the <112>−direction. The vertical growth of the facet nanowire was induced by the strong interface anisotropy between the deposit and electrolyte due to the ultra-dilute concentration of electrolyte and high reduction potential. The thickness of Ag nanosheets was controllable by the adjustment of the reduction/oxidation potential and frequency of the reverse-pulse potentiodynamic mode.

A dispersive scattering centers-based strategy for dramatically enhancing the photocatalytic efficiency of photocatalysts in liquid-phase photochemical processes: a case of Ag nanosheets

A dispersive scattering centers-based strategy was proposed to enhance the photocatalytic efficiency of photocatalysts in liquid-phase photochemical processes. Photocatalytic efficiencies of the photocatalyst, Degussa P25, in water splitting and photodegradation were markedly enhanced by using Ag nanosheets as dispersive scattering centers.

Generation of Ag–Ag2O complex nanostructures by excimer laser ablation of Ag in water

Pulsed laser ablation in liquid (PLAL) has been well established as a facile method to produce nanoparticles from bulk materials, but it is still insufficient for fabricating anisotropic and complex nanostructures, especially without the use of surfactants. Here, we demonstrate that silver (Ag) nanosheets can be produced by pulsed excimer laser ablation of bulk Ag in water via laser re-processing of the laser-produced primary clusters. We also show that by combining PLAL and drop evaporation, rice-shaped Ag-Ag(2)O particles and their assemblies can be generated on Si substrates, because the interior flow of an evaporating colloidal drop could redistribute the laser-produced primary clusters, which results in the formation of complex nanostructures. These results show that PLAL is able to fabricate novel micro-/nanostructures while keeping its merit of "clean" fabrication.

Plasmon-enhanced organic solar cells with solution-processed three-dimensional Ag nanosheets

The silver nanosheets (AgNSs) prepared via normal silver mirror reaction were used to improve the performance of organic solar cells. AgNSs with a size of about 100nm in width and 10nm in thickness formed a 3-D network on an indium tin oxide (ITO) surface. Organic solar cells with a structure of ITO/AgNSs/poly(3,4-ethylene dioxythiophene) poly(styrenesulfonate) (PEDOT:PSS)/poly(3-hexylthiophene) and [6,6]-phenyl C61 butyric acid methyl ester (P3HT:PC61BM)/LiF/Al exhibited an open circuit voltage (Voc) of 0.60±0.01V, short circuit current density (Jsc) of 11.16±0.08mA/cm2, a fill factor (FF) of 53.69±0.92%, and power conversion efficiency (PCE) of 3.60±0.06%. The PCEs of organic solar cells with 3-D AgNSs layers were 1.29 times that of the control device without 3-D AgNSs layer. We attributed the improvement of the efficiency to localized surface plasmon resonance (LSPR) induced by the 3-D network of AgNSs, which enhanced the light harvest of active layers, increased the probability of exciton generation and dissociation.

Spectroscopic Properties of Multilayered Gold Nanoparticle 2D Sheets

We report the fabrication technique and optical properties of multilayered two-dimensional (2D) gold nanoparticle sheets ("Au nanosheet"). The 2D crystalline monolayer sheet composed of Au nanoparticles shows an absorption peak originating from a localized surface plasmon resonance (LSPR). It was found that the absorption spectra dramatically change when the monolayers are assembled into the multilayers on different substrates (quartz or Au). In the case of the multilayers on Au thin film (d = 200 nm), the LSPR peak is shifted to longer wavelength at the near-IR region by increasing the number of layers. The absorbance also depends on the layer number and shows the nonlinear behavior. On the other hand, the multilayers on quartz substrate show neither such LSPR peak shift nor nonlinear response of absorbance. The layer number dependence on metal surfaces can be interpreted as the combined effects between the near-field coupling of the LSPR and the far-field optics of the stratified metamaterial films, as proposed in our previous study. We also report the spectroscopic properties of hybrid multilayers composed of two kinds of monolayers, i.e., Au nanosheet and Ag nanosheet. The combination of the different metal nanoparticle sheets realizes more flexible plasmonic color tuning.

Facile synthesis of large-scale Ag nanosheet-assembled films with sub-10 nm gaps as highly active and homogeneous SERS substrates

We report a facile low-cost synthetic approach to large-scale Ag nanosheet-assembled films with a high density of uniformly distributed sub-10nm gaps between the adjacent nanosheets on Si substrates via galvanic cell reactions. The distribution density of Ag nanosheets on substrates could be tailored by tuning the duration of the HF-etching and the concentration of citric acid in the solution. Furthermore, in conjunction with a conventional photolithography, highly uniform patterned Ag nanosheet-assembled structures with different morphologies can be achieved on Si substrates via galvanic-cell-induced growth. By using rhodamine 6G as a standard test molecule, the large-scale Ag nanosheet-assembled films exhibit highly active and homogenous surface-enhanced Raman scattering (SERS) effect and also show promising potentials as reliable SERS substrates for rapid detection of trace polychlorinated biphenyls (PCBs).

Highly Sensitive Surface-Enhanced Raman Spectroscopy (SERS) Platforms Based on Silver Nanostructures Fabricated on Polyaniline Membrane Surfaces

Here, we demonstrate a facile synthesis of homogeneous Ag nanostructures fully covering the polyaniline (PANI) membrane surface simply by introducing organic acid in the AgNO(3) reaction solution, as an improved technique to fabricate well-defined Ag nanostructures on PANI substrates through a direct chemical deposition method [Langmuir2010, 26, 8882]. It is found that the chemical nature of the acid is crucial to create a homogeneous nucleation environment for Ag growth, where, in this case, homogeneous Ag nanostructures that are assembled by Ag nanosheets are produced with the assistance of succinic acid and lactic acid, but only scattered Ag particles with camphorsulfonic acid. Improved surface wettability of PANI membranes after acid doping may also account for the higher surface coverage of Ag nanostructures. The Ag nanostructures fully covering the PANI surface are extremely sensitive in the detection of a target analyte, 4-mercaptobenzoic acid (4-MBA), using surface-enhanced Raman spectroscopy (SERS), with a detection limit of 10(-12) M. We believe the facilely fabricated SERS-active substrates based on conducting polymer-mediated growth of Ag nanostructures can be promising in the trace detection of chemical and biological molecules.

Template-assisted synthesis of uniform nanosheet-assembled silver hollow microcubes

Uniform silver hollow microcubes assembled by nanosheets have been synthesized by using Cu(2)O cubes as chemical template at room temperature. In the reaction system, the Ag(+) ions were reduced by Cu(+) ions released from Cu(2)O cubes, meanwhile the morphology of silver growth units were controlled by trisodium citrate in the form of nanosheets around the template during the reaction. It was found that the concentrations of acid, citrate ions and AgNO(3) were critical to the formation of perfect nanosheet-assembled hollow microcubes. According to the experiment results, an interface redox growth mechanism of nanosheet-assembled Ag hollow microcubes was proposed. Since the obtained Ag hollow cubes are composed of Ag nanosheets, the hierarchical shells are bestrewed with pores or gaps which created abundant active "hot spots" for highly sensitive surface enhanced Raman scattering (SERS) detection. The SERS experiments using rhodamine 6G (R6G) as probing molecules showed that the pack density and porous structure of the shell in the final products strongly affected the SERS signals. The product with higher porous shell structure exhibited stronger SERS signals than others, indicating the rough Ag hollow microcubes could act as excellent substrates for ultrasensitive detection.

Electrochemical growth and oxygen reduction property of Ag nanosheet arrays on a Ti/TiO 2 electrode

A standing Ag nanosheet array was successfully deposited using an electrochemical method. The results demonstrated that the adsorption of polyvinylpyrrolidone (PVP) over the Ag (111) plane during deposition (1) inhibits the crystalline growth in the [111] direction, (2) stacks atomic faults in the fcc structure, and (3) forms a standing Ag nanosheet composed essentially of (111) planes. In an application, this Ag nanosheet array can be successfully used as an oxygen reduction catalyst. Based on Koutecky–Levich equation, the involved electron number at −0.2 V was 3.97.

Characterization of Remote Photocatalytic Activity of TiO2 with Ag Nanosheet

Remote photocatalytic reaction of a Pt-modified TiO2 thin film was investigated by using Ag nanosheet as a marker. The Ag nanosheet is a two-dimensional crystalline film composed of myristate-capped silver nanoparticles (d = 5 nm), which has a strong localized plasmon absorption band at λmax = 470 nm. The Ag nanosheet on a 50 nm gold film was set on a measurement cell at 10 μm distance from the Pt-modified TiO2 film. Then the refractive index change of Ag nanosheet was real-time monitored by a surface plasmon resonance (SPR) technique under UV light irradiation (wavelength: 365 nm) from the back side of the TiO2 film. The plasmon resonance angle shifted to lower angle in consequence of the degradation of Ag nanosheet due to the remote photocatalytic reaction. We found the reaction was continued even after stopping UV irradiation, i.e., a chain reaction in Ag nanosheet was suggested. The chain reaction was influenced by N2 gas purge as well as the ligand exchange of myristate capping molecules to alkyl thiolate.

Collective plasmon modes excited on a silver nanoparticle 2D crystalline sheet

This paper describes unique plasmonic characteristics of two dimensional (2D) crystalline sheets composed of homogeneous Ag nanoparticles (AgNPs) fabricated by the Langmuir-Schaefer method at an air-water interface. The localized surface plasmon resonance (LSPR) band of the Ag nanosheet was tuned by changing the interparticle distance of AgNPs via the length of the organic capping molecules. Red shift of the LSPR band of the AgNPs sheet followed an exponential law against the interparticle distance in a similar manner to the previous reports of metal nanodisc pairs. However, the shift was much larger and less dependent on the interparticle separation gap. This phenomenon is reasonably interpreted as the long-range interaction of LSPR in the 2D sheet ('delocalized' LSPR) confirmed by simulation using the finite difference time domain (FDTD) method. The FDTD simulation also revealed additional enhancement of local electric fields on the 2D sheet compared to those on the single or paired particles.

Facile Fabrication of Homogeneous 3D Silver Nanostructures on Gold-Supported Polyaniline Membranes as Promising SERS Substrates

We report a facile synthesis of large-area homogeneous three-dimensional (3D) Ag nanostructures on Au-supported polyaniline (PANI) membranes through a direct chemical reduction of metal ions by PANI. The citric acid absorbed on the Au nuclei that are prefabricated on PANI membranes directs Ag nanoaprticles (AgNPs) to self-assemble into 3D Ag nanosheet structures. The fabricated hybrid metal nanostructures display uniform surface-enhanced Raman scattering (SERS) responses throughout the whole surface area, with an average enhancement factor of 10(6)-10(7). The nanocavities formed by the stereotypical stacking of these Ag nanosheets and the junctions and gaps between two neighboring AgNPs are believed to be responsible for the strong SERS response upon plasmon absorption. These homogeneous metal nanostructure decorated PANI membranes can be used as highly efficient SERS substrates for sensitive detection of chemical and biological analytes.

Synthesis of homogeneous silver nanosheet assemblies for surface enhanced Raman scattering applications

Conducting polymers have been proved to be effective reducing agents in the synthesis of noble metal nanoparticles. We demonstrate here the fabrication of homogeneous Ag nanosheet assemblies on conducting polymer membranes with 5 wt% polyaniline (PANI) substituted by conductive additives like graphite (G) or multi-walled carbon nanotubes (CNTs). The inclusion of conductive additives that act as electrical connectors for the PANI particles changes the surface property and creates a homogeneous nucleation environment, leading to the membrane surface completely covered by the Ag nanosheet structures. The pack density of the nanosheets can be simply tuned by modulating the concentration of AgNO3 aqueous solution. The as-prepared Ag nanosheet assemblies with abundant interstitial sites show strong SERS responses toward the mercaptobenzoic acid (MBA) molecules, with a detection sensitivity down to 5 ppm. A proper acid etching of these Ag nanosheet structures in 0.1 M HNO3 aqueous solution makes the nanoparticles that form the nanosheets much more exposed to the analyte molecules, and an even stronger Raman enhancement can be obtained. We believe the homogeneous Ag nanosheet assemblies supported on conducting polymer membranes can be sensitive and cost-effective SERS substrates in molecule detection.

New Method to Single-Crystal Micrometer-Sized Ultra-Thin Silver Nanosheets: Synthesis and Characterization

We reported a new method, which uses Cu+ as the efficient and clean reducing agent, to synthesize micrometer-sized ultra-thin silver (Ag) nanosheets in organic solvent containing oleylamine (OAm). The as-synthesized Ag nanosheets are single-crystal, with regular triangular, truncated triangular, hexagonal, and dodecahedral (truncated hexagonal) shapes, with 3−8 μm edge length and 25 ± 15 nm thickness, which are in contrast to the previous reported micrometer-sized metal nanosheets with thickness above 40 nm. Analysis is performed by X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, transmission electron microscopy, selected area electron diffraction, X-ray photoelectron spectroscopy, UV−vis-NIR absorption and transmittance spectroscopy, and optical microscopy, indicating that single-crystal Ag nanosheets are of high quality with a large in-plane size, ultra-thin thickness, and top and bottom enclosed by {111} facets. The present study provides a simple and extendable method to synthesis of micrometer-scale ultra-thin metal nanosheets holding promises for novel physical properties and functional nanodevices.

Trapeziform Ag Nanosheet Arrays Induced by Electrochemical Deposition on Au-Coated Substrate

Trapeziform Ag nanoplate arrays are successfully fabricated on Au-coated silicon substrate by electrochemical deposition. The trapeziform Ag nanoplates are standing on the substrate and dispersed uniformly. The nanoplates are 1−2 μm in edge length and 40 nm in thickness. Further experiments have revealed that the presence of PVP in the electrolyte and low deposition current density together with the Au-coated substrate are indispensable to fabrication of such arrays. The formation of trapeziform Ag nanoplate arrays is attributed to selectively oriented nucleation of Ag and quasi-equilibrium preferential growth on the Au film-coated substrate. This study is of importance in vertical immobilization Ag nanoplates on a solid substrate, which could provide new substrates for some catalysis or surface-enhanced Raman scattering.