Graphene Silver Research Articles

One-pot environmentally friendly amino acid mediated synthesis of N-doped graphene–silver nanocomposites with an enhanced multifunctional behavior

The present paper reports the one-pot synthesis of N-doped graphene-Ag nanocomposites (N-GrAg) involving the in situ generation of Ag nanoparticles (NPs). The simultaneous reduction of GO and Ag(+) to produce N-GrAg has been achieved under mild reaction conditions using an environmentally benign reducing agent, glycine, in aqueous medium without adding any external stabilizer. XRD and SAED analyses revealed the presence of Ag in the fcc structure. HRTEM analysis shows a 'd' spacing of 0.236 nm corresponding to the highest intensity (111) reflection of Ag which matches the fcc structure. The N-doping of graphene and its uniform decoration by Ag NPs (with an av. dia. of 17.5 nm) having a relatively low surface atomic % of Ag (0.309) are evidenced by TEM and XPS analyses. Raman spectroscopy has also revealed that the decoration of N-Gr with Ag NPs resulted in the enhancement of the D and G bands by about 365%. The presence of Ag in N-GrAg prevents the folding of the graphene sheet as was revealed by TEM analysis. The supramolecular interactions of Ag with different moieties of N in N-GrAg were evidenced by IR, (13)C NMR and XPS analyses, which resulted in the enhancement of its surface area and electrical conductivity as compared to that of N-Gr. The presence of Ag NPs on N-Gr increased the current response in cyclic voltammetry by more than seven fold as compared to that of N-Gr. These nanocomposites exhibited a fairly high SERS activity for 4-aminothiophenol, employed as the probe molecule, and allowed its detection at a 50 nM concentration even for the fairly small sized Ag NPs used in the present work.

Synergistic antibacterial activity of PEGylated silver–graphene quantum dots nanocomposites

The emergence of antibiotic-resistant bacteria is a major threat to world-wide public health. Functionalized nanoparticles could offer novel strategies in this post-antibiotic era. In this study, we developed nanocomposites of silver nanoparticles decorated with graphene quantum dots (Ag-GQDs) using pulsed laser synthesis. The nanocomposites were PEGylated, which increases their biocompatibility and solubility in aqueous solutions. The HR-TEM micrographs of bare GQDs show that their size is in the range of 1.6–4nm, and the lattice spacing is 0.214nm, which corresponds to the (100) lattice fringes of graphene. The antibacterial activity of Ag-GQDs was evaluated and compared to that of bare GQDs and commercial silver nanoparticles (Ag-NPs) against both Gram-negative and Gram-positive bacteria, using Pseudomonas aeruginosa and Staphylococcus aureus as model bacteria, respectively. Concentration values of 25 and 50μg/mL are required for Ag-GQDs to inhibit the growth of S. aureus and P. aeruginosa bacteria, respectively. The fractional inhibitory concentration (FIC) index is below 0.5 indicating that there is a synergistic effect between Ag-NPs and GQDs. Kirby–Bauer tests showed that Ag-GQDs inhibit P. aeruginosa and S. aureus, in contrast to bare GQDs and Ag-NPs alone. Cell viability of normal mammalian cells treated with Ag-GQDs showed that cell viability is maintained at 100% for cells incubated with Ag-GQDs. The decoration of Ag-NPs with GQDs minimizes their cytotoxicity in mammalian cells and increases their biocompatibility. Ag-GQDs have potential applications in the fabrication of antibacterial coatings, self-sterile textiles, and personal care products.

Flexible Cellulose-Based Films of Polyaniline–Graphene–Silver Nanowire for High-Performance Supercapacitors

We report a facile fabrication of a high-performance supercapacitor (SC) using a flexible cellulose-based composite film of polyaniline (PANI), reduced graphene oxide (RGO), and silver nanowires (AgNWs). The flexibility, high capacitive behavior, cyclic stability, and enhanced rate capability of the entire device make it a good candidate for flexible and wearable SCs. Our results demonstrate that a capacitance as high as 73.4 F/g (1.6 F/cm2) at a discharge rate of 1.1 A/g is achieved. In addition, the SC shows a power density up to 468.8 W/kg and an energy density up to 5.1 Wh/kg. The flexibility of the composite film is owing to the binding effect of cellulose fibers as well as AgNWs. The superb electrochemical performance of the device is found to be mainly attributed to the synergistic effect between PANI/RGO/AgNWs ternary in a cushiony cellulose scaffold and porous structure of the composite.

Environmentally friendly synthesis of graphene–silver composites with surface-enhanced Raman scattering and antibacterial activity via reduction with l-ascorbic acid/water vapor

Free-standing reduced graphene oxide–Ag composite films with different Ag contents not only possess high Raman enhancement, but also have antibacterial activity.

Oxides in silver-graphene nanocomposites: electrochemical signatures and electrocatalytic implications.

Herein we report an electrochemical approach to establish the presence of silver oxides in silver-reduced graphene oxide (Ag-rGO) nanocomposites synthesised under alkaline conditions. The recorded electrochemical signatures, further supported and validated by UV-Vis spectroscopy, XRD and TEM analysis, clearly establish the presence of an oxide phase of silver in the nanodimensional silver present in Ag-rGO. The Ag-rGO was tested for its electrocatalytic and electrosensing activity for hydroquinone (H2Q) and ascorbic acid (AA). The presented results establish that the electrocatalytic and electrosensing potential of the Ag-rGO for H2Q and AA can be enhanced through electroreduction of the oxide phase of silver in these nanocomposites. Our results prove that the electrocatalytic and electroanalytic activities of electroreduced Ag-rGO for AA are better than most of the electrode materials reported so far in the literature.

The silver–graphene electrode. Building, stability, and catalytic efficiency

The cathodic polarization of smooth silver surfaces covered with natural graphite in dimethylformamide or acetonitrile containing tetraalkylammonium salts induces a spectacular exfoliation process followed by the release of almost all deposited graphite particles; the ablation goes practically to the last (few) layer(s) of graphene in immediate contact with Ag. Another efficient method to form such interesting interfaces consists in the deposit of graphite micro-flakes (pre-exfoliated at a mercury pool at −2V) by rubbing them onto small size Ag electrodes. The as-prepared silver/graphite surfaces are stable and exhibit reproducible voltammetric responses related to the reduction (doping) of remaining graphene layers. Their nature and intensities (not related to diffusion and quasi perfectly proportional to the scan rate) essentially depend on the size of the concerned TAA+ cations. Total amounts of electricity involved in reduction/oxidation are quite stable and can be assigned to the doping of remaining graphene layers attached to Ag. The average coverage based on TAA+ mono-layer formation was estimated to be <10−9molcm−2. Chemical modifications of these carbon layers and first experiments concerning catalytic properties assigned both to graphene and Ag are presented.

Synthesis and characterization of a poly-tetraaniline-urethane/Ag-nanowire or/graphene conductive elastomer

Tetraaniline-containing poly(urethane-urea) (TAPU), a new material, was synthesized in this study and blended with Ag nanowire (≤ 3 wt.%), denoted as TAPU/A, or graphene (≤ 3 wt.%), denoted as TAPU/G, to form a conductive elastomer. The conductivities can be improved from less than 10−10 S/cm, for pure PU, to 6 × 10−2 S/cm, for the TAPU/A 3 %. The tensile strength and modulus were increased twofold and 20- to 60-fold, respectively, for TAPU/A 3 % or TAPU/G 3 %. The viscoelastic creep was simulated effectively using a Burgers model. Additionally, TAPU/A and TAPU/G demonstrate a higher viscosity, a higher retardation time, and a lower compliance D 1 than regular TAPU does. TAPU/Ag and TAPU/G exhibit less elasticity but more insignificant permanent deformation than TAPU does, because the additives function as a chain holder. The stretching tension induces the orientation of silver nanowire or graphene. Such orientation is believed to affect electrical conductivity positively. The solid form of the elastomer, TAPU/A or TAPU/G, can be heated and dissolved in a solvent to be reshaped, indicating that this compound is uniquely reworkable.

Three-Dimensional Highly Conductive Graphene–Silver Nanowire Hybrid Foams for Flexible and Stretchable Conductors

Graphene foams have showed huge application potentials owing to their unique 3D structure and superior properties. Thus, it is highly desired to develop a simple and effective pathway to fabricate high performance graphene-based foams. Here, we present a polymer template-assisted assembly strategy for fabricating a novel class of graphene/AgNW hybrid foams. The hybrid foams show 3D ordered microstructures, high thermal stability, and excellent electrical and mechanical properties, and demonstrate huge application potential in the fields of flexible and stretchable conductors. Importantly, the polymer-template assisted assembly technique is simple, scalable, and low-cost, providing a new synthesis protocol for various multifunctional graphene hybrid foam-based composites.

A biorecognition system for concanavalin a using a glassy carbon electrode modified with silver nanoparticles, dextran and glucose oxidase

Concanavalin A (Con A) was chosen as a model lectin protein for an electrochemical study on the interaction between lectins and carbohydrates. A composite prepared from reduced graphene oxide and silver nanoparticles (rGO-AgNPs) acted as a redox probe, and phenoxy-derivatized dextran (DexP) and glucose oxidase (GOx) acted as recognition elements. The rGO-AgNPs, DexP and GOx were deposited on the surface of a glassy carbon electrode. The immobilized DexP and GOx showed high affinity for the target lectin Con A. The surface-modified biosensor was characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, UV–vis absorption spectra, cyclic voltammetry and electrochemical impedance spectroscopy. Due to the high affinity of Con A for both DexP and GOx, the biosensor displays a detection limit for Con A that is as low as 0.67 ng mL−1 at a working voltage of 48 mV. The response is linear in the 2.0–322 ng mL-1 concentration range, thus offering a sensitive means for the determination of Con A.

A facile and eco-friendly synthesis of graphene–silver hybrid materials for transparent conductive films

Recently, graphene–silver (GN–Ag) hybrid material has attracted a great attention to substitute indium tin oxide (ITO) and/or fluorine tin oxide (FTO) in the transparent conductive electrodes (TCE) due to their multifunctional extraordinary properties. However, the synthesis process of this hybrid material requires some toxic chemicals and complicated processes. Herein, we report a simple, an efficient and an environment-friendly approach to synthesize the graphene–silver nanoparticles (GN–AgNPs) hybrid material for transparent, conductive and flexible films, which can further be used in various modern optoelectronic devices. The morphological and structural characteristics of hybrids are studied via several techniques such as scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and Raman spectroscopy. The results of these analysis confirmed that silver AgNPs were successfully decorated on the surface of GN. Furthermore, the sheet resistance of the flexible films with this hybrid structure was significantly lower (~10-fold) than that of the GN-only deposited films at the wide range of transmittance.

ChemInform Abstract: Synthesis of Silver—Graphene Nanocomposite and Its Catalytic Application for the One‐Pot Three‐Component Coupling Reaction and One‐Pot Synthesis of 1,4‐Disubstituted 1,2,3‐Triazoles in Water.

AbstractA new heterogeneous graphene based catalyst with silver nanoparticles is developed and successfully applied as catalyst for the three component condensation of aldehydes, terminal alkynes, and amines as well as the 1,3‐dipolar cycloaddition of organic azides with terminal alkynes.

In situ green synthesis of silver–graphene oxide nanocomposites by using tryptophan as a reducing and stabilizing agent and their application in SERS

Silver–graphene oxide (Ag–GO) nanocomposites were in situ fabricated rapidly through a green one-pot method by using tryptophan (Trp) as a reducing and stabilizing agent. The morphologies of synthesized Ag–GO nanocomposites were characterized by UV–vis absorption spectroscopy, transmission electron microscopy (TEM), and micro-Raman system. The results indicated silver nanoparticles (Ag NPs) with spherical size were well dispersed on the surface of graphene oxide (GO). The role of pH has been explored to obtain optimum reaction conditions during the growth process. Raman signals of GO were greatly enhanced after Ag NPs loaded on its surface. More importantly, the synthesized Ag–GO nanocomposites exhibited excellent surface-enhanced Raman scattering (SERS) activity as SERS substrates to detect crystal violet (CV) in aqueous solution, and the enhancement factor (EF) from the intensity of the vibrational mode at 1621 cm−1 was calculated to be 1.6 × 105.

Efficiency enhancement of nanorod green light emitting diodes employing silver nanowire-decorated graphene electrode as current spreading layer

We report nanorod green light emitting diodes (NGR-LEDs) with a silver nanowire-decorated graphene electrode (S-DGE) as a current spreading electrode to connect each individual nanorod and to give improved emission efficiency. The current–voltage and electroluminescence characteristics of NGR-LEDs with an S-DGE are enhanced remarkably compared to NGR-LEDs with a graphene electrode. The effective current spreading in the whole emission area after thermal annealing of the S-DGE was attributed to reduced sheet and contact resistances caused by the p-type doping of graphene and enhanced adhesion at the graphene–GaN and graphene–silver nanowire interfaces.

A highly electrically conductive graphene–silver nanowire hybrid nanomaterial for transparent conductive films

Uniform and high-quality graphene oxide thin films were prepared using a dip-coating approach and were reduced to highly electrically conductive graphene nanosheet (GN) transparent conductive films (TCFs) using hydriodic acid. Silver nanowires (AgNWs), which were modified using thiophenol and exhibited a high aspect ratio and high electrical conductivity, were deposited on the surfaces of the GN TCFs through π–π interactions between the aromatic functional groups on the AgNWs and GNs to form high-performance GN/AgNW TCFs. The GN/AgNW hybrid nanomaterial films exhibited a sheet resistance of 71 Ω □−1 and 85% light transmittance.

Graphene–silver nanohybrids for ultrasensitive surface enhanced Raman spectroscopy: size dependence of silver nanoparticles

The surface-enhanced Raman scattering (SERS) mechanism of graphene–silver (GE–Ag) nanohybrids was investigated by studying the Raman signals of rhodamine 6G (R6G) adsorbed onto nanohybrids with different sizes of Ag nanoparticles (NPs). The results showed that the SERS intensity ratios between GE–Ag NPs with Ag NPs with sizes of 9, 25 and 35 nm and pure Ag substrate were estimated to be 2.7, 5.0 and 8.9 respectively. GE sheets did improve the SERS activity due to their high adsorption ability, strong fluorescence quenching and additional chemical enhancement mechanism (CM)-based SERS effect. However, Ag NPs with relatively larger size (∼nm) play a major role in SERS activity of molecules adsorbed on the nanohybrids. Furthermore, the free-standing GE–Ag NP nanohybrid film was fabricated through the vacuum filtration of the optimized GE–Ag NP composite suspension followed by thermal annealing. The as-prepared film has the larger size of Ag NPs and narrower interparticle distance, which provides more “hot spots” for sensitive detection of R6G molecules, with a detection limit at 1 × 10−12 M. Additionally, the relative standard deviation (RSD) values are measured to be below 0.13, revealing a good consistency and reproducibility across the entire area of the film, suggesting this substrate holds a promise for routine SERS detection.

Conductivity improvement of silver flakes filled electrical conductive adhesives via introducing silver–graphene nanocomposites

In this study, silver–graphene nanocomposites (SGNs) were successfully prepared by spontaneous reduction of silver ions and graphene oxide. Silver nanoparticles (about 30 nm) with narrow size distribution were distributed randomly on the surface of graphene. Different amounts of SGNs were introduced into silver flakes filled electrical conductive adhesives (ECAs) to study the effect of SGNs on the properties of the ECAs. The results showed that the volume resistivity of the ECAs decreased first and then increased with the increase of weight ratios of SGNs to silver flakes. While the weight ratio of SGNs to silver flakes was 20:80 (%), the resistivity reached the lowest value of 2.37 × 10−4 Ω cm. The lap shear strength decreased with the increase of the content ration of SGNs. And when the weight ratio of SGNs to silver flakes was 20:80 (%), the lap shear strength of ECA was about 10 MPa. According to the thermogravimetric analysis, the addition of SGNs can cause a slight decrease in the thermal stability of the ECA. In summary, SGNs are the promising candidates for the conductivity improvement of silver flakes filled electrical conductive adhesives.

Synthesis of silver–graphene nanocomposite and its catalytic application for the one-pot three-component coupling reaction and one-pot synthesis of 1,4-disubstituted 1,2,3-triazoles in water

A graphene based composite with silver nanoparticles has been synthesized via a simple chemical route and its catalytic activity has been tested for multi-component reactions and click reaction in a one-pot approach. This silver–graphene nanocomposite shows excellent catalytic activity at room temperature for three-component couplings between aldehydes, alkynes and amines (A3-coupling) and one-pot synthesis of 1,4-disubstituted 1,2,3-triazole via click reaction between in situ generated azides (derived from anilines or amines) and terminal acetylenes. This solid silver–graphene catalyst has been characterized by TEM, Raman, XRD and UV-Visible absorption spectra. The developed catalyst is air-stable, inexpensive, easy to prepare and can be facilely recovered and reused five times without significant decrease in activity and selectivity.

Facile synthesis of flexible graphene–silver composite papers with promising electrical and thermal conductivity performances

Free-standing and flexible graphene–silver (GE–Ag) composite paper has been successfully fabricated through an evaporation of graphene oxide–AgNO3 aqueous aerosol followed by a chemical reduction.

Graphene–silver nanowire hybrid films as electrodes for transparent and flexible loudspeakers

We report a hybrid structure employing two-dimensional graphene and networks of one-dimensional silver nanowires as transparent and flexible electrodes. The hybrid films have sheet resistances as low as ~16 Ω □−1 with a high transmittance of 91.1% at 550 nm, and exhibit impressive stability against oxidation and mechanical flexibility. These properties are superior to commercial transparent electrodes such as indium tin oxides and comparable to the best reported results in transparent electrodes. The hybrid films were successfully applied as transparent and flexible electrodes in acoustic devices that show a high sound pressure level, demonstrating their potential applications for a wide range of optoelectronic and photovoltaic devices.

Graphene as an Electron Shuttle for Silver Deoxidation: Removing a Key Barrier to Plasmonics and Metamaterials for SERS in the Visible

The role of graphene in enabling deoxidation of silver nanostructures, thereby contributing to enhance plasmonic properties and to improve the temporal stability of graphene/silver hybrids for both general plasmonic and meta‐materials applications, as well as for surface enhanced Raman scattering (SERS) substrates, is demonstrated. The chemical mechanism occurring at the graphene–silver oxide interface is based on the reduction of silver oxide triggered by graphene that acts as a shuttle of electrons and as a kind of catalyst in the deoxidation. A mechanism is formulated, combining elements of electron transfer, role of defects in graphene, and electrochemical potentials of graphene, silver, and oxygen. Therefore, the formulated model represents a step forward from the simple view of graphene as barrier to oxygen diffusion proposed so far in literature. Single layer graphene grown by chemical vapor deposition is transferred onto silver thin films, a periodic silver fishnet structure fabricated by nanoimprint lithography, and onto silver nanoparticle ensembles supporting a localized surface plasmon resonance in the visible range. Through the study of these nanostructured graphene/Ag hybrids, the effectiveness of graphene in preventing and reducing oxidation of silver plasmonic structures, keeping silver in a metallic state over months at air exposure, is demonstrated. The enhanced and stable plasmonic properties of the silver‐fishnet/graphene hybrids are evaluated through their SERS response for detecting benzyl mercaptane.