Graphene Silver Research Articles

Microstructure-tunable highly conductive graphene–metal composites achieved by inkjet printing and low temperature annealing

We present a method for fabricating highly conductive graphene–silver composite films with a tunable microstructure achieved by means of an inkjet printing process and low temperature annealing. This is implemented by starting from an aqueous ink formulation using a reactive silver solution mixed with graphene nanoplatelets (GNPs), followed by inkjet printing deposition and annealing at 100 °C for silver formation. Due to the hydrophilic surfaces and the aid of a polymer stabilizer in an aqueous solution, the GNPs are uniformly covered with a silver layer. Simply by adjusting the content of GNPs in the inks, highly conductive GNP/Ag composites (>106 S m−1), with their microstructure changed from a large-area porous network to a compact film, is formed. In addition, the printed composite films show superior quality on a variety of unconventional substrates compared to its counterpart without GNPs. The availability of composite films paves the way to the metallization in different printed devices, e.g. interconnects in printed circuits and electrodes in energy storage devices.

In vitro assessment of activity of graphene silver composite sheets against multidrug-resistant bacteria and Tomato Bushy Stunt Virus

Purpose: To synthesize graphene-based silver nanocomposites and evaluate their antimicrobial and anti-Tomato Bushy Stunt Virus (TBSV) activities.Methods: A graphene-based silver composite was prepared by adsorbing silver nanoparticles AgNPs to the surfaces of graphene oxide (GO) sheets. Scanning electron microscopy was used to analyze the morphology of the synthesized graphene-based silver nanocomposite. This compound was investigated for its antimicrobial activity against several multidrug-resistant human pathogens using the agar well diffusion technique. Moreover, the biocompatibility and antiviral activity of the graphene-based nanocomposite against TBSV was studied in lettuce.Results: The graphene-based silver composite exhibited remarkable antimicrobial effects against pathogenic bacteria including Shigella sonnei and Pseudomonas aeruginosa with zones of inhibition of 32 ± 0.11 and 29 ± 0.05 mm, respectively. They inhibited TBSV better than graphene and GO.Conclusion: The synthesized graphene-based silver composite exhibits potent activity against TBSV and multidrug resistant bacteria, indicating that they are good candidates for future therapeutic applications.Keywords: Graphene oxide, Graphene-based nanocomposite, Antiviral, Antimicrobial, Multidrugresistant (MDR) human pathogens

Синтез, характеристика и применение нанокомпозитов на основе серебряных наночастиц и оксида графена

Синтез, характеристика и применение нанокомпозитов на основе серебряных наночастиц и оксида графена

Graphene-silver hybrid devices for sensitive photodetection in the ultraviolet.

The weak light-matter interaction in graphene can be enhanced with a number of strategies, among which sensitization with plasmonic nanostructures is particularly attractive. This has resulted in the development of graphene-plasmonic hybrid systems with strongly enhanced photodetection efficiencies in the visible and the IR, but none in the UV. Here, we describe a silver nanoparticle-graphene stacked optoelectronic device that shows strong enhancement of its photoresponse across the entire UV spectrum. The device fabrication strategy is scalable and modular. Self-assembly techniques are combined with physical shadow growth techniques to fabricate a regular large-area array of 50 nm silver nanoparticles onto which CVD graphene is transferred. The presence of the silver nanoparticles resulted in a plasmonically enhanced photoresponse as high as 3.2 A W-1 in the wavelength range from 330 nm to 450 nm. At lower wavelengths, close to the Van Hove singularity of the density of states in graphene, we measured an even higher responsivity of 14.5 A W-1 at 280 nm, which corresponds to a more than 10 000-fold enhancement over the photoresponse of native graphene.

Facile synthesis, biofilm disruption properties and biocompatibility study of a poly-cationic peptide functionalized graphene-silver nanocomposite.

Bacterial colonization and biofilm formation is a growing challenge in the biomedical field. Although nanotechnology has emerged as an alternative strategy to combat biofilm formation, the toxicity of nanomaterials is a major concern. In this study, we report a safe-by-design strategy for the synthesis of a poly-cationic peptide functionalized graphene-silver nanocomposite (designated as GAPP) and its enhanced biofilm inhibition and disruption properties to eliminate the biofilm development of Gram-negative bacteria. The graphene-silver (rGOAg) nanocomposite was synthesized by microwave reduction, and subsequently functionalized with an antimicrobial poly-cationic peptide through covalent bonding. The results demonstrated that GAPP effectively killed the planktonic cells and biofilms of Escherichia coli and Pseudomonas aeruginosa depending upon the concentration and duration of the interaction. The complete eradication of preformed biofilm was achieved when treated with 10 μg mL-1 of GAPP for 5 h. The GAPP exerted bactericidal and biofilm inhibition activity through a "contact-kill-release" mode of action, wherein the electrostatic interaction of GAPP with the bacterial cells induced physical disruption accompanied by ROS-mediated biochemical changes. The internalization of GAPP into the cytoplasm through the damaged membrane led to metabolic imbalance in the cells. The peptide functionalization further prevented the dissolution of Ag+ ions, thus minimizing the cytotoxicity of GAPP to adult zebrafish. More importantly, the poly-cationic peptide functionalization enhanced the bioavailability, biofilm inhibition and disruption activities of GAPP, while minimizing its toxicological impact. The results obtained thereby provide an effective strategy in the design of alternative antibacterial agents for fighting biofilms of Gram-negative bacteria.

Synthesis, Characterization, and Applications of Nanographene-Armored Enzymes.

The unexpected discovery of graphene and especially the follow-up explosion of interest in its properties and applications marked the beginning of a new carbon era. Graphene-based nanostructured materials are highly useful because they show great promise in the field of biotechnology and biomedicine. Owing to their unique structural features, exceptional chemical, electrical, and mechanical properties, and their ability to affect the microenvironment of biomolecules, graphene-armored nanomaterials are suitable for use in various applications, such as immobilization of enzymes, field-effect transistors, photovoltaic devices, and biosensors, which in turn is extremely vital to the development of biomedical instruments, clinical diagnosis, and disease treatment. In this chapter, we present our recently reported work to armor hydrolytic enzymes on graphene-based nanomaterial in order to develop novel scaffolds to build robust nanobiocatalysts. Synthesized graphene-Fe3O4 and polyaniline-coated silver graphene nanocomposite have been used to immobilize β-galactosidase and lipase, using noncovalent and covalent strategies, respectively. Herein, the methodologies of both techniques have been discussed in detail. Owing to the large surface area offered by the honeycomb like structure of graphene, very high amount of enzyme has been loaded on small amounts of the nanocomposite. The stability and reusability of the fabricated nanobiocatalysts have been compared with their free forms. Nanographene-armored enzymes demonstrated high catalytic stability and easy recovery from the reaction medium and can be applied in various biotechnological applications. Lastly, future prospects and possible challenges in this rapidly developing area have also been discussed.

Graphene–bimetal plasmonic platform for ultra-sensitive biosensing

A graphene–bimetal plasmonic platform for surface plasmon resonance biosensing with ultra-high sensitivity was proposed and optimized. In this hybrid configuration, graphene nanosheets was employed to effectively absorb the excitation light and serve as biomolecular recognition elements for increased adsorption of analytes. Coating of an additional Au film prevents oxidation of the Ag substrate during manufacturing process and enhances the sensitivity at the same time. Thus, a bimetal Au–Ag substrate enables improved sensing performance and promotes stability of this plasmonic sensor. In this work we optimized the number of graphene layers as well as the thickness of the Au film and the Ag substrate based on the phase-interrogation sensitivity. We found an optimized configuration consisting of 6 layers of graphene coated on a bimetal surface consisting of a 5 nm Au film and a 30 nm Ag film. The calculation results showed the configuration could achieve a phase sensitivity as high as 1.71×106 deg/RIU, which was more than 2 orders of magnitude higher than that of bimetal structure and graphene–silver structure. Due to this enhanced sensing performance, the graphene–bimetal plasmonic platform proposed in this paper is potential for ultra-sensitive plasmonic sensing.

Hybrid Copper-Silver-Graphene Nanoplatelet Conductive Inks on PDMS for Oxidation Resistance Under Intensive Pulsed Light.

A simple, low-cost, and reliable process of production for conductive tracks and their transfer to poly(dimethylsiloxane) (PDMS) substrate has been proposed. Flexible electrodes were fabricated using conductive nanoparticulates under intensive pulsed light, which were then transferred on to a PDMS substrate via a pouring, curing, and peeling process. The combination of copper-silver nitrate-graphene nanoplatelets (GnPs) provided multiple benefits to the conductive tracks, such as oxidation resistance and increased durability on PDMS. The addition of silver nitrate reduced the speed of oxidation during the curing process of PDMS in the presence of heat and air. The addition of GnPs then increased the stability of conductive tracks on PDMS, whereas the films without GnPs were not conductive on PDMS due to mechanical cracks. The copper-silver-GnP electrodes on PDMS were successfully demonstrated as flexible electrodes and reveal the enhancement of oxidation resistance during thermal oxidation for Joule heater application.

Toward the ultra-transparent electrode by using patterned silver nanowire and graphene layered material

Silver nanowires (AgNWs) and graphene can be used in a high-performance electrode to obtain a transparency over 95% due to their exceptional properties as transparent-electrode materials. However, even though the electrical conductivity of the AgNW is excellent, it cannot obtain a further performance improvement such as a higher transparency without changed parameters. Here, we are proposing a technique to improve the performance of highly transparent electrodes by introducing an AgNW-grid patterning that can enhance the contact density between nanowires (NWs) for the enhancement of their electrical properties. The electrical performance of the patterned AgNW-grid depends on the channel width and the fill factor. The 95 %-transparent-patterned-AgNW grid reduced the sheet resistance by 9.22% compared with the unpatterned-AgNW network under an identical transparency condition, and further, the effect is more dominant under much higher transparency conditions. The contribution of graphene is important for the transparent electrode since it can completely cover the electrode surface while improving electrical properties of the patterned-AgNW grid by 100.59% with a 98.06% transparency, which is higher than that of the unpatterned-AgNW network under an identical transparency condition.

Gamma Irradiation Assisted Synthesis of Ag/rGO Composites and their Surface Properties

Ag/rGO composites were synthesized under gamma irradiation using silver nitrate and graphene oxide (GO) as the starting materials. Comparing with traditional methods, gamma irradiation is a simple and “green” technique. In the irradiation system, silver ions were reduced to silver nanoparticles (AgNPs) by the electrons generated from the radiolysis of solvent. GO nanosheets provided reactive sites for the formation of AgNPs and acted as a colloidal surfactant preventing the aggregation of AgNPs. Meanwhile, GO were partially reduced to reduced graphene oxide (rGO). X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscope, transmission electron microscope, Raman spectra and UV-Vis absorption spectra were applied for the characterization of Ag/rGO composites. The results showed that the absorbed dose (3.1 kGy, 4.7 kGy, 9.4 kGy and 27.4 kGy) plays an important role in the size distribution of AgNPs and the reduction degree of GO nanosheetes. The Ag/rGO composites exhibit a broad absorption band at visible light due to the surface plasmon resonance of AgNPs. Because of the unique surface properties, Ag/rGO composites behave enhanced performance for the adsorption of organic dye from water.

Silver–graphene oxide based plasmonic spacer for surface plasmon-coupled fluorescence emission enhancements

We report the application of single layered graphene oxide (SLGO) and silver decorated SLGO (Ag-SLGO) as plasmonic spacer material for obtaining enhanced fluorescence from a Rhodamine 6G (Rh6G) radiating dipole in a surface plasmon-coupled emission platform. To this end, we have decorated SLGO with biphasic silver nanoparticles using an in situ deposition technique to achieve 112-fold fluorescence enhancements.

Coherent resonance of quantum plasmons in Stone–Wales defected graphene–silver nanowire hybrid system

Defected graphene has a more important practical significance than graphene. Silver nanoparticles can modify the optical properties of defected graphene. We present herein a detailed theoretical analysis about the coherent resonance of quantum plasmons in the Stone–Wales (SW) defected graphene–silver nanowire hybrid system by using time-dependent density functional theory. The plasmon coherent effect is mainly attributed to the electromagnetic field coupling between the Stone–Wales defected graphene and silver nanowires. As a result, the optical response of the hybrid system exhibits a remarkable enhancement. Plasmon resonance, which depends on polarization and selectable tuning, is enhanced in wide frequency regions. Moreover, it reveals that the resonance frequency of an optical absorption spectrum depends on the space configuration of the SW defected graphene in the hybrid system. This investigation provides a better understanding of the plasmon enhancement effect used in a graphene-based photoelectric device. The study also offers an effective means of detecting the defects existing in graphene.

Exfoliation and Decoration of Graphene Sheets with Silver Nanoparticles and Their Antibacterial Properties

High quality graphene sheets (GRP) have been exfoliated using facile one pot method through direct ultrasonication of graphite in the presence of polyvinyl alcohol. The GRP were decorated with silver nanoparticles (AgNPs) producing graphene–silver nanoparticle composites. The effect of variation of graphite and silver salt mass ratios on the morphology and performance of produced composites was studied. The size of AgNPs decorated on GRP has been tuned with synthesis method optimization. The average size of AgNPs was found to be in the range of 8.6–15.6 nm. Cotton–polyester blend textile fabrics were treated with the new smart developed composite as antibacterial agent producing new composites. A significant inhibition of bacterial growth has been observed for graphene–silver nanoparticle composite and the antibacterial efficiency was optimized. The clear inhibition zone for textiles treated with new developed composite and AgNPs alone was recorded as 12 and 1.75 mm respectively, achieving more than six fold improvement.

Wrinkled Graphene–AgNWs Hybrid Electrodes for Smart Window

Over the past few years, there has been an increasing demand for stretchable electrodes for flexible and soft electronic devices. An electrode in such devices requires special functionalities to be twisted, bent, stretched, and deformed into variable shapes and also will need to have the capacity to be restored to the original state. In this study, we report uni- or bi-axially wrinkled graphene–silver nanowire hybrid electrodes comprised of chemical vapor deposition (CVD)-grown graphene and silver nanowires. A CVD-grown graphene on a Cu-foil was transferred onto a bi-axially pre-strained elastomer substrate and silver nanowires were sprayed on the transferred graphene surface. The pre-strained film was relaxed uni-(or bi-)axially to produce a wrinkled structure. The bi-axially wrinkled graphene and silver nanowires hybrid electrodes were very suitable for high actuating performance of electro-active dielectric elastomers compared with the wrinkle-free case. Present results show that the optical transparency of the highly stretchable electrode can be successfully tuned by modulating input voltages.

Graphene sandwiched platform for surface-enhanced Raman scattering

The gold nanoparticle–monolayer graphene–silver nanoarray sandwich structure exhibits excellent SERS activity of high sensitivity and good reproducibility.

Well-controlled silver nanowire/graphene hybrid from full solution process

The surface of a one-dimensional silver nanowire was covered with amphiphilic materials, N-(2-aminoethyl)-3a-hydroxy-5b-cholan-24-amide, and patched with two-dimensional graphene to form individually controlled hybrid. Graphene was prepared from ultrasonic in o-dichlorobenzene without any additives. As N-(2-aminoethyl)-3a-hydroxy-5b-cholan-24-amide between silver nanowires and graphene tightly held each other, silver nanowire was individually covered with graphene without introducing ultrasonic power, the necessary process to evenly mix silver nanowires and graphene but lead to damage and oxidize silver nanowires. Although the quality of graphene was inferior, the properties of hybrid were superior compared with pristine silver nanowire/graphene except introducing N-(2-aminoethyl)-3a-hydroxy-5b-cholan-24-amide. All processes to form the hybrid were carried out in solution. Therefore, this makes the processes less expensive and more useful and opens up opportunities for the mass production for conductive materials.

Mortiño (Vaccinium floribundum Kunth) berry assisted green synthesis and photocatalytic performance of Silver–Graphene nanocomposite

Mortiño (Vaccinium floribundum Kunth) is a wild shrub native to South America, whose berries are widely consumed in Ecuador as fresh fruit, juice and jam. We reported a green synthesis of Silver–Graphene (Ag-G) nanocomposite through the reduction of Ag+ and graphene oxide using berry extract of Mortiño. Silver nanoparticles were anchored onto the graphene sheets by ultrasonication and solar light irradiation. The as-prepared Ag-G nanocomposite was characterized by Fourier transform infrared spectroscopy, UV–vis spectroscopy, Scanning transmission electron microscopy, Scanning electron microscopy with energy dispersive X-ray spectrometry, and X-ray diffraction techniques. The photocatalytic activities of the Ag-G nanocomposite were evaluated by the degradation of methylene blue (MB) and methylene orange (MO) in an aqueous medium under sunlight irradiation. The photocatalytic activity of Ag-G nanocomposite for the degradation of MB (k = 0.0163283 min−1) > MO (k = 0.0140985 min−1), due to the anchoring of Ag nanoparticles on the graphene sheets and thiazine ring of MB is more susceptible to photodegradation than the azo bond of MO. This ecofriendly and green reduction method avoids the use of toxic reagents, and it might be useful for biocompatible materials in the future engineering applications.

Enhanced performance of polyimide hybrid membranes for benzene separation by incorporating three-dimensional silver–graphene oxide

Graphene oxide-Ag nanoparticle composites were prepared through impregnation reduction using different reactants. Transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and Fourier transform infrared spectroscopy analyses were performed to characterize differences in the morphologies of three different Ag–GO composites. Scanning electron microscopy, transmission electron microscopy, and differential scanning calorimetry analyses were also applied to evaluate the morphology and thermal stability of the hybrid membranes. Swelling–sorption and pervaporation experiments of benzene and cyclohexane were conducted to evaluate the separation performance of hybrid membranes containing different Ag–GO composites. Results demonstrated that small Ag nanoparticles generated through impregnation reduction using Ag(NH3)2+ and PEG were homogeneously distributed in the hybrid membranes because of moderate reduction rate. The polymide (PI) hybrid membrane exhibited high separation performance. Increase in Ag content in the Ag–GO samples led to the formation of Ag particles on the GO surface; these particles enhanced the separation performance of the hybrid membranes. When Ag-GO samples with 15 mass percent added, the hybrid membrane showed the highest separation performance and its maximum separation factor in the pervaporation experiments reached 35. It is more than three times higher than that of the GO/PI hybrid membrane. Moreover, large Ag particles were formed and aggregated during the preparation and polymerization of Ag–GO samples with high Ag contents; these particles reduced the separation performance of the hybrid membranes.

Antiviral Activity of Graphene-Silver Nanocomposites against Non-Enveloped and Enveloped Viruses.

The discovery of novel antiviral materials is important because many infectious diseases are caused by viruses. Silver nanoparticles have demonstrated strong antiviral activity, and graphene is a potential antimicrobial material due to its large surface area, high carrier mobility, and biocompatibility. No studies on the antiviral activity of nanomaterials on non-enveloped viruses have been reported. To investigate the antiviral activity of graphene oxide (GO) sheets and GO sheets with silver particles (GO-Ag) against enveloped and non-enveloped viruses, feline coronavirus (FCoV) with an envelope and infectious bursal disease virus (IBDV) without an envelope were chosen. The morphology and sizes of GO and GO-Ag were characterized by transmission, scanning electron microscopy, and X-ray diffraction. A virus inhibition assay was used to identify the antiviral activity of GO and GO-Ag. Go-Ag inhibited 25% of infection by FCoV and 23% by IBDV, whereas GO only inhibited 16% of infection by FCoV but showed no antiviral activity against the infection by IBDV. Further application of GO and GO-Ag can be considered for personal protection equipment to decrease the transmission of viruses.

One-pot preparation of graphene–Ag nano composite for selective and environmentally-friendly recognition of trace mercury(ii)

A graphene–silver nano composite was prepared by a simple one-pot redox method, using ascorbic acid as a catalytic reagent, which was applied for colorimetric Hg2+ detection. The proposed method is selective and sensitive with little secondary pollution.