Green synthesis of nanosilver‐decorated graphene oxide sheets

A green facile method has been successfully used for the synthesis of graphene oxide sheets decorated with silver nanoparticles (rGO/AgNPs), employing graphite oxide as a precursor of graphene oxide (GO), AgNO₃ as a precursor of Ag nanoparticles (AgNPs), and geranium (Pelargonium graveolens) extract as reducing agent. Synthesis was accomplished using the weight ratios 1:1 and 1:3 GO/Ag, respectively. The synthesised nanocomposites were characterised by scanning electron microscopy, transmission electron microscopy, atomic force microscopy, X‐ray diffraction, UV‐visible spectroscopy, Raman spectroscopy, energy dispersive X‐ray spectroscopy and thermogravimetric analysis. The results show a more uniform and homogeneous distribution of AgNPs on the surface of the GO sheets with the weight ratio 1:1 in comparison with the ratio 1:3. This eco‐friendly method provides a rGO/AgNPs nanocomposite with promising applications, such as surface enhanced Raman scattering, catalysis, biomedical material and antibacterial agent.Inspec keywords: silver, nanoparticles, graphene, nanocomposites, scanning electron microscopy, transmission electron microscopy, atomic force microscopy, X‐ray diffraction, ultraviolet spectra, visible spectra, X‐ray chemical analysis, surface enhanced Raman scattering, catalysis, nanofabricationOther keywords: antibacterial agent, biomedical material, catalysis, surface enhanced Raman scattering, rGO‐AgNP nanocomposite, eco‐friendly method, homogeneous distribution, thermogravimetric analysis, energy dispersive X‐ray spectroscopy, Raman spectroscopy, UV‐visible spectroscopy, X‐ray diffraction, atomic force microscopy, transmission electron microscopy, scanning electron microscopy, nanocomposites, reducing agent, geranium, graphene oxide sheets, graphite oxide, silver nanoparticles, green facile method     

Biocompatibility enhancement of graphene oxide‐silver nanocomposite by functionalisation with polyvinylpyrrolidone

Several materials such as silver are used to enhance graphene oxide (GO) sheets antimicrobial activity. However, these toxic materials decrease its biocompatibility and hinder its usage in many biological applications. Therefore, there is an urgent need to develop nanocomposites that can preserve both the antimicrobial activity and biocompatibility simultaneously. This work highlights the importance of functionalisation of GO sheets using Polyvinylpyrrolidone (PVP) and decorating them with silver nanoparticles (AgNPs) in order to enhance their antimicrobial activity and biocompatibility at the same time. The structural and morphological characterisations were performed by UV‐Visible, Fourier transform infrared (FTIR), and Raman spectroscopic techniques, X‐ray diffraction (XRD), and high‐resolution transmission electron microscopy (HR‐TEM). The antimicrobial activities of the prepared samples against Staphylococcus aureus, Pseudomonas aeruginosa, and Candida albicans were studied. The cytotoxicity of prepared materials was tested against BJ1 normal skin fibroblasts. The results indicated that the decoration with AgNPs showed a significant increase in the antimicrobial activity of GO and FGO sheets, and functionalisation of GO sheets and GO‐Ag nanocomposite with PVP improved the cell viability about 40 and 35%, respectively.Inspec keywords: biomedical materials, nanocomposites, visible spectra, ultraviolet spectra, X‐ray diffraction, cellular biophysics, nanoparticles, Raman spectra, filled polymers, transmission electron microscopy, silver, microorganisms, antibacterial activity, nanomedicine, nanofabrication, graphene compounds, toxicology, Fourier transform infrared spectraOther keywords: graphene oxide‐silver nanocomposite, polyvinylpyrrolidone, toxic materials, biocompatibility, antimicrobial activity, morphological characterisations, structural characterisations, UV‐visible spectra, Fourier transform infrared spectra, Raman spectra, X‐ray diffraction, high‐resolution transmission electron microscopy, Staphylococcus aureus, Pseudomonas aeruginosa, Candida albicans, cytotoxicity, BJ1 normal skin fibroblasts, cell viability, CO‐Ag     

Negligible particle-specific antibacterial activity of silver nanoparticles

For nearly a decade, researchers have debated the mechanisms by which AgNPs exert toxicity to bacteria and other organisms. The most elusive question has been whether the AgNPs exert direct "particle-specific" effects beyond the known antimicrobial activity of released silver ions (Ag(+)). Here, we infer that Ag(+) is the definitive molecular toxicant. We rule out direct particle-specific biological effects by showing the lack of toxicity of AgNPs when synthesized and tested under strictly anaerobic conditions that preclude Ag(0) oxidation and Ag(+) release. Furthermore, we demonstrate that the toxicity of various AgNPs (PEG- or PVP- coated, of three different sizes each) accurately follows the dose-response pattern of E. coli exposed to Ag(+) (added as AgNO(3)). Surprisingly, E. coli survival was stimulated by relatively low (sublethal) concentration of all tested AgNPs and AgNO(3) (at 3-8 μg/L Ag(+), or 12-31% of the minimum lethal concentration (MLC)), suggesting a hormetic response that would be counterproductive to antimicrobial applications. Overall, this work suggests that AgNP morphological properties known to affect antimicrobial activity are indirect effectors that primarily influence Ag(+) release. Accordingly, antibacterial activity could be controlled (and environmental impacts could be mitigated) by modulating Ag(+) release, possibly through manipulation of oxygen availability, particle size, shape, and/or type of coating.     

Synthesis of bio-inspired Ag–Au nanocomposite and its anti-biofilm efficacy

In the present study, bio-inspired Ag–Au nanocomposite was synthesized using banana peel extract (BPE) powder. The Ag–Au nanocomposite was characterized using various techniques such as UV–vis spectrophotometry, transmission electron microscopy (TEM) attached with energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). Efficiency of AuNPs, AgNPs and Ag–Au nanocomposite was tested for their antibacterial activity against Pseudomonas aeruginosa NCIM 2948. The Ag–Au nanocomposite exhibits enhanced antimicrobial activity over its monometallic counterparts. Anti-biofilm activity of AgNPs, AuNPs and Ag–Au nanocomposite against P. aeruginosa was evaluated on glass surfaces. The Ag–Au nanocomposite exhibited the highest biofilm reduction (70–80%) when compared with individual AgNPs and AuNPs. Effect of AuNPs, AgNPs and Ag–Au nanocomposite on biofilm formation was evaluated in 96 wells microtiter plates. The percentage of biofilm inhibition was sharply increased with increasing concentration of AuNPs, AgNPs and Ag–Au composite. However, Au–Ag nanocomposite showed the highest biofilm inhibition when compared with individual AuNPs and AgNPs. This synergistic anti-biofilm activity of Ag–Au nanocomposite has an importance in the development of novel therapeutics against multidrug-resistant bacterial biofilm.     

Effect of leavening agent on structural and photocatalytic properties of ZnO nanorods

In the present work, we have demonstrated a simple, facile, one-step, rapid and cost effective synthesis of ZnO nanorods through the thermal decomposition of zinc acetate and leavening agent (NaHCO₃). The silver nanoparticles (AgNPs) were deposited on the surface of ZnO nanorods by photocatalytic reduction of Ag (I) to Ag(0). As synthesized ZnO nanorods and Ag–ZnO nanocomposites were characterized by using X-ray Diffraction, field emission scanning electron microscope, high-resolution transmission electron microscope and diffuse reflectance spectroscopy. The photocatalytic activities of the ZnO nanorods and Ag–ZnO nanocomposites were evaluated for the photodegradation of Methyl Orange (MO) under UV and sunlight irradiation. The use of common leavening agent helps to prevent the aggregation of ZnO nanorods, further it hinders crystallite growth and narrowing the diameter of nanorods by the evolution of carbon dioxide during calcination. The ZnO nanorods and Ag–ZnO nanocomposite exhibited an enhanced photocatalytic activity and separation of photogenerated electron and hole pairs. Due to effect of leavening agent and AgNPs deposited on surface of ZnO nanorods finds best catalyst for the 99% degradation of MO within 30 min compared to ZnO.     

Rapid synthesis of highly stable silver nanoparticles and its application for colourimetric sensing of cysteine

A modified green approach for the synthesis of stable silver nanoparticles (AgNPs) using tea leaf extract is described. The method involves the reduction of silver salt by the polyphenols present in the green tea leaf extract and requires no additional capping/stabilising agents. Compared to other biogenic methods for the synthesis of AgNPs, the uniqueness of the approach described here lies in its simplicity, low-cost, and rapid synthesis rate; the reaction being completed within 10–15 min at room temperature. The reaction was carried out in alkaline medium without stirring and heating, and requires no special cleaning or drying of the glassware used. The synthesised AgNPs were characterised by UV–Vis spectroscopy and transmission electron microscopy (TEM). The results showed that AgNPs with a strong surface plasmon resonance peak around 410 nm and particle size in the 5–30 nm range were prepared. The synthesised AgNPs show excellent chemical stability for more than six months in aqueous solution. Additionally, we showed that the as-synthesised AgNPs can be used as highly selective colorimetric and optical sensors for the detection of cysteine. Thus, with a simple synthesis strategy, and enhanced stability, these green-tea-functionalised AgNPs have the potential for further applications as biosensors and antimicrobial agents.     

Graphene in Photocatalysis: A Review

In recent years, heterogeneous photocatalysis has received much research interest because of its powerful potential applications in tackling many important energy and environmental challenges at a global level in an economically sustainable manner. Due to their unique optical, electrical, and physicochemical properties, various 2D graphene nanosheets‐supported semiconductor composite photocatalysts have been widely constructed and applied in different photocatalytic fields. In this review, fundamental mechanisms of heterogeneous photocatalysis, including thermodynamic and kinetics requirements, are first systematically summarized. Then, the photocatalysis‐related properties of graphene and its derivatives, and design rules and synthesis methods of graphene‐based composites are highlighted. Importantly, different design strategies, including doping and sensitization of semiconductors by graphene, improving electrical conductivity of graphene, increasing eloectrocatalytic active sites on graphene, strengthening interface coupling between semiconductors and graphene, fabricating micro/nano architectures, constructing multi‐junction nanocomposites, enhancing photostability of semiconductors, and utilizing the synergistic effect of various modification strategies, are thoroughly summarized. The important applications including photocatalytic pollutant degradation, H₂ production, and CO₂ reduction are also addressed. Through reviewing the significant advances on this topic, it may provide new opportunities for designing highly efficient 2D graphene‐based photocatalysts for various applications in photocatalysis and other fields, such as solar cells, thermal catalysis, separation, and purification.     

Specific Capacitance and Cyclic Stability of Graphene Based Metal/Metal Oxide Nanocomposites:A Review

Graphene has become a worldwide admired material among researchers and scientists equally due to its unique richness in mechanical strength,electrical conductivity,optical and thermal properties.Researchers have explored that the composite materials based on graphene and metal/metal oxide nanostructures possess excellent potential for energy storage technologies.In particular,supercapacitors based on such composite materials have engrossed the extreme interest of researchers for its rapid charging/discharging time,safe operation and longer cyclic constancy.Till now,several fabrication techniques for composite materials and their energy storage applications have been explored.Here,specially,we have concentrated on the hottest research progress for the fabrication of graphene oxide and metal/metal oxide nanocomposites.We also emphasized on the characteristics and properties of supercapacitors fabricated using these composite materials.Moreover,our study is focused on the specific capacitance and cyclic stability of various composites to haul out the most efficient material for supercapacitor applications.     

Recent development in 2D materials beyond graphene

Discovery of graphene and its astonishing properties have given birth to a new class of materials known as “2D materials”. Motivated by the success of graphene, alternative layered and non-layered 2D materials have become the focus of intense research due to their unique physical and chemical properties. Origin of these properties ascribed to the dimensionality effect and modulation in their band structure. This review highlights the recent progress of the state-of-the-art research on synthesis, characterization and isolation of single and few layer nanosheets and their assembly. Electronic, magnetic, optical and mechanical properties of 2D materials have also been reviewed for their emerging applications in the area of catalysis, electronic, optoelectronic and spintronic devices; sensors, high performance electrodes and nanocomposites. Finally this review concludes with a future prospective to guide this fast evolving class of 2D materials in next generation materials science.     

Reduced graphene oxide-based photocatalysts containing Ag nanoparticles on a TiO2 nanotube array

A simple one-step electrochemical deposition method was demonstrated to fabricate reduced graphene oxide/Ag nanoparticle co-decorated TiO₂ nanotube arrays (RGO/Ag–TiO₂NTs) photocatalyst in this study. The structures and properties of these photocatalysts were characterized using scanning electron microscope, X-ray diffraction, UV–Vis diffuse reflection spectra, and photoluminescence. By taking the advantages of TiO₂, graphene, and Ag nanoparticles (AgNPs), RGO/Ag–TiO₂NTs showed a greatly improved photocatalytic activity compared with the bare TiO₂NTs, Ag–TiO₂NTs or RGO–TiO₂NTs. The deposited RGO and AgNPs not only reduce the recombination of photogenerated electrons and holes, but also increase the surface area of the catalyst. Both photocatalytic performance and adsorptivity of the catalyst have been improved. The ternary photocatalyst exhibited over 93 % removal efficiency of typical herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) under simulated solar light irradiation with good stability and easy recovery, which justifies the photocatalytic system, a promising application for herbicide or other organic pollutant removal from water.     

Recent Progress in Graphene‐Based Noble‐Metal Nanocomposites for Electrocatalytic Applications

The fast industrialization process has led to global challenges in the energy crisis and environmental pollution, which might be solved with clean and renewable energy. Highly efficient electrochemical systems for clean‐energy collection require high‐performance electrocatalysts, including Au, Pt, Pd, Ru, etc. Graphene, a single‐layer 2D carbon nanosheet, possesses many intriguing properties, and has attracted tremendous research attention. Specifically, graphene and graphene derivatives have been utilized as templates for the synthesis of various noble‐metal nanocomposites, showing excellent performance in electrocatalytic‐energy‐conversion applications, such as the hydrogen evolution reaction and CO₂ reduction. Herein, the recent progress in graphene‐based noble‐metal nanocomposites is summarized, focusing on their synthetic methods and electrocatalytic applications. Furthermore, some personal insights on the challenges and possible future work in this research field are proposed.     

Recent progress in the development and properties of novel metal matrix nanocomposites reinforced with carbon nanotubes and graphene nanosheets

One-dimensional carbon nanotubes and two-dimensional graphene nanosheets with unique electrical, mechanical and thermal properties are attractive reinforcements for fabricating light weight, high strength and high performance metal-matrix composites. Rapid advances of nanotechnology in recent years enable the development of advanced metal matrix nanocomposites for structural engineering and functional device applications. This review focuses on the recent development in the synthesis, property characterization and application of aluminum, magnesium, and transition metal-based composites reinforced with carbon nanotubes and graphene nanosheets. These include processing strategies of carbonaceous nanomaterials and their composites, mechanical and tribological responses, corrosion, electrical and thermal properties as well as hydrogen storage and electrocatalytic behaviors. The effects of nanomaterial dispersion in the metal matrix and the formation of interfacial precipitates on these properties are also addressed. Particular attention is paid to the fundamentals and the structure–property relationships of such novel nanocomposites.     

Highly Stable and Dispersive Silver Nanoparticle–Graphene Composites by a Simple and Low‐Energy‐Consuming Approach and Their Antimicrobial Activity

A simple and low‐energy‐consuming approach to synthesize highly stable and dispersive silver nanoparticle–graphene (AgNP–GE) nanocomposites has been developed, in which the stability and dispersivity of the composites are varied greatly with the pH value and temperature of the reaction. The results demonstrate that the optimal reaction conditions are pH 11 at room temperature for 70 min. As‐synthesized composites display excellent antimicrobial activity, and can completely inhibit the growth of Escherichia coli cells at a concentration of 20 mg L^?1 (20 ppm). After treatment with 10 ppm AgNP–GE composites, the cells are killed completely within 3 h. The unique structure imparts such good antimicrobial properties to the composites. Firstly, the sheetlike AgNP–GE tends to be adsorbed and accumulated onto the surface of cells, which can change the permeability and enhance the antimicrobial activity. Secondly, Ag⁺ released from AgNPs can act on the cells effectively and fully, thereby resulting in cell death.     

石墨烯及其纳米复合材料作为锂离子电池负极的研究进展

自2004年被发现以来,石墨烯及其纳米复合材料因其特殊的结构和优异的性能而受到广泛关注,并在锂离子电池负极方面展现出巨大的应用价值.首先简单介绍了石墨烯及其常用制备方法,然后详细介绍了石墨烯及其纳米复合材料作为锂离子电池负极材料的研究现状,并阐述了各自的优势与不足,提出了一些改进方案,最后展望了其在锂电负极的应用前景和未来面临的挑战.     

Magnesia supported Au and Ag catalysts for the preparation of few-layer graphene–metal nanocomposites: relationship between catalyst structure and the properties of graphene composites

Magnesia supported Au, Ag, and Au–Ag nanostructured catalysts were prepared, characterized, and used to synthesize few-layer graphene–metal nanoparticle (Gr–MeNP) composites. The catalysts have a mezoporous structure and a mixture of MgO and MgO·H₂O as support. The gold nanoparticles (AuNPs) are uniformly dispersed on the surface of the Au/MgO catalysts, and have a uniform round shape with a medium size of ~8 nm. On the other hand, the silver nanoparticles (AgNPs) present on the Ag/MgO catalyst have an irregular shape, larger diameters, and less uniform dispersion. The Au–Ag/MgO catalyst contains large Au–Ag bimetallic particles of ~20–30 nm surrounded by small (5 nm) AuNPs. Following the RF-CCVD process and the dissolution of the magnesia support, relative large, few-layer, wrinkled graphene sheets decorated with metal nanoparticles (MeNPs) are observed. Graphene–gold (Gr–Au) and graphene–silver (Gr–Ag) composites had 4–7 graphitic layers with a relatively large area and similar crystallinity for samples prepared in similar experimental conditions. Graphene–gold–silver composites (Gr–Au–Ag) presented graphitic rectangles with round, bent edges, higher crystallinity, and a higher number of layers (8–14). The MeNPs are encased in the graphitic layers of all the different samples. Their size, shape, and distribution depend on the nature of the catalyst. The AuNPs were uniformly distributed, had a size of about 15 nm, and a round shape similar to those from Au/MgO catalyst. In Gr–Ag, the AgNPs have a round shape, very different from that of the Ag/MgO catalyst, large size distribution and are not uniformly distributed on the surface. Agglomerations of AgNPs together with large areas of pristine few-layer graphene were observed. In Gr–Au–Ag composites, almost exclusively large bimetallic particles of about 25–30 nm, situated at the edge of graphene rectangles have been found.     

Safe and Effective Ag Nanoparticles Immobilized Antimicrobial NanoNonwovens

Silver nanoparticles (AgNPs) with large surface‐to‐volume ratio have been widely studied as a valuable material for their strong antimicrobial effect. However, the practical applications of AgNPs in health care and water purification are often hampered by the concern of their toxicity and possibility of introduction of secondary pollution. Here, we present a novel strategy to produce a safe and effective antimicrobial nanononwoven material by immobilizing AgNPs on a rigid polymer nanofibrous matrix through simple co‐electrospinning of pre‐prepaired AgNPs and polystyrene (PS). Distribution of the AgNPs on the surface of PS fibers was achieved by tuning fiber diameters during electrospinning. Atomic force microscopy (AFM) analysis revealed that the AgNPs distributed at the fiber surface were still covered by a layer of polymer, which inhibited their antimicrobial activity. UV/ozone treatment was thus employed to degrade the polymer coating without loosening the AgNPs, resulting in an active antimicrobial nonwoven against Gram‐positive Staphylococcus xylosus. The mechanism based on cellular uptake of silver ions via close contact to the surface of AgNPs is proposed. The novel nanononwoven retains the enhanced antimicrobial activities from nanofeatured AgNPs without detectable AgNPs leaching, which holds great potential for safe and recyclable use.     

石墨烯及其纳米复合材料作为锂离子电池负极的研究进展

自2004年被发现以来,石墨烯及其纳米复合材料因其特殊的结构和优异的性能而受到广泛关注,并在锂离子电池负极方面展现出巨大的应用价值。首先简单介绍了石墨烯及其常用制备方法,然后详细介绍了石墨烯及其纳米复合材料作为锂离子电池负极材料的研究现状,并阐述了各自的优势与不足,提出了一些改进方案,最后展望了其在锂电负极的应用前景和未来面临的挑战。     

Sub‐10 nm Ag Nanoparticles/Graphene Oxide: Controllable Synthesis,Size‐Dependent and Extremely Ultrahigh Catalytic Activity

While tremendous advancements in Ag nanoparticle (AgNP)‐based materials have been made, the development of a facile protocol for preparing sub‐10 nm AgNPs with controllable size and ultrahigh performance remains a formidable challenge. It is shown that AgNPs/graphene oxide (AgNPs/GO) bearing 2.5, 4.3, and 6.2 nm AgNPs (2.5‐AgNPs/GO, 4.3‐AgNPs/GO, and 6.2‐AgNPs/GO, respectively) could be fabricated via light‐induced synthesis. Their catalytic activity toward 4‐nitrophenol (4‐NP) reduction, which is a “gold standard” for evaluating the performance of noble metal–based catalysts, is studied. When normalized by mole and area, the activity exhibits an order of 4.3‐AgNPs/GO > 6.2‐AgNPs/GO > 2.5‐AgNPs/GO and 6.2‐AgNPs/GO > 4.3‐AgNPs/GO > 2.5‐AgNPs/GO, respectively. This trend is a result of GO‐induced electron concentration reduction with decreasing AgNP size. Significantly, under similar conditions, the activity of 4.3‐AgNPs/GO is substantially superior to that of numerous state‐of‐the‐art noble metal–based catalysts. The ultrafine size of the AgNPs and their surface accommodation on the unobstructed 2D GO scaffolds without capping reagents/covers, which make the abundantly exposed catalytically active sites highly accessible to substrate molecules, play an important role in their extremely ultrahigh performance. This work paves a new avenue for high‐performance AgNP‐based materials, and by taking 4‐NP reduction as a proof‐of‐concept, provides new scientific insights into the rational design of surface‐based advanced materials.     

Mechanical and tribological performance of polyamide 12 reinforced with graphene nanoplatelets and paraffin oil nanocomposites

With polymeric nanocomposites many problems due to their extensive applications such as aerospace, automobiles, coatings, and packaging materials were solved. In this study, polyamide 12/graphene nanoplatelets impregnated by paraffin oil were fabricated by a hot compression technique. Elastic modulus has been determined by compression tests using a universal testing machine. Microhardness of unfilled polyamide 12 and its nanocomposites has been measured by Vickers microhardness testing machine. Tribological properties of the unfilled polyamide 12 and its nanocomposites have been investigated by pin‐on‐disc tester under applied normal loads of 10 N, 20 N and 30 N, 1.2 m/s sliding speed, and 212 m sliding distance. The results showed that the elastic modulus and microhardness of polyamide 12/graphene nanoplatelets (PA12/GNPs) nanocomposites are higher than that of the unfilled polyamide 12, and then gradually increased by adding paraffin oil contents. Tribological properties showed that polyamide 12/graphene nanoplatelets nanocomposites have lower coefficient of friction and wear rates in comparison with polyamide 12. By adding paraffin oil contents to the unfilled polyamide 12 and its nanocomposites, coefficient of friction and wear rates gradually decreased. Worn surfaces were imaged using scanning electron microscope.     

High concentration exfoliation of graphene in ethyl alcohol using block copolymer surfactant and its influence on properties of epoxy nanocomposites

In this work, high concentration exfoliation (～0.2 mg/ml) of graphene in ethyl alcohol is achieved in presence of block copolymer of polyethylene oxide–polypropylene oxide–polyethylene oxide (PEO–PPO–PEO) using sonication followed by centrifugation. The obtained graphene solution is used to prepare epoxy nanocomposites. Flexural tests were conducted over epoxy nanocomposites. The 0.018 wt% of PEO–PPO–PEO block copolymer exfoliated graphene in epoxy matrix shows 21.7% and 15.8% enhancement in flexural modulus and flexural strength respectively as compared to pure epoxy. Transmission electron microscopy reveals well dispersion of graphene in epoxy matrix; and fractography of flexural fractured sample shows graphene dispersion restricts the crack propagation. The well-dispersed graphene in epoxy matrix increase the dielectric constant and thermal stability of epoxy nanocomposites. Further, the enhanced graphene dispersion in epoxy nanocomposites reduces the glass transition temperature (T_g). Thus, enhanced mechanical properties achieved by dispersion of block copolymer exfoliated graphene in epoxy nanocomposites make it suitable for several applications.