Graphene Nanopowder Research Articles

A Simple and Efficient Method to Fabricate Graphene 2D Nanomaterial into a thin Film to Serve as a Saturable a bsorber for Fiber Laser Application

A passively pulsed fiber laser using saturable absorbers such as graphene has been increased dramatically in recent years. Up to now, researchers have been proposed many methods to fabricate graphene saturable absorber such as (evanescent coupling structure, electrochemical exfoliation, and mechanical exfoliation) for light pulse generation in a fiber laser. However, each of these methods has got some limitations which reduce the saturable absorber performance and restrict its range of applications. In this paper, we propose a simple but very efficient fabrication way of graphene saturable absorber by converting graphene Nano powder into a thin film using polyvinyl alcohol (PVA) as a host material. The fabricated film can then be easily sandwiched between two fiber pigtails and inserted inside the laser cavity to form the saturable absorber. when compared with other methods, this method is much preferable because it provides saturable absorber with combat structure, maximum interaction area, reasonable insertion loss, polarization insensitive, controllable concentration, and safe to handle. The fabricated graphene saturable absorber in this paper was characterized and found to have a uniform distribution of the graphene nanomaterial in the PVA and have a modulation depth of 6.1% which make it a very promising saturable absorber for ultra-fast fiber laser demonstration.

Investigation the in vitro biological performance of graphene/bioactive glass scaffolds using MC3T3-E1 and ATDC5 cells

ABSTRACTSilicate-based bioactive glass constructs were fabricated by polymer foam replication method for tissue engineering applications. Composites were prepared by coating the surface of bioactive glass scaffolds with poly(ε-caprolactone) involving graphene nanopowders at different concentrations. In vitro bioactivity of the composite constructs was tested in simulated body fluid. Additionally, the response of pre-osteoblastic MC3T3-E1 and chondrogenic ATDC5 cells were investigated under in vitro conditions. Results revealed that a decrease was not observed in acellular bioactivity of the scaffolds. Cell viability experiments showed that graphene involving samples were not cytotoxic to the MC3T3-E1 and ATDC5 cells (except for the samples containing 10 wt% graphene) and cells proliferated well on the scaffolds. Additionally, the pre-osteoblastic cells seeded onto the composite scaffolds differentiated into osteoblasts. The scaffolds prepared in this study may find applications for bone and cartilage tissue engineering in the presence of electric stimulation.

Response of mouse bone marrow mesenchymal stem cells to graphene-containing grid-like bioactive glass scaffolds produced by robocasting.

In the study, three-dimensional, grid-like silicate-based bioactive glass scaffolds were manufactured using a robotic deposition technique. Inks were prepared by mixing 13-93 bioactive glass particles in Pluronic® F-127 solution. After deposition, scaffolds were dried at room temperature and sintered at 690°C for 1 h. The surface of the sintered scaffolds was coated with graphene nanopowder (1, 3, 5, 10 wt%) containing poly(ε-caprolactone) solution. The in vitro mineralization ability of the prepared composite scaffolds was investigated in simulated body fluid. The surface of the simulated body fluid-treated scaffolds was analyzed using scanning electron microscopy to investigate the hydroxyapatite formation. Mechanical properties were tested under compression. Results revealed that graphene coating has no detrimental effect on the hydroxyapatite forming ability of the prepared glass scaffolds. On the other hand, it decreased the compression strength of the scaffolds at high graphene concentrations. The prepared grid-like bioactive glass-based composite scaffolds did not show toxic response to bone marrow mesenchymal stem cells. It was shown that stem cells seeded onto the scaffolds attached and proliferated well on the surface. Cells seeded on the scaffolds surface also demonstrated osteogenic differentiation under in vitro conditions in the absence of transforming growth factors.

Study of tensile and compressive behaviour of the in-house synthesized al-alloy nano composite

The present study is focused on the in-house synthesis of graphene reinforced Al-alloy nanocomposites using stir casting process. The concentration of graphene nanopowder (size range: 3-8 nm) is taken as 2 wt. % and 6 wt. %. Tensile and compressive characterization study has carried out on the prepared synthesized specimens as per the ASTM standard, and further examined the microstructure of the specimens to study the behaviour of nanopowder dispersed in Al-alloy matrix. The results reveal that the tensile and compressive strength of the graphene reinforced (increasing concentration to 6 wt. %) Al-alloy nanocomposite has increased by 49% and 44% respectively as compared to un-reinforced material. Moreover, it has been observed that with increasing concentration of reinforcement, the specimen exhibits brittle character and accordingly the percentage of elongation found to be reduced. The effect of graphene nanoparticles on the tensile and compressive behaviour of the composites has also documented in this article.

Preparation and characterization of PCL-coated porous hydroxyapatite scaffolds in the presence of MWCNTs and graphene for orthopedic applications

Macro-channeled porous hydroxyapatite (HA) scaffolds were fabricated by a polymer foam replication method. Composites were prepared by coating the surface of HA scaffolds with polycaprolactone (PCL) in the presence of graphene nanopowders (in the form of flakes) and multi-walled carbon nanotubes (MWCNTs) at different concentrations. Compression strength of the scaffolds was investigated as a function of additive concentration. Results revealed that the use of PCL coating increased the mechanical strength of HA scaffolds. Besides, addition of graphene or MWCNTs further improved the compression strength of the constructs when they were used at 0.25 wt% and a decrease was observed at higher graphene and MWCNT concentrations. Highest mechanical performance was obtained in composite HA scaffolds involving MWCNTs. In vitro acellular bioactivity experiments revealed that both graphene and MWCNT-incorporated HA scaffolds showed higher bioactivity in simulated body fluid compared to bare scaffolds. However, HA formation ability was more pronounced with MWCNTs compared to graphene nanoflakes where they were possibly acted as an effective nucleation sites to induce the formation of a biomimetic apatite. Additionally, scaffolds prepared in the study were found to be nontoxic to the mouse bone marrow mesenchymal stem cells.

Wetting of water on graphene nanopowders of different thicknesses

We study the wetting of graphene nanopowders by measuring the water adsorption in nanopowder flakes of different flake thicknesses. Chemical analysis shows that the graphene flakes, especially the thin ones, might exist in the partially oxidized state. We observe that the thinnest graphene nanopowder flakes do not adsorb water at all, independent of the relative humidity. Thicker flakes, on the other hand, do adsorb an increasing amount of water with increasing humidity. This allows us to assess their wetting behavior which is actually the result of the competition between the adhesive interactions of water and graphene and the cohesive interactions of water. Explicit calculation of these contributions from the van der Waals interactions confirms that the adhesive interactions between very thin flakes of graphene oxide and water are extremely weak, which makes the flakes superhydrophobic. “Liquid marble” tests with graphene nanopowder flakes confirm the superhydrophobicity. This shows that the origin of the much debated “wetting transparency” of graphene is due to the fact that a single graphene or graphene oxide layer does not contribute significantly to the adhesion between a wetting phase and the substrate.

Graphene-containing PCL- coated Porous 13-93B3 Bioactive Glass Scaffolds for Bone Regeneration

Borate-based 13-93B3 bioactive glass scaffolds were coated with the graphene-containing poly-caprolactone (PCL) solution to prepare electrically conductive composites for biomedical applications. Results revealed that electrical conductivity of the scaffolds increased with increasing concentration of graphene nanoparticles. Significant difference was not observed in hydroxyapatite forming ability of the bare and the graphene-containing scaffolds immersed in simulated body fluid. In vitro cytotoxicity experiments (XTT tests) showed that pre-osteoblastic MC3T3-E1 cell viability percentages of the graphene- containing samples was higher than control group samples after 7 days of incubation. However, a decrease in cell viability rates was obtained after 14 days of incubation for samples coated with PCL containing graphene starting from 3 wt%. Additionally, results obtained in the live-dead assay were consistent with the results of XTT tests. A higher ALP activity was detected in cells cultured on the graphene-containing borate glass scaffolds than those on the bare PCL coated 13-93B3 scaffolds suggesting the presence of graphene nanopowders stimulated an early stage of osteoblastic differentiation. SEM analysis showed that MC3T3-E1 cells exhibited a flat appearance and spread out through the surface in all groups of scaffolds starting from 3 days of incubation.

Thermal interface materials based on graphene and silver nanopowder

PurposeThe purpose of this paper is to present results of the studies on modification of ethylene-vinyl acetate (EVA) encapsulation foil to be used as thermal interface material (TIM). It is estimated that poor thermal management in electronic devices can cause over 50 per cent of failures. As the junction temperature rises, the failure rate for electronics increases exponentially. To ensure sufficient heat transfer from its source, TIMs are used in various circuits. On the other hand, it is important to ensure high electric resistivity of the designed TIM.Design/methodology/approachThe focus of the investigation was twofold: modification of EVA with both graphene oxide (GO) and silver nanopowder (nAg); and TIM applicability through lamination of photovoltaic cells with standard and modified EVA foil. The main problem of a new type of encapsulant is proper gas evacuation during the lamination process. For this reason, reference and modified samples were compared taking into account the percentage of gas bubbles in visible volume of laminated TIM. Finally, reference and modified TIM samples were compared using differential scanning calorimetry (DSC) and laser flash analysis (LFA) measurements.FindingsThe proper parameters of the lamination process for the modified EVA foil - with both GO and organometallic nAg particles - were selected. The nAg addition results in an increase in thermal conductivity of the proposed compositions with respect to unmodified EVA foil, which was confirmed by DSC and LFA measurements.Originality/valueThe experiments confirmed the potential application of both EVA foil as a matrix for TIM material and nAg with GO as an active agent. Proposed composition can bring additional support to a solar cell or other electronic components through effective heat removal, which increases its performance.

Preparation and properties of amine functionalized graphene filled epoxy thin film nano composites for electrically conductive adhesive

The study was carried out to investigate the effect of amine coupling agent of graphene nanopowder (GNP) on the properties of epoxy-based electrically conductive adhesives. Amine-based coupling agent for GNP (m-GNP)/epoxy thin film nanocomposites and GNP/epoxy thin film nanocomposites were fabricated using an ultrasonication and spin-coating techniques. Subsequently, the effect of GNP with different filler loading (0.05–1 vol%) on the tensile properties and electrical properties of the epoxy composites was studied. The GNPs functionalized with amine coupling agent was confirmed with FTIR, AFM and Raman spectroscopy. Generally, it was found that the addition of GNPs decreased the tensile properties of epoxy composites. However, m-GNP/epoxy composites showed higher tensile properties than GNP/epoxy composites at the same filler loading. While, it was found that the percolation threshold of the m-GNP/epoxy composites (0.6 vol%) was much higher than that of the GNP/epoxy (0.1 vol%). Morphological analysis of the GNP fillers by TEM images showed that the average dimensions of m-GNPs layers were far smaller than the average dimensions of GNPs before functionalization. SEM images of the tensile samples cross section confirmed the existence of strong interfacial bonding between m-GNP and the epoxy matrix.

Graphene: A new activator of sodium persulfate for the advanced oxidation of parabens in water

Graphene was successfully employed as a catalyst for the activation of sodium persulfate, towards the effective degradation of propylparaben, an emerging micro-pollutant, representative of the parabens family. A novel process is proposed which utilizes a commercial graphene nano-powder as the catalyst and sodium persulfate as the oxidizing agent. It was found that over 95% of micro-pollutant degradation occurs within 15 min of reaction time. The effects of catalyst loading (75 mg/L to 1 g/L), sodium persulfate (SPS) concentration (10 mg/L to 1 g/L), initial solution pH (3–9) and initial paraben concentration (0.5 mg/L to 5 mg/L) were examined. Experiments were carried out in different aqueous conditions, including ultrapure water, bottled water and wastewater in order to investigate their effect on the degradation rate. The efficiency of the process was lower at complex water matrices signifying the role of organic matter as scavenger of the oxidant species. The role of radical scavengers was also investigated through the addition of methanol and tert-butanol in several concentrations, which was found to be important only in relatively high values. An experiment in which propylparaben was substituted by methylparaben was conducted and similar results were obtained. The consumption of SPS was found to be high in all pH conditions tested, surpassing 80% in near neutral environment. However, the results indicate that the sulfate radicals formed react with water in alkaline conditions, which are the optimal for the reaction, producing hydroxyl radicals which appear to be the dominant species leading to the rapid degradation of propylparaben.To the best of our knowledge, this is the first time pristine graphene has been implemented as an activator of sodium persulfate for the effective oxidation of micro-pollutants.

Graphene-Decorated Nanocomposites for Printable Electrodes in Thin Wafer Devices

Printable electrodes that induce less stress and require lower curing temperatures compared to traditional screen-printed metal pastes are needed in thin wafer devices such as future solar cells, and in flexible electronics. The synthesis of nanocomposites by incorporating graphene nanopowders as well as silver nanowires into epoxy-based electrically conductive adhesives (ECA) is examined to improve electrical conductivity and to develop alternate printable electrode materials that induce less stress on the wafer. For the synthesized graphene and Ag nanowire-decorated ECA nanocomposites, the curing kinetics were studied by dynamic and isothermal differential scanning calorimetry measurements. Thermogravimetric analysis on ECA, ECA-AG and ECA/graphene nanopowder nanocomposites showed that the temperatures for onset of decomposition are higher than their corresponding glass transition temperature (T g) indicating an excellent thermal resistance. Printed ECA/Ag nanowire nanocomposites showed 90% higher electrical conductivity than ECA films, whereas the ECA/graphene nanocomposites increased the conductivity by over two orders of magnitude. Scanning electron microscopy results also revealed the effect of fillers morphology on the conductivity improvement and current transfer mechanisms in nanocomposites. Residual stress analysis performed on Si wafers showed that the ECA and nanocomposite printed wafers are subjected to much lower stress compared to those printed with metallic pastes. The observed parameters of low curing temperature, good thermal resistance, reasonably high conductivity, and low residual stress in the ECA/graphene nanocomposite makes this material a promising alternative in screen-printed electrode formation in thin substrates.

Supported Liquid Membrane Using Hybrid Polyethersulfone/Graphene Flat Sheet Membrane for Acetic Acid Removal

Acetic acid is one of the inhibitors mainly found in biomass hydrolysates after acid hydrolysis of lignocellulose biomass. The presence of this compound can affect the final yield of bioethanol. Supported liquid membrane (SLM) is an efficient method for solute extraction from aqueous solution. However, unsuitable membrane structure and insufficient membrane strength are the typical problems experienced by the membrane support in the SLM system. In the current study, graphene nanopowder was incorporated into polyethersulfone (PES) dope polymer solution to fabricate flat sheet PES membrane support. The hydrophobicity of the PES membrane was increased from 85° to 120° when the graphene was added. The force required to break the PES/graphene membrane was 4.3N. This force was higher compared to the pristine PES membrane which was 1.9N. Both membranes however showed almost similar acetic acid removal percentages which were 86% and 83% for pristine PES and PES/graphene membrane, respectively.

Synergy effects of graphene and multiwalled carbon nanotubes hybrid system on properties of epoxy nanocomposites

Tensile and electrical properties of graphene nanopowder (GNP) and multiwalled carbon nanotubes (MWCNT) filled epoxy thin film nanocomposites were investigated. In addition, synergy effects of various mixture ratios of GNP–MWCNT hybrids on the properties of the epoxy thin film nanocomposites were evaluated. It was found that the addition of GNPs or MWCNTs decreased the tensile properties compared to that of unfilled epoxy. The electrical percolation threshold of MWCNT/epoxy was found to be 0.8 vol%. Addition of only 0.1 vol% GNPs results in significant improvement in the electrical properties of the composites. Enhanced tensile and electrical properties in the GNP–MWCNT/epoxy hybrid were achieved with GNP–MWCNT ratio of 0.1:0.4. Morphological analysis confirmed the uniform dispersion of both GNPs and MWCNTs within the epoxy matrix. For the hybrid GNP–MWCNT filler system (i.e., with the 0.1:0.4 ratio), MWCNTs were seen to align themselves on the GNPs surfaces creating an interconnected strong nanofiller network in the epoxy.

The Nature of Metastable AA' Graphite: Low Dimensional Nano- and Single-Crystalline Forms.

Over the history of carbon, it is generally acknowledged that Bernal AB stacking of the sp2 carbon layers is the unique crystalline form of graphite. The universal graphite structure is synthesized at 2,600~3,000 °C and exhibits a micro-polycrystalline feature. In this paper, we provide evidence for a metastable form of graphite with an AA’ structure. The non-Bernal AA’ allotrope of graphite is synthesized by the thermal- and plasma-treatment of graphene nanopowders at ~1,500 °C. The formation of AA’ bilayer graphene nuclei facilitates the preferred texture growth and results in single-crystal AA’ graphite in the form of nanoribbons (1D) or microplates (2D) of a few nm in thickness. Kinetically controlled AA’ graphite exhibits unique nano- and single-crystalline feature and shows quasi-linear behavior near the K-point of the electronic band structure resulting in anomalous optical and acoustic phonon behavior.

Graphene nanoparticle dispersion in epoxy thin film composites for electronic applications: effect on tensile, electrical and thermal properties

Graphene nanopowder (GNP)/epoxy thin film composites were fabricated using an ultrasonication and spin-coating technique. This study aims to investigate the effect of dispersion state and filler loading (0.025–1 vol%) of GNP on the tensile, electrical and thermal properties of the GNP/epoxy composites. GNP/epoxy composites with different dispersion states were prepared, and a combination of sonication and chloroform (as the dispersion solution) was used in one of the samples. The addition of GNP decreased the tensile properties of the epoxy composites. However, among the tested samples, the chloroform GNP (ch-GNP)/epoxy composites had higher tensile properties, especially at low filler loading (0.05–0.2 vol%). Although the ch-GNP/epoxy formed clusters, a higher degree of dispersion and exfoliation of GNP was observed in each cluster, due to improve dispersion by chloroform compared to the system without chloroform. The rolling of GNP was found to be dominant in the ch-GNP/epoxy composite. Electrical properties showed that the ch-GNP/epoxy composites exhibit higher electrical conductivity with lower percolation thresholds value than that the GNP/epoxy composites. From the thermal properties it was determined that composites with the dispersion solution showed a higher glass transition temperature (Tg) than those without the dispersion solution.

Sticky gecko-inspired material conducts electricity

A new take on adhesives inspired by sticky gecko feet has led to stretchy silicone patches that conduct electricity and cling fast to skin, even underwater (ACS Nano 2016, DOI: 10.1021/acsnano.6b01355). The material could be used as comfortable, low-cost, reusable electrodes for heart monitors, fitness sensors, or wearable electronics. A team led by materials scientist Seokwoo Jeon of the Korea Advanced Institute of Science & Technology (KAIST) mixed conductive carbon nanotubes and graphene nanopowder into polydimethylsiloxane and poured the composite into a silicon mold dotted with holes. After curing the elastomer at 120 °C for two hours, they had a 10- by 10-cm square patch covered with 15-µm-tall golf-tee-shaped pillars. These shapes mimic the microscopic, hairlike features on gecko feet that can cling to surfaces via van der Waals interactions. When a volunteer wore the patch wired to an electrocardiography recorder, the team measured heartbeat signals that matched those from

Bioinspired, Highly Stretchable, and Conductive Dry Adhesives Based on 1D-2D Hybrid Carbon Nanocomposites for All-in-One ECG Electrodes.

Here we propose a concept of conductive dry adhesives (CDA) combining a gecko-inspired hierarchical structure and an elastomeric carbon nanocomposite. To complement the poor electrical percolation of 1D carbon nanotube (CNT) networks in an elastomeric matrix at a low filler content (∼1 wt %), a higher dimensional carbon material (i.e., carbon black, nanographite, and graphene nanopowder) is added into the mixture as an aid filler. The co-doped graphene and CNT in the composite show the lowest volume resistance (∼100 ohm·cm) at an optimized filler ratio (1:9, total filler content: 1 wt %) through a synergetic effect in electrical percolation. With an optimized conductive elastomer, gecko-inspired high-aspect-ratio (>3) microstructures over a large area (∼4 in.(2)) are successfully replicated from intaglio-patterned molds without collapse. The resultant CDA pad shows a high normal adhesion force (∼1.3 N/cm(2)) even on rough human skin and an excellent cycling property for repeatable use over 30 times without degradation of adhesion force, which cannot be achieved by commercial wet adhesives. The body-attachable CDA can be used as a metal-free, all-in-one component for measuring biosignals under daily activity conditions (i.e., underwater, movements) because of its superior conformality and water-repellent characteristic.

Copper and Graphene activated ZnO nanopowders for enhanced photocatalytic and antibacterial activities

ZnO, ZnO:Cu and ZnO:Cu:Graphene nanopowders were synthesized via a facile wet chemical method. The XRD studies show that the synthesized samples have hexagonal wurtzite structure. It is found that graphene addition induces a decrease in crystallite size. UV–vis absorption spectra of the samples show sharp absorption edges around 380nm. Photoluminescence studies reveal that the incorporation of copper and graphene in ZnO facilitates the efficient photo generated electron–hole pair separation. It is found that the ZnO:Cu and ZnO:Cu:Graphene nanopowder exhibit improved photocatalytic efficiency for the photodegradation of Methylene Blue (MB) under visible light irradiation. Moreover, improved antibacterial activity of ZnO:Cu:Graphene nanopowder against Escherichia coli and Staphylococcus aureus bacteria is observed.

Effects of Carbon Allotropic Forms on Microstructure and Thermal Properties of Cu-C Composites Produced by SPS

Combination of extreme service conditions and complex thermomechanical loadings, e.g., in electronics or power industry, requires using advanced materials with unique properties. Dissipation of heat generated during the operation of high-power electronic elements is crucial from the point of view of their efficiency. Good cooling conditions can be guaranteed, for instance, with materials of very high thermal conductivity and low thermal expansion coefficient, and by designing the heat dissipation system in an accurate manner. Conventional materials such as silver, copper, or their alloys, often fail to meet such severe requirements. This paper discusses the results of investigations connected with Cu-C (multiwall carbon nanotubes (MWNTs), graphene nanopowder (GNP), or thermally reduced graphene oxide (RGO)) composites, produced using the spark plasma sintering technique. The obtained composites are characterized by uniform distribution of a carbon phase and high relative density. Compared with pure copper, developed materials are characterized by similar thermal conductivity and much lower values of thermal expansion coefficient. The most promising materials to use as heat dissipation elements seems to be copper-based composites reinforced by carbon nanotubes (CNTs) and GNP.

Graphene addition to MgB2 superconductor obtained by ex-situ spark plasma sintering technique

Graphene nanopowder (G) with average thickness particle size of about 6–8nm was added to MgB2 commercial powder. Starting composition was (MgB2)(1−x)(G)x, x=0.0125, 0.025, 0.05. Processing was performed by Spark Plasma Sintering (SPS) technique. All added samples have high density (above 95%). The critical temperature (Tc) and the lattice parameter a (c-axis lattice parameter is constant) show a small variation suggesting that carbon substitution for boron is low. TEM observations show the presence of un-reacted graphene plates supporting the Tc and structural results. It also indicates that G-addition does not modify the MgB2 microstructure. Despite this, there is an optimum doped sample (MgB2)0.9875(G)0.0125 for which the critical current density at temperatures below 25K is slightly higher at high magnetic fields than for the pristine sample. The addition of G is found as one of the least effective C-source additions enhancing Jc. We discuss results as being strongly related to variation of the residual stress.