Synthesized Graphene Nanosheets Research Articles

Plasma‐Based Synthesis of Freestanding Graphene from a Natural Resource for Sensing Application

AbstractAtmospheric pressure microwave plasma has the lead in synthesizing freestanding and scalable graphene within seconds without the need for high vacuum and temperature. However, the process is limited in utilizing chemical sources for synthesis, such as methane and ethanol. Herein, the usage of an extract of a sustainable precursor, that is, Melaleuca alternifolia, commonly known as tea tree, is for the first time reported to synthesize graphene nanosheets in atmospheric pressure microwave plasma. The synthesis is carried out in a single step at a remarkably low microwave power of 200 W. The morphology, structure, and electrochemical properties of graphene are studied using state‐of‐the‐art characterization techniques such as Raman spectroscopy, X‐ray diffraction, transmission electron microscopy (TEM) and electrochemical impedance spectroscopy. The TEM images reveal the presence of a combination of nanostructures such as nano‐horns, nano‐rods, or nano‐onions consisting of multi‐layer graphitic architectures. An excellent sensing capability of as‐synthesized graphene is demonstrated through the detection of diuron herbicide. A commendable linear range of 20 µm to 1 mm and a limit of detection of 5 µm of diuron is recorded.

Decoration of graphene sheets with silver nanoparticles and their characterization

Graphene has been an emerging area of research since last decade. This fantastic material promises a wide variety of applications starting from electronics to biomedical fields. The properties of graphene can be enhanced by conjugating it with various other elements. The present work describes about the deposition of silver nano-particles via chemical synthesis onto in-house synthesized graphene nanosheets. It can be pointed out that application of infrared accelerates the synthesis process. Few layered graphene nanosheets (FLGNs) has been synthesized through electrochemical exfoliation technique. The colloidal graphene solution stabilized by citrate ions helps in the chemical reduction of AgNO3, which is essential in the formation of a nano-sized silver particulate layer (Ag NPs) over the graphene sheets. The presence of Ag NPs over the as-synthesized graphene was established by XRD, UV–VIS, FE-SEM and STM studies. The change in colloidal stability for the as-synthesized graphene and Ag NPs coated graphene was explained by the dynamic light scattering studies. The electronic characteristics of graphene coated Ag NPs was studied by scanning tunneling spectroscopy (STS) technique. The STS studies revealed that graphene with various numbers of coupled layers is responsible for the variations in the density of states (DOS) pattern. For Ag NPs-FLGNs, the spatial variations in the DOS spectra can be correlated to the size effects of the Ag NPs over the FLGNs. The local density of states (LDOS) spectra originates from the quantized electronic structure of the Ag NPs–FLGs system.

Active sites engineering via tuning configuration between graphitic-N and thiophenic-S dopants in one-step synthesized graphene nanosheets for efficient water-cycled electrocatalysis

• N, S co-doped graphene nanosheets (NSG) were synthesized via a bottom-up strategy. • All NSG are characterized by high surface area and highly graphitization degree. • The ratio of graphitic N and thiophenic S dopants in NSG affects their selectivity. • The optimized NSG exhibit efficient activity and stability for ORR, OER and HER. • The work provides a new insight on engineering active site of doped carbon materials. Precisely tuning synergetic effect between multi-heteroatom dopants in carbon matrix for water-cycled reactions such as hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) is critical for fuel cell and water splitting technologies. Herein, an effective active sites engineering strategy of bottom-up synthesized N, S co-doped graphene (NSG) nanosheets was developed via a facile pyrolysis of the mixed solid power of 2,6-diaminopyridine (DAP) as N source and ammonium persulfate (AP) as S source. All NSG nanosheets prepared with various mass ratio of DAP and AP possess high surface area up to more than 1000 m 2 g −1 and highly degree of crystallinity, but display significant differentiation in electrocatalytic selectivity, in which, the NSG prepared by DAP and AP with the mass ratio of 1:1 displays the highest ORR performance with a half-wave potential of 0.87 V vs . RHE, while the NSG with the mass ratio of 3:1 and 1:3 exhibit the highest activity for OER and HER respectively, achieving the corresponding potential of 1.58 V vs . RHE and 0.118 V vs . RHE at 10 mA cm −2 , respectively. These activities are comparable and even better than their precious metal counterparts, outperforming the vast majority of reported doped carbon materials prepared using other strategies and precursors. The excellent eletrocatalytic activity and selectivity essentially originate from the optimized intermediates energy of three-reaction pathways via active sites engineering constructed by tuning the ratio of graphitic-N and thiophenic-S dopants in NSG nanosheets, obtained by controlling the ratio of precursors of DAP and AP. This tuning strategy of active sites provides an effective and convenient way to develop precisely function-orientated water-cycled electrocatalysts based on a certain platform of N-containing precursor.

Controlled high temperature stability of microwave plasma synthesized graphene nanosheets

High temperature stability of nanomaterials plays an important role for their application in the field of nanocomposites, batteries, and sensors. Few-layer graphene nanosheets prepared by microwave plasma based decomposition of ethanol exhibited high thermal stability in the oxidation atmosphere in dependence on controlled formation of structural disorder. Analysis of differential thermogravimetry (DTG) curve profile showed three temperature regions, around 345 °C, 570 °C and above 700 °C, related to amorphous phase with a carbon–oxygen functional groups, small defective nanostructures and highly crystalline structure of graphene nanosheets, respectively. Raman spectroscopy and x-ray photoelectron spectroscopy (XPS) analysis of the nanosheets showed an increase of D/G Raman band ratio as well as increasing of sp3 phase content, from 6.1 at% to 15.2 at%, for highly crystalline and highly disordered structure of the nanosheets. Thermal annealing under synthetic air was used to investigate the variation in D/G and 2D/G Raman band ratio of the samples and to estimate activation energy of oxidation and disintegration process of graphene nanosheets. The highest oxidation resistance exhibited sample with high 2D/G band ratio (1.54) and lowest oxygen content of 1.7 at%. The synthesis process led to stabilization of nanosheet structure by formation of curved edges and elimination of free dangling bonds. The nanosheets prepared in microwave plasma exhibited high surface area, over 350 m2 g−1, and superior thermal stability with defect activation energy in an oxidation atmosphere higher than 2 eV. Heat release rate during the oxidation process was in correlation with the amount of disorder in the samples. Fast and easy to use technique based on high power Raman spectroscopy was developed for assessment of nanomaterial oxidation resistance.

Graphene nanosheets loaded Fe3O4 nanoparticles as a promising anode material for lithium ion batteries

A novel synthesis strategy has been developed to synthesize graphene nanosheets loaded Fe3O4 nanoparticles (GNSs/Fe3O4 NPs) via a freeze-drying of graphene and iron ion suspension and by a solvent thermal synthesis method sequentially. The size of Fe3O4 loaded on the graphene nanosheets can be regulated from 20 nm to 100 nm by controlling the mass ratio of GNSs and Fe3O4. When the ratio of GNSs to Fe3O4 is 1:2, the obtained Fe3O4 nanoparticles have ∼40 nm in diameter. Lithium ion battery anode made from GNSs/Fe3O4 (1:2) without adding any other conductive agent can exhibit a high reversible capacity (∼1145 mAh g−1 after 120 cycles at 100 mA g−1) and a remarkable rate capability (650 and 530 mAh g−1 at 0.5 and 1 A g−1, respectively). This excellent performance is caused by the uniform dispersion of Fe3O4 nanoparticles on the graphene nanosheet surfaces, and thus achieving a large specific surface area and the structural integrity during the Li+ insertion/extraction process.

Temperature sensor based on exfoliated graphene sheets produced by microwave assisted freezing induced volumetric expansion of carbonated water

In this report, we demonstrate the temperature sensing performance of exfoliated pristine few-layered graphene nanosheets. Fabrication of sensor material has been carried out by employing rapid, inexpensive and environmentally benign exfoliation approach based on microwave assisted freezing induced volumetric expansion of carbonated water. The structural and morphological characterization studies of as synthesized graphene nanosheets have been systematically accomplished by means of X-ray diffraction, Raman microscopic technique, scanning electron microscopy and transmission electron microscopy. The performance of assembled sensor is typically based upon resistive type temperature detection, which exhibits an exponential temperature dependence of resistance in temperature range of 28–250 °C. The resultant device exhibits a negative temperature coefficient resistance values of − 1.41% (°C)−1 and − 0.53% (°C)−1 in the temperature ranges of 28–45 °C and 50–160 °C respectively which are relatively higher than commercially available counterparts. The plausible underlying mechanism for temperature sensing has been explained on the basis of thermal generation of electron–hole pairs and carrier scattering by acoustic phonons. Captivatingly, the significant responsivity in temperature range of 28–45 °C has been obtained which makes the sensor competent for real time monitoring of body temperature. Such kind of temperature sensors may find their applications in customized health care and human–machine interface systems.

Growth of Tin Dioxide Nanostructures on Chemically Synthesized Graphene Nanosheets

금속산화물/그래핀 복합체는 고감도 가스센서 및 고용량의 이차전지와 같은 첨단 응용 분야에 활용될 수 있는 유망한 기능성 소재로 알려져 있다. 본 연구에서는 이산화주석( $SnO_2$ ) 나노구조물을 두 영역 전기로 장치를 이용하여 화학적으로 합성된 그래핀 나노시트 위에 성장시켰다. 대면적의 그래핀 나노시트는 Cu ...

High-quality liquid phase-pulsed laser ablation graphene synthesis by flexible graphite exfoliation

This work reports a one-pot procedure of laser ablation on a graphite target in a liquid medium, based on the variation of different parameters such as target type, laser wavelength, and ablation medium, to obtain high-quality graphene nanosheets. The morphology of derived products was characterized by the field emission scanning electron microscopy (FE-SEM). Then, the morphology and structure of the optimized sample were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), ultraviolet-visible-near infrared (UV–vis-NIR) spectroscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). By controlling the laser ablation parameters, we were able to prepare micrometer-sized few-layer graphene nanosheets with mainly less than ten layers. Such synthesized graphene nanosheets were grown at the surface of a flexible graphite target, indicating many potential applications in fundamental research, electrochemical and as hydrophobic surfaces.

SIMPLE SYNTHESIS OF GRAPHENE NANOSHEETS USING A MICROWAVE–ASSISTED METHOD

In this research, few–layer–graphene (FLG) sheets had been successfully fabricated by using a microwave–assisted method. First, graphite intercalation compounds were prepared from potassium–tetrahydrofuran (K–THF) –expanded graphite by solvothermal process, and then the exfoliation was assisted by microwave radiation and sonication process. The resulted nano–graphene has average thickness about ~ 2 nm with a lateral size of 3–7 μm. Raman analysis showed that the as–synthesized graphene nanosheets contain only a few numbers of structural defects or impurities. X–ray photoelectron spectroscopy and Fourier transform infrared spectroscopy spectra revealed that the nano–graphene consisted of several peaks similar to those of graphite, indicating the effectiveness of the solvothermal reduction method in lowering the oxygen level. The electrical conductivity of the as–synthesized nano–graphene was measured to be 170 S/m. In contrast to the Hummer method, the method is simple, inexpensive, and does not generate toxic gas. This simple method could provide the synthesis of high quality nano–graphene on a large scale.

Pulsed Nd:YAG laser assisted fabrication of graphene nanosheets in water

AbstractGraphene nanosheets were prepared by pulsed Nd:YAG laser ablation of graphite target in H2O under ambient conditions. The synthesized graphene nanosheets were characterized by high resolution transmission electron microscope (HRTEM), X-ray diffraction (XRD), Raman spectroscopy and Selected Area Electron Diffraction (SAED). The obtained structural and morphological analysis confirmed that the graphene nanosheets could be formed in an aqueous medium via one step method where a nanosecond pulsed near-infrared (NIR) laser (λ = 1064 nm) is used to ablate the surface of a pure graphite target. Compared to other used chemical methods to synthesis graphene nanosheets, laser ablation is an easy, versatile, environmental friendly and rapidly growing method for the synthesis of nanostructured materials such as graphene nanosheets. This technique showed normal operation in liquid medium (i.e. water or organic) under ambient conditions. Our study confirmed the great potential of laser ablation in liquid method for the fabrication of graphene nanosheets based nanofluids wich has a potential applicatiuon as a heat transfer fluid.

Urea-assisted low temperature green synthesis of graphene nanosheets for transparent conducting film

Present work demonstrates the fabrication of graphene nanosheet (GN) based transparent conducting film (TCF) using spray coating. Green synthesis of GN is carried out by reduction of graphene oxide (GO) using urea as green reducing agent. The reductive ability of urea with varied concentration is studied for GO at low temperature (i.e., 90 °C). As synthesized graphene nanosheets (GNs) are characterized by Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), UV–visible spectroscopy, field emission scanning electron microscopy (FESEM), atomic force microscope (AFM), and X-ray Photon spectroscopy (XPS). Raman analysis confirms that the maximum reduction of oxygen species is noticed using 30 mg/ml urea concentration at 90 °C from GO, and found Raman D to G band ratio (ID/IG) of ∼1.30. XPS analysis validates the Raman signature of removal of oxygen functional groups from GO, and obtained C/O ratio of ∼5.28. Further, transparent conducting films (TCFs) are fabricated using synthesized GNs. Thermal graphitization is carried out to enhance the optical and electrical properties of TCFs. TCF shows best performance when it is annealed at 900 °C for 1 h in vacuum, and obtained sheet resistance is ∼1.89 kΩ/□ with transmittance of ∼62.53%.

Facile synthesis of graphene nanosheets from humic acid for supercapacitors

A simple, cost-effective, and environmentally friendly route was developed to synthesize graphene nanosheets from humic acid via preliminary carbonization coupled with oxidation-exfoliation-thermal reduction. Such graphene nanosheets have a high specific surface area (495m2·g−1) with large pore volume (2.987cm3·g−1), unique interconnected mesoporous structure and uniform oxygen-containing functional groups in layered graphene framework, which offer a favorable and efficient pathway for the electrolyte propagation and transportation. The electrodes of supercapacitors made from these graphene nanosheets exhibit a maximum specific capacitance of 272F·g−1 at the current density of 50mA·g−1 in aqueous electrolyte, and possess excellent rate capability, low resistance, superior cycling performance with over 96.5% initial capacitance retention after 8000cycles. The corresponding supercapacitors deliver a desirable energy density of 6.47Wh·kg−1 at a powder density of 2250W·kg−1. This study demonstrates a promising synthesis route for large-scale production of graphene nanosheets from renewable and green humic acid for high performance supercapacitors.

Rapid detection of single nucleotide mutation in p53 gene based on gold nanoparticles decorated on graphene nanosheets

A simple and highly sensitive electrochemical DNA sensor for the rapid detection of a specific DNA sequence related to the p53 gene is described. The structure and morphology of the synthesized graphene nanosheets and Au nanoparticles were characterized through transmission electron microscopy, UV–Vis spectroscopy and energy dispersion X-ray spectroscopy techniques. The new electrochemical biosensor was prepared by modifying a graphite screen printed electrode (SPE) with gold nanoparticles decorated on graphene (AuNPs/G) nanocomposite. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) techniques were employed to clarify the changes in charge transfer during the fabrication and utilization of the DNA biosensor. The DNA hybridization event was monitored by differential pulse voltammetry (DPV). Under optimal conditions, the decrease of the peak current had a linear relation with the logarithm of the concentration of target complementary DNA in the range 0.5 fM to 0.05 nM, with a detection limit of 0.36 ± 0.04 fM. Rapid detection of DNA hybridization and single nucleotide mutation is reported by using gold nanoparticle-decorated, graphene nanosheets-modified screen printed electrode. Under optimal conditions, the peak current had a linear relation with the logarithm of the concentration of target complementary DNA in the range 0.5 fM to 0.05 nM, with a detection limit of 0.36 ± 0.04 fM.

Multiplex electrochemiluminescence DNA sensor for determination of hepatitis B virus and hepatitis C virus based on multicolor quantum dots and Au nanoparticles

In this work, a novel multiplex electrochemiluminescence (ECL) DNA sensor has been developed for determination of hepatitis B virus (HBV) and hepatitis C virus (HCV) based on multicolor CdTe quantum dots (CdTe QDs) and Au nanoparticles (Au NPs). The electrochemically synthesized graphene nanosheets (GNs) were selected as conducting bridge to anchor CdTe QDs551-capture DNAHBV and CdTe QDs607-capture DNAHCV on the glassy carbon electrode (GCE). Then, different concentrations of target DNAHBV and target DNAHCV were introduced to hybrid with complementary CdTe QDs-capture DNA. Au NPs-probe DNAHBV and Au NPs-probe DNAHCV were modified to the above composite film via hybrid with the unreacted complementary CdTe QDs-capture DNA. Au NPs could quench the electrochemiluminescence (ECL) intensity of CdTe QDs due to the inner filter effect. Therefore, the determination of target DNAHBV and target DNAHCV could be achieved by monitoring the ECL DNA sensor based on Au NPs-probe DNA/target DNA/CdTe QDs-capture DNA/GNs/GCE composite film. Under the optimum conditions, the ECL intensity of CdTe QDs551 and CdTe QDs607 and the concentration of target DNAHBV and target DNAHCV have good linear relationship in the range of 0.0005–0.5 nmol L−1 and 0.001–1.0 nmol L−1 respectively, and the limit of detection were 0.082 pmol L−1 and 0.34 pmol L−1 respectively (S/N = 3). The DNA sensor showed good sensitivity, selectivity, reproducibility and acceptable stability. The proposed DNA sensor has been employed for the determination of target DNAHBV and target DNAHCV in human serum samples with satisfactory results.

Determination of copper ions in foodstuff products with a newly modified potentiometric carbon paste electrode based on a novel nano-sensing layer

In the present study, a novel nano-layer sensing materials for the fabrication of a newly modified potentiometric carbon paste electrode was introduced. Its sensing layer was prepared with the incorporation of 1-(3-imino-4-hydroxophenylazo-4 nitrobenzene) isonicotinohydrazide “as an efficient ionophore” into the matrix consisting of graphite powder, synthesized graphene nanosheets, synthesized CdO nanowires, and diphenylacetylene (a typical molecular wire as the conductive binder). The suggested nanocomposite carbon paste electrode gave a Nernstian behavior in the linear range of 3.50 × 10−9 to 1.00 × 10−2 M with the detection limit of 1.44 × 10−9 M. For investigation of the electrochemical behavior of Cu2+ at the surface of the unmodified and modified electrodes, the differential pulse voltametric method was used. The proposed sensor was successfully applied in the determination of copper ions in some foodstuff real samples with satisfactory results.

Electrocatalytic Study of Efficient Synthesized Graphene Nanosheets Incorporated with Pt Nanoparticles for Methanol Oxidation Reaction

AbstractGraphene nanosheets/Pt (GNS/Pt) nanocomposite was successfully fabricated via clean chemical reduction method. The nanocomposite was characterized by X‐ray diffraction, field emission scanning electron microscope and high resolution transmission electron microscope, which revealed that Pt nanoparticles were completely formed and homogenously distributed on the GNS. The electrochemical activities of the catalysts were investigated by cyclic voltammogram. The experimental results showed that GNS/Pt nanocomposites catalyst exhibited superior electrocatalytic activity for methanol oxidation. These results suggest that GNS/Pt nanocomposites would be a promising anode catalyst for DMFC.

Designing and fabrication of new molecularly imprinted polymer-based potentiometric nano-graphene/ionic liquid/carbon paste electrode for the determination of losartan

In this study, a novel losartan molecularly imprinted polymer was synthesized and used as a sensing agent in a sensing layer of the new modified potentiometric nano-graphene/carbon paste electrode incorporated with graphite powder, synthesized graphene nano-sheets and an ionic liquid, as the conducting binder, for the selective determination of losartan. Methacrylic acid as functional monomer, ethylene glycol dimethacrylate as a cross linker, 2-2′-azoisobutyronitrile as an initiator and chloroform as polymerization solvent were used. The characteristic of the synthesized molecularly imprinted polymer were investigated by Fourier transform infrared analysis and scanning electron microscopy. The molecularly imprinted polymer-modified electrode exhibited a Nernstian response (59.64±0.20mVdecade−1) in a wide linear dynamic range of 3.00×10−9 to 1.00×10−2M with a lower detection limit of 1.82×10−9M. The suggested potentiometric sensor demonstrated a fast response time of ∼6s, a high performance, fairly high selectivity over some interfering compounds and a satisfactory long-term stability (more than 3months). It was successfully applied for the highly sensitive determination of losartan in pharmaceutical products and urine samples with satisfactory results.

Facile synthesis of graphene sheets for heat sink application

A mechanical cleavage (MC) approach has been demonstrated to synthesize graphene nanosheets (GNs) as heat sink materials from artificial graphite paper (GP). The facile MC method is composed of three main steps: GP isolation, GP exfoliation, and GN collection. The method is capable of preparing few layers of GNs repeatedly without using chemical oxidizing agents and costly deposition apparatus. The as-prepared GN powders are well characterized by X-ray diffraction and Raman spectroscopy. On the basis of the experimental results, the MC method shows a great feasibility to synthesize high-quality GN products with high repeatability and environmental friendliness. We also report that the addition of GN onto Cu foil induces an improved capability for heat dissipation, as compared with original GP and Cu heat foil. According to the calculations of Fourier's law, the thermal conductivity of the GN/Cu composite heat sink can reach as high as 2142 W/mK, leading to 26% increase of thermal conductivity compared to the GP heat sink.

Nanoporous graphene materials by low-temperature vacuum-assisted thermal process for electrochemical energy storage

Graphene supercapacitors with a high electrode surface area have great potential in efficient energy storage. For practical applications, it is critical to develop highly-manufacturable methods to synthesize graphene nanosheets with high ion accessibility and uniform pore-sizes. Here we demonstrate a nontoxic approach for graphene synthesis which involves a low vacuum annealing at an easy-to-reach temperature. The supercapacitors based on the low-temperature exfoliated graphene materials show excellent electrochemical performance superior to those synthesized by high-temperature methods. Our investigation presents an efficient, yet industry-compatible and low cost way that can be scaled up for mass production of graphene for electrochemical energy storage application.

Direct growth of cobalt aluminum double hydroxides on graphene nanosheets and the capacitive properties of the resulting composites

We synthesized graphene nanosheets (GNs)/cobalt aluminum (CoAl) double hydroxide composites through a layer-by-layer deposition process while varying the concentration of the graphene precursor used. The CoAl layered double hydroxide particles were uniformly distributed on the surfaces of the graphene layers and effectively prevented the agglomeration of the GNs, resulting in a higher reactive surface area and easier ion transport. We employed X-ray diffraction analysis, energy-dispersive X-ray spectroscopy, field-emission scanning electron microscopy, and field-emission transmission electron microscopy to investigate the microstructures and morphologies of the composites. In addition, cyclic voltammetry, electrochemical impedance spectroscopy, and galvanostatic charge/discharge measurements were performed to analyze the electrochemical behaviors of the composites. The as-prepared composites showed desirable electrochemical characteristics, including high specific capacitances, low resistances, and high cycling stabilities. In particular, the composite formed by optimizing the GNs/CoAl ratio (the electrolyte used was a 6M aqueous KOH solution) exhibited the maximum specific capacitance, which was 974Fg−1.