Assembly Of Graphene Research Articles

Simplified Fabrication Strategy of Graphene Liquid Cells for the in Situ Transmission Electron Microscopy Study of Au Nanoparticles

Graphene liquid cells (GLCs) have recently attracted increasing attention in multiple research fields because this technique has provided unique opportunities for studying liquid-phase reactions. Here, we report a simplified approach for the fabrication of GLCs using ultrasonication assistance. We demonstrate that morphologies of fabricated GLCs depend on the number of graphene layers. With the appropriate ultrasound, few-layer graphene assemblies to graphene shells and multilayer graphene (mlG) transforms to graphene scrolls that preserve the liquid pocket inside. We reveal that liquid cells made from mlG offer superior spatial resolution to achieve sub-nanometer detection. More importantly, we investigate the in situ coalescence processes of Au nanoparticles both in the liquid cell and on solid graphene support. From the direct comparison, we show a jump to the contact mode only associated with the coalescence of Au nanoparticles in water. Our study provides a simplified route to prepare GLCs and enhan...

Molecular investigations on the interactions of graphene, crude oil fractions and mineral aggregates at low, medium and high temperatures

Performance of the nanoparticle-modified asphalt binder is greatly influenced by adhesion properties between asphalt binder and nanoparticle. In this work, the adhesion properties of crude oil fractions (e.g., Saturate, Asphaltene, Resin and Aromatic components of asphalt binder), graphene and mineral aggregates (silicon dioxide) at various temperatures are investigated through molecular dynamic simulation and REAXFF force field. The results from SARA-graphene interface demonstrations that aromatic and asphaltene have 30% higher adhesion properties than saturate and resin. Also, while using graphene is valuable for the adhesion properties of the binder, it has no significant advantage over binder in binder-aggregate interactions.

High-performance antistatic acrylic coating by incorporation with modified graphene

Abstract

Green Synthesis and Layer-by-Layer Assembly of Amino-Functionalized Graphene Oxide/Carboxylic Surface Modified Trimetallic Nanoparticles Nanocomposite for Label-Free Electrochemical Biosensing

In this context, a novel, scalable and facile method for the green synthesis of graphene oxide (GO) to facilitate effective and safe oxidation of graphite using sodium periodate (NaIO4) is demonstrated. The optimized value of the oxidizing agent NaIO4 ensured effective oxidation, minimized defects on sp2 C-C plane (ID/IG = 0.645) and increased C/O atomic ratio of ∼5.146. Subsequently, we successfully synthesized the amino-functionalized reduced graphene oxide (NH2-rGO) and carboxylic surface modified AgPtPd (COOH-AgPtPd) trimetallic nanoparticles (TNPs), in order to fabricate a label-free electrochemical sensing platform using the conventional immersive layer-by-layer (LBL) assembly. The superior synergetic effect between LBL-assembled NH2-rGO and COOH-AgPtPd (COOH-AgPtPd/NH2-rGO) significantly boosts the electron transfer rate of the electrode as well as electrocatalytic efficiency. Therefore, the as-prepared COOH-AgPtPd/NH2-rGO nanocomposite-based sensing material was first employed for nonenzymatic electrochemical detection of H2O2, with a low detection limit of 0.2 nM. Moreover, COOH-AgPtPd/NH2-rGO nanocomposite can also be utilized as a sensing platform for label-free accurate electrochemical detection of prostate-specific antigen (PSA) over a large linear range of 4 fg mL−1 to 300 ng mL−1, with an ultra-low detection limit (LOD) of 4 fg mL−1.

Layer-layer assembly of water-based graphene for facile fabrication of sensitive strain gauges on paper

Paper has been proposed as an alternative substrate material for graphene-based strain gauges due to its high flexibility and accessibility when compared to the conventional substrates such as polymer that is not only rigid but also not recyclable. In the fabrication of graphene-based strain gauges on paper, inkjet printing is commonly used as the main deposition method of graphene on paper as this process allows a systematic control of strain gauge resistance by manipulating several factors such as print passes and drop spacing. However, the availability of inkjet printers that allows the printing of graphene solution is an issue as industrial inkjet printers can be obtained only at a premium price while modification of commercial inkjet printers is a must to replace the original ink with graphene ink. To counter this issue, a commercial photo paper has been used for the first time as a substrate during vacuum filtration of graphene solution for layer–layer assembly of strain gauges on paper. With the resulting gauge factor of up to 83 at the maximum and minimum strain of 1.4% and 0.03% (sensitivity of 1.25%) respectively, the fabricated strain gauge from photo paper shows the potential of paper to be used as a component in the future wearable device. Meanwhile, the advantages of using vacuum filtration as the selected technique for the deposition of graphene meanwhile are demonstrated in this work by varying the gauge factor through controlling the graphene deposition volume.

Stabilization of 2D graphene, functionalized graphene, and Ti2CO2 (MXene) in super-critical CO2: a molecular dynamics study.

The stabilization of nanoparticles is a main concern to produce an efficient nanofluid. Here, we carry out Molecular Dynamics (MD) modeling to evaluate the stabilization of 2D graphene, oxygen- and hydrogen-functionalized graphene, and Ti2CO2 MXene nano-sheets in carbon dioxide (CO2) liquid under supercritical conditions. The rheological properties (i.e., viscosity and self-diffusion) of the nanofluids with the corresponding nano-sheets are also calculated. The results show that pristine graphene aggregates in the liquid and the adsorbed CO2 molecules on the graphene surfaces could not provide enough repulsive forces to avoid their aggregation. The stabilization of graphene is improved by surface functionalization of graphene with oxygen and hydrogen functional groups. This is because, first, the presence of the corresponding surface groups can alter the electrostatic forces of the graphene nano-sheets and, second, a larger number of CO2 molecules attracted by the functionalized nano-sheets can provide additional repulsive forces between the nano-sheets. The results demonstrate that Ti2CO2 MXene nano-sheets aggregate severely although they are covered by oxygen surface terminations and attract more CO2 molecules than the pristine graphene. This is attributed to the strong interlayer coupling between the MXene nano-sheets so that the electrostatic repulsion of the MXene surfaces could not overcome the interlayer coupling. Based on our results, the stabilization of the corresponding 2D nano-sheets in CO2 liquid is in the order: oxygen-functionalized graphene > hydrogen-functionalized graphene > pristine graphene > Ti2CO2 MXene. The calculation of the rheological properties of the nanofluids with different nano-sheets demonstrates that immersing the nano-sheets in the CO2 liquid affords a superior viscosity enhancement as much as possible to be dispersed in the liquid. This study expands the potential applications of these 2D materials in producing SC-CO2 based nanofluids.

Numerical study on the field-emission properties of a graphene–C60 composite

A new model of a graphene–C60 composite is constructed to explore its electronic structure and field-emission characteristics. We investigate the structural stability, energy levels, local electron density distribution, work function, ionization potential, and Mulliken, Hirshfeld, and electrostatic potential fitting (ESP) charges of this composite by using first-principles methods. The results indicate that the electronic structure of the composite can be modulated obviously by applying an external electric field. The energy gap decreases as the electric field is increased, and the change in the local electron density distribution plays the role of a tip emission point. We find that the binding energy increases as the electric field is increased, which confirms that the assembly of graphene and C60 directly improves the stability of the compound and results in excellent semiconducting properties. With the increasing electric field, we also find that the work functions and ionization potentials of this composite decrease linearly, and the Mulliken, Hirshfeld and ESP charge move efficiently. All of those and the change of energy gap and the local electron density distribution show the improvement of graphene–C60 composite’s field emission properties. We conclude that the graphene–C60 composite may be a promising candidate for use in field-emission devices.

Synthesis and Characterization of Graphene/Binary Metal Molybdate (Graphene/Zn1−xNixMoO4) Nanocomposite for Supercapacitors

A novel graphene/binary metal molybdate (Zn1‐xNixMoO4) is synthesized via a facile and simple microwave synthesis route (x = 0.0, 0.2, 0.4, 0.6, 0.8). Electrochemical studies are performed for all the samples to study their charge storage mechanism and frequency dependence in a three‐electrode set up with 2m KOH electrolyte solution. Among the samples, Zn0.6Ni0.4MoO4 shows better electrochemical performance which is combined with graphene so as to obtain graphene/Zn1‐xNixMoO4 (x = 0.4) nanocomposite. XRD and Raman analyses have confirmed formation of complexation of graphene/binary metal molybdate nanocomposite. TEM morphological profile illustrates little aggregation and interconnected layers of graphene interspersed with rice‐like grains of binary metal molybdate. Graphene/Zn1‐xNixMoO4 (x = 0.4) exhibits good energy density and power density of 62.3 Wh kg−1 and 448.5 W kg−1 respectively with a specific capacitance of 555.5 F g−1 at 1 A g−1. The electrode material with good cyclic stability of 85% even after 5000 charge/discharge cycles may be explored as a novel option for supercapacitors.

One‐Pot Synthesis of a Highly Active 3‐Dimensional Fe−Nx−CNTs/rGO Composite Catalyst for Oxygen Reduction

AbstractA facile one‐pot method to synthesize a Fe−Nx−CNTs/rGO catalyst by using melamine and FeCl2⋅4H2O as low‐cost precursors is reported.The 3‐dimensional porous structure and the dispersion of precursor were completed at the same time. Suitable precursor and concentration selection not only solved the aggregation of graphene but also improved its effective iron content and activity. The obtained catalysts exhibited oxygen reduction activitycomparable to commercial Pt/C with a half‐wave potential (the potential when current density reaches the half of the diffusion‐limited current density) at 0.875 V(vs. RHE) in alkaline media. In addition, it also showed a better stability than Pt/C with a lower decay of E1/2 (10 mV) after 2000 cycles. From the systematic physical characterizations including aberration‐corrected scanning transmission electron microscopy, 57Fe Mössbauer spectroscopy and X‐ray absorption spectroscopy, it was discovered that a unique structure with the coexistence of nitrogen‐coordinated single iron atoms and Fe/Fe2C nanocrystals had been formed.

Assembly of graphene on Ag3PO4/AgI for effective degradation of carbamazepine under Visible-light irradiation: Mechanism and degradation pathways

A highly efficient visible-light-driven photocatalyst Ag3PO4/AgI-Graphene (Ag3PO4/AgI-G) was synthesized through a chemical coprecipitation procedure. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) were performed to study the physicochemical structural of the photocatalysts. The photocatalytic activity of the samples was examined by the carbamazepine (CBZ) degradation under artificial visible light and natural sunlight irradiation. Experimental results indicated that the introduction of low mass content of graphene enhanced the photocatalytic performance of Ag3PO4/AgI, and the photocatalytic degradation efficiency of CBZ over Ag3PO4/AgI-3%G (mass ratio of graphene:Ag3PO4/AgI = 3:100) reached 93.06% within 21 min, which was much higher than that over pure Ag3PO4 (26.92%) and Ag3PO4/AgI (74.38%). UV–vis diffuse reflectance spectra, photoluminescence (PL) spectra, transient photocurrent responses and electrochemical impedance spectra (EIS) of the samples were conducted to verify the high photocatalytic performance of the Ag3PO4/AgI-3%G. In addition, possible photocatalytic degradation pathways of CBZ were proposed based on the analysis of transformation products during the reaction. The reactive species trapping experiments and Electron spin resonance (ESR) analysis demonstrated that h+ and O2− were the main active oxidant species responsible for CBZ photodegradation. The photocatalytic degradation mechanism of CBZ over Ag3PO4/AgI-3%G under visible light irradiation was schematically proposed. This study not only provides a new technique for the synthesis of Ag3PO4-based photocatalysts with high photocatalytic activity, but also demonstrates that the Ag3PO4/AgI-3%G composite could be a promising photocatalyst for the treatment of waters containing CBZ.

A facile and general approach for production of nanoscrolls with high-yield from two-dimensional nanosheets

Nanoscrolls (NSs) assembled from two-dimensional nanosheets have emerged as a novel type of one-dimensional nanomaterials because of their unique topological features and properties. The scale-up preparation of the NSs is crucial for their foundational and applied research. Herein, we report a general and straightforward approach for efficiently converting two-dimensional nanosheets into the NSs with high yield. We demonstrated the converting process by illustrating the formation of the graphene nanoscrolls through characterizing their morphology and structure using a scanning electron microscope, transmission electron microscope, Raman spectra, and X-ray diffraction spectra. The graphene sheets with a few-lay number were converted immediately and entirely into the graphene nanoscrolls when they mixed with an ethanol solution of silver nitrate at room temperature. The as-prepared graphene nanoscrolls were confirmed to be formed via the layer-by-layer assembly of graphene triggered by silver cyanide formed in site. Also, we extended this approach to construct the nanoscrolls of the hexagonal boron nitride, molybdenum disulfide, and tungsten disulfide, respectively, from their corresponding two-dimensional nanomaterials. In a broader context, this approach paves a significant new way for the large production of the NSs with cost-efficiency.

Graphene-dye supramolecular assembly for parts per trillion level F− monitoring

An innovative and simple displacement approach based on Graphene and Rhodamine supramolecular assembly that could sense fluoride ion in aqueous solution is demonstrated. Graphene-Rhodamine unit engages in the formation of a supramolecular complex between Rhodamine (indicator) and Graphene (receptor), followed by the displacement of the indicator with the advent of F− ion. These changes alter optical characteristics of the supramolecular entity which can be quantified using spectroscopic techniques. The findings of UV–vis and Photoluminescence analysis together with the life-time measurement studies reveal that through the interactions of Graphene sheets with Rhodamine dye quenches the optical response of the dye which can be selectively restored by introducing traces of F−. The detection limit was found to be 11 ppb and 850 ppt by UV–vis and Photoluminescence studies respectively, falling admirably below the permissible F- level in drinking water i.e. 1.5 ppm. The proof of concept for this sensing strategy is demonstrated through paper-based testing strips that can function as a portable layman’s tool for sub ppb level detection of the test anion. Investigations on real water samples spiked with Fluoride ion assures that the proposed sensor moiety can swiftly monitor the test ion levels in complex samples and affirm the utility of the system for practical applications.

Reliable and quantitative electrochemical platform for direct detection of CYP707A1 gene expression from wheat leaves

Gene-expression analysis is increasingly important in biological research, measuring the level of a particular gene expressed within a cell or tissue can provide a lot of valuable information. In this paper, we present a simple electrochemical (EC) biosensor that is capable of detecting CYP707A1 gene expression. Briefly, the target CYP707A1 gene was amplified by reverse transcription-polymerase chain reaction (RT-PCR) extraction from the leaves of Triticum aestivum (wheat). Due to the 5′ end of primers for PCR amplification modified with biotin and thiol separately, signal tag (Thi-dsDNA@SA-MB bioconjugate) was formed. The sensing platform was simply constructed by the assembly of typical gold nanostar and graphene with good repeatability. When the Thi-dsDNA@SA-MB bioconjugate was captured onto the sensing interface, numerous redox molecule thionine (Thi) could be introduced, producing a significant EC response. As a result, the proposed EC biosensor sensitively detects CYP707A1 express products of T. aestivum with the detection limit is as low as 13 pM. Importantly, the accuracy and reproducibility of this methodology, is comparable favorably with that of real-time RT-PCR (qRT-PCR), the benchmark technology for expression profiling of selected CYP707A1 gene in different drought-treated samples of T. aestivum.

Graphene Reinforced Epoxy Adhesive For Fracture Resistance

The fracture resistance of construction adhesive has attracted tremendous interests in the past decades. This paper conducts an experimental study on the mode I fracture resistance of epoxy construction adhesive reinforced with graphene nanoplatelets (GNPs) through double cantilever beam (DCB) specimens. The experimental results show that the mode I fracture toughness of nanocomposites increases compared with the neat epoxy. It is worth noting that the mode I fracture toughness of nanocomposites at a graphene content of only 0.25 wt% exhibits a 5 times enhancement compared with neat epoxy adhesive. When the graphene content continues to increase, the mode I fracture toughness of adhesive decreases as the aggregation of graphene in adhesive. The mechanical behavior of the DCB specimens with different nanocomposites adhesive are predicted using finite elements analysis (FEA). The mode I fracture properties of nanocomposites obtained from the experimental results are used as cohesive zone model parameters in FEA. The prediction agrees very well with the experimental results.

Preparation of stable and high-efficient poly(m-phenylenediamine)/reduced graphene oxide composites for hexavalent chromium removal

Structural instability of polymers under strong acidic condition severely limits their application in the field of environment. A synthetic strategy for the preparation of poly(m-phenylenediamine)/reduced graphene oxide (PmPD/rGO) composites was proposed for Cr(VI) removal in strong acidic solution, which involved in situ reduction of graphene oxide (GO) and assembly of PmPD nanoparticles. Effects of in situ reduction of GO on oxidation polymerization, property and Cr(VI) adsorption capacity of composites were investigated methodically. Compared to pure PmPD, PmPD/rGO composites exhibited favorable stability in strong acidic solution. Moreover, the polymerization yield of PmPD/rGO composites increased from 75 to 91%. The maximum Cr(VI) adsorption capacity of composites calculated by the Langmuir model reached 526.24 mg g−1. The mechanisms of PmPD/rGO composites preparation and Cr(VI) removal were analyzed in detail. The synthetic strategy shows promising prospect to expand application of polymers, especially for Cr(VI) removal in strong acidic solution.

Mechanical properties and simulation of nanographene/polyvinylidene fluoride composite films

Nanographene possesses unique mechanical and electrical properties. The mechanical properties of nanographene/polyvinylidene fluoride (PVDF) composite films are studied by experiment and simulation analysis in this paper. Different amounts of nanographene/PVDF samples were prepared to obtain general field emission scanning electron microscopy overviews and perform tensile experiments for obtaining the equivalent elastic moduli. Materials Studio was used to establish nanographene microscopic models to obtain linear elasticity data. The digital simulation models were established using ANSYS to conduct the finite element simulation for the equivalent elastic modulus of the composites in different graphene contents and assumptions.Results of the experiments and simulations showed that the equivalent elastic modulus of the composites increases first with increasing graphene content and then decreases after the mass fraction of graphene reaches 10%. The change in the mechanical properties of nanographene/PVDF composites is due to graphene aggregation. The agglomeration phenomenon increases with the increase in graphene.

Stacking-Controlled Assembly of Cabbage-Like Graphene Microsphere for Charge Storage Applications.

Nanostructured graphene electrodes generally have a low density, which can limit the volumetric performance for energy storage devices. The liquid-phase mild reduction process of graphene oxide sheets is combined with the continuous aerosol densification process to produce high-density graphene agglomerates in the form of microspheres. The produced graphene assembly shows the cabbage-like morphology with a high density of 0.75 g cm-3 . In spite of such high density, the cabbage-like graphene microspheres have narrow-ranged mesopores and a high surface area. The cabbage-like graphene microsphere exhibits both high gravimetric and volumetric energy densities due to the optimized microstructure, which shows a high gravimetric capacitance of 177 F g-1 and volumetric capacitance of 117 F cm-3 in supercapacitors. As a cathode for lithium-ion capacitors, the cabbage-like graphene delivers a reversible capacity of ≈176 mAh g-1 . The stacking-control approach provides a new pathway to control the microstructure of the graphene assembly and corresponding charge storage characteristics for energy storage applications.

Solder-free electrical Joule welding of macroscopic graphene assemblies

Welding is an important convenient methodology to realize robust coalescence of individual metallic or polymeric objects through local melting of contact boundaries. However, how to firmly conjoin the refractory graphene-based materials via conventional welding remains an open question because of their non-melting nature. In this work, we report an efficient solder-free approach to weld individual macroscopic graphene assemblies via electrical Joule heating. Graphene-based materials with different architectures, including graphene fibers, films, and foams, are covalently welded together with high joint strength. The welding mechanism was studied by in situ transmission electron microscope and molecular dynamic simulations. We attributed the unique welding behavior to the defect-facilitated cross-linking between graphene layers at contact interface. The facile electrical Joule welding strategy provides a new reliable connection method for carbon materials, enabling the direct assembling of macroscopic graphene materials to sophisticated three-dimensional configurations.

Wet‐spinning assembly of continuous and macroscopic graphene oxide/polyacrylonitrile reinforced composite fibers with enhanced mechanical properties and thermal stability

ABSTRACTPolyacrylonitrile (PAN) composite microfibers with different contents of graphene oxide (GO) were fabricated via wet‐spinning route in this work. Based on nonsolvent‐induced phase separation theory, N,N‐dimethyl formamide/water mixture system was employed as coagulation bath, nonsolvent (water) diffused into PAN spinning solution and led to a quick PAN fiber solidification. Nematic liquid crystal state of GO dispersions and GO/PAN spinning solutions were determined via polarized optical microscopy images, and the morphology and structure of the composite fibers were characterized via scanning electron microscope, Transmission electron microscopy, Fourier transform infrared spectra, and X‐ray diffraction. 1 wt % GO/PAN composite fibers exhibited outstanding mechanical properties, 40% enhancement in tensile strength and 34% enhancement in Young's modulus compared with pure PAN fiber. The results of dynamic mechanical analysis indicated that the composite fiber with 1 wt % GO performed the best thermal mechanical property with 5.5 GPa and 0.139 in storage modulus and loss tangent, respectively. In addition, thermogravimetric analysis showed that thermal stability of the composite fibers enhanced with the increasing GO contents. GO/PAN composite fibers can be as the candidate of carbon fiber precursor, high performance fibers, and textiles applications. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 46950.

Fine Regulate the Process of Exfoliation of Graphite to Prepare Graphene

The use of graphene (Gr) has led to great breakthroughs because of its excellent mechanical strength, high electric and thermal conductivity, catalytic properties, etc. Industrial applications of this material are hindered by the absence of high-volume production method of high-quality Gr. Electrochemical exfoliation of graphite is a promising method for mass production of Gr. The key issue is the difficulty of controlling the intercalation and tailing processes, which occur in almost the same potential region. Nevertheless, we realized that these processes are different kinetically and designed various programmed strategies of potential modulation for electrochemical exfoliation. High-quality Gr (≤ 5 layers) was obtained from highly oriented pyrolytic graphite (HOPG), with a yield of 96% and an average area greater than 230 μm2. The programmed electrolysis applies to commercial graphite rods with a yield of 58% (≤ 5 layers) and an average area about 50 μm2. The molecular ratio of carbon over oxygen (C/O) was confirmed as 22.7, indicating an oxidation degree as low as 4.4 %, and excellent electron transport and electron transfer properties. The specific capacitance of the prepared layer Gr by commercial graphite rods was 135 F g-1. The programmed electrolysis opens a promising route to the mass production of Gr, which is crucial for the follow-up modification and assembly of graphene for industrial applications.