Nanographite Sheets Research Articles

Aptasensor Integrated with Two-Dimensional Nanomaterial for Selective and Sensitive Electrochemical Detection of Ketamine Drug.

Ketamine is one of the most commonly abused drugs globally, posing a severe risk to social stability and human health, not only it is being used for recreational purposes, but this tasteless, odourless, and colourless drug also facilitates sexual assaults when it is mixed with drinks. Ketamine abuse is a threat for safety, and this misuse is one of the main uses of the drug. The crucial role of ketamine detection is evident in its contributions to forensic investigations, law enforcement, drug control, workplace integrity, and public health. Electrochemical sensors have gained considerable interest among researchers due to their various advantages, such as low cost and specificity, and particularly screen-printed paper-based electrode (SPBE) biosensors have gained attention. Here, we reported an ePAD (electrochemical paper-based analytical device) for detecting the recreational drug ketamine. The advantages of using a paper-based electrode are that it reduces the electrode's production costs and is disposable and environmentally friendly. At the same time, nanographite sheets (NGSs) assisted in amplifying the signals generated in the cyclic voltammetry system when ketamine was present. This ePAD was developed by immobilizing a ketamine aptamer on NGS electrodes. The characterization of proper synthesized NGSs was performed by Scanning Electron Microscopy (SEM), XRD (X-ray Diffraction), Fourier-transform infrared spectroscopy (FTIR), and UV-Vis spectroscopy. Electrochemical techniques, including cyclic voltammetry (CV) and linear sweep voltammetry (LSV), were employed to validate the results and confirm each attachment. Furthermore, the versatility of the proposed sensor was explored in both alcoholic and non-alcoholic beverages. The developed sensor showed a low LOD of about 0.01 μg/mL, and the linear range was between 0.01 and 5 μg/mL. This approach offers a valid diagnostic technique for onsite service with minimal resources. This cost effective and portable platform offers desirable characteristics like sensitivity and selectivity and can also be used for POC (point of care) testing to help in the quick identification of suspicious samples and for testing at trafficking sites, amusement parks, and by the side of the road.

Graphene reinforced-graphitized nanodiamonds matrix composites: Fabrication, microstructure, mechanical properties, thermal and electrical conductivity

The inherent defects of traditional graphite bulks, such as microcracks and brittleness, have a severe impact on their application performances. The introduction of graphene (Gr) into graphite materials is considered as an effective strategy to improve their properties. Herein, Gr reinforced graphite bulk composites with nanodiamonds (NDs) as a matrix precursor and Gr as reinforcement were successfully synthesized by spark plasma sintering. After sintering, the NDs phase was completely transformed into nanographite sheets, and the volume expansion during the transformation endows the graphite bulks with dense structure. The introduction of Gr can not only reduce the internal stress in the sintered composites, but effectively promote the deflection of the crack propagation path. As a result, the prepared composites reinforced by doping 1 wt% of Gr (Gr-1) demonstrates the highest flexural strength (57 MPa) and compressive strength (245 MPa), which are 90% and 82.6% higher than those of the NDs graphitized compacts (Gr-0), respectively. Gr-1 exhibits the lowest friction coefficient (0.1) and higher thermal conductivity and electrical conductivity in all the Gr/nanographite composites. It is attributed to the fact that Gr maintains its planar structure in the matrix and forms a good interface bond with nanographite sheets.

Synthesis of stable anisotropic carbon particle aggregates covered by surface nano-graphitic sheets

For this study, pyrolytic carbon particles were synthesized in a pyrolytic reactor in which a moderate electric field by DC power was generated between two electrodes at the center of the pyrolysis zone at 1573K. The resulting carbon particles, which were collected on the top of the electrode, were analyzed to assess their microstructure and nanostructure using TEM observation, Raman spectroscopy, X-ray diffraction measurement, and light scattering size distribution measurements. Results showed that the resulting carbon particles formed a characteristic structure; the anisotropic chain-like configuration (fractal dimension, Df=1.65±0.02), with graphitic thin nanolayers having high crystallinity covering the surface of these aggregates. Morphological analysis with the concept of the fractal dimension of the aggregate indicates that the electric field regulates the aggregate morphology. The other experiment which the carbon source was fed onto prefabricated pyrolysis carbon particles under 1537K showed that surface graphitic layers on the aggregate was derived from gas phase carbon sources, not from graphitizing of the surface structure of carbon particles. The ultrasonication of carbon particles with/without surface graphitic layers in the ethanol solution also confirmed that the specific role of the layers that supports stabilization of the aggregate configuration.

Preparation of nanographite sheets supported Si nanoparticles by in situ reduction of fumed SiO2 with magnesium for lithium ion battery

This work explores low cost methods for the preparation of Si/nano-graphite sheets (NanoGs) composite materials for Li ion battery. The Si/NanoGs composites are prepared by magnesium thermal reduction of mechanical mixture of fumed SiO2 and NanoGs under Ar atmosphere. The structure of the samples is characterized by XRD, Raman spectroscope, SEM, and HRTEM. The results show that highly crystallized Si nanoparticles with a sheet-like morphology are uniformly distributed on the surface of NanoGs (both edge and a-b plane). The average diameter of Si nanoparticles is ∼20 nm. Electrochemical characterization shows that an electrode has an initial lithium storage capacity of 1702.9 mAh g−1 at a current of 100 mA g−1. The storage capacity decreases to 975.7 mAh g−1 after 100 cycles. Since cheap commercial fumed SiO2 and graphite are used and the process is simple and easy to scale up, with further improvement, the method has potential for use in large scale production of high energy density Si/NanoGs anode materials at low cost.

Fabrication of NanoGs/PPy/Polymethacrylate (PMMA)-Epoxy Conductive Films

Nanographite sheets (NanoGs)/polypyrrole (PPy)/polymethacrylate (PMMA)–epoxy conductive films have been successfully prepared. NanoGs were prepared by treating the expanded graphite with sonication in aqueous alcohol solution. Then nanocomposite films were fabricated by in-situ polymerization of pyrrole in the presence of NanoGs by using epoxy resin and PMMA blends as copolymer matrix. From the thermogravimetric analysis, the introduction of epoxy resin and a few PMMA blends exhibited a beneficial effect on the thermal stability of pure PPy. According to the four-point probe test, the conductivity of the final nanocomposite films was about 1.5 × 10−3 s/cm.

Synthesis of PPy/Nano-Graphite Sheets/TbCl3 Composites with High Conductivity

Nano-graphite sheets (NanoGs) were prepared by treating the expanded graphite with sonication in 95% alcohol solution. The polypyrrole (PPy)/NanoGs/TbCl3 nanocomposites were successfully prepared by in-situ polymerization. The structure, morphology, and stability of the composites are characterized by transmission electron microscope (TEM), scanning electron microscope (SEM), and thermogravimetric analysis (TG). The PPy/NanoGs/TbCl3 nanocomposites exhibited much higher electrical conductivity and better thermal property than the pristine PPy. The electrical conductivity of these nanocomposites were adjusted by changing different wt% of the NanoGs and TbCl3, the conductivity of the composites was reached 80.0 S/cm with the 7 wt% of TbCl3 and 3 wt% of NanoGs.

Nanographite sheets derived from polyaniline nanocoating of cellulose nanofibers

A simple chemical approach for the fabrication of nanographite sheets has been developed by denitrogenation of polyaniline thin layers deposited as a coating on natural cellulose nanofibers as in ordinary filter paper. The crystalline domains on the cellulose nanofiber surface directed the adsorption and further polymerization of aniline monomers to form well-aligned polyaniline layers. Treatment of the filter paper with the deposited polyaniline with a sodium hydroxide/urea aqueous solution at −20°C resulted in both the removal of the cellulose and the formation of well-structured nanographite sheets.

Preparation for Graphite Materials and Study on Electrochemical Degradation of Phenol by Graphite Cathodes

Nanographite flake through ultrasound dispersing expanded graphite which got by chemical oxidation and microwave puffing method have been prepared by natural flake graphite. The microstructures of natural flake graphite, expanded graphite and nanographite sheets were characterized by means of SEM, XRD, FTIR and Raman; the cathodes were made by NG, EG and nanographite, respectively; the electrolysis phenol was conducted by the diaphragm cell prepared cathode and the Ti/RuO2 anode. The results showed that the thickness of graphite flake was 18 nm, and the grain size and particle size decreased compared with the NG and EG; Nano-G showed the best electrochemical properties; in the diaphragm electrolysis system with the aeration conditions, the degradation rate of phenol reached 89.5% COD reached 81.3% under 120 min’s electrolysis, which was far above the degradation rate of phenol of EG cathode and NG cathode.

Differential conductance fluctuation of curved nanographite sheets in the mesoscopic regime

Excess conductance fluctuations with peculiar temperature dependence from 1.4 to 250 K were observed in curved nanographite sheets with electrode gap lengths of 300 and 450 nm, whereas the conductance fluctuation is greatly suppressed above 4.2 K when the electrode gap lengths increase to 800 and 1000 nm. The former is discussed in the context of the presence of a small energy bandgap in the nanographite sheets, while the latter is attributed to the crossover from the coherent transport to diffusive transport regime.

Structural phase transition and failure of nanographite sheets under high pressure: amolecular dynamics study

Nanographite sheets under high compressive stresses at ambient temperaturehave been investigated through molecular dynamics simulations using theTersoff–Brenner potential. Nanographite undergoes a soft to hard phasetransition at a certain compressive stress, about 15 GPa. With increasingcompressions, the bonding structures of nanographite are changed, interlayersp3-bonds are formed, and nanographite transforms into a superhard carbon phase(SCP). Further compressions lead to the instabilities of the SCP. Although thedetailed lattice structure of the SCP remains elusive, its compressive strength canapproach 150 GPa, comparable to that of diamond. The maximum failure stresses ofnanographite sheets are sensitive to the inter-and intra-layer interstices. Ourresults may explain paradoxical experimental results in the available literature.

Cracking diamond anvil cells by compressed nanographite sheets near the contact edge

Uniformly cold-compressed nanographite sheets in diamond anvil cells (DAC) are found to transform from soft into hard phase at about 17 GPa using molecular dynamics simulations. The hard phase can reach the compressive strength of about 150 GPa. Finite element analyses show that high stress concentrations occur along the boundary of interface on the diamond-anvil culets contacted with the nanographite sheets. The concentrated compressive stress can exceed the strength of diamond in a ring region with the width about 0.2μm, when the average pressure in the graphite sample is 17 GPa as in [W. L. Mao et al., Science 302, 425 (2003)]. Within the narrow ring, superhard carbon phase can be formed from the nanographite sheets, which leads to cracking of the DAC near the contact edge.

Ordered Monolayers of Nanographitic Sheets Processed from Solutions via Oxidative Cyclodehydrogenation

We describe a new approach for solution processing of crystalline monolayers of an alkyl-substituted polycyclic aromatic hydrocarbon molecule on the basal plane of graphite. These layers are prepared by first adsorbing a soluble oligophenyl precursor at a solid−liquid interface and subsequently performing the oxidative cyclodehydrogenation reaction to the final fused product in-situ. Scanning tunneling microscopy imaging with submolecular resolution allowed visualization of the ordered nanostructures of both the precursors and the final organic adlayer, proving that the reaction had occurred.

New type of antiferromagnetic state in stacked nanographite

Nanographite systems show novel magnetic properties. We theoretically investigate stacking effects in the zigzag nanographite sheets to find a remarkable difference in the magnetic properties. For the simple stacking, there are no magnetic solutions. For the A–B stacking, we find antiferromagnetic solutions for strong onsite repulsions. The local magnetic moments tend to exist at the edge sites in each layer due to the large amplitude of wavefunctions at these sites. We study variations between the A–A and A–B stackings, and find that the magnetism between the two stackings experiences the first-order phase transition.

Pore Structures and Adsorption Properties of Fluorinated Activated Carbon Fiber

N2 adsorption and XPS elucidated the surface states of fluorinated activated carbon fiber (F-ACF) and fluorinated carbon black. The XPS examination showed that the C-F bonds are not ionic, but covalent. The N2 adsorption isotherms of F-ACF was of Type I and the adsorption was predominant at a low P/P0 region, although the total adsorption amount of F-ACF decreased. The fluorination reduced the pore width of ACF by 0.21nm. Only external nanographitic layers of three stacking sheets were fluorinated, considering from the crystallite size from X-ray diffraction and the chemical analysis. The increase of the pore-wall thickness by the fluorination of the nanographitic sheets agreed with the decrease of the pore width by fluorination. Adsorption isotherms of H20, CH3OH, and C2H5OH were measured. The fluorinated ACF showed a perfect hydrophobicity. Also adsorption isotherms of CH3OH and C2H5OH on F-ACF had an S-shaped nature at the low P/P0 region, while their adsorption isotherms ofACF were of Type I.