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The use of non-thermal plasma at atmospheric pressure has emerged as a technique for the substrate-free, gas-phase synthesis of graphene nanoflakes (GNFs). In this paper, a non-thermal plasma based...

A novel approach for the preparation of few-layer graphene nano-flakes (GNFs) is presented in this paper. The GNFs are continuously synthesized by thermal decomposition of hydrocarbons using a magnetically rotating arc at atmospheric pressure. The effects of magnetic field, arc current, feedstock gas flow rate, and feedstock gas type on the morphologies and microstructures of pyrolysis products are investigated and discussed. Results show that the microscopic characteristics of pyrolysis products are affected by the operating parameters. High temperature and high hydrogen concentration are considered the essential condition for the formation of GNFs. The synthesized GNFs are agglomerative flakes, where each flake is between 50 and 300 nm. Material analyses indicates that the GNFs have excellent properties such as a good crystalline structure, a low number of layers, and a large specific surface area. This indicates that the GNFs could be applied in fuel cells and energy storages. This method is suitable for mass production of few-layer GNFs since it is a continuous process with a relatively high yield (∼14%) and a relatively low energy cost (∼0.4 kWh/g).

In this study, a cylindrical plasma generator with an axial magnetic field is constructed to obtain the magnetically stabilized gliding arc discharge (MSGAD). Using high speed photography, voltage waveform analysis and spectral diagnostics, the MSGAD physical characteristics, such as arc voltage, rotation speed, electric field, excitation/rotational temperature, etc., are investigated under different magnetic field. The experimental results reveal that as the magnetic field increases, the arc voltage, rotation speed, electric field and non-equilibrium level increase, and the MSGAD is more stable under the larger magnetic field. Additionally, carbon black nanoparticles with “crumpled paper sheet” structure are prepared by the MSGAD. The results indicate that the enhanced magnetic field can promote the transition from amorphous carbon to crystalline graphite. It is inferred that the transition is likely relevant to the rotation speed and electron energy of the arc plasma.

Potassium ion batteries (PIBs) have drawn considerable attention owing to the low cost and high natural abundance of potassium. However, risks associated with the extremely high activity of potassium metal have motivated the search for alternative anode materials with high performance and good safety. Herein, an essential element of the human body, vitamin K, is applied as an organic redox-active electrode material for PIBs. This biomolecule has a quinone structure with two active redox carbonyl groups, which can provide a theoretical specific capacity of 313.5 mA h g−1. After hybridization with graphene nanotubes (GNTs), the composite delivered a high reversible capacity of 300 mA h g−1 and maintained 222.3 mA h g−1 after 100 cycles at a current density of 100 mA g−1 with a coulombic efficiency of ∼99%. Moreover, at higher current densities of 200, 500, and 1000 mA g−1, it maintained high discharge capacities of 203, 181, and 165 mA h g−1, respectively. The enhanced electrochemical performance of the composite might be attributed to the improved electronic conductivity and inhibition of vitamin K dissolution into the organic electrolyte. This biomolecule-based electrode offers a new alternative approach to the development of PIBs.

A cluster-like AuAg alloy hollow-nanoparticles (HNPs), synthesized by facile one-pot co-reduction under the guidance of bovine serum albumin (BSA), enhanced the electrochemiluminescence (ECL) of luminol, thus to be served as the sensing matrix of the enzymatic glucose biosensor. The prepared HNPs were characterized by electronic microscopy, UV–Vis spectrometry, IR spectrometry, X-ray diffraction analysis, X-ray photoelectron spectroscopy and electrochemistry. Using hydrolyzed APTMS to connect AuAg HNPs on indium tin oxide (ITO) coated glass, the synergistic effect between two metals makes it had 20 multiple enhancement of ECL, and shows sensitive response toward reactive oxygen species. After loading GOD on this matrix to build the glucose sensor, it has a wide linear response range for the glucose from 5.0 μM to 1.0 mM with a detection limit as 0.40 μM. It can be applied for noninvasive detection of glucose with saliva as specimen, the results indicated the high-degree correlation of glucose contents between saliva and blood.

Herein, a novel cell-based electrochemiluminescent (ECL) sensing matrix was developed for probing reactive oxygen species (ROSs) produced from mouse macrophage cells. Uniformly sized Au nanoparticles (AuNPs) with an average diameter of 16 nm were decorated on the surface of indium tin oxide (ITO) glass through the connection of hydrolyzed 3-aminopropyl trimethoxysilane (APTMS) serving as a sensor substrate. Then, the surface was covered with a poly-l-lysine thin film, where mouse macrophage cells were successfully cultured. The morphology of the electrodes obtained was characterized by scanning electron microscopy and atomic force microscopy, and their electrochemical properties were investigated by electrochemical impedance spectroscopy. A linear response was observed from the AuNPs/APTMS/ITO substrate with a sensitivity of 0.465 units per mg/l of H(2)O(2), and a higher sensitivity of 207 units per mg/l of zymosan. Thereafter, a factor of 84 molecules of H(2)O(2) produced by a single glycogen was estimated. The results demonstrated that the ECL response of this cell-based sensor quantitatively correlated with yielded ROSs during cell oxygen metabolism under the stimulation of zymosan. This work suggests that the prepared sensing matrix is efficient for monitoring the oxygen metabolism of living cells and can be applied in biological and clinical fields to provide significant information on the regular or abnormal function of cells.

A non-thermal plasma source based on magnetically stabilized gliding arc discharge (MSGAD) was used to prepare carbon nanoparticles via methane decomposition. Spherical carbon nanoparticles (SCNs), few-layer graphene nanoflakes (GNFs), and nitrogen-doped carbon nanoparticles were obtained. The results showed that the product microstructure was influenced by the buffer gas. In pure methane and argon, the products were a mixture of SCNs and GNFs. In helium and hydrogen, all products were highly crystalline GNFs with low defects, few layers, large BET surface areas, and excellent thermal stability. Under a nitrogen atmosphere, nitrogen-doped nanoparticles were formed, and the products were a mixture of GNFs, disordered graphitic layers, and tiny spots similar to carbon dots. The formation of GNFs was possibly related to the high input power and abundant hydrogen atoms, while the complex product morphology obtained under a nitrogen atmosphere was likely caused by the incorporation of nitrogen atoms.

Few-layer graphene nano-flakes (GNFs) are successfully prepared via hydrocarbon pyrolysis using a non-thermal plasma process based on a magnetically stabilized gliding arc discharge (MSGAD) at atmospheric pressure. The effects of feedstock gas type and hydrogen flow rate on the morphology of carbon nanomaterials are investigated. When the hydrogen/carbon (H/C) molar ratio is 4, the synthesized GNFs consist of 10 layers per stack with dimensions between 100 and 300 nm in a 4.57.2% yield. The energy cost is 0.1–0.2 kWh/g, which makes this process feasible for large-scale GNFs production. The results show that appropriately increasing the H/C molar ratio promotes the morphological transformation of carbon nanomaterials from spherical carbon nanoparticles (SCNs) to GNFs, improve the quality of GNFs and reduce the stacking of graphite layers. However, increasing the H/C ratio reduces the yields of carbon nanomaterials, so as to increase the energy cost. Analysis suggests that increasing the H/C ratio reduces the concentration of polycyclic aromatic hydrocarbon (PAH) and generates more H atoms, which helps form a two-dimensional nucleation and promotes planar growth. However, an excessive H/C ratio may introduce some defects due to an etching effect.

A novel non-thermal plasma process based on magnetically stabilized gliding arc discharge (MSGAD) is developed for continuous synthesis of carbon nano-onions (CNOs). CNOs with a diameter range of 70–200 nm are continuously prepared by propane decomposition. Results indicate that with increased residence time in the plasma region, the product morphology gradually changes from graphene nanoflakes (GNFs) to CNOs. It is proposed that CNOs synthesis mainly includes three stages: formation of GNFs, curving and closure of multiple GNFs, further graphitization. In addition, H2 content has a key role in CNOs formation since hydrogen has a significant effect on the formation and morphology of GNFs.

A thermal plasma process at atmospheric pressure is an attractive method for continuous synthesis of graphene flakes. In this paper, a magnetically rotating arc plasma system is employed to investigate the effects of buffer gases on graphene flakes synthesis in a thermal plasma process. Carbon nanomaterials are prepared in Ar, He, Ar-H2, and Ar-N2 via propane decomposition, and the product characterization is performed by transmission electron microscopy (TEM), Raman spectroscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and the Brunauer&ndash, Emmett&ndash, Teller (BET) method. Results show that spherical particles, semi-graphitic particles, and graphene flakes coexist in products under an Ar atmosphere. Under an He atmosphere, all products are graphene flakes. Graphene flakes with fewer layers, higher crystallinity, and a larger BET surface area are prepared in Ar-H2 and Ar-N2. Preliminary analysis reveals that a high-energy environment and abundant H atoms can suppress the formation of curved or closed structures, which leads to the production of graphene flakes with high crystallinity. Furthermore, nitrogen-doped graphene flakes with 1&ndash, 4 layers are successfully synthesized with the addition of N2, which indicates the thermal plasma process also has great potential for the synthesis of nitrogen-doped graphene flakes due to its continuous manner, cheap raw materials, and adjustable nitrogen-doped content.