All-carbon field emission device by direct synthesis of graphene and carbon nanotube

In this paper, an all carbon-based field emission device (FED) fabricated by graphene and carbon nanotubes (CNTs) is presented. Through the combination of highly conductive graphene and photolithographically patterned CNT, the resistivity of the interface is lowered and the FED performance is enhanced. FE measurements indicated that the fabricated all carbon-based FED demonstrated stable electron emission properties with uniform luminance.     

Electron-beam-induced direct etching of graphene

We present electron-beam-induced oxidation of single- and bilayer graphene devices in a low-voltage scanning electron microscope. We show that the injection of oxygen leads to targeted etching at the focal point, enabling us to pattern graphene with a resolution of better than 20 nm. Voltage-contrast imaging, in conjunction with finite-element simulations, explain the secondary-electron intensities and correlate them to the etch profile.     

Controlled synthesis of bilayer graphene on nickel

ABSTRACT: We report uniform and low-defect synthesis of bilayer graphene on evaporated polycrystalline nickel films. We use atmospheric pressure chemical vapor deposition with ultra-fast substrate cooling after exposure to methane at 1000C. The optimized process parameters i.e. growth-time, annealing profile and flow rates of various gases are reported. By using Raman spectroscopy mapping, the ratio of 2D to G peak intensities (I2D/IG) is in the 0.9-1.6 range over 96 percent of 200umx200um area. Moreover, the average ratio of D to G peak intensities (ID/IG) is about 0.1.     

氧化铁浸染型石英中性正浮选制备低铁石英砂

氧化铁含量是决定石英在不同领域应用的主要因素,尤其是氧化铁浸染型石英砂,因氧化铁的赋存状态、共伴生、浸染程度及粒度差异,常规擦洗、强磁选及酸法反浮选难以有效降低石英中三氧化二铁含量。中性条件下,以抑制剂抑制含铁矿物、采用捕收剂使充分解离的石英上浮,通过粗选、精选进一步降低石英精砂中三氧化二铁含量。研究表明：自然pH下,采用淀粉基抑制剂CTSS、两性捕收剂兼起泡剂ZD-3联合作用,可将此类石英砂三氧化二铁含量由130～150mg/kg降至60～100mg/kg,满足超白光伏玻璃用硅质原料的质量要求;入浮砂粒度上限为0.6mm,以≤0.5mm为宜;对含铁铝硅酸盐矿物、氧化铁浸染型石英砂,中性正浮选石英精砂三氧化二铁含量低于酸性反浮选石英精砂中该指标;热力学计算表明pH≥5.5时淀粉基抑制剂CTSS与氧化铁表面铁离子发生化学键合的标准自由能变化ΔG为负值,化学键合具有自发趋势,抑制剂CTSS与含铁矿物的优先吸附是实现石英中性正浮选提纯的关键之一。     

Few-layer graphene synthesis on a dielectric substrate

We report on few-layer graphene synthesis on fused silica, with the help of pre-deposited copper films with thickness of few hundred nanometers, by using chemical vapor deposition technique. Depending on the copper film thickness, the deposited graphene samples on copper/silica interface were either micron sized graphene flakes or uniform graphene films of a sub-millimeter width. The quality of graphene grown beneath the pre-deposited copper film was found to be comparable with that of graphene grown on bulk copper. The developed technique opens new route towards the space-selective CVD graphene growth on dielectric substrates.     

Combustion synthesis of graphene materials

Combustion synthesis (CS) of graphene by a novel type of exothermic self-sustain reaction between a refractory ceramic compound (silicon carbide) and polymer (polytetrafluoroethylene, PTFE) under the inert gas (argon) environment is reported. The synthesis of graphene is confirmed by both transmission electron microscopy and Raman spectroscopy. It is important that the produced graphene has low (<1 wt.%) oxygen content. The mechanism for CS of graphene is also discussed. It is experimentally shown that fluorocarbon gases (e.g. tetrafluoroethylene, C₂F₄) released due to PTFE decomposition in the combustion wave, reduces SiC to tetrafluorosilane (SiF₄) gas and meso-porous carbon particles with folded “native” graphene layers on their surfaces. The continuous supply of carbon, in the form of fluorocarbon gases, and the high reaction temperature (∼1400 K) enables further rapid growth of “free-standing” graphene sheets on the surface of those graphene-coated particles. The developed method for synthesis of graphene does not require an external energy source, since it occurs in a self-sustained synergetic manner. This approach is also flexible in terms of tuning the synthesis conditions, and allows easy scale-up.     

Structure and synthesis of graphene oxide

Graphene oxide (GO) is one typical two-dimension structured and oxygenated planar molecular material. Researchers across multiple disciplines have paid enormous attention to it due to the unique physiochemical properties. However, models used to describe the structure of GO are still in dispute and ongoing to update. And currently, synthesis methods for mass production are seemingly abundant but in fact, dominated by a few core methodologies. To update with the state-of-art opinions and progresses, herein we present a mini critical review regarding the synthesis of GO as well as its models and simulations of structure. Also, we discuss the perspectives.     

A review on direct synthesis of dimethoxymethane

Polyoxymethylene dimethyl ethers are recognized as the prospective diesel additive to decrease the pollutant emission from the light-duty vehicles, which can be polymerize form the monomer of dimethoxymethane (DMM). The industrial synthesis of DMM is mainly involved two-step process: methanol is oxidized to form the formaldehyde in fixed bed reactor and then reacted with the generated formaldehyde through acetalization in continuous stirred-tank reactor. Due to huge energy consumption, this typical synthesis route of DMM needs to be upgraded and more green routes should be determined. In this review, four state-of-the-art one-step direct synthetic routes, including two upgrading routes (methanol direct oxidation and direct dehydrogenation) and two green routes (methanol diethyl ether direct oxidation and carbon oxides direct hydrogenation), have been summarized and compared. Combination with the reaction mechanism and catalytic performance on the different catalysts, the challenges and opportunities for every synthetic route are proposed. The relationships between catalyst structure and property in different synthesis strategy are also investigated and then the suggestions of the design of catalyst are given about future research directions that efforts should be made in. Hopefully, this review can bridge the gap between newly developed catalysts and synthesis technology to realize their commercial applications in the near future.     

Flexible conductive graphene paper obtained by direct and gentle annealing of graphene oxide paper

We report the fabrication of flexible conductive graphene paper through a direct and gentle annealing process of graphene oxide paper. Thermal treatments at 700 °C under argon or hydrogen atmosphere directly applied to parent graphene oxide paper lead to a significant removal of disruptive oxygen-containing functional groups, and to a considerable recovery of the sp² network structure. Detailed comparison of chemical and combined chemical–thermal treatments by scanning electronic microscopy (SEM), Raman, X-photoelectron spectroscopy (XPS) and conductivity measurements underline the high efficiency of the direct annealing process. The resulting highly reduced graphene oxide paper exhibits electrical conductivities as high as 8100 S/m representing an increase of five orders of magnitude with respect to the parent graphene oxide paper, which significantly outperforms the results of chemical treatments. Moreover, our direct and gentle thermal reduction allows maintaining the structural integrity and mechanical flexibility of the parent graphene oxide paper thus overcoming problems of brittleness typically encountered in annealing processes. Our approach sets the base for an easy, cost-effective and environmentally friendly fabrication route for flexible conducting graphene paper of great application potential as flexible electrodes in various fields of technology.     

Few layer graphene synthesis on transition metal ferrite catalysts

Development of cheap, green and up scalable production methods for graphene is one of the most challenging problems in its manufacture on an industrial scale. We report here a large scale substrate-free fluidized bed catalytic chemical vapour deposition (FB-CCVD) process for few layer graphene (FLG) powder production that uses a crystalline oxide catalyst of the general formula A_xB_3−xO₄, wherein the FLG layer thickness and domain sizes can be varied. A and B can be chosen from a list of transition elements including Co, Fe, Ni, Mn, Cu and Zn. The best results in terms of activity and selectivity are obtained for the Co_xFe_3−xO₄ system. We also investigated the reaction mechanism using in situ EXAFS and Raman spectroscopy, and electron tomography. Since FB-CCVD processes are already used for industrial scale production of carbon nanotubes, this process should enable the large scale production of free standing FLG in the near future.     

A review on synthesis and properties of polymer functionalized graphene

This review highlights the functionalization chemistry of graphene with polymers by both covalent and non-covalent approaches. Due to the strong cohesive interactions graphene platelets agglomerate, causing difficulty to attain its optimum properties. The covalent functionalization is illuminated both from ‘grafting to’ and ‘grafting from’ techniques discussing the merits and demerits of the processes. The controlled free radical polymerization techniques used for this purpose e.g. ATRP, SET–LRP and RAFT etc. are discussed along with the conventional free radical polymerization. We have also noted the various approaches used in non-covalent functionalization e.g. π–π, H-bonding and hydrophobic interactions. These functionalized graphenes show good and stable dispersion facilitating composite formation with commodity plastics enhancing it's mechanical, thermal and conductivity properties. The optoelectronic properties of these functionalized graphene are interesting to fabricate sensors, photovoltaics, supercapacitors etc. A short account of the properties of these modified graphenes is also embodied with an emphasis on different area where future developments are expected.     

聚合物功能化石墨烯的合成及应用研究进展(二)

着重评述了采用共价连接和非共价连接技术制备聚合物功能化石墨烯的方法,介绍了聚合物功能化石墨烯的应用概况。     

聚合物功能化石墨烯的合成及应用研究进展(一)

着重评述了采用共价连接和非共价连接技术制备聚合物功能化石墨烯的方法,介绍了聚合物功能化石墨烯的应用概况。     

Ultra-fast synthesis of graphene by melt spinning

Large-scale few-layer graphene (FLG) films were prepared by an industrial single-roller melt spinning technique based on molten alloy quenched carbon self-segregation using nickel and carbon as precursors. A formation mechanism of FLG based on rapid diffusion and non-equilibrium segregation of carbon is discussed. This ultra-fast thin film preparation technique can be extended and used to produce ultrathin sheets of two-dimensional materials other than graphene.     

石墨烯及化学改性石墨烯的胶状悬浮物合成研究进展

详细综述了石墨烯及化学改性石墨烯(CMG)的胶状悬浮物的合成工艺进展,从氧化石墨、氧化石墨烯及石墨其他衍生物的溶解性质和合成路径等方面展开论述。石墨烯的胶状悬浮物合成工艺既提供了大批量生产石墨烯的可能性,在化学改性修饰方面也有普遍的适用性。     

聚乳酸直接合成的研究

综述了近年来国内外研究聚乳酸直接合成的进展情况,概述了乳酸直接合成的几种方法,研究了熔融聚合、溶液聚合中影响聚乳酸相对分子质量的因素,探讨了固相聚合机理。     

生物质气一步法合成二甲醚中试实验

在列管式连续固定床中试系统上,采用自制二甲醚(DME)合成催化剂,以玉米芯经两段式固定床富氧气化合成气为气源,进行一步法合成DME实验研究.考察了催化剂反应温度(210-295℃)、空速(650-3 000 h-1)对合成过程的影响.并对合成DME催化剂反应前后进行XRD表征.实验结果表明:反应空速为1 200 h-1时,最佳反应温度为270℃时.此时CO转化率最高为73.55%;空速在650-3 000 h-1时,CO转化率为82.00%～67.74%,时空产率为124.28～281.24 kg/(m3·h).