Synthesis of Blue‐, Green‐, Yellow‐, and Red‐Emitting Graphene‐Quantum‐Dot‐Based Nanomaterials with Excitation‐Independent Emission

A one‐pot method is described for the preparation of graphene quantum dots/graphene oxide (GQDs/GO) hybrid composites with emission in the visible region, through heteroatom doping and hydroxyl‐radical‐induced decomposition of GO. The NH₄OH‐ and thiourea‐mediated dissociation of H₂O₂ produces hydroxyl radicals. Treatment of GO with hydroxyl radicals results in the production of small‐sized GO sheets and GQDs, which self‐assemble to form GQDs/GO through strong π–π interactions. For example, the reaction of GO with a mixture of NH₄OH and H₂O₂ for 40, 120, and 270 min generates yellow‐emitting GQDs/GO (Y‐GQDs/GO), green‐emitting GQDs/GO, and blue‐emitting GQDs, while red‐emitting GQDs/GO (R‐GQDs/GO) are prepared by incubating GO with a mixture of thiourea and H₂O₂. From the analysis of these four GQD‐based nanomaterials by transmission electron microscopy, atomic force microscopy, and fluorescence lifetime spectroscopy, it is found that this tunable fluorescence wavelength results from the differences in particle size. All four GQD‐based nanomaterials exhibit moderate quantum yields (1–10%), nanosecond fluorescence lifetimes, and excitation‐independent emissions. Except for R‐GQDs/GO, the other three GQD‐based nanomaterials are stable in a high‐concentration salt solution (e.g., 1.6 m NaCl) and under high‐power irradiation, enabling the sensitive (high‐temperature resolution and large activation energy) and reversible detection of temperature change. It is further demonstrated that Y‐GQD/GO can be used to image HeLa cells.     

Liquid Crystalline Dispersions of Graphene‐Oxide‐Based Hybrids: A Practical Approach towards the Next Generation of 3D Isotropic Architectures for Energy Storage Applications

We report the use of the spray pyrolysis method to design self‐assembled isotropic ternary architectures made up of reduced graphene oxide (GO), functionalized multiwalled carbon nanotubes, and nickel oxide nanoparticles for cost‐effective high‐performance supercapacitor devices. Electrodes fabricated from this novel ternary system exhibit exceptionally high capacitance (2074 Fg^?1) due to the highly conductive network, synergistic link between GO and carbon nanotubes and achieving high surface area monodispersed NiO decorated rGO/CNTs composite employing the liquid crystallinity of GO dispersions. To further assess the practicality of this material for supercapacitor manufacture, we assembled an asymmetric supercapacitor device incorporating activated carbon as the anode. The asymmetric supercapacitor device showed remarkable capacity retention (>96%), high energy density (23 Wh kg^?1), and a coulombic efficiency of 99.5%.     

基于中性水凝胶/取向碳纳米管阵列高电压柔性固态超级电容器

随着科技发展和时代进步,发展质轻便携、安全环保的高性能储能器件变得日趋重要,对柔性固态超级电容器的研究也应运而生.柔性电极材料及电解质的选用是设计柔性固态超级电容器的关键因素,近年来一直是研究的热点.考虑到环境污染及实际需求问题,本文采用中性凝胶电解质对具有高比表面积、良好导电性及取向性的碳纳米管阵列进行包埋处理,所形成的柔性复合薄膜作为电极材料,设计制备三明治结构的柔性超级电容器件.通过改变凝胶电解质中所加入的无机盐电解质种类,调控器件的电化学储能性质.最终在聚乙烯醇PVA-NaCl作为凝胶电解质时,整个器件比容量最高达104.5 mF·cm~(–3),远高于有机离子凝胶与碳管阵列形成的复合器件以及无规分布的碳纳米管与水凝胶形成的复合器件,同时获得了0.034 mW·h·cm~(–3)的最大能量密度,并且具有良好的倍率性能、循环稳定性及抑制自放电的效果,并在高电压1.6 V下依然保持良好的化学稳定性.这种中性凝胶/碳管阵列复合超级电容器件不仅满足了绿色安全、柔性便携的要求,未来在医学可植入器件等领域也具有很好的应用前景.     

Liquid‐Crystal‐Mediated Self‐Assembly of Porous α‐Fe2O3 Nanorods on PEDOT:PSS‐Functionalized Graphene as a Flexible Ternary Architecture for Capacitive Energy Storage

A novel aqueous‐based self‐assembly approach to a composite of iron oxide nanorods on conductive‐polymer (CP)‐functionalized, ultralarge graphene oxide (GO) liquid crystals (LCs) is demonstrated here for the fabrication of a flexible hybrid material for charge capacitive application. Uniform decoration of α‐Fe₂O₃ nanorods on a poly(3,4‐ethylene‐dioxythiophene): poly(styrenesulfonate) (PEDOT:PSS)‐functionalized, ultralarge GO scaffold results in a 3D interconnected layer‐by‐layer (LBL) architecture. This advanced interpenetrating network of ternary components is lightweight, foldable, and possesses highly conductive pathways for facile ion transportation and charge storage, making it promising for high‐performance energy‐storage applications. Having such structural merits and good synergistic effects, the flexible architecture exhibits a high specific discharge capacitance of 875 F g^?1 and excellent volumetric specific capacitance of 868 F cm^?3 at 5 mV s^?1, as well as a promising energy density of 118 W h kg^?1 (at 0.5 A g^?1) and promising cyclability, with capacity retention of 100% after 5000 charge–discharge (CD) cycles. This synthesis method provides a simple, yet efficient approach for the solution‐processed LBL insertion of the hematite nanorods (HNR) into CP‐functionalized novel composite structure. It provides great promise for the fabrication of a variety of metal‐oxide (MO)‐nanomaterial‐based binder and current collector‐free flexible composite electrodes for high‐performance energy‐storage applications.     

Graphene‐Based Phosphorus‐Doped Carbon as Anode Material for High‐Performance Sodium‐Ion Batteries

Graphene‐based phosphorus‐doped carbon (GPC) is prepared through a facile and scalable thermal annealing method by triphenylphosphine and graphite oxide as precursor. The P atoms are successfully doped into few layer graphene with two forms of P–O and P–C bands. The GPC used as anode material for Na‐ion batteries delivers a high charge capacity 284.8 mAh g^?1 at a current density of 50 mA g^?1 after 60 cycles. Superior cycling performance is also shown at high charge?discharge rate: a stable charge capacity 145.6 mAh g^?1 can be achieved at the current density of 500 mA g^?1 after 600 cycles. The result demonstrates that the GPC electrode exhibits good electrochemical performance (higher reversible charge capacity, super rate capability, and long‐term cycling stability). The excellent electrochemical performance originated from the large interlayer distance, large amount of defects, vacancies, and active site caused by P atoms doping. The relationship of P atoms doping amount with the Na storage properties is also discussed. This superior sodium storage performance of GPC makes it as a promising alternative anode material for sodium‐ion batteries.     

Substrate‐Induced Synthesis of Nitrogen‐Doped Holey Graphene Nanocapsules for Advanced Metal‐Free Bifunctional Electrocatalysts

The development of efficient metal‐free electrocatalysts for oxygen electrocatalysis is of great significance for various energy conversion devices. Herein, novel nitrogen‐doped holey graphene nanocapsules (NHGNs) are reported prepared by self‐assembly of graphene oxide nanosheets on the surface of amino‐functionalized silica template and NH₃ activation with simultaneously enhanced nitrogen doping and etching of nanopores in graphene, followed by template etching. The silica template is demonstrated to show a substrate‐enhanced effect on nitrogen doping and etching of nanopores in graphene based on density functional theory calculations. Benefiting from the large surface area, unique pore distribution, and high surface functionality of nitrogen doping, the resulting NHGNs exhibit superior bifunctional electrocatalytic activity and durability for both oxygen reduction reaction and oxygen evolution reaction, which is similar to that of the commercial Pt/C and RuO₂ electrocatalysts, respectively. This work presents an advance in developing new nitrogen‐doped graphene species for highly efficient metal‐free electrocatalysis.     

Full Protection for Graphene‐Incorporated Micro‐/Nanocomposites Containing Ultra‐small Active Nanoparticles: the Best Li‐Storage Properties

In recent years, graphene‐incorporated micro‐/nanocomposites represent one of the hottest developing directions for the composite materials. However, a large number of active nanoparticles (NPs) are still in the unprotected state in most constructed graphene‐containing designs, which will seriously impair the effects of the graphene additives. Here, a fully protected Fe₃O₄‐based micro‐/nanocomposite (G/Fe₃O₄@C) is rationally developed by carbon‐boxing the common graphene/Fe₃O₄ microparticulates (G/Fe₃O₄). The processes and results of full protection are tracked in detail and characterized by X‐ray diffraction, X‐ray photoelectron spectroscopy, and nitrogen absorption–desorption isotherms, as well as scanning and transition electron microscopy. When used as the anode for lithium‐ion batteries, the fully protected G/Fe₃O₄@C exhibits the best lithium‐storage properties in terms of the highest rate capabilities and the longest cycle life compared to the common G/Fe₃O₄ composites and commercial Fe₃O₄ products. These much improved properties are mainly attributed to its novel structural features including complete protection of active Fe₃O₄ nanoparticles by the surface carbon box, a robust conductive network composed of nitrogen‐doped graphene nanosheets, ultra‐small Fe₃O₄ NPs of 4–5 nm, abundant mesopores to accommodate the volume variation during cycling, and micrometer‐sized secondary particles.     

碳纳米管制备蓝光石墨烯量子点及其在柔性有机存储器上的应用

通过化学裁剪法打开碳纳米管获得了粒径一致、性能稳定、具有蓝色荧光的石墨烯量子点。该方法属于化学溶液法，具有成本低廉、工艺简单、条件易控等优势。将该样品与半导体聚合物按一定比例混溶，通过旋涂技术形成基于石墨烯量子点掺杂的聚合物复合薄膜，进而制成柔性存储器。该柔性可弯曲存储器具有低驱动电压、接近10³的ON/OFF 比率、较好的循环次数，较好的重复性和稳定性。该研究结果为柔性有机存储器领域的研究展开了新的方向。     

Graphene and Graphene‐Based Materials in Biomedical Science

Graphene and its composite materials are very important in many disciplines of science and have been used enormously by researchers since their discovery in 2004. These are a new group of compounds, and are also wonderful model systems for quantum behavior studies. Their properties like exceptional conductivity, biocompatibility, surface area, mechanical strength, and thermal properties make them rising stars in the scientific community. Graphene and its composite compounds are utilized widely in different medical applications, for example, biosensing of biological compounds responsible for disease development, bioimaging of various cells, tissues, microorganisms, animal models, etc. In addition, they are used for enhancing and supporting the stem cell differentiation, i.e., regenerative medicine for regeneration studies of various human organs, tissue engineering in biology for the development of carrier materials, as well as in bone reformation. This review focuses on the modification procedure involved in the fabrication of graphene‐based biomaterials for various applications and recent developments in research related to graphene and graphene‐based materials in biosensing, optical sensing, gas sensing, drug, gene, protein delivery, tissue engineering, and bioimaging. In addition, the potential toxicological effects of graphene‐based biomaterials are discussed.     

Towards Excellent Anodes for Li‐Ion Batteries with High Capacity and Super Long Lifespan: Confining Ultrasmall Sn Particles into N‐Rich Graphene‐Based Nanosheets

Sn is regarded as a promising anode material for Li‐ion batteries due to high capacity and cost effectiveness. Hitherto large‐scale fabrication of Sn‐based materials while achieving both high capacity and long cycle life remains challenging, but it is highly required for its realization in practical applications. Furthermore, low melting point always casts shadow over the morphology‐controllable preparation, and leads to multistep or high‐cost processes. Here, a facile and scalable method is devised for a 2D hybrid structure of Sn@graphene‐based nanosheets incorporating of optimized nitrogen species (≈13 wt%). Distinct from conventional Sn–C composites, the fairly N‐rich carbon nanosheets liberate limited potential of low N doping, induce massive extra Li‐storage sites, and encourage a high capacity significantly. In addition, these abundantly anchored heteroatoms also promote the homogeneous dispersion and robust confinement of ultrasmall Sn nanoparticles into the flexible graphene‐based nanosheets. This elastic encapsulation towards Sn nanoparticles admirably maintains structural integrity through effective remission of volume expansion, demonstrating a super long‐term cyclic stability for 1000 cycles. This structural and componential engineering offers a significant implication for rational design of materials in extended areas of energy conversion and storage.     

Scalable bottom‐up assembly of suspended carbon nanotube and graphene devices by dielectrophoresis

Bottom‐up assembly by dielectrophoresis (DEP) has emerged in recent years as a viable alternative to conventional top–down fabrication of electronic devices from nanomaterials, particularly carbon nanotubes and graphene. Here, we demonstrate how this technique can be extended to fabricate devices containing carbon nanotubes and graphene suspended between two electrodes over a back‐gate electrode. The suspended device geometry is critical for the development of nano‐electromechanical devices and to extract maximum performance out of electronic and optoelectronic devices. This technique allows for parallel assembly of devices over large scale. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Carbon nanotube transistors with graphene oxide films as gate dielectrics

Carbon nanomaterials,including the one-dimensional(1-D) carbon nanotube(CNT) and two-dimensional(2-D) graphene,are heralded as ideal candidates for next generation nanoelectronics.An essential component for the development of advanced nanoelectronics devices is processing-compatible oxide.Here,in analogy to the widespread use of silicon dioxide(SiO2) in silicon microelectronic industry,we report the proof-of-principle use of graphite oxide(GO) as a gate dielectrics for CNT field-effect transistor(FET) via a...     

Real‐Time and Broadband Terahertz Wave Scattering Manipulation via Polarization‐Insensitive Conformal Graphene‐Based Coding Metasurfaces

Here, for the first time, the real‐time and broadband manipulation of terahertz (THz) waves are acquired by introducing a multifunctional graphene‐based coding metasurface (GBCM). The designed structure consists of subwavelength patterned graphene units whose operational statuses can be dynamically switched between two digital states of “0” and “1”. By engineering the spatial distribution of chemical potentials across the GBCM, various scattering patterns having single, two, four, and numerous reflection beams are elaborately achieved just within one planar structure. To compute the far‐field pattern of GBCM, an inverse discrete Fourier transform (IDFT) is established, providing a fast and efficient design method. The proposed GBCM provides a low reflection bellow ?10 dB over a broad frequency band ranging from 1 THz to 1.9 THz. In addition, the metasurface retains its low reflection behavior in a wide range of incident wave angles for both TE and TM polarizations. According to conformal invariance of graphene sheets, the stealth property of GBCM is well preserved while wrapping around a curved object. The proposed technique of real‐time scattering manipulation leads to multifunctional THz devices, opening new routes contributing to numerous applications such as imaging and stealth technology.     

Controllable Formation of Niobium Nitride/Nitrogen‐Doped Graphene Nanocomposites as Anode Materials for Lithium‐Ion Capacitors

Niobium nitride/nitrogen‐doped graphene nanosheet hybrid materials are prepared by a simple hydrothermal method combined with ammonia annealing and their electrochemical performance is reported. It is found by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) that the as‐obtained niobium nitride nanoparticles are about 10–15 nm in size and homogeneously anchored on graphene. A non‐aqueous lithium‐ion capacitor is fabricated with an optimized mass loading of activated carbon cathode and the niobium nitride/nitrogen‐doped graphene nanosheet anode, which delivers high energy densities of 122.7–98.4 W h kg^?1 at power densities of 100–2000 W kg^?1, respectively. The capacity retention is 81.7% after 1000 cycles at a current density of 500 mA g^?1. The high energy and power of this hybrid capacitor bridges the gap between conventional high specific energy lithium‐ion batteries and high specific power electrochemical capacitors, which holds great potential applications in energy storage for hybrid electric vehicles.     

Site‐specific fabrication of graphitic microporous carbon terminated with ordered multilayer graphene walls

The site‐specific fabrication of metal‐incorporated graphitic microporous carbon terminated by highly ordered multilayer graphene walls via an ambient‐temperature vacuum‐based process is presented for the first time. Sputtering of Cr nano‐particles on the ultrathin amorphous carbon film manifests a dual effect of activation via dry‐etching by the sputtering plasma and of ‘knock‐on' inelastic collision between nanoparticles and C atoms for structural ordering. This novel and simple method is very useful for fabricating high surface area carbon nanostructures for hydrogen storage and clean energy applications. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Near‐3‐MeV protons from target‐normal‐sheath‐acceleration femtosecond laser irradiating advanced targets

Advanced targets based on graphene oxide and gold thin film were irradiated at high laser intensity (10¹⁸–10¹⁹ W/cm²) with 50‐fs laser pulses and high contrast (10⁸) to investigate ion acceleration in the target‐normal‐sheath‐acceleration regime. Time‐of‐flight technique was employed with SiC semiconductor detectors and ion collectors in order to measure the ion kinetic energy and to control the properties of the generated plasma. It was found that, at the optimized laser focus position with respect to the target, maximum proton acceleration up to about 3 MeV energy and low angular divergence could be generated. The high proton energy is explained as due to the high electrical and thermal conductivity of the reduced graphene oxide structure. Dependence of the maximum proton energy on the target focal position and thickness is presented and discussed.     

Electro‐optic switching with liquid crystal graphene

Graphene oxide (GO) particles in aqueous dispersions can form liquid crystal (LC) phases at extremely low concentrations due to the extremely high aspect ratio of the flakes and noticeably, they possess an extremely large Kerr coefficient attractive for low power consumption electro‐optic devices. Reduced graphene does not easily form LC phases in water due to its hydrophobic nature but here we show that stable dispersions of reduced graphene oxide can be realized with surfactants and that they exhibit birefringence upon shearing as well as under application of electric fields. The performance of the system is largely superior to GO LC possessing longer time stability and drastically improved electro‐optic properties with an induced birefringence twice as large at the same field strength thanks to the almost recovery of graphene properties upon reduction. (© 2016 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

电化学超级电容器电极材料的研究进展

超级电容器是一种利用电化学双电层储能或在电极材料表面及近表面发生快速可逆氧化还原反应而储能的装置,具有高的比功率、比能量和长的循环寿命.文章综述了超级电容器电极材料的储能机理、特点及应用,并重点介绍了石墨烯、二氧化锰及其复合电极材料在超级电容器中应用的最新研究进展.     

基于收缩高密度碳纳米管阵列的柔性固态超级电容器

柔性超级电容器因其加工方式灵活,具有高的能量密度和可剪裁可弯曲的特性,近年来受到广泛的关注.碳纳米管阵列凭借其自身良好的电化学性能、高效的电荷转移率和良好的循环寿命被视为理想的能量储存材料.然而原始碳纳米管阵列密度较小,且因管间较弱的相互作用力使得其在加工和转移过程中容易倒塌散落,从而限制了碳纳米管阵列直接用于组装柔性电子器件.本文应用无水乙醇对阵列进行收缩处理,在保持阵列高度取向优势的前提下大大增加了阵列的密度和机械强度,同时使用生物相容性好的聚乙烯醇(PVA)导电凝胶包埋碳纳米管阵列来制备柔性固态超级电容器件.PVA包埋的阵列复合体在折叠、弯曲过程中既能保持良好的机械稳定性和柔性,又能保持碳纳米管的高度取向性.使用原位电氧化对碳纳米管阵列外壁进行简单的电化学修饰,可以进一步提高该复合器件的性能.该方法为未来研发可穿戴电子器件以及可植入医学器件提供了新思路.     

Nanocarbon hybrids of graphene‐based materials and ultradispersed diamond: investigating structure and hierarchical defects evolution with electron‐beam irradiation

We report the influence of electron‐beam (E‐beam) irradiation on the structural and physical properties modification of monolayer graphene (Gr), reduced graphene oxide (rGO) and graphene oxide (GO) with ultradispersed diamond (UDD) forming novel hybrid composite ensembles. The films were subjected to a constant energy of 200 keV (40 nA over 100 nm region or electron flux of 3.9 × 10¹⁹ cm⁻²s⁻¹) from a transmission electron microscope gun for 0 (pristine) to 20 min with an interval of 2.5 min continuously – such conditions resemble increased temperature and/or pressure regime, enabling a degree of structural fluidity. To assess the modifications induced by E‐beam, the films were analyzed prior to and post‐irradiation. We focus on the characterization of hierarchical defects evolution using in situ transmission electron microscopy combined with selected area electron diffraction, Raman spectroscopy (RS) and Raman mapping techniques. The experiments showed that the E‐beam irradiation generates microscopic defects (most likely, interstitials and vacancies) in a hierarchical manner much below the amorphization threshold and hybrids stabilized with UDD becomes radiation resilient, elucidated through the intensity, bandwidth, and position variation in prominent RS signatures and mapping, revealing the defects density distribution. The graphene sheet edges start bending, shrinking, and generating gaps (holes) at ~10–12.5 min owing to E‐beam surface sputtering and primary knock‐on damage mechanisms that suffer catastrophic destruction at ~20 min. The microscopic point defects are stabilized by UDD for hybrids in the order of GO > rGO ≥ Gr besides geometric influence, i.e. the int erplay of curvature‐induced (planar vs curved) energy dispersion/absorption effects. Furthermore, an attempt was made to identify the nature of defects (charged vs residual) through inter‐defect distance (i.e. L_D). The trends of L_D for graphene‐based hybrids with E‐beam irradiation implies charged defects described in terms of dangling bonds in contrast to passivated residual or neutral defects. More importantly, they provided a contrasting comparison among variants of graphene and their hybrids with UDD. Copyright © 2015 John Wiley & Sons, Ltd.