Reduction and functionalization of graphene oxide sheets using biomimetic dopamine derivatives in one step

An easy and environmentally friendly chemical method for the simultaneous reduction and noncovalent functionalization of graphene oxide (GO) using dopamine derivatives is described. The reaction takes place at room temperature under ultrasonication of an aqueous suspension of GO and a dopamine derivative. X-ray photoelectron spectroscopy, FT-IR spectroscopy, and cyclic voltammetry characterizations revealed that the resulting material consists of graphene functionalized with the dopamine derivative. This one-step protocol is applied for simultaneous reduction and functionalization of graphene oxide with a dopamine derivative bearing an azide function. The chemical reactivity of the azide function was demonstrated by a postfunctionalization with ethynylferrocene using the Cu(I) catalyzed 1,3-dipolar cyloaddition.     

Chemical functionalization of graphene enabled by phage displayed peptides

The development of a general approach for the nondestructive chemical and biological functionalization of graphene could expand opportunities for graphene in both fundamental studies and a variety of device platforms. Graphene is a delicate single-layer, two-dimensional network of carbon atoms whose properties can be affected by covalent modification. One method for functionalizing materials without fundamentally changing their inherent structure is using biorecognition moieties. In particular, oligopeptides are molecules containing a broad chemical diversity that can be achieved within a relatively compact size. Phage display is a dominant method for identifying peptides that possess enhanced selectivity toward a particular target. Here, we demonstrate a powerful yet benign approach for chemical functionalization of graphene via comprehensively screened phage displayed peptides. Our results show that graphene can be selectively recognized even in nanometer-defined strips. Further, modification of graphene with bifunctional peptides reveals both the ability to impart selective recognition of gold nanoparticles and the development of an ultrasensitive graphene-based TNT sensor. We anticipate that these results could open exciting opportunities in the use of graphene in fundamental biochemical recognition studies, as well as applications ranging from sensors to energy storage devices.     

Noncovalent Functionalization of Pnictogen Surfaces: From Small Molecules to 2D Heterostructures

Beyond graphene, 2D pnictogen polymers are rapidly growing among the family of 2D materials. Due to their unique properties, this group has received considerable interest in recent years. Those properties include tunable electronic band gaps, high charge carrier mobility, and in‐plane anisotropic properties. This Review covers the noncovalent functionalization of pnictogen surfaces considering experimental and theoretical studies. Noncovalent functionalization is of great importance for effective modulation of the electronic structure of these materials as well as improvement of their stability toward surface oxidation. This Review highlights their noncovalent modification by organic molecules, in which enhanced surface stability of phosphorene and generated functionalized materials for applications in biomedical, supercapacitors, energy storage, and biosensors. Moreover, the noncovalent interactions with small molecules show its significance for sensing applications. Lastly, the interactions of pnictogen sheets with other 2D materials and their applications for van der Waals heterostructure formation are discussed. Current state‐of‐the‐art as well as future perspectives in this field are covered.     

Immobilization of carbon nanotubes on functionalized graphene film grown by chemical vapor deposition and characterization of the hybrid material

We report the surface functionalization of graphene films grown by chemical vapor deposition and fabrication of a hybrid material combining multi-walled carbon nanotubes and graphene (CNT–G). Amine-terminated self-assembled monolayers were prepared on graphene by the UV-modification of oxidized groups introduced onto the film surface. Amine-termination led to effective interaction with functionalized CNTs to assemble a CNT–G hybrid through covalent bonding. Characterization clearly showed no defects of the graphene film after the immobilization reaction with CNT. In addition, the hybrid graphene material revealed a distinctive CNT–G structure and p–n type electrical properties. The introduction of functional groups on the graphene film surface and fabrication of CNT–G hybrids with the present technique could provide an efficient, novel route to device fabrication.     

Dynamic Fluid‐Like Graphene with Ultralow Frictional Molecular Bearing

Fluid‐like sliding graphenes but with solid‐like out‐of‐plane compressive rigidity offer unique opportunities for achieving unusual physical and chemical properties for next‐generation interfacial technologies. Of particular interest in the present study are graphenes with specific chemical functionalization that can predictably promote adhesion and wetting to substrate and ultralow frictional sliding structures. Lubricity between stainless steel (SS) and diamond‐like carbon (DLC) is experimentally demonstrated with densely functionalized graphenes displaying dynamic intersheet bonds that mechanically transform into stable tribolayers. The macroscopic lubricity evolves through the formation of a thin film of an interconnected graphene matrix that provides a coefficient of friction (COF) of 0.01. Mechanical sliding generates complex folded graphene structures wherein equilibrated covalent chemical linkages impart rigidity and stability to the films examined in macroscopic friction tests. This new approach to frictional reduction has broad implications for manufacturing, transportation, and aerospace.     

Highly conducting graphene sheets and Langmuir-Blodgett films

Graphene is an intriguing material with properties that are distinct from those of other graphitic systems. The first samples of pristine graphene were obtained by 'peeling off' and epitaxial growth. Recently, the chemical reduction of graphite oxide was used to produce covalently functionalized single-layer graphene oxide. However, chemical approaches for the large-scale production of highly conducting graphene sheets remain elusive. Here, we report that the exfoliation-reintercalation-expansion of graphite can produce high-quality single-layer graphene sheets stably suspended in organic solvents. The graphene sheets exhibit high electrical conductance at room and cryogenic temperatures. Large amounts of graphene sheets in organic solvents are made into large transparent conducting films by Langmuir-Blodgett assembly in a layer-by-layer manner. The chemically derived, high-quality graphene sheets could lead to future scalable graphene devices.     

Zwitterionic Conjugated Surfactant Functionalization of Graphene with pH‐Independent Dispersibility: An Efficient Electron Mediator for the Oxygen Evolution Reaction in Acidic Media

The functionalization of graphene has been extensively used as an effective route for modulating the surface property of graphene, and enhancing the dispersion stability of graphene in aqueous solutions via functionalization has been widely investigated to expand its use for various applications across a range of fields. Herein, an effective approach is described for enhancing the dispersibility of graphene in aqueous solutions at different pH levels via non‐covalent zwitterion functionalization. The results show that a surfactant with electron‐deficient carbon atoms in its backbone structure and large π–π interactive area enables strong interactions with graphene, and the zwitterionic side terminal groups of the molecule support the dispersibility of graphene in various pH conditions. Experimental and computational studies confirm that perylene diimide amino N‐oxide (PDI–NO) allows efficient functionalization and pH‐independent dispersion of graphene enabled by hydration repulsion effects induced by PDI–NO. The PDI–NO functionalized graphene is successfully used in the oxygen evolution reaction as an electron mediator for boosting the electrocatalytic activity of a Ru‐based polyoxometalate catalyst in an acidic medium. The proposed strategy is expected to bring significant advances in producing highly dispersible graphene in aqueous medium with pH‐independent stability, thus broadening the application range of graphene.     

Peptide-functionalized colloidal graphene via interdigited bilayer coating and fluorescence turn-on detection of enzyme

Synthesis of colloidal functional graphene is challenging because graphene is water-insoluble and its relatively inert surface made the functionalization a difficult task. Here we report interdigited bilayer type coating that provide both colloidal stability and functionalization option for graphene. Colloidal graphene oxide is first converted into interdigited bilayer coated graphene oxide and next they are transformed into colloidal graphene by hydrazine reduction. These coated graphenes can be further transformed into colloidal functional graphene using covalent conjugation chemistry. Functional graphene has been synthesized for optical detection of enzyme where a fluorescent dye is covalently linked through a peptide so that the dye fluorescence is quenched by graphene but switches on once enzymes cleave the peptide bond. The interdigited bilayer coating reported here is unique as it provides coating thickness <3 nm, offering optically responsive graphene-fluorophore substrate with high colloidal stability.     

One-step reduction, characterization and magnetic behaviour of exfoliated graphene oxide

The functionalized graphene (GO) was fabricated by a simple method of chemical reduction in a polar aprotic solvent. This paper therefore, describes a versatile and synthetic route for the preparation of reduced graphene oxide (RGO) and its behavior when exposed to magnetic field environment. The characterization results of transmission electron microscopy (TEM), scanning electron microscopy (SEM), Raman spectroscopy and the attenuated total reflectance-Fourier transform infra-red (ATR-FTIR) analysis indicate that graphite was exfoliated and reduced to graphene layers.     

混杂功能化多壁碳纳米管/环氧树脂复合材料的制备及性能

对多壁碳纳米管(MWCNTs)分别进行共价、非共价和混杂功能化改性, 然后采用溶液共混法, 将三种功能化类型的MWCNTs按不同质量分数分别加入环氧树脂(EP)制备MWCNTs/EP复合材料。通过拉伸试验和热重分析, 研究MWCNTs的功能化类型及含量对复合材料力学性能和热学性能的影响, 并对复合材料拉伸试件断面进行SEM观察分析。结果表明: 与共价功能化复合材料(MWCNTs-Epon828/EP)和非共价功能化复合材料(MWCNTs-PPA/EP)相比, 混杂功能化复合材料(MWCNTs-Epon828-PPA/EP)的力学性能和热学性能最佳。当MWCNTs质量分数为0.3%时, 其拉伸强度、弹性模量和断裂伸长率较纯EP分别提高30%, 62%和26%。      

The preparation of high performance and conductive poly (vinyl alcohol)/graphene nanocomposite via reducing graphite oxide with sodium hydrosulfite

Sodium hydrosulfite is used to reduce graphite oxide in current study. The preparation of poly (vinyl alcohol) (PVA)/graphene nanocomposites is realized using two simple steps: the synthesis of PVA/graphite oxide (GO) nanocomposites film and immersion of such a film in the reducing agent aqueous solution. This method prohibits the agglomeration of GO during direct reduction in PVA/GO aqueous solution, and opens a new way to scale up the production of graphene nanocomposites using a simple reducing agent. A 40% increase in tensile strength and 70% improvement in elongation at break have been obtained with only the addition of 0.7 wt.% of reduced graphite oxide. Furthermore, a good level of conductivity and a variation in the surface property of the prepared films have been observed for the composites containing graphene.     

石墨的纳米结构组装

本文在分析石墨微观结构和性能基础上, 综合分析了石墨加工改性方法, 提出了石墨纳米结构组装的概念, 介绍了几种石墨纳米结构组装的方法。通过结构组装, 引入纳米功能粒子, 制造活性功能空间, 合成新型石墨功能材料; 通过制备石墨层间化合物、碳石墨合金等方法引入纳米功能粒子组装碳石墨材料; 通过打开石墨层片, 制备二维层状材料制备纳米石墨烯片, 可以采用氧化活化等制造孔隙结构增加活性空间; 通过调节石墨晶体排布方向减少石墨材料的性能异向性, 提高性能均匀性; 通过石墨结构纳米组装设计, 设计新型石墨功能材料。纳米尺度的石墨加工和改性有可能推动石墨矿物资源的有效利用, 开发新型石墨储能材料和石墨烯片材料。     

Functionalized cubic mesostructured silica films

Cubic Pm3n mesoporous silica films have been prepared on silicon wafers and quartz crystal microbalance (QCM) devices covered with gold electrodes by a spin-coating process from preformed silica/CTABr/ethanol/water assemblies under acidic conditions. Post-synthesis functionalization of mesoporous films with amino- and thiol-containing organosilanes is performed in order to modify the mesoporous surface for further confinement of nanoscale structures. The type of mesophase structure and the functionalization process was followed with surface sensitive techniques such as grazing incidence diffraction (GID), reflection-absorption FT-IR spectroscopy and gravimetric measurements by applying QCMs technique. Nitrogen sorption data using QCM devices were obtained for the calcined and functionalized mesoporous films.     

How Do the Electrical Properties of Graphene Change with its Functionalization?

Functionalization of graphene is essential to interface it with other moieties to expand the scope of its electrical/electronic applications. However, chemical functionalization and/or molecular interactions on graphene sensitively modulate its electrical properties. To evaluate and take advantage of the properties of functionalized graphene, it is important to understand how its electrical attributes (such as carrier scattering, carrier concentration, charge polarity, quantum‐capacitance enhanced doping, energy levels, transport mechanisms, and orbital hybridization of energy‐bands) are influenced by a change in carbon's structural conformation, hybridization state, chemical potential, local energy levels, and dopant/interface coupling induced via functionalization or molecular interactions. Here, a detailed and integrated model describes factors influencing these electrical characteristics of functionalized graphene (covalent bonds, adsorption, π–π bonds, and lattice incorporation). The electrical properties are governed via three mechanisms: (a) conversion of carbon's hybridized state, (b) dipole interactions enhanced via quantum capacitance, and (c) orbital hybridization with an interfacing molecule. A few graphenic materials are also identified where further studies are essential to understand the effect of their functionalization.     

Recent Progress on Germanene and Functionalized Germanene: Preparation,Characterizations, Applications,and Challenges

A new family of single‐atom‐thick 2D germanium‐based materials with graphene‐like atomic arrangement, germanene and functionalized germanene, has attracted intensive attention due to their large bandgap and easily tailored electronic properties. Unlike carbon atoms in graphene, germanium atoms tend to adopt mixed sp²/sp³ hybridization in germanene, which makes it chemically active on the surface and allows its electronic states to be easily tuned by chemical functionalization. Impressive achievements in terms of the applications in energy storage and catalysis have been reported by using germanene and functionalized germanene. Herein, the fabrication of epitaxial germanene on different metallic substrates and its unique electronic properties are summarized. Then, the preparation strategies and the fundamental properties of hydrogen‐functionalized germanene (germanane or GeH) and other ligand‐terminated forms of germanene are presented. Finally, the progress of their applications in energy storage and catalysis, including both experimental results and theoretical predictions, is analyzed.     

Nylon-6/Graphene composites modified through polymeric modification of graphene

The covalent functionalization of graphene oxide (GO) with poly(vinyl alcohol) (PVA) via ester linkages (GO-es-PVA) as well as the characterization of modified graphene based Nylon-6 (PA6) composite prepared by solution mixing techniques was examined. The anchoring of PVA chains on GO sheets was confirmed by XPS and FTIR measurements. The resulting functionalized sample became soluble in formic acid, allowing solution-phase processing for preparation of PA6/GO composites. Answering to the efficient polymer-chain grafting, a homogeneously dispersion of GO sheets in PA6 matrix and a dramatic improvement of interface adhesion between nanosheets and matrix were observed in PA6/GO-es-PVA composites by SEM and TEM. The depressed crystallization of PA6 chains in PA6/GO-es-PVA composites was investigated by their DSC and XRD results.     

Magnetomicelles: composite nanostructures from magnetic nanoparticles and cross-linked amphiphilic block copolymers

We report the synthesis, characterization, and covalent surface chemistry of "magnetomicelles", cross-linked, amphiphilic block-copolymer micelles that encapsulate superparamagnetic iron oxide nanoparticles. Because these composite nanostructures assemble spontaneously from solution by simultaneous desolvation of nanoparticle and amphiphilic poly(styrene(250)-block-acrylic acid(13)) components, explicit surface functionalization of the particles is not required, and the encapsulation method was applied to different magnetic nanoparticle sizes and compositions. TEM images of the magnetomicelles illustrated that the number of encapsulated particles could be dictated rationally by synthetic conditions. The magnetic properties of the particles were characterized by SQUID magnetometry and followed the general Langevin magnetic model for superparamagnetic materials. The micellar shells of these particles were functionalized using covalent chemistry that would not ordinarily be possible on the magnetic particle surface. As a result, this noncovalent approach provides a new route to technological applications of hydrophobic magnetic nanomaterials that lack appropriate conjugate surface chemistry.     

Surface charge induced tuning of electrical properties of CVD assisted graphene and functionalized graphene sheets

We demonstrate a new approach to tune the electrical properties of graphene and functionalized graphene. Graphene was synthesized using thermal chemical vapour deposition(TCVD) method on copper foil using precursor gas acetylene and co-catalyst H2 gas. TCVD assisted graphene was successfully transferred onto a silicon wafer. Transferred graphene sheet was then functionalized to prepare graphene oxide(GO) and reduced graphene oxide(rGO). Different surface charge carbon nanoparticles, e.g. carbon nanoparticle with net positive charge and carbon nanoparticle with net negative charge were then immobilized on transferred graphene and functionalized graphene sheets. The functionalized graphene and charge mobilized functionalized graphene were characterized by Uv–vis spectroscopy,Fourier transformed infrared spectroscopy, scanning electron microscopy, and Raman spectroscopy. After immobilization of carbon nanomaterials, the ac electrical conductivity was found to increase due to enhancement of the surface charge, electron density, and mobility. It was observed that negative surface charge immobilized graphene and functionalized graphene show higher conductivity. Thus, the electrical property of graphene and functionalized graphene can be tuned by surface modification with different surface charge carbon nanomaterials.     

Mechanism of Functionalization of the Surfaces of Detonation Nanodiamonds: Mass-Spectrometric Investigation

The comparison of the formation processes of volatile products at heating mixtures of detonation nanodiamonds with perfluorochemical alcohol and nanodiamonds subjected to directed chemical modification with perfluorochemical alcohol was made using the thermodesorption mass-spectrometry. A change of the destruction mechanism and increase of the thermostability of perfluorochemical alcohol by ~ 100°C as a result of a directional chemical modification was revealed, the most possible models of functionalization through hydrogen and covalent bonds of the hydroxyl group of fluorine radicals with carboxyl groups of surfaces of nanodiamond particles are suggested, the degrees of the functionalization and energy of the desorption activation of the products of the destruction functionalized molecules are assessed.     

羧基功能化和表面活性剂修饰对石墨烯电化学性能的影响

通过简单的两步溶液法对石墨烯进行羧基接枝和表面活性剂修饰, 并研究其电化学性能。研究结果表明, 与纯石墨烯(比电容50 F/g)相比, 表面活性剂本身并不能有效提高石墨烯的比电容(45 F/g), 羧基功能化可以将石墨烯的比电容提高至130 F/g。而羧基功能化和表面活性剂修饰双处理工艺能够将石墨烯的比电容提高到230 F/g, 且经800次充放电循环后其比电容仍然具有95%的保持率, 表明该材料具有良好的循环稳定性。因此, 调控石墨烯的表面化学特性对提高其电化学性能具有重要的意义。