Towards Novel Multifunctional Pillared Nanostructures: Effective Intercalation of Adamantylamine in Graphene Oxide and Smectite Clays

Multifunctional pillared materials are synthesized by the intercalation of cage‐shaped adamantylamine (ADMA) molecules into the interlayer space of graphite oxide (GO) and aluminosilicate clays. The physicochemical and structural properties of these hybrids, determined by X‐ray diffraction (XRD), Fourier transform infrared (FTIR), Raman and X‐ray photoemission (XPS) spectroscopies and transmission electron microscopy (TEM) show that they can serve as tunable hydrophobic/hydrophilic and stereospecific nanotemplates. Thus, in ADMA‐pillared clay hybrids, the phyllomorphous clay provides a hydrophilic nanoenvironment where the local hydrophobicity is modulated by the presence of ADMA moieties. On the other hand, in the ADMA‐GO hybrid, both the aromatic rings of GO sheets and the ADMA molecules define a hydrophobic nanoenvironment where sp³‐oxo moieties (epoxy, hydroxyl and carboxyl groups), present on GO, modulate hydrophilicity. As test applications, these pillared nanostructures are capable of selective/stereospecific trapping of small chlorophenols or can act as cytotoxic agents.     

The Exfoliation of Graphene in Liquids by Electrochemical,Chemical, and Sonication‐Assisted Techniques: A Nanoscale Study

The different exfoliation routes of graphite to produce graphene by sonication in solvent, chemical oxidation and electrochemical oxidation are compared. The exfoliation process and roughening of a flat graphite substrate is directly visualized at the nanoscale by scanning probe and electron microscopy. The etching damage in graphite and the properties of the exfoliated sheets are compared by Raman spectroscopy and X‐ray diffraction analysis. The results show the trade‐off between exfoliation speed and preservation of graphene quality. A key step to achieve efficient exfoliation is to couple gas production and mechanical exfoliation on a macroscale with non‐covalent exfoliation and preservation of graphene properties on a molecular scale.     

Facile Physical Route to Highly Crystalline Graphene

A physical route is proposed to obtain highly crystalline graphene sheets with minimal oxygen content similar to the precursor graphite. The functional graphene sheets obtained from graphite oxide by low temperature thermal exfoliation are annealed at high temperature (1900 °C) in a vacuum (10^?6 torr). The D band intensity in Raman spectroscopy is reduced significantly, while the G band intensity is recovered, similar to the level of precursor graphite. No appreciable oxygen content is observed from X‐ray photoelectron spectroscopy and an electrical conductivity of ～56 500 S m^?1 is obtained, comparable to 100 900 S m^?1 of the precursor graphite.     

A Facile Approach to Chemically Modified Graphene and its Polymer Nanocomposites

A scalable approach for the mass production of chemically modified graphene has yet to be developed, which holds the key to the large‐scale production of stable graphene colloids for optical electronics, energy conversion, and storage materials, catalysis, sensors, composites, etc. Here, a facile approach to fabricating covalently modified graphene and its polymer nanocomposites is presented. The method involves: i) employing a common furnace, rather than a furnace installed with a quartz tube and operated in inert gas as required in previous studies, to treat a commercial graphite intercalation compound with thermal shocking and ultrasonication and fabricate graphene platelets (GnPs) with a thickness of 2.51 ± 0.39 nm that contain only 7 at% oxygen; ii) grafting these GnPs with a commercial, long‐chain surfactant, which is able to create molecular entanglement with polymer matrixes by taking advantage of the reactions between the epoxide groups of the platelets and the end amine groups of the surfactant, to produce chemically modified graphene platelets (m‐ GnPs); and iii) solution‐mixing m‐GnPs with a commonly used polymer to fabricate nanocomposites. These m‐GnPs are well dispersed in a polymer with highly improved mechanical properties and a low percolation threshold of electrical conductivity at 0.25 vol%. This novel approach could lead to the future scalable production of graphene and its nanocomposites.     

Epoxide Speciation and Functional Group Distribution in Graphene Oxide Paper‐Like Materials

The electronic structure and chemical bonding of three differently prepared samples of graphene oxide paper‐like sheets are studied. Two are created by water filtration of fully oxidized graphene sheets, although one is later intercalated with dodecylamine. The third is created by reducing graphene oxide with hydrazine hydrate. The spectroscopic fingerprints of the aligned epoxide functional groups that unzip the carbon basal plane are found. This unzipping appears to be a result of aging, and the extent to which the basal plane is unzipped can be controlled via the preparation method. In particular, reduction with hydrazine enhances line defect formation, whereas intercalation inhibits the process.The hydroxyl functional group also has a tendency to gather in zones of dense oxidation on the carbon basal plane, a predilection that is not shared by the other prominent functional group species. Finally, the non‐functionalized carbon sites exhibit very similar bonding despite the increase in the sp²/sp³ ratio, confirming that reduction alone is insufficient for producing pristine graphene from graphene oxide. These results are obtained by directly probing the electronic structure of the graphene oxide samples via X‐ray absorption near‐edge structure spectroscopy (XANES) and resonant X‐ray emission spectroscopy (RXES). This work has important significance for the development of graphene oxide as a band gap‐engineered electronic material, as preparation methodology strongly affects not only the initial condition of the sample, but how the electronic structure evolves over time.     

General Synthesis of N‐Doped Macroporous Graphene‐Encapsulated Mesoporous Metal Oxides and Their Application as New Anode Materials for Sodium‐Ion Hybrid Supercapacitors

A general method to synthesize mesoporous metal oxide@N‐doped macroporous graphene composite by heat‐treatment of electrostatically co‐assembled amine‐functionalized mesoporous silica/metal oxide composite and graphene oxide, and subsequent silica removal to produce mesoporous metal oxide and N‐doped macroporous graphene simultaneously is reported. Four mesoporous metal oxides (WO_{3? x} , Co₃O₄, Mn₂O₃, and Fe₃O₄) are encapsulated in N‐doped macroporous graphene. Used as an anode material for sodium‐ion hybrid supercapacitors (Na‐HSCs), mesoporous reduced tungsten oxide@N‐doped macroporous graphene (m‐WO_{3? x} @NM‐rGO) gives outstanding rate capability and stable cycle life. Ex situ analyses suggest that the electrochemical reaction mechanism of m‐WO_{3? x} @NM‐rGO is based on Na⁺ intercalation/de‐intercalation. To the best of knowledge, this is the first report on Na⁺ intercalation/de‐intercalation properties of WO_{3? x} and its application to Na‐HSCs.     

Mechanical Reinforcement of Polyethylene Using Polyethylene‐Grafted Multiwalled Carbon Nanotubes

The incorporation of carbon nanotubes to a polymer generally improves the stiffness and strength of the polymer, but the ductility and toughness of the polymer are compromised in most cases. Here we report the mechanical reinforcement of polyethylene (PE) using polyethylene‐grafted multiwalled carbon nanotubes (PE‐g‐MWNTs). The stiffness, strength, ductility and toughness of PE are all improved by the addition of PE‐g‐MWNTs. The grafting of PE onto MWNTs enables the well‐dispersion of nanotubes in the PE matrix and improves MWNT/PE interfacial adhesion. The grafting was achieved by a reactive blending process through melt blending of PE containing 0.85 wt % of maleic anhydride and amine‐functionalized MWNTs. The reaction between maleic anhydride and amine groups, as evidenced by X‐ray photoelectron spectroscopy and Raman spectroscopy, leads to the grafting of PE onto the nanotubes.     

Sodium Storage and Electrode Dynamics of Tin–Carbon Composite Electrodes from Bulk Precursors for Sodium‐Ion Batteries

Here, a Sn–C composite material prepared from bulk precursors (tin metal, graphite, and melamine) using ball milling and annealing is reported. The composite (58 wt% Sn and 42 wt% N‐doped carbon) shows a capacity up to 445 mAh g_Sn+C^?1 and an excellent cycle life (1000 cycles). For the graphite, the ball milling leads to graphene nanoplatelets (GnP) for which the storage mechanism changes from solvent co‐intercalation to conventional intercalation. The final composite (Sn at nitrogen‐doped graphite nanoplatelets (SnNGnP)) is obtained by combining the GnPs with Sn and melamine as the nitrogen source. Rate‐dependent measurements and in situ X‐ray diffraction are used to study the asymmetric storage behavior of Sn, which shows a more sloping potential profile during sodiation and more defined steps during desodiation. The disappearance of two redox plateaus during desodiation is linked to the preceding sodiation current density (memory effect). The asymmetric behavior is also found by in situ electrochemical dilatometry. This method also shows that the effective electrode expansion during sodiation is much smaller (about +14%) compared to what is expected from Sn (+420%), which gives a reasonable explanation for the excellent cycle life for the SnNGnP (and likely other nanocomposites in general). Next to the advantages, challenges, which result from the nanocomposite approach, are also discussed.     

Crystalline CoFeB/Graphite Interfaces for Carbon Spintronics Fabricated by Solid Phase Epitaxy

Structurally ordered interfaces between ferromagnetic electrodes and graphene or graphite are of great interest for carbon spintronics, since they allow spin‐filtering due to k‐vector conservation. By solid phase epitaxy of amorphous/nanocrystalline CoFeB at elevated temperatures, the feasibility of fabricating crystalline interfaces between a 3d ferromagnetic alloy and graphite is demonstrated, without suffering from the unwetting problem that was commonly seen in many previous studies with 3d transition metals. The films fabricated on graphite in this way are found to have a strong body‐centered‐cubic (110) texture, albeit without a unique, well‐defined in‐plane epitaxial relationship with the substrate lattice. Using various X‐ray spectroscopic techniques, it is shown that boron suppresses the formation of CoFe‐O during CoFeB deposition, and then diffuses out of the CoFe lattice. Segregation of B occurred exclusively to the film surface upon in situ annealing, and not to the interface between CoFeB and graphite. This is favorable for obtaining a high spin polarization at the hybrid CoFe/graphite crystalline interface. The Co and Fe spin moments in the crystalline film, determined by X‐ray magnetic circular dichroism, are found to be bulk‐like, while their orbital moments show an unusual giant enhancement which has yet to be understood.     

One‐Step Electrochemical Synthesis of Graphene/Polyaniline Composite Film and Its Applications

This work describes a new one‐step large‐scale electrochemical synthesis of graphene/polyaniline (PANI) composite films using graphite oxide (GO) and aniline as the starting materials. The size of the film could be controlled by the area of indium tin oxide (ITO). Scanning electron microscopy (SEM), transmission electron microscopy (TEM), X‐ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), and ultraviolet–visible absorption spectrum (UV–vis) results demonstrated that the graphene/PANI composite film was successfully synthesized. The obtained graphene/PANI composite film showed large specific area, high conductivity, good biocompatibility, and fast redox properties and had perfect layered and encapsulated structures. Electrochemical experiments indicated that the composite film had high performances and could be widely used in applied electrochemical fields. As a model, horseradish peroxidase (HRP) was entrapped onto the film‐modi?ed glassy carbon electrode (GCE) and used to construct a biosensor. The immobilized HRP showed a pair of well‐de?ned redox peaks and high catalytic activity for the reduction of H₂O₂. Furthermore, the graphene/PANI composite film could be directly used as the supercapacitor electrode. The supercapacitor showed a high specific capacitance of 640 F g^?1 with a retention life of 90% after 1000 charge/discharge cycles.     

X‐Ray Spectroscopic Investigation of Chlorinated Graphene: Surface Structure and Electronic Effects

Chemical doping of graphene represents a powerful means of tailoring its electronic properties. Synchrotron‐based X‐ray spectroscopy offers an effective route to investigate the surface electronic and chemical states of functionalizing dopants. In this work, a suite of X‐ray techniques is used, including near edge X‐ray absorption fine structure spectroscopy, X‐ray photoemission spectroscopy, and photoemission threshold measurements, to systematically study plasma‐based chlorinated graphene on different substrates, with special focus on its dopant concentration, surface binding energy, bonding configuration, and work function shift. Detailed spectroscopic evidence of C–Cl bond formation at the surface of single layer graphene and correlation of the magnitude of p‐type doping with the surface coverage of adsorbed chlorine is demonstrated for the first time. It is shown that the chlorination process is a highly nonintrusive doping technology, which can effectively produce strongly p‐doped graphene with the 2D nature and long‐range periodicity of the electronic structure of graphene intact. The measurements also reveal that the interaction between graphene and chlorine atoms shows strong substrate effects in terms of both surface coverage and work function shift.     

Preparation,Structure, and Electrochemical Properties of Reduced Graphene Sheet Films

This paper describes the preparation, characterization, and electrochemical properties of reduced graphene sheet films (rGSFs), investigating especially their electrochemical behavior for several redox systems and electrocatalytic properties towards oxygen and some small molecules. The reduced graphene sheets (rGSs) are produced in high yield by a soft chemistry route involving graphite oxidation, ultrasonic exfoliation, and chemical reduction. Transmission electron microscopy (TEM), X‐ray diffraction (XRD), scanning electron microscopy (SEM), X‐ray photoelectron spectroscopy (XPS) and Raman spectroscopy clearly demonstrate that graphene was successfully synthesized and modified at the surface of a glassy carbon electrode. Several redox species, such as Ru(NH₃)₆^3+/2+, Fe(CN)₆^3?/4?, Fe^3+/2+ and dopamine, are used to probe the electrochemical properties of these graphene films by using the cyclic voltammetry method. The rGSFs demonstrate fast electron‐transfer (ET) kinetics and possess excellent electrocatalytic activity toward oxygen reduction and certain biomolecules. In our opinion, this microstructural and electrochemical information can serve as an important benchmark for graphene‐based electrode performances.     

Graphene‐Based Nanoporous Materials Assembled by Mediation of Polyoxometalate Nanoparticles

A kind of graphene‐based nanoporous material is prepared through assembling graphene sheets mediated through polyoxometalate nanoparticles. Owing to the strong interaction between graphene and polyoxometalate, 2D graphene sheets with honeycomb‐latticed carbon atoms could assemble into a porous structure, in which 3D polyoxometalate nanoparticles serve as the crosslinkers. Nitrogen and hydrogen sorption analysis reveal that the as‐prepared graphene‐based hybrid material possesses a specific surface area of 680 m² g^?1 and a hydrogen uptake volume of 0.8?1.3 wt%. Infrared spectrometry is used to probe the electron density changes of polyoxometalate particle in the redox‐cycle and to verify the interaction between graphene and polyoxometalate. The as‐prepared graphene‐based materials are further characterized by Raman spectroscopy, X‐ray diffraction, scanning electron microscopy, and transmission electron microscopy.     

Simultaneous Electrochemical Dual‐Electrode Exfoliation of Graphite toward Scalable Production of High‐Quality Graphene

Developing scalable methods to produce large quantities of high‐quality and solution‐processable graphene is essential to bridge the gap between laboratory study and commercial applications. Here an efficient electrochemical dual‐electrode exfoliation approach is developed, which combines simultaneous anodic and cathodic exfoliation of graphite. Newly designed sandwich‐structured graphite electrodes which are wrapped in a confined space with porous metal mesh serve as both electrodes, enabling a sufficient ionic intercalation. Mechanism studies reveal that the combination of electrochemical intercalation with subsequent thermal decomposition results in drastic expansion of graphite toward high‐efficiency production of graphene with high quality. By precisely controlling the intercalation chemistry, the two‐step approach leads to graphene with outstanding yields (85% and 48% for cathode and anode, respectively) comprising few‐layer graphene (1–3 layers, >70%), ultralow defects (I_D/I_G < 0.08), and high production rate (exceeding 25 g h^?1). Moreover, its excellent electrical conductivity (>3 × 10⁴ S m^?1) and great solution dispersibility in N‐methyl pyrrolidone (10 mg mL^?1) enable the fabrication of highly conductive (11 Ω sq^?1) and flexible graphene films by inkjet printing. This simple and efficient exfoliation approach will facilitate the development of large‐scale production of high‐quality graphene and holds great promise for its wide application.     

Electrical Conductivity and Ferromagnetism in a Reduced Graphene–Metal Oxide Hybrid

The rare coexistence of ferromagnetism and electrical conductivity is observed in the reduced graphene oxide–metal oxide hybrids, rGO‐Co, rGO‐Ni, and rGO‐Fe, using chemical reduction with hydrazine or ultraviolet photoirradiation of the graphene oxide–metal complexes, GO‐Co, GO‐Ni, and GO‐Fe. The starting and final materials are characterized by X‐ray photoelectron spectroscopy, transmission electron microscopy (TEM), elemental analysis, Mössbauer spectroscopy, and Raman spectroscopy. In contrast to graphene, where the electrical conductivity and magnetic properties are controlled by carrier (electron or hole) doping, those of graphene oxide can be controlled by complexation with Co²⁺, Ni²⁺, and Fe³⁺ cations through the strong electrostatic affinity of negatively charged graphene oxide towards metal cations. The presence of ferromagnetism and electrical conductivity in these hybrids can promote significant applications including magnetic switching and data storage.     

Hierarchical Graphene–Carbon Fiber Composite Paper as a Flexible Lateral Heat Spreader

As a low dimensional crystal, graphene attracts great attention as heat dissipation material due to its unique thermal transfer property exceeding the limit of bulk graphite. In this contribution, flexible graphene–carbon fiber composite paper is fabricated by depositing graphene oxide into the carbon fiber precursor followed by carbonization. In this full‐carbon architecture, scaffold of one‐dimensional carbon fiber is employed as the structural component to reinforce the mechanical strength, while the hierarchically arranged two‐dimensional graphene in the framework provides a convenient pathway for in‐plane acoustic phonon transmission. The as‐obtained hierarchical carbon/carbon composite paper possesses ultra‐high in‐plane thermal conductivity of 977 W m^?1 K^?1 and favorable tensile strength of 15.3 MPa. The combined mechanical and thermal performances make the material highly desirable as lateral heat spreader for next‐generation commercial portable electronics.     

Structural,Electrical, and Thermal Behavior of Graphite‐Polyaniline Composites with Increased Crystallinity

Conductive materials are at the forefront of materials science research because of the large number of applications that have been developed around their interesting and unique properties. This work reports for the first time a correlation between the structural, electrical, and thermal behavior of novel graphite‐polyaniline (G‐PANI) composites with electrical conductivities greater than either of the individual components. The G:PANI mass ratio was varied during synthesis of the composites (90:10, 95:5, 96:4, 97:3, and 98:2 G:PANI mass ratios) and the highest electrical conductivity was determined for the composite having a G:PANI mass ratio of 96:4. The structural changes related to this increase in electrical conductivity were clearly reflected by the Raman spectra of the new composites, which indicated an improved crystallinity through a better stacking along the c‐axis of graphite when PANI was present (as evidenced by the G and 2 × D modes at 1582 and 2684 cm⁻¹). X‐ray diffraction data showed a slight increase in the (0 0 2) graphite crystal plane distance that was associated with a dilute stage intercalation or a possible “pseudo‐intercalation” of the polymer species between the graphite layers facilitating charge transfer in the composites. It is proposed that polyaniline acts as a charge transfer component between basal planes of graphite. Thermogravimetric analyses of the samples showed similar trends for the thermal stability in accordance with the electrical conductivity, the Raman and X‐ray diffraction data. The potential impact of this work is evident in the many areas that utilize graphite as conductive filler in electrically conducting materials. The composites can be used for a large number of applications in nanoelectronics, electromagnetic interference shielding, rechargeable batteries or as other advanced nanocomposite materials with improved electrical, structural, and thermal properties.     

Dual‐Functionalized Polymer Nanotubes as Substrates for Molecular‐Probe and DNA‐Carrier Applications

Bifunctionalized polymer nanotubes have been fabricated using vapor‐deposition polymerization in FeCl₃‐adsorbed anodic aluminum oxide membranes followed by attachment of amine‐functionalized silica nanoparticles. The prepared bifunctionalized polymer nanotubes are applied as both a molecular probe and a DNA carrier by conjugating pyreneacetic acid with the amine groups and immobilizing DNA with the carboxylic acid groups on the surface. The number of amine functional groups on the nanotubes' surface can be measured by means of the photoluminescence intensity of pyreneacetic acid conjugated with amine groups, and the number of the residual carboxylic acid groups is calculated by titration with sodium hydroxide. Fourier‐transform infrared spectroscopy, X‐ray photoelectron spectroscopy, transmission electron microscopy, scanning electron microscopy, and confocal laser scanning microscopy have been performed to confirm the complete polymerization of the monomer and the attachment of photoluminescent molecules and single‐stranded DNA.     

Enhancement of Thermal Energy Transport Across Graphene/Graphite and Polymer Interfaces: A Molecular Dynamics Study

Understanding thermal energy transport in polymeric nanocomposite materials is important to the engineering of polymer composites with better engineered heat transfer properties. Interfacial thermal resistance between the filling particles and the polymer matrices is a major bottleneck for the thermal conductivity improvement of polymer composite materials. Here, thermal energy transport in graphene/graphite‐polymer (paraffin wax‐C₃₀H₆₂) composite systems are systematically studied using molecular dynamics simulations. The influences of graphene size, interfacial bonding strength, and polymer density on the interfacial thermal transport are studied. According to the simulation results, approaches to improve interfacial thermal transport are proposed. Spectral analysis is performed to explore the mechanism of thermal transport. It is found that thermal energy transport across graphene/graphite‐polymer interfaces can be enhanced by increasing the polymer density and graphene size or forming covalent bonds between the graphite edges and polymer molecules. The results offer valuable guidance on improving thermal transport properties of polymeric nanocomposite.     

石墨烯的制备及表征研究进展

简述了石墨烯的力、热、电学特性;重点分析了制备石墨烯的几种不同方法,包括:机械剥离法、加热SiC法、石墨插层法、电弧放电法、化学气相沉积法、溶剂剥离法与溶剂热法等,并且评述了这几种方法的特点及存在的问题。介绍了石墨烯的几种表征方法,并阐述了其未来的发展前景。