Polarised infrared microspectroscopy of edge-oriented graphene oxide papers

We have performed FTIR transmission microspectroscopy on graphene oxide papers oriented with the nominal lattice planes parallel to the infrared optical axis. By polarising the IR light for samples of this geometry, spectral contributions of oriented oxide species are isolated from broad convoluted bands. Analysing the data alongside previous works, including experiments where samples were perturbed by reduction, dehydration and deuteration, we tabulate the most likely assignments for the observed spectral bands.     

Controllable synthesis of graphene sheets with different numbers of layers and effect of the number of graphene layers on the specific capacity of anode material in lithium-ion batteries

High quality graphene sheets are synthesized through efficient oxidation process followed by rapid thermal expansion and reduction by H₂. The number of graphene layers is controlled by tuning the oxidation degree of GOs. The higher the oxidation degree of GOs is getting, the fewer the numbers of graphene layers can be obtained. The material is characterized by elemental analysis, thermo-gravimetric analysis, scanning electron microscopy, atomic force microscopy, transmission electron microscopy and Fourier transform infrared spectroscopies. The obtained graphene sheets with single, triple and quintuplicate layers as anode materials exhibit a high reversible capacity of 1175, 1007, and 842 mA h g⁻¹, respectively, which show that the graphene sheets with fewer layers have higher reversible capacity.     

Low-temperature synthesis of SrAl2O4 by a modified sol-gel route: XRD and Raman characterization

Among other alkaline-earth aluminates, the monoclinic (M) polymorph of SrAl₂O₄ can be used as host material for Eu²⁺ luminescence based phosphors. With the aim of reducing the synthesis temperature of this polymorph, we have produced and characterized by XRD and Raman scattering solid solutions of the SrAl_2−xB_xO₄ system (x?0.3) obtained by two different methods, a ceramic route and a modified sol-gel synthesis. Though the addition of boron lowers the temperature of obtention of the M polymorph in both type of samples, lower B contents are needed to stabilize the M form as single phase for samples prepared by the sol-gel method than through the ceramic route. In the sol-gel method, the M polymorph can be obtained at temperatures as low as 1200 °C, with a Boron content of just 1%. Rietveld profile analysis allows us to conclude that coexistence of the monoclinic and hexagonal polymorphs of SrAl₂O₄ occurs for samples synthesized below an onset temperature of about 1000-1100 °C, that depends on the sample composition. Above those temperatures, only the monoclinic phase is formed.     

Raman spectroscopy as a tool for the analysis of carbon-based materials (highly oriented pyrolitic graphite,multilayer graphene and multiwall carbon nanotubes) and of some of their elastomeric composites

Raman spectra of highly oriented pyrolitic graphite, multilayer graphene and multiwall carbon nanotubes are carried out at different laser powers and different excitation energies. The effects of the laser heating and the double resonance Raman scattering are investigated as a prerequisite for a correct interpretation of the Raman spectra of carbon materials-based composites. The Raman spectra of multilayer graphene and multiwall carbon nanotubes embedded in a silicone matrix are also analyzed in an attempt to get some insights into the polymer–filler interface.     

Green synthesis of graphene nanosheets/ZnO composites and electrochemical properties

A green and facile approach was demonstrated to prepare graphene nanosheets/ZnO (GNS/ZnO) composites for supercapacitor materials. Glucose, as a reducing agent, and exfoliated graphite oxide (GO), as precursor, were used to synthesize GNS, then ZnO directly grew onto conducting graphene nanosheets as electrode materials. The small ZnO particles successfully anchored onto graphene sheets as spacers to keep the neighboring sheets separate. The electrochemical performances of these electrodes were analyzed by cyclic voltammetry, electrochemical impedance spectrometry and chronopotentiometry. Results showed that the GNS/ZnO composites displayed superior capacitive performance with large capacitance (62.2 F/g), excellent cyclic performance, and maximum power density (8.1 kW/kg) as compared with pure graphene electrodes. Our investigation highlight the importance of anchoring of small ZnO particles on graphene sheets for maximum utilization of electrochemically active ZnO and graphene for energy storage application in supercapacitors.     

Number of graphene layers exhibiting an influence on oxidation of DNA bases: Analytical parameters

This article investigates the analytical performance of double-, few- and multi-layer graphene upon oxidation of adenine and guanine. We observed that the sensitivity of differential pulse voltammetric response of guanine and adenine is significantly higher at few-layer graphene surface than single-layer graphene. We use glassy carbon electrode as substrate coated with graphenes. Our findings shall have profound influence on construction of graphene based genosensors.     

Effect of MWCNTs and graphene on the crystallization of polyurethane based nanocomposites,analyzed via calorimetry,rheology and AFM microscopy

Isothermal crystallization of two nanocomposites composed of multiwalled carbon nanotubes (MWCNT) and graphene dispersed in a hot melt adhesive polyurethane (PUR) is investigated. Rheological percolation is reached for PUR/MWCNT, but not for PUR/Graphene nanocomposites. Analysis of the elastic modulus versus time indicates that the crystallization process is more hastened by MWCNTs than by graphene, favouring the welding process of the corresponding adhesives. Correlative AFM images show that the crystal size follows the order: Crystals in neat PUR > Crystals in PUR/Graphene > Crystals in PUR/MWCNT. The nucleation density is higher in the case of MWCNTs due to the poorer dispersion of graphene in the PUR matrix. Analysis of DSC results by the Avrami equation and the fitting of G′-time results to a rheological equation adapted from the Avrami equation, show that the parameter n decreases from n = 3 for neat PUR to n = 2 for both nanocomposites. The coherence between the value n = 2 and AFM images is demonstrated: The lamellae organization in two dimensional growth, that brings about nucleated axialites, as expected for n = 2, is confirmed by AFM microscopy.     

退火时间对6H-SiC(0001)表面外延石墨烯形貌和结构的影响

在分子束外延(MBE)设备中,采用高温退火的方法在6H-SiC(0001)表面外延石墨烯,并研究了退火时间对外延石墨烯形貌和结构的影响.利用反射式高能电子衍射(RHEED)、原子力显微镜(AFM)、激光拉曼光谱(Raman)和近边X射线吸收精细结构(NEXAFS)等实验技术对制备的样品进行了表征.RHEED结果发现,不同退火时间的样品在SiC衍射条纹的外侧都出现了石墨烯的衍射条纹.AFM测试表明,外延石墨烯的厚度随退火时间增加而增大,且样品孔洞减少、表面更加平整.Raman测试表明,外延石墨烯拉曼谱中2D峰和G峰的位置相对高定向热解石墨(HOPG)中2D峰和G峰的位置蓝移,且退火时间增加,峰的蓝移量减小.对样品中碳原子K边NEXAFS谱测量显示,样品中存在sp2杂化的碳原子,退火时间增加使碳原子的1s→π以及1s→σ吸收的强度增大,且1s电子到π态的吸收峰相对HOPG的向高能偏移.     

Electrochemical interfacial capacitance in multilayer graphene sheets: Dependence on number of stacking layers

We engineered the number of stacking layers of multilayer graphene sheets by selective post-treatments. The most probable number of layers of graphene was determined according to specific surface area. The interfacial capacitance of multilayer graphene sheets relates to the number of layers. This result is attributed to the dependence of space charge layer capacitance on the number of layers.     

Facile synthesis and excellent catalytic activity of gold nanoparticles on graphene oxide

For the first time,Au nanoparticles on graphene oxide（GO-AuNPs） were successfully fabricated without applying any additional reductants,just by the redox reaction between AuCl₄^-1 and GO.Their structure was characterized by transmission electron microscopy and X-ray powder diffraction.The results show that flower-like AuNPs were successfully dispersed on GO surface.Importantly,they showed a high catalytic activity for the Suzuki-Miyaura coupling reaction in an aqueous medium.     

纳米金汞核-壳粒子的电化学制备及其光谱性质

在聚乙烯吡啶修饰导电玻璃电极表面进行了金纳米粒子的二维单层结构组装,通过电沉积方法在金粒子表面制备了纳米汞壳层.研究结果表明,汞壳层的形成导致了内部金粒子表面等离子体共振的谱峰红移和强度衰减.吸附于汞壳表面的结晶紫分子因可承受被金核增强的电磁场,而使其拉曼散射得到极大的增强.     

铁酸钴纳米晶的低温合成、谱学表征及磁性

以十六烷基三甲基溴化铵（CTAB）为模板,Fe(NO3)3·9H2O和Co(NO3)2·6H2O为前躯体,NaOH为沉淀剂,低温回流合成了磁性铁酸钴纳米晶。利用X射线衍射、透射电子显微镜、红外光谱、拉曼光谱等测试技术对产品的结构进行了表征,借助振动样品磁强计测定了样品的室温磁性能。结果表明,铁酸钴纳米晶为单相立方尖晶石结构,纳米晶的平均粒径为15-20 nm。铁酸钴纳米晶在室温外加磁场下表现出明显的磁滞现象,饱和比磁化强度MS=36.5 A.m2/kg,矫顽力HC=5.89×104 A/m。     

Impact of graphene on the enhancement of electrochemical and photocatalytic performance of Gd2O3 - Graphene nanocomposites

Gadolinium oxide - Graphene (Gd₂O₃-G) nanocomposites were prepared with different weight ratio of graphene using low temperature solution process. The structural, morphological, electrochemical and photocatalytic properties of the composites were investigated by X-ray diffraction, Raman, FE-SEM, HRTEM, Cyclic voltammetric and photo-degradation analysis. The chemical composition of the composites was studied by elemental mapping analysis using EPMA. The binding states of various elements present in the composites were analyzed by XPS. Cyclic voltammetric studies revealed that the nanocomposite with 5% graphene exhibits the specific capacitance of 26 F g⁻¹, which is higher than that of pure Gd₂O₃ (18 F g⁻¹). The presence of graphene has greatly enhanced the photocatalytic performance of Gd₂O₃G composites as the rate of degradation of MB dye is relatively higher in the composites compared to pure Gd₂O₃. The significant increase in the specific capacitance and rate of degradation of dye suggest that the Gd₂O₃G is a promising material for energy storage and environmental applications.     

Surface-enhanced Raman scattering of single- and few-layer graphene by the deposition of gold nanoparticles

Surface-enhanced Raman scattering (SERS) of graphene on a SiO(2)(300 nm)/Si substrate was investigated by depositing Au nanoparticles using thermal evaporation. This provided a maximum enhancement of 120 times for single-layer graphene at 633 nm excitation. SERS spectra and scan images of single-layer and few-layer graphene were acquired. Single-layer graphene provides much larger SERS enhancement compared to few-layer graphene, while in single-layer graphene the enhancement of the G band was larger than that of the 2D band. Furthermore, the D bands were identified in the SERS spectra; these bands were not observed in a normal Raman spectrum without Au deposition. Appearance of the D band is ascribed to the considerable SERS enhancement and not to an Au deposition-induced defect. Lastly, SERS enhancement of graphene on a transparent glass substrate was compared with that on the SiO(2)(300 nm)/Si substrate to exclude enhancement by multiple reflections between the Si substrate and deposited Au nanoparticles. The contribution of multiple reflections to total enhancement on the SiO(2)(300 nm)/Si substrate was 1.6 times out of average SERS enhancement factor, 71 times.     

Facile synthesis of cobalt oxide/reduced graphene oxide composites for electrochemical capacitor and sensor applications

Reduced graphene oxide sheets decorated with cobalt oxide nanoparticles (Co₃O₄/rGO) were produced using a hydrothermal method without surfactants. Both the reduction of GO and the formation of Co₃O₄ nanoparticles occurred simultaneously under this condition. At the same current density of 0.5 A g⁻¹, the Co₃O₄/rGO nanocomposites exhibited much a higher specific capacitance (545 F g⁻¹) than that of bare Co₃O₄ (100 F g⁻¹). On the other hand, for the detection of H₂O₂, the peak current of Co₃O₄/rGO was 4 times higher than that of Co₃O₄. Moreover, the resulting composite displayed a low detection limit of 0.62 μM and a high sensitivity of 28,500 μA mM⁻¹cm⁻² for the H₂O₂ sensor. These results suggest that the Co₃O₄/rGO nanocomposite is a promising material for both supercapacitor and non-enzymatic H₂O₂ sensor applications.     

溶液相合成卤化石墨烯及其对氧化还原反应的电催化活性(英文)

Metal-free carbon electrocatalyts for the oxygen reduction reaction (ORR) are attractive for their high activity and economic advantages. However, the origin of the activity has never been clearly elucidated in a systematic manner. Halogen group elements are good candidates for elucidating the effect, although it has been a difficult task due to safety issues. In this report, we demonstrate the synthesis of Cl-, Br- and I-doped reduced graphene oxide through two solution phase syntheses. We have evaluated the effectiveness of doping and performed electrochemical measurements of the ORR activity on these halogenated graphene materials. Our results suggest that the high electroneg-ativity of the dopant is not the key factor for high ORR activity; both Br- and I-doped graphene promoted ORR more efficiently than Cl-doped graphene. Furthermore, an unexpected sulfur-doping in acidic conditions suggests that a high level of sulfide can degrade the ORR activity of the graphene material.     

Determination of Graphene Sheets Content in Carbon Materials by Raman Spectroscopy

Graphene layer is a monolayer of graphite. Graphene single layer has confirmed to have a higher electron and hole mobility than silicon and has high heat conduction and special optical properties. And un‐perfect graphene sheets exist in any carbon materials. In our previous result to determine the graphene sheets content in any carbon material can be determined by X‐ray spectrum combination with a peak decomposition method. In this study, we have prepared two serious carbon materials from wood wastes, with and without MnO₂ catalytic pyrolysis processes. Results show that all the G band intensity of all synthesized samples including a commercial graphene powder in Raman spectrum has a proportional relation with the graphene sheets content in these carbon materials.     

Online tracking of the thermal reduction of graphene oxide by two-dimensional correlation infrared spectroscopy

Thermal reduction of graphene oxide (GO) via rapid heating is an environment-friendly and cost-effective method. However, the detailed reduction mechanism remains unclear because of lack of methods for online monitoring of GO thermal reduction. In this study, the thermal reduction of GO (from 20 °C up to 400 °C in argon atmosphere) was successfully monitored online and investigated through temperature-dependent FTIR spectroscopy combined with scaling-MW2D FTIR spectroscopy and generalized 2D correlation analyses. Raman spectroscopy, XPS, and XRD studies were also conducted to characterize the structural changes before and after reduction. SEM and AFM analyses were performed to directly observe the formation of defects in GO after thermal reduction. According to scaling-MW2D results, the thermal reduction of GO was divided into two processes, namely, 35 °C–182 °C (process I) and 182 °C–385 °C (process II). Process I rapidly eliminates oxygen functional groups, and process II gradual removes them. The 2D correlation analysis for each process indicated the sequential order of movements of the oxygen-containing functional groups during thermal reduction. Process I comprised six steps, and process II contained four sequential steps. This work elucidated the complex deoxygenation steps and the mechanism of GO thermal reduction.