Electrical and spectroscopic investigations on the reduction mechanism of graphene oxide

Ultra-large graphene oxide sheets of monolayer thickness were obtained by removing ultrasonication during the conventional oxidation process of graphite. In situ electrical conductivity measurement during the reduction by hydrazine monohydrate vapor and thermal annealing revealed the existence of an onset temperature at which electrical conduction started to occur. Corresponding X-ray photoelectron spectra indicated that an approximately 65% restoration of the sp² network led to the occurrence of electrical conduction. Reduction by ring-opening of epoxide group by hydrazine treatment seemed to restore the sp² network, while thermal annealing left a considerable number of defects in the graphene sheet through the formation of volatile gases.     

Chitosan–graphene oxide nanocomposites: Effect of graphene oxide nanosheets and glycerol plasticizer on thermal and mechanical properties

In this study, graphite oxide (GO) is synthesized from natural graphite flakes by the modified Hummers method. Characterization by Fourier transform infrared, X‐ray photoelectron, Raman and ultraviolet‐visible spectroscopies, X‐ray diffraction, and thermogravimetric analysis is conducted on GO to confirm the oxidation of graphite. Unplasticized and glycerol plasticized chitosan/graphene oxide (CS/GO) nanosheets nanocomposites with different GO loadings are prepared by solution casting. The combined effect of GO and glycerol on structure, thermal and mechanical properties of nanocomposite films is studied. GO nanosheets are well dispersed throughout the CS matrix due to the hydrogen bonding and electrostatic interactions between CS and GO nanosheets. The incorporation of GO within the CS matrix results in a decrease of the crystallinity, an improvement of thermal stability, and a significant enhancement of the stiffness and tensile strength that is emphasized by the glycerol. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45092.     

不同氧化程度氧化石墨烯对羧基丁腈橡胶力学性能的影响:实验和分子模拟

制备了不同氧化程度的氧化石墨烯（GO）,并用以增强羧基丁腈橡胶（XNBR）,通过实验和分子模拟研究了其拉伸性能和结合能。结果表明,m（高锰酸钾）/m（石墨）为3时得到的GO与XNBR的相容性最好,界面相互作用最强,有利于应力传递,对XNBR具有最好的增强效果。     

氧化石墨烯对羰基铁粉吸波性能影响

将氧化石墨烯和羰基铁粉制成复合吸收材料,并作为填料制备了聚硫体系吸波密封剂,对比分析氧化石墨烯的加入对羰基铁粉的电磁参数和垂直反射率影响。研究结果表明:氧化石墨烯加入羰基铁粉后,其电磁参数随频率的变化趋势有较为复杂的影响;垂直反射率的峰逐渐向低频方向移动,同时峰值变高,峰宽变窄。     

Mechanical properties of free-standing graphene oxide

The mechanical properties of free-standing graphene oxide (GO) films were investigated using nanoindentation on a dynamic contact module (DCM) system. The Young's modulus, stiffness, and ultimate strength of thin films were evaluated. Nanoindentation measurements were combined with the DCM to evaluate the mechanical properties of thin films and to predict the crack length and critical energy. Electrophoretically deposited GO film, 50 ~ 60 nm in thickness, was found to have a Young's modulus of 695 ± 53 ~ 697 ± 15 GPa. The critical energy values for 50- and 60-nm-thick films were 0.142 ~ 0.201 and 0.479 ~ 0.596 J/m², respectively. Nanoindentation combined with the DCM can thus be used to obtain the mechanical properties and critical energy of thin films.     

Effect of graphene oxide on the properties of compatibilized polypropylene/ethylene-propylene-rubber blend

In this work, the effect of graphene oxide (GO) and its derivatives on the mechanical, thermal and morphological properties of nanocomposites based on polypropylene/ethylene-propylene rubber (PP/EPR) were investigated. In order to achieve a better dispersion of the nanofiller and to enhance its interaction with the polymer matrix, amine and alcohol grafted polypropylene were used as compatibilizers. These compatibilizers were synthesized by the reaction of polypropylene-grafted anhydride maleic (PP-g-MAH) with 1,12-dodecanediamine and 1,12-dodecanediol, respectively in the presence of dicumyl peroxide (DCP) by melt mixing. The nanocomposites were prepared via melt blending masterbatch process using Brabender mixer. The addition of functionalized GO and compatibilizers improved the tensile strength and Young’s modulus of PP/EPR nanocomposite. While the elongation and Izod impact strength were adversely affected. Furthermore, the TGA analysis showed that the incorporation of GO and compatibilizers improve significantly the thermal stability. SEM micrographs of the fractured surfaces of the nanocomposites revealed a good dispersion of functionalized GO in the polymer matrix.     

对负离子对氧化石墨烯/聚苯胺电磁性能的影响

以过硫酸铵为引发剂,控制掺杂质子浓度为1 mol/L,分别以Cl–、CSA–(樟脑磺酸根)和SO42–为对负离子,通过原位化学氧化聚合法制备得到掺杂态氧化石墨烯/聚苯胺复合材料.采用SEM、FTIR和XRD对复合材料进行形貌和结构表征,采用四探针法、矢量网络分析仪分别测试复合材料的电磁参数,并计算材料的阻抗和反射损耗(...     

氧化石墨烯掺杂对低碳钢表面硅烷涂层性能的影响

利用浸渍法在Q235低碳钢表面制备了氧化石墨烯(GO)掺杂的双?[3?(三乙氧基)硅丙基]四硫化物(BTESPT)硅烷涂层.分别采用扫描电镜、傅里叶变换红外光谱仪、电化学工作站和摩擦磨损试验机研究了氧化石墨烯掺杂对硅烷涂层的表面形貌、相结构、耐蚀性和耐磨性的影响.结果表明:氧化石墨烯掺杂后硅烷涂层表面更加致密,耐蚀性和耐磨性得到提高.     

Wet-spinning assembly of continuous and macroscopic graphene oxide/polyacrylonitrile reinforced composite fibers with enhanced mechanical properties and thermal stability

Polyacrylonitrile (PAN) composite microfibers with different contents of graphene oxide (GO) were fabricated via wet-spinning route in this work. Based on nonsolvent-induced phase separation theory, N,N-dimethyl formamide/water mixture system was employed as coagulation bath, nonsolvent (water) diffused into PAN spinning solution and led to a quick PAN fiber solidification. Nematic liquid crystal state of GO dispersions and GO/PAN spinning solutions were determined via polarized optical microscopy images, and the morphology and structure of the composite fibers were characterized via scanning electron microscope, Transmission electron microscopy, Fourier transform infrared spectra, and X-ray diffraction. 1 wt % GO/PAN composite fibers exhibited outstanding mechanical properties, 40% enhancement in tensile strength and 34% enhancement in Young's modulus compared with pure PAN fiber. The results of dynamic mechanical analysis indicated that the composite fiber with 1 wt % GO performed the best thermal mechanical property with 5.5 GPa and 0.139 in storage modulus and loss tangent, respectively. In addition, thermogravimetric analysis showed that thermal stability of the composite fibers enhanced with the increasing GO contents. GO/PAN composite fibers can be as the candidate of carbon fiber precursor, high performance fibers, and textiles applications. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 46950.     

Effect of high-temperature thermal treatment on the structure and adsorption properties of reduced graphene oxide

We present the study on the structure and adsorption properties of reduced graphene oxide subjected to thermal treatment in temperature range of 1100–2000 °C under flowing argon. The morphology and composition analyses reveal that the defective carbon materials remaining after volatilization of oxygen and hydrogen rearrange into highly ordered hexagonal carbon layers during thermal treatment at 2000 °C. The surface area of the resulting carbon layers increases to a value more than fourfold over that of the starting precursor materials. These results offer useful insights to understand the thermal behavior of the carbonaceous decomposition materials.     

A structural and spectroscopic investigation of reduced graphene oxide under high pressure

The effect of high pressure on reduced graphene oxide (RGO) has been investigated using X-ray diffraction (XRD) and infrared (IR) absorption spectroscopy. Our XRD measurements show two-step reversible compression in the inter-layer spacing of RGO whereas intra-layer ordering exhibits a high pressure behavior similar to that of graphite up to 20 GPa. The line shape analysis of (1 0 0) peak, representing the intra-layer ordering, suggests presence of local out of plane distortions in RGO in the form of puckered regions which progressively straighten out as a function of pressure. IR measurements show reversible changes in spectroscopic features attributed to remnant functional groups in the inter-layer region. These measurements suggest high stability and recovering ability of RGO under pressure cycling.     

The aniline-to-azobenzene oxidation reaction on monolayer graphene or graphene oxide surfaces fabricated by benzoic acid

The oxidation of aniline to azobenzene was conducted in the presence of either monolayer graphene (EG) or graphene-oxide-like surface, such as GOx, under ultra-high vacuum conditions maintaining a 365-nm UV light exposure to enhance the oxidation reaction. The surface-bound products were investigated using micro Raman spectroscopy, high-resolution photoemission spectroscopy, and work function measurements. The oxygen carriers present on the GOx surfaces, but not on the EG surfaces, acted as reaction reagents to facilitate the oxidation reaction from aniline to azobenzene. Increasing the aniline concentration at 300 K confirmed that the exchange ratio from the aniline to the azobenzene was enhanced, as determined by the intensity ratio between the aniline- and azobenzene-induced N 1 s core-level spectra. The work function changed dramatically as the aniline concentration increased, indicating that the aniline on the GOx surface conveyed n-type doping characteristics at a low coverage level. A higher aniline concentration increased the p-type doping character by increasing the azobenzene concentration on the GOx surface. A comparison of the oxidation reactivity of aniline molecules on the EG or GOx surfaces revealed the role of the oxygen carriers on the GOx surfaces in the context of catalytic oxidation.     

Reduction dependent wetting properties of graphene oxide

This study reports contact angle measurements of standard, diol and aromatic solvents on graphene oxide thin films thermally reduced in ultra-high vacuum up to 900 °C. The films were chemically and morphologically characterized using respectively X-ray photoemission spectroscopy and atomic force microscopy. The characterization shows that the wetting occurs in the chemically heterogeneous regime, namely the surface roughness (3 nm) does not influence the wetting properties of the samples. Zisman, Owens–Wendt and Neumann methods have been applied in order to calculate the surface free energy of the thin films showing that the Owens–Wendt method best fit the data trends. The surface free energy varies from 51 mN/m (pristine graphene oxide) to 39 mN/m (900 °C reduced graphene oxide). A correlation between the surface chemical composition, the surface free energy and its polar and dispersive components is reported, giving a rationale to the wetting properties of graphene oxide and reduced graphene oxide.     

Effect of incorporation of graphene oxide and graphene nanoplatelets on mechanical and gas permeability properties of poly(lactic acid) films

Nanocomposite thin films of poly(lactic acid) (PLA) were produced incorporating small amounts (0.2 to 1 wt%) of graphene oxide (GO) and graphene nanoplatelets (GNP). The films were prepared by solvent‐casting. Mechanical properties were evaluated for plasticized (by residual solvent) and unplasticized films. Plasticized nanocomposite films presented yield strength and Young's modulus about 100% higher than those of pristine PLA. For unplasticized films improvements in tensile strength and Young's modulus were about 15 and 85%, respectively. For both film types, a maximum in mechanical performance was identified for about 0.4 wt% loadings of the two filler materials tested. Permeabilities towards oxygen and nitrogen decreased, respectively, three‐ and fourfold in films loaded with both GO or GNP. The glass transition temperature showed maximum increases, in relation to unloaded PLA films, of 5 °C for 0.4 wt% GO and 7 °C for 0.4 wt% GNP, coinciding with the observed maxima in mechanical properties. Copyright © 2012 Society of Chemical Industry     

Co(salen) supported on graphene oxide for oxidation of lignin

Co(salen) was supported on graphene oxide (GO) (Co‐GO) by covalently grafting. Spectroscopy analyses confirmed its successful synthesis. Co‐GO demonstrated a high activity in the cleavage of βO4 linkage in lignin model compounds. The catalyst was also effective in depolymerizing an organosolv lignin polymer. The polymer residues were separated, and extensively analyzed by FTIR and NMR in order to understand the various structural changes of the polymer occurring versus catalyst. In catalytic oxidation, the βO4 ether linkages were cleaved and the side‐chains were oxidized occurring in the polymer. The polymer was thus converted into smaller monomers called degradation products which were detected by GC‐MS. The evolution of the polymer found that Co‐GO exhibited a significant catalytic effect as compared with Co‐NaY, Co‐MCM‐48, Co‐SSZ‐13. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44133.     

Effect of graphene oxide on the solution rheology and the film structure and properties of cellulose carbamate

Highly ordered, homogeneous and reinforced cellulose carbamate (CC)/graphene oxide (GO) composite films were prepared using an easy, aqueous and solution-mixing method. The dynamic rheology measurement showed that the addition of 2 wt.% GO decreased the complex viscosity of CC solution and significantly prolonged the valid spinning time of CC solution. X-ray diffraction characterization revealed that GO promoted the transition of crystalline structure of CC from cellulose I to II, and the addition of 2 wt.% GO improved the orientation and crystallinity of the CC molecules. Scanning electron microscope images indicated that the GO layers were aligned parallel to the surface of the composite films. The incorporation of GO also showed profound effects on the macroscopic properties of the CC film. Compared to the pure CC, the composite showed a 280% increase in Young’s modulus and 180% increase in tensile strength by the addition of 2 wt.% of GO. Moreover, the carbon yields of all the composite films were higher than that of pure CC film.     

Electronic properties and atomic structure of graphene oxide membranes

We have performed a near-edge X-ray absorption fine-structure (NEXAFS) and a transmission electron microscopy (TEM) investigation of freely suspended graphene oxide (GO) sheets. We utilized a photoemission electron microscope to identify GO membranes and to acquire C K and O K absorption spectra. The overall line shape of C K-edge spectra demonstrates that the honeycomb carbon network of graphene is the scaffold of GO. However, the intensity ratio of π^∗ and σ^∗ resonances, and a broad feature at about 20 eV from the edge, indicate the presence of new carbon bonds. The O K-edge spectra show that oxidized regions are made of carbonyl, epoxide, and hydroxyl groups attached to the plane of graphene, while carboxyl groups might also be present at the edges. Further, our study indicates the presence of ordered arrangements of oxygen atoms in GO sheets. Our investigation provides a new and efficient route to study the electronic structure of suspended membranes.     

PET石墨烯复合材料的制备及性能研究

将氧化石墨烯(GO)与精对苯二甲酸(PET)、乙二醇(EG)进行原位聚合,制备了氧化石墨烯/PET(GO/PET)复合材料,研究了氧化石墨烯对PET聚酯的热性能、结晶性能的影响,并制备复合材料纤维,测试了其力学性能.结果表明:GO的加入提高了PET的热稳定性、结晶温度及结晶速率但没有改变PET的成核方式和生长方式.与纯PET相比,加入GO后纤维的拉伸强度降低,断裂伸长率提高,但与低GO含量的PET纤维相比,GO含量较高的PET纤维的拉伸强度更高.     

Effect of nickel oxide synthesis conditions on its physical properties and electrocatalytic oxidation of methanol

Nickel oxide (NiO) was synthesized using several methods and the various physical characteristics observed were correlated to differences in electrocatalytic activity, specifically relating to the oxidation of methanol in alkaline media. Room temperature NaOH-precipitated NiO showed the highest activity and stability towards methanol oxidation in hydroxide (0.005 M KOH) and carbonate (0.1 M Na₂CO₃) media of similar alkalinity. Rapid degradation of NiO electrodes was attributed to microcracking and disintegration associated with the formation of the γ-NiOOH/α-Ni(OH)₂ redox couple, in addition to repeated scans through the oxygen evolution reaction region. Carbonate electrolytes also exhibited average current ranges 3–4 times higher and charge transfer resistances around 85% lower than hydroxide electrolytes. This suggests carbonate may provide a better medium in terms of higher activity and more moderate alkalinity for electrochemical reactions than hydroxide solutions.