Spectroscopic studies of large sheets of graphene oxide and reduced graphene oxide monolayers prepared by Langmuir-Blodgett technique

Graphene oxide (GO) sheets prepared by chemical exfoliation were spread at the air-water interface and transferred to silicon substrates by Langmuir-Blodgett technique as closely spaced monolayers of 20-40 μm size. Hydrazine exposure followed by annealing in vacuum and argon ambient results in the formation of reduced graphene oxide (RGO) monolayers, without significantly affecting the overall morphology of the sheets. The monolayer character of both GO and RGO sheets was ascertained by atomic force microscopy. X-ray photoelectron spectroscopy supported by Fourier transform infrared spectroscopy revealed that the reduction process results in a significant decrease in oxygen functionalities, accompanied by a substantial decrease in the ratio of non-graphitic to graphitic (sp² bonded) carbon in the monolayers from 1.2 to 0.35. Raman spectra of GO and RGO monolayers have shown that during the reduction process, the G-band shifts by 8-12 cm^− 1 and the ratio of the intensities of D-band to G-band, I(D)/I(G) decreases from 1.3 ± 0.3 to 0.8 ± 0.2, which is in tune with the smaller non-graphitic carbon content of RGO monolayers. The significant decrease in I(D)/I(G) has been explained by assuming that substantial order is present in precursor GO monolayers as well as RGO monolayers obtained by solid state reduction.     

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.     

Reduced graphene oxide–nickel oxide composites with high electrochemical capacitive performance

Reduced graphene oxide (RGO)–NiO composites have been fabricated by a simple solvothermal route starting with graphite oxide (GO). The morphology, composition and microstructure of the as-obtained samples are systematically characterized by thermogravimetric (TG) analysis, X-ray diffraction (XRD), and field emission scanning electron microscopy (FESEM). Moreover, the electrochemical performances of composites were evaluated by cyclic voltammogram (CV) and galvanostatic charge–discharge. Interestingly, it was found that the electrochemical performance of the composites could be affected by the mass ratio between RGO and NiO. The composite with the mass ratio up to 79:21 (NiO:RGO) exhibits the highest specific capacitance of 576 F g⁻¹ at 1 A g⁻¹, which is much higher than that of pure NiO (240 F g⁻¹) and pure RGO (98 F g⁻¹). In addition, the cycling measurements showed that RGO–NiO composite exhibited excellent cycling stability with no decay in the available capacity over 1100 cycles. The enhancement in specific capacitance and cycling stability may be attributed to the increased electrode conductivity owing to RGO network, the increased effective interfacial area between NiO and the electrolyte, as well as the contact area between NiO and RGO.     

Nitrogen-doped carbon nanotube arrays grown on graphene substrate

Nitrogen-doped carbon nanotube (N-doped CNT) arrays have been synthesized on graphene substrate by chemical vapor deposition process, in which iron nanoparticles (NPs) assembled on the graphene sheet were generated in situ from the reduction of Fe₃O₄ NPs/reduced graphene oxide (RGO) and were used as catalyst. The morphology and structure of the N-doped CNT arrays were investigated by field emission scanning electron microscope and high-resolution transmission electron microscope. The N-doped CNTs were bamboo-shaped and the density can be controlled by modulating the density of catalyst NPs on RGO sheets. The concentration and incorporation of nitrogen were studied by elemental analysis, X-ray photoelectron spectroscope and Raman analysis, and the results showed that the nitrogen content was around 3 wt.%. Because of the good conductivity of graphene structure, N-doped CNT arrays grown on graphene substrate may be promising candidates as noble metal-free electrodes for oxygen reduction reaction in the future.     

Graphene/thermoplastic polyurethane nanocomposites: Surface modification of graphene through oxidation,polyvinyl pyrrolidone coating and reduction

Herein, oxidation, polyvinyl pyrrolidone (PVP) coating and reduction are used to modify the surface of graphene in thermoplastic polyurethane (TPU)/graphene nanocomposites. It is demonstrated that graphene could be easily dispersed in TPU with PVP absorbed on reduced graphene oxide (RGO) as stabilizer during reduction. In the stress–strain curves for these composites containing GO, PVP coated GO (GO/PVP) and reduced GO/PVP (RGO/PVP) as filler, PVP coating and reduction can largely enhance the stress in low modulus region. It is thought to largely related with enhanced interfacial interaction between filler and matrix and healing of graphene structure during reduction. Consequently, the modulus of TPU/GO/PVP and TPU/RGO/PVP is significantly increased. Meanwhile, an electrical percolation threshold of 0.35 wt.% is obtained for TPU/RGO/PVP. Comparing with the results in literature, the filler surface modification used in this study has created nanocomposites with a good balance between electrical conductivity and mechanical properties.     

Electrochemical actuator based on polypyrrole/sulfonated graphene/graphene tri-layer film

A tri-layer electrochemical actuator was fabricated by the electrodeposition of polypyrrole (PPy) onto a sulfonated graphene (SG)/reduced graphene oxide (RGO) bi-layer film. In this actuator, PPy and RGO were acted as actuation and conductive inert layers, respectively. The SG layer was used to enhance the interfacial interactions. The tri-layer actuator exhibited high and stable actuating performance for over 1000 actuation cycles, and the lifetime of the actuator was tested to be about 5000 cycles. The bending angle of the actuator is larger than 360° and its movement rate was higher than 150° s^− 1 under a driving potential of 1.0 V versus saturated calomel electrode. Furthermore, the low weight density of graphene based supporting layer greatly lowered the energy or charge consuming of the actuator during electrochemical actuation.     

Zn还原氧化石墨烯(RGO)和ZnO/RGO自组装复合材料的电磁响应行为

以天然鳞片石墨为原料制备氧化石墨烯（GO）,通过Zn将其还原为石墨烯（RGO）,且生成的ZnO附着在RGO表面。采用XRD、SEM、FTIR、Raman、TEM和矢量网络分析仪（VNA）研究了不同还原温度对ZnO/RGO复合材料形貌、结构、氧化程度、电磁损耗特性、德拜弛豫模型及电磁响应行为的影响。结果表明:还原温度为50℃时RGO还原后结构更加完整,层间距为0.89 nm时ZnO/RGO复合材料的介电常数和磁导率均较高,在17.15 GHz时反射率达到-41.2 dB,反射损耗小于-10 dB的带宽为3.67 GHz。      

How can graphene reduce the flammability of polymer nanocomposites?

Nanocomposites based on poly(vinyl alcohol) (PVA) and graphene nanosheets have been prepared by polymer solution blending and their flame retardant properties have been evaluated by a cone calorimetry test. It has been shown that there is a strong influence of graphene nanosheets on the fire behaviour of the composites with a significant reduction in peak heat release rate (PHRR) and a much longer time to ignition. Compared to pure PVA, the PHRR of PVA filled with 3 wt.% graphene is reduced by 49%. The flame retardancy of graphene for PVA matrix surpasses that of both Na-MMT and MWNTs with the same addition content. Such a remarkable behaviour might be explained by the forming of a compact, dense and uniform char during combustion.     

功能石墨烯/热塑性聚氨酯复合材料膜的制备及性能

采用双十二烷基二甲基溴化铵(DDAB)插层改性氧化石墨烯(DD-GO),再用抗坏血酸进行还原制得功能石墨烯(DDRGO)。采用溶液成形的方法在涂膜机上制备功能石墨烯(DD-RGO)/热塑性聚氨酯(TPU)复合材料膜,并利用FTIR、XRD、FE-SEM、高阻计、氧气透过仪对DD-RGO/TUP复合材料膜结构和性能进行表征。结果表明:经DDAB改性后的石墨烯能在TPU基体中能以褶皱层状的形式均匀的分散,并提高TPU的热稳定性、阻隔性与抗静电性。当DD-RGO的添加量为2%时,复合材料膜的阻隔性与导电性相对于纯TPU分别提高了50%与7个数量级,阻隔性与抗静电性明显提高。     

In situ thermal reduction of graphene oxide for high electrical conductivity and low percolation threshold in polyamide 6 nanocomposites

Electrically conductive and thermally stable polyamide 6 (PA 6) nanocomposites were prepared through one-step in situ polymerization of ε-caprolactam monomer in the presence of electrically insulating and thermally unstable graphene oxide (GO) nanosheets. These nanocomposites show a low percolation threshold of ∼0.41 vol.% and high electrical conductivity of ∼0.028 S/m with only ∼1.64 vol.% of GO. Thermogravimetric analysis and X-ray photoelectron spectroscopy results of GO before and after thermal treatment at the polymerization temperature indicate that GO was reduced in situ during the polymerization process. X-ray diffraction patterns and scanning electron microscopy observation confirm the exfoliation of the reduced graphene oxide (RGO) in the PA 6 matrix. The low percolation threshold and high electrical conductivity are attributed to the large aspect ratio, high specific surface area and uniform dispersion of the RGO nanosheets in the matrix. In addition, although GO has a poor thermal stability, its PA 6 nanocomposite is thermally stable with a satisfactory thermal stability similar to those of neat PA 6 and PA 6/graphene nanocomposite. Such a one-step in situ polymerization and thermal reduction method shows significant potential for the mass production of electrically conductive polymer/RGO nanocomposites.     

A low-cost method for preliminary separation of reduced graphene oxide nanosheets

Reduced graphene oxide (RGO) nanosheets were produced by chemical reduction of exfoliated graphite oxide. Atomic force microscopy (AFM) images show that the obtained RGO nanosheets vary greatly in lateral-dimensional sizes, ranging from less than 100  100 nm to more than 2000  2000 nm. In order to separate these nanosheets, one simple and low-cost method mainly based on magnetic-stirring and centrifugation treatments was proposed. Preliminary statistical analysis of RGO nanosheets, based on AFM images, shows that the dot-like RGO nanosheets (with lateral dimensions less than 100  100 nm) and leaf-like RGO nanosheets (with lateral dimensions more than 500  500 nm) were effectively separated by this simple method.     

氮掺杂石墨烯的制备及其电催化氧气还原性能

通过改良Hummers法制备氧化石墨(Graphite oxide,GO),采用爆炸辅助还原法将GO还原剥离并原位掺杂得到氮掺杂石墨烯(Nitrogen-doped graphene,N-RGO)。采用TEM、SEM、FI-IR、XPS、XRD及Raman等分析手段对N-RGO的形貌、组成以及结构进行了表征,利用旋转环盘电极技术测试了其电催化氧气还原活性。TEM和SEM结果表明,爆炸条件下GO被很好地剥离开来,得到只有几层厚度的石墨烯;FI-IR及XPS结果表明,GO中大部分含氧官能团被脱除,C/O原子比达到26.2,是目前所得GO还原程度非常高的方法之一,且氮元素成功掺杂进石墨烯晶格中,掺杂氮的原子质量分数约为2.11%;电化学测试结果显示,氧气还原的极限扩散电流由非氮掺杂石墨烯(Reduced graphene oxide,RGO)的0.24mA提高到N-RGO的0.49 mA,尽管爆炸辅助还原得到的RGO对氧气还原也显示出较好的催化活性,但掺杂之后的N-RGO具有更高的催化活性。     

还原氧化石墨烯/天然橡胶-丁腈橡胶复合材料的制备与性能

采用水合肼还原氧化石墨烯（GO）制备了还原氧化石墨烯（RGO）,以RGO作为分散介质加入到天然橡胶（NR）和丁腈橡胶（NBR）基体中,通过乳液共混法制备了RGO/NR-NBR复合材料。采用FTIR、Raman、XRD及SEM等手段表征了RGO的结构和形貌,测试结果表明,水合肼还原GO效果较好,基本除去含氧官能团,同时RGO还保留了GO的片层结构。RGO/NR-NBR复合材料的SEM测试结果显示,纳米尺寸的RGO均匀分散在橡胶基体中,且复合材料的拉伸断面粗糙程度显著增加。RGO/NR-NBR复合材料的硫化性能测试结果表明,随RGO的含量增加,复合材料的交联密度、最大扭矩及扭矩差均增大。RGO/NR-NBR复合材料的力学性能随RGO含量的增加而提高,当RGO含量为3.0%时,材料的拉伸强度、100%定伸强度和邵氏硬度分别提高了65.7%、90.3%和21.1%,断裂伸长率降低了13.1%。     

Structures of thermally and chemically reduced graphene

This study investigated the structures and compositions of two types of graphene (GP) produced by the reduction of graphene oxide (GO): GP_TR, produced by thermal reduction at 1073 K in N₂; and GP_CR, chemically reduced with hyrdazine. GP_TR and GP_CR have a small number of surface oxide groups with the compositions C₁₀₀O_3 ± 1 and C₁₀₀O_6.5 ± 2 and consist of six layers and three layers, respectively. The interlayer spaces are slightly larger than those in typical graphene produced by “top-down” exfoliation from graphite. These structures and compositions are intrinsic properties of graphene produced by the “bottom-up” layer-by-layer stacking process.     

A facile preparation of graphene/reduced graphene oxide/Ni(OH)2 two dimension nanocomposites for high performance supercapacitors

A Ni(OH)₂ composite with good electrochemical performances was prepared by a facile method. Ni(OH)₂ was homogeneously grown on the hydrophilic graphene/graphene oxide (G/GO) nanosheets, which can be prepared in large scale in my lab. Then G/GO/Ni(OH)₂ was reduced by L-Ascorbic acid to obtain G/RGO/Ni(OH)₂. Caused by the synergy effects among the components, the G/RGO/Ni(OH)₂ electrode showed good electrochemical properties. The G/RGO/Ni(OH)₂ electrode possessed a specific capacitance as high as 1510 F g⁻¹ at 2 A g⁻¹ and even 890 F g⁻¹ at 40 A g⁻¹. An asymmetric supercapacitor device consisting of G/RGO/Ni(OH)₂ and reduced graphene oxide (RGO) was installed and displayed a high energy density of 44.9 W h kg⁻¹ at the power energy density of 400.1 W kg⁻¹. It was verified that the G/GO nanosheets are ideal supporting material in supercapacitor.     

石墨烯/低密度聚乙烯复合膜的制备及性能

目的以石墨烯/低密度聚乙烯(LDPE)复合包装材料为研究对象,讨论石墨烯、石墨烯微片对低密度聚乙烯薄膜力学性能、颜色、透光率及透氧率的影响。方法使用熔融共混方法制备不同石墨烯质量分数的石墨烯/LDPE复合材料,检测并比较其性能变化。结果石墨烯以及石墨烯微片的加入,使LDPE薄膜的弹性模量提高了9%~50%,横纵向拉伸强度提高了2%~30%,透光率降低了10%~60%,透氧率提高了10%~15%。结论由于石墨烯比表面积大、刚性高,对LDPE材料的拉伸强度、弹性模量等力学性能有明显改善,同时可提高薄膜透氧率,加深LDPE材料的颜色,降低薄膜透光率。     

Transparent, luminescent, antibacterial and patternable film forming composites of graphene oxide/reduced graphene oxide

Multifunctional graphene oxide/reduced graphene oxide (GO/RGO) composites were prepared through electrostatic interaction using biocompatible ingredients. Different functionalities were added to GO/RGO by anchoring materials such as native lactoferrin (NLf), NLf protected Au clusters (designated as Au@NLf), chitosan (Ch) and combinations thereof. Anchoring of Ch and NLf enhances the antibacterial property of RGO/GO. The addition of Ch to RGO/GO not only helped in forming stable dispersions but also helped in fabricating large (cm(2)) area films through a simple solvent evaporation technique. Functionalities such as photoluminescence were added to Ch-RGO/GO composites by anchoring Au@NLf on it. The composites thus formed showed stable luminescence in presence of various metal ions in the solid state. The composite showed reasonable stability against pH and temperature variations as well. The as-prepared films were transparent and the transparency could be modulated by controlling the concentration of RGO/GO in the composite. The antibacterial property and ability to form stable thin films may provide an opportunity to use such composites for medical and environmental remediation applications as well. Erasable patterns were fabricated on the film by stamping required patterns under compressive pressure. Luminescent patterns can be inscribed on the film and can be erased by simply wetting it. Such films with erasable information may be useful for security applications.     

Synthesis of manganese dioxide/reduced graphene oxide composites with excellent electrocatalytic activity toward reduction of oxygen

MnO₂/reduced graphene oxide(RGO) composites were synthesized by a facile and effective polymer-assisted chemical reduction method. The synthetic MnO₂/RGO composites have a uniform surface distribution and large coverage of MnO₂ nanoparticles onto graphene, which were characterized with scanning electron microscopy, high-resolution transmission electron microscopy, X-ray diffraction and cyclic voltammetry. The synthetic MnO₂/RGO composites were studied with respect to its electrocatalytic activity toward the reduction of oxygen in alkaline media and were found to possess a good electrocatalytic activity toward the four-electron reduction of oxygen.     

石墨烯/纳米银复合材料的制备、微结构及其导电性能

将不同比例的氧化石墨烯(GO)和硝酸银混合,采用水合肼一步还原制备石墨烯/纳米银(RGO/Ag)复合材料。采用UV-vis、XRD、FTIR和SEM对RGO/Ag复合材料结构组成进行表征分析,并结合热流量和结构变化研究其构成和热处理工艺对导电性的影响。结果表明:Ag基本以类似球形与石墨烯(RGO)复合;RGO/Ag复合材料的导电性与其构成有很大关系,只有当GO加入量小于50wt%时,Ag含量的提高和热处理工艺的优化可以明显改善复合材料的导电性,其中,GO加入量为16wt%的RGO/Ag片方阻值可达到8mΩ/□;当GO加入量高于50wt%时,复合材料导电性与RGO接近,受Ag含量的提高和热处理工艺优化的影响较小。     

Biodegradable amylose films reinforced by graphene oxide and polyvinyl alcohol

Graphene oxide/amylose (GO/amylose) composite films with different amounts of graphene oxide (GO), glycerol and polyvinyl alcohol (PVA) were prepared by a solution casting method. The structure, morphologies, and properties of the films were characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction, thermal gravimetric analysis, UV–vis spectroscopy and tensile tests. The results indicated good dispersion of the GO nanosheets in the GO/amylose composite films and consequently a significant improvement in their mechanical properties. The addition of GO increased the tensile strength of the GO/amylose films, significantly. When glycerol was used as a plasticizer, the elongation at break of the films increased. When PVA was also added to the composite films, the films were mechanically strong and flexible. The incorporation of GO also decreased the moisture absorbability and UV transmittance of the films. The stability of the GO/amylose films in acidic and alkaline solutions was also studied and the films had excellent stability in both acidic and alkaline aqueous mediums.