Preparation and properties of polystyrene nanocomposites with graphite oxide and graphene as flame retardants

In this study, graphite oxides (GOs) with different oxidation degrees and graphene nanosheets were prepared by a modified Hummers method and thermal exfoliation of the prepared GO, respectively. Polystyrene (PS)/GO and PS/graphene nanocomposites were prepared via melt blending. X-ray diffraction results showed that GOs and graphene were exfoliated in the PS composites. It could be observed from the scanning electron microscope images that GOs and graphene were well dispersed throughout the matrix without obvious aggregates. Dynamic mechanical thermal analysis suggested that the storage modulus for the PS/GO1 and PS/graphene nanocomposites was efficiently improved due to the low oxygen content of GO1 and the elimination of the oxygen groups from GO. The flammability of nanocomposites was evaluated by thermal gravimetric analysis and cone calorimetry. The results suggested that both the thermal stability and the reduction in peak heat release rate (PHRR) decreased with the increasing of the oxygen groups in GOs or graphene. The optimal flammability was obtained with the graphene (5 wt%), in which case the reduction in the PHRR is almost 50 % as compared to PS.     

Appropriate conditions for preparing few-layered graphene oxide and reduced graphene oxide

Oxidation time and exfoliated conditions of graphite oxides (GOs) were investigated to prepare few–layer graphene oxide and reduced graphene oxide via a modified Hummers approach. Different oxidative degree of GOs was prepared by changing oxidation time, and the effects of oxidative degree of GOs in different oxidation time were studied by XRD, FT-IR. Afterwards, highly oxidized GOs were used as precursor to prepare graphene oxide and reduced graphene oxide by ultrasonic dispersion method and thermal expansion method. The exfoliated conditions (ultrasonic power and ultrasonic time, thermal exfoliated temperature) were investigated to prepare few-layered graphene oxide and reduced graphene oxide.     

Synthesis of graphene soluble in organic solvents by simultaneous ether-functionalization with octadecane groups and reduction

Octadecane-functionalized graphene (OD-G) soluble in organic solvents was produced by combining the Hummers process for graphite oxidation and a simultaneous ether-functionalization and reduction approach with 1-bromooctadecane in pyridine and dimethylformamide (DMF). The exfoliated OD-Gs were testified to be monolayer sheets by transmission electron microscope (TEM) and atomic force microscopy (AFM). The functionalization with octadecane (OD) groups and the effective deoxygenation of graphene oxide (GO) were confirmed by Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and thermogravimetric analysis (TGA). It is proved that the effective reduction and functionalization of GO could be simultaneously completed during the refluxing process. The functionalization with OD groups can effectively prevent the aggregation of GO during the reduction.     

Preparation and properties of exfoliated graphite modified with iron compounds

Using the anodic oxidation of graphite in Fe(NO₃)3-HNO₃ mixed electrolytes, followed by heat treatment, we obtained exfoliated graphite modified with iron oxides. All of the samples obtained were characterized by X-ray diffraction, M?ssbauer spectroscopy, and scanning electron microscopy. The results demonstrate that the proposed approach allows one to produce exfoliated graphite containing up to 14% Fe in the form of oxides and hydroxides, whose composition depends on the exfoliation temperature.     

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。     

An electrochemical route to graphene oxide

Large-scale graphene oxide (GO) with adjustable resistivity was synthesized from graphite via an electrochemical method using KCl solution as an effective electrolyte. During the exfoliation process, electrostatic force intercalates chloride ions between the expanded graphite layers on the anode. These chloride ions form small gas bubbles between the graphite layers in the electrochemical reaction. It is believed that the gas bubbles expand the gap between graphite sheets and produce a separating force between adjacent graphene layers. This separating force overcomes the Van der Waals force between adjacent sheets and exfoliates graphene layers from the starting graphite. Because the graphene is electrochemically oxidized by chorine during the exfoliation, the exfoliated GO sheets are hydrophilic and easily dispersed in the electrolyte solution. The GO solution prepared by the electrochemical exfoliation can be simply sprayed or spin-coated onto any substrate for device applications. The measured average thicknesses of a monolayer, bilayer, and trilayer exfoliated GO on SiO2 substrate were 1.9, 2.8, and 3.9 nm, respectively. It was observed that the measured resistance of the exfoliated GO sheets increases due to electrochemical oxidation in the solution. This electrochemical approach offers a low-cost and efficient route to the fabrication of graphene based devices.     

磺化石墨烯及其导电炭薄膜的制备与性能

以石墨为原料, 采用Hummers法液相氧化合成了氧化石墨(GO), 通过低温真空剥离预还原、磺化反应、葡萄糖二次还原, 合成了高质量的磺化石墨烯(S-GNS), 有效避免了在此过程中石墨烯大量团聚的现象. 采用傅里叶变换红外(FTIR)光谱、X射线光电子能谱(XPS)、热重分析仪(TG)、X射线衍射(XRD)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)和原子力显微镜(AFM)等分析手段对磺化石墨烯样品进行了表征. 实验结果表明: 对氨基苯磺酸成功地接枝到了石墨烯上, 磺化石墨烯还原彻底, 热稳定性能高; 石墨烯表面平整, 缺陷少; 单层磺化石墨烯厚度约为1.2 nm. 水溶性、分散性实验结果表明: 磺化石墨烯拥有高水溶性和高分散性. BET比表面积及电性能测试表明: 磺化石墨烯的比表面积高达806.4 m²/g, 薄膜材料的导电率为1150 S/m.     

Tailor made exfoliated reduced graphene oxide nanosheets based on oxidative-exfoliation approach

This study presents a versatile and scalable strategy of ‘oxidation controlled exfoliation’ of rGO nanosheets synthesized from both Hummers and modified Hummers method. A co-relation between degree of oxidation of graphite oxide (GO) sheets and exfoliation of resulting synthesized rGO nanosheets has been successfully developed which in turn reflects in various properties of rGO sheets. The extent of exfoliation of rGO sheets has been well analyzed by XRD, SEM, BET and TEM techniques. Moreover, the quantitative analysis of degree of oxidation of GO has been estimated from FTIR spectra using quotient law method. The variations in number of rGO layers, defect density and sp² domain size have been investigated in detail by Raman spectroscopic technique. Both qualitative-quantitative analysis of rGO nanosheets have been discussed from their SAED pattern and HR-TEM images. The optical characterization of GO and corresponding rGO nanosheets has been studied in detail by UV- Vis spectroscopic technique.     

氧化石墨烯还原制备石墨烯的方法研究

以天然鳞片石墨为原料,对Hummers法制备的氧化石墨烯,分别采用氢碘酸、葡萄糖、乙二胺、氢氧化钠进行化学还原,同时对比用快速热处理制备石墨烯。利用傅立叶红外光谱（FT—IR）、拉曼光谱（Raman）、扫描电子显微镜（SEM）对所得产物进行了比较分析。结果表明：对Hummers法制备的氧化石墨烯还原,葡萄糖的还原效果比较好;通过热处理可有效地将氧化石墨烯的含氧官能团还原,是一种高效、可行的方法。     

Influence of graphene oxide with different degrees of oxidation on the conductivity of graphene/poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) composites

A modified Hummers method was used to synthesize graphene oxide (GO) with different degrees of oxidation. Single-factor and orthogonal experiments were designed to analyze the influence of the oxidant dose on the properties of the GO. The GO series were characterized by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, elemental analysis, and zeta potential measurements. We synthesized RGO/PEDOT:PSS composites by an in situ polymerization with the GO. Through analysis of the specific conductance of the composites, we determined the optimum conditions for forming RGO/PEDOT:PSS which can improve the specific conductance to 114.06 S/cm. Thus, by changing the oxidation degree of GO we were able to improve the conductivity of RGO/PEDOT:PSS composites.     

碳纤维-氧化石墨烯/环氧树脂复合材料的制备及表征

采用改进的Hummers法制备了五种具有不同氧化程度的氧化石墨烯（GO）。借助元素分析、X射线光电子能谱及FTIR红外光谱测试对所制备GO的组成及结构衍变进行了表征。利用光学显微镜对不同GO在固化剂异佛尔酮二胺（IPDA）中的分散状态进行观察,并将分散效果最佳的GO试样用于改性碳纤维/环氧树脂（CF/EP）复合材料。结果表明,随着氧化剂用量及反应时间的增加,GO的氧化程度也随之增加。在氧化程度较低时,GO表面官能团主要以羰基、羧基和酚羟基为主。随着氧化程度的不断提高,GO表面官能团主要为醚、环氧和醇羟基结构。GO在IPDA中的分散状态与其氧化程度密切相关,氧化程度最低和最高的GO均出现明显的聚集现象。另外,GO表面在分散过程中可被IPDA化学改性。在EP基体中加入分散效果最佳的GO（0.2wt%）后,与CF/EP复合材料相比,CF-GO/EP复合材料的弯曲强度、层间剪切强度和Ⅱ型层间断裂韧性分别提高了14%、17%和14%。     

氧化程度对氧化石墨改性环氧树脂涂层摩擦学性能的影响

通过改变H2SO4／KMnO4氧化体系,制备出几种不同氧化程度的氧化石墨,分别对环氧树脂涂层进行填充耐磨改性。通过红外光谱和扫描电镜分析、电性能测试及摩擦磨损性能试验,研究硫酸用量、氧化石墨电阻与氧化程度三者之间的关系,考察氧化程度对氧化石墨结构及其填充改性环氧树脂耐磨涂层摩擦学性能的影响。结果表明：硫酸用量的增加引起氧化石墨电阻和氧化程度非线性增大,同时氧化石墨层状结构剥离成氧化石墨片的程度增加。氧化程度在95％以上的氧化石墨已失去固体润滑特性,导致填充改性环氧涂层摩擦性能下降,磨损增加,氧化程度约85％的氧化石墨填充改性涂层的综合性能最佳。     

Gas permeability of graphite foil modified with iron,cobalt, and nickel oxides

Graphite foils containing iron(III), cobalt(II), and nickel(II) oxides have been prepared via the impregnation of oxidized graphite in aqueous FeCl₃, Co(NO₃)₂, and Ni(NO₃)₂ solutions, followed by exfoliation via thermal shock and pressing of the resultant exfoliated graphite. The materials thus prepared have been characterized by X-ray diffraction, scanning electron microscopy, and energy dispersive X-ray spectroscopy. We have studied the gas transport properties of the modified graphite foil samples and observed a considerable increase in the nitrogen and hydrogen permeabilities of the metal oxide-modified graphite foils relative to the unmodified graphite foil. The thermal properties of the samples have been studied by thermogravimetry and differential scanning calorimetry. The results demonstrate that their oxidation onset temperature reaches 570°C.     

硫氮共掺杂石墨烯修饰电极的制备及电化学性能研究

以天然鳞片石墨为原料,采用改进的Hummers法制备了氧化石墨(GO),以GO和硫氰酸铵为前驱体,采用一步水热法制备了硫氮共掺杂石墨烯(SNG)。X射线衍射、扫描电子显微镜和拉曼光谱分析结果显示,硫和氮成功掺入石墨烯晶格中,SNG表面褶皱明显且形成了三维孔道结构。通过交流阻抗、循环伏安法和差分脉冲伏安法考察了对苯二酚(HQ)、邻苯二酚(CC)和间苯二酚(RC)在修饰玻碳电极(SNG-180/GCE)上的电化学行为。结果表明:硫氮共掺杂能有效改善石墨烯的电化学性能,修饰电极实现了对HQ、CC和RC的同时检测,线性范围在5.5~43.06μmol/L和90.91~245.28μmol/L之间,检出限为1.83μmol/L(信噪比为3)。     

Preparation and tribological properties of graphene oxide/nitrile rubber nanocomposites

Graphene oxide (GO)/nitrile rubber (NBR) nanocomposites with various contents of GO were prepared by a solution-mixing method,in this study. The GO sheets were exfoliated from natural fake graphite by an improved Hummers method and could be further dispersed homogeneously in NBR matrix. The thickness and size of the GO sheets were observed by atomic force microscopy and transmission electron microscopy. The tribological properties of the GO/NBR nanocomposites were evaluated on a ring-block MRH-3 wear tester under dry sliding and water-lubricated conditions. The worn surface morphologies of the GO/NBR nanocomposites were observed by a scanning electron microscopy. It was found that under dry sliding, both the friction coefficient (COF) and specific wear rate of the nanocomposites decreased dramatically at first, then increased with increasing GO contents, while under water-lubricated condition, both the COF and specific wear rate of the nanocomposites decreased with increasing GO contents. Finally, the friction and wear mechanisms of the GO/NBR nanocomposites were tentatively proposed.     

Morphological and optoelectronic characteristics of nanocomposites comprising graphene nanosheets and poly(3-hexylthiophene)

P3HT/graphene nanocomposite was prepared via in-situ reduction of exfoliated graphite oxide in the P3HT polymer matrix, where the exfoliated graphite oxide was formed beforehand via the oxidation of graphite via the Hummers method. The oxidation reaction not only imparts functional groups, such as C=O, C-OH, and C-O-C, to graphite but also causes exfoliation of the resulting graphite oxide. The functional groups render graphite oxide an additional, lower thermal degradation temperature (T(d)) and the exfoliation shifts the XRD pattern towards a much smaller angle. The oxidation of graphite into graphite oxide creates a pleated flaking morphology for graphite oxide as opposed to that of graphite. UV/Vis and photoluminescence (PL) spectra of P3HT/graphene nanocomposite indicate that the existence of graphene does not alter the UV/Vis and PL excitation characteristics of P3HT, and the P3HT/graphene composite has higher electron mobility, a smaller band gap and higher conductivity than the pristine P3HT.     

Size-specified graphene oxide sheets: ultrasonication assisted preparation and characterization

The preparation of graphene oxide (GO) sheets with specified size was developed by simply controlling the time of ultrasonication to the large-size GO (LGO) sheets. The LGO sheets were synthesized by choosing large parent graphite, mild oxidation condition and a two-step centrifugation. The different-sized GO samples prepared under different ultrasonication times, are characterized by Scanning electron microscopy, X-ray photoelectron spectroscopy, Ultraviolet–visible spectroscopy, and X-ray diffraction. It is found that the size of the GO sheets, which has a Gaussian distribution, decreases from 231 to 17 μm² as the ultrasonication time increases. Moreover, the ultrasonication not only can exfoliate and break GO sheets, but also increase the oxidation degree of GO sheets, especially when the GO sheets have a weak oxidation degree. It is reasonable to believe that the size of GO sheets is closely correlated to the C–O content, which enables the size of GO sheets to be controlled. Our work demonstrates that ultrasonication is an important method to control the size and the oxidation degree of GO sheets, to a certain extent.     

Study on preparation and performance of Ru-Fe/GO catalyst for sodium borohydride alcoholysis to produce hydrogen

Abstract

Ru-Fe bimetallic alloy nanoparticle catalyst (Ru-Fe/GO) was prepared by chemical reduction method on graphene oxide prepared using Hummers modified method. The structure and morphology of both GO and Ru-Fe/GO were analyzed using X-ray diffraction (XRD), Transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS, Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS).The effect of catalyst components on hydrogen generation rate for NaBH₄ methanolysis was investigated. When Ru:Fe is 6:1, the catalytic activity is the highest, and the average rate is about 473?mL·min^?1·g^?1. The effect of temperature, Sodium hydroxide concentration, and sodium borohydride concentration on reaction rate is also discussed, and the activation energy for the methanolysis of sodium borohydride is 59.33?kJ·mol^?1 based on the data.     

氧化还原法制备石墨烯及其表征

采用改进的Hummers法氧化处理石墨粉制得氧化石墨,利用超声波作用将氧化石墨剥离,得到均匀分散的氧化石墨烯胶状悬浮液,然后在水合肼的还原作用下得到石墨烯。采用SEM、XRD以及Raman光谱对样品进行了形貌、结构以及谱学的表征分析。考察了还原过程中温度对还原效果的影响,以及中性条件下、碱性条件下水合肼用量对还原效果的影响。     

In situ thermal preparation of polyimide nanocomposite films containing functionalized graphene sheets

Graphene oxides (GO) were exfoliated in N,N-dimethylformamide by simple sonication treatment of the as-prepared high quality graphite oxides. By high-speed mixing of the pristine poly(amic acid) (PAA) solution with graphene oxide suspension, PAA solutions containing uniformly dispersed GO can be obtained. Polyimide (PI) nanocomposite films with different loadings of functionalized graphene sheets (FGS) can be prepared by in situ partial reduction and imidization of the as-prepared GO/PAA composites. Transmission electron microscopy observations showed that the FGS were well exfoliated and uniformly dispersed in the PI matrix. It is interesting to find that the FGS were highly aligned along the surface direction for the nanocomposite film with 2 wt % FGS. Tensile tests indicated that the mechanical properties of polyimide were significantly enhanced by the incorporation of FGS, due to the fine dispersion of high specific surface area of functionalized graphene nanosheets and the good adhesion and interlocking between the FGS and the matrix.