Conductive composites based on chitosan and polyvinylpyrrolidone-stabilized graphene

Highly concentrated dispersions of polyvinylpyrrolidone-stabilized graphene were prepared. Using transmission electron microscopy, it was found that the graphene particles consisted, on average, of one to four layers, with the lateral size of 50–400 nm. From these dispersions, new film composites of chitosan with the filler content up to 4 wt % characteristic of electrical conductivity as high as 1.9 × 10^–2 S/cm were formed.     

Graphene dispersions

Aqueous dispersions of graphene are of interest to afford environmentally safe handing of graphene for coating, composite, and other material applications. The dispersion of graphene in water and some other solvents using surfactants, polymers, and other dispersants is reviewed and results show that nearly completely exfoliated graphene may be obtained at concentrations from 0.001 to 5% by weight in water. The molecular features promoting good dispersion are reviewed. A critical review of optical extinction shows that the visible absorption coefficients of graphene have been reported over the ranges of 12 to 66 cm²/mg at various wavelengths. The practice of energetically activating graphene in various solvents with various stabilizers followed by centrifugation to isolate the “good” dispersion components is fine for producing samples amenable to TEM analysis and quantification, but cannot be expected to drive value added production of products on the kg or higher scale. Such approaches lack practical application and often involve 90–99% wasted graphene. However, alternative approaches omitting centrifugation are yielding dispersions 0.5 to 5% by weight graphene, with higher yields likely in the near future. These dispersions yield effective extinctions of about 49 cm²/mg, in conformity with macroscopic optical analysis of single and few layer graphene.     

P3HT/graphene composites synthesized using In situ GRIM methods

Poly(3‐hexylthiophene)/graphene (P3HT/G) materials are synthesized using an in situ Grignard metathesis approach. The structural properties and spectroscopy of the materials are studied using NMR, FTIR, and UV–vis absorption spectroscopies, wide‐angle X‐ray scattering, atomic force microscopy and cyclic voltammetry. P3HT regioregularities ≥90% are observed in composites with approximate graphene compositions as high as 20% by weight. ¹H and ¹³C NMR spectra of liquid phase dispersions reveal signals that are not observed in pristine P3HT. The intensity of these signals correlates with the graphene content, thereby indicating that the graphene is influencing the polymerization process. Anomalous features in the FTIR spectra of P3HT/G powders are also observed. AFM images of P3HT/G films show morphological differences between P3HT on graphene compared with P3HT domains on the silicon substrates. Cyclic voltammetry reveals a monotonic decrease in the energy of the HOMO and LUMO levels of P3HT with increasing graphene loading. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 60–76     

Highly Concentrated Aqueous Dispersions of Graphene Exfoliated by Sodium Taurodeoxycholate: Dispersion Behavior and Potential Application as a Catalyst Support for the Oxygen‐Reduction Reaction

A high‐yielding exfoliation of graphene at high concentrations in aqueous solutions is critical for both fundamental study and future applications. Herein, we demonstrate the formation of stable aqueous dispersions of pristine graphene by using the surfactant sodium taurodeoxycholate under tip sonication at concentrations of up to 7.1 mg mL^?1. TEM showed that about 8 % of the graphene flakes consisted of monolayers and 82 % of the flakes consisted of less than five layers. The dispersions were stable regardless of freezing (?20 °C) or heat treatment (80 °C) for 24 h. The concentration could be significantly improved to about 12 mg mL^?1 by vacuum‐evaporation of the dispersions at ambient temperature. The as‐prepared graphene dispersions were readily cast into conductive films and were also processed to prepare Pt/graphene nanocomposites that were used as highly active electrocatalysts for the oxygen‐reduction reaction.     

Poly(methyl methacrylate)-Assisted Exfoliation of Graphite and Its Use in Acrylonitrile-Butadiene-Styrene Composites

One of the applications of graphene in which its scalable production is of utmost importance is the development of polymer composites. Among the techniques used to produce graphene flakes, the liquid-phase exfoliation (LPE) of graphite stands out due to its versatility and scalability. However, solvents suitable for the LPE process are generally toxic and have a high boiling point, making the processing challenging. The use of low boiling point solvents could be convenient for the processing, due to the easiness of their removal. In this study, the use of poly(methyl methacrylate) (PMMA) as a stabilizing agent is proposed for the production of graphene flakes in a low boiling point solvent, that is, acetone. The graphene dispersions produced in the mixture acetone-PMMA have higher concentration, +175 %, and contain a higher percentage of few-layer graphene flakes (<5 layers), that is, +60 %, compared to the dispersions prepared in acetone. The as-produced graphene dispersions are used to develop graphene/acrylonitrile-butadiene-styrene composites. The mechanical properties of the pristine polymer are improved, that is, +22 % in the Young's modulus, by adding 0.01 wt. % of graphene flakes. Moreover, a decrease of ≈20 % in the oxygen permeability is obtained by using 0.1 wt. % of graphene flakes filler, compared to the unloaded matrix.     

石墨烯/钴镍双金属氢氧化物复合材料的制备及电化学性能研究

采用微波辐射与高温裂解相结合的二步还原法制备石墨烯。二步还原使氧化石墨被充分还原和剥离,所得到的石墨烯有较好的传导性,其比表面达675.4 m2.g-1。以此石墨烯为原料,水热法合成出石墨烯/钴镍双金属氢氧化物复合材料,并考察了复合材料作为超级电容电极材料的电化学性能。研究发现,褶皱的石墨烯纳米片均匀分散在钴镍双金属氢氧化物中,这改善了钴镍双金属氢氧化物的传导性和结构稳定性。在0.25 A.g-1电流密度下,复合材料的比电容量是800.2 F.g-1。当电流密度增加至10 A.g-1,比电容量为386.5 F.g-1,恒电流充-放电500次后比电容量仍能保持99%以上,这些呈示该复合材料具有优良的电化学性能。     

Efficient and Scalable Production of 2D Material Dispersions using Hexahydroxytriphenylene as a Versatile Exfoliant and Dispersant

Thin‐layer 2D materials have been attracting enormous interest, and various processes have been investigated to obtain these materials efficiently. In view of their practical applications, the most desirable source for the preparation of these thin‐layer materials is the pristine bulk materials with stacked layers, such as pristine graphite. There are many options in terms of conditions for the exfoliation of thin‐layer materials, and these include wet and dry processes, with or without additives, and the kind of solvent. In this context, we found that the versatile exfoliant hexahydroxytriphenylene works efficiently for the exfoliation of typical 2D materials such as graphene, MoS₂, and hexagonal boron nitride (h‐BN) by both wet and dry processes by using sonication and ball milling, respectively, in aqueous and organic solvents. As for graphene, stable dispersions with relatively high concentrations (up to 0.28 mg mL^?1) in water and tetrahydrofuran were obtained from graphite in the presence of hexahydroxytriphenylene by a wet process with the use of bath sonication and by a dry process involving ball milling. Especially, most of the graphite was exfoliated and dispersed as thin‐layer graphene in both aqueous and organic solvents through ball milling, even on a large scale (47–86 % yield). In addition, the exfoliant was easily removed from the precipitated composite by heat treatment without disturbing the graphene structure. Bulk MoS₂ and h‐BN were also exfoliated by both wet and dry processes. Similar to graphene, dispersions of MoS₂ and h‐BN of high concentrations in water and DMF were produced in high yields through ball milling.     

Al3+/graphene composites for electrochemical detection of DNA cleavage

Herein, we present the electrochemical co-deposition of Al3+/graphene composites directly from an aqueous mixture containing graphene oxide (GO) and Al3+. The obtained Al3+/graphene composites with good electrochemical activity were regarded as an appropriate immobilization platform for double-stranded DNA (dsDNA). The nontoxic redox probe xanthurenic acid (XA) was successfully applied to recognize single-stranded DNA and dsDNA. We illustrated that the scission of dsDNA caused by GO combining with some metal ions could be detected by monitoring the electrochemical signals of XA.     

Facile Preparation and Lithium Storage Properties of TiO2@Graphene Composite Electrodes with Low Carbon Content

Over the past decade, TiO₂/graphene composites as electrodes for lithium ion batteries have attracted a great deal of attention for reasons of safety and environmental friendliness. However, most of the TiO₂/graphene electrodes have large graphene content (9–40 %), which is bound to increase the cost of the battery. Logically, reducing the amount of graphene is a necessary part to achieve a green battery. The synthesis of TiO₂ nanosheets under solvothermal conditions without additives is now demonstrated. Through mechanical mixing TiO₂ nanosheets with different amount of reduced graphene (rGO), a series of TiO₂@graphene composites was prepared with low graphene content (rGO content 1, 2, 3, and 5 wt %). When these composites were evaluated as anodes for lithium ion batteries, it was found that TiO₂+3 wt % rGO manifested excellent cycling stability and a high specific capacity (243.7 mAh g^?1 at 1 C; 1 C=167.5 mA g^?1), and demonstrated superior high‐rate discharge/charge capability at 20 C.     

Interlayer-expanded MoS<Subscript>2</Subscript>/graphene composites as anode materials for high-performance lithium-ion batteries

A facile strategy was developed to prepare interlayer-expanded MoS₂/graphene composites through a one-step hydrothermal reaction method. MoS₂ nanosheets with several-layer thickness were observed to uniformly grow on the surface of graphene sheets. And the interlayer spacing of MoS₂ in the composites was determined to expand to 0.95 nm by ammonium ions intercalation. The MoS₂/graphene composites show excellent lithium storage performance as anode materials for Li-ion batteries. Through gathering advantages including expanded interlayers, several-layer thickness, and composited graphene, the composites exhibit reversible capacity of 1030.6 mAh g^?1 at the current density of 100 mA g^?1 and still retain a high specific capacity of 725.7 mAh g^?1 at a higher current density of 1000 mA g^?1 after 50 cycles.     

石墨烯/硫复合正极材料的一步水热法制备与电化学性能

将硫代硫酸钠（Na₂S₂O₃）与氧化石墨烯（GO）的混合溶液,在酸性条件下经过一步水热反应制备还原氧化石墨烯/硫（RGO/S）复合正极材料. 实验探索了水热温度、反应时间、碳硫质量比例对材料的影响. 通过X射线衍射（XRD）、扫描电镜（SEM）、透射电镜（TEM）和恒电流充放电对材料进行分析. 结果表明在180 ℃下,碳硫质量比为3：7时,水热12 h得到的RGO/S复合材料具有优异的循环性能,首次放电比容量为931 mAh·g^-1,50次循环之后其比容量还保持在828.16 mAh·g^-1;RGO/S复合材料的充放电库仑效率在95%以上;同时RGO/S复合材料的倍率性能相比于单质硫有很大提高. 一步水热法能够使硫分子均匀分布在石墨烯片层结构中,同时加强了石墨烯表面基团对硫分子的固定作用.     

High‐Concentration Graphene Dispersions with Minimal Stabilizer: A Scaffold for Enzyme Immobilization for Glucose Oxidation

Modified acrylate polymers are able to effectively exfoliate and stabilize pristine graphene nanosheets in aqueous media. Starting with pre‐exfoliated graphite greatly promotes the exfoliation level. The graphene concentration is significantly increased up to 11 mg mL^?1 by vacuum evaporation of the solvent from the dispersions under ambient temperature. TEM shows that 75 % of the flakes have fewer than five layers with about 18 % of the flakes consisting of monolayers. Importantly, a successive centrifugation and redispersion strategy is developed to enable the formation of dispersions with exceptionally high graphene‐to‐stabilizer ratio. Characterization by high‐resolution transmission electron microscopy, X‐ray photoelectron spectroscopy, X‐ray diffraction, and Raman spectroscopy shows the flakes to be of high quality with very low levels of defects. These dispersions can act as a scaffold for the immobilization of enzymes applied, for example, in glucose oxidation. The electrochemical current density was significantly enhanced to be approximately six times higher than an electrode in the absence of graphene, thus showing potential applications in enzymatic biofuel cells.     

Multi-stage Ordered Mesoporous Carbon-graphene Aerogel-Ni3S2/Co4S3 for Supercapacitor Electrode

Transition metal sulfides have emerged as promising materials in supercapacitor. In this work, we firstly developed an interface-induced superassembly approach to fabricate NiS_x and CoS_x nanoparticles, which based on ordered mesoporous carbon-graphene aerogel composites for supercapacitor electrodes. The obtained multi-component superassembled nanoparticles-carbon matrix composites have controllable 3D porous structure of multi-stage composite. The two-dimensional graphene interlaced to form a 3D framework with large sponge-like pores, and then the graphene surface was loaded with mesoporous carbon with mesoporous pore size and vertical orientation. The composites display high specific capacitance of 958.1 F g⁻¹ at 0.1 A g⁻¹. The capacitance retains about 97.3 % after 3000 charging-discharging cycles at 2 A g⁻¹. These results indicate that the obtained OMC−GA−Ni₃S₂/Co₄S₃ is a promising material for electrochemical capacitors, which providing new technical methods and ideas for the research of new energy and analytical sensor materials in the fields of energy storage, photocatalysis, point-of-care testing devices and other fields.     

One‐pot synthesis of magnetic zeolitic imidazolate framework/grapheme oxide composites for the extraction of neonicotinoid insecticides from environmental water samples

Magnetic zeolitic imidazolate framework 67/graphene oxide composites were synthesized by one‐pot method at room temperature for the first time. Electrostatic interactions between positively charged metal ions and both negatively charged graphene oxide and Fe₃O₄ nanoparticles were expected to chemically stabilize magnetic composites to generate homogeneous magnetic products. The additional amount of graphene oxide and stirring time of graphene oxide, Co²⁺, and Fe₃O₄ solution were investigated. The zeolitic imidazolate framework 67 and Fe₃O₄ nanoparticles were uniformly attached on the surface of graphene oxide. The composites were applied to magnetic solid‐phase extraction of five neonicotinoid insecticides in environmental water samples. The main experimental parameters such as amount of added magnetic composites, extraction pH, ionic strength, and desorption solvent were optimized to increase the capacity of adsorbing neonicotinoid insecticides. The results show limits of detection at signal‐to‐noise ratio of 3 were 0.06–1.0 ng/mL under optimal conditions. All analytes exhibited good linearity with correlation coefficients of higher than 0.9915. The relative standard deviations for five neonicotinoid insecticides in environmental samples ranged from 1.8 to 16.5%, and good recoveries from 83.5 to 117.0% were obtained, indicating that magnetic zeolitic imidazolate framework 67/graphene oxide composites were feasible for analysis of trace analytes in environmental water samples.     

石墨烯/硫酸铅复合材料的制备及其在铅酸电池中的电化学性能

利用简单的浸渍法制备了石墨烯/硫酸铅复合材料,使得硫酸铅可以直接用作铅酸电池负极材料。该复合材料分别以100 mA.g-1、200 mA.g-1和300 mA.g-1电流密度放电时,平均放电比容量分别可达到110、94和69 mAh.g-1,而硫酸铅仅为49、5和0.5 mAh.g-1,显示出复合材料在高倍率充放电下更好的比容量和再接受充电能力。循环伏安测试表明石墨烯的电容效应随扫描速率增大而增强,同时析氢也变得严重,使得复合材料在充放电过程中充电效率比纯硫酸铅低20%。在充放电过程中,石墨烯能够提高硫酸铅1倍以上的放电容量,并将充电电压提高0.1 V。XRD和SEM结果显示硫酸铅均匀分布在石墨烯片层上,没有出现团聚现象。     

An in situ oxidation route to fabricate graphene nanoplate-metal oxide composites

We report our studies on an improved soft chemical route to directly fabricate graphene nanoplate-metal oxide (Ag₂O, Co₃O₄, Cu₂O and ZnO) composites from the in situ oxidation of graphene nanoplates. By virtue of H⁺ from hydrolysis of the metal nitrate aqueous solution and NO₃⁻, only a small amount of functional groups were introduced, acting as anchor sites and consequently forming the graphene nanoplate-metal oxide composites. The main advantages of this approach are that it does not require cumbersome oxidation of graphite in advance and no need to reduce the composites due to the lower oxidation degree. The microstructures of as-obtained metal oxides on graphene nanoplates can be dramatically controlled by changing the reaction parameters, opening up the possibility for processing the optical and electrochemical properties of the graphene-based nanocomposites.     

Nonlinear optical properties of polyvinylcarbazole composites with graphene

The study has focused on polyvinylcarbazole (PVK) composites with graphene. It has been shown that there is a noticeable nonadditive shoulder on the long-wavelength edge of the optical absorption of PVK in these samples, which can be attributed to the formation of a charge-transfer complex between PVK as a donor and graphene as an acceptor. The formation of the complex causes a significant nonlinear optical effect in the PVK/graphene composite. The revealed increase in both the nonlinearity coefficient with increasing laser intensity and the cross section with increasing incident energy density is due to the formation of the graphene^?· radical anion, an additional species contributing to nonlinear absorption, with an increase in the radiation energy density. Nonlinear optical properties of PVK composites with graphene isolated from a solution in tetrachloroethane after 1.5-h centrifugation (sample 1) have been considered. It has been suggested that a significant decrease in optical transmission of laser radiation by the composite T _OA = 0.4 at an energy density at focus of 502 J/cm² is due to the formation of the PVK/graphene charge-transfer complex responsible for the nonadditive shoulder on the long-wavelength optical absorption edge of PVK. During photoexcitation of graphene in the PVK/graphene composites at a laser wavelength of 1064 nm, mobile holes are generated in PVK, indicating the formation of graphene^?· radical anions as a result of charge transfer from PVK to photoexcited graphene. The observed increase in both β with an increase in the laser radiation intensity and the cross section (σ_exc — σ₀) with an increase in the incident energy density may be due to either the contribution of nonlinear transitions (S ₀ → S ₂, S ₀ → S ₁ → S ₂, T ₁ → T ₂) or the formation of the additional species, the graphene-· radical anions, participating in nonlinear absorption by increasing the energy density at the focus (F _foc, J/cm²).     

High thermal conductivity polylactic acid composite for 3D printing: Synergistic effect of graphene and alumina

With the continuous development of the electronics industry, in order to meet the requirements of electronic equipment to reduce the size and increase power consumption, the development of high thermal conductivity materials is crucial. In this study, thermally conductive polylactic acid (PLA) composites were prepared by constructing graphene and alumina (Al₂O₃) hybrid filler network, and it was further successfully used in additive manufacturing. Due to the synergistic effect of Al₂O₃ and graphene, the resulting composite achieved the thermal conductivity of 2.4 Wm^?1 K^?1 with 70 wt% Al₂O₃ and 1 wt% graphene, which are superior to data reported in the literature in the same filler condition. The Al₂O₃ and graphene hybrid filler network reduced the agglomeration of graphene and the thermal contact resistance between the fillers, thereby leading a faster cooling rate. Furthermore, the obtained thermally conductive PLA composite has good thermal stability at a normal temperature. The PLA composite powder obtained by the cryogenic pulverization can be used in the laser sintering additive manufacturing process to prepare a heat conductive material with a complicated shape.     

金红石相TiO2-石墨烯复合材料的制备及其光催化性能

以鳞片石墨为原料, 用改进的Hummers法制备氧化石墨烯(GO), 以异丙醇钛为钛源经一步水热法制备得到金红石相TiO₂-石墨烯复合材料(rGO-TiO₂), 考察了氧化石墨烯用量对复合材料光催化性能的影响. 采用X射线衍射(XRD), 比表面积(BET), 透射电镜(TEM), 扫描电镜(SEM), 拉曼光谱, 紫外-可见(UV-Vis)吸收光谱和荧光光谱(PL)等测试手段对复合材料进行表征. 结果表明: 复合材料中TiO₂为针簇状结构的金红石相, 与石墨烯能够均匀复合; 与纯金红石相TiO₂相比, 复合材料具有较大的比表面积. 研究了该复合材料在紫外光下对罗丹明B 以及可见光下对甲基橙光降解效果. 当氧化石墨烯浓度为0.5 mg·mL^-1时, 制备得到的复合材料rGO-TiO₂具有较好的光催化效果.     

干燥方式对高氯酸铵/石墨烯复合材料的结构和热分解行为的影响

通过溶胶-凝胶法制备了石墨烯水凝胶, 并将其与高氯酸铵(AP)复合, 然后分别采用自然干燥、冷冻干燥和超临界CO₂干燥三种干燥方式制备了AP/石墨烯复合材料, 并通过扫描电镜(SEM)、元素分析、X射线衍射(XRD)、差示扫描量热仪(DSC)和热重-红外联用技术(TG-FTIR)研究了不同干燥方式对其结构和热分解行为的影响. 结果表明, 干燥方式对AP/石墨烯复合材料的形貌具有明显影响, 其中通过超临界CO₂干燥制备的AP/石墨烯复合材料基本能保持与石墨烯气凝胶相似的外观和多孔结构. 通过自然干燥、冷冻干燥和超临界CO₂干燥制备的AP/石墨烯复合材料中AP的质量分数分别为89.97%、92.41%和94.40%, 其中通过超临界CO₂干燥制备的复合材料中AP的粒径尺寸为69 nm. DSC测试结果表明, 石墨烯对AP的热分解过程具有明显的促进作用, 能使AP的低温分解过程大大减弱, 高温分解峰温明显降低. 三种干燥方式相比, 通过超临界CO₂干燥制备的AP/石墨烯复合材料中石墨烯的促进作用最明显. 与纯AP相比, 其高温分解峰温降低了83.7℃, 表观分解热提高到2110 J·g^-1. TG-FTIR分析结果表明, AP/石墨烯复合材料的热分解过程中, AP分解产生的氧化性产物与石墨烯发生了氧化反应, 生成了CO₂.