Dispersion Of Graphite Oxide Research Articles

The influence of metal ions on aqueous dispersions of graphite oxide

ABSTRACT The residual metallic impurities in the graphite oxide (GO) dominate their properties and have a negative influence on the potential applications. The swelling of the GO suspensions is mainly affected by electrostatic forces and special interactions between water molecules, metal ions and hydrophilic groups. Bivalent and trivalent cations give rise to ionic crosslinking of the charged network within the particles. The CaCl2 solution has the best purification effect. A new purification method is proposed in the purification process, the origin metal ions in GO suspensions are replaced by homogeneous metal ions first, and GO suspensions are desalted by electrodialysis device. Free ionic calcium is removed by electrodialysis, and only the calcium that interact with GO particles is remained. The content of fixed calcium is 0.0049 g/g (nearly clear) after washing with 1.5 mmol/L CaCl2 solution and electrodialyzing for 20 min. The new method improves the purification efficiency and save energy.

A Novel Cryogenic Adhesive Retaining Fluidity at Dry-Ice Temperature for Low-Temperature Scanning Electron Microscopy.

Scanning electron microscopy operated at cryogenic temperature (cryo-SEM) is a powerful tool for investigating surface and cross-sectional nanostructures of water-containing samples. Typically, cryo-SEM samples are frozen just before observation in specific metal carriers. However, pre-frozen samples are also of interest, such as frozen food and freeze-stored animal samples. In such cases, sample mounting with a defined orientation is required, but there has been a lack of ideal conductive adhesives that can be used without increasing the sample temperature. Here, we developed a mixture of graphite oxide and 1,3-butanediol as an adhesive, capable of gluing samples at dry-ice temperature and is frozen below that temperature. Dispersion of graphite oxide increased the conductivity and reduced the charge-up contrast. Acquisition of energy-dispersive X-ray spectrum, cross-sectional ion milling, and high-resolution imaging were successfully achieved using the adhesive. We tested and confirmed the usefulness of this new adhesive by applying it to cryo-SEM surface imaging of diatomite, freeze-fractured cross-sectional imaging of chicken liver, and ion milling cross-sectional imaging of a deep-sea snail. The new adhesive is not only useful for food science and field-preserved biological samples but also potentially applicable to wider fields such as archaeological and biological samples preserved under permafrost.

Study the Effects of Carbon Nanotubes and Graphene Oxide Combinations on the Mechanical Properties and Flame Retardance of Epoxy Nanocomposites

Carbon-based fillers have attracted a lot of interest in polymer composites because of their ability to alter beneficial properties at low filler concentrations, good surface bonding with polymers, availability in different forms, etc. Carbon-based materials (such as fullerene, CNTs, graphene, and graphite) have been studied as fillers with enhanced fire resistance to epoxy resins. In order to reduce the flammability and improve the thermal stability of epoxy resin-based nanocomposite materials, which can be achieved by a simultaneous combination of graphene oxide and multiwall carbon nanotubes, the graphite oxide (GO) epoxy nanomaterial was developed by 1% wt.% GO combined with 0.02 wand 0.04 wt.% MWCNT. The homogeneous dispersion of GO and MWCNTs in epoxy resins is supported by ultrasonic vibrations. The results showed that when nanocomposite materials were present at the same time MWCNTs and GO, their mechanical properties and fire resistance were significantly improved. Nanomaterials are characterized by FT-IR spectroscopy and SEM imaging, mechanical strength, and flame retardant properties (LOI, UL94).

Polypyrrole nanospheres@graphene aerogel with high specific surface area, compressibility, and proper water wettability prepared in dimethylformamide-dependent environment

A polar functionalization modification is put forward to prepare polypyrrole nanospheres@graphene aerogel (PPys@GA) with high specific surface area, compressibility, and proper water wettability. Polarity of mixed solutions is regulated by controlling the volume ratio of H2O to N,N-dimethylformamide (DMF) to realize better dispersion of graphite oxide (GO), while PPys prepared by weak oxidant (FeCl2/H2O2) own excellent water wettability and can be easily adsorbed on GO sheets to restrain the aggregation of graphene sheets during the reduction self-assembly process more efficiently than PPys synthesized using strong oxidants. The finally resultant PPys@GA enjoys the advantages of high specific surface area (686 m2 g−1), ultralow density (7.8 mg cm−3), high Young's modulus (45.33 kPa) as well as proper wettability (a contact angle of 86°). And such excellent comprehensive properties for PPys@GA outperform many of their counterparts, which qualifies PPys@GA acting as a promising candidate for extensive applications such as adsorption, catalysis, sensors and energy storage materials.

Microstructure evolution of sandwich graphite oxide/interlayer-embedded Au nanoparticles induced from γ-rays for carcinoembryonic antigen biosensor

With the capability of inducing small particle sizes of supported metal in graphite oxide (GO), the γ-ray irradiation method applied for preparing graphite oxide-gold (GO-Au) nanocomposites as electrochemical immunosensors has attracted specific attention recently. To study the accurate factors influencing the precise morphology and final performance of the prepared composites in the γ-irradiation system, we proposed a facile method to investigate the evolution of the GO structure, size and dispersion of Au nanoparticles (AuNPs) produced with the addition of isopropyl alcohol to the system. The GO-Au nanocomposites were characterized by Fourier transform infrared spectroscopy, x-ray diffraction spectra, Raman spectra, x-ray photoelectron spectroscopy and high resolution transmission electron microscopy. These nanocomposites with sandwich morphology exhibited an excellent immunosensor performance with a low detection limit of 15.8 pg ml−1 (S/N = 3) and a wide linear range from 1 to 40 ng ml−1 for detecting carcinoembryonic antigens. The enhanced biosensing performance is attributed to the synergistic effect of γ-irradiation and the precise structure of GO, which endows the smaller size and more uniform distribution of AuNPs on the GO as well as the good signal amplification capability. Furthermore, adopting the γ-irradiation method and use of GO as a precursor is propitious for application in large-scale production because of its high-efficiency and high-yielding characteristics.

Synthesis of graphene on Ni foam with enhanced capacitive performance by embedding PS spacers

ABSTRACTReduced graphene oxide (rGO) has attracted great attention as a promising electrode material for supercapacitors. Herein, polystyrene (PS) colloidal microsphere was used as spacers embedded in the interlayer of graphite oxide (GO) sheets when mixed with GO dispersion. The resulting rGO/PS on Ni foam was prepared using the above-mentioned GO/PS mixed dispersion and vitamin C as reducing agent. To what extent do different volume ratios of GO and PS have effect on the electrochemical performance of as-prepared rGO materials is of great interest to us. As a results, the rGO/PS achieved the highest specific capacitance of 140.4 F g−1, given that the specific capacitance of pure rGO was prepared using pure GO dispersion at the absence of PS particles is only 122.5 F g−1. Therefore, the specific capacitance of rGO can be increased a lot in this way of using GO/PS mixed dispersion.

Engineering Novel Fiber Structures As Wearable Supercapacitors

Recently, fiber/yarn-based energy-storage systems have attracted enormous attention due to their remarkable promises in smart textiles and high-tech sportswear etc., mainly as more pliable energy-storage units being truly “wearable”. Scalable, inexpensive manufacturing processes that produce yarns capable of storing energy are required for new breakthroughs within the wearable electronics sector. For example, US Army is looking for the manufacturing processes capable of producing kilometers of energy-storage yarns that retain desirable mechanical attributes and can be knitted or woven into wearable fabrics. However, so far such processes are still missing. Current technologies include modified textile yarns, composite yarns containing metal wires, polymers, carbon nanotubes (CNTs), metal oxides, and conductive carbon yarns etc. However, several issues exist in current systems, including the biosafety of CNTs, the weight and corrosion of metal wires, and long-term stability of conductive polymers. These issues need to be addressed before they can be employed for practical use. Here we introduce a unique process of making graphitic yarns (yarns made of graphitic carbon flakes) that has attracted enormous attention internationally. Yarns made of graphite flakes are lighter and more corrosion-resistive than metal wires, and more stable in electrical conductivity than polymers. More importantly, graphite flakes are generally considered to be biofriendly, since they have been used as the major component in pencils for decades. Furthermore, the process of making graphite fibers has several advantages: 1) large-scale availability of the wet-spinning dope, which is graphite oxide dispersions in water; 2) fiber/yarn precursors labile for various chemical/physical modifications; 3) graphite used as the major precursor, which is low cost and abundant in nature; 4) several prototypes have been demonstrated. This talk will introduce our recent research on process engineering and chemical modification of the detailed yarn structures for high energy density and mechanical flexibility.

In Situ Synthesis of Ultrahigh Molecular Weight Polyethylene/Graphene Oxide Nanocomposite Using the Immobilized Single-site Catalyst

ABSTRACTWe address the immobilization of single-site catalyst on the graphite oxide (GO) surface using methylaluminoxane. Ethylene polymerization was performed using the immobilized catalyst and the nanocomposite of ultrahigh molecular weight polyethylene (UHMWPE)/GO with less entanglement density was obtained. It was observed that the drawability, mechanical and thermal properties of the produced polymer significantly are affected by the anchoring of polymer chains to the GO nanosheets. The orientation and location of crystalline lamellae and nanosheets were verified by microscopic techniques. Besides, X-ray analysis demonstrated the dispersion of GO within the UHMWPE phase and crystallinity of UHMWPE/GO nanocomposites enhanced during drawing process.

Direct laser scribed graphene/PVDF-HFP composite electrodes with improved mechanical water wear and their electrochemistry

As a recent addition to carbon nanomaterials, graphene has been widely investigated in sensing and energy applications due of its specific two-dimensional nanostructure and attractive intrinsic properties. Laser scribing of graphite oxide (GO) is a facile and cost-effective technology for fabricating patterned reduced graphene oxide electronics in a single-step. However, if the laser scribing does not occur through all of the layers of the graphite oxide, the existence of water-soluble graphite oxide underneath the laser scribed graphene (LSG) may result in an unexpected low-stability of the produced electronic elements in aqueous media. This study investigates the electrochemical performance and mechanical stability of LSG films that contained various amounts of poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) as a binder, blended into the GO dispersion. The laser scribed composite graphene electrodes not only showed improved water mechanical wear resistance, but were largely unaffected in terms of electrochemical behaviour when compared with the binder-free LSG. The findings are significant in terms of the development of robust bioelectronics, to be employed in aqueous environments, based on the simple methodology of laser scribing of GO.

Preparation and characterization of reduced graphene oxide using ascorbic acid and sodium citrate as binary reductant

ABSTRACTIn this article, we successfully prepared transparent and gauze-like reduced graphene oxide (RGO) film with the thickness of only 1.32 nm using modified Hummers method and binary reductant consisting of ascorbic acid and sodium citrate. SEM, TEM, AFM, XRD, UV-Vis, and FTIR results all convincingly demonstrated that the reduction of graphite oxide using binary reductant is a feasible method to prepare RGO. In addition, the results also revealed that extending the oxidation time and increasing the ultrasonic oscillation reasonably might improve the oxidation degree of the graphite oxide, the ratio of the D-band Raman intensity to that of the G band (ID/IG) reached up to 1.244 in the as-obtained graphite oxide. Moreover, sodium citrate not only increased the reducibility of binary reduction system but also improved the dispersion of graphite oxide. Furthermore, reasonable annealing treatment could reduce the defects of RGO. It is a potential route to prepare RGO films and increase practical applications in large-scale production of graphene.

Optimization of operating conditions in the purification of graphite oxide dispersions

In the graphite oxide (GO) suspension purification process, some metallic impurities in GO cannot be separated. The residual metallic impurities dominate graphite oxide properties and have a negative influence on applications. Therefore, the removal of metallic impurities from graphite oxide has been brought into focus now. Single factor experiments and orthogonal experiments are used to get the optimal purification condition. The results show that purification agent, temperature, stirring intensity and contact time affect the purification degree, and the purification agent is the most important element for the purification efficiency. The optimal purification condition is 10% hydrochloric acid (H10), 20 °C, 0 rpm and 60 min. Besides, the theoretical stage is calculated by the mass conservation equation and distribution balance equation and the minimum stage is 3 under the optimal purification condition.

Effect of Graphite Oxide Dispersion Evaluated with Multifractal on Mechanical Properties and Thermal Stability of Poly(3hydroxybutyrate‐co‐4hydroxybutyrate)/Graphite Oxide Biocomposites

ABSTRACTPoly(3hydroxybutyrate‐co‐4hydroxybutyrate) [P(3HB‐co‐4HB)]/graphite oxide (GO) composites were fabricated using a solution mixing method. The GO structures in the composites were analyzed by using transmission electron microscopy, Raman spectroscopy, and X‐ray diffraction. The fracture morphology of the samples was evaluated by the multifractal, and the effect of GO dispersion on the mechanical properties and the thermal stability were discussed for the P(3HB‐co‐4HB) and the composites. It was found that the interlayer spacing of the GO increased due to the intercalation of the polymer into the GO platelets. As the GO content increased, the relative multifractal spectrum increased, but the mechanical properties declined for the composites, indicating that the filler agglomeration effect overcame the reinforcement benefits for the high loadings of the GO. Moreover, both good dispersion and high content of the GO platelets increased the thermal stability of the composites. Therefore, the relative multifractal spectrum width of the fracture morphology was related to the mechanical properties and the thermal stability of the composites.

Desalination of graphite oxide by electrodialysis

Graphite oxide (GO) has got more and more attention for its excellent performance. However, the desalination of GO dispersions is a challenge because of its easy swelling and electronegativity. A new electrodialysis (ED) system was developed specially by adding an interception medium (IM), to solve the membrane fouling of conventional ED system and achieve efficient desalination. The salt removal rate and efficiency were achieved about 85% and 88%, respectively, for GO by this designed ED system under the optimum conditions. The results showed that the designed ED system was more suitable for the desalination of GO dispersions, which intercepted charged particles and ensured the continuous work of anion exchange membrane (AEM). These results provide important technical basis for a large-scale procedure of GO and the desalination of charged colloid dispersions.

Effect of hydrothermal reaction time and alkaline conditions on the electrochemical properties of reduced graphene oxide

Reduced graphene oxide sheets (rGO) were prepared by hydrothermal treatment of aqueous dispersions of graphite oxide (GtO) applied for short (4h) and prolonged reaction times (19–24h). The effect of process duration as well as the alkaline conditions (pH ∼10) by addition of K2CO3 on the quality characteristics of the produced rGO materials was investigated. Both reduction and exfoliation occurred during this process as it was evidenced by FTIR and XRD data. SEM, TEM and HRTEM microscopy displayed highly exfoliated rGO materials. XPS verified that the re-establishment of the conjugated graphene network is more extensive for prolonged times of hydrothermal processing in accordance to Raman spectroscopy measurements. The sample produced under alkaline conditions bore fewer defects and almost 5 times higher BET surface area (∼181m2/g) than the sample with no pH adjustment (∼34m2/g) for the same hydrothermal reaction time (19h), attributed to the developed microporosity. The specific capacitance of this material estimated by electrochemical impedance using three-electrode cell and KCl aqueous solution as an electrolyte was ∼400–500F/g. When EDLC capacitors were fabricated from rGO materials the electrochemical testing in organic electrolyte i.e. TEABF4 in PC, revealed that the shortest hydrothermal reaction time (4h) was more efficient resulting in capacitance around 60F/g.

Rheological Behavior of High Concentrated Dispersions of Graphite Oxide

The rheological properties of graphite oxide (GO) of high concentrations were studied, which is important for pumping and translating design. Steady test indicated GO displayed shear thinning behaviors at low shear rates. The viscosity and particle increased quickly above certain shear rates. The Herschel–Bulkley model represented flow behavior accurately. Correlations between solid content, temperature, and viscosity were expressed by an exponential equation and a modified Arrhenius type equation, respectively. The dynamic test indicated viscoelasticity of GO decreased remarkably at lower concentrations. Under shearing, network structure of GO broke down gradually, and viscosity decreased with time, causing flow acceleration.

Polyimide nanocomposites with novel functionalized‐graphene sheet: thermal property, morphology, gas permeation, and conductivity

4‐Amino‐N‐hexadecylbenzamide‐graphene sheets (AHB‐GSs), used in the preparation of polyimide (PI) nanocomposite films, were synthesized by mixing a dispersion of graphite oxide with a solution of the ammonium salt of AHB. The atomic force microscopy image of the AHB‐GSs on mica and a profile plot revealed the average sheet thickness to be ~3.21 nm. PI films were prepared by reacting 4,4'‐biphthalic anhydride and bis(4‐aminophenyl) sulfide. PI nanocomposite films containing different amounts of AHB‐GS (0–10 wt%) were compared for their morphologies, thermal properties, gas permeation, and electrical and thermal conductivities. The graphenes, for the most part, were well dispersed in the polymer matrix despite some agglomeration. However, micrometer‐scale particles were not detected. The average thickness of the particles was less than 10 nm, as revealed from the transmission electron microscope images. Only a small amount of AHB‐GS was required to improve the coefficient of thermal expansion, gas permeation, and electrical and thermal conductivities. In contrast, the glass transition temperature and initial decomposition temperature of the PI hybrid films continued to decrease with increasing AHB‐GS content up to 10 wt%. Copyright © 2015 John Wiley & Sons, Ltd.

열 이미드화 온도에 따른 작용기화 그래핀/폴리이미드 나노복합재료

폴리이미드(PI) 나노복합체 필름 제조에 사용된 작용기화 4-amino-N-hexadecylbenzamide graphene sheets (AHB-GSs)는 graphene oxide 분산액에 4-amino-N-hexadecylbenzamide(AHB)를 반응시켜 합성하였다. AHB-GS의 주사탐침 현미경(atomic force microscope, AFM) 이미지와 모식도를 통해서 AHB-GS의 평균 두께가 약 3.21 nm임을 확인하였다. PI는 4,4'-biphthalic anhydride와 bis(4-aminophenyl)sulfide를 사용하여 합성하였다. PI 나노복합체는 0-10 wt%의 다양한 함량의 AHB-GS를 용액 삽입(solution intercalation) 방법을 사용하여 합성하였고, 이미드화는 각각 <TEX>$250^{\circ}C$</TEX> 및 <TEX>$350^{\circ}C$</TEX>까지 열 처리하였다. AHB-GS는 대부분 고분자 매트릭스에 잘 분산되었고 약간 뭉친 것도 있었지만 마이크로미터 수준의 입자는 관찰되지 않았다. TEM으로 관찰하였을 때, 평균적으로 입자의 두께는 10 nm 미만이었다. PI 복합체 필름 중 소량의 AHB-GS만으로도 가스 투과도와 전기 전도도는 향상되었지만, 반대로 유리전이 온도와 초기 분해 온도는 AHB-GS의 함량이 10 wt%까지 증가함에 따라 지속적으로 감소되는 경향을 보였다. 전체적으로는, <TEX>$250^{\circ}C$</TEX>까지 이미드화한 PI에 비해 <TEX>$350^{\circ}C$</TEX>까지 열처리한 PI 필름이 보다 향상된 특성을 보였다. 4-Amino-N-hexadecylbenzamide-graphene sheets (AHB-GSs), used in the preparation of the polyimide (PI) nanocomposite films, were synthesized by mixing a dispersion of graphite oxide with a solution of the ammonium salt of AHB. The atomic force microscope image of functionalized-GS on mica and a profile plot revealed the average thickness of AHB-GS to be ~3.21 nm. PI films were synthesized by reacting 4,4'-biphthalic anhydride and bis(4-aminophenyl) sulfide. PI nanocomposite films containing various contents of AHB-GS over the range of 0-10 wt% were synthesized using the solution intercalation method. The PI nanocomposite films under different thermal imidization temperatures, 250 and <TEX>$350^{\circ}C$</TEX>, were examined. The graphenes, for the most part, were well dispersed in the polymer matrix despite some agglomeration. However, micrometer-scale particles were not detected. The average thickness of the particles was <10 nm, as revealed from the transmission electron microscope images. Only a small amount of AHB-GS was required to improve the gas barrier, and electrical conductivity. In contrast, the glass transition and initial decomposition temperatures of the PI hybrid films continued to decrease with increasing content of AHB-GS up to 10 wt%. In general, the properties of the PI hybrid films heat treated at <TEX>$350^{\circ}C$</TEX> were better than those of films heat treated at <TEX>$250^{\circ}C$</TEX>.

Highly dispersed carbon nanotube in new ionic liquid-graphene oxides aqueous dispersions for ultrasensitive dopamine detection

Graphite oxide (GO) is a pH-dependent amphiphile with hydrophilic edges and a more hydrophobic basal plane. It was found that when the hydrophobic prototype ionic liquid (IL) of 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF6]) was added into GO water, it experienced changes from coagulation to being redispersed in water phase by constantly turning its pH to alkali condition. Then new aqueous dispersions of GO-[BMIM][PF6] “water” formed after facile sonicate. The introduction of [BMIM][PF6] not only minimize the defects of poor electrical conductivity of GO and more interesting is that the carbon nanotube (CNT) can be highly dispersed in this GO-[BMIM][PF6] water through a simple and facile ultrasonic method at room temperature, forming a new composite of GO-[BMIM][PF6]-CNT with high dispersibility. This novel composite enhanced its electrochemical signal obviously in the measurement of dopamine (DA) in biological systems and exhibited a wider linear response ranging from 8.0×10−12–1.5×10−5M. The detection limit of 3.0×10−12M at a signal to-noise ratio of 3 was two orders of magnitude lower than that reported previously.

Electrical anisotropies of carbon-nanotube-embedded graphene composite films

Graphite oxide (GO) was prepared by using the chemical oxidation of pristine graphite, and the GO dispersions in water were sprayed onto substrates. The prepared GO film was soaked in a hydrogen iodide (HI) water solution to make reduced graphite oxide (rGO) film. The resulting rGO film was analyzed using a 4-pin probe analyzer and current-voltage measurements, and the film’s conductivities were compared in both the in-plane and the out-of-plane directions. In addition, the film’s conductivities were analyzed according to the loadings (10–30 wt.%) of multiwalled carbon nanotubes (MWNTs) added to the rGO films. The experimentally-measured conductivities were compared and are discussed based on the film structures of rGO and MWNT-embedded rGO.

Scale-up and purification of graphite oxide as intermediate for functionalized graphene

High purity graphite oxide (GO) and scale-up of GO synthesis is in high demand for enabling GO applications in catalysis and the synthesis of functionalized carbon nanomaterials. Although Hummers method, which involves oxidizing graphite with KMnO4 in sulfuric acid, is highly attractive with respect to its cost-effective raw materials and low energy demand, still purification, scale-up and safety problems prompt numerous challenges in large scale production. Conventional dead-end-filtration (DE) is difficult, owing to the severe plugging of the filters by water-swollen GO, whereas dialysis requires massive amounts of water. Plugging problems are solved when using membrane separation with average membrane pores smaller than the lateral micrometer dimensions of GO nanoplatelets. In contrast to DE and dialysis, a short DE prefiltration of acidified GO dispersions, combined with subsequent cross-flow filtration (CF) enables easy GO scale-up and production of high purity GO. Equipped with on-line monitoring of waste-water, this CF process is automated and enables concentration of GO dispersions in the final stage. In GO purification, pH switching represents the key to removing Mn and S impurities.