Graphene Oxide Aqueous Suspension Research Articles

Characterization of graphene oxide nanofilms obtained by the SAW atomization

Due to its ability to absorb water molecules, graphene oxide (GO) is considered a promising material for sensitive coatings in fast surface acoustic wave (SAW) humidity sensors. In this work, we characterize GO films obtained by the SAW atomization technique. It is shown that the atomized submicroliter droplets of aqueous suspension of GO can be deposited onto the surface of Si, LiNbO3 or quartz substrates forming discrete or continuous films of nanometer thickness. The deposited films were examined using AFM and electron microscopy. We discuss the dependence of thickness and structure of the obtained GO films on the parameters of deposition: the number of atomized droplets, a volume of the initial droplet, a distance between the atomizer and the sample, etc. To evaluate the adsorption characteristics of the obtained GO films, we used them as sensitive coatings of the SAW humidity sensors. We found that the adsorption characteristics of the GO films are determined by fast adsorption on the surface of GO sheets and slow adsorption, attributed to limited penetration of water molecules between the sheets, and depend on the number of deposited layers.

Removal of Pb(II) using silver nanoparticles deposited graphene oxide: equilibrium and kinetic studies

Silver nanoparticles-decorated graphene oxide (Ag-GO) composites as advanced metal ion adsorbents have been synthesized. The silver nanoparticles (Ag-NPs) were homogeneously deposited onto graphene oxide (GO) surface by an optimal method, in which N,N-dimethylformamide as a co-dispersant is added to an aqueous suspension of GO and AgNO3. The Fourier transform infrared spectroscopy, scanning electron microscopy, and transmission electron microscopy indicates that GO and Ag-GO are fully exfoliated. The synthesized Ag-GO NPs were used for removal of Pb(II) metal ions. The experiments showed that the removal of metal ions followed a pseudo-second-order kinetic model and equilibrium adsorption studies confirmed that the Langmuir model provided a better fit than others as revealed by high correlation coefficients and low Chi-square values. These Ag-GO NPs can be successfully used for the separation of Pb(II) from aqueous solutions.

Highly enhanced electrochemical responses of rutin by nanostructured Fe2O3/RGO composites

Fe2O3/reduced graphene oxide (RGO) nanocomposites were prepared by a hydrothermal reduction using Fe(OH)3 and graphene oxide (GO) precursors, which were assembled electrostatically by mixing a negatively charged GO aqueous suspension with a positively charged Fe(OH)3 solution at room temperature. The resulting composites were characterized using XRD, SEM, FTIR, and TGA, and then were used to modify the glassy carbon electrode (GCE). The electrochemical behavior of rutin on different types of electrode was compared, and the Fe2O3/RGO composite enhanced electrochemical catalysis effect on rutin, and suitable for rutin detection with high sensitivity and short response time. After 90 s, under open circuit potential, the linear range was increased from 1.5 × 10−8 to 1.8 × 10−5 M, and the detection limit was reduced to 9.8 × 10−9 M. This method of analysis has high recovery ratio of rutin up to 99.5 %.

Surface modification of aramid fibres by graphene oxide nano-sheets for multiscale polymer composites

Aramid fibre–graphene oxide (GO) multiscale reinforcement fibres were prepared by a novel technique where a plasma co-polymerized functional primer coating was initially applied on fibres followed by chemically attaching GO unilamellar sheets to the functionalized surface of the fibres. The functionalized fibres were immersed in purified GO aqueous suspensions at 60°C under two pH conditions (slightly acidic GO suspension at pH6 and alkaline ammonia water GO suspension at pH9). The multiscale hybrid fibres were characterized by XPS, FTIR, Raman spectroscopy, SEM, AFM and tensile measurements. The fibres treated in alkaline ammonia aqueous suspension showed better strength and adhesion characteristics. The mean tensile strength value for the modified fibres showed an improvement over 7.9% whereas the interfacial shear strength in modified fibre–epoxy model composites, as determined by micro-bond technique, improved by 44.68%.

Facile preparation of large-scale graphene nanoscrolls from graphene oxide sheets by cold quenching in liquid nitrogen

Graphene nanoscrolls (GNSs) are receiving intense interest because they are expected to possess some peculiar properties quite distinct from both graphene and carbon nanotubes. Research on GNS, however, has been hindered by limitations of the available preparation methods. Here we demonstrate a novel strategy for the large-scale preparation of GNSs from graphene oxide (GO) sheets by cold quenching, freeze-drying and subsequent thermal reduction. When a plastic box with a heated GO aqueous suspension is immersed in liquid nitrogen, GO sheets are able to roll up and most GNSs have diameters ranging from 200 to 600nm. More interestingly, these GNSs connect each other to form a 3D network. The structural conversion is closely correlated with the initial temperature of GO suspension, the size of GO sheets and the immersion way. The liquid nitrogen cold quenching is a simple and controllable method for large-scale preparation of GNSs. The liquid nitrogen cold quenching is a simple and controllable method for large-scale preparation of GNSs.

One-step synthesis of a sulfur–graphene composite with enhanced photocatalytic performance

• Sulfur–graphene (SG) composites were prepared by one-step approach at room temperature, without addition of any reducing agent, only using Na 2 S·9H 2 O, Na 2 SO 3 and GO aqueous suspension as precursors. • SG composites show high photocatalytic activity toward methylene blue degradation under both UV and visible light. • The electron transfer between sulfur and graphene greatly retard the recombination of photoinduced charge carriers. Sulfur–graphene (SG) composites were prepared by one-pot, one step method at room temperature, without addition of any reducing agent, only using Na 2 S·9H 2 O, Na 2 SO 3 and graphene oxide aqueous suspension as precursors. Transmission electron microscopy images show a thin layer of cloud-like sulfur as well as a few small sulfur particles (<0.3 μm) were attached firmly on the surface of graphene. The photoluminescence spectroscopy implies the presence of electron transfer between sulfur and graphene. The electron transfer at the sulfur/graphene interface will greatly retard the recombination of photoinduced charge carriers and prolong electron lifetime, which contribute to the enhancement of photocatalytic performance. As a result, the SG composites exhibit high photocatalytic activity toward methylene blue degradation under both UV and visible light, probably due to the intimate contact between sulfur and graphene, the efficient charge transport of graphene sheets and hence reduced recombination rate of excited carriers, and great adsorptivity of dyes.

Reduced graphene oxide–bismuth oxide composite as electrode material for supercapacitors

We have reported a new reduced graphene oxide–bismuth oxide composite that can be used as a supercapacitor electrode. Bi2O3 was synthesized from bismuth nitrate pentahydrate and oxalic acid as a precipitating agent using a hydrothermal process in an aqueous graphene oxide suspension. Instead of mixing graphene oxide with bismuth oxide, we have developed a bismuth oxalate precipitation between the layers. As prepared, composite of hydrated bismuth oxalate and graphene oxide was converted to bismuth oxide and reduced graphene oxide by thermal decomposition in a muffle stove. The material exhibited the specific capacitance of 94 F/g at current density 0.2 A/g. Using the cyclic voltammetry, the specific capacitance was as high as 55 F/g at scan rate 5 mV/s over the potential range 0–1 V. The material exhibited long-term cycle stability retaining 90 % specific capacitance after 3,000 cycles. Except Bi3+ ions present in Bi2O3, some amount of higher energy Bi5+ was confirmed.

A simple approach to synthesize nanosized sulfur/graphene oxide materials for high-performance lithium/sulfur batteries

We report on a simple and facile synthesis route for the sulfur/graphene oxide composite via ultrasonic mixing of the nano-sulfur and graphene oxide aqueous suspensions followed by a low-temperature heat treatment. High-resolution transmission and scanning electronic microscopy observations revealed the formation of a highly porous structure consisting of sulfur with uniform graphene oxide coating on its surface. The resulting sulfur/graphene oxide (S/GO) composite exhibited high and stable specific discharge capacities of 591 mAh g−1 after 100 cycles at 0.1 C and good rate capability. This enhanced electrochemical performance could be attributed to the effective confining the polysulfides dissolution and accommodation of the volume changes during the Li-S electrochemical reaction by the functional groups on the graphene oxide coating layer. Furthermore, the highly developed porous structure of S/GO composite favors the enhanced ion transport and electrolyte diffusion.

High Efficiency Anti-Reflectance Graphene-based Coating through Electrochemical Etching and Deposition

Antireflection (AR) coating is of great significance in controlling the reflection index (RI), which influences optical performance of the system. Comparing to the traditional absorbing materials, single layer graphene with much lower mass density, absorbs 2.3% of light at visible frequencies, which makes it an ideal candidate for use in mass-sensitive systems. The electrochemical anisotropic etching and electrophoretic deposition of graphene can minimize the RI of Aluminum material to 1%, meanwhile the mechanical properties of the coating is acceptable. Electrochemical anisotropic etching (EAE) with prior cathodic polarization during anodic etching, forms homogeneous digital AR structure on the centimeter-scale Aluminum material surface, with pit number density and size distribution controllable and improved interfacial binding force. Electrophoretic deposition (EPD) forms graphene-oxide-based nanostructures on the three-dimensional Aluminum surface from Graphene oxide aqueous suspension. The graphene-based AR coating is achieved through the catalytic reduction of graphene oxide by visible light with N-doped TiO2 as photocatalyst. By electrochemical treatment, we manufacture the high efficiency absorbtion ability and low RI optical surface of Aluminum material, through conducting digital AR structure and homogeneous AR coating.

Synthesis of silanized maghemite nanoparticles onto reduced graphene sheets composites

Novel γ-Fe2O3@APTES@rGO composites are successfully synthesized by using graphene oxide and silanized maghemite nanoparticles. Graphene oxide and maghemite were obtained by Hummers and Massart methods, respectively. The silanization process was done to functionalize maghemite surface with a controllable quantity of amino groups. Then, by adding aqueous graphene oxide suspension, the bonding between graphene oxide and silanized maghemite nanoparticles was done in refluxing conditions. Afterwards, chemical reduced graphene oxide reaction was realized by addition of hydrazine solution. The characterization of γ-Fe2O3@APTES@rGO composites was studied by X-ray Diffraction, Fourier Transformed Infrared Spectroscopy, thermogravimetric analysis and scanning electron microscopy.

Photocatalytic activities of heterostructured TiO2-graphene porous microspheres prepared by ultrasonic spray pyrolysis

Abstract TiO 2 -graphene porous microspheres were prepared by ultrasonic spray pyrolysis (USP) of aqueous suspension of graphene oxide containing TiO 2 nanoparticles (Degussa P25). The composite microspheres were characterized with SEM, XPS, photoluminescence, Raman and UV–Vis absorption spectra. TiO 2 -graphene porous microspheres displayed higher photocatalytic activity for the degradation of methylene blue solution than pristine TiO 2 microspheres under the irradiation of Xe lamp, and the highest activity was obtained at a weight percentage of graphene around 1%. The effect of graphene on photocatalytic activity of porous microsphere was discussed in terms of the enhanced charge separation by TiO 2 -graphene heterojunction, increased absorption of the visible light, as well as the possible hindrance of mass transportation in microspheres.

Cationically Charged MnIIAlIII LDH Nanosheets by Chemical Exfoliation and Their Use As Building Blocks in Graphene Oxide-Based Materials

We report on the synthesis and exfoliation of Mn(II)Al(III) sulfonate and sulfate layered double hydroxides (LDHs) and their combination with graphene oxide by charge-directed self-assembly. The synthesis of the LDH compounds has been accomplished either directly by coprecipitation of the respective hydroxides with sulfonate anions or by ion-exchange of the chloride-containing LDH with sodium dodecylsulfate. Exfoliation of the bulk material in formamide yields colloidal suspensions of positively charged nanosheets with lateral dimensions of tens to hundreds of nanometers and thicknesses down to 1.3 nm, ascertained by TEM and AFM. Flocculation of the LDH nanosheets with an aqueous graphene oxide suspension yields a hybrid material that can be converted to a reduced graphene oxide/LDH composite by hydrazine reduction. The hybrid materials were tested for pseudocapacitive electrochemical storage capacity and electrocatalytic oxygen evolution reactions and showed significant increases compared to the pristine materials.

A stable silicon/graphene composite using solvent exchange method as anode material for lithium ion batteries

Current research has demonstrated the combination of the high theoretical capacity offered by silicon nanoparticles (Si NPs) with graphene-based matrices in order to produce a high energy density and stable lithium ion battery system. However, Si NPs do not mix well with graphene oxide aqueous suspensions and thus create severe segregation of the materials. In this letter, we propose a simple, cost-effective and commercially-viable solvent exchange process to improve the interaction of the Si NPs in poor solvent environments such as in aqueous media. Using N-methylpyrrolidone (NMP) to disperse the Si NPs and followed by a solvent exchange process, we are able to improve the dispersion and stability of Si NPs in aqueous graphene oxide aqueous suspension. Consequently, this also improves the output and the stability of the lithium ion battery using the aforementioned composite system.

Self-Assembled Free-Standing Graphene Oxide Fibers

It is a great challenge to directly assemble two-dimensional (2D) graphene oxide (GO) sheets into 1D fibers without any polymer or surfactant for their promising multifunctional applications. Herein, a facile self-assembly strategy is proposed to fabricate neat GO fibers from cost-efficient, aqueous GO suspension at a liquid/air interface based on the repulsive electrostatic forces, attractive van der Waals forces, and π-π stacking. During the self-assembly process and ultrasonic cleaning, the morphology variated from the source graphite powder through GO sheets to GO fibers and finally to neat GO fiber films. It is interesting to note that the electrical property of the GO fiber films was improved dramatically after subsequent low-temperature thermal annealing. The morphological evolution process and formation mechanism were analyzed on the basis of optical microscopy, scanning electron microscopy, and transmission electron microscopy observation, and the electrical characteristics was also discussion.

Facile and rapid synthesis of highly crumpled graphene sheets as high-performance electrodes for supercapacitors

Highly crumpled graphene sheets (HCGSs) have been prepared by a facile and rapid route through freezing a chemically reduced graphene oxide aqueous suspension with liquid nitrogen. The porous and highly crumpled graphene structure with a large surface area and pore volume facilitates fast ionic transport within the electrode while preserving excellent electrical conductivity and thus endows HCGSs with excellent electrochemical properties. As the electrodes for supercapacitors, the HCGSs exhibit high specific capacitance (259 F g−1), excellent rate capability and cycling stability (93% retention after 5000 cycles).

Hydrogenated Graphene as Metal-free Catalyst for Fenton-like Reaction

Carbonaceous catalysts are potential alternatives to metal catalysts. Graphene has been paid much attention for its high surface area and light weight. Here, hydrogenated graphene has been prepared by a simple gamma ray irradiation of graphene oxide aqueous suspension at room temperature. Transmission electron microscopic, element analysis, X-ray photoelectron spectroscopy, and UV-Vis spectrophotometer studies verified the hydrogenation of graphene. The as-prepared hydrogenated graphene can be used as a metal-free carbonaceous catalyst for the Fenton-like degradation of organic dye in water.

Reduction and Functionalization of Graphene Oxide Sheets Using Biomimetic Dopamine Derivatives in One Step

An easy and environmentally friendly chemical method for the simultaneous reduction and noncovalent functionalization of graphene oxide (GO) using dopamine derivatives is described. The reaction takes place at room temperature under ultrasonication of an aqueous suspension of GO and a dopamine derivative. X-ray photoelectron spectroscopy, FT-IR spectroscopy, and cyclic voltammetry characterizations revealed that the resulting material consists of graphene functionalized with the dopamine derivative. This one-step protocol is applied for simultaneous reduction and functionalization of graphene oxide with a dopamine derivative bearing an azide function. The chemical reactivity of the azide function was demonstrated by a postfunctionalization with ethynylferrocene using the Cu(I) catalyzed 1,3-dipolar cyloaddition.

Chemical reduction of an aqueous suspension of graphene oxide by nascent hydrogen

One of the major challenges in the chemical reduction of graphene oxide is increasing the C/O atomic ratio of the chemically converted graphene. In this paper, we report a simple and effective method to reduce aqueous suspensions of graphene oxide using nascent hydrogen generated in situ by the reaction between Al foil and HCl, Al foil and NaOH and Zn powder and NaOH. The nascent hydrogen-reduced graphene oxides (nHRGOs) were characterized by elemental analysis, UV-vis spectra, Raman spectra, X-ray photoelectron spectroscopy, thermogravimetric analysis and electrical conductivity measurements. The reduction efficiency of graphene oxide strongly depended on the reaction medium and the rate of nascent hydrogen generation. The best nHRGO achieved a C/O atomic ratio greater than 21 and a bulk electrical conductivity as high as 12 500 S m−1, corresponding to the nascent hydrogen generated from the reaction between Al foil and HCl. Since nascent hydrogen could be produced on a metal surface upon oxidation in solution, other metals with low standard reduction potentials, such as Mg, Mn, and Fe, can be applied to reduce graphene oxide.

Tough and highly stretchable graphene oxide/polyacrylamide nanocomposite hydrogels

Polyacrylamide (PAM)/graphene oxide (GO) nanocomposite hydrogels (PGH) with GO nanosheets as cross-linkers were synthesized via in situ free radical polymerization of acrylamide in an aqueous suspension of GO. The tensile properties of the hydrogels were investigated in terms of type and content of cross-linkers. Compared to conventional PAM hydrogels (PBH) cross-linked chemically with N,N′-methylenebisacrylamide, PGH exhibits high tensile strength, high toughness and especially a large elongation at break. The tensile strength of PGH is about 4.5 times higher than that of PBH, and the elongation at break is over 3000%, nearly one order higher than that of PBH even when the content of GO is only 0.0079 wt%. By analyzing the cross-linked structure of PGH and the theoretical calculation on the number of cross-linked polymer chains per unit volume of gels, a structure model was thus proposed.

Study on the Catalytic Activity of Graphene Oxide

Graphene oxide (GO), an oxygen-rich carbonaceous layered material, is produced by the strong oxidation of graphite. The GO aqueous suspension is very stable and can be fabricated to porous GO aerogels by a green method, unidirectional freeze-drying technology. GO shows catalytic activities in both solution and solid state. It can also act as reductant or oxidant depending on the reaction patterns. The product of the reaction was analyzed and the component change of the graphene oxide (GO) was monitored by x-ray photoelectron spectrometer, scanning electron microscopy and transmission electron microscopy. The results confirm that GO not only acts as the reactant in the reaction, but also as the catalyst to catalyze the reaction.