As-prepared Graphene Oxide Research Articles

An Investigation of a Polydopamine-Graphene Oxide Composite as a Support for an Anode Fuel Cell Catalyst

Home-made graphene oxide (GO) with a high surface area was functionalized by polydopamine (PDA) and was labeled PDA-GO, while GO without PDA was labeled as GO. With different compositions of metals (Pt and/or Pd), the electrodeposition of the metals onto the prepared GO and PDA-GO supports was prepared for the anode electrocatalyst. The electrocatalytic activities of the electrocatalysts (xPtPd/GO and xPtPd/PDA-GO, where x = 1–5) were studied in the oxidation of alcohols (e.g., methanol and ethanol). Morphologies obtained from transmission electron microscopy (TEM), scanning electron microscopy (SEM), and atomic force microscopy (AFM) images showed that the as-prepared GO and PDA-GO supports can accommodate electrodeposited metals loaded on the topmost layer of the support surfaces, although the size of nanoparticles is somewhat different. The electrochemical results indicated that the xPtPd/PDA-GO catalysts offered outstanding oxidation efficiencies. The prepared 5PtPd/PDA-GO catalyst provided enhanced activity and long-time stability in the oxidation reactions. The GO surface modified by the polymer and the other electrodeposited metal catalysts provided a larger number of available active sites, as the PDA offered a greater electric connection between the metal catalysts and the GO support during alcohol oxidation.

Natural polysaccharides-modified graphene oxide for adsorption of organic dyes from aqueous solutions

Three polysaccharide- graphene oxide composite materials (PS-GO) were synthesized from graphene oxide (GO) and natural polysaccharides, which compounds were tested for removal of organic dyes from aqueous solutions. These adsorbents were characterized by Fourier transform infrared spectroscopy (FT-IR), Raman spectrometer, X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), N2 adsorption-desorption isotherms and UV–vis spectrum. The adsorption properties of PS-GO towards four organic dyes were investigated along with measured effects on adsorption by initial concentration, temperature, contact time and pH value. Resulting adsorption isotherms, thermodynamics and kinetics were analyzed systematically. In these tests, PS-GO composite materials were found to be more efficient than as-prepared GO as adsorbents for the removal of both cationic and anionic organic dyes.

Synthesis of graphene oxide sheets with controlled sizes from sieved graphite flakes

Graphene oxide (GO) sheets with desired sizes and narrow size distribution were synthesized via a modified Hummers method by using sieved graphite flakes as the starting materials. This method outweighs previous post-synthesis fractionation methods in efficiency and scalability; thus it is more promising for large-scale synthesis of size-controlled GO. The as-prepared GO suspensions exhibited size-dependent liquid crystal behavior. The importance of hydrolysis step on exfoliation and preserving the sizes of GO sheets, and the removal of their sulfate species was also discussed.

Direct Observation, Molecular Structure, and Location of Oxidation Debris on Graphene Oxide Nanosheets.

The presence of oxidation debris (OD) complicates the structures and properties of graphene oxide (GO) nanosheets, thereby impacting their potential applications. However, the origin of OD is still in dispute. Moreover, characterizing the structure and location of supposed OD on nanosheets of GO produced during the oxidation process is difficult. Herein, the attached state and size of OD on graphene oxide nanosheets were directly observed using HRTEM, the molecular structure of OD was initially proposed based on the spectroscopic characterization and Q-TOF mass spectrometry, and the locations of OD on the GO nanosheets were detected through the adsorption of probe molecules onto as-prepared GO (a-GO) and base-washed GO (bw-GO). The results indicated that OD possesses a highly crystalline structure and can be defined as several nanometre-sized polyaromatic molecules with a considerable number of oxygen-containing functional groups attached on the edges. The dark nanodot seated on a-GO was clearly observed in the HRTEM images, whereas it appeared as a clean nanosheet in the image of bw-GO, indicating that OD is removed by base-washing treatment. Following the base-washing treatment, the contents of carboxyl groups on bw-GO unexpectedly increased and subsequently contributed to the desorption of OD from a-GO due to the electrostatic repulsion being stronger than primary π-π interactions. Compared with a-GO, the adsorption of phenanthrene, as an aromatic probe, onto bw-GO increased by 6-fold via π-π stacking interactions, whereas the increase in the adsorption of m-dinitrobenzene, as a defect probe, was not as remarkable as that of phenanthrene. Reasonably, the OD nanoparticles were primarily located at the sp(2) structures on the GO nanosheets through π-π interactions rather than attached on defects/edges. The insights regarding the existence, molecular structures and attached sites of OD nanoparticles on GO nanosheets provide a theoretical basis for preparing OD-free GO for optimizing the potential applications of GO nanosheets.

Reduction and structural evolution of graphene oxide sheets under hydrothermal treatment

This work carefully investigated the hydrothermal reduction of graphene oxide (GO) sheets. To evaluate the reduced extent, the as-prepared GO and RGO sheets in different conditions were measured by FT-IR, UV–Vis, Raman spectra and TEM morphologies. It revealed that the hydrothermal reduction of GO sheets was undergone four steps and the optimal condition was treated at 180 °C for 24 h. These RGO sheets exhibited the expectant morphologies and maintained the original sizes.

Facile synthesize of free standing highly conducting flexible reduced graphene oxide paper

We report a facile fabrication of free standing, highly conducting flexible reduced graphene oxide (rGO) paper by an evaporation-induced self-assembly process. The impact of heat treatment conditions on the structural, mechanical and electrical properties of rGO paper has been investigated. The effect of annealing temperature on the structural variations of GO (graphene oxide) and rGO papers was confirmed by X-ray diffraction studies. The removal of oxygen and other functional groups from the GO paper by heat-treatment process was confirmed using FTIR analysis. Raman spectra confirmed the effective control of defects in rGO paper by means of heat-treatment, which has also been inferred from the Raman mapping analysis. The morphology of rGO paper studied by FESEM emphasized the stacking of rGO layers. The electrical conductivity was significantly enhanced for 400 °C heat-treated rGO paper (4.82 × 103 S/cm) compared to the as-prepared GO paper (7 × 10−3 S/cm). The tensile strength of the rGO paper was also relatively higher than that of GO paper. The experimental results demonstrated that the present approach is simple and reducing agent free green approach for preparing large-area rGO paper with high electrical conductivity and mechanical flexibility.

Synthesis of r-GO/TiO2 composites via the UV-assisted photocatalytic reduction of graphene oxide

Reduced graphene oxide/TiO2 (rGO/TiO2) composites were synthesized by combined TiO2 and graphene oxide (GO) under ultraviolet (UV) irradiation. The influences of TiO2 content on the reduction degree of GO during synthesis of the rGO/TiO2 composites were investigated and characterized by XRD, Raman, FTIR, SEM and TEM. It is shown that the XRD diffraction peak of 2θ at 10° of the as-prepared GO decreases with the increasing amount of TiO2 added. When the weight ratio of GO:TiO2 is 2:1, the XRD diffraction peak of 2θ at 10° of graphene oxide almost disappears. At a GO:TiO2 of 1:2, the OH functional groups, carboxylic and carbonyl, on the edge of the graphene oxide are effectively removed. Moreover, a morphological study shows the observation of graphene has a corrugated titanium oxide load and intercalation. The as-prepared rGO/TiO2 obtained from weight ratios of GO: TiO2 at 1: 2.5 showed a specific capacitance of 226.45Fg−1 at a scan rate of 10mVs−1 in 1M H2SO4 electrolyte solution.

Formation process of holey graphene and its assembled binder-free film electrode with high volumetric capacitance

Holey graphene with abundant in-plane nanopores is achieved through a mild defect-etching reaction between graphene oxide (GO) and hydrogen peroxide (H2O2) then followed by a reduction process in hydrazine solution. The porosity of the obtained holey graphene is systematically investigated by optimizing the reaction conditions between GO and H2O2. The optimum reaction conditions are that GO is hydrothermally treated in 0.4mL H2O2 at 100°C for 10h and the as-prepared holey graphene oxide (HGO) is refluxed in hydrazine solution at 100°C for 1h, by which holey reduced graphene oxide (HRGO) suspension with good dispersity is obtained. By vacuum filtration of the HRGO suspension, the binder-free porous graphene film electrodes are successfully assembled. The obtained film electrodes exhibit high specific capacitance (251Fg−1 at a current density of 1Ag−1), high volumetric capacitance (up to 216Fcm−3), and enhanced rate capability (73% capacitance retention from 1–60Ag−1) due to their high packing density (0.86gcm−3). The suitable porosity of the assembled porous graphene film keeps a balance between electrolyte ion diffusion rate and conductivity, which can bridge the gap between gravimetric capacitance and volumetric capacitance for the obtained electrode material.

Solvothermal fabrication and enhanced visible light photocatalytic activity of Cu2O-reduced graphene oxide composite microspheres for photodegradation of Rhodamine B

The addition of graphene oxide (GO) in the semiconductors has been regarded as one of the effective methods to enhance their photocatalytic activity. In this study, Cu2O-reduced graphene oxide (Cu2O-rGO) composites with low loading (0–0.5wt.%) of graphene oxide (GO) were produced by a one-step green solvothermal method in ethanol system by using Cu(NO3)2·3H2O and glutamic acid as copper precursor and reducing agent, respectively. During the solvothermal treatment, GO was reduced to rGO. The as-prepared Cu2O-reduced graphene oxide composite microspheres exhibited enhanced photocatalytic activity toward the degradation of RhB aqueous solution under visible light irradiation. At the optimal loading of graphene oxide (0.05wt.%), Cu2O-rGO composites showed the highest photocatalytic activity, exceeding that of pure Cu2O and commercial Degussa P25 by a factor of 2.9 and 7.9, respectively. The enhanced photocatalytic activity may be ascribed to the strong coupling interaction between Cu2O particles and rGO nanosheets, which reduces the recombination of charge carriers.

Non-Contact Local Conductance Mapping of Individual Graphene Oxide Sheets during the Reduction Process

We used electrostatic force microscopy (EFM) to investigate local conducting states of atomically thin individual graphene oxide (GO) sheets and monitor the spatial evolution of their conducting properties during the reduction process. Because of the thinness of the GO sheets and finite carrier density, the electric field is partially screened in the reduced GO, which is manifested in the EFM phase signals. We found inhomogeneous oxidation states in as-prepared GO sheets and followed the evolution of reduction process in the individual GO sheets during both thermal and chemical reduction. We also compared the EFM measurement results with simultaneous IV characteristics to assess correlations between two measurements.

Graphene oxide-confined synthesis of Li4Ti5O12 microspheres as high-performance anodes for lithium ion batteries

This paper reports a graphene oxide (GO) confined strategy to synthesize reduced GO-coated lithium titanate (Li4Ti5O12, LTO) microspheres using as-prepared TiO2 microspheres and GO as raw materials. The obtained samples are characterized by X-ray diffraction, field emission scanning electron microscopy and spectrophotometer. Results show that the spherical LTO is formed with approximate 1μm diameter after hydrothermal reactions, which is due to a confined effect of GO on the surface of TiO2 spheres. Electrochemical tests reveal that the presence of rGO can increase the capacity and cycling stability of LTO anodes, especially at higher C rate. The 3wt% rGO-coated LTO anodes present a higher reversible Li-ion storage with a specific discharge capacity of 131.6mAhg−1 at 5C and 97% retention even after 500 cycles, which are more excellent than those of pristine LTO. The GO-confined method is anticipated to synthesize other electrode materials with high electrochemical performances.

Biological relevance of oxidative debris present in as-prepared graphene oxide.

The influence of oxidative debris (OD) present in as-prepared graphene oxide (GO) suspensions on proteins and its toxicity to human embryonic kidney cells (HEK-293T) are reported here. The OD was removed by repeated washing with aqueous ammonia to produce the corresponding base-washed GO (bwGO). The loading (w/w) of bovine serum albumin (BSA) was increased by 85% after base washing, whereas the loading of hemoglobin (Hb) and lysozyme (Lyz), respectively, was decreased by 160% and 100%. The secondary structures of 13 different proteins bound to bwGO were compared with the corresponding proteins bound to GO using the UV circular dichroism spectroscopy. There was a consistent loss of protein secondary structure with bwGO when compared with proteins bound to GO, but no correlation between either the isoelectric point or hydrophobicity of the protein and the extent of structure loss was observed. All enzymes bound to bwGO and GO indicated significant activities, and a strong correlation between the enzymatic activity and the extent of structure retention was noted, regardless of the presence or absence of OD. At low loadings (<100 μg/mL) both GO and bwGO showed excellent cell viability but substantial cytotoxicity (~40% cell death) was observed at high loadings (>100 μg/mL). In control studies, OD by itself did not alter the growth rate even after a 48-h incubation. Thus, the presence of OD in GO played a very important role in controlling the chemical and biological nature of the protein-GO interface and the presence of OD in GO improved its biological compatibility when compared to bwGO.

Graphene-oxide (GO)–Fe3+ hybrid nanosheets with effective sonocatalytic degradation of Reactive Red 120 and study of their kinetics mechanism

This work demonstrates the preparation of graphene-oxide (GO)–Fe3+ hybrids nanosheets and their high bleaching efficiency on the dye “Reactive Red 120 (RR 120)” by using sonocatalytic degradation. Sonocatalytic degradation was enhanced by using oxidants like PMS (peroxomonosulphate), PDS (peroxodisulphate), H2O2 (hydrogen peroxide) and KIO4 (potassium periodate). Our observations manifested that the degradation of the dye “RR 120” was found to be multiplied by addition of oxidants in the order of PMS>H2O2>PDS>KIO4. The effect of inorganic ions was studied by the addition of SO42−, Cl−, H2PO4− and HCO3−. These results revealed that an addition of inorganic anionic decreases the degradation efficiency of RR 120 at high concentration. The trend of decreased degradation efficiency was SO−4<Cl−<HPO4. In identical conditions, upon addition of HCO3−, the degradation rate of RR 120 degradation was increased. As-prepared GO–Fe3+ hybrid nanosheets were characterised by using X-ray diffraction technique, X-ray photoelectron spectroscopy (XPS), transmission electron microscopy, Raman spectroscopy and Energy Dispersive Analysis of Spectroscopy. Raman and XPS results confirmed the existence of Fe3+ ions in GO sheet.

Single and Multiple Doping in Graphene Quantum Dots: Unraveling the Origin of Selectivity in the Oxygen Reduction Reaction

Singly and multiply doped graphene oxide quantum dots have been synthesized by a simple electrochemical method using water as solvent. The obtained materials have been characterized by photoemission spectroscopy and scanning tunneling microscopy, in order to get a detailed picture of their chemical and structural properties. The electrochemical activity toward the oxygen reduction reaction of the doped graphene oxide quantum dots has been investigated by cyclic voltammetry and rotating disk electrode measurements, showing a clear decrease of the overpotential as a function of the dopant according to the sequence: N ∼ B > B,N. Moreover, assisted by density functional calculations of the Gibbs free energy associated with every electron transfer, we demonstrate that the selectivity of the reaction is controlled by the oxidation states of the dopants: as-prepared graphene oxide quantum dots follow a two-electron reduction path that leads to the formation of hydrogen peroxide, whereas after the reduction with ...

Ultrasensitive and simultaneous detection of heavy metal ions based on three-dimensional graphene-carbon nanotubes hybrid electrode materials

A green and facile method was developed to prepare a novel hybrid nanocomposite that consisted of one-dimensional multi-walled carbon nanotubes (MWCNTs) and two-dimensional graphene oxide (GO) sheets. The as-prepared three-dimensional GO–MWCNTs hybrid nanocomposites exhibit excellent water-solubility owing to the high hydrophilicity of GO components; meanwhile, a certain amount of MWCNTs loaded on the surface of GO sheets through π–π interaction seem to be “dissolved” in water. Moreover, the graphene(G)-MWCNTs nanocomposites with excellent conductivity were obtained conveniently by the direct electrochemical reduction of GO–MWCNTs nanocomposites. Seeing that there is a good synergistic effect between MWCNTs and graphene components in enhancing preconcentration efficiency of metal ions and accelerating electron transfer rate at G-MWCNTs/electrolyte interface, the G-MWCNTs nanocomposites possess fast, simultaneous and sensitive detection performance for trace amounts of heavy metal ions. The electrochemical results demonstrate that the G-MWCNTs nanocomposites can act as a kind of practical sensing material to simultaneously determine Pb2+ and Cd2+ ions in terms of anodic stripping voltammetry (ASV). The linear calibration plots for Pb2+ and Cd2+ ranged from 0.5μgL−1 to 30μgL−1. The detection limits were determined to be 0.2μgL−1 (S/N=3) for Pb2+ and 0.1μgL−1 (S/N=3) for Cd2+ in the case of a deposition time of 180s. It is worth mentioning that the G-MWCNTs modified electrodes were successfully applied to the simultaneous detection of Cd2+ and Pb2+ ions in real electroplating effluent samples containing lots of surface active impurities, showing a good application prospect in the determination of trace amounts of heavy metals.

Tungsten oxide nanowire-reduced graphene oxide aerogel for high-efficiency visible light photocatalysis

A light, 3-D, porous aerogel was fabricated by way of a simple approach from 1-D tungsten oxide nanowires and 2-D reduced graphene oxide sheets. The as-prepared graphene oxide, tungsten oxide nanowires, and tungsten oxide-reduced graphene oxide (W18O49-RGO) aerogel were characterised. The photocatalytic activities of as-prepared aerogel under visible light irradiation were investigated through the degradation of six different organic dyes including Rhodamine B, reactive black 39, reactive yellow 145, weak acid black BR, methyl orange, and weak acid yellow G. In comparison with the pure W18O49 nanowires, the prepared W18O49-RGO aerogel had significantly improved photocatalytic efficiency. Also, the photocatalysis of W18O49-RGO aerogel maintained its efficiency after 30 cycles for each of the six dyes. The photocatalytic mechanism was studied by adding hole and radical scavengers: the results confirmed that the holes generated in W18O49-RGO aerogel played a key role in the visible light photocatalytic process.

Preparation of Fe3O4-Embedded Graphene Oxide for Removal of Methylene Blue

Fe3O4-embedded graphene oxide was developed as a magnetic adsorbent for removal of methylene blue from aqueous solution. Fe3O4 nanoparticles were embedded on the surface of the as-prepared graphene oxide via a co-precipitation procedure with cheap and environmentally friendly iron salts. The weight percentage of graphene oxide was estimated by calcination to be about 18.5 %. In the aqueous solution of methylene blue at 20 °C, the adsorption data agreed well with the Langmuir adsorption model with a maximum adsorption capacity of 246 mg/g and a Langmuir adsorption equilibrium constant of 8.926 mL/mg. The adsorption amount increased with the increase of the solution pH (3–11), decreased with the increase of KCl concentration until it was up to 60 mM. The adsorbed methylene blue could be desorbed by using the methanol solution of acetic acid. In addition, both the adsorption and desorption rate were very quick that the equilibrium was achieved within 5 min due to the absence of the internal diffusion resistance. Fe3O4-embedded graphene oxide with large adsorption capacity and easy separation could be regarded as a potential adsorbent for removal of cationic dye in wastewater treatment process.

Organic fragments from graphene oxide: Isolation, characterization and solvent effects

As-prepared graphene oxide (GO) contains oxidative debris which can be washed using basic solutions. We present the isolation and characterization of these debris. Dynamic light scattering (DLS) is used to monitor the separation of the debris in various solvents in the presence of different protic and aprotic alkylamino bases. The study reveals that the debris are rich in carbonyl functional groups and water is an essential component for separation and removal of the debris from GO under oxidative reaction conditions.

Identifying the magnetic properties of graphene oxide

Highly oxidative debris (OD) was obtained by aqueous ammonia wash of as-prepared graphene oxide (GO) which composed of OD and lightly oxidative GO sheets. The magnetic properties of OD and GO were studied. The results showed that OD has a low magnetization of 0.16 emu/g, and the magnetization of GO can be increased from 0.38 to 0.42 emu/g by discarding low-magnetization OD. Thus, this study provided a reliable method to increase the magnetization of GO. Hydroxyl groups were proposed to be the magnetic source.

Preparation of graphene oxide-based surface plasmon resonance biosensor with Au bipyramid nanoparticles as sensitivity enhancer

A sensitive and selective wavelength-modulation surface plasmon resonance (SPR) biosensor based on graphene oxide (GO) and Au bipyramids (AuBPs) is reported for determination of bovine IgM. GO sheets with lengths of 100–300nm are synthesized and assembled on amine-modified Au film. The large surface area and abundant functional groups of GO allow the efficient immobilization of antibody. AuBPs are nanoparticles with a penta-twinned crystal structure, which have a sharp localized surface plasmon resonance (LSPR) band because of their high monodispersity. In the optimal conditions, the GO-based biosensor with AuBPs as sensitivity enhancers shows a satisfactory response to bovine IgM in the concentration range of 0.03–32μgmL−1. For contrast, traditional biosensor, GO-based biosensor and GO-based biosensor with Au nanorods (AuNRs) as sensitivity enhancers for antigen detection were also investigated. Consequently, the as-prepared GO sheets function as promising support for antibody and GO-based SPR biosensor using AuBPs as enhancers has the highest sensitivity among the four types of biosensors.