Pristine GO Research Articles

Methylpiperidine-functionalized graphene oxide for efficient curing acceleration and gas barrier of polymer nanocomposites

We synthesized methylpiperidine-functionalized graphene oxide (MP-GO) by introducing 4-amino-1-methylpiperidine into reactive epoxy and/or carboxylic acid groups on pristine GO. Then, we applied the MP-GO as a curing catalyst for polyimide (PI) nanocomposites. The MP-GO was found to be an effective base-catalysts for the thermal conversion of polyamic acid (PAA) precursor to PI. Interestingly, when 3 wt% of MP-GO was added to the PI matrix, the complete imidization of nanocomposites was achieved at a temperature lower than 200 °C. In addition, the PI/MP-GO nanocomposite films exhibited reinforcement of the oxygen barrier properties which were even better than those of pristine PI, due to the excellent dispersion state of MP-GO and the favorable non-covalent interaction between MP-GO and the PI matrix. Comparison to pristine PI, the oxygen permeability of nanocomposite films that contained only 1 wt% of MP-GO loading was significantly decreased, by about 80%. Furthermore, all the PI/MP-GO nanocomposites exhibited high thermal stability.

Core-shell flame retardant/graphene oxide hybrid： a self-assembly strategy towards reducing fire hazard and improving toughness of polylactic acid

Biobased flame retardant/graphene oxide hybrid (GOH) as a multifunctional flame retardant for polylactic acid (PLA) was synthesized through organic-solvent-free self-assembly. The electrostatic interactions deposited the polyethylenimine (PEI) and biobased polyelectrolyte (BPE) coating on the surface of ammonium polyphosphate (APP) in water, which gave the negatively charged core-shell flame retardant. Then, GOH was obtained via aqueous self-assembling between the positively charged graphene oxide (pGO) obtained by grafting pristine GO with PEI and the core-shell flame retardant. Subsequently, GOH was employed as multifunctional flame retardant to PLA, aiming to enhance both flame retardancy and toughness. Based on the investigation via LOI, UL94 test and the cone calorimetry, it clearly showed that GOH endowed PLA significantly enhanced flame retardancy. The flame retardancy of GOH in PLA was performed in both of the gas-phase and condensed-phase mechanisms according to the analysis of the volatile gases and the residues. As for the mechanical properties of PLA/GOH composites, an over 6 folds increment in elongation at break (52.4%) and 86.7% increase in notched impact strength (5.6 kJ/m2) were achieved for PLA/10%GOH, compared with that of the neat PLA. It meant the introduction of GOH remarkably improved toughness of PLA.

Investigation of graphene oxide-hydrogen interaction using in-situ X-ray diffraction studies

Hydrogen is one of the alternatives as clean fuel for our growing demands for energy. However, its storage for practical applications is a challenge due to low energy density. The interaction mechanism between the hydrogen gas and the host involved plays a vital role to explore its potential application as hydrogen storage material. So, in the present work, we have studied the interaction of Graphene oxide with hydrogen gas at different pressures varying from 70 mbar to 900 mbar at room temperature using reliable in-situ X-ray diffraction technique. XRD patterns showed that the hydrogen gas induced strain up to ∼6.3% in GO films for 1% and 10% hydrogen atmosphere. The interaction mechanism was studied qualitatively using Raman spectroscopy and Fourier transform infra-red (FTIR) spectroscopy. Elastic recoil detection analysis (ERDA) technique was employed to determine the concentration of hydrogen in GO film which increased from ∼1.7 × 1022 atoms/cc (for pristine GO) to ∼ 9.5 × 1022 atoms/cc after exposing to 100% hydrogen environment at 900 mbar pressure.

Pyridinic-N-Doped Graphene Paper from Perforated Graphene Oxide for Efficient Oxygen Reduction.

We report a simple approach to fabricate a pyridinic-N-doped graphene film (N-pGF) without high-temperature heat treatment from perforated graphene oxide (pGO). pGO is produced by a short etching treatment with hydrogen peroxide. GO perforation predominated in a short etching time (∼1 h), inducing larger holes and defects compared to pristine GO. The pGO is advantageous to the formation of a pyridinic N-doped graphene because of strong NH3 adsorption on vacancies with oxygen functional groups during the nitrogen-doping process, and the pyridinic-N-doped graphene exhibits good electrocatalytic activity for oxygen reduction reaction (ORR). Using rotating-disk electrode measurements, we confirm that N-pGF undergoes a four-electron-transfer process during the ORR in alkaline and acidic media by possessing sufficient diffusion pathways and readily available ORR active sites for efficient mass transport. A comparison between Pt/N-pGF and commercial Pt/C shows that Pt/N-pGF has superior performance, based on its more positive onset potential and higher limiting diffusion current at −0.5 V.

Incorporating attapulgite nanorods into graphene oxide nanofiltration membranes for efficient dyes wastewater treatment

Graphene oxide/attapulgite (GO/APT) composite membranes were successfully fabricated by the vacuum-assisted filtration for efficient dyes wastewater treatment. By characterization of FTIR, XPS, Raman, XRD and FESEM, APT nanorods were confirmed to be incorporated into GO laminar layers via grafting modification, which would influence GO interlayer distance (d-spacing), membrane surface microstructure (laminate morphology, structure, and hydrophilicity) and even water separation performance. Comparison of those of pristine GO membrane, the calculated d-spacing of GO/APT membranes gradually increased from 0.90 nm to 1.07 nm, while water contact angles decreased from 71.0° to 43.3° with the increasing APT/GO ratios. Moreover, GO/APT membranes exhibited rough hierarchical microstructure and higher surface hydrophilicity, which was in conjunction with larger interlayer spacing to synergistically improve separation performance. The water permeated flux increased from 3.4 of pristine GO membrane to 13.3 L m−2 h−1 of GO/APT membrane with preserving high rejection nearly to 100% for 7.5 mg L−1 Rh B wastewater under optimized conditions. Similarly, membrane thickness, dye concentrations and separating species in feed solutions were also found to affect membrane separation performance. Dye molecules were efficiently rejected through GO/APT nanofiltration membranes by the synergistic separation mechanism: size exclusion effect because of the unimpeded water channels formed into 3D network laminate structure, and electrostatic interactions between the oxygen-containing functional groups on membrane surface and charged molecules. Such these GO/APT membranes demonstrated efficiently separation properties and thus provided new insight into the potential applications in water purification and dyes wastewater treatment.

Improving the thermal conductivity and mechanical property of epoxy composites by introducing polyhedral oligomeric silsesquioxane‐grafted graphene oxide

In this work, polyhedral oligomeric silsesquioxane‐graphene oxide (POSS‐GO) was prepared by 1,6‐Hexanediamine (HDM) as a bridge and characterized using Fourier transform infrared spectroscopy, thermogravimetric analysis, X‐ray diffraction, and transmission electron microscope. High thermal conductivity toughening composites were prepared by introducing POSS‐GO into epoxy resin (EP) with solution blending. The introduction of HDM‐POSS molecular chain can not only improve the dispersion of GO in epoxy, but also as “stent” prevent the accumulation of GO. Results show that when the weight loading of GO and POSS‐GO was 1.0 phr, the thermal conductivity of composites improved by 26.32 and 63.16% as compared with neat epoxy. Impact strength of POSS‐GO/EP is 29.29% higher than that of GO/EP at 0.8phr and bending strength tests also showed similar results. When compared with pristine GO, POSS‐GO possessed better thermal conductivity and toughening effect for epoxy, moreover, the mechanism is discussed in this paper. POLYM. COMPOS., 39:E1890–E1899, 2018. © 2018 Society of Plastics Engineers

Semi-aromatic polyamide-based nanocomposites: I. in-situ polymerization in the presence of graphene oxide

In-situ interfacial polymerization method was employed to synthesize nanocomposites based on a semi-aromatic polyamide (PA) and pristine or sulfonated graphene oxides (GO or SGO, respectively). The PA chains were produced at the interface of a nonaqueous solution of isophthaloyl dichloride and an aqueous triethylenetetramine solution containing different amounts of GO or SGO dispersed nanosheets. The effects of SGO and pristine GO on the structure, thermal stability and dynamic mechanical and electrical properties of PA were studied. Favorable interfacial interactions between SGO and PA were confirmed using Fourier transform infrared spectroscopy and X-ray diffractometry. Consequently, SGO significantly increased the thermal stability and char residues of PA. Furthermore, adding both pristine and sulfonated GO nanosheets led to an enhancement in storage modulus and a shift in glass transition temperature of the polyamide. Finally, the facile sulfonation of GO resulted in partial reduction of the electrically insulating nanosheets and hence the electrical conductivity and dielectric constant of PA were increased by 10 and 3 times, respectively, at SGO content of 1.0 wt%.

Nanocomposite of γ-Fe2O3 immobilized on graphene oxide for remediation of Ni(II) ions - kinetics, isotherm and thermodynamics studies

Facile sonication method was used to immobilize ?-Fe2O3 nanoparticles (NPs) on graphene oxide (GO) to obtain environmentally stable ?-Fe2O3-GO nanocomposite (NC). Structure, surface morphology and composition of NC were thoroughly studied. M?ssbauer analysis confirmed the presence of maghemite (?-Fe2O3) as dominant phase of iron oxide. TEM images of NC revealed homogeneous distribution of ?-Fe2O3 NPs over the GO nanosheet. A comparative analysis of GO, ?-Fe2O3 NPs and NC for the removal of Ni(II) ions from water was carried out by batch method and adsorption kinetics, thermodynamics and isotherms were also studied. The adsorption data fitted better to Langmuir and Freundlich adsorption isotherms as compared to Dubinin Radushkevich (D-R) and Temkin adsorption isotherms. NC showed higher qmax value (615.0mg/g) as compared to the pristine GO (403.7mg/g) and ?-Fe2O3 NPs (572.4mg/g). The adsorption kinetics followed pseudo-second-order model. NC displayed greater affinity for Ni(II) ions in comparison to pristine GO and ?-Fe2O3 NPs. The results suggested that the synthesized ?-Fe2O3-GO nanocomposite can be used as a promising novel material for the removal of Ni(II) from water due to its higher adsorption capacity, stability, convenient magnetic separation and regeneration.

Enhanced desalination performance of capacitive deionization using zirconium oxide nanoparticles-doped graphene oxide as a novel and effective electrode

Abstract Due to its eco-friendly and low energy technique for removing salt ions from saline water, capacitive deionization (CDI) is highly recommended as a desalination process. Based on its good features, large surface area and good electric conductivity, graphene oxide is a promising electrode in the CDI technology if the specific capacitance could be enhanced. In this study, to improve the electrochemical performances, novel ZrO 2 nanoparticles-incorporated graphene oxide nanosheets with different concentrations were successfully synthesized by hydrothermal treatment, their electrosorption characteristics in CDI unit were examined. The morphology, structure and electrochemical performance of the fabricated materials were investigated by scanning electron microscopy, transmission electron microscopy (TEM), X-ray diffraction (XRD), cyclic voltammetry and electrochemical impedance spectroscopy. The capacitive and electrosorption performances in NaCl solution were studied. Moreover, the role of ZrO 2 loading was investigated. The introduced ZrO 2 -doped graphene oxide showed a distinct improvement in the electrosorption capacity and revealed higher specific capacitance compared to the pristine graphene oxide. The obtained results indicated that the synthesized ZrO 2 -doped graphene oxide nanocomposite having 10 wt.% ZrO 2 displayed a significant increase in the specific capacitance as the corresponding value (452.06 F/g) was nine folds more than that of the pristine GO at 10 mV/s. Moreover, the same electrode exhibits great cycling stability, excellent salt removal efficiency (93.03%), and distinct electrosorptive capacity (4.55 mg/g). Overall, the proposed GO/ZrO 2 nanoparticle composite electrode is appropriate for utilizing as optimum electrodes for the CDI technique.

Ammonia reduced graphene oxides as a hole injection layer for CdSe/CdS/ZnS quantum dot light-emitting diodes

In this study, we report quantum-dot light-emitting devices (QD-LEDs) using ammonia reduced graphene oxide (rGO) as a hole injection layer (HIL). Compared with pristine GO, QD-LEDs employing rGO as a HIL show higher maximum luminance (936 cd m−2 versus 699 cd m−2) and lower turn-on voltage (Vth, 5.0 V versus 7.5 V). The improved performance can be attributed to the synergistic effect of the improved conductivity (1.27 μS cm−1 versus 0.139 μS cm−1) and decreased work function (5.27 eV versus 5.40 eV) of the GO after the reduction process. The above results indicate that ammonia functionalized graphene may be a promising hole injection material for QD-LEDs.

Enhanced β Crystalline Phase in Poly(vinylidene fluoride) via the Incorporation of Graphene Oxide Sheets assisted by Supercritical CO2 Treatment

ABSTRACTGraphene oxide (GO) sheets were pre-modified with a typical piezoelectric polymer, poly(vinylidene fluoride) (PVDF), using a simple supercritical carbon dioxide (SC CO2) method, and then the PVDF-decorated GO was added into a PVDF matrix by solution blending. Transmission electron microscopy (TEM) revealed that the decorating degree of PVDF on the surface of the GO increased significantly with increasing of SC CO2 pressure and PVDF concentration. The mechanism of the polymer adsorption on the GO sheets through favorable interaction between the GO and PVDF chains was identified via Fourier transform infrared spectroscopy (FTIR). Further, the crystallization behavior of PVDF/GO composites was investigated by differential scanning calorimetry (DSC), FTIR and polarized optical microscopy (POM). Interestingly, the composite with PVDF-decorated GO as the filler showed higher β-phase content compared to the composite with pristine GO as the filler. The study showed that the supercritical fluid-induced epitaxial crystallization process has significant potential for fabricating functional GO-based nanocomposties containing piezoelectric or conducting materials.

Comparative in vitro toxicity of a graphene oxide-silver nanocomposite and the pristine counterparts toward macrophages.

BackgroundGraphene oxide (GO) is a highly oxidized graphene form with oxygen functional groups on its surface. GO is an excellent platform to support and stabilize silver nanoparticles (AgNP), which gives rise to the graphene oxide-silver nanoparticle (GOAg) nanocomposite. Understanding how this nanocomposite interacts with cells is a toxicological challenge of great importance for future biomedical applications, and macrophage cells can provide information concerning the biocompatibility of these nanomaterials. The cytotoxicity of the GOAg nanocomposite, pristine GO, and pristine AgNP was compared toward two representative murine macrophages: a tumoral lineage (J774) and peritoneal macrophages collected from Balb/c mouse. The production of reactive oxygen species (ROS) by J774 macrophages was also monitored. We investigated the internalization of nanomaterials by transmission electron microscopy (TEM). The quantification of internalized silver was carried out by inductively coupled plasma mass spectrometry (ICP-MS). Nanomaterial stability in the cell media was investigated overtime by visual observation, inductively coupled plasma optical emission spectrometry (ICP OES), and dynamic light scattering (DLS).ResultsThe GOAg nanocomposite was more toxic than pristine GO and pristine AgNP for both macrophages, and it significantly induced more ROS production compared to pristine AgNP. TEM analysis showed that GOAg was internalized by tumoral J774 macrophages. However, macrophages internalized approximately 60 % less GOAg than did pristine AgNP. The images also showed the degradation of nanocomposite inside cells.ConclusionsAlthough the GOAg nanocomposite was less internalized by the macrophage cells, it was more toxic than the pristine counterparts and induced remarkable oxidative stress. Our findings strongly reveal a synergistic toxicity effect of the GOAg nanocomposite. The toxicity and fate of nanocomposites in cells are some of the major concerns in the development of novel biocompatible materials and must be carefully evaluated.Electronic supplementary materialThe online version of this article (doi:10.1186/s12951-016-0165-1) contains supplementary material, which is available to authorized users.

Exploring complex structural evolution of graphene oxide/ZnO triangles and its impact on photoelectrochemical water splitting

Different morphologies of ZnO (Hollow spheres and Bucky bowls) and graphene oxide/ZnO hybrid structures (nanorod and triangle shaped) were synthesized via a facile hydrothermal method. The structural evolution of pristine ZnO and GO–ZnO hybrid structures were examined in detail over both the experimental and analytical means (deformation models). Herein, the simultaneous effect of dislocation driven growth and Layer by Layer growth is a favored mechanism for GO–ZnO triangles. Furthermore, the oxygen vacancies (VO) in GO–ZnO strongly influence the photoelectrochemical (PEC) performances in two faced effect. The GO–ZnO triangle-shaped composites exhibit the maximum overall water splitting photocurrent density of ∼1.517mA/cm−2 at 1.45V vs RHE with the highest enhancement in the Incident Photon to Current conversion Efficiency (IPCE) of 10.41%, which is ∼3.30 and 2.08 times higher than pristine ZnO Hollow spheres and Bucky bowls respectively. Besides, the similar strategy of GO–ZnO triangle shaped nanocomposites exhibit ∼1.82 times higher than the GO–ZnO nanorod. Hence, the overall improvement in the GO–ZnO triangle shape in comparisons with pristine ZnO samples and/or GO–ZnO rods is due to the increased amounts of oxygen vacancies to some extent.

Synthesis of SnO2 pillared carbon using long chain alkylamine grafted graphene oxide: an efficient anode material for lithium ion batteries.

With the objective of developing new advanced composite materials that can be used as anodes for lithium ion batteries (LIBs), herein we describe the synthesis of SnO2 pillared carbon using various alkylamine (hexylamine; dodecylamine and octadecylamine) grafted graphene oxides and butyl trichlorotin precursors followed by its calcination at 500 °C for 2 h. While the grafted alkylamine induces crystalline growth of SnO2 pillars, thermal annealing of alkylamine grafted graphene oxide results in the formation of amorphous carbon coated graphene. Field emission scanning electron microscopy (FE-SEM) results reveal the successful formation of SnO2 pillared carbon on the graphene surface. X-ray diffraction (XRD), transmission electron microscopy (TEM) and Raman spectroscopy characterization corroborates the formation of rutile SnO2 crystals on the graphene surface. A significant rise in the BET surface area is observed for SnO2 pillared carbon, when compared to pristine GO. Electrochemical characterization studies of SnO2 pillared carbon based anode materials showed an enhanced lithium storage capacity and fine cyclic performance in comparison with pristine GO. The initial specific capacities of SnO2 pillared carbon are observed to be 1379 mA h g(-1), 1255 mA h g(-1) and 1360 mA h g(-1) that decrease to 750 mA h g(-1), 643 mA h g(-1) and 560 mA h g(-1) depending upon the chain length of grafted alkylamine on the graphene surface respectively. Electrochemical impedance spectral analysis reveals that the exchange current density of SnO2 pillared carbon based electrodes is higher, corroborating its enhanced electrochemical activity in comparison with GO based electrodes.

Lipoxygenase-modified Ru-bpy/graphene oxide: Electrochemical biosensor for on-farm monitoring of non-esterified fatty acid

Elevated concentrations of non-esterified fatty acids (NEFA) in biological fluids are recognized as critical biomarkers for early diagnosis of dairy cow metabolic diseases. Herein, a cost-effective, electrochemically active, and bio-friendly sensor element based on ruthenium bipyridyl complex-modified graphene oxide nanosheets ([Ru(bpy)3]2+-GO) is proposed as a biosensor platform for NEFA detection. Electrochemical analysis demonstrates that the [Ru(bpy)3]2+-GO electrodes exhibit superior and durable redox properties compared to the pristine carbon and GO electrodes. Target specificity is accomplished through immobilization of the enzyme, lipoxygenase, which catalyzes the production of redox active species from NEFA. Lipoxygenases retain their catalytic ability upon immobilization and exhibit changes to amperometric signals upon interaction with various concentrations of standard NEFA and serum samples. Our study demonstrates that the [Ru(bpy)3]2+-GO electrode has the potential to serve as a biosensor platform for developing a field deployable, rapid, and user-friendly detection tool for on-farm monitoring of dairy cow metabolic diseases.

Role of oxygen functional groups in graphene oxide for reversible room-temperature NO2 sensing

Reduced graphene oxide (rGO) is one of the promising sensing elements for high-performance chemoresistive sensors because of its remarkable advantages such as high surface-to-volume ratio, outstanding transparency, and flexibility. In addition, the defects on the surface of rGO, including oxygen functional groups, can act as active sites for interaction with gaseous molecules. However, the major drawback of rGO-based sensors is the extremely sluggish and irreversible recovery to the initial state after a sensing event, which makes them incapable of producing repeatable and reliable sensing signals. Here, we show that pristine GO can be used as the active sensing material with reversible and high response to NO2 at room temperature. First-principles calculations, in conjunction with experimental results, reveal the critical role of hydroxyl groups rather than epoxy groups in changing metallic graphene to the semiconducting GO. We show that the adaptive motions of the hydroxyl groups, that is, the rotation of these groups for the adsorption of NO2 molecules and relaxation to the original states during the desorption of NO2 molecules, are responsible for the fast and reversible NO2 sensing behavior of GO. Our work paves the way for realizing high-response, reversible graphene-based room-temperature chemoresistive sensors for further functional convergence.

Vacuum-ultraviolet photoreduction of graphene oxide: Electrical conductivity of entirely reduced single sheets and reduced micro line patterns

We here report a scanning probe method to locally and directly research the electrical properties of vacuum-ultraviolet (VUV) reduced graphene oxide. The measured electrical conductivity of individual VUV-reduced GO (VUV-rGO) sheets by using conductive atomic force microscopy (CAFM) reached 0.20 S·m−1 after 64 min irradiation, which was clearly enhanced compared with the pristine GO. According to the X-ray photoelectron spectroscopy results, the recovered conductivity of VUV-rGO could be ascribed to the partial elimination of oxygen-containing functional groups and the rapid reconstruction of the C=C bonds. Heterogeneously distributed low- and high-conductivity domains (with a diameter of tens of nanometer to ca. 500 nm) were found from current mapping of the VUV-rGO sheet. By applying photomask lithography, rGO regions were drawn into single GO sheet and were researched by CAFM. The in-plane lateral conductivity of rGO regions increased obviously compared with pristine GO regions.

One-step codoping of reduced graphene oxide using boric and nitric acid mixture and its use in metal-free electrocatalyst

In this study, the preparation of a highly efficient metal-free electrocatalyst, boron and nitrogen codoped reduced graphene oxide (BN-rGO), with an excellent durability is reported. The BN-rGO were prepared in one step using boric and nitric acid mixture, exhibiting highly improved oxygen reduction reaction (ORR) activity than those of the pristine GO and single doped rGOs. The electrocatalyst also showed the excellent long-term durability and CO tolerance than those of the commercial Pt/C catalysts.

Chemical and magnetic functionalization of graphene oxide as a route to enhance its biocompatibility.

The novel approach for deposition of iron oxide nanoparticles with narrow size distribution supported on different sized graphene oxide was reported. Two different samples with different size distributions of graphene oxide (0.5 to 7 μm and 1 to 3 μm) were selectively prepared, and the influence of the flake size distribution on the mitochondrial activity of L929 with WST1 assay in vitro study was also evaluated. Little reduction of mitochondrial activity of the GO-Fe3O4 samples with broader size distribution (0.5 to 7 μm) was observed. The pristine GO samples (0.5 to 7 μm) in the highest concentrations reduced the mitochondrial activity significantly. For GO-Fe3O4 samples with narrower size distribution, the best biocompatibility was noticed at concentration 12.5 μg/mL. The highest reduction of cell viability was noted at a dose 100 μg/mL for GO (1 to 3 μm). It is worth noting that the chemical functionalization of GO and Fe3O4 is a way to enhance the biocompatibility and makes the system independent of the size distribution of graphene oxide.

Highly NO2 sensitive caesium doped graphene oxide conductometric sensors.

Here we report on the synthesis of caesium doped graphene oxide (GO-Cs) and its application to the development of a novel NO2 gas sensor. The GO, synthesized by oxidation of graphite through chemical treatment, was doped with Cs by thermal solid-state reaction. The samples, dispersed in DI water by sonication, have been drop-casted on standard interdigitated Pt electrodes. The response of both pristine and Cs doped GO to NO2 at room temperature is studied by varying the gas concentration. The developed GO-Cs sensor shows a higher response to NO2 than the pristine GO based sensor due to the oxygen functional groups. The detection limit measured with GO-Cs sensor is ≈90 ppb.