Reduced graphene oxide anchored with δ-MnO2 nanoscrolls as anode materials for enhanced Li-ion storage

We developed a one-pot in situ synthesis procedure to form nanocomposite of reduced graphene oxide (RGO) sheets anchored with 1D δ-MnO₂ nanoscrolls for Li-ion batteries. The as-prepared products were characterized by X-ray diffraction (XRD), Raman spectra, X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscope (FESEM) and transmission electron microscope (TEM). The electrochemical performance of the δ-MnO₂ nanoscrolls/RGO composite was measured by galvanostatic charge/discharge cycling and electrochemical impedance spectroscopy. The results show that the δ-MnO₂ nanoscrolls/RGO composite displays superior Li-ion battery performance with large reversible capacity and high rate capability. The first discharge and charge capacities are 1520 and 810 mAh g⁻¹, respectively. After 50 cycles, the reversible discharge capacity is still maintained at 528 mAh g⁻¹ at the current density of 100 mAh g⁻¹. The excellent electrochemical performance is attributed to the unique nanostructure of the δ-MnO₂ nanoscrolls/RGO composite, the high capacity of MnO₂ and superior electrical conductivity of RGO.     

Facile hydrothermal synthesis and optical limiting properties of TiO2-reduced graphene oxide nanocomposites

TiO₂/reduced graphene oxide (RGO) nanocomposites Gx (RGO titania nanocomposite, x grams tetrabutyl titanate per 0.03 g RGO, x = 0.25, 0.50, 1.00) were prepared by a hydrothermal method: graphene oxide was reduced to RGO in a 2:1 water:ethanol mixture in the presence of varying quantities of tetrabutyl titanate, which deposited as TiO₂ on the RGO sheets. The nanocomposites were characterized by a combination of Fourier transform infrared spectroscopy, diffuse reflectance ultraviolet–visible spectroscopy, photoluminescence spectroscopy, Raman spectroscopy, X-ray powder diffraction, X-ray photoelectron spectroscopy and transmission electron microscopy studies. The nanocomposite G0.25 exhibits enhanced nonlinear optical properties compared to its individual components, which is ascribed to a combination of mechanisms. The role of defects and electron/energy transfer in the optical limiting performance of G0.25 was clarified with the help of Raman and photoluminescence spectroscopies. Intensity-dependent switching between reverse saturable absorption and saturable absorption behavior was observed with the G0.50 nanocomposite.     

Low-cost preparation of a conductive and catalytic graphene film from chemical reduction with AlI3

AlI₃ synthesized by I₂ and Al in ethanol was used as reductive agent to directly obtain flexible reductive graphene oxide (RGO) films with high conductivity of 5320 S/m from graphene oxide (GO) films at a low temperature of 80 °C. This reductive method has provided a low-cost and effective route for large-scale production of graphene with high catalytic activity. Structural evolution during the reduction of GO was studied by Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy. The RGO films served as counter electrode exhibited high electrochemical activity.     

Highly thermal conductive composites with polyamide-6 covalently-grafted graphene by an in situ polymerization and thermal reduction process

The thermal conductive polyamide-6/graphene (PG) composite is synthesized by in situ ring-opening polymerization reaction using ε-caprolactam as the monomer, 6-aminocaproic acid as the initiator and reduced graphene oxide (RGO) as the thermal conductive filler. The generated polyamide-6 (PA6) chains are covalently grafted onto graphene oxide (GO) sheets through the “grafting to” strategy with the simultaneous thermal reduction reaction from GO to RGO. The homogeneous dispersion of RGO sheets in PG composite favors the formation of the consecutive thermal conductive paths or networks at a relatively low GO sheets loading, which improves the thermal conductivity (λ) from 0.196 W m⁻¹ K⁻¹ of neat PA6 to 0.416 W m⁻¹ K⁻¹ of PG composite with only 10 wt% GO sheets loading.     

MoO3/reduced graphene oxide composites as anode material for sodium ion batteries

MoO₃/reduced graphene oxide (MoO₃/RGO) composites were successfully prepared via a facile one-step hydrothermal method, and evaluated as anode materials for sodium ion batteries (SIBs). The crystal structures, morphologies and electrochemical properties of the as-prepared samples were characterized by X-ray diffraction, field-emission scanning electron microscopy, cyclic voltammetry, electrochemical impedance spectroscopy, and galvanostatic charge/discharge tests, respectively. The results show that the introduction of RGO can enhance the electrochemical performances of MoO₃/RGO composites. MoO₃/RGO composite with 6 wt% RGO delivers the highest reversible capacity of ~208 mA h g⁻¹ at 50 mA g⁻¹ after 50 cycles with good cycling stability and excellent rate performance for SIBs. The excellent sodium storage performance of MoO₃/RGO should be attributed to the synergistic effect between MoO₃ and RGO, which offers the increased electrical conductivity, the facilitated electron transfer ability and the buffering of volume expansion.     

Increasing the antioxidant activity of green tea polyphenols in the presence of iron for the reduction of graphene oxide

An easy method for green and low-temperature (40 °C) reduction of graphene oxide (GO) by increasing the antioxidant activity of green tea polyphenols (GTPs) in the presence of iron was developed. The reduction level (obtained by X-ray photoelectron spectroscopy) and electrical conductivity (obtained by current–voltage measurement) of the GO sheets reduced by GTPs in the presence of iron were comparable to those of hydrazine-reduced GO and much better than those of the GO reduced by only GTPs (in the absence of iron) at reduction temperatures of 40–80 °C. Raman spectroscopy indicated that application of GTPs in the presence of iron, in contrast to hydrazine, resulted in better recovering of the sp²-hybridized structure of the sheets. The lasting water dispersion of the polyphenolic-reduced GO sheets in the presence of iron was assigned to π–π adsorption of Fe²⁺-polyphenol radicals on surface of the reduced sheets. A mechanism describing the role of iron in the reduction of the GO by epicatechin gallate and epigallocatechin gallate of green tea was also proposed.     

One-step hydrothermal synthesis of Sb2S3/reduced graphene oxide nanocomposites for high-performance sodium ion batteries anode materials

Sb₂S₃/reduced graphene oxide (SSR) nanocomposites were successfully synthesized through a facile one-step hydrothermal process, as used as anode materials for sodium ion batteries (SIBs). The characterization and electrochemical performance of the as-prepared samples were characterized by X-ray diffraction, field-emission scanning electron microscopy, transmission electron microscopy, nitrogen adsorption-desorption isotherms, cyclic voltammetry, electrochemical impedance spectroscopy, and galvanostatic charge/discharge tests, respectively. The results show that the introduction of reduced graphene oxide (RGO) can improve the electrochemical performances of SSR nanocomposites. SSR nanocomposites with 10 wt% RGO exhibits the highest reversible capacity of 581.2 mAh g⁻¹ at the current density of 50 mA g⁻¹ after 50 cycles, and excellent rate performance for SIBs. The improved electrochemical performance is attributed to the smaller Sb₂S₃ nanoparticles dispersed on RGO crumpled structure and synergetic effects between Sb₂S₃ and RGO matrix, which can increase specific surface area and improve electrical conductivity, reduce sodium ion diffusion distance, and effectively buffer volume changes during cycling process.     

One-step electrodeposition synthesis of silver-nanoparticle-decorated graphene on indium-tin-oxide for enzymeless hydrogen peroxide detection

Silver-nanoparticles-decorated reduced graphene oxide (rGO) was electrodeposited on indium tin oxide (ITO) by a cyclic voltammetry method. The results of X-ray diffraction, Fourier-transform infrared transmission spectroscopy and Raman spectroscopy confirmed the simultaneous formation of cubic phase silver nanoparticles and reduction of GO through the electrodeposition process. Field emission scanning electron microscope images showed a uniform distribution of nanometer-sized silver nanoparticles with a narrow size distribution on the RGO sheets, which could only be achieved using silver ammonia complex instead of silver nitrate as precursor. The composite deposited on ITO exhibited notable electrocatalytic activity for the reduction of H₂O₂, leading to an enzymeless electrochemical sensor with a fast amperometric response time less than 2 s. The corresponding calibration curve of the current response showed a linear detection range of 0.1–100 mM (R² = 0.9992) while the limit of detection was estimated to be 5 μM.     

Green reduction of graphene oxide by aqueous phytoextracts

The reduction of graphene oxide (GO) by phytochemicals was investigated using aqueous leaf extracts of Colocasia esculenta and Mesua ferrea Linn. and an aqueous peel extract of orange (Citrus sinensis). The prepared GO and phytoextract reduced GO (RGO) were characterized by ultraviolet–visible spectroscopy, Raman spectroscopy and Fourier transform infrared analyses to provide a clear indication of the removal of oxygen-containing groups from the graphene and the formation of RGO. The extent of reduction was determined from elemental analysis. Formation of few layers of graphene was indicated by transmission electron microscopy. The obtained RGO exhibited good specific capacitance (17–21 Fg^?1), high electrical conductivity (3032.6–4006 Sm^?1) and high carbon to oxygen ratio (5.97–7.11).     

Fabrication and properties of reduced graphene oxide reinforced yttria-stabilized zirconia composite ceramics

Fully dense yttria-stabilized zirconia (YSZ) ceramics reinforced with reduced graphene oxide (RGO) were fabricated by spark plasma sintering (SPS), and their electrical, thermal, and mechanical properties were investigated. Graphene oxide (GO) was exfoliated by a short sonification in dimethylformamide (DMF)/water solution and uniformly mixed with ZrO₂ powders. The microstructure of the composites showed that undamaged RGO sheets were homogeneously distributed throughout matrix grains. The electrical conductivity of YSZ composites drastically increased with the addition of RGO, and it reached 1.2 × 10⁴ S/m at 4.1 vol.%. However, the thermal diffusivity increased only 12% with RGO addition. The hardness decreased slightly with RGO addition, whereas the fracture toughness significantly increased from 4.4 to 5.9 MPa^1/2. The RGO pull-out and crack bridging contributed to the improved fracture toughness.     

Structural,magnetic, and textural properties of iron oxide-reduced graphene oxide hybrids and their use for the electrochemical detection of chromium

Superparamagnetic Fe₃O₄ nanoparticles were anchored on reduced graphene oxide (RGO) nanosheets by co-precipitation of iron salts in the presence of different amounts of graphene oxide (GO). A pH dependent zeta potential and good aqueous dispersions were observed for the three hybrids of Fe₃O₄ and RGO. The structure, morphology and microstructure of the hybrids were examined by X-ray diffraction, transmission electron microscopy (TEM), Fourier transform infrared spectroscopy, Raman and X-ray photoelectron spectroscopy. TEM images reveal lattice fringes (d₃₁₁ = 0.26 nm) of Fe₃O₄ nanoparticles with clear stacked layers of RGO nanosheets. The textural properties including the pore size distribution and loading of Fe₃O₄ nanoparticles to form Fe₃O₄–RGO hybrids have been controlled by changing the concentration of GO. An observed maximum (～10 nm) in pore size distribution for the sample with 0.25 mg ml^?1 of GO is different from that prepared using 1.0 mg ml^?1 GO. The superparamagnetic behavior is also lost in the latter and it exhibits a ferrimagnetic nature. The electrochemical behavior of the hybrids towards chromium ion was assessed and a novel electrode system using cyclic voltammetry for the preparation of an electrochemical sensor platform is proposed. The textural properties seem to influence the electrochemical and magnetic behavior of the hybrids.     

High quality graphene sheets from graphene oxide by hot-pressing

We report a simple and effective route to convert graphene oxide sheets to good quality graphene sheets using hot pressing. The reduced graphene oxide sheets obtained from graphene oxide by low temperature thermal exfoliation are annealed at 1500 °C and 40 MPa uniaxial pressures for 5 min in vacuum. No appreciable oxygen content was observed from X-ray photoelectron spectroscopy and no D peak was detected in the Raman spectrum. The graphene sheets produced had a much higher electron mobility (1000 cm² V⁻¹ S⁻¹) than other chemically modified graphenes.     

Phenolic resin-based composite sheets filled with mixtures of reduced graphene oxide, γ-Fe2O3 and carbon fibers for excellent electromagnetic interference shielding in the X-band

Composite sheets consisting of phenolic resin filled with a mixture of reduced graphene oxide (RGO), γ-Fe₂O₃ and carbon fibers have been produced by compression molding. Its electrical conductivity lies in the range 0.48–171.21 S/cm. Transmission and scanning electron microscopy observations confirm the presence of nano particles of γ-Fe₂O₃ (～9.8 nm) and carbon fiber (～1 mm) which gives flexural strength to composite sheets. Thermogravimetric analysis show that the thermal stability of the sheets depend upon the amount of RGO and phenol resin in the composite. Complex parameters, i.e., permittivity (ε* = ε′ ? iε″) and permeability (μ* = μ′ ? iμ″) of RGO/γ-Fe₂O₃/carbon fiber have been calculated from experimental scattering parameters (S₁₁ and S₂₁) using theoretical calculations given in Nicholson?Ross and Weir algorithms. The microwave absorption properties of the sheets have been studied in the 8.2–12.4 GHz (X-Band) frequency range. The maximum shielding effectiveness observed is 45.26 dB, which strongly depends on dielectric loss and volume fraction of γ-Fe₂O₃ in RGO matrix.     

A green and facile one-pot synthesis of Ag–ZnO/RGO nanocomposite with effective photocatalytic activity for removal of organic pollutants

In this study, Ag–ZnO/reduced graphene oxide (Ag–ZnO/RGO) composite was synthesized by a green and facile one-step hydrothermal process. Aqueous suspension containing Ag and ZnO precursors with graphene oxide (GO) sheets was heated at 140 °C for 2 h. The morphology and structure of as-synthesized particles were characterized by field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Raman spectroscopy, and Photoluminescence (PL) spectroscopy which revealed the formation of composite of metal, metal oxide and RGO. It was observed that the presence of Ag precursor and GO sheets in the hydrothermal solution could sufficiently decrease the size of ZnO flowers. The hybrid nanostructure, with unique morphology, obtained from this convenient method (low temperature, less time, and less number of reagents) was found to have good photocatalytic and antibacterial activity. The perfect recovery of catalyst after reaction and its unchanged efficiency for cyclic use showed that it will be an economically and environmentally friendly photocatalyst.     

Platinum supported on reduced graphene oxide as a catalyst for hydrogenation of nitroarenes

Reduced graphene oxide (RGO)-supported platinum (Pt) catalyst was prepared by simple ethylene glycol (EG) reduction and used for hydrogenation of nitroarenes. Characterizations showed that EG as a reductant exhibited more advantages than the widely used hydrazine hydrate to fabricate monodispersed, small sized Pt nanoparticles on the surface of RGO. The yield of aniline over the Pt/RGO-_EG catalyst reached 70.2 mol-_AN/(mol-_Pt min) at 0 ^oC, which is 12.5 and 19.5 times higher than that of multi-walled carbon nanotube- and active carbon-supported Pt catalysts, respectively. When the reaction temperature was increased to 20 ^oC, the catalytic activity of Pt/RGO-_EG jumped to 1138.3 mol-_AN/(mol-_Pt min), and it was also extremely active for the hydrogenation of a series of nitroarenes. The unique catalytic activity of Pt/RGO-_EG is not only related to the well dispersed Pt clusters on the RGO sheets but also the well dispersion of Pt/RGO-_EG in the reaction mixture.     

The effect of graphene dispersion on the mechanical properties of graphene/epoxy composites

The effect of dispersion state of graphene on mechanical properties of graphene/epoxy composites was investigated. The graphene sheets were exfoliated from graphite oxide (GO) via thermal reduction (thermally reduced GO, RGO). Different dispersions of RGO sheets were prepared with and without ball mill mixing. It was found that the composites with highly dispersed RGO showed higher glass transition temperature (T_g) and strength than those with poorly dispersed RGO, although no significant differences in both the tensile and flexural moduli are caused by the different dispersion levels. In particular, the T_g was increased by nearly 11 °C with the addition of 0.2 wt.% well dispersed RGO to epoxy. As expected, the highly dispersed RGO also produced one or two orders of magnitude higher electrical conductivity than the corresponding poorly dispersed RGO. Furthermore, an improved quasi-static fracture toughness (K_IC) was measured in the case of good dispersion. The poorly and highly dispersed RGO at 0.2 wt.% loading resulted in about 24% and 52% improvement in K_IC of cured epoxy thermosets, respectively. RGO sheets were observed to bridge the micro-crack and debond/delaminate during fracture process due to the poor filler/matrix and filler/filler interface, which should be the key elements of the toughening effect.     

Excellent electrocatalytic performance of Pt nanoparticles on reduced graphene oxide nanosheets prepared by a direct redox reaction between Na2PtCl4 and graphene oxide

A simple and environment-friendly method was used to prepare Pt/reduced graphene oxide (Pt/RGO) hybrids. This approach used a redox reaction between Na₂PtCl₄ and graphene oxide (GO) nanosheets and a subsequent thermal reduction of the material at 200 °C for 24 h in a vacuum oven. In contrast to other methods that use an additional reductant to prepare Pt nanoparticles, the Pt²⁺ was directly reduced to Pt⁰ in the GO solution. GO was used as the reducing agent, the stabilizing agent and the carrier. The resulting Pt/RGO hybrid was characterized by X-ray diffraction, thermo-gravimetric analysis, X-ray photoelectron spectroscopy, transmission electron microscopy and energy-dispersive X-ray spectroscopy. Electrochemical measurements showed that the Pt/RGO hybrids exhibit good activity as catalysts for the electro-oxidation of methanol and ethanol in acid media. Interestingly, the Pt/RGO hybrids showed better electrocatalytic activity and stability for the oxidation of methanol than Pt/C and Pt/RGO hybrids made from other Pt precursors. This indicates that the Pt/RGO hybrids should have great potential applications in direct methanol and ethanol fuel cells.     

Fabrication of manganese oxide/three-dimensional reduced graphene oxide composites as the supercapacitors by a reverse microemulsion method

Manganese oxide (MnO₂)/three-dimensional (3D) reduced graphene oxide (RGO) composites were prepared by a reverse microemulsion (water/oil) method. MnO₂ nanoparticles (3–20 nm in diameter) with different morphologies were produced and dispersed homogeneously on the macropore surfaces of the 3D RGO. Scanning electron microscopy and transmission electron microscopy were applied to characterize the microstructure of the composites. The MnO₂/3D RGO composites, which were annealed at 150 °C, displayed a significantly high specific capacitance of 709.8 F g⁻¹ at 0.2 A g⁻¹. After 1000 cycles, the capacitance retention was measured to be 97.6%, which indicates an excellent long-term stability of the MnO₂/3D RGO composites.     

A high capacity NiFe2O4/RGO nanocomposites as superior anode materials for sodium-ion batteries

NiFe₂O₄/reduced graphene oxide (NFO/RGO) nanocomposites were prepared by a facile one-step hydrothermal method and used as anode for sodium ion batteries (SIBs). The crystal structures, morphologies and electrochemical properties of as-prepared samples were evaluated by X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and galvanostatic charge/discharge tests. The results show that NFO/RGO-20 (20 wt%) delivers the highest reversible capacity of ~450 mA h g⁻¹ at 50 mA g⁻¹ after 50 cycles with good cycling stability. The excellent sodium storage performance of NFO/RGO should be attributed to the synergistic effect between NFO and RGO to form conductive network structure, which offers the increased specific surface area, the facilitated electron transfer ability and the buffering of volume expansion.     

An efficient method of producing stable graphene suspensions with less toxicity using dimethyl ketoxime

A highly stable graphene suspension has been prepared using dimethyl ketoxime (DMKO) as reductant. Nitrogen was doped into the graphene plane at the same time as the graphene oxide (GO) sheets were reduced. X-ray photoelectron spectroscopy indicated that the C/O ratio of graphene was significantly increased after GO was treated with DMKO and the quantity of nitrogen incorporated into the graphene lattice was 3.67 at.%. The electrical conductivity of the graphene paper was found to be ～10² S m^?1, which was 5 orders of magnitude better than that of GO, and this demonstrated the effective chemical reduction of GO. The mechanism of the chemical reaction of GO with DMKO was also discussed. The as-produced graphene material showed good capacitive behavior and long cycle life with a specific capacitance of ～140 F g^?1.