Synthesis of water dispersible reduced graphene oxide via supramolecular complexation with modified β-cyclodextrin

A noncovalent functionalization of the edges of reduced graphene oxide (RGO) with β-cyclodextrin-graft-hyperbranched polyglycerol (β-CD-g-HPG) was successfully performed via a host-guest interaction. The results showed that β-CD-g-HPG disperses the graphene sheets better than pure β-CD or HPG. The resulted supramolecular structure is stable in neutral water medium more than one week. However, in acidic medium the host-guest interaction is collapsed and graphene nanosheets precipitate.     

Reduced graphene oxide for Li–air batteries: The effect of oxidation time and reduction conditions for graphene oxide

Reduced graphene oxide (rGO) has shown great promise as an air-cathode for Li–air batteries with high capacity. In this article we demonstrate how the oxidation time of graphene oxide (GO) affects the ratio of different functional groups and how trends of these in GO are extended to chemically and thermally reduced GO. We investigate how differences in functional groups and synthesis may affect the performance of Li–O₂ batteries. The oxidation timescale of the GO was varied between 30 min and 3 days before reduction. Powder X-ray diffraction, micro-Raman, FE-SEM, BET analysis, and XPS were used to characterize the GO’s and rGO’s. Selected samples of GO and rGO were analyzed by solid state ¹³C MAS NMR. These methods highlighted the difference between the two types of rGO’s, and XPS indicated how the chemical trends in GO are extended to rGO. A comparison between XPS and ¹³C MAS NMR showed that both techniques can enhance the structural understanding of rGO. Different rGO cathodes were tested in Li–O₂ batteries which revealed a difference in overpotentials and discharge capacities for the different rGO’s. We report the highest Li–O₂ battery discharge capacity recorded of approximately 60,000 mAh/g_carbon achieved with a thermally reduced GO cathode.     

A chemiluminescence sensor for determination of epinephrine using graphene oxide–magnetite-molecularly imprinted polymers

A chemiluminescence (CL) sensor for the determination of epinephrine using the system of luminol–NaOH–H₂O₂ based on a graphene oxide–magnetite-molecularly imprinted polymer (GM-MIP) is described. The epinephrine GM-MIP was synthesized using graphene oxide (G) which improved the adsorption capacity, and magnetite nanoparticles which made the polymers easier to use in the sensor. The adsorption performance and properties were characterized. The GM-MIP was used in CL analysis to increase the selectivity and the possible mechanism was also discussed. The CL sensor responded linearly to the concentration of epinephrine over the range 1.04 × 10^?7–7.06 × 10^?3 mol/L with a detection limit of 1.09 × 10^?9 mol/L (3σ). The relative standard deviation for determination was 3.87%. On the basis of speediness and sensitivity, the sensor is reusable and shows a great improvement in selectivity and adsorption capacity over other sensors. The sensor had been used for the determination of epinephrine in drug samples.     

Ultrasonic assisted synthesis of TiO2–reduced graphene oxide nanocomposites with superior photovoltaic and photocatalytic activities

In this work, TiO₂–reduced graphene oxide (RGO) nanocomposites were successfully produced by an ultrasonication-assisted reduction process. The reduction of graphene oxide (GO) and the formation TiO₂ crystals occurred simultaneously. The synthesized nanocomposite was characterized by SEM, EDX, Raman spectroscopy, FTIR, XRD, XPS, UV–vis spectroscopy, photoluminescence spectrometer and electrochemical impedance spectroscopy. As a result of the introduction of RGO, the light absorption of octahedral TiO₂ was markedly improved. The photocatalytic results revealed that weight percent of RGO has substantial influence on degradation of Rhodamine B under visible light irradiation. The enhancement of the photocatalytic activity can be attributed to the enhancement of the visible-light irradiation harvesting and efficiently separation of the photogenerated charge carriers. Meanwhile, upon the RGO loading, the photoelectric conversion efficiency of TiO₂–RGO nanocomposite modified electrode was also highly improved.     

The doping of reduced graphene oxide with nitrogen and its effect on the quenching of the material’s photoluminescence

N-doped graphene (NG) was synthesized by annealing reduced graphene oxide (RGO) in an ammonia atmosphere. The dependence of the nitrogen content on the annealing temperature and the type of doping of NG were investigated. The photoluminescence (PL) properties of the RGO and NG samples were studied. The results show that RGO exhibits strong ultraviolet (UV) PL at 367 nm. The PL of RGO can be quenched by doping it with N and the quenching efficiency depends on the pyridine N content.     

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.     

Hierarchical 3D starfish-like Ni3S4–NiS on reduced graphene oxide for high-performance supercapacitors

In this research, Ni₃S₄–NiS with starfish morphology was synthesized with a simple hydrothermal method and then hybridized with reduced graphene oxide (rGO) as a material for high-performance supercapacitors. The crystal structure and morphology of the as-prepared materials were studied by X-ray diffraction spectroscopy and electron microscopy. Uniform distribution of Ni₃S₄–NiS on rGO was observed from electron microscopy images. The results showed that Ni₃S₄–NiS/rGO with a specific capacitance of 1578 Fg^-1 and discharge time of 603 s at the current density of 0.5 Ag^-1 has more capacity and stability relative to Ni₃S₄–NiS. The cyclic stability after 5000 cycles showed that the Ni₃S₄–NiS/rGO electrode is stable, and 91% of its corresponding initial capacitance retained at the end of 5000 cycles. The good results in capacitance and stability of this electrode can be regarded as an improvement for the development of highly efficient and economic supercapacitors for portable electronic devices.     

Synthesis of three-dimensional hierarchically porous reduced graphene oxide–TiO2 nanocomposite for enhanced hydrogen storage

Three-dimensional hierarchically porous graphene-TiO₂ (3D-HPGT) nanocomposites were synthesized through electrostatic assembly method. The obtained 3D-HPGT nanocomposites exhibited hierarchically porous structure with multi-level pores (macro-, meso- and micropores), high specific surface area (705?m²/g), large pore volume (0.41?cm³/g) and higher hydrogen storage capacity. At the pressure of 5?bar, 3D-HPGT nanocomposite showed a maximum hydrogen capacity of 4.11 and 1.48?wt% at 77 and 298?K, respectively, which were much higher than those of previously reported graphene-based materials. The enhanced hydrogen storage capacities were attributed to the three-dimensional hierarchically porous structure, evenly distributed TiO₂ nanoparticles on the graphene nanosheets, strong attachment of TiO₂ nanoparticles to the underlying graphene nanosheets, and hydrogen spillover effect originated from TiO₂ nanoparticles.     

Synthesis of SBA 15 graphene oxide composite membrane using phenol–formaldehyde resin pore modifier for CO2 separation

Present study highlights the development of carbon-loaded SBA 15 membrane on clay-alumina tubular support and its performance on the CO₂ separation efficiencies from different mixture gases. To modify the large pores of SBA 15 by graphitic carbon, low molecular weight phenol–formaldehyde (PF) resin was incorporated into the mesoporous channel followed by calcination under inert atmosphere. The modified ordered pore structure of the membrane has been characterized by low-angle XRD, TEM, and pore size distribution analysis. The chemical state of the deposited carbon phase into the SBA 15 pores was analyzed by X-ray photoelectron and Raman spectroscopy. Carbon having graphitic nature mainly in graphene oxide has been deposited into the mesopore of SBA 15 resulting decrease in pore size from 8.9 to 1.0 nm. Finally, the developed SBA 15 carbon membranes were characterized by CO₂ permeation and separation selectivity of CO₂/CH₄, CO₂/CO. Highest CO₂/CH₄ separation factor was achieved as 16.9 with CO₂ permeance 13.6 × 10^–8 mol/m²/s/Pa at 200 kPa feed pressure by the 20% resin with 2 times coated membrane. In flue gas analysis, highest CO₂/CO separation factor of 32.8 was achieved. This study offers an observation on CO₂ separation from simulated BF gas for the first time and the results show the potential of the developed SBA 15/C composite membranes in commercial application.     

Combustion synthesis of graphene oxide–TiO2 hybrid materials for photodegradation of methyl orange

Graphene oxide (GO)–TiO₂ hybrid materials with enhanced photocatalytic properties were synthesized by a one-step combustion method using urea and titanyl nitrate as the fuel and oxidizer, respectively. During the synthesis procedure, the precursors containing GO, fuel, and oxidizer were maintained at different combustion temperatures (300–450 °C) for 10 min to ignite the combustion reaction. The effects of combustion temperatures on the weight loss, chemical status and photocatalytic properties were studied by thermogravimetry and differential scanning calorimetry, X-ray photoelectron spectroscopy, Raman, and photoluminescence. GO in the GO–TiO₂ hybrids were not oxidized, but thermally reduced by decomposition of partial oxygen-containing groups. Meantime, the nitrogen doping of GO was achieved. Compared to the neat TiO₂ obtained at same condition, GO–TiO₂ hybrid obtained at 350 °C exhibited enhanced photodegradation performance, which is attributed to the effective photo-generated electron transferring from TiO₂ to partially reduced GO, which confirmed by the photoluminescence quenching of TiO₂.     

Hydrothermal synthesis of 3D NixCo1−xS2 particles/graphene composite hydrogels for high performance supercapacitors

In this work, three dimensional (3D) Ni_xCo_1−xS₂/graphene composite hydrogels with different Ni contents (denoted as Ni_xCo_1−xS₂/GH (x = 0, 0.31, 0.56, 0.66, 1)) have been synthesized by a simple one-step hydrothermal method and utilized as the active materials of supercapacitors. The as-prepared samples present a 3D interconnected porous network with the pore sizes in the range of several to tens micrometers. Interestingly, the Ni_xCo_1−xS₂ particles are uniformly located on the graphene network and the particle size is evolved from ∼50 nm to ∼1.5 μm with the increase of Ni content. The electrochemical measurements revealed that the specific capacitance, rate capability and cyclability of different Ni_xCo_1−xS₂/GH electrodes are strongly affected by their different Ni content. Among these, the 3D Ni_0.31Co_0.69S₂/GH composite has the highest specific capacitance of 1166 F/g at a current density of 1 A/g. Furthermore, a specific capacitance of 559 F/g can be still maintained at high current density of 20 A/g. After 1000 charge–discharge cycles at 5 A/g, the specific capacitance remains a high value of 755 F/g.     

A facile one step electrostatically driven electrocodeposition of polyviologen–reduced graphene oxide nanocomposite films for enhanced electrochromic performance

Polyviologen (PV)–reduced graphene oxide (rGO) nanocomposite films were fabricated by simple, one-step reductive electropolymerization of cyanopyridinium based precursor monomer (CNP) in an aqueous dispersion of graphene oxide (GO). Since the polymer formation and reduction of graphene oxide occurs within the same potential window, electrocodeposition method was preferred for obtaining nanostructured PV–rGO films. Cyclic voltammetry experiments of PV–rGO displayed two well resolved, reversible one-electron redox processes typical of viologen. Being a redox polymer, incorporation of rGO further enhances the electroactivity of the PV in the composite films. Vibrational spectral analysis with surface characterization revealed structural changes after composite formation along with subsequent reduction of GO within the polymer matrix. The PV–rGO nanostructured film exhibits a high-contrast electrochromism with low driving voltage induced striking color changes from transparent (0 V) to purple (−0.6 V), high coloration efficiency, fast response times and better cycling stability compared to a pristine PV film. This improved performance can be attributed to the high stability of the electrochrome in the composite assembly induced by electrostatically driven non-covalent interactions between redox PV²⁺ and negatively charged rGO, improved electrical conductivity and enlarged surface area accessed through reinforced nanostructured graphene sheets for tethering PV molecules.     

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.     

Modification of poly(vinylidene fluoride) membranes with aluminum oxide nanowires and graphene oxide nanosheets for oil–water separation

To improve the hydrophilic and oleophobic properties of membrane, we adopted aluminum oxide (Al₂O₃) nanowires and graphene oxide (GO) nanosheets to modify poly(vinylidene fluoride) (PVDF) membranes. The experimental results show that the intercalation of Al₂O₃ nanowires between GO nanosheets effectively improved the roughness of the GO–Al₂O₃–PVDF membrane, and the permeability of the membrane with an optimal mass ratio of Al₂O₃ to GO of 7.5 was 31 times that of the GO–PVDF membrane. Furthermore, the addition of Al₂O₃ nanowires significantly enhanced both the hydrophilic and oleophobic properties of the GO–Al₂O₃–PVDF membrane. On the basis of the extended Derjaguin–Landau–Verwey–Overbeek theory, the energy barriers between the oil droplets and GO–PVDF and GO–Al₂O₃–PVDF membranes were 0.63 and 0.9 KT, respectively; this indicated improvements in the anti-oil-fouling ability of the GO–Al₂O₃–PVDF membranes. We also found that both the GO–PVDF and GO–Al₂O₃–PVDF membranes had great oil–water separation rates (97.9 and 99.4%, respectively) with an initial oil concentration of 200 mg/L. The findings of this study show that the GO–Al₂O₃–PVDF membrane is a promising oil–water separation membrane, and further investigation of the cleaning procedure is needed to promote its practical application in oil–water separation. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47493.     

Bio-inspired composite films with integrative properties based on the self-assembly of gellan gum–graphene oxide crosslinked nanohybrid building blocks

Mimicking natural structures to synthesize novel structural materials is attracting considerable attention, but progress in practical applications remains slow. Natural composites achieve excellent balance between strength and toughness from the “brick-and-mortar” arrangement of organic and inorganic layers, accompanied with various toughening mechanisms. We emulate the structural features of natural nacre by combining graphene oxide (GO) and a gellan gum (GG) biopolymer. We also reveal the mechanism of integrative mechanical performance. Several GO nanosheets with GG coating and crosslinking are used as optimal building blocks with intrinsic hard/soft features. These materials are induced to rapidly self-assemble into aligned nacre-like films by vacuum filtration to produce strong and tough bio-inspired composite films with fracture strength of 88.7 MPa, fracture stain of 0.84%, tensile modulus of 25.4 GPa and good biocompatibility. This study has merit of unrestricted fabrication of a homogeneous colloidal suspension of crosslinked nanohybrid building blocks of GO. Composite films constructed using these building blocks are innovative because of combined interactions, including coordination bonding, ionic bonding, and hydrogen bonding among their constituents. These films differ from other reported bio-inspired GO composite films with single adhesion interaction and thus provide good integrative mechanical performance through a multiple energy dissipation mechanism.     

Synthesis and characterization of novel PbS–graphene/TiO2 composite with enhanced photocatalytic activity

In this study novel material PbS–graphene/TiO₂ composites were prepared by sol–gel method. The “as-prepared” composites were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) with an energy dispersive X-ray (EDX) analysis, transmission electron microscopy (TEM), UV–vis diffuse reflectance spectra (DRS) and Raman spectroscopic analysis. The photocatalytic activities were investigated by the degradation of methylene blue (MB) as a standard dye. We observed that coupling of PbS with TiO₂ extends the photoresponse to visible region. This revealed that the excellent photoinduced charge separation abilities and transport properties of graphene make these hybrids as potential candidates for developing high-performance next-generation devices.     

Tailored interphase and thermal interface resistance of self-assembled thermally reduced graphene oxide–polyamide hybrid/epoxy composites with enhanced thermal conductivity

Thermally reduced graphene oxide–polyamide (TrGO-PA) hybrids were fabricated by self-assembly between TrGO nanosheets and PA microparticles, and the dispersibility, interphase extension, and thermal conduction mechanism of TrGO-PA/epoxy (EP) composites were investigated. Most of the oxygen-containing functional groups of TrGO were removed, and a conjugated structure of graphene was recovered. TrGO was distributed evenly on the PA surface via electrostatic adsorption between TrGO and PA, which resulted in the inhibition of TrGO aggregation in the epoxy matrix. Compared with that of TrGO/EP and PA/EP composites, the thermal interface resistance (R_TIM) of TrGO-PA/EP composites was greatly decreased to 38.3 mm² kW⁻¹ and the thermal conductivity was improved to 0.268 W/(m K), which was attributed to the enhanced dispersibility of TrGO-PA and the enlarged interphase in TrGO-PA/EP composites. A schematic model of thermal conduction mechanisms was proposed based on the formation of contiguous thermal transfer pathways by bridged TrGO adsorbed on well-dispersed PA microparticles in TrGO-PA/EP composites. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47826.     

Probing the engineered sandwich network of vertically aligned carbon nanotube–reduced graphene oxide composites for high performance electromagnetic interference shielding applications

Herein, we developed a strategy for fabrication of iron oxide infiltrated vertically aligned multiwalled carbon nanotubes (MWCNT forest) sandwiched with reduced graphene oxide (rGO) sheets network for high performance electromagnetic interference (EMI) shielding application which offers a new avenue in this area. Such engineered sandwiched network exhibits enhanced shielding effectiveness compared to conventional EMI shielding materials. This network of exotic carbons demonstrates the shielding effectiveness value more than 37 dB (>99.98% attenuation) in Ku-band (12.4–18 GHz), which is greater than the recommended limit (∼30 dB) for techno-commercial applications.     

Microwave-assisted synthesis of Ag–TiO2/graphene composite for hydrogen production under visible light irradiation

Novel photocatalysts based on silver (Ag), TiO₂, and graphene were successfully synthesized by microwave-assisted hydrothermal method. The prepared photocatalysts were characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), Brunauer–Emmett–Teller (BET) specific surface area analysis, X-ray photoelectron spectroscopy (XPS) and electrochemical impedance spectroscopy (EIS). The influence of silver loading and graphene incorporation on photocatalytic hydrogen (H₂) production of as-prepared samples was investigated in methanolic aqueous solution under visible light irradiation (λ≥420 nm). The results showed that Ag–TiO₂/graphene composite had appreciably enhanced photocatalytic H₂ production performance under visible light illumination compared to pure TiO₂, Ag–TiO₂ and TiO₂/graphene samples. The enhanced photocatalytic hydrogen production activity of Ag–TiO₂/graphene composite under visible light irradiation could be attributed to increased visible light absorption, reduced recombination of photogenerated charge carriers and high specific surface area. This novel study provides more insight for the development of novel visible light responsive TiO²⁻ graphene based photocatalysts for energy applications.     

The excellent performance of amorphous Cr2O3, SnO2, SrO and graphene oxide–ferric oxide in glucose conversion into 5-HMF

Amorphous Cr₂O₃, SnO₂ and SrO presented an excellent performance in the conversion of glucose to 5-hydroxymethylfurfural (5-HMF), and 5-HMF yields achieved 84%, 81% and 99%, however, the calcined metal oxides almost completely lost the catalytic activities. Although Fe₂O₃ exhibited very poor catalytic activity, the graphene oxide–Fe₂O₃ (GO–Fe₂O₃) displayed a better performance in catalytic glucose conversion to 5-HMF (86% yield) in 1-ethyl-3-methylimidazolium bromide ([EMIM]Br). The plausible mechanisms of glucose conversion to 5-HMF over amorphous Cr₂O₃, SnO₂, SrO and GO–Fe₂O₃ were proposed.