Chemically modified graphene oxide/polybenzimidazobenzophenanthroline nanocomposites with improved electrical conductivity

Graphene/polybenzimidazobenzophenanthroline nanocomposites were prepared through the liquid-phase exfoliation of graphene oxide (GO) and reduced graphene oxide (rGO) in methanesulfonic acid with subsequent solution mixing. Various chemical and combined chemical-thermal methods were examined to be effective for producing rGO with highly graphitic structure and excellent electrical conductivity. Raman and X-ray photoelectron spectroscopy showed higher degree of reduction of the GO with the combined chemical-thermal method compared to other chemical reduction processes. Structural characterization of the nanocomposites by X-ray diffraction, scanning electron microscopy and transmission electron microscopy showed good exfoliation and dispersion of both GO and rGO fillers in the polymer matrix. The thermogravimetric analysis found that the nanocomposites with rGO have higher onset and maximum weight loss temperatures than those with GO. Compared with the pure polymer, the electrical conductivity of the nanocomposites containing 10 wt% GO and GO reduced by the combined chemical-thermal treatment showed a remarkable increase by four and seven orders of magnitude, respectively. Long-term in-situ thermal reduction was performed to further improve the conductivities of the nanocomposites.     

Facile Preparation of LaFeO<Subscript>3</Subscript>/rGO Nanocomposites with Enhanced Visible Light Photocatalytic Activity

The present work demonstrates a facile route for preparing LaFeO₃/rGO nanocomposites comprising of metal oxide nanoparticles and graphene. Structural, morphology, optical and photocatalytic studies of the samples were characterized using powder X-ray diffraction (XRD), FT-IR, Raman, high resolution scanning electron microscopy (HRSEM), high resolution transmission electron microscope (HRTEM), atomic force microscopy (AFM), thermogravimetry (TGA), X-ray photoelectron spectroscopy, UV–visible and photocatalytic. LaFeO₃/rGO nanocomposites believed as an effective photocatalyst for the degradation of methyl orange (MO) dye under visible light irradiation. The inclusion of carbon enhances the light absorption of LaFeO₃, resulting in the enhanced photocatalytic activity of the nanocomposite. The degradation of MO dye under visible light source was completely achieved using LaFeO₃/rGO as a catalyst.     

Effect of electrolyte on the supercapacitive behaviour of copper oxide/reduced graphene oxide nanocomposite

Cupric oxide/reduced graphene oxide (CuO/rGO) nanocomposites were synthesized through a chemical reduction method using hydrazine hydrate as the reducing agent. The morphology, elemental composition, and bonding network of the CuO/rGOnanocomposites were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy respectively. The XRD results reveal lattice spacing and lattice strain from 3.371 to 3.428 Å and 1.05 × 10⁻³to 5.44 × 10⁻³ respectively, with the increasing ratio of rGO: CuO from 1:1 to 1:5. The cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS)and galvanostatic charge-discharge (GCD) studyofCuO/rGOas the electrode material showed excellent super-capacitive behavior in H₂SO₄ over Na₂SO₄ electrolytes. Moreover CuO/rGO nanocomposites exhibited better capacitance retention in H₂SO₄(75.69%) compared to Na₂SO₄(12.06%).     

Fabrication of ZrO2/rGO nanocomposites by flash sintering under AC electric fields

Ceramic matrix nanocomposites containing graphene possess superior mechanical properties. However, these nanocomposites are very difficult to be prepared using the conventional methods due to severe grain growth and simultaneous degradation of the graphene at high sintering temperatures and long dwell time. Herein, the dense ZrO₂/rGO (reduced graphene oxide) nanocomposites are successfully fabricated by flash sintering of the green compacts consisting of ZrO₂ nanoparticles and graphene oxide (GO) at 893–951℃ in merely 5 seconds under the alternating current (AC) electric fields of 130–150 V cm⁻¹. The GO can be in situ thermal reduced during the flash sintering. The as-prepared ZrO₂/rGO nanocomposites exhibit excellent mechanical properties. This study presents a green and simple approach to fabricate the dense ceramic matrix nanocomposites reinforced with graphene at low temperatures in a short time.     

Preparation of functional reduced graphene oxide and its influence on the properties of polyimide composites

Homogeneous dispersion and strong filler–matrix interfacial interactions were vital factors for graphene for enhancing the properties of polymer composites. To improve the dispersion of graphene in the polymer matrix and enhance the interfacial interactions, graphene oxide (GO), as an important precursor of graphene, was functionalized with amine‐terminated poly(ethylene glycol) (PEG–NH₂) to prepare GO–poly(ethylene glycol) (PEG). Then, GO–PEG was further reduced to prepare modified reduced graphene oxide (rGO)–PEG with N₂H₄·H₂O. The success of the modification was confirmed by Fourier transform infrared spectroscopy, thermogravimetric analysis, and Raman spectroscopy. Different loadings of rGO–PEG were introduced into polyimide (PI) to produce composites via in situ polymerization and a thermal reduction process. The modification of PEG–NH₂ on the surface of rGO inhibited its reaggregation and improved the filler–matrix interfacial interactions. The properties of the composites were enhanced by the incorporation of rGO–PEG. With the addition of 1.0 wt % rGO–PEG, the tensile strength of PI increased by 81.5%, and the electrical conductivity increased by eight orders of magnitude. This significant improvement was attributed to the homogeneous dispersion of rGO–PEG and its strong filler–matrix interfacial interactions. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45119.     

Development of photo-anodes based on strontium doped zinc oxide-reduced graphene oxide nanocomposites for improving performance of dye-sensitized solar cells

The goal of this study was to create highly efficient dye-sensitized solar cells (DSSCs) using strontium doped zinc oxide-reduced graphene oxide (Sr-doped ZnO/rGO) nanocomposites. As photo-anodes of DSSCs, ZnO, ZnO/rGO (with weight percent rGO in composites: 0, 0.01, 0.1, 0.5, and 1 wt%) and Sr-doped ZnO/rGO (with Zn_1-xSr_xO nanoparticle stoichiometry: x = 0, 0.02, 0.04, 0.06 and 0.08) nanocomposites were designed and characterized. AFM, FESEM, XRD, EDS, XPS, PL, and FTIR analyses were used to investigate the morphology and structure properties of prepared nanocomposites. UV–vis spectroscopy and photo-electrochemical measurements were used to investigate the efficiency of prepared photo-anodes. The efficiency (η) and short-circuit photocurrent density (JSC) of DSSCs based on Zn_0.92Sr_0.08O/rGO nanocomposite were 7.98 % and 18.4 mA cm⁻², respectively. The results showed that doping Sr on ZnO/rGO nanocomposites resulted in a wide bandgap energy and increased the values of η, J_SC, IPCE, and photo-anode electron transportability. These findings suggest that Sr-doped ZnO/rGO nanocomposites can provide a novel approach for increasing photo-electrochemical activity in ZnO-based DSSCs.     

Electrochemical hydrogen peroxide nanosensor using a reduced graphene oxide-poly(6-(4H-dithieno[3,2-b:2′,3′-d]pyrrol-4-yl)hexan-1-amine) hybrid-modified electrode

The construction and biofunctionalization of graphene-based conjugated polymer nanocomposite that included reduced graphene oxide-poly DTP-NH₂ hybrid-modified glassy carbon electrode (GCE) for the electrochemical H₂O₂ sensing were accomplished in this work. For the construction of the hydrogen peroxide bioassay, as an initial step of fabrication of the nanobiosensor, a novel conductive polymer structure was synthesized by the Suzuki-Miyaura coupling reaction and structural characterization was carried out by ¹H-NMR and Mass spectroscopy techniques. Then, graphene oxide was chemically synthesized according to Hummers' method to expand the effective surface area to enhance the interaction between enzymes and conjugated polymers. This synthesized structure was assembled by an electrochemically polymerized conductive polymer with graphene oxide on a GCE. The modified glassy electrode surface was obtained by covalent bonding of the electrochemically polymerized DTP-NH₂ with graphene oxide and coated on each well as biomimetic material. The structure and sensing properties of the nanosensing hybrid structure were investigated using UV–vis, AFM, SEM, and XRD. Thanks to the fast electron transfer at the poly(DTP-NH2)/rGO nanocomposite electrode interface, the developed biosensor exhibits a fast and linear amperometric response upon H₂O₂. Finally, a biosensor that is more selective and sensitive to H₂O₂ was developed. Also, the Poly(DTP-NH2)/rGO nanocomposite based Hydrogen Peroxide Nano sensor displayed excellent selectivity as well as good reproducibility and stability. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48538.     

High acetic acid sensing performance of Mg-doped ZnO/rGO nanocomposites

Mg-doped ZnO/reduced graphene oxide (rGO) nanocomposites were synthesized using a facile and cost-effective sol-gel procedure to detect acetic acid vapor. Field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), ultraviolet-visible (UV–vis) diffuse reflectance spectroscopy, and photoluminescence (PL) analysis were utilized to characterize morphologies, compositions of the nanocomposites, and optical properties of the synthesized nanostructures. The gas sensing measurements of spin-coated Mg-doped ZnO/rGO thin films were carried out for a temperature range of 150–350?°C at various acetic acid vapor concentrations. It was found that the Mg-doped sample with 20?wt%/v of GO solution concentration exhibited the response/recovery time of 60?s/35?s with the best response of ~?200% for 100?ppm of acetic acid at 250?°C.     

Photovoltaic and UV detector applications of ZnS/rGO nanocomposites synthesized by a green method

The effect of graphene concentration on the photovoltaic and UV detector applications of ZnS/graphene nanocomposites was investigated. The nanocomposites were synthesized by a green, cost-effective, and simple co-precipitation method with different graphene concentrations (5, 10, and 15 wt%) using L-cysteine amino acid as a surfactant and graphene oxide (GO) powder as a graphene source. Transmission electron microscopy (TEM) images showed that the ZnS NPs were decorated on GO sheets and the GO caused a significant decrease in ZnS diameter size. The results of X-ray diffraction (XRD) patterns, Raman, and Fourier transform infrared (FTIR) spectroscopy indicated that the GO sheets were changed into reduced graphene oxide (rGO) during synthesis process. Therefore, L-cysteine amino acid played its role as a reducing agent to reduce the GO. Photovoltaic measurements showed that the graphene caused to increase the efficiency of solar-cell application of ZnS/rGO nanocomposites. In addition, our observation showed that the nanocomposites were suitable as ultraviolet (UV) detectors and graphene concentration increased the responsibility of the detectors.     

Effect of oxygen functional groups of reduced graphene oxide on the mechanical and thermal properties of polypropylene nanocomposites

Reduced graphene oxide (rGO) with various surface structures was prepared by reducing graphene oxide (GO) with hydrazine hydrate (N₂H₄), sodium borohydride (NaBH₄) and l ‐ascorbic acid, respectively. The resulting rGO were used to fabricate rGO/polypropylene (PP) nanocomposites by a melt‐blending method. The surface structure of rGO as well as multifunctional properties of rGO/PP nanocomposites were thoroughly investigated. It was shown that rGO with highest C/O ratio could be obtained by reducing GO with N₂H₄. The crystallization behaviors, tensile strength, thermal conductivity and thermal stability of rGO/PP nanocomposites were significantly improved with the increase of C/O ratio of rGO. For example, with only 1 phr (parts per hundred PP) rGO reduced by N₂H₄, the degree of crystallinity, tensile strength, maximum heat decomposition temperature and thermal conductivity of PP nanocomposite were increased by 6.2%, 20.5%, 48.0 °C and 54.5%, respectively, compared with those of pure PP. Moreover, the thermal degradation kinetics indicated that the decomposition activation energy of rGO/PP nanocomposites could be enhanced by adding rGO with higher C/O ratio. © 2018 Society of Chemical Industry     

UV-assisted sonochemical synthesis and optoelectrical properties of Bi2S3/rGO nanocomposites

In the present study, a simple UV-assisted sonication method is used for the development of bismuth sulfide (Bi₂S₃) nanostructures on graphene sheets. X-ray diffraction (XRD) and Raman results indicated that graphene oxide (GO) layers are reduced. Field emission scanning electron microscopy (FESEM) images also indicated that Bi₂S₃ particles without rGO sheets are agglomerated. In comparison, when adding these sheets, the particles are uniformly spread (decorated) and their size is reduced significantly due to the incorporation of rGO sheets. UV–Vis studies reveal that the band gap in Bi₂S₃/rGO nanocomposites compared with Bi₂S₃ has a shift toward shorter wavelengths, suggesting some changes in the electronic band structure of Bi₂S₃ due to the existence of rGO sheets. Photoluminescence (PL) analysis indicated emission bands in infrared and visible regions resulting from the band edge emission and crystal defects in the samples, respectively. The electrical investigations showed reduced recombination of photogenerated carriers in the nanocomposites. Moreover, the results indicated that the concentration of rGO is an important factor in determining the optoelectrical behavior of these devices.     

Effect of annealing temperature and graphene concentrations on photovoltaic and NIR-detector applications of PbS/rGO nanocomposites

The effect of annealing temperature on photovoltaic and near-infrared (NIR) detector applications of PbS nanoparticles (NPs) and PbS/graphene nanocomposites was investigated. The products were synthesized by a simple co-precipitation method and graphene oxide (GO) sheets were used as graphene source. Several characterization techniques were used to show transfer of the GO into reduced graphene oxide (rGO) during the synthesis process. In addition, the effect of graphene concentrations on morphology, structure, photovoltaic, and detector parameters of the samples were studied. Transmission electron microscope (TEM) images showed that, the PbS NPs were agglomerated, while, the PbS/rGO nanocomposites were dispersed completely after annealing under H₂/Ar gas atmosphere. UV–visible spectrometer showed an absorption peak for all samples in the near infrared red (NIR) region of the electromagnetic spectrum. The results indicated that, photocurrent intensity, responsivity of the samples to an NIR source, and solar-cell efficiency were affected by annealing of samples and graphene concentrations.     

Flexible rGO-SnO2 supercapacitors converted from pastes containing SnCl2 liquid precursor using atmospheric-pressure plasma jet

Reduced graphene oxide (rGO)-SnO₂ nanocomposites are fabricated on carbon cloth from screen-printed pastes containing rGO nanoflakes and SnCl₂ liquid precursor by using a nitrogen atmospheric-pressure plasma jet (APPJ). RGO-SnO₂-coated carbon cloth is then used as the electrode of gel-electrolyte supercapacitors (SCs). Experiments conducted with various APPJ processing times suggest that the optimal APPJ processing time is 300 s. Cyclic voltammetry (CV) measurements indicate that 300-s APPJ processing results in the best areal capacitance of 97.53 mF/cm². The capacitance retention rate is ~85% after a 10,000-cycle CV test. Further, capacitance increases by 11% after a 1000-cycle bending test under a bending radius of 7.5 mm, possibly owing to the better electrolyte/electrode contact and decrease in the charge transport resistance after mechanical bending. This study also characterized APPJ-processed rGO-SnO₂ nanocomposites by scanning electron microscopy with energy dispersive spectroscopy, X-ray photoelectron spectroscopy, X-ray diffractometry, Raman spectroscopy, and water contact angle measurements.     

Microwave-assisted one-pot synthesis of metal/metal oxide nanoparticles on graphene and their electrochemical applications

An effective synthesis strategy of hybrid metal (PtRu)/metal oxide (SnO₂) nanoparticles on graphene nanocomposites is developed using a microwave-assisted one-pot reaction process. The mixture of ethylene glycol (EG) and water is used as both solvent and reactant. In the reaction system for the synthesis of SnO₂/graphene nanocomposite, EG not only reduces graphene oxide (GO) to graphene, but also results in the formation of SnO₂ facilitated by the presence of a small amount of water. On the other hand, in the reaction system for preparation of PtRu/graphene nanocomposites, EG acts as solvent and reducing agent for reduction of PtRu nanoparticles from their precursors and reduction of graphene from graphene oxide. Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM) characterizations confirm the feasibility of the microwave-assisted reaction system to simultaneously reduce graphene oxide and to form SnO₂ or PtRu nanoparticles. The as-synthesized SnO₂/graphene hybrid composites show a much higher supercapacitance than the pure graphene, and the as-prepared PtRu/graphene show much better electrocatalytic activity for methanol oxidation compared to the commercial E-TEK PtRu/C electrocatalysts.     

Multiscale patterning of graphene oxide and reduced graphene oxide for flexible supercapacitors

A simple and facile method for multiscale, in-plane patterning of graphene oxide and reduced graphene oxide (GO–rGO) was developed by region-specific reduction of graphene oxide (GO) under a mild irradiation. The UV-induced reduction of graphene oxide was monitored by various spectroscopic techniques, including optical absorption, X-ray photoelectron spectroscopy (XPS), Raman, and X-ray diffraction (XRD), while the resultant GO–rGO patterned film morphology was studied on optical microscope, scanning electron microscope (SEM), and atomic force microscope (AFM). Flexible symmetric and in-plane supercapacitors were fabricated from the GO–rGO patterned polyethylene terephthalate (PET) electrodes to show capacitances up to 141.2 F/g.     

In Situ Synthesis of Reduced Graphene Oxide and Gold Nanocomposites for Nanoelectronics and Biosensing

In this study, an in situ chemical synthesis approach has been developed to prepare graphene–Au nanocomposites from chemically reduced graphene oxide (rGO) in aqueous media. UV–Vis absorption, atomic force microscopy, scanning electron microscopy, transmission electron microscopy, and Raman spectroscopy were used to demonstrate the successful attachment of Au nanoparticles to graphene sheets. Configured as field-effect transistors (FETs), the as-synthesized single-layered rGO-Au nanocomposites exhibit higher hole mobility and conductance when compared to the rGO sheets, promising its applications in nanoelectronics. Furthermore, we demonstrate that the rGO-Au FETs are able to label-freely detect DNA hybridization with high sensitivity, indicating its potentials in nanoelectronic biosensing.     

Effect of the sheet size on the thermal stability of silicone rubber–reduced graphene oxide nanocomposites

The structures of differently sized reduced graphene oxides (rGOs), the dispersion state, and the compatibility of rGO with silicone rubber (SR) are important impact factors on the properties of SR–rGO nanocomposites. To analyze the influence of the size of rGO on the properties of SR-based nanocomposites, three differently sized rGO sheets were introduced into SR to fabricate a series of SR-based nanocomposites. The SR–middle-sized reduced graphene oxide (MrGO) nanocomposites showed the best mechanical and thermal properties. Compared with the blank sample, the SR–MrGO nanocomposites presented remarkable two-fold and three-fold increases in the tensile modulus and strength values. The initial degradation temperature increased nearly 40 °C. In this study, we investigated the size effect of graphene on the thermal stability by examining the thermal degradation mechanism of the different SR–rGO nanocomposites in detail. Ultimately, this research may suggest a facile approach for improving the thermal stability of SR. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47034.     

A selective determination of levodopa in the presence of ascorbic acid and uric acid using a glassy carbon electrode modified with reduced graphene oxide

A selective determination of levodopa (LD) in the presence of ascorbic acid (AA) and uric acid (UA) has been investigated at a glassy carbon electrode modified with reduced graphene oxide (rGO). The graphene oxide was synthesized chemically by Hummers method and characterized by energy-filtered transmission electron microscopy (EF-TEM). The reduced graphene oxide modified glassy carbon electrode (rGO/GCE) showed excellent electrochemical performance in the simultaneous electrochemical detection of LD, AA, and UA due to the unique properties of graphene, such as large surface area, facile electronic transport and high electrocatalytic activity. The redox characteristics of rGO/GCE were investigated with cyclic voltammetry (CV) and differential pulse voltammetry (DPV). Well-resolved oxidation peak potentials, corresponding to the oxidation of AA, LD, and UA, were observed from their mixture solution at 0.098, 0.285, and 0.423 V, respectively. The rGO/GCE showed that LD can be detected without the interference of AA and UA. Under the optimized conditions, the oxidation peak current of LD is linear with the concentration of LD from 2.0 to 100 μM with the detection limit of 1.13 μM (S/N = 3). The present electrode system was also successfully applied to direct determination of LD in commercially available tablets and urine samples.     

Preparation of Ag/reduced graphene oxide reinforced copper matrix composites through spark plasma sintering: An investigation of microstructure and mechanical properties

The reduced graphene oxide (rGO) decorated with Ag nanoparticles was synthesized by the chemical reduction of graphene oxide in an aqueous solution containing AgNO₃, in the presence of hydrazine hydrate as a reducing agent. The reduction of graphene oxide was confirmed by FT-IR and raman spectroscopy analyses. The x-ray diffraction pattern and UV–visible investigations demonstrated the formation of Ag particles on the surface of rGO sheets. After successful decoration, the Ag/rGO nano-composite was used as the reinforcement in the copper matrix composite. Cu–Ag/rGO composites with different percentages of Ag/rGO (0.4, 0.8, 1.6 and 3.2 vol%.) were prepared by mechanical milling and spark plasma sintering (SPS). The effects of the Ag/rGO content on the consolidation process, micro-hardness, bending strength and also, fracture surface of the prepared samples were then investigated. The three-point bending strength of the sintered samples was increased from 285 to 472 MPa by the addition 0.8 vol%. of Ag/rGO, as compared to the pure Cu. Moreover, increasing the reinforcement content to the 3.2 vol%. Ag/rGO led to decreasing the bending strength to 433 MPa. The highest micro-hardness (81 Hv) was obtained for the composite sample containing the 1.6 vol%. Ag/rGO. By increasing Ag/r-GO as the reinforcement (3.2 vol%.), the Vickers hardness was decreased to 69 Hv. Also, investigation of the fracture surface morphology showed transformation of fracture mechanism from plastic changes to brittle ones by raising the Ag/rGO content volume from 0.8 to 1.6 vol %.     

Effect of oxidation debris on spectroscopic and macroscopic properties of graphene oxide

Oxidation debris (OD) and graphene oxide (GO) before and after OD removal were characterized by Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy, mass spectroscopy, X-ray diffraction, transmission electron microscopy and potentiometric titration, respectively. OD removal decreased GO absorption intensity in UV/Vis spectra, caused changes in peak position and absorption intensity in FTIR spectra, and resulted in the decrease of I_D/I_G in Raman spectra. OD was amorphous and had higher content of acidic groups than purified GO. OD contributed 10–25% of overall surface charge density to unpurified GO in spite of small amount (ca. 1% mass). OD removal decreased significantly GO dispersibility in aqueous solution, but increased obviously the electrical conductivity of reduced graphene oxide (rGO) and the apparent density of compacted rGO. The removal of OD was necessary because of its striking effects on both GO spectroscopic and macroscopic properties. Batch desorption in NaOH solution was recommended for OD removal from as-prepared graphite oxide because of slow OD desorption kinetics.