Fabrication and characterization of graphene oxide/zinc oxide nanorods hybrid

This work presented a hybrid architecture of graphene oxide (GO)/ZnO nanorods (ZNs) with ZNs attached parallel onto GO sheets. ZNs were synthesized by refluxing zinc acetate dehydrate in methanol solution under basic conditions followed by surface modification of 3-aminopropyl triethoxysilane (ATS), and then the preformed ZNs were attached onto GO sheets by reaction of the amino groups on the outer wall of ZNs with the carboxyl groups on the GO surface. Transmission electron microscopy (TEM) image of the as-prepared hybrid reveals the morphology of the architecture of GO/ZNs hybrid. Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), thermogravimetric analysis (TGA) ultraviolet-visible (UV-vis) and fluorescence spectroscopy were also performed to characterize the structure and properties of the GO/ZNs hybrid. It was shown that ZNs maintained their initial morphology and crystallinity in the hybrid and the luminescence quenching of yellow-green emission of ZNs confirmed the electron transfer from excited ZnO to GO sheets.     

Gold nanoparticles produced by laser ablation in water and in graphene oxide suspension

The comparison between two different approaches based on the use of the laser ablation in medium to synthetise gold nanoparticles is presented and discussed. Deionised water as well as a graphene oxide (GO) suspension in deionised water have been employed as solution to produce gold nanoparticles by laser ablation. In the former case, the nanoparticles assembly has been stabilised by using surfactants, but in the latter case to avoid undesired effects the use of chemicals was not necessary and Au reduced graphene oxide (Au-rGO) nanocomposites have been obtained. The structure, size and composition of the gold nanoparticles and of the Au–rGO nanocomposites have been monitored by UV–Vis–NIR absorption spectroscopy and Raman spectroscopy, the transmission and scanning electron microscopies and the X-ray energy-dispersive spectroscopy. The presented methodology of Au rGO nanocomposites preparation could represent a green alternative on the production of metallic nanoparticles in biocompatible environment.     

Investigation on thermal conductivity and physical properties of polythiophene/p-phenylenediamine-graphene oxide and polythiophene-co-poly(methyl methacrylate)/p-phenylenediamine graphene oxide composites

An efficient approach was employed to simultaneously functionalize and reduce the graphene oxide (GO) with p-phenylene diamine (PPD) using simple refluxing. There was a possibility of nucleophilic substitution of amino moieties of PPD with the epoxy groups of GO. The polythiophene (PTh) and polythiophene-co-poly(methylmethacrylate) (PTh-co-PMMA) nanocomposites with chemically modified GO were prepared using in situ polymerization technique. Two series of nanocomposites that is PTh/PPD-GO and PTh-co-PMMA/PPD-GO were designed. The nanocomposites were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction, scanning electron microscopy (SEM), thermal conductivity, and electrical conductivity measurement. The FTIR spectra depicted the characteristic absorption peaks for the formation of copolymer and their composites with PPD-GO. The SEM micrographs showed that the PPD-GO nanosheets were homogeneously dispersed in copolymer matrix forming nano-granular morphology. The nanofluids were prepared by suspending modified GO particles inside the basefluid of polythiophene and PTh-co-PMMA. The thermal conductivity of nanocomposites was significantly improved even with low PPD-GO loading. The thermal conductivity of PTh-co-PMMA/PPD-GO with 1.5 wt.% filler was increased to 1.42 W/mK at a higher temperature. The XRD patterns confirmed the presence of chemical interactions between the copolymer and filler particles. The electrical conductivity of PTh-co-PMMA/PPD-GO was also found to increase in the range of 6.1 × 10^?3–2.5 × 10^?2 S/cm. Novel PTh-co-PMMA/PPD-GO-based nanocomposite is potentially significant in high-performance thermal systems.     

Investigation of Raman and photoluminescence studies of reduced graphene oxide sheets

In this paper, we are investigating the Raman and photoluminescence properties of reduced graphene oxide sheets (rGO). Moreover, graphene oxide (GO) sheets are synthesized using Hummer’s method and further reduced into graphene sheets using D-galactose. Both GO and rGO are characterized by UV-vis spectroscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Thermogravimetric (TGA) analysis. Raman analysis of rGO shows the restoration of graphitic domains in GO after reduction. The photoluminescence of rGO showed emission in the UV region which is blue shifted along with luminescent quenching as compared to GO. This blue shift and quenching in photoluminescence arises due to the newly formed crystalline sp² clusters in rGO which created percolation pathways between the sp² clusters already present.     

Ultrasound assisted reduction of graphene oxide to graphene in l-ascorbic acid aqueous solutions: Kinetics and effects of various factors on the rate of graphene formation

The reduction of graphene oxide (GO) to graphene (rGO) was achieved by using 20 kHz ultrasound in l-ascorbic acid (l-AA, reducing agent) aqueous solutions under various experimental conditions. The effects of ultrasound power, ultrasound pulse mode, reaction temperature, pH value and l-AA amount on the rates of rGO formation from GO reduction were investigated. The rates of rGO formation were found to be enhanced under the following conditions: high ultrasound power, long pulse mode, high temperature, high pH value and large amount of l-AA. It was also found that the rGO formation under ultrasound treatment was accelerated in comparison with a conventional mechanical mixing treatment. The pseudo rate and pseudo activation energy (E_a) of rGO formation were determined to discuss the reaction kinetics under both treatment. The E_a value of rGO formation under ultrasound treatment was clearly lower than that obtained under mechanical mixing treatment at the same condition. We proposed that physical effects such as shear forces, microjets and shock waves during acoustic cavitation enhanced the mass transfer and reaction of l-AA with GO to form rGO as well as the change in the surface morphology of GO. In addition, the rates of rGO formation were suggested to be affected by local high temperatures of cavitation bubbles.     

Reduced graphene oxide foils for ion stripping applications

ABSTRACT

Reduced graphene oxide (rGO) films can be employed as ion strippers in an accelerator. They show some advantages with respect to the graphite foils, due to their high thermal and electrical conductivity, low density, high mechanical resistance and high stability. Thin graphene oxide (GO) films with a sub-micron thickness have been synthesized and transformed into reduced GO (rGO) by ion beam irradiations. Physical characterizations of the pristine and ion irradiated GO films have been performed. Measurements of stripping efficiency have been carried out by using helium, lithium, carbon and oxygen ion beams. The rGO stripper films demonstrate a significantly high charge production, comparable to that of the graphite films but with the advantage of a longer lifetime.     

Investigation of reduced graphene oxide effects on ultra-violet detection of ZnO thin film

The reduced graphene oxide (rGO) incorporated ZnO thin films were fabricated by dip-coating method. The Raman and FT-IR spectra of 0.075 wt% incorporated composite film showed reduction of GO in composite film. The transmittanceProd. Type: FTP spectra have shown that rGO incorporation increase the visible light absorption of ZnO thin film while the calculated band gaps of samples were decreased from 3.28 to 3.25 eV by increasing the rGO content. The linear trend of I–V curve suggests an ohmic contact between ZnO and rGO. Besides, it was found that by increasing the rGO content, the electrical resistivity was decreased from 4.32×10² Ω cm for pure ZnO film to 2.4×10¹ Ω cm for 0.225 wt% rGO incorporated composite film. The composite photodetectors not only possessed a desirable UV photosensitivity, but also the response time of optimum sample containing 0.075 wt% rGO was reduced to about one-half of pure ZnO thin film. Also, the calculated signal to noise (SNR) showed that highly conductive rGO in composite thin films facilitate the carrier transportation by removing the trapping centers. The mechanism of photoresponsivity improvement of composite thin films was proposed by carrier transportation process.     

Structural,electrical and optical properties of MgO-reduced graphene oxide nanocomposite for optoelectronic applications

MgO-reduced graphene oxide nanocomposites (NCs) were synthesized by a simple two-step chemical method. The microstructure, surface morphology, and composition of the prepared samples have been studied. X-ray diffractometer (XRD) analysis confirmed the crystalline cubic MgO nanoparticle and rGO sheets. Scanning electron microscope (SEM) showed the spherical MgO nanoparticles well dispersed over the graphene sheets. UV–visible spectroscopy analysis demonstrated that a red shift in the wavelength dependent absorbance curve. The band gap of the samples was found to be decreased with the increase of rGO content. The dielectric studies have been examined in the frequency range 500 Hz−5 MHz and found significant improvement in the dielectric constant, dielectric loss, and electric properties due to rGO addition.This is mainly attributed to the strong interfacial polarization (Maxwell–Wagner polarization) between MgO and rGO sheets. Further, the modulation of charge carrier density with rGO additions help to enhance the electrical conductivity of NCs and thus, encouraging to have wider application in electronic and energy technologies.     

Synthesis and characterization of nanocomposites films with graphene oxide and reduced graphene oxide nanosheets

Graphene oxide (GO) and reduced graphene oxide (CRGO), as a graphene derivatives, possess unique properties and a high aspect ratio, indicating great potential in nanocomposite fields. The present work reports the fabrication of the nanocomposite films by a simple and environmentally friendly process using aqueous solution and optimized time sonication for better exfoliation of the graphene sheets within Poly(Vinyl alcohol) (PVA) as matrix. The films were characterized using high-resolution TEM (HRTEM), X-ray diffraction (XRD), Microtensile testing, Differential scanning calorimetry (DSC) and Thermogravimetric analysis (TGA). The TEM images revealed a successfully exfoliation of the GO/CRGO nanosheets. XRD combined with TGA and DSC measurements showed an improvement in the thermal stability and tunable thermal properties. In addition, the Young's modulus and tensile yield strength of the composite films containing 1 wt% GO were obtained to be 4.92 GPa and 66 MPa respectively. These excellent reinforcement effects were achieved by the strong interaction between the components.     

Improvement of water softening efficiency in capacitive deionization by ultra purification process of reduced graphene oxide

Capacitive deionization (CDI) is the next generation of water desalination and softening technology by using relatively low capacitive current of electrochemical double layer. Among various carbon-based materials used for making electrode, reduced graphene oxide (rGO) has been intensively studied due to its excellent electrical conductivity and high surface area. Although Hummer method for making graphene oxide (GO) and rGO is a simple process, it remains some impurities in inherent GO and rGO which affect negatively to the CDI performance. In this work, we successfully prepared ultra purified GO and rGO by modifying Hummer method in order to remove entirely excess elements degrading the CDI performance. The electrosorption capacity of ultra purified rGO is considerably better than that of previous rGO, and maximum removal achieves 3.54 mg g⁻¹ at applied voltage of 2.0 V. Thus, this result could be comparable to other researches in CDI process.     

Hydrothermal synthesis of flower-like TiO2 nanocrystals/graphene oxide nanocomposites

A facile hydrothermal method has been developed to be capable of decorating graphene oxide (GO) with flower-like TiO₂ nanocrystals without using any bridging species. The flower-like TiO₂ nanocrystals were uniformly self-assembled on the surface of GO nanosheets. The photocatalytic activity experiment indicated that the prepared TiO₂/GO nanocomposites exhibited a higher photocatalytic activity for the photocatalytic degradation of rhodamine B (RB) aqueous solution under the UV illumination, this methodology made the synthesis of TiO₂/GO nanocomposites possible and may be further extended to prepare more complicated nanocomposites based on GO for technological applications.     

Thermoelectric characteristics of flexible reduced graphene oxide/silver selenide nanowire composites prepared by a facile vacuum filtration process

The reduced graphene oxide/silver selenide nanowire (rGO/Ag₂Se NW) composite powders were fabricated via a wet chemical approach, and then flexible rGO/Ag₂Se NW composite film was prepared by a facile vacuum filtration method combined with cold-pressing treatment. A highest power factor of 228.88 μW·m^-1·K^-2 was obtained at 331 K for the cold-pressed rGO/Ag₂Se NW composite film with 0.01 wt% rGO. The rGO/Ag₂Se NW composite film revealed superior flexibility as the power factor retained 94.62% after bending for 500 times with a bending radius of 4 mm, which might be due to the interwoven network structures of Ag₂Se NWs and pliability of rGO as well as nylon membrane. These results demonstrated that the GO/Ag₂Se NW composite film has a potential for preparation of flexible thermoelectric devices.     

Solvothermal synthesis and characterization of sandwich-like graphene/ZnO nanocomposites

Graphene-based nanocomposites are emerging as a new class of materials that hold promise for many applications. In this paper, we present a general approach for the preparation of sandwich-like graphene/ZnO nanocomposites in ethylene glycol (EG) medium using graphene oxide as a precursor of graphene and zinc acetylacetonate as a single-source precursor of zinc oxide. The samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared (FT-IR) spectroscopy, ultraviolet-visible (UV-vis) spectroscopy and thermogravimetry analysis. It was shown that the as-formed ZnO nanoparticles with a diameter of about 5 nm were densely and uniformly deposited on both surfaces of the graphene sheets to form a sandwich-like composite structure and as a result, the restacking of the as-reduced graphene sheets was effectively prevented. The ZnO-coated graphene nanocomposites can be expected to effectively improve the photocatalysis and sensing properties of ZnO and would be promising for practical applications in future nanotechnology.     

Laser and ion beams graphene oxide reduction for microelectronic devices

Reduced graphene oxide (rGO) is a two-dimensional material, which is attracting increasing attention due to its special properties. It can be obtained by laser or ion beam irradiations of pristine graphene oxide (GO). It shows high mechanical resistance, considerable electric and thermal conductivity. All these rGO characteristics together with the high number of molecular species that can be embedded between its layers, make graphene oxide a potential material for electronic sensors or efficient support on which conductive strips, condensers, and micrometric electronic devices can be designed. In particular, as it is described in this paper, it is possible to carry out high spatial resolution lithography in GO by using a focused laser or micro ion beam in order to design macro, micro, and submicron geometrical structures. The use of the reduced graphene oxide for the laser and ion beam fabrication of electrical resistances and capacitances is presented.     

Probing the role of hydrolytically stable, 3-aminopropyl triethoxysilane crosslinked chitosan/graphene oxide membrane towards Congo red dye adsorption

In this investigation, the practicability of utilizing 3-aminopropyl triethoxysilane (3-APTES) crosslinked chitosan (Ch)/graphene oxide (GO) membranes were explored for adsorptive removal of anionic dyes from aqueous medium. Membranes were successfully fabricated through solution casting technique. Strong interactions amongst matrix (chitosan), 3-APTES, polyvinylpyrrolidone (PVP) and GO were confirmed by Infrared spectroscopy. Thermal stability of the chitosan was improved by adding graphene oxide and results were verified via thermogravimetric (TGA) analysis. Swelling and hydrolytic results confirmed that 2 %-Ch/PVP was a stable membrane while increasing the amount of 3-APTES in the chitosan nanocomposites membrane decreased its stability in aqueous medium. The adsorption characteristics of the membranes were evaluated by the adsorption of Congo red (CR) dye from aqueous medium. The adsorbent can remove 80% of CR from aqueous medium and follows second order kinetics. This study outlines the possibility of exploring green membranes which can be easily fit in various flow systems.     

Investigation on fluorescence quenching of dyes by graphite oxide and graphene

Rhodamine B (Rh B), eosin (E) and methylene blue (MB) were used as a probe to investigate the molecular structure and charge of the dyes on the sensitized efficiency of graphite oxide (GO) and graphene (G). The structure of the prepared GO and G were characterized by X-ray diffraction (XRD) and atomic force microscopy (AFM), respectively. To study the electron transfer between dyes and GO or G, UV-vis absorption spectra (UV-vis), steady state fluorescence spectra (FL) and time resolved fluorescence spectra have been determined. It has been found that the electron transfer from the excited dyes to G was more efficient than to GO, and the transfer from excited MB to G was easier than to Rh B and E, because of the different electrostatic attraction between the dye and G.     

Sulfonated reduced graphene oxide as a highly efficient catalyst for direct amidation of carboxylic acids with amines using ultrasonic irradiation

Sulfonated reduced graphene oxide nanosheets (rGO-SO₃H) were prepared by grafting sulfonic acid-containing aryl radicals onto chemically reduced graphene oxide (rGO) under sonochemical conditions. rGO-SO₃H catalyst was characterized by Fourier-transform infrared (FT-IR) spectroscopy, Raman spectroscopy, scanning electron microscopy (SEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and X-ray photoelectron spectroscopy (XPS). rGO-SO₃H catalyst was successfully applied as a reusable solid acid catalyst for the direct amidation of carboxylic acids with amines into the corresponding amides under ultrasonic irradiation. The direct sonochemical amidation of carboxylic acid takes place under mild conditions affording in good to high yields (56–95%) the corresponding amides in short reaction times.     

A new analytical device incorporating a nitrogen doped lanthanum metal oxide with reduced graphene oxide sheets for paracetamol sensing

The novel N-CeO₂ nanoparticles decorated on reduced graphene oxide (N-CeO₂@rGO) composite has been synthesized by sonochemical method. The characterization of as prepared nanocomposite was intensely performed by UV–Vis, FT-IR, EDX, FE-SEM, HR-TEM, XRD, and TGA analysis. The synthesized nanomaterial was further investigated for its selective and sensitive sensing of paracetamol (PM) based on a N-CeO₂@rGO modified glassy carbon electrode. A distinct and improved reversible redox peak of PM is obtained at N-CeO₂@rGO nanocomposite compared to the electrodes modified with N-CeO₂ and rGO. It displays a very good performance with a wide linear range of 0.05–0.600 μM, a very low detection limit of 0.0098 μM (S/N = 3), a high sensitivity of 268 μA µM⁻¹ cm⁻² and short response time (<3 s). Also, the fabricated sensor shows a good sensibleness for the detection of PM in various tablet samples.     

Electrochemical performance of CeO<Subscript>2</Subscript> nanoparticle-decorated graphene oxide as an electrode material for supercapacitor

Cerium oxide nanoparticles and cerium oxide nanoparticle-decorated graphene oxide (GO) are synthesized via a facile chemical coprecipitation method in the presence of hexadecyltrimethylammonium bromide (CTAB). Nanostructure studies and electrochemical performances of the as-prepared samples were systematically investigated. The crystalline structure and morphology of the nanocomposites were examined by X-ray diffraction (XRD), scanning electron microscopy (SEM), transition electron microscopy (TEM), Raman spectrum, and X-ray photoelectron spectroscopy (XPS). Electrochemical properties of the CeO₂ electrode, the GO electrode, and the nanocomposites electrodes were investigated by cyclic voltammetry (CV), galvanostatic charge/discharge (GCD), and electrochemical impedance spectroscopy (EIS) measurements. The CeO₂ nanoparticle-decorated GO (at the mole ratio of CeO₂/GO = 1:4) electrode exhibited excellent supercapacitive behavior with a high specific capacitance of 382.94 F/g at the current density of 3.0 A/g. These superior electrochemical features demonstrate that the CeO₂ nanoparticle-decorated GO is a promising material for next-generation supercapacitor systems.     

双酚A在氧化石墨烯表面吸附的分子动力学模拟

双酚A(bisphenol A,BPA)是一种内分泌干扰物,会对机体多方面产生不良影响,包括生殖系统、神经系统、胚胎发育等.因此,在水环境中如何检测和去除BPA显得尤为重要.实验研究表明,氧化石墨烯(graphene oxide,GO)对BPA具有优异的吸附去除性能,但在分子层面的吸附机制尚不清楚.分子动力学模拟,能提供BPA在GO表面的动态吸附过程以及吸附构象等详细信息,可以弥补实验的不足.本文利用GROMACS分子动力学模拟软件,系统模拟了BPA在含GO的水溶液中的吸附过程,并计算了吸附自由能.结果显示:所有的BPA均被吸附在GO两侧,通过分析BPA的吸附构象以及与GO的相互作用,发现π-π疏水作用对吸附起主导作用,且显示出很好的稳定性,而静电和氢键作用增加了GO的吸附能力.通过自由能计算,BPA在GO表面的结合能达30 k J/mol,远大于水分子的5 k J/mol.这些结果进一步证实GO对BPA具有很强的吸附能力以及GO作为吸附剂在水溶液中去除BPA的可行性.