Graphene nanosheets: Ultrasound assisted synthesis and characterization

A facile sonochemical route for the synthesis of graphene nanosheets via reduction of graphene oxide (GO) has been reported. The synthesized graphene sheets are characterized using UV–vis spectra, Fourier transform infra-red (FT-IR) spectra, transmission electron microscope, X-ray photoelectron spectra (XPS) and Raman spectroscopic techniques. The UV–vis spectroscopy results showed that the absorption peak was red shifted due to the reduction of GO into graphene. FT-IR and XPS spectra revealed the removal of oxygenated functional groups in graphene after the reduction process. Raman spectra confirmed the restoration of new sp² carbon domains in graphene sheets after the reduction. The sonochemical approach for the synthesis of graphene nanosheets is relatively fast, cost-effective and efficient as compared to other methods.     

Tuned CuCr layered double hydroxide/carbon-based nanocomposites inducing sonophotocatalytic degradation of dimethyl phthalate

This study is the first to explore the possibility of utilizing CuCr LDH decorated on reduced graphene oxide (rGO) and graphene oxide (GO) as sonophotocatalysts for the degradation of dimethyl phthalate (DMP). CuCr LDH and its nanocomposites were successfully fabricated and characterized. Scanning electron microscopy (SEM) along with high-resolution transmission electron microscope (HRTEM) both evidenced the formation of randomly oriented nanosheet structures of CuCr LDH coupled with thin and folded sheets of GO and rGO. The impact of diverse processes on the degradation efficiency of DMP in the presence of the so-prepared catalysts was compared. Benefiting from the low bandgap and high specific surface area, the as-obtained CuCr LDH/rGO represented outstanding catalytic activity (100 %) toward 15 mg L⁻¹ of DMP within 30 min when subjected to light and ultrasonic irradiations simultaneously. Radical quenching experiments and visual spectrophotometry using an O-phenylenediamine revealed the crucial role of hydroxyl radicals compared to holes and superoxide radicals. Overall, outcomes disclosed that CuCr LDH/rGO is a stable and proper sonophotocatalyst for environmental remediation.     

Synthesis of graphene oxide sheets decorated by silver nanoparticles in organic phase and their catalytic activity

The graphene oxide(GO) sheets decorated by Ag nanoparticles were prepared using a liquid–liquid two-phase method at the room temperature. The synthesized samples existed in the organic phase and were characterized by X-ray diffraction, transmission electron microscopy, UV–vis spectroscopy and Raman spectra. The results demonstrate that these silver-nanoparticles with diameter of about 10 nm assembled on graphene oxide sheets are flexible and can form stable suspensions in organic phase. Raman signals of graphene oxide sheets are increased by the attached silver nanoparticles, displaying higher surface-enhanced Raman scattering activity. Furthermore, Ag/GO are found to serve as effective catalysts to activate the reduction of 4-nitrophenol (4NP) in the presence of NaBH₄.     

Graphene Modified Lipophilically by Stearic Acid and its Composite With Low Density Polyethylene

Graphene, prepared by the thermal reduction of graphite oxide (GO), was modified with stearic acid to enhance its lipophilicity. A novel method, using the intrinsic epoxy groups on the graphene, was utilized for reaction with stearic acid to minimize the negative impact of the normal functionalization method on the π-electronic system of graphene. Gravimetric analysis, thermogravimetric analysis (TGA), Fourier transform infrared (FTIR) spectroscopy, and X-ray photoelectron spectroscopy (XPS) showed that the stearic acid was effectively attached to the graphene. In addition, Raman spectroscopy and electric conductivity of the graphene showed that this novel modification method, utilizing intrinsic defects, did not damage the π-electronic system of the sp² bonded carbons. The dispersion of graphene in a low density polyethylene (LDPE) matrix was enhanced; consequently, the reinforcing effect in tensile testing was improved by the lipophilic modification. The crystallization behavior observed by differential scanning calorimetry (DSC) showed that the crystallization of LDPE was hindered by dispersed graphene, more evidently when dispersed uniformly.     

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.     

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.     

Molecular responses of cells to 2-mercapto-1-methylimidazole gold nanoparticles (AuNPs)-mmi: investigations of histone methylation changes

Reduced graphene oxide (RGO) sheet was functionalized with nanocrystalline cellulose (NCC) via click coupling between azide-functionalized graphene oxide (GO-N₃) and terminal propargyl-functionalized nanocrystalline cellulose (PG-NCC). First, the reactive azide groups were introduced on the surface of GO with azidation of 2-chloroethyl isocyanate-treated graphene oxide (GO-Cl). Then, the resulted compounds were reacted with PG-NCC utilizing copper-catalyzed azide-alkyne cycloaddition. During the click reaction, GO was simultaneously reduced to graphene. The coupling was confirmed by Fourier transform infrared, Raman, DEPT135, and ¹³C NMR spectroscopy, and the complete exfoliation of graphene in the NCC matrix was confirmed with X-ray diffraction measurement. The degree of functionalization from the gradual mass loss of RGO-NCC suggests that around 23 mass % has been functionalized covalently. The size of both NCC and GO was found to be in nanometric range, which decreased after click reaction.     

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.     

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.     

Fabrication of functionalized nitrogen-doped graphene for supercapacitor electrodes

A unique and convenient one-step hydrothermal process for synthesizing functionalized nitrogen-doped graphene (FGN) via ethylenediamine, hydroquinone, and graphene oxide (GO) is described. The graphene sheets of FGN provide a large surface area for hydroquinone molecules to be anchored on, which can greatly enhance the contribution of pseudocapacitance. X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Raman spectroscopy, and electrochemical workstation are used to characterize the materials. The nitrogen content exhibited in FGN can be up to 9.83 at.%, and the as-produced graphene material shows an impressive specific capacitance of 364.6 F g^?1 at a scan rate of 10 mV s^?1, almost triple that of the graphene (GN)-based one (127.5 F g^?1). Furthermore, the FGN electrodes show excellent electrochemical cycle stability with 94.4 % of its initial capacitance retained after 500 charge/discharge cycles at the current density of 3 A g^?1.     

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 of rGO–Ag nanoparticles for high-performance SERS and the adsorption geometry of 2-mercaptobenzimidazole on Ag surface

The sliver nanoparticles (AgNPs) with diameters of 30～50 nm were self-assembled onto the surfaces of reduced graphene oxide (rGO) sheets simply by mixing AgNO₃ aqueous solution and GO dispersion via a synchronous reduction process. Structure and morphology of the rGO–AgNPs hybrids were well characterized. More significantly, the surface-enhanced Raman scattering (SERS) spectrum of 2-mercaptobenzimidazole (MBI) adsorbed on the solid rGO–AgNPs surface shown that the rGO–AgNPs system gives a very strong SERS intensity at in-plane vibrational modes in comparison to the out-of-plane vibrational modes. This large enhancement effect is most likely a result of charge-transfer (CT) mechanism. Based on the surface selection rules and the information provided by the highly enhanced in-plane vibrational modes, it can be found that MBI molecule was adsorbed on AgNPs surface as a thiol form via the sulphur and nitrogen atoms with a slightly tilted geometric conformation.     

Ecofriendly Route for the Synthesis of Highly Conductive Graphene Using Extremophiles for Green Electronics and Bioscience

Highly conductive biocompatible graphene is synthesized using ecofriendly reduction of graphene oxide (GO). Two strains of non‐pathogenic extremophilic bacteria are used for reducing GO under both aerobic and anaerobic conditions. Degree of reduction and quality of bacterially reduced graphene oxide (BRGO) are monitored using UV–vis spectroscopy, X‐ray photoelectron spectroscopy, and Raman spectroscopy. Structural morphology and variation in thickness are characterized using electron microscopy and atomic force microscopy, respectively. Electrical measurements by three‐probe method reveal that the conductivity has increased by 10⁴–10⁵ fold from GO to BRGO. Biocompatibility assay using mouse fibroblast cell line shows that BRGO is non‐cytotoxic and has a tendency to support as well as enhance the cell growth under laboratory conditions. Hereby, a cost effective, non‐toxic bulk reduction of GO to biocompatible graphene for green electronics and bioscience application is achieved using halophilic extremophiles for the first time.     

Structural and magnetic properties of reduced graphene oxide-TiO2 nanoflower composite

We have focused on the structural and magnetic properties of hazardous acid free synthesis of anatase titanium dioxide (TiO₂) phase nanoflower and reduced graphene oxide-TiO₂ (rGO-TiO₂) nanocomposite using hydrothermal process. Because, strong acids free synthesis is environmental friendly and reduce overall cost of synthesized samples. In the synthesis of rGO-TiO₂, synthesized TiO₂ nanoflower and graphene oxide (GO) were used as reagents. The resulting materials have analyzed using different techniques such as, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and Fourier Transformation Infrared spectrophotometer for confirmation of flower like morphology, crystalline phase and chemical composition. Moreover, VSM analysis has revealed the ferromagnetism induced in the rGO-TiO₂ composite at room temperature. The values of saturation magnetization were found to be 0.002 and ~ 0.243±0.04 emu/g for TiO₂ nanoflower and rGO-TiO₂ nanocomposite, respectively. In comparison of pure TiO₂, rGO-TiO₂ exhibited larger magnetization at room temperature. This is because presences of various edge and site defects such as topological and point defects like vacancies, which create localized unpaired spins in reduced graphene oxide (rGO), induce the ferromagnetism behavior in rGO-TiO₂ nanocomposite.     

A green synthetic approach to graphene nanosheets for hydrogen adsorption

A green and facile strategy of preparing graphene by reducing exfoliated graphite oxide (GO) with glucose was developed in this study. The as-prepared samples were characterized by X-ray diffraction (XRD), Raman spectroscopy, Fourier transform infrared spectroscopy (FT-IR), Scanning electron microscopy (SEM), Transmission electron microscopy (TEM) and Atomic force microscopy (AFM). The characterization results indicated that the graphene sheets (GS) were of high quality with smooth surface, rich pore structure and few layer graphene. The samples have a BET specific surface area of 1205.8 m² g⁻¹ measured by N₂ adsorption at 77 K. The hydrogen storage capacity of 2.7 wt.% at 298 K and 25 bar demonstrated that the as-prepared graphene employing glucose as reductant is supposed to be a promising material with outstanding property for hydrogen storage.     

NiCoP/rGO复合材料的合成及其性能研究

以六水合氯化镍、七水合硫酸钴、氧化石墨烯(GO)和赤磷为原料,利用原位水热法,在不添加任何表面活性剂的情况下,合成了磷化钴镍/还原氧化石墨烯(NiCoP/rGO)纳米复合材料,并通过XRD、SEM、TEM、IR、Raman等对该复合材料进行了表征.结果表明,所得复合材料由NiCoP纳米颗粒和还原氧化石墨烯片层结构组成,NiCoP纳米颗粒尺寸大约为20 nm,均匀分布在rGO片层结构表面上,同时探讨了复合材料的形成过程.另外,复合材料的吸附脱除实验表明,所得复合材料对多种染料都具有非常好的吸附作用,因此,在污水处理方面有较大的应用价值.     

等离子体增强化学气相沉积法制备含氢类金刚石膜的紫外Raman光谱和X射线光电子能谱研究

利用脉冲辉光放电的方法,在硅片上采用不同的沉积工艺制备了含氢类金刚石膜层,并采用Raman光谱和X射线光电子能谱(XPS)对膜层进行表征.用Raman光谱仪在波长为325 nm的紫外光源的激励下观察膜层的键结构.紫外Raman光谱对含氢类金刚石膜是非常有用的,它能有效避免可见光Raman光谱测量时的荧光干扰,清晰地得到膜层的D峰和G峰.同时利用XPS分析得到膜层的sp3键含量,并与Raman光谱所得数据进行比较.通过Raman光谱和XPS分析可以发现,在紫外光源的激励下,膜层的G峰峰位向高频移方向移动,G峰峰位、I(D)/I(G),G峰半高宽和sp3键含量之间存在一定的关系.     

A Self‐Assembly Route to an Iron Phthalocyanine/Reduced Graphene Oxide Hybrid Electrocatalyst Affording an Ultrafast Oxygen Reduction Reaction

Graphene oxide (GO) is an attractive freestanding support that can be decorated with ultrathin organic layers for facile and low‐cost fabrication of novel devices with controllable functional properties and microstructures. Here, it is reported that a hybrid material consisting of an ultrathin iron phthalocyanine (FePc) layer self‐assembled on reduced graphene oxide (rGO) exhibits excellent catalytic activity that is superior to that of commercial Pt/C for an oxygen reduction reaction (ORR). During solution processing, the FePc layer is first self‐organized onto GO sheets and then reduced electrochemically to form an FePc/rGO hybrid electrocatalyst. Kinetics studies reveal that the hybrid architecture affords an ultrafast ORR rate caused by a strongly dominant four‐electron process, and the durability of the catalyst shows significant improvement by forming the hybrid structure. Spectroscopic studies suggest that these advantages are afforded by synergistic effects between FePc and rGO, which are enriched by the hybrid structure and the appropriate reduction step.     

Superior dielectric properties and bandgap modulation in hydrothermally grown Gr/MgO nanocomposite

MgO nanoparticles (NPs) and Gr/MgO nanocomposite (NC) have been synthesized by hydrothermal route. X-ray diffraction (XRD) analysis confirmed the crystalline cubic phase of MgO and Gr/MgO NC. Raman spectroscopy was used to study the defects in the NCs. Electron microscopy study display spherical NPs of MgO on graphene sheets. UV-visible spectroscopy shows a red shift in the absorption band and a significant reduction in the bandgap for Gr/MgO NC. The improvements in dielectric properties of NC can be ascribed to interfacial polarization between rGO and MgO. The rGO in the NCs supports the electron transfer and improves the electrical conductivity.     

Preparation and electrochemical properties of LiFePO<Subscript>4</Subscript>/graphene composites from tailoring graphene oxides

LiFePO₄/graphene composites have been prepared by using tailoring graphene oxide (GO) nanosheets as precursors. The structure and electrochemical properties of the composites were investigated by X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), Raman microscopy, and a variety of electrochemical testing techniques. The decrease in graphene size reduces the contact resistance between activated materials, and enhances the lithium-ion transport in LiFePO₄/graphene composites. With low weight fractions of small-size graphene sheets, the composites show better electrochemical performance than those with large size graphene sheets.