Preparation of graphene nanosheets/SnO2 composites by pre-reduction followed by in-situ reduction and their electrochemical performances

The Graphene nanosheets/SnO₂ composites were synthesized using stannous chloride to restore the semi-reduction graphene oxide (SRGO) under a simple hydrothermal reduction procedure. First graphene oxide was pre-reduced by glucose for a certain time to get SRGO, which keeps the good water-solubility of graphite oxide (GO) and has a good conductivity like graphene nanosheets. The higher electrostatic attraction between SRGO and Sn²⁺ makes SnO₂ nanoparticles tightly anchor on the graphene sheets in the hydrothermal reduction process. The formation mechanism of the composite was investigated by SEM, TEM, XRD, AFM and Raman. Moreover, the electrochemical behaviors of the Graphene nanosheets/SnO₂ nanocomposites were studied by cyclic voltammogram, electrical impedance spectroscopy (EIS) and chronopotentiometry. Results showed that the Graphene nanosheets/SnO₂ composites have excellent supercapacitor performances: the specific capacitance reached 368 F g⁻¹ at a current density of 5 mA cm⁻², and the energy density was much improved to 184 Wh kg⁻¹ with a power density of 16 kW kg⁻¹, and capacity retention was more than 95% after cycling 500 cycles with a constant current density of 50 mA cm⁻². The experimental results and the thorough analysis described in this work not only provide a potential electrode material for supercapacitors but also give us a new way to solve the reunification of the graphene sheets.     

Facile synthesis and application of Ag-chemically converted graphene nanocomposite

An in situ chemical synthesis approach has been employed to prepare an Ag-chemically converted graphene (CCG) nanocomposite. The reduction of graphene oxide sheets was accompanied by generation of Ag nanoparticles. The structure and composition of the nanocomposites were confirmed by means of transmission electron microscopy (TEM), atomic force microscopy (AFM) and X-ray diffraction. TEM and AFM results suggest a homogeneous distribution of Ag nanoparticles (5–10 nm in size) on CCG sheets. The intensities of the Raman signals of CCG in such nanocomposites are greatly increased by the attached silver nanoparticles, i.e., there is surface-enhanced Raman scattering activity. In addition, it was found that the antibacterial activity of free Ag nanoparticles is retained in the nanocomposites, which suggests they can be used as graphene-based biomaterials.      

Effects of functional groups on the graphene sheet for improving the thermomechanical properties of polyurethane nanocomposites

Dispersibility of graphene sheets in polymer matrices and interfacial interaction are challenging for producing graphene-based high performance polymer nanocomposites. In this study, three kinds nanofillers; pristine graphene nanoplatelets (GNPs), graphene oxide (GO), and functionalized graphene sheet (FGS) were used to prepare polyurethane (PU) composite by in-situ polymerization. To evaluate the efficacy of functional groups on the graphene sheets, PU reinforced with GNPs, GO, and FGS were compared through tensile testing and dynamic mechanical thermal analysis. The Young's moduli of 2 wt% GO and FGS based PU nanocomposites were found significantly higher than that of same amount of GNPs loading as an evidence of the effect of functional groups on graphene sheets for the mechanical reinforcement. The strong interaction of FGS with PU was responsible to exhibit notably high modulus (25.8 MPa) of 2 wt% FGS/PU composite than the same amount of GNPs and GO loading even at elevated temperature (100 °C).     

In situ synthesis of graphene/cobalt nanocomposites and their magnetic properties

Graphene, which possesses unique nanostructure and excellent properties, is considered as a low cost alternative to carbon nanotubes in nanocomposites. In this study, we present a simple in situ approach for the deposition of cobalt (Co) nanoparticles onto surfaces of graphene sheets by hydrazine hydrate reduction. The as-synthesized composites were characterized by X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, Raman spectroscopy, transmission electron microscopy (TEM) and thermogravimetry and differential scanning calorimetry. It was shown that the as-formed Co nanoparticles were densely and homogeneously deposited on the surfaces of the graphene sheets and as a result, the restacking of the as-reduced graphene sheets was effectively inhibited. Magnetic studies reveal that the graphene/Co nanocomposite displays ferromagnetic behavior with saturation magnetizations of 53.4 emu g⁻¹, remanent magnetization of 6.0 emu g⁻¹ and coercivity of 226 Oe at room temperature, which make it promising for practical applications in future nanotechnology.     

Facile preparation and electrochemical characterization of graphene/ZnO nanocomposite for supercapacitor applications

Graphene/ZnO nanocomposites were successfully synthesized by microwave-assisted method. The structure, morphology, optical and composition of the obtained samples were characterized using XRD, FT-IR, laser Raman, UV–Vis spectroscopy and XPS analysis. XRD analysis confirmed the presence of graphene/ZnO nanocomposite. FE-SEM image reveals that the homogenous distribution of ZnO nanoparticles on the graphene nanosheets. The electrochemical properties of the graphene/ZnO electrodes were analyzed by cyclic voltammetry and impedance spectroscopy. The results confirmed that the incorporation of ZnO nanoparticles enhanced the capacitive performance of graphene electrode. Graphene/ZnO nanocomposite electrode showed higher capacitance value of 109 F g⁻¹ at a scan rate of 5 mV s⁻¹ in 1 M KCl solution as compared to the graphene electrodes. These results demonstrated the importance and great potential of graphene based composites in the development of high-performance energy-storage systems.     

Preparation and characterisation of graphene/ZnS nanocomposites via a surfactant-free method

In this article, we present a surfactant-free method for the preparation of graphene/ZnS nanocomposites. The as-synthesised products were characterised by the X-ray diffraction, transmission electron microscopy, Fourier transform infrared spectroscopy and ultraviolet-visible spectroscopy. It is shown that in the nanocomposites, individual ZnS nanoparticles are well-spread out on the graphene sheets. The good distribution of ZnS nanoparticles on graphene sheets would be promising for practical applications in future nanotechnology.     

TiO<Subscript>2</Subscript>/graphene composite from thermal reaction of graphene oxide and its photocatalytic activity in visible light

In this study, the P25 TiO₂ nanoparticles and graphene sheets (GSs) composite were prepared from a facile thermal reaction of graphene oxide. Its microstructures and photocatalytic properties were characterized and measured using X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), Brunauer–Emmett–Teller (BET) specific area analysis, X-ray photoelectron spectroscopy (XPS), FT-IR spectra, and ultraviolet–visible (UV–vis) diffuse reflectance spectroscopy. Compared with pure P25 nanoparticles, the results reveal that (1) there is a red shift about 20 nm in the absorption edge of the P25/graphene composite; (2) the photocurrent of the composite is about 15 times higher than that of pure P25; (3) the visible light photocatalytic activity of the composite is enhanced greatly on decomposition of methylene blue (MB). The photocatalytic mechanism of the P25/graphene composite is also discussed.     

An investigation on post-fire behavior of hybrid nanocomposites under bending loads

This work focuses on residual bending properties of hybrid nanocomposites after intense heat conditions. Carbon fiber/epoxy-nanoclay and carbon fiber/epoxy-graphene nanosheets were manufactured. The nanoparticles employed were Cloisite 30B nanoclay and surface modified graphene nanosheets. The epoxy system was RemLam M/HY956. For short beam samples exposed to 800 KW/m² heat flux, for a various period of time up to 120 s, the addition of nanoparticles (nanoclay and graphene nanosheets) increased the unburned thickness from 0.16 mm (original) to 2.63 mm and 2.74 mm, respectively. When the two-dimensional (plates) samples were tested, the improvement on heat performance was reduced. The unburned thickness improved close to 10% with the presence of nanoclay. The addition of graphene nanosheets leads to a decrease in unburned thickness of 12.8%. This result can be due to the good thermal protection properties of the graphene nanosheets. Using SEM analysis, it was observed that when the hybrid nanocomposites were subjected to a large heat flux, nanoparticles remained trapped inside the char layers. Finally, the proposed model seems to overestimate the residual bending response by 8%.     

Effect of ZnO nanoparticles doped graphene on static and dynamic mechanical properties of natural rubber composites

In this work, effect of ZnO nanoparticles doped graphene (Nano-ZnO–GE) on static and dynamic mechanical properties of natural rubber composites were studied. Nano-ZnO–GE was synthesized by sol–gel method and thermal treatment. With the incorporation of nano-ZnO–GE into the matrix, the mechanical properties of NR nanocomposite significantly improved over that of NR composite containing with 5 phr of conventional-ZnO. The results demonstrated that the presence of nano-ZnO on the surface of graphene sheets not only conduces to suppressing aggregation of graphene sheets but also acts as a more efficient cure-activator in vulcanization process, with the formation of excellent crosslinked network at low nano-ZnO–GE content. This work also showed that NR/Nano-ZnO–GE nanocomposites exhibited higher wet grip property and lower rolling resistance compared with NR/Conventional-ZnO composite, which makes nano-ZnO–GE very competitive for the green tire application as a substitute of conventional-ZnO, enlarging versatile practical application to prepare high-performance rubber nanocomposites.     

Preparation and characterization of graphene/NiO nanocomposites

Graphene-based nanocomposites are emerging as a new class of materials that hold promise for many applications. In this article, we present a facile approach for the preparation of graphene/NiO nanocomposites using graphite oxide and nickel chloride as starting materials. The as-synthesized composites were characterized using X-ray diffraction, Fourier transform-Infrared spectroscopy, transmission electron microscopy, ultraviolet–visible spectroscopy, thermogravimetry, and differential scanning calorimetry analyses. It was shown that graphene sheets were decorated by the in situ-formed NiO nanoparticles to form a film-like composite structure and as a result, the restacking of the as-reduced graphene sheets was effectively prevented. The NiO-coated graphene nanocomposites can be expected to remarkably improve the electrochemical properties of NiO and would be the promising candidates for a variety of applications in future nanotechnology.     

Click coupled stitched graphene sheets and their polymer nanocomposites with enhanced photothermal and mechanical properties

The chemically stitched graphene oxide (GO) sheets were obtained using a click chemistry reaction between azide-functionalized GO and alkyne-functionalized GO. The click coupled GO (GO-click-GO) sheets showed the largely increased electrical conductivity and near infrared laser-induced photothermal properties compared to the GO sheets, which result from formation of triazole ring as a bridging linker between the GO sheets. The polyurethane (PU) nanocomposites incorporating the GO-click-GO sheets exhibited enhanced mechanical properties of breaking stress and modulus than the GO/PU nanocomposites. The modulus of GO-click-GO/PU nanocomposites was higher than that of the GO/PU nanocomposites at the same filler loading of 0.1 and 0.5 wt%. The GO-click-GO/PU nanocomposites also showed a significantly improved photothermal properties compared to the GO/PU nanocomposites at the same filler loading. The click coupled stitched GO sheets in this study can be used as the superior reinforcing fillers for mechanically and photothermally high performance polymer nanocomposites.     

Titania-reduced graphene oxide nanocomposite as a promising visible light-active photocatalyst for continuous degradation of VVOC in air purification process

Titania-reduced graphene oxide nanocomposites have been prepared through facile hydrothermal method by a reaction between P25 as TiO₂ source and graphene oxide. Reduction of graphene oxide and its reaction with P25 nanoparticles were achieved simultaneously at high temperature and pressure during the hydrothermal process with the minimum organic solvents. Chemical bonds, crystalline structure, morphology, porosity and light absorption of composites along with their photocatalytic activity under UV and visible light irradiation were investigated. Transmission electron microscopy images showed that P25 nanoparticles, with diameters about 25 nm, were dispersed on the sheets of reduced graphene oxide (RGO) homogeneously. A stronger interaction between P25 and RGO provided a red shift about 20 nm in the absorption edge of the composites. To set up a continuous tubular reactor made from thin layer of the prepared material, composite films were coated on the external surface of a steel tube to make an annular reactor. The reactor was equipped with UV or visible light sources to investigate the photocatalytic activity of the prepared composites in a continuous air flow contaminated with specified amount of acetaldehyde as a VVOC (very volatile organic compound) model molecule. Degradation efficiency of P25–RGO with 0.5 wt% RGO was significantly high under visible light irradiation, and about 70% conversion was observed using an air flow at normal conditions with specific flow rate of 17 ml min^?1 and 500 ppm acetaldehyde, by 30 mg of the coated composite in the reactor. Composites with low amount of RGO would be an appropriate photosensitizer and electron acceptor to suppress the recombination of photogenerated electron–hole pairs to enhance the photocatalytic performance.     

Enhanced electrochemical capacitance of polyaniline/graphene hybrid nanosheets with graphene as templates

Polyaniline/graphene nanocomposites (PANi/GR) were prepared via PANi covalent grafting from the surface of GR. The unique structure of hybrid nanosheets was formed with uniform PANi layer coating GR without phase separation appearing when the weight ratio of aniline-to-graphene was 1:1. The unique PANi/GR hybrid nanosheets as electrode material for supercapacitors have a specific capacitance as high as 922 F/g at 10 mV/s and still retain a specific capacitance of 106 F/g at a high scan rate of 1 V/s due to synergistic effect between PANi and GR. The capacitance retention was ∼90% after 1000 cycles, which is much better than that of pure PANi or other PANi nanocomposites. The enhanced capacitive performance of PANi/GR hybrid nanosheets makes them have potential application in developing high performance energy storage devices.     

Graphene sheets anchored with ZnO nanocrystals as electrode materials for electrochemical capacitors

An efficient approach consisted of modified Hummers' method, pulse microwave heating, and homogenizing dispersion has been demonstrated to prepare ZnO/graphene hybrid as electrode material for electrochemical capacitors (ECs). Highly-crystalline ZnO nanoparticles are anchored with graphene sheets, forming three-dimensional framework. The electrochemical properties of ZnO/graphene hybrids are characterized by cyclic voltammetry, electrochemical impedance spectroscopy, and galvanostatic charge–discharge cycling. The EC equipped with ZnO/graphite hybrid (1:5 in w/w) exhibit the improved performance in terms of specific capacitance, high rate capability, and excellent cycling stability, as compared with blank graphene electrode. The maximum energy and power densities of ZnO/graphite capacitor can be obtained as high as 66 Wh kg⁻¹ and 15.2 kW kg⁻¹, respectively. The improved performance can be ascribed to the insertion of ZnO nanocrystals between individual graphite sheets, creating a conducting framework that provides more active sites for the formation of electric double layer. The unique framework allows the electrolyte ions to diffuse easily into the interior channels, leading to small inner resistance.     

氧化锡粒子/石墨烯纳米复合材料真空热还原制备及其在近红外胰腺癌热疗中的应用

利用真空热还原法制备得到氧化锡粒子/石墨烯纳米复合材料(SnO2/GR),该过程中,石墨烯氧化物原料既是氧化锡粒子的有效载体来源,也是新型的活泼氧给体,可同步将零价锡氧化为正四价锡,石墨烯氧化物原料则被还原为石墨烯。利用透射电镜(TEM)、扫描电镜(SEM)、X射线衍射(XRD)和傅里叶变换红外光谱等分别对氧化锡粒子/石墨烯纳米复合材料的形貌和尺寸、结构进行了表征。利用该新型材料在近红外(NIR)激光照射下的强光热转化性能,使相比健康细胞更易受到温度影响的胰腺肿瘤细胞内部产生过高热(Hyperthermia),从而诱导胰腺肿瘤细胞热损伤及细胞凋亡。实验结果表明,在1064nm近红外激光照射下,对照组胰腺肿瘤细胞仍保持较高活性,而实验组的胰腺肿瘤细胞活力则大幅降至5.03%,充分显示了氧化锡粒子/石墨烯纳米复合材料在胰腺肿瘤热疗领域的潜力。     

Highly aligned,ultralarge-size reduced graphene oxide/polyurethane nanocomposites: Mechanical properties and moisture permeability

Polyurethane (PU) nanocomposite films containing highly-aligned graphene sheets are produced. Aqueous dispersion of ultralarge-size graphene oxide (GO) is in situ reduced in waterborne polyurethane, resulting in fine dispersion and high degree of orientation of graphene sheets, especially at high graphene contents. The PU/reduced GO nanocomposites present remarkable 21- and 9-fold increases in tensile modulus and strength, respectively, with 3 wt.% graphene content. The agreement between the experiments and theoretical predictions for tensile modulus proves that the graphene sheets are indeed dispersed individually on the molecular scale and oriented in the polymer matrix to form a layered structure. The moisture permeability of the nanocomposites presents a systematic decrease with increasing graphene content, clearly indicating the impermeable graphene sheets acting as moisture barrier. The synergy arising from the very high aspect ratio and horizontal alignment of the graphene sheets is responsible for this finding.     

Depositing ZnO nanoparticles onto graphene in a polyol system

In this work, graphene-ZnO nanocomposites were prepared through a one-step solvothermal approach, using ethylene glycol as the solvent and reducing agent. ZnO particles can attach on the surfaces and edges of graphene oxide sheets. The in situ formed ZnO nanoparticles were randomly decorated on the surfaces of graphene oxide sheets, which were simultaneously reduced directly capable of forming the graphene sheets by the ethylene glycol. In addition, photoluminescence spectra of graphene-ZnO nanocomposites display the fluorescence quenching property.     

Self-assembly of nitrogen-doped TiO2 with exposed {001} facets on a graphene scaffold as photo-active hybrid nanostructures for reduction of carbon dioxide to methane

Tailored synthesis of well-defined anatase TiO₂-based crystals with exposed {001} facets has stimulated incessant research interest worldwide due to their scientific and technological importance. Herein, anatase nitrogen-doped TiO₂ (N-TiO₂) nanoparticles with exposed {001} facets deposited on the graphene (GR) sheets (N-TiO₂-001/GR) were synthesized for the first time via a one-step solvothermal synthetic route using NH₄F as the morphology-controlling agent. The experimental results exemplified that GR was uniformly covered with anatase N-TiO₂ nanoparticles (10–17 nm), exposing the {001} facets. The percentage of exposed {001} facets in the N-TiO₂-001/GR nanocomposites was calculated to be ca. 35%. Also, a red shift in the absorption edge and a strong absorption in the visible light range were observed due to the formation of Ti-O-C bonds, resulting in the successful narrowing of the band gap from 3.23 to 2.9 eV. The photocatalytic activities of the as-prepared photocatalysts were evaluated for CO₂ reduction to produce CH₄ in the presence of water vapor under ambient temperature and atmospheric pressure using a low-power 15 W energy-saving daylight lamp as the visible light source—in contrast to the most commonly employed high-power xenon lamps—which rendered the process economically and practically feasible. Among all the studied photocatalysts, the N-TiO₂-001/GR nanocomposites exhibited the greatest CH₄ yield of 3.70 μmol·g_catalyst ^?1, approximately 11-fold higher activity than the TiO₂-001. The enhancement of photocatalytic performance was ascribed to the effective charge anti-recombination of graphene, high absorption of visible light region and high catalytic activity of {001} facets relative to the {101} facets.      

The effects of S-doping concentration on the photocatalytic performance of SnSe/S-GO nanocomposites

The effects of S-doped graphene oxide (S-GO) on the photocatalytic performance of SnSe nanostructures have been investigated. Different concentrations of S-doping as 2S-GO, 4S-GO, and 6S-GO (2, 4, and 6% in weight) have been synthesized. Characterization results indicated sulfur not only has successfully placed in the GO structure and a part of the GO sheet has been changed into reduced GO (rGO) by sulfur doping but also the surface morphology of the GO sheets has been changed from a smooth surface to fractured crack surfaces. The results showed that the increase of sulfur content caused the morphology of the SnSe nanostructures was changed from nanoparticles (NPs) into nanorods (NRs). The photocatalytic activity of the samples to degrade dyes under the visible-light irradiation conditions was carried out and it was observed an enhancement photocatalytic performance for the SnSe/2S-rGO nanocomposites in comparison to the other samples. More than 95% of dyes were degraded by the SnSe/2S-rGO nanocomposites for only 60 min. Brunauer–Emmett–Teller (BET) and electrical measurement results indicated the textural properties and conductivity of GO sheets were improved by sulfur doping. In addition, the photogenerated electron lifetime (τ_r) of the SnSe/rGO and SnSe/S-rGO nanocomposites has been measured by the Bode phase plot and it was observed a lifetime of τ_r = 71.1 and 31.7 μs for the SnSe/S-rGO and SnSe/rGO nanocomposites, respectively.     

One-step synthesis of Co–Ni ferrite/graphene nanocomposites with controllable magnetic and electrical properties

Co_1−xNi_xFe₂O₄/graphene nanocomposites were synthesized through a one-step solvothermal method. The as-synthesized products were characterized by X-ray powder diffraction, field emission scanning microscopy, transmission electron microscope, and high-resolution transmission electron microscope. The results show that the Co_1−xNi_xFe₂O₄ nanoparticles are uniformly dispersed on graphene sheets. The dependence of structure, magnetic and electrical properties of Co_1−xNi_xFe₂O₄/graphene nanocomposites on the Ni²⁺ concentration and the graphene content were also studied. The saturation magnetization and electrical conductivity of the as-prepared products reached 51.82 emu/g and 1.00 × 10² S/m, respectively.