•Weakly negative permittivity was first obtained from the graphene composites.•Negative permittivity resulted from formation of graphene conductive networks.•Negative permittivity was easily adjusted by controlling the graphene contents.•High dielectric loss (above 25) was obtained from 13 vol% graphene.Three-dimensional (3D) graphene (GR) network/phenolic resin composites with tunable and weakly negative permittivity were prepared by mechanical mixed method. Dielectric properties including permittivity, dielectric loss tangent and alternating current conductivity (σac), were investigated in detail. When the GR content was increased from 8 to 13 vol%, a ladder-shape increase of σac was observed, indicating a percolation phenomenon. It was found that, when the GR content exceeded 13 vol% the negative permittivity appeared attributed to the formation of 3D interconnected GR network. Moreover, the negative permittivity was easily adjusted by controlling the GR content. Compared with the metal-ceramics in our previous work, the absolute values of negative permittivity were low, which was in favor of impedance matching. For the GR content of 13 vol%, high dielectric loss above 25 over the whole frequency was also observed. Finally, the equivalent circuits were used to analyze the reason of the negative permittivity.Download high-res image (132KB)Download full-size image

Graphene (GR)/acrylic polyurethane (APU) composites with low percolation threshold and tunable negative permittivity were prepared by coating and pressing method. The microstructures and dielectric properties including alternating current conductivity (σac), reactance (Z″) and permittivity (ɛ′ and ɛ″) were investigated in detail. A percolation phenomenon from σac was observed when the GR content was increased from 0.9 to 6 vol%, and the percolation threshold was 1.8 vol%. The percolation threshold was obviously lower than those from the reported carbon/silicon nitride, carbon nanotube/phenolic resin and GR/phenolic resin composites, which was possibly attributed to the well dispersion and unique microstructure of GR in APU. Moreover, the negative permittivity was obtained from the much lower GR content (only 3 vol%) than the previously reported composites. In addition, compared with other composites with negative permittivity, the dielectric loss (ɛ″) from the GR/APU composites was obviously reduced.

•Iron (II) phthalocyanine (FePc) nanoclusters were prepared by solvent evaporation.•The FePc-graphene sandwich composite was fabricated by combining FePc nanoclusters and graphene.•The FePc-graphene sandwich composite exhibited good electrocatalytical performance towards oxygen reduction reaction.Iron (II) phthalocyanine (FePc) nanoclusters were synthesized by solvent evaporation with poly(diallyldimethlammonium chloride) as a stabilizer. Combining FePc nanoclusters with graphene (GR), the FePc-GR sandwich composite was produced. Morphologies of the resulted FePc-GR composite were characterized by field emission scanning electron microscopy. It was found that the FePc-GR composite exhibited sandwich structure, and the FePc nanoclusters (~ 500 nm) consisted of small nanoparticles were uniformly distributed between GR sheets. Electrochemical and electrocatalytical properties of the FePc-GR composite were studied by cyclic voltammetry and linear sweep voltammetry methods. Compared with the pure FePc nanoclusters or GR, the FePc-GR composite showed improved electrocatalytical performance towards oxygen reduction reaction (ORR). The electrocatalytical performance of FePc-GR composite was related to the ratio of FePc nanoclusters and GR. It was observed that the FePc-GR composite showed the highest current density when the volume ratio of FePc nanoclusters to GR was 2:1. The electron transfer number of the FePc-GR composite was 4.05, indicating the direct four electron process for the ORR. In addition, the FePc-GR composite also exhibited good stability and excellent resistance to methanol compared with the commercial 20% Pt/C catalyst.Download high-res image (182KB)Download full-size image

The carbon/silicon nitride (C/Si3N4) composites consisting of amorphous carbon dispersed in porous Si3N4 matrix were herein prepared by facile impregnation-carbonization process at low temperature. The microstructures and electrical properties of C/Si3N4 composites were investigated in detail. A percolation phenomenon and an insulator–conductor transition appeared in the composites with the increase of carbon content. The formation of continuous conducting carbon network led to the plasma-like negative permittivity behavior in the composites above the percolation threshold (between 8.1 and 10.9 vol%), and the frequency dispersions of negative permittivity can be fitted well by Drude model. Carbon materials can be regarded as a good candidate for realizing negative permittivity, and the preparation of C/Si3N4 composites by the facile impregnation-carbonization approach offers the important possibility of tuning the negative permittivity.

•Structure of porous graphene is easily controlled by surfactant and oil droplets.•The porous graphene is used for immobilization of glucose oxidase (GOD).•Using oil droplets improves electrochemical response of GOD.•The surfactant introduces mesopores and decreases electron transfer rate of GOD.We first reported a facile method to prepare porous graphene with tunable structure for glucose oxidase (GOD) immobilization based on freeze-drying. The produced porous graphene (PGR) exhibited three-dimensional interconnected porous structure. Moreover, their microstructure was easily tuned by addition of surfactant and oil droplets into the graphene oxide dispersion. Field emission scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy and nitrogen physisorption were used to characterize microstructures, composition and surface area of the produced PGR. The addition of surfactant introduced mesopores in the PGR and the oil droplets can improve the pore volume. It was found that the PGR structure obviously affected the electrochemical behavior of GOD. Electrocatalytical activity towards glucose was also investigated, and the maximum electrocatalytical current reached 6.3 times for 5 mM glucose. The modified electrode was used to detect the glucose, and a low detection limit of 8.7 μM and a high sensitivity of 16.3 μA mM cm−2 were obtained. The good sensing performance was attributed to the good three-dimensional porous structure and conductivity of the PGR.

We first reported tunable negative permittivity from phenolic resin (PhR) and multi-walled carbon nanotubes (MWNTs). Different amount of MWNTs were incorporated into the PhR matrix, and the morphologies of the PhR–MWNT materials were characterized using field emission scanning electron microscopy. Dielectric, conductive and impedance performance were investigated in detail. When the MWNT content was above 14.00 vol%, negative permittivity was obtained which was obviously different from that with a low MWNT content. Moreover, the negative permittivity was tuned by adjusting the MWNT content in the matrix. The equivalent circuit analysis indicated that the PhR–MWNT material with negative permittivity corresponded to an inductive element. The appearance of negative permittivity was attributed to the presence of three-dimensional conductive networks of MWNT in the PhR matrix.

•Three-dimensional porous graphene–MnO2 composites were fabricated.•MnO2 particles were formed and uniformly distributed on the graphene sheets.•The composites exhibited interpenetrating porous structure.•The composites gave a high specific capacitance of 800 F g−1.Three dimensional (3D) porous graphene–MnO2 (PGR–MnO2) composites as electrode materials for supercapacitors were fabricated via deposition of MnO2 particles on 3D PGR produced from freeze–drying method. Field emission scanning electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy were used to characterize morphologies and composition of the produced PGR–MnO2 composites. By immersing PGR into 0.1 M KMnO4/K2SO4 for different time, it was found that MnO2 particles with the size of about 200 nm were formed and uniformly distributed on the GR sheets. The obtained PGR–MnO2 composites still remained 3D interpenetrating porous structures. Electrochemical methods including cyclic voltammetry, electrochemical impedance spectroscopy and galvanostatic charge–discharge were carried out to investigate electrochemical properties and capacitive performance. The results showed that the PGR–MnO2-2 h composite (immersing the PGR into 0.1 M KMnO4/K2SO4 for 2 h) gave the best capacitive performance among these produced composites. The PGR–MnO2-2 h composite gave the maximum specific capacitance of 800 F g−1 with the maximum energy density of 40 W h kg−1 at the current density of 0.1 A g−1. The good capacitive performance was attributed to the unique 3D porous structure of the PGR–MnO2 composites and the synergistic effect of GR with high conductivity and MnO2 particles with good pseudocapacitive properties.

Three dimensional porous graphene–chitosan (GR–CS) composites via ice-induced assembly for glucose oxidase (GOD) immobilization were reported for the first time. By adjusting the GR amount, the porous GR–CS composites containing different GR content could be produced. It was found that the GR amount played an important role in their morphologies. Higher GR amount resulted in more pores appearing in the GR–CS composites. When the GR amount was 70 wt%, the GR–CS composites (GR70–CS) had good flexibility and interpenetrating porous structures. The GR70–CS composite showed good stability, and still kept a porous structure even after dispersing and coating on the substrates. Current response from the GR70–CS composite modified glassy carbon electrode (GR70–CS/GCE) was about two times that from the bare GCE with Fe(CN)63−/4− as a probe. The direct electrochemical behavior was observed when GOD was immobilized onto the GR70–CS/GCE. The GOD modified GCE also showed good electrocatalytic activity for glucose. Using ferrocenecarboxylic acid as a mediator, a linear relationship from 0.14 to 7.0 mM (R = 0.995) between currents and the glucose concentration with a detection limit of 17.5 μM was obtained.

As a new type of nano-metal materials, nanoporous gold has gradually received widespread concern of researchers in recent years. It exhibits many characteristics such as high specific surface area, good electrical conductivity, controllable structure and etc. Because of its special structure and properties, nanoporous gold has been widely used in many fields such as catalysis, sensors, separation and energy. This review summarizes the applications and development of nanoporous gold in analytical chemistry in recent five years.

We first reported a new method to prepare Prussian blue (PB) nanocubes through reducing a single-source precursor with graphene oxide (GO). By mixing GO and K3Fe(CN)6 at 80 °C for 3 h, K3Fe(CN)6 was reduced by GO and this resulted in the formation of PB nanocubes with average size of 200 nm on GO surfaces. The obtained PB–GO nanocomposites were characterized by UV–Vis spectroscopy, X-ray diffraction, Fourier transform infrared spectroscopy, and field emission scanning electron microscopy. Effects of the mass ratio of K3Fe(CN)6 to GO, and the reaction time on PB nanocubes were investigated. Electrochemical experiments demonstrated that the prepared PB–GO nanocomposites exhibited good electrochemical properties. The PB–GO-modified electrodes also showed good electrocatalytic activity for the reduction of hydrogen peroxide and the current response to the concentration of H2O2 had a good linear range from 0.5 μM to 1.0 mM (R2 = 0.997) with a detection limit of 0.4 μM at a signal-to-noise ratio of 3. This method provided a novel, simple, and low-cost route for fabrication of PB nanocubes and PB–GO nanocomposites.

We report on the single-step preparation of a composite consisting of graphene oxide (GO), Prussian blue (PB) and chitosan (Chit) that was deposited on a glassy carbon electrode and then used to determine hydrogen peroxide. The composite was obtained by mixing GO, Chit, potassium ferricyanide and ferric chloride and keeping it at 90 °C for 1 h. This method is simple and inexpensive, and does not require purification, centrifugation or sedimentation. Scanning electron microscopy, UV-vis spectroscopy, Fourier transform IR spectroscopy and X-ray diffraction were used to characterize the GO-PB-Chit composites and revealed that PB nanoparticles were formed and uniformly distributed on the surfaces of the GO due to the integrating effects of Chit and GO. The composite displayed electrocatalytic activity in the reduction of hydrogen peroxide to which it responded with good linear relationship in the 1.0 μM to 1.0 mM concentration range, with a detection limit of 0.1 μM (at S/N = 3).

Silicon nitride composites were fabricated by adding Fe3Al and carbon nanotubes and hot-pressing at a low sintering temperature of 1600 °C. The resulted composites were characterized by X-ray diffraction, Fourier-transform infrared spectrum, and field emission scanning electron microscopy. It was found that the Fe3Al could react with Si3N4 to form the series of compound of FexSiy, and CNTs could keep chemical stability in the system. Mechanical properties of the composites were also investigated. For Fe3Al as the additive, the relative density could reach to 93.6 % with the maximum hardness of 15.7 GPa. When the Fe3Al and CNTs were added into matrix simultaneously, the relative density reached to 92.6 %, and the maximum fracture toughness was 6.7 MPa m1/2. Finally, the toughening mechanism of Fe3Al and CNTs in sialon composites, containing crack deflection and bridging, and nanotubes pullout and bridging, were also discussed.