•High quality PG dispersions are prepared in ethanol assisted by organic salts.•The PG is used to fabricate electrochemical immunosensor for rapid detection of ractopamine.•The prepared electrochemical immunosensor exhibits remarkable detection performance.A new electrochemical immunosensor for fast determination of ractopamine (RAC) is fabricated based on pristine graphene (PG). The PG provides a microenvironment beneficial the immobilization of RAC, promotes the electron transfer, and raises the sensitivity of the immunosensor. The free RAC in solution can be effectively measured based on the competitive immunoreaction between RAC-antibody and RAC. The calibration graph shows linearity over the concentration ranges of 0.1–10 and 10–4000 ng mL−1. The proposed immunosensor displays a satisfactory stability, selectivity, and reproducibility and has been applied to the quantificational detection of RAC in real pork samples.Preparation of pristine graphene in organic solvent assisted by organic salt for immunodetection of ractopamine.Download high-res image (99KB)Download full-size image

•Sulfonated graphene/polypyrrole composite was prepared by one-step electrodeposition method.•The composite exhibits high specific capacitance and good cycling stability.•A symmetric supercapacitor was also fabricated and showed high specific capacitance.•The high-risk hydrazine was avoided during the synthesis of sulfonated graphene.A sulfonated graphene/polypyrrole (s-G/PPy) composite was successfully prepared by a method of one-step electrodeposition using water soluble sulfonated graphene (s-G) and polypyrrole as the starting materials. The morphology, structure and thermal stability of s-G/PPy were characterized using transmission electron microscope, scanning electron microscope, thermogravimetric analysis, and Raman spectroscopy. The electrochemical performance of s-G/PPy is evaluated with galvanostatic charge/discharge, cyclic voltammetry and electrochemical impedance spectroscopy in 1 mol L−1 KCl. The composite exhibits high specific capacitance and good cycling stability. The specific capacitance of s-G/PPy is as high as 310 F g−1 at a current density of 0.3 A g−1 and retains 71% after 1500 cycles at a scan rate of 50 mV s−1. The equivalent series resistance of s-G/PPy film is only 0.6 Ω. In addition, a s-G/PPy//s-G/PPy symmetric supercapacitor was also fabricated and in which the s-G/PPy showed specific capacitance still up to 253 F g−1.

Metalloporphyrinic frameworks have been studied in many fields. However, their electrochemical properties were seldom reported. This work reports the synthesis and the electrochemical application of a new bimetallic metalloporphyrinic framework, [Cu2-Co[5,10,15,20-(4-carboxyphenyl)porphyrin](H2O)2]·0.5DMF·5H2O (Cu-CoTCPP) in which [5,10,15,20-(4-carboxyphenyl)porphyrin]Co(II) (CoTCPP) struts are bound by Cu(II)–carboxylate clusters (Cu2(COO)4). Cu-CoTCPP was synthesized by the solvothermal method and characterized by various techniques, including XRD, IR, UV-vis, elemental analysis, TG, and TEM. Cu-CoTCPP showed novel bifunctional electrocatalytic ability toward the reduction/oxidation of H2O2 and the oxidation of NaNO2, which might be due to Cu and Co central ions, respectively. With the assistance of multi-walled carbon nanotubes (MWCNTs), Cu-CoTCPP showed further improved sensing performance toward H2O2. The linear detection ranges of the Cu-CoTCPP/MWCNTs/GCE for H2O2 and NaNO2 are 5.0 × 10−7 to 1.8 × 10−4 M and 2.5 × 10−6 to 1.1 × 10−3 M, respectively, with the detection limits of 2.4 × 10−7 M and 1.7 × 10−7 M, and the sensitivity of 168 and 439 mA mol−1 L cm−2. The bifunctional electrocatalytic ability and the excellent performance imply that the metalloporphyrinic frameworks are promising candidates for fabricating electrochemical sensors.

In this article, a novel electrochemical sensor based on pristine graphene (PG) is successfully constructed to detect ascorbic acid (AA), dopamine (DA), and uric acid (UA). The PG is obtained by liquid-phase exfoliation of graphite and characterized by transmission electron microscopy and X-ray photoelectron spectroscopy. The sensor based on PG prepared by this method to realize simultaneous determination of AA, DA, and UA is firstly reported. The linear detection ranges for AA, DA, and UA are 9.00–2314 μM, 5.00–710 μM, and 6.00–1330 μM, respectively, with detection limits of 6.45, 2.00, and 4.82 μM. This PG based sensor exhibits excellent performance for detection of AA, DA, and UA, which is much better than those electrochemical sensors based on chemical converted graphene.

An easy electrochemical technique is proposed to prepare electrochemically reduced graphene oxide (ERGO)/polyaniline (PANI) composites in a single step. The technique uses a two-electrode cell in which a separator soaked with an acid solution is sandwiched between graphene oxide (GO)/aniline films deposited on conductive substrates and an alternating voltage was applied to the electrodes. Successful preparations of ERGO/PANI composites were evidenced by characterizations due to UV–vis-NIR, FT-IR, XPS, XRD, and SEM measurements with free-standing films of ERGO/PANI obtained easily by disassembling the two-electrode cells. The ERGO/PANI films exhibited a high mechanical stability, flexibility, and conductivity (68 S cm−1 for the composite film containing 80% ERGO) with nanostructured PANI particles (smaller than 20 nm) embedded homogeneously between the ERGO layers. The two-electrode cells acted as electrochemical capacitors (ECs) after a sufficient voltage cycling and exhibited relatively large specific capacitances (195–243 F g−1 at a scan rate of 100 mV s−1) with an excellent cycle life (retention of 83% capacitance after 20,000 charge–discharge cycles). Influences of the GO/aniline ratio, the sort of electrolytes, and the weight of the composite on the energy storage characteristics of ECs comprising the ERGO/PANI composites were also studied.

An easy technique is proposed to prepare a new surfactant-free water-processable supercapacitive material composed of graphene oxide (GO) and pristine graphene (PG). GO and PG are prepared by a modified Hummer's method and direct liquid phase exfoliation of graphite in dimethyl sulfoxide (DMSO) respectively. Water-processable GO/PG composites can be conveniently fabricated by mixing colloidal GO/H2O and PG/DMSO dispersions. The GO/PG composites can be re-dispersed in water to form stable colloidal dispersions. Capacitive behaviors of GO, PG and GO/PG composites were tested by cyclic voltammetry, galvanostatic charge/discharge curves and electrochemical impedance spectroscopy in aqueous electrolyte solutions. GO/PG composites exhibited improved capacitive properties in terms of specific capacitance and cycling stability, compared to those of individual components. The enhanced performances of the GO/PG composites signify the importance of the surface chemical property and conductivity of carbon-based materials for supercapacitor applications.

•A good electrode material based on graphene oxide patched with pristine graphene is proposed.•This composite material exhibits very fast electron transfer kinetics.•The charge transfer ability benefits from the healing role of pristine graphene patches.A new electrode material composed of graphene oxide (GO) and pristine graphene (PG) was simply fabricated, and a very fast electron transfer kinetics on GO/PG electrodes was exhibited. This improved electrochemical performance of the GO/PG composites should be ascribed to a unique structure formed when GO combined with PG nanosheets serving as patches.

Graphene, a two-dimensional crystalline form of carbon, has attracted wide and intense interest owing to its excellent physical properties and because its surface and edges can be chemically modified readily. Development of a method for producing high-quality graphene in large quantities is essential for further investigation of its properties and applications. The direct liquid-phase exfoliation of graphite to produce graphene is a convenient method for generating ideal graphene samples in large quantities. This direct method, which involves the use of colloidal suspensions, is based on the one-step physical transformation of graphite into graphene and has many unique advantages. A large number of liquids have been employed as exfoliation media and show a range of exfoliation efficiencies. In this review, we highlight the recent progress made on the exfoliation of bulky graphite powders or flakes into single- and few-layered graphene sheets in various liquids, including organic solvents, ionic liquids, and water/surfactant solutions. The qualities and yields of the exfoliated graphene samples, as well as their use in various applications, are also reviewed. Furthermore, future research directions for the development of novel exfoliation media and more efficient techniques for producing well-exfoliated pristine graphene are proposed.

•Certain common organic salts are first used for liquid-phase exfoliation of graphene.•They exhibit efficient assistance for graphite exfoliation in some organic solvents.•Up to 123 times enhanced exfoliation efficiency is achieved in DMSO.•The organic salt-assisted exfoliation method is simple, efficient, safe and economical.Certain ordinary organic salts, such as edetate disodium, sodium tartrate, potassium sodium tartrate and sodium citrate were found to have universal and efficient assistant effect for liquid-phase exfoliation of graphite in common organic solvents to produce pristine graphene. Up to 123 times enhanced exfoliation efficiency was observed when sodium citrate was introduced into an exfoliation system consisting of natural graphite powder and dimethyl sulfoxide. TEM, AFM, Raman spectroscopy, EDX, TGA, and FTIR analysis showed graphite was successfully exfoliated into single or few-layer graphene nanosheets which were free of defects and oxides. The method is simple, effective, safe and economical.

Fe3O4 and Pd nanoparticles were assembled on sulfonated graphene (s-G) by an easy chemical approach and characterized by transmission electron microscopy, X-ray diffraction and energy dispersive X-ray spectroscopy. The resulting material could be dispersed homogeneously in water or water/ethanol and further used as an excellent semi-heterogeneous catalyst for the Suzuki–Miyaura cross-coupling reaction in an environmentally friendly solvent under ligand-free ambient conditions. The high heterogeneous catalytic activity appears to be due to the small size of Pd nanoparticles and homogeneous distribution of the nanoparticles on the Fe3O4/s-G matrix. In addition, the catalytic activity did not deteriorate even after repeated applications, which may be due to the easy and efficient magnetic separation of the catalyst and the high dispersion and stability of the catalyst in an aqueous solution.

UV-vis absorption, photoluminescence (PL), and electroluminescence (EL) properties of a series of monosilylene–oligothienylene copolymer films have been studied. Both the absorption and PL spectra of these films exhibited a red shift with increasing the number of thienylene rings in the repeat unit of a polymer, indicating that the optical properties of these polymers are controlled mainly by the aromatic units, i.e. oligothienylene in the main chain. Polymer light-emitting diodes with a simple structure of Al/electrolyte-doped copolymer/ITO were fabricated using these copolymers as an emitting layer. Clear and stable EL spectra were observed only when the EL devices were in the reverse bias, i.e.Al as anode and ITO as cathode. The EL spectra resembled the corresponding PL spectra and also exhibited a red shift with the increase in the number of thienylene rings. It was also found that the turn-on voltage of the EL devices decreased with the increase in the number of thienylene rings, which is due, most likely, to the increase of charge carrier mobility and decrease of the bandgap as the π-conjugation length increases.

Low frequency noise properties of the poly(3-methylthiophene) film prepared by electrochemical polymerization on two-band Pt electrode are investigated. The relation between flicker noise and conducting properties under different doping potential is discussed on the basis of the Hooge empirical equation. Under light doping state, the Hooge parameter almost remains constant with increasing doping potential. However, in the case of heavy doping, it increases with doping potential. The dependence of the Hooge parameter on doping level reflects the evolution of metallic domains and the transport process of charge carriers. It is believed that the amorphous structure and high carrier concentration in the poly(3-methylthiophene) film lead to a greater Hooge parameter value.

A simple and renewable four-band platinum electrode for in situ conductivity measurement of polymers is described. A model is developed to evaluate contact resistance between the electrode and polyaniline film and calibrate the film resistances obtained by two-probe and four-probe methods. The conductivity of the film is calculated from the calibrated resistance. By comparing the effects of band thickness, gap width, and film thickness, it is found that the ratio K of the middle gap width to the thickness of the internal two platinum bands is the most important parameter to characterize one four-band electrode. An ideal four-band electrode should have large K and wide middle gap as possible so long as the film can uniformly cover the electrode. Under this case, the influence of contact resistance on the four-probe measurement of film resistance is negligible. It is shown that contact resistance depends on the oxidation state of the film. It rises nonlinearly with increasing film resistance.

Fe3O4 and Pd nanoparticles were assembled on sulfonated graphene (s-G) by an easy chemical approach and characterized by transmission electron microscopy, X-ray diffraction and energy dispersive X-ray spectroscopy. The resulting material could be dispersed homogeneously in water or water/ethanol and further used as an excellent semi-heterogeneous catalyst for the Suzuki–Miyaura cross-coupling reaction in an environmentally friendly solvent under ligand-free ambient conditions. The high heterogeneous catalytic activity appears to be due to the small size of Pd nanoparticles and homogeneous distribution of the nanoparticles on the Fe3O4/s-G matrix. In addition, the catalytic activity did not deteriorate even after repeated applications, which may be due to the easy and efficient magnetic separation of the catalyst and the high dispersion and stability of the catalyst in an aqueous solution.

Graphene, a two-dimensional crystalline form of carbon, has attracted wide and intense interest owing to its excellent physical properties and because its surface and edges can be chemically modified readily. Development of a method for producing high-quality graphene in large quantities is essential for further investigation of its properties and applications. The direct liquid-phase exfoliation of graphite to produce graphene is a convenient method for generating ideal graphene samples in large quantities. This direct method, which involves the use of colloidal suspensions, is based on the one-step physical transformation of graphite into graphene and has many unique advantages. A large number of liquids have been employed as exfoliation media and show a range of exfoliation efficiencies. In this review, we highlight the recent progress made on the exfoliation of bulky graphite powders or flakes into single- and few-layered graphene sheets in various liquids, including organic solvents, ionic liquids, and water/surfactant solutions. The qualities and yields of the exfoliated graphene samples, as well as their use in various applications, are also reviewed. Furthermore, future research directions for the development of novel exfoliation media and more efficient techniques for producing well-exfoliated pristine graphene are proposed.

Metalloporphyrinic frameworks have been studied in many fields. However, their electrochemical properties were seldom reported. This work reports the synthesis and the electrochemical application of a new bimetallic metalloporphyrinic framework, [Cu2-Co[5,10,15,20-(4-carboxyphenyl)porphyrin](H2O)2]·0.5DMF·5H2O (Cu-CoTCPP) in which [5,10,15,20-(4-carboxyphenyl)porphyrin]Co(II) (CoTCPP) struts are bound by Cu(II)–carboxylate clusters (Cu2(COO)4). Cu-CoTCPP was synthesized by the solvothermal method and characterized by various techniques, including XRD, IR, UV-vis, elemental analysis, TG, and TEM. Cu-CoTCPP showed novel bifunctional electrocatalytic ability toward the reduction/oxidation of H2O2 and the oxidation of NaNO2, which might be due to Cu and Co central ions, respectively. With the assistance of multi-walled carbon nanotubes (MWCNTs), Cu-CoTCPP showed further improved sensing performance toward H2O2. The linear detection ranges of the Cu-CoTCPP/MWCNTs/GCE for H2O2 and NaNO2 are 5.0 × 10−7 to 1.8 × 10−4 M and 2.5 × 10−6 to 1.1 × 10−3 M, respectively, with the detection limits of 2.4 × 10−7 M and 1.7 × 10−7 M, and the sensitivity of 168 and 439 mA mol−1 L cm−2. The bifunctional electrocatalytic ability and the excellent performance imply that the metalloporphyrinic frameworks are promising candidates for fabricating electrochemical sensors.

UV-vis absorption, photoluminescence (PL), and electroluminescence (EL) properties of a series of monosilylene–oligothienylene copolymer films have been studied. Both the absorption and PL spectra of these films exhibited a red shift with increasing the number of thienylene rings in the repeat unit of a polymer, indicating that the optical properties of these polymers are controlled mainly by the aromatic units, i.e. oligothienylene in the main chain. Polymer light-emitting diodes with a simple structure of Al/electrolyte-doped copolymer/ITO were fabricated using these copolymers as an emitting layer. Clear and stable EL spectra were observed only when the EL devices were in the reverse bias, i.e.Al as anode and ITO as cathode. The EL spectra resembled the corresponding PL spectra and also exhibited a red shift with the increase in the number of thienylene rings. It was also found that the turn-on voltage of the EL devices decreased with the increase in the number of thienylene rings, which is due, most likely, to the increase of charge carrier mobility and decrease of the bandgap as the π-conjugation length increases.