Qingli Hao

Effect of Graphene Oxide on the Properties of Its Composite with Polyaniline

Graphene oxide, a single layer of graphite oxide (GO), has been used to prepare graphene oxide/polyaniline (PANI) composite with improved electrochemical performance as supercapacitor electrode by in situ polymerization using a mild oxidant. The composites are synthesized under different mass ratios, using graphite as start material with two sizes: 12 500 and 500 mesh. The result shows that the morphology of the prepared composites is influenced dramatically by the different mass ratios. The composites are proposed to be combined through electrostatic interaction (doping process), hydrogen bonding, and pi-pi stacking interaction. The highest initial specific capacitances of 746 F g(-1) (12 500 mesh) and 627 F g(-1) (500 mesh) corresponding to the mass ratios 1:200 and 1:50 (graphene oxide/aniline) are obtained, compared to PANI of 216 F g(-1) at 200 mA g(-1) by charge-discharge analysis between 0.0 and 0.4 V. The improved capacitance retention of 73% (12 500 mesh) and 64% (500 mesh) after 500 cycles is obtained for the mass ratios 1:23 and 1:19 compared to PANI of 20%. The enhanced specific capacitance and cycling life implies a synergistic effect between two components. This study is of significance for developing new doped PANI materials for supercapacitors.

Nanostructured ternary composites of graphene/Fe2O3/polyaniline for high-performance supercapacitors

Well-designed nanostructures of a ternary nanocomposite, graphene/Fe2O3/polyaniline, are fabricated via a two-step approach. Graphene oxide is reduced by Fe2+ and well-dispersed by loading α-Fe2O3 nanoparticles (20–70 nm in size). A thin film of polyaniline is in situ polymerized on the graphene/Fe2O3 surfaces for the fabrication of its ternary composite. Among the composites obtained at different ratios of graphene/Fe2O3 to polyaniline, the ternary graphene/Fe2O3/polyaniline with a ratio of 2 : 1 exhibits a high specific capacitance of 638 F g−1 in 1 M KOH at a scan rate of 1 mV s−1 and experiences only a negligible decay of 8% after 5000 cycles. It also shows a higher energy density at high power density than other ternary or binary composites of the three components, respectively. The extraordinary electrochemical performance of the composite arises from the well-designed structural advantages of the ternary nanocomposite, and the good combination and synergistic effects among the three components. Graphene sheets, as the conducting frameworks for sustaining polyaniline and Fe2O3, can separate and disperse well in the composite due to the existence of Fe2O3. On the other hand, the thin film of polyaniline on the surface of graphene/Fe2O3 not only enhances the surface area, but also restricts the dissolution, aggregation and volume changes of Fe2O3 during charge–discharge cycling. Additionally, the existence of Fe2O3 is helpful to increase the rate stability of the ternary composite. The ternary composites with synergistic effects can take advantage of both Faradaic and non-Faradaic processes for capacity-charge storage with excellent electrochemical properties.

Graphene/SnO2/polypyrrole ternary nanocomposites as supercapacitor electrode materials

A ternary electrode material, based on graphene, tin oxide (SnO2) and polypyrrole (PPy) was obtained via one–pot synthesis. The graphene/SnO2/PPy (GSP) nanocomposite is composed of a thin conducting film of PPy on the surface of graphene/SnO2 (GS). An enhanced specific capacitance (616 F g−1) of GSP was obtained at 1 mV s−1 in 1 M H2SO4 compared with GS (80.2 F g−1) and PPy (523 F g−1). The GSP electrode shows better cycle stability and no obvious decay after 1000 galvanostatic cycles at 1 A g−1. Its specific power density and energy density can reach 9973.26 W kg−1, and 19.4 W h kg−1, respectively. The excellent electrochemical performance arises from the well-designed structure advantages, the good combination of components and the synergistic effect between the three components. Well-dispersed graphene is used as a framework for sustaining the pseudocapacitive materials of SnO2 and PPy. The PPy film restricts the aggregation and volume change of SnO2 during charge–discharge cycling, and also enhances the surface area. The electrochemical results show that the ternary composite of GSP is a promising candidate electrode material for high-performance supercapacitors.

Reduced-graphene oxide/molybdenum oxide/polyaniline ternary composite for high energy density supercapacitors: Synthesis and properties

Reduced-graphene oxide/molybdenum oxide/polyaniline ternary composites, RGO(MP), for use as electrode materials for high energy density supercapacitors, were firstly synthesized using a one-step method with Mo3O10(C6H8N)2·2H2O and graphene oxide (GO) as precursors. When the mass ratio of Mo3O10(C6H8N)2·2H2O to GO is 8 : 1, the resulting composite RGO(MP)8 shows excellent electrochemical performance with a maximum specific capacitance of 553 F g−1 in 1M H2SO4 and 363 F g−1 in 1 M Na2SO4 at a scan rate of 1 mV s−1. Its energy density reaches 76.8 W h kg−1 at a power density of 276.3 W kg−1, and 28.6 W h kg−1 at a high power density of 10294.3 W kg−1 in H2SO4. While in Na2SO4, the energy density achieves 72.6 W h Kg−1 at a power density of 217.7 W kg−1 and 13.3 W h Kg−1 at power density of 3993.8 W kg−1, respectively. The composite also presents good cycling stability (86.6, 73.4% at 20 mV s−1 after 200 cycles in 1 M H2SO4 and Na2SO4, respectively).

Experimental and density functional studies on 4-(4-cyanobenzylideneamino)antipyrine

4-(4-cyanobenzylideneamino)antipyrine (CBAP) has been synthesized and characterized by elemental analysis, FT-IR, UV-VIS and X-ray single crystal diffraction techniques. Crystallographic study reveals that the compound adopts trans configuration about the Schiff base imine double bond. The substituted p-cyanophenyl ring indirectly linked to the pyrazoline ring by the C=N double bond is almost coplanar with the pyrazole ring, whereas the phenyl ring directly attached to the pyrazoline ring forms an effective dihedral angle. Density functional calculations have been carried out to optimize and to characterize the title compound by using B3LYP method at 6-31G(d) basis set. The calculated results show that the optimized geometry can well reproduce the crystal structural parameters and the theoretical vibrational frequencies show good agreement with experimental values. On the basis of theoretical vibrational analyses, the thermodynamic properties (standard heat capacities, standard entropies, and standard enthalpy changes) of the title compound at different temperatures have been calculated, revealing the correlations between , , and temperatures. The total molecular dipole moment, mean linear polarizability and mean first hyperpolarizability obtained by calculation are 3.4724 Debye, 40.154 Å3 and 4.5424 × 10−29 cm5/esu, respectively. Three absorption bands in UV-VIS are mainly derived from the contribution of bands π → π* and electrons transfer from HOMO to LUMO, LUMO + 1, LUMO + 2, respectively.

Conducting polymer composites with graphene for use in chemical sensors and biosensors

AbstractThis review (with 79 references) summarizes the recent work on the development of chemical sensors and biosensors based on the use of composites made from conducting polymers (CPs) and graphene. Owing to the unique electrical, mechanical, optical, chemical and structural properties of CP and graphene, these kinds of composites have generated increasing interest in senor field. In this review, we first discuss methods for preparation of CP/GE composites by chemical, electrochemical, or physical methods including electrostatic interactions. We then cover aspects of the fabrication of modified electrodes and the performance of respective sensors with electrochemical, electronic or optical signal transduction. We then discuss sensors for the determination of inorganic and organic species, gases and vapors. We also review the state of the art in respective biosensors for hydrogen peroxide and glucose, for oligomers (DNA, RNA, and aptamers), for biogenic amines, NAD^+/NADH, cytochromes and the like, and in immunosensors. Finally, the perspective and current challenges of CP/GE composites for use in (bio)sensors are outlooked. FigureConducting polymer composites with graphene have attracted increasing research interest in the modified electrodes for the application in chemical sensors and biosensors, due to the unique intrinsic properties of each component.

Investigation of contact and bulk resistance of conducting polymers by simultaneous two- and four-point technique

A conventional resistance measured by two-point technique includes bulk and contact components. The contact resistance can be excluded by a four-point technique. A simultaneous use of the two- and four-point techniques allows to separate the total resistance between two electrodes for the contact and bulk parts. This approach has been used to analyze electrical coupling between metal electrodes of interdigitated structures and chemically sensitive coating formed by polyaniline (PANI). The polymer layers were deposited by electropolymerization on bare gold and platinum electrodes as well as on gold electrodes precoated by a self-assembled monolayer of 4-aminothiophenol. An exposure of the PANI films formed on interdigitated structures to gaseous HCl displays proportional changes of resistance measured by the two- and four- point techniques for platinum electrodes and for the precoated gold electrode, while a strong deviation from this proportionality was observed for the gold electrodes without precoating. The results demonstrate a high contribution of the contact resistance between PANI and bare gold electrodes into the resistance measured by the two-point technique. This contribution is small and therefore not measurable for bare platinum electrodes or for gold electrodes coated by 4-aminothiophenol.

Experimental and theoretical studies on vibrational spectra of 4-(2-furanylmethyleneamino)antipyrine, 4-benzylideneaminoantipyrine and 4-cinnamilideneaminoantipyrine

This work deals with the IR and Raman spectroscopy of 4-(2-furanylmethyleneamino) antipyrine (FAP), 4-benzylideneaminoantipyrine (BAP) and 4-cinnamilideneaminoantipyrine (CAP) by means of experimental and quantum chemical calculations. The equilibrium geometries, harmonic frequencies, infrared intensities and Raman scattering activities were calculated by density functional B3LYP method with the 6-31G(d) basis set. The comparisons between the calculated and experimental results covering molecular structures, assignments of fundamental vibrational modes and thermodynamic properties were investigated. The optimized molecular geometries have been compared with the experimental data obtained from XRD data, which indicates that the theoretical results agree well with the corresponding experimental values. For the three compounds, comparisons and assignments of the vibrational frequencies indicate that the calculated frequencies are close to the experimental data, and the IR spectra are comparable with some slight differences, whereas the Raman spectra are different clearly and the strongest Raman scattering actives are relative tightly to the molecular conjugative moieties linked through their Schiff base imines. The thermodynamic properties (heat capacities, entropies and enthalpy changes) and their correlations with temperatures were also obtained from the harmonic frequencies of the optimized structures.

Well-Combined Magnetically Separable Hybrid Cobalt Ferrite/Nitrogen-Doped Graphene as Efficient Catalyst with Superior Performance for Oxygen Reduction Reaction.

Catalysts with low-cost, high activity and stability toward oxygen reduction reaction (ORR) are extremely desirable, but its development still remains a great challenge. Here, a novel magnetically separable hybrid of multimetal oxide, cobalt ferrite (CoFe2O4), anchored on nitrogen-doped reduced graphene oxide (CoFe2O4/NG) is prepared via a facile solvothermal method followed by calcination at 500 °C. The structure of CoFe2O4/NG and the interaction of both components are analyzed by several techniques. The possible formation of Co/Fe-N interaction in the CoFe2O4/NG catalyst is found. As a result, the well-combination of CoFe2O4 nanoparticles with NG and its improved crystallinity lead to a synergistic and efficient catalyst with high performance to ORR through a four-electron-transfer process in alkaline medium. The CoFe2O4/NG exhibits particularly comparable catalytic activity as commercial Pt/C catalyst, and superior stability against methanol oxidation and CO poisoning. Meanwhile, it has been proved that both nitrogen doping and the spinel structure of CoFe2O4 can have a significant contribution to the catalytic activity by contrast experiments. Multimetal oxide hybrid demonstrates better catalysis to ORR than a single metal oxide hybrid. All results make the low-cost and magnetically separable CoFe2O4/NG a promising alternative for costly platinum-based ORR catalyst in fuel cells and metal-air batteries.

Vibrational spectroscopic study of o-, m- and p-hydroxybenzylideneaminoantipyrines.

Three structurally similar antipyrine derivatives of o-hydroxybenzylideneaminoantipyrine (o-HBAP), m-hydroxybenzylideneaminoantipyrine (m-HBAP) and p-hydroxybenzylideneaminoantipyrine (p-HBAP) were characterized by FT-IR, FT-Raman experimental techniques and density functional theoretical (DFT) calculations. The comparisons between the calculated and experimental results covering molecular structures, assignments of fundamental vibrational modes and thermodynamic properties were investigated. The optimized molecular geometries agree well with the corresponding experimental values by comparing with the XRD data. The comparisons and assignments of the vibrational frequencies indicate that the experimental spectra also coincide satisfactorily with those of theoretically simulated spectrograms except the hydrogen-bond coupling infrared vibrations, and compounds can be distinguished by the IR and Raman spectra due to the differences of the hydroxyl-substituted positions and molecular packing, and the strong Raman scattering activities of the compounds are tightly relative to the molecular conjugative moieties linked through the Schiff base imines. The thermodynamic functions and their correlations with temperatures were also obtained from the theoretical harmonic frequencies.