Excellent electrocatalytic performance of Pt nanoparticles on reduced graphene oxide nanosheets prepared by a direct redox reaction between Na2PtCl4 and graphene oxide

A simple and environment-friendly method was used to prepare Pt/reduced graphene oxide (Pt/RGO) hybrids. This approach used a redox reaction between Na₂PtCl₄ and graphene oxide (GO) nanosheets and a subsequent thermal reduction of the material at 200 °C for 24 h in a vacuum oven. In contrast to other methods that use an additional reductant to prepare Pt nanoparticles, the Pt²⁺ was directly reduced to Pt⁰ in the GO solution. GO was used as the reducing agent, the stabilizing agent and the carrier. The resulting Pt/RGO hybrid was characterized by X-ray diffraction, thermo-gravimetric analysis, X-ray photoelectron spectroscopy, transmission electron microscopy and energy-dispersive X-ray spectroscopy. Electrochemical measurements showed that the Pt/RGO hybrids exhibit good activity as catalysts for the electro-oxidation of methanol and ethanol in acid media. Interestingly, the Pt/RGO hybrids showed better electrocatalytic activity and stability for the oxidation of methanol than Pt/C and Pt/RGO hybrids made from other Pt precursors. This indicates that the Pt/RGO hybrids should have great potential applications in direct methanol and ethanol fuel cells.     

Fabrication of graphene nanosheet (GNS)–Fe3O4 hybrids and GNS–Fe3O4/syndiotactic polystyrene composites with high dielectric permittivity

Graphene nanosheet–Fe₃O₄ (GNS–Fe₃O₄) hybrids were obtained by a one-step solvothermal reduction of iron (III) acetylacetonate [Fe(acac)₃] and graphene oxide (GO) simultaneously, which had several advantages: (1) the Fe₃O₄ nanoparticles were firmly anchored on GNS surface even after mild ultrasonication; (2) the loading amount of Fe₃O₄ nanoparticles could be effectively controlled by changing the initial feeding weight ratio of Fe(acac)₃ to GO; (3) the Fe₃O₄ nanoparticles were homogeneously distributed on the GNS surface without much aggregation. Composites based on syndiotactic polystyrene (sPS) and GNS–Fe₃O₄ were prepared by a solution-blending method and the electric and dielectric properties of the resultant GNS–Fe₃O₄/sPS composites were investigated. The percolation threshold of GNS–Fe₃O₄ in the sPS matrix was determined to be 9.41 vol.%. Slightly above the percolation threshold with 9.59 vol.% of GNS–Fe₃O₄, the GNS–Fe₃O₄/sPS composite showed a high dielectric permittivity of 123 at 1000 Hz, which was 42 times higher than that of pure sPS. The AC electrical conductivity at 1000 Hz increased from 3.6 × 10⁻¹⁰ S/m for pure sPS to 2.82 × 10⁻⁴ S/m for GNS–Fe₃O₄/sPS composite containing 10.69 vol.% of GNS–Fe₃O₄, showing an obvious insulator-semiconductor transition.     

Magnetic reduced graphene oxide nanocomposite as an effective electromagnetic wave absorber and its absorbing mechanism

A magnetic reduced graphene oxide (MRGO) composite consisting of graphene oxide and Fe₃O₄ particles in the range of 5–20 nm has been prepared by the one-pot hydrothermal process. RGO nanosheets provide flexible substrates for nanoparticle decoration, while Fe₃O₄ nanoparticles can also effectively prevent nanosheets to restack each other. Compared with previously literature, the synthesized RGO-Fe₃O₄ composite exhibits excellent electromagnetic wave absorption. The minimum reflection loss (R_L) value of −49.05 dB has been observed at 14.16 GHz with a thickness of 2.08 mm. The absorption bandwidth (R_L<−10 dB) corresponding to the minimum R_L is 4.60 GHz. The electromagnetic wave absorption properties of the RGO-Fe₃O₄ composite have been interpreted through the quarter-wavelength matching model.     

Effect of core-shell reversal on the structural,magnetic and adsorptive properties of Fe2O3-GO nanocomposites

Effect of core-shell reversal on the nanocomposites of graphene oxide (GO) and ferric oxide (Fe₂O₃) was studied. Fe₂O₃@GO core-shell nanosheets were synthesized by sonication method, while the GO@Fe₂O₃ core-shell nanospheres by employing N,N′-dicyclohexylcarbodimide as the binding agent for the wrapping of GO sheets on pre-formed Fe₂O₃ nanoparticles (NPs). The phase composition, crystallinity and morphology of the nanocomposites were characterized by FT-IR, TEM, SEM-EDS, VSM, BET surface area study and XRD techniques. The saturation magnetization (M_s) was 1.25 and 0.51 emu g⁻¹ for GO@Fe₂O₃ and Fe₂O₃@GO respectively owing to the dependence of magnetic properties on the reversal of core-shell. BET analysis revealed the surface area of 100.32 m² g⁻¹ and 45.69 m² g⁻¹ for GO@Fe₂O₃ and Fe₂O₃@GO nanocomposites respectively. The fabricated nanocomposites were analyzed as adsorbents for the uptake of Pb (II) ions. The impact of various factors affecting adsorption process such as pH, adsorbent dose, contact time, temperature and metal ion concentration was also investigated. GO@Fe₂O₃ core-shell nanospheres showed a higher adsorption capacity for Pb (II) ions as compared to Fe₂O₃@GO core-shell nanosheet with the maximum adsorption capacities (q_m) of 303.0 and 125.0 mg g⁻¹ respectively. The equilibrium data was estimated by Freundlich, Langmuir, D-R and Temkin isotherm models. Thermodynamic analysis confirmed the spontaneous and exothermic nature of the adsorption process. The adsorption kinetics was significantly fitted to pseudo-second order model. The results confirmed that core-shell reversal can significantly alter the adsorptive properties of Fe₂O₃-GO nanocomposite     

One-pot solvothermal preparation of magnetic reduced graphene oxide-ferrite hybrids for organic dye removal

A one-pot solvothermal synthesis method was developed to prepare reduced graphene oxide (RGO) supported ferrite (MFe₂O₄, M = Mn, Zn, Co and Ni) hybrids using graphite oxide and metal ions (Fe³⁺ and M²⁺) as starting materials. The hybrids were characterized by X-ray powder diffraction, Raman spectra, field emission scanning electron microscopy, energy dispersive X-ray spectroscopy, transmission electron microscopy, and vibrating sample magnetometer. It was shown that monodispersed MFe₂O₄ microspheres with uniform size were homogeneously deposited on RGO nanosheets. The influence of the metal ion concentration on the morphology of the hybrids was investigated. The hybrids possess considerable saturation magnetization, lower remanence and coercivity. Importantly, the obtained hybrids are effective adsorbents for removal of dye pollutants. It was found that over 92% rhodamine B (RhB) and 100% methylene blue (MB) with a concentration of 5 mg/L can be removed by the hybrids within 2 min when the concentration of the hybrids is 0.6 g/L. In addition, the hybrids also show enhanced photocatalytic activity in the degradation of RhB and MB. Benefiting from their bigger saturation magnetization, the hybrids can be easily separated from the solution by a magnet. This research would provide a new easy separating platform for wastewater decontamination.     

PtPd nanowire arrays supported on reduced graphene oxide as advanced electrocatalysts for methanol oxidation

Novel reduced graphene oxide (RGO) nanosheet/PtPd nanowire hybrids were prepared by a mild wet chemical approach. Uniform Pt nanowire arrays are successfully supported on functionalized RGO nanosheets with Pd nanoparticles as growing seeds. The whole deposition process was achieved in aqueous solution at room temperature. TEM and HR-TEM analysis indicated the single-crystal feature of the Pt nanowires with a diameter of ca. 4 nm in average and a length of 20–200 nm. Electrochemical characterization demonstrated that the hybrid nanostructures have a higher catalytic activity and stability than commercial state-of-the-art platinum black catalysts (Hispec1000) toward the methanol oxidation reaction (MOR). An initial mass activity of 0.51 A mg⁻¹ and a degradation ratio of 17.2% after 1000 potential sweeping cycles were achieved for the hybrid nanostructures, compared with 0.44 A mg⁻¹ and 27.5% for Pt black, respectively, demonstrating a great potential of this RGO/PtPd hybrids for DMFC applications.     

Highly efficient synthesis of graphene/MnO2 hybrids and their application for ultrafast oxidative decomposition of methylene blue

A highly efficient method has been reported to fabricate the reduced graphene oxide/MnO₂ (RGO/MnO₂) hybrid materials, a kind of catalysts for oxidative decomposition of methylene blue (MB). The pristine suspension of graphene oxide/manganese sulfate (GO/MnSO₄) produced by the modified Hummers method is in situ transformed into GO/MnO₂ composites in combination with KMnO₄, and then further into RGO/MnO₂ composites by means of glucose-reduction. It is found that MnO₂ nanoparticles with the size of 20–30 nm are uniformly distributed in the structure of RGO. A series of composites with different mass ratios of RGO to MnO₂ has been proved superior catalytic activities, much higher than that of the bare MnO₂ for decomposition of MB dye in the presence of H₂O₂. Typically, 50 mL of MB (50 mg L⁻¹) can be completely decolorized and nearly 66% mineralized at 50 °C in 5 min with 10 mg of the RGO/MnO₂ hybrid. According to the adsorption–oxidation–desorption mechanism, the high activity of RGO/MnO₂ composites for decomposition of MB is closely related to the positive synergistic effect of RGO and MnO₂ with the assistance of H₂O₂.     

Electrochemically synthesized graphene/polypyrrole composites and their use in supercapacitor

Composite films consisting of polypyrrole (PPy) and graphene oxide (GO) were electrochemically synthesized by electrooxidation of 0.1 M pyrrole in aqueous solution containing appropriate amounts of GO. Simultaneous chronoamperometric growth profiles and frequency changes on a quartz crystal microbalance showed that the anionic GO was incorporated in the growing GO/PPy composite to maintain its electrical neutrality. Subsequently, the GO was reduced electrochemically to form a reduced GO/PPy (RGO/PPy) composite by cyclic voltammetry. Specific capacitances estimated from galvanostatic discharge curves in 1 M H₂SO₄ at a current density of 1 A g^?1 indicated that values for the RGO/PPy composite were larger than those of a pristine PPy film and the GO/PPy composite. In the case of 6 mg mL^?1 GO for the preparation of GO/PPy, a high specific capacitance of 424 F g^?1 obtained at the electrochemically prepared RGO/PPy composite indicated its potential for use as an electrode material for supercapacitors.     

Controlled synthesis of Fe3O4@SnO2/RGO nanocomposite for microwave absorption enhancement

A ternary nanocomposite of Fe₃O₄@SnO₂/reduced graphene oxide (RGO) with different contents of SnO₂ nanoparticles was synthesized by a simple and efficient three-step method. The transmission electron microscopy and field emission scanning electron microscopy characterization display that plenty of Fe₃O₄@SnO₂ core–shell structure nanoparticles are well distributed on the surface of RGO sheets. The X-ray diffractograms show that the products consist of highly crystallized cubic Fe₃O₄, tetragonal SnO₂ and disorderedly stacked RGO sheets. The magnetic hysteresis measurement reveals the ferromagnetic behavior of the products at room temperature. The microwave absorption properties of paraffin containing 50 wt% products were investigated at room temperature in the frequency range of 2–18 GHz by a vector network analyzer. The electromagnetic data show that the maximum reflection loss is −45.5 dB and −29.5 dB for Fe₃O₄@SnO₂/RGO-1 and Fe₃O₄@SnO₂/RGO-2 nanocomposite, respectively. Meanwhile, the reflection loss less than −10 dB is up to 14.4 GHz and 13.8 GHz for Fe₃O₄@SnO₂/RGO-1 and Fe₃O₄@SnO₂/RGO-2 nanocomposite, respectively. It is believed that such nanocomposite could be used as promising microwave absorbers.     

Synthesis of Mn3O4/N-doped graphene hybrid and its improved electrochemical performance for lithium-ion batteries

Mn₃O₄/N-doped graphene (Mn₃O₄/NG) hybrids were synthesized by a simple one-pot hydrothermal process. The scanning electron microscopy (SEM), transition electron microscopy (TEM), X-ray powder diffraction (XRD), Thermogravimetric analysis (TG), Raman Spectroscopy and X-ray photoelectron spectroscopy (XPS) were used to characterize the microstructure, crystallinity and compositions. It is demonstrated that Mn₃O₄ nanoparticles are high-dispersely anchored onto the individual graphene nanosheets, and also found that, in contrast with pure Mn₃O₄ obtained without graphene added, the introduction of graphene effectively restricts the growth of Mn₃O₄ nanoparticles. Simultaneously, the anchored well-dispersed Mn₃O₄ nanoparticles also play a role as spacers in preventing the restacking of graphene sheets and producing abundant nanoscale porous channels. Hence, it is well anticipated that the accessibility and reactivity of electrolyte molecules with Mn₃O₄/NG electrode are highly improved during the electrochemical process. As the anode material for lithium ion batteries, the Mn₃O₄/NG hybrid electrode displays an outstanding reversible capacity of 1208.4 mAh g⁻¹ after 150 cycles at a current density of 88 mA g⁻¹, even still retained 284 mAh g⁻¹ at a high current density of 4400 mA g⁻¹ after 10 cycles, indicating the superior capacity retention, which is better than those of bare Mn₃O₄, and most other Mn₃O₄/C hybrids in reported literatures. Finally, the superior performance can be ascribed to the uniformly distribution of ultrafine Mn₃O₄ nanoparticles, successful nitrogen doping of graphene and favorable structures of the composites.     

Immobilization of Aspergillus niger xylanase A on Fe3O4-coated chitosan magnetic nanoparticles for xylooligosaccharide preparation

Aspergillus niger xylanase A (XylA) was immobilized onto Fe₃O₄-coated chitosan magnetic nanoparticles prepared by the layer-by-layer self-assembly approach. The Fe₃O₄-coated chitosan magnetic nanoparticles showed a high binding capacity of 162.2 mg ∙ g^− 1-particles and a recovery activity of 56.5% for XylA. The immobilized XylA showed improved thermostability and storage stability compared with free XylA. The immobilized XylA retained 87.5% activity after seven successive reactions by magnetic separation. Xylotriose and xylohexaose were the main products released from birchwood xylan and wheat bran insoluble xylan by immobilized XylA, respectively.     

In situ sonochemical synthesis of Fe3O4–graphene nanocomposite for lithium rechargeable batteries

In this paper, we have presented experimental results for preparation of Fe₃O₄–graphene nanocomposite that uses an ultrasound assisted method. The graphene oxide (GO) was prepared from graphite powder using modified Hummers–Offeman method. Subsequently, the synthesis of graphene-Fe₃O₄ nanocomposite was carried out by ultrasound assisted co-precipitation of iron (II) and (III) chlorides in the presence of GO. The formation of GO and graphene-Fe₃O₄ nanocomposite was confirmed by X-ray diffraction (XRD), Energy dispersive X-ray (EDX) analysis and Fourier transform-infrared (FTIR) analysis. The particle size of Fe₃O₄ nanoparticles loaded on graphene nanosheets (observed from TEM image) was found to be smaller than 20 nm. The use of ultrasonic irradiations during synthesis of graphene-Fe₃O₄ nanocomposite resulted in uniform loading of Fe₃O₄ nanoparticles on graphene nanosheets. The prepared graphene-Fe₃O₄ nanocomposite material was used for the preparation of anode for lithium ion batteries. The electrochemical performance of the material was tested by cyclic voltammetry (CV) and charge/discharge cycles. It was observed that the capacity of Li-battery when the anode material was made using graphene-Fe₃O₄ nanocomposite showed stable electrochemical performance for around 120 cycles and the battery could repeat stable charge–discharge reaction.     

Controlled synthesis and electromagnetic wave absorption properties of core-shell Fe3O4@SiO2 nanospheres decorated graphene

Fe₃O₄/reduced graphene oxide (RGO) nanocomposite was synthesized by a simple hydrothermal method and then SiO₂ coated onto Fe₃O₄ by a modified Stӧber method. The transmission electron microscopy and field emission scanning electron microscopy characterization indicate that masses of Fe₃O₄@SiO₂ core-shell structure nanospheres attached to the RGO sheets, and that the thicknesses of SiO₂ shells are about 20–40 nm. The X-ray diffractograms and Raman spectra illustrate that the synthesized samples consist of highly crystallized cubic Fe₃O₄, amorphous SiO₂ and disorderedly stacked RGO sheets. The magnetic hysteresis loops reveal the ferromagnetic behavior of the samples at room temperature. In addition, the Fe₃O₄@SiO₂/RGO paraffin composite exhibit excellent electromagnetic wave absorption properties at room temperature in the frequency range of 2–18 GHz, which are attributed to the effective complementarities between the dielectric loss and magnetic loss. For Fe₃O₄@SiO₂/RGO-1 and Fe₃O₄@SiO₂/RGO-2 nanocomposite, the minimum reflection loss can reach −26.4 dB and −16.3 dB with the thickness of 1.5 mm, respectively. The effective absorption bandwidth of the samples can reach more than 10.0 GHz with the thickness in the range of 1.5–3.0 mm. It is demonstrated that such nanocomposite could be used as a promising candidate in electromagnetic wave absorption area.     

Three-dimensional hierarchical ZnCo2O4 flower-like microspheres assembled from porous nanosheets: Hydrothermal synthesis and electrochemical properties

In this work, three-dimensional hierarchical ZnCo₂O₄ flower-like microspheres have been synthesized on a large scale via a facile and economical citrate-mediated hydrothermal method followed by an annealing process in air. The as-synthesized ZnCo₂O₄ flower-like microspheres are constructed by numerous interweaving porous nanosheets. According to the experimental results, a formation mechanism involving the assembly of the nanosheets from nanoparticles into flower-like microsphere is proposed. As a virtue of their beneficial structural features, the ZnCo₂O₄ flower-like microspheres exhibit a high lithium storage capacity and excellent cycling stability (1136 mA h g⁻¹ at 100 mA g⁻¹ after 50 cycles). This remarkable electrochemical performance can be ascribed to the hierarchical structure and porous structures in the nanosheets, which effectively increases the contact area between the active materials and the electrolyte, shortening the Li⁺ diffusion pathway and buffering the volume variation during cycling.     

RGO/KMn8O16 composite as supercapacitor electrode with high specific capacitance

Reduced graphene oxide/cryptomelane (RGO/KMn₈O₁₆) composites are successfully synthesized from α-MnO₂ nanorods and GO using a water-bathing precipitation method. The unique structure of KMn₈O₁₆ nanorods, with a length of 2–4 μm, dispersed on the surface of RGO leads to a much enhanced electrical conductivity and ionic transport, finally achieving composites with an improved electrochemical performance. Electrochemical measurement results show a specific capacitance of 222.3 F/g at a current density of 0.2 A/g, much higher than that of the original α-MnO₂. After 500 cycles at 2.0 A/g, the RGO/KMn₈O₁₆ composite electrode still retains 92.6% of its initial specific capacitance. The excellent electrochemical performance and durability observed for this composite electrode suggest its potential application for electrochemical capacitors.     

Fe3O4 nanoparticles encapsulated in electrospun porous carbon fibers with a compact shell as high-performance anode for lithium ion batteries

Fe₃O₄ nanoparticles encapsulated in porous carbon fibers (Fe₃O₄@PCFs) as anode materials in lithium ion batteries are fabricated by a facile single-nozzle electrospinning technique followed by heat treatment. A mixed solution of polyacrylonitrile (PAN) and polystyrene (PS) containing Fe₃O₄ nanoparticles is utilized to prepare hybrid precursor fibers of Fe₃O₄@PS/PAN. The resulted porous Fe₃O₄/carbon hybrid fibers composed of compact carbon shell and Fe₃O₄-embeded honeycomb-like carbon core are formed due to the thermal decomposition of PS and PAN. The Fe₃O₄@PCF composite demonstrates an initial reversible capacity of 1015 mAh g⁻¹ with 84.4% capacity retention after 80 cycles at a current density of 0.2 A g⁻¹. This electrode also exhibits superior rate capability with current density increasing from 0.1 to 2.0 A g⁻¹, and capacity retention of 91% after 200 cycles at 2.0 A g⁻¹. The exceptionally high performances are attributed to the high electric conductivity and structural stability of the porous carbon fibers with unique structure, which not only buffers the volume change of Fe₃O₄ with the internal space, but also acts as high-efficient transport pathways for ions and electrons. Furthermore, the compact carbon shell can promote the formation of stable solid electrolyte interphase on the fiber surface.     

Integration of tailored reduced graphene oxide nanosheets and electrospun polyamide-66 nanofabrics for a flexible supercapacitor with high-volume- and high-area-specific capacitance

Nanofiber fabric is firstly introduced to replace common microfiber fabrics as the platform for flexible supercapacitors. Nanofiber and microfiber electrodes can be simply fabricated using a dipping process that impregnates reduced graphene oxide (RGO) nanosheets into electrospun polyamide-66 (PA66) nanofiber and microfiber fabrics. RGO nanosheets are tailored to various sizes and only RGO with a medium diameter of 250–450 nm (denoted as M-RGO) can effectively penetrate the pores of nanofiber fabrics for constructing smooth conductive paths within PA66 nanofiber fabrics. The synergistic effect between suitable sizes of RGO nanosheets and nanofiber fabrics with a high specific area provides a symmetric supercapacitor composed of M-RGO/PA66 nanofiber fabric electrodes with high-volume and high-area specific capacitance (C_S,V and C_S,A, equal to 38.79 F cm⁻³ and 0.931 F cm⁻² at 0.5 A g⁻¹, respectively), which are much larger than that of a symmetric supercapacitor composed of RGO/PA66 microfiber fabric electrodes (8.52 F cm⁻³ and 0.213 F cm⁻² at 0.5 A g⁻¹). The effect of impregnating nanofiber fabrics with suitably sized RGO to promote C_S,V and C_S,A of flexible supercapacitors has been demonstrated.     

Fabrication of carbon encapsulated Co3O4 nanoparticles embedded in porous graphitic carbon nanosheets for microwave absorber

Carbon-encapsulated Co₃O₄ nanoparticles homogeneously embedded 2D (two-dimensional) porous graphitic carbon (PGC) nanosheets were prepared by a facile and scalable synthesis method. With assistance of sodium chloride, the Co₃O₄ nanoparticles (10–20 nm) with magnetic loss were well encapsulated by onion-like carbon shells homogeneously embedded porous graphitic carbon nanosheets (thickness of less than 50 nm) with dielectric loss. In the architecture, the well impedance matching for microwave absorption can be obtained by the synergetic effect between Co₃O₄ nanoparticles and encapsulated porous carbon nanosheets. The minimum reflection loss value of −32.3 dB was observed at 11.4 GHz with a matching thickness of 2.3 mm for 2D Co₃O₄@C@PGC nanosheets. The 2D Co₃O₄@C@PGC nanosheets can be used as a kind of candidate for microwave absorbing materials.     

One-step electrodeposition synthesis of silver-nanoparticle-decorated graphene on indium-tin-oxide for enzymeless hydrogen peroxide detection

Silver-nanoparticles-decorated reduced graphene oxide (rGO) was electrodeposited on indium tin oxide (ITO) by a cyclic voltammetry method. The results of X-ray diffraction, Fourier-transform infrared transmission spectroscopy and Raman spectroscopy confirmed the simultaneous formation of cubic phase silver nanoparticles and reduction of GO through the electrodeposition process. Field emission scanning electron microscope images showed a uniform distribution of nanometer-sized silver nanoparticles with a narrow size distribution on the RGO sheets, which could only be achieved using silver ammonia complex instead of silver nitrate as precursor. The composite deposited on ITO exhibited notable electrocatalytic activity for the reduction of H₂O₂, leading to an enzymeless electrochemical sensor with a fast amperometric response time less than 2 s. The corresponding calibration curve of the current response showed a linear detection range of 0.1–100 mM (R² = 0.9992) while the limit of detection was estimated to be 5 μM.     

MoO3/reduced graphene oxide composites as anode material for sodium ion batteries

MoO₃/reduced graphene oxide (MoO₃/RGO) composites were successfully prepared via a facile one-step hydrothermal method, and evaluated as anode materials for sodium ion batteries (SIBs). The crystal structures, morphologies and electrochemical properties of the as-prepared samples were characterized by X-ray diffraction, field-emission scanning electron microscopy, cyclic voltammetry, electrochemical impedance spectroscopy, and galvanostatic charge/discharge tests, respectively. The results show that the introduction of RGO can enhance the electrochemical performances of MoO₃/RGO composites. MoO₃/RGO composite with 6 wt% RGO delivers the highest reversible capacity of ~208 mA h g⁻¹ at 50 mA g⁻¹ after 50 cycles with good cycling stability and excellent rate performance for SIBs. The excellent sodium storage performance of MoO₃/RGO should be attributed to the synergistic effect between MoO₃ and RGO, which offers the increased electrical conductivity, the facilitated electron transfer ability and the buffering of volume expansion.