Preparation and electrochemical performances of graphite oxide/polypyrrole composites

Graphite oxide/polypyrrole composites (GPys) were prepared by in situ polymerization and reduced by NaBH₄ to prepare reduced graphite oxide/polypyrrole composites (R-GPys). On the basis of the morphological and structural characterization of the composites by Fourier transform infrared spectrometer (FTIR), X-ray diffraction (XRD) and transmission electron microscopy (TEM) tests, the electrochemical performances of the composites were investigated by cyclic voltammetry, galvanostatic charge–discharge and electrochemical impedance techniques. The experimental results showed that the specific capacitances of the composites before and after reduction (197 and 180 F/g) were highly improved compared with that of pristine graphite oxide (11 F/g) and polypyrrole (112 F/g), respectively. The capacitance retention of about 73% for R-GPys compared with 12% for PPy and 47% for GPys after 1200 cycles indicated the high cycle stability of the R-GPys and its potential as an electrode material for supercapacitor applications.     

Intercalation compounds of graphite: Chemical identity and reactivity

Although both the true intercalation compound “C₁₃CrO₃” and the commercially available Seloxcette graphite/chromium trioxide mixture are reduced by various inorganic reagents, only the Seloxcette is efficacious in oxidizing primary alcohols to aldehydes. The nature of this divergence is probed by chemical and physical techniques. Curiously, while both the Seloxcette and the “C₁₃CrO₃” are found to contain chromium in a mixture of oxidation states, just as many intercalation compounds contain metals of different oxidation states, the immobility of the chromium in “C₁₃CrO₃” precludes reaction with organic species. The results found for these chromium systems are generalized to a discussion of the chemical reactivity of other intercalation compounds.     

Synthesis and studies of properties of graphite oxide and thermally expanded graphite

Graphite oxide is synthesized using various reaction parameters. Stagewise evaluation of graphite oxidation dynamics in the course of synthesis is carried out using the method of sample collection and thermogravimetric analysis. Thermally expanded graphite with high texture characteristics was obtained from graphite oxide. Properties of graphite oxide and thermally expanded graphite were determined using scanning electron microscopy, X-ray diffraction, thermogravimetry, differential scanning calorimetry, energy dispersive spectroscopy, and low-temperature adsorption of nitrogen. The values of capacity of supercapacitors based on graphite oxide and expanded graphite are found.     

Intercalation of stable organic radicals into layered copper hydroxides

We report the intercalation of a stable organic radical, 3-carboxy-2,2,5,5-tetramethyl-1-pyrrolidine-1-oxyl anion (PROXYL⁻) into the layered copper hydroxides, Cu₂(OH)₃(CH₃CO₂)·H₂O, by means of the anion exchange. The powder X-ray diffractions reveal the anion exchange, showing an increase in the interlayer distance. However, the elemental analyses indicate that the obtained material is Cu₂(OH)_3.5(PROXYL)_0.5·H₂O. The temperature dependence of the magnetic susceptibilities for the intercalation compound indicates a dominant antiferromagnetic interaction in contrast to the intralayer ferromagnetic interaction in the parent compound. The EPR spectra of the intercalation compound consist of the absorption of the organic radical, whose temperature-variable follows the Curie law. The observed antiferromagnetic properties can be ascribed to a transition in the magnetic properties of the [Cu₂(OH)₃]⁺ layer from ferromagnetic to antiferromagnetic upon intercalation.     

Intercalation of formic acid into carbon fibers and their exfoliation

Intercalation of formic acid in a mesophase-pitch-based fibers was successfully carried out by electrolysis in 50% solution. The formation of intercalation compounds was confirmed by X-ray diffraction (XRD), which showed a broad peak at the interlayer spacing of 0.92 nm. By rapid heating of the intercalated compounds of carbon fibers thus produced up to 1000 °C, exfoliation was occurred instantaneously. Changes of potential was found to depend on electrolysis temperature to prepare intercalation compounds of carbon fibers with formic acid; at the higher temperature potential saturated at the less electrical charge supplied. Suitable synthesis condition of the intercalation compounds was determined to be the current density of 200 A/g at the electrolysis temperature 10 °C. The exfoliation of carbon fibers started at the free end of fibers and proceeds gradually to the fixed end along the fiber axis with increasing charge. This electrolysis behavior suggests that the intercalation of formic acid into the present carbon fibers proceeds from the free end of carbon fibers towards the fixed end with increasing charge.     

The preparation and gas sensitivity study of polypyrrole/zinc oxide

Polypyrrole (PPy) was prepared by chemical oxidation polymerization, analyzed by FT-IR, elemental analysis and HRTEM, and studied for gas sensitivity. It suggested that PPy had sensitivity to NH₃, H₂S and NO_x, and showed irreversibility to NO_x gas. The organic–inorganic hybrid materials PPy/ZnO with different PPy weight percents were prepared by mechanical mixing, and the sensitivity study of the materials to toxic gases NH₃, H₂S, NO_x was carried out at different operating temperatures 30, 60, and 90 °C. It was found that PPy/ZnO materials (PPy(1%)/ZnO, PPy(3%)/ZnO, PPy(5%)/ZnO, PPy(10%)/ZnO, PPy(20%)/ZnO) had better selectivity and reversibility to NO_x than pure PPy, and much lower working temperature than the reported working temperature of ZnO (about 350–450 °C). Their sensitivity increased with the increasing concentration of NO_x at particular working temperature, and among them PPy(10%)/ZnO had the maximum sensitivity to NO_x in the same condition. They showed no response to 1000, 1500, 2000 ppm NH₃ or H₂S. The response mechanism of PPy/ZnO materials to NO_x was discussed.     

The incorporation of silver nanoparticles into polypyrrole: Conductivity changes

Silver nanoparticles obtained by the electro-exploding wire technique were used to deposit on polypyrrole films prepared electrochemically. The presence of silver nanoparticles deposited was confirmed by X-ray diffraction. Energy dispersive X-ray spectroscopy was used to estimate the amount of silver nanoparticles deposited on polypyrrole.     

Intercalation of MoCl5 into graphite-determining factor to control stage structure

The mechanism of formation of MoCl₅–graphite intercalation compounds (MoCl₅–GICs) was proposed on the basis of the experimental results obtained in the present and previous works. The amount of reactive chlorine formed in the reaction system was concluded to be the determining factor for the stage structure in resulting MoCl₅–GICs. Reactive atomic chlorine produced during the decomposition of only 2% MoCl₆, which was formed from MoCl₅ at high temperature, seemed not enough for the formation of pure stage 1 MoCl₅–GIC and therefore only stage 2 structure was obtained. Heating the MoCl₅ in presence of either MoOCl₃ or MoO₃ formed MoOCl₄, which evolved high amount of reactive chlorine which formed the stage 1 MoCl₅–GIC in single phase.     

Modification of graphite oxide nanoparticles prepared via electrochemically oxidizing method

Graphite oxide nanoparticles (GONPs), prepared via electrochemically oxidizing technique, were chemically reduced by hydrazine hydrate in water medium. The electrical conductivity of the samples showed an improvement by three orders of magnitude from 1.38 × 10⁻⁶ s cm⁻¹ (before reduction) to 1.02 × 10⁻³ s cm⁻¹ (after reduction). UV–vis measurement was used to explained the restoration of the conducting conjugated networks in graphite nanoparticles. The hydrophilic GONPs or their reduced samples could be further organically modified, using cetyltrimethylammoniumbromide (CTAB) as a modifier, turned to a hydrophobic nanoparticles which could form homogeneous and stable dispersion in toluene, and other organic media.     

Synthesis and characterization of poly acrylic acid/graphite oxide nanocomposite

1　INTRODUCTIONOrganic intercalatedlayeredsolidshavebeenstudiedbyscientistsindifferentfieldsformanyyearsbecauseoftheirnew physicalandchemicalpropertiessuchaselectricalproperties[1] ,mechanicalproper ties ,thermalbehavior[2 ] ,surfaceandinterfacialproperties[3] .Graphiteoxide (GO)hasbeenstudiedformany years ,itsstructuralmodel[4 6 ] ,formationprocessandkinetics[7,8] havebeenstudiedindetail.IthasbeenreportedthatGOpossessesC OHande poxidefunctionalgroups[9] whichmakegraphiteox ideeasilyabs…     

碳纳米管与还原氧化石墨烯构建高倍率石墨电极

通过在金属铜箔上均匀排布碳纳米管宏观膜(carbon nanotubes (CNTs) macro film,CMF),制成复合集流体(Cu-CMF),从而改善活性物质与集流体的结合性,降低电池界面电阻,在活性材料石墨中掺杂还原氧化石墨烯(r GO),增大了活性物质石墨颗粒间的接触位点,最后获得高比容量和化学稳定性的电池。采用扫描电子显微镜和电化学测试对复合集流体的微观形貌及电化学性能等进行表征。结果表明,基于Cu-CMF复合集流体掺杂r GO的石墨电极,在2 C倍率下发挥101.5 m Ah·g^-1的比容量,是未掺杂基于铜箔集流体的石墨电极(26.3 m Ah·g^-1)的3.7倍以上,表现出优异的倍率性能。     

Carrier transport properties of aluminum oxide/polypyrrole films doped with naphthalene-1,5-disulfonic acid

The electrical structure of the Al/Al₂O₃/PPy-NDSA/Au has been investigated by means of current–voltage (I–V) and capacitance–voltage (C–V) measurements, in a temperature range of 90–350 K. The forward C–V measurements have been carried out in the range of frequency of 1 kHz to 20 MHz. The effects of series resistance, interfacial layer and interface states on I–V and C–V characteristics are investigated. At high current densities in the forward direction, the series resistance effect has been observed for voltages greater than 0.7 V. The analysis of I–V characteristics based on the thermionic emission mechanism has been explained by the assumption of a Gaussian distribution of barrier heights, due to barrier height inhomogeneities that prevail at the interface. It has been observed that the forward C–V plot exhibits a peak, whose position shifts towards lower voltages and that decreases with increasing frequency. The non-linearity of 1/C² versus V plot at high frequency was explained with the assumption that only some of the interface states follow the applied ac signal. Surface analysis by X-ray photoelectron spectroscopy (XPS) was performed in order to evaluate the chemical states of the constituents of the Al/Al₂O₃/PPy-NDSA/Au sample.     

人造金刚石提纯及氧化石墨制备一体化工艺研究

综合采用磁选法、Hummers法及沉降分离法对人造金刚石一次摇床分选尾料进行提纯处理。利用X射线衍射仪、拉曼光谱仪和扫描电子显微镜进行物相组成和显微结构分析。结果表明:所得人造金刚石纯度高、回收率接近100%;同时,尾料中的石墨被转化为氧化石墨,达到了节约资源、变废为宝的目的。      

Intercalation behavior of salicylic acid into calcined Cu-Al-layered double hydroxides for a controlled release formulation

Owing to their layered structure and memory effect property, layered double hydroxides (LDHs), also called anionic clays, have received considerable attention in recent years. We have studied the effect of the operating conditions on the formation of the Cu-Al-CO₃ by co-precipitation and a series of Cu-Al-LDHs has been synthesized by this method. The Cu/Al molar ratio varied between 0.5 and 3 and the pH between 6 and 12. The effect of the aging time on the cristallinity of the Cu-Al-CO₃ hydrotalcite was also investigated. By the reconstruction method, the calcined Cu-LDHs were tested for their ability to intercalate salicylic acid into the interlayer space. Powder X-ray diffractogrammes show that the basal spacing of the Cu-Al-LDHs bearing salicylate as the intergallery anion expanded from 7.52 Å in the precursors to 15.7 Å, these values suggesting the organic molecules form bilayers in the interlayer space. The Fourier transform infrared study further confirmed intercalation of salicylate into the interlayers of the LDHs. The thermal stability of the intercalated salicylic acid is significantly enhanced compared with the pure form before intercalation. Using the X-ray diffraction results combined with a molecular simulation model, a possible representation of the salicylate anion positioning between the lamellar layers has been proposed. The in vitro release rate was remarkably lower than that from the corresponding physical mixture at pH 7.5. The kinetic analysis shows the importance of the diffusion through the control of the drug release rate. The obtained results demonstrate show that hydrotalcites may be used to prepare modified release formulations.     

Promoting performance of lithium-sulfur battery via in situ sulfur reduced graphite oxide coating

Activated graphene/sulfur structure sheathed in a flexible graphene layer is presented as the cathode material of lithium-sulfur battery.The surface coating gra...     

Intercalation of graphite by silicon tetrafluoride and fluorine to yield a second-stage salt C24SiF5

Powdered graphite (either finely broken HOPG or Union Carbide SP1) interacts with 1:1 SiF₄/F₂ mixture (～50 atmospheres) at 40°, to yield a second-stage compound (a₀ = 2.46(1), c₀ = 11.29(1) Å) of composition C～₂₄SiF₅. This product interacts with excess PF₅ with quantitative displacement of SiF₄ to yield a first-stage fluorophosphate (a₀ = 2.46(1); $\text{c}{}_0\text{= 7.65(1)}\text{A}\text{?}\text{)}$ according to the equation: C₂₄SiF₅ + 2PF₅ → C₂₄PF₆. PF₅ + SiF₄. The first-stage fluorophosphate falls to a second-stage salt (a₀ = 2.46(1); $\text{c}{}_0\text{= 10.87}\text{A}\text{?}\text{)}$ under vacuum: $\text{C}{}_{24}\text{PF}{}_6\text{.}\text{PF}{}_5\text{20°}\text{→}\text{C}{}_{24}\text{PF}{}_6\text{+}\text{PF}{}_5$. This is identical to that prepared directly: $\text{24}\text{C}\text{+}\text{PF}{}_5\text{+}\text{1}\text{2}\text{F}{}_2\text{→}\text{C}{}_{24}\text{PF}{}_6$. Extensive reduction of C₂₄PF₆, at ≈20° : 2C₂₄PF₆ + PF₃ → 48C + 3PF₅ to graphite of crystallinity comparable to that of the starting graphite establishes that the initial C₂₄SiF₅ does not involve extensive fluorination of the graphite. The ease of displacement of SiF₄ by superior fluoroacids indicates that C₂₄SiF₅ can be a valuable precursor for other graphite salts. Ready formation of a first-stage fluoroborate, $\text{C}{}_7\text{BF}{}_4\text{, I}{}_{\mathrm{<mtext>c</mtext>}}\text{= 7.70(1)}\text{A}\text{?}$ contrasts with the failure to prepare similarly a first-stage SiF₅^? salt.     

Diffusion of potassium atoms into rhenium covered with two-dimensional graphite film

The effective diffusion of K atoms into Re (1010) stimulated by a graphite monolayer on its surface is discovered. The activation energies of the diffusion of potassium into rhenium and from it, as well as the effectiveness of the diffusion of potassium atoms, are determined. The following values are obtained: E _f1 = 5.4 ± 0.05 eV, E _1f = 5.75 ± 0.05 eV, and δ_dif(K) ≈ 0.25. The difference in the energies of the diffusion of potassium into rhenium is lower than the energy of the diffusion of potassium into iridium. It is shown that the diffusion length in the process of the diffusion of potassium adatoms into rhenium is greater than in the case of diffusion into iridium. The noticeable diffusion of potassium atoms are observed when the voltage U ≥ +200 V is applied to the specimen and intensifies approximately following the linear law as U increases to 4000 V. The formation of a graphite monolayer on the rhenium surface due to the enormous prolongation of the lifetime of K adatoms under the graphite island compared to the lifetime of adatoms on the exposed rhenium surface increases greatly the effectiveness of potassium diffusion, which grows by ～10⁸ times, then approaches unity. This phenomenon can be used as a method for the active alloying of subsurface layers of solids by atoms.