Preparation and characterization of a tetrabutylammonium graphite intercalation compound

The intercalation of tetrabutylammonium (TBA) cations into graphite by cation exchange from a sodium-ethylenediamine graphite intercalation compound yields a single-phase first-stage product, C(44)TBA, with a gallery expansion of 0.47 nm. The gallery dimension requires an anisotropic "flattened" cation conformation.     

Thermal characterization of the intercalation compound ofp-toluenesulfonate into a layered double hydroxide

On intercalation ofp-toluenesulfonate (PTS) into Mg/Al (0.73/0.27) layered double hydroxide (LDH), the layer expanded from 4.77 Å to 17.7 Å, indicating that the plane of PTS was perpendicular to the plane of the LDH layers. Thermal treatment of the PTS intercalate resulted in 82% of the included PTS being evolved as decomposition products. This value was higher than the value of 32.5% obtained with sodium PTS and 43.8% with a mixed sample of PTS and Mg/Al (0.73/0.27) LDH. It was considered that the intercalated PTS in Mg/Al (0.73/0.27) LDH was easy to decompose because interaction between intercalated PTS and Mg/Al (0.73/0.27) LDH was smaller than that between sodium and PTS in sodium PTS.     

Thermal exfoliation of electrochemically synthesized graphite intercalation compound with perrhenic acid

In present work, we describe the synthesis of graphite intercalation compounds with perrhenic acid (HReO₄-GIC) through the anodic oxidation of graphite in aqueous perrhenic acid solution and their thermal exfoliation. Due to electrochemical treatment of graphite in perrhenic acid solution, ReO₄⁻ ions are intercalated into interlayer spaces of graphite. Anodic oxidation of graphite in HReO₄ solution leads to the formation of 3-stage GIC. Simultaneously, some amount of perrhenic acid becomes deposited on the graphite surface and edges. In the next step, thermal treatment of the previously synthesized GIC was performed, causing both the exfoliation of graphitic structure and transformation of perrhenic acid into rhenium oxides on the surface of graphene layers. The yielded product was exfoliated graphite-ReO₂/ReO₃ composite. The obtained composite was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and Raman spectroscopy. Additionally, specific surface area of the exfoliated materials was measured.

     

Determination of oxidants with photoreduced methylviologen

Summary Determination of Oxidants with Photoreduced Methylviologen Optimal conditions for photogeneration of the reduced form of methylviologen are described in detail. The generation is done by photochemical reaction of the system 3,10-dimethyl-5-deazaisoalloxazine-methylviologen-electron donor (EDTA, oxalate or arginine). The methylviologen radical cation is suitable as a reductimetric titrant. A method has been developed for the determination of micromolar quantities of organic and inorganic substances byin situ photochemical generation of the reduced form of methylviologen. Spectrophotometric end-points can be utilized because of the intense blue colour of the titrant. Amperometric end-points can also be utilized. A precision of 1.5% can be obtained with both detection methods.     

Synthesis and characterisation of a novel europium-based graphite intercalation compound

In the lithium-europium-graphite system, a novel ternary compound was synthesised by direct immersion of a pyrolytic graphite platelet in a molten lithium-based alloy with a well chosen Li/Eu ratio at 400 °C. The ternary compound exhibits poly-layered intercalated sheets mainly constituted of two europium planes. Its chemical formula can be written Li_xEuC₄, since the amount of lithium is still not determined. The ¹⁵¹Eu Mössbauer spectra clearly indicate a +II valence for europium. The magnetic susceptibility and the magnetisation versus temperature reveal a complex behaviour which is qualitatively described thanks to structural hypothesis and analogies with the magnetic properties of the binary EuC₆ compound. A first ferromagnetic transition occurring at 225 K is attributed to interactions between both intercalated europium planes. The lower temperature susceptibility behaviour can be interpreted by antiferromagnetic interactions between in-plane neighbours and ferromagnetic interactions along the c-axis.     

Thermal desorption of bromine from a graphite-bromine intercalation compound

Gas chromatography and static adsorption have been used to examine the bromine-graphite acceptor system, which has intercalant structures comparable with the adjacent graphite: layers. The bromine adsorption-desorption isobars and isotherms have been determined at 278–393 K, whose shapes indicate reversible phase transitions between intercalation stages 2 and 4. Measurements at 390–550 K give the desorption activation energies for the two forms of intercalated bromine; the heat involved in the conversion of the ionized intercalant form to the molecular one is 10.4 kJ/mole.Translated from Teoreticheskaya i Ékperimental'naya Khimiya, Vol. 25, No. 1, pp. 120–123, January–February, 1989.     

Investigation of hydrolysed TaCl5-graphite intercalation compounds with PIXE

Graphite intercalation compounds combine low density with high electrical conductivity. These physical properties makes these compounds interesting as components of carbon epoxy composites, but the high reactivity of graphite intercalation compounds to moisture is an obstacle for practical applications.Earlier investigations showed that tantalum chloride forms with graphite flakes an intercalation compound, which is stable against humidity for a few days. We studied the stability against moisture of a stage-2 tantalum chloride intercalation compound after one year. A fresh tantalum chloride intercalation compound was exposed for 2 h in water and afterwards stored at room humidity for ca. 1 year. Some of the flakes were embedded in epoxy resin after a few months. After 1 year all flakes were highly altered. The non-embedded flakes showed coatings of tantalum oxide on the surface. The epoxy-resin-mounted flakes showed an irregular surface with many cracks. The edges of the flakes were sealed by epoxy resin, whereas the basal planes of the flakes are not coated. With particle-induced X-ray emission (PIXE) we performed Ta and Cl analyses across the flakes. The ClTa ratios varied over a wide range and, especially near the cracks, were very low. In other regions of the flake we found that tantalum oxychloride or a mixture of tantalum chloride and tantalum oxide had been formed. In a few regions we found evidence that tantalum chloride was encapsulated in the interior of the flakes.     

层间化合物hNB—Cu稳定性的理论研究

以分子簇为模型，用从头算方法，在６－３１Ｇ＾＊基组水平上对六方氮化硼（ｈＢＮ）进行几何全优化，再用优化构型对Ｃｕ的六方氮化硼层间化合物（ｈＮＢ－Ｃｕ）做单点计算，根据计算结果，从层间距、Ｍｕｌｌｉｋｅｎ布居、轨道相互作用、原子净电荷及前线轨道等角度分析了ｈＢＮ－Ｃｕ的电子结构及其稳定性，通过劝分析计算确认了这一层间化合物只是一个介稳结构，阐明了Ｃｕ使六方氮化硼陶瓷致密化的作用机理以及ｈＮＢ－Ｃｕ的弱抗氧化性。     

Possibility of superconductivity in intercalation compound related to MgB2

We investigated the electronic structure of MgB₂ and intercalation compounds, MgBX (X = Li, Be, C), with fully relaxed crystal structure by using density functional theory. The compounds MgBLi and MgBBe could be similar two‐band superconductors to MgB₂ because the Fermi surface crosses σ and π bands. Our results indicate that changing the lattice constants, hole or electron doping, and stacking of B? X effect the energy levels of the σ and π bands in MgBX compounds. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2004     

Photoelectrochemical characterization of several semiconducting compounds of palladium with sulfur and/or phosphorus

Semiconducting compounds of palladium with sulfur and/or phosphorus were prepared as crystals and their semiconducting and photoelectrochemical properties studied. The compounds include PdS, PdPS, Pd₃(PS₄)₂, and PdP₂ and crystal growth was accomplished by chemical vapor transport with halogens and Bridgeman methods. Photoelectrochemical techniques were used to measure bandgap, transition type, doping level, majority carrier type, flatband potential, quantum yield for electron flow, and stability in a photoelectrochemical cell. The previously undetermined bandgap of PdP₂ is reported (1.08 eV, indirect).     

The oxidation of aqueous thiols on a graphite intercalation compound adsorbent

Aqueous phase adsorption of thiols onto a graphite intercalation compound (GIC) adsorbent was shown to be accompanied by surface assisted oxidation of the thiols to their disulfide dimer. This effect was studied for three thiols; ethanethiol, propanethiol and sec-butanethiol. Unlike the case of thiol oxidation on activated carbons in aqueous conditions, the generation of dimer did not affect the adsorbent’s ability to oxidise the thiols in solution in the concentration range studied (0–100 ppm). This was attributed to the non-porous, crystalline nature of the adsorbent. This meant that once formed the dimers migrated from the active sites for thiol oxidation, believed to be mainly at the edges of the graphite planes, onto the hydrophobic basal plane where they could be adsorbed. Oxidation of the GIC adsorbent in the anodic compartment of an electrochemical cell was shown to attenuate the adsorbent’s ability to oxidise thiols. It was inferred that this was a result of a decrease in the amount of CO groups at the plane edges caused by this oxidation process.     

Structural study and crystal chemistry of the first stage calcium graphite intercalation compound

A novel and efficient synthesis method concerning the preparation of the first stage calcium graphite intercalation compound is provided. It makes use of a reaction between liquid metallic alloy and pyrolytic graphite. From now on it is especially easy to obtain bulk CaC₆ samples. Thanks to such samples, it was possible to study in detail the crystal structure of this binary intercalation compound. It has been entirely specified, so that we know that CaC₆ crystal is rhombohedral and belongs to the space group with the following parameters: and α=49.55°. The elemental unit cell contains one calcium atom and six carbon atoms. In this paper, we show also how the various MC₆ structures evolve according to the size of the intercalated element and to the bond nature that appears in the final compound. CaC₆ is unique, since all the other MC₆ compounds exhibit a hexagonal symmetry.     

Study of intercalation of BrF5 in graphite

Conclusions In the formation of intercalation compounds of graphite with BrF₅, the intercalation reaction rate significantly exceeds the reaction rate of fluorination of the graphite lattice. The stage nature of the reaction of intercalation of BrF₅ in graphite was demonstrated.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, pp. 953–957, May, 1988.     

Charge transfer complex between methylviologen and ferrocyanide

Charge transfer complex between methylviologen and ferrocyanide has been studied spectrophotometrically at different temperatures. From the thermodynamic association constants (320 ± 30 M⁻¹, 380 ± 30 M⁻¹ and 460 ± 40 M⁻¹ at 15, 25 and 30°C respectively), the enthalpy of formation, ΔH° (− 3.4 ± 1.5 kcal/mole), and the related entropy change, ΔS°(0.4 ± 5 e.u), have been calculated. The average extinction values of coefficients are 69±6 M⁻¹ cm⁻¹, 70±4 M⁻¹ cm⁻¹ and 72±5 M⁻¹ cm⁻¹ at 15, 25 and 35°C respectively.     

Photoelectrochemical Properties of Sol-Gel Nb2O5 Films

Structural, optical, electro and photoelectrochemical properties of amorphous and crystalline sol-gel Nb₂O₅ coatings have been determined. The coatings are n-type semiconductor with indirect allowed transition and present an overall low quantum efficiency ( < 4%) for UV light to electric conversion. The photoconducting behavior of the coatings is discussed within the framework of the Gärtner and Södergren models. Improvement can be foreseen if Nb₂O₅ coatings can be made of 10–20 nm size nanoparticles.     

碳化钨-石墨烯插层复合物的制备及作为甲醇氧化助催化剂的性能研究

直接甲醇燃料电池(DMFCs)作为一种环境友好、高效的新能源,对解决世界目前面临的“能源危机”与“环境危机”这两大问题有着至关重要的意义,具有较广阔的应用前景.目前,甲醇氧化催化剂仍然以 Pt基为主,但是 Pt价格昂贵,且容易受甲醇氧化中间产物的毒化,从而影响了 DMFCs的商业化进程.碳化钨(WC)作为非贵金属催化剂,在催化方面具有类铂的性能.在 WC上负载适量的 Pt,可以通过两者的协同效应加强催化剂的抗 CO中毒能力.但是,由于 WC的导电性能不佳,比表面积较小,因此寻找合适的载体显得尤为必要.在碳载体中,石墨烯(RGO)具有优良的导电性以及独特的片层结构,是电催化剂的理想载体.以 RGO为载体, WC为插层物质制备的 WC-RGO插层复合物具有化学稳定性好、电导率高且电化学活性面积大等优势.但是,由于石墨烯表面光滑且呈惰性,同时使用传统的碳化方法制备的碳化钨颗粒较大,因此,制备较小颗粒且分散均匀的 WC-RGO插层复合物具有较大难度.一般以偏钨酸铵和氧化石墨烯(GO)为前驱体制备 WC-RGO插层复合物,但是由于偏钨酸根和 GO都带负电,因此不能成功地将偏钨酸根引入到石墨烯的片层结构中,造成 WC-RGO插层复合物组装上的困难.本文采用硫脲成功地合成了具有高分散性 WC纳米颗粒插层在少层 RGO里的 WC-RGO插层复合物.硫脲((NH2)2CS)作为阴离子接受器,具有较强的结合阴离子形成稳定复合物的能力,同时它也是合成具有片层结构的过渡金属硫化物的原料之一.因此在 WC-RGO插层复合物组装过程中,硫脲既作为锚定及诱导剂,又是制备片层二硫化钨(WS2)的硫源.材料具体制备方法如下：首先利用浸渍法,将偏钨酸根阴离子([H2W12O40]6?)牵引到(NH2)2CS改性过的 GO上形成[H2W12O40]6?-(NH2)2CS-GO前驱体;然后将前驱体放入管式炉中还原碳化,前驱体先反应生成 WS2;由于 WS2自身的2D片层结构,反应中可以得到 WS2-RGO插层复合物,接着原位碳化生成 WC-RGO插层复合物.碳化钨-石墨烯负载铂电催化剂(Pt/WC-RGO)通过微波辅助法制得,并采用 X射线衍射、扫描电子显微镜、透射电子显微镜及激光拉曼光谱等手段对其结构与形貌进行了表征.结果显示,在 WC-RGO插层复合物中, WC的平均粒径为1.5 nm, RGO的层数约为5层.在甲醇电氧化反应中,相比于商用 Pt/C催化剂, Pt/WC-RGO插层复合物催化剂具有更高的电化学活性面积(ECSA)和较高的峰电流密度(246.1 m2/g Pt,1364.7 mA/mg Pt),分别是 Pt/C的3.66和4.77倍.我们分别利用 CO溶出伏安法、计时电流法及加速耐久性试验法验证了 Pt/WC-RGO催化剂优秀的抗 CO中毒能力及稳定性. Pt/WC-RGO催化剂特殊的插层结构,在增加 WC与 Pt接触机会以加强协同作用的同时,促进了催化过程中质量及电荷的转移,因而具有比 Pt/C更高的催化活性.可见,通过制备WC-RGO插层复合物可降低 Pt用量,从而大大地降低燃料电池中电催化剂的成本.同时,我们使用的是一种高效,可大批量生产纳米材料的方法,有助于催化剂的商业化.     

The intercalation reaction of 2,2′-bipyridine with layered compound MnPS3

The intercalation process of 2,2′-bipyridine into layered MnPS₃ is studied with powder X-ray powder diffraction (XRD) technology as the monitoring tool. From the XRD results, it is found that the absence or presence of acid greatly influences the existing form and the arranged orientation of the guest. Two series of the reactions are carried out. In Series A, only MnPS₃ and 2,2′-bipyridine are present. While in Series B, a variety of acetic acid is added. During the intercalation of Series A, there coexist four phases: the 00l phase (with lattice spacing of 6.47 Å) is pristine MnPS₃; the 00l′ phase (with lattice spacing of 9.81 Å), indicating the parallel orientation of the 2,2′-bipyridine molecular ring to the layer; the 00l″ phase (with lattice spacing of 12.20 Å), indicating the perpendicular orientation of the 2,2′-bipyridine molecular ring to the layer of the host, which is only an intermediate phase for the formation of the 00l′′′ phase; the 00l′′′ phase (with the lattice spacing of 15.33 Å), indicating the existence of the complex cation [Mn(bipy)₃]²⁺ coming from the in situ coordination of the inserted guest with intralayered Mn²⁺ ions between the interlayer space of host. As the intercalation proceeds, the 00l, 00l′ and 00l″ phases finally disappear, and 00l′′′ phase is intensified and a complete intercalate is obtained. In Series B, due to the presence of the acid, the formation of the complex cation [Mn(bipy)₃]²⁺ is inhibited, and the amount of the acid in the intercalation plays a key role in the formation of the guest. With the increase of the acid, the protonated bipyridine becomes the main existing form of the guest, which is arranged in the perpendicular orientation of molecular ring to the layer. From the experimental evidences, the possible intercalation mechanisms are proposed and the novel intercalation phenomenon of in situ coordination of the inserted 2,2′-bipyridine with Mn²⁺ of the host is elucidated.     

Photoelectrochemical and optical characterization of Prussian blue onto p-Si(100)

In this study, we examined the characterization of Prussian blue deposited onto p-Si(100). A cyclic voltammetry analysis was carried out under illumination showing quasi-reversibility responses of high and low-spin iron centres in the deposit. Optical measurements were done, where XRD analysis allowed to determine crystallinity while EDS analysis indicated that there is influence in the number of cycles on the film composition. Reflectance measurements confirm the coloration observed in the films. However a Kubelka–Munk analysis demonstrates the presence of blue greenish coloration which is an indication of a mix between Prussian blue and Berlin green films. Finally, this research is oriented to construct electrochemical storage devices which can be in situ loaded by the photovoltaic action of the semiconductor base material-doped silicon._.     

The synthesis and properties of a methylviologen analogue

A novel derivative of methylviologen, prepared by transannular reaction of [2.2] (3,5) pyridinophane, shows large bathochromic shift in the electronic spectrum and nearly equal redox potential compared with methylviologen.