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Abstract: Alkali metal–graphite intercalation compounds with the composition of MC24 (M=K, Rb, Cs) were prepared by heating a mixture of MC8 (saturated compound) and graphite sheet (Grafoil) at 350–450°C. The resistivity perpendicular to the layer planes (ρ c) of the resulting compounds was determined by the two-terminal method. The anisotropy factor of the resistivity, (ρ c/ρ a), of KC24 prepared from Grafoil was ∼130, being about 1/6–1/10 in magnitude compared with that of KC24 prepared from highly oriented pyrolytic graphite. The resistivity change during sorption of hydrogen (at 90K), ethylene (at 194K) and acetylene (at 194K) was determined. The resistivity of MC24 increased with increase of the sorbed amount of H2. The magnitude of the increase was in the order KC24>RbC24>CsC24. This resistivity increase was considered to be due to the expansion along c-direction which reduces the charge-transfer interaction between the carbon layers and potassium ions, resulting in the decrease of the density of the conduction electron. The resistivity of MC24 increased extensively during sorption of C2H4 and C2H2. It was discussed in connection with the in-plane structural transition and chemical interaction between alkali metal ions and sorbed molecules. [Copyright &y& Elsevier]

Electrical conductivity change of alkali metal–graphite intercalation compounds such as MC8 and MC24 (M=K, Rb, Cs) was determined during ternarization with ammonia. The conductivity of MC8 decreased by the ammoniation. A remarkable decrease of the conductivity during initial stage of ammoniation was observed for KC8. The conductivity of RbC8 decreased rather moderately and that of CsC8 was most insensitive to the ammoniation. The energy of interaction of alkali metal ion with ammonia molecule was evaluated by theoretical calculation using density functional theory and obtained the following result: K+–NH3, −28.9 kcal/mol; Rb+–NH3, −24.4 kcal/mol; Cs+–NH3, −19.3 kcal/mol. This result clearly explained the observed difference in the degree of the conductivity decrease of the MC8 compounds against the ammoniation. Thus, the conductivity decrease can be considered to be originated from the interaction of ammonia molecules with alkali metal ions, resulting in the backtransfer of conduction electrons from carbon layers to alkali metal ions. The conductivity change for KC24–NH3 and KC48–NH3 systems was relatively small compared to the system KC8–NH3. This was explained by taking into account the fact that the nanospace of KC24 and KC48 is larger than that of KC8. [Copyright &y& Elsevier]

Preparation and characterization of sodium-graphite intercalation compounds were investigated. It was confirmed that the resulting compound (NaC x ) had the stage 8 structure with identity period of 2.8 nm. The Raman spectroscopy showed that the G-band signal of NaC x was observed at 1582 cm −1 and at 1608 cm −1 , which is a typical indication of the formation of intercalation compounds. The g-value of NaC x was determined to be 2.0018 by the ESR measurement, which was very close to the reported values for the other alkali metal-graphite intercalation compounds. The electrical resistivity of NaC x was about 1/3 of that of host graphite at room temperature and showed metallic temperature dependence. [ABSTRACT FROM PUBLISHER]

Conduction electron spin resonance (CESR) of alkali metal-graphite intercalation compounds (AM-GICs) such as KC 8 , KC 24 , KC 36 , RbC 8 , RbC 24 etc. and their ternary compounds with NH 3 was investigated. It was shown that ternary compound of RbC 8 with ammonia gave a clear ESR signal, in contrast to no signal for binary RbC 8 and that the line width of ESR spectra of KC 8 (NH 3 ) x decreased monotonically with increasing ammonia content. These observations suggested that ammonia molecules reduce the spin-orbit interaction. [ABSTRACT FROM PUBLISHER]

Preparation and characterization of sodium-graphite intercalation compounds were investigated. It was confirmed that the resulting compound (NaC x ) had the stage 8 structure with identity period of 2.8 nm. The Raman spectroscopy showed that the G-band signal of NaC x was observed at 1582 cm -1 and at 1608 cm -1 , which is a typical indication of the formation of intercalation compounds. The g-value of NaC x was determined to be 2.0018 by the ESR measurement, which was very close to the reported values for the other alkali metal-graphite intercalation compounds. The electrical resistivity of NaC x was about 1/3 of that of host graphite at room temperature and showed metallic temperature dependence. [ABSTRACT FROM AUTHOR]

Conduction electron spin resonance (CESR) of alkali metal-graphite intercalation compounds (AM-GICs) such as KC 8 , KC 24 , KC 36 , RbC 8 , RbC 24 etc. and their ternary compounds with NH 3 was investigated. It was shown that ternary compound of RbC 8 with ammonia gave a clear ESR signal, in contrast to no signal for binary RbC 8 and that the line width of ESR spectra of KC 8 (NH 3 ) x decreased monotonically with increasing ammonia content. These observations suggested that ammonia molecules reduce the spin-orbit interaction. [ABSTRACT FROM AUTHOR]

Magnetoresistance and Hall coefficient of air-stable potassium-intercalated graphite sheets (hereafter abbreviated as K-PGS) were determined at room temperature. The magnitude of the magnetoresistance and the absolute value of Hall coefficient of K-PGS decreased with increasing potassium content of K-PGS, n K/n C. Two-carrier model was used for calculating carrier density and mobility. The electron density increased with increasing n K/n C: 3.07×1020 cm−3 (n K/n C=0.005), 5.67×1020 cm−3 (n K/n C=0.008) and 6.40×1020 cm−3 (n K/n C=0.011). The value of the electron density of K-PGS with n K/n C=0.011 (nominal composition KC91) was about 80% of the reported value, 7.8×1020 cm−3, for KC48 (n K/n C=0.021) prepared from HOPG (highly oriented pyrolytic graphite). The mobility decreased with increasing n K/n C: 2.11×103 cm2 V−1 s−1 (n K/n C=0.005), 1.42×103 cm2 V−1 s−1 (n K/n C=0.008) and 1.34×103 cm2 V−1 s−1 (n K/n C=0.011). The value of the mobility of K-PGS with n K/n C=0.011 was about 60% of the reported value (2300cm2 V−1 s−1) for KC48 prepared from HOPG. [ABSTRACT FROM AUTHOR]

Potassium–graphite intercalation compounds with chemical compositions of KC84, KC48, KC36 and KC8 were prepared from PGS graphite sheet and then treated with 6M-HCl aqueous solution. After washing with water and drying under open air, chemical composition, stage structure and electrical conductivity of the resulting air-stable compounds were determined. It was found that about 40% of potassium in the starting potassium–graphite intercalation compounds remained in the matrix after treated with 6M-HCl aqueous solution for KC84, KC48 and KC36, while 15% for KC8. The room temperature electrical conductivity of an air-stable compound, containing potassium of 0.008 in molar ratio of potassium to carbon, was determined to be 1.3×105 Scm−1. This is comparable to that of iron (1.0×105 Scm−1) and about 1/3 of that of aluminum (3.6×105 Scm−1). [ABSTRACT FROM AUTHOR]

The present paper describes the desalination performance of reverse osmosis (RO) membranes of multi-walled carbon nanotube-polyamide complex (CNT-PA) and commercial polyamide membranes in NaCl, MgCl 2 , MgSO 4 and Na 2 SO 4 aqueous solutions. The permeate flux, salt rejection, and salt flux were determined in a cross-flow experiment. The CNT-PA and commercial RO (PA) membranes (SWC5, Nitto Denko Co.) showed 96.0% and 99.7% salt rejection, respectively, for 0.2% NaCl aqueous solution at 0.7 MPa. The calculated salt flux was 0.38 g·m −2 ·h −1 (CNT-PA) and 0.07 g·m −2 ·h −1 (SWC5). The salt rejection increased with increasing running pressure and decreasing salt concentration. The zeta potential measurement of CNT-PA demonstrated that it is negatively charged due to the presence of CNT. Accordingly, it showed salt rejection performances against the four salt solutions (Na 2 SO 4  > MgSO 4  > NaCl > MgCl 2 ) that differed from that of the usual PA membranes (Na 2 SO 4  > MgSO 4  > MgCl 2  > NaCl). These data are explained based on the Donnan model (CNT-PA) and steric hindrance pore model (SWC5), except for the case of chlorides under low-flux or high ionic strength conditions, where the diffusion and molecular size exclusion of the salts dominate over their mas-transport. Positron annihilation lifetime spectroscopy (PALS) enabled the estimation of the pore diameters of these membranes: 0.55 nm (CNT-PA) and 0.58 nm (SWC5). [ABSTRACT FROM AUTHOR]

Abstract: The practical use of graphite intercalation compounds (GICs) as industrial materials has been considered to be unfeasible because their air stability is fairly low, notwithstanding their high electrical conductivities and low densities. On the other hand, some air-stable GICs that exhibit p-type conduction have been reported. In this study, air-stable and electrically conductive GICs that exhibited n-type conduction were prepared from commercially available flexible graphite sheets (PGS graphite sheets). We observed that K-GIC and Cs-GIC were air-stable enough to be used in practical applications and were highly electrically conductive. The air stability of Cs-GIC was slightly higher than that of K-GIC. In addition, the stage-2 structure of Cs-GIC was more stable in that it maintained ten times higher electrical conductivity than that of the host graphite after 10years of exposure to air. Moreover, Cs-ethylene-GIC was the most stable and exhibited a blue colored surface after 10years of exposure to air. We assumed that the significantly improved air stability of the alkali-metal-GICs prepared from PGS graphite sheets is caused by the large crystalline size and the bending graphite layer structure of the host PGS graphite. [Copyright &y& Elsevier]

Abstract: The effects of two different halogen dopants (bromine and iodine) at different concentrations on the higher frequency modes (the so-called G and G′ bands) of the Raman spectra of double-wall carbon nanotube (DWCNT) “buckypaper” are investigated. The effects of dopants on different DWCNT configurations (metallic inner/semiconducting outer and vice versa) are studied by changing the laser excitation energy. The doping causes the loss of the Breit–Wigner–Fano line shape and the appearance of less metallic behavior. An increase of the relative intensity of the G+ band, which is more sensitive for the outer metallic tubes, is clearly observed with increasing Br2 concentration in the sample. By analysis of the G+ band and the G′ band it is possible to measure the changes in the electron–phonon coupling, due to the charge-transfer between the dopant (Br2 or I2) and the tubes in the DWCNT. The doping effect causes an upshift of the G+ band and a suppression of the contribution of the inner tubes to the G′ band signal and as a consequence, the observed G′ band is dominated by the contribution from the outer tubes. [Copyright &y& Elsevier]

The structure of bromine residue compounds was investigated by X-ray absorption fine structure (XAFS) in order to interpret where and how bromine is present in carbons with different degrees of graphitization. The residue compounds can be classified into three groups, as obtained from X-ray absorption near edge structure (XANES) spectra and the values of the intramolecular distance rBr–Br determined by extended X-ray absorption fine structure (EXAFS). In Group I, prepared from the host carbons heat treated at temperatures higher than 1900 °C, bromine exists in the interlayer space of graphite in the form of Br2 molecules with interaction of the π electrons of graphite. In Group III, from carbon heat treated at 1000 °C, most of the bromine probably reacts with carbon atoms having a dangling bond or functional groups. For Group II, where the host carbons are heat treated at intermediate temperatures, it is likely that bromine exists in undeveloped defects with a unique electronic state. [Copyright &y& Elsevier]

Carbon films were prepared from polyimide films (Kapton and Upilex-s with thickness of 50μm) by heat treatment at 750°C under Ar atmosphere. The electrical resistance of the carbon films was remarkably increased with the adsorption of acetone and decreased with its desorption. The magnitude of the resistance change increased with increasing vapor pressure of acetone and with decreasing temperature. The weight and resistance changes during the adsorption of acetone were simultaneously determined. A linear relationship was confirmed between them. It was also found that similar resistance changes were observed for adsorption of aqueous ammonia and nitric acid. [TANSO 2013 (No. 257) 141–144] [ABSTRACT FROM AUTHOR]