Dielectric relaxation studies of 1-hexanol and 1,2-hexanediol in heptane

Solutions of 1-hexanol and 1,2-hexanediol in heptane have been investigated tigated by means of dielectric time domain spectroscopy (TDS). The permittivity spectrum of 1-hexanol in heptane is characterized by a model function containing a sum of three elementary Debye dispersions, while 1,2-hexanediol in heptane is best described by a Cole-Davidson model function. It is shown that dilute solutions of 1-hexanol in heptane have a completely different behavior to that of 1,2-hexanediol. For the diol, the relaxation time levels off at a high value indicating an existence of higher hydrogen bonded complexes. It is possible to quantify the relative amount of monomeric 1-alcohol molecules from the dielectric spectrum. The monomerization rate for 1-hexanol upon dilution with heptane is initially low, but increases rapidly for mole fractions of heptane exceeding 0.4.     

甲醇催化分解动力学之研究

甲醇的裂解产物为H_2与CO,故甲醇被视为一种方便、安全的贮氢材料,可作为汽油的代用燃料;其裂解气作为保护气氛可广泛应用于热处理工业。甲醇裂解有两种方法,高温热裂解(约930℃)与低温催化裂解(约300℃)由于低温催化裂解有诸多优点,在工业上的应用正在发展。     

Mechanism of the thermal decomposition of nitrates from graphite furnace mass spectrometry studies

A basically new mechanism of the thermal decomposition of solids is proposed to explain the mass spectral observations of gaseous molecules of CoO, CuO, Cu₂O, NiO, PbO and Mg(OH)₂ during the low-temperature decomposition of the anhydrous and hydrated nitrates of these metals. The mechanism consists of two stages: congruent gasification of all reaction products irrespective of their saturated vapor pressure and subsequent condensation of the low-volatility species (oxides and hydroxides). The partial pressures of these species at the appearance temperatures calculated from this theory for the first stage of the process (1–50 mPa) are in agreement with the detection limits of the quadrupole mass spectrometers used in these experiments. The proposed mechanism is supported by other available data obtained by thermal analysis.     

Plasma-chemical decomposition of methane during diamond synthesis

Using a mass spectrometric sampling method, we have observed the decomposition of CH₄ in an rf plasma usedfor diamond deposition. The gas samples were extracted through an orifice located downstream of the plasma zone and analyzed online. For the experiments a dilute mixture of H₂ and CH₄ containing 0.1–3% CH₄ has been used. CH₄ is converted to C₂H₂ and C₂H₄ quantitatively. Small amounts of heavier hydrocarbons are formed. A comparison of the experimental results with a recent kinetic model treating a purely thermal environment is made and the differences between our experiment and the model are explained. The role of acetylene as a species formed in an atmosphere rich in atomic hydrogen is proposed. The electron impact dissociation process is suggested as the rare-determining step in the plasma-chemical decomposition of methane.     

四种溴代甲苯异构体的质谱区分

本工作用四种较新的质谱技术(碰撞诱导解离(CID),电荷剥离(CS),电荷分离(CSe),电子捕获诱导解离(ECID)谱研究了邻、间、对溴甲苯和溴化苄四种异构体。四种技术在一定程度上都可区分这些异构体。其中比较四种异构体ECID谱中ECID峰的相对强度可得到满意的区分效果。     

Defect-induced anisotropic surface reactivity and ion transfer processes of anatase nanoparticles

Surface reactivity and ion transfer processes of anatase TiO₂ nanocrystals were studied using lithium bis(trifluoromethylsulfone)imide (LiTFSI) as a probing molecule. Analysis of synthesized anatase TiO₂ by electron microscopy reveals aggregated nanoparticles (average size ~8 nm) with significant defects (holes and cracks). With the introduction of LiTFSI salt, the Li⁺-adsorption propensity towards the surface along the anatase (100) step edge plane is evident in both x-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) analysis. Ab initio molecular dynamics (AIMD) analysis corroborates the site-preferential interaction of Li⁺ cations with oxygen vacancies and the thermodynamically favorable transport through the (100) step edge plane. Using ⁷Li nuclear magnetic resonance (NMR) chemical shift and relaxometry measurements, the presence of Li⁺ cations near the interface between TiO₂ and the bulk LiTFSI phase was identified, and subsequent diffusion properties were analyzed. The lower activation energy derived from NMR analysis reveals enhanced mobility of Li⁺ cations along the surface, in good agreement with AIMD calculations. On the other hand, the TFSI^– anion interaction with defect sites leads to CF₃ bond dissociation and subsequent generation of carbonyl fluoride-type species. The multimodal spectroscopic analysis including NMR, electron paramagnetic resonance (EPR), and x-ray photoelectron spectroscopy (XPS) confirms the decomposition of TFSI^– anions near the anatase surface. The reaction mechanism and electronic structure of interfacial constituents were simulated using AIMD calculations. Overall, this work demonstrates the role of defects at the anatase nanoparticle surface on charge transfer and interfacial reaction processes.     

The Adsorption and Photocatalytic Decomposition of Citric Acid on Pt/TiO_2

The adsorption and photocatalutic decomposition of citric acid on both Pt/TiO2 powder and n-TiO2 single crystal electrode were studied in aqueous solutions of various pH. It was found that citrate ions were chemisorbed on TiO2, which could increase the interfacial capacity and the filling factor of photocurrent-potential curves. The quantity of adsorption, slope of mott-Shottky plot and the rate of photocatalytic decomposition of citric acid were found to depend strongly on pH of solution. The phot ocatalytic decomposition of citric acid was discussed in light of its adsorption on TiO2.