The thermal stability of oxidized single‐walled carbon nanotubes (SWNTs) with various degrees of oxidation was investigated. The oxidized SWNTs exhibited lower absorption and radial breathing mode (RBM) peaks and a higher intensity ratio of the D band to the G band (D/G) in their absorption and Raman spectra than those of the pristine SWNTs. After the thermal treatment, the D/G ratio of the oxidized SWNTs almost recovered its original intensity, regardless of the degree of oxidation. The absorption, photoluminescence (PL), and RBM peaks could not recover their original intensities when the oxidation degree was high. The results indicate that the elimination and decomposition reactions proceeded competitively depending on the degree of oxidation. In addition, a new PL peak was observed in the near‐infrared region, and the PL peak intensity increased with the subsequent thermal treatment. The theoretical calculations provided an insight into the possible pathways for the decomposition of oxidized SWNTs, showing that the O2 elimination and CO/CO2 evolution proceed competitively during thermal treatment. 相似文献
This paper reviews recent mathematical results on the half-space problem for the Boltzmann equation. The case of a phase transition is discussed in detail. 相似文献
This contribution reports for the first time on the synthesis and the main physical properties of single-phase pure α-Cr2O3 nanoparticles synthesized by a facile, rapid and eco-friendly process using Callistemon viminalis flower's extract as an effective oxidizing/reducing agent. These crystalline nanoparticles exhibit a cubic-like platelet shape with sharp edges with an average particle diagonal size of ~92.2?nm. The room temperature physical properties of these pure highly crystalline Eskolaite α-Cr2O3 nanoparticles were carried out using complementary techniques such as high-resolution transmission electron microscopy (HRTEM), energy-dispersive X-ray spectroscopy (EDS), XRD, FTIR-ATR, Raman and XPS. 相似文献
Lidar data observed by two continuously operated portable automated lidar (PAL) systems and images from the visible and thermal
infrared channels of the advanced very high resolution radiometer (AVHRR) sensor on board the noaa16 satellite are employed for the characterization of cloud heights and cloud types. The PAL systems are located in Chiba
and Ichihara city areas, separated by approximately 10 km. Measurements from October 2003 to March 2005 reveal that monthly
averages of cloud base height and cloud cover ratio show good agreement between the two sites. The characteristics of the
vertical (Chiba) and slant (Ichihara) measurements are also discussed. The PAL data are used to adjust threshold values of
a cloud-type classification method in split-window data of noaa16-AVHRR. Comparisons between the lidar signals and the cloud classification results from the concurrent AVHRR images show
that the classification method can reasonably be applied to this mid-latitude case, although the split-window technique was
originally developed for tropical clouds. 相似文献
Better the second time around : The title compounds were synthesized by using a one‐pot double methylene transfer catalyzed by a heterobimetallic La/Li complex. Chiral amplification in the second step was the key to obtaining oxetanes in high enantiomeric excess (see scheme).
We describe here a comprehensive study of solution and solid-state properties of self-assembling triblock molecules composed of a hydrophilic dendron covalently linked to an aromatic rigid rod segment, which is in turn connected to a hydrophobic flexible coil. These dendron-rod-coil (DRC) molecules form well-defined supramolecular structures that possess a ribbonlike morphology as revealed by transmission-electron and atomic-force microscopy. In a large variety of aprotic solvents, the DRC ribbons create stable networks that form gels at concentrations as low as 0.2% by weight DRC. The gels are thermally irreversible and do not melt at elevated temperatures, indicating high stability as a result of strong noncovalent interactions among DRC molecules. NMR experiments show that the strong interactions leading to aggregation involve mainly the dendron and rodlike blocks, whereas oligoisoprene coil segments remain solvated after gelation. Small-angle X-ray scattering (SAXS) profiles of different DRC molecules demonstrate an excellent correlation between the degree-of-order in the solid-state and the stability of gels. Studies on two series of analogous molecules suggest that self-assembly is very sensitive to subtle structural changes and requires the presence of at least four hydroxyl groups in the dendron, two biphenyl units in the rod, and a coil segment with a size comparable to that of the rodlike block. A detailed analysis of crystal structures of model compounds revealed the formation of stable one-dimensional structures that involve two types of noncovalent interactions, aromatic pi-pi stacking and hydrogen bonding. Most importantly, the crystal structure of the rod-dendron compound shows that hydrogen bonding not only drives the formation of head-to-head cyclic structures, but also generates multiple linkages between them along the stacking direction. The cyclic structures are tetrameric in nature and stack into ribbonlike objects. We believe that DRC molecules utilize the same arrangement of hydrogen bonds and stacking of aromatic blocks observed in the crystals, explaining the exceptional stability of the nanostructures in extremely dilute solutions as well the thermal stability of the gels they form. This study provides mechanistic insights on self-assembly of triblock molecules, and unveils general strategies to create well-defined one-dimensional supramolecular objects. 相似文献
The photochemical C,C-bond cleavage of trisubstituted aziridines 3-6 and consequent [3+2] cycloaddition with electron-deficient alkenes afforded the novel head-to-head adducts (1,2,3,5-tetrasubstituted pyrrolidines) selectively and efficiently. The aziridines 3 and 5 reacted with molecular oxygen, affording dioxazolidine 26 and cleaved products, respectively. The results may suggest that the C,C-bond of aziridine cleaves biradically. The photoreactions of N-tritylaziridines 7-9 possessing diester, dinitrile, and butadiene groups in the side chain with electron-deficient alkenes yielded 2,3-cis-pyrrolidine derivatives 29, 30, and 33 exclusively. In particular, the dinitrile 8 also reacted with non-electron-deficient alkenes. The formal synthesis of the indolizidine fragment 10 of stellettamides starting from the pyrrolidine (E)-33 was achieved in a convenient manner. 相似文献
Summary A new mixed nickel(II) chelate, Ni(tmen)(acac)(NCS) · 0–1 H2O, was prepared. It was found that this (anhydrous) chelate changes from a 6-coordinate, probably dimeric structure in the solid state to (i) a 5-coordinate square pyramidal, (ii) a 4-coordinate square planar and (iii) 6-coordinate solvated structure, according to the solvent used. 相似文献