ABSTRACT
Embedding both boron and nitrogen into the backbone of acenes to generate their isoelectronic structures has significantly enriched the acene chemistry to offer appealing properties. However, only small BN-heteroacenes have been extensively investigated, with BN-heptacenes as the hitherto longest homologue. Herein, we report the synthesis of three new nonacene BN-isosteres via incorporating a pair of antiaromatic B2 C4 and N2 C4 heterocycles, representing a new length record for BN-heteroacenes. The distance between the B2 C4 and N2 C4 rings affects the contribution of the charge-separated resonance forms, leading to tunable antiaromaticity of the two heterocycles. The adjusted local antiaromaticity manifests substantial influence on the molecular orbital arrangement, and consequently, the radiative transition rate of BN-3 is greatly enhanced compared with BN-1 and BN-2, realizing a high fluorescence quantum yield of 92 %. This work provides a novel design concept of large acene BN-isosteres and reveals the importance of BN/CC isosterism on their luminescent properties.
ABSTRACT
A novel kind of carbon nanotubes/titanium dioxide (CNTs/TiO2) composite photocatalyst was prepared by a modified sol-gel method in which the nanoscaled TiO2 particles were uniformly deposited on the CNTs modified with poly(vinyl pyrrolidone) (PVP). The composites were characterized by a range of analytical techniques including high resolution transmission electron microscopy (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The results show the successful covering of the CNTs with PVP, forming core-shell structure. The nanoscaled TiO2 particles were uniformly deposited on the surface of CNTs reducing the bare CNTs which avoid losing the absorption and scattering of photons. The combination of CNTs and TiO2 particles imply the enhanced interactions between the CNTs and TiO2 interface which possibly becomes heterojunction. The composites become mesoporous crystalline TiO2 (anatase) clusters after annealing at 500 degrees C, and the surface area increases obviously. The photocatalytic activities of surface modification CNTs/TiO2 (smCNTs/TiO2) composites are extremely enhanced from the results of the photodegradation of methylene blue (MB).
ABSTRACT
Hydrous oxides of cerium, aluminum, nickel and copper were prepared by alkaline precipitation method. Langmuir adsorption isotherm was studied and specific surface area was measured by BET method through N2 adsorption-desorption process. IR characterization of hydrous metal oxides before and after fluoride adsorption was also studied. Results show that different hydrous metal oxides have different specific surface areas and their pore size distributions also are not all the same. Adsorption capacity is not directly dependent on the specific surface area. Isotherm study indicates that the adsorption follows Langmuir model and shows the feature of monolayer adsorption. IR study before and after fluoride adsorption shows that different hydrous metal oxides have similar adsorption sites in the same IR region as well as adsorption sites in the different IR region. The comprehensive interaction of these adsorption sites with fluoride ions results in the different adsorption capacity of different hydrous metal oxides.
ABSTRACT
Ferrocene was used as a catalyst, and xylene as carbon source. Chemical vapor deposition method was used to synthesize carbon nanotubes (CNTs). The CNTs were treated by oxidation method with concentrated nitric acid. Magnetic carbon nanotubes were prepared by using chemical co-precipitation. The products were characterized by field emission scanning electron microscope. This paper is concerned with the adsorption of methyl orange by magnetic carbon nanotubes. The best experimental conditions were found. Adsorbent solution was analyzed by UV-Vis adsorption spectra. At the same time, desorption and re-adsorption of methyl orange from magnetic CNTs were studied.
