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Liu W.,Chinese Research Academy of Environmental Sciences | Liu W.,CAS Lanzhou Cold and Arid Regions Environmental and Engineering Research Institute | Chen D.,Chinese Research Academy of Environmental Sciences | Chen D.,National Research Center for Certified Reference Materials | And 5 more authors.
Environmental Science and Technology | Year: 2010

The distribution of organochlorine pesticides and polychlorinated biphenyls in air along an altitudinal transect on Balang Mountain in western China was measured by deploying XAD-2 resin based passive air samplers in duplicate at seven sites with elevations ranging from 1242 to 4485 m above sea level for five consecutive six-month periods between 2005 and 2008. Analyzed by gas chromatography-high resolution mass spectrometry, concentrations of hexachlorobenzene were highest, followed by hexachlorocyclohexanes, DDT-related compounds and PCB congeners 28 and 52. Except for hexachlorobenzene, which had largely uniform concentrations in space and time, there were clear seasonal variations with concentrations in summer being higher than in winter. With a few exceptions, concentrations that vary little with altitude suggest that the presence of these chemicals in the area is almost entirely due to atmospheric transport, most likely from the Chengdu plain. This is supported by similarities in the relative abundance of different compounds and in the differences between summer and winter concentrations measured in the city of Chengdu and in the mountains. Furthermore, air mass trajectories during the sampling period often originate to the East, passing over the Western part of the Sichuan basin, including the Chengdu plain, prior to arriving at the sampling sites. Higher summer time values in the mountains are due to more contaminated air being blown into the region, presumably due either to higher pesticide usage in summer or due to higher temperatures leading to higher evaporation in source regions. Air and soil from the region are in equilibrium with respect to α-HCH, γ-HCH, and HCB, whereas a situation of net deposition prevails for p,p'-DDE and p,p'-DDT. © 2010 American Chemical Society. Source


Li L.,Beijing University of Chemical Technology | Zhang L.,Beijing University of Chemical Technology | Wen Z.,Beijing University of Chemical Technology | Chen D.,National Research Center for Certified Reference Materials
Chinese Journal of Chemistry | Year: 2010

A pair of chromophores with donor-acceptor properties, coumarin-3-carboxylic acid (3-CCA) and 9-anthracene carboxylic acid (9-ACA), have been successfully intercalated into the layered double hydroxide (LDH), [Zn0.66Al0.34(OH)2](CO3)0.17•0.33H2O by an ion-exchange method. The obtained co-intercalation compounds were characterized by X-ray diffraction, FTIR spectral, thermogravimetry techniques and chemical composition. The guest molecular sizes and structures were investigated utilizing an ab initio (HF/6-31G) method by G98w. These anions were steadily arranged between the metal hydroxide layers by their carboxylate functional groups interacting with the layer plane. The photophysical properties of the obtained compounds were studied by UV-Vis absorption and fluorescence spectroscopy. These results indicate that the confinement of the pair of chromophores, 3-CCA and 9-ACA, within the interlayer region of the host is in favor of guest-host interaction and guest-guest interaction, and that the pair of chromophores, 3-CCA and 9-ACA can give rise to energy transfer processes because of the characteristics of their excited states. © 2010 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source


Li L.,Beijing University of Chemical Technology | Liu P.,Beijing University of Chemical Technology | Zhang L.,Beijing University of Chemical Technology | Chen D.,National Research Center for Certified Reference Materials
Journal of Solid State Chemistry | Year: 2013

Ethyl Orange (EO) and 4-aminoazobenzene-4-sulfonic (AS) anions with Donor-∏-Acceptor structure have been intercalated into the layered double hydroxide (LDH), [Mg0.66 Al0.34 (OH)2] (CO 3)0.17·0.67H2O or adsorbed on the external surface of the host by the method of ion-exchange procedures. The photoabsorption and fluorescence properties of the obtained compounds were different from the pure solid phase of EO and AS. It was suggested that the photophysical properties of guests were closely related to the geometry and electrical structure of the guest molecule, which can affect the distribution and orientation of the guests in the layers or on the surface of the host. The host-guest interactions modulate photophysical properties of guest. In addition, the guest having higher molecular dipole moments surface exchanged on MgAlCO3LDH are beneficial to the enhancement of the blue emission than that of intercalation into LDH. © 2012 Elsevier Inc. Source


Li L.,Beijing University of Chemical Technology | Zhang L.,Beijing University of Chemical Technology | Chen D.-Z.,National Research Center for Certified Reference Materials | Tang H.,National Research Center for Certified Reference Materials
Wuji Cailiao Xuebao/Journal of Inorganic Materials | Year: 2010

Ethyl orange (EO-) and 4-aminoazobenzene-4-sulfonic anion(4A-) were intercalated into the layered double hydroxide (LDH), [Mg0.66Al0.34(OH)2] (CO3)0.17 · 0.67H2O or exchanged on the external surface of the host by the method of ion-exchange procedures. The obtained compounds were characterized by X-ray diffraction, infrared and thermogravimetry techniques. The photophysical properties of the obtained compounds were studied by UV-Vis absorption and fluorescence spectroscope. The guest molecular sizes and structures were investigated utilizing an ab initio (HF/6-31G) method by G03w. These anions were arranged in the interlayer space as a monolayer of species with the main axis perpendicular to the layer plane. These results indicated that the fluorescence of intercalated sample of Mg-Al-EO-LDH increased greatly due to a more rigid and constrained environment of the host. However, the fluorescence of intercalated sample of Mg-Al-4A-LDH decreased due to the concentration quenching. Compared with those observed in the pure microcrystalline EO and 4A, the fluorescence intensity of the samples containing only surface-exchanged EO or 4A reduced because the charge transfer between EO or 4A molecules was enhanced. It suggests that the photophysical properties of guests can be changed by the guest-host interaction or guest-guest interaction. Source

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