| 1. |
- Dong, Kun, et al.
(författare)
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Structural Evidence for the Ordered Crystallites of Ionic Liquid in Confined Carbon Nanotubes
- 2009
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 113:23, s. 10013-10020
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Tidskriftsartikel (refereegranskat)abstract
- Ionic liquids (ILs) are a class of new green materials that have attracted extensive attention in recent decades. Many novel properties not evident under normal conditions may appear when ionic liquids are confined to a nanometer scale. As was observed in the experiment, an anomalous phase behavior from liquid to high melting point perfect crystal occurred when 1-n-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF6]) ionic liquid was confined in a carbon nanotube. In this work, we performed molecular dynamics (MD) simulations for [bmim][PF6] ionic liquid and provided direct structural evidence that the ionic crystallizes in a carbon nanotube. The ordered ionic arrangement in both the radial and the axial directions can be observed inside the channels of the CNTs to induce the form of crystallites. The ionic stacking and distributing can be determined by the sizes of the CNTs. Hydrogen bonds remain the dominant interactions between cations and anions when the ionic liquid enters into the CNT from the bulk phase. The free energies as the thermal driven forces were calculated, and it is found that it is very difficult for a single anion to enter into the channel of the CNT spontaneously. A more favorable way is through an ion-pair in which a cation “pulls” an anion to enter into the channel of the CNT together. It is predicted that other ionic liquids that possess similar structures, even including the pyridinium-based ionic liquids, can show higher melting points when confined in CNTs.
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| 2. |
- Wang, Pu, et al.
(författare)
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Altitude dependence of polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) in surface soil from Tibetan Plateau, China
- 2009
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Ingår i: Chemosphere. - : Elsevier. - 0045-6535 .- 1879-1298. ; 76:11, s. 1498-1504
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Tidskriftsartikel (refereegranskat)abstract
- Remote mountain areas besides high latitude regions are beginning to receive increased attention in studying the transport and behavior of persistent organic pollutants (POPs). In the present work, surface soil samples were collected from the Tibetan Plateau, the highest plateau in the world which includes the northern slope of Mt. Qomolangma, to investigate the levels and trends of polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) along the altitudinal gradient. The average PCB and PBDE concentrations were 185.6 ng kg-1 dry weight (dw) (range 47.1-422.6 ng kg-1 dw) and 11.1 ng kg-1 dw (range 4.3-34.9 ng kg-1 dw), respectively. Regression analysis between the log-transformed TOC-normalized concentrations and the altitudes of the sampling sites showed two opposite trends with regard to altitude dependence: negative relationship with altitude below about 4500 m followed by a positive altitude dependence above this point. Considering minimum anthropogenic activities and very sparse precipitation in the north of Himalayas, the trends above 4500 m imply that the significant altitude dependence of these two groups of POPs were irrespective of pollution sources, but could be predicted by the global distillation effect involving cold condensation in high altitude mountain areas. Increasing levels of heavier congeners were found in higher altitude sites, although the lighter congeners were the main contributors to the total amount, suggesting that less volatile congeners seem to become enriched easier than those more volatile at higher altitudes in this region.
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