Tuesday, May 11, 2010

Journal of Physical Chemistry C, vol. 114, Issue 18

The Role of the Cluster on the Relaxation of Endohedral Fullerene Cage Carbons: A NMR Spin−Lattice Relaxation Study of an Internal Relaxation Reagent

Sabrina Klod, Lin Zhang and Lothar Dunsch*

J. Phys. Chem. C, 2010, 114 (18), pp 8264–8267
DOI: 10.1021/jp101218p

Abstract: The endohedral cluster fullerenes Ih-Sc3N@C80, Ih-Y3N@C80, and Ih-Lu3N@C80 were investigated with respect to the strategy of an internal relaxation reagent by following the cluster size effects and the influence of f-electrons on the carbon relaxation. For endohedral nitride cluster fullerenes of Ih-C80 cage symmetry increased relaxation rates are observed. In general, the enlarged cage size increases the relaxation of the carbons. The encapsulated metal atoms give an additional dipole−dipole interaction to the relaxation rate of the carbon atoms depending on their magnetic character. For different metals the increased nitride cluster size is one reason for the observed stronger dipole−dipole interaction. In contrast, a higher shielding of a metal nucleus by its electron shell leads to a reduced magnetic effect. The negative charge on the cage increases the electron density, thus decreasing T1. In temperature-dependent studies, the diffusion is fast compared to the rotation of the molecule at higher temperatures which is typical for the spherical shape of the fullerene cage. Thus, only a minor deformation of the cage by the endohedral voluminous cluster is found. The shape of the cage is preserved and less influenced by the type and size of the cluster.

Fabrication of Hierarchical Channel Wall in Al-MCM-41 Mesoporous Materials to Enhance Their Adsorptive Capability: Why and How?

Fang Na Gu†‡, Feng Wei†, Jia Yuan Yang†, Ying Wang*‡ and Jian Hua Zhu*†
Key Laboratory of Mesoscopic Chemistry of MOE, College of Chemistry and Chemical Engineering, and Ecomaterials and Renewable Energy Research Center (ERERC), Nanjing University, Nanjing 210093, China
J. Phys. Chem. C, 2010, 114 (18), pp 8431–8439
DOI: 10.1021/jp1009143

Abstract:To overcome the inefficiency of mesoporous materials in the adsorption of small molecules, this article reports the effort how to create hierarchical channel wall in Al-MCM-41 and more important, how to distinguish the contribution of the newly formed micropores in adsorption by the mesoporous materials. Fabrication of hierarchical channel wall is realized through extracting framework aluminum of sample by acid leach to create micropores and defects, providing the fine geometric confinement toward tiny targets. The influence of original Al content of Al-MCM-41 on the controlled dealumination was studied, and X-ray diffraction, N2 adsorption−desorption, 27Al and 29Si MAS NMR, Fourier transform IR techniques were employed to characterize the resulting samples. Besides, volatile nitrosamine N-nitrosopyrrolidine (NPYR) was chosen as a probe to assess the adsorption of the resulting samples. Hierarchical channel wall in Al-MCM-41 significantly increased its ability to trap NPYR, and for the first time the adsorptive contribution of newly formed micropores and defects in the mesoporous silica was distinguished by the instantaneous adsorption under the carrier gas with different flow rate, which is beneficial for developing new functional materials to protect environment.

Structure, Connectivity, and Configurational Entropy of GexSe100−x Glasses: Results from 77Se MAS NMR Spectroscopy

E. L. Gjersing and S. Sen*, B. G. Aitken
J. Phys. Chem. C, 2010, 114 (18), pp 8601–8608
DOI: 10.1021/jp1014143

Abstract:High-resolution 77Se MAS NMR spectroscopy has been conducted at 11.7 T to investigate the short-and intermediate- range structure and chemical order in binary GexSe100−x glasses with 5 ≤ x ≤ 33.33. Four distinct Se environments are observed for the first time, corresponding to Se−Se−Se and Ge−Se−Se linkages as well as Ge−Se−Ge sites where the Se atom is shared by two GeSe4 tetrahedra in either corner-sharing or edge-sharing configuration. Assignments of corner and edge-shared tetrahedra were made based on the 77Se MAS NMR spectrum of crystalline β-GeSe2. Analysis of the compositional variation of the relative concentrations of these Se sites indicates that the structure of GexSe100−x glasses in this composition range can be described as a randomly interconnected network of GeSe4 tetrahedra and chains of Se atoms. The implications of this structural model are discussed in relation to the composition dependence of the glass-forming ability and kinetic fragility of the corresponding parent liquids.

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