Hua Ning

Au42: A possible ground-state noble metallic nanotube

A large hollow tubelike Au(42) is predicted as a new ground-state configuration based on the scalar relativistic density functional theory. The shape of this new Au(42) cluster is similar to a (5,5) single-wall gold nanotube, the two ends of which are capped by half of a fullerenelike Au(32). In the same way, a series of Au(n) (n = 37, 42, 47, 52, 57, 62, 67, 72, ..., Delta n = 5) tubelike structures has been constructed. The highest occupied molecular orbital-lowest unoccupied molecular orbital gaps suggested a significant semiconductor-conductor alternation in n is an element of [32,47]. Similar to the predictions and speculation of Daedalus [D. E. H. Jones, New Sci. 32, 245 (1966); E. Osawa, Superaromaticity (Kagaku, Kyoto, 1970), Vol. 25, pp. 854-863; Z. Yoshida and E. Osawa, Aromaticity Chemical Monograph (Kagaku Dojin, Kyoto, Japan, 1971), Vol. 22, pp. 174-176; D. A. Bochvar and E. G. Galpern, Dokl. Akad. Nauk SSSR 209, 610 (1973)], here a large hollow ground-state gold nanotube was predicted theoretically.

Catalytic action of Y2O3@graphene nanocomposites on the hydrogen-storage properties of Mg–Al alloys

An Y2O3@rGO nanocomposite was synthesized via an impregnation method and the catalytic effect of the nanocomposite on the hydrogen-storage properties of a Mg–Al alloy was investigated. The pressure composition isotherm measurement results revealed that the Mg–Al–Y2O3@rGO composite underwent a reversible hydrogenation/dehydrogenation process at 250 °C. Furthermore, the onset temperatures of hydrogenation and dehydrogenation were significantly (i.e., 102 °C and 122 °C, respectively) lower than the respective values corresponding to the Mg–Al alloy. The Y2O3@rGO nanocomposite enhanced the hydriding kinetic properties of the alloy. The hydrogenation kinetic parameter of the Mg–Al alloy increased from 0.008 to 0.195 at 300 °C with 5 wt% of the Y2O3@rGO composite. The values of 162.6 kJ mol−1 H2 and 145.9 kJ mol−1 H2 were obtained for the dehydrogenation energy barrier (evaluated by means of a Kissinger plot) of the Mg–Al alloy and the Mg–Al–Y2O3@rGO hydride, respectively. The reaction enthalpy of hydrogenation/dehydrogenation (determined from a vant Hoff plot) of the alloy decreased with the addition of the Y2O3@rGO nanocomposite. For example, the values of 70.7 kJ mol−1 H2 and 54.3 kJ mol−1 H2 were obtained for the reaction enthalpy of hydrogenation associated with the Mg–Al alloy and the Mg–Al–Y2O3@rGO composite, respectively. Therefore, the addition of the Y2O3@rGO nanocomposite is conducive for improving the thermodynamic and kinetic properties of hydrogenation/dehydrogenation of the Mg–Al alloy.

Nitric Oxide Adsorption and Dissociation on Nb(100) Surface

We have studied nitric oxide (NO) adsorption and dissociation on the Nb(100) surface by using the density-functional theory and total-energy calculations. On the Nb(100) surface, at high coverage the tilted NO prefers to adsorb on hollow sites as the most stable adsorption configuration, while at lower coverage the tilted bridge site is the most favorable site. For vertical NO adsorption, similar structural features on top and bridge sites are found in different coverage. Moreover, NO molecules adsorbed on hollow sites of c(2×2) and p(2×2) cells are easy to dissociate to forming the atomic adsorption states from PES calculations. The further analysis based on electronic states reveal that the essential interaction between NO and metal substrate is the hybridization of NO 2π * -orbital and the d-bands of surface niobium atoms. For the tilted NO adsorption, NO 1π and 5σ states are superposed, which are hybridized with niobium d orbitals strongly.