Palladium nanowires (of length a few tens of nanometers) are synthesized in a hexagonal mesophase formed by a quaternary system (Pd-doped water, surfactant, cosurfactant, and oil) by electron beam irradiation. The mesophases can be doped by high concentrations of palladium (0.1 M) without any disturbance of the structure of the mesophases which allows the quantitative synthesis of 1D Pd nanostructures. We found an increase in the average length of the nanowires with the amount of cosurfactant (pentanol) that assists the reduction/growth processes. The electrocatalytic oxidation of ethanol was selected as a test reaction in alkaline medium where Pd is known to be among the best electrode materials. We found that the Pd nanowires exhibit both a very important electrocatalytic activity for ethanol oxidation and a very high stability.

We studied liquid water confined within nanopores which present a high level of hydrophobicity thanks to a new method of synthesis. We found that the liquid state persists down to temperatures much lower than in the bulk and in hydrophilic materials of comparable sizes, allowing us to define a thermodynamic limit for the melting/crystallization of water.

Grand canonical Monte Carlo simulations are used to study the adsorption of benzene on atomistic silica surfaces and in cylindrical nanopores. The effect of temperature and surface chemistry is addressed by studying the adsorption of benzene at 293 and 323 K on both fully and partially hydroxylated silica surfaces or nanopores. We also consider the adsorption of benzene in a cylindrical nanopore of diameter D=3.6 nm and compare our results with those obtained for planar surfaces. The structure of benzene in the vicinity of the planar surface and confined in the cylindrical nanopore is determined by calculating orientational order parameters and examining positional pair correlation functions. The density profiles of adsorbed benzene reveal the strong layering of the adsorbate, which decays with the distance from the silica surface. At a given temperature and at low pressures, the film adsorbed at the fully hydroxylated silica surface is larger than that for the partially hydroxylated silica surface. This result is due to an increase in the density of silanol groups that induces an increase in the polarity of the silica surface, which becomes more attractive for the adsorbate. Our results also suggest that the benzene molecules prefer an orientation in which their ring is nearly perpendicular to the surface when fully hydroxylated surfaces are considered. When partially hydroxylated surfaces are considered, a second preferential orientation is observed where the benzene ring forms an angle of approximately 50 degrees with the silica surface. In this case, the average orientation of the benzene molecules appears disordered as in the bulk phase. These results suggest that determining the experimental orientation of benzene in the vicinity of a silica surface is a difficult task even when the surface chemistry is known. Capillary condensation in the nanopores involves a transition from a partially filled pore (a thin film adsorbed at the pore surface) to a completely filled pore configuration where the confined liquid coexists at equilibrium with the external gas phase. The disordered orientation of the adsorbed benzene molecules in the case of the partially hydroxylated surface favors the condensation of benzene molecules (the condensation pressure for this substrate is lower than that for the fully hydroxylated surface). Finally, these results are consistent with the structural analysis, showing that (1) benzene tends to relax its liquid structure a little in order to optimize its molecular arrangement near the pore wall and (2) the disordering of the liquid structure induced by the surface becomes stronger as the interaction with the pore wall increases.

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The catalytic activity of porous platinum nanostructures, viz. platinum nanonets (PtNNs) and platinum nanoballs (PtNBs), synthesized by radiolysis were studied using two model reactions (i) electron transfer reaction between hexacyanoferrate (III) and sodium thiosulfate and (ii) the reduction of p-nitrophenol by sodium borohydride to p-aminophenol. The kinetic investigations were carried out for the platinum nanostructure-catalyzed reactions at different temperatures. The pseudofirst-order rate constant for the electron transfer reaction between hexacyanoferrate (III) and sodium thiosulfate catalyzed by PtNNs and PtNBs at 293 K are (9.1 ± 0.7) × 10(-3) min(-1) and (16.9 ± 0.6) × 10(-3) min(-1), respectively. For the PtNN- and PtNB-catalyzed reduction of p-nitrophenol to p-aminophenol by sodium borohydride, the pseudofirst-order rate constant was (8.4 ± 0.3) × 10(-2) min(-1) and (12.6 ± 2.5) × 10(-2) min(-1), respectively. The accessible surface area of the PtNNs and PtNBs determined before the reaction are 99 and 110 m(2)/g, respectively. These nanostructures exhibit significantly higher catalytic activity, consistent with the largest accessible surface area reported so far for the solid platinum nanoparticles. The equilibrium of the reactants on the surface of the platinum nanostructures played an important role in the induction time (t0) observed in the reaction. A possible role of structural modifications of PtNBs catalyzed the reaction leading to change in the accessible surface area of PtNBs is being explored to explain the nonlinear behavior in the kinetic curve. The activation energy of the PtNN- and PtNB-catalyzed reduction of p-nitrophenol are 26 and 6.4 kJ/mol, respectively. These observations open up new challenges in the field of material science to design and synthesize platinum nanostructures which could withstand such reaction conditions.

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