Self-supported Pd(x)Bi catalysts for the electrooxidation of glycerol in alkaline media.

Highly active self-supported PdxBi catalysts are synthesized by the sacrificial support method. Self-supported PdxBi catalysts have a porous nanostructured morphology with high surface areas (in the range from 75 to 100 m(2) g(-1)), making PdxBi a state-of-the-art catalyst. Pd4Bi displays the highest activity toward glycerol oxidation. In situ Fourier transform infrared spectroscopy highlights the unique catalytic behavior of self-supported PdxBi materials due to their particular structure and morphology. The confinement of reactants and intermediates in pores acting as nanoreactors is responsible for the high selectivity as a function of the electrode potential: aldehyde and ketone at low potentials, hydroxypyruvate at moderate potentials, and CO2 at high potentials. Moreover, the selectivity depends on the electrode history: it is different for the positive potential scan direction than for the reverse direction, where the catalyst becomes selective toward the production of carboxylates.

Stable and fluid multilayer phospholipid-silica thin films: mimicking active multi-lamellar biological assemblies.

Phospholipid-based nanomaterials are of interest in several applications including drug delivery, sensing, energy harvesting, and as model systems in basic research. However, a general challenge in creating functional hybrid biomaterials from phospholipid assemblies is their fragility, instability in air, insolubility in water, and the difficulty of integrating them into useful composites that retain or enhance the properties of interest, therefore limiting there use in integrated devices. We document the synthesis and characterization of highly ordered and stable phospholipid-silica thin films that resemble multilamellar architectures present in nature such as the myelin sheath. We have used a near room temperature chemical vapor deposition method to synthesize these robust functional materials. Highly ordered lipid films are exposed to vapors of silica precursor resulting in the formation of nanostructured hybrid assemblies. This process is simple, scalable, and offers advantages such as exclusion of ethanol and no (or minimal) need for exposure to mineral acids, which are generally required in conventional sol-gel synthesis strategies. The structure of the phospholipid-silica assemblies can be tuned to either lamellar or hexagonal organization depending on the synthesis conditions. The phospholipid-silica films exhibit long-term structural stability in air as well as when placed in aqueous solutions and maintain their fluidity under aqueous or humid conditions. This platform provides a model for robust implementation of phospholipid multilayers and a means toward future applications of functional phospholipid supramolecular assemblies in device integration.

Facile fabrication of scalable, hierarchically structured polymer/carbon architectures for bioelectrodes.

This research introduces a method for fabrication of conductive electrode materials with hierarchical structure from porous polymer/carbon composite materials. We describe the fabrication of (3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) scaffolds doped with carbon materials that provide a conductive three-dimensional architecture that was demonstrated for application in microbial fuel cell (MFC) anodes. Composite electrodes from PHBV were fabricated to defined dimensions by solvent casting and particulate leaching of a size-specific porogen (in this case, sucrose). The cellular biocompatibility of the resulting composite material facilitated effective immobilization of a defined preparation of Shewanella oneidensis DSP-10 as a model microbial catalyst. Bacterial cells were immobilized via chemical vapor deposition (CVD) of silica to create an engineered biofilm that exhibits efficient bioelectrocatalysis of a simple-carbon fuel in a MFC. The functionalized PHBV electrodes demonstrate stable and reproducible anodic open circuit potentials of -320 ± 20 mV (vs Ag/AgCl) with lactate as the electron donor. Maximum power densities achieved by the hierarchically structured electrodes (~5 mW cm(3)) were significantly higher than previously observed for graphite-felt electrodes. The methodology for fabrication of scalable electrode materials may be amenable to other bioelectrochemical applications, such as enzyme fuel cells and biosensors, and could easily be adapted to various design concepts.

Convective assembly of 2D lattices of virus-like particles visualized by in-situ grazing-incidence small-angle X-ray scattering.

The rapid assembly of icosohedral virus-like particles (VLPs) into highly ordered (domain size > 600 nm), oriented 2D superlattices directly onto a solid substrate using convective coating is demonstrated. In-situ grazing-incidence small-angle X-ray scattering (GISAXS) is used to follow the self-assembly process in real time to characterize the mechanism of superlattice formation, with the ultimate goal of tailoring film deposition conditions to optimize long-range order. From water, GISAXS data are consistent with a transport-limited assembly process where convective flow directs assembly of VLPs into a lattice oriented with respect to the water drying line. Addition of a nonvolatile solvent (glycerol) modified this assembly pathway, resulting in non-oriented superlattices with improved long-range order. Modification of electrostatic conditions (solution ionic strength, substrate charge) also alters assembly behavior; however, a comparison of in-situ assembly data between VLPs derived from the bacteriophages MS2 and Qß show that this assembly process is not fully described by a simple Derjaguin-Landau-Verwey-Overbeek model alone.

Morphology of nanoclusters and nanopillars formed in nonequilibrium surface growth for catalysis applications.

We consider growth of nanoclusters and nanopillars in a model of surface deposition and restructuring yielding morphologies of interest in designing catalysis applications. Kinetic Monte Carlo numerical modeling yields examples of the emergence of face centered cubic (fcc) symmetry surface features in Pt-type metal nanostructures, allowing evaluation of the fraction of the resulting active sites with desirable properties, such as (111)-like coordination, as well as suggesting the optimal growth regimes.

High electrocatalytic activity of tethered multicopper oxidase-carbon nanotube conjugates.

Multicopper oxidases linked to multiwall carbon nanotubes via the molecular tethering reagent, 1-pyrenebutanoic acid, succinimidyl ester, displayed high bioelectrocatalytic activity for oxygen reduction.

Microparticles with bimodal nanoporosity derived by microemulsion templating.

Oil, water, and surfactant liquid mixtures exhibit very complex phase behavior. Depending on the conditions, such mixtures give rise to highly organized structures. A proper selection of the type and concentration of surfactants determines the structuring at the nanoscale level. In this Article, we show that hierarchically bimodal porous structures can be obtained by templating silica microparticles with a specially designed surfactant micelle/microemulsion mixture. Tuning the phase state by adjusting the surfactant composition and concentration allows for the controlled design of a system where microemulsion droplets coexist with smaller surfactant micellar structures. The microemulsion droplet and micellar dimensions determine the two types of pore sizes. We also demonstrate the fabrication of carbon and carbon/platinum replicas of the silica microspheres using a "lost-wax" approach. Such particles have great potential for the design of electrocatalysts for fuel cells, chromatography separations, and other applications.

CVD for the facile synthesis of hybrid nanobiomaterials integrating functional supramolecular assemblies.

In this letter, we present a simple one-step, versatile, scalable chemical vapor deposition (CVD)-based process for the encapsulation and stabilization of a host of single or multicomponent supramolecular assemblies (proteoliposomes, microbubbles, lipid bilayers, and photosynthetic antennae complexes and other biological materials) to form functional hybrid nanobiomaterials. In each case, it is possible (i) to form thin silica layers or gels controllably that enable the preservation of the supramolecular assembly over time and under adverse environmental conditions and (ii) to tune the structure of the silica gels so as to optimize solute accessibility while at the same time preserving functional dynamic properties of the encapsulated phospholipid assembly. The process allows precise temporal and spatial control of silica polymerization kinetics through the control of precursor delivery at room temperature and does not require or produce high concentrations of injurious chemicals that can compromise the function of biomolecular assemblies; it also does not require additives. This process differs from the conventional sol-gel process in that it does not involve the use of cosolvents (alcohols) and catalysts (acid or base).