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The packing of electronic molecules into planar structures and an ensured pi-pi interaction within the plane are preferred for efficient organic transistors. Thin films of organic electronics are exemplar, but the widely adopted molecular design and associated fabrication lead to limited ordering in multistack construction motifs. Here we demonstrate self-assembled nanolayers of organic molecules having potential electronic utility using an amphiphilic silane as a building block. Unlike a cross-linked (tetrahedral) configuration found in conventional siloxane networks, a linear polymer chain is produced following silane polycondensation. As a result, hydrophobic branches plus a noncovalent pi-pi interlocking between the molecules promote planar packing and continuous stacking along the surface normal. In contrast to conventional pi-pi stacking or hydrogen bonding pathways in a fibrous construct, multistacked nanolayers with coexisting pi-pi and herringbone interlocking can provide unmatched properties and processing convenience in molecular electronics.
ACS Nano 2010 Jul 27
PMID:Self-assembled nanolayers of conjugated silane with pi-pi interlocking. 2051 69

For decades, ethanol has been in use as a fuel for the storage of solar energy in an energy-dense, liquid form. Over the past decade, the ability to reform ethanol into hydrogen gas suitable for a fuel cell has drawn interest as a way to increase the efficiency of both vehicles and stand-alone power generators. Here we report the use of extremely small nanocrystalline materials to enhance the performance of 1% Rh/10% Ni@CeO(2) catalysts in the oxidative steam reforming of ethanol with a ratio of 1.7:1:10:11 (air/EtOH/water/argon) into hydrogen gas, achieving 100% conversion of ethanol at only 300 degrees C with 60% H(2) in the product stream and less than 0.5% CO. Additionally, nanocrystalline 10% Ni@CeO(2) was shown to achieve 100% conversion of ethanol at 400 degrees C with 73% H(2), 2% CO, and 2% CH(4) in the product stream. Finally, we demonstrate the use of biological templating on M13 to improve the resistance of this catalyst to deactivation over 52 h tests at high flow rates (120 000 h(-1) GHSV) at 450 degrees C. This study suggests that the use of highly nanocrystalline, biotemplated catalysts to improve activity and stability is a promising route to significant gains over traditional catalyst manufacture methods.
ACS Nano 2010 Jun 22
PMID:Production of hydrogen using nanocrystalline protein-templated catalysts on m13 phage. 2052 95

Vertically aligned ZnO--CdSSe core-shell nanocable arrays were synthesized with a controlled composition and shell thickness (10-50 nm) by the chemical vapor deposition on the pregrown ZnO nanowire arrays. They consisted of a composition-tuned single-crystalline wurtzite structure CdS1-xSex (x=0, 0.5, and 1) shell whose [0001] direction was aligned along the [0001] wire axis of the wurtzite ZnO core. The analysis of structural and optical properties shows the formation of Zn containing alloy in the interface region between the ZnO core and shell, which can facilitate the growth of single-crystalline shell layers by reducing both the lattice mismatch and the number of defect sites. In contrast, the TiO2 (rutile) nanowire array can form the polycrystalline shell under the same condition. The photoelectrochemical cell using the ZnO--CdS photoelectrode exhibits a higher photocurrent and hydrogen generation rate than that using the TiO2-CdS one. We suggest that the formation of the CdZnSSe intermediate layers contributes to the higher photoelectrochemical cell performance of the ZnO--CdSSe nanocables.
ACS Nano 2010 Jul 27
PMID:Composition-tuned ZnO--CdSSe core--shell nanowire arrays. 2052 2

Hydrogen is recognized as a potential, extremely interesting energy carrier system, which can facilitate efficient utilization of unevenly distributed renewable energy. A major challenge in a future "hydrogen economy" is the development of a safe, compact, robust, and efficient means of hydrogen storage, in particular, for mobile applications. Here we report on a new concept for hydrogen storage using nanoconfined reversible chemical reactions. LiBH4 and MgH2 nanoparticles are embedded in a nanoporous carbon aerogel scaffold with pore size Dmax approximately 21 nm and react during release of hydrogen and form MgB2. The hydrogen desorption kinetics is significantly improved compared to bulk conditions, and the nanoconfined system has a high degree of reversibility and stability and possibly also improved thermodynamic properties. This new scheme of nanoconfined chemistry may have a wide range of interesting applications in the future, for example, within the merging area of chemical storage of renewable energy.
ACS Nano 2010 Jul 27
PMID:A reversible nanoconfined chemical reaction. 2053 50

We have studied the electronic structural characteristics of hydrogenated bilayer graphene under a perpendicular electric bias using first-principles density functional calculations. The bias voltage applied between the two hydrogenated graphene layers allows continuous tuning of the band gap and leads to transition from semiconducting to metallic state. Desorption of hydrogen from one layer in the chair conformation yields a ferromagnetic semiconductor with a tunable band gap. The implications of tailoring the band structure of biased system for future graphene-based device applications are discussed.
ACS Nano 2010 Jul 27
PMID:Tunable band gap in hydrogenated bilayer graphene. 2053 19

Supramolecular self-assembly on surfaces, guided by hydrogen bonding interactions, has been widely studied, most often involving planar compounds confined directly onto surfaces in a planar two-dimensional (2-D) geometry and equipped with structurally rigid chemical functionalities to direct the self-assembly. In contrast, so-called molecular Landers are a class of compounds that exhibit a pronounced three-dimensional (3-D) structure once adsorbed on surfaces, arising from a molecular backboard equipped with bulky groups which act as spacer legs. Here we demonstrate the first examples of extended, hydrogen-bonded surface architectures formed from molecular Landers. Using high-resolution scanning tunnelling microscopy (STM) under well controlled ultrahigh vacuum conditions we characterize both one-dimensional (1-D) chains as well as five distinct long-range ordered 2-D supramolecular networks formed on a Au(111) surface from a specially designed Lander molecule equipped with dual diamino-triazine (DAT) functional moieties, enabling complementary NH...N hydrogen bonding. Most interestingly, comparison of experimental results to STM image calculations and molecular mechanics structural modeling demonstrates that the observed molecular Lander-DAT structures can be rationalized through characteristic intermolecular hydrogen bonding coupling motifs which would not have been possible in purely planar 2-D surface assembly because they involve pronounced 3-D optimization of the bonding configurations. The described 1-D and 2-D patterns of Lander-DAT molecules may potentially be used as extended molecular molds for the nucleation and growth of complex metallic nanostructures.
ACS Nano 2010 Jul 27
PMID:Supramolecular architectures on surfaces formed through hydrogen bonding optimized in three dimensions. 2055 Jan 41

The ability to assess the risks of human exposure to engineered nanomaterials requires fundamental understanding of the fate and potential cytotoxicity of nonbiodegradable nanoparticles, for instance, after oral uptake. In this study, we quantify the impact of nanoparticles with low chemical toxicity on the intestinal membrane in a human intestinal in vitro model. Differentiated human colorectal adenocarcinoma cells, Caco-2, were cultured on a permeable support where they form an epithelial monolayer separating an apical and basal compartment. This model system allows a systematic characterization of the effect of nanoparticles on the cell viability as a function of size, surface chemistry, concentration, and incubation time. We used polystyrene (PS) nanoparticles (20 and 40 nm diameter) with two different surface chemistries (carboxylic acid and amines). The experiments performed show a strong decrease in cell viability as a response to nanoparticle exposure. Incubation times of <or=4 h are sufficient to induce dramatic losses in cell viability after an additional induction period of 4-12 h. Mapping the temporospatial distribution of dead cells in the Caco-2 cell monolayer using optical microscopy reveals that the nanoparticles induce apoptosis in individual cells, which then propagate across the cell monolayer through a "bystander killing effect". Addition of catalase, which selectively decomposes hydrogen peroxide, leads to a significant decrease in apoptosis levels, indicating that hydrogen peroxide causes the spread of apoptosis across the monolayer. Our findings confirm that ingested nonbiodegradable nanoparticles represent a potential health risk due to their detrimental impact on the intestinal membrane by destroying their barrier protection capability over time.
ACS Nano 2010 Jul 27
PMID:Nanoparticle-induced apoptosis propagates through hydrogen-peroxide-mediated bystander killing: insights from a human intestinal epithelium in vitro model. 2056 Jun 58

This study compares the electrocatalytic activity of nitrogen-doped carbon nanotubes (NCNTs) with multiwalled carbon nanotubes (MWCNTs). Results indicate that NCNTs possess a marked electrocatalytic activity toward oxygen reduction reaction (ORR) by an efficient four-electron process in the alkaline condition, while the process of MWCNTs is through a two-electron pathway. Meanwhile, NCNTs show a very attractive electrochemical performance for the redox reaction of hydrogen peroxide (H2O2) and could be employed as a H2O2 sensor at a low potential of +0.3 V. The sensitivity of the NCNT-based biosensor reaches 24.5 microA/mM, more than 87 times that of the MWCNT-based one. Moreover, NCNTs exhibit striking analytical stability and reproducibility, which enables a reliable and sensitive determination of glucose by monitoring H2O2 produced by an enzymatic reaction between glucose oxidase/glucose or choline oxidase/choline at +0.3 V without the help of the electron mediator. The NCNT-based glucose biosensor has a linear range from 2 to 140 microM with an extremely high sensitivity of 14.9 microA/mM, and the detection limit is estimated to be 1.2 microM at a signal-to-noise ratio of 3. The results indicate that the NCNTs are good nanostructured materials for potential application in biosensors.
ACS Nano 2010 Jul 27
PMID:Nitrogen-doped carbon nanotubes: high electrocatalytic activity toward the oxidation of hydrogen peroxide and its application for biosensing. 2056 21

p-Type surface conductivity is a uniquely important property of hydrogen-terminated diamond surfaces. In this work, we report similar surface-dominated electrical properties in silicon nanowires (SiNWs). Significantly, we demonstrate tunable and reversible transition of p(+)-p-i-n-n(+) conductance in nominally intrinsic SiNWs via changing surface conditions, in sharp contrast to the only p-type conduction observed on diamond surfaces. On the basis of Si band energies and the electrochemical potentials of the ambient (pH value)-determined adsorbed aqueous layer, we propose an electron-transfer-dominated surface doping model, which can satisfactorily explain both diamond and silicon surface conductivity. The totality of our observations suggests that nanomaterials can be described as a core-shell structure due to their large surface-to-volume ratio. Consequently, controlling the surface or shell in the core-shell model represents a universal way to tune the properties of nanostructures, such as via surface-transfer doping, and is crucial for the development of nanostructure-based devices.
ACS Nano 2010 Jun 22
PMID:Tunable electrical properties of silicon nanowires via surface-ambient chemistry. 2056 40

In hydrodesulfurization (HDS) of fossil fuels, the sulfur levels are reduced by sulfur extraction from hydrocarbons through a series of catalyzed reaction steps on low-coordinated sites on molybdenum disulfide (MoS(2)) nanoclusters. By means of scanning tunneling microscopy (STM), we show that the adsorption properties of MoS(2) nanoclusters toward the HDS refractory dibenzothiophene (DBT) vary dramatically with small changes in the cluster size. STM images reveal that MoS(2) nanoclusters with a size above a threshold value of 1.5 nm react with hydrogen to form so-called sulfur vacancies predominately located at edge sites, but these edge vacancies are not capable of binding DBT directly. In contrast, MoS(2) nanoclusters below the threshold perform remarkably better. Here, sulfur vacancies form predominantly at the corner sites, and these vacancies show a high affinity for DBT. The results thus indicate that very small MoS(2) nanoclusters may have unique catalytic properties for the production of clean fuels.
ACS Nano 2010 Aug 24
PMID:Size threshold in the dibenzothiophene adsorption on MoS2 nanoclusters. 2060 73


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