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Optimizing product selectivity and conversion efficiency are primary goals in catalysis. However, efficiency and selectivity are often mutually antagonistic, so that high selectivity is accompanied by low efficiency and vice versa. Also, just increasing the temperature is very unlikely to change the reaction pathway. Here, by constructing hierarchical plasmonic nanoreactors, we show that nanoconfined thermal fields and energetic electrons, a combination of attributes that coexist almost uniquely in plasmonic nanostructures, can overcome the antagonism by regulating selectivity and promoting conversion rate concurrently. For propylene partial oxidation, they drive chemical reactions by not only regulating parallel reaction pathways to selectively produce acrolein but also reducing consecutive process to inhibit the overoxidation to CO2, resulting in valuable products different from thermal catalysis. This suggests a strategy to rationally use plasmonic nanostructures to optimize chemical processes, thereby achieving high yield with high selectivity at lower temperature under visible light illumination.

Plasmon-mediated chemical reactions (PMCRs) constitute a vibrant research field, advancing such goals as using sunlight to convert abundant precursors such as CO2 and water to useful fuels and chemicals. A key question in this burgeoning field which has not, as yet, been fully resolved, relates to the precise mechanism through which the energy absorbed through plasmonic excitation, ultimately drives such reactions. Among the multiple processes proposed, two have risen to the forefront: plasmon-increased temperature and generation of energetic charge carriers. However, it is still a great challenge to confidently separate these two effects and quantify their relative contribution to chemical reactions. Here, we describe a strategy based on the construction of a plasmonic electrode coupled with photoelectrochemistry, to quantitatively disentangle increased temperature from energetic charge carriers effects. A clear separation of the two effects facilitates the rational design of plasmonic nanostructures for efficient photochemical applications and solar energy utilization.

We present a sensitive and quantitative protein detection assay that can efficiently distinguish between specific and nonspecific target binding. Our technique combines dual affinity reagents with surface-enhanced Raman spectroscopy (SERS) and chemometric analysis. We link one Raman reporter-tagged affinity reagent to gold nanoparticles and another to a gold film, such that protein-binding events create a "hot spot" with strong SERS spectra from both Raman reporter molecules. Any signal generated in this context is indicative of recognition by both affinity labels, whereas signals generated by nonspecific binding lack one or the other label, enabling us to efficiently distinguish true from false positives. We show that the number of hot spots per unit area of our substrate offers a quantitative measure of analyte concentration and demonstrate that this dual-label, SERS-linked aptasensor assay can sensitively and selectively detect human α-thrombin in 1% human serum with a limit of detection of 86 pM.

Plasmonic metal/semiconductor heterostructures show promise for visible-light-driven photocatalysis. Gold nanorods (AuNRs) semi-coated with TiO2 are expected to be ideally structured systems for hydrogen evolution. Synthesizing such structures by wet-chemistry methods, however, has proved challenging. Here we report the bottom-up synthesis of AuNR/TiO2 nanodumbbells (NDs) with spatially separated Au/TiO2 regions, whose structures are governed by the NRs' diameter, and the higher curvature and lower density of CnTAB surfactant at the NRs' tips than on their lateral surfaces, as well as the morphology's dependence on concentration, and alkyl chain length of CnTAB. The NDs show plasmon-enhanced H2 evolution under visible and near-infrared light.

The optical resonances of plasmonic nanostructures depend critically on the geometrical details of the absorber. We show that this unique property of plasmons can potentially be used to create panchromatic absorbers covering most of the useful solar spectrum, by measuring the light-to-hydrogen conversion capabilities of a series multielectrode photocatalytic devices, based on functionalized gold nanorods of appropriately chosen aspect ratios. Judiciously combining nanorods of various aspect ratios almost doubles the H2 production of the device over what is optimally possible with a device using gold nanorods of a single aspect ratio (all other key parameters being equal). The estimated quantum efficiency (absorbed photons-to-hydrogen) averaged over the entire solar spectrum of the best performing plasmonic multielectrode array was approximately 0.1%, and the measured H2 production rate for all of the devices was found to be approximately proportional to the hot electron generation. The device was monitored continuously for over 200 hr of operation without measurable diminution in the rate.

The conversion of sunlight into electricity by photovoltaics is currently a mature science and the foundation of a lucrative industry. In conventional excitonic solar cells, electron-hole pairs are generated by light absorption in a semiconductor and separated by the "built in" potential resulting from charge transfer accompanying Fermi-level equalization either at a p-n or a Schottky junction, followed by carrier collection at appropriate electrodes. Here we report a stable, wholly plasmonic photovoltaic device in which photon absorption and carrier generation take place exclusively in the plasmonic metal. The field established at a metal-semiconductor Schottky junction separates charges. The negative carriers are high-energy (hot) electrons produced immediately following the plasmon's dephasing. Some of the carriers are energetic enough to clear the Schottky barrier or quantum mechanically tunnel through it, thereby producing the output photocurrent. Short circuit photocurrent densities in the range 70-120 μA cm(-2) were obtained for simulated one-sun AM1.5 illumination with devices based on arrays of parallel gold nanorods, conformally coated with 10 nm TiO2 films and fashioned with a Ti metal collector. For the device with short circuit currents of 120 μA cm(-2), the internal quantum efficiency is ∼2.75%, and its wavelength response tracks the absorption spectrum of the transverse plasmon of the gold nanorods indicating that the absorbed photon-to-electron conversion process resulted exclusively in the Au, with the TiO2 playing a negligible role in charge carrier production. Devices fabricated with 50 nm TiO2 layers had open-circuit voltages as high as 210 mV, short circuit current densities of 26 μA cm(-2), and a fill factor of 0.3. For these devices, the TiO2 contributed a very small but measurable fraction of the charge carriers.

An approach based on a solution-based synthesis that produces a thermally stable Ag/oxide/S₂ Te₃ -Te metal-semiconductor heterostructure is described. With this approach, a figure of merit of zT = 1.0 at 460 K is achieved, a record for a heterostructured material made using wet chemistry. Combining experiments and theory shows that the large increase in the material's Seebeck coefficient results from hot carrier filtering.

We report a method for preparing p-type silicon germanium bulk alloys directly from a boron-doped silica germania nanocomposite. This is the first successful attempt to produce and characterize the thermoelectric properties of SiGe-based thermoelectric materials prepared at temperatures below the alloy's melting point through a magnesiothermic reduction of the silica-germania nanocomposite. We observe a thermoelectric power factor that is competitive with the literature record obtained for high energy ball milled nanocomposites. The large grain size in our hot pressed samples limits the thermoelectric figure of merit to 0.5 at 800 C for an optimally doped Si80Ge20 alloy. © 2013 American Chemical Society.

The field of plasmonics--the study of collective electron excitation in nanostructured metal and other conductors--is currently highly active with research foci in a number of related fields, including plasmon-enhanced spectroscopies and plasmon-mediated photochemical and photocatalytic processes through which the energy stored temporarily as plasmons can be used to enable and (or) accelerate photochemistry. This enhancement is accomplished either by the action of the large optical fields produced in the vicinity of plasmonic nanostructures or mediated by the energetic electrons and holes surviving transiently following the dephasing of the plasmon. This article traces the early contributions to the foundation of the current field of plasmonics by two scientists working in Canada in the early 1970s, J. P. Marton at McMaster University and Welwyn Corporation and the current author while he was at the University of Toronto. Key words: plasmonics. La plasmonique, l'etude de l'excitation collective d'electrons dans des metaux et autres conducteurs nanostructures, est un domaine qui suscite actuellement un grand interet et dont les activites de recherche se concentrent dans de nombreux domaines connexes, notamment les techniques de spectroscopie amelioree par plasmons ainsi que les processus photochimiques et catalytiques a mediation plasmonique, dans lesquels l'energie emmagasinee temporairement dans les plasmons peut etre utilisee pour rendre possibles ou accelerer des reactions photochimiques. Cette acceleration est attribuable soit a l'action des champs optiques etendus produits dans le voisinage des nanostructures plasmoniques, soit a celle des electrons et des trous energetiques qui survivent transitoirement apres le dephasage du plasmon. Cet article relate les premieres decouvertes qui ont jete les bases du domaine de la plasmonique actuelle. Ces travaux ont ete realises par deux scientifiques travaillant au Canada au debut des annees 1970 : J. P. Marton a l'Universite McMaster et a la Welwyn Corporation, et l'auteur du present article alors qu'il etait affilie a l'Universite de Toronto. [Traduit par la Redaction] Mots-cles : plasmonique., Plasmonics, the photophysical and photochemical excitation of collective electron oscillations in conducting media, and their photonic and chemical consequences and applications, is currently a high-flying field of research. Searching the [...]

Efficient and cost-effective conversion of solar energy to useful chemicals and fuels could lead to a significant reduction in fossil hydrocarbon use. Artificial systems that use solar energy to produce chemicals have been reported for more than a century. However the most efficient devices demonstrated, based on traditionally fabricated compound semiconductors, have extremely short working lifetimes due to photocorrosion by the electrolyte. Here we report a stable, scalable design and molecular level fabrication strategy to create photoelectrochemically active heterostructure (PAH) units consisting of an efficient semiconductor light absorber in contact with oxidation and reduction electrocatalysts and otherwise protected by alumina. The functional heterostructures are fabricated by layer-by-layer, template-directed, electrochemical synthesis in porous anodic aluminum oxide membranes to produce high density arrays of electronically autonomous, nanostructured, corrosion resistant, photoactive units (~10(9)-10(10) PAHs per cm(2)). Each PAH unit is isolated from its neighbor by the transparent electrically insulating oxide cellular enclosure that makes the overall assembly fault tolerant. When illuminated with visible light, the free floating devices have been demonstrated to produce hydrogen at a stable rate for over 24 h in corrosive hydroiodic acid electrolyte with light as the only input. The quantum efficiency (averaged over the solar spectrum) for absorbed photons-to-hydrogen conversion was 7.4% and solar-to-hydrogen energy efficiency of incident light was 0.9%. The fabrication approach is scalable for commercial manufacturing and readily adaptable to a variety of earth abundant semiconductors which might otherwise be unstable as photoelectrocatalysts.

Nanostructured Schottky inorganic-organic solar cells provide overall power conversion efficiencies exceeding 3%, with extremely large short-circuit photocurrents. The device EQE faithfully tracks the absorptance of the CdSe nanorods, and the IQE is approximately constant over the entire visible spectrum as opposed to a p-n junction hybrid solar cell fabricated with a highly absorbing organic polymer.

Previously reported TiO2 nanowire fabrication from Ni catalysts shows a surprising amount of phosphorous (P) contamination incorporated into the seed particle. We proposed this unintentional P-doping of Ni particles aids the mechanism for nanowire growth and occurs by an alternative pathway from the Vapor-Liquid-Solid (VLS) mechanism. To confirm this new mechanism, mixed phase NiP/Ni2P (NixPy) and Ni2P nanoparticles were fabricated and the central role of phosphorous in TiO 2 nanowire synthesis confirmed. This newly developed P-assisted fabrication method yielded crystalline rutile TiO2 nanowires. In this mechanism solid, quasi-spherical catalyst particles attached to the ends of nanowires and surrounded by a Ni/P liquid shell are responsible for the nanowire growth. The growing end of the nanowire appears to form a "tangent- plane" to the solid catalyst core with the liquid shell wetting and occupying the interstice between the catalyst and the nanowire. In Ni xPy assisted growth, nanowire diameters occurred as small as 12.3 nm, some of the thinnest yet reported TiO2 nanowires resulting from atmospheric-pressure chemical vapor deposition (APCVD) growth. © The Royal Society of Chemistry 2013.

Very thin films deposited using atomic layer deposition (ALD) on aluminum mirrors showed extraordinary resistance toward concentrated alkali solutions, various chemical etchants, and solvents. Aluminum mirrors with no surface protection dissolved immediately in 24% aqueous KOH. Mirrors protected with 30 nm electron-beam deposited silica film were fully removed in 30 min. Mirrors with 10, 30, and 120 nm films grown by ALD required, respectively, 10, 15, and 60 h of exposure to the alkali for the mirror to be fully removed. Likewise, large-scale hydrogen bubbling was observed immediately upon immersing mirrors coated with electron-beam deposited silica in aqueous KOH, whereas no visible hydrogen bubbling was detected for the mirror protected by ALD silica. For mirrors protected by 120 nm ALD silica, a 2 h soak in various acid and solvent media produced no discernible change. OCIS codes: 310.1515, 310.1860, 240.0310, 160.6030.

The development of low-cost, stable, and robust electrocatalysts for the hydrogen evolution reaction (HER) is significantly indispensable and is of urgent need for electrocatalytic water splitting and clean energy. Herein, a hydrothermal and phosphorization approach is reported for the construction of a sandwich Ti3C2Tx/MoS2−xPx heterostructure, in which ultrathin MoS2 nanosheets doped with P are vertically grown on a 2D layered Ti3C2Tx MXene. The as-prepared Ti3C2Tx/MoS2−xPx heterostructure delivers outstanding activity for the HER, affording a low overpotential of 157 mV at 10 mA cm−2, as well as superior long-term durability with a negligible attenuation after 2000 CV cycles and constant activity after the chronoamperometric test. An excellent HER performance is induced by ultrathin MoS2 nanosheets, which bring abundant active sites to accelerate mass transport. Furthermore, the sandwich heterostructure shows an abundant interface and a 3D porous network, which can facilitate electron transfer capability and promote the contact of electrolytes. In addition, P doping provides good conductivity and has appropriate adsorption and desorption energy for the H intermediate. This work enriches the catalyst family and presents an alternative and efficient route to accelerate the hydrogen activity of non-noble metal catalysts. [ABSTRACT FROM AUTHOR]