Visible-light-enhanced catalytic oxidation reactions on plasmonic silver nanostructures

In-situ plasmon-driven chemical reactions revealed by high vacuum tip-enhanced Raman spectroscopy

With strong surface plasmons excited at the metallic tip, tip-enhanced Raman spectroscopy (TERS) has both high spectroscopic sensitivity and high spatial resolution, and is becoming an essential tool for chemical analysis. It is a great challenge to combine TERS with a high vacuum system due to the poor optical collection efficiency. We used our innovatively designed home-built high vacuum TERS (HV-TERS) to investigate the plasmon-driven in-situ chemical reaction of 4-nitrobenzenethiol dimerizing to dimercaptoazobenzene. The chemical reactions can be controlled by the plasmon intensity, which in turn can be controlled by the incident laser intensity, tunneling current and bias voltage. The temperature of such a chemical reaction can also be obtained by the clearly observed Stokes and Anti-Stokes HV-TERS peaks. Our findings offer a new way to design a highly efficient HV-TERS system and its applications to chemical catalysis and synthesis of molecules, and significantly extend the studies of chemical reactions.

Molecular thinking for nanoplasmonic design

The development of nanoplasmonics has been tremendous during the past two decades, driven in part by the improvements in colloidal synthesis of nanocrystals and manipulation of nanoparticle surface functionalities. This has granted access not only to exquisite control over the morphology of nanoparticles but also to novel multiparticle nanostructures with a variety of organizational motifs. Driven by such new possibilities, completely unforeseen plasmonic effects have been found, which let us think about applications in a variety of fields. In this Perspective, we discuss the evolution of plasmonic nanomaterials and their corresponding properties and correlations with molecular concepts that have been around for a long time. Additional thinking along these lines may lead to further expansion of nanoplasmonics and to multiple surprising discoveries in this field.

Topotaxial fabrication of vertical Aux Ag1-x nanowire arrays: plasmon-active in the blue region and corrosion resistant

Topotaxial growth of Au(x) Ag(1-x) alloy nanowires (NWs) by postepitaxial deposition of Ag vapor on Au NWs and investigation of their plasmonic properties are reported. Ag vapor is supplied onto the epitaxially grown Au NWs, topotaxially turning them into Au(x) Ag(1-x) alloy NWs. The original geometries and alignments of the Au nanostructures are well preserved, while the composition of the alloy NWs is controlled by varying the Ag vapor supply time. The Au(0.5) Ag(0.5) NWs show high surface-enhanced Raman scattering (SERS) activity comparable to that of Ag NWs as well as highly increased oxidation resistance. The plasmon-active wavelength range of the Au(0.5) Ag(0.5) NW is significantly extended to the blue region compared to Au NWs. The Au(x) Ag(1-x) alloy NWs that have plasmonic activity in the blue region in addition to high corrosion resistance will make a superb material for practical plasmonic devices including SERS sensors and optical nanoantennas.

Mangrove Streptomyces sp. BDUKAS10 as nanofactory for fabrication of bactericidal silver nanoparticles

Biosynthesis has led to the development of various biomimetic approaches for the fabrication of nanoscale materials. The present study reveals a unique procedure for the biosynthesis of bactericidal silver nanoparticles (AgNPs) using a novel Streptomyces sp. BDUKAS10, an isolate of mangrove sediment. Aqueous silver nitrate (AgNO(3)) solution was treated with cell free supernatant (CFS) of the isolate to synthesize bactericidal silver nanoparticles. Initial characterization was performed by visual observation for color change to intense brown color. UV-visible spectrophotometry (UV-vis) for measuring surface plasmon resonance indicated a maximum absorption peak at 441 nm. Fourier Transform Infrared Spectroscopy (FTIR) analysis provides evidence for proteins as possible reducing, and capping agents. Energy dispersive X-ray (EDAX) spectroscopy analysis showed elemental silver as major signal. Transmission Electron Microscopy (TEM) study indicated spherical silver nanoparticles in the size range of 21-48 nm. Compared to the CFS, the biosynthesized AgNPs exemplified superior bactericidal efficacy towards the tested bacterial strains. Results from this study suggested that Streptomyces sp. BDUKAS10 can be advantageous for the synthesis of AgNPs by extracellular method in the view of sustainable and ecofriendly approach.

Nano Pinstripes: TiO2 Nanostripe Formation by Nanoparticle-Mediated Pinning of Step Edges

The present scanning tunneling microscopy study describes the high-temperature growth of TiO2 nanostripes with tunable width, orientation, and spacing, mediated by thermally stable micellar Pt and Au NPs deposited on TiO2(110). This phenomenon could not be explained by spillover effects but is based on the preferential stabilization of [11̅0] step edges on TiO2(110) by the metal NPs. Contrary to the behavior of physical-vapor-deposited NPs, which are known to move toward step edges upon annealing, our micellar NPs remain immobile up to 1000 °C. Instead, the mobility of TiO2 step edges toward the micellar NPs, where they become stabilized, is observed. Our findings are relevant to the technological application of nanostructured materials in the fields of catalysis, molecular electronics, and plasmonics.

Synthesis of silver nanoparticles by solar irradiation of cell-free Bacillus amyloliquefaciens extracts and AgNO3

Silver nanoparticles (AgNPs) were obtained by solar irradiation of cell-free extracts of Bacillusamyloliquefaciens and AgNO3. Light intensity, extract concentration, and NaCl addition influenced the synthesis of AgNPs. Under optimized conditions (solar intensity 70,000 lx, extract concentration 3 mg/mL, and NaCl content 2 mM), 98.23±0.06% of the Ag+ (1 mM) was reduced to AgNPs within 80 min, and the ζ-potential of AgNPs reached -70.84±0.66 mV. TEM (Transmission electron microscopy) and XRD (X-ray diffraction) analysis confirmed that circular and triangular crystalline AgNPs with mean diameter of 14.6 nm were synthesized. Since heat-inactivated extracts also mediated the formation of AgNPs, enzymatic reactions are likely not involved in AgNPs formation. A high absolute ζ-potential value of the AgNPs, possibly caused by interaction with proteins likely explains the high stability of AgNPs suspensions. AgNPs showed antimicrobial activity against Bacillussubtilis and Escherichiacoli in liquid and solid medium.

Plasmonic-metal nanostructures for efficient conversion of solar to chemical energy

Recent years have seen a renewed interest in the harvesting and conversion of solar energy. Among various technologies, the direct conversion of solar to chemical energy using photocatalysts has received significant attention. Although heterogeneous photocatalysts are almost exclusively semiconductors, it has been demonstrated recently that plasmonic nanostructures of noble metals (mainly silver and gold) also show significant promise. Here we review recent progress in using plasmonic metallic nanostructures in the field of photocatalysis. We focus on plasmon-enhanced water splitting on composite photocatalysts containing semiconductor and plasmonic-metal building blocks, and recently reported plasmon-mediated photocatalytic reactions on plasmonic nanostructures of noble metals. We also discuss the areas where major advancements are needed to move the field of plasmon-mediated photocatalysis forward.

Selective sulfuration at the corner sites of a silver nanocrystal and its use in stabilization of the shape

This paper describes a new approach to site-selective sulfuration at the corner sites of Ag nanocrystals including triangular nanoplates and nanocubes. The reaction simply involved mixing an aqueous suspension of the Ag nanocrystals with an aqueous solution of polysulfide at room temperature. As a precursor to elemental S, polysulfide is highly soluble in water and can directly react with elemental Ag upon contact to generate Ag(2)S in the absence of oxygen. The reaction was easily initiated at the corner sites and then pushed toward the center. By controlling the reaction time and/or the amount of polysulfide added, the reaction could be confined to the corner sites only, generating Ag-Ag(2)S hybrid nanocrystals with greatly improved stability against aging at 80 and 100 °C in air than their counterparts made of pure Ag.