DNA Origami Directed Au Nanostar Dimers for Single-Molecule Surface-Enhanced Raman Scattering

We demonstrate the synthesis of Au nanostar dimers with tunable interparticle gap and controlled stoichiometry assembled on DNA origami. Au nanostars with uniform and sharp tips were immobilized on rectangular DNA origami dimerized structures to create nanoantennas containing monomeric and dimeric Au nanostars. Single Texas red (TR) dye was specifically attached in the junction of the dimerized origami to act as a Raman reporter molecule. The SERS enhancement factors of single TR dye molecules located in the conjunction region in dimer structures having interparticle gaps of 7 and 13 nm are 2 × 10¹⁰ and 8 × 10⁹, respectively, which are strong enough for single analyte detection. The highly enhanced electromagnetic field generated by the plasmon coupling between sharp tips and cores of two Au nanostars in the wide conjunction region allows the accommodation and specific detection of large biomolecules. Such DNA-directed assembled nanoantennas with controlled interparticle separation distance and stoichiometry, and well-defined geometry, can be used as excellent substrates in single-molecule SERS spectroscopy and will have potential applications as a reproducible platform in single-molecule sensing

Core-Size-Dependent Catalytic Properties of Bimetallic Au/Ag Core–Shell Nanoparticles

Bimetallic core–shell nanoparticles have recently emerged as a new class of functional materials because of their potential applications in catalysis, surface enhanced Raman scattering (SERS) substrate and photonics etc. Here, we have synthesized Au/Ag bimetallic core–shell nanoparticles with varying the core diameter. The red-shifting of the both plasmonic peaks of Ag and Au confirms the core–shell structure of the nanoparticles. Transmission electron microscopy (TEM) analysis, line scan EDS measurement and UV–vis study confirm the formation of core–shell nanoparticles. We have examined the catalytic activity of these core–shell nanostructures in the reaction between 4-nitrophenol (4-NP) and NaBH₄ to form 4-aminophenol (4-AP) and the efficiency of the catalytic reaction is found to be increased with increasing the core size of Au/Ag core–shell nanocrystals. The catalytic efficiency varies from 41.8 to 96.5% with varying core size from 10 to 100 nm of Au/Ag core–shell nanoparticles, and the Au₁₀₀/Ag bimetallic core–shell nanoparticle is found to be 12-fold more active than that of the pure Au nanoparticles with 100 nm diameter. Thus, the catalytic properties of the metal nanoparticles are significantly enhanced because of the Au/Ag core–shell structure, and the rate is dependent on the size of the core of the nanoparticles

Intrinsic Specific Activity Enhancement for Bifunctional Electrocatalytic Activity toward Oxygen and Hydrogen Evolution Reactions via Structural Modification of Nickel Organophosphonates

A comprehensive knowledge of the structure–activity relationship of the framework material is decisive to develop efficient multifunctional electrocatalysts. In this regard, two different metal organophosphonate compounds, [Ni(Hhedp)2]·4H2O (I) and [Ni3(H3hedp)2(C4H4N2)3]·6H2O (II) have been isolated through one-pot hydrothermal strategy by using H4hedp (1-hydroxyethane 1,1-diphosphonic acid) and N-donor auxiliary ligand (pyrazine; C4H4N2). The structures of synthesized materials have been established through single-crystal X-ray diffraction studies, which confirm that compound I formed a one-dimensional molecular chain structure, while compound II exhibited a three-dimensional extended structure. Further, the crystalline materials have participated as efficient electrocatalysts for the oxygen evolution and hydrogen evolution reactions (OER and HER) as compared to the state-of-the-art electrocatalyst RuO2. The electrocatalytic OER and HER performances show that compound II displayed better electrocatalytic performances toward OER (η10 = 305 mV) and HER (η10 = 230 mV) in alkaline (1 M KOH) and acidic (0.5 M H2SO4) media, respectively. Substantially, the specific activity has been assessed in order to measure the inherent electrocatalytic activity of the title electrocatalyst, which displays an enrichment of fourfold higher activity of compound II (0.64 mA/cm2) than compound I (0.16 mA/cm2) for the OER experiments. Remarkably, inclusion of an auxiliary pyrazine ligand into the metal organophosphonate structure (compound II) not only offers higher dimensionality along with significant enhancement of the overall bifunctional electrocatalytic performances but also improves the long-term stability, which is noteworthy for the family of hybrid framework materials

Electrochemical Oxygen Evolution Catalyzed by Zn_0.76Co_0.24S‑Enriched ZnCo₂S₄/ZnCr₂O₄ Nanostructures

Finding a suitable replacement for expensive and scarce precious metal electrocatalysts for the oxygen evolution reaction (OER) remains a challenging task. There is a need to research highly efficient and long-lasting catalysts based on transition metals that are readily available on Earth for electrochemical oxygen evolution. In this study, zinc cobalt sulfide (ZnCo2S4) was derived by hydrothermal treatment of metal salt precursors and thioacetamide, followed by calcination at 700 °C for ZnCr2O4 to create a ZnCo2S4/ZnCr2O4 composite nanostructure enriched with Zn0.76Co0.24S. The electrochemical performance of the composition-dependent ZnCo2S4/ZnCr2O4 nanostructure enriched with Zn0.76Co0.24S was then tested along with its constituents, and it was found that the OER activity is not linearly proportional to the composition. We also evaluated the OER activity at pH 7.0 in a neutral medium and the OER electrochemical performance in an alkaline medium. Zn–Co–S is preferable to Zn- and Cr-based thio-spinel as it increases electronic conductivity and decreases charge transfer resistance. Both of these properties are necessary for generating the high oxidative valency of Co species during the OER process. The material’s unique composition and remarkable stability make it highly desirable for future research in this field

Europium Molybdate/Molybdenum Disulfide Nanostructures with Efficient Electrocatalytic Activity for the Hydrogen Evolution Reaction

The design of hybrid nanostructures of molybdenum disulfide (MoS2) has been extensively explored as potent electrocatalysts for hydrogen generation reactions. Here, we report the in situ synthesis of a nanocomposite containing europium molybdate [Eu2(MoO4)3] and molybdenum disulfide (MoS2) for an enhanced electrochemical hydrogen evolution reaction (HER). The characteristic X-ray diffraction (XRD) peaks of both 2H–MoS2 and α-Eu2(MoO4)3 confirm the formation of the nanocomposite. The nanoflower (NF) architecture of MoS2 coupled with flakes of europium molybdate is observed in the transmission electron microscopy (TEM) and scanning electron microscopy (SEM) images, which lead to an enhanced surface area of the nanocomposite. Raman and X-ray photoelectron spectroscopy (XPS) studies reveal a variation in the layer thickness of MoS2 and a significant interfacial electronic interaction between Eu2(MoO4)3 and MoS2. As evident from the small onset potential of −0.05 V vs reversible hydrogen electrode (RHE) and a lower overpotential value of 186 mV (at a current density of 10 mA/cm2), the nanocomposite outperforms pristine MoS2 nanoflowers in terms of electrocatalytic HER. The charge-transfer resistance of the nanocomposite (80.02 Ω) is significantly low compared to pristine MoS2 (158.37 Ω), thus confirming the enhanced interfacial charge transfer. The Tafel slope value of the nanocomposite (189 mV/dec) is notably less than that of pristine MoS2 (313 mV/dec), indicating the enhanced HER activity of the nanocomposite. The fabrication of lanthanide-containing MoS2 nanocomposites appears to be promising for an efficient electrocatalytic activity for the hydrogen evolution reaction