Selective growth of Ag nanodewdrops on Au nanostructures: a new type of bimetallic heterostructure

Probing Chemical-Composition-Induced Heterostructures and Interfaces in Lead Halide Perovskites

Lead halide perovskites (LHP) are of great interest for their optoelectronic properties and photovoltaic applications. Various heterostructures are created in these materials to achieve favorable optical properties and improved stability at the interfaces during the fabrication of devices. Such heterostructures are often assumed to be formed based on the reactivity of precursors and are not directly probed. In this Feature Article, we report how various strategies have been employed in LHP thin films and nanocrystals (NCs) that generate heterostructures to boost their stability and photovoltaic (PV) efficiencies and how variable energy photoelectron spectroscopy (VEPES) can probe the chemical composition variation in heterostructured materials and interfaces. We specifically discussed the internal heterostructures of LHP NCs generated due to the surface chemistry and postsynthesis anion exchange followed by a detailed discussion of the heterostructures induced by the chemical composition (anion, cation, and degradation) of LHP thin films. The difficulties in determining heterostructures as well as the potential scope of the application of VEPES in unwrapping heterostructures in diverse materials are also discussed.

Sunlight-assisted route to antimicrobial plasmonic aminoclay catalysts

We present a straightforward, environmentally-benign, one-pot photochemical route to generate alloyed AgAu bimetallic nanoparticle decorated aminoclays in water at room temperature. The protocol uses no reducing agent (e.g., NaBH4) nor is photocatalyst required. These hybrid materials show excellent promise as dual catalysts/antibacterial agents.

Novel formation of Ag/Au bimetallic nanoparticles by physical mixture of monometallic nanoparticles in dispersions and their application to catalysts for aerobic glucose oxidation

Ag/Au bimetallic nanoparticles (BNPs) with a size less than 2 nm were prepared by physical mixture of colloidal dispersions of Ag and Au nanoparticles (NPs). This provides an example of fabrication of BNPs with self-organization by the reaction between metal NPs. Although Ag/Au BNPs having different structures and compositions are one of the most widely studied bimetallic systems in the literature due to their wide range of uses such as in catalysis, electronics, plasmonics, optical sensing, and surface-enhanced Raman scattering, we first prepared such BNPs by physical mixture and characterized them by UV-vis spectroscopy, SERS, XPS, TEM, and EDS in HR-STEM. The present fabrication method has the advantage of avoiding the unfavorable formation of AgCl precipitates in the reaction process which are always produced when Ag(+) ions are used as a starting material in combination with a HAuCl4 precursor. These Ag/Au BNPs showed high catalytic activities for aerobic glucose oxidation, and the highest activity of 11,510 mol of glucose·h(-1)·mol of metal(-1) was observed for the BNPs with a Ag/Au atomic ratio of 1/4; the activity value is about 2 times higher than that of Au NPs with nearly the same particle size. XPS and DFT calculation results show that the negatively charged Au atoms due to the electron charge transfer effects from neighboring Ag atoms and poly(N-vinyl-2-pyrrolidone) act as catalytically active sites and play an important role in the aerobic glucose oxidation.

Gold nanoparticles assembling on smooth silver spheres for surface-enhanced Raman spectroscopy

A simple and cost-effective chemical method was introduced to assemble gold (Au) nanoparticles on smooth silver (Ag) spheres for realizing surface-enhanced Raman scattering (SERS) enhancement by the replacement reaction between chloroauric acid and Ag spheres. In addition, the Ag-Au core-shell spheres were fabricated when a certain amount of chloroauric acid was used in the reaction solution. We found that the Ag particles decorated with small Au nanoparticles demonstrated the strongest SERS enhancement, while Ag-Au core-shell spheres showed the weakest enhancement.

Signal-enhanced electrochemiluminescence immunosensor based on synergistic catalysis of nicotinamide adenine dinucleotide hydride and silver nanoparticles

A new metal-organic nanocomposite with synergistic catalysis function was prepared and developed to construct an electrochemiluminescence (ECL) immunosensor for ultrasensitive detection of tumor biomarker CA125. Silver nanoparticles (AgNPs) and nicotinamide adenine dinucleotide hydride (NADH) that can participate and catalyze the ECL reaction of Ru(bpy)(3)(2+) were employed as the metal component and the organic component to synthesize the metal-organic nanocomposite of NADH-AgNPs (NA). The novel ECL immunosensor was assembled via Ru(bpy)(3)(2+)-doped silica nanoparticles (Ru-SiO(2)) modified electrode with the NA as immune labels. First, the chitosan-suspended Ru-SiO(2) nanoparticles were cast on the gold electrode surface to immobilize the ECL probes of Ru(bpy)(3)(2+) and link gold nanoparticles. Then, the primary antibodies were loaded onto the modified electrode via the gold sulfhydryl covalent binding. After immunobinding the analytes of antigen, NA-attached secondary antibodies could be captured as a sandwich type on the electrode. Finally, based on the circularly synergistic catalysis by the silver and NADH for the solid-phase ECL of Ru(bpy)(3)(2+), the proposed immunosensor sensed the concentration of antigen. The synergistic ECL catalysis of metal-organic nanocomposite amplified response signal and pushed the detection limit down to 0.03 U ml(-1), which initiated a new ECL labeling field and has great significance for ECL immunoassays.

Surface-enhanced Raman scattering imaging of a single molecule on urchin-like silver nanowires

Urchin-like silver nanowires are prepared by reacting AgNO(3)(aq) with copper metal in the presence of cetyltrimethylammonium chloride and HNO(3)(aq) on a screen-printed carbon electrode at room temperature. The diameters of the nanowires are about 100 nm, and their lengths are up to 10 μm. Using Raman spectroscopy, the detection limit of Rhodamine 6G (R6G) on the urchin-like silver nanowire substrate can be as low as 10(-16) M, while the analytical enhancement factor is about 10(13). Raman mapping images confirm that a single R6G molecule on the substrate can be detected.

Nanoporous bimetallic Pt-Au alloy nanocomposites with superior catalytic activity towards electro-oxidation of methanol and formic acid

We present a facile route to fabricate novel nanoporous bimetallic Pt-Au alloy nanocomposites by dealloying a rapidly solidified Al(75)Pt(15)Au(10) precursor under free corrosion conditions. The microstructure of the precursor and the as-dealloyed sample was characterized using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy, and energy dispersive X-ray (EDX) analysis. The Al(75)Pt(15)Au(10) precursor is composed of a single-phase Al(2)(Au,Pt) intermetallic compound, and can be fully dealloyed in a 20 wt.% NaOH or 5 wt.% HCl aqueous solution. The dealloying leads to the formation of the nanoporous Pt(60)Au(40) nanocomposites (np-Pt(60)Au(40) NCs) with an fcc structure. The morphology, size and crystal orientation of grains in the precursor can be conserved in the resultant nanoporous alloy. The np-Pt(60)Au(40) NCs consist of two zones with distinct ligament/channel sizes and compositions. The formation mechanism of these np-Pt(60)Au(40) NCs can be rationalized based upon surface diffusion of more noble elements and spinodal decomposition during dealloying. Electrochemical measurements demonstrate that the np-Pt(60)Au(40) NCs show superior catalytic activity towards the electro-oxidation of methanol and formic acid in the acid media compared to the commercial JM-Pt/C catalyst. This material can find potential applications in catalysis related areas, such as direct methanol or formic acid fuel cells. Our findings demonstrate that dealloying is an effective and simple strategy to realize the alloying of immiscible systems under mild conditions, and to fabricate novel nanostructures with superior performance.