Abstract
We herein report a simple chemical route to prepare Au–Ag and Ag–Au core–shell bimetallic nanostructures by reduction of two kinds of noble metal ions in the presence of a water-soluble polymer such as poly(vinyl alcohol) (PVA). PVA was intentionally chosen as it can play a dual role of a supporting matrix as well as stabilizer. The simultaneous reduction of metal ions leads to an alloy type of structure. Ag(c)–Au(s) core–shell structures display tendency to form prismatic nanostructures in conjunction with nanocubes while Au(c)–Ag(s) core–shell structures show formation of merely nanocubes. Although UV–visible spectroscopy and X-ray photoelectron spectroscopy analyses of the samples typically suggest the formation of both Ag(c)–Au(s) and Au(c)–Ag(s) bimetallic nanostructures, the definitive evidence comes from high-resolution transmission electron microscopy–high-angle annular dark field elemental mapping in the case of Au(c)–Ag(s) nanomorphs only. The resultant nanocomposite materials are used to fabricate resistors on ceramic rods having two electrodes by drop casting technique. These resistors are examined for their relative humidity (RH) response in the range (2–93% RH) and both the bimetallic nanocomposite materials offer optimized sensitivity of about 20 Kohm/% RH and 300 ohm/% RH at low and higher humidity conditions, respectively, which is better than that of individual nanoparticles.
Highlights
Bimetallic nanoparticles have emerged as an increasingly important research area, because of their interesting catalytic, electronic and optical properties which are quite distinct from those of the corresponding monometallic counterparts [1,2,3,4,5,6]
In order to acquire high imaging resolution and spatial resolution for atom to atom chemical mapping of the material, we employed high-resolution transmission electron microscopy equipped with a high-angle annular dark-field detector (STEMHAADF) and electron energy loss spectroscopy (EELS) elemental mapping using a JEOL, JEM ARM200F operated at 200 kV with spherical aberration corrector
The most salient aspect of our work is the synthesis of prismatic nanostructures of Ag(c)–Au(s) core–shell with such a simple method
Summary
Bimetallic nanoparticles have emerged as an increasingly important research area, because of their interesting catalytic, electronic and optical properties which are quite distinct from those of the corresponding monometallic counterparts [1,2,3,4,5,6]. Several types of core–shell nanostructures, such as heterogeneous metal/metal [7,8,9], metal/semiconductor [10,11,12], metal/polymer and other combinations [13,14,15,16], have been explored hitherto Among such systems, noble metal core–shell nanostructures have received a lot of attention due to their fascinating optical and electronic properties. We report a simple chemical route for the synthesis of Au(c)– Ag(s) and Ag(c)–Au(s) core–shell bimetallic nanocubes and nanoprisms in PVA matrix. These core–shell nanocomposites when tested for humidity sensing applications disclosed better sensitivity than that of the individual monometallic nanoparticles
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