Chemistry Reference
In-Depth Information
2.5.
Materials characterization
The crystallographic information of as-synthesized materials was
investigated using powder X-ray diffraction technique (PAN analytical
X-ray BV diffractometer, Cu Kα radiation λ = 1.506 Ǻ at a scan rate of
2°
per minute). Scanning electron microscopy (ESEM, Quanta) was
employed to examine the morphology of the nanocomposites.
Electrochemical studies were carried out using a potentiostat (CH
Instruments, USA, Model CH 660A) in aqueous phosphate buffer with
saturated calomel reference electrode (SCE) and a large area Pt foil
counter electrode.
3. RESULTS AND DISCUSSION
Bimetallic and alloy surfaces, both in the planar and nanoparticulate
form, attract wide interest because of their distinctive properties that
distinguish them from their monometallic counter parts. Alloys
containing Au as one of their components are particularly interesting,
since Au, which is a very inert metal behaves quite differently when it is
in conjunction with another metal. The structure of Au-Ag bimetallic
nanoparticle has generated a lot of interest since both Au and Ag
have very similar lattice constants and are completely miscible
over entire composition range, forming homogeneous alloys in bulk
phase. Graphene and Au-Ag alloy composites are expected to possess
properties of both the components (graphene as well as alloy
counterparts) and hence these hybrid materials may have good features
for (electro)catalysis.
The absorption spectra (not shown) of graphene - Au-Ag alloys
of different compositions reveal only one surface plasmon band
corresponding to the particular alloy composition. The change in position
of the λ
max
depends on the composition and falls in between the surface
plasmon band positions of gold and silver. The reduced graphene oxide
shows an absorption band near 266 nm. However, a physical mixture of
individual colloids shows two surface plasmon bands corresponding to
the monometallic counter parts. Powder X-ray diffractommograms
(Fig. 1) of graphene-Au-Ag alloy nanocomposites show a peak around
