Homogeneously-Alloyed Au-Ag Nanoparticles as per Feeding Moles
Ranguwar Rajendra,§ Parnika Bhatia,‡ Anita Justin,§ Shilpy Sharma‡ and Nirmalya Ballav*§
§
Department of Chemistry, Indian Institute of Science Education and Research (IISER), Pashan, Pune – 411008
‡
Department of Biotechnology, Savitribai Phule Pune University, Ganeshkhind, Pune – 411007
Figure S1. UV-vis absorption spectra were recorded after reduction of Ag+ ions in AgCl (blue curve) and Ag(NH3)+
(AgCl precipitate was treated with NH4OH) (red curve) solutions by NaBH4 in presence of Na3Ct. Blue curve indicates
very minute amount of Ag+ ions were reduced to Ag NPs (NaBH4 could not reduce AgCl). Red curve indicates
complete reduction of Ag(NH3)+ to Ag NPs. (Inset: optical images of the corresponding solutions).
Figure S2. UV-vis absorption spectra for Au NPs, Au-Ag (50:50) alloy NPs and Ag NPs synthesized in presence of
excess amount of CH3NH2 ( Inset: optical images for the corresponding samples.)
Figure S3. UV-vis absorption spectra (Normalized) for Au NPs, Au-Ag (75:25; 50:50; 25:75) alloy NPs and Ag
NPs synthesized in presence of (a) polyvinylpyrrolidone, (b) polyethyleneglycol, (c) cyclodextrin and (d)
glucose as stabilizers. Optical images for the respective samples are shown above the spectra.
Figure S4. UV-vis spectra were recorded for the samples made of mixing the as synthesized pure Au (100%)
and Ag (100%) NPs with varying their respective quantities while total volume of each solution kept constant.
Figure S5. (a) TEM image of the Au-Ag alloy NPs prepared without using NH4OH (initial feeding mole ratio of
HAuCl4 to AgNO3 was 1:1). (b) A high-resolution image of a single particle. (c) SAED pattern.
Figure S6. UV-vis absorption spectra for Au NPs, Au-Ag (75:25; 50:50; 25:75) alloy NPs and Ag NPs synthesized
with the help of hydrazine (NH2NH2) as reducing agent – instead of NaBH4. Inset: optical images for the
corresponding samples.
Figure S7. FESEM images and EDXS data collected on the ensembles of 1:3 (a, d), 1:1 (b, e) and 3:1 (c, f)
Au-Ag alloy NPs prepared with using NH4OH. Notably, the EDXS data on the elemental ratio of Au:Ag
matched very closely to the initial feeding mole ratio of HAuCl4 to AgNO3.
Figure S8. A graphical summary on the correlation of feeding moles of Au and Ag with the elemental compositions
of Au and Ag in three batches (Each batch consists of 7 different alloy compositions) of Au-Ag alloy compositions.
Table S1. EDXS data on Batch 1 samples of seven different alloy compositions along with feeding % of Ag.
Table S2. EDXS data on Batch 2 samples of seven different alloy compositions along with feeding % of Ag.
Table S3. EDXS data on Batch 3 samples of seven different alloy compositions along with feeding % of Ag.
Figure S9. FESEM images and EDXS data collected on the ensembles of Au-Ag alloy NPs prepared without
using NH4OH. Notably, the EDXS data on the elemental ratio of Au:Ag is not at all matching with the initial
feeding mole ratio of HAuCl4 to AgNO3.
Figure S10. PXRD patterns of Au-Ag alloy NPs prepared with an initial feed of 1:3 (Au:Ag) in absence of NH4OH.
Green arrows indicate the impurity peaks characteristic of Ag2O and/or AgCl.
Figure S11. FESEM images of Ag NPs, seven different Au-Ag alloy NPs and Au NPs. Each image is labelled with
size distribution plot, number of particles analyzed and average size. Specifically the Au-Ag alloy NPs were sub-10nm.
Table S4. Analytical enhancement factors (AEFs) of NPs. Area under the curve has been estimated from Lorentzian
fit of Raman signal (ISERS) and CSERS represents analyte concentration.
Figure S12. Plot of optical density values of various NPs solutions as a function of the mole fraction of Au. The
experimental data points (blue spheres) can be best fitted exponentially (red line). Such a plot is a figure of merit for
the extinction coefficient values for various systems of NPs.
Figure S13. Catalytic conversion of p-nitrophenol to p-aminophenol in presence of Au-Ag alloy NPs prepared
without the use of NH4OH.
Figure S14. UV-vis spectra revealing the vanishing of characteristic Au--Cl metal-to-ligand charge-transfer band
(highlighted by grey shade) upon addition of NH4OH to the aqueous solution of HAuCl4 (inset: visible colorimetric
change in higher concentration).
Figure S15. UV-vis absorption spectra for Au NPs prepared in presence (blue) and absence (red) of excess of
NH4OH. With the use of NH4OH, maybe it leads to the formation of sub-3 nm particles which are not stabilized and
got settle down after 3 min; and the UV-vis spectrum was measured for the clear solution (upper part).
Figure S16. Schematic representation of ‘homogeneous-alloying’ concept of Au and Ag in fcc-lattice (golden sphere
is Au and grey sphere is Ag)
Figure S17. UV-vis absorption spectra of Au-Ag alloy NPs and of pure Au and Ag NPs, collected before and after
one hour of treatment with H2O2+NH4OH.
Table S5. Change in the SPR peak position of Au-Ag alloy NPs after one hour of treatment with H2O2+NH4OH
mixture.
Figure S18. UV-vis absorption spectra (before and after one hour of treatment with H2O2+NH4OH) of Au-Ag alloy
NPs having Ag concentration in the range of 80-95%.
Table S6. Change in the SPR peak position of Au-Ag alloy NPs with Ag concentration in the range of 80-95% after
one hour of treatment with H2O2+NH4OH mixture.