Synergistic effect of Au-Ag nano-alloying: Intense SEIRA and

Enhanced Catalysis

Manoj Verma, M.Boazbou Newmai, P. Senthil Kumar1*

Department of Physics & Astrophysics, University of Delhi, Delhi-110007, India

Supplementary Information:

d- values of different (hkl) planesNanoparticles

111 200 220 311

Average Crystallite

size (nm)

Au Nanoparticles 2.3489 2.0321 1.4355 1.2237 34.2

Ag Nanoparticles 2.3571 2.0432 1.4373 1.2248 28.2

ANP1 Nanoparticles 2.3515 2.0347 1.4354 1.2237 28.0

ANP2 Nanoparticles 2.3530 2.0361 1.4365 1.2242 23.1

ANP3 Nanoparticles 2.3544 2.0368 1.4367 1.2246 12.7

Table S1 Average crystallite size calculated for each type of nanoparticles synthesized by using

scherrer formula on most dominating <111> diffraction peak.

Electronic Supplementary Material (ESI) for Dalton Transactions.This journal is © The Royal Society of Chemistry 2017

Strain along different (hkl) planes ( x 10-3)

Type of

Nanoparticle

200111

220111

311111

111 200 220 311

Au 0.25 0.12 0.09 1.29 1.68 1.03 2.17

Ag 0.29 0.18 0.15 1.38 1.91 1.42 2.93

ANP1 0.27 0.16 0.11 1.57 1.88 2.19 2.99

ANP2 0.39 0.22 0.20 1.90 2.33 2.84 3.53

ANP3 0.46 0.30 0.28 3.45 3.90 4.51 4.92

Table S2 Illustrate the change in relative intensity ratio of high energy facets with <111> facets

for different synthesized nanoparticles

Nelson Riley function is given by

SE12 21 cos cos

2 sinF

For calculating “a” value precisely and free from systematic error using Nelson and Riley

function

SE22 21 cos cos

2 sina

a

Simplest mathematical expression for Vegard’s law in case of Au and Ag alloys can be written

as

SE30 0(1 ) ( )Au Aga a x a x

Where “x” is the mole fraction Ag and a0 is the lattice parameters of pure gold and silver

nanoparticles.

The dislocation density has been determined using the following expression

SE4a15 cos

4hkl

aD

This can be rewritten as

SE4b cos 4 /15hkl a D

Where lattice constant “a” used in this equation is taken from Nelson Riley approximation

method and D is the particle size obtained from Debye-Scherrer formula

% CompositionSample Lattice Constant “a”

Au Ag

Normalised Microstrain ε(*10-2)

Dislocation Densityδ (*1015 m-2)

Pure Au 4.05421 100 0 4.76 3.80Pure Ag 4.06752 0 100 7.13 6.46ANP1 4.05769 71.9 28.1 7.46 5.75ANP2 4.06041 51.8 48.2 8.30 8.22ANP3 4.06302 37.3 62.7 9.91 17.64

Table S3: Variation of dislocation density due to alloying process

Fig. S1 Plot of lattice constant vs Nilson Riley function, βcosθ vs D values and Microstrain Vs

Nilson Riley function for each samples with varying concentration of Au/Ag ratio.

Fig. S2 Size distribution histogram of different nanoparticles synthesized and their respective

average size calculation by Gaussian fitting of size histograms.(a) pure Au nanoparticle, size is

about 36 nm (b) pure Ag nanoparticle, size is about 30 nm (c) ANP1, size is about 28 nm(d)

ANP2, size is about 25 nm (e) ANP, size is about 18nm (f) size distribution graph of different

samples containing pure Au, pure Ag and alloy samples.

Fig. S3 Absorbance spectra of synthesized nanoparticles after formation, after 10 days of

formation and after heating them at 100o C for 1 hour.

Fig. S4 Absorbance spectra of alloy nanoparticles in low wavelength region. Low intensity of

absorbance in UV region shows the marginal effect of small size particles on colloid overall

absorbance.

Fig. S5 Plot between mean particle size and nucleation time revealing fast nucleation timegive

rise to comparatively large nanoparticles.

Fig. S6 shows decrease in polydispersity with increase in growth time.

Fig. S7 Plot of Tauc relation to find the optical band gap of synthesized nanoparticles with

different Au/Ag compositions.

Fig. S8 Determination of Urbach energy estimation, the slope on the linear region gives urbach

energy.

Fig. S9 Full range FTIR spectra of pure PVP and PVP adsorped on different nanoparticles

systems.

Fig. S10 Time dependent UV-visible absorption spectra of reduction of 4-NA by NaBH4 in

presence of different nanoparticles and their rate constants in first and second cycles of catalysis.