Hye Hun Park
1
, Kyoungja Woo
1
*, and Jae-Pyoung Ahn
2
1
Molecular Recognition Research Center,
2
Advanced Analysis Center, Korea Institute of Science and
Technology, P. O. Box 131, Cheongryang, Seoul 130-650 (Korea)
*E-mail: kjwoo@kist.re.kr
EXPERIMENTAL SECTION
Materials : Ammonium hydroxide aqueous solution (28~30%), Sodium borohydride (NaBH
4
, 98+%),
Sodium hydroxide (NaOH, >93.0%), Sodium citrate tribasic dihydrate (Na
3
Cit·2H
2
O, > 99.0
%),
Tetraethylorthosilicate (TEOS, 98%), hydrogen tetrachloroaurate(
Ⅲ
) trihydrate (HAuCl
4
·3H
2
O,
99.9+%), silver nitrate (AgNO
3
, >99.0%), iron (
Ⅲ
) chloride (FeCl
3
, 97%), palladium chloride(
Ⅱ
) (PdCl
2
,
99%), formaldehyde solution (37% in water), L-ascorbic acid, ( 3-aminopropyl)trimethoxysilane (APS,
97%), p -nitrophenol (Nip, >99%), and tetrakis(hydroxymethyl)phosphonium chloride (THPC, 80% solution in water) were used as purchased.
1

Synthesis of AP-MSM (Fe
3
O
4
– SiO
2
core – shell structured magnetic silica sub-microsphere with aminopropyl moiety) : The superparamagnetic Fe
3
O
4
core (~300 nm) was synthesized by a solvothermal reaction at 200 ° C from the mixture of 0.65 g (4.0 mmol) FeCl
3
, 0.20 g (0.68 mmol)
Na
3
Cit ·2H
2
O
, and 1.2 g (8.8 mmol) sodium acetate·3H
2
O in
20 mL of ethylene glycol as reported in reference 1. The resultant Fe
3
O
4
core was dispersed in 20 mL of ethanol and encapsulated with silica using St öber process. Typically, 5 mL of the Fe
3
O
4
core in ethanol was diluted to 500 mL and then, 50 mL of de-ionized water (DW), 15 mL of aqueous ammonia, and 0.225 g of Na
3
Cit ·2H
2
O
were added and stirred with a mechanical stirrer at room temperature. After 1 hr, 22.5 mL of TEOS was injected to the reaction mixture and stirred for 12 hr. The obtained Fe
3
O
4
– SiO
2
was purified with ethanol and water for at least 5 times using centrifugation and magnetic decantation and then, dispersed in 20 mL of ethanol (MSM solution). To this solution, 80 mL of ethanol, 3 mL of aqueous ammonia, 3 mL of DW, and 0.011 mL of APS were added in turn and the mixture was stirred for 12 hr with a mechanical stirrer at room temperature. At the end of the reaction, the AP-functionalized Fe
3
O
4
– SiO
2
(AP-MSM) was purified with ethanol using magnetic decantation five times and dispersed in 20 mL of ethanol for further reactions (AP-MSM stock solution containing 5.68
 10 10 particles/mL). 1 mL portion was fully dried, yielding 0.010 g/mL AP-MSM. Most of the AP-MSM sample was attracted to an external magnet outside the vial within 1 min. The TEM images of Fe
3
O
4
core, MSM, and AP-MSM are displayed in Fig.
S1 and Fig. 1a.
Calculation of the number of MSM particles : We have utilized the number of SiO
2
shell to estimate the number of MSM particles, where the two numbers should match in theory. The number of SiO
2
shell was calculated from the weight difference (0.117 g when dried from 20 mL solution) before and after silica encapsulation, mean diameter of MSM = 500 nm, mean thickness of silica shell = 100 nm, and porous amorphous silica density = 2.0 g/cm 3 as follows, assuming Fe
3
O
4
core and MSM are spherical.
The number of MSM particles (in 1 mL solution)
2

= weight difference before and after silica encapsulation/weight of single silica shell
= 0.117g/(20mL)(4/3)
π(r after
3
- r before
3
)d
= 0.117/2.06
 10 -12 mL
= 5.68
 10 10 /mL
Synthesis of Au seeds: 1~2 nm sized gold seeds were synthesized by using THPC as a reducing reagent according to reference 2 and 3. More specifically, 5 mL of NaOH (0.1 M), 0.012 mL of THPC (80% in water), and 2 mL of HAuCl
4
·3H
2
O (1 wt/v %) were added to the 45 mL of DW. The mixture was stirred for 30 min with a magnetic stirrer. The resultant Au seeds were used without further purification.
References
1.
Liu, J. et al. Highly water-dispersible biocompatible magnetite particles with low cytotoxicity stabilized by citrate groups. Angew. Chem., Int. Ed.
48, 5875-5879 (2009).
2.
Duff, D. G. & Baiker, A. A new hydrosol of gold clusters. 1. Formation and particle size variation. Langmuir 9, 2301-2309 (1993).
3.
Duff, D. G. & Baiker, A. A new hydrosol of gold clusters. 2. A comparison of some different measurement techniques. Langmuir 9, 2310-2317 (1993).
3

a b
Figure S1. TEM images of (a) superparamagnetic Fe
3
O
4
core
and (b)
Fe
3
O
4
–SiO
2
core–shell (
MSM).
MSM nM@MSM a few APs
M n+
Reduction nAg@MSM nAu@MSM nPd@MSM
Figure S2. TEM images of Ag, Au and Pd nanoparticles directly grown from AP-MSM without Au seeding process.
4

d1 d2 d3 e1 e2 e3 f1 f2
Figure S3. Size distributions histograms of the nanoparticles on the dn , en , and fn samples (d = average
±
standard deviation).
5

a b
Figure S4. TEM images showing coalescence of self-assembled Au seeds (left) to Au cores (right) upon addition of (a) Ag
+
and (b) Pd
2+
solution.
6

d2
Figure S5. SEM and TEM image of nAg/Au@MSM ( d2 ). e1 e2
Figure S6. SEM and TEM images of nAu/Au@MSM ( en ).
7 e3

f1 f2
Figure S7. SEM and TEM images of nPd/Au@MSM ( fn ). f3
8

Figure S8. EDS data of nAg/Au@MSM ( d2 ), nAu/Au@MSM ( e2 ), and nPd/Au@MSM ( f2 ).
(a)
(b)
Figure S9. TEM (a), HRTEM (inset of a), and Z-contrast HAADF-STEM (b) image of Au – Ag bimetallic nanoparticles torn down from nAg/Au@MSM ( d2 ).
9

a b1 c b5 c5
Figure S10. Extinction spectra at every 2 min for the reaction of p -nitrophenol with NaBH
4
(a) without composite system and with (b1 & b5) nAg/Au@MSM ( d2 ) and (c1 & c5) nAu/Au@MSM ( e2 ) showing the first and fifth cycle.
10

nAg/Au@MSM ( d2 ) nAu/Au@MSM ( e2 )
Figure S11. TEM image of d2 and e2 samples after the fifth cycle of catalytic reaction. a b c
Figure S12.
Magnetization curves of (a) Fe
3
O
4
core, (b) Fe
3
O
4
–SiO
2
core–shell composite (MSM), and
(c) nAg/Au@MSM ( d2 ). The inset shows d2 solution without (left) and with (right) an external magnet.
11

Figure S13. TEM images of nAg/Au@SM system.
12

Table S1 The reaction rate constants and TOF (turn over frequency) for the catalyzed reduction of p nitrophenol by d2 and e2 systems in the repeated cycles cycle k (10
-2 d2 system
/min) e2 system
TOF a
(s
-1 ) × 10 3 k
1
(10
-2
/min) k
2
(10
-2
/min)
1
2
(recovered from 1)
3
(recovered from 2)
4
(recovered from 3)
5
(recovered from 4)
9.5
6.4
8.1
12.1
15.8
3.5
2.3
3.0
4.4
5.8
3.2
2.1
1.9
2.3
1.7
1.2
1.0
1.0
1.4
1.0
TOF was calculated assuming 100% recovery of the catalyst. a
TOF = moles of Amp @90% conversion/(moles of total surface Ag atoms)(time for 90% conversion)
= 3.6 × 10 -7 mol/(7.15 × 10 -8 mol)(time for 90% conversion)
TOF (average) = 3.8
×
10
-3
s
-1
13