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Facile synthesis of polymer and carbon spheres decorated with highly dispersed metal nanoparticles

Nilantha P. Wickramaratne and Mietek Jaroniec*

Department of Chemistry and Biochemistry, Kent State University, Kent, Ohio, 44242, USA

EXPERIMENTAL

Synthesis of cysteine-stabilized polymer spheres. Cysteine-stabilized polymer spheres (PS) were synthesized using a slightly modified recipe reported in our previous work.23 In a typical experiment, an aqueous-alcoholic solution was prepared by mixing 48 mL of ethanol and 120 mL of distilled water under refluxing conditions at 70 oC. Subsequently, 0.6 mL of 28 wt% ammonia and 1.2 g of cysteine were added under continuous stirring for 1 hour. Then, 1.2 g of resorcinol was added and stirred for another 30 minutes. Next, 1.2 mL of 37 wt% formaldehyde was slowly added and stirred for 24 h under reflux conditions. Finally, the reaction mixture was transferred to a closed polypropylene bottle, which was placed in an oven at 100 oC for 24 h under static conditions. The solid product (cysteine-stabilized PS) was obtained by centrifugation and washing several times with water. Finally, this product was dispersed in 100 mL of water and freeze-dried.

Synthesis of polymer spheres decorated with metal nanoparticles. To decorate PS with metal nanoparticles, 0.1 g of cysteine-stabilized PS was dispersed in 100 mL of various metal salts (10 mM) and stirred for 4 hours. Next, these metal-containing polymeric spheres were centrifuged and freeze-dried as described in the aforementioned section. The resulting polymeric spheres were labeled as PS-x and PS-x** in the case of metal-polymer composites obtained using 10 mM and 20mM solutions of metal salts, respectively; symbol “x” denotes metal, whereas “CS” refers to carbon spheres. In order to obtain CS, polymeric spheres were subjected to thermal treatment at 600 oC (carbonization) in flowing nitrogen in a tube furnace using a heating rate of 2 oC/min up to 600 oC and dwell for 2h. The resulting carbon spheres were labeled as CS-x and CS-x* in the case of metal-carbon composites carbonized at 600 oC and 800 oC, respectively; symbol “x” denotes metal. Measurements and Characterization. Transmission electron microscopy (TEM) imaging was carried out using a FEI Tecnai F20ST/STEM instrument operated at 200 keV. The preparation of samples for TEM analysis involved their sonication in ethanol for 2 to 5 min and deposition on a 400 mesh lacey carbon coated copper grid.

Electronic Supplementary Material (ESI) for ChemComm.This journal is © The Royal Society of Chemistry 2014

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The X-ray diffraction (XRD) measurements were recorded for the carbonized samples using a PANanalytical, Inc. X’Pert Pro (MPD) Multi-Purpose Diffractometer with Cu Kα radiation (1.5406 Å) at an operating voltage of 45 kV.

Nitrogen adsorption isotherms were measured at -196 °C on ASAP 2010 volumetric adsorption analyzer manufactured by Micromeritics (Norcross, GA, USA) using nitrogen of 99.998% purity. Before adsorption measurements, each sample was degassed under vacuum for at least 2 h at 200 °C. The specific surface area of the samples was calculated using the Brunauer-Emmett-Teller (BET) method within the relative pressure range of 0.05-0.20. Pore size distributions were calculated using the BJH algorithm for cylindrical pores according to the KJS method.

Thermogravimetric analysis (TGA) was performed on a TA instrument TGA Q500 thermogravimetric analyzer using a high resolution mode. The curves were recorded in flowing air with a heating rate of 10 oC/min from 30 to 800 oC. Two types of plots were obtained from the TGA data: (1) weight loss % vs. temperature; this plot is used to obtain the residue amount, and (2) –derivate weight % vs. temperature; this plot is used to estimate the decomposition temperatures of organic components in the samples studied.

Table S1. Surface area in m2/g calculated from N2 adsorption isotherms using BET equation and residue % obtained from the TGA profiles.

Sample CS CS-Ru CS-Ag CS-Mn CS-Gd CS-Fe CS-Au

Surface area (m2/g) 714 766 446 681 474 530 162

Residue % < 0.5 18.9 25.3 4.9 15.3 4.8 77.8

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Fig. S1 TEM images of the metal-containing PS and CS studied.

CS‐Fe* CS‐Fe* CS‐Fe*

PS‐Gd PS‐Gd PS‐Gd

PS‐Fe CS‐Fe

PS‐Au CS‐Au CS‐Au

CS‐Mn

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Fig. S2. The TEM and EDX spectra of PS-Fe (A), PS-Ru (B), and PS-Gd (C).

B

A

C

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Fig. S3. TG and differential weight change (DTG, inset) profiles for the PS-Ag (A) and CS-Fe series of carbons.

Temperature (oC)0 200 400 600 800

We

igh

t (%

)

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40

60

80

100

PS-Ag (4h)PS-Ag (2h)PS-Ag**

Temperature (oC)

200 300 400

-De

riv

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t (%

/oC

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0

2

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Temperature (oC)0 200 400 600 800

We

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t (%

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CS-FeCS-Fe*

Temperature (oC)

400 450 500

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15

A

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Fig. S4. Differential weight change (DTG) profiles for the metal-containing PS (A) and CS (B). Note that the oxidation temperatures of carbon can vary due to the metal present in the carbon sample. For example, it has been shown that the presence of K, Na, etc. can catalyze the oxidation of carbon in oxygen-containing atmosphere at elevated temperatures (Ogura, M.;

Morozumi, K.; Elangovan, S. P.; Tanada, H.; Ando, H.; Okubo, T. Applied Catalysis B, Environmental 2008,

77, 294-299).

Temperature (oC)200 300 400

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riv

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igh

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/oC

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0

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PS-AuPS-AgPS-RuPS-Fe

Temperature (oC)

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CS-AuCS-AgCS-RuCS-Fe

A

B

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Fig. S5. Wide angle XRD patterns for selected metal-containing polymer and carbon spheres studied.

Fig. S6. N2 adsorption isotherms for the metal-containing carbon spheres studied.

Relative Pressure 0.0 0.2 0.4 0.6 0.8 1.0

Vo

lum

e A

dso

rbed

(cm

3 ST

Pg

-1)

0

100

200

300

400

500 CSCS-RuCS-AgCS-MnCS-GdCS-Fe CS-Au

2/ degree20 40 60 80

Inte

nsi

ty (

arb

.un

its)

CS-Au

PS-AgCS-Ag

CS-Ru

�

�

�

�

++ +

+ +

+ = Ru, � = RuS2