Electronic Supplementary Material

Enhanced Non-enzymatic Amperometric Sensing of Glucose Using Co(OH)2 Nanorods

Deposited on a Three Dimensional Graphene Network as an Electrode Material

Iman Shackery ‡,a, Umakant Patil ‡a, Atiye Pezeshki b, Nanasaheb M Shinde a, Seongil Imb and

Seong Chan Jun a*

a School of Mechanical Engineering, Yonsei University, Seoul 120-749, Republic of Korea

b Institute of Physics and Applied Physics, Yonsei University, Seoul 120-749, Republic of

Korea

‡ These authors contribute equally.

* Corresponding author, E-mail: scj@yonsei.ac.kr

Growth of 3D graphene networks by chemical vapor deposition

Nickel foams were placed in the center of a quartz tube furnace and annealed at

1,000°C for 60 min in H2 at a pressure of 1.4 Torr with a constant flow of 200 sccm1 of H2 in

order to reduce the oxide layers of the Ni foam. Methane (CH4) gas was then flowed into the

tube while increasing the pressure of the hydrogen mixture to 2.1 Torr at 1,000 oC. The

concentration of carbon atoms that dissolve in the foam can be adjusted by varying the ratio

of CH4 to H2. After 10 min of CH4 flow, the quartz tube was taken out of the furnace and

cooled down to room temperature at a cooling rate of 10 °C s-1. During all the steps, Ar was

flowed in the tube with a rate of 5 sccm. After the growth of graphene, to remove the Ni

foam, the 3D graphene network was first coated with poly(methyl methacrylate) (PMMA) by

dipping it in a PMMA solution for several seconds followed by drying at room temperature

for 4 hrs. Next, the network was immersed in an etchant solution containing 1 mol L-1 FeCl3

and 2 mol L-1 HCl at room temperature for at least 3 days. After removal of the Ni foam, the

1 Standard Cubic Centimeters per Minute

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PMMA coated on the 3D graphene network was removed by acetone vapor for another 3

days. Finally, we developed the continuous interconnected porous 3D graphene framework.

Growing mechanism of Co(OH)2/3DG

Graphene networks were grown by CVD method on Ni foam using methane as

precursor. Fig. 1 (see the manuscript) shows the schematic procedure for preparation of

Co(OH)2 nanorods on 3DG. A porous structure with an interconnected 3D scaffold of nickel

was used as a template for the growth of 3DGs. Formerly, methane (CH4) was introduced into

a nickel foam as source of carbon. At 1,000 °C under low pressure ( ), graphene films

were then precipitated on the surface of the nickel foam (see the manuscript, Fig.1, step 1).

Before etching away, the nickel skeleton by etchant (1 mol L-1 FeCl3 and 2 mol L-1 HCl)

solution, graphene films was dipped in poly(methyl methacrylate) (PMMA). Consequently, a

thin layer of PMMA was coated on the surface of the graphene films as a support to prevent

the graphene network from collapsing during nickel etching (Fig. 1-step 2). After etching

away the nickel skeleton (Fig.1, step 3), the PMMA layer was carefully removed by acetone

vapor (Fig.1, step 4). During the above process ripples and wrinkles were formed on the

graphene films due to the difference between the thermal expansion coefficients of nickel

foam and graphene. Furthermore, during the chemical etching and other process some

functional groups such as carboxyl groups were formed on the 3DG. These ripples, wrinkles

and functional groups probably result in an improved mechanical and chemical interlocking,

consequently better adhesion. Synthesis of Co(OH)2 on 3DG, was achieved by using the CBD

method (Fig.1, step 5). The CBD method is based on the formation of a solid phase from

solution which involves two steps: nucleation and particle growth [1]. The Co(OH)2 has been

deposited on a 3DG substrate by the slow hydrolysis of cobalt chloride. As the temperature of

solution bath increased to 95oC, decomposition of urea (reactions 1) took place, producing

CO2 and NH3 gradually [2]:

(1)

Simultaneously NH3 reacts with Co2+ that is formed from CoCl2.6H2O:

(2)

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Torr4.1

23222 2 CONHOHCONHNH

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2 )(4 NHCoNHCo

Such amine complex metal ions easily get adsorbed on the surface of the 3DG by

electrostatic or Van-der Waals force. At alkalescent bath condition, the Co(NH3)42+ is unstable

and formed metal hydroxide nanorods on the graphene surface according to following

reaction:

(3)

Fig. S1 (a) Raman spectra of 3DG at different positions (b) The XRD patterns of 3

dimensional graphene (3DG) and Co(OH)2/3DG electrode

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32243 4)(2)( NHOHCoOHNHCo

Fig. S2 (a) TGA plots of 3DG (black) and Co(OH)2/3DG (red) in air (b) FT-IR spectrum of

Co(OH)2/3DG

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Fig. S3: EDX element mappings of carbon, oxygen, and Cobalt atoms obtained from the SEM

images of Co(OH)2/3DG

Fig. S4: The point EDX. (a) shows 80% of carbon with a little amount of Ni. This data

indicates that almost all Ni was removed. (b) the point EDX data of Co(OH)2 flower like

nanorods. The inset images show the SEM of the samples.

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Fig. S5 (a) The CV curves of Co(OH)2/3DG at different scan rates ( from 10 to 100 mVs−1) in

1 M KOH. (b) The graph of anodic and cathodic peak vs. square root of scan rates.

Fig. S6: (a) The CV curves of Co(OH)2/3DG in 3 M KCl containing 10 mM of K3Fe(CN)6 at

different scan rates (b) The relationships between the peak current (Ip) and the square root of

the potential scan rate (ν1/2)

Table S1: The reproducibility of Co(OH)2/3DG electrode was tested with 3 samples in 5

concentration from 0.1 mM up to 0.5 mM

Concentratio

n (mM)

Response current density (mA) Mean RSD (%)

Sensor #1 Sensor #2 Sensor #3

0.1 0.429 0.441 0.436 0.435

3

1.95

0.2 0.485 0.487 0.428 0.466

6

8.29

0.3 0.451 0.460 0.452 0.454

3

1.49

0.4 0.391 0.444 0.426 0.420

3

9.01

0.5 0.442 0.398 0.439 0.426

3

7.87

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Table S2: The reproducibility of Co(OH)2/3DG electrode was tested three times with same

sample in five concentration of glucose from 0.1 mM up to 1 mM

Concentration

(mM)

Response current density (mA) Mean RSD (%)

1st experiment 2nd experiment 3rd experiment

0.1 0.501 0.462 0.476 0.479 1.97

0.4 1.802 1.681 1.724 1.735 6.13

0.6 0.875 0.910 0.892 0.892 1.75

0.9 1.412 1.289 1.332 1.344 6.24

1 0.483 0.521 0.461 0.488 3.03

References:

1. Hodes, G., Semiconductor and ceramic nanoparticle films deposited by chemical bath

deposition. Physical Chemistry Chemical Physics, 2007. 9(18): p. 2181-2196.

2. Jayalakshmi, M., et al., Optimum conditions to prepare high yield, phase pure α-Ni

(OH) 2 nanoparticles by urea hydrolysis and electrochemical ageing in alkali

solutions. Journal of power sources, 2005. 150: p. 272-275.

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