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Supplementary Information for:

Ionic Block Copolymer Doped Reduced Graphene Oxide

Supports with Ultra-fine Pd Nanoparticles: Strategic

Realization of Ultra-accelerated Nanocatalysis

Kie Yong Cho,a,b Yong Sik Yeom,a Heun Young Seo,a Pradip Kumar,b Albert S. Lee,b Kyung-Youl

Baekb,c and Ho Gyu Yoona,*

a Department of Materials Science and Engineering, Korea University, Seoul 136-701, Korea.b Materials Architecting Research Center, Korea Institute of Science and Technology, 39-1 Hawolgok-dong,

Seongbuk-gu, Seoul 136-791, Korea.c KIST-UNIST Ulsan Center for Convergent Materials, Ulsan National Institute of Science and Technology, Ulsan

689-698, Korea.

List of Supplementary Information

1. Experimental Section

2. Characterization of Pyrene-functionalized Ionic Block Copolymer.

3. Characterization of GO and rGO.

4. Characterization of Hybrid Catalysts.

5. Evaluation of Catalytic Activities.

6. References

Electronic Supplementary Material (ESI) for Journal of Materials Chemistry A.This journal is © The Royal Society of Chemistry 2015

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1. Experimental Section

Materials. All reagents were purchased from Alfa Aesar and Sigma-Aldrich and

were used as received, unless otherwise noted. Dimethylaminoethyl methacrylate

(DMAEMA) monomer was refined by distillation after removal of the moisture with calcium

hydride. Poly(ethylene glycol) methyl ether methacrylate (PEGMEMA) monomer was refined

using the inhibitor remover resin (AL-154, Sigma-Aldrich).

Characterization. The number-average molecular weight (Mn) and molecular weight

distributions (Mw/Mn) of the samples were measured using a JASCO PU-2080 plus SEC

system equipped with RI-2031 and UV-2075 (254 nm detection wavelength) attachments,

using THF as the eluent at 40°C (flow rate: 1 mL/min). The samples were separated through

four columns: Shodex-GPC KF-802, KF-803, KF-804, and KF-805. 1H NMR spectra were

acquired in CDCl3 at 25°C on a 300 MHz Varian Unity INOVA instrument. The size

distribution of the Ag NPs was determined using dynamic light scattering (DLS) (Photal,

ELSZ-1000) analysis. UV-Vis absorption spectra were acquired in air with a JASCO V-670

spectrophotometer. The X-ray diffraction patterns were acquired on a Rigaku diffractometer

(Rigaku Smart Lab, Rigaku Co., Japan) operated at 45 kV and 40 mA with CuKα radiation (λ

= 1.5406 A°) using a diffracted beam monochromator. Data were collected between 2θ = 5°

and 100° at 0.01° intervals. The phase was identified by matching each characteristic peak

with the JCPDS files. Identification and characterization of functional groups were carried out

using a Raman spectrometer (LabRam ARAMIS IR2, Horiba, Japan) with a laser excitation

wavelength of 532 nm. X-ray photoelectron spectroscopy (XPS) analysis was performed

under reduced pressure using an X-ray photoelectron spectrometer (X-TOOL, ULVAC-PHI)

with a monochromatic AlKα source. The sample morphologies were investigated by field-

emission transmission electron microscopic analysis (FE-TEM, Tecnai G2 F30 S-Twin, FEI

Co., USA) at an accelerating voltage of 300 kV.

Synthesis of PDMAEMA-b-PPEGMEMA Block Copolymer. Typical controlled

radical polymerizations were carried out by the syringe technique under argon using

baked flasks with three-way stopcocks. CuCl1 (0.75 mmol, 77.7 mg), Anisole (10.5

mL), dNbpy (1.5 mmol, 0.64 mg), DMAEMA (18.8 mmol, 3.2 mL), and a solution of

2-EBP (0.6 mmol, 0.9 mL, 700 mM in toluene) were sequentially added to a 50 mL

round-bottom flask in the stated order at 25°C under argon. The reaction solution was

then placed in an oil bath set at 80°C. After achieving around 97% conversion by

polymerization for 14 h, 0.1 mL of the sample was withdrawn from the reaction

solution. The conversion was determined by integrating the ratio of the 1H NMR

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spectra of the polymer versus that of the unreacted monomer. The molecular weight

and PDI of the PDMAEMA product were measured by GPC and calculated to be 4.6 k

and 1.17 respectively. PPEGMEMA copolymerization was sequentially conducted via

an in-situ process with the injection of the PEGMEMA monomer (18.8 mmol, 8.97 mL)

into the reaction solution. After the polymerization reached around 97% conversion

(16 h), the reaction was terminated by cooling to −78°C. The quenched solution was

diluted with THF (30 mL) and then passed through the aluminum oxide column using

extra THF. The solution was collected and the solvent was removed under reduced

pressure. The concentrated solution was dropped into hexane. This precipitation

procedure was repeated 3 times. The product was obtained by decantation and dried at

25°C for 48 h under reduced pressure (MW: 19 k, PDI: 1.09). The weight fractions of

the PDMAEMA and PEGMEMA blocks were calculated to be 0.16 and 0.84,

respectively.

Synthesis of Pyrene-functionalized Ionic Block Copolymer (PIB). Pyrene

functionalization of the PDMAEMA-b-PPEGMEMA block copolymer was carried out by

simple addition of 1-(bromomethyl)pyrene. PDMAEMA-b-PPEGMEMA copolymers (0.5 g)

were placed into a pre-baked 100 mL RB flask and 9.6 mL of DMF was subsequently injected.

The solution was refluxed after connection of the condenser. After half-hour, 1-

(bromomethyl)pyrene (0.39 mM, 0.116 g) was added to the solution. The reaction was

completed after 24 h. The conversion was measured by 1H NMR analysis of samples taken

directly from the reaction solution, which contained PIB and unreacted methyl pyrene. The

reaction conversion was over 95% and the number of pyrene groups per chain was calculated

to be 14. Purification was simply performed by precipitation in 200 mL of hexane after

removal of DMF, followed by dilution with 30 mL of THF. The product was dried at RT for

48 h under reduced pressure.

Synthesis of Graphene Oxide (GO). The graphene oxide dispersion was prepared by

oxidative exfoliation of natural graphite flakes according to a literature modified Hummer's

method.1,2 One gram of graphite powder was oxygenated in 40 mL H2SO4 while stirring for

15 min, followed by slow addition of 3.5 g potassium permanganate in an ice bath. The

mixture was then continuously stirred for 24 h at 35oC. Thereafter, excess deionized water

and 35% H2O2 were added to the mixture. The obtained yellow mixture was thoroughly

filtered and washed with 1 M HCl solution and deionized water and then re-dispersed in 1 L

of water. Monolayer exfoliation was achieved by mild sonication of the washed graphite

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oxide. To remove the non-exfoliated flakes, the obtained graphene oxide dispersion was

centrifuged 3 times. The monolayer exfoliated GO dispersion was then purified by passing

through a dialysis membrane to remove ionic impurities. A predetermined amount of the

concentrated dispersion was diluted in water to prepare the GO dispersions with a desired

composition.

Synthesis of Reduced Graphene Oxide (rGO). A predetermined amount (2 mg/mL) of

colloidal GO dispersion was placed in a sealed Teflon cuvette.3 1 μL hydrazine monohydrate

per 3 mg of GO was added to the dispersion and the cuvette was placed in an 80oC oil bath for

12 h. After cooling to room temperature, the black, precipitated reduced graphene oxide

powder was filtered through a membrane filter (0.2 μm in pore size) and washed with excess

water under reduced pressure. The resulting black rGO was vacuum-dried and used for further

study.

Synthesis of oxidized CNT. Oxidization of pristine CNT was performed by using an

acidic solution (nitric acid/sulfuric acid = 1:3). After adding pristine CNTs to the acidic

solution, the suspension was refluxed at 80oC for 4 h. The obtained oxidized CNTs were

filtered and rinsed with excess water to neutralize the solution. The products were redispersed

in water for further use.

Preparation of PIB-functionalized rGO (PIBrGO). To accomplish effective integration

of rGO with PIB, 20 mg of rGO was pre-dispersed in 200 mL of NMP by sonication for 30

min. Thereafter, 80 mg of PIB was added to the rGO suspension and then stirred in an ice

bath for 30 min. Thereafter, the PIB-rGO mixture was sonicated for 20 min and then agitated

in an ice bath for 30 min. This procedure was repeated thrice. After the foregoing procedure,

well-dispersed PIBrGO nanocomposites were obtained and free PIB was removed by simple

filtration under reduced pressure. The products were redispersed in water (0.2 mg/mL) for

further use.

Synthesis of Pd-decorated hybrid catalyst (Pd-PIBrGO, Pd-rGO, Pd-CNT, and Pd-AC).

An aqueous suspension of the carbon support (PIBrGO, rGO, CNT, and activated carbon) (5

mL, 0.2 mg/mL) was mixed with the Na2PdCl4 precursor aqueous solution (0.2 mL, 5 mM).

After sonication for 1 min, an aqueous solution of NaBH4 (0.2 mL, 50 mM) was added to the

prepared reaction solution. The reaction solution was placed in an ice bath with mild agitation

and maintained for 20 min. The reaction solution was diluted with 30 mL of water, followed

by centrifugation. Thereafter, the clear supernatant was removed and 30 mL of fresh water

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was added. This procedure was repeated 3 times. The final precipitated product was re-

dispersed in water for further use in catalytic studies (0.1 mg/mL).

Evaluation of Catalytic Activities for Reduction of Methylene Blue (MB). The catalytic

activity of the hybrid catalysts (Pd-PIBrGO, Pd-rGO, and Pd-CNT) for the reduction of

methylene blue to leuco methylene blue was evaluated. 1 mL of fresh aqueous NaBH4

solution (0.5 M) was added to 2 mL of aqueous methylene blue solution (5 mg/L) in a UV

quartz cuvette. Thereafter, the mixed solution was agitated for 5 sec. Thirty microliters of the

hybrid catalyst (0.1 mg/mL) was injected into the aforementioned solution. The reduction

reaction was monitored by UV-Vis monitoring of the methylene blue peak at 662.7 nm.

Evaluation of Catalytic Activities for Reduction of 4-Nitrophenol (4-NP). The catalytic

activity of the metal NP-incorporated hybrid nanocomposites for the reduction reaction of 4-

nitrophenol to 4-aminophenol was evaluated. One milliliter of fresh aqueous NaBH4 solution

(0.1 M) was added to 1.5 mL of aqueous 4-nitrophenol solution (1 10-4 M) in a quartz UV ×

cuvette. Thereafter, the mixed solution was agitated for 1 min, accompanied by a color change

from light yellow to yellowish green. One hundred microliters of catalyst (0.1 mg/mL) was

injected into the afore-described solution. The reduction reaction was monitored by UV-Vis

analysis of the 4-nitrophenolate peak at 400 nm.

Control of the Sequential Catalytic Reduction of Methylene Blue using Pd-PIBrGO

Hybrid Catalyst. To evaluate the catalytic activity with sequential addition of MB, two

solutions comprising 1 mL of fresh aqueous NaBH4 solution (0.5 M) and 2 mL of aqueous

methylene blue solution (5 mg/L) were placed into separate vials. Thereafter, 30 μL of the

hybrid catalyst (0.1 mg/mL) was injected into one vial only, and the change in color was

monitored. Subsequently, 10 μL of aqueous MB solution (500 mg/L) was injected into each

vial, and the color change was monitored. These procedures were repeated several times.

2. Characterization of Pyrene-functionalized Ionic Block Copolymer.

The PDMAEMA-b-PPEGMEMA block copolymer was synthesized using a simple in-

situ process via atom transfer radical polymerization (ATRP). The molecular weight and PDI

of the synthesized block copolymer evaluated using GPC (Fig. S1) were 19,000 g/mol and

1.09, respectively. This result is indicative of well-controlled copolymerization for the

PDMAEMA-b-PPEGMEMA block copolymer. Furthermore, the molecular structure of the

polymer was investigated using 1H NMR (Fig. S2). Proton peaks from the PDMAEMA

backbone appeared in the range of 0.7 to 2 ppm (a and b) and three other peaks appeared at

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2.3, 2.6, and 4.1 ppm, corresponding to dimethyl protons (e) and methylene protons (d and c),

respectively. After copolymeriztion of PEGMEMA with the PDMAEMA precursor, a peak

with the highest intensity appeared at 3.6 ppm, corresponding to ethylene protons (g); the

methylene and methyl protons appeared at 4 ppm (f) and 3.35 ppm (h), respectively. The

backbone proton signals of PPEGMEMA overlapped with those of the PDMAEMA backbone,

appearing in the range of 0.7 to 2 ppm. For the quaternization reaction using 1-

(bromomethyl)pyrene, the number of DMAEMA monomers per chain was estimated to be 29

by integration of the 1H NMR peaks (d and h). To accomplish rational design of the solubility,

we aimed for 50% conversion during pyrene functionalization of PDMAEMA and achieved

around 48% conversion, indicating that 14 pyrene moieties were introduced into the

PDMAEMA block via the simple amine quaternization reaction. After incorporation of

pyrene groups into the tertiary amine, the NMR peaks shifted to 2.87 ppm (e`) and 2.94 ppm

(d`) with a decrease of the intensity (Fig. S2), while the (d) methylene absorption peak was

strongly shifted from 4.21 to 4.36 ppm (c`). In addition, two broad peaks corresponding to

methyl pyrene protons (i and j) appeared in the range of 5.68 to 6.26 ppm and 7.38 to 8.57

ppm, respectively.

Scheme S1 Synthesis of pyrene functionalized ionic PDMAEMA-b-PPEGMEMA block

copolymer.

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Fig. S1 GPC curves of PDMAEMA and PDMAEMA-b-PPEGMEMA.

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6 4(ppm)

2 135789

c

ba

d

e

O

OmBr

O

PDMAEMA(Precursor)

O

N

ba

e

dc

b,b"a,a"

gf

PDMAEMA-b-PPEGMEMA(Diblock Copolymer)

O

Om

O

Br

OO

O

7.5

n

O

N

a b

c d

e

a" b"

Oc, f

g h

h

e

d

f

Br

OO

O

7.5

n

a' b'

O

g

h

O

O

OOx

N

OOy

NBr(x+y=m)

a b

c d

e b,b"a,a"

a' b'

c' d'

j

ie'

ji

g h e

dd',e'c,c', f

Py-PDMAEMA-b-PPEGMEMA(PIB)

Fig. S2 1H NMR spectra of PDMAEMA, PDMAEMA-b-PPEGMEMA, and Py-PDMAEMA-

b-PPEGMEMA.

3. Characterization of GO and rGO.

The prepared GO was characterized by XPS, Raman, and XRD analyses. The XPS

spectrum of the C 1s core-level region on the GO surface (Fig. S3) showed two predominant

peaks and was deconvoluted into 3 three peaks attributed to C–C and C–H bonds at 284.6 eV,

C–O bonds at 286.6 eV, and C=O bonds at 288.2 eV. The surface condition of GO may be

indicative of successful synthesis of GO. The oxygenated functional groups on the surface of

GO conferred a good dispersion stability to GO in water. After chemical reduction of GO to

rGO, a predominant peak corresponding to non-oxygenated carbon bonds appeared,

accompanied by significant reduction of the peaks arising from oxygenated carbon bonds (Fig.

2C). These reduction behaviors supported the successful synthesis of rGO. Raman

spectroscopic analysis was used for further characterization of GO and rGO. GO exhibited

two typical peaks at 1349.6 and 1588.4 cm−1, corresponding to the sp3 electronic

configuration of disordered carbon bonds and the in-plane vibrations of sp2 carbon bonds,

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respectively (Fig. S4A). After reduction of GO to rGO, these D and G bands of GO were

shifted to lower wavenumber, centered at 1339.1 and 1582.8 cm−1, respectively. In addition,

the ID/IG ratio increased from 0.905 to 1.01. These changes in the Raman spectrum can be

explained by the self-healing characteristics of rGO, resulting in regeneration of the typical

hexagonal networks of graphite with defects.4 The successful synthesis of GO and rGO was

further confirmed by XRD (Fig. S4B). The typical peak of GO at 10.8o is attributed to the

(001) plane reflection derived from the introduction of oxygenated functional groups into

graphite. The interlayer spacing was calculated to be 0.84 nm. After reduction of GO to rGO,

the peak of the (001) plane disappeared and only the peak of the (002) plane was observed at

25o, indicating efficient reduction of GO. Furthermore, the thickness of rGO was measured by

AFM, resulting in a thickness of 1 nm, representative of a single layer of rGO.

Fig. S3 XPS spectrum of C 1s on GO.

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(A) (B)

Fig. S4 (A) Raman spectra and (B) XRD patterns of GO and rGO

Fig. S5 AFM height image of rGO (inset: thickness curve of rGO along the line).

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4. Characterization of hybrid catalysts.

Fig. S6 TEM images of the Pd-PIBrGO hybrid catalysts prepared by addition of different

molar concentrations of Na2PdCl4: (A) 2.5 mM, (B) 5 mM, (C) 10 mM, and (D) 20 mM.

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Fig. S7 TEM images of variety of Pd-PIBrGO hybrid catalysts, synthesized by the addition of

different molar concentrations of Na2PdCl4:(A) 2.5 mM, (B) 5 mM, (C) 10 mM, and (D) 20

mM.

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Fig. S8 (A) Dark-field TEM image and (B) energy-dispersive X-ray spectroscopy (EDX)

analysis of Pd-PIBrGO (2.98% of Pd).

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Fig. S9 Survey XPS spectrum of Pd-PIBrGO.

The survey XPS spectrum of Pd-PIBrGO indicated an elemental atomic composition of

58.7% C 1s, 32.5% O 1s, 3% Pd, and 1.1% N 1s (Fig. S9).

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Fig. S10 TEM image of Pd-CNT

Pd NP decorated CNTs were prepared as one of the reference hybrid catalysts. The oxidized

CNT was utilized as a support for Pd NP deposition. Pd NPs of a few nanometers in size were

incorporated onto the surface of the CNTs, as shown in Fig. S10. However, significant

aggregation of the Pd NPs was also observed. This may be attributed to the lack of driving

force for Pd NP deposition on the oxidized CNT because of the low level of oxygenated

functional groups (lower than 8%).5

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Fig. S11 (A) STEM images and (B) STEM-EDX anlaysis of Pd-AC (inset: STEM image of

Pd-AC with EDX analysis point).

Pd NP decorated activated carbon (Pd-AC) was prepared as one of the reference hybrid

catalysts. In Fig. S11A, STEM images exhibited large size and porous structure of activated

carbon and a few nanometer sized Pd NPs were observed on the surface of AC. STEM-EDX

result indicated Pd NP was well-incorporated onto the surface of AC (Fig. S11B).

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5. Evaluation of Catalytic Activity.

Fig. S12 Catalytic reduction mechanism of methylene blue and 4-nitrophenol with Pd-

PIBrGO.

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Fig. S13 Schematic illustrations of the formation of (A) Pd-rGO and (B) Pd-PIBrGO hybrid

catalysts and their process for catalytic reduction reaction of methylene blue (MB) to leuco

methylene blue (LMB).

In the methylene blue aqueous solution, the MB molecules can be dispersed in the

molecular level owing to its good solubility in water. After presence of NaBH4 and Pd-

PIBrGO into the MB aqueous solution, MB molecules may be attracted by an electrically

negative brush (PEGMEMA) because of the effect of the static interaction, and can be relayed

onto the electron-doped Pd metal catalysts by the presence of NaBH4. These catalytic

reductions of MB led to the color change from blue to colorless.

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300 400 500 600 7000.0

0.2

0.4

0 s4 min.

Wavelength (nm)

Absorbance(a.u.)

8 min.12 min.

20 min.24 min.

0.6

0.8

0

1.2

Reaction Time (min.)

Ct/ C

0

1.0

10 20 30

rGO (30 L)

0.8

0.6

0.4

0.2

0.0

16 min.

28 min.32 min.36 min.

(C) (D)

300 400 500 600 7000.0

0.2

0.4

0.6

0 s30 s

Wavelength (nm)

Absorbance(a.u.) 1 min.

2 min.3 min.

0.8(A) (B)

300 400 500 600 7000.0

0.2

0.4

0 s2 min.

Wavelength (nm)

Absorbance(a.u.)

4 min.6 min.

10 min.12 min.

0.6

0.8

8 min.

Pd-AC (30 L)

Fig. S14 (A) – (C) Successive reductions of methylene blue using 10 μL of Pd-PIBrGO, and

30 μL of Pd-AC and rGO aqueous solution (0.1 mg/mL), respectively; (D) Ct/C0 vs. reaction

time (t) plots for rGO and Pd-activated carbon (AC) catalysts.

Pd NP-decorated activated carbon (Pd-AC) was synthesized for comparing its catalytic

performance in the reduction of MB to Pd-PIBrGO. The catalytic reaction was monitored by

UV-Vis spectroscopy (Fig. S14B). Although Pd-AC showed relatively lower catalytic activity

(12 min) in comparison to Pd-PIBrGO (almost one second), the reaction time was much

shorter than other references including rGO, Pd-rGO and Pd-CNT (Fig. S14D). This catalytic

performance of Pd-AC can be explained by its morphologic properties, which are large

surface area and highly porous structure. In addition, its conducting properties can aid the

effective catalytic reaction. In addition, the catalytic properties of rGO without Pd NP were

monitored by UV-Vis spectroscopy (Fig. S14C). In the beginning of the reaction, MB

concentration decreased about 10% due to the sorption onto the rGO surface. However, after

4 minutes, the concentration of MB did not change much up to 36 min, indicating that the

main role of rGO was just a support for metal and a diffusion agent for reagents (Fig. S14D).

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Fig. S15 TEM images of the Pd-PIBrGO hybrid catalyst with different magnified-scales after

10-times catalytic reactions.

Fig. S16 Color change during catalytic reduction of 4-nitrophenol to 4-aminophenol by Pd-

PIBrGO hybrid catalyst in the presence of NaBH4.

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Fig. S17 Successive reductions of 4-nitrophenol using (A) Pd-PIBrGO (50 μL), (B) Pd-

PIBrGO (100 μL), and (C) Pd-rGO (100 μL) aqueous solution (0.1 mg/mL). (D) ln(Ct/C0) vs.

reaction time (t) plots for Pd-PIBrGO (100 and 50 μL) and Pd-rGO (100 μL) hybrid catalysts.

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6. References

1. J. E. Kim, T. H. Han, S. H. Lee, J. Y. Kim, C. W. Ahn, J. M. Yun and S. O. Kim, Angew. Chem. Int. Ed., 2011, 50, 3043.

2. P. Kumar, U. N. Maiti, K. E. Lee and S. O. Kim, Carbon, 2014, 80, 453.3. S. Park, J. An, J. R. Potts, A. Velamakanni, S. Murali and R. S. Ruoff, Carbon, 2011, 49,

3019.4. Q. Zheng, B. Zhang, X. Lin, X. Shen, N. Yousefi, Z.-D. Huang, Z. Li and J.-K. Kim, J.

Mater. Chem., 2012, 22, 25072.5. X. Chen, G. Wu, J. Chen, X. Chen, Z. Xie and X. Wang, J. Am. Chem. Soc., 2011, 133, 1693