S-1

1 Supporting Information

2

3 Controllable ionic liquid-assisted electrochemical exfoliate

4 carbon fibers for the green and large-scale preparation of

5 functionalized graphene quantum dots endowed with multicolor

6 emitting and size tunability

7 Yuting Yana, Henan Lib, Qirui Wanga, Hanping Maoa, Wang Kun*a,b

8 aKey Laboratory of Modern Agriculture Equipment and Technology, Institute of

9 Agricultural Engineering, Jiangsu University, Zhenjiang, 212013, P.R. China

10 bSchool of Chemistry and Chemical Engineering, Jiangsu University, Zhenjiang,

11 212013, P. R. China.

12

13 Corresponding author. Tel.: +86 511 88791800; fax: +86 511 88791708. 14 E–mail address: wangkun@ujs.edu.cn; maohp@ujs.edu.cn

Electronic Supplementary Material (ESI) for Journal of Materials Chemistry C.This journal is © The Royal Society of Chemistry 2017

S-2

1 Fig. S1

2

3

4

5 Fig. S1. Time evolution of ILs electrolyte and carbon fiber anode during exfoliation in

6 [Bmim][BF4] electrolyte in different stages (A: before exfoliation; B: the beginning of

7 exfoliation; C: an hour in exfoliation; D: the end of exfoliation).

A B

D C

S-3

1 Quantum Yields (QYs) Measurements

2 The quantum yields of as-prepared G-GQDs were measured and calculated by

3 using a comparative method (Table S1). Rhodamine B in water (QYs=0.31) was

4 chosen as the standard fluorophore with excitation at 340 nm as the reference. And the

5 quantum yields of the GQDs were calculated according to:

6

2R

R 2R R

AI nI A n

7 Where Φ, I, n and A designates the quantum yield, measured integrated emission

8 intensity, refractive index and the optical absorbance, respectively. The subscript "R"

9 refers to standard with known quantum yield.

10 Table S1. QYs of the as-prepared G-GQDs

Sample Integrated

emissions

intensity (I)

Abs. at 340

nm (A)

Refractive

index of

solvent (n)

Quantum yield

(Φ)

Rhodamine B 19568 0.017 1.33 0.31 (known)

G-GQDs 13412 0.042 1.33 0.086

11 In addition, with the assistance of ionic liquid, G-GQDs with a quantum yield up to

12 8.6% are successfully prepared via electrochemical exfoliate, which is higher than that

13 of the hydrothermal cleaving routes (< 8%).1,2

S-4

1 Characterization of the CFs

2 Raman spectroscopy is considered to be a powerful and efficient technique for

3 characterizing the carbonization and graphitization on carbon-based materials.3 The

4 D- and G-band (ID/IG) ratio of Raman spectra is a parameter to estimate the disorder

5 degree and the sp2 domains. Thus, the Raman spectrum of starting material (CFs) as

6 showed in Fig. S2A. The characteristic peaks at around 1359 cm1 (D-band) and 1589

7 cm1 (G-band), corresponding to the sp3 hybridized and the sp2 hybridized,

8 respectively. Form the Raman spectra, it was observed that the small domain structure

9 of the sp2 in original CFs (Integrated intensity), which is beneficial to get size

10 controlled synthesis of GQDs in accordance with Peng’s report.4 Meanwhile, the

11 higher ratio of ID/IG (Integrated intensity) on original CFs indicated that the existence

12 of non-graphitized structure in original CFs.5,6

13 Further, XRD tool was employed to study the crystalline structure of the original

14 CFs presented in Fig. S2B. There is an obvious diffraction peak at ∼25.0° can be

15 observed in the spectrum, corresponding to the (002) diffraction of graphitic

16 structures, the absence of the (110) band at ∼44.0°even indicates a non-graphitized

17 carbonaceous structure in original CFs.7

18 Combined with the analysis of Raman and XRD, it is clearly confirmed that CFs

19 were possessed with carbonized structure. Such a carbonized CFs can be easily

20 broken down, leading to the creation of GQDs with different size distribution in

21 scalable amounts.

22

S-5

1 Fig. S2

2

10 20 30 40 50 60 70 80

Inte

nsity

/ a.

u.

2 Theta / degree

B

500 1000 1500 2000 2500

17933.5

G

In

tens

ity /

a.u.

Raman shift / cm-1

DA

51727.3

3 Fig. S2. Raman spectra (A) and XRD pattern (B) of original CFs.

S-6

1 Fig. S3

2

3500 3000 2500 2000 1500 1000

b

17421421

15501638

Tr

ansm

ittan

ce

Wavenumber / cm-1

3450

a

A

800 700 600 500 400 300 200 100

O 1s

C 1s

aInte

nsity

/ a.

u.

Binding energy / eV

b

B

3 Fig. S3. (A) FTIR and (B) XPS spectra of G-GQDs (a) and Y-GQDs (b) were

4 synthesized with ratios of H2O/ILs at 15% and 30% as electrolyte, respectively.

S-7

1 Fig. S4

2

300 400 500 600 700

PL

Inte

nsity

(a.u

)

Wavelength / nm

350nm 370nm 390nm 410nm 430nm 450nm 470nmB-GQDs

A

400 500 600 700

PL In

tens

ity(a

.u)

Wavelength / nm

420nm 430nm 440nm 450nm 460nm 470nm 480nm 490nmG-GQDs

B

450 500 550 600 650 700

PL In

tens

ity(a

.u)

Wavelength / nm

470nm 480nm 490nm 500nm 510nm 520nm 530nmY-GQDs

C

3 Fig. S4. The PL spectra of the (A) B-GQDs, (B) G-GQDs and (C) Y-GQDs aqueous

4 solution excited by various wavelengths, respectively.

S-8

1 The effect of the water on the electrochemical properties of ILs

2 In order to investigate the influence of the water on the electrochemical properties

3 of ILs, the cyclic voltammetrys (CVs) recorded in ILs contain different content of

4 H2O, as shown in Fig. S5. It is seen that the electrochemical potential window of the

5 IL/water was decreased with the content of water from 0 vt % H2O to 30 vt % H2O

6 (Fig. S5A). Thus, we can infer that the trend of decreasing activation voltages with

7 increasing water content is correlated to the smaller over potential required for the

8 electrochemical oxidation of water. As such, hydroxyl radicals released from the

9 oxidation of water may play an important role. Meanwhile, the viscosity of ILs may

10 be changed by other means such as stirring, so we also investigate the effect of

11 stirring on viscosity of ILs by CV test. However, there is no any change on

12 electrochemical potential window of pure ILs before and after stirring from CV

13 curves (Fig. S5B).

S-9

1 Fig. S5

2

-2 -1 0 1 2 33

2

1

0

-1

-2

-3

-4

E1

E2

cb

Cu

rren

t /

A

Potential / V

a

E3

A

-2 -1 0 1 2 31.0

0.5

0.0

-0.5

-1.0

-1.5

-2.0

Curr

ent /

A

Potential / V

before stirring after stirring

B

3 Fig. S5. (A) CVs curve recorded in different electrolyte with volume ratio of H2O/ILs

4 at (a) 0%, (b) 15% and (c) 30%, respectively; (B) CVs curve recorded in pure ILs

5 before and after stirring.

S-10

1 Fig. S6

2

0.0 0.3 0.6 0.9 1.2 1.5

0

700

1400

2100

2800

3500

ba

ECL

Inte

nsity

/ a.

u.Potential / V

cB

0.0 0.3 0.6 0.9 1.2 1.5

0.00

0.04

0.08

0.12

0.16 cb

Curr

ent /

mA

Potential / V

a

A

3 Fig. S6. (A) CV and (B) ECL-potential curves of (a) G-GQDs/Ru(bpy)32+, (b) G-

4 GQDs/Ru(bpy)32+ and (c) B-GQDs/ Ru(bpy)3

2+ in 0.1 M pH 9.0 PBS.

S-11

1 Fig. S7

2

0

800

1600

2400

3200

4000

pH 11

pH 10

pH 9

pH 8

pH 7

ECL

Inte

nsity

/ a.

u.

Time

pH 6

3 Fig. S7. ECL-potential curves of the B-GQDs/Ru(bpy)32+ in PBS with different pH

4 values.

S-12

1 Fig. S8

2

0

3000

6000

9000

12000

15000

18000

0.0 0.5 1.0 1.5 2.0 2.5 3.02.4

2.8

3.2

3.6

4.0

4.4

Log

[ECL

Inte

nsity

/ a.

u.]

Log [Ru(bpy)32+/ M]

1000M

200M

100M

50M30M

16M6M

ECL

Inte

nsity

/ a.

u.

Time

2M

A

0

2000

4000

6000

8000

I

ECL

Inte

nsity

/ a.

u.

Time

B

I

I

3 Fig. S8. (A) ECL-potential curves of the B-GQDs/Ru(bpy)32+ in PBS (pH 9.0) with

4 different Ru(bpy)32+ concentration, inset: Calibration curve for Ru(bpy)3

2+; (B) Effect

5 of Ru(bpy)32+ concentration on the change of ECL intensity with PCP.

S-13

1 Selectivity, reproducibility and stability of the ECL senseing

2 Further, the long-term stability of the as-constructed ECL sensor was investigated

3 during 25 days by measuring the ECL response upon of B-GQDs/Ru(bpy)32+ system

4 in 0.1 M PBS (pH 9.0) with adding 50 pg mL−1 PCP (Fig.S9A). In a series of five

5 electrodes prepared in the same way, a relative standard deviation (RSD) of 4.5% was

6 obtained, indicating the reliability of the 25 days.

7 In addition, the specifity of this ECL sensor was studied using 3-chlorophenol (3-

8 CP), 2,4,6-trichlorophenol (1,3,5-TCP), and 2,4-dichlorophenol (2,4-DCP) as

9 inerferents. As shown in Fig. S9B, only PCP enhanced the ECL emission of B-

10 GQDs/Ru(bpy)32+ system dramatically, whereas the analogs of PCP changed the ECL

11 emission slightly (e.g., 3-CP, 1,3,5-TCP, 2,4-DCP). The reason might be attributed to

12 that the above interferents possess more stable chemical properties, which did not

13 make a better facilitate effect to electrochemical reaction of Ru(bpy)32+.

S-14

1 Fig. S9

2

0

2000

4000

6000

8000

10000

DNPTCP

DCPPCP

Blank

ECL

Inte

nsity

/ a.

u.

B

0 5 10 15 20 250

3000

6000

9000

12000

ECL

Inte

nsity

/ a.

u.

Time / day

A

3 Fig. S9. (A) Stability of the ECL sensor over 25 days in 0.1 mol L1 PBS (pH 9.0)

4 with 50 pg mL−1 PCP; (B) ECL of 10 pg mL−1 DCP, TCP, DNP and PCP on the

5 responses of the sensor in 0.1 mol L1 PBS (pH 9.0).

S-15

1 Table S2 Comparison of other ECL systems for determination of PCP

Materials Linear range Detection limit Ref.

GQDs-CdS NCs 0.01 ~ 500 ng mL−1 3 pg mL−1 [8]

CuO NWs/rGO 0.027 ~ 266.3 ng mL−1 9 pg mL−1 [9]

MWCNTs@GONR

s0.002 ~ 10 ng mL−1 0.7 pg mL−1 [10]

B-GQDs 0.02 ~ 150 pg mL-1 6.7 fg mL-1 this work

S-16

1 Notes and references

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22