Supporting Information physiological oxidant graphene ...3 graphene quantum dots and their...

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1 Supporting Information 2 Title Direct transformation of lignin into fluorescence-switchable 3 graphene quantum dots and their application in ultrasensitive profiling of 4 physiological oxidant 5 Ruibin Wang, a† Guangjie Xia, b† Wentao Zhong, a Lei Chen, a Liheng Chen ,c Yanggang 6 Wang, b* Yonggang Min a* and Kaixin Li a* 7 8 Experimental Section 9 A-acid recyclability 10 We conducted a preliminary evaluation of the reusability of A-acid by fractionating 11 AL under the same condition. First, after the above-mentioned second filtration, the 12 obtained filter cake was thoroughly washed by DI water, and then air-dried (Fig. S2a). 13 Second, we calculated the amount of fresh makeup A-acid needed for the next cycle 14 on the basis of the mass of the as-dried solids with the assumption that A-acid 15 consumption by reaction was negligible. Next, the predetermined amount of makeup 16 A-acid was mixed with the as-dried solids along with the desire amount of DI water in 17 prior to heating liquor to the desired reaction temperature. Finally, 2 g of A-acid was 18 added then initiate the second cycle of the fractionation. We compared the chemical 19 compositions from the first and second cycles (Fig. S2b). The differences were within 20 measurement error, suggesting good reusability and (reactivity) of A-acid. The A-acid Electronic Supplementary Material (ESI) for Green Chemistry. This journal is © The Royal Society of Chemistry 2019

Transcript of Supporting Information physiological oxidant graphene ...3 graphene quantum dots and their...

Page 1: Supporting Information physiological oxidant graphene ...3 graphene quantum dots and their application in ultrasensitive profiling of 4 physiological oxidant 5 Ruibin Wang,a† Guangjie

1 Supporting Information

2 Title Direct transformation of lignin into fluorescence-switchable

3 graphene quantum dots and their application in ultrasensitive profiling of

4 physiological oxidant

5 Ruibin Wang,a† Guangjie Xia,b† Wentao Zhong,a Lei Chen,a Liheng Chen,c Yanggang

6 Wang,b* Yonggang Min a* and Kaixin Li a*

7

8 Experimental Section

9 A-acid recyclability

10 We conducted a preliminary evaluation of the reusability of A-acid by fractionating

11 AL under the same condition. First, after the above-mentioned second filtration, the

12 obtained filter cake was thoroughly washed by DI water, and then air-dried (Fig. S2a).

13 Second, we calculated the amount of fresh makeup A-acid needed for the next cycle

14 on the basis of the mass of the as-dried solids with the assumption that A-acid

15 consumption by reaction was negligible. Next, the predetermined amount of makeup

16 A-acid was mixed with the as-dried solids along with the desire amount of DI water in

17 prior to heating liquor to the desired reaction temperature. Finally, 2 g of A-acid was

18 added then initiate the second cycle of the fractionation. We compared the chemical

19 compositions from the first and second cycles (Fig. S2b). The differences were within

20 measurement error, suggesting good reusability and (reactivity) of A-acid. The A-acid

Electronic Supplementary Material (ESI) for Green Chemistry.This journal is © The Royal Society of Chemistry 2019

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21 recovery rate for 5 consecutive cycles is obtained as 85.18 % (Details are listed in

22 Table S1).

23 A HPLC system (Dionex Ultimate 3000, Thermo Fisher Scientific, Germany)

24 equipped with the RefractoMax521 RI Detector that could be used for gel permeation

25 chromatography (GPC) characterization, of which the mobile phase was

26 tetrahydrofuran (0.6 mL/min at a column temperature of 35 °C) with linear

27 polystyrene standards for the molecular weight calibration curve. By means of a

28 sample loop, aliquots of 20 μL of the liquor were analyzed at a time.

29

30 Table S1. The single cycle recovery rate with corresponding rate data obtained by

31 conducting the A-acid fractionation of AL in a consecutive five cycles.

Cycle 1 2 3 4 5

RX (%) * 95.82 97.49 97.36 96.67 96.88

R (%) ** 95.82 93.42 90.95 87.92 85.18

32 * The singe cycle recovery rate, RX, could be calculated by referring eq. 1 shown

33 below, where mX is the weight of the A-acid recovered after the cycle X was finished

34 (X=1, 2, 3, 4, 5 and m0=1.0022 g).

35 eq.1𝑅𝑋 = 𝑚𝑋/𝑚𝑋 ‒ 1 ∗ 100 %

36 ** Recovery rate, R, could be calculated by referring eq. 2 shown below, where RX was

37 obtained above (X=1, 2, 3, 4, 5).

38 eq.2𝑅 =

𝑋

∏𝑘 = 1

𝑅𝑘 ∗ 100 %

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40 The cytotoxicity test of LGQDs

41 The cytotoxicity of LGQDs was evaluated in vitro by using the mouse fibroblast cell

42 L929 with the Cell-Counting Kit-8 assay as reported in our previous study. In brief,

43 cells of the mouse fibroblast cell line L929 were seeded onto 96-well plates (7×103

44 cells/well) and incubated at 37 °C for 8 h. Then, the cell medium was replaced with

45 fresh medium containing various concentrations of LGQDs. The cells treated with

46 LGQDs, and phosphate-buffered saline (PBS), respectively, were incubated at 37 °C

47 for 48 h. After the incubation, all the cells were washed with PBS and then incubated

48 in 100 μL of Dulbecco’s modified Eagle’s medium containing 10 μL of CCK-8 (5

49 mg/mL in PBS) for another 4 h. The absorbance in each well was measured using a

50 microplate reader at a wavelength of 450 nm, to calculate the number of viable cells.

51 Computational details

52 Density functional theory (DFT) calculations were performed within the generalized

53 gradient approximation with the exchange correlation functional of PBE by

54 employing the CP2K package.1-3 The atomic core regions are described by

55 Goedecker-Teter-Hutter (GTH) pseudopotentials,4-6 while the valence wave functions

56 were expanded in terms of double-ζ Gaussian basis sets.7 An additional auxiliary

57 plane-wave basis set with a 360 Ry cutoff is also implemented in electrostatic

58 calculation. The Grimme’s third-generation correction is also involved during the

59 calculation to take into account the dispersion interactions.2 The simulated system is

60 typically consisted of the LGQDs and H2O2 with 294 explicit water molecules(with a

61 density around 0.99 g/mL) inside a periodic cubic box with length of 30 x 30 x 12 Å.

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62 When NaH2PO4 is added, the number of water molecules is reduced to 288 to

63 maintain the water density.

64

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66 Table S2. GQD-based H2O2 detection from the reported literatures and this study.

Method Material Linear

range (M)

Limit of

detection (M)

Reference

Fluorescence MnO2-nanosheet-

modified

upconversion

nanoparticles

1-35 × 10-5 10 × 10-6 8

Fluorescence AgNP-

DNA@GQDs

4-2000 ×

10-7

1 × 10-7 9

Fluorescence FeTMPyP@GQD

s

2-300 × 10-6 3 × 10-7 10

Colorimetry AgNPs@GQDs 1-1000 ×

10-7

3.3 × 10-7 11

Colorimetry GQDs 1 -1000×

10-8

1 × 10-8 12

Fluorescence Graphitic C3N4

nanosheets

1-20000 ×

10-7

5 × 10-8 13

Electrochemistry GQDs 2-8000 ×

10-6

7 × 10-8 14

Fluorescence tyramine@GQDs 1-150 × 10-9 3.2 × 10-10 15

Fluorescence LGQDs 1-150 × 10-9 1.3 × 10-11 Our data

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69 Fig. S1. The structural differences between A-acid, P-acid, B-acid, and C-acid.

70

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73 Fig. S2. (a) Schematic flow diagram shows the recycling process of A-acid for the

74 recyclability test, the inset is the filtrate obtained from the first vacuum filtration

75 (Filtration Ⅰ) and has been air-cooled to room temperature. (b) Elemental

76 composition comparison between LGQDs and the LGQDs prepared by using recycled

77 A-acid.

78

79

80

81

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83 Fig. S3. UV-vis absorbance spectra of the AL aqueous solution.

84

85

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86

87 Fig. S4. (a) PLE spectra of LGQDs at 377, 490 and 576 nm. Single-particle PL

88 emission images of LGQDs under excitations at (b) 535 nm, (c) 475 nm, (d) 360 nm,

89 and (e) their overlaid image.

90

91

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92

93 Fig. S5. (a) Particle size comparison among AL, LGQDs, and other three LGQDs. (b)

94 PL spectra of AL excited within 280-500 nm.

95

96

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97

98

99 Fig. S6. High resolution XPS spectra of (a) C 1s, (b) O 1s, (c) N 1s and (d) S 2p of

100 LNPs.

101

102

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103

104 Fig. S7. The side-chain regions in the two-dimensional HSQC NMR spectra of AL,

105 LNPs, and LGQDs with the chemical structures of three main components.

106 The HSQC data of Alkaline-lignin (AL) indicate the native structure of lignin

107 includes the β-aryl-ether linkages (A), phenylcoumarane structures (B), resinol

108 linkages (C) and methoxyl groups (OCH3).

109 In comparison, the spectrum of LNPs shows no A (α & γ) compounds, which

110 qualitatively demonstrates that AL is strongly de-etherified under A-acid treatment

111 via β-aryl-ether bond cleavage. Meanwhile, the XPS data (Fig. 4b) displayed the N

112 and S dual-doping in LNP, resulting in asymmetric charge density distribution of the

113 host carbon domain (which is also evidenced by our DFT calculations in Fig.6). A lot

114 of active sites will be exposed for further transformation of LNPs (Angewandte

115 Chemie International Edition, 2012, 51(46): 11496-11500.).

116 After further hydrothermal treatment, the obtained LGQDs share a similar HSQC

117 spectrum with LNPs, indicating that the aromatic skeleton is reserved in LGQD. That

118 is, under hydrothermal treatment, the edge groups (eg. epoxy groups, hydroxy groups,

119 carboxylic groups and ketone groups) adjacent to doped N, S are decomposed into

120 CO2, CO, and H2O (J. Mater. Chem., 2012, 22, 25471-25479). In this regard, the

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121 hydrogen bonding and electrostatic interactions in LNPs will be strongly weakened.

122 Accordingly, LNPs were transformed into LGQDs due to the prompt π-π stacking and

123 the increased sp2 hybridization. These results are in consistent with the XPS spectra.

124 According to the data shown above, the chemical mechanism of the

125 transformation of lignin into GQDs has been proposed as follows: The mechanism for

126 chemical transformation of lignin into LGQDs includes two steps. In the 1st step, AL

127 is transformed into LNPs by de-etherification via β-aryl-ether bond cleavage and N, S

128 dual-doping via convalent conjugation. In the 2nd step,the edge groups (mostly the

129 oxygen containing groups) adjacent to doped N, S in LNPs are decomposed into CO2,

130 CO, and H2O. Subsequently LGQDs are formed via π-π stacking and sp2

131 hybridization under hydrothermal treatment. The detailed pathway is shown below:

132

133

134

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136 Fig. S8. Designed LGQDs with (a) SO in the middle and (b) SO2 on the edge.

137

138

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139

140

141 Fig. S9. 3D structures of designed LGQDs in the water box. For brevity the water

142 molecules are omitted in the right column.

143

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145 400 450 500 550 600 650 700

0

40000

80000

120000

160000PL

inte

nsity

(a.u

.)

Wavelength (nm)

DI water NMP 2-Propanol CS2

(a)

400 500 600 700

10000

20000

30000

40000

50000

60000

70000

80000(b)

PL in

tens

ity (a

.u.)

Wavelength (nm)

0 15nM 150nM

146400 500 600 700

10000

20000

30000

40000

50000

60000

70000

80000(c)

PL in

tens

ity (a

.u.)

Wavelength (nm)

0 15nM 150nM

147 Fig. S10. (a) The PL intensity of LGQDs in various solution with different polarity

148 (N-Methyl pyrrolidone (NMP) > DI water > 2-prapanol > CS2); (b) A PL spectra

149 summary of LGQDs in sodium tetraborate buffer(pH=9.18) with H2O2 concentration

150 of 15 and 150 nM; (c) A PL spectra summary of LGQDs in KMnO4 solutions of 15

151 and 150 nM.

152 According to the XPS analysis, the molar ratio of C/S/N/O of LGQDs is

153 0.061667/0.0003688/N 0.0015286/0.014156, which is close to: C167S1N4O38. By

154 further comparing and referring the previous theoretical study that C170H32 with doped

155 S and N is used as the model, we choose C167S1N4O37-38Hn since it has the similar size

156 as theirs (25-26 Å), though the terminal groups of LGQDs are -OH, -COOH, etc.,

157 considering they are originated from alkaline lignin.16, 17

158 According to the reported literature,18 the doped S can exist as C-S unit and C-SO2

Page 17: Supporting Information physiological oxidant graphene ...3 graphene quantum dots and their application in ultrasensitive profiling of 4 physiological oxidant 5 Ruibin Wang,a† Guangjie

159 unit on the edge or C¬SO in the middle of LGQDs. Given that C-S without O

160 obviously cannot have a strong interaction with H2O2, we build two models of

161 C167S1N4O37-38Hn: one with C-SO in the middle, C167S1N4O38H42 (Fig. S7a); and the

162 other with C-SO2 on the edge, C167S1N4O37H34 (Fig. S7b). In both cases the four N

163 exit as two CO-NH2, one C=NH-OH, and one NH2.

164 a) Edge groups: 6 -COOH, [1 =O, 1 -COH-NH2], 1 -CO-NH2, 1 -C=NH-OH, 1

165 -NH2, 21 -OH, 1 center –SO;

166 b) Edge groups: 6 -COOH, [1 =O, 1 -COH-NH2], 1 -CO-NH2, 1 -C=NH-OH, 1

167 -NH2, 19 -OH, 1 edge -SO2.

168 [1 =O, 1 -COH-NH2] is initially 1-OH and 1-CO-NH2. After optimization, as the

169 phenol -OH is acidic, the near -CO-NH2 will be protonated. When water molecules

170 are introduced, the -COH-NH will also be potentiated by a near phenol -OH. In

171 addition, with water solvation, sometimes one extra phenol -OH and -COOH will lose

172 the proton to form the anion. For all the structures, both the -CO-NH2 and -COH-NH2

173 groups will capture an adjacent H on -OH to form the -O- ~ -COH+-NH2

174 intramolecular ion pair. At the beginning of the design, we implement one -NH2, two

175 -CO-NH2 and one -COH-NH2. In most cases, one -CO-NH2 and one -COH-NH2 will

176 be protonated while the remaining one -CO-NH2 is unable to be protonated.

177

178 References

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180 2. J. H. Parrinello and Michele, Mol. Phys., 1997, 92, 477-488.

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181 3. J. VandeVondele, M. Krack, F. Mohamed, M. Parrinello, T. Chassaing and J. Hutter, Comput.

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