Facile and High-Yield Synthesis of Carbon Quantum Dots from

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Facile and High-yield Synthesis of Carbon Quantum Dots from Biomass-derived Carbons at Mild Condition Shuangshuang Jing, Yushuang Zhao, Run-Cang Sun, Linxin Zhong, and Xinwen Peng ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.9b00027 • Publication Date (Web): 20 Mar 2019 Downloaded from http://pubs.acs.org on March 21, 2019

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ACS Sustainable Chemistry & Engineering

Facile and High-yield Synthesis of Carbon Quantum Dots from Biomass-derived Carbons at Mild Condition Shuangshuang Jing,a Yushuang Zhao,a Run-Cang Sun, b, c Linxin Zhong,*a and Xinwen Penga a

State Key Laboratory of Pulp and Paper Engineering, South China University of

Technology, NO. 381 Wushan Road, Tianhe District, Guangzhou 510640, China. b

Beijing Key Laboratory of Lignocellulosic Chemistry, Beijing Forestry University,

NO.35 Qinghua East Road, Haidian District, Beijing 100083, China c

Center for Lignocellulose Science and Engneering, Dalian Polytechnic University,

NO.1 Qinggong Road, Ganjingzi District, Dalian 116034, China *Corresponding authors. E-mail: [email protected] (Linxin Zhong). Tel. and Fax: +86 02087111861.

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Abstract Hydrothermal synthesis of carbon quantum dots (CQDs) from biomass is a green and sustainable route for CQDs applications in various fields. However, one of the major problems is the low CQDs yield since the traditional hydrothermal treatment would produce large amounts of hydrochar byproduct. In this work, we present a novel, facile, and effective method for large-scale synthesis of CQDs from biomass-derived carbon including hydrochar and carbonized biomass through mild oxidation (NaOH/H2O2 solution). An ultrahigh CQDs yield of 76.9 wt% can be obtained, which is much higher than those obtained from traditional hydrothermal and strong acid oxidation processes. Furthermore, the CQDs have excellent quantum yield (QY) that is higher than (or comparable to) those from other methods. In addition, the CQDs have uniform size (~2.4 nm) and their surface states can be regulated to significantly improve the QY by adjusting the concentration of oxidants. The CQDs displayed excellent sensitivity for Pb2+ detection along with good linear correlation ranging from 1.3 to 106.7 μM. These advantages, together with low cost, sustainability, and green process, make this approach have great potential in the synthesis and applications of CQDs in large scale.

Keywords: carbon quantum dots, hydrothermal, alkaline-peroxide, hydrochar, biomass


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Introduction As a new class of “zero-dimensional” nano materials, carbon quantum dots (CQDs) attract increasingly interest in recent years because of their outstanding properties including good conductivity, low toxicity 1, unique optical, photoelectronic and fluorescent performances 2. These advantages make them excellent alternatives to toxic metallic quantum dots for applications in photocatalysis 3, electrocatalysis 4, chemical probe 5, bioimaging 6, drug delivery 7 and LED 8. The fabrication of CQDs can generally be classified into “top-down” and “bottom-up” approaches.9 Top-down method involves decomposing macroscopic carbon materials such as graphite, active carbon, carbon nanotubes, coal 10, soot 11, carbonized waste carbon paper12 and biomass 13 by serious treatments, including arc-discharge 14,

laser ablation 15, electronic oxidation

solvethermal treatment

10a.

10b,12-13,16,

chemical oxidation 17, ultrasonic treatment

18

and

Bottom-up method refers to the synthesis of CQDs from precursors such

as organic acid, saccharides, amino acids and some natural products (e.g. foxtail millet 19 and lemon peel

20)

through microwave irradiation

21,

thermal decomposition

22,

hydrothermal/solvothermal

treatment 23, template 24, and plasma 25. As compared with other methods, hydrothermal treatment is a powerful, sustainable and facile technology for synthesizing CQDs from various carbon sources. Among numerous precursors, biomass is the most promising one due to its low cost, renewability, abundance, environmental friendliness, and the natural doping of multi-heteroatom (including N, S, P. etc). 26

It is widely accepted that hydrothermal carbonization of biomass is a green method for the preparation of CQDs. However, one of the major problems this method faces is the low yield because hydrothermal treatment produces large amount of hydrochar as a major byproduct, and the quantity of CQDs in the



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liquid is very low.27 Therefore, it is still a big challenge to synthesize CQDs in high yield from biomass. Considering that hydrochar can be easily produced from various hydrothermal biomass resources in large scale, transferring hydrochar into value-added materials is an interesting topic in biomass conversion. As a kind of macroscopic carbon material, hydrohcar have a potential in synthesizing CQDs through “top-down” methods. Very recently, Zhou et al. 28 synthesized CQDs from hydrochar with concentrated sulfuric acid and nitric acid. However, this method is high cost and the corrosion of strong acid brings severe environmental problem, and thus limiting the application of it.

Herein, we propose a facile and effective path to synthesize CQDs from biomass-derived carbon in a large-scale way through mild oxidation of diluted NaOH/H2O2 solution (at room temperature). As compared with other oxidation reagents such as concentrated sulfuric and nitride acid, NaOH/H2O2 is much more environment-friendly and less corrosive. Exceptionally high yield of CQDs (43.8 wt%, glucose as a precursor) can be obtained, which is much higher than those of CQDs prepared through traditional method (0.62 wt%, glucose as a precursor). This method is universal, and high-yield CQDs also can be produced from various biomass resources, including cellulose, chitosan, and hemicellulose. Furthermore, NaOH/H2O2 solution can effectively decompose carbon from glucose annealing into CQDs at low temperature with an ultrahigh yield of 76.9 wt% (glucose as a precursor), which is superior to those of CQDs obtained from other methods. The as-prepared CQD has high quantum yield and excellent sensitivity for Pb2+ detection. These advantages allow this method hold great promise for sustainably producing CQDs in large scale and potential industrial applications in various fields.

Experiment Section


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Materials D-glucose (ACS reagent), α-cellulose (90 μm), hemicellulose and quinine sulfate dehydrate (99.0%, Biotech) were purchased from Aladdin Industrial Corporation (China). Chitosan (DAC ≥ 95%) was purchased from Jinan Haidebei Marine Bioengineering Co. Ltd. Hydrogen peroxide (AR, 30%), sodium hydroxide (ACS, 97%), hydrochloric acid (AR, 36%~38%), and the other chemical reagents were purchased from Guangzhou Chemical Reagent. The Biotech cellulose ester (CE) membrane (MWCO 500-1000D) was purchased from Shanghai Yuanye Bio-Technology Co., Ltd. All reagents are of analytical grade and used without further purification.

Synthesis of CQDs The synthesis of CQDs involved the hydrothermal treatment of various biomass resources or carbonization of glucose and decomposition of these hydrochar or carbon. Biomass substrates (1.0 g) were dispersed in 10 mL deionzied water and added into a 15 mL teflon container that was packed into a stainless steel autoclave. The mixture was hydrothermally treated at 200 oC for 6 hours, and then cooled to room temperature by fan. The products were centrifuged to separate the suspension and hydrochar. The yellow suspension was than filtrated with 0.22 μm filter membrane and dialyzed to obtain traditional CQDs. The hydrochar was washed with deionized water and ethanol for three times, respectively, and then dried at 60 oC for 24 h in an oven. The glucose-derived carbon was obtained from carbonizing glucose at 250 oC (with a heating rate of 7.5 oC min-1) for 2 h in a tube furnace under N2 atmosphere.

To synthesis CQDs from biomass carbon, 0.1 g carbon material was dispersed in 50 mL diluted NaOH



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solution (0.05, 0.1, 0.2, and 0.3 mol/L), which was followed by adding a spot of H2O2 (2 or 4 mL) to the mixture and stirring for 8 h at room temperature to obtain golden brown transparent liquor. After adjusting pH to 5-9 with HCl, this liquor was dialyzed for 3-5 days to remove salts and harvest pure CQDs. These pure samples were named as 0.05-2, 0.05-4, 0.1-2, 0.1-4, 0.2-2, 0.2-4, 0.3-2 and 0.3-4.

To carry out the scale-up synthesis of CQDs, 120 g glucose was dissolved in 600 mL deionized water and transferred to a 1 L stainless steel autoclave. The thermal reaction was carried out for 3 times under the same reaction conditions mentioned above. The suspension was than filtrated and dialyzed to obtain traditional CQDs. The hydrochar was washed with deionized water for five times, and then dried at 80 oC for 48 h in an oven. After that, hydrochar was added into diluted 0.2 mol/L NaOH solution (the ratio of hydrochar to solution was 10:1, g/L), which was followed by adding 400 mL H2O2 (30 wt%) to the mixture and stirred for 8 h at room temperature. After neutralization with HCl solution, this liquor was dialyzed to remove salts and harvest pure CQDs.

Characterization UV-vis absorption spectra were recorded on a S3100 spectrophotometer (Scinco, Korea) in 1 cm quartz cells. PL spectra measurements were conducted using a Hitachi F-7000 fluorescence spectrophotometer instrument apparatus. Fourier transform infrared spectrum (FT-IR) was characterized at room temperature by a Bruker VERTEX 70 spectrophotometer. Morphology and sizes of CQDs were determined by using transmission electron microscope (TEM, JEM-2100F) and atomic force microscopy (AFM, Muitimode 8, Bruker). Morphology of hydrochar was observed through scanning electron microscopy (SEM, ZEISS Merlin, Germany). The crystalline was determined by


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using a powder X-ray diffractometer (XRD, Bruker D8 ADVANCE). Raman spectra were recorded on a LabRAM Armis (H. J. Y., France) Raman spectrometer with a 532 nm laser beam. The X-ray photoelectron spectroscopy (XPS) analysis was performed by an K-Alpha+ photoelectron spectrometer (Termo Fisher Scientifc, USA) with mono Al Kα (1486.6 eV) as the X-ray source. Elemental analysis was performed by Vario EL cube (Elementar, Germany).

Quantum yield (QY) measurements The quantum yield (QY) of the CQDs was calculated through the following equation: 𝐼𝑥 𝐴𝑠𝑡𝑑 𝜂2𝑥

𝜑𝑥 = 𝜑𝑠𝑡𝑑𝐴𝑥 𝐼𝑠𝑡𝑑 𝜂2

𝑠𝑡𝑑

(1)

where φx is the fluorescence quantum yield; x represents the samples. std is the reference compound. Quinine sulfate dissolved in 0.1 M H2SO4 (φstd = 0.54) was chosen as the reference. η is the refractive index (1.33 for aqueous solution). A is the absorbance at the excitation wavelength. I is the integrated fluorescence intensity under the fluorescence emission spectrum. In order to minimize re-absorption effects, the optical absorbency values were below 0.1 at the excitation wavelength.

Detection of Pb2+ ion For the selectivity test towards Pb2+, the detection of Pb2+ was carried out by adding metal ion stock solutions (including Ni2+, Fe3+, Fe2+, Pb2+, Co2+, Zn2+, Cr3+, Cu2+ and Mn2+) and determining the PL intensity at pH=7.3 in Tris buffer (10 mM). The concentrations of CQDs and these metal ions were 25 μg/mL and 100 μM, respectively. To evaluate the sensitivity towards Pb2+, different concentrations of Pb2+ (pH=7.3) were added into the aqueous solution of CQDs (25 μg/mL) with stirring for 2 min before PL spectral measurement. The fluorescence was recorded at the excitation wavelength of 340 nm. All



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experiments were performed at room temperature.

Results and Discussion Fabrication of CQDs from Digesting Hydrothermal Carbon (Hydrochar) Fig. 1a summarizes the traditional and our new methods for the synthesis of CQDs from biomass via hydrothermal treatment. Traditionally, CQDs are obtained from the suspension of hydrothermal product with a low yield. For example, in this work, when glucose was used as a raw material, only 0.62 wt% CQDs could be obtained from the hydrothermal suspension (the glucose concentration is 10 wt%). However, about 40% solid byproduct (hydrochar) was obtained from the hydrothermal treatment of glucose. After the hydrochar was treated with diluted NaOH/H2O2 solution, a high yield of 43.8 wt% (basing on glucose) of CQDs would obtain at room temperature. This is in sharp contrast with traditional method. CQDs could be easily synthesized through treating hydrochar with low content of NaOH (0.05-0.3 mol/L) and H2O2 (1.2-2.4 wt%) at room temperature. The as-prepared CQDs with a concentration of 0.1 mg/mL in aqueous solution emit blue-green light under the irradiation of UV light (365 nm, Fig. 1 b).


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Fig. 1 (a) Scheme of facile process for fabricating CQDs, and (b) images of CQDs solutions under irradiation of daylight and UV-light (365 nm).

Biomass undergoes structural rearrangement through hydrolysis, dehydration, decarboxylation, aromatization and re-condensation during the hydrothermal treatment.

29

Aromatization occurs

because of the elimination of hydroxyl groups and carboxyl groups caused by dehydration and decarboxylation. Thus, functional groups with double bonds including C=C and C=O replace the hydroxyl and carboxyl groups.30 The re-condensation of small compounds also leads to the formation of hydrochar.31 To understand the synthesis mechanism of CQDs from hydrochar, the morphology and chemical structure of hydrochar from hydrothermal treatment of glucose were investigated. Fig. 2 shows that the hydrochar consists of microspheres with a diameter of 0.2-1 μm, which is coincident to the typical size of glucose-derived hydrochar.32 The XRD pattern (Fig. S1) displays a broad diffraction



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peak (2θ = 22o) and a low-density diffraction peak (2θ = 44o), revealing the amorphous carbon phase and the presence of graphitic carbon, respectively.33

Fig. 2 The structure of hydrochar and the possible mechanism for synthesizing CQDs from alkaline-peroxide treatment. (a) Glucose. (b) SEM image of hydrochar. (c) Possible structure and chemical fracture of hydrochar in

NaOH/H2O2. (d) Carbon quantum dots.

As shown in Fig. 3a, the band at 1633 cm-1 attributed to C=C vibration and the bands at 875-750 cm-1 assigned to aromatic C–H out-of-plane bending vibrations demonstrate the existence of aromatic rings. 30,34 The band at 3000-2810 cm-1 is corresponding to the stretching vibration of aliphatic C-H, revealing

the presence of aliphatic structures. Besides, the presence of oxygen groups in hydroxyl, carbonyl and ether are suggested by the bands at 3000-3715 cm-1 (υO-H), 1705 cm-1 (υC=O), and 100-1460 cm-1 (υC-O and δO-H)

30,35.

Therefore, the hydrochar is composed of abundant aromatic or unsaturated structure

and oxygen groups, as shown in Fig. 2. Quinone or ether also forms as a result of the linkage of chemical species on the surface of nuclei nucleated by aromatic cluster.30


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Fig. 3 FT-IR spectra of hydrochar (a) and CQDs (b).

Comparing with the FT-IR spectra of hydrochar, the decreasing intensity of C=C and C=O and the increasing intensity of –OH in the FT-IR spectra of CQDs (Fig. 3a) indicate the destruction of conjugated double bond and the formation of hydroxyl. As shown in Table 1, the O/C ratio of hydrochar is 0.47 (Sample 2), which is far less than that of CQDs (2.12, Sample 0.3-2), suggesting that more oxygen groups were introduced by the oxidation of NaOH/H2O2. Alkaline-peroxide treatment is widely used in delignification and bleaching in pulping industry through the oxidation of hydrogen peroxide. Under alkaline condition, hydrogen peroxide dissociates as follows: H2O2 + OH– ⇋ H2O + HOO–. The conjugated double bond, carbonyl group and quinoid structure in lignin are destroyed and the carboxyl is introduced, resulting in the degradation of lignin and the generation of soluble aromatic and dicarboxylic acid.36 Similarly, there are abundant aromatic and unsaturated structures, as well as carbonyl groups in hydrochar, which makes it possible to oxidize hydrochar with NaOH/H2O2 and then generate hydrophilic carbonaceous fragments (Fig. 2).

The microstructure of CQDs was investigated by TEM and AFM, as shown in Fig. 4. The CQDs have a uniform diameter ranging from 1.5 to 4.0 nm (Fig. 4a). High-resolution TEM image (HR-TEM) (Fig. 4b) clearly exhibits lattice fringes with inter-planar spacing of 0.20 nm, corresponding to the [1-11]



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facet of graphitic carbon. AFM image (Fig. 4c) further reveals that the CQDs are quasi-spherical carbon nanoparticles. And the typical topographic height of CQDs is 1-3 nm (Fig. 3d).

Fig. 4 The TEM (a), HR-TEM (b) and AFM (c, d) images of the CQDs (sample 0.2-2).

The XRD patterns of the CQDs (Fig. 5a) display a broad diffraction peak at 2θ = 22o, revealing an amorphous carbon phase and abundant defects at the edges of CQDs 37. A low-density diffraction peak at 2θ = 44o ascribed to (100) graphite lattice can also be observed.7,38 The Raman spectra (Fig. 5b) exhibit two broad bands at about 1352 cm-1 (D band) and 1584 cm-1 (G band), corresponding to the sp3 and sp2 hybrid carbon, respectively. The ID/IG ratios for all of the samples are higher than 1, indicating that there are abundant defects at the surface of CQDs. With the increasing concentration of H2O2 and NaOH, ID/IG of CQDs decreases. It is assumed that the CQDs are generated from the degradation of hydrochar by the oxidation of peroxide ion. There is ionization equilibrium in the hydrogen peroxide solution as follows: H2O2 ⇋ H+ + HOO–. Both the increasing contents of H2O2 and NaOH are expected to increase the concentration of HOO– in the solution, which will enhance the


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oxidation of hydrochar. Therefore, the structure of CQDs can be tailored by varying the concentrations of alkali and peroxide.

Fig. 5 XRD pattern (a), Raman spectrum (b), XPS survey (c) and XPS high resolution scan of the C1 s region of CQDs samples: (d) 0.1-2, (e) 0.1-4, (f) 0.2-2, (g) 0.2-4, (h) 0.3-2, (i) 0.3-4.

XPS was performed to analyze the surface elements and their binding states of CQDs. Fig. 5c reveals that the as-prepared CQDs mainly contain carbon and oxygen. The XPS survey spectra of CQDs show an obvious peak of C1s at about 285.0 eV and a peak of O1s at about 531.9 eV. The high resolution spectra of C1s exhibit four main peaks (Fig. 5d-i). The binding energy peak at 284.8 eV confirms the presence of graphitic or aliphatic structure (C=C and C–C). The peak at about 286.3 eV suggests the presence of C–O, and the peak at 288.6 eV can be assigned to C=O. The peak at 289.1 eV assigned to O=C–OH

37

is evident in all samples except the one treated by 0.1 mol/L NaOH and 1.2 wt% H2O2



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(0.1-1, Fig. 5d). The presences of C=C, C–O and O=C–OH clearly indicate that the CQDs possess hydroxyl, epoxy and carbonyl groups, which is also evidenced by FT-IR (Fig. 3b). These groups improve the hydrophilicity and stability of CQDs in aqueous solution. The relative areas of these peaks shown in Table S1 demonstrate that the increment of H2O2 oxidizes C=O and forms more C–O or – COOH. This result is also confirmed by element analysis (Table 1). The ratio of oxygen to carbon rises with increasing concentrations of NaOH and H2O2, suggesting the increment of oxygen groups on the surface of CQDs. Therefore, the surface chemistry can also be tailored by the concentrations of NaOH and H2O2.

Table 1 Element analysis of CQDs fabricated from alkaline peroxide treatment of glucose-derived hydrochar with different concentrations of NaOH and H2O2. Sample

NaOH (mol/L)

H2O2 (wt%)

C

H

Oa

O/C

0.1-2

0.1

1.2

40.3

4.3

55.4

1.4

0.1-4

0.1

2.4

33.4

3.8

62.8

1.9

0.2-2

0.2

1.2

34.1

6.5

59.3

1.7

0.2-4

0.2

2.4

32.0

6.5

61.5

1.9

0.3-2

0.3

1.2

37.9

4.0

58.1

1.5

0.3-4

0.3

2.4

30.7

4.1

65.0

2.1

64.6

5.9

30.4

0.5

2b a

The content of oxygen was calculated. b Hydrochar from hydrothermal treatment of glucose. Reaction condition:

10 wt% glucose aqueous, 200 oC, 6 h.

As shown in Table 2, the yield of CQDs from glucose ranges from 32 wt% to 43.8 wt%, which is at least 50 times more than that of CQDs from traditional route (0.6%, sample 1). And the increasing


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concentration of NaOH or H2O2 doesn’t lead to the decrease in the yield of CQDs. It is also found that, apart from glucose, different biomass resources including cellulose, chitosan, and hemicellulose can be used to synthesize CQDs in a high yield (28-43 wt%), as shown in Table 2. Interestingly, treating the carbonized glucose with NaOH/H2O2 produced CQDs with a yield high up to 76.9%. During the carbonization of glucose in this research, a carbon-rich solid product (carbonized glucose) was obtained with higher yield of 70-85 wt%. Thus, a higher CQDs yield would be achieved from the carbonized glucose.

Table 2 Yields and Quantum Yields (QY) of CQDs synthesized via NaOH/H2O2 treatment. The substrate is hydrochar obtained from hydrothermal conversion of glucose.

a

Sample

NaOH (mol/L)

H2O2 (wt%)

Yield (wt %)a

QY (%)

1b

0

0

0.6

4.03

0.05-2

0.05

1.2

32.0

4.50

0.05-4

0.05

2.4

39.7

5.06

0.1-2

0.1

1.2

36.3

5.39

0.1-4

0.1

2.4

40.0

17.88

0.2-2

0.2

1.2

42.6

12.99

0.2-4

0.2

2.4

43.8

18.90

0.3-2

0.3

1.2

34.7

13.52

0.3-4

0.3

2.4

40.1

22.67

Glucose c

0.1

1.2

76.9

14.99

The yield is related to quality of glucose. b The CQDs was obtained from the suspension in hydrothermal treatment

of glucose. c The glucose was carbonized in tube furnace at 250 oC for 2 h for producing CQDs.

Table 3 shows the comparison of CQDs yield from different methods and materials. Taking glucose



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as a substrate, the yields of CQDs synthesized from NaOH/H2O2 treatment is higher than those of CQDs synthesized from hydrothermal treatment with L-aspartic acid

39

and lysine40. The yield of

CQDs from the carbonized glucose in this work is double of that from hydrothermal treatment of glucose

41.

The yield of CQDs synthesized from cellulose in this work is superior to not only the

ultrasonic treatment of food waste

18,

but also the hydrothermal treatment of cabbage

42,

hair

43,

chitosan 44 and cellulose 45. With the treatment of strong oxidizing acids (sulfuric and nitric acid), hair fiber

46,

waste frying oil

47,

and petroleum coke

48

also generated comparable yields of CQDs (23-

29%). However, this method is high-cost, equipment erosive, and environmentally harmful. Lowconcentration NaOH/H2O2 solution can obtain high-yield CQDs from various biomass at a mild condition. As shown in Fig. 6, a scale-up synthesis of CQDs from traditional method and alkalineperoxide treatment were carried out with 1 L stainless steel autoclave. Three pots of hydrothermal reactions produced 9.03 g and 138.30 g CQDs from the suspension and hydrochar, respectively, which demonstrates the application of our method in a large scale way. The cost of 1 g CQDs is estimated to be 6 dollars (containing chemical and energy costs) in this experiment.

Table 3 The yields and QYs of CQDs synthesized from various methods.


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Materials

Methods

Yield (wt%)

QY (%)

Reference

Hydrothermal treatment

34.5

7.5

39

Glucose, lysine


25

16.3

40

Glucose


34

1.8

41

Cabbage


7.076

16.5

42

Hair


14

10.75

43

Chitosan


~10

13

44

Cellulose


9

Food waste

Ultrasound

0.12

2.85

18

Hair fiber

H2SO4 etching

29

11

46

23.2

3.66

47

24

8.7-15.8

48

Glucose, L-aspartic acid

Waste frying oil

Concentrated H2SO4

45

carbonization Oxidized in concentrated Petroleum coke

H2SO4 and HNO3 Hydrothermal treatment

a

Glucose

NaOH/H2O2 treatment

40.1

22.67

This work

Glucosea

NaOH/H2O2 treatment

76.9

14.99

This work

Celluloseb

NaOH/H2O2 treatment

29.7

7.54

This work

Chitosanb

NaOH/H2O2 treatment

28.1

8.35

This work

Hemicelluloseb

NaOH/H2O2 treatment

29.0

7.44

This work

The substrate is carbonized glucose. b Cellulose, chitosan, and hemicelluloses were hydrothermally treated at 200

oC

for 12 h to obtain hydrochar. Hydrochar from cellulose and chitosan were treated with 0.1 mol/L NaOH and 1.2

wt% H2O2, while hydrochar from hemicelluloses was treated with 0.05 mol/L NaOH and 1.2 wt% H2O2.



Page 18 of 28

Fig. 6 Scheme of Scale-up synthesis of CQDs from hydrothermal treatment of glucose and alkaline treatment of glucose derived hydrochar. (a) Glucose was hydrothermally treated in the reactor. (b) Suspension containing CQDs. (c) Hydrochar collected from hydrothermal treatment of glucose. (d) Pure and dried CQDs from the suspension. (2) Pure and dried CQDs from the hydrochar.

Optical properties of CQDs To study the optical properties of the CQDs, UV-vis absorption and PL spectrum were carried out in details. As illustrated in Fig. 7, the CQDs exhibit a broad absorption at UV band, with absorption features at around 250 nm and 350 nm, which is ascribed to the typical absorption of aromatic π system or the n-p* transition of carbonyl

49,

and n-π* transition of C=O 7. The CQDs solutions show no

obvious fluorescent emission when they are excited at 250 nm, which indicates that the inherent aromatic π system is not the efficient emission center.

50

The emission peak gradually shifts to long

wavelength with the increasing excitation wavelength, suggesting that the photoluminescence of the CQDs is dependent on the excitation wavelength. The excitation-dependent PL behavior can be arisen from exactions of carbon 51, emissive traps 52, aromatic conjugate structure 53, free zig-zag sites 54, and


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the presence of “surface states” 55. Upon increasing the excitation wavelength from 320 to 400 nm, the emission peak shifts from 445 to 495 nm in Fig 7a. The different excitation wavelengths might affect the subsequent excited state energy distribution, the charge separation, and/or the confinement of electrons and holes on CQDs’ surface and their radiative recombination.18,37 This narrow photoluminescence emission area (445-495 nm) confirms that the size distribution of the CQDs is narrow because of similar quantum effects and emission traps on the surface, 18 which well agrees with the results of TEM (Fig 4a). Therefore, the shift results from different energy levels associated with various surface state is caused by the functional groups (e.g., C–OH, C=O, C–O–C, C–H) on the surface of CQDs. 7,55 Table S2 summarizes the maximum emission peaks and corresponding excitation wavelengths from PL spectra. It is obvious that the PL peak shifts to shorter wavelength with the increasing concentration of NaOH/H2O2, demonstrating that the surface state changes with the oxidation of NaOH/H2O2. This result is coincident with the increment of oxygen groups on the surface of CQDs, as demonstrated by the XPS and element analysis.

Fig. 7 UV-vis absorption spectra and the PL emission spectra of the as-prepared CQDs: (a) 0.1-2, (b) 0.1-4, (c) 0.22, (d) 0.2-4, (e) 0.3-2, and (f) 0.3-4.



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The PL excitation (PLE) spectra of CQDs are displayed in Fig S2. The excitation peaks locate at 366, 356, 351, 353, 350, and 341 nm for 0.1-2, 0.1-4, 0.2-2, 0.2-4, 0.3-2, and 0.3-4, respectively, which are corresponding to the adsorption at about 350 nm (Fig. 7). Under the irradiation of excitation wavelength from 720 to 820 nm, the corresponding emission spectra show an up-converted property (Fig. S3). This implies that the CQDs can be used as a potential energy transfer component in biology application or photocatalyst design.38,56 Fig. 8a shows the PL stability in a wide range of pH values. It remains stable at pH=3-11 and declines slightly at strong acidic (pH=2) and alkaline (pH= 12 and 13) conditions. The PL intensity almost does not change even under continuous excitation with a 298 W Xe lamp for 10 h, indicating that the as-synthesized CQDs have excellent photostability (Fig. 8b).

Fig. 8 PL intensity of sample 0.3-2 at different pH values (a), and to the continued illumination (b) for 1, 2, 3, 4, 5, 6, 7, 8, 9, and 10 h with a 294 W Xe lamp.

The quantum yields (QYs) of the as-prepared CQDs are calculated and summarized in Table 2. For sample 0.05-1 and 0.05-2, low-concentration NaOH makes no difference on improving their QYs. This might be attributed to the low content of HOO- in solution. However, with the increasing concentration of NaOH from 0.5 to 1.0 mol/L (sample 0.05-4 and 0.1-4), the QY significantly increases from 5.06% to 17.88%. At the same time, when H2O2 concentration arising from 1.2 wt% to 2.4 wt%, the QY also remarkably increases from 5.39% to 17.88% (sample 0.1-2 and 0.1-4). The increasing


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photoluminescence efficiency caused by the QY change can also be observed by naked eye (Fig 1b, sample 0.1-2 and 0.1-4). Therefore, the concentrations of NaOH and H2O2 have an important impact on the QY of CQDs. As we mentioned in the XPS, elemental and PL analysis, the surface state (the species and proportion of oxygen groups) of CQDs is remarkably affected by the content of HOO– (the oxidation degree). The PL spectra confirm that it is the surface state rather than the aromatic structure of CQDs contributing to the effective emission center. Thus, the increase of oxygen groups on the surface of CQDs with increasing concentrations of NaOH and H2O2 affects the surface state of CQDs and thus causes the rise of QY. Our new method can synthesize CQDs with a high QY of 22.67%, which is higher than those of CQDs not only from hydrothermal treatment of glucose 39-41, cabbage 42, hair 43, chitosan 44, cellulose 45, but also from ultrasonic treatment of food waste 18, and even strong oxidizing acids treatment of hair fiber 46, waste frying oil 47, and petroleum coke

48

(Table 3). With

ultrahigh yield, excellent QY, adjustable surface chemistry, and environment friendliness, our approach opens up a universal and highly effective way for large-scale fabrication and applications of biomass-derived CQDs.

Sensitivity of Pb2+ detection The potential application of the as-prepared CQDs as probes for metallic ions was investigated by measuring the fluorescence changes of the CQDs in Tris buffer. The metal ions tested include Ni2+, Fe2+, Fe3+, Pb2+, Co2+, Zn2+, Cr3+, Cu2+ and Mn2+. As shown in Fig. 9a, Pb2+ shows the highest selectivity towards the fluorescence quenching of CQDs among 9 metal ions, implying that CQDs can be used as a nanosensing platform for Pb2+ ion detection. The fluorescence response of CQDs to Pb2+ was then investigated. The fluorescence intensity of the CQDs at 440 nm gradually declines with the



Page 22 of 28

increasing concentration of Pb2+ from 0 to 220 μM, suggesting that this system is sensitive to Pb2+ ion. The fluorescence quenching data follows the Stern-Volmer equation: I0/I=1+K[C]

(2)

where I and I0 are the fluorescence intensities of the CQDs at 440 nm in the solutions with and without Pb2+, respectively. K is the Stern-Volmer quenching constant, and [C] is the concentration of Pb2+. A good linear correlation (R2 = 0.992) was observed over the concentration range of 1.3-106.7 μM (Fig. 9c). These results clearly confirm that the CQDs can be used as a nanoprobe for Pb2+ detection.

Fig. 9 (a) Comparison of PL intensities of CQDs solutions with different metal ions (pH=7.3, the concentration of CQDs is 25 μg/mL; the concentration of metal ions is 100 μM). (b) PL emission spectra of the CQDs solutions with various concentrations of Pb2+. (c) Stern-Volmer plot as a function of Pb2+ concentration.

Conclusions We present a facile, low-cost, and highly effective method for large-scale synthesis of carbon quantum dots from biomass-derived hydrothermal hydrochar through NaOH/H2O2 treatment. The abundant conjugated double bond, carbonyl group and quinoid groups in the hydrochar are oxidized during the treatment, thus producing CQDs with abundant carboxyl and hydroxyl groups on the surface. The surface state of CQDs can be regulated by adjusting the oxidation condition, and thus their fluorescence efficiency can be significantly improved. The as-prepared CQDs also show potential application in


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Pb2+ detection. Comparing with the traditional hydrothermal method and concentrated strong acid treatment, our new approach displays an ultrahigh production yield and excellent QY. Considering other prominent merits including low cost, sustainability, simple and green process, our method has great potential in industrial applications of CQDs.

Associated Content Supporting Information. The Supporting Information is available free of charge on the ACS Publications website. XRD patterns of hydrochar, PL excitation spectra and up-converted PL emission spectra, tables for further analysis of XPS high resolution scan and PL spectra.

Author Information Corresponding authors L. X. Zhong, Email: [email protected] Tel. and Fax: +86 02087111861 Notes The authors declare no competing financial interest.

Acknowledgements This work was supported by Guangdong Natural Science Funds for Distinguished Young Scholar (2017A030306029 and 2016A030306027), Guangdong Special Support Program (2017TQ04Z837), Natural Science Foundation of Guangdong Province (2016A030313487), Fundamental Research Funds for the Central Universities and State Key Laboratory of Pulp and Paper Engineering.



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Reference (1)

Lim, S. Y.; Shen, W.; Gao, Z., Carbon quantum dots and their applications. Chem. Soc. Rev. 2015, 44, 362, DOI: 10.1039/C4CS00269E.

(2)

Du, Y.; Guo, S., Chemically doped fluorescent carbon and graphene quantum dots for bioimaging, sensor, catalytic and photoelectronic applications. Nanoscale 2016, 8, 2532, DOI: 10.1039/C5NR07579C.

(3)

(a) Xu, X.; Bao, Z.; Zhou, G.; Zeng, H.; Hu, J., Enriching photoelectrons via three transition channels in aminoconjugated carbon quantum dots to boost photocatalytic hydrogen generation. ACS Appl. Mater. Interfaces 2016, 8, 14118, DOI: 10.1021/acsami.6b02961. (b) Wu, W.; Zhang, Q.; Wang, R.; Zhao, Y.; Li, Z.; Ning, H.; Zhao, Q.; Wiederrecht, G. P.; Qiu, J.; Wu, M., Synergies between unsaturated Zn/Cu doping sites in carbon dots provide new pathways for photocatalytic oxidation. ACS Catal. 2017, 8, 747, DOI: 10.1021/acscatal.7b03423.

(4)

Hu, C.; Yu, C.; Li, M.; Wang, X.; Dong, Q.; Wang, G.; Qiu, J., Nitrogen-doped carbon dots decorated on graphene: a novel all-carbon hybrid electrocatalyst for enhanced oxygen reduction reaction. Chem. Commun. 2015, 51, 3419, DOI: 10.1039/c4cc08735f.

(5)

Miao, X.; Yan, X.; Qu, D.; Li, D.; Tao, F. F.; Sun, Z., Red emissive sulfur, nitrogen codoped carbon dots and their application in ion detection and theraonostics. ACS Appl. Mater. Interfaces 2017, 9, 18549, DOI: 10.1021/acsami.7b04514.

(6)

Demir, B.; Lemberger, M. M.; Panagiotopoulou, M.; Medina Rangel, P. X.; Timur, S.; Hirsch, T.; Tse Sum Bui, B.; Wegener, J.; Haupt, K., Tracking hyaluronan: molecularly imprinted polymer coated carbon dots for cancer cell targeting and imaging. ACS Appl. Mater. Interfaces 2018, 10, 3305, DOI: 10.1021/acsami.7b16225.

(7)

Feng, T.; Ai, X.; An, G.; Yang, P.; Zhao, Y., Charge-convertible carbon dots for imaging-guided drug delivery with enhanced in vivo cancer therapeutic efficiency. ACS Nano 2016, 10, 4410, DOI: 10.1021/acsnano.6b00043.

(8)

Chen, Y.; Zheng, M.; Xiao, Y.; Dong, H.; Zhang, H.; Zhuang, J.; Hu, H.; Lei, B.; Liu, Y., A Self-quenchingresistant carbon-dot powder with tunable solid-state fluorescence and construction of dual-fluorescence morphologies for white light-emission. Adv. Mater. 2016, 28, 312, DOI: 10.1002/adma.201503380.

(9)

Wang, R.; Lu, K.-Q.; Tang, Z.-R.; Xu, Y.-J., Recent progress in carbon quantum dots: synthesis, properties and applications in photocatalysis. J. Mater. Chem. A 2017, 5, 3717, DOI: 10.1039/c6ta08660h.

(10)

(a) Li, M.; Yu, C.; Hu, C.; Yang, W.; Zhao, C.; Wang, S.; Zhang, M.; Zhao, J.; Wang, X.; Qiu, J., Solvothermal conversion of coal into nitrogen-doped carbon dots with singlet oxygen generation and high quantum yield. Chem. Eng. J. 2017, 320, 570, DOI: 10.1016/j.cej.2017.03.090. (b) Hu, C.; Yu, C.; Li, M.; Wang, X.; Yang, J.; Zhao, Z.; Eychmuller, A.; Sun, Y. P.; Qiu, J., Chemically tailoring coal to fluorescent carbon dots with tuned size and their capacity for Cu(II) detection. Small 2014, 10, 4926, DOI: 10.1002/smll.201401328.

(11)

Devi, S.; Gupta, R. K.; Paul, A. K.; Kumar, V.; Sachdev, A.; Gopinath, P.; Tyagi, S., Ethylenediamine mediated luminescence enhancement of pollutant derivatized carbon quantum dots for intracellular trinitrotoluene detection: soot to shine. RSC Adv. 2018, 8, 32684, DOI: 10.1039/c8ra06460a.

(12)

Devi, S.; Gupta, R. K.; Paul, A. K.; Tyagi, S., Waste carbon paper derivatized carbon quantum dots/(3aminopropyl)triethoxysilane based fluorescent probe for trinitrotoluene detection. Mater. Res. Express 2019, 6, 025605, DOI: 10.1088/2053-1591/aaf03c.

(13)

Tripathi, K. M.; Tyagi, A.; Ashfaqa, M.; Gupta, R. K., Temperature dependent, shape variant synthesis of photoluminescent and biocompatible carbon nanostructures from almond husk for applications in dye removal. RSC Adv. 2016, 6, 29545, DOI: 10.1039/c5ra27432j.

(14)

Xu, X.; Ray, R.; Gu, Y.; Ploehn, H. J.; Gearheart, L.; Raker, K.; Scrivens, W. A., Electrophoretic analysis and


Page 25 of 28 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


purification of fluorescent single-walled carbon nanotube fragments. J. Am. Chem. Soc. 2004, 126, 12736, DOI: 10.1021/ja040082h. (15)

Li, X.; Wang, H.; Shimizu, Y.; Pyatenko, A.; Kawaguchi, K.; Koshizaki, N., Preparation of carbon quantum dots with tunable photoluminescence by rapid laser passivation in ordinary organic solvents. Chem. Commun. 2011, 47, 932, DOI: 10.1039/c0cc03552a.

(16)

Lu, J.; Yang, J.-x.; Wang, J.; Lim, A.; Wang, S.; Loh, K. P., One-pot synthesis of fluorescent carbon nanoribbons, nanoparticles, and graphene by the exfoliation of graphite in ionic liquids. ACS Nano 2009, 3, 2367, DOI: 10.1021/nn900546b.

(17)

Liu, H.; Ye, T.; Mao, C., Fluorescent carbon nanoparticles derived from candle soot. Angew. Chem. Int. Ed. 2007, 46, 6473, DOI: 10.1002/anie.200701271.

(18)

Park, S. Y.; Lee, H. U.; Park, E. S.; Lee, S. C.; Lee, J. W.; Jeong, S. W.; Kim, C. H.; Lee, Y. C.; Huh, Y. S.; Lee, J., Photoluminescent green carbon nanodots from food-waste-derived sources: large-scale synthesis, properties, and biomedical applications. ACS Appl. Mater. Interfaces 2014, 6, 3365, DOI: 10.1021/am500159p.

(19)

Chen, Z.; Zhao, Z.; Wang, Z.; Zhang, Y.; Sun, X.; Hou, L.; Yuan, C., Foxtail millet-derived highly fluorescent multi-heteroatom doped carbon quantum dots towards fluorescent inks and smart nanosensors for selective ion detection. New J. Chem. 2018, 42, 7326, DOI: 10.1039/c8nj01072b.

(20)

Tyagi, A.; Tripathi, K. M.; Singh, N.; Choudhary, S.; Gupta, R. K., Green synthesis of carbon quantum dots from lemon peel waste: applications in sensing and photocatalysis. RSC Adv. 2016, 6, 72423, DOI: 10.1039/c6ra10488f.

(21)

Zhu, H.; Wang, X.; Li, Y.; Wang, Z.; Yang, F.; Yang, X., Microwave synthesis of fluorescent carbon nanoparticles with electrochemiluminescence properties. Chem. Commun. 2009, 5118, DOI: 10.1039/b907612c.

(22)

(a) Chen, B.; Li, F.; Li, S.; Weng, W.; Guo, H.; Guo, T.; Zhang, X.; Chen, Y.; Huang, T.; Hong, X.; You, S.; Lin, Y.; Zeng, K.; Chen, S., Large scale synthesis of photoluminescent carbon nanodots and their application for bioimaging. Nanoscale 2013, 5, 1967, DOI: 10.1039/c2nr32675b. (b) Tripathi, K. M.; Sonker, A. K.; Bhati, A.; Bhuyan, J.; Singh, A.; Singh, A.; Sarkar, S.; Sonkar, S. K., Large-scale synthesis of soluble graphitic hollow carbon nanorods with tunable photoluminescence for the selective fluorescent detection of DNA. New J. Chem. 2016, 40, 1571, DOI: 10.1039/c5nj02037a.

(23)

(a) Dong, Y.; Pang, H.; Yang, H. B.; Guo, C.; Shao, J.; Chi, Y.; Li, C. M.; Yu, T., Carbon-based dots co-doped with nitrogen and sulfur for high quantum yield and excitation-independent emission. Angew. Chem. Int. Ed. 2013, 52, 7800, DOI: 10.1002/anie.201301114. (b) Briscoe, J.; Marinovic, A.; Sevilla, M.; Dunn, S.; Titirici, M., Biomass-derived carbon quantum dot sensitizers for solid-state nanostructured solar cells. Angew. Chem. Int. Ed. 2015, 54, 4463, DOI: 10.1002/anie.201409290.

(24)

Liu, R.; Wu, D.; Liu, S.; Koynov, K.; Knoll, W.; Li, Q., An aqueous route to multicolor photoluminescent carbon dots using silica spheres as carriers. Angew. Chem. Int. Ed. 2009, 48, 4598, DOI: 10.1002/anie.200900652.

(25)

Jiang, H.; Chen, F.; Lagally, M. G.; Denes, F. S., New strategy for synthesis and functionalization of carbon nanoparticles. Langmuir 2010, 26, 1991, DOI: 10.1021/la9022163.

(26)

(a) Zhao, S.; Lan, M.; Zhu, X.; Xue, H.; Ng, T. W.; Meng, X.; Lee, C. S.; Wang, P.; Zhang, W., Green synthesis of bifunctional fluorescent carbon dots from garlic for cellular imaging and free radical scavenging. ACS Appl. Mater. Interfaces 2015, 7, 17054, DOI: 10.1021/acsami.5b03228. (b) Zhang, M.; Wang, W.; Yuan, P.; Chi, C.; Zhang, J.; Zhou, N., Synthesis of lanthanum doped carbon dots for detection of mercury ion, multi-color imaging of cells and tissue, and bacteriostasis. Chem. Eng. J. 2017, 330, 1137, DOI: 10.1016/j.cej.2017.07.166.

(27)

Zhang, X.; Jiang, M.; Niu, N.; Chen, Z.; Li, S.; Liu, S.; Li, J., Natural-product-derived carbon dots: from natural products to functional materials. ChemSusChem 2018, 11, 11, DOI: 10.1002/cssc.201701847.

(28)

Zhou, Y.; Liu, Y.; Li, Y.; He, Z.; Xu, Q.; Chen, Y.; Street, J.; Guof, H.; Nelles, M., Multicolor carbon nanodots from food waste and their heavy metal ion detection application. RSC Adv. 2018, 8, 23657, DOI:



Page 26 of 28

10.1039/c8ra03272f. (29)

(a) Funke, A.; Ziegler, F., Hydrothermal carbonization of biomass: a summary and discussion of chemical mechanisms for process engineering. Biofuel. Bioprod. Bior. 2010, 4, 160, DOI: 10.1002/bbb.198. (b) Fakkaew, K.; Koottatep, T.; Polprasert, C., Effects of hydrolysis and carbonization reactions on hydrochar production. Bioresour. Technol. 2015, 192, 328, DOI: 10.1016/j.biortech.2015.05.091.

(30)

Sevilla, M.; Fuertes, A. B., The production of carbon materials by hydrothermal carbonization of cellulose. Carbon 2009, 47, 2281, DOI: 10.1016/j.carbon.2009.04.026.

(31)

Libra, J. A.; Ro, K. S.; Kammann, C.; Funke, A.; Berge, N. D.; Neubauer, Y.; Titirici, M.-M.; Fühner, C.; Bens, O.; Kern, J.; Emmerich, K.-H., Hydrothermal carbonization of biomass residuals: a comparative review of the chemistry, processes and applications of wet and dry pyrolysis. Biofuels 2014, 2, 71, DOI: 10.4155/bfs.10.81.

(32)

Sevilla, M.; Fuertes, A. B., Chemical and structural properties of carbonaceous products obtained by hydrothermal carbonization of saccharides. Chem. Eur. J. 2009, 15, 4195, DOI: 10.1002/chem.200802097.

(33)

(a) Zheng, M.; Liu, Y.; Jiang, K.; Xiao, Y.; Yuan, D., Alcohol-assisted hydrothermal carbonization to fabricate spheroidal

carbons

with

a

tunable

shape

and

aspect

ratio.

Carbon

2010,

48,

1224,

DOI:

10.1016/j.carbon.2009.11.045. (b) Zheng, M.; Liu, Y.; Xiao, Y.; Zhu, Y.; Guan, Q.; Yuan, D.; Zhang, J., An easy catalyst-free hydrothermal method to prepare monodisperse carbon microspheres on a large scale. J. Phys. Chem. C 2009, 113, 8455, DOI: 10.1021/jp811356a. (c) Schwan, J.; Ulrich, S.; Batori, V.; Ehrhardt, H.; Silva, S. R. P., Raman spectroscopy on amorphous carbon films. J. Appl. Phys. 1996, 80, 440, DOI: 10.1063/1.362745. (34)

Lua, A. C.; Yang, T., Effect of activation temperature on the textural and chemical properties of potassium hydroxide activated carbon prepared from pistachio-nut shell. J Colloid. Interf. Sci. 2004, 274, 594, DOI: 10.1016/j.jcis.2003.10.001.

(35)

(a) Bacon, R.; Tang, M. M., Carbonization of cellulose fibers—II. Physical property study. Carbon 1964, 2, 221, DOI: 10.1016/0008-6223(64)90036-3. (b) Kabyemela, B. M.; Adschiri, T.; Malaluan, R. M.; Arai, K., Glucose and fructose decomposition in subcritical and supercritical water: detailed reaction pathway, mechanisms, and kinetics. Ind. Eng. Chem. Res. 1999, 38, 28888, DOI: 10.1021/ie9806390.

(36)

Ma, R.; Xu, Y.; Zhang, X., Catalytic oxidation of biorefinery lignin to value-added chemicals to support sustainable biofuel production. ChemSusChem 2015, 8, 24, DOI: 10.1002/cssc.201402503.

(37)

Sahu, S.; Behera, B.; Maiti, T. K.; Mohapatra, S., Simple one-step synthesis of highly luminescent carbon dots from orange juice: application as excellent bio-imaging agents. Chem. Commun. 2012, 48, 8835, DOI: 10.1039/c2cc33796g.

(38)

Ming, H.; Ma, Z.; Liu, Y.; Pan, K.; Yu, H.; Wang, F.; Kang, Z., Large scale electrochemical synthesis of high quality carbon nanodots and their photocatalytic property. Dalton. T. 2012, 41, 9526, DOI: 10.1039/c2dt30985h.

(39)

Zheng, M.; Ruan, S.; Liu, S.; Sun, T.; Qu, D.; Zhao, H.; Xie, Z.; Gao, H.; Jing, X.; Sun, Z., Self-targeting fluorescent carbon dots for diagnosis of brain cancer cells. ACS Nano 2015, 9, 11455, DOI: 10.1021/acsnano.5b05575.

(40)

Li, D.; Na, X.; Wang, H.; Xie, Y.; Cong, S.; Song, Y.; Xu, X.; Zhu, B. W.; Tan, M., Fluorescent carbon dots derived from maillard reaction products: their properties, biodistribution, cytotoxicity, and antioxidant activity. J. Agric. Food Chem. 2018, 66, 1569, DOI: 10.1021/acs.jafc.7b05643.

(41)

Cailotto, S.; Amadio, E.; Facchin, M.; Selva, M.; Pontoglio, E.; Rizzolio, F.; Riello, P.; Toffoli, G.; Benedetti, A.; Perosa, A., Carbon dots from sugars and ascorbic acid: role of the precursors on morphology, properties, toxicity, and drug uptake. ACS Med. Chem. Lett. 2018, 9, 832, DOI: 10.1021/acsmedchemlett.8b00240.

(42)

Alam, A.-M.; Park, B.-Y.; Ghouri, Z. K.; Park, M.; Kim, H.-Y., Synthesis of carbon quantum dots from cabbage with down- and up-conversion photoluminescence properties: excellent imaging agent for biomedical applications. Green Chem. 2015, 17, 3791, DOI: 10.1039/c5gc00686d.


Page 27 of 28 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(43)


Guo, Y.; Zhang, L.; Cao, F.; Leng, Y., Thermal treatment of hair for the synthesis of sustainable carbon quantum dots and the applications for sensing Hg2+. Sci. Rep. 2016, 6, 35795, DOI: 10.1038/srep35795.

(44)

Liang, Z.; Kang, M.; Payne, G. F.; Wang, X.; Sun, R., Probing energy and electron transfer mechanisms in fluorescence quenching of biomass carbon quantum dots. ACS Appl. Mater. Interfaces 2016, 8, 17478, DOI: 10.1021/acsami.6b04826.

(45)

Yang, G.; Wan, X.; Liu, Y.; Li, R.; Su, Y.; Zeng, X.; Tang, J., Luminescent poly(vinyl alcohol)/carbon quantum dots composites with tunable water-induced shape memory behavior in different pH and temperature environments. ACS Appl. Mater. Interfaces 2016, 8, 34744, DOI: 10.1021/acsami.6b11476.

(46)

Sun, D.; Ban, R.; Zhang, P.-H.; Wu, G.-H.; Zhang, J.-R.; Zhu, J.-J., Hair fiber as a precursor for synthesizing of sulfur- and nitrogen-co-doped carbon dots with tunable luminescence properties. Carbon 2013, 64, 424, DOI: 10.1016/j.carbon.2013.07.095.

(47)

Hu, Y.; Yang, J.; Tian, J.; Jia, L.; Yu, J.-S., Waste frying oil as a precursor for one-step synthesis of sulfur-doped carbon dots with pH-sensitive photoluminescence. Carbon 2014, 77, 775, DOI: 10.1016/j.carbon.2014.05.081.

(48)

Wu, M.; Wang, Y.; Wu, W.; Hu, C.; Wang, X.; Zheng, J.; Li, Z.; Jiang, B.; Qiu, J., Preparation of functionalized water-soluble photoluminescent carbon quantum dots from petroleum coke. Carbon 2014, 78, 480, DOI: 10.1016/j.carbon.2014.07.029.

(49)

Liang, Q.; Ma, W.; Shi, Y.; Li, Z.; Yang, X., Easy synthesis of highly fluorescent carbon quantum dots from gelatin

and

their

luminescent

properties

and

applications.

Carbon

2013,

60,

421,

DOI:

10.1016/j.carbon.2013.04.055. (50)

(a) Zeng, Y.-W.; Ma, D.-K.; Wang, W.; Chen, J.-J.; Zhou, L.; Zheng, Y.-Z.; Yu, K.; Huang, S.-M., N, S co-doped carbon dots with orange luminescence synthesized through polymerization and carbonization reaction of amino acids. Appl. Surf. Sci. 2015, 342, 136, DOI: 10.1016/j.apsusc.2015.03.029. (b) Hou, J.; Wang, W.; Zhou, T.; Wang, B.; Li, H.; Ding, L., Synthesis and formation mechanistic investigation of nitrogen-doped carbon dots with high quantum yields and yellowish-green fluorescence. Nanoscale 2016, 8, 11185, DOI: 10.1039/c6nr02701f.

(51)

Zhou, J.; Booker, C.; Li, R.; Zhou, X.; Sham, T.-K.; Sun, X.; Ding, Z., An electrochemical avenue to blue luminescent nanocrystals from multiwalled carbon nanotubes (MWCNTs). J. Am. Chem. Soc. 2007, 129, DOI: 10.1021/ja0669070.

(52)

Mochalin, V. N.; Gogotsi, Y., Wet chemistry route to hydrophobic blue fluorescent nanodiamond. J. Am. Chem. Soc. 2009, 131, 4594, DOI: 10.1021/ja9004514.

(53)

Zhu, S.; Zhang, J.; Qiao, C.; Tang, S.; Li, Y.; Yuan, W.; Li, B.; Tian, L.; Liu, F.; Hu, R.; Gao, H.; Wei, H.; Zhang, H.; Sun, H.; Yang, B., Strongly green-photoluminescent graphene quantum dots for bioimaging applications. Chem. Commun. 2011, 47, 6858, DOI: 10.1039/c1cc11122a.

(54)

Pan, D.; Zhang, J.; Li, Z.; Wu, M., Hydrothermal route for cutting graphene sheets into blue-luminescent graphene quantum dots. Adv. Mater. 2010, 22, 734, DOI: 10.1002/adma.200902825.

(55)

Tang, L.; Ji, R.; Cao, X.; Lin, J.; Jiang, H.; Li, X.; Teng, K. S.; Luk, C. M.; Zeng, S.; Hao, J.; Lau, S. P., Deep ultraviolet photoluminescence of water-soluble self-passivated graphene quantum dots. ACS Nano 2012, 6, 5102, DOI: 10.1021/nn300760g.

(56)

Li, H.; He, X.; Kang, Z.; Huang, H.; Liu, Y.; Liu, J.; Lian, S.; Tsang, C. H.; Yang, X.; Lee, S. T., Water-soluble fluorescent carbon quantum dots and photocatalyst design. Angew. Chem. Int. Ed. 2010, 49, 4430, DOI: 10.1002/anie.200906154.



A facile, universal, and highly effective method is developed to synthesize fluorescent CDs from biomassderived carbons with exceptionally high yield 369x250mm (96 x 96 DPI)


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Facile and High-Yield Synthesis of Carbon Quantum Dots from

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