臺灣博碩士論文加值系統

因為獨特的物理、化學及光學性質，近年來石墨烯量子點材料逐漸受到注視。除了延續石墨烯原先具有的物化特性如: 大比表面積、化學物理穩定性、非毒性等之外，因為其奈米尺寸的大小，電子受到量子侷限效應與邊界效應而產生具有與半導體相似的性質，因此從原先零能隙衍生出具有可調控能隙的性質。近幾年來各界學者積極投入研究可調式能隙的石墨烯量子點，以理論與實驗方法探討量子點特性與影響能隙的因子，並將影響的因子主要歸納為粒子大小、表面官能基組成、邊緣結構與表面型態。
目前用以合成石墨烯量子點的方法多數以水熱法、溶熱法或濕式化學法合成，然而上述方法均涉及耗時、複雜的反應程序與化合物使用，將不利於工業化發展與後續應用。本研究提出一個簡易且快速的合成技術是利用大氣常壓微電漿系統製備石墨烯量子點，所使用的微電漿設備、製程程序與前驅物簡單，所合成的石墨烯量子點其平均粒徑為4.9 nm，為典型的藍光螢光性質，而量子螢光效率則約為1.5%。隨後透過改變製程物理參數如反應時間與前驅物濃度可得到不同光學特性之石墨烯量子點，研究結果顯示隨著反應時間增長或提高前驅物濃度都將增加石墨烯量子點的粒徑，且其螢光性質也產生紅位移，意味著石墨烯量子點能隙的減少是由於量子侷限效應所影響。在探討合成機制上，透過實行不同反應條件如改變氣體環境、前驅物與加入添加物等，從中推測在電漿環境中具有自由基聚合的反應程序，微電漿系統提供一個可初始化自由基聚合的環境與條件，使得前驅物分子在液面下可以自由基化並隨後聚合形成石墨烯量子點。
此外，本研究亦探討使用其他不同鏈長分子作為前驅物，經由大氣常壓微電漿處理後，其粒徑大小隨著使用的鏈長增加而變大，在螢光性質上同樣產生紅位移，進一步闡述量子侷限效應對其光學與物理性質的影響，這將有助於可調式螢光性質石墨烯量子點的發展與研究，並將可應用於特定技術或生醫領域上。

Graphene quantum dots (GQDs) have attracted attention due to its unique and superior physical, chemical and optical properties. On the basis of graphene structure, it possess large specific surface area, physiochemical stability and non-toxic. Electrons in GQDs would be limited by structure because of their nanoscale size. Hence, band gap opening of GQDs should be highly size-dependent, which is called quantum confinement. For this reason, GQDs have similar property which is non-zero band gap to semiconductor. In recent years, continuously increasing researches interest in tunable fluorescence GQDs. They probably categorize the effect factors of band gap into particle size, functional groups, edges structure and surface state.
Currently, most synthesis methods are using hydrothermal, solvothermal and wet chemistry. All of which are time-consuming, complex reaction procedure and chemicals unfavorable to its development and applications. Here, we presented a facile and rapid method to synthesize GQDs by atmospheric-pressure microplasma. The average diameter of as-product GQDs were 4.9 nm. They were typical blue fluorescence with quantum yield around 1.5%. Subsequently, through changing physical parameters like reaction time and precursor concentration, we can get different optical properties GQDs. PL emission wavelength were red shift, which suggested that band gap were decreased when the reaction time or precursor concentration were increased. Based on TEM and XPS analysis, their particles size had increasing tendency with analogous surface compositions, suggesting that PL red shift reason was originated from quantum confinement effect predominantly. The influence of using microplasma towards GQDs formation was also investigated. Through a series of experiments and paper review, we considered that radical polymerization were existed in solution. Microplasma can be as a radical initiator and induce precursor radicalized. Radicalized molecule subsequently were cyclized and finally polymerized to form GQDs.
Additionally, we also studied using different chain length molecule as precursor to implement microplasma. The characteristic analysis results exhibited a consistent of surface composition of as-product by XPS. GQDs particle size and PL emission wavelength were increased with using longer chain molecule. It meant that GQDs band gap were decreased. These results further prove quantum confinement effect and chemical formula effect on GQDs physical and optical properties. This study will contribute to the development of tunable fluorescence GQDs and be applied in specific fields or biomedical techniques.

Content
List of figures VIII
1 Introduction 1
1.1 Graphene quantum dots (GQDs) structure 1
1.2 GQDs Properties 3
1.2.1 Optical properties 3
1.2.3 Cytotoxicity 13
1.2.3 Electrochemical luminescence 15
1.3 GQDs Synthesis 16
1.3.1 Top-down approach 17
1.3.2 Bottom-up approach 19
1.4 Atmospheric-pressure microplasma system 22
2 Experiment 28
2.1 Chemicals 28
2.2 Characterizations 28
2.2.1 UV-visible spectroscopy 28
2.2.2 Raman spectroscopy 29
2.2.3 Photoluminescence spectroscopy (PL) 29
2.2.4 Transmission Electron Microscopy (TEM) 29
2.2.5 Atomic Force Microscopy (AFM) 29
2.2.6 Fourier Transform Infrared Spectrometer (FT-IR) 29
2.2.7 X-ray photoelectron spectroscopy (XPS) 30
2.2.8 Gas chromatography mass spectrometry (GC-Mass) 30
2.3 Microplasma-liquid system synthesis 30
2.3.1 GQDs synthesis method 30
2.3.2 Synthesis mechanism experiment 31
2.4 Quantum yield calculation 32
3 Results and Discussion 34
3.1 Synthesize GQDs using SDS as precursor by Microplasma 34
3.2 Synthesis parameters effect on PL property 42
3.3 Synthesis mechanism 47
3.4 Other precursors for discussing PL property 53
4 Conclusion 56
5 Supporting information 58
6 Reference 61

1. Namdari P, Negahdari B, Eatemadi A. Synthesis, properties and biomedical applications of carbon-based quantum dots: An updated review. Biomed Pharmacother. 2017;87:209-222.
2. Li L, Wu G, Yang G, Peng J, Zhao J, Zhu JJ. Focusing on luminescent graphene quantum dots: current status and future perspectives. Nanoscale. 2013;5(10):4015-4039.
3. Lin L, Rong M, Luo F, Chen D, Wang Y, Chen X. Luminescent graphene quantum dots as new fluorescent materials for environmental and biological applications. TrAC Trends in Analytical Chemistry. 2014;54:83-102.
4. Wang Z, Zeng H, Sun L. Graphene quantum dots: versatile photoluminescence for energy, biomedical, and environmental applications. J. Mater. Chem. C. 2015;3(6):1157-1165.
5. Ponomarenko LA, Schedin F, Katsnelson MI, et al. Chaotic Dirac Billiard in Graphene Quantum Dots. Science. 2008;320(5874):356-358.
6. Benítez-Martínez S, Valcárcel M. Graphene quantum dots in analytical science. TrAC Trends in Analytical Chemistry. 2015;72:93-113.
7. Dong Y, Lin J, Chen Y, Fu F, Chi Y, Chen G. Graphene quantum dots, graphene oxide, carbon quantum dots and graphite nanocrystals in coals. Nanoscale. 2014;6(13):7410-7415.
8. Zhu S, Song Y, Wang J, et al. Photoluminescence mechanism in graphene quantum dots: Quantum confinement effect and surface/edge state. Nano Today. 2016.
9. Zheng XT, Ananthanarayanan A, Luo KQ, Chen P. Glowing graphene quantum dots and carbon dots: properties, syntheses, and biological applications. Small. 2015;11(14):1620-1636.
10. Li X, Rui M, Song J, Shen Z, Zeng H. Carbon and Graphene Quantum Dots for Optoelectronic and Energy Devices: A Review. Advanced Functional Materials. 2015;25(31):4929-4947.
11. Jin SH, Kim DH, Jun GH, Hong SH, Jeon S. Tuning the Photoluminescence of Graphene Quantum Dots through the Charge Transfer Effect of Functional Groups. ACS Nano. 2013;7(2):1239-1245.
12. Ye R, Peng Z, Metzger A, et al. Bandgap engineering of coal-derived graphene quantum dots. ACS Appl Mater Interfaces. 2015;7(12):7041-7048.
13. Pu C, Qin H, Gao Y, Zhou J, Wang P, Peng X. Synthetic Control of Exciton Behavior in Colloidal Quantum Dots. J Am Chem Soc. 2017;139(9):3302-3311.
14. Shen J, Zhu Y, Yang X, Li C. Graphene quantum dots: emergent nanolights for bioimaging, sensors, catalysis and photovoltaic devices. Chem Commun (Camb). 2012;48(31):3686-3699.
15. Li X, Zhang S, Kulinich SA, Liu Y, Zeng H. Engineering surface states of carbon dots to achieve controllable luminescence for solid-luminescent composites and sensitive Be2+ detection. Scientific Reports. 2014;4.
16. Gan Z, Xu H, Hao Y. Mechanism for excitation-dependent photoluminescence from graphene quantum dots and other graphene oxide derivates: consensus, debates and challenges. Nanoscale. 2016;8(15):7794-7807.
17. Yuan F, Wang Z, Li X, et al. Bright Multicolor Bandgap Fluorescent Carbon Quantum Dots for Electroluminescent Light-Emitting Diodes. Adv Mater. 2017;29(3).
18. Yeh TF, Huang WL, Chung CJ, et al. Elucidating Quantum Confinement in Graphene Oxide Dots Based On Excitation-Wavelength-Independent Photoluminescence. J Phys Chem Lett. 2016;7(11):2087-2092.
19. Li Y, Zhao Y, Cheng H, et al. Nitrogen-doped graphene quantum dots with oxygen-rich functional groups. J Am Chem Soc. 2012;134(1):15-18.
20. Tetsuka H, Asahi R, Nagoya A, et al. Optically Tunable Amino-Functionalized Graphene Quantum Dots. Advanced Materials. 2012;24(39):5333-5338.
21. Sk MA, Ananthanarayanan A, Huang L, Lim KH, Chen P. Revealing the tunable photoluminescence properties of graphene quantum dots. Journal of Materials Chemistry C. 2014;2(34):6954.
22. Bao L, Liu C, Zhang ZL, Pang DW. Photoluminescence-tunable carbon nanodots: surface-state energy-gap tuning. Adv Mater. 2015;27(10):1663-1667.
23. Yang Z-C, Wang M, Yong AM, et al. Intrinsically fluorescent carbon dots with tunable emission derived from hydrothermal treatment of glucose in the presence of monopotassium phosphate. Chemical Communications. 2011;47(42):11615-11617.
24. Kim S, Hwang SW, Kim M-K, et al. Anomalous Behaviors of Visible Luminescence from Graphene Quantum Dots: Interplay between Size and Shape. ACS Nano. 2012;6(9):8203-8208.
25. Zhu S, Meng Q, Wang L, et al. Highly photoluminescent carbon dots for multicolor patterning, sensors, and bioimaging. Angew Chem Int Ed Engl. 2013;52(14):3953-3957.
26. Ding H, Yu S-B, Wei J-S, Xiong H-M. Full-Color Light-Emitting Carbon Dots with a Surface-State-Controlled Luminescence Mechanism. ACS Nano. 2015.
27. Tetsuka H, Nagoya A, Fukusumi T, Matsui T. Molecularly Designed, Nitrogen-Functionalized Graphene Quantum Dots for Optoelectronic Devices. Adv Mater. 2016;28(23):4632-4638.
28. Huang P, Shi JJ, Zhang M, et al. Anomalous Light Emission and Wide Photoluminescence Spectra in Graphene Quantum Dot: Quantum Confinement from Edge Microstructure. J Phys Chem Lett. 2016;7(15):2888-2892.
29. Liu R, Wu D, Feng X, Mullen K. Bottom-up fabrication of photoluminescent graphene quantum dots with uniform morphology. J Am Chem Soc. 2011;133(39):15221-15223.
30. Tan J, Zou R, Zhang J, Li W, Zhang L, Yue D. Large-scale synthesis of N-doped carbon quantum dots and their phosphorescence properties in a polyurethane matrix. Nanoscale. 2016;8(8):4742-4747.
31. Niu W-J, Li Y, Zhu R-H, Shan D, Fan Y-R, Zhang X-J. Ethylenediamine-assisted hydrothermal synthesis of nitrogen-doped carbon quantum dots as fluorescent probes for sensitive biosensing and bioimaging. Sensors and Actuators B: Chemical. 2015;218:229-236.
32. Pan D, Zhang J, Li Z, Wu M. Hydrothermal route for cutting graphene sheets into blue-luminescent graphene quantum dots. Adv Mater. 2010;22(6):734-738.
33. Gan Z, Xiong S, Wu X, et al. Mechanism of Photoluminescence from Chemically Derived Graphene Oxide: Role of Chemical Reduction. Advanced Optical Materials. 2013;1(12):926-932.
34. Deng Y, Chen X, Wang F, Zhang X, Zhao D, Shen D. Environment-dependent photon emission from solid state carbon dots and its mechanism. Nanoscale. 2014;6(17):10388-10393.
35. Cushing SK, Li M, Huang F, Wu N. Origin of Strong Excitation Wavelength Dependent Fluorescence of Graphene Oxide. ACS Nano. 2014;8(1):1002-1013.
36. Dong Y, Pang H, Yang HB, et al. Carbon-Based Dots Co-doped with Nitrogen and Sulfur for High Quantum Yield and Excitation-Independent Emission. Angewandte Chemie International Edition. 2013;52(30):7800-7804.
37. Cao L, Wang X, Meziani MJ, et al. Carbon Dots for Multiphoton Bioimaging. Journal of the American Chemical Society. 2007;129(37):11318-11319.
38. Lee E, Ryu J, Jang J. Fabrication of graphene quantum dots via size-selective precipitation and their application in upconversion-based DSSCs. Chem Commun (Camb). 2013;49(85):9995-9997.
39. Zhu S, Zhang J, Liu X, et al. Graphene quantum dots with controllable surface oxidation, tunable fluorescence and up-conversion emission. RSC Advances. 2012;2(7):2717.
40. Shen J, Zhu Y, Chen C, Yang X, Li C. Facile preparation and upconversion luminescence of graphene quantum dots. Chem Commun (Camb). 2011;47(9):2580-2582.
41. Wen X, Yu P, Toh YR, Ma X, Tang J. On the upconversion fluorescence in carbon nanodots and graphene quantum dots. Chem Commun (Camb). 2014;50(36):4703-4706.
42. Zhu S, Zhang J, Qiao C, et al. Strongly green-photoluminescent graphene quantum dots for bioimaging applications. Chem Commun (Camb). 2011;47(24):6858-6860.
43. Dong Y, Chen C, Zheng X, et al. One-step and high yield simultaneous preparation of single- and multi-layer graphene quantum dots from CX-72 carbon black. Journal of Materials Chemistry. 2012;22(18):8764.
44. Zhu S, Zhang J, Tang S, et al. Surface Chemistry Routes to Modulate the Photoluminescence of Graphene Quantum Dots: From Fluorescence Mechanism to Up-Conversion Bioimaging Applications. Advanced Functional Materials. 2012;22(22):4732-4740.
45. Peng J, Gao W, Gupta BK, et al. Graphene quantum dots derived from carbon fibers. Nano Lett. 2012;12(2):844-849.
46. Frigerio C, Ribeiro DS, Rodrigues SS, et al. Application of quantum dots as analytical tools in automated chemical analysis: a review. Anal Chim Acta. 2012;735:9-22.
47. Li L-L, Ji J, Fei R, et al. A Facile Microwave Avenue to Electrochemiluminescent Two-Color Graphene Quantum Dots. Advanced Functional Materials. 2012;22(14):2971-2979.
48. Chen Y, Dong Y, Wu H, Chen C, Chi Y, Chen G. Electrochemiluminescence sensor for hexavalent chromium based on the graphene quantum dots/peroxodisulfate system. Electrochimica Acta. 2015;151:552-557.
49. Du X, Jiang D, Liu Q, Zhu G, Mao H, Wang K. Fabrication of graphene oxide decorated with nitrogen-doped graphene quantum dots and its enhanced electrochemiluminescence for ultrasensitive detection of pentachlorophenol. Analyst. 2015;140(4):1253-1259.
50. Dong Y, Shao J, Chen C, et al. Blue luminescent graphene quantum dots and graphene oxide prepared by tuning the carbonization degree of citric acid. Carbon. 2012;50(12):4738-4743.
51. Zhou X, Zhang Y, Wang C, et al. Photo-Fenton Reaction of Graphene Oxide: A New Strategy to Prepare Graphene Quantum Dots for DNA Cleavage. ACS Nano. 2012;6(8):6592-6599.
52. Zhuo S, Shao M, Lee S-T. Upconversion and Downconversion Fluorescent Graphene Quantum Dots: Ultrasonic Preparation and Photocatalysis. ACS Nano. 2012;6(2):1059-1064.
53. Wang L, Chen X, Lu Y, Liu C, Yang W. Carbon quantum dots displaying dual-wavelength photoluminescence and electrochemiluminescence prepared by high-energy ball milling. Carbon. 2015;94:472-478.
54. Zhang M, Bai L, Shang W, et al. Facile synthesis of water-soluble, highly fluorescent graphene quantum dots as a robust biological label for stem cells. Journal of Materials Chemistry. 2012;22(15):7461-7467.
55. Li Y, Hu Y, Zhao Y, et al. An electrochemical avenue to green-luminescent graphene quantum dots as potential electron-acceptors for photovoltaics. Adv Mater. 2011;23(6):776-780.
56. Shinde DB, Pillai VK. Electrochemical preparation of luminescent graphene quantum dots from multiwalled carbon nanotubes. Chemistry. 2012;18(39):12522-12528.
57. Ananthanarayanan A, Wang X, Routh P, et al. Facile Synthesis of Graphene Quantum Dots from 3D Graphene and their Application for Fe3+Sensing. Advanced Functional Materials. 2014;24(20):3021-3026.
58. Zhou J, Booker C, Li R, et al. An electrochemical avenue to blue luminescent nanocrystals from multiwalled carbon nanotubes (MWCNTs). J Am Chem Soc. 2007;129(4):744-745.
59. Qu D, Zheng M, Zhang L, et al. Formation mechanism and optimization of highly luminescent N-doped graphene quantum dots. Sci Rep. 2014;4:5294.
60. Gu J, Zhang X, Pang A, Yang J. Facile synthesis and photoluminescence characteristics of blue-emitting nitrogen-doped graphene quantum dots. Nanotechnology. 2016;27(16):165704.
61. Zheng B, Chen Y, Li P, et al. Ultrafast ammonia-driven, microwave-assisted synthesis of nitrogen-doped graphene quantum dots and their optical properties. Nanophotonics. 2017;6(1).
62. Qu S, Zhou D, Li D, et al. Toward Efficient Orange Emissive Carbon Nanodots through Conjugated sp -Domain Controlling and Surface Charges Engineering. Adv Mater. 2016.
63. Wang Z, Long P, Feng Y, Qin C, Feng W. Surface passivation of carbon dots with ethylene glycol and their high-sensitivity to Fe3+. RSC Adv. 2017;7(5):2810-2816.
64. Schneider J, Reckmeier CJ, Xiong Y, et al. Molecular Fluorescence in Citric Acid-Based Carbon Dots. The Journal of Physical Chemistry C. 2017;121(3):2014-2022.
65. Krysmann MJ, Kelarakis A, Dallas P, Giannelis EP. Formation mechanism of carbogenic nanoparticles with dual photoluminescence emission. J Am Chem Soc. 2012;134(2):747-750.
66. Li Y, Zhong X, Rider AE, Furman SA, Ostrikov K. Fast, energy-efficient synthesis of luminescent carbon quantum dots. Green Chemistry. 2014;16(5):2566.
67. Fang Q, Dong Y, Chen Y, et al. Luminescence origin of carbon based dots obtained from citric acid and amino group-containing molecules. Carbon. 2017;118:319-326.
68. Tian L, Yang S, Yang Y, et al. Green, simple and large scale synthesis of N-doped graphene quantum dots with uniform edge groups by electrochemical bottom-up synthesis. RSC Adv. 2016;6(86):82648-82653.
69. Huang X, Li Y, Zhong X, Rider AE, Ostrikov KK. Fast Microplasma Synthesis of Blue Luminescent Carbon Quantum Dots at Ambient Conditions. Plasma Processes and Polymers. 2015;12(1):59-65.
70. Wang Z, Lu Y, Yuan H, Ren Z, Xu C, Chen J. Microplasma-assisted rapid synthesis of luminescent nitrogen-doped carbon dots and their application in pH sensing and uranium detection. Nanoscale. 2015;7(48):20743-20748.
71. Akolkar R, Sankaran RM. Charge transfer processes at the interface between plasmas and liquids. Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films. 2013;31(5):050811.
72. Chiang W-H, Richmonds C, Sankaran RM. Continuous-flow, atmospheric-pressure microplasmas: a versatile source for metal nanoparticle synthesis in the gas or liquid phase. Plasma Sources Science and Technology. 2010;19(3):034011.
73. Rumbach P, Bartels DM, Sankaran RM, Go DB. The solvation of electrons by an atmospheric-pressure plasma. Nature Communications. 2015;6:7248.
74. Stratton GR, Dai F, Bellona CL, Holsen TM, Dickenson ER, Mededovic Thagard S. Plasma-Based Water Treatment: Efficient Transformation of Perfluoroalkyl Substances in Prepared Solutions and Contaminated Groundwater. Environ Sci Technol. 2017;51(3):1643-1648.
75. Bruggeman PJ, Kushner MJ, Locke BR, et al. Plasma–liquid interactions: a review and roadmap. Plasma Sources Science and Technology. 2016;25(5):053002.
76. Go DB. Atmospheric-pressure ionization: New approaches and applications for plasmas in contact with liquids. Journal of Physics: Conference Series. 2015;646:012052.
77. Mariotti D, Sankaran RM. Microplasmas for nanomaterials synthesis. Journal of Physics D: Applied Physics. 2010;43(32):323001.
78. Lin L, Wang Q. Microplasma: A New Generation of Technology for Functional Nanomaterial Synthesis. Plasma Chemistry and Plasma Processing. 2015;35(6):925-962.
79. Shi JJ, Kong MG. Evolution of discharge structure in capacitive radio-frequency atmospheric microplasmas. Phys Rev Lett. 2006;96(10):105009.
80. Kaufmann W. Elektrodynamische Eigentümlichkeiten leitender Gase. Annalen der Physik. 1900;307(5):158-178.
81. Wang C, Xu Z, Cheng H, Lin H, Humphrey MG, Zhang C. A hydrothermal route to water-stable luminescent carbon dots as nanosensors for pH and temperature. Carbon. 2015;82:87-95.
82. Zhang Y, He J. Facile synthesis of S, N co-doped carbon dots and investigation of their photoluminescence properties. Phys. Chem. Chem. Phys. 2015;17(31):20154-20159.
83. Yoon H, Chang YH, Song SH, et al. Intrinsic Photoluminescence Emission from Subdomained Graphene Quantum Dots. Adv Mater. 2016.
84. Hu S, Trinchi A, Atkin P, Cole I. Tunable photoluminescence across the entire visible spectrum from carbon dots excited by white light. Angew Chem Int Ed Engl. 2015;54(10):2970-2974.
85. Sun Y, Wang S, Li C, et al. Large scale preparation of graphene quantum dots from graphite with tunable fluorescence properties. Phys Chem Chem Phys. 2013;15(24):9907-9913.
86. Song L, Shi J, Lu J, Lu C. Structure observation of graphene quantum dots by single-layered formation in layered confinement space. Chemical Science. 2015;6(8):4846-4850.
87. Gupta A, Chen G, Joshi P, Tadigadapa S, Eklund. Raman Scattering from High-Frequency Phonons in Supported n-Graphene Layer Films. Nano Letters. 2006;6(12):2667-2673.
88. Loukanov A, Sekiya R, Yoshikawa M, Kobayashi N, Moriyasu Y, Nakabayashi S. Photosensitizer-Conjugated Ultrasmall Carbon Nanodots as Multifunctional Fluorescent Probes for Bioimaging. The Journal of Physical Chemistry C. 2016.
89. Hou J, Wang L, Zhang P, Xu Y, Ding L. Facile synthesis of carbon dots in an immiscible system with excitation-independent emission and thermally activated delayed fluorescence. Chem Commun (Camb). 2015.
90. Zhao L, Gao L. Coating multi-walled carbon nanotubes with zinc sulfide. Journal of Materials Chemistry. 2004;14(6):1001.
91. Ding H, Xiong H-M. Exploring the blue luminescence origin of nitrogen-doped carbon dots by controlling the water amount in synthesis. RSC Adv. 2015;5(82):66528-66533.
92. Lu L, Zhu Y, Shi C, Pei YT. Large-scale synthesis of defect-selective graphene quantum dots by ultrasonic-assisted liquid-phase exfoliation. Carbon. 2016;109:373-383.
93. Ye R, Xiang C, Lin J, et al. Coal as an abundant source of graphene quantum dots. Nat Commun. 2013;4:2943.
94. Jovanović SP, Marković ZM, Syrgiannis Z, et al. Enhancing photoluminescence of graphene quantum dots by thermal annealing of the graphite precursor. Materials Research Bulletin. 2017;93:183-193.
95. Li X, Lau SP, Tang L, Ji R, Yang P. Multicolour light emission from chlorine-doped graphene quantum dots. Journal of Materials Chemistry C. 2013;1(44):7308.
96. Li X, Lau SP, Tang L, Ji R, Yang P. Sulphur doping: a facile approach to tune the electronic structure and optical properties of graphene quantum dots. Nanoscale. 2014;6(10):5323-5328.
97. Liu X, Wang J, Li Y, Xue W. Size controllable preparation of graphitic quantum dots and their photoluminescence behavior. Materials Letters. 2016;162:56-59.
98. Zhang F, Liu F, Wang C, et al. Effect of Lateral Size of Graphene Quantum Dots on Their Properties and Application. ACS Appl Mater Interfaces. 2016.
99. Zhang W, Liu Y, Meng X, et al. Graphenol defects induced blue emission enhancement in chemically reduced graphene quantum dots. Phys Chem Chem Phys. 2015;17(34):22361-22366.
100. Brouwer AM. Standards for photoluminescence quantum yield measurements in solution (IUPAC Technical Report). Pure and Applied Chemistry. 2011;83(12).
101. Li B, Guo Y, Iqbal A, et al. Insight into excitation–related luminescence properties of carbon dots: synergistic effect from photoluminescence centers in carbon core and on the surface. RSC Adv. 2016.
102. Fumiyoshi T, Naoki S, Satoshi U. Liquid-phase reactions induced by atmospheric pressure glow discharge with liquid electrode. Journal of Physics: Conference Series. 2014;565(1):012010.
103. Le Caër S. Water Radiolysis: Influence of Oxide Surfaces on H2 Production under Ionizing Radiation. Water. 2011;3(1):235.
104. Marotta E, Paradisi C. A mass spectrometry study of alkanes in air plasma at atmospheric pressure. J Am Soc Mass Spectrom. 2009;20(4):697-707.
105. Rumbach P, Witzke M, Sankaran RM, Go DB. Decoupling interfacial reactions between plasmas and liquids: charge transfer vs plasma neutral reactions. J Am Chem Soc. 2013;135(44):16264-16267.
106. Megan W, Paul R, David BG, Sankaran RM. Evidence for the electrolysis of water by atmospheric-pressure plasmas formed at the surface of aqueous solutions. Journal of Physics D: Applied Physics. 2012;45(44):442001.
107. Gorbanev Y, Leifert D, Studer A, O'Connell D, Chechik V. Initiating radical reactions with non-thermal plasmas. Chem. Commun. 2017;53(26):3685-3688.
108. Teng C-Y, Yeh T-F, Lin K-I, Chen S-J, Yoshimura M, Teng H. Synthesis of graphene oxide dots for excitation-wavelength independent photoluminescence at high quantum yields. J. Mater. Chem. C. 2015;3(17):4553-4562.
109. Gao F, Ma S, Li J, et al. Rational design of high quality citric acid-derived carbon dots by selecting efficient chemical structure motifs. Carbon. 2017;112:131-141.