Different synthesis routes of CQDs from different precursors, their optical properties and applications.

Precursors	Synthesis route	Quantum yield (QY)	Application	Reference
Citric acid, ethylenediamine	Hydrothermal			48
Ammonium citrate, ethylenediamine	Hydrothermal		Photocatalysis	49
Sodium citrate, ethylenediamine	Hydrothermal		H2O2 sensor	50
Folic acid, ethylene glycol	Hydrothermal	15.7%	Hg2+ sensor	51
CCl4, 1,2-ethylenediamine	Solvothermal	36.3%	pH, Ag+, Fe3+, H2O2 sensor, bioimaging	32
N-Methyl-2-pyrrolidone, dimethyl-imidazolidinone	Pyrolysis	11.6%	Bioimaging, electrocatalysts	52
Petroleum coke	Chemical oxidation with acid	15.8%		53
Graphite rods	Electrochemical	12%	Catalyst	54
Citric acid monohydrate, l-cysteine	Hydrothermal	73%	Bioimaging	55
Carbon target	Laser ablation	>10%		14
Diammonium hydrogen citrate, urea	Solid state reaction	46.4%	Sensor, bioimaging, fluorescent ink	56
Citric acid, linear-structured polyethyleneimine	Hydrothermal	37.4%		57
Citric acid, diethylenetriamine, gadolinium chloride	Hydrothermal	69.86%	Bioimaging	58
Citric acid, branched polyethylenimine	Pyrolysis	42.5%	Sensor	59
Coal	Chemical oxidation with acid	18.6%	Composites	60
Hair	Carbonization-microwave	86.06%	Bioimaging	61
Gelatin	Hydrothermal	31.6%	Bioimaging, fluorescent ink	62
Citric acid, cysteamine	Hydrothermal	81%	Composites, bioimaging	63
Activated carbon	Chemical oxidation with acid	26%	Sensor	64
Citric acid, dicyandiamide	Solid state reaction	73.2%	Sensor	65
Alanine, ethylenediamine	Hydrothermal	46.2%	Biosensing, bioimaging	66
Anthracite, dimethyl formamide	Solvothermal	47.0%	Composite	67
Citric acid, diethylenetriamine	Hydrothermal	98%		68
Activated carbon	Chemical oxidation	>10%	Electrochemiluminescence	69
Citric acid, ethylenediamine	Hydrothermal	80%	Biosensor, fluorescent ink, composites	70
Bergamot (a plant)	Hydrothermal	50.78%	Sensor	71
l-Glutamic acid	Pyrolysis	28%	Biological detection	72
Citric acid, branched polyethyleneimine	Microwave pyrolysis	12–13%	In vivo gene delivery	73
Anhydrous citric acid, NaBH4, ammonia	Hydrothermal	36%	Sensor	74
Citric acid, urea, H2SO4, H3PO4	Microwave		Screening of oxygen-states in CQDs	75
Tetraphenylporphyrin or its metal complex, nitric acid, ethanediamine	Hydrothermal	10.1–17.8%	Sensor, bioimaging	76
Activated carbon, KOH	High-energy ball milling	7.6%	Electrochemiluminescence	28
Amino acids	Electrochemical/electroanalytical	7–46.2%	Bioimaging, sensor	77