Table 1.

Natural carbon quantum dots (NCDs) synthesized by different method.

S. No.	NCDs	Methods	Quantum Yield (%)	Size (nm)	Reference
‘Bottom-up’ approach
1	White flowering plant	Hydrothermal, 250 °C, 4 h	28.2	5	[11]
2	Ascorbic acid	Hydrothermal, 180 °C, 12 h	47	4.5	[12]
3	Orange juice	Hydrothermal,120 °C, 150 min	26	1.5−4.5	[13]
4	Lemon juice	Hydrothermal, 120–280 °C, 12 h	14.86 to 24.89	12−15 (200 °C), 3−5 (280 °C)	[14]
5	Carrot roots	Hydrothermal, 170 °C, 12 h	7.6	2.3	[15]
6	Pomelo peels	Hydrothermal, 220 °C,2 h	6.9	3	[26]
7	Papaya	Hydrothermal, 200 °C, 5 h	18.39−18.98	20	[64]
8	Tulsi leaves	Hydrothermal, 200 °C, 4 h	3.06	5	[79]
9	Curcumin	Hydrothermal, 180, 1h	3.6	1.6	[86]
10	Egg yolk oil	Hydrothermal, 200 °C,60 min	5.01	10	[16]
11	Chitosan	Microwave,450 W, 5 min	2−10	20	[17]
12	Sucrose	Microwave, 100 W, 3 min 40 s	–	3−10	[18]
13	Raw cashew gum	Microwave, 800 W, 30 - 40 min	–	9	[19]
14	Lotus root	Microwave, 800 W, 6 min	–	–	[20]
15	L-Asparagine	Microwave, 180 W, 15 min	–	2.17 ± 0.70	[42]
16	Konjac flour	Pyrolysis, 470 °C, 1.5 h	–	–	[21]
17	Curcumin	Pyrolysis,180 °C	17	2−8	[22]
18	Aloe vera	Pyrolysis, 160–250 °C	12.37		[44]
‘Top-down’ approach
19	Curcumin	Ultrasonic	–	13.7+4.9	[45]
20	Fruit juice (Avacado, kiwi, pear)	Ultrasonic,30 °C, hydrothermal treatment 200 °C for 12 h	35, 23, 20	4.42 + 0.05, 4.35 + 0.04, 4.12 +0.03	[32]
21	N-acetyl-l-cysteine	Laser ablation	–	34.1−40.8	[24]
22	Neem Leaves	Chemical oxidation	1−2	5−6	[27]