Overview of Carbon Quantum Dots Synthesis Strategies

Carbon quantum dots (CQDs) have attracted much attention since their discovery in 2004^[1]. Compared with conventional organic dyes, CQDs have good biocompatibility, good water solubility, fluorescent signal stability, the light can be coordinated, etc. And have been widely researched and applied in biological imaging, biological sensing, optical diagnosis and treatment, photocatalysis, solar cells, light emitting components areas. CQDs is a kind of extremely potential carbon matrix material.

At present, the synthesis methods are mainly divided into "top-down" and "bottom-up". The "top-down" synthesis strategy is conducive to the synthesis of carbon quantum dots with high crystalline and complete structure, while the "bottom-up" synthesis strategy usually produces carbon quantum dots with amorphous carbon nuclei, rich doping sites and many surface functional groups.

"Top-down" synthesis strategy

Synthesis strategy	Advantages	Disadvantages
Arc discharge method	The earliest method to prepare CDQs Product had good fluorescence properties	Production rate is low The purification process is complicated
Electrochemical method	The product has good uniformity High utilization rate for carbon source	The early processing work is tedious and time-consuming Purification takes a long time The quantum yield is low
Laser ablation	Light is adjustable Organic solvents can modify the surface ^[2]	Expensive instrument Complex synthesis Production rate is low Many impurities

"Bottom-up" synthesis strategy

Synthesis strategy	Advantages	Disadvantages
Template method	Fluorescence quantum yield is high Uniform particle size distribution Good solubility in water Low biotoxicity	Complex preparation steps
Microwave digestion synthesis method	Simple and quick operation	The particle size distribution of the product is not uniform, and further separation is needed
Ultrasonic oscillation	The operation is simple	Reaction time is long Production rate is low
Solvent hot method	Simple preparation process High yield	Organic solvents have certain toxicity
Strong acid oxidation	The products all contain carboxyl group, which is favorable for further modification	Cumbersome separation steps Uneven particle size
Hydrothermal method	The most commonly used preparation method Simple synthesis process Uniform particle size distribution Small toxicity

References

Xu X.; et al. Electrophoretic analysis and purification of fluorescent single-walled carbon nanotube fragments. J.Am.Chem.Soc.2004,126(40):12736- 12737.
Hu.; et al. One-step synthesis of fluorescent carbon nanoparticles by laser irradiation. J. Mater. Chem., 2009,19(4):484-488.

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