GQDs find application in displays, sensors, biomedicine, electronics and anti-counterfeiting.
Carbon dots and graphene quantum dots (CDs, GQDs) represent relatively new members of the carbon nanomaterials family. Studies have demonstrated that quantum confinement could appear in graphene with finite size and edge effects-graphene quantum dots (GQDs).1 GQDs display properties derived from both graphene and carbon dots, combining the structure of graphene with the quantum confinement and edge effects of CDs. They possess unique optical and electrical properties such as:
- strong photoluminescence
- biocompatibility
- exhibit band gap (unlike graphene sheets).
Figure 1: Commercially available Graphene Quantum Dots. Image credit: Dotz Nano.
As a result they are being widely investigated for applications in optoelectronics, biomedicine and sensors.
Properties
Carbon quantum dots (CDs) are quasi-spherical nanoparticles less than 10 nm in diameter, formed by crystalline sp2 graphite cores, or amorphous aggregations, which have a quantum confinement effect.
Graphene quantum dots (GDs) are composed of single or very few graphene lattices (<10) that have quantum confinement effect and edge effects.. Unlike graphene sheets, they exhibit band gap that is responsible for their unique electrical and optoelectronic properties.
GQDs are promising materials as substitutes for Cd, Ir, Ga, S, Se and P quantum dots (QDs) and possess unique structural and photophysical properties. Compared with QDs, GQDs are potentially superior due to their high photostability against photobleaching and blinking, biocompatibility, and low toxicity.
Theoretical and demonstrated properties include:
• high quantum yield
• high electrical conductivity
• high thermal conductivity
• excellent photostability
• biocompatibility
• highly tunable photoluminescence (PL)
• exceptional multi-photon excitation (up-conversion) property
• low-toxicity.
|
Types |
Optical properties |
Optical properties |
Optical properties |
Stability |
Toxicity |
Cost |
|
Quantum yield |
Emission |
Half-height |
||||
|
Graphene QDs |
90+ % (potentially) |
380-570nm (no red) |
>40nm (ca. 70nm) |
Yes |
No |
Low |
|
Semiconductor QDs |
• CdSe 10-25% • ZnSe/CdSe 30-50% |
480-640nm |
40nm> |
No |
Yes |
High |
Table 1: Properties of graphene QDs and semiconductor QDs.
They are especially interesting in the biomedical field as they are water-soluble, they can be decorated exploiting different chemical approaches and they possess intrinsic characteristics of fluorescence.
Synthesis
There are two main strategies for synthesizing GQDs:
Top-down method: Graphene oxide is manufactured then the graphene sheet is cut through controlled oxidation or the reduction process to the desired size to fabricate GQDs. Specific approaches for preparation include:
• molecular assembly of carbon ring structures.
• chemical exfoliation of graphite nanofibers. 2
• chemical synthesis.
• modification of graphite nanoparticles.
• electron beam lithography. 3
• pulsed laser synthesis.
• microwave pyrolysis. 4 5 6 7
• hydrothermal graphene oxide reduction, resulting in the fracture of GO sheets into ultra-small pieces. 8 9
Bottom-up method: Low molecular weight compounds are polymerized to nm-size to obtain GQDs. Various carbon starting materials are utilized.
The bottom-up approach only produces a small quantity of GQDs, limiting its use. The top-down method potentially offers low-cost and high yield and is the main focus of commercial production.
There are a number of technical hurdles that need to be overcome for successful production with low synthesis yields at present due to aggregation that limit industrial scale-up. 10 11 Also the synthesized GQDs currently display low quantum yield, poor control of the emission wavelength and optical instability. 12 Researchers have recently turned their attentions to developing new methods for synthesis.
Applications
GQDs be used in various applications, such as sensing, consumer electronics, computer storage, medical imaging, sensing, solar cells and energy storage.
Applications of graphene QDs that have been identified include:
Optoelectronics, electronics and photonics
• Optoelectronics (LEDs). 13 14 15
• Photodetectors.16
• Sensors.
• Quantum computing.
Energy
• Batteries and supercapacitors. 17
• Fuel cells.
• Photovoltaics.
• Lighting (OLED).
Biomedicine and healthcare
• Bioimaging (e.g. membrane markers, cancer cell imaging, protein analysis, cell tracking). 18 19
• Biosensors.
• Theranostic agents.
• Cancer therapy.
Figure 4: Graphene quantum dots have many advantages over metallic quantum dots, including their ability to better reproduce the color blue (Credit: Dotz Nano).
Advantages
The advantage of GQDs is that demonstrate similar properties to cadmium-based QDs but without the potentially hazardous health and environmental effects, and at lower cost. In the coming years they could be utilized as inexpensive and eco-friendly alternatives to QDs for opto-electronic devices such as displays and lighting devices. GQDs strong photoluminescence can be tailored for specific applications by controlling their size, shape, defects, and functionality.
Pricing
GQDs are currently commercially available, with materials selling for up to $2.5 million/kg, although recent producers have manufactured materials for less. Competing materials such as high quality, non-toxic Cadmium Quantum Dots selling for up to $8 million/kg.
Recent commercial activity
Fuji Pigment
In April 2016, Fuji Pigment announced the development of a large-scale manufacturing process for carbon and graphene quantum dots (QDs). Fuji Pigment stated that its toxic-metal-free QDs exhibit a high light-emitting quantum efficiency and stability comparable to the toxic metal-based quantum dots. Read more at http://www.fuji-pigment.co.jp/en/Graphene_Quantum_Dot_en.pdf
Dotz Nano
In January 2017, Dotz Nano signed a marketing agreement with Strem Chemicals, a manufacturer and distributor of specialty chemicals headquartered in the U.S. Strem Chemicals will become a global distributor of Graphene Quantum Dots. Dotz Nano Ltd. uses low-cost, raw material to make high-quality, cost-effective products.
Dotz Nano’s patented technology was developed at Rice University. In February 2017, the company announced its first commercial shipment of GQDs to China.
Read more at http://www.dotznano.com/ and https://secure.strem.com/catalog/family/Quantum+Dots/
Other Producers
ACS Materials, LLC, USA
The company is a graphene producer. They also produce a range of graphene QDs.
KRI, Inc., Japan
The company produces graphene quantum dots and has developed proprietary synthesis methods.
Shanghai Simbatt Energy Technology Co., Ltd., China
The company produces GQD powder and in solution.
References
1. L Li, X Yan, The Journal of Physical Chemistry Letters, 1(17), 2572 (2010).
2. S Schnez, F Molitar, C Stampfer, et al., Applied Physics Letters, 94(1), (2009).
3. H Zhu, X Wang, Y LI, Z Wang, F Yang, X Yang, Chem. Commun, no. 34, 5118 (2009).
4. X Wang, K Qu, B Xu, J Ren, X Qu, Journal of Materials Chemistry, 21(8), 2445 (2011).
5. Libin Tang, Rongbin Ji, et al., ACS Nano, 6(6), 5102 (2012).
6. J Lu, P S E Yeo, C K Gan, et al., Nature nanotechnology, 6(4), 247 (2011).
7. http://pubs.rsc.org/en/content/articlelanding/2015/nr/c5nr00814j#!divAbstract
8. D Pan, J Zhang, Z Li, M Wu, Advanced Materials, 22(6), 734 (2010).
9. D Pan, L Guo, J Zhang, C Xi, Q Xue, H Huang, et al., Journal of Materials Chemistry.
10. Zhu, S. J. et al. Strongly Green-Photoluminescent Graphene Quantum Dots for Bioimaging Applications. Chem. Commun. 47, 6858–6860 (2011).
11. Pan, D. Y., Zhang, J. C., Li, Z. & Wu, M. H. Hydrothermal Route for Cutting Graphene Sheets into Blue-Luminescent Graphene Quantum Dots. Adv. Mater. 22, 734–738 (2010).
12. Lin, L. X. & Zhang, S. W. Creating High Yield Water Soluble Luminescent Graphene Quantum Dots Via Exfoliating and Disintegrating Carbon Nanotubes and Graphite Flakes. Chem. Commun. 48, 10177–10179 (2012).
13. Luk C, Tang L, Zhang W, Yu S, Teng K and Lau S 2012 J. Mater. Chem. 22 22378.
14. http://www.nature.com/articles/srep11032
15. Kwon, W. et al. Electroluminescence from graphene quantum dots prepared by amidative cutting of tatterd graphite. Nano Lett.14, 1306–1311 (2014).
16. http://www.nature.com/articles/srep05603
17.http://www.sciencedaily.com/releases/2015/06/150614225649.htm
18. Zhu S, Zhang J, Tang S, Qiao C, Wang L, Wang H, Liu X, Li B, Li Y and Yu W 2012 Adv. Funct. Mater. 22 4732
19. S. Nandi, R. Malishev, K. Parambath Kootery, Y. Mirsky, S. Kolusheva, R. Jelinek, Chem. Commun. 2014, 50, 10299 – 10302.
20. Zhuo S, Shao M and Lee S T 2012 ACS Nano 6 1059.
21. Li Y, Zhao Y, Cheng H, Hu Y, Shi G, Dai L and Qu L 2012 J. Am. Chem. Soc. 134
22. J. Wang, C.-F. Wang, S. Chen, Angew. Chem. Int. Ed. 2012, 51, 9297 – 9301; Angew. Chem. 2012, 124, 9431 – 9435.
Further information
The Global Market for Quantum Dots 2017-2027
Published by Future Markets, January 2017, Read more at https://www.futuremarketsinc.com/the-global-market-for-quantum-dots-2/
