Overview of Graphene Quantum Dots (GQDs)

Graphene quantum dots refer to an emerging carbonaceous fluorescent material with a graphene sheet size of less than 100nm and a number of sheets of less than 10 layers. Generally speaking, graphene quantum dots include graphene quantum dots, graphene oxide quantum dots, and partially reduced graphene oxide quantum dots, a general term for carbonaceous fluorescent materials and their derivatives with similar structures and the same performance.

Practical applications of graphene quantum dots (GQDs)

Graphene quantum dots have important potential applications in the fields of biology, medicine, and new semiconductor devices. The realization of single-molecule sensors may also lead to the creation of ultra-small transistors or on-chip communication using semiconductor lasers to make chemical sensors, solar cells, medical imaging devices, or nano-scale circuits, and so on.

Application of GQDs in LED

(a) The physical and energy band structure of LEDs using GQDs as electroluminescent phosphors; (b) The structure of LEDs using original GQDs as phosphors that emit blue light; (cd) Organic light-emitting diodes using GQDs as light emitters The physical and electronic structure of (OLED) and the electroluminescence spectrum with a bias voltage of 13V; (e) GQDs are used as color conversion agents for LEDs.

Application of GQDs in photodetectors

a) A photodetector based on GQD-sensitized Si nanowires; (b) A deep ultraviolet photodetector using large band gap GQDs; (c) GQD/ZnO heterojunction as a visible light-UV detector; (d) using a light emitting diode Red light GQD/graphene/BN nanosheets are used as photodetectors to realize a wide range of photoelectric detection from ultraviolet to near-infrared.

Application of GQDs in Catalysis

a) GQD with intramolecular Z-scheme structure as photocatalyst; (b) N-GQDs catalyzes hydrogen evolution reaction; (c) N-GQD/Vo-NaTaON for catalyzing CO2 emission reduction; (d) for catalyzing NO oxidation GQD/N-Bi2O2CO3 heterojunction; (e) GQD/C3N4 heterojunction for photocatalytic degradation of pollutants; (f) GQD-based NiCo2P2 nanocatalyst for bi-functional overall water splitting; (g) GQD -The rhenium complex has an ultra-low initial potential for reducing CO2 to CO.

Application of GQDs in biological therapy

(a) Use FA functionalized IR780/GQD photothermal therapy to kill cancer cells and eradicate mouse tumors;

(b) Photodynamic therapy using photosensitizer (Ce6) to functionalize GQD.

The advantages of graphene quantum dots (GQDs) over other quantum dots

"Quantum dots" are something that TV and solar cell manufacturers have been boasting about in the past few years. These tiny semiconductor crystals are usually made of metals such as cadmium selenide and are good at absorbing invisible light and emitting it as visible light of a specific wavelength. Quantum dots are basically a kind of mini-disc, which can absorb ultraviolet light and release it in the visible light spectrum. We can change the color in the visible spectrum according to the size of the dot.

Although the effect of quantum is very large, the production of quantum dots is a difficult and energy-intensive process. Due to the presence of cadmium, some of them are very toxic. Companies like Samsung have begun to use safer alternatives in their products, but several other issues still hinder their full potential-many of which can be solved by graphene substitution.

Graphene quantum dots have other properties that metal quantum dots do not have, such as electrical conductivity and thermal conductivity. It is 200 times stronger than steel. Since graphene is just carbon, the toxicity of GQDs is very low, and the "quantum yield"-the ratio of energy consumed to dots generated-is much higher.

Graphene is also easier to get blues. In displays, metal quantum dots cannot replicate blue well, because only the smallest dots about two nanometers wide emit blue light, making them very difficult to manufacture.

They are problematic because they are too small and the crystal structure is not large enough to provide them with enough quantum yield. The quantum yield of blue metal quantum dots is about 4-6%, so they do not use blue quantum dots, they use blue LED backlight.

All these advantages make graphene quantum dots more attractive than their metal cousins, and they can generally open up the range of applications of quantum dots. In addition to displays, these fluorescent spots may appear in pigments and dyes, cosmetics, anti-counterfeiting technologies, batteries, solar cells, sensors, lights, lasers, water or ultraviolet monitoring systems, and biological imaging technologies.

Graphene quantum dots can be used as optical brighteners, especially as additives in existing laundry detergents. Graphene quantum dots are a more effective and cleaner alternative to the fluorophores widely used in detergents.

Potential bottlenecks in graphene quantum dot manufacturing

The preparation of graphene quantum dots is mainly divided into the enlargement method and the reduction method (also called "bottom-up" and "top-down" method)

Table 1 Comparison of preparation technologies of graphene quantum dots

The preparation technology of graphene quantum dot reduction method has the advantages of easy availability of raw materials, simple production process, and suitable for large-scale preparation, but it has disadvantages such as difficult control, low yield, and unstable product size; the expansion method preparation process is highly controllable , But the operation is relatively cumbersome, and the product purification is difficult, etc.

Development and opportunities

The development background of our company's quantum dot project

The quantum dot project was launched in September 2017. The technical team of Jiangsu Huada Group Company inspected foreign advanced quantum dot technology companies and markets, and cooperated with corresponding foreign technical teams to introduce them to jointly develop industrialized mass production processes. With the cooperation and promotion of the technical teams of both parties, the project achieved a phased success in May 2018. In the same month, Changzhou Huada Nano Material Technology Co., Ltd. was established for this purpose. As of January 2021, with the goal of stably supplying qualified samples, our company has now fully developed two stable experimental process routes for quantum dots (GQD, RQD). From the adaptive optimization and adjustment of equipment, formula, process, etc., a stable domestic raw material supply channel is basically determined.

Project performance advantage

At present, most companies at home and abroad have graphene quantum dot synthesis processes. At present, there are reports that there are mainly two methods, top-down (reduction method) and bottom-up (enlargement method). The reduction method preparation technology has the advantages of easy availability of raw materials, simple production process, and suitable for large-scale preparation, but it has disadvantages such as difficult control, low yield, and unstable product size; the expansion method has strong controllability, but relative operation It is cumbersome and difficult to purify the product. So compared to this, our current results appear to have more advantages:

1. The main production process of our company's graphene quantum dots uses unique raw materials and dispersants to carry out chain rearrangement and cracking reactions under highly specific conditions to generate graphene quantum dots. Its raw materials are all industrialized raw materials, which are relatively cheap and easy to obtain, and the supply is stable. At the same time, it has reached an agreement with some raw material suppliers to jointly develop higher-quality raw materials.

2. The success of the special reaction process directly solves the problem that cannot be scaled up due to the limitation of the mechanism, increases the output per unit time, and the waste liquid produced is far lower than other companies' production processes.

3. The reaction temperature is close to 500℃, and the mixing time of each material is accurately controlled. Other process production is prone to errors, resulting in poor repeatability. Our current chemical reaction has basically effectively reduced the above risks and has strong stability.

4. Graphene quantum dot products under our company's unique process have stable quality and higher quality than the current quantum dot products on the European and American markets.

The above advantages have formed a unique quantum dot synthesis process and raw material formula of our company, forming a unique technical barrier.

Project Outlook

At present, the company's quantum dot project has basically been feasible for mass production after technical evaluation. Our company is currently planning to put into production a graphene quantum dot with an annual output of 12kg. The unit price of quantum dot materials is 200-1000 US dollars/g, and about 1.315 million-6.5 million yuan. /kg. Since our graphene quantum dots are of relatively high-end quality, our annual output value can reach 30-40 million yuan, with profits and taxes above 25 million yuan. Since the annual output of solids is 12 kg, the raw materials and three wastes involved in the entire process are not large, and the actual production area requires a small area (about 80 square meters), so the operability is strong!

Graphene Quantum Dot Synthesis Technology Service

At present, most companies at home and abroad have graphene quantum dot synthesis processes. At present, there are reports that there are mainly two methods, top-down (reduction method) and bottom-up (enlargement method). The reduction method preparation technology has the advantages of easy availability of raw materials, simple production process, and suitable for large-scale preparation, but it has disadvantages such as difficult control, low yield, and unstable product size; the expansion method has strong controllability, but relative operation It is cumbersome and difficult to purify the product. So compared to this, our current results appear to have more advantages:

1 The main production process of our company's graphene quantum dots is to carry out chain rearrangement and cracking reactions under specific process conditions with unique raw materials and dispersants to generate graphene quantum dots. Its raw materials are all industrialized raw materials, which are relatively cheap and easy to obtain, and the supply is stable. At the same time, it has reached an agreement with some raw material suppliers to jointly develop higher-quality raw materials.

2 The success of the special reaction process directly solves the problem that cannot be scaled up due to the limitation of the mechanism, improves the output per unit time, and the waste liquid produced is far lower than other companies' production processes.

3 The reaction temperature is close to 500℃, the mixing time of each material is accurately controlled, and other process production is prone to errors, resulting in poor repeatability. Our current response has basically effectively reduced the above risks with strong stability.

The graphene quantum dot products produced by our company's unique process have stable quality and higher quality than the graphene quantum dot products currently on the European and American markets.

The above advantages have formed a unique quantum dot synthesis process and raw material formula of our company, forming a unique technical barrier.

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