CN105692581A - Preparation method of high-crystallization graphene quantum dots capable of replacing fullerene - Google Patents

Abstract

The invention discloses a method for preparing high-crystallinity graphene-like quantum dots that can replace fullerenes, using small molecular carbohydrates as carbon sources to carry out one-step hydrothermal synthesis of nanoscale carbon quantum dots, and performing these carbon quantum dots Temperature-controlled microwave reduction treatment removes oxygen-containing groups on the surface. The chloroform solvent is mixed with the treated carbon quantum dot aqueous solution, the mixed solution is extracted and separated, the chloroform solution in the lower layer is collected, and the chloroform solvent in the lower layer is removed by vacuum distillation to obtain the final product. The preparation method of the present invention is easy to operate, has short time and high yield, and can realize large-scale preparation. Graphene quantum dots with soluble organic phase and uniform size can be obtained through one-step solvent selection and separation. It is expected that this material will be applied to light detection devices, solar cells and other organic photovoltaic fields.

Description

Preparation method of highly crystalline graphene-like quantum dots that can replace fullerenes

technical field

The invention belongs to the field of preparation of carbon nanomaterials, and more specifically, relates to a graphene-like quantum dot (GQD) with a high crystal structure dominated by ^sp2 hybridized carbon atoms, which can be used as a substitute for fullerene-derived Electron acceptor materials for organic solar cells.

Background technique

Among renewable energy sources such as solar energy, wind energy, hydrogen energy, and coal vaporization, photovoltaic energy, which converts solar energy into electricity, is one of the most promising energy sources in the future. At present, the mainstream inorganic solar cells, such as monocrystalline silicon and polycrystalline silicon solar cells, have high power conversion efficiency (PCE), but the high energy consumption production process and high price limit their wide application. In contrast, polymer solar cells have unique advantages such as light weight, good flexibility, low production cost and easy realization of large-area processing, and have great potential in widely utilizing solar energy (LiG, ShrotriyaV, YangY, et al. - organization of Polymer Blends. Nat. Mater., 2005, 4:864—868. Koster LJA, Mihailetchi VD, Blom PWM. Ultimate Efficiency of Polymer/fullerene Bulk Heterojunction Solar Cells. Appl. Phys. Lett., 2006, 88:093511.). In the field of polymer solar cells, polymer/fullerene solar cells (PFSCs) using conjugated polymers as electron donors and fullerene and its derivatives as electron acceptors are the hottest research direction. . However, as a three-dimensional aromatic compound with a unique cage structure, the preparation of fullerene is generally very complicated, and chemical modification is usually required to better realize its application. Therefore, the development of new acceptor materials may provide new ideas for the preparation of organic solar cells.

Carbon is the basis of all known life on earth. Due to its various electron orbital characteristics (sp, sp ² , sp ³ ), many substances with strange structures and properties are formed. At the beginning of the 21st century, scientists at Clemson University in the United States first developed a new type of carbon nanomaterial - carbon quantum dots (CQD), because its structure is similar to a disc or circle formed by stacking graphene sheets with a size of a few nanometers. Spheres are also reported to be called "graphene quantum dots" (GQD) (XuX, RayR, GuY, et al., Electrophoretic Analysis and Purification of Fluorescent Single-Walled Carbon Nanotube Fragments, J.Am.Chem.Soc., 2004, 126, 12736-12737.), very Soon, the superior performance of this material has attracted widespread attention. Further studies have shown that GQDs have high chemical stability, photostability and special optical properties (STYang, L.Cao, PGJLuo, et al., CarbonDotsforOpticalImaginginVivo, J.Am.Chem.Soc.,2009,131,11308–11309 .ZP Zhang, J. Zhang, N. Chen, etal., Graphene Quantum Dots: An Emerging Material for Energy-related Applications and Beyond, Energy Environ. Sci., 2012, 5, 8869–8890); as a nanoscale "quantum dot" material, it also has particle Small diameter (generally less than 10nm), adjustable excitation wavelength and excellent biocompatibility. In addition, compared with traditional quantum dots and organic dyes, it has the advantages of low toxicity, stability, easy preparation and easy chemical modification (ZAQiao, YFWang, Y.Gao, et al., Commercially Activated Carbon as the Source for Producing Multicolor Photoluminescent Carbon Dots by Chemical Oxidation, Chem.Commun., 2010, 46, 8812-8814. F. Wang, Z. Xie, H. Zhang, et al., Highly Luminescent Organosilane-Functionalized Carbon Dots, Adv. Funct. Mater., 2011, 21, 1027-1031). GQD can be divided into oil-soluble carbon dots and water-soluble carbon dots according to whether they are soluble in water. Among them, the surface of water-soluble GQD has a large number of hydrophilic groups such as carboxyl and hydroxyl groups. Based on these surface active sites, researchers have extensively and effectively discussed their potential application value (SN Baker and G.A. Baker, Luminescent Carbon Nanodots: Emergent Nanolights, Angew. Chem., Int. Ed., 2010, 49, 6726–6744.), they can be compatible with a variety of organic, inorganic, and biomolecules and have attracted widespread attention. In fact, these water-soluble oxygen-containing groups are usually inevitably generated and attached to the surface of GQDs during the formation process, so GQDs were once considered as "carbogenic nanodots" (AB Bourlinos, A. Stassinopoulos, D. Anglos, et al., Photoluminescent Carbogenic Dots, Chem. Mater., 2008, 20, 4539–4541). However, everything has two sides. While these active sites provide unlimited possibilities for the application of GQDs, they also become constraints that limit their use in certain fields: on the one hand, they lead to poor solubility of the organic phase of GQDs; This greatly limits the electron transport capability of GQDs. Therefore, if you want to exploit its semiconductor application properties, you need to explore a method to prepare "pure" GQDs, that is, GQDs without oxygen-containing defects on the surface.

At present, there are few reports on the preparation of GQDs with a relatively perfect structure. Liu et al. used graphite nano-particles (GNPs) as raw materials to prepare "zero-defect" pure graphene quantum dots (Oxygen -free pristine GQD) (F. Liu, Min-Ho Jang, Hyun Dong Ha, et al., Facile Synthetic Method for Pristine Graphene Quantum Dots and Graphene Oxide Quantum Dots: Origin of Blue and Green Luminescence, Adv. Mater., 2013, 25, 3657–3662). The GQDs obtained by this method hardly contain any oxygen-containing components, and most of the carbons are sp ² hybridized. However, the raw materials used in this method, that is, nano-scale pure graphite particles (GNPs), are very expensive and generally only available to a few specialized research groups, so this method is difficult to achieve large-scale production.

Contents of the invention

The purpose of the present invention is to overcome the deficiencies in the prior art, to provide a kind of preparation method of organic phase soluble GQD with specific structure: the product obtained has the high crystallinity structure dominated by sp ² hybridized carbon atoms, just this This structure enables it to have a π-π conjugated "channel" for photoelectron transport, so that its photoinduced charge transport ability is much higher than that of CQD prepared by general methods; at the same time, because the surface of this product has few oxygen-containing functional group defects , so it has the characteristics of hydrophobic and lipophilic (organic solvent), which further provides the basis for its application in organic photovoltaic devices. The preparation process of the entire material does not involve any toxic reagents and complicated equipment. On the contrary, this method has the advantages of simple and easy operation, wide source of raw materials, low cost, and high final product yield, which is suitable for large-scale production.

Technical purpose of the present invention is achieved through the following technical solutions:

The preparation method of the highly crystalline graphene-like quantum dot that can replace fullerene is carried out according to the following steps:

Step 1, after the aqueous solution of glycerol with a volume fraction of 70% and the concentrated sulfuric acid with a mass percentage of 98% are uniformly dispersed by ultrasonic waves, the temperature is raised to 160-220° C. in a sealed environment for 12-24 hours, and then naturally cooled to room temperature to generate Pour out the yellow-brown solution, filter to remove solid impurities therein and carry out dialysis purification operation on the remaining solution part, the solution obtained after purification is recorded as A;

In step 1, the volume ratio of the aqueous solution of glycerol to concentrated sulfuric acid is (10000-5000): (10-50).

Step 2: Mix A solution with anhydrous N, N-dimethylformamide solvent 5 times the volume of A solution, and ultrasonically disperse evenly, then microwave heating, take out the suspension after the end, and distill off the remaining solvent under reduced pressure , add 50-200mL ultrapure water to dissolve and dilute the solute part, and record the diluted solution as solution B;

In step 2, the microwave heating power is 600-800W, and the microwave reduction treatment is performed for 1-8min under N2 protection condition.

Step 3, after ultrasonically dispersing solution B, pour it into a separatory funnel and add an equal volume of chloroform, stir to make the two evenly mixed, let the mixed solution stand until an obvious layered interface is formed, collect the lower layer of chloroform solution, and record it as Solution C;

In step 3, the volume of the solution B is 50-200mL.

Step 4, the solution C is subjected to rotary evaporation to remove the solvent chloroform to obtain the final product, which is highly crystalline graphene-like quantum dots;

In step 4, a rotary evaporator was used for the operation, and after completion, the flask was placed in a vacuum drying oven, and dried for 48-72 hours at a vacuum degree of -0.1Mpa and 60°C.

The technical solution of the present invention uses small molecular carbohydrates as carbon sources to carry out one-step hydrothermal synthesis of CQDs with a size of several nanometers, and then performs temperature-controlled microwave reduction treatment on these CQDs to remove oxygen-containing groups on their surfaces. Then, using the hydrophobic and lipophilic characteristics of the target GQD, the chloroform solvent was mixed with the treated CQD aqueous solution, the mixed solution was extracted and separated, and the chloroform solution in the lower layer was collected. The chloroform solvent in the lower layer was removed by vacuum distillation to obtain the final product, namely highly crystalline GQDs dominated by sp ² hybridized carbon atoms.

The PHI1600 XPS instrument from PERKINELMZR in the United States, the Dimension3100 AFM instrument from BRUKER in Germany, and the JEM-2100F TEM from Japan Electronics Co., Ltd. were used to characterize the prepared quantum dots as follows: (1) The product quantum dots have a uniform height distribution without any agglomeration , its height is roughly 2-4nm, the height of each layer of carbon nanodiscs is 0.8-1nm, and the actual number of layers of the product quantum dots is a carbon nanodisc structure of 2-5 layers; (2) the size distribution of GQD is also relatively uniform , the diameter of a single GQD is about 3-5nm; (3) Most of the carbon atoms in GQD are sp ² hybrid type, which account for 90.92% of the total carbon distribution after analysis, and the oxygen-containing carbon peak only accounts for less than 10% , is almost negligible. This characterization proves that: GQD has a highly crystalline structure with sp ² hybridized carbon atoms dominating and few oxygen-containing defects, that is, sp ² hybridized carbon atoms account for 90% of all carbons.

The technical scheme of the present invention uses the method of microwave heat treatment and reduction to deeply reduce the carbon source small molecules through the bottom-up assembly of CQD under hydrothermal conditions, and remove the oxygen-containing groups attached to the surface, thereby obtaining an organic It is a GQD product with high crystalline structure that is soluble in phase, almost free of oxygen-containing defects, and mainly composed of sp ² hybridized carbon atoms. Then, the target product is extracted from the aqueous dispersion into an organic solvent by utilizing its hydrophobic and lipophilic properties. A method of reduction, deoxygenation and extraction separation of a large number of CQD primary products with complex components has been developed, and the high carbon content and high crystal structure of the target product have been realized. The method has a wide range of raw material sources, simple operation, and can be completed in a short period of time, and any step involved has no special requirements on preparation conditions, and large-scale preparation can be realized.

Description of drawings

Figure 1 is an AFM image of the GQD prepared in the present invention.

Fig. 2 is a TEM image of the GQD prepared in the present invention.

Fig. 3 is the high-resolution XPS-C1s spectrum of the GQD prepared by the present invention.

detailed description

Three embodiments of the present invention are given below, which are further descriptions of the present invention, rather than limiting the scope of the present invention.

Example 1:

Add 15 μL of concentrated sulfuric acid as an ion catalyst to 15 mL of an aqueous solution of glycerol with a volume fraction of 70%, ultrasonically disperse the mixed solution for 3 minutes, put it into a polytetrafluoroethylene hydrothermal reaction kettle, cover and seal Afterwards, the reaction kettle was put into a muffle furnace, and the temperature was raised to 180° C. for 16 hours. After the reaction was completed, the reaction kettle was cooled to room temperature, and the yellow-brown solution generated in the reaction kettle was poured out, the solid impurities were removed by filtration, and the remaining solution was purified by dialysis. Mix the solution obtained after purification with 5 times the volume of anhydrous DMF solvent and disperse evenly by ultrasonic. After completion, put it into a chemical microwave reactor, set the heating power to 600W, and perform microwave reduction treatment under N2 protection conditions for 2 minutes. After the end, the suspension was taken out and the remaining solvent was distilled off under reduced pressure. The solute was dissolved and diluted by adding 100mL ultrapure water. The two are mixed evenly. The mixture was allowed to stand for 5 minutes until an obvious layered interface was formed. Collect the chloroform solution in the lower layer and add it to a round-bottomed flask, use a rotary evaporator to remove the chloroform solvent, put the flask in a vacuum drying oven, and dry it at -0.1Mpa at 60°C for 48 hours to obtain The final product is a highly crystalline GQD sample soluble in the organic phase.

Example 2:

Add 30 μL of concentrated sulfuric acid as an ion catalyst to 30 mL of an aqueous solution of glycerol with a volume fraction of 70%, sonicate the mixed solution for 4 minutes to disperse it evenly, then place it in a polytetrafluoroethylene hydrothermal reaction kettle, cover and seal Afterwards, the reaction kettle was put into a muffle furnace, and the temperature was raised to 200° C. for 20 h. After the reaction was completed, the reaction kettle was cooled to room temperature, and the yellow-brown solution generated in the reaction kettle was poured out, the solid impurities were removed by filtration, and the remaining solution was purified by dialysis. Mix the solution obtained after purification with 5 times the volume of anhydrous DMF solvent and disperse evenly by ultrasonic. After completion, put it into a chemical microwave reactor, set the heating power to 720W, and perform microwave reduction treatment under N2 protection conditions for 3 minutes. After the end, the suspension was taken out and the remaining solvent was distilled off under reduced pressure. The solute was dissolved and diluted by adding 150mL ultrapure water. The two are mixed evenly. The mixture was allowed to stand for 6 minutes until an obvious layered interface was formed. Collect the chloroform solution in the lower layer and add it to a round-bottomed flask, use a rotary evaporator to remove the chloroform solvent, put the flask in a vacuum drying oven, and dry it at -0.1Mpa vacuum at 60°C for 72 hours to obtain The final product is a highly crystalline GQD sample soluble in the organic phase.

Example 3:

Add 40 μL of concentrated sulfuric acid as an ion catalyst to 40 mL of an aqueous solution of glycerol with a volume fraction of 70%, ultrasonically disperse the mixed solution for 5 minutes, put it into a polytetrafluoroethylene hydrothermal reaction kettle, cover and seal Afterwards, the reaction kettle was put into a muffle furnace, and the temperature was raised to 220° C. for 24 hours. After the reaction was completed, the reaction kettle was cooled to room temperature, and the yellow-brown solution generated in the reaction kettle was poured out, the solid impurities were removed by filtration, and the remaining solution was purified by dialysis. The solution obtained after purification was mixed with 5 times the volume of anhydrous DMF solvent and dispersed uniformly by ultrasonic. After completion, it was placed in a chemical microwave reactor, and the heating power was set to 800W, and microwave reduction treatment was performed under _N2 protection conditions for 5 minutes. After the end, the suspension was taken out and the remaining solvent was distilled off under reduced pressure. The solute was dissolved and diluted by adding 200mL ultrapure water. The two are mixed evenly. Let the mixture stand for 7 minutes until an obvious layered interface is formed. Collect the chloroform solution in the lower layer and add it to a round-bottomed flask, use a rotary evaporator to remove the chloroform solvent, put the flask in a vacuum drying oven, and dry it at -0.1Mpa vacuum at 60°C for 72 hours to obtain The final product is a highly crystalline GQD sample soluble in the organic phase.

The present invention has been described as an example above, and it should be noted that, without departing from the core of the present invention, any simple deformation, modification or other equivalent replacements that can be made by those skilled in the art without creative labor all fall within the scope of the present invention. protection scope of the invention.

Claims (4)

1. the preparation method of the highly crystalline graphene-like quantum dot that can replace fullerene, it is characterized in that, carry out according to the following steps: Step 1, after the aqueous solution of glycerol with a volume fraction of 70% and the concentrated sulfuric acid with a mass percentage of 98% are uniformly dispersed by ultrasonic waves, the temperature is raised to 160-220° C. in a sealed environment for 12-24 hours, and then naturally cooled to room temperature to generate The yellow-brown solution is poured out, the solid impurities are removed by filtration and the remaining solution part is subjected to dialysis and purification operation, and the purified solution is denoted as A; in step 1, the volume ratio of the aqueous solution of glycerol and the concentrated sulfuric acid is (10000-5000): (10-50); Step 2: Mix A solution with anhydrous N, N-dimethylformamide solvent 5 times the volume of A solution, and ultrasonically disperse evenly, then microwave heating, take out the suspension after the end, and distill off the remaining solvent under reduced pressure , add 50-200mL ultrapure water to dissolve and dilute the solute part, and record the diluted solution as solution B; Step 3, after ultrasonically dispersing solution B, pour it into a separatory funnel and add an equal volume of chloroform, stir to make the two evenly mixed, let the mixed solution stand until an obvious layered interface is formed, collect the lower layer of chloroform solution, and record it as Solution C; Step 4, the solution C is subjected to rotary evaporation to remove the solvent chloroform to obtain the final product, that is, highly crystalline graphene-like quantum dots. 2. the preparation method of the highly crystalline graphene-like quantum dot that can replace fullerene according to claim 1 is characterized in that, in step ₂ , described microwave heating power is 600-800W, under N protection Microwave reduction treatment under the condition of 1-8min. 3. The method for preparing highly crystalline graphene-like quantum dots that can replace fullerenes according to claim 1, characterized in that, in step 3, the volume of the solution B is 50-200mL. 4. the preparation method of the highly crystalline graphene-like quantum dot that can replace fullerene according to claim 1 is characterized in that, in step 4, use rotary evaporator to operate, after finishing, flask is put into vacuum In a drying oven, dry at -0.1Mpa vacuum and 60°C for 48-72h.