CN107117600A - A kind of method that graphene quantum dot is prepared by raw material of 3D graphenes - Google Patents

Abstract

The present invention discloses one kind using 3D graphenes as raw material, the method that the graphene quantum dot with fluorescence property is prepared by solvent-thermal method.Specifically include following steps：a）3D graphenes are prepared using CVD under the high temperature conditions using tube furnace；b）3D graphene powders is scattered in ethanol, and add after a certain amount of alkali lye, ultrasonic dissolution, it is put into reactor and seals, under the high temperature conditions reaction a period of time；c）Filtrate is collected after being cooled to room temperature, vacuum filtration, filtrate is dialysed to neutrality in the bag filter of certain molecular cut off, fluorescence graphene quantum dot is obtained.The preparation method technique that the present invention is provided is simple, it is easy to operate, and cost is low and environmental protection, and obtained graphene quantum dot purity and yield is higher, with good dispersiveness and stability and fluorescence intensity is high.There is potential application prospect in fields such as lithium ion battery, photocatalysis.

Description

A method for preparing graphene quantum dots using 3D graphene as raw material

technical field

The invention relates to a method for preparing graphene quantum dots by using 3D graphene as a raw material, and belongs to the technical field of nanomaterials.

Background technique

With the development of science and technology, semiconductor quantum dots have been widely used in biomedical imaging, disease diagnosis, biosensing and other research. However, the heavy metal components it contains are highly toxic, which limits the transformation of semiconductor quantum dots from animal experiments to clinical applications. As a new member of the graphene family, graphene quantum dots (GQDs), in addition to the excellent properties of graphene, also exhibit a series of new characteristics due to quantum confinement effects and boundary effects, and have obtained chemical, physical, It is widely concerned by scientists in various fields such as materials and biology.

The research on GQDs began in recent years. People found that when two-dimensional graphene was cut into a zero-dimensional structure through some physical and chemical means, it showed many special properties that two-dimensional structures did not have. It has stimulated the research enthusiasm of domestic and foreign scientists for zero-dimensional nanomaterials. Compared with traditional semiconductor quantum dots and organic dyes, GQDs have high water solubility, strong chemical stability, easy functionalization, resistance to photobleaching, and excellent biological characteristics, good biocompatibility, and are widely used in biomedicine (bioimaging , biosensing, drug delivery, etc.) have potential application prospects.

At present, there are few reports on the preparation of graphene quantum dots from 3D graphene. Ananthanarayanan et al. (“Facile Synthesis of Graphene Quantum Dots from 3D Graphene and their Application for Fe ³⁺ Sensing” Adv. Funct. Mater. 2014, 24 , 3021-3026) first reported the preparation of 3D graphene prepared by CVD method as raw material Graphene quantum dots. They successfully obtained fluorescent graphene quantum dots through the electrochemical exfoliation method under the action of ionic liquids, and applied them to the specific detection of Fe ³⁺ . Zhu et al. (“One-stepsynthesis of graphene quantum dots from defective CVD graphene and their application in IGZO UV thin film phototransistor” Carbon. 2016, 100, 20-207) used CVD method to prepare graphene (non-3D graphene) as raw material, using Graphene quantum dots were prepared by ultrasonic method. Graphene quantum dots with fluorescent properties can be successfully prepared by the above method, but there are still disadvantages such as long reaction time, cumbersome experimental process, harsh reaction conditions and expensive reagents. The yield and fluorescence efficiency of graphene quantum dots prepared by existing reports are still low, which also greatly limits its industrial production and application. Therefore, it remains a challenge to develop a simple, environmentally friendly method that can be applied to the large-scale production of graphene QDs.

Contents of the invention

The purpose of the present invention is to overcome the disadvantages of the above method, and provide a simple, quick, environmentally safe, and high-yield method for preparing graphene quantum dots.

The present invention is realized by adopting the following technical solutions: a method for preparing graphene quantum dots using 3D graphene as a raw material, using 3D graphene as a raw material and utilizing solvothermal method to prepare graphene quantum dots, comprising the following steps:

(1) Preparation of 3D graphene:

Firstly, the nickel foam substrate was cut into 50×50 ^mm2 squares, and ultrasonically cleaned in absolute ethanol and deionized water for 30 min to remove the oil on the surface of the nickel foam; the cleaned nickel foam was placed in a vacuum tube furnace at constant temperature The area was heated to 1000°C in an atmosphere of 500 sccm argon and 200 sccm hydrogen, and the gas flow and temperature were kept constant for 10 minutes to remove the oxide layer on the surface of the nickel foam; after that, the temperature and the flow of hydrogen and argon were kept constant, and methane gas was introduced After keeping for 10 minutes, stop feeding methane, then cool to room temperature at a cooling rate of 100-200°C/min, and turn off all gases, and then a 3D graphene/nickel foam composite material can be obtained. Finally, put the 3D graphene/nickel foam composite in 4M nitric acid solution for two hours, take it out and clean it with deionized water to obtain 3D graphene with nickel foam removed;

(2) Preparation of graphene quantum dots:

A. Disperse the 3D graphene powder obtained in step (1) in an alcoholic solvent to prepare a dispersion. The concentration of 3D graphene in the prepared dispersion is 10-30 mg/L; Add 100 ~ 500 mg/L sodium hydroxide to the mixture, and ultrasonically mix to obtain a mixed solution;

B. Evenly transfer the mixed solution obtained in step A to the reaction kettle through a graduated cylinder, seal it; place it in an oven with a temperature of 100-200°C for 6-24 h, wait to cool to room temperature, and collect it after vacuum filtration to obtain yellow filtrate;

C. The filtrate obtained in step B is dialyzed to neutrality in a dialysis bag with a molecular weight cut-off of 8000~14000 Da, removes excess alkali ions, obtains a graphene quantum dot dispersion, and obtains a graphene quantum dot powder after drying.

The alcohol solvent described in A of step (2) of the present invention can be absolute ethanol, which can better disperse 3D graphene powder; saturated aqueous solution of sodium hydroxide is used as saturated lye, and its ion size is smaller than the distance between graphene layers, Intercalation and exfoliation can be performed efficiently.

The reaction kettle described in B of the step (2) of the present invention is a polytetrafluoroethylene-lined reaction kettle; the filter membrane used in the vacuum suction filtration is an organic filter membrane with a pore size of 0.45 um, which can remove unreacted residual thing.

The dialysis time in C of the step (2) of the present invention is 3 to 4 days until neutral, effectively removing redundant alkali ions.

The drying method described in C of the step (2) of the present invention is to freeze-dry under the conditions of a temperature of -40°C and an air pressure of 20 Pa to obtain solid graphene quantum dot powder.

Compared with the prior art, the present invention has the following advantages:

1. The present invention adopts solvothermal method to prepare graphene quantum dots. The required ethanol and sodium hydroxide are all convenient and easy-to-get raw materials on the market, and can effectively disperse and peel off 3D graphene powders. The obtained graphene quantum dots The purity and yield are relatively high, and it has good dispersibility, water solubility and stable fluorescence performance.

2. The production method of the present invention is green and environmentally friendly, the required experimental equipment is easy to operate, the production cost is low and the cycle is short, and it has potential application prospects in the fields of lithium-ion batteries, micro-supercapacitors, biological imaging and solar cells, and is expected to achieve large-scale industrialization. Mass production.

Description of drawings

Fig. 1 is the high-resolution transmission electron microscope picture of the graphene quantum dot prepared in embodiment 1.

Fig. 2 is the graphene quantum dot prepared in embodiment 1 fluorescence spectra under different excitation wavelengths.

Fig. 3 is the Raman spectrogram of the graphene quantum dot prepared in embodiment 1.

Fig. 4 is the X-ray diffraction figure of the graphene quantum dot prepared in embodiment 1.

5 is an ultraviolet-visible absorption spectrum diagram of graphene quantum dots prepared in Example 1.

Fig. 6 is the Fourier transform infrared spectrogram of the graphene quantum dot prepared in embodiment 1.

detailed description

The technical solution of the present invention will be further clarified below in conjunction with specific embodiments. It is worth mentioning that the 3D graphene powders involved in all the following examples are all prepared by the preparation method of the 3D graphene powders in Example 1.

Example 1:

(1) Preparation of 3D graphene powder

Firstly, the nickel foam substrate was cut into 50×50 ^mm2 squares, and ultrasonically cleaned in absolute ethanol and deionized water for 30 min to remove the oil on the surface of the nickel foam; the cleaned nickel foam was placed in a vacuum tube furnace at constant temperature The area was heated to 1000°C in an atmosphere of 500 sccm argon and 200 sccm hydrogen, and the gas flow and temperature were kept constant for 10 minutes to remove the oxide layer on the surface of the nickel foam; after that, the temperature and the flow of hydrogen and argon were kept constant, and methane gas was introduced After keeping for 10 minutes, stop feeding methane, then cool to room temperature at a cooling rate of 100-200°C/min, and turn off all gases, and then a 3D graphene/nickel foam composite material can be obtained. Finally, put the 3D graphene/nickel foam composite material in a 4M nitric acid solution for two hours, take it out and clean it with deionized water to obtain 3D graphene with the nickel foam removed.

(2) Preparation of graphene quantum dots

Disperse 1 mg of 3D graphene powder in step (1) into 50 mL of absolute ethanol solution, add 20 mg of sodium hydroxide, and mix ultrasonically for 5 min. Transfer the mixed solution into a reaction kettle, seal it, put it in an oven, raise the temperature to 180 °C, maintain it for 10 h, and cool it down to room temperature naturally. The treated dispersion was collected by vacuum filtration to obtain a pale yellow filtrate. The filtrate was dialyzed into a 10000Da dialysis bag until neutral. The obtained dialysate was frozen, and then freeze-dried at a temperature of -40 °C and an air pressure of 20 Pa to obtain graphene quantum dot powder.

Figure 1 is a high-resolution transmission electron microscope picture of the graphene quantum dots obtained in Example 1. It can be seen from the figure that the size of the obtained quantum dots is mainly distributed in the range of 5-9 nm, and the interplanar spacing is 0.21 nm. Fig. 2 is the fluorescence spectrogram of the graphene quantum dot that embodiment 1 obtains, as can be seen with the variation of excitation wavelength, the emission wavelength of graphene quantum dot is also changing, illustrates that the fluorescence emission spectrum of graphene quantum dot has wavelength dependence sex. Fig. 3 is the Raman spectrogram of the graphene quantum dot obtained in embodiment 1, as can be seen from the figure, the ID/IG ratio is 0.42, indicating that the graphene quantum dot has a higher degree of graphitization. Figure 4 is the X-ray diffraction pattern of the graphene quantum dots obtained in Example 1. It can be seen that the graphene quantum dots have a sharp peak at 2θ=28.1°. According to the Bragg equation 2dsinθ=nλ, the lattice spacing of the sheets is 0.32 nm. Fig. 5 is the ultraviolet-visible absorption spectrogram of the graphene quantum dot obtained in Example 1, and it can be seen that the absorption peaks appear at 262 and 304 nm. Figure 6 is the Fourier transform infrared spectrum of graphene quantum dots obtained in Example 1. It can be observed from the figure that COC (1145 cm ^-1 ), C-OH (1380 cm ^-1 ), -C=O (1628 cm ^-1 ) stretching vibration peak, and -OH (3410 cm ^-1 ) stretching vibration peak, indicating that the surface of graphene quantum dots contains abundant oxygen-containing functional groups.

Example 2

Disperse 1.5 mg of the 3D graphene powder obtained in step (1) of Example 1 into 50 mL of absolute ethanol solution, add 10 mg of sodium hydroxide, and ultrasonically mix for 5 min. Transfer the mixed solution to a reaction kettle, seal it, put it in an oven, raise the temperature to 200 °C, maintain it for 9 h, and cool it down to room temperature naturally. The treated dispersion was collected by vacuum filtration to obtain a pale yellow filtrate. The filtrate was dialyzed in a 10000 Da dialysis bag until neutral. The obtained dialysate was frozen, and then freeze-dried at a temperature of -40 °C and an air pressure of 20 Pa to obtain solid graphene quantum dots.

Example 3

Disperse 0.5 mg of the 3D graphene powder obtained in step (1) of Example 1 into 30 mL of absolute ethanol solution, add 15 mg of sodium hydroxide, and ultrasonically mix for 5 min. The mixed dispersion was transferred to a reaction kettle, sealed, put into an oven, heated to 120 °C, maintained for 12 h, and cooled to room temperature naturally. The treated dispersion was collected by vacuum filtration to obtain a pale yellow filtrate. Fill the filtrate into a 10,000 Da dialysis bag until neutral. The obtained dialysate was frozen, and then freeze-dried at a temperature of -40 °C and an air pressure of 20 Pa to obtain solid graphene quantum dots.

Example 4

Disperse 1 mg of the 3D graphene powder obtained in step (1) of Example 1 into 40 mL of absolute ethanol solution, add 12 mg of sodium hydroxide, and mix ultrasonically for 5 min. Transfer the mixed solution to a reaction kettle, seal it, put it in an oven, raise the temperature to 100 °C, maintain it for 20 h, and cool it down to room temperature naturally. The treated dispersion was collected by vacuum filtration to obtain a pale yellow filtrate. The filtrate was dialyzed in a 10000 Da dialysis bag until neutral. The obtained dialysate was frozen, and then freeze-dried at a temperature of -40 °C and an air pressure of 20 Pa to obtain solid graphene quantum dots.

The above embodiments have only described several modes of the present invention, and are only used to further elaborate on the technical solution in detail, and are not intended to limit the invention. It should be pointed out that those skilled in the art will not depart from the present invention. Under the premise of the idea, the non-essential improvements and adjustments all belong to the protection scope of the technical solution of the present invention.

Claims (5)

1. a kind of method that graphene quantum dot is prepared by raw material of 3D graphenes, it is characterised in that comprise the following steps：

（1）The preparation of 3D graphenes：

Foam nickel base is cut to 50 × 50 mm first²Square, and each ultrasound is clear in absolute ethyl alcohol and deionized water respectively 30 min are washed, with the greasy dirt for the nickel surface that defoams；The nickel foam that cleaning is finished is placed in vacuum tube furnace flat-temperature zone 500 1000 DEG C are heated in sccm argon gas, 200 sccm atmosphere of hydrogen, gas flow and temperature-resistant 10 min are kept, to go de-bubble The oxide layer of foam nickel surface；Keeping temperature and hydrogen argon flow amount are constant afterwards, are passed through methane gas and keep stopping after 10 min Methane is passed through, then room temperature is cooled to 100-200 DEG C/min cooldown rate, all gas are closed, you can obtain 3D graphenes/bubble The composite of foam nickel；Finally by 3D graphenes/foam nickel composite material two hours in 4M salpeter solutions, spent after taking-up from Sub- water is cleaned up, and obtains washing the 3D graphenes of nickel foam；

（2）The preparation of graphene quantum dot：

A. by step（1）Obtained 3D graphene dispersions are made dispersion liquid, configure obtained dispersion liquid in alcohols solvent The concentration of middle 3D graphenes is 10 ~ 30 mg/L；100 ~ 500 mg/L sodium hydroxides are added into the dispersion liquid again, ultrasound is mixed Mixed liquor is made；

B. the obtained mixed liquors of step A are uniformly transferred in reactor by graduated cylinder, sealed；Be placed on temperature for 100 ~ 6 ~ 24 h of reaction in 200 DEG C of baking oven, are cooled to collection after room temperature, vacuum filtration and obtain flaxen filtrate；

C. the filtrate that step B is obtained is dialysed to neutrality in molecular cut off is 8000 ~ 14000 Da bag filter, removes many Remaining basic ion, obtains graphene quantum dot dispersion, and solid graphite alkene quantum dot is obtained after drying.

2. according to a kind of method that graphene quantum dot is prepared by raw material of 3D graphenes described in claim 1, it is characterised in that： Step（2）A described in alcohols solvent be absolute ethyl alcohol, can preferably disperse 3D graphene powders；Sodium hydroxide is used as saturation Alkali lye, its ion size is less than spacing between graphene layer, can effectively carry out intercalation and stripping.

3. a kind of method that graphene quantum dot is prepared by raw material of 3D graphenes according to claim 1, its feature exists In：Step（2）B described in reactor be polytetrafluoroethyllining lining reactor；Filter membrane used in the vacuum filtration is to have Machine filter film, aperture is 0.45 um, can remove the complete residue of unreacted.

4. a kind of method that graphene quantum dot is prepared by raw material of 3D graphenes according to claim 1 or 2, its feature It is：Step（2）C in dialysis time be 3 ~ 4 days, until neutral, effectively remove unnecessary basic ion.

5. a kind of method that graphene quantum dot is prepared by raw material of 3D graphenes according to claim 1 or 2, its feature It is：Step（2）C described in drying means be temperature be -40 DEG C, air pressure be 20 Pa under conditions of be freeze-dried, obtain To the graphene quantum dot powder of solid-state.