WO2021120800A1 - Lignin-based graphene quantum dot, preparation method therefor and use thereof - Google Patents

Abstract

A lignin-based graphene quantum dot, a preparation method therefor and use thereof, belonging to the field of the preparation of novel nanomaterials. The method comprises the following steps: performing laccase pre-treatment on lignin; performing a high pressure hydrothermal reaction; and performing centrifugal and dialysis separation and purification. The lignin-based graphene quantum dot is derived from renewable, rich-source and low-price initial raw material alkali lignin. The preparation process is green, environmentally friendly, simple and easy to operate, uses a mild and friendly chemical reagent, is beneficial for protecting environment and reducing power consumption, and conforms to the concept of sustainable development. The finally obtained lignin-based graphene quantum dot has the characteristics of being uniform in size, high in yield, good in water solubility and the like. The stable and efficient green preparation method is of great practical significance for the macro preparation of the graphene quantum dot, and can be applied to the field of information encryption.

Description

A lignin-based graphene quantum dot and preparation method and application thereof Technical field

The invention belongs to the field of preparation of novel nano materials, and specifically relates to a lignin-based graphene quantum dot and a preparation method and application thereof.

Background technique

Graphene quantum dots (GQDs) are nano-scale semiconducting carbon materials that will transition to a higher energy level excited state when exposed to specific external stimuli such as ultraviolet light, and then quickly return to a low energy state while emitting electromagnetic radiation of a specific wavelength. Studies have shown that GQDs have a series of outstanding properties, such as good solubility, biocompatibility, biological non-toxicity, low chemical activity, easy processing, fluorescent properties, etc., so they are expected to be used in bioimaging, biosensing, light-emitting diodes, etc. , Anti-counterfeiting encryption and photocatalysis and other fields.

At present, the preparation of GQDs still has problems such as non-renewable raw materials, poor environmental protection process, and unstable product performance, and its promotion and application have been difficult to achieve. With the increasingly serious energy crisis and environmental problems, domestic and foreign experts and scholars have successively proposed a series of improvement plans, including the use of renewable natural polymers such as cellulose and lignin as raw materials and the use of improved "bottom-up" "Method, cooperating with microwave/ultrasonic auxiliary processing, etc. However, most of these preparation methods currently have disadvantages such as complex preparation processes, the use of toxic and hazardous chemicals, and high energy consumption.

As a renewable resource with abundant sources, natural polymer has become an important raw material for the preparation of advanced functional materials. Therefore, it has attracted wide attention and attention of scientists from all over the world. In particular, lignin has the largest reserves in nature. The aromatic compound is an excellent precursor for the preparation of GQDs. In plants, lignin is mainly found in the amorphous area of the xylem, and its function is to harden the cell wall by forming an interwoven network to improve the plant's ability to withstand pressure. Therefore, wood usually has good mechanical strength, elasticity and rheology, reactivity, chemical compatibility and higher carbon content.

Summary of the invention

In order to overcome the shortcomings and deficiencies of the prior art, the primary purpose of the present invention is to provide a method for preparing lignin-based graphene quantum dots.

Another object of the present invention is to provide lignin-based graphene quantum dots prepared by the above-mentioned preparation method.

Another object of the present invention is to provide applications of the above-mentioned lignin-based graphene quantum dots.

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

A method for preparing lignin-based graphene quantum dots includes the following operation steps:

(1) Enzymatic pretreatment of lignin: add a certain amount of enzyme to the reactor containing lignin to perform enzymatic hydrolysis to obtain pretreated lignin;

(2) Hydrothermal reaction: Put the lignin pretreated in step (1) into an autoclave for hydrothermal reaction;

(3) Separation and purification: the reaction product in step (2) is centrifuged first, and then dialyzed to obtain an aqueous solution of lignin-based graphene quantum dots (L-GODs), which is stored for later use.

The lignin in step (1) refers to alkali lignin, and enzyme refers to laccase, and the amount of enzyme added is 5-8mg/g lignin (5-8mg enzyme is added per gram of lignin).

In step (1), after adding the enzyme, the pH of the reaction system is adjusted to 5.4-6.0, the temperature of the enzymatic hydrolysis reaction is 50-60°C, and the time of the enzymatic hydrolysis reaction is 40-60 min.

The solvent of the hydrothermal reaction in step (2) is water, and the absolute dry mass ratio of the mass of water to the lignin is 3-5:2-3.

In step (2), the temperature of the hydrothermal reaction is 230 to 260° C., the pressure is 8.0 to 10.0 MPa, and the reaction time is 21 to 24 hours.

In step (2), water is used as a solvent, and within an appropriate range, the lignin is well dispersed and the hydrothermal reaction is more thorough. At the same time, the ratio range of the present invention has moderate requirements for the temperature and pressure of the hydrothermal reaction, the reaction is mild, the yield of L-GODs obtained is greater, and the mass ratio of 3 to 5: 2 to 3 is the best ratio.

The centrifugal treatment described in step (3) specifically refers to centrifugal treatment at 15000-25000 rpm for 5-10 minutes to remove the lower layer sediment and collect the upper layer liquid.

The dialysis treatment described in step (3) refers to filling the collected liquid into a dialysis bag with a molecular weight of 14,000 to 20,000 and dialysis with deionized water until the pH value of the dialysate is constant.

A lignin-based graphene quantum dot is prepared by the above-mentioned preparation method.

The performance index of the lignin-based graphene quantum dots: the average particle size of L-GODs is 0.6-3.0 nm; the yield is 18.2-24.5%.

The application of the lignin-based graphene quantum dots in the field of information encryption.

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

(1) The present invention uses laccase to pretreat alkali lignin, which destroys the benzene ring structure of lignin, which is a green pretreatment method and further reduces energy consumption for subsequent hydrothermal separation. And laccase has high efficiency and reusability in degrading lignin.

(2) The present invention uses alkali lignin as raw material, water as green solvent, and hydrothermal reaction to prepare L-GODs. The reaction system is free of toxic and harmful chemicals, is green and safe, and is simple to operate, which can realize the green large-scale preparation of GODs.

(3) The L-GODs prepared by the present invention have uniform size, high yield, simple and controllable preparation process conditions, green and low energy consumption, and conform to the concept of sustainable development. This stable and efficient green preparation method has important practical significance for the macro-preparation of GODs.

Detailed ways

The present invention will be further described in detail below in conjunction with the examples and drawings, but the implementation of the present invention is not limited to this.

The alkali lignin used in the examples of the present invention was purchased from a paper mill in Hubei Province, and laccase, xylanase, and amylase were purchased from Sigma-Aldrich. Other reagents and drugs can be purchased from the market or prepared according to the prior art method. Got.

The method for calculating the yield of the lignin-based graphene quantum dots of the present invention=the mass of the obtained lignin-based graphene quantum dots/the mass of the initial alkali lignin.

Comparative Example 1

The method for preparing lignin-based graphene quantum dots of this embodiment, the specific preparation steps are as follows:

(1) Enzymatic pretreatment of alkali lignin: add xylanase at a ratio of 5 mg/g alkali lignin to the reactor containing alkali lignin, and carry out enzymatic hydrolysis at a pH of 5.4 and a temperature of 50°C. 40min reaction;

(2) Hydrothermal reaction: The alkali lignin pretreated by xylanase in step (1) is charged into an autoclave, and distilled water is used as a solvent. The ratio of the mass of distilled water to the absolute dry mass of alkali lignin is 3 : 2. Hydrothermal reaction for 21h at 230℃ and pressure of 8.0MPa;

(3) Separation and purification: Centrifuge the reaction product in step (2) at 15000 rpm for 5 minutes, remove the lower layer of sediment, and collect the upper layer of liquid. The collected liquid is then put into a dialysis bag with a molecular weight of 14,000 to 20,000 and continuously dialysis treated with deionized water until the pH value of the dialysate is constant. Collect the aqueous solution of L-GODs and save for later use.

The performance index of the lignin-based graphene quantum dots of this embodiment: the average particle size of L-GODs is 5.6 nm; the yield is 10.7%.

Comparative Example 2

The method for preparing lignin-based graphene quantum dots of this embodiment, the specific preparation steps are as follows:

(1) Enzymatic pretreatment of alkali lignin: add amylase at the ratio of 5mg/g alkali lignin to the reactor containing alkali lignin, and carry out enzymatic hydrolysis reaction for 40 minutes under the conditions of pH 5.4 and temperature 50°C ；

(2) Hydrothermal reaction: Put the alkali lignin pretreated by amylase in step (1) into an autoclave, using distilled water as a solvent, and the ratio of the mass of distilled water to the absolute dry mass of alkali lignin is 3:2 , Hydrothermal reaction for 21h at 230℃ and pressure of 8.0MPa;

(3) Separation and purification: Centrifuge the reaction product in step (2) at 15000 rpm for 5 minutes, remove the lower layer of sediment, and collect the upper layer of liquid. The collected liquid is then put into a dialysis bag with a molecular weight of 14,000 to 20,000 and continuously dialysis treated with deionized water until the pH value of the dialysate is constant. Collect the aqueous solution of L-GODs and save for later use.

The performance index of the lignin-based graphene quantum dots of this embodiment: the average particle size of L-GODs is 4.2 nm; the yield is 12.5%.

Example 1

The method for preparing lignin-based graphene quantum dots of this embodiment, the specific preparation steps are as follows:

(1) Enzymatic pretreatment of alkali lignin: add laccase at the ratio of 5mg/g alkali lignin to the reactor containing alkali lignin, and carry out enzymatic hydrolysis reaction for 40 minutes under the conditions of pH 5.4 and temperature 50℃ ；

(2) Hydrothermal reaction: Put the alkali lignin pretreated by laccase in step (1) into an autoclave, using distilled water as a solvent, and the ratio of the mass of distilled water to the absolute dry mass of alkali lignin is 3:2 , Hydrothermal reaction for 21h at 230℃ and pressure of 8.0MPa;

(3) Separation and purification: Centrifuge the reaction product in step (2) at 15000 rpm for 5 minutes, remove the lower layer of sediment, and collect the upper layer of liquid. The collected liquid is then put into a dialysis bag with a molecular weight of 14,000 to 20,000 and continuously dialysis treated with deionized water until the pH value of the dialysate is constant. Collect the aqueous solution of L-GODs and save for later use.

The performance index of the lignin-based graphene quantum dots of this embodiment: the average particle size of L-GODs is 3.0 nm; the yield is 18.2%.

Example 2

The method for preparing lignin-based graphene quantum dots of this embodiment, the specific preparation steps are as follows:

(1) Enzymatic pretreatment of alkali lignin: Add laccase at the ratio of 6mg/g alkali lignin to the reactor containing alkali lignin, and carry out enzymatic hydrolysis reaction at pH 5.6 and temperature 55°C for 40 minutes ；

(2) Hydrothermal reaction: Put the alkali lignin pretreated by laccase in step (1) into an autoclave, using distilled water as a solvent, and the ratio of the mass of distilled water to the absolute dry mass of alkali lignin is 4:2 , Hydrothermal reaction for 22h at 240℃ and pressure of 9.0MPa;

(3) Separation and purification: Centrifuge the reaction product in step (2) at 18000 rpm for 7 minutes to remove the lower layer sediment and collect the upper layer liquid. Then put the collected liquid into a dialysis bag with a molecular weight of 14,000 to 20,000, and continue dialysis treatment with deionized water until the pH value of the dialysate is constant. Collect the aqueous solution of L-GODs and save for later use.

The performance index of the lignin-based graphene quantum dots of this embodiment: the average particle size of L-GODs is 2.1 nm; the yield is 19.7%.

Example 3

The method for preparing lignin-based graphene quantum dots of this embodiment, the specific preparation steps are as follows:

(1) Enzymatic pretreatment of alkali lignin: Add laccase at the ratio of 7mg/g alkali lignin to the reactor containing alkali lignin, and carry out enzymatic hydrolysis reaction at pH 5.8 and temperature 60°C for 50 minutes ；

(2) Hydrothermal reaction: Put the alkali lignin pretreated by laccase in step (1) into an autoclave, using distilled water as a solvent, and the ratio of the mass of distilled water to the absolute dry mass of alkali lignin is 4:3 , Hydrothermal reaction for 23h at 250℃ and pressure of 10.0MPa;

(3) Separation and purification: Centrifuge the reaction product in step (2) at 22000 rpm for 8 minutes, remove the lower layer of sediment, and collect the upper layer of liquid. The collected liquid is then put into a dialysis bag with a molecular weight of 14,000 to 20,000 and continuously dialysis treated with deionized water until the pH value of the dialysate is constant. Collect the aqueous solution of L-GODs and save for later use.

The performance index of the lignin-based graphene quantum dots of this embodiment: the average particle size of L-GODs is 1.3 nm; the yield is 21.8%.

Example 4

The method for preparing lignin-based graphene quantum dots of this embodiment, the specific preparation steps are as follows:

(1) Enzymatic pretreatment of alkali lignin: add laccase at the ratio of 8mg/g alkali lignin to the reactor containing alkali lignin, and carry out the enzymatic hydrolysis reaction at a pH of 6.0 and a temperature of 55°C for 60 minutes ；

(2) Hydrothermal reaction: Put the alkali lignin pretreated by laccase in step (1) into an autoclave, using distilled water as a solvent, and the ratio of the mass of distilled water to the absolute dry mass of alkali lignin is 5:3 , Hydrothermal reaction at 260℃ and pressure of 9.0MPa for 24h;

(3) Separation and purification: Centrifuge the reaction product in step (2) at 25000 rpm for 10 minutes, remove the lower layer of sediment, and collect the upper layer of liquid. The collected liquid is then put into a dialysis bag with a molecular weight of 14,000 to 20,000 and continuously dialysis treated with deionized water until the pH value of the dialysate is constant. Collect the aqueous solution of L-GODs and save for later use.

The performance index of the lignin-based graphene quantum dots of this embodiment: the average particle size of L-GODs is 0.6 nm; the yield is 24.5%.

The above-mentioned embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited by the above-mentioned embodiments, and any other changes, modifications, substitutions, combinations, etc. made without departing from the spirit and principle of the present invention Simplified, all should be equivalent replacement methods, and they are all included in the protection scope of the present invention.

Claims (10)

1. A preparation method of lignin-based graphene quantum dots is characterized by comprising the following operation steps:

   (1) Enzymatic pretreatment of lignin: adding enzyme to the reactor containing lignin for enzymatic pretreatment to obtain pretreated lignin;

   (2) Hydrothermal reaction: Put the lignin pretreated in step (1) into an autoclave for hydrothermal reaction;

   (3) Separation and purification: the reaction product obtained in step (2) is first subjected to centrifugal separation, followed by dialysis treatment to obtain an aqueous solution of lignin-based graphene quantum dots.
2. The method for preparing lignin-based graphene quantum dots according to claim 1, wherein the lignin in step (1) refers to alkali lignin, the enzyme refers to laccase, and the addition of enzyme The amount is 5-8mg/g lignin.
3. The method for preparing lignin-based graphene quantum dots according to claim 1, characterized in that: in step (1), after adding enzymes, the pH of the reaction system is adjusted to 5.4-6.0, and the enzymatic hydrolysis reaction temperature is 50- At 60°C, the reaction time is 40-60 min.
4. The method for preparing lignin-based graphene quantum dots according to claim 1, wherein the solvent for the hydrothermal reaction in step (2) is water, and the absolute dry mass ratio of water to lignin is 3 to 5: 2～3.
5. The method for preparing lignin-based graphene quantum dots according to claim 1, characterized in that: in step (2), the temperature of the hydrothermal reaction is 230 to 260°C, the pressure is 8.0 to 10.0 MPa, and the reaction time is 21. ~24h.
6. The method for preparing lignin-based graphene quantum dots according to claim 1, wherein the centrifugal treatment in step (3) is specifically a centrifugal treatment at 15000-25000rpm for 5-10min to remove the lower sediment , Collect the upper liquid.
7. The method for preparing lignin-based graphene quantum dots according to claim 1, wherein the dialysis treatment in step (4) refers to filling the collected liquid in a dialysis bag with a molecular weight of 14,000 to 20,000. Dialysis with deionized water until the pH value of the dialysate is constant.
8. A lignin-based graphene quantum dot, which is characterized by being prepared by the preparation method according to any one of claims 1-7.
9. 8. The lignin-based graphene quantum dots according to claim 8, wherein the average particle size of the lignin-based graphene quantum dots is 0.6-3.0 nm.
10. The application of the lignin-based graphene quantum dots of claim 8 or 9 in the field of information encryption.