CN107936266B

CN107936266B - Cellulose/black phosphorus nanosheet composite hydrogel and preparation method thereof

Info

Publication number: CN107936266B
Application number: CN201711129778.2A
Authority: CN
Inventors: 张晗; 邢晨阳; 陈世优
Original assignee: Shenzhen University
Current assignee: Shenzhen University
Priority date: 2017-11-15
Filing date: 2017-11-15
Publication date: 2021-10-26
Anticipated expiration: 2037-11-15
Also published as: CN107936266A; WO2019095752A1

Abstract

The invention provides a cellulose/black phosphorus nanosheet composite hydrogel which is characterized by comprising a cellulose three-dimensional network structure and black phosphorus nanosheets loaded in the cellulose three-dimensional network structure. The black phosphorus nanosheet can be stably loaded in the composite hydrogel system and is not easy to agglomerate, and the composite hydrogel has uniform and stable high photothermal conversion efficiency, good compatibility with biological body fluid, complete biodegradability and high biosafety and can be used in the field of biomedicine. The invention also provides a preparation method of the composite hydrogel.

Description

Cellulose/black phosphorus nanosheet composite hydrogel and preparation method thereof

Technical Field

The invention belongs to the field of preparation of black phosphorus-based nano materials, and particularly relates to a cellulose/black phosphorus nanosheet composite hydrogel and a preparation method thereof.

Background

Black phosphorus (Black phosphorus) is a novel direct band gap two-dimensional material, the band gap of which can be adjusted from 0.3eV (bulk state) to 1.5eV (single layer) through the number of layers, and which can absorb light with wavelength from visible light to infrared for communication, and in addition, the Black phosphorus has high carrier mobility, high cut-off ratio, and good photothermal conversion effect and biocompatibility, so that the Black phosphorus (Black phosphorus) shows great potential advantages in the semiconductor field, the photoelectric field, the biological field and the like.

In the biomedical field, the inorganic nano material-black phosphorus has insufficient dispersibility in biological body fluid, is easy to precipitate, and has obvious regional difference in photo-thermal effect. In addition, the structure of the existing black phosphorus-based material is too single, and the black phosphorus in the material has poor stability and is easy to dissociate, so that the targeting property and the durability required in the tumor treatment process cannot be met. Therefore, there is a need to expand the existence forms of black phosphorus in the biomedical field.

Cellulose is the most abundant renewable resource on the earth, has the advantages of complete biocompatibility, complete biodegradability and the like, but is difficult to process and form due to the difficult dissolution and refractory property of the cellulose under the restriction of high crystallinity and intramolecular/intermolecular hydrogen bonds, so that the development of the cellulose in biomedical materials is greatly limited.

Disclosure of Invention

In view of the above, the invention provides a cellulose/black phosphorus nanosheet composite hydrogel, which has high stability of black phosphorus nanosheets in the composite hydrogel, has good dispersibility in biological body fluid, shows excellent characteristics such as high photothermal conversion efficiency, complete biodegradability, complete biocompatibility and biosafety, has good mechanical strength, and is expected to be applied in the biomedical field.

In a first aspect, the invention provides a cellulose/black phosphorus nanosheet composite hydrogel, which comprises a cellulose three-dimensional network structure and black phosphorus nanosheets supported on the cellulose three-dimensional network structure.

According to the invention, the black phosphorus nanosheets are wound into a cellulose three-dimensional network structure mainly by means of the three-dimensional network structure formed by cellulose molecules, so that the black phosphorus nanosheets are loaded into the system to form the cellulose/black phosphorus nanosheet composite hydrogel. The composite hydrogel remarkably improves the dispersibility of the black phosphorus nanosheets and prevents agglomeration among the black phosphorus nanosheets.

Preferably, the thickness of the black phosphorus nanosheet is 1-25 nm. More preferably 3 to 18 nm. Two-dimensional layered materials of nanometer-scale thickness can be more strongly loaded into the cellulose three-dimensional network structure.

Preferably, the number of layers of the two-dimensional layered material is 1-20, and more preferably 2-10.

Preferably, the lateral dimension of the two-dimensional layered material is 100-800 nm. The transverse dimension refers to the length or width of the two-dimensional layered material.

Wherein the cellulose three-dimensional network structure comprises a three-dimensional network structure formed by connecting cellulose or cellulose derivatives with the cellulose or the cellulose derivatives, or a three-dimensional network structure formed by the cellulose and/or the cellulose derivatives through a cross-linking agent.

Wherein the cellulose derivative comprises cellulose modified by at least one of graphene oxide, chitosan, cyclodextrin and gelatin, or carboxylated and silanized cellulose.

Preferably, the crosslinking agent includes at least one of epichlorohydrin and isocyanate, but is not limited thereto.

Wherein the cellulose three-dimensional network structure has a pore structure with a pore diameter of 30-300 μm. Preferably, the pore size of the pore structure is 50-280 μm. More preferably 80 to 250. mu.m.

Wherein the water content of the composite hydrogel is 85-98%. The composite hydrogel has a large water content, is easy to disperse in aqueous solution or organism body fluid, has excellent compatibility with the body fluid, and can improve the adhesion of the black phosphorus nanosheet with organism cells and tissues.

Wherein the mass ratio of the cellulose to the black phosphorus nanosheet in the cellulose three-dimensional network structure is 100: (0.0001-50), preferably 100: (0.001-10), more preferably 100: (0.001-5), more preferably 100: 0.05.

in one embodiment of the present invention, the cellulose three-dimensional network structure is a three-dimensional network structure formed by crosslinking cellulose molecules and a crosslinking agent.

Wherein the mass ratio of the cellulose to the cross-linking agent in the cellulose three-dimensional network structure is 100: (1.372-13.71). Preferably 100: (4.116-13.71), more preferably 100: (4.116-6.86).

Wherein the cellulose is one or more of lignocellulose, bamboo cellulose, wood cellulose pulp, cotton cellulose, microcrystalline cellulose, hydroxyethyl cellulose and carboxymethyl cellulose.

According to the cellulose/black phosphorus nanosheet composite hydrogel provided by the first aspect of the invention, a cellulose three-dimensional network structure is used as a carrier, and the black phosphorus nanosheets are stably loaded in the three-dimensional network structure, so that the dispersibility of the black phosphorus nanosheets is improved, the agglomeration among the black phosphorus nanosheets is prevented, and the product form of black phosphorus is expanded. The cellulose/black phosphorus nanosheet composite hydrogel has good dispersibility in biological body fluid, shows excellent characteristics of high photothermal conversion efficiency, complete biodegradability, complete biocompatibility, biological safety and the like, has good mechanical strength, and is expected to be applied to the field of biomedicine, particularly the field of tumor treatment.

In a second aspect, the invention provides a preparation method of a cellulose/black phosphorus nanosheet composite hydrogel, which comprises the following steps:

(1) preparing a mixed solvent containing strong base, urea and water, precooling, adding cellulose powder into the precooled mixed solvent, and violently stirring to obtain a cellulose solution;

(2) under the condition of high-speed stirring, mixing the black phosphorus nanosheet and the cross-linking agent with the cellulose solution, carrying out ultrasonic treatment, and carrying out cross-linking reaction for 0.5-2 hours at 65-90 ℃ to obtain a cross-linking reactant;

(3) and adding cellulose regeneration liquid into the crosslinking reactant, soaking for 30-60min, and then putting the regenerated crosslinking reactant into water for dialysis to obtain the cellulose/black phosphorus nanosheet composite hydrogel.

The cellulose/black phosphorus nanosheet composite hydrogel prepared by the method comprises a cellulose three-dimensional network structure formed by crosslinking cellulose and a crosslinking agent, and also comprises black phosphorus nanosheets loaded in the cellulose three-dimensional network structure. Further, the surface of the black phosphorus nanosheet is covered by the three-dimensional network structure of cellulose.

Wherein, in the step (1), the mixed solvent is pre-cooled to-15 to-5 ℃. This facilitates a better dissolution of the cellulose powder. Preferably, the mixed solvent is pre-cooled to-12 ℃.

Optionally, the cellulose powder has a particle size of 10-30 microns.

Wherein in the step (1), the rotation speed of the violent stirring is 7000-10000 rpm, and the time of the violent stirring is 1-3 minutes.

In step (2), the crosslinking agent is preferably a substance that is not completely hydrophobic. The cross-linking agent contains at least one of epoxy group (C-O-C) and isocyanate group (NCO), so that the functional groups in the cross-linking agent can perform cross-linking reaction with-OH in the cellulose molecular chain.

Preferably, the crosslinking agent is selected from one or more of epichlorohydrin and isocyanate, but is not limited thereto. Further preferably, the crosslinking agent is epichlorohydrin. At the moment, a hydroxyl functional group (-OH) on a cellulose molecular chain and a carbon atom on an epoxy functional group (C-O-C) in the epoxy chloropropane generate nucleophilic reaction, and a hydrogel system is formed by crosslinking.

In the step (2), the high-speed stirring speed is 7000-10000 rpm, and the high-speed stirring time is 1-3 minutes. The stirring speed and the stirring time of the violent stirring and the high-speed stirring can be the same or different.

Wherein, in the step (2), the power of the ultrasonic treatment is 300-.

Preferably, in step (2), the temperature of the crosslinking reaction is 70-85 ℃. For example, 72, 75, 78, 80 or 82 deg.c.

In the step (3), the cellulose regeneration liquid is a dilute sulfuric acid solution with the mass fraction of 5% -10%.

Preferably, the volume ratio of the crosslinking reactant to the dilute sulfuric acid solution is 1: (2-3). Further, the volume of the dilute sulfuric acid solution used was 10 to 15 mL. Wherein the crosslinking reactant is cellulose/crosslinking agent/black phosphorus nanosheet/sodium hydroxide/urea hydrogel.

Wherein in the step (3), the dialysis time is 3-7 days. The purpose of dialysis is mainly to remove strong alkali, urea and regeneration liquid.

In the step (1), the mass concentration of the strong base in the mixed solvent is 5-15%, and the mass concentration of the urea in the mixed solvent is 10-15%.

Wherein the strong base is one or more of sodium hydroxide, potassium hydroxide and lithium hydroxide.

In the step (1), the mass ratio of the mixed solvent to the cellulose in the cellulose solution is 100: (1-4).

Preferably, the volume ratio of the cellulose solution to the cross-linking agent is 100: (0.2-2.0).

Preferably, the mass ratio of the volume of the cellulose solution to the cross-linking agent is 100: (0.236-2.36) mL/g.

Preferably, the mass ratio of the cellulose solution to the cross-linking agent is 100: (0.212-2.12).

Wherein the mass ratio of the cellulose to the black phosphorus nanosheet is 100: (0.0001-50). For example, it may be 100: 0.01, 100: 0.03, 100: 0.05, 100: 0.1, 100: 0.5, 100: 1,100: 5,100: 10. preferably 100: (0.001-10), more preferably 100: (0.001-5), more preferably 100: 0.05.

the black phosphorus nanosheet can generate heat under the irradiation of near infrared light (such as 808nm), the temperature can be increased from room temperature to 150 ℃, the temperature (such as 43-60 ℃) required for killing cancer cells can be reached by regulating the content of the black phosphorus nanosheet in the composite hydrogel, and compared with other common photothermal reagents (such as nanogold, nano Pd, CuS, porphyrin and the like), the black phosphorus nanosheet can generate biodegradation behaviors in a living body, the degradation product of the black phosphorus nanosheet is safe phosphate, and the black phosphorus nanosheet has better biocompatibility and biosafety.

Optionally, the mass ratio of the cellulose to the black phosphorus nanoplates is 100: (0.0001-0.01). At this time, the composite hydrogel can be irradiated at an irradiation power of 0.5/cm²The photo-thermal equilibrium temperature reaches 43.5-60 ℃ under the irradiation of 808nm laser, so that the composite hydrogel can be irradiated at the irradiation power of 1.0/cm²The photo-thermal equilibrium temperature reaches 48-75 ℃ under the irradiation of 808nm laser. Therefore, when the composite hydrogel contains the low-quality black phosphorus nanosheets, the composite hydrogel can have a good photo-thermal effect of killing tumor cells.

Preferably, the thickness of the black phosphorus nanosheet is 1-25 nm. More preferably 3 to 18 nm.

In the invention, the preparation method of the black phosphorus nanosheet is not limited, and the black phosphorus nanosheet can be prepared by adopting the following method:

mixing the blocky black phosphorus and an organic solvent, grinding, and supplementing the organic solvent into the mixture obtained by grinding to obtain a dispersion liquid; and carrying out probe type ultrasonic treatment on the dispersion liquid under the power of 1000-1400W for 30-60 hours, carrying out low-speed centrifugation on the solution obtained after ultrasonic treatment, collecting supernatant, carrying out high-speed centrifugation on the supernatant, collecting solid precipitate, and carrying out vacuum drying on the solid precipitate to obtain the black phosphorus nanosheet.

Optionally, the ratio of the mass of black phosphorus to the total volume of the organic solvent is (0.25-1) mg/mL.

Optionally, the milling is performed in an oxygen-free condition for a time period of 20-60 min.

The surface energy of the organic solvent is matched with the surface energy of the two-dimensional black phosphorus, and a certain interaction exists between the organic solvent and the two-dimensional black phosphorus to balance the energy required for stripping the block-shaped black phosphorus. Wherein the organic solvent is selected from one or more of N-methylpyrrolidone (NMP), Dimethylsulfoxide (DMSO), N-Dimethylformamide (DMF), N-cyclohexyl-2-pyrrolidone (CHP), and isopropyl alcohol (IPA), but is not limited thereto.

Preferably, the rotation speed of the low-speed centrifugation is 5000-. Further preferably, the rotation speed of the low-speed centrifugation is 6000-.

Preferably, the rotating speed of the high-speed centrifugation is 15000-18000rpm, and the time is 30-60 min. Further preferably, the rotation speed of the high-speed centrifugation is 16000-.

Preferably, the drying temperature of the vacuum drying is 50-80 ℃, and the drying time is 12-24 h.

The forming mechanism of the cellulose/black phosphorus nanosheet composite hydrogel provided by the invention is as follows: 1) firstly, a low-temperature alkaline mixed solvent of sodium hydroxide, urea and water is adopted to dissolve cellulose, a hydrogen bond network among molecular chains of the cellulose can be gradually opened to form sodium ions and hydroxyl ions of hydrate, a new hydrogen bond network is formed with the molecular chains of the cellulose, the urea molecular hydrate prevents the self-association of the molecular chains of the cellulose, and finally the molecular chains of the cellulose are dissolved in an aqueous solution in the form of a tubular inclusion compound, so that the problem that the cellulose with high crystallinity and strong hydrogen bonds in molecules/between molecules is difficult to dissolve in a common solvent comprising a water solvent is solved. In addition, the alkaline solution also helps to improve the stability of the black phosphorus nanoplatelets, protecting the black phosphorus from oxidation. 2) After mixing and ultrasonically treating a cellulose aqueous solution, black phosphorus nanosheets and a cross-linking agent under high-speed stirring, performing nucleophilic reaction on a cellulose molecular chain and the cross-linking agent at a certain temperature, and simultaneously embedding the black phosphorus nanosheets into the mixture to enable the black phosphorus nanosheets to be in an extremely stable state, so as to form the cellulose/cross-linking agent/black phosphorus nanosheets/sodium hydroxide/urea hydrogel with a three-dimensional network structure. 3) After the cellulose/cross-linking agent/black phosphorus nanosheet/sodium hydroxide/urea hydrogel is soaked in a dilute sulfuric acid solution, cellulose is regenerated, namely a cellulose molecular chain is separated out, so that the regenerated hydrogel can be taken out conveniently, and after the hydrogel is soaked in water, the sodium hydroxide and the urea can be removed, so that the cellulose/black phosphorus nanosheet composite hydrogel is finally obtained.

In the cellulose/black phosphorus nanosheet composite hydrogel, the black phosphorus nanosheets are stably loaded in a three-dimensional network structure formed by crosslinking of cellulose and a crosslinking agent, and due to the blocking of cellulose macromolecular chains, the black phosphorus nanosheets are in an extremely stable state and are not prone to agglomeration and sedimentation, so that the composite hydrogel has a uniform and stable photo-thermal effect, and the photo-thermal effect is almost free of regional difference. Secondly, the composite hydrogel contains enough moisture, is easy to disperse in aqueous solution or organism body fluid, has excellent compatibility with the body fluid, and can improve the adhesiveness of the black phosphorus nanosheet with organism cells and tissues. Furthermore, due to the gel property of the composite hydrogel, when the composite hydrogel is used as an anti-cancer treatment system, the composite hydrogel can be directly injected into a tumor part in an intratumoral injection mode. In addition, the gel framework taking cellulose as a main body in the composite hydrogel can also fix other hydrophilic anticancer drugs, so that the composite hydrogel can realize multi-mode comprehensive treatment of targeted therapy, photothermal therapy and chemotherapy on tumor cells. Finally, the cellulose and the black phosphorus nanosheets are degradable materials with good biocompatibility, so that the composite hydrogel also has excellent characteristics of complete biodegradability, complete biocompatibility, biological safety and the like.

The preparation method of the cellulose/black phosphorus nanosheet composite hydrogel provided by the second aspect of the invention is simple in process, green and environment-friendly, and the obtained product is excellent in performance, stable and uniform.

Advantages of embodiments of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of embodiments of the invention.

Drawings

Fig. 1 is a Transmission Electron Microscope (TEM) photograph of black phosphorus nanoplates employed in the examples of the present invention: (a) low resolution pictures (100 nm on scale); (b) high resolution topography (10 nm scale).

Fig. 2 is an Atomic Force Microscope (AFM) photograph of black phosphorus nanoplates employed in embodiments of the present invention, including an AFM height map (left side) and thicknesses of the corresponding three different sized black phosphorus nanoplates (right side).

Figure 3 is a macroscopic physical photograph of a cellulose hydrogel (comparative example 4) and a cellulose/black phosphorus nanosheet composite hydrogel (example 4).

FIG. 4 is a Scanning Electron Microscope (SEM) photograph of an aerogel obtained after freeze-drying the cellulose/black phosphorus nanosheet composite hydrogel in example 4 of the present invention; wherein (b) is an enlargement of the area in (a).

FIG. 5 is an SEM photograph of an aerogel obtained after freeze-drying the cellulose hydrogel in comparative example 4; wherein (b) is an enlargement of the area in (a).

Detailed Description

While the following is a description of the preferred embodiments of the present invention, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention.

The following examples are intended to illustrate the invention in more detail. The embodiments of the present invention are not limited to the following specific embodiments. The present invention can be modified and implemented as appropriate within the scope of the main claim.

Unless otherwise specified, the raw materials and other chemicals used in the examples of the present invention are commercially available.

Example 1

Preparation of a cellulose/black phosphorus nanosheet composite hydrogel, comprising:

step (1), preparing a black phosphorus nanosheet solid with uniform size by a liquid phase stripping method, which comprises the following specific steps:

1-a), adding blocky black phosphorus and N-methyl pyrrolidone (NMP) into an agate mortar according to the solid content ratio of 500mg/10mL for mechanical grinding for 30 minutes; after milling, the black phosphorus/N-methylpyrrolidone (NMP) complex was transferred to a 100mL reaction flask and 90mL of NMP was added to give a dispersion with a final black phosphorus solids content of 5mg/mL in total NMP.

And 1-b) performing probe ultrasound on the dispersion liquid, wherein the ultrasonic power is 600W, and the ultrasonic time is 50 hours, so as to obtain a solution containing the black phosphorus nanosheet for later use.

1-c) carrying out low-speed centrifugation on the black phosphorus nanosheet solution at 7000rpm for 25 minutes, and slowly taking out 3/4 supernatant.

And 1-d) centrifuging the supernatant at a high speed of 17000rpm for 35 minutes, slowly pouring out the supernatant, and collecting the black phosphorus nanosheet solid.

1-e) drying the black phosphorus nanosheet solid in a vacuum drying oven for 20 hours at the temperature of 75 ℃ to finally obtain the dried black phosphorus nanosheet solid for later use.

Through tests, the transverse dimension of the obtained black phosphorus nanosheet is 200-400nm, the number of layers is 15, and the thickness is 9 nm.

Step (2), preparing transparent and uniform cellulose alkaline aqueous solution, which comprises the following steps:

2-a), adding sodium hydroxide, urea and deionized water into a 200mL beaker according to the mass ratio of 7%/12%/81% to obtain a mixed solvent, wherein the mass of the deionized water is 81.0g, namely the total volume of the mixed solvent is 100 mL; precooling the mixed solvent for 30 minutes to ensure that the temperature of the mixed solvent reaches-12 ℃ for standby.

And 2-b) adding cellulose powder into the pre-cooled mixed solvent, wherein the mass ratio of the mixed solvent to the cellulose is 100: 4; and then, violently stirring the obtained cellulose suspension at the stirring speed of 7500rpm for 2 minutes to finally obtain a uniform and transparent cellulose solution, namely a mixed solution of cellulose/sodium hydroxide/urea/deionized water for later use.

Step (3), preparing the cellulose/black phosphorus nanosheet composite hydrogel, which comprises the following specific steps:

and 3-a) taking 5mL of the cellulose solution in the step (2), and taking the black phosphorus nanosheet solid in the step (1), wherein the mass ratio of the cellulose to the black phosphorus nanosheet solid is 100: 0.0001, taking 0.05mL of epoxy chloropropane, namely, the volume ratio of the cellulose solution to the epoxy chloropropane is 100: 1; stirring the three materials at a high speed of 7500rpm for 2 minutes; and then performing water bath ultrasound with the ultrasonic power of 300W for 15 minutes to obtain an ultrasonic mixed solution, namely a mixed solution of cellulose/epichlorohydrin/black phosphorus nanosheet/sodium hydroxide/urea/deionized water.

And 3-b) placing the mixed solution after ultrasonic treatment in an oil bath at 70 ℃ for chemical crosslinking reaction for 1.5 hours to obtain a crosslinking reactant, namely the hydrogel of cellulose/epichlorohydrin/black phosphorus nanosheet/sodium hydroxide/urea/deionized water.

And 3-c) adding 15mL of dilute sulfuric acid solution with the mass fraction of 8% into the crosslinking reactant, and carrying out acid soaking for 40 minutes to ensure that cellulose regeneration behavior, namely, cellulose molecular chains are separated out. And then, putting the regenerated crosslinking reactant into deionized water, dialyzing for 5 days to ensure that sodium hydroxide, urea and sulfuric acid are gradually dialyzed out, and finally obtaining the cellulose/black phosphorus nanosheet composite hydrogel.

The cellulose/black phosphorus nanosheet composite hydrogel prepared in embodiment 1 of the present invention includes a three-dimensional network structure formed by crosslinking cellulose molecules and a crosslinking agent, and black phosphorus nanosheets loaded in the three-dimensional network structure.

Example 2

Preparing the composite hydrogel of the cellulose/black phosphorus nanosheet, which is different from the composite hydrogel prepared in example 1 in that in the step 3-a), the mass ratio of the cellulose to the black phosphorus nanosheet solid is 100: 0.01.

example 3

Preparing the composite hydrogel of the cellulose/black phosphorus nanosheet, which is different from the composite hydrogel prepared in example 1 in that in the step 3-a), the mass ratio of the cellulose to the black phosphorus nanosheet solid is 100: 0.03.

example 4

Preparing the composite hydrogel of the cellulose/black phosphorus nanosheet, which is different from the composite hydrogel prepared in example 1 in that in the step 3-a), the mass ratio of the cellulose to the black phosphorus nanosheet solid is 100: 0.05.

example 5

Preparing the composite hydrogel of the cellulose/black phosphorus nanosheet, which is different from the composite hydrogel prepared in example 1 in that in the step 3-a), the mass ratio of the cellulose to the black phosphorus nanosheet solid is 100: 5.

example 6

Preparing the composite hydrogel of the cellulose/black phosphorus nanosheet, which is different from the composite hydrogel prepared in example 1 in that in the step 3-a), the mass ratio of the cellulose to the black phosphorus nanosheet solid is 100: 10.

example 7

Preparing the composite hydrogel of the cellulose/black phosphorus nanosheet, which is different from the composite hydrogel prepared in example 1 in that in the step 3-a), the mass ratio of the cellulose to the black phosphorus nanosheet solid is 100: 50.

in order to highlight the beneficial effects of the present invention, the present invention also provides the following comparative examples:

comparative example 1

Preparing a cellulosic hydrogel comprising:

the method comprises the following steps of (1) preparing transparent and uniform cellulose alkaline aqueous solution:

1-a), adding sodium hydroxide, urea and deionized water into a 200mL beaker according to the mass ratio of 7%/12%/81% to obtain a mixed solvent, wherein the mass of the deionized water is 81.0g, namely the total volume of the mixed solvent is 100 mL; precooling the mixed solvent for 30 minutes to ensure that the temperature of the mixed solvent reaches-12 ℃ for standby.

1-b) adding cellulose powder into the pre-cooled mixed solvent, wherein the mass ratio of the mixed solvent to the cellulose is 100: 1; the resulting cellulose suspension was then vigorously stirred at 7500rpm for 2 minutes to obtain a uniform, transparent cellulose solution, i.e., a mixed solution of cellulose/sodium hydroxide/urea/deionized water.

Step (2) preparing the cellulose hydrogel, which comprises the following specific steps:

2-a) taking 5mL of the cellulose solution in the step (1), taking 0.01mL of epoxy chloropropane, namely the volume ratio of the cellulose solution to the epoxy chloropropane is 100: 0.2; stirring the three materials at a high speed of 7500rpm for 2 minutes; and then performing water bath ultrasound with the ultrasonic power of 300W for 15 minutes to obtain a mixed solution after ultrasound, namely the mixed solution of cellulose/epichlorohydrin/sodium hydroxide/urea/deionized water for later use.

And 2-b) placing the mixed solution after ultrasonic treatment in an oil bath at 70 ℃ for chemical crosslinking reaction for 1.5 hours to obtain a crosslinking reactant, namely the hydrogel of cellulose/epichlorohydrin/sodium hydroxide/urea/deionized water for later use.

2-c) adding 15mL of dilute sulfuric acid solution with the mass fraction of 8% into the crosslinking reactant, and soaking for 40 minutes to regenerate the cellulose. Then, the regenerated crosslinking reactant is placed in deionized water, and dialyzed for 5 days to ensure that sodium hydroxide and urea are gradually dialyzed out, and finally the cellulose/epichlorohydrin hydrogel (simply referred to as cellulose hydrogel) is obtained.

Comparative example 2: the difference from comparative example 1 is that the mass ratio of the mixed solvent to the cellulose is 100: 2, the volume ratio of the cellulose solution to the epichlorohydrin is 100: 0.4.

comparative example 3: the difference from comparative example 1 is that the mass ratio of the mixed solvent to the cellulose is 100: 3, the volume ratio of the cellulose solution to the epichlorohydrin is 100: 0.6.

comparative example 4: the difference from comparative example 1 is that the mass ratio of the mixed solvent to the cellulose is 100: 4, the volume ratio of the cellulose solution to the epichlorohydrin is 100: 1.0.

comparative example 5: the difference from comparative example 1 is that the mass ratio of the mixed solvent to the cellulose is 100: 4, the volume ratio of the cellulose solution to the epichlorohydrin is 100: 1.4.

comparative example 6: the difference from comparative example 1 is that the mass ratio of the mixed solvent to the cellulose is 100: 4, the volume ratio of the cellulose solution to the epichlorohydrin is 100: 2.0.

fig. 1 is a transmission electron microscopy micrograph of a black phosphorus nanoplate used in an embodiment of the invention, (a) is a low resolution photograph; (b) is a high-resolution photo.

The microscopic morphology test conditions of the black phosphorus nanosheets are as follows: the instrument equipment comprises: a high resolution transmission electron microscope; the model is as follows: FEI Tecnai G²F30; testing high pressure: 300 kV.

As can be seen from fig. 1 (a), the size of the black phosphorus nanoplate is about 100nm × 400 nm; as can be seen from fig. 1b, the black phosphorus nanosheet exhibits distinct lattice fringes, indicating that the black phosphorus nanosheet of the present invention has a good crystal structure; the lattice size was 0.223 nm, corresponding to the (014) diffraction plane.

Fig. 2 is an atomic force microscope photograph of black phosphorus nanoplates used in the present invention. The test conditions for the height map of the black phosphorus nanoplates are as follows: the instrument equipment comprises: high resolution atomic force microscopy; the model is as follows: a Brooks scanning probe microscope; scanning mode: intelligent scanning mode.

As can be seen from FIG. 2, the thickness of these black phosphorus nanoplates is in the distribution range of 1.4-25 nm.

Figure 3 provides a macroscopic physical photograph of a cellulose hydrogel (comparative example 4) and cellulose/black phosphorus nanoplates (example 4). As can be seen from FIG. 3, the pure cellulose hydrogel (comparative example 4) has a colorless translucent "jelly-like" macro-morphology as a whole; after the black phosphorus nanosheet is successfully introduced, the obtained cellulose/black phosphorus nanosheet composite hydrogel (example 4) is coffee-colored as a whole, and the two have bright color contrast.

Fig. 4 and 5 provide scanning electron microscope photographs of the corresponding aerogels obtained after freeze-drying of the cellulose/black phosphorus nanosheet composite hydrogel (example 4) and the cellulose hydrogel (comparative example 4), respectively.

The test conditions were as follows:

to preserve the macromolecular porous structure in the cellulose hydrogel, the tested hydrogel (the cellulose hydrogel of comparative example 4 and the cellulose/black phosphorus nanosheet composite hydrogel of example 4) was first subjected to a freeze-drying treatment to obtain a corresponding aerogel structure, wherein the freeze-drying experimental conditions were as follows: temperature: -80 ℃; time: for 72 hours. Then, the microscopic morphology is tested by adopting the following instruments and equipment: a cold field emission scanning electron microscope; the model is as follows: SEM-Hitachi SU 8010; testing voltage: 3 kV; silver plating time on the surface of the sample: for 20 seconds.

As can be seen from a comparison of fig. 4 and 5, both types of aerogels exhibit significant porosity, which is determined by the three-dimensional gel network structure of cellulose. But obviously, the porous structure of the aerogel corresponding to the cellulose/black phosphorus nanosheet composite hydrogel prepared by the method is relatively uniformly distributed, the pore diameter is 80-280 mu m, and the porosity is about 85%.

The cellulose hydrogel prepared in comparative examples 1 to 6 and the cellulose/black phosphorus nanosheet composite hydrogel prepared in examples 1 to 7 were subjected to mechanical property test and photo-thermal property test, respectively, and the results are shown in table 1.

TABLE 1 basic ingredients and Performance parameters of hydrogels in comparative examples 1-6 and examples 1-7

Table 1 shows typical compositions and physical properties of comparative examples 1-6 and examples 1-7 in the patent of the present invention. As can be seen from table 1, in comparative examples 1 to 6, as the volume fraction of the crosslinking agent epichlorohydrin was increased, the mechanical strength of the finally obtained cellulose hydrogel was substantially increased significantly. For example, when the volume ratio of the cellulose solution to epichlorohydrin is 100: 0.2 (i.e., comparative example 1), the compressive modulus was 19.4 kPa; when the volume ratio of the cellulose solution to the epichlorohydrin is increased to 100: 1 (i.e., comparative example 4) and 100: at time 2 (i.e., comparative example 6), the corresponding compressive moduli increased to 60.8kPa and 79.1kPa, respectively, due to the greater crosslinker content resulting in a substantial increase in the degree of chemical crosslinking of the cellulose hydrogel. However, pure cellulose hydrogels lack any functionality, do not exhibit any photothermal effect, and have a photothermal equilibrium temperature of 25 ℃, which is substantially the same as room temperature.

However, as a strong comparison, in the composite hydrogels of examples 1 to 7, i.e., cellulose/epichlorohydrin/black phosphorus nanosheets, the final photo-thermal equilibrium temperature thereof was greatly increased due to the introduction of the black phosphorus nanosheets. For example, when the mass ratio of cellulose to black phosphorus nanoplatelets is 100: at 0.0001 (i.e., example 1), the final photothermal equilibrium temperature of the composite hydrogel was between 0.5 and 1.0W/cm²Can reach 43.5 ℃ and 49.7 ℃ respectively, and are respectively improved by 18.5 ℃ and 24.7 ℃ compared with pure cellulose hydrogel. When the mass fraction of the black phosphorus nanosheet in the cellulose/epichlorohydrin/black phosphorus nanosheet composite hydrogel is continuously increased, the photo-thermal equilibrium temperature is greatly increased and even exceeds the detection range of a thermal imaging instrument. For example, when the mass ratio of cellulose to black phosphorus nanoplatelets is 100: 5 (i.e., example 5), the final photothermal equilibrium temperature of the composite hydrogel was between 0.5 and 1.0W/cm²At the time of heating, respectively 110 ℃ and 130.4 ℃; when the mass ratio of the cellulose to the black phosphorus nanosheets is 100: 10 (i.e., example 6) and 100: at 50 f (i.e., example 7), the final photothermal equilibrium temperature of the composite hydrogel was above 150 c, which exceeded the detection range of the thermal imager.

The results show that the introduction of the black phosphorus nanosheet not only remarkably improves the mechanical strength of the cellulose hydrogel, but also can really endow the cellulose hydrogel with excellent photo-thermal characteristics, and the characteristics can be adjusted through the content of the black phosphorus nanosheet. And when the black phosphorus nanosheet with lower quality is adopted, the composite hydrogel can reach a higher photo-thermal equilibrium temperature.

The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the present invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.

Claims

1. A preparation method of cellulose/cross-linking agent/black phosphorus nanosheet composite hydrogel is characterized by comprising the following steps:

(1) preparing a mixed solvent containing strong base, urea and water, precooling to-15 to-5 ℃, adding cellulose powder into the precooled mixed solvent, and violently stirring to obtain a cellulose solution;

(3) adding cellulose regeneration liquid into the crosslinking reactant, soaking for 30-60min, and then putting the regenerated crosslinking reactant into water for dialysis to obtain cellulose/black phosphorus nanosheet composite hydrogel; in the composite hydrogel, the mass ratio of the cellulose to the black phosphorus nanosheets is 100: (0.0001-0.03), wherein the water content of the composite hydrogel is 85% -98%.

2. The method according to claim 1, wherein the mixed solvent contains the alkali at a concentration of 5 to 15% by mass and the urea at a concentration of 10 to 15% by mass.

3. The method according to claim 1, wherein the mass ratio of the mixed solvent to the cellulose in the cellulose solution is 100: (1-4); the mass ratio of the cellulose solution to the cross-linking agent is 100: (0.212-2.12).

4. The preparation method according to claim 1, wherein in the step (3), the cellulose regeneration liquid is a dilute sulfuric acid solution with a mass fraction of 5% -10%; the volume ratio of the crosslinking reactant to the dilute sulfuric acid solution is 1: (2-3).

5. The method according to claim 1, wherein the high speed stirring is performed at 7000 to 10000rpm for 1 to 3 minutes.

6. A cellulose/black phosphorus nanoplate composite hydrogel prepared by the preparation method according to any one of claims 1 to 5, wherein the composite hydrogel comprises a cellulose three-dimensional network structure and black phosphorus nanoplates supported in the cellulose three-dimensional network structure; wherein the mass ratio of the cellulose to the black phosphorus nanosheet in the cellulose three-dimensional network structure is 100: (0.0001-0.03), the water content of the composite hydrogel is 85% -98%, and the cellulose three-dimensional network structure is a three-dimensional network structure formed by cellulose and a cross-linking agent.

7. The composite hydrogel according to claim 6, wherein the cellulose three-dimensional network structure has a pore structure with a pore size of 30 to 300 μm.

8. The composite hydrogel according to claim 6, wherein the mass ratio of the cellulose to the crosslinking agent in the cellulose three-dimensional network structure is 100: (1.372-13.71).