Janus structured mxene-cnf aerogel and preparation method and application thereof

Abstract

The application discloses Janus structure MXene-CNF aerogel as well as a preparation method and application thereof. The Janus structure MXene-CNF aerogel comprises a CNF layer and a MXene-CNF layer, wherein the CNF layer and the MXene-CNF layer can be self-assembled to form a Janus structure. The Janus structure MXene-CNF aerogel provided by the application is composed of the CNF layer with a porous microstructure morphology, low thermal conductivity, low light absorbance and high infrared emissivity, and the MXene-CNF layer with a sheet layer microstructure morphology, higher thermal conductivity, high light absorbance and low infrared emissivity, and can be widely applied to the thermal management field through the difference of the double-layer optical properties, physical properties and thermal conductivity, and meanwhile, the preparation process is simple, green, energy-saving and low in price, and can meet the demand of industrial production.

Description

TECHNICAL FIELD

[0001] The present application relates to a new type of aerogel fiber material, in particular to a Janus structure MXene-CNF aerogel and a preparation method and application thereof, and belongs to the technical field of nanoporous materials and functional materials. BACKGROUND

[0002] In recent years, the influence of extreme high and low temperature weather has caused human body discomfort, crop freeze damage, material aging and even fire, which increasingly harms human health and economy. In recent years, about 12% of the global energy is consumed to meet the needs of global human beings through temperature regulation of heating and refrigeration infrastructure. However, the widely used compression-based air conditioning system consumes a large amount of electricity and produces a large amount of carbon dioxide, which has a bad impact on energy and environment. Reducing energy consumption has become one of the most effective and practical solutions in thermal management applications. Therefore, in order to alleviate the negative excessive impact, it is desirable to draw on the process and material that meets the economic, scalable, environmentally friendly and green energy saving.

[0003] As a super-light material, aerogel has low density, ultra-high porosity, high specific surface area and excellent optical performance. Therefore, aerogel shows greater potential in thermal management applications. After decades of development, there are many types of aerogels at present, mainly including silica aerogel, graphene aerogel, MXene aerogel and Kevlar aerogel, etc.

[0004] Patent CN113101877A, patent CN109679146A and patent CN112011094A all disclose a MXene aerogel, but the MXene aerogel material disclosed in the above patents is mainly in block form, which has poor flexibility, low strength and poor wet stability, limiting the feasibility of MXene aerogel in the field of thermal management. At the same time, traditionally, a large amount of energy is needed for freeze-drying to prepare aerogel, which does not meet the principle of energy and environmental sustainability. Patent CN113718371A discloses a preparation method and application of MXene aerogel fiber, although the strength is improved, but in the aspect of thermal management application, only a single heating process can be realized, and the temperature cannot be reduced in a high temperature environment. In view of the above various situations, under the condition of green energy saving, how to improve the performance of MXene aerogel and withstand complex environment in realizing full-season thermal management and large-scale application is a severe challenge, and also a problem to be solved urgently at present to meet the social needs. SUMMARY

[0005] The main purpose of the present application is to provide a Janus structure MXene-CNF aerogel to overcome the shortcomings of the prior art.

[0006] Another purpose of the present application is to provide a preparation method of the Janus structure MXene-CNF aerogel.

[0007] In addition, the present application also provides the application of the Janus structure MXene-CNF aerogel in all-season thermal management.

[0008] To achieve the aforementioned purposes of the application, the present application adopts the following technical solutions:

[0009] The present application provides a Janus structure MXene-CNF aerogel, comprising a CNF layer and a MXene-CNF layer, wherein the CNF layer and the MXene-CNF layer can self-assemble to form a Janus structure.

[0010] Another purpose of the present application is to provide a preparation method of the Janus structure MXene-CNF aerogel, comprising:

[0011] The CNF dispersion liquid, the biocompatible dispersion liquid, and the crosslinking agent are uniformly dispersed to obtain a CNF layer mixed solution;

[0012] The CNF dispersion liquid, the MXene dispersion liquid, the biocompatible dispersion liquid, and the crosslinking agent are uniformly dispersed to obtain a MXene-CNF layer mixed solution;

[0013] The CNF layer mixed solution and the MXene-CNF layer mixed solution are sequentially frozen in a set order to obtain a Janus structure MXene-CNF ice gel;

[0014] The Janus structure MXene-CNF ice gel is subjected to crosslinking reaction through an acidic solution, followed by solvent replacement and drying to obtain a Janus structure MXene-CNF aerogel.

[0015] The present application also provides a Janus structure MXene-CNF aerogel prepared by the above preparation method.

[0016] In addition, the present application also provides the application of the Janus structure MXene-CNF aerogel in all-season thermal management.

[0017] Compared with the prior art, the present application has at least the following beneficial effects:

[0018] 1) The Janus structure MXene-CNF aerogel prepared by adjusting the concentration and relative content of raw materials such as CNF and MXene, and the freezing temperature and time, etc., can simultaneously realize indoor temperature rise and fall due to the differences in double-layer optical properties, micro-morphology structure, and thermal conductivity, meet the demand of different seasons for suitable temperature, and can reduce the temperature by 6-10℃ in summer and increase the temperature by 4-6℃ in winter.

[0019] 2) The raw materials required for the prepared Janus structure MXene-CNF aerogel in the application are biodegradable and have high biocompatibility, and will not have a negative impact on the ecological environment; the freeze-drying process required for traditional aerogel preparation is broken, greatly reducing energy consumption, meeting the current social development requirements for energy and environment.

[0020] 3) The Janus structure MXene-CNF aerogel preparation method provided by the application has a simple process, does not require expensive preparation instruments, high temperature action and catalysts, etc., has low cost and takes less time, and has good application prospects for large-scale preparation. BRIEF DESCRIPTION OF DRAWINGS

[0021] In order to more clearly illustrate the technical solutions in the embodiments of the application or the prior art, the drawings needed to be used in the embodiments or prior art description will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments described in the application, and other drawings can also be obtained by those skilled in the art without creative labor on the basis of these drawings.

[0022] Figure 1 Scanning electron microscope image of the Janus structure MXene-CNF aerogel obtained in Example 1 of the application.

[0023] Figure 2 Cyclic compression performance test diagram of the Janus structure MXene-CNF aerogel obtained in Example 1 of the application.

[0024] Figure 3a CNF layer tensile strength characterization diagram of the Janus structure MXene-CNF aerogel obtained in Example 1 and Example 2 of the application with different concentrations of CNF.

[0025] Figure 3b CNF layer porosity characterization diagram of the Janus structure MXene-CNF aerogel obtained in Example 1 and Example 2 of the application with different concentrations of CNF.

[0026] Figure 3c CNF layer pore size characterization diagram of the Janus structure MXene-CNF aerogel obtained in Example 1 and Example 2 of the application with different concentrations of CNF.

[0027] Figure 4a Schematic diagram of a thermal management house model constructed based on the Janus structure MXene-CNF aerogel, single-layer CNF aerogel and single-layer MXene-CNF aerogel of Example 1, Comparative Example 1 and Comparative Example 2 of the application.

[0028] Figure 4bSchematic diagram of the device based on Janus structured MXene-CNF aerogel, single-layer CNF aerogel and single-layer MXene-CNF aerogel of Example 1, Comparative Example 1 and Comparative Example 2 of the present application.

[0029] Figure 5 Schematic diagram of the winter warming thermal management mechanism of the Janus structured MXene-CNF aerogel of Example 1 of the present application.

[0030] Figure 6a Absorbance characterization diagram of the CNF layer and MXene-CNF layer aerogel of Example 1, Comparative Example 1 and Comparative Example 2 of the present application.

[0031] Figure 6b Infrared emissivity characterization diagram of the CNF layer and MXene-CNF layer aerogel of Example 1, Comparative Example 1 and Comparative Example 2 of the present application.

[0032] Figure 7 Winter thermal management simulation indoor and outdoor temperature test diagram of the Janus structured MXene-CNF aerogel of Example 1 of the present application.

[0033] Figure 8 Schematic diagram of the summer cooling thermal management mechanism of the Janus structured MXene-CNF aerogel of Example 1 of the present application.

[0034] Figure 9 Summer thermal management simulation indoor and outdoor temperature test diagram of the Janus structured MXene-CNF aerogel of Example 1 of the present application.

[0035] Figure 10a Absorbance characterization diagram of the MXene-CNF layer of the Janus structured MXene-CNF aerogel with different MXene contents of Example 3 of the present application.

[0036] Figure 10b Infrared emissivity performance test diagram of the MXene-CNF layer of the Janus structured MXene-CNF aerogel with different MXene contents of Example 3 of the present application.

[0037] Figure 11 Optical photograph morphology and schematic diagram of the Janus structured MXene-CNF aerogel when the mass ratio of CNF to MXene is 2:1 of Example 3 of the present application.

[0038] Figure 12a Summer thermal management simulation indoor and outdoor temperature test diagram of the single-layer CNF aerogel of Comparative Example 1 and Comparative Example 2 of the present application.

[0039] Figure 12bThe winter thermal management simulation indoor and outdoor temperature test chart of the single-layer MXene-CNF aerogel of the present application Comparative Example 1 and Comparative Example 2. DETAILED DESCRIPTION

[0040] In view of the defects of the prior art, the present inventors have obtained the technical solutions of the present application through long-term research and a large number of practices. The technical solutions of the present application will be described clearly and completely below. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor fall within the scope of protection of the present application.

[0041] Specifically, as one aspect of the technical solutions of the present application, the Janus structure MXene-CNF aerogel includes a CNF layer and a MXene-CNF layer, wherein the CNF layer and the MXene-CNF layer can self-assemble to form a Janus structure.

[0042] In some specific embodiments, the material of the CNF layer includes any one or a combination of two or more of TEMPO-CNF, sulfonated CNF, quaternized CNF, and bacterial CNF. TEMPO-CNF is preferred due to its excellent optical properties and higher specific surface area and porous structure, but is not limited thereto.

[0043] Further, the thickness of the CNF layer is 0.5-2.5 cm.

[0044] Further, the CNF layer has an ultrahigh specific surface area and a porous structure, a porosity of 96-99%, and a pore size of the contained pores of 80-300 μm.

[0045] Further, the absorbance of the CNF layer is 5-20%, and the infrared emissivity is above 90%, so that the internal temperature is reduced mainly through the low absorbance of the CNF layer for sunlight reflection and the high infrared emissivity for solar energy dissipation.

[0046] In some specific embodiments, the MXene-CNF layer is prepared by mixing MXene and CNF in a certain mass ratio.

[0047] Further, the concentration of MXene in the MXene-CNF layer is 0.05-0.3 wt.%.

[0048] Further, the MXene-CNF layer of the present application is prepared by mixing MXene and CNF according to a certain mass ratio, wherein the MXene in the MXene-CNF layer comprises any one or a combination of two or more of Ti3AlC2, Ti2AlC, Nb2AlC, V2AlC, Mo3AlC2, and Ti3SiC2.

[0049] Further, the mass ratio of the CNF to the MXene is 6-2:1, preferably one of 6:1, 5:1, 4:1, 3:1, 2:1, etc.

[0050] Further, the thickness of the MXene-CNF layer is 0.5-2.5 cm.

[0051] Further, the micro-morphological structure of the MXene-CNF layer is a sheet structure.

[0052] Further, the absorbance of the MXene-CNF layer is 80-98%, and the minimum infrared emissivity is 60-90%. The MXene-CNF layer mainly absorbs solar energy through high absorbance and transfers it to the CNF layer, and radiates energy to the internal space through high infrared emissivity to increase the internal temperature.

[0053] In some specific embodiments, the Janus-structured MXene-CNF aerogel is self-assembled from a CNF layer and a MXene-CNF layer according to a certain thickness ratio. Specifically, the thickness ratio of the CNF layer to the MXene-CNF layer is between 2:1 and 1:3.

[0054] In some specific embodiments, the Janus-structured MXene-CNF aerogel comprises: (1) a CNF layer having a porous microstructure morphology, low thermal conductivity, low absorbance, and high infrared emissivity; and (2) a MXene-CNF layer having a sheet microstructure morphology, higher thermal conductivity, high absorbance, and low infrared emissivity.

[0055] Further, the total thickness of the Janus-structured MXene-CNF aerogel is between 1-5 cm.

[0056] Further, the Janus-structured MXene-CNF aerogel has excellent physicochemical properties, with a tensile property of 1-2.5 MPa and a cyclic compression property of 100-200 kPa, and the mechanical properties are superior to most existing biomass-based aerogels.

[0057] Further, in summer, the Janus structure MXene-CNF aerogel can reduce the indoor temperature by 6-10℃ compared with the ambient temperature, and in winter, the Janus structure MXene-CNF aerogel can increase the indoor temperature by 4-6℃ compared with the ambient temperature.

[0058] Another aspect of the embodiment of the present application provides a preparation method of the Janus structure MXene-CNF aerogel, which is mainly prepared by an ice template strategy, and the preparation process includes freezing, thawing, solvent exchange, cross-linking and normal temperature drying processes.

[0059] In some embodiments, the preparation method specifically includes:

[0060] The CNF aqueous dispersion, the biocompatible aqueous dispersion and the cross-linking agent are uniformly dispersed in water to obtain a CNF layer mixed solution;

[0061] The CNF aqueous dispersion, the MXene aqueous dispersion, the biocompatible aqueous dispersion and the cross-linking agent are uniformly dispersed in water to obtain a MXene-CNF layer mixed solution;

[0062] The CNF layer mixed solution and the MXene-CNF layer mixed solution are sequentially frozen in a set order to obtain a Janus structure MXene-CNF ice gel;

[0063] The Janus structure MXene-CNF ice gel is cross-linked by an acid solution reaction, and then solvent replacement and drying are performed to obtain a Janus structure MXene-CNF aerogel.

[0064] In some specific embodiments, the CNF in the CNF aqueous dispersion includes any one or a combination of two or more of TEMPO-CNF, sulfonated CNF, quaternized CNF and bacterial CNF, and is preferably TEMPO-CNF.

[0065] Further, the concentration of the CNF in the CNF aqueous dispersion is 0.4-1.4wt.%.

[0066] Further, the concentration of the MXene in the MXene aqueous dispersion is 0.05-0.3wt.%.

[0067] In some specific embodiments, the biocompatible substance contained in the biocompatible aqueous dispersion includes any one or a combination of two or more of sodium alginate, tannic acid, polyvinyl alcohol and chitin.

[0068] Further, the concentration of the biocompatible substance in the biocompatible aqueous dispersion is 0.1-1wt.%.

[0069] Further, the mass ratio of the CNF aqueous dispersion solution to the biocompatible aqueous dispersion solution is 20:1-60:1.

[0070] In some specific embodiments, the cross-linking agent comprises any one or a combination of two or more of ferric chloride, calcium chloride, calcium carbonate, and copper chloride.

[0071] Further, the concentration of the cross-linking agent in the CNF layer mixed solution is 0.05-0.2 wt.%.

[0072] In some specific embodiments, the freezing mold is a three-dimensional geometric shape, preferably any one of a cube or a cylinder.

[0073] Further, the freezing temperature is -30 to -10℃, and the freezing time is 5-10 h.

[0074] In some specific embodiments, the acidic solution comprises any one or a combination of two or more of carbonic acid, hydrochloric acid, acetic acid, and hypochlorous acid, and the concentration of the acidic solution is 1M.

[0075] In some specific embodiments, the displacing agent used in the solvent displacement comprises any one or a combination of two or more of acetone, anhydrous ethanol, tetrahydrofuran, and isopropanol, and the purity of the displacing agent is 99%.

[0076] Further, the acid solution reaction cross-linking time is 0.5-2 h, the displacing agent solvent displacement time is 10-40 min, and the number of times of displacing agent solvent displacement is 3.

[0077] Further, the drying temperature is 40-100℃, and the time is 1-4 h. The present application reduces the large amount of time and energy consumed in the freeze-drying process through normal temperature drying.

[0078] In some more specific embodiments, the preparation method of the Janus structure MXene-CNF aerogel comprises:

[0079] (1) First, the CNF deionized water dispersion solution and the biocompatible deionized water dispersion solution are stirred and ultrasonically treated at a mass ratio of 20:1-60:1, and a cross-linking agent is added to the mixed solution to uniformly disperse in the mixed solution of CNF and biocompatible deionized water dispersion solution, to obtain a CNF layer mixed solution raw material (i.e., the "CNF layer mixed solution" in the foregoing), the stirring time is 30 min, and the ultrasonic treatment time is 30 min:

[0080] (2) Secondly, MXene-CNF layer mixed solution raw materials are prepared: CNF dispersion liquid, biocompatible dispersion liquid and MXene deionized water dispersion liquid are mixed, stirred and ultrasonically treated, the mass ratio of CNF to MXene is 6:1, 5:1, 4:1, 3:1 and 2:1, and a crosslinking reagent is added in the mixed solution to uniformly disperse in the mixed solution of MXene, CNF and biocompatible deionized water dispersion liquid, to obtain MXene-CNF layer mixed solution raw materials (namely the "MXene-CNF layer mixed solution" in the foregoing), and the concentration of the crosslinking agent is 0.05-0.2wt.%;

[0081] (3) Thirdly, the CNF layer mixed solution raw materials prepared in step (1) are poured into a mold to freeze to obtain CNF ice gel, and then a second layer of MXene-CNF layer mixed solution raw materials is poured on top, and after sufficient freezing, Janus structure MXene-CNF ice gel is obtained.

[0082] (4) Finally, the obtained Janus structure MXene-CNF ice gel is reacted by an acidic solution, crosslinked and replaced by a displacement agent through multiple solvent replacement, and then placed in a dry environment (or an oven) to dry to obtain the required Janus structure MXene-CNF aerogel.

[0083] In summary, by adjusting the concentration and relative content of CNF, MXene and other raw materials, and the freezing temperature and time, the thickness (1-5cm), double-layer thickness ratio (2:1-1:3), CNF layer pore size (80-300μm), MXene-CNF layer absorbance (80-98%) and infrared emissivity (60-90%) of the Janus structure MXene-CNF aerogel can be precisely adjusted and controlled.

[0084] Another aspect of the embodiments of the present application also provides the Janus structure MXene-CNF aerogel prepared by the above preparation method.

[0085] In addition, another aspect of the embodiments of the present application also provides the application of the Janus structure MXene-CNF aerogel in full-season thermal management.

[0086] According to the difference in optical properties, the Janus structure MXene-CNF aerogel exhibits a dual-function thermal regulation performance in different seasons. In winter, the MXene-CNF layer is on the outside, mainly absorbing solar energy through high absorbance to increase the indoor temperature; in summer, the CNF layer is on the outside, mainly reflecting sunlight through low absorbance and high infrared emissivity to radiate outward infrared radiation to reduce the indoor temperature. Through thermal management, the indoor temperature can be regulated in different seasons. In summer, the indoor temperature can be reduced by 6-10℃ compared with the ambient temperature; in winter, the indoor temperature can be increased by 4-6℃. Therefore, the Janus structure MXene-CNF aerogel prepared in the application can adjust the indoor temperature to a comfortable temperature, and is a dual-function thermal management system suitable for all-season home indoor thermal regulation.

[0087] In summary, the Janus structure MXene-CNF aerogel provided by the application has comprehensive performance improvement, and is widely used in all-season thermal management, such as indoor temperature regulation, to meet the human body's suitable temperature in different seasons. At the same time, the application has low requirements for environmental factors, simple preparation process, low price, energy saving and emission reduction, does not need expensive and complex experimental equipment, and will not cause adverse effects on the surrounding environment, and can meet the needs of industrial production.

[0088] The technical solutions of the application will be further described in detail below in combination with several preferred embodiments and the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the application, rather than all the embodiments. It should be noted that the following described embodiments are intended to facilitate the understanding of the application, and do not have any limiting effect. Based on the embodiments in the application, all other embodiments obtained by those of ordinary skill in the art without creative labor are within the scope of protection of the application. The experimental methods not specified in the following embodiments are usually carried out according to the conventional conditions or the conditions recommended by the manufacturer.

[0089] Example 1

[0090] Preparation of Janus structure MXene-CNF aerogel and test of thermal management performance.

[0091] (1) 1wt.% TEMPO-CNF deionized water dispersion and 0.5wt.% sodium alginate dispersion were stirred and ultrasonicated at a mass ratio of 40:1, and 0.1wt.% iron chloride was added to the mixed solution to uniformly disperse in the mixed solution of TEMPO-CNF and sodium alginate dispersion, to obtain a CNF layer mixed solution raw material;

[0092] (2) Next, prepare the raw materials for the MXene-CNF layer mixture: 1 wt.% TEMPO-CNF dispersion and 0.5 wt.% sodium alginate are stirred and sonicated at a mass ratio of 40:1. At the same time, 1 wt.% TEMPO-CNF and 0.2 wt.% Ti3AlC2 type MXene dispersion are stirred and sonicated at a mass ratio of 3:1. 0.1 wt.% ferric chloride is added to the mixture to make it uniformly dispersed in the mixture of MXene, TEMPO-CNF and sodium alginate dispersion to obtain the raw materials for the MXene-CNF layer mixture.

[0093] (3) Next, the CNF layer mixture raw material prepared in (1) is poured into a cylindrical mold and frozen (-20℃) to obtain CNF ice gel. Then, the second layer of MXene-CNF layer mixture raw material (double layer ratio 1:1) is poured onto the top and fully frozen to obtain Janus structure MXene-CNF ice gel.

[0094] (4) Finally, the obtained Janus structure MXene-CNF ice gel was reacted and crosslinked in 1M acetone solution for 1 h and then replaced with pure acetone reagent multiple times for 25 min. After that, it was placed in a dry environment (or oven) and dried at ~60℃ for 4 h to obtain the desired Janus structure MXene-CNF aerogel.

[0095] (5) The prepared Janus-structured MXene-CNF aerogel has distinct layers and uniform morphology, possessing both a microporous CNF layer and a microsheet-like structure of the MXene-CNF layer. Figure 1 ),and Figure 2 This indicates that the prepared Janus-structured MXene-CNF aerogel possesses compression recovery properties, with a strength of approximately 150 kPa after three compression cycles. Furthermore, from... Figure 3a and 3b It is known that the Janus-structured MXene-CNF aerogel prepared with 1 wt.% TEMPO-CNF has a tensile strength of approximately 2.2 MPa and a porosity of approximately 98.2%.

[0096] (6) The Janus-structured MXene-CNF aerogel prepared in this way is used for thermal management to regulate indoor temperature in different seasons: such as Figure 4a The constructed thermal management house model device is shown, which adjusts to simulate the winter environment, and the thermal management mechanism is as follows: Figure 5As shown, the MXene-CNF layer of the obtained Janus structured MXene-CNF aerogel is outward as a smart window model, in which the Janus structured MXene-CNF aerogel can perform efficient and continuous thermal management under sunlight irradiation. The solar simulator simulates sunlight irradiation on the surface of the aerogel. The high light absorption (97%) of the MXene-CNF layer absorbs solar energy to the CNF layer, and the high infrared emissivity (95%) of the CNF layer radiates heat to the indoor to increase the temperature of the internal space, achieving the effect of warming in winter. Figure 6a and 6b ).

[0097] Through the winter thermal management simulation test of the Janus structured MXene-CNF aerogel, the indoor temperature is increased to about 26°C under the condition of environmental temperature of about 21°C by absorbing solar energy and infrared heat radiation by the Janus structured MXene-CNF aerogel. Figure 7

[0098] (7) Further, the simulated summer environment is adjusted, such as Figure 8 As shown, the CNF layer of the obtained Janus structured MXene-CNF aerogel is outward as a smart window model, in which the Janus structured MXene-CNF aerogel can perform efficient and continuous thermal management under sunlight irradiation. The solar simulator simulates sunlight irradiation on the surface of the aerogel. The CNF layer reflects sunlight with extremely low light absorption, and radiates energy dissipation to the outside through high infrared emissivity (about 95%). A small part of energy is absorbed through the MXene-CNF layer by the relatively low infrared emissivity (about 60%) of the layer, thereby minimizing the internal space heat energy, reducing the indoor temperature, and achieving the effect of cooling in summer. Figure 6a and 6b ).

[0099] Through the summer thermal management simulation test of the Janus structured MXene-CNF aerogel, the indoor temperature is reduced to about 31°C under the condition of environmental temperature of about 40°C extremely hot, by reflecting sunlight, radiating dissipation of solar energy and absorbing heat energy by the Janus structured MXene-CNF aerogel. Figure 9

[0100] Example 2

[0101] Compared with Example 1, the influence of CNF concentration on the porosity, pore size and tensile strength of the Janus structured MXene-CNF aerogel.

[0102] ​​(1) 0.4 wt.%, 0.6 wt.%, 0.8 wt.%, 1.2 wt.% and 1.4 wt.% sulfonated CNF dispersions were respectively stirred and ultrasonicated with 0.5 wt.% tannic acid dispersion at a mass ratio of 20:1, 30:1, 40:1, 50:1 and 60:1, and 0.05 wt.% calcium chloride was added to the mixed solution to uniformly disperse in the mixed solution of CNF and tannic acid dispersion, to obtain five different concentrations of CNF layer mixed solution raw materials;

[0103] (2) Secondly, MXene-CNF layer mixed solution raw materials were prepared: 0.4 wt.%, 0.6 wt.%, 0.8 wt.%, 1.2 wt.% and 1.4 wt.% sulfonated CNF dispersions were respectively stirred and ultrasonicated with 0.5 wt.% tannic acid dispersion at a mass ratio of 20:1, 30:1, 40:1, 50:1 and 60:1, and 0.05 wt.% Ti2AlC type MXene dispersion was stirred and ultrasonicated at a mass ratio of 6:1, 5:1, 4:1, 3:1 and 2:1, and 0.05 wt.% calcium chloride was added to the mixed solution to uniformly disperse in the mixed solution of MXene, CNF and tannic acid dispersion, to obtain five different concentrations of MXene-CNF layer mixed solution raw materials;

[0104] (3) Thirdly, the five different concentrations of CNF layer mixed solution raw materials prepared in (1) were respectively poured into five cylindrical molds and frozen (-30°C) to obtain five different concentrations of sulfonated CNF ice gels, and then the second layer of MXene-CNF layer mixed solution raw materials corresponding to the concentration was poured on top (double-layer ratio 1:1), and after sufficient freezing, five different concentrations of Janus structure MXene-CNF ice gels were obtained.

[0105] (4) Finally, the five different concentrations of Janus structure MXene-CNF ice gels obtained were respectively reacted and crosslinked in 1M hydrochloric acid in anhydrous ethanol solution for 1.5h, and after pure anhydrous ethanol reagent solvent replacement for 30min, they were placed in a dry environment (or oven) at ~80°C for 3h to obtain the required five concentrations of Janus structure MXene-CNF aerogels.

[0106] The prepared Janus structure MXene-CNF aerogel of five CNF concentrations, the change of sulfonated CNF concentration affects the tensile strength, porosity and pore size of the CNF layer of the aerogel. As shown in Figure 3, with the increase of sulfonated CNF concentration, the degree of crosslinking network increases, and the tensile strength gradually increases (1-2.5 MPa), and with the increase of concentration, the density increases, the porosity gradually decreases (96-99%), and the pore size also gradually decreases (80-300 um). By comparing with Example 1, the mechanical stability of the aerogel is ensured under the premise of high porosity, and the mechanical properties also need to be improved. Through comparison, the Janus structure MXene-CNF aerogel prepared by 1 wt.% sulfonated CNF is finally selected, at this time the tensile strength of the CNF layer is 2.2 MPa, the porosity is about 98.2, and the pore size is about 200 um.

[0107] Example 3

[0108] Effect of MXene content on absorbance and infrared emissivity of Janus structure MXene-CNF aerogel.

[0109] (1) 1.0 wt.% quaternary ammonium CNF dispersion liquid was respectively mixed with 0.1 wt.% polyvinyl alcohol dispersion liquid at a mass ratio of 40:1, and 0.2 wt.% calcium carbonate was added to the mixed liquid to uniformly disperse in the mixed liquid of quaternary ammonium CNF and polyvinyl alcohol dispersion liquid, to obtain CNF layer mixed liquid raw material;

[0110] (2) Secondly, the MXene-CNF layer mixed liquid raw material was prepared: 1.0 wt.% quaternary ammonium CNF dispersion liquid, 0.1 wt.% polyvinyl alcohol dispersion liquid and 0.3 wt.% V2AlC type MXene dispersion liquid were mixed and ultrasonically stirred at a mass ratio of 20:1, 30:1, 40:1, 50:1 and 60:1, and 1.0 wt.% quaternary ammonium CNF and 0.3 wt.% MXene were mixed and ultrasonically stirred at a mass ratio of 6:1, 5:1, 4:1, 3:1 and 2:1, and 0.2 wt.% calcium carbonate was added to the five mixed liquids to uniformly disperse in the mixed liquid of MXene, quaternary ammonium CNF and polyvinyl alcohol dispersion liquid, to obtain five MXene-CNF layer mixed liquid raw materials with different MXene mass ratios;

[0111] (3) Thirdly, the CNF layer mixed liquid raw material prepared in (1) was respectively poured into 5 cylindrical molds and frozen (-10℃) to obtain 5 quaternary ammonium CNF ice gels, and then the second layer of MXene-CNF layer mixed liquid raw material with different mass ratios of MXene was respectively poured on top (double-layer ratio 1:1), and after sufficient freezing, 5 Janus structure MXene-CNF ice gels with different mass ratios of MXene were obtained.

[0112] (4) Finally, the obtained 5 pieces of Janus structured MXene-CNF ice hydrogel with different mass ratios of MXene were respectively reacted and cross-linked in 1M acetic acid tetrahydrofuran solution for 2h and solvent replaced by pure tetrahydrofuran reagent for 40min, and then placed in a dry environment (or oven) at ~100℃ for 1h to obtain the required 5 kinds of Janus structured MXene-CNF aerogel with different mass ratios of MXene.

[0113] The prepared 5 kinds of Janus structured MXene-CNF aerogel with different mass ratios of MXene, the change of MXene content affects the absorbance, infrared emissivity and structural stability of the MXene-CNF layer of the aerogel. As shown in Figure 10a and Figure 10b : With the increase of MXene content, the blackness of the MXene-CNF layer gradually deepens, so the absorbance increases (80-98%), which is more conducive to absorbing solar energy in cold environments (MXene-CNF layer on the outside), and the indoor temperature rising effect is more significant; Similarly, with the increase of MXene content, the infrared emissivity of the MXene-CNF layer gradually decreases (60-90%), which is more conducive to energy storage in hot environments (MXene-CNF layer on the inside), and the indoor temperature lowering effect is more significant. Therefore, the increase of MXene content is conducive to the improvement of the thermal management performance of the Janus structured MXene-CNF aerogel. However, if the content of MXene is too high, the content of quaternized CNF will decrease, which will lead to the decrease of the stability of the layer and the instability of the structure, as shown in Figure 11 : When the mass ratio of quaternized CNF and MXene is 2:1, the aerogel will present a concave state, the structure will be damaged, and the stability will be reduced. Considering various factors and performance comparisons, the Janus structured MXene-CNF aerogel prepared by selecting the mass ratio of quaternized CNF and MXene as 3:1 is finally selected, at this time the absorbance of the MXene-CNF layer is about 97%, and the infrared emissivity is about 60%.

[0114] Example 4

[0115] Preparation of Janus structured MXene-CNF aerogel.

[0116] (1) 1.0wt.% bacterial CNF dispersion was respectively mixed with 0.5wt.% chitin dispersion at a mass ratio of 20:1, and 0.1wt.% copper chloride was added to the mixed solution to make it uniformly dispersed in the mixed solution of bacterial CNF and chitin dispersion, to obtain the CNF layer mixed solution raw material;

[0117] (2) Secondly, MXene-CNF layer mixed solution raw materials are prepared: 1.0 wt.% bacterial CNF dispersion liquid, 0.1 wt.% chitin dispersion liquid and 0.2 wt.% Mo3AlC2 type MXene dispersion liquid are mixed, the bacterial CNF and the MXene are stirred and ultrasonically mixed at a mass ratio of 4:1, and 0.05 wt.% copper chloride is added in the mixed solution to uniformly disperse in the mixed solution of the MXene, the CNF and the chitin dispersion liquid, to obtain the MXene-CNF layer mixed solution raw materials;

[0118] (3) Thirdly, the CNF layer mixed solution raw materials prepared in (1) are poured into a cylindrical mold and frozen (-20°C) to obtain CNF ice gel, and then a second layer of MXene-CNF layer mixed solution raw materials (double layer ratio 2:1) is poured on top, and after sufficient freezing, a Janus structure MXene-CNF ice gel is obtained;

[0119] (4) Finally, the obtained Janus structure MXene-CNF ice gel is reacted and crosslinked in 1M hypochlorous acid isopropyl alcohol solution for 1 h, and isopropanol reagent is replaced with solvent for multiple times for 30 min, and then is placed in a 40°C drying environment (or in an oven) for drying for 1 h to obtain the required Janus structure MXene-CNF aerogel.

[0120] Example 5

[0121] Preparation of Janus structure MXene-CNF aerogel.

[0122] (1) 1.0 wt.% bacterial CNF dispersion liquid is respectively stirred and ultrasonically mixed with 0.5 wt.% chitin dispersion liquid at a mass ratio of 60:1, and 0.1 wt.% copper chloride is added in the mixed solution to uniformly disperse in the mixed solution of the bacterial CNF and the chitin dispersion liquid, to obtain CNF layer mixed solution raw materials;

[0123] (2) Secondly, MXene-CNF layer mixed solution raw materials are prepared: 1.0 wt.% bacterial CNF dispersion liquid, 1.0 wt.% chitin dispersion liquid and 0.2 wt.% Ti3SiC2 type MXene dispersion liquid are mixed, the bacterial CNF and the MXene are stirred and ultrasonically mixed at a mass ratio of 4:1, and 0.2 wt.% copper chloride is added in the mixed solution to uniformly disperse in the mixed solution of the MXene, the CNF and the chitin dispersion liquid, to obtain the MXene-CNF layer mixed solution raw materials;

[0124] (3) Thirdly, the CNF layer mixed solution raw materials prepared in (1) are poured into a cylindrical mold and frozen (-20°C) to obtain CNF ice gel, and then a second layer of MXene-CNF layer mixed solution raw materials (double layer ratio 3:1) is poured on top, and after sufficient freezing, a Janus structure MXene-CNF ice gel is obtained;

[0125] (4) Finally, the obtained Janus structured MXene-CNF cryogel was cross-linked by 1M carbonic acid acetone solution for 1 h and solvent exchanged with pure acetone reagent for 15 min, and then placed in a dry environment at 40°C (or in an oven) for 4 h to obtain the desired Janus structured MXene-CNF aerogel.

[0126] Example 6

[0127] Preparation of Janus structured MXene-CNF aerogel.

[0128] (1) 1.0 wt.% bacterial CNF dispersion liquid was stirred and ultrasonicated with 0.5 wt.% chitin dispersion liquid at a mass ratio of 60:1, and 0.1 wt.% copper chloride was added to the mixed liquid to uniformly disperse in the mixed liquid of bacterial CNF and chitin dispersion liquid, to obtain CNF layer mixed liquid raw material;

[0129] (2) Secondly, MXene-CNF layer mixed liquid raw material was prepared: 1.0 wt.% bacterial CNF dispersion liquid, 1.0 wt.% chitin dispersion liquid and 0.2 wt.% Nb2AlC type MXene dispersion liquid were mixed, and bacterial CNF and MXene were stirred and ultrasonicated at a mass ratio of 4:1, and 0.2 wt.% copper chloride was added to the mixed liquid to uniformly disperse in the mixed liquid of MXene, CNF and chitin dispersion liquid, to obtain MXene-CNF layer mixed liquid raw material;

[0130] (3) Again, the CNF layer mixed liquid raw material prepared in (1) was poured into a cylindrical mold and frozen (-20°C) to obtain CNF cryogel, and then the second layer of MXene-CNF layer mixed liquid raw material was poured on top (double layer ratio 3:1), and after sufficient freezing, Janus structured MXene-CNF cryogel was obtained;

[0131] (4) Finally, the obtained Janus structured MXene-CNF cryogel was cross-linked by 1M carbonic acid acetone solution for 1 h and solvent exchanged with pure acetone reagent for 15 min, and then placed in a dry environment at 40°C (or in an oven) for 4 h to obtain the desired Janus structured MXene-CNF aerogel.

[0132] Comparative Example 1

[0133] Thermal management performance application test of single-layer CNF aerogel

[0134] (1) 1.0 wt.% bacterial CNF dispersion was stirred and ultrasonicated with 0.5 wt.% chitin dispersion at a mass ratio of 50:1, and 0.1 wt.% copper chloride was added to the mixture to uniformly disperse in the bacterial CNF and chitin dispersion mixture to obtain CNF layer mixture raw materials;

[0135] (2) Next, the prepared CNF layer mixture raw materials were poured into a cylindrical mold and frozen (-20°C) to obtain a single-layer CNF ice gel with a thickness of 2.5 em;

[0136] (3) Finally, the obtained quaternized CNF ice gel was reacted and cross-linked in 1M hypochlorous acid isopropyl alcohol reagent for 0.5h and solvent replaced by pure isopropyl alcohol reagent for 20min, and then placed in a dry environment (or oven) at ~80°C for 1.5h to obtain the desired single-layer CNF aerogel;

[0137] (4) The prepared single-layer CNF aerogel has a porous structure Figure 1 ), and the prepared single-layer CNF aerogel has compression recovery performance, 3 compression cycle strength of about 150kPa, tensile strength of about 2.2MPa, and porosity of about 98.2%.

[0138] (5) Similarly, as shown in the thermal management house model device constructed in Figure 4, the single-layer CNF aerogel was used for thermal management simulation test. Through the thermal management simulation test, the single-layer CNF aerogel has low light absorption intensity and high infrared emissivity, so it cannot achieve indoor heating in winter, but can be used for indoor cooling in summer Figure 11 ;

[0139] In summer, as shown in Figure 6, the single-layer CNF aerogel can achieve indoor cooling to ~33°C under the extremely hot condition of ambient temperature of about 40°C due to its extremely high infrared emissivity (95%) and extremely low light absorption intensity (10%), but the cooling performance is still slightly lower than that of the Janus structure MXene-CNF aerogel Figure 12a ;

[0140] Comparative Example 2

[0141] Comparison of thermal management performance application test of single-layer MXene-CNF aerogel.

[0142] (1) Preparation of MXene-CNF layer mixed solution raw materials: 1.0 wt.% TEMPO-CNF dispersion liquid, 0.5 wt.% chitin dispersion liquid and 0.2 wt.% Nb2AlC type MXene dispersion liquid are mixed, TEMPO-CNF and MXene are stirred and ultrasonically treated at a mass ratio of 6:1, and 0.1 wt.% calcium chloride is added in the mixed solution to make it uniformly dispersed in the mixed solution of MXene, CNF and chitin dispersion liquid, to obtain MXene-CNF layer mixed solution raw materials;

[0143] (2) Secondly, the prepared MXene-CNF layer mixed solution raw materials are poured into a cylindrical mold and frozen (-20°C) to obtain a single-layer MXene-CNF ice gel with a thickness of 2.5 cm;

[0144] (3) Finally, the obtained MXene-CNF ice gel is reacted and cross-linked in 1M acetic acid anhydrous ethanol solution for 2h, and after multiple solvent replacement for 10min in pure anhydrous ethanol reagent, it is placed in a dry environment (or in an oven) at 70°C for 2h to obtain the required single-layer MXene-CNF aerogel;

[0145] (4) The prepared single-layer MXene-CNF aerogel has a micro lamellar structure Figure 1 ). Similarly, as shown in the thermal management house model device constructed in Figure 4, the single-layer MXene-CNF aerogel is used for thermal management simulation test. The MXene-CNF aerogel has very high light absorption intensity (about 97%) and low infrared emissivity (about 60%), so it cannot achieve summer cooling, but can be used for winter indoor heating application (Figure 6);

[0146] At noon in winter, under sufficient sunlight conditions, the MXene-CNF aerogel absorbs sunlight through its very high light absorption intensity, and transmits the energy to the indoor, so that the indoor temperature is increased by about 4°C, but the heating performance is still not as good as that of the Janus structure MXene-CNF aerogel Figure 12b ).

[0147] Therefore, the single-layer CNF and the single-layer MXene-CNF aerogel can only achieve thermal management application in a single season, and cannot achieve full-season thermal management application, and the thermal management performance is not as good as that of the Janus structure MXene-CNF aerogel of the above embodiments 1-3.

[0148] It should be noted that the specific embodiments of the application described above do not constitute a limitation on the scope of protection of the application. Any other corresponding changes and modifications made in accordance with the technical concept of the application shall be included in the scope of protection of the claims of the application.

Claims

1. A method for preparing a Janus structured MXene-CNF aerogel, characterized in that, Comprising: The CNF aqueous dispersion, the biocompatible aqueous dispersion, and the crosslinking agent are uniformly dispersed to obtain a CNF layer mixed solution; the CNF aqueous dispersion, the MXene aqueous dispersion, the biocompatible aqueous dispersion, and the crosslinking agent are uniformly dispersed to obtain a MXene-CNF layer mixed solution; wherein the biocompatible substance contained in the biocompatible aqueous dispersion is selected from any one or a combination of two or more of sodium alginate, tannic acid, polyvinyl alcohol, and chitin, the CNF contained in the CNF aqueous dispersion is selected from any one or a combination of two or more of TEMPO-CNF, sulfonated CNF, quaternized CNF, and bacterial CNF, and the MXene contained in the MXene aqueous dispersion is selected from any one or a combination of two or more of Ti3AlC2, Ti2AlC, Nb2AlC, V2AlC, Mo3AlC2, and Ti3SiC2; the crosslinking agent is selected from any one or a combination of two or more of ferric chloride, calcium chloride, calcium carbonate, and copper chloride; The CNF layer mixed solution and the MXene-CNF layer mixed solution are sequentially frozen in a set order to obtain a Janus structure MXene-CNF cryogel; The Janus structure MXene-CNF cryogel is subjected to acid solution reaction crosslinking for 0.5-2 h, the acid solution includes any one or a combination of two or more of carbonic acid, hydrochloric acid, acetic acid, and hypochlorous acid, and then solvent replacement and normal temperature drying are performed to obtain a Janus structure MXene-CNF aerogel.

2. The method of claim 1, wherein: The concentration of CNF in the CNF aqueous dispersion is 0.4-1.4 wt .

3. The method of claim 1, wherein: The concentration of MXene in the MXene aqueous dispersion is 0.05-0.3 wt .

4. The method of claim 1, wherein: The concentration of the biocompatible substance in the biocompatible aqueous dispersion is 0.1-1 wt .

5. The method of claim 1, wherein: The mass ratio of the CNF aqueous dispersion to the biocompatible aqueous dispersion is 20:1-60:

1.

6. The method of claim 1, wherein: The concentration of the crosslinking agent in the CNF layer mixture solution is 0.05-0.2 wt .

7. The method of claim 1, wherein: The freezing mold used in the freezing is a three-dimensional geometric shape.

8. The method of claim 7, wherein: The freezing mold used in the freezing is any one of a cube and a cylinder.

9. The method of claim 1, wherein: The freezing temperature is -30--10℃, and the freezing time is 5-10 h.

10. The method of claim 1, wherein: The replacement agent used in the solvent replacement includes any one or a combination of two or more of acetone, anhydrous ethanol, tetrahydrofuran, and isopropanol.

11. The method of claim 1, wherein: The solvent replacement time is 10-40 min.

12. The method of claim 1, wherein: The drying temperature is 40-100℃, and the drying time is 1-4 h.

13. A Janus structure MXene-CNF aerogel prepared by the preparation method of any one of claims 1-12.

14. Use of the Janus structure MXene-CNF aerogel of claim 13 in all-season thermal management.

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