阅读说明：本技术 一种具有Janus特性的复合气凝胶及其制备方法与应用 (Composite aerogel with Janus characteristics and preparation method and application thereof ) 是由 王树荣 韩昕宏 丁少秋 邢博 周雍皓 朱玲君 于 2021-06-25 设计创作，主要内容包括：本发明公开了一种具有Janus特性的复合气凝胶,包括复合气凝胶本体,所述复合气凝胶本体包括具有疏水性的上层和具有亲水性的下层,上层为硅烷改性的纤维素纳米纤丝/Ti-(3)C-(2)T-(x) MXene气凝胶,下层为纤维素纳米纤丝气凝胶,上层和下层的交界处通过化学交联作用联结为整体,所述复合气凝胶本体内开设有若干通孔,所述通孔一体贯穿所述复合气凝胶本体的上层和下层。复合气凝胶上部疏水下部亲水的Janus特性,使其可以独立地、稳定地漂浮于空气-水界面处,其下半部分充分吸水并浸于水中,上半部分保持干燥暴露于空气中,而且由于复合气凝胶的上下层通过化学作用联结在一起,其间没有缝隙,避免了热量通过缝隙向外界耗散,进而上层的热量可以高效地用于水蒸发。(The invention discloses a composite aerogel with Janus characteristics, which comprises a composite aerogel body, wherein the composite aerogel body comprises an upper layer with hydrophobicity and a lower layer with hydrophilicity, and the upper layer is silane-modified cellulose nanofibrils/Ti 3 C 2 T x MXene aerogel, the lower floor is cellulose nanofibril aerogel, and the juncture of upper strata and lower floor is through chemical crosslinking connection for whole, set up a plurality of through-holes in the compound aerogel body, the integrative upper strata and the lower floor that run through the compound aerogel body of through-hole. Composite aerogelThe hydrophobic hydrophilic Janus characteristic in lower part of its upper portion makes it independently, float in air-water interface department steadily, and its the latter half fully absorbs water and soaks in aquatic, and the upper half keeps dry and exposes in the air, and owing to the upper and lower layer of compound aerogel links together through chemical action, does not have the gap between them, has avoided the heat to dissipate to the external world through the gap, and then the heat of upper strata can be used for water evaporation high-efficiently.)

1. A composite aerogel having Janus properties, comprising a composite aerogel body, wherein: the composite aerogel body comprises an upper layer (1) with hydrophobicity and a lower layer (2) with hydrophilicity, wherein the upper layer (1) is hydrophobically modified cellulose nanofibrils/Ti₃C₂T_xMXene aerogel, lower floor (2) are cellulose nanofibril aerogel, and the juncture of upper strata (1) and lower floor (2) is as an organic whole through the chemical crosslinking connection, a plurality of through-holes (3) have been seted up in the composite aerogel body, through-hole (3) an organic whole run through upper strata (1) and lower floor (2) of composite aerogel body.

2. The composite aerogel having Janus properties of claim 1, wherein: the Ti₃C₂T_xMXene surface contains-OH, ═ O, -F groups, the cellulose nanofibril surface contains-OH groups, and the boundary between the upper layer (1) and the lower layer (2) is crosslinked and linked into a whole through hydrogen bonds and covalent bonds.

3. The composite aerogel having Janus properties of claim 1, wherein: the aperture of through-hole (3) is the micron level, the cross section of through-hole (3) is class spindle shape, through-hole (3) distribute evenly, vertically run through in compound aerogel body, the porosity in the compound aerogel body is more than 90%.

4. The composite aerogel having Janus properties of claim 1, wherein: the composite aerogel body is also provided with a pore structure with the pore diameter at the nanometer level.

5. The composite aerogel having Janus properties of claim 1, wherein: what is needed isThe cellulose nanofibrils/Ti₃C₂T_xThe MXene aerogel takes cellulose nano-fibrils as basic skeletons and Ti₃C₂T_xAerogel structure with MXene as photothermal functional filler, cellulose nanofibrils/Ti₃C₂T_xMXene aerogel is hydrophobically modified by a hydrophobic modifier.

6. The composite aerogel having Janus properties of claim 5, wherein: the cellulose nano-fibril/Ti₃C₂T_xMXene aerogel, cellulose nanofibrils and Ti₃C₂T_xThe mass ratio of MXene is 1:1-4: 1.

7. A method of preparing a composite aerogel having Janus properties as claimed in any one of claims 1 to 6, comprising the steps of:

a. cellulose nanofibrils/Ti₃C₂T_xPreparation of mixed dispersion of MXene: to Ti₃C₂T_xAdding cellulose nano-fibril powder into MXene dispersion liquid, and stirring uniformly to obtain cellulose nano-fibril/Ti₃C₂T_xMixed dispersion of MXene;

b. crosslinking and hydrophobic modification: adding a cross-linking agent into the mixed dispersion liquid, stirring for the first time, adding a hydrophobic modifier into the mixed dispersion liquid, and stirring for the second time to obtain the hydrophobically modified cellulose nanofibril/Ti₃C₂T_xMXene dispersion liquid;

c. double-layer combination: pouring the cellulose nanofibril dispersion into a mould and freezing to obtain lower-layer ice gel, and pouring the cellulose nanofibril/Ti prepared in the step b on the lower-layer ice gel₃C₂T_xMXene dispersion to form gel whole;

d. molding: the mould in the step c has an auxiliary axial freezing function, the whole gel obtained in the step c is axially frozen, and freeze drying is carried out after solidification;

e. heating: and d, heating the aerogel obtained in the step d to obtain the composite aerogel with Janus characteristics.

8. The method of preparing a composite aerogel having Janus properties as claimed in claim 7,

in said step a, Ti₃C₂T_xMXene dispersion is adjusted to be alkaline, Ti in the mixed dispersion₃C₂T_xThe concentration of MXene is 3-7.5g/L, and the concentration of cellulose nanofibrils is 7.5-12 g/L;

in the step b, the first stirring is carried out for 3 to 5 hours, and the second stirring is carried out for 1 to 3 hours;

in the step b, the cross-linking agent is selected from one or more of epichlorohydrin, ethylene glycol diglycidyl ether, 1, 4-butanediol diglycidyl ether and glutaraldehyde;

in the step b, the hydrophobic modifier is a silane coupling agent, and the silane coupling agent is selected from one or more of methyltrimethoxysilane, methyltriethoxysilane, perfluorooctyltriethoxysilane, 3- (methacryloyloxy) propyltrimethoxysilane and 3- (2, 3-glycidoxy) propyltrimethoxysilane;

in the step b, the concentration of the cross-linking agent is 6-9g/L, and the concentration of the hydrophobic modifier is 6-9 g/L;

in the step c, the freezing mode is liquid nitrogen freezing, and the freezing time is 5-15 minutes;

after the step c, further carrying out solvent replacement treatment on the whole formed gel, adding a tert-butyl alcohol aqueous solution into a mold, carrying out solvent replacement on the whole formed gel at the step c at room temperature, and sucking out the tert-butyl alcohol solution on the upper layer after the solvent replacement is finished to obtain a gel block;

the solvent replacement treatment time is 10-18 hours, and the concentration of the tert-butyl alcohol aqueous solution is 20 wt% -40 wt%;

in the step d, the bottom of the mold is made of metal with good thermal conductivity, the periphery of the mold is made of plastic with poor thermal conductivity, and the bottom of the mold is immersed into liquid nitrogen to enable the internal gel to be directionally frozen along the axial direction, wherein the freezing time is 20-40 minutes;

in the step d, the temperature of freeze drying is-70 ℃ to-55 ℃, the vacuum degree is 1-3Pa, and the time is 36-72 hours;

in the step e, the heating temperature is 80-100 ℃ and the time is 0.5-3 hours.

9. The method of making a composite aerogel having Janus properties of claim 7, wherein said step c comprises: firstly, the cellulose nano fibril/Ti prepared in the step b is prepared₃C₂T_xThe MXene dispersion was poured into a mold and frozen to give a lower layer of ice gel, and then the cellulose nanofibril dispersion was poured over the lower layer of ice gel to form the gel monolith.

10. An interfacial evaporator comprising the composite aerogel having Janus properties of any of claims 1 to 9, wherein: composite aerogel has hydrophilic lower floor (2) and absorbs moisture, for upper strata (1) that have hydrophobicity provide water, and upper strata (1) that have light and heat conversion characteristic absorb solar energy and turn into heat energy and be used for evaporating moisture, the interface evaporator is applied to in sea water desalination, sewage treatment or the evaporation purification of water.

[ technical field ] A method for producing a semiconductor device

The invention relates to the technical field of aerogel materials, in particular to the technical field of composite aerogel with Janus characteristics.

[ background of the invention ]

From the perspective of alleviating energy crisis and environmental problems, the rapid evaporation of water driven by solar photothermal conversion is a promising fresh water supply technology. While the evaporation efficiency of the solar energy directly acting on the water body is only 30-45 percent generally. In order to realize higher solar energy utilization rate, scientific research personnel continuously innovate a solar photo-thermal conversion technology, and the current novel interface evaporation system is concerned by the higher evaporation efficiency.

The interface evaporation system has the advantages that the photothermal material is positioned on the surface of the water body, and the heat generated by solar energy conversion can be limited to the air-water interface and directly used for evaporation of surface water, so that the transfer of the heat to the water body is limited, and the evaporation efficiency is obviously improved. Generally, photothermal materials only have single wettability, in the application of interface evaporation, a hydrophobic material needs to be supplemented with a water transmission component, while a hydrophilic material has the upper surface below the water surface with the use time to weaken the light absorption capacity, and the water evaporation is gradually unstable. In order to stably locate the photothermal material at the air-water interface and achieve good thermal management and water transfer, the interface evaporation system is mostly composed of several components, including a photothermal conversion component, a supporting heat insulation component, a water transfer component, and the like.

Zhan et al (ACS appl. Nano mate. 2020,3,5, 4690-4698) designed an interface photothermal evaporation system with double-layer structure, in which the carbon nano tube aerogel is positioned in the lower layer as heat-insulating layer and C/SiO aerogel is positioned in the lower layer₂Au aerogel is positioned on the upper layer and used as a light absorption layerBetween the two layers there is felt for water transfer, the system is under a standard sun illumination (1000W/m)²) The water evaporation rate was 1.32kg m^-2h^-1The evaporation efficiency was 79.6%. Patent CN110183572A discloses an aerogel, its preparation method and its application as solar evaporator, wherein the aerogel is composed of polyacrylamide aerogel as water supply layer and polyacrylamide-carbon nanotube aerogel as light absorption layer, the two-layer structure of the aerogel is composed of two independent aerogels, and in the application as solar evaporator, additional plastic foam is needed for fixing support.

In order to realize self-floating of the photothermal material, development of the photothermal material having Janus characteristics (i.e., opposite wettability) is gradually focused. Yu et al (Research 2020,2020,3241758) obtained Janus polyvinylidene fluoride film by oriented cooling crystallization template method, chemical vapor deposition and one-sided hydrophilic modification method, which has water evaporation rate of 1.08kg m under a standard solar irradiation^-2h^-1. The lack of high water evaporation performance achieved by the Janus film may be attributed to the poor thermal management properties of the film material itself. After the film is further assembled with polyurethane foam and absorbent paper, the water evaporation rate of the film can be increased to 1.58kg m^-2h^-1. Therefore, the development of the photo-thermal material integrating the functions of self-floating, light absorption and conversion, heat management and water transmission for efficient interfacial water evaporation is of great significance.

[ summary of the invention ]

The invention aims to solve the problems in the prior art, and provides a composite aerogel with Janus characteristics, a preparation method and application thereof, wherein the composite aerogel can independently and stably float on the water surface and can be used as an independent solar interface evaporator.

In order to achieve the above purpose, the present invention provides a composite aerogel with Janus characteristics, which comprises a composite aerogel body, wherein the composite aerogel body comprises an upper layer with hydrophobicity and a lower layer with hydrophilicity, and the upper layer is hydrophobically modified cellulose nanofibrils/Ti₃C₂T_xMXene air condensationGlue, the lower floor is cellulose nanofibril aerogel, and the juncture of upper strata and lower floor is as a whole through the chemical crosslinking connection, this internal a plurality of through-holes of having seted up of composite aerogel, the through-hole is integrative to run through the upper strata and the lower floor of composite aerogel body.

Preferably, the Ti is₃C₂T_xMXene surface comprises-OH, ═ O, -F groups, and the cellulose nanofibril surface comprises-OH groups. Janus means that the upper part and the lower part of the composite aerogel have opposite wettabilities.

Ti in the invention₃C₂T_xMXene is a two-dimensional nanomaterial, wherein T is_xRepresents a surface group including-OH, ═ O, -F, and the like. Ti₃C₂T_xMXene has a semimetal-like energy band structure and can induce a local surface plasmon resonance effect, so that the MXene has an outstanding photothermal conversion characteristic, and the photothermal conversion efficiency of the MXene can reach 100% when the MXene is measured by a liquid drop light heating system. Ti in the invention₃C₂T_xMXene is Ti selectively etched by using LiF/HCl mixed solution₃AlC₂Obtaining the Al atomic layer, and combining ultrasonic treatment to obtain the nanosheet structure. Since the etching system is a fluorine-containing aqueous solution system, Ti₃C₂T_xMXene has a group such as-OH, -O, -F, etc. on the surface.

The cellulose nanofibrils according to the invention are filamentous cellulose material isolated from natural biomass, with diameters on the nanometer scale and lengths on the micrometer scale, and having both crystalline and amorphous regions. The aerogel obtained by winding and crosslinking the cellulose nano fibrils not only has unique hydrophilicity and biocompatibility of natural cellulose, but also has higher mechanical stability.

Preferably, the boundary between the upper layer and the lower layer is integrally cross-linked by hydrogen bonds and covalent bonds.

abundant-OH group and Ti on surface of cellulose nanofibrils₃C₂T_xHydrogen bond interaction is formed between-OH, ═ O and-F groups on the surface of MXene, and the existence of the cross-linking agent also makes the fibers of the upper layer and the lower layerVitamin nanofibrils and Ti₃C₂T_xMXene is crosslinked by formation of covalent bonds. Because the upper layer and the lower layer of the composite aerogel are of an integral structure, no gap exists, and the thermal insulation performance is good, dissipation in the heat transfer process is avoided, and efficient heat utilization is realized.

Preferably, the aperture of the through hole is in the order of micrometers.

Preferably, the cross section of the through hole is spindle-like.

Preferably, the through holes are uniformly distributed and vertically penetrate through the composite aerogel body.

The cross section of the through hole is similar to a spindle shape, the size of a long axis of the cross section is between dozens and two hundred micrometers, and the size of a short axis of the cross section is about dozens of micrometers. In the interface evaporation application, the micron-sized through holes with low tortuosity and uniformly distributed in the composite aerogel are beneficial to light capture (multiple reflection, scattering and absorption in the holes), water vapor escape and capillary action water absorption of the lower layer on the upper layer, and salt can be diffused back to a water body through the shortest path in the seawater desalination application process, so that the composite aerogel has excellent salt resistance.

Preferably, the porosity of the composite aerogel body is above 90%.

Porosity refers to the volume of pores (including any form of pores present inside the aerogel) in the aerogel as a percentage of the total volume of the aerogel.

Preferably, the composite aerogel body is further provided with a pore structure with the pore diameter at the nanometer level.

Pores with a diameter of several hundred nanometers, which are formed by cellulose nanofibrils and Ti, are also observed at the cross-links of the lamellar network structure inside the composite aerogel₃C₂T_xMXene is formed by mutual connection.

Preferably, the cellulose nanofibrils/Ti₃C₂T_xThe MXene aerogel takes cellulose nano-fibrils as basic skeletons and Ti₃C₂T_xAerogel structure with MXene as photothermal functional filler, the fiberVitamin nanofibrils/Ti₃C₂T_xMXene aerogel is hydrophobically modified by a hydrophobic modifier.

Using cellulose nanofibrils as a matrix, with Ti₃C₂T_xMXene is crosslinked to form a double network, so that Ti is effectively prevented₃C₂T_xAnd due to the accumulation of MXene nanosheets, rich pore structures are formed, and the improvement of light absorption and the reduction of heat conductivity are facilitated.

Preferably, the cellulose nanofibrils/Ti₃C₂T_xMXene aerogel, cellulose nanofibrils and Ti₃C₂T_xThe mass ratio of MXene is 1:1-4: 1.

Preferably, the cellulose nanofibrils/Ti₃C₂T_xIn MXene aerogel, the cellulose nano-fibrils and Ti₃C₂T_xThe mass ratio of MXene is 4:1, 11:4, 2:1, 3:2 or 1: 1.

The invention also provides a preparation method of the composite aerogel with Janus characteristics, which comprises the following steps:

a. cellulose nanofibrils/Ti₃C₂T_xPreparation of mixed dispersion of MXene: to Ti₃C₂T_xAdding cellulose nano-fibril powder into MXene dispersion liquid, and stirring uniformly to obtain cellulose nano-fibril/Ti₃C₂T_xMixed dispersion of MXene;

b. crosslinking and hydrophobic modification: adding a cross-linking agent into the mixed dispersion liquid, stirring for the first time, adding a hydrophobic modifier into the mixed dispersion liquid, and stirring for the second time to obtain the hydrophobically modified cellulose nanofibril/Ti₃C₂T_xMXene dispersion liquid;

c. and (c) double-layer combination, namely pouring the cellulose nanofibril dispersion liquid into a mould and freezing to obtain lower-layer ice gel, and pouring the cellulose nanofibril/Ti prepared in the step (b) on the lower-layer ice gel₃C₂T_xMXene dispersion to form gel whole;

because the lower layer is in the ice gel state, a distinct interface is formed between the two layers and no miscibility occurs. Since the cellulose nanofibril dispersion and the cellulose nanofibril/Ti₃C₂T_xAqueous MXene dispersions all have a high viscosity so that returning to room temperature the two layers are not miscible. Cellulose nanofibrils and Ti at upper and lower layer interfaces₃C₂T_xThe MXene has hydrogen bond interaction, and the cross-linking agent at the interface can react with the cellulose nano-fibrils and Ti₃C₂T_xMXene is subjected to covalent crosslinking, so that the upper layer and the lower layer are chemically combined and can be seamlessly connected into a whole;

d. molding: the mould in the step c has an auxiliary axial freezing function, the gel whole obtained in the step c is axially frozen, and freeze drying is carried out after solidification;

in the axial freezing process, the solvent in the gel directionally grows into ice crystals from bottom to top, the ice crystals can be used as template agents, the ice crystals are gradually sublimated in the subsequent freeze drying process, and finally through holes are reserved in the aerogel.

e. Heating: and d, heating the aerogel obtained in the step d to obtain the composite aerogel with Janus characteristics.

Preferably, the step c is: firstly, the cellulose nano fibril/Ti prepared in the step b is prepared₃C₂T_xPouring the MXene dispersion liquid into a mould and freezing to obtain lower-layer ice gel, and then pouring the cellulose nanofibril dispersion liquid on the lower-layer ice gel to form a gel whole;

the same ice gel can be prepared by changing the pouring sequence of the upper layer dispersion liquid and the lower layer dispersion liquid;

preferably, in the step a, Ti₃C₂T_xMXene dispersion is adjusted to be alkaline, Ti in the mixed dispersion₃C₂T_xThe concentration of MXene is 3-7.5g/L, and the concentration of cellulose nanofibrils is 7.5-12 g/L.

Preferably, in the step b, the first stirring is performed for 3 to 5 hours, and the second stirring is performed for 1 to 3 hours.

Preferably, in the step b, the crosslinking agent is selected from one or more of epichlorohydrin, ethylene glycol diglycidyl ether, 1, 4-butanediol diglycidyl ether and glutaraldehyde.

Preferably, in the step b, the hydrophobic modifier is a silane coupling agent.

Preferably, in the step b, the silane coupling agent is one or more selected from methyltrimethoxysilane, methyltriethoxysilane, perfluorooctyltriethoxysilane, 3- (methacryloyloxy) propyltrimethoxysilane and 3- (2, 3-glycidoxy) propyltrimethoxysilane.

Preferably, in the step b, the concentration of the cross-linking agent is 6-9g/L, and the concentration of the hydrophobic modifier is 6-9 g/L.

Preferably, in the step c, the freezing mode is liquid nitrogen freezing, and the freezing time is 5-15 minutes.

Ultra-low temperature (-196 ℃) conditions formed by liquid nitrogen can promote ice crystal nucleation and limit ice crystal growth (prevent the formation of large spherical ice crystals), thereby forming rich pores in the gel network.

Preferably, after the step c, the whole gel is further subjected to a solvent substitution treatment, an aqueous solution of t-butanol is added to a mold, the whole gel formed in the step c is subjected to a solvent substitution at room temperature, and after the solvent substitution is completed, the t-butanol solution in the upper layer is sucked out to obtain a gel block.

The tert-butyl alcohol has small surface tension, and can replace the filling solvent in the gel pores, so that the shrinkage deformation of the gel structure in the drying process can be avoided.

Preferably, the solvent replacement treatment time is 10 to 18 hours, and the concentration of the tert-butanol aqueous solution is 20 wt% to 40 wt%.

Research shows that the gel obtained after solvent replacement is carried out by using a tert-butyl alcohol solution with the concentration of about 30 wt% can form a tert-butyl alcohol-water eutectic structure with the smallest size in the gel when the gel is frozen, and the porosity of the finally obtained aerogel is favorably improved.

Preferably, in the step d, the bottom of the mold is made of metal with good thermal conductivity, the periphery of the mold is made of plastic with poor thermal conductivity, and the bottom of the mold is immersed in liquid nitrogen to directionally freeze the internal gel along the axial direction, wherein the freezing time is 20-40 minutes.

Because only the bottom of the mould with good thermal conductivity is immersed in the liquid nitrogen and the thermal conductivity around the mould is poor, the upper part and the lower part of the gel can form a temperature gradient, so that the solvent ice crystals in the gel grow in a single direction along the axial direction and penetrate through the whole body.

Preferably, in the step d, the temperature of freeze drying is-70 ℃ to-55 ℃, the vacuum degree is 1-3Pa, and the time is 36-72 hours.

Preferably, in the step e, the heating temperature is 80-100 ℃ and the heating time is 0.5-3 hours.

The heat treatment can enhance covalent crosslinking within the composite aerogel.

The invention further protects an interface evaporator, the interface evaporator adopts composite aerogel with Janus characteristics, the composite aerogel has a hydrophilic lower layer for absorbing water and providing water for a hydrophobic upper layer, and the upper layer with photo-thermal conversion characteristics absorbs solar energy and converts the solar energy into heat energy for evaporating water.

The upper part and the lower part of the composite aerogel have opposite wettabilities, the structure enables the composite aerogel to stably float on the water surface independently, and the upper part is exposed to the air and kept dry; the lower half part is immersed in water to fully absorb water; the upper layer of the composite aerogel has a light-heat conversion characteristic, can absorb sunlight and convert the sunlight to generate heat, and has heat preservation performance, so that the heat can be limited in the aerogel. The upper layer and the lower layer of the composite aerogel are combined into an integral structure without gaps, so that when the composite aerogel is used as an interface evaporator, other auxiliary components can be omitted, the dissipation of heat in the processes of transmission and conversion can be avoided, efficient heat utilization is realized, and the energy absorbed by the upper layer from the sun can be transmitted to the water in the lower layer of the gel network to the maximum extent for rapid water evaporation.

The invention also protects the application of the interface evaporator, and the interface evaporator is applied to seawater desalination, sewage treatment or water evaporation and purification.

The composite aerogel has excellent salt tolerance, salt is not easy to separate out on the surface, and the composite aerogel has good durability, can be used for a long time and is suitable for seawater desalination and sewage treatment. The evaporation of the water at the interface of the composite aerogel is more efficient than the direct evaporation of water, the evaporation rate of the water is at least 7.5 times faster than that of the water alone under 1 sun illumination, and the water evaporation purification method is suitable for the evaporation and the purification of the water.

The invention has the beneficial effects that:

1. the Janus characteristic of hydrophobic lower part hydrophile in composite aerogel upper portion makes it can independently, stably float in air-water interface department, and its the latter half fully absorbs water and soaks in water, and the upper half keeps dry and exposes in the air, and because composite aerogel's upper and lower layer links together through chemical action, does not have the gap between them, has avoided the heat to dissipate to the external world through the gap, and then the heat of upper strata can be used for water evaporation high-efficiently. The composite aerogel realizes excellent water evaporation performance, and the water evaporation rate can reach 2.3kg m under the irradiation of standard sun^-2h^-1The evaporation efficiency can reach more than 88%.

2. The upper half part of the composite aerogel has a photothermal conversion characteristic, can absorb sunlight and convert the sunlight into heat energy, and has low thermal conductivity (axial thermal conductivity of 0.04-0.06W m)^-1K^-1Radial coefficient of thermal conductivity of 0.02-0.04W m^-1K^-1) The composite aerogel heat insulation material has excellent heat insulation performance, and can reduce the dissipation of heat to the surrounding environment, so that the composite aerogel does not need an additional heat insulation component in the water evaporation process.

3. The lower half of the composite aerogel has hydrophilic characteristics, and can continuously and stably transfer water to the upper-lower layer interface through capillary action in the water evaporation process.

4. The rich pores (the porosity is more than 90%) of the composite aerogel are beneficial to reducing the outward reflection of sunlight, and the high-efficiency absorption of the sunlight (the absorption rate can reach about 95.8%) is realized through multiple reflection and scattering in the pores. And run through in the holistic low tortuosity of compound aerogel through-hole structure of lining up the range be favorable to the escape of vapor, the water of water is upwards transmitted through the capillary action of hydrophilicity gel through-hole, directly follows the through-hole behind the water absorption heat in the through-hole when transmitting to the upper and lower layer interface near and escape the aerogel. In the evaporation application process of seawater desalination, the salt deposited on the lower part can be diffused back to the seawater again by the shortest path, so that the deposition of a large amount of salt particles is avoided.

5. In the sea water desalination is used, the Janus structure of compound aerogel also is favorable to preventing the separation out of salt granule, because the hydrophobicity of upper strata, the sea water can only be restricted to the lower floor, consequently, the salinity can not be transmitted to the upper strata, can not lead to the jam of upper through-hole, vapor can not spill over unimpededly, and the outstanding hydrophilicity of lower floor, can upwards absorb water continuously, the salinity can be dissolved in aquatic, and salt concentration gradient between gel inside and the water can promote the salinity to diffuse back to the water again, consequently, the gel lower part can not form a large amount of salt granule and block the through-hole.

6. The preparation process adopts a mold with an auxiliary axial freezing function, the composite gel forms a temperature gradient in the axial direction during freezing, the solvent in the gel can grow into ice crystals from bottom to top in a one-way mode and penetrates through the whole gel, and through holes are formed in the aerogel after the solvent is sublimated.

7. The composite aerogel is prepared by firstly freezing the lower layer, pouring the upper layer of gel, and finally freeze-drying the whole gel, when the upper layer of gel is poured, because the lower layer is in an ice-gel state, an obvious interface can be formed between the two layers, the phenomenon of mixing and dissolving can not occur, and after the room temperature is recovered, because the viscosity of the upper layer and the lower layer is large, the mixing and dissolving can not occur, so that the upper layer and the lower layer are mutually separated except for the interface.

The features and advantages of the present invention will be described in detail by embodiments in conjunction with the accompanying drawings.

[ description of the drawings ]

FIG. 1 is a schematic structural view of a composite aerogel having Janus properties according to the present invention;

FIG. 2 is a schematic diagram of the chemical crosslinking mechanism of a composite aerogel having Janus properties according to the present invention;

FIG. 3 is a schematic illustration of axial freezing during the preparation of a composite aerogel having Janus properties according to the present invention;

FIG. 4 is a scanning electron microscope image of example 2 of the present invention;

FIG. 5 is an absorption spectrum in the wavelength range of 200-2500nm in example 2 of the present invention;

FIG. 6 is a lower water contact angle test chart of example 2 of the present invention;

FIG. 7 is a test chart of water contact angles of upper layers of examples 1 to 5 of the present invention;

FIG. 8 is a plot of water evaporation versus time for examples 1-5 of the present invention;

FIG. 9 is a plot of water evaporation rate over time for various concentrations of brine in accordance with example 2 of the present invention;

FIG. 10 is a plot of water evaporation rate over time for 3.5 wt% NaCl brine evaporating over ten consecutive days for example 2 of the present invention;

fig. 11 is a schematic view of three cross-sections of a fusiform through-hole.

In the figure: 1-upper layer, 2-lower layer, 3-through hole.

[ detailed description ] embodiments

Example 1:

referring to fig. 1 and 2, a composite aerogel having Janus properties, comprising a composite aerogel body, wherein: the composite aerogel body comprises an upper layer 1 with hydrophobicity and a lower layer 2 with hydrophilicity, wherein the upper layer 1 is hydrophobically modified cellulose nanofibril/Ti₃C₂T_xMXene aerogel, lower floor 2 are cellulose nanofibril aerogel, and the juncture of upper strata 1 and lower floor 2 links as an organic whole through chemical crosslinking, a plurality of through-holes 3 have been seted up in the composite aerogel body, through-hole 3 an organic whole runs through upper strata 1 and lower floor 2 of composite aerogel body, the juncture of upper strata 1 and lower floor 2 links as an organic whole through hydrogen bond and covalent bond crosslinking, the aperture of through-hole 3 is the micron level, the porosity of composite aerogel body is more than 90%, the cross section of through-hole 3 is spindle-like shape, through-hole 3 dividesThe cloth is even, through-hole 3 vertically run through in compound aerogel body, compound aerogel body has still been seted up the pore structure of aperture at nanometer level, cellulose nanofibril/Ti₃C₂T_xThe MXene aerogel takes cellulose nano-fibrils as basic skeletons and Ti₃C₂T_xAerogel structure with MXene as filler, cellulose nanofibrils/Ti₃C₂T_xMXene aerogel is hydrophobically modified by silane coupling agent.

Referring to fig. 3 and 11, the through holes are formed by axial freezing, during the axial freezing process, the solvent in the gel directionally grows into ice crystals from bottom to top, the ice crystals can be used as a template agent, the ice crystals gradually sublimate in the subsequent freeze drying process, and finally the through holes are left in the aerogel, and the cross section of the obtained through holes is in a spindle-like shape. The preparation method of the composite aerogel with Janus characteristics comprises the following steps:

the method comprises the following steps: weighing 1.5g of cellulose nanofibril powder, adding the cellulose nanofibril powder into 100mL of NaOH aqueous solution with the pH value of 10, magnetically stirring the mixture for 30 minutes, adding 0.75g of epoxy chloropropane, and continuously stirring the mixture for 6 hours to obtain cellulose nanofibril dispersion liquid;

step two: to a mixed solution containing 2g LiF and 40mL 9M HCl was added 2g Ti₃AlC₂Stirring at 35 deg.C for 24 hr, centrifuging with deionized water until the supernatant has pH of 6, redispersing the precipitate with deionized water, ultrasonic treating in ice water bath for 1 hr, centrifuging to obtain supernatant (Ti)₃C₂T_xMXene dispersion liquid; more Ti can be obtained by repeated redispersion, ultrasonication and centrifugation of the precipitate₃C₂T_xMXene dispersion liquid;

step three: 4g/L Ti was adjusted by dropwise addition of 1M aqueous NaOH solution₃C₂T_xMXene dispersion pH 10 to 100mL Ti of pH 10₃C₂T_xAdding 1.1g of cellulose nano fibril powder into MXene dispersion liquid, magnetically stirring for 30 minutes, adding 0.75g of epichlorohydrin, and continuously magnetically stirring for 4 hoursThen, 0.75g of methyltrimethoxysilane was added, and magnetic stirring was continued for 2 hours to obtain cellulose nanofibrils/Ti₃C₂T_xMXene dispersion liquid;

step four: pouring 20mL of the dispersion obtained in the first step into a mold with copper as a substrate and polytetrafluoroethylene at the periphery, immersing the bottom of the mold into liquid nitrogen, freezing for 10 minutes and taking out;

step five: pouring 20mL of the dispersion obtained in the third step onto the ice gel obtained in the fourth step;

step six: adding 40mL of 30 wt% tert-butyl alcohol aqueous solution into the mold along the wall surface at room temperature, carrying out solvent replacement for 12 hours, and sucking out the upper tert-butyl alcohol solution by using a dropper after the solvent replacement is finished;

step seven: immersing the bottom of the mold into liquid nitrogen for freezing for 30 minutes, and then carrying out freeze drying for 48 hours at the temperature of minus 65 ℃ and the vacuum degree of 1 Pa;

step eight: the aerogel obtained was heated at 90 ℃ for 1 hour to give a finished product, reference JC11M 4.

Example 2:

example 2 is essentially the same as example 1, except that example 2 is prepared as follows:

the method comprises the following steps: same as the first step of the embodiment 1;

step two: same as the first step of the embodiment 1;

step three: 5g/L Ti was adjusted by dropwise addition of 1M aqueous NaOH solution₃C₂T_xMXene dispersion pH 10 to 100mL Ti of pH 10₃C₂T_xAdding 1g of cellulose nanofibril powder into MXene dispersion liquid, magnetically stirring for 30 minutes, adding 0.75g of epichlorohydrin, continuously magnetically stirring for 4 hours, adding 0.75g of methyltrimethoxysilane, and continuously magnetically stirring for 2 hours to obtain the cellulose nanofibril/Ti₃C₂T_xMXene dispersion liquid;

step four: pouring 20mL of the dispersion obtained in the first step into a mold with copper as a substrate and polytetrafluoroethylene at the periphery, immersing the bottom of the mold into liquid nitrogen, freezing for 10 minutes and taking out;

step five: pouring 20mL of the dispersion obtained in the third step onto the ice gel obtained in the fourth step;

step six: adding 40mL of 30 wt% tert-butyl alcohol aqueous solution into the mold along the wall surface at room temperature, carrying out solvent replacement for 12 hours, and sucking out the upper tert-butyl alcohol solution by using a dropper after the solvent replacement is finished;

step seven: immersing the bottom of the mold into liquid nitrogen for freezing for 30 minutes, and then carrying out freeze drying for 48 hours at the temperature of minus 65 ℃ and the vacuum degree of 1 Pa;

step eight: the aerogel obtained was heated at 90 ℃ for 1 hour to give a finished product, reference JC10M 5.

Example 3:

example 3 is essentially the same as example 1, except that example 3 is prepared as follows:

the method comprises the following steps: same as the first step of the embodiment 1;

step two: same as the first step of the embodiment 1;

step three: 6g/L Ti was adjusted by dropwise addition of 1M aqueous NaOH solution₃C₂T_xMXene dispersion pH 10 to 100mL Ti of pH 10₃C₂T_xAdding 0.9g of cellulose nanofibril powder into the MXene dispersion liquid, magnetically stirring for 30 minutes, adding 0.75g of epichlorohydrin, continuously magnetically stirring for 4 hours, adding 0.75g of methyltrimethoxysilane, and continuously magnetically stirring for 2 hours to obtain the cellulose nanofibril/Ti₃C₂T_xMXene dispersion liquid;

step four: pouring 20mL of the dispersion obtained in the first step into a mold with copper as a substrate and polytetrafluoroethylene at the periphery, immersing the bottom of the mold into liquid nitrogen, freezing for 10 minutes and taking out;

step five: pouring 20mL of the dispersion obtained in the third step onto the ice gel obtained in the fourth step;

step six: adding 40mL of 30 wt% tert-butyl alcohol aqueous solution into the mold along the wall surface at room temperature, carrying out solvent replacement for 12 hours, and sucking out the upper tert-butyl alcohol solution by using a dropper after the solvent replacement is finished;

step seven: immersing the bottom of the mold into liquid nitrogen for freezing for 30 minutes, and then carrying out freeze drying for 48 hours at the temperature of minus 65 ℃ and the vacuum degree of 1 Pa;

step eight: the aerogel obtained was heated at 90 ℃ for 1 hour to give the finished product, reference JC9M 6.

Example 4:

example 4 is essentially the same as example 1, except that example 4 is prepared as follows:

the method comprises the following steps: same as the first step of the embodiment 1;

step two: same as the first step of the embodiment 1;

step three: 4g/L Ti was adjusted by dropwise addition of 1M aqueous NaOH solution₃C₂T_xMXene dispersion pH 10 to 100mL Ti of pH 10₃C₂T_xAdding 0.8g of cellulose nanofibril powder into MXene dispersion, magnetically stirring for 30 minutes, adding 0.6g of glutaraldehyde, continuously magnetically stirring for 4 hours, adding 0.6g of 3- (methacryloyloxy) propyltrimethoxysilane, and continuously magnetically stirring for 2 hours to obtain the cellulose nanofibril/Ti₃C₂T_xMXene dispersion liquid;

step four: pouring 20mL of the dispersion obtained in the first step into a mold with copper as a substrate and polytetrafluoroethylene at the periphery, immersing the bottom of the mold into liquid nitrogen, freezing for 15 minutes and taking out;

step five: pouring 20mL of the dispersion obtained in the third step onto the ice gel obtained in the fourth step;

step six: adding 40mL of 30 wt% tert-butyl alcohol aqueous solution into the mold along the wall surface at room temperature, carrying out solvent replacement for 12 hours, and sucking out the upper tert-butyl alcohol solution by using a dropper after the solvent replacement is finished;

step seven: immersing the bottom of the mold into liquid nitrogen for freezing for 40 minutes, and then carrying out freeze drying for 72 hours at the temperature of minus 70 ℃ and the vacuum degree of 2 Pa;

step eight: the aerogel obtained was heated at 80 ℃ for 3 hours to give the finished product, reference JC8M 4.

Example 5:

example 5 is essentially the same as example 1, except that example 5 is prepared as follows:

the method comprises the following steps: same as the first step of the embodiment 1;

step two: same as the first step of the embodiment 1;

step three: 6g/L Ti was adjusted by dropwise addition of 1M aqueous NaOH solution₃C₂T_xMXene dispersion pH 10 to 100mL Ti of pH 10₃C₂T_xAdding 1.2g of cellulose nanofibril powder into MXene dispersion liquid, magnetically stirring for 30 minutes, adding 0.9g of ethylene glycol diglycidyl ether, continuously magnetically stirring for 3 hours, adding 0.9g of perfluorooctyltriethoxysilane, and continuously magnetically stirring for 1 hour to obtain the cellulose nanofibril/Ti₃C₂T_xMXene dispersion liquid;

step four: pouring 20mL of the dispersion obtained in the first step into a mold with copper as a substrate and polytetrafluoroethylene at the periphery, immersing the bottom of the mold into liquid nitrogen, freezing for 5 minutes and taking out;

step five: pouring 20mL of the dispersion obtained in the third step onto the ice gel obtained in the fourth step;

step six: adding 40mL of 30 wt% tert-butyl alcohol aqueous solution into the mold along the wall surface at room temperature, carrying out solvent replacement for 12 hours, and sucking out the upper tert-butyl alcohol solution by using a dropper after the solvent replacement is finished;

step seven: immersing the bottom of the mold into liquid nitrogen for freezing for 20 minutes, and then carrying out freeze drying for 36 hours at the temperature of minus 55 ℃ and the vacuum degree of 3 Pa;

step eight: the aerogel obtained was heated at 100 ℃ for 0.5 hour to give a finished product, reference JC12M 6.

Example 6:

example 6 is essentially the same as example 1, except that example 6 is prepared as follows:

the method comprises the following steps: same as the first step of the embodiment 1;

step two: same as the first step of the embodiment 1;

step three: 3g/L Ti was adjusted by dropwise addition of 1M aqueous NaOH solution₃C₂T_xMXene dispersion pH 10.5 to 100mLTi of pH 10.5₃C₂T_xAdding 1.2g of cellulose nanofibril powder into MXene dispersion, magnetically stirring for 30 minutes, adding 0.75g of 1, 4-butanediol diglycidyl ether, continuously magnetically stirring for 5 hours, adding 0.75g of methyltriethoxysilane, and continuously magnetically stirring for 1 hour to obtain the cellulose nanofibril/Ti₃C₂T_xMXene dispersion liquid;

step four: pouring 15mL of the dispersion obtained in the third step into a mold with copper as a substrate and polytetrafluoroethylene at the periphery, immersing the bottom of the mold into liquid nitrogen, freezing for 5 minutes and taking out;

step five: pouring 15mL of the dispersion liquid obtained in the step one on the ice gel obtained in the step four;

step six: adding 30mL of 20 wt% tert-butyl alcohol aqueous solution into the mold along the wall surface at room temperature, carrying out solvent replacement for 18 hours, and sucking out the upper tert-butyl alcohol solution by using a dropper after the solvent replacement is finished;

step seven: immersing the bottom of the mold into liquid nitrogen for freezing for 20 minutes, and then carrying out freeze drying for 36 hours at the temperature of minus 60 ℃ and the vacuum degree of 2 Pa;

step eight: the aerogel obtained is heated at 80 ℃ for 0.5 hour to obtain the finished product.

Example 7:

example 7 is essentially the same as example 1 except that example 7 is prepared as follows:

the method comprises the following steps: same as the first step of the embodiment 1;

step two: same as the first step of the embodiment 1;

step three: 7.5g/L Ti was adjusted by dropwise addition of 1M aqueous NaOH solution₃C₂T_xMXene dispersion pH 9.5 to 100mL Ti of pH 9.5₃C₂T_xAdding 0.75g of cellulose nanofibril powder into MXene dispersion, magnetically stirring for 30 minutes, adding 0.75g of glutaraldehyde, continuously magnetically stirring for 3 hours, adding 0.75g of 3- (2, 3-epoxypropoxy) propyltrimethoxysilane, and continuously magnetically stirring for 3 hours to obtain the cellulose nanofibril/Ti₃C₂T_xMXene dispersion liquid;

step four: pouring 15mL of the dispersion obtained in the third step into a mold with copper as a substrate and polytetrafluoroethylene at the periphery, immersing the bottom of the mold into liquid nitrogen, freezing for 15 minutes and taking out;

step five: pouring 15mL of the dispersion liquid obtained in the step one on the ice gel obtained in the step four;

step six: adding 30mL of 40 wt% tert-butyl alcohol aqueous solution into the mold along the wall surface at room temperature, carrying out solvent replacement for 10 hours, and sucking out the upper tert-butyl alcohol solution by using a dropper after the solvent replacement is finished;

step seven: immersing the bottom of the mold into liquid nitrogen for freezing for 30 minutes, and then carrying out freeze drying for 48 hours at the temperature of minus 70 ℃ and the vacuum degree of 2 Pa;

step eight: the aerogel obtained is heated at 100 ℃ for 2 hours to obtain the finished product.

Example 2 was characterized by a scanning electron microscope, and the results are shown in fig. 4, in which a-c are the cross-section of the upper layer part of example 2, c is the nano-scale pore structure, d is the longitudinal section of the upper layer part of example 2, and e is the cross-section of the lower layer part of example 2, and it can be observed that the through-hole in example 2 has low tortuosity and the cross-section of the through-hole is like a spindle.

The open through hole structure is favorable for the escape of water vapor, the water in the water body is upwards transferred through the capillary action of the hydrophilic gel through holes, and the water in the through holes directly escapes the aerogel along the through holes after absorbing heat when being transferred to the vicinity of the upper-layer and lower-layer interfaces.

The absorption spectrum of example 2 was characterized by an ultraviolet-visible-near infrared spectrophotometer, and the characterization result is shown in fig. 5, in which the abscissa represents the test wavelength range in nm. The dotted line is the solar radiation spectrum corresponding to the right ordinate, which is the irradiance at a particular wavelength, in W m^-2nm^-1. The light absorption of example 2 is shown by a solid line and corresponds to the left ordinate, and the left ordinate is the light absorption in%. The light absorption of example 2 was about 95.8% over the range tested.

The water contact angle test was performed on the lower layer portions of examples 1 to 5, wherein the test results of example 2 are shown in fig. 6, and the results showed that the lower layer portions of examples 1 to 5 had strong hydrophilicity.

The water contact angle test was performed on the upper layer portions of examples 1 to 5, and the test results are shown in FIG. 7, in which a represents example 1, b represents example 2, c represents example 3, d represents example 4, and e represents example 5. The results show that the upper portions of examples 1-5 have strong hydrophobicity.

The method comprises the following steps of directly placing examples 1-5 into a glass container filled with deionized water, enabling the composite aerogel to independently float, placing the glass container under the irradiation of a solar simulator after the lower half part of the composite aerogel fully absorbs water, and under the illumination of standard sunlight, when stable water evaporation is achieved, wherein the curve rate of water evaporation amount changing along with time is shown in a figure 8, and the water evaporation rate is shown in a table 1:

TABLE 1

In FIG. 8, the abscissa represents time in units of s and the ordinate represents the evaporation in units of kg m^-2。

Experiments prove that the evaporation of the composite aerogel interface water is obviously more efficient than the direct evaporation of water, and the evaporation rate of the composite aerogel interface water is at least 7.5 times faster than that of pure water under 1 sun illumination.

A simulation test for the interfacial evaporator application was performed for example 2:

the example 2 was placed directly in a glass container containing deionized water, and after the lower half had absorbed sufficient water, the glass container was placed under the irradiation of a solar simulator. At two standard solar intensities (2000W/m)²) Under irradiation, when stable water evaporation is achieved, the water evaporation rate is 3.199kg m^-2h^-1。

The example 2 was placed directly in a glass container containing deionized water, and after the lower half had absorbed sufficient water, the glass container was placed under the irradiation of a solar simulator. In three standard sunlightStrong (3000W/m)²) Under irradiation, when stable water evaporation is achieved, the water evaporation rate is 3.928kg m^-2h^-1。

Example 2 was placed directly in a glass container containing 3.5 wt%, 7 wt% and 10.5 wt% aqueous NaCl solutions and, after the lower half had absorbed sufficient water, the glass container was placed under the irradiation of a solar simulator. After 6 hours of continuous standard solar illumination, the water evaporation rate can reach 2.13, 2.03 and 1.80kg m^-2h^-1The results of the experiment are shown in FIG. 9, where the abscissa is time in h and the ordinate is the evaporation rate in kg m^-2h^-1And no salt particle deposition was observed on the upper surface of the composite aerogel. Compared with the intricate network structure, the aligned micron-sized through holes with low tortuosity enable the salt to diffuse back into the water body in the shortest path, so that example 2 exhibits excellent salt tolerance.

Example 2 was placed directly in a glass container containing 3.5 wt% NaCl aqueous solution and after the lower half had absorbed sufficient water, the glass container was placed under the irradiation of a solar simulator. After one standard solar illumination of 6 hours per day for 10 consecutive days, the water evaporation rate can still reach 1.95kg m^-2h^-1. The results of the experiment are shown in FIG. 10, where X is time in units of h, Y is time in units of days, and Z is the evaporation rate in units of kg m^-2h^-1. The experiment proves that the example 2 has good durability.

Example 2 was placed directly in a simulated seawater (Na)⁺：11505mg/L，Mg²⁺：1375mg/L，Ca²⁺: 299mg/L) and placed under the irradiation of a sunlight simulator. Recovering the resulting desalinated seawater by condensation, wherein Na is present⁺，Mg^{2 +}And Ca²⁺The concentration of (A) is obviously reduced to 1.486, 0.025 and 0.584 mg/L. Example 2 demonstrates excellent desalting performance.

The simulation application experiments prove that the composite aerogel disclosed by the invention can be used as an interface evaporator to be applied to seawater desalination, sewage treatment and water evaporation purification, and has good stability and high efficiency.

The above embodiments are illustrative of the present invention, and are not intended to limit the present invention, and any simple modifications of the present invention are within the scope of the present invention.