CN113603935B - Composite aerogel with Janus characteristics and preparation method and application thereof - Google Patents
Composite aerogel with Janus characteristics and preparation method and application thereof Download PDFInfo
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Abstract
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. 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.
Description
[ 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 photothermal material in the interface evaporation system 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 interfacial evaporation system is generally 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 2 The Au aerogel is arranged on the upper layer as a light absorption layer, wool felt is arranged between the two layers for water transfer, and the system is under standard solar illumination (1000W/m) 2 ) The water evaporation rate was 1.32kg m -2 h -1 The evaporation efficiency was 79.6%. Patent CN110183572A discloses an aerogel, a preparation method and its application as a solar evaporator, said aerogel is made of polyacrylamide aerogel as water supply layer and polyacrylamide-carbon nanotube aerogel as light absorption layer, the two-layer structure of the aerogel is made 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, 3241758) obtained Janus polyvinylidene fluoride film by oriented cooling crystallization template method, chemical vapor deposition and one-sided hydrophilization modification method, which has water evaporation rate of 1.08kg m under a standard solar irradiation -2 h -1 . The higher water evaporation performance of the Janus film can not be attributed to the heat pipe with the poorer film materialPhysical properties. 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 -2 h -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 purpose, the 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 made of hydrophobically modified cellulose nanofibrils/Ti 3 C 2 T x The MXene aerogel comprises a lower layer which is cellulose nanofibril aerogel, the junction of the upper layer and the lower layer is connected into a whole through a chemical crosslinking effect, a plurality of through holes are formed in the composite aerogel body, and the through holes integrally penetrate through the upper layer and the lower layer of the composite aerogel body.
Preferably, the Ti is 3 C 2 T x MXene 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 invention 3 C 2 T x MXene is a two-dimensional nanomaterial, wherein T is x Represents a surface group, including-OH, = O, -F, etc. Ti 3 C 2 T x MXene 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 invention 3 C 2 T x MXene is Ti selectively etched by using LiF/HCl mixed solution 3 AlC 2 Obtaining the Al atomic layer, and combining ultrasonic treatment to obtain the nanosheet structure. Since the etching system is a fluorine-containing aqueous solution system, ti 3 C 2 T x MXene surface contains-OH, = O, -F and other groups.
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 nanofibrils 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 nanofibrils 3 C 2 T x Hydrogen bond interaction is formed among-OH, = O and-F groups on the MXene surface, and the existence of the cross-linking agent enables the cellulose nano-fibrils of the upper layer and the lower layer and Ti 3 C 2 T x MXene 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 aerogel 3 C 2 T x MXene is formed by mutual connection.
Preferably, the cellulose nanofibrils/Ti 3 C 2 T x The MXene aerogel takes cellulose nano-fibrils as basic skeletons and Ti 3 C 2 T x Aerogel structure with MXene as photothermal functional filler, cellulose nanofibrils/Ti 3 C 2 T x MXene aerogel is hydrophobically modified by a hydrophobic modifier.
Using cellulose nanofibrils as a matrix with Ti 3 C 2 T x MXene is crosslinked to form a double network, so that Ti is effectively prevented 3 C 2 T x And 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/Ti 3 C 2 T x In MXene aerogel, cellulose nano-fibril and Ti 3 C 2 T x MXene mass ratio is 1-4.
Preferably, the cellulose nanofibrils/Ti 3 C 2 T x In MXene aerogel, the cellulose nano-fibrils and Ti 3 C 2 T x MXene mass ratio is 4.
The invention also provides a preparation method of the composite aerogel with Janus characteristics, which comprises the following steps:
a. cellulose nanofibrils/Ti 3 C 2 T x Preparation of mixed dispersion of MXene: to Ti 3 C 2 T x Adding cellulose nano-fibril powder into MXene dispersion liquid, and stirring uniformly to obtain cellulose nano-fibril/Ti 3 C 2 T x Mixed 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/Ti 3 C 2 T x MXene dispersion;
c. and (c) double-layer combination, namely pouring the cellulose nano fibril dispersion liquid into a mould and freezing to obtain ice gel at the lower layer, and then pouring the cellulose nano fibril/Ti prepared in the step (b) on the ice gel at the lower layer 3 C 2 T x MXene 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/Ti 3 C 2 T x Aqueous 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 interfaces 3 C 2 T x The MXene has hydrogen bond interaction, and the cross-linking agent at the interface can react with the cellulose nano-fibrils and Ti 3 C 2 T x MXene 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 prepared 3 C 2 T x Pouring the MXene dispersion liquid into a mould, freezing to obtain lower-layer ice gel, and pouring the cellulose nano fibril 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, ti 3 C 2 T x MXene dispersion is adjusted to be alkaline, ti in the mixed dispersion 3 C 2 T x The concentration of MXene is 3-7.5g/L, and the concentration of cellulose nanofibrils is 7.5-12g/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 selected from one or more of 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 6-9g/L.
Preferably, in the step c, the freezing mode is liquid nitrogen freezing, and the freezing time is 5-15 minutes.
The ultra-low temperature (-196 ℃) conditions created by liquid nitrogen can promote ice crystal nucleation and limit ice crystal growth (prevent the formation of large spherical ice crystals), which in turn form 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-butyl alcohol aqueous solution is 20wt percent to 40wt percent.
Research shows that the gel obtained by using a tert-butyl alcohol solution with the concentration of about 30wt% for solvent replacement can form a tert-butyl alcohol-water eutectic structure with the smallest size in the gel when the gel is frozen, and the method is favorable for improving the porosity of the finally obtained aerogel.
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 heat conductivity is immersed into the liquid nitrogen and the heat conductivity around the mould is poorer, the upper part and the lower part of the gel can form a temperature gradient, so that the solvent ice crystals in the gel can grow along the axial direction in a unidirectional way and penetrate through the whole.
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 into 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 performanceUnder the irradiation of standard sun, the water evaporation rate can reach 2.3kg m -2 h -1 The 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) -1 K -1 Radial coefficient of thermal conductivity 0.02-0.04W m -1 K -1 ) The composite aerogel insulation board has excellent insulation performance, and can reduce the dissipation of heat to the surrounding environment, so that the composite aerogel does not need additional insulation components 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 with reference to the accompanying drawings.
[ description of the drawings ]
FIG. 1 is a schematic representation of the structure of a composite aerogel having Janus properties according to the present invention;
FIG. 2 is a schematic illustration of the chemical cross-linking 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 a graph showing an absorption spectrum in a wavelength region of 200 to 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 graph of the water evaporation rate by time of 3.5wt% NaCl brine evaporated for ten consecutive days in example 2 of the present invention;
fig. 11 is three schematic cross-sectional views of a spindle-like 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/Ti 3 C 2 T x MXene aerogel, lower floor 2 are cellulose nanofibril aerogel, and the juncture of upper strata 1 and lower floor 2 is linked 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 is linked as an organic whole through hydrogen bond and covalent bond crosslinking, the aperture of through-hole 3 is 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 distributes evenly, through-hole 3 vertically run through in the composite aerogel body, the pore structure of aperture at nanometer level is still seted up to the composite aerogel body, cellulose nanofibril/Ti 3 C 2 T x The MXene aerogel takes cellulose nano-fibrils as basic skeletons and Ti 3 C 2 T x Aerogel structure with MXene as filler, cellulose nanofibrils/Ti 3 C 2 T x MXene 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, 2g Ti was added 3 AlC 2 Stirring 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) 3 C 2 T x MXene dispersion liquid; more Ti can be obtained by repeated redispersion, ultrasonication and centrifugation of the precipitate 3 C 2 T x MXene dispersion;
step three: 4g/L Ti was adjusted by dropwise addition of 1M aqueous NaOH solution 3 C 2 T x MXene dispersion pH 10 to 100mL of Ti having pH 10 3 C 2 T x Adding 1.1g of cellulose nano-fibril powder into MXene dispersion, 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 cellulose nano-fibril/Ti 3 C 2 T x MXene dispersion;
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 30wt% 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 1Pa;
step eight: the aerogel obtained was heated at 90 ℃ for 1 hour to give a finished product, reference JC11M4.
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 solution 3 C 2 T x MXene dispersion pH 10 to 100mL Ti of pH 10 3 C 2 T x Adding 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/Ti 3 C 2 T x MXene 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 30wt% 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 1Pa;
step eight: the aerogel obtained was heated at 90 ℃ for 1 hour to give a finished product, designated JC10M5.
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 solution 3 C 2 T x MXThe ene dispersion had a pH of 10 and 100mL of Ti having a pH of 10 3 C 2 T x Adding 0.9g 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/Ti 3 C 2 T x MXene dispersion;
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 30wt% 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 1Pa;
step eight: the aerogel obtained was heated at 90 ℃ for 1 hour to give a finished product, designated JC9M6.
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 solution 3 C 2 T x MXene dispersion pH 10 to 100mL of Ti having pH 10 3 C 2 T x Adding 0.8g of cellulose nano-fibril 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 cellulose nano-fibril/Ti 3 C 2 T x MXene 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 30wt% 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 2Pa;
step eight: the aerogel obtained was heated at 80 ℃ for 3 hours to give a finished product, reference JC8M4.
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 solution 3 C 2 T x MXene dispersion pH 10 to 100mL Ti of pH 10 3 C 2 T x Adding 1.2g of cellulose nano fibril 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 nano fibril/Ti 3 C 2 T x MXene 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 30wt% 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 3Pa;
step eight: the aerogel obtained was heated at 100 ℃ for 0.5 hour to give a finished product, mark JC12M6.
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 solution 3 C 2 T x MXene dispersion pH 10.5 to 100mL Ti of pH 10.5 3 C 2 T x Adding 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/Ti 3 C 2 T x MXene dispersion;
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 obtained in the first step onto the ice gel obtained in the fourth step;
step six: adding 30mL of 20wt% 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 2Pa;
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 solution 3 C 2 T x MXene dispersion pH 9.5 to 100mL Ti of pH 9.5 3 C 2 T x Adding 0.75g of cellulose nano-fibril 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 nano-fibril/Ti 3 C 2 T x MXene 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 obtained in the first step onto the ice gel obtained in the fourth step;
step six: adding 30mL of 40wt% 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 2Pa;
step eight: the obtained aerogel is heated for 2 hours at 100 ℃ to obtain a 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.
This kind of open through-hole structure is favorable to the effusion of vapor, and 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 and escapes the aerogel when transmitting to the lower floor interface near.
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 -2 nm -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, indicating that the lower layer portions of examples 1 to 5 have strong hydrophilicity.
The upper layer portions of examples 1-5 were subjected to the water contact angle test, and the 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 a water body, 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 -2 h -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. At three standard solar intensities (3000W/m) 2 ) Under irradiation, when stable water evaporation is achieved, the water evaporation rate is 3.928kg m -2 h -1 。
Example 2 was directly placed in a glass container containing 3.5wt%,7wt% and 10.5wt% aqueous NaCl solution, and after the lower half thereof had sufficiently absorbed water, the glass container was placed under 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 -2 h -1 The 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 -2 h -1 And 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 directly placed in a glass vessel containing a 3.5% by weight aqueous NaCl solution, and after the lower half thereof had sufficiently absorbed water, the glass vessel was placed under irradiation with 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 -2 h -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 -2 h -1 . Experiments prove that example 2 has good durability.
Example 2 was placed directly in a simulated seawater (Na) + ：11505mg/L，Mg 2+ ：1375mg/L，Ca 2+ :299 mg/L) and placed under the irradiation of a sunlight simulator. Recovering the resulting desalinated seawater by condensation, wherein Na is present + ，Mg 2 + And Ca 2+ The concentration of (A) is obviously reduced to 1.486,0.025,0.584mg/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.
Claims (27)
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/Ti 3 C 2 T x MXene 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 Ti 3 C 2 T x MXene surface comprises-OH, = O, -F groups and the cellulose nanofibril surface comprises-OH groups.
3. A composite aerogel having Janus properties as claimed in claim 1, wherein: the junction of the upper layer (1) and the lower layer (2) is linked into a whole through hydrogen bonds and covalent bonds.
4. A composite aerogel having Janus properties as claimed in claim 1, wherein: the aperture of the through hole (3) is in a micron scale.
5. A composite aerogel having Janus properties as claimed in claim 1, wherein: the cross section of the through hole (3) is in a spindle-like shape.
6. The composite aerogel having Janus properties of claim 1, wherein: the through holes (3) are uniformly distributed and vertically penetrate through the composite aerogel body.
7. The composite aerogel having Janus properties of claim 1, wherein: the porosity in the composite aerogel body is above 90%.
8. 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.
9. The composite aerogel having Janus properties of claim 1, wherein: the cellulose nanofibrils/Ti 3 C 2 T x The MXene aerogel takes cellulose nano-fibrils as basic skeletons and Ti 3 C 2 T x Aerogel structure of MXene as photo-thermal functional filler, cellulose nano-filament/Ti 3 C 2 T x MXene aerogel is carried out by a hydrophobic modifierAnd (4) performing hydrophobic modification.
10. A composite aerogel having Janus properties as claimed in claim 9, wherein: the cellulose nano-fibril/Ti 3 C 2 T x In MXene aerogel, cellulose nano-fibril and Ti 3 C 2 T x MXene mass ratio is 1-4.
11. The composite aerogel having Janus properties of claim 10, wherein: the cellulose nano-fibril/Ti 3 C 2 T x In MXene aerogel, cellulose nano-fibril and Ti 3 C 2 T x The mass ratio of MXene is 4.
12. A method of preparing a composite aerogel having Janus properties as claimed in any one of claims 1 to 11, comprising the steps of:
a. cellulose nanofibrils/Ti 3 C 2 T x Preparation of mixed dispersion of MXene: to Ti 3 C 2 T x Adding cellulose nano-fibril powder into MXene dispersion liquid, and stirring uniformly to obtain cellulose nano-fibril/Ti 3 C 2 T x Mixed 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 hydrophobic modified cellulose nano-fibril/Ti 3 C 2 T x MXene 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 gel 3 C 2 T x MXene 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.
13. A method of making a composite aerogel having Janus properties as in claim 12, wherein: in said step a, ti 3 C 2 T x MXene dispersion is adjusted to be alkaline, ti in the mixed dispersion 3 C 2 T x The concentration of MXene is 3-7.5g/L, and the concentration of cellulose nanofibrils is 7.5-12g/L.
14. A method of making a composite aerogel having Janus properties as in claim 12, wherein: in the step b, the first stirring is carried out for 3-5 hours, and the second stirring is carried out for 1-3 hours.
15. A method of making a composite aerogel having Janus properties as in claim 12, wherein: 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.
16. A method of making a composite aerogel having Janus properties as in claim 12, wherein: in the step b, the hydrophobic modifier is a silane coupling agent.
17. A method of making a composite aerogel having Janus properties as in claim 16, wherein: in the step b, the silane coupling agent is selected from one or more of methyltrimethoxysilane, methyltriethoxysilane, perfluorooctyltriethoxysilane, 3- (methacryloyloxy) propyltrimethoxysilane and 3- (2, 3-glycidoxy) propyltrimethoxysilane.
18. A method of making a composite aerogel having Janus properties as in claim 12, wherein: in the step b, the concentration of the cross-linking agent is 6-9g/L, and the concentration of the hydrophobic modifier is 6-9g/L.
19. A method of making a composite aerogel having Janus properties as in claim 12, wherein: in the step c, the freezing mode is liquid nitrogen freezing, and the freezing time is 5-15 minutes.
20. The method of making a composite aerogel having Janus properties as claimed in claim 12, wherein said step c comprises: firstly, the cellulose nano fibril/Ti prepared in the step b is prepared 3 C 2 T x The MXene dispersion was poured into a mold and frozen to give an ice gel, and then the cellulose nanofibril dispersion was poured onto the ice gel to form the gel monolith.
21. A method of making a composite aerogel having Janus properties as in claim 12, wherein: and c, 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.
22. A method of making a composite aerogel having Janus properties as claimed in claim 21, wherein: the solvent replacement treatment time is 10-18 hours, and the concentration of the tertiary butanol aqueous solution is 20wt% -40wt%.
23. A method of making a composite aerogel having Janus properties as claimed in claim 12, wherein: in the step d, the bottom of the mold is made of metal with good heat conductivity, the periphery of the mold is made of plastic with poor heat conductivity, the bottom of the mold is immersed into liquid nitrogen, so that the inner gel is directionally frozen along the axial direction, and the freezing time is 20-40 minutes.
24. A method of making a composite aerogel having Janus properties as in claim 12, wherein: 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.
25. A method of making a composite aerogel having Janus properties as in claim 12, wherein: in the step e, the heating temperature is 80-100 ℃ and the time is 0.5-3 hours.
26. An interfacial evaporator, comprising: a composite aerogel with Janus properties comprising the lower layer (2) with hydrophilicity absorbing moisture, providing the upper layer (1) with hydrophobicity with water, the upper layer (1) with photothermal conversion properties absorbing solar energy into thermal energy for evaporating moisture according to any of claims 1 to 11.
27. The interfacial evaporator of claim 26, wherein: the interface evaporator is applied to seawater desalination, sewage treatment or water evaporation and purification.
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