CN116251720A - A solar water evaporation sponge based on amphoteric Janus nanofibers and its preparation method - Google Patents

Abstract

A solar water evaporation sponge based on amphoteric Janus nanofibers and a preparation method thereof, belonging to the technical field of water resource regeneration. The matrix of the solar water evaporation sponge is composed of hydrophilic/hydrophobic amphoteric Janus nanofibers, and the surface is covered with a layer of photothermal conversion material. The solar water evaporation sponge is prepared by parallel electrospinning technology and freeze-drying technology, and can float on the water surface. Under sunlight, the water layer on the upper surface of the solar water evaporation sponge is heated by a photothermal conversion material to realize water evaporation. . The solar water evaporation sponge can desalinate simulated seawater, and the concentration of salt ions in the condensed water obtained after treatment is lower than the drinking water standards of the World Health Organization and the United States Environmental Protection Agency. In addition, the solar water evaporation sponge can effectively remove organic pollutants in water, and has good recyclability.

Description

A solar water evaporation sponge based on amphoteric Janus nanofibers and its preparation method

technical field

The invention belongs to the technical field of water resource regeneration, and relates to a solar water evaporation sponge based on amphoteric Janus nanofibers and a preparation method thereof.

Background technique

The shortage of fresh water resources has always been a major problem in the process of human development. Nowadays, many areas in the world are still affected by the shortage of fresh water resources. How to produce fresh water cleanly and efficiently is a major challenge. Solar energy is an inexhaustible and inexhaustible clean energy. Solar energy-driven water evaporation technology is a new water purification technology. This technology uses various photothermal conversion materials to absorb sunlight and convert it into heat energy to accelerate water Evaporation, so as to obtain fresh water from sewage, this technology is expected to become one of the most convenient ways to solve the shortage of fresh water resources. The basic strategy is to use solar energy to convert sewage, wastewater or seawater into water vapor, which is then collected and concentrated into drinkable fresh water. The process by which solar water evaporation separates water from pollutants and impurities is similar to the water cycle in the natural environment. Therefore, this technology is an environmentally friendly and low-cost water purification solution that does not require additional energy input. Due to the low solar light absorption rate and poor energy conversion efficiency of natural water, it is necessary to place materials with high light-to-heat conversion performance on the surface of the water body to achieve interface heating. Typical interfacial photothermal materials include photothermal aerogels, hydrogels, porous polymer networks, sponges, membranes, etc.

Three-dimensional interfacial photothermal materials are currently a research hotspot in solar-driven water evaporation technology. The combination of electrospinning and freeze-drying is a common method for preparing three-dimensional interfacial photothermal materials. However, in existing reports, the three-dimensional materials directly obtained by electrospinning and freeze-drying techniques are either completely hydrophilic or completely hydrophobic, which leads to some problems in their application in solar-driven water evaporation technology: hydrophilic Although water materials can pump water to the evaporating surface, the excess water inside the material acts as a "thermal bridge", resulting in severe heat dissipation from the evaporating surface to the water body. In addition, since hydrophilic materials cannot float on the water surface, usually Additional support materials are required; in contrast, completely hydrophobic materials are hardly suitable for the preparation of interfacial photothermal materials due to their inability to pump water to the evaporation surface.

In view of the above problems, the present invention proposes a three-dimensional sponge composed of hydrophilic/hydrophobic amphoteric Janus nanofibers, and modifies the photothermal conversion material on its outer surface, thereby obtaining a three-dimensional interfacial photothermal material. Among them, the hydrophilic structural unit mainly plays the role of pumping water to the evaporating surface; the hydrophobic structural unit enables the sponge to float on the water surface, and at the same time ensures that the water content in the sponge is moderate, reducing the heat loss from the evaporating surface to the water body, thereby speeding up the water flow. evaporation rate.

Contents of the invention

The purpose of the present invention is to provide a solar water evaporation sponge based on amphoteric Janus nanofibers, which overcomes the shortcomings of traditional hydrophilic three-dimensional interface photothermal materials such as excessive water content, the need for additional supports, easy swelling in water, and poor salt resistance. , to provide new strategies and technical support for the development of three-dimensional interfacial photothermal materials.

To achieve said purpose, the present invention takes the following technical solutions:

A method for preparing a solar water evaporation sponge based on amphoteric Janus nanofibers by using an electrospinning process, wherein the matrix of the material is a sponge-like cube composed of hydrophilic/hydrophobic amphoteric Janus nanofibers. A single Janus nanofiber consists of a hydrophilic organic polymer on one half; a hydrophobic organic polymer on the other half. The photothermal conversion material is sprayed on the surface of the substrate to form a three-dimensional interface photothermal material. The specific preparation steps are as follows:

Mix a hydrophilic organic polymer and an organic solvent, stir continuously for a certain period of time, and then stand for defoaming to obtain an electrospinning solution A; mix a hydrophobic organic polymer and an organic solvent, stir continuously for a certain period of time, and then stand for defoaming to obtain an electrospinning solution Liquid B. Add the above two electrospinning liquids to two identical syringes respectively, connect the two syringes to the same parallel spinneret, and perform electrospinning at a certain propulsion rate and spinning voltage. The electrospun fibers were collected by aluminum foil paper to obtain the hydrophilic/hydrophobic amphoteric Janus nanofiber membrane. The obtained amphoteric Janus nanofiber membrane is crushed by a homogenizer, and the amphoteric Janus nanofiber sponge is obtained by a freeze-drying technique. Finally, a photothermal conversion material is sprayed on its surface to obtain a solar water evaporation sponge based on amphoteric Janus nanofibers;

Preferably, the hydrophilic organic polymer for preparing the electrospinning solution A can be at least one of cellulose acetate, polyacrylonitrile, polylactic acid, and polyethylene glycol;

Preferably, the hydrophobic organic polymer used to prepare the electrospinning solution B can be one of polyvinyl butyral, polyvinylidene fluoride, polyethersulfone, polyurethane, and polystyrene;

Preferably, the light-to-heat conversion material can be at least one of carbon nanotubes, graphene, nano-graphite powder, polypyrrole, and polydopamine;

Preferably, the stirring time of the mixed solution of organic polymer and organic solvent is 6-24 h, and it can be heated to no more than 90 ^o C to increase the dissolution rate of the organic polymer, and the standing defoaming time is 12-24 h;

Preferably, the propulsion rate of the spinning solution is 0.2-0.5 mL/h, the spinning voltage is 10-20 kV, and the receiving distance is 10-20 cm;

Preferably, the temperature of the electrospinning environment is 15-40 ^o C, and the humidity is 20-50%.

Advantage and positive effect of the present invention are:

1. The substrate of the solar water evaporation sponge involved in the present invention is a hydrophilic/hydrophobic Janus nanofiber sponge, in which hydrophilic materials and hydrophobic materials are combined on a nanometer scale, which overcomes the inability of traditional hydrophilic three-dimensional interface photothermal materials to float on the water surface and the inability of hydrophobic 3D materials to pump water to evaporating surfaces.

2. In the hydrophilic/hydrophobic Janus nanofiber sponge of the present invention, the hydrophobic material can limit the volume expansion caused by the swelling effect of the hydrophilic material in water, and improve the cycle life.

3. In the hydrophilic/hydrophobic Janus nanofiber sponge involved in the present invention, the hydrophobic material can play a better role in salt resistance, and effectively inhibit the formation rate of salt crystals on the evaporation surface.

4. The solar evaporation film involved in the present invention has high water evaporation and photothermal desalination performance, and can also remove organic pollutants in water at the same time.

Description of drawings

Fig. 1 is the structural representation of embodiment 1 to embodiment 5 in the present invention;

Fig. 2 is the scanning electron micrograph of hydrophilic/hydrophobic Janus nanofiber and hydrophilic nanofiber in comparative example 1 in embodiment 1 to embodiment 5 of the present invention;

Fig. 3 is embodiment 1 to embodiment 5 and comparative example 1 in the present invention under 1 times of simulated sunlight and process the evaporation curve of pure water;

Fig. 4 is the desalination performance of Example 1 of the present invention when dealing with simulated seawater under 1 times simulated sunlight irradiation;

Fig. 5 is under 1 times of simulated sunlight irradiation, embodiment 1 of the present invention is the removal performance of the different organic dyes that concentration is 0.01 g/L;

Fig. 6 is the stability of the 10-cycle experiment of Example 1 of the present invention.

Implementation

The present invention will be further described in detail below in conjunction with the accompanying drawings and through specific embodiments. The following embodiments are only descriptive, not restrictive, and cannot limit the protection scope of the present invention.

A method for preparing a solar water evaporation sponge based on amphoteric Janus nanofibers by using an electrospinning process, the specific preparation steps are as follows:

(1) Mix the hydrophilic organic polymer and the organic solvent, stir continuously for a certain period of time, and then stand for degassing to obtain the electrospinning liquid A;

(2) Mix the hydrophobic organic polymer and the organic solvent, stir continuously for a certain period of time, and then stand for defoaming to obtain the electrospinning solution B;

(3) Place the two electrospinning liquids A and B in parallel electrospinning equipment for electrospinning, and collect the electrospun fibers with aluminum foil;

(4) Break the collected electrospun fibers through a homogenizer, and obtain the amphoteric Janus nanofiber sponge through freeze-drying technology;

(5) Spray photothermal conversion materials on the surface of the amphoteric Janus nanofiber sponge to obtain a solar water evaporation sponge based on the amphoteric Janus nanofiber.

Moreover, the hydrophilic organic polymer in the spinning solution A is preferably a mixture of cellulose acetate and polyethylene glycol, and the solvent is a mixed solution of acetone and N,N-dimethylformamide;

Moreover, the parameters of the cellulose acetate are acetyl: 39.8 wt%, hydroxyl: 3.5 wt%, and the molecular weight Mw of polyethylene glycol is 2000;

And, the mass ratio of described cellulose acetate and polyethylene glycol is preferably 2:1;

Moreover, the mass ratio of acetone and N,N-dimethylformamide in the spinning solution A is preferably 1:1.5;

And, the mass ratio of hydrophilic organic polymer and solvent in described spinning solution A is preferably 0.4:1;

Moreover, the hydrophobic organic polymer in the spinning solution B is preferably polyvinyl butyral, and the solvent is dimethyl sulfoxide;

Moreover, the molecular weight Mw of the polyvinyl butyral is 40000-70000;

And, the mass ratio of hydrophobic organic polymer and solvent in described spinning solution B is preferably 0.18:1;

Moreover, the ambient temperature of the electrospinning is 25 ^o C, and the humidity is 30 ± 5%;

Moreover, the propulsion rate of the spinning solution is preferably 0.3 mL/h, the spinning voltage is preferably 14 kV, and the receiving distance is preferably 15 cm;

Moreover, the shape of the amphoteric Janus nanofiber sponge is preferably a cube with a side length of 3 cm;

Moreover, the composition of the light-to-heat conversion material is preferably a mixture of multi-walled carbon nanotubes, silica nanoparticles and polydopamine;

Example

(1) Add 0.8 g of polyethylene glycol, 1.6 g of cellulose acetate, 2.4 g of acetone, and 3.6 g of N,N-dimethylformamide into an Erlenmeyer flask, and magnetically stir for 36 h to obtain spinning solution A; Add 1.4 g of polyvinyl butyral and 7.7 g of dimethyl sulfoxide into another Erlenmeyer flask with magnetic stirring for 36 h to obtain spinning solution B.

(2) The method of making parallel spinnerets is as follows: use two 5 mL syringes with truncated 12# stainless steel needles respectively, bend the two stainless steel needles at an angle of 30°, so that the two needle tips can be closely parallel, and use A 1 mL plastic spray gun head is set on two parallel stainless steel needles so that the tips of the two stainless steel needles are in the middle part of the plastic spray gun head. During parallel electrospinning, the spinning solution A and B were added to two 5 mL syringes respectively, and aluminum foil was used as the spinning device. After electrospinning, the product was peeled off from the aluminum foil to obtain a nanofibrous membrane. The process parameters of parallel electrospinning were as follows: the voltage was 14 kV, the distance between the spinning needle and the receiving net was 15 cm, and the flow rate of both spinning solutions was 0.3 mL/h.

(3) Crush the obtained nanofibrous membrane with a homogenizer, disperse it into a mixture of water and N,N-dimethylformamide, and stir vigorously for 20 min. Immediately after the stirring is stopped, the above dispersion is soaked in liquid nitrogen After being frozen into a solid and freeze-dried for 7 days, the product was thermally crosslinked in an oven at 100 ^o C for 90 min to obtain amphoteric Janus nanofibrous sponges, which were cut into cubes with a side length of 3 cm. In the above process, the mass ratio of water and N,N-dimethylformamide in the mixed liquid is 10:1, and the mass ratio of the crushed nanofibers to the mixed liquid is 0.05:1.

(4) Mix and stir the multi-walled carbon nanotubes, tetraethyl orthosilicate and absolute ethanol for 10 min, add deionized water to it and continue stirring for 20 min. The mass ratio of multi-walled carbon nanotubes, tetraethyl orthosilicate, absolute ethanol and water is 0.1:0.3:1:3. A few drops of hydrofluoric acid were slowly added to the above solution to hydrolyze the tetraethyl orthosilicate into silica nanoparticles. The above product was centrifuged, the liquid phase was discarded, and the solid phase was dried in an oven at 80 ^o C for 24 h to obtain a composite of multi-walled carbon nanotubes and silica nanoparticles, which was then ground. The composite of the above-mentioned multi-walled carbon nanotubes and silica nanoparticles and dopamine hydrochloride were added to the Tris buffer solution, and stirred at room temperature for 8 h to polymerize the dopamine hydrochloride into polydopamine. The composites of multi-walled carbon nanotubes and silica nanoparticles and the concentration of dopamine hydrochloride in Tris buffer solution were 5.0 g/L and 2.4 g/L respectively, the concentration of Tris buffer solution was 1.7 g/L, and the pH was 8.5 . The above product was centrifuged, dried and ground, then added to deionized water, and ultrasonically dispersed for 30 min to obtain a spray coating solution containing photothermal conversion materials, wherein the mass ratio of photothermal conversion materials to deionized water was 1:100.

(5) Spray the spray liquid containing the light-to-heat conversion material on the six surfaces of the amphoteric Janus nanofiber sponge with an air spray gun, and obtain the solar water evaporation sponge after natural drying. The dry solid matter loading per surface was 0.016 g/cm ² .

The specific test method of the solar water evaporation sponge based on amphoteric Janus nanofibers in the water evaporation process is as follows:

Using a solar simulator to generate columnar uniform (irradiation non-uniformity < 2%) simulated sunlight, the spot can completely cover the solar water evaporation sponge. Before lighting, 20 g of water was added to the beaker, and the solar water evaporation sponge was forced to soak in water for 10 min and then placed on the water surface. The beaker is placed on an electronic balance to record the mass loss of water during evaporation. When the simulated sunlight hits the upper surface of the solar water evaporation sponge, the light is absorbed and converted into heat energy. Solar water evaporation The water on the surface of the sponge evaporates rapidly after being heated.

Example

The preparation method and test method of the solar water evaporation sponge are the same as in Example 1, the difference is that the solid matter loading of each surface after drying in step (5) is 0.008 g/cm ² ;

Example

The preparation method and test method of the solar water evaporation sponge are the same as in Example 1, the difference is that the solid matter loading of each surface after drying in step (5) is 0.012 g/cm ² ;

Example

The preparation method and test method of the solar water evaporation sponge are the same as in Example 1, the difference is that the solid matter loading of each surface after drying in step (5) is 0.020 g/cm ² ;

Example

The preparation method and test method of the solar water evaporation sponge are the same as in Example 1, except that the solid matter loading of each surface after drying in step (5) is 0.024 g/cm ² ;

The preparation method and test method of the hydrophilic solar water evaporation sponge are the same as in Example 1, except that the hydrophilic solar water evaporation sponge is composed of hydrophilic nanofibers prepared by electrospinning the spinning solution A through a single needle.

Although the embodiments and accompanying drawings of the present invention are disclosed for the purpose of illustration, those skilled in the art can understand that various replacements, changes and modifications are possible without departing from the spirit and scope of the present invention and the appended claims Therefore, the scope of the present invention is not limited to what is disclosed in the embodiments and drawings.

Claims (7)

1. A solar water evaporation sponge based on amphoteric Janus nanofiber and a preparation method thereof are characterized in that: the matrix of the solar water evaporation sponge consists of hydrophilic/hydrophobic amphoteric Janus nano fibers, and the surface of the solar water evaporation sponge is covered with a layer of photo-thermal conversion material; under the irradiation of sunlight, the energy of the sunlight can be converted into heat, so that the evaporation of water is realized, and meanwhile, the removal of salt ions and organic pollutants in the water is realized; the specific preparation steps of the solar water evaporation sponge are as follows:

mixing a hydrophilic organic polymer and an organic solvent, continuously stirring for a certain time, and standing for defoaming to obtain an electrostatic spinning solution A; mixing a hydrophobic organic polymer and an organic solvent, continuously stirring for a certain time, and standing for deaeration to obtain an electrostatic spinning solution B; respectively adding the two electrostatic spinning solutions into two identical injectors, connecting the two injectors to the same parallel spinning nozzle, carrying out electrostatic spinning at a certain propulsion rate and spinning voltage, and collecting electrostatic spinning fibers at a fixed receiving distance by adopting aluminum foil paper to obtain hydrophilic/hydrophobic Janus nano fibers; crushing the obtained nanofiber membrane by a homogenizer, and obtaining the amphoteric Janus nanofiber sponge by a freeze drying technology; finally, spraying a photo-thermal conversion material on the surface of the porous material to obtain the solar water evaporation sponge based on the amphoteric Janus nanofiber.

2. The method of manufacturing according to claim 1, characterized in that: the hydrophilic organic polymer for preparing the electrostatic spinning solution A can be at least one of cellulose acetate, polyacrylonitrile, polylactic acid and polyethylene glycol.

3. The method of manufacturing according to claim 1, characterized in that: the hydrophobic organic polymer for preparing the electrostatic spinning solution B can be one of polyvinyl butyral, polyvinylidene fluoride, polyether sulfone, polyurethane and polystyrene.

4. The method of manufacturing according to claim 1, characterized in that: the photothermal conversion material can be at least one of carbon nano tube, graphene, nano graphite powder, polypyrrole and polydopamine.

5. The method of manufacturing according to claim 1, characterized in that: the mixing time of the mixed solution of the organic polymer and the organic solvent is 6-24 h, and the mixed solution can be heated to not more than 90 ^o C, standing and defoaming for 12-24 h to improve the dissolution rate of the organic polymer.

6. The method of manufacturing according to claim 1, characterized in that: the advancing speed of the spinning solution is 0.2-0.5 mL/h, the spinning voltage is 10-20 kV, and the receiving distance is 10-20 cm.

7. The method of manufacturing according to claim 1, characterized in that: the electrostatic spinning environment temperature is 15-40 ^o And C, the humidity is 20-50%.

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