CN111116976B

CN111116976B - Nanofiber aerogel-based solar water evaporator and preparation method thereof

Info

Publication number: CN111116976B
Application number: CN201911394128.XA
Authority: CN
Inventors: 樊玮; 杨帆; 刘天西; 赵兴宇; 田婧
Original assignee: Donghua University
Current assignee: Donghua University
Priority date: 2019-12-30
Filing date: 2019-12-30
Publication date: 2022-03-04
Anticipated expiration: 2039-12-30
Also published as: CN111116976A

Abstract

The invention relates to a nanofiber aerogel-based solar water evaporator and a preparation method thereof. The method comprises the following steps: mixing and dispersing the polyamide acid nano-fiber and water-soluble polyamide acid, freezing the obtained dispersion liquid, freeze-drying, performing thermal imidization, soaking the obtained polyimide nano-fiber aerogel in an initiator solution, and dropwise adding a pyrrole monomer solution on the surface of the aerogel for polymerization reaction. The method has simple preparation process and low cost; the prepared solar water evaporator has the advantages of light density, low thermal conductivity, high photothermal conversion efficiency and the like, and is a good solar water evaporator.

Description

Nanofiber aerogel-based solar water evaporator and preparation method thereof

Technical Field

The invention belongs to the field of photo-thermal conversion materials and preparation thereof, and particularly relates to a nanofiber aerogel-based solar water evaporator and a preparation method thereof.

Background

With the increasingly serious problems of uneven water source distribution, water environment pollution and the like, water resource shortage becomes a global problem to be solved urgently. To solve this problem, great efforts are made to find a practical and effective solution. Solar water evaporation is considered as an environment-friendly and renewable water purification technology, can effectively relieve the severe situation of water resource shortage at present, and is the most common solar energy collection and conversion technology in the world.

To date, two materials have been commonly used to implement solar water evaporation devices. One is the photo-thermal conversion of noble metal nanoparticles, such as gold nanoparticles, by absorbing incident light energy through the surface plasmon resonance effect, but most of the materials involved in these works are high in cost, complex in preparation process, and poor in stability of the metal particles in corrosive media, which largely hinders the further practical application of the solar water evaporation device. Another commonly used is a carbon-based material, for example, graphite, graphene, and carbon nanotubes are used to achieve photothermal conversion. However, the carbon-based materials have poor mechanical properties and low sunlight absorption, and the application of the evaporator is influenced by the factors. In summary, the problems of the existing solar evaporation device include high thermal conductivity, need of a thermal insulation layer, high cost, complex preparation, difficulty in large-scale production and application, and the like, so that a design strategy with low thermal conductivity, low cost, simplicity and high efficiency is needed to be explored to realize high-efficiency solar water evaporation.

Aerogel is a porous material with a solid appearance and a space network structure filled with gas, and has attracted much attention due to its characteristics of low thermal conductivity, low density, high porosity, and the like. For example, Zhonghu et al (DOI:10.1021/acsami.7b15125) prepared Cellulose Nanofiber (CNF) aerogel by freezing, freeze-drying method, then repeatedly deposited isopropanol suspension of Carbon Nanotubes (CNT) on CNF aerogel to ensure complete coverage, then dried under vacuum to get double layer CNF-CNT aerogel evaporator.

Disclosure of Invention

The invention aims to solve the technical problem of providing a nanofiber aerogel-based solar water evaporator and a preparation method thereof, and aims to overcome the defects of poor thermal conductivity, complex preparation and the like of the solar water evaporator in the prior art.

The invention provides a nanofiber aerogel-based solar water evaporator which is prepared by mixing and dispersing polyamide acid nanofibers and water-soluble polyamide acid in water, freezing, freeze-drying, performing thermal imidization, soaking the obtained aerogel in an initiator solution, and dropwise adding a pyrrole monomer solution on the surface of the aerogel for polymerization reaction.

The initiator is ammonium persulfate or ferric trichloride; the solvent of the initiator solution is water.

The invention also provides a preparation method of the nanofiber aerogel-based solar water evaporator, which comprises the following steps:

(1) performing electrostatic spinning on the polyamic acid spinning solution, mixing the obtained polyamic acid nanofiber and water-soluble polyamic acid in water according to a mass ratio of 4: 1-1: 1, and dispersing to obtain a dispersion solution of the polyamic acid nanofiber and the water-soluble polyamic acid, wherein the solid content of the dispersion solution of the polyamic acid nanofiber and the water-soluble polyamic acid is 10-20 mg/mL;

(2) freezing, freeze-drying and heat imidizing the dispersion liquid of the polyamide acid nanofiber and the water-soluble polyamide acid obtained in the step (1) to obtain polyimide nanofiber aerogel;

(3) soaking the polyimide nanofiber aerogel obtained in the step (2) in an initiator solution, dropwise adding a pyrrole monomer solution on the surface of the aerogel for polymerization reaction, washing and drying to obtain the nanofiber aerogel-based solar water evaporator, wherein the dropwise adding amount of the pyrrole monomer solution is 100-150 mg/cm²。

The preparation method of the polyamic acid spinning solution in the step (1) comprises the following steps: dissolving diamine monomer in polar solvent, adding dicarboxylic anhydride monomer, and polymerizing.

The polar solvent is N, N-dimethylacetamide, N-methylpyrrolidone or N, N-dimethylformamide.

The diamine monomer is p-phenylenediamine or 4,4' -diaminodiphenyl ether.

The binary anhydride monomer is pyromellitic dianhydride, biphenyl tetracarboxylic dianhydride or diphenyl ether tetracarboxylic dianhydride.

The polymerization temperature is-5-5 ℃, and the polymerization time is 4-6 h.

The electrostatic spinning process parameters in the step (1) are as follows: the voltage is 15-20 kV, the pushing speed is 0.05-0.10 mm/min, and the receiving speed is 65-100 r/min.

The preparation method of the water-soluble polyamic acid in the step (1) includes: dissolving diamine monomer in polar solvent, adding dicarboxylic anhydride monomer, polymerizing, adding triethylamine, reacting, precipitating the obtained water-soluble polyamic acid solution, washing, and freeze-drying.

The diamine monomer is p-phenylenediamine or 4,4' -diaminodiphenyl ether.

The polymerization reaction and the continuous reaction temperature are-5-5 ℃, and the polymerization reaction and the continuous reaction time are 4-6 h.

And (2) dispersing by using a dispersing machine in the step (1), wherein the rotating speed of the dispersing machine is 10000-15000 r/min, and the dispersing time is 30-60 min.

The step (2) of freezing is carried out in a liquid nitrogen atmosphere.

The freeze drying process parameters in the step (2) are as follows: the drying temperature is-50 ℃, the vacuum degree is 20Pa, and the drying time is 24-72 h.

The thermal imidization process parameters in the step (2) are as follows: heating from room temperature to 120-150 ℃ at a heating rate of 1-3 ℃/min, preserving heat for 1-2 h, heating to 320-360 ℃ at a heating rate of 1-3 ℃/min, and preserving heat for 1-2 h.

In the step (3), the solid content of the initiator solution is 100-200 mg/mL.

The dipping time in the step (3) is 30 min-1 h.

The polymerization reaction temperature in the step (3) is 0-5 ℃, and the polymerization reaction time is 30-60 min.

And (4) drying at the temperature of 30-60 ℃ for 1-3 h in the step (3).

The invention also provides an application of the nanofiber aerogel-based solar water evaporator. For example for desalination of sea water or treatment of sewage.

According to the invention, a polypyrrole layer is polymerized on the surface of the polyimide nanofiber aerogel. The organic polymer polypyrrole has good sunlight absorption capacity and photothermal conversion performance. When illumination, because the thermal-insulated effect of aerogel, surface steam temperature is higher than bottom surface of water temperature far away, greatly reduced to the heat loss of non-evaporation part, and then improve steam generation efficiency. The hydrophilic nature of the aerogel and the three-dimensional interconnected network allow it to transport water by capillary action. And the polyimide nanofiber aerogel has good mechanical properties and chemical corrosion resistance and can be recycled. Therefore, the solar water evaporation device based on the nanofiber aerogel material has a good application prospect in the fields of seawater desalination, sewage treatment and the like.

Advantageous effects

(1) The preparation method is simple in preparation process and low in cost, and is a convenient and efficient preparation method;

(2) the prepared nanofiber aerogel has a three-dimensional porous network structure, so that the nanofiber aerogel can absorb water through capillary action; the weight is light, and the solar cell can float on a water-gas evaporation interface for photo-thermal conversion, so that heat loss is reduced; the solar water heater has high sunlight absorptivity and low heat conductivity, can effectively prevent heat from being dissipated into massive water, and improves the photothermal conversion efficiency; has good mechanical property and chemical corrosion resistance, can be recycled, and is a good solar water evaporation device.

Drawings

FIG. 1 is a graph of water weight loss versus time for nanofiber aerogel-based solar water evaporators prepared in examples 1-3;

FIG. 2 is a surface infrared thermal image of the nanofiber aerogel-based solar water evaporator prepared in examples 1-3 after being placed in a beaker with water and irradiated under sunlight for 5 min;

FIG. 3 shows the transmittance and reflectance of the nanofiber aerogel-based solar water evaporator prepared in example 3 in the wavelength range of 500-2500 nm;

fig. 4 is a digital photograph of the self-floating of the nanofiber aerogel-based solar water evaporator prepared in example 3 in water;

fig. 5 is a 1000 cycle stress-strain curve of the nanofiber aerogel-based solar water evaporator prepared in example 3;

fig. 6 is a digital photograph of the nanofiber aerogel-based solar water evaporator prepared in example 3 before and after being immersed in an aqueous HCl solution having a PH of about 1 for 12 hours.

Detailed Description

The invention will be further illustrated with reference to the following specific examples. It should be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the present invention. Further, it should be understood that various changes or modifications of the present invention may be made by those skilled in the art after reading the teaching of the present invention, and such equivalents may fall within the scope of the present invention as defined in the appended claims.

4,4' -diaminodiphenyl ether (ODA), pyromellitic dianhydride (PMDA), N, N-dimethylacetamide (DMAc), Triethylamine (TEA), and ammonium persulfate were purchased from Chemicals, Inc., national drug group. Pyrrole was purchased from Shanghai Tantake technologies, Inc. All commercial chemicals were used directly without further purification. Deionized water was used for all experiments.

Example 1

The embodiment provides a nanofiber aerogel-based solar water evaporator and a preparation method thereof, and the preparation method comprises the following specific steps:

step 1): preparing polyamide acid nano-fiber:

4.0048g of 4,4' -diaminodiphenyl ether is dissolved in 50g N, N-dimethylacetamide solvent, 4.4278g of pyromellitic dianhydride is added, and the mixture reacts in an ice-water bath for 5 hours to obtain polyamic acid spinning solution; adding the prepared polyamic acid spinning solution into an injector, and carrying out electrostatic spinning, wherein electrostatic spinning parameters are as follows: the voltage is 15kV, the injection speed is 0.06mm/min, and the receiving speed is 100r/min, so as to obtain the polyamic acid nanofiber;

step 2): preparation of Water-soluble Polyamic acid:

n, N-dimethylacetamide is used as a solvent, and 4,4' -diaminodiphenyl ether and terephthalic anhydride in equal molar ratio are subjected to condensation polymerization in an ice-water bath to prepare polyamic acid with the solid content of 15%. The specific process is as follows: 8.0096g of 4,4' -diaminodiphenyl ether is dissolved in 95.57g N, N-dimethylacetamide, 8.8556g of pyromellitic dianhydride is added, and the mixture is reacted in an ice-water bath for 5 hours. Then, 4.0476g of triethylamine was added, and the reaction was continued for 5 hours to prepare a water-soluble polyamic acid solution having a solid content of 15%. Precipitating the prepared water-soluble polyamic acid by using deionized water, and then washing and freeze-drying to obtain the water-soluble polyamic acid for later use.

Step 3): preparing polyimide nanofiber aerogel:

taking 30mL of deionized water, 0.27g of nanofiber membrane and 0.09g of water-soluble polyamic acid, dispersing the nanofiber membrane and the water-soluble polyamic acid in the deionized water at a dispersion speed of 10000r/min for 30min to obtain uniform dispersion liquid, then placing the obtained dispersion liquid in a mold, freezing for 1h in a liquid nitrogen atmosphere, then placing the mold in a freeze dryer for drying, wherein the drying temperature is-50 ℃, the vacuum degree is 20Pa, the drying time is 72h, and finally performing thermal imidization to obtain the polyimide nanofiber aerogel. The technological parameters of the thermal imidization are as follows: heating to 120 ℃ from room temperature at the heating rate of 2 ℃/min and preserving heat for 2h, and then heating to 360 ℃ at the heating rate of 2 ℃/min and preserving heat for 1 h.

Step 4): preparing a nanofiber aerogel-based solar water evaporator:

firstly, preparing 100mg/mL ammonium persulfate aqueous solution, then soaking the polyimide nanofiber aerogel with the surface size of 2cm multiplied by 2cm and the height of 1cm in the solution for 30min, then dropwise adding 100mg pyrrole monomer solution with the concentration of 0.967g/mL on the surface of the polyimide nanofiber aerogel, then polymerizing (polymerizing for 30min at 0 ℃) to form black polypyrrole, and finally drying for 30min at 50 ℃ to obtain the nanofiber aerogel-based solar water evaporator which is marked as PI-PPy-1.

Example 2

The present embodiment is different from embodiment 1 in that: the same procedure as in example 1 was repeated except that the amount of the pyrrole monomer added dropwise in step 4) was 300 mg. Namely, 300mg of pyrrole monomer solution is dripped on the surface of the polyimide nanofiber aerogel with the surface size of 2cm multiplied by 2cm and the height of 1cm to obtain the nanofiber aerogel-based solar water evaporator which is marked as PI-PPy-2.

Example 3

The present embodiment is different from embodiment 1 in that: the same procedure as in example 1 was repeated except that the amount of the pyrrole monomer added dropwise in step 4) was 500 mg. Namely, 500mg of pyrrole monomer solution is dripped on the surface of the polyimide nanofiber aerogel with the surface size of 2cm multiplied by 2cm and the height of 1cm to obtain the nanofiber aerogel-based solar water evaporator which is marked as PI-PPy-3.

FIG. 1 is a graph of water weight loss versus time for the nanofiber aerogel-based solar water evaporators prepared in examples 1-3, wherein the weight loss of water for PI-PPy-3 is the greatest, followed by PI-PPy-2, and the least is PI-PPy-1, indicating that the evaporation effect of PI-PPy-3 is the best. Because the more the weight loss of water is, the more water vapor is generated in the evaporation process, and the higher the evaporation efficiency is. (the sample was placed in a beaker containing water, placed under a solar simulator, the mass of water loss in the beaker was calculated using an electronic balance, and the mass of water lost at a specific time was divided by the surface area of the sample to obtain the amount of water lost in weight; test conditions: ambient temperature 26 ℃, relative humidity 40%, and light intensity 1KW m^-2。)

FIG. 2 is a surface temperature infrared thermal imaging graph of the nanofiber aerogel-based solar water evaporator prepared in examples 1-3 after being placed in a beaker with water and irradiated under sunlight for 5min, wherein the surface temperature of PI-PPy-1 is 39.2 ℃, the surface temperature of PI-PPy-2 is 55.2 ℃, and the surface temperature of PI-PPy-3 is 59.6 ℃, which shows that the PI-PPy-3 has the best absorption effect on light. Since a higher surface temperature means that the evaporator absorbs more solar energy, which in turn converts the absorbed light energy into heat energy for efficient steam generation.

Fig. 3 shows transmittance and reflectance of the nanofiber aerogel-based solar water evaporator prepared in example 3 in the wavelength range of 500-2500 nm, which indicates that the nanofiber aerogel-based solar water evaporator has good sunlight absorbance.

Fig. 4 is a digital photograph of the self-floating of the nanofiber aerogel-based solar water evaporator prepared in example 3 in water. It can be seen that the evaporator can easily float at the water-vapor evaporation interface, showing its light weight.

Fig. 5 is a 1000 cycle stress-strain curve of the nanofiber aerogel-based solar water evaporator prepared in example 3. It can be seen that the test piece still can keep a complete curve after 1000 cycles, which indicates good mechanical properties. (mechanical Property test using Universal testing machine (SANS UTM2102), load 50N, compression speed 10 mm/min.)

Fig. 6 is a digital photograph of the nanofiber aerogel-based solar water evaporator prepared in example 3 before and after being immersed in an aqueous HCl solution having a PH of about 1 for 12 hours. It can be seen that the morphology remained intact after the evaporator was immersed in the strong acid solution for 12h, indicating that it had good corrosion resistance.

Comparative example 1

CNF aerogel assembly was carried out in literature (DOI:10.1021/acsami.7b15125) Zhonghu et al using TEMPO ((2,2,6, 6-tetramethylpiperidin-1-yl) oxy) oxidation (5 mmol NaClO loading per gram of cellulose) of softwood Cellulose Nanofibers (CNFs). 10mL of CNF aqueous suspension (0.7 wt%) was frozen in a small beaker at-20 ℃ for 6 h. The frozen CNF suspension was immediately transferred to the chamber of a freeze dryer to sublimate the ice (-50 ℃, 20Pa, 48h) to give a white porous CNF aerogel. The aerogel was cut to a thickness of 5mm and 2mL of an isopropanol suspension of CNTs (2.5mg/mL) was repeatedly deposited on top of the CNF aerogel to ensure complete coverage, then dried under vacuum, resulting in a two-layer CNF-CNT aerogel evaporator. The double-layer evaporator has the light absorption of 97.5 percent in the spectral range of 300-1200nm and the light absorption of 1kW m^-2The surface temperature of the sunlight can reach 32.7 ℃, and is 1kW m^-2The water evaporation rate of the solar radiation is 1.11kg m^-2h^-1The solar energy conversion efficiency was 76.3%.

Claims

1. A nanofiber aerogel-based solar water evaporator is characterized in that polyamide acid nanofibers and water-soluble polyamide acid are mixed and dispersed in water, the mixture is frozen, freeze-dried and then thermally imidized, the obtained aerogel is immersed in an initiator solution, and a pyrrole monomer solution is dropwise added to the surface of the aerogel for polymerization reaction to obtain the nano-fiber aerogel-based solar water evaporator, wherein the freezing is carried out in the liquid nitrogen atmosphere, the polymerization reaction temperature is 0-5 ℃, and the polymerization reaction time is 30-60 min.

2. The water evaporator of claim 1, wherein the initiator is ammonium persulfate or ferric chloride.

3. A preparation method of a nanofiber aerogel-based solar water evaporator comprises the following steps:

(2) freezing, freeze-drying and thermal imidization the dispersion liquid of the polyamide acid nanofiber and the water-soluble polyamide acid obtained in the step (1) to obtain the polyimide nanofiber aerogel, wherein the freezing is carried out in the liquid nitrogen atmosphere;

(3) soaking the polyimide nanofiber aerogel obtained in the step (2) in an initiator solution, dropwise adding a pyrrole monomer solution on the surface of the aerogel for polymerization reaction, washing and drying to obtain the nanofiber aerogel-based solar water evaporator, wherein the dropwise adding amount of the pyrrole monomer solution is 100-150 mg/cm²The polymerization temperature is 0-5 ℃, and the polymerization time is 30-60 min.

4. The method of claim 3, wherein the method for preparing the polyamic acid dope of the step (1) comprises: dissolving diamine monomer in polar solvent, adding dicarboxylic anhydride monomer, and polymerizing.

5. The method according to claim 3, wherein the electrostatic spinning in the step (1) comprises the following process parameters: the voltage is 15-20 kV, the pushing speed is 0.05-0.10 mm/min, and the receiving speed is 65-100 r/min; the dispersion time is 30-60 min.

6. The method according to claim 3, wherein the freeze-drying of step (2) comprises the following process parameters: the drying temperature is-50 ℃, the vacuum degree is 20Pa, and the drying time is 24-72 h.

7. The method according to claim 3, wherein the thermal imidization in step (2) is performed according to the following process parameters: heating from room temperature to 120-150 ℃ at a heating rate of 1-3 ℃/min, preserving heat for 1-2 h, heating to 320-360 ℃ at a heating rate of 1-3 ℃/min, and preserving heat for 1-2 h.

8. The method as claimed in claim 3, wherein the solid content of the initiator solution in the step (3) is 100-200 mg/mL; the dipping time is 30 min-1 h.

9. Use of the water evaporator of claim 1 in desalination of sea water or treatment of sewage.