CN115198519B - High-efficiency photothermal conversion hydrophilic/hydrophobic fiber mat and its preparation method - Google Patents

Abstract

The invention provides a high-efficiency photo-thermal conversion hydrophilic/hydrophobic fiber mat and a preparation method thereof. The preparation method comprises the following steps: carrying out surface activation treatment on the carbon-based material fiber felt; receiving an ultrafine polyvinyl alcohol fiber layer on the surface-activated carbon-based fiber felt by using an electrostatic spinning technology; acetalation treatment is carried out on the superfine polyvinyl alcohol fiber layer to obtain the high-efficiency photo-thermal conversion hydrophilic/hydrophobic fiber felt. The high-efficiency photo-thermal conversion hydrophilic/hydrophobic fiber felt prepared by the invention has excellent water evaporation rate, the upper hydrophobic carbon-based material fiber layer can improve photo-thermal conversion efficiency, the lower layer is hydrophilic superfine polyvinyl acetal fiber, water can be pumped efficiently, and salt gathered by the hydrophilic layer can be dissolved rapidly; the method has the advantages of high efficiency, stability and portability, avoids the defect of reduced evaporation rate caused by evaporation rate due to evaporation of water, salt deposition and blockage of a water vapor escape channel in the sea water desalination process, and simultaneously avoids the problems of unstable performance, film pollution and the like of the photo-thermal conversion material.

Description

High-efficiency photothermal conversion hydrophilic/hydrophobic fiber mat and its preparation method

technical field

The invention relates to the technical field of seawater desalination, in particular to a high-efficiency photothermal conversion hydrophilic/hydrophobic fiber mat and a preparation method thereof.

Background technique

Although about 71% of the earth's surface is covered by water, fresh water resources only account for 2.5% of all water resources, and the fresh water resources available for human use account for only 1% of the total fresh water resources. The crisis of fresh water resources has become a century-old challenge faced by mankind, and how to convert seawater into fresh water for human use has become a research hotspot.

Desalination technology has gradually become one of the important means of obtaining clean water in the field of water treatment. Traditional energy-driven desalination technologies such as thermal-driven and membrane-driven desalination processes have disadvantages such as high consumption of fossil energy and pollution to the environment. Compared with traditional energy sources, solar energy, as a green and sustainable resource, can provide a new energy source for desalination technology. In the solar evaporative desalination system, the use of photothermal conversion materials can effectively convert the absorbed sunlight into heat energy, so that water can be evaporated to achieve the purpose of water purification.

Solar evaporation desalination technology is divided into three types: bottom heating type, volume heating type and interface heating type. Bottom-heated solar evaporation system is the most primitive distillation desalination method. The temperature of brine gradually decreases from the bottom of the system to the evaporation surface, which will cause unnecessary heat loss and cause the evaporation efficiency of this type of evaporation system to be generally low, about 30 -45%. In order to reduce the heat loss of the system, the volume heating solar evaporation system based on nanofluids can move the heat generated by sunlight to the inside of the fluid, and the volume heating strategy can only improve the evaporation efficiency of the system to a certain extent; at the same time, in the long-term solar Under irradiation, the strong dispersion effect of nanofluids is also not conducive to solar evaporation desalination. The interface heating type uses solar energy to heat the interface photothermal material, and the interface photothermal material transfers heat to the interface brine, so that the interface water molecules quickly evaporate to obtain clean water. The interface heating evaporation desalination is under the condition of no light concentration. Generally above 80%, the evaporation efficiency is obviously higher than the other two types.

At present, the photothermal film materials used for solar evaporation are mainly hydrophilic materials, and most of the hydrophilic photothermal films face the severe problem of salt deposition (salt deposition is mainly because in the process of solar-driven desalination, salt The rate of upward transport and surface deposition of ions in the 2D film is greater than the rate of release of salt ions into the bulk solution). In order to solve the problem of salt deposition, people began to study photothermal conversion materials with hydrophobic/hydrophilic structure. The Chinese patent with the application number CN201911146604.6 discloses a preparation method of light and hot water evaporation nanofiber knitted aggregates. Firstly, electrospinning is used to prepare nanofiber hollow yarn; Fiber-based knitted fabric; finally, a light-to-heat conversion layer is plated on the obtained nanofiber-based fabric by using an evaporation device. The disadvantages of this method are: (1) the light-to-heat conversion is deposited on the fabric by evaporation, the bonding force between the fabric and the light-to-heat conversion layer is weak, and the light-to-heat conversion layer is easy to fall off; (2) the light-to-heat conversion layer deposited on the fabric The light-to-heat conversion layer on the surface is dense and the pores are small, and the water evaporated at the interface is not easy to escape, which reduces the evaporation efficiency; (3) The light-to-heat conversion layer is a metal coating, and the metal is expensive, and it is easy to cause secondary pollution of water .

Carbon-based materials have been used as light absorbers for solar evaporation due to their high light absorption rate, low cost, and high stability. Vinylon (the trade name of polyvinyl acetal fiber, also called Vinylon) is similar in nature to cotton, and its strength and abrasion resistance are superior to cotton; it has good durability, moisture absorption, warmth retention, abrasion resistance and sunlight resistance It is known as "synthetic cotton" and is the most hygroscopic variety among existing synthetic fibers. In addition, vinylon is insoluble in general organic acids, alcohols, esters, petroleum and other solvents, and is not easy to be moulded, and the strength loss is not large when exposed to sunlight. Therefore, how to use carbon-based materials and vinylon to prepare efficient interfacial evaporation materials is an urgent problem to be solved.

In view of this, it is necessary to design an improved photothermal conversion hydrophilic/hydrophobic fiber mat and its preparation method to solve the above problems.

Contents of the invention

The purpose of the present invention is to provide a high-efficiency photothermal conversion hydrophilic/hydrophobic fiber mat and its preparation method. First, the carbon-based material fiber mat is immersed in an organic solvent to dissolve the adhesive layer and its attachments on the surface of the carbon-based material fiber mat. Finally, the hydrophobic carbon-based material fiber mat is subjected to corona treatment to increase the surface roughness, specific surface area and the number of active groups, and then it is used as an electrospinning receiving device to receive hydrophilic polyvinyl alcohol fibers on its surface Layer, polyvinyl alcohol is bonded on its surface through chemical bonds, and the specific surface area of ultrafine fibers is large at the same time, intertwining occurs between different ultrafine fibers to make the pores of the polyvinyl alcohol fiber layer uniform, and finally the polyvinyl alcohol fiber layer Acetalization treatment produces hydrophilic polyvinyl acetal fibers with better performance in terms of durability, moisture absorption, warmth retention, abrasion resistance and sunlight resistance, and finally obtains high-efficiency photothermal conversion of hydrophilic/hydrophobic fiber mats, Salt deposits are avoided while the evaporation rate is high.

In order to achieve the purpose of the above invention, the present invention provides a method for preparing a high-efficiency light-to-heat conversion hydrophilic/hydrophobic fiber mat, comprising the following steps:

S1. Carry out surface activation treatment to carbon-based material fiber felt;

S2. Using electrospinning technology to receive an ultrafine polyvinyl alcohol fiber layer on the surface-activated carbon-based material fiber mat;

S3. Performing acetalization treatment on the ultrafine polyvinyl alcohol fiber layer to obtain a highly efficient light-to-heat conversion hydrophilic/hydrophobic fiber mat.

As a further improvement of the present invention, in the high-efficiency light-to-heat conversion hydrophilic/hydrophobic fiber mat, the thickness of the carbon-based material fiber mat is 1-20 mm, and the pore diameter is 1-20 μm; the ultrafine polyvinyl alcohol fiber layer The thickness is 30-2000 μm, the hole diameter is 0.1-10 μm, and the fiber diameter is 160-200 nm, and the acetalization degree of the superfine polyvinyl alcohol fiber layer is 16-65%.

As a further improvement of the present invention, the carbon-based material fiber felt includes one of carbon fiber felt, graphite felt, hard carbon felt, and hard graphite felt, and the activation treatment includes one of corona treatment and plasma treatment. kind.

As a further improvement of the present invention, in step S2, the electrospinning specifically includes: first preparing a polyvinyl alcohol spinning solution with a mass concentration of 5%-30%, and then adding the polyvinyl alcohol spinning solution into the electrospinning solution. Electrospinning was carried out in a silk machine.

As a further improvement of the present invention, the electrospinning voltage is 10-40kV, the receiving distance is 10-25cm, the advance rate of the syringe is 0.1-1mL/h, the ambient temperature is 20-40°C, and the humidity is 45%- 65%.

As a further improvement of the present invention, in step S3, the acetalization treatment specifically includes: immersing the ultrafine polyvinyl alcohol fiber layer in an aldehyde solution containing a strong acid catalyst, and reacting at 60-90° C. for 20-30 minutes; Wherein, the strong acid catalyst includes one or both of concentrated sulfuric acid, hydrochloric acid, and nitric acid; the aldehyde solution is one or both of formaldehyde solution, acetaldehyde solution, butyraldehyde solution, and glutaraldehyde solution; The mass ratio of the aldehyde content to the ultrafine polyvinyl alcohol fiber is (1-3):(3-8).

As a further improvement of the present invention, the irradiation temperature of the corona treatment is 10-50°C, the voltage is 10-30kV, the treatment time is 1-20min, the distance between the electrodes of the corona device and the carbon-based material fiber mat 0.1-5mm.

As a further improvement of the present invention, the cleaning specifically includes: immersing the carbon-based material fiber mat in an organic solvent, dissolving the adhesive layer and its attachments on the surface of the carbon-based material fiber mat, and then removing the carbon-based material fiber mat Clean in an ultrasonic cleaner and blow dry with compressed nitrogen; wherein, the organic solvent includes one or both of alcohol, acetone, chloroform, and isopropanol.

In order to achieve the purpose of the above invention, the present invention also provides a high-efficiency photothermal conversion hydrophilic/hydrophobic fiber mat, which is prepared by the preparation method of the high-efficiency photothermal conversion hydrophilic/hydrophobic fiber mat described in any one of the above.

The beneficial effects of the present invention are:

(1) The preparation method of the high-efficiency photothermal conversion pro-/hydrophobic fiber mat provided by the present invention first cleans the carbon-based material fiber felt and then corona treats the hydrophobic carbon-based material fiber felt, and then uses it as an electrospinning The receiving device receives the hydrophilic polyvinyl alcohol fiber layer on its surface, and finally acetalizes the polyvinyl alcohol fiber layer to generate hydrophilic polyvinyl acetal fibers, and finally obtains highly efficient photothermal conversion hydrophilic/hydrophobic fibers felt.

First of all, corona treatment is performed on the carbon-based material fiber mat to increase the surface roughness and specific surface area of the carbon-based material fiber mat, which not only provides more attachment sites for the subsequent polyvinyl alcohol fibers, but also improves both. In addition, the low-temperature ions generated during the corona process will destroy the surface molecular structure of the carbon-based material fiber mat, causing free radical reactions on the surface to cause cross-linking between molecules, further improving the surface roughness of the material, and at the same time More active groups will be exposed on the surface, and the active groups on the surface of the material can bond with polyvinyl alcohol molecules through chemical bonds; a large amount of ozone will also be generated during corona discharge, and ozone, as a strong oxidant, can oxidize carbon molecules And generate strong polar groups such as carbonyl and peroxide, thereby improving the surface energy of the carbon-based material fiber mat, making it have higher adhesion and easier to bond with polyvinyl alcohol fibers. The tight combination of the two is more conducive to the moisture transfer between different materials.

Secondly, the electrospinning technology is used to spin polyvinyl alcohol into ultrafine polyvinyl alcohol fibers, and the activated carbon-based material fiber mat is directly used as a receiving device. On the surface of the material fiber felt, the polyvinyl alcohol molecules and the carbon-based material fiber molecules are bonded by chemical bonds, and at the same time, the ultrafine polyvinyl alcohol fibers are entangled to different degrees, so that the polyvinyl alcohol fiber layer forms uniform pores and generates a special structure Polyvinyl alcohol/carbon-based material composite fiber mat. In addition, the ultra-fine polyvinyl alcohol fiber obtained by electrospinning has a finer fiber diameter, a larger specific surface area and a rich pore structure, which can not only effectively improve the moisture transfer efficiency, but also make it easier for water to be pumped to the hydrophobic carbon-based material. The junction of the fiber mat and the hydrophilic polyvinyl acetal fiber layer; at the same time, it provides more channels for the escape of water vapor and increases the evaporation rate of water.

Finally, acetalize ultrafine polyvinyl alcohol fibers to produce ultrafine polyvinyl acetal fibers. Polyvinyl acetal fibers are insoluble in general organic acids, alcohols, esters, petroleum and other solvents, and are not easy to be moldy. There is little loss of strength when exposed to sunlight, and it has excellent moisture absorption, sun resistance, and abrasion resistance (polyvinyl alcohol fibers will dissolve after long-term use, and the hot water resistance is poor), so as to improve the high-efficiency photothermal conversion. /Hydrophobic fiber felt durability; at the same time, during the reaction of polyvinyl alcohol, the cross-linking structure between fibers changes, resulting in an efficient light-thermal conversion hydrophilic/hydrophobic fiber felt with a better structure and special pore structure. When the sun shines, the carbon-based material absorbs solar energy and converts it into heat energy, and heats the water above the junction of the carbon-based material fiber mat and the ultrafine polyvinyl acetal fiber layer, and the water vapor generated from the carbon-based material The fiber mat and the ultra-fine polyvinyl acetal fiber layer escape in the rich pores, and the water evaporation rate is excellent, which is twice as efficient as the bottom heating type.

(2) The high-efficiency light-to-heat conversion hydrophilic/hydrophobic fiber mat prepared by the present invention, the upper layer is a hydrophobic carbon-based material fiber layer with a higher light absorption rate, and the light-to-heat conversion efficiency can be improved by using the principle of interface evaporation; the lower layer is hydrophilic Ultra-fine polyvinyl acetal fibers can pump water efficiently; during the water evaporation process, salt can only accumulate in the hydrophilic fiber layer. Due to the high water pumping efficiency of the hydrophilic layer, water continues to accumulate to the hydrophilic layer, and the accumulated salt quickly It will dissolve and will not block the water delivery channel of the hydrophilic fiber layer. This flexible and high-efficiency photothermal conversion hydrophilic/hydrophobic fiber mat provides an efficient, stable and portable solar steam generator for seawater desalination, avoiding salt deposition and blocking the escape channel of water vapor during the desalination process , leading to the disadvantages of reducing the evaporation rate, and avoiding the occurrence of problems such as unstable performance of photothermal conversion materials and membrane fouling.

Description of drawings

Fig. 1 is a schematic structural view of the high-efficiency light-to-heat conversion hydrophilic/hydrophobic fiber mat of the present invention.

Figure 2 is a schematic diagram of the acetalization reaction of polyvinyl alcohol and formaldehyde.

reference sign

1-carbon fiber felt; 2-rough interface produced by corona treatment; 3-acetalized ultrafine polyvinyl alcohol fiber layer.

Detailed ways

In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be described in detail below in conjunction with the accompanying drawings and specific embodiments.

Here, it should also be noted that, in order to avoid obscuring the present invention due to unnecessary details, only the structures and/or processing steps closely related to the solution of the present invention are shown in the drawings, and the steps related to the present invention are omitted. Invent other details that don't really matter.

Additionally, it should be noted that the term "comprises", "comprises" or any other variation thereof is intended to cover a non-exclusive inclusion such that a process, method, article or apparatus comprising a set of elements includes not only those elements, but also Other elements not expressly listed, or inherent to the process, method, article, or apparatus are also included.

The invention provides a method for preparing a high-efficiency photothermal conversion hydrophilic/hydrophobic fiber mat, comprising the following steps:

S1. Surface activation:

First immerse the hydrophobic carbon-based material fiber felt in an organic solvent for 20-40 minutes to dissolve the adhesive layer and its attachments on the surface of the carbon-based material fiber felt; then put the carbon-based material fiber felt into an ultrasonic cleaner for cleaning 1- 3h, and then blow dry with compressed nitrogen to obtain a carbon-based material fiber mat with a clean surface. Wherein, the organic solvent includes one or both of alcohol, acetone, chloroform, and isopropanol.

The surface-activated carbon-based material fiber mat is subjected to surface activation treatment to obtain a surface-activated carbon-based material fiber mat. Wherein, the carbon-based material fiber felt includes one of carbon fiber felt, graphite felt, hard carbon felt, and hard graphite felt; the activation treatment includes one of corona treatment and plasma treatment, preferably corona treatment. The irradiation temperature of the corona treatment is 10-50°C, the voltage is 10-30kV, the treatment time is 1-20min, and the distance between the electrode of the corona device and the carbon-based material fiber mat is 0.1-5mm. The carbon-based material fiber felt has a thickness of 1-20 mm and a pore size of 1-20 μm.

Carbon-based materials have the advantages of high light absorption rate, low cost, and high stability, and are used as light absorbers for solar evaporation. Among them, carbon fiber felt has the advantages of excellent carbonization degree, good electrical conductivity, strong flexibility and excellent macroporous structure (providing more channels for water vapor to escape to increase the evaporation rate of water), etc., and can be used Widely used in photothermal conversion materials.

Corona treatment is a kind of electric shock treatment, which uses high-frequency and high-voltage corona discharge on the surface of carbon-based material fiber felt (high-frequency AC voltage up to 5000-15000V/m ² ), the process will generate low-temperature plasma, plasma electric shock Erosion of the surface of the material increases the surface roughness and increases the specific surface area, which not only provides more attachment sites for the subsequent polyvinyl alcohol fibers, but also improves the bonding strength between the two. In addition, the low-temperature ions generated during the corona process will change the surface molecular structure of the carbon-based material fiber mat, causing free radical reactions on the surface to cause cross-linking between molecules, further improving the surface roughness of the material, and at the same time, the surface of the material will be exposed more. There are many active groups, and the active groups on the surface of the material can be bonded with polyvinyl alcohol molecules through chemical bonds. Furthermore, a large amount of ozone will be produced during corona discharge. As a strong oxidant, ozone can oxidize carbon molecules to produce carbonyl and peroxide and other polar groups, thereby improving the carbon-based material fiber felt. Surface energy, so that carbon-based materials can better bond with polyvinyl alcohol.

S2. Electrospinning:

Dissolving polyvinyl alcohol in water to configure a polyvinyl alcohol spinning solution with a mass concentration of 5%-30%, adding the configured polyvinyl alcohol spinning solution to an electrospinning machine for electrospinning, and the surface prepared in step S1 The activated carbon-based material fiber mat is used as an electrospinning receiving device, and an ultrafine polyvinyl alcohol (PVA) fiber layer with a preset thickness is deposited on its surface to obtain a polyvinyl alcohol/carbon-based material composite fiber mat. Polyvinyl alcohol fiber has high strength, high modulus, low elongation, wear resistance, acid and alkali resistance, good weather resistance, sunlight resistance, and low loss rate of strength after long-term sun exposure.

Specifically, the electrospinning voltage is 10-40kV, the receiving distance is 10-25cm, the advance rate (flow rate) of the syringe is 0.1-1mL/h, the ambient temperature is 20-40°C, and the humidity is 45%-65%. By adjusting the parameters of the electrospinning process, it can be found that (1) the diameter of the polyvinyl alcohol fiber increases with the increase of the concentration of the spinning solution; (2) the diameter of the polyvinyl alcohol fiber changes with the change of the voltage: when the voltage changes from 15kV When the voltage increased to 25kV, the fiber diameter decreased gradually; when the voltage increased from 25kV to 30kV, the fiber diameter began to increase instead; (3) The fiber diameter of polyvinyl alcohol decreased with the increase of the receiving distance. When the mass concentration of the spinning solution was 15%, the voltage was 25kV, the receiving distance was 15cm, and the flow rate was 0.2mL/h, the shape and diameter of PVA fibers were the best, and the electrospinning process was also the most stable.

The influence of spinning temperature on electrospun fibers is multifaceted: on the one hand, increasing the temperature is conducive to the volatilization of the solvent, making the jet solidify rapidly in the electric field, and increasing the diameter of nanofibers; on the other hand, the spinning temperature also increases It will affect the viscosity and surface tension of the spinning solution. The influence of humidity on electrospun fibers is mainly reflected in the volatility of solvents: increasing humidity will reduce the volatilization rate of solvents, and vice versa. Therefore, the morphology of nanofibers obtained by electrospinning can be adjusted by adjusting the temperature and humidity of the spinning environment, and then the structure of the prepared high-efficiency photothermal conversion hydrophilic/hydrophobic fiber mat can be adjusted.

The ultra-fine polyvinyl alcohol fiber prepared by electrospinning is only one-thousandth of the cotton fiber in diameter. The ultra-fine polyvinyl alcohol fiber layer can improve the moisture transfer efficiency through the differential capillary effect (the differential capillary effect is the one-way moisture transfer effect of the fabric. , when the fiber linear density of the inner layer of the fabric, that is, the polyvinyl alcohol fiber layer, is greater than the fiber linear density of the outer layer, that is, the carbon-based material fiber layer, an additional pressure difference of the capillary effect will be formed on the inner and outer layers of the fabric. Under the action of this pressure difference , the liquid moisture in the fabric automatically diffuses from the inner layer to the outer layer), and the water is more easily drawn to the junction of the hydrophobic carbon-based material fiber mat and the hydrophilic polyvinyl acetal fiber layer; at the same time, the ultrafine polyethylene Alcohol fiber has a larger specific surface area and richer pore structure, which provides more channels for water vapor to escape, so as to increase the evaporation rate of water. The ultrafine polyvinyl alcohol fiber layer has a thickness of 30-2000 μm, a hole diameter of 0.1-10 μm, and a fiber diameter of 160-200 nm.

The corona-treated carbon-based material fiber mat not only has a rough surface and a large specific surface area, but also has a large number of active groups on the surface. The ultra-fine polyvinyl alcohol fibers obtained by electrospinning can not only be chemically bonded to the carbon-based material fiber mat At the same time, the superfine fibers of different roots are entangled to different degrees to form a special structure of superfine polyvinyl alcohol fiber layers with uniform pore size.

S3. Acetalization treatment:

Immerse the ultrafine polyvinyl alcohol fiber layer of the polyvinyl alcohol/carbon-based material composite fiber mat prepared in step S2 in an aldehyde solution containing a strong acid catalyst (the entire polyvinyl alcohol/carbon-based material composite fiber mat floats on the solution, and the process In the process, the carbon-based material fiber felt is not in contact with the solution, only the ultrafine polyvinyl alcohol fiber layer is in contact with the solution), and reacted at 60-90°C for 20-30min, and the ultrafine polyvinyl alcohol fiber layer is acetalized. Make it into an ultrafine polyvinyl acetal fiber layer to obtain a high-efficiency light-to-heat conversion hydrophilic/hydrophobic fiber mat.

Among them, the strong acid catalyst includes one or both of concentrated sulfuric acid, hydrochloric acid, and nitric acid; the aldehyde solution is one or both of formaldehyde solution, acetaldehyde solution, butyraldehyde solution, and glutaraldehyde solution; The mass ratio of polyvinyl alcohol fibers is (1-3):(3-8). The acetalization reaction must be carried out under acidic conditions. The higher the acidity, the faster the reaction speed. However, if the reaction speed is too fast, the acetalization reaction will be incomplete, resulting in high free aldehyde content; if the reaction speed is too slow, the reaction time will be too long. When the pH is adjusted to 2.0-2.5, the reaction conditions are more suitable. The acetalization degree of the ultrafine polyvinyl alcohol fiber layer is 16-65%, and the thickness of the ultrafine polyvinyl acetal fiber layer is basically the same as that of the ultrafine polyvinyl alcohol fiber layer; the pore diameter is slightly smaller than that of the ultrafine polyvinyl alcohol fiber layer; The fiber diameter is slightly larger than the ultrafine polyvinyl alcohol fiber layer.

The polyvinyl alcohol molecule contains a large number of hydroxyl groups, and the aldehyde molecule contains a strong polar carbonyl group. The carbon of the aldehyde carbonyl group has a strong positive charge, while the hydroxyl oxygen in the polyvinyl alcohol molecule has a lone pair of electrons. The lone pair of electrons attacks the carbonyl carbon to form hemiacetal; the hydroxide ion of hemiacetal is unstable, and it is easy to dehydrate and condense with another molecule of alcohol to form acetal. The specific reaction principle of polyvinyl acetalization is shown in Figure 2, in which formaldehyde is taken as an example.

The schematic diagram of the structure of the obtained high-efficiency photothermal conversion hydrophilic/hydrophobic fiber mat is shown in Figure 1, 1 is a carbon fiber felt, 2 is a rough interface produced by corona treatment, and 3 is an acetalized ultrafine polyvinyl alcohol fiber layer (i.e. ultra-fine polyvinyl alcohol fiber layer). fine polyvinyl acetal fiber layer).

The present invention also provides a high-efficiency photothermal conversion hydrophilic/hydrophobic fiber mat, which is prepared by the above-mentioned high-efficiency photothermal conversion hydrophilic/hydrophobic fiber mat. When the high-efficiency photothermal conversion hydrophilic/hydrophobic fiber mat is used for seawater desalination, the carbon-based material fiber mat naturally floats on the water surface due to its hydrophobicity, and the ultrafine polyvinyl acetal fiber layer is immersed in water to achieve efficient water supply; The carbon-based material absorbs solar energy and converts it into heat energy, heats the water absorbed by the capillary of the carbon-based material fiber mat and the water above the junction with the ultrafine polyvinyl acetal fiber layer, and the water vapor generated from the carbon-based material Escape from the abundant pores of the fiber mat and ultrafine polyvinyl acetal fiber layer.

The present invention is described in detail below by a plurality of embodiments:

Example 1

A kind of preparation method of high-efficiency photothermal conversion hydrophilic/hydrophobic fiber mat, comprises the following steps:

S1. Surface activation:

First soak the hydrophobic carbon fiber felt with a thickness of 10mm in propanol for 30 minutes to dissolve the adhesive layer and its attachments on the surface of the carbon fiber felt; then put the carbon fiber felt in an ultrasonic cleaner for cleaning for 2 hours, and then dry it with compressed nitrogen. A carbon-based material fiber mat with a clean surface is obtained.

Corona treatment is carried out on the surface of the clean carbon fiber felt to obtain a surface activated carbon fiber felt. Among them, the irradiation temperature of the corona treatment is 25° C., the voltage is 15 kV, the treatment time is 10 minutes, and the distance between the electrodes of the corona device and the carbon fiber felt is 2 mm.

S2. Electrospinning:

Configure polyvinyl alcohol with a mass concentration of 15% polyvinyl alcohol spinning solution, add the configured polyvinyl alcohol spinning solution to an electrospinning machine for electrospinning, and use the surface-activated carbon fiber felt prepared in step S1 as an electrostatic spinning solution. Spinning receiving device, deposited on its surface an ultrafine polyvinyl alcohol fiber layer with a thickness of 2mm, to obtain a polyvinyl alcohol/carbon fiber composite fiber mat.

Specifically, the electrospinning voltage was 25kV, the receiving distance was 15cm, the flow rate was 0.2mL/h, the ambient temperature was 25°C, and the humidity was 60%.

S3. Acetalization treatment:

Add a certain amount of concentrated sulfuric acid to 200mL deionized water to adjust the pH value to 2-2.5, add the prepared nitric acid solution to the formaldehyde solution, and mix well. Immerse the ultra-fine polyvinyl alcohol fiber layer of the polyvinyl alcohol/carbon fiber composite fiber mat prepared in step S2 into the prepared formaldehyde solution, the mass ratio of formaldehyde content to ultra-fine polyvinyl alcohol fiber is 2:5, at 70 ° C After reacting for 25 minutes, the hydrophilic polyvinyl alcohol fibers were acetalized to generate hydrophilic polyvinyl formal fibers, and finally a highly efficient photothermal conversion hydrophilic/hydrophobic fiber mat was obtained.

The high-efficiency photothermal conversion hydrophilic/hydrophobic fiber mat prepared in Example 1 was placed under a standard simulated sunlight (ie 1kW/m ² ) and simultaneously placed in different concentrations of NaCl solutions for 30 consecutive days of photothermal evaporation tests. Among them, the mass fraction of the NaCl solution is 2%, 3.5%, and 5%, respectively. It can be seen from the test that the surface and interior of the carbon fiber mat do not produce salt in different concentrations of the NaCl solution of the high-efficiency photothermal conversion hydrophilic/hydrophobic fiber mat. The deposition shows that the evaporation rate and stability of the fiber mat are good, and it can work stably for a long time. The evaporation efficiency of the high-efficiency photothermal conversion hydrophilic/hydrophobic fiber felt in 3.5% NaCl solution is 86%, and the evaporation rate is 2.62kg·m ^-2 ·h ^-1 .

Example 2-3

A kind of preparation method of high-efficiency photothermal conversion hydrophilic/hydrophobic fiber mat, compared with embodiment 1, the difference is that, in step S1, the voltage of corona treatment process is different, others are roughly the same as embodiment 1, not here Let me repeat.

The high-efficiency photothermal conversion hydrophilic/hydrophobic fiber mat prepared in Examples 1-3 was placed under a standard simulated sunlight (ie 1kW/m ² ) and simultaneously placed in a NaCl solution with a mass concentration of 3.5% to perform a photothermal evaporation test , and the results are shown in Table 1.

The relevant properties of the high-efficiency light-to-heat conversion hydrophilic/hydrophobic fiber mat prepared in Table 1 Example 1-3

Example Voltage (kV) Evaporation efficiency (%) Evaporation rate (kg·m ^-2 ·h ^-1 ) Example 1 15 86 2.62 Example 2 10 80 2.24 Example 3 30 83 2.43

It can be seen from Table 1 that with the increase of the voltage in the corona treatment process, the evaporation efficiency and evaporation rate of the prepared high-efficiency photothermal conversion hydrophilic/hydrophobic fiber mat gradually increased and then decreased. This is mainly because as the voltage increases during corona treatment, the surface roughness of carbon fiber felt increases, and at the same time, more polar groups are introduced on the surface of the fiber, which increases the content of crystal domains, which is more conducive to the subsequent production of polyvinyl alcohol. The attachment and intertwining of microfibers can form a more efficient light-to-heat conversion hydrophilic/hydrophobic fiber mat with a better structure, so that its performance is better. However, when the voltage is too high, the surface of the carbon fiber mat will be etched more severely, thereby affecting the performance of the highly efficient light-to-heat conversion hydrophilic/hydrophobic fiber mat.

At the same time, the etching effect of corona treatment on the carbon fiber mat makes the surface rough and enhances the friction between fibers, thus improving the strength of the prepared high-efficiency light-to-heat conversion hydrophilic/hydrophobic fiber mat. However, when the corona treatment voltage is too high, the molecular chains on the surface of the carbon fiber mat are severely broken, which reduces the strength, which in turn affects the strength of the prepared high-efficiency photothermal conversion hydrophilic/hydrophobic fiber mat. Generally, although corona treatment has the characteristics of high electron density, high energy, and is more likely to occur or initiate related physical and chemical reactions, its depth of action is still limited to the surface layer of the fiber (<10 ^-8 m), and will not affect the fiber. The main chain of macromolecules constitutes damage, so under normal conditions, it will not damage the strength of fibers and fabrics, and will not affect the performance of fabrics.

Corona treatment also needs to be carried out within a reasonable time. As the treatment time continues to increase, the molecular chains on the fiber surface are broken to form small molecular substances, and then the small molecular substances will be removed by long-term corona treatment, causing the surface structure of the fiber to be formed. Severe damage will affect the performance of the prepared high-efficiency light-to-heat conversion hydrophilic/hydrophobic fiber mat.

Example 4-9

A method for preparing a high-efficiency photothermal conversion hydrophilic/hydrophobic fiber felt, compared with Example 1, the difference is that in step S2, the parameters of the electrospinning process are set differently, and the others are roughly the same as Example 1, here No longer.

Put the high-efficiency photothermal conversion hydrophilic/hydrophobic fiber mat prepared in implementation 4-9 under a standard simulated sunlight (ie 1kW/m ² ) and at the same time place it in a NaCl solution with a mass concentration of 3.5% to conduct a photothermal evaporation test. The results are shown in Table 2.

The relevant properties of the high-efficiency light-to-heat conversion hydrophilic/hydrophobic fiber mat prepared in Table 2 Example 4-9

It can be seen from Table 2 that with the increase of the concentration of the electrospinning spinning solution (Example 1, 4, 5), the evaporation efficiency and evaporation rate of the prepared high-efficiency photothermal conversion hydrophilic/hydrophobic fiber mat first increase and then decrease . This is mainly because when the concentration of the spinning solution is low, the diameter of the obtained polyvinyl alcohol ultrafine fiber is too small, it is easy to break, and cannot be well adhered and entangled on the carbon fiber felt; and when the concentration of the spinning solution is high , high viscosity, high surface tension, and difficult spinning process, resulting in poor performance of the obtained fiber, which ultimately affects the performance of the prepared high-efficiency photothermal conversion hydrophilic/hydrophobic fiber mat.

With the increase of electrospinning voltage (Example 1/6/7), the evaporation efficiency and evaporation rate of the prepared high-efficiency photothermal conversion hydrophilic/hydrophobic fiber mat still increase first and then decrease. This is mainly because, with the increase of electrospinning voltage, the jet of electrospinning liquid has a larger surface charge density, so there is a greater electrostatic repulsion, but if the voltage is too large, the static electricity between the spinning streams If the repulsion force is too large, the fibers cannot be fully entangled, and the structure of the polyvinyl alcohol ultrafine fiber layer is loose, which affects the performance of the high-efficiency photothermal conversion hydrophilic/hydrophobic fiber mat; when the voltage is small, the spinning fine flow The electrostatic repulsion between them is small, and the entanglement between different fine streams is serious, so that the pore size of the prepared polyvinyl alcohol ultrafine fiber layer is too small, which seriously affects its transportation of water, so that the efficient photothermal conversion of hydrophilic/hydrophobic fiber mats Evaporation efficiency and evaporation rate are small.

By adjusting the applied voltage and breaking the balance of surface tension and electric field force, the droplets at the tip of the needle will have different surface shapes, which will affect the size distribution and fiber morphology of the sprayed droplets and fine streams, and finally affect the preparation. Properties of efficient photothermal conversion of hydrophilic/hydrophobic fiber mats.

With the increase of the receiving distance of electrospinning (Example 1/8/9), the evaporation efficiency and evaporation rate of the prepared high-efficiency photothermal conversion hydrophilic/hydrophobic fiber mat still increase first and then decrease. During the fiber preparation process, after the polymer droplets are ejected from the needle, the solvent is volatilized in the air, and the polymer is concentrated and solidified into fibers, which are finally accepted by the receiver. If the receiving distance is too large, the stretching distance of the spinning fine stream is longer, which reduces the diameter of the fiber; while the collecting distance is too small, the fine spinning stream has been deposited on the carbon fiber felt without sufficient stretching. The situation is not conducive to obtaining a high-efficiency light-to-heat conversion hydrophilic/hydrophobic fiber mat with a better structure, so the performance is poor.

Examples 10-14

A method for preparing a high-efficiency photothermal conversion hydrophilic/hydrophobic fiber felt, compared with Example 1, the difference is that in step S3, the parameters of the acetalization process are set differently, and the others are roughly the same as Example 1, here No longer.

Put the high-efficiency photothermal conversion hydrophilic/hydrophobic fiber mat prepared in Examples 10-14 under a standard simulated sunlight (ie 1kW/m ² ) and at the same time place it in a NaCl solution with a mass concentration of 3.5% for photothermal evaporation test , and the results are shown in Table 3.

The relevant properties of the high-efficiency photothermal conversion pro-/hydrophobic fiber mat prepared in Table 3 Example 10-14

It can be seen from Table 3 that with the increase of pH (Example 1/10/11), the evaporation efficiency and evaporation rate of the prepared high-efficiency photothermal conversion hydrophilic/hydrophobic fiber mat still increase first and then decrease. This is mainly because when the pH is too low, the catalyst is excessive and the reaction is too violent, resulting in excessive local acetalization and water-insoluble substances; when the pH is too high, the reaction is too slow or even stops, resulting in the polymerization The degree of vinyl acetalization is too low. Both of these conditions will affect the acetalization reaction, and then affect the performance of the efficient photothermal conversion hydrophilic/hydrophobic fiber mat.

When the aldehyde used is glutaraldehyde, the performance of the prepared high-efficiency photothermal conversion hydrophilic/hydrophobic fiber mat can still be excellent.

Comparative example 1

A method for preparing a high-efficiency photothermal conversion pro-/hydrophobic fiber felt, compared with Example 1, the difference is that the carbon fiber felt is not subjected to the corona treatment of step S1, and the hydrophobic carbon fiber felt is directly used as an electrospinning receiving device , and others are substantially the same as those in Embodiment 1, and will not be repeated here. The evaporation efficiency of the resulting high-efficiency photothermal conversion hydrophilic/hydrophobic fiber mat was 69%, and the evaporation rate was 1.27kg·m ^-2 ·h ^-1 , significantly lower than that of Example 1. This is mainly because the carbon fiber mat has not been treated with corona, the bonding force between the carbon fiber and the polyvinyl acetal fiber layer is weak, and the content of the polyvinyl acetal fiber adhered to the carbon fiber is small, the structure is disordered, and the pore structure is disordered. , thereby affecting the properties of the material.

Comparative example 2

A kind of preparation method of high-efficiency photothermal conversion hydrophilic/hydrophobic fiber mat, compared with embodiment 1, the difference is that the polyvinyl alcohol fiber layer is not processed through acetalization, and others are roughly the same as embodiment 1, and are not described here. Let me repeat. The evaporation efficiency of the obtained high-efficiency photothermal conversion hydrophilic/hydrophobic fiber mat is 73%, and the evaporation rate is 1.66kg·m ^-2 ·h ^-1 , obviously lower than that of Example 1. At the same time, due to the poor hot water resistance of polyvinyl alcohol, At the contact point between polyvinyl alcohol and carbon fiber felt (where the temperature is higher), the polyvinyl alcohol fiber is prone to damage, and the polyvinyl alcohol will dissolve slowly.

Comparative example 3

A kind of preparation method of high-efficiency photothermal conversion hydrophilic/hydrophobic fiber mat, compared with Example 1, the difference is that first adopts electrospinning to prepare polyvinyl alcohol fiber, then acetalizes it to obtain polyvinyl formal Fiber, and then the polyvinyl formal fiber is supported on the carbon fiber felt. The evaporation efficiency of the resulting high-efficiency photothermal conversion hydrophilic/hydrophobic fiber mat was 69%, and the evaporation rate was 1.28 kg·m ^-2 ·h ^-1 , significantly lower than that of Example 1.

Comparative example 4

A method for preparing a high-efficiency photothermal conversion hydrophilic/hydrophobic fiber mat. Compared with Example 1, the difference is that in step S2, centrifugal spinning is used to prepare polyvinyl alcohol fibers. The evaporation efficiency of the obtained high-efficiency photothermal conversion hydrophilic/hydrophobic fiber mat is 67%, and the evaporation rate is 1.06kg·m ^-2 ·h ^-1 , significantly lower than that of Example 1, indicating that the pore size of the special structure obtained by electrospinning is more Facilitate the evaporation of water.

In summary, the present invention provides a high-efficiency light-to-heat conversion hydrophilic/hydrophobic fiber mat and its preparation method. Polyvinyl alcohol molecules and carbon-based material fiber molecules are bonded by chemical bonds, and at the same time, the polyvinyl alcohol fiber layer forms uniform pores. , in addition, the ultra-fine polyvinyl alcohol fibers obtained by electrospinning technology have a finer fiber diameter, a larger specific surface area and a rich pore structure, which can not only effectively improve the moisture transfer efficiency, but also make it easier for water to be pumped to the hydrophobic carbon. The junction of the base material fiber mat and the hydrophilic polyvinyl acetal fiber layer; at the same time, it provides more channels for the escape of water vapor and improves the evaporation rate of water; during the water evaporation process, salt can only be deposited on the hydrophilic fiber layer In the process, due to the high water pumping efficiency of the hydrophilic layer, water continues to accumulate to the hydrophilic layer, and the deposited salt will dissolve quickly, and will not form salt deposits on the carbon-based material fiber mat.

The above embodiments are only used to illustrate the technical solutions of the present invention without limitation. Although the present invention has been described in detail with reference to preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced. Without departing from the spirit and scope of the technical solution of the present invention.

Claims (8)

1. A preparation method of a high-efficiency photo-thermal conversion hydrophilic/hydrophobic fiber mat is characterized by comprising the following steps: the method comprises the following steps:

s1, carrying out surface activation treatment on a carbon-based material fiber felt; the activation treatment is corona treatment; the irradiation temperature of the corona treatment is 10-50 ℃, the voltage is 10-30kV, the treatment time is 1-20min, and the distance between an electrode of a corona device and the carbon-based material fiber felt is 0.1-5mm;

s2, receiving an ultrafine polyvinyl alcohol fiber layer on the carbon-based material fiber felt with the surface activated by utilizing an electrostatic spinning technology;

s3, carrying out acetalation treatment on the superfine polyvinyl alcohol fiber layer to obtain a high-efficiency photo-thermal conversion hydrophilic/hydrophobic fiber felt; the acetalation treatment specifically comprises: immersing the superfine polyvinyl alcohol fiber layer into aldehyde solution containing a strong acid catalyst, and reacting for 20-30min at 60-90 ℃; wherein the strong acid catalyst comprises one or two of concentrated sulfuric acid, hydrochloric acid and nitric acid; the aldehyde solution is one or two of formaldehyde solution, acetaldehyde solution, butyraldehyde solution and glutaraldehyde solution; the mass ratio of the aldehyde solution to the superfine polyvinyl alcohol fiber is (1-3) to (3-8).

2. The method for preparing the high-efficiency photothermal conversion hydrophilic/hydrophobic fiber mat according to claim 1, wherein the method comprises the following steps: the thickness of the carbon-based material fiber felt is 1-20mm, and the aperture is 1-20 mu m; the thickness of the superfine polyvinyl alcohol fiber layer is 30-2000 mu m, the aperture is 0.1-10 mu m, and the fiber diameter is 160-200nm; the acetalization degree of the superfine polyvinyl alcohol fiber layer is 16-65%.

3. The method for preparing the high-efficiency photothermal conversion hydrophilic/hydrophobic fiber mat according to claim 1, wherein the method comprises the following steps: the carbon-based material fiber felt comprises one of a carbon fiber felt and a graphite felt.

4. The method for preparing the high-efficiency photothermal conversion hydrophilic/hydrophobic fiber mat according to claim 1, wherein the method comprises the following steps: in step S2, the electrospinning specifically includes: firstly preparing a polyvinyl alcohol spinning solution with the mass concentration of 5% -30%, and then adding the polyvinyl alcohol spinning solution into an electrostatic spinning machine for electrostatic spinning.

5. The method for preparing the high-efficiency photothermal conversion hydrophilic/hydrophobic fiber mat according to claim 4, wherein the method comprises the following steps: the voltage of the electrostatic spinning is 10-40kV, the receiving distance is 10-25cm, the advancing speed of the injector is 0.1-1mL/h, the ambient temperature is 20-40 ℃, and the humidity is 45% -65%.

6. The method for preparing the high-efficiency photothermal conversion hydrophilic/hydrophobic fiber mat according to claim 1, wherein the method comprises the following steps: before the carbon-based fiber mat is subjected to surface activation treatment, the carbon-based fiber mat needs to be cleaned.

7. The method for preparing the high-efficiency photothermal conversion hydrophilic/hydrophobic fiber mat according to claim 6, wherein the method comprises the following steps: the cleaning is specifically as follows: immersing the carbon-based material fiber felt into an organic solvent, dissolving a glue layer and attachments on the surface of the carbon-based material fiber felt, and then placing the carbon-based material fiber felt into an ultrasonic cleaner for cleaning and then drying by compressed nitrogen; wherein the organic solvent comprises one or two of alcohol, acetone, chloroform and isopropanol.

8. A high-efficiency photo-thermal conversion hydrophilic/hydrophobic fiber mat is characterized in that: is prepared by the preparation method of the high-efficiency photo-thermal conversion hydrophilic/hydrophobic fiber mat according to any one of claims 1 to 7.