Optical transparency-optical confinement composite nanofiber membrane as well as preparation method and application thereof

Abstract

The invention provides an optical transparency-optical confinement composite nanofiber membrane as well as a preparation method and application thereof. The optical transparency-optical confinement composite nanofiber membrane comprises a PDMS (Polydimethylsiloxane) / PS (Polystyrene) / TPU (Thermoplastic Polyurethane) nanofiber membrane and a photothermal conversion material layer loaded on the PDMS / PS / TPU nanofiber membrane, the PDMS / PS / TPU nanofiber membrane is prepared by taking PDMS, PS and TPU as raw materials and adopting an electrostatic spinning technology; the photothermal conversion material layer comprises honeycomb porous carbon nanofibers and PDA (Personal Digital Assistant). The optical transparency-optical confinement composite nanofiber membrane and the PDMS / PS / TPU nanofiber membrane have excellent light transmittance and hydrophobicity, the photo-thermal conversion material layer has excellent light absorptivity and high photo-thermal conversion capacity, and the optical transparency-optical confinement composite nanofiber membrane has high membrane flux when being used for photo-thermal membrane distillation desalination. And the photo-thermal film is excellent in distillation performance stability.

Description

Technical Field

[0001] The present invention belongs to the technical field of nanofiber membranes, and particularly relates to an optically transparent-light confinement composite nanofiber membrane, a preparation method thereof, and an application thereof. Background Art

[0002] Utilizing seawater resources through seawater desalination technology is an effective way to solve the water resource problem. Membrane distillation (MD) technology uses a highly porous hydrophobic membrane as the separation medium and the temperature difference across the membrane as the driving force. Fresh water in the hot-side brine enters the cold side through three steps of "evaporation - transfer - condensation", thereby achieving the concentration of brine and the production of fresh water. Membrane distillation (MD) technology has attracted much attention due to its advantages such as high-quality effluent, low operating pressure, and low operating temperature. Chinese patent document with publication number CN118988001A discloses a novel Janus composite hollow fiber membrane for membrane distillation and a preparation method thereof. The novel Janus composite hollow fiber membrane is composed of a carbon nanotube layer, a polyvinyl alcohol layer, and a polytetrafluoroethylene hollow fiber membrane attached and combined. Its permeation flux is stable, the rejection rate is high, and the outer surface of the membrane has good hydrophilicity, avoiding the problem of oil pollution, which is of great significance for solving the problems of membrane fouling and membrane wetting easily caused by the membrane for membrane distillation. Chinese patent document with publication number CN106868712B discloses a nanofiber membrane for membrane distillation and a preparation method thereof. The nanofiber membrane is composed of nanofibers and nano-branch structures distributed on the nanofibers. The method of this invention simply synchronously implements the spraying (or atomizing) technology and the electrospinning technology to jointly prepare a nanofiber membrane for membrane distillation with superhydrophobic properties, effectively solving the problems of low membrane flux and easy wetting.

[0003] However, membrane distillation technology requires heating the feed liquid, resulting in high energy consumption. And due to the influence of temperature polarization, that is, the temperature difference (ΔT m,f between the hot-side membrane surface temperature T m,p and the cold-side membrane surface temperature T eff = T m,f - T m,p ) and the temperature difference (T f between the bulk temperature of the feed liquid T p and the bulk temperature of the permeate liquid T f - T p ) are inconsistent, resulting in a significant reduction in ΔT eff , a decrease in the mass transfer driving force, thus significantly reducing the permeation flux of the MD process and having a low energy utilization efficiency, usually between 20% and 50%.

[0004] With the development of photothermal conversion technology in recent years, the photothermal membrane distillation (PMD) technology has attracted wide attention. It uses solar energy as the driving force and conducts local heating at the membrane-feed water interface through the photothermal effect, thus replacing the overall heating of the feed liquid in the traditional MD technology, alleviating the temperature polarization phenomenon of the MD technology and further reducing energy consumption. It has become a research hotspot at home and abroad, and researchers have carried out preliminary exploratory experiments on the selection and preparation of photothermal conversion materials, the design of water vapor channels, etc. However, the energy utilization efficiency of the photothermal membrane is still relatively low. In addition, actual seawater contains dissolved salts and other substances, and is mixed with suspended particles, microorganisms and other substances, resulting in strong light scattering, which significantly weakens the light intensity when light penetrates seawater to reach the surface of the photothermal membrane, reduces the energy utilization efficiency, and restricts the actual application process of the PMD technology. Summary of the Invention

[0005] The technical problem solved by the present invention is to provide an optically transparent-light confinement composite nanofiber membrane, its preparation method and application. The optically transparent-light confinement composite nanofiber membrane, the PDMS / PS / TPU nanofiber membrane has excellent light transmittance and hydrophobic properties, the photothermal conversion material layer has excellent light absorption rate and high photothermal conversion ability, and the optically transparent-light confinement composite nanofiber membrane has a high membrane flux for photothermal membrane distillation desalination, and the photothermal membrane distillation performance has excellent stability.

[0006] To solve the above problems, the first aspect of the present invention provides an optically transparent-light confinement composite nanofiber membrane, including a PDMS / PS / TPU nanofiber membrane and a photothermal conversion material layer loaded on the PDMS / PS / TPU nanofiber membrane; the PDMS / PS / TPU nanofiber membrane is prepared by an electrospinning technique using PDMS, PS, and TPU as raw materials; the photothermal conversion material layer includes honeycomb porous carbon nanofibers and PDA.

[0007] Preferably, the thickness of the PDMS / PS / TPU nanofiber membrane is 40-200 μm.

[0008] Preferably, the thickness of the photothermal conversion material layer is 0.5-20 μm.

[0009] Preferably, in the photothermal conversion material layer, the mass ratio of honeycomb porous carbon nanofibers to PDA is 1:0.1-10.

[0010] The second aspect of the present invention provides a preparation method of the above-mentioned optically transparent-light confinement composite nanofiber membrane, including the following steps:

[0011] S1. Prepare a PDMS / PS / TPU nanofiber membrane;

[0012] S2. Attach the honeycomb porous carbon nanofibers to the surface of the PDMS / PS / TPU nanofiber membrane by vacuum self-assembly method;

[0013] S3. Prepare a dopamine solution, immerse one side of the PDMS / PS / TPU nanofiber membrane attached with honeycomb porous carbon nanofibers into the dopamine solution, and then let it stand to obtain the optically transparent-light confinement composite nanofiber membrane.

[0014] Preferably, in step S2, before attaching the honeycomb porous carbon nanofibers to the surface of the PDMS / PS / TPU nanofiber membrane by vacuum self-assembly method, hydroxylation of the honeycomb porous carbon nanofibers is also included, which specifically includes the following steps: Hydroxylate the honeycomb porous carbon nanofibers with NaOH solution, disperse the honeycomb porous carbon nanofibers in the sodium hydroxide solution, and stir and wash at 50-70 °C.

[0015] Preferably, the preparation of the PDMS / PS / TPU nanofiber membrane specifically includes the following steps:

[0016] Dissolve PS and TPU in a solvent, blend with PDMS, and prepare an electrospinning solution; transfer the electrospinning solution to the liquid storage bin of the electrospinning equipment, adjust the liquid supply rate to 0.5-2.0 ml·h -1 , voltage to 25-40 kV, receiving distance to 16-22 cm, spinneret diameter to 0.5-0.8 cm, temperature to 20-30 °C, humidity to 25-50%, carry out spinning, and then transfer to a roller to obtain the PDMS / PS / TPU nanofiber membrane; the mass ratio of PS to TPU is 1-10:1; the addition amount of PDMS is 1%-20% of the total mass of PS and TPU.

[0017] Preferably, the attachment of the honeycomb porous carbon nanofibers to the surface of the PDMS / PS / TPU nanofiber membrane by vacuum self-assembly method specifically includes the following steps:

[0018] Add the honeycomb porous carbon nanofibers to a dispersant to obtain a honeycomb porous carbon nanofiber dispersion; then use the method of vacuum-induced self-assembly to pump the honeycomb porous carbon nanofibers onto the PDMS / PS / TPU nanofiber membrane.

[0019] Preferably, step S3 specifically includes: Add hydrochloric acid dopamine monomer to a hydrochloric acid buffer solution with pH = 8.5 to obtain a dopamine solution; then immerse one side of the PDMS / PS / TPU nanofiber membrane attached with honeycomb porous carbon nanofibers into the dopamine solution, and keep it standing in a sealed environment at 20-30 °C for 5-7 hours; finally, rinse to remove the residual polymer particles on the surface and dry at 50-70 °C for 7-9 hours to obtain the optically transparent-light confinement composite nanofiber membrane.

[0020] The third aspect of the present invention provides an application of the above-mentioned optically transparent-light confinement composite nanofiber membrane in photothermal membrane distillation.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] 1) The optically transparent nanofiber layer (PDMS / PS / TPU nanofiber membrane) in the optically transparent-light confinement composite nanofiber membrane of the present invention has a high light transmittance, enabling the light path to effectively pass through its membrane body to reach the photothermal layer (photothermal conversion material layer), and the hydrophobic property of the optically transparent nanofiber layer endows it with super moisture resistance;

[0023] 2) The honeycomb porous carbon nanofibers in the optically transparent-light confinement composite nanofiber membrane of the present invention have a multi-level nanoporous structure, realizing multiple reflections of light, forming light "trapping" and "confinement", thereby improving the light absorption rate and promoting the efficient increase of the membrane body temperature;

[0024] 3) The optically transparent-light confinement composite nanofiber membrane of the present invention is prepared based on the electrospinning technology and is composed of several overlapping nanofibers, forming a relatively high porosity, which can effectively reduce the thermal conductivity of the membrane, and at the same time can provide more water vapor permeation paths, contributing to achieving a high permeation flux and long-term operation stability. Description of the Drawings

[0025] Figure 1 In [the figure], a and b are respectively the SEM images of the optically transparent layer PDMS / PS / TPU nanofiber membrane and the optically confinement layer honeycomb porous carbon nanofiber membrane in the optically transparent-light confinement composite nanofiber membrane prepared in Example 1;

[0026] Figure 2 are the ultraviolet-visible-near-infrared transmittance and the physical image of the optically transparent layer PDMS / PS / TPU nanofiber membrane in the optically transparent-light confinement composite nanofiber membrane of the present invention;

[0027] Figure 3 is the light path diagram of the optically confinement layer honeycomb porous carbon nanofiber membrane in the optically transparent-light confinement composite nanofiber membrane of the present invention;

[0028] Figure 4 is the preparation flow chart of the optically transparent-light confinement composite nanofiber membrane of the present invention. Detailed Embodiments

[0029] Next, in combination with the embodiments of the present invention, the technical solutions of the present invention will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0030] In the first aspect of the embodiments of the present invention, an optically transparent-light confinement composite nanofiber membrane is provided, which includes a PDMS / PS / TPU nanofiber membrane and a photothermal conversion material layer loaded on the PDMS / PS / TPU nanofiber membrane; the PDMS / PS / TPU nanofiber membrane is prepared from PDMS, PS, and TPU as raw materials by an electrospinning technique; the photothermal conversion material layer includes honeycomb porous carbon nanofibers and PDA.

[0031] In the present invention, a photothermal conversion material is introduced onto the PDMS / PS / TPU nanofiber membrane to form a bilayer composite of an optically transparent material and a light absorption and heat generation material. This composite nanofiber membrane can utilize solar energy to provide power and perform local heating at the membrane-feed water interface through the photothermal effect, thereby replacing the overall heating of the feed liquid in the traditional MD technology, alleviating the temperature polarization phenomenon in the MD technology, and further reducing energy consumption.

[0032] In a conventional photothermal membrane distillation (PMD) system, usually the side loaded with the photothermal material is placed on the feed liquid side, and the simulated light source is directly irradiated onto this surface to stimulate the photothermal effect. This configuration is usually referred to as the "upright" configuration. Since actual seawater contains dissolved salts and other substances, and is mixed with suspended particles, microorganisms and other substances, resulting in strong light scattering, the light intensity when light penetrates seawater to reach the photothermal membrane surface will be significantly weakened, reducing the energy utilization efficiency. The present invention uses a PDMS / PS / TPU nanofiber membrane as the base membrane. The PDMS / PS / TPU nanofiber membrane is an optically transparent nanofiber membrane prepared from PS, TPU, and PDMS low-crystalline or amorphous polymers with a relatively small refractive index and good optical transparency by an electrospinning process, and has excellent properties such as high porosity and good hydrophobicity. By combining this optically transparent material with the photothermal conversion material in a bilayer, the membrane is "inverted" during the membrane distillation operation, so that sunlight irradiates the permeate side and passes through the optically transparent layer of the composite membrane to irradiate the photothermal layer, thereby realizing the heating of the seawater on the feed side, and effectively solving the problem of difficult light transmission caused by seawater pollution. Upright means that sunlight irradiates the feed side to realize the heating of the seawater on the feed side; inverted means that sunlight irradiates the permeate side and passes through the optically transparent layer of the composite membrane to irradiate the photothermal layer, thereby realizing the heating of the seawater on the feed side.

[0033] Moreover, the PDMS / PS / TPU nanofiber membrane has a high light transmittance, enabling the light path to effectively pass through its membrane body and reach the photothermal layer, and the hydrophobic property of the optically transparent nanofiber layer endows it with super moisture resistance.

[0034] The energy utilization efficiency is related to the photothermal conversion efficiency and is restricted by the intrinsic properties of the photothermal conversion material and the light utilization rate of the entire active region. It is directly related to the increase in the surface temperature of the membrane distillation membrane, which in turn determines the mass transfer driving force and ultimately affects the permeation flux of the membrane distillation membrane. In the present invention, honeycomb porous carbon nanofibers are used. The honeycomb porous carbon nanofibers have a hierarchical nanoporous structure, which realizes multiple reflections of light, forms light "trapping" and "confining", thereby increasing the light absorption rate and promoting the efficient increase in the membrane body temperature.

[0035] In the optically transparent-light confinement composite nanofiber membrane of the present invention, the honeycomb porous carbon nanofibers are adhered to the PDMS / PS / TPU nanofiber membrane by interfacial polymerization of PDA. Adding PDA can adhere the honeycomb porous carbon nanofibers more firmly to the PDMS / PS / TPU nanofiber membrane. Moreover, PDA also has a certain photothermal conversion effect and can increase the light absorption rate.

[0036] The thickness of the base membrane is one of the key influencing factors in membrane distillation and has a certain impact on the transfer of photothermal effects and heat conduction during the membrane distillation process. Considering the inversion adopted in the present invention, if the base membrane is too thick, it will increase the difficulty of light penetration and the vapor mass transfer resistance to a certain extent, resulting in a decrease in energy utilization efficiency. And a too thin base membrane may cause a low salt rejection rate or even membrane wetting. Preferably, the thickness of the PDMS / PS / TPU nanofiber membrane is 40 - 200 μm; the thickness of the photothermal conversion material layer is 0.5 - 20 μm. Further preferably, the thickness of the PDMS / PS / TPU nanofiber membrane is 50 - 180 μm; the thickness of the photothermal conversion material layer is 1 - 15 μm.

[0037] Preferably, in the photothermal conversion material layer, the mass ratio of the honeycomb porous carbon nanofibers to PDA is 1:0.1 - 10. Further preferably, the mass ratio of the honeycomb porous carbon nanofibers to PDA is 1:1 - 8.

[0038] The second aspect of the embodiments of the present invention provides a preparation method of the above-mentioned optically transparent-light confinement composite nanofiber membrane, including the following steps:

[0039] S1. Prepare a PDMS / PS / TPU nanofiber membrane;

[0040] S2. Attach the honeycomb porous carbon nanofibers to the surface of the PDMS / PS / TPU nanofiber membrane by vacuum self-assembly method;

[0041] S3. Prepare a dopamine solution, immerse one side of the PDMS / PS / TPU nanofiber membrane with honeycomb porous carbon nanofibers attached therein into the dopamine solution, and then let it stand to obtain the optically transparent-light confinement composite nanofiber membrane.

[0042] Preferably, in step S2, before attaching the honeycomb porous carbon nanofibers to the surface of the PDMS / PS / TPU nanofiber membrane by vacuum self-assembly method, hydroxylation of the honeycomb porous carbon nanofibers is also included, which specifically includes the following steps: hydroxylate the honeycomb porous carbon nanofibers with an NaOH solution, disperse the honeycomb porous carbon nanofibers in the sodium hydroxide solution, and stir and wash at 50-70 °C.

[0043] Preferably, the preparation of the PDMS / PS / TPU nanofiber membrane specifically includes the following steps:

[0044] Dissolve PS and TPU in a solvent, blend with PDMS, and prepare an electrospinning solution; transfer the electrospinning solution to the liquid storage bin of the electrospinning equipment, adjust the liquid supply rate to 0.5-2.0 ml·h -1 、voltage 25-40 kV, receiving distance 16-22 cm, spinning head diameter 0.5-0.8 cm, temperature 20-30 °C, humidity 25-50%, carry out spinning, and then transfer it to a roller to obtain a PDMS / PS / TPU nanofiber membrane; the mass ratio of PS to TPU is 1-10:1; the addition amount of PDMS is 1%-20% of the total mass of PS and TPU. Preferably, the mass ratio of PS to TPU is 2:1; the addition amount of PDMS is 10% of the total mass of PS and TPU.

[0045] Traditional optically transparent materials are difficult to simultaneously meet the basic requirements of membrane distillation membranes. For example, for transparent metal materials, their preparation process is difficult and the application range is limited; for transparent inorganic non-metallic materials (such as glass, transparent ceramics, etc.), although they have high optical transparency and good mechanical properties, their preparation process requirements are high, the materials are rigid and solid and non-porous, and they are airtight; transparent organic polymer materials have high optical transparency and good flexibility, but they are also solid and non-porous, lack connected pores, and have a single function. The present invention uses the above-mentioned method to use low-crystalline or amorphous polymers of PS, TPU, and PDMS with relatively small refractive indices and good optical transparency as raw materials, combines the electrospinning process, prepares a PDMS / PS / TPU nanofiber membrane, and adjusts the structural characteristics such as fiber diameter and porosity through process parameters, and combines mechanical rolling to realize the controllable preparation of a hydrophobic (contact angle 138±2°), optically transparent (light transmittance 83±3%) nanofiber membrane on the basis of retaining the high porosity (>80%) of electrospinning.

[0046] Preferably, the attachment of the photothermal conversion material to the surface of the PDMS / PS / TPU nanofiber membrane by the vacuum self-assembly method specifically includes the following steps:

[0047] Add the honeycomb porous carbon nanofibers to a solvent to obtain a honeycomb porous carbon nanofiber dispersion; then use the method of vacuum-induced self-assembly to draw the honeycomb porous carbon nanofibers onto the PDMS / PS / TPU nanofiber membrane, and then wash until the honeycomb porous carbon nanofibers do not fall off.

[0048] Preferably, step S3 specifically includes: adding hydrochloric acid dopamine monomer to a hydrochloric acid buffer solution with pH = 8.5 to obtain a dopamine solution; then immersing one side of the PDMS / PS / TPU nanofiber membrane attached with honeycomb porous carbon nanofibers in the dopamine solution, and keeping it static in a closed environment at 20 - 30 °C for 5 - 7 hours; finally, rinsing to remove the polymer particles remaining on the surface, and drying at 50 - 70 °C for 7 - 9 hours to obtain the optically transparent-light confinement composite nanofiber membrane.

[0049] The third aspect of the present invention provides an application of the above-mentioned optically transparent-light confinement composite nanofiber membrane in photothermal membrane distillation.

[0050] In the following examples, the honeycomb porous carbon nanofibers are self-made. The preparation method is as follows: (Mix a PVA solution (10 wt%, as a carbon precursor) and a PTFE emulsion (60 wt%, as a pore-forming agent) and continuously stir for 1 hour to prepare a spinning solution. Control the mass ratio of PVA to PTFE to be 1:15. Use the above spinning solution to prepare honeycomb porous carbon nanofibers by the electrostatic solution blowing method, at 40 kV (electrostatic voltage), 0.1 MPa (air pressure), 20 mL / h (solution flow rate) and 800 mm (collection distance) at a temperature of 20 °C and a humidity of 60%. The composite nanofibers are pretreated in an air atmosphere (held at 260 °C for 1 h, heating rate 3 °C / min) and carbonized (held at 800 °C for 1 h, heating rate 2 °C / min) to obtain honeycomb porous carbon nanofibers. For the specific preparation steps, refer to Patent ZL201510675761.1.

[0051] Example 1

[0052] The optical transparent-light confinement composite nanofiber membrane of this embodiment includes a PDMS / PS / TPU nanofiber membrane and a photothermal conversion material layer loaded on the PDMS / PS / TPU nanofiber membrane. The photothermal conversion material layer includes honeycomb porous carbon nanofibers and PDA. The mass ratio of the honeycomb porous carbon nanofibers to PDA is 1:5. The honeycomb porous carbon nanofibers are adhered to the PDMS / PS / TPU nanofiber membrane through PDA. The thickness of the PDMS / PS / TPU nanofiber membrane is 100 μm; the thickness of the photothermal conversion material layer is 10 μm.

[0053] The preparation method of the optical transparent-light confinement composite nanofiber membrane of this embodiment includes the following steps:

[0054] S1. Prepare the PDMS / PS / TPU nanofiber membrane. Add PS and TPU to the solvent DMF respectively, place them on a magnetic stirrer at room temperature and stir for 6 h until dissolved uniformly to prepare PS and TPU spinning solutions with a concentration of 18 wt%. Mix the uniformly configured PS and TPU solutions in a ratio of 2:1 to obtain a PS / TPU mixed solution. Add PDMS at 10% of the total mass of PS and TPU to the PS / TPU mixed solution, place it on a magnetic stirrer at room temperature and stir for 2 h until dispersed uniformly to obtain a PDMS / PS / TPU electrospinning solution. Transfer the electrospinning solution to the liquid storage bin of the electrospinning equipment, adjust the liquid supply rate to 1 ml·h -1 、voltage 30 kV, receiving distance 18 cm, spinneret diameter 0.5 cm, temperature 25 °C, humidity 35%, carry out spinning, and then transfer it to a roller to prepare a PDMS / PS / TPU nanofiber membrane with a thickness of 100 μm.

[0055] S2. To make the honeycomb porous carbon nanofibers have better hydrophilicity and dispersibility, hydroxylate the honeycomb porous carbon nanofibers, which specifically includes the following steps: Hydroxylate the honeycomb porous carbon nanofibers with an NaOH solution, disperse the honeycomb porous carbon nanofibers in the sodium hydroxide solution, stir at 60 °C, wash repeatedly after stirring, and finally dry to obtain hydroxylated honeycomb porous carbon nanofibers. Add the hydroxylated honeycomb porous carbon nanofibers to an appropriate amount of distilled water, and under continuous stirring until dispersed uniformly, prepare a 1% honeycomb porous carbon nanofiber dispersion. Use the method of vacuum-induced self-assembly to uniformly attach the honeycomb porous carbon nanofibers to the surface of the PDMS / PS / TPU nanofiber membrane, wash three times with distilled water to ensure that the water is clear and turbid-free and the honeycomb porous carbon nanofiber particles no longer fall off, realizing the uniform distribution of the honeycomb porous carbon nanofiber particles.

[0056] S3. Prepare a dopamine solution by adding dopamine hydrochloride (DA) monomer into a hydrochloric acid buffer solution with pH = 8.5, such that the mass ratio of honeycomb porous carbon nanofibers to dopamine is 1:5; then immerse the PDMS / PS / TPU nanofiber membrane with attached honeycomb porous carbon nanofibers unilaterally into the above solution, and keep it standing for 6 hours in a normal temperature and airtight environment. After the reaction, take out the membrane sample, rinse it with deionized water to remove the residual particles on the membrane surface, and dry it in an oven at 60 °C for 8 hours to finally obtain an optically transparent - optical confinement composite nanofiber membrane. The thickness of the PDMS / PS / TPU nanofiber membrane is 100 μm; the thickness of the photothermal conversion material layer is 10 μm.

[0057] Example 2

[0058] The optically transparent - optical confinement composite nanofiber membrane of this example is different from that of Example 1 in that the thickness of the photothermal conversion material layer is 1 μm, and the remaining structures and preparation methods are the same as those of Example 1.

[0059] Example 3

[0060] The optically transparent - optical confinement composite nanofiber membrane of this example is different from that of Example 1 in that the thickness of the photothermal conversion material layer is 15 μm, and the remaining structures and preparation methods are the same as those of Example 1.

[0061] Example 4

[0062] The optically transparent - optical confinement composite nanofiber membrane of this example is different from that of Example 1 in that the thickness of the photothermal conversion material layer is 0.5 μm, and the remaining structures and preparation methods are the same as those of Example 1.

[0063] Example 5

[0064] The optically transparent - optical confinement composite nanofiber membrane of this example is different from that of Example 1 in that the thickness of the photothermal conversion material layer is 20 μm, and the remaining structures and preparation methods are the same as those of Example 1.

[0065] Example 6

[0066] The optically transparent - optical confinement composite nanofiber membrane of this example is different from that of Example 1 in that the thickness of the PDMS / PS / TPU nanofiber membrane is 50 μm, and the remaining structures and preparation methods are the same as those of Example 1.

[0067] Example 7

[0068] The optically transparent - optical confinement composite nanofiber membrane of this example is different from that of Example 1 in that the thickness of the PDMS / PS / TPU nanofiber membrane is 180 μm, and the remaining structures and preparation methods are the same as those of Example 1.

[0069] Example 8

[0070] The optically transparent - optical confinement composite nanofiber membrane of this example is different from that of Example 1 in that the thickness of the PDMS / PS / TPU nanofiber membrane is 40 μm, and the rest of the structure and preparation method are the same as those of Example 1.

[0071] Example 9

[0072] The optically transparent - optical confinement composite nanofiber membrane of this example is different from that of Example 1 in that the thickness of the PDMS / PS / TPU nanofiber membrane is 200 μm, and the rest of the structure and preparation method are the same as those of Example 1.

[0073] Example 10

[0074] The optically transparent - optical confinement composite nanofiber membrane of this example is different from that of Example 1 in that in the photothermal conversion material layer, the mass ratio of honeycomb porous carbon nanofibers to PDA is 1:1. The rest of the structure and preparation method are the same as those of Example 1.

[0075] Example 11

[0076] The optically transparent - optical confinement composite nanofiber membrane of this example is different from that of Example 1 in that in the photothermal conversion material layer, the mass ratio of honeycomb porous carbon nanofibers to PDA is 1:8. The rest of the structure and preparation method are the same as those of Example 1.

[0077] Example 12

[0078] The optically transparent - optical confinement composite nanofiber membrane of this example is different from that of Example 1 in that in the photothermal conversion material layer, the mass ratio of honeycomb porous carbon nanofibers to PDA is 1:0.1.

[0079] Example 13

[0080] The optically transparent - optical confinement composite nanofiber membrane of this example is different from that of Example 1 in that in the photothermal conversion material layer, the mass ratio of honeycomb porous carbon nanofibers to PDA is 1:10.

[0081] Comparative Example 1

[0082] The nanofiber membrane of this comparative example is a PDMS / PS / TPU nanofiber membrane with a thickness of 100 μm. The preparation method is the same as step S1 in Example 1.

[0083] Comparative Example 2

[0084] The nanofiber membrane of this comparative example is different from that of Example 1 in that dopamine is not used to bond the photothermal conversion material layer, that is, step S3 is not included.

[0085] Such as Figure 1Figures a and b are SEM images of the optically transparent-light confined composite nanofiber membrane prepared in Example 1. It can be seen that the optically transparent layer PDMS / PS / TPU nanofiber membrane presents a uniform fiber state, proving that the morphology of the fiber itself is not affected during the light pressure transparency process, and the excellent pore structure is maintained. The optically confined layer honeycomb porous carbon nanofiber membrane presents a honeycomb porous structure, which is conducive to achieving multiple reflections of light. Figure 2 The UV-Vis-NIR transmittance and physical picture of PDMS / PS / TPU nanofiber membrane show that PDMS / PS / TPU nanofiber membrane has good optical transparency. Figure 3 This is the optical path diagram of the honeycomb porous carbon nanofiber membrane of the optical confinement layer. It can be seen that the honeycomb porous structure is conducive to achieving multiple reflections of light, providing an effective way to improve the light absorption rate. Figure 4 The present invention is a flow chart for preparing the optically transparent-optically confined composite nanofiber membrane.

[0086] The transmittance and hydrophobicity of the optically transparent layer (PDMS / PS / TPU nanofiber membrane layer) of the nanofiber membrane obtained in the above embodiments and comparative examples, and the light absorption rate and photothermal conversion capacity of the photothermal layer (photothermal conversion material layer) were measured. The nanofiber membranes obtained in the above embodiments and comparative examples were applied to photothermal membrane distillation desalination, and their permeation flux and salt retention rate were measured. The permeation flux measurement conditions were: the feed liquid was 3.5wt% NaCl, 0.5wt% dye, and the light intensity was 1.0kW m -2 , no other heat source is added. The test results are shown in Table 1 below.

[0087] It can be seen from the data in the table below that the permeation flux of the photothermal membrane distillation of the single PDMS / PS / TPU nanofiber membrane in the upright and inverted positions in Comparative Example 1 is 0, and dopamine is not added in Comparative Example 2, and the honeycomb porous carbon falls off during operation. The optically transparent-light confined composite nanofiber membranes of each embodiment of the present application have a high permeation flux in both upright and inverted positions, and the honeycomb porous carbon does not fall off during operation.

[0088] Among them, compared with Examples 1-5, the difference is that the thickness of the photothermal layer is different, among which the thickness of the photothermal layer of Example 1-3 is in the preferred range, and the permeation flux is higher when it is placed upright or inverted. Compared with Examples 1, 6-9, the difference is that the thickness of the optically transparent layer is different, among which the thickness of the photothermal layer of Examples 1, 6, and 7 is in the preferred range. Although the permeation flux of Example 8 is higher, the salt interception rate is lower. Compared with Examples 1, 10-13, the difference is that the ratio of honeycomb porous carbon to PDA in the photothermal layer is different, among which Examples 1, 10, and 11 are preferred ratios. Although the permeation flux of Example 12 is higher, the honeycomb porous carbon falls off slightly during operation.

[0089] Table 1

[0090]

[0091]

[0092]

[0093] Obviously, the above embodiments are merely examples given for clear illustration and are not limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to enumerate all implementation manners here. And the obvious changes or modifications derived therefrom still fall within the protection scope of the present invention.

Claims

1. An optically transparent - optical confinement composite nanofiber membrane, characterized in that: It includes a PDMS / PS / TPU nanofiber membrane and a photothermal conversion material layer loaded on the PDMS / PS / TPU nanofiber membrane; the PDMS / PS / TPU nanofiber membrane is prepared from PDMS, PS, and TPU as raw materials by an electrospinning technique; the photothermal conversion material layer includes honeycomb porous carbon nanofibers and PDA.

2. The optically transparent - optical confinement composite nanofiber membrane according to claim 1, characterized in that: The thickness of the PDMS / PS / TPU nanofiber membrane is 40 - 200 μm.

3. The optically transparent - optical confinement composite nanofiber membrane according to claim 1, characterized in that: The thickness of the photothermal conversion material layer is 0.5 - 20 μm.

4. The optically transparent - optical confinement composite nanofiber membrane according to claim 1, characterized in that: In the photothermal conversion material layer, the mass ratio of honeycomb porous carbon nanofibers to PDA is 1:0.1 - 10.

5. A method for preparing an optically transparent-light confinement composite nanofiber membrane according to any one of claims 1-4, characterized in that, It includes the following steps: S1. Prepare a PDMS / PS / TPU nanofiber membrane; S2. Attach honeycomb porous carbon nanofibers to the surface of the PDMS / PS / TPU nanofiber membrane by vacuum self - assembly; S3. Prepare a dopamine solution, immerse one side of the PDMS / PS / TPU nanofiber membrane with attached honeycomb porous carbon nanofibers into the dopamine solution, and then let it stand to obtain the optically transparent - optical confinement composite nanofiber membrane.

6. The preparation method according to claim 5, characterized in that: In step S2, before attaching honeycomb porous carbon nanofibers to the surface of the PDMS / PS / TPU nanofiber membrane by vacuum self - assembly, hydroxylation of the honeycomb porous carbon nanofibers is also included, which specifically includes the following steps: hydroxylate the honeycomb porous carbon nanofibers with an NaOH solution, disperse the honeycomb porous carbon nanofibers in the sodium hydroxide solution, and stir and wash at 50 - 70 °C.

7. The preparation method according to claim 5, characterized in that, The preparation of the PDMS / PS / TPU nanofiber membrane specifically includes the following steps: Dissolve PS and TPU in a solvent, blend with PDMS, and prepare an electrospinning solution; transfer the electrospinning solution to the liquid storage bin of the electrospinning equipment, and adjust the liquid supply rate to 0.5 - 2.0 ml·h -1 , voltage to 25 - 40 kV, receiving distance to 16 - 22 cm, spinneret diameter to 0.5 - 0.8 cm, temperature to 20 - 30 °C, humidity to 25 - 50%, carry out spinning, and then transfer to a roller to obtain a PDMS / PS / TPU nanofiber membrane; the mass ratio of PS to TPU is 1 - 10:1; the addition amount of PDMS is 1% - 20% of the total mass of PS and TPU.

8. The preparation method according to claim 5, characterized in that, The attachment of honeycomb porous carbon nanofibers to the surface of the PDMS / PS / TPU nanofiber membrane by vacuum self - assembly specifically includes the following steps: Add honeycomb porous carbon nanofibers to a dispersant to obtain a honeycomb porous carbon nanofiber dispersion; then use the method of vacuum - induced self - assembly to draw the honeycomb porous carbon nanofibers onto the PDMS / PS / TPU nanofiber membrane.

9. The preparation method according to claim 5, characterized in that, Step S3 specifically includes: Add hydrochloric acid dopamine monomer to a hydrochloric acid buffer solution with pH = 8.5 to obtain a dopamine solution; then immerse one side of the PDMS / PS / TPU nanofiber membrane with attached honeycomb porous carbon nanofibers into the dopamine solution, and keep it standing in a sealed environment at 20 - 30 °C for 5 - 7 hours; finally, rinse to remove residual polymer particles on the surface and dry at 50 - 70 °C for 7 - 9 hours to obtain the optically transparent - optical confinement composite nanofiber membrane.

10. Application of an optically transparent-light confinement composite nanofiber membrane as described in any one of claims 1-4 in photothermal membrane distillation.

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