Self-crosslinking photo-thermal pervaporation composite membrane, preparation method and application

Abstract

The invention discloses a self-crosslinking photo-thermal pervaporation composite membrane which comprises a basement membrane (1) subjected to plasma treatment and graphene oxide (2) directly self-crosslinked on the surface of the basement membrane, and a preparation method of the composite membrane comprises the following steps: preparing a graphene oxide dispersion liquid by adopting a hammers method; the particle size of the graphene oxide is 100 to 200 nm; the preparation method comprises the following steps: preparing a graphene oxide dispersion liquid, carrying out plasma treatment on a substrate membrane, uniformly adding the graphene oxide dispersion liquid onto the substrate membrane subjected to plasma treatment in a fixed mold, carrying out blast drying at 75-85DEG C for 1.5-2.5 h so that graphene oxide is self-crosslinked, and carrying out crosslinking between graphene oxide and the substrate membrane to obtain the self-crosslinked photo-thermal pervaporation composite membrane. The composite membrane is high in flux, blockage and pollution caused by temperature control or salt crystallization are avoided, the preparation method is simple and environmentally friendly, the composite membrane is applied to solar seawater desalination equipment and systems, the membrane flux is high, and the system operation stability is good.

Description

Technical Field

[0001] The present invention relates to the technical field of solar seawater desalination, and in particular to a self-crosslinking photothermal pervaporation composite membrane, a preparation method and applications thereof. Background Art

[0002] Common membrane-based desalination technologies for seawater desalination include reverse osmosis, membrane distillation, and pervaporation. Pervaporation, as a membrane-based separation technology, has the advantages of low energy consumption, high separation capacity, and high energy efficiency. The membrane flux and system operation stability have become the key to seawater desalination separation technology.

[0003] Patent publication number CN119680399A provides a polytetrafluoroethylene composite nanofiltration membrane and a preparation method thereof. The invention uses polytetrafluoroethylene as a base membrane, places it in anhydrous ethanol for ultrasonic cleaning and drying, then soaks the polytetrafluoroethylene membrane in a surfactant solution, and then immerses it in a dopamine deposition solution for reaction. Finally, it is washed with deionized water and vacuum dried to obtain a hydrophilic modified polytetrafluoroethylene membrane. The patent has a complex and costly hydrophilic modification process at the polytetrafluoroethylene surface, increases membrane thickness, and uses a large amount of modification and cross-linking chemical reagents, which not only pollutes the environment, but also the residual or failure of the modification and cross-linking chemical reagents will cause water pollution after desalination.

[0004] All-waste-based solar evaporator in interfacial solar-driven seawater desalination, Journal of Environmental Chemical Engineering 11(5) (2023) A solar evaporator was built using waste to solve the problem of fresh water shortage. Each square meter of solar evaporator produces about 5.3m per day. 3 Fresh water. A new solar membrane distillation system with high photothermal conversion efficiency based on Ti3C2Tx MXene nanofluid was designed. Desalination 539 (2022) designed a solar membrane distillation system that combines solar energy with membrane distillation technology. Combined with the photothermal conversion material MXene, it eliminates additional energy input and the membrane energy is 2.375 kg / m 2 *h.

[0005] The membrane flux of the system currently in use is Figure 5 As shown, specifically Figure 5 ① is a bio-derived ultrathin film for solar-driven water purification, Nano Energy 60 (2019) 567-575; Figure 5 ② is the solar desalination of seawater using double dye modified PTFE membrane, Water Research 127 (2017) 96-103; Figure 5③ is a new type of solar membrane distillation achieved by locally heated PDMS / CNT / PVDF membrane, Desalination 489 (2020) 114529; ①-③ are the combination of solar energy and evaporator, and the photothermal composite membrane for solar evaporator is prepared by designing novel materials, with a membrane flux of 0.98~1.33kg / m 2 * between h. Figure 5 ④ is a biomimetic MXene texture with strong light-to-heat conversion function, which is used for solar steam generation and wearable thermal management. Advanced Energy Materials 9 (34) (2019) 1901687; Figure 5 ⑤ in the figure is MXene Ti3C2: an efficient two-dimensional light-to-heat conversion material, ACS Nano (2017) 3752-3759; Figure 5 ⑥ is the successful preparation of a hydrophobic MXene membrane by filtering PFDTMS, with modified d-Ti3C2 nanosheets acting as a light absorber, vapor evaporator, and solute blocker on the filter membrane. Journal of Materials Chemistry A 33 (2018) 16196-16204. ④-⑥ are the system fluxes obtained by combining solar energy with membrane distillation technology, ranging from 0.9 to 1.43 kg / m 2 * between h.

[0006] However, during the above-mentioned seawater osmosis vaporization process, if the salt concentration is too high or the temperature is improperly controlled, salt crystals will clog the osmotic membrane, and pollutants such as bacteria will adhere to the membrane, affecting its photothermal conversion performance. Summary of the Invention

[0007] In response to the problems existing in the above technologies, the present invention provides a self-crosslinked photothermal pervaporation composite membrane and preparation method with high flux, avoiding blockage and pollution due to temperature control or salt crystallization, and a simple and environmentally friendly preparation method. The present invention also provides a self-crosslinked photothermal pervaporation composite membrane for application in solar seawater desalination equipment and systems, with high flux and high system operation stability.

[0008] To achieve the above objectives, the present invention adopts the following technical solutions: A self-crosslinked photothermal pervaporation composite membrane comprises a plasma-treated base membrane and graphene oxide directly self-crosslinked on the surface of the base membrane.

[0009] The present invention provides a method for preparing a self-crosslinked photothermal pervaporation composite membrane, comprising the following steps: S1. A graphene oxide dispersion was prepared by a hammers method; the graphene oxide particle size was 100 to 200 nm; S2. The basement membrane was plasma treated, wherein the plasma treatment was performed using a voltage of 75 to 85 V and a current of 1.4 to 1.6 A for 3 to 4 seconds. S3 self-crosslinking: The graphene oxide dispersion of step S1 is evenly added to the fixed mold in step S2 of the plasma-treated base film at 75~85 O C and dried with forced air for 1.5 to 2.5 h to cause self-crosslinking of the graphene oxide, and crosslinking of the graphene oxide and the substrate membrane to obtain a self-crosslinked photothermal pervaporation composite membrane.

[0010] Furthermore, the base membrane is a PTFE base membrane.

[0011] The present invention installs the self-crosslinking photothermal pervaporation composite membrane in a seawater desalination tank, with the graphene oxide surface facing the sun and located on the seawater circulation side, and the base membrane surface facing the water collection side, and a mesh gasket is used to support the self-crosslinking photothermal pervaporation composite membrane; when the equipment is operated, the self-crosslinking photothermal pervaporation composite membrane converts light energy into heat energy for heating seawater to generate water vapor, and the water vapor then permeates to the other side of the self-crosslinking photothermal pervaporation composite membrane.

[0012] The present invention has the following advantages: 1. The present invention uses plasma technology to modify the basement membrane to change the chemical properties and physical structure of the basement membrane surface, increase its surface roughness and polar groups, so that the PTFE basement membrane and graphene oxide and the graphene oxide form stronger chemical bonds and physical bonds. During the blast drying process, the graphene oxide dispersion spontaneously undergoes a cross-linking reaction during the deposition process, avoiding the use of surface treatment agents and cross-linking agents, reducing environmental pollution and the effect of cross-linking agents on the thickness of the self-crosslinked photothermal pervaporation composite membrane; the increase in polar groups improves the hydrophilicity of the self-crosslinked photothermal pervaporation composite membrane and improves the water vapor passage efficiency; 2. The photothermal particles of the self-crosslinked photothermal pervaporation composite membrane of the present invention directly convert light into heat, reducing the heat loss in the traditional pervaporation process. At the same time, the increase in the surface temperature of the composite membrane effectively inhibits the crystallization of salt molecules on the membrane surface, and has a certain degradation effect on pollutants and bacteria.

[0013] 3. The self-crosslinked photothermal pervaporation composite membrane of the present invention uses photothermal particles of graphene oxide as a photothermal conversion medium to heat seawater for pervaporation of seawater. The photothermal pervaporation composite membrane is at 1 kW·m -2 Under the sunshine condition, the total water productivity reaches 4.175kg / m 2 *h high flux and more than 99.9% salt rejection rate.

[0014] 4. The application of the self-crosslinked photothermal pervaporation composite membrane of the present invention is based on existing technical equipment, including a sunlight simulation device (using a xenon lamp to simulate sunlight), a seawater circulation device, a desalination box and a clean fresh water collection device. The self-crosslinked photothermal pervaporation composite membrane of the present invention is located in the desalination box. Since the desalination box is made of transparent PVC material, the photothermal material in the photothermal pervaporation composite membrane can absorb light energy to achieve efficient heating of seawater, causing the seawater to evaporate and produce water vapor. Driven by the concentration difference, the water vapor penetrates from the feed liquid side of the membrane to the other side, and is condensed to form liquid water to be collected; at the same time, during desalination, the xenon lamp continuously irradiates the photothermal pervaporation membrane, and the temperature of the permeation membrane surface reaches 60~70 O C. Salt molecules will not crystallize on the membrane surface. At the same time, the high temperature of the permeable membrane will also have a certain disinfection and degradation effect on pollutants and bacteria, increasing the stability of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 The self-crosslinked photothermal pervaporation composite membrane of the present invention; Figure 2 Schematic diagram of the cross-linking process of the PTFE base membrane and graphene oxide of the present invention; Figure 3 This is a flux diagram of the self-crosslinked photothermal pervaporation composite membrane of Examples 1 and 2 of the present invention; Figure 4 This is a comparison chart of the salt rejection and conductivity of the self-crosslinked photothermal pervaporation composite membrane filtration products of Examples 1 and 2 of the present invention; Figure 5 This is a comparison chart of water productivity of the self-crosslinked photothermal pervaporation composite membranes of Examples 1 and 2 of the present invention and other solar desalination technologies; Figure 6 Graphs showing the flux of the self-crosslinked photothermal pervaporation composite membranes of Examples 1 to 4 of the present invention; Figure 7 Characterization diagram of the self-crosslinked photothermal pervaporation composite membrane of Examples 1 and 2 of the present invention; Figure 8 This is an application diagram of the self-crosslinking photothermal pervaporation composite membrane of the present invention.

[0016] Among them, 1. PTFE base membrane; 2. Graphene oxide photothermal layer; 3. Vacuum pump; 4. Connecting hose; 5. Support frame; 6. Product collection bottle; 7. Straight condenser; 8. Low-temperature condenser 9. Desalination box; 10. Photothermal pervaporation composite membrane; 11. Guarantee bottle; 12. Circulation pump; 13. Xenon lamp; 14. Seawater holding bottle. DETAILED DESCRIPTION Example 1

[0017] A method for preparing a self-crosslinked photothermal pervaporation composite membrane comprises the following steps: S1. 1 g of 150 nm graphene nanosheets was weighed and dissolved in 50 ml of concentrated sulfuric acid solution. A total of 1 g of potassium permanganate was slowly added in portions in an ice bath. After complete addition, the mixture was stirred at 500 rpm at 37°C for 1 h. Subsequently, 100 ml of deionized water was slowly added in small portions and stirred at the same speed for 15 min. An appropriate amount of hydrogen peroxide (H2O2) was then added to reduce the residual strong oxidant until the gas was completely released. The resulting graphene oxide was immediately isolated and washed twice with 10 wt% HCl solution by centrifugation (11,000 rpm). The collected graphene oxide was further purified by repeated centrifugation (11,000 rpm) and redispersion until the supernatant was neutral. The supernatant was then sonicated at 125 W in an ice bath for 5 minutes. Finally, the suspension was centrifuged at 3,000 rpm for 1 hour to remove unexfoliated graphite oxide particles. The resulting slurry was dried in a vacuum oven for two days to remove excess water, resulting in GO powders with varying degrees of oxidation. Finally, 0.2 g of GO powder was mixed with 100 ml of deionized water. The mixture was homogenized by stirring at 5000 rpm for 5 min using a homogenizer. S2. A PTFE base membrane was plasma treated using a PT-1 3D surface treatment machine at 80 V and 1.5 A for 3 s at a height of 3 cm from the base membrane. S3 self-crosslinking: The graphene oxide dispersion of step S1 was stirred evenly using a dropper and added to the fixed mold in step S2 of the plasma-treated PTFE substrate membrane, vibrated to make it evenly distributed at 80 O C for 2.5 h to allow the graphene oxide to self-crosslink and the graphene oxide to crosslink with the substrate membrane. Figure 2 As shown, the carbon-oxygen ratio of cross-linked graphene oxide is Figure 7 As shown in c, the deposition amount of low-oxidation graphene oxide is 3.025 mg / cm 2 Self-crosslinked photothermal pervaporation composite membranes such as Figure 1 As shown, the graphene oxide thickness is 280 μm. Figure 7 As shown in b, the surface flatness of low-oxidation graphene oxide is as follows Figure 7 As shown in a in . Example 2

[0018] A method for preparing a self-crosslinked photothermal pervaporation composite membrane comprises the following steps: S1. 1 g of 150 nm graphene nanosheets was weighed and dissolved in 50 ml of concentrated sulfuric acid solution. A total of 5 g of potassium permanganate was slowly added in portions in an ice bath. After complete addition, the mixture was stirred at 500 rpm at 37°C for 1 h. Subsequently, 100 ml of deionized water was slowly added in small portions and stirred at the same speed for 15 min. An appropriate amount of hydrogen peroxide (H2O2) was then added to reduce the residual strong oxidant until the gas was completely released. The resulting graphene oxide was immediately isolated and washed twice with 10 wt% HCl solution by centrifugation (11,000 rpm). The collected graphene oxide was further purified by repeated centrifugation (11,000 rpm) and redispersion until the supernatant was neutral. The supernatant was then sonicated at 125 W in an ice bath for 5 minutes. Finally, the suspension was centrifuged at 3,000 rpm for 1 hour to remove unexfoliated graphite oxide particles. The resulting slurry was dried in a vacuum oven for two days to remove excess water, resulting in GO powders with varying degrees of oxidation. Finally, 0.2 g of GO powder was mixed with 100 ml of deionized water. The mixture was homogenized by stirring at 5000 rpm for 5 min using a homogenizer. S2. A PTFE base membrane was plasma treated using a PT-1 3D surface treatment machine at 75 V and 1.4 A for 4 s at a height of 3 cm from the base membrane. S3 self-crosslinking: The graphene oxide dispersion of step S1 was stirred evenly using a dropper and added to the fixed mold in step S2 of the plasma-treated PTFE substrate membrane, vibrated to make it evenly distributed at 80 O C for 1.5 h to allow the graphene oxide to self-crosslink and the graphene oxide to crosslink with the substrate membrane. Figure 2 As shown, the carbon-oxygen ratio of self-crosslinked graphene oxide is Figure 7 As shown in f, the deposition amount of highly oxidized graphene oxide is 2.468 mg / cm 2 The self-crosslinked photothermal pervaporation composite membrane, graphene oxide thickness is 3 microns Figure 7 As shown in e, the surface flatness of highly oxidized graphene oxide is as follows Figure 7 As shown in d. Example 3

[0019] A method for preparing a self-crosslinked photothermal pervaporation composite membrane comprises the following steps: S1. A graphene oxide dispersion having a low degree of oxidation was prepared as in Example 1 (S1); S2. A PTFE base membrane was plasma treated using a PT-1 3D surface treatment machine at 85 V and 1.5 A for 3 s at a height of 3 cm from the base membrane. S3. Self-crosslinking: The graphene oxide dispersion of step S1 is stirred evenly and added to the PTFE substrate membrane treated with plasma in step S2 in the fixed mold using a dropper, and vibrated to make it evenly distributed at 85 O C for 2 h to allow the graphene oxide to self-crosslink and the graphene oxide to crosslink with the substrate membrane. Figure 2 As shown in the figure, the deposition amount of low-oxidation graphene oxide was 1.433 mg / cm 2 , 2.229mg / cm 2 、3.821mg / cm 2 Self-crosslinked photothermal pervaporation composite membranes such as Figure 1 shown. Example 4

[0020] A method for preparing a self-crosslinked photothermal pervaporation composite membrane comprises the following steps: S1. A highly oxidized graphene oxide dispersion was prepared as in Example 2 (S1); S2. A PTFE base membrane was plasma treated using a PT-1 3D surface treatment machine at 80V and 1.6A for 3 seconds at a height of 3 cm from the base membrane. S3 self-crosslinking: The graphene oxide dispersion of step S1 was stirred evenly using a dropper and added to the fixed mold in step S2 of the plasma-treated PTFE substrate membrane, vibrated to make it evenly distributed at 75 O C for 2.5 h to allow the graphene oxide to self-crosslink and the graphene oxide to crosslink with the substrate membrane. Figure 2 As shown in Figure 2, the amount of low-oxidation graphene oxide deposition is 1.627 mg / cm 2 、3.264mg / cm 2 , 4.060mg / cm 2 Self-crosslinked photothermal pervaporation composite membranes such as Figure 1 shown. Example 5

[0021] like Figure 8As shown, the self-crosslinked photothermal pervaporation composite membrane prepared in Examples 1 to 4 of the present invention is installed in a seawater desalination tank of a solar pervaporation equipment system in the prior art, with the graphene oxide surface facing the sun and located on the seawater circulation side, the substrate membrane surface facing the water collection side, and a mesh gasket supporting the self-crosslinked photothermal pervaporation composite membrane; the equipment is operated, and the self-crosslinked photothermal pervaporation composite membrane converts light energy into heat energy for heating seawater to generate water vapor, which then permeates to the other side of the self-crosslinked photothermal pervaporation composite membrane. The rest are all prior art.

[0022] The feed solution (3.5 wt% NaCl) was heated by simulating sunlight irradiation on the photothermal pervaporation composite membrane, and the membrane flux of the self-crosslinked photothermal pervaporation composite membrane prepared in Examples 1 and 2 was tested as follows: Figure 3 、 4 shown.

[0023] The conductivity of the self-crosslinked photothermal pervaporation composite membrane prepared in Examples 3 and 4 was tested on the permeate side: The test method is: the conductivity of the produced water during the test is 40μs·cm −1 Below, the salt resistance of the photothermal pervaporation composite membrane is high, all greater than 99.9% as shown in Table 1 and Table 2;

[0024] The self-crosslinked photothermal pervaporation composite membranes prepared in Examples 1 and 2 were characterized by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). Figure 7 As shown; Table 1 The test results of the properties of the self-crosslinked photothermal pervaporation composite membrane prepared in Examples 1 and 2 and applied in the seawater desalination tank:

[0025] Table 2 The test results of the properties of the self-crosslinked photothermal pervaporation composite membranes prepared in Examples 3 and 4 and their application in seawater desalination tanks:

[0026] Compared with other solar desalination technologies, the polytetrafluoroethylene graphene oxide self-crosslinked photothermal pervaporation composite membrane disclosed in the present invention has a membrane flux of up to 4.175 kg / m 2 *h, which shows that the high oxidation degree self-crosslinked photothermal pervaporation composite membrane can significantly improve the flux of seawater desalination.

[0027] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A self-crosslinking photothermal pervaporation composite membrane, characterized in that: The invention comprises a plasma-treated base film (1) and graphene oxide (2) directly self-crosslinked on the surface of the base film.

2. The method for preparing a self-crosslinked photothermal pervaporation composite membrane according to claim 1, characterized in that: The following steps are involved: S1. A graphene oxide dispersion was prepared by a hammers method; the graphene oxide particle size was 100 to 200 nm; S2. The basement membrane was plasma treated, wherein the plasma treatment was performed using a voltage of 75 to 85 V and a current of 1.4 to 1.6 A for 3 to 4 seconds. S3 self-crosslinking: the graphene oxide dispersion of step S1 is evenly added to the fixed mold on the plasma-treated base film of step S2, at 75~85 O C and dried with forced air for 1.5 to 2.5 h to cause self-crosslinking between graphene oxide and crosslinking between graphene oxide and substrate membrane to obtain a self-crosslinked photothermal pervaporation composite membrane.

3. The self-crosslinking photothermal pervaporation composite membrane according to claim 1, characterized in that: The basement membrane is a PTFE basement membrane.

4. Use of the self-crosslinked photothermal pervaporation composite membrane according to claim 1 or the self-crosslinked photothermal pervaporation composite membrane prepared by the method according to any one of claims 2 to 3, characterized in that: The self-crosslinked photothermal pervaporation composite membrane is installed in a seawater desalination tank, with the graphene oxide surface facing the sun and located on the seawater circulation side, and the base membrane surface facing the water collection side. A mesh gasket is used to support the self-crosslinked photothermal pervaporation composite membrane.

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