Two-dimensional tetracarboxyl phenyl porphyrin copper nanosheet, photo-thermal pervaporation desalination membrane modified by same and application of photo-thermal pervaporation desalination membrane

Abstract

The two-dimensional copper tetracarboxylphenylporphyrin (Cu-TCPP) nanosheet is successfully synthesized through a solvothermal method, the surface of the material is of a uniform sheet structure, the transverse size is 2-4 nm, and the thickness is about 5 nm. Cu-TCPP is successfully introduced into a PVA membrane to participate in a cross-linking reaction of a separation layer, the prepared photo-thermal pervaporation desalination membrane has good permeability and separation performance, when the relative content of Cu-TCPP is 100%, the pervaporation flux of the nano-composite membrane can reach 95.26 L.m <-2 >. H <-1 >, the salt rejection rate can reach 99.51%, the nano-composite membrane shows excellent pervaporation desalination performance, and the prepared photo-thermal pervaporation desalination membrane has good application prospects. The membrane has wide application prospects in the fields of seawater desalination, brackish water desalination, salt-containing wastewater treatment and the like.

Description

Technical Field

[0001] The invention relates to a preparation method of a nanosheet material and application thereof in a photothermal pervaporation membrane; in particular, to the preparation and application of a two-dimensional tetracarboxylphenylporphyrin copper nanosheet; and belongs to the technical field of preparation of novel functional membrane materials. Background Art

[0002] Photothermal conversion technology uses photothermal conversion agents to directly and efficiently convert received sunlight into thermal energy, thereby achieving the purposes of sterilization, catalysis, desalination, treatment, etc. Photothermal conversion agents include two major categories: inorganic and organic. Inorganic ones are mainly based on precious metals and transition metals. Although they have good photothermal conversion efficiency, they have disadvantages such as high cost and potential biological toxicity. In contrast, organic photothermal conversion agents have higher safety while meeting high photothermal conversion efficiency, showing greater application potential. Organic photothermal agents mainly include cyanines, porphyrins, porphines and polymer nanoparticles. Among them, porphyrin and porphine derivatives are eco-friendly and biosafe. At the same time, the presence of amine active groups in the molecular structure can further enhance the hydrophilic properties; and porphyrin molecules have a photothermal effect, and the temperature can be controlled by in-situ illumination.

[0003] The current pervaporation desalination technology has certain advantages over traditional desalination technology, but it still faces disadvantages such as high energy consumption and difficulty in regenerating energy. On the one hand, during the preparation of the pervaporation desalination membrane, the membrane needs to be heated to carry out a cross-linking reaction to obtain a polymer separation layer with a dense and stable structure; on the other hand, during operation, the feed liquid needs to be heated to a higher temperature to produce a large temperature difference on both sides of the membrane, prompting the vaporization of water molecules to complete the pervaporation separation process. This production mode must rely on external high temperature to achieve cross-linking of the separation layer, and the reaction takes a long time, which seriously limits the large-scale preparation of pervaporation desalination membranes.

[0004] Inspired by the existing photothermal desalination technology, the photothermal effect of photothermal molecules themselves is expected to provide thermal energy for the cross-linking reaction, thereby promoting further innovation in pervaporation desalination technology. Summary of the invention

[0005] To address the deficiencies of the prior art, the present invention aims to provide two-dimensional copper tetracarboxyphenylporphyrin (Cu-TCPP) nanosheets and introduce them into the preparation and application of photothermal pervaporation composite membranes to reduce the energy consumption of the membrane making process and obtain photothermal pervaporation desalination membranes with excellent performance.

[0006] In order to achieve the above objectives, the present invention adopts the following technical solution: The present invention first discloses a method for preparing a two-dimensional tetracarboxylphenylporphyrin copper nanosheet material, comprising the following steps:

[0007] S1, Cu(NO 3 ) 2 ·3H 2 O and polyvinyl pyrrolidone PVP are added to the mixed solvent to form a mixed solution, and then trifluoroacetic acid TFA is dropped into the mixed solution and uniformly dispersed by ultrasonication to obtain solution 1;

[0008] S2, dissolving tetrakis(4-carboxyphenyl)porphine TCPP in a mixed solvent, and uniformly dispersing by ultrasonication to obtain solution 2;

[0009] S3, slowly dripping solution 2 into solution 1, after completely mixing, transferring the obtained mixed solution to a hydrothermal reactor lined with polytetrafluoroethylene, and placing the reactor in an oven for heating and reaction for a period of time;

[0010] S4. After the reaction is completed, the reactor is cooled naturally to room temperature, and the solution after the reaction is transferred to a centrifuge tube for centrifugal washing, and then dried to obtain the product.

[0011] Preferably, the mixed solvent is composed of ethanol and N,N-dimethylformamide (DMF), and the volume ratio of ethanol to DMF is 1:3.

[0012] More preferably, in the aforementioned step S3, the oven is heated to 70-100° C., and the reaction time is 2-6 hours.

[0013] Further preferably, in the aforementioned step S4, the drying method is vacuum drying; the centrifugal washing method is: at room temperature, washing once with DMF, the washing time is 5 to 20 minutes, and the rotation speed is 8000 to 15000 rpm; and then washing at least twice with ethanol, the washing time is 5 to 20 minutes, and the rotation speed is 8000 to 15000 rpm.

[0014] More preferably, the surface of the nanosheet material prepared above is flat, with a lateral dimension of 2 to 4 nm, and multiple layers of nanosheets are stacked to form a nano-deposit with a thickness of about 5 nm, which is beneficial for the nanosheets to play a photothermal conversion role in the composite film and will not cause local defects in the dense layer of the composite film.

[0015] The present invention also discloses a photothermal pervaporation desalination membrane modified by the above-prepared two-dimensional tetracarboxylphenylporphyrin copper nanosheets, and the preparation method of the membrane is as follows:

[0016] (1) dissolving PVA and the tetracarboxylphenylporphyrin copper nanosheet material prepared above in deionized water in a certain ratio, stirring at high temperature in an oil bath pot, to obtain a uniform and stable PVA solution;

[0017] (2) After the solution cools to room temperature, P(AA / AMPS) is added as a cross-linking agent, and magnetic stirring is performed at room temperature to obtain a uniform PVA casting solution;

[0018] (3) After static degassing, the casting solution is coated on a substrate and a photothermal pervaporation desalination membrane is prepared by photothermal crosslinking.

[0019] Further preferably, the temperature in the aforementioned oil bath is 80-100° C., and the substrate is a PMIA substrate, which is prepared using the invention patent with application number 202211588036.7 (the applicant's previous research results).

[0020] More preferably, the mass ratio of the aforementioned PVA to the P(AA / AMPS) cross-linking agent is 7:3.

[0021] Further preferably, the specific process of the photothermal crosslinking is: using a xenon lamp light source for irradiation to carry out the crosslinking reaction, and the light power of the xenon lamp light source is set to 0.4-0.8 W·cm -2 , the distance between the light source and the film is 5 to 30 cm.

[0022] The present invention also discloses the application of the above-mentioned photothermal pervaporation desalination membrane in seawater desalination, brackish water desalination and saline wastewater treatment.

[0023] The present invention is beneficial in that:

[0024] (1) The present invention first successfully synthesized two-dimensional copper tetracarboxylphenylporphyrin (Cu-TCPP) nanosheets by a solvothermal method, and the surface of the material showed a uniform sheet structure, with a lateral size of 2 to 4 nm and a thickness of about 5 nm. The nano-stacked structure of large lateral size and ultra-thin nanosheets prepared by the present invention can provide a relatively high photothermal temperature, avoiding the need for PVA cross-linking in the prior art to rely on the long-term cross-linking reaction of the oven during heating, which is beneficial for the nanosheets to play a photothermal conversion role in the composite film and will not cause local defects in the dense layer of the composite film, overcoming the defects of the photothermal effect of the photothermal material in the prior art, such as weak stability, avoiding the problems of reduced photothermal effect caused by agglomeration of nanoparticles, mixing of larger sizes into the polymer layer, and thus avoiding defects in the PVA layer during the film formation process, causing a decrease in separation performance.

[0025] (2) The present invention successfully introduced Cu-TCPP nanosheets into the PVA membrane to participate in the cross-linking reaction of the separation layer. The membrane was characterized by SEM and FTIR, confirming that the nanomaterial Cu-TCPP was successfully introduced. The prepared photothermal pervaporation desalination membrane has good permeability and separation performance. When the relative content of Cu-TCPP is 80% (NM4), the pervaporation flux of the PVA nanocomposite membrane can reach 95.26L·m -2 ·h -1The salt rejection rate was as high as 99.51%. When the relative content of Cu-TCPP was 125% (NM6), the pervaporation flux of the PVA nanocomposite membrane further increased to 103.78 L·m -2 ·h -1 , the salt rejection rate can reach 97.95%, both showing excellent pervaporation desalination performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 is the XRD diffraction pattern of Cu-TCPP nanosheets;

[0027] Figure 2 FT-IR spectra of TCPP and Cu-TCPP nanosheets;

[0028] Figure 3 UV-visible absorption spectra of TCPP and Cu-TCPP nanosheets;

[0029] Figure 4 XPS spectrum of Cu-TCPP. (a) Full spectrum; (b) C 1s; (c) O 1s; (d) N 1s; (e) Cu2p;

[0030] Figure 5 is the SEM image of Cu-TCPP nanosheets;

[0031] Figure 6 AFM images and thickness measurement structures of Cu-TCPP nanosheets;

[0032] Figure 7 This is the SEM image of the surface of the photothermal pervaporation composite membrane;

[0033] Figure 8 This is the EDS image of the photothermal pervaporation composite membrane surface;

[0034] Fig. 9 This is the temperature change diagram of the photothermal pervaporation composite membrane under light;

[0035] Fig.10 This is the temperature change difference trend diagram of the photothermal pervaporation composite membrane under light;

[0036] Fig.11 This is a rendering of the separation performance of the photothermal pervaporation composite membrane;

[0037] Fig.12 This is a diagram showing the effect of pervaporation testing of the photothermal pervaporation composite membrane using real Bohai Sea water at 75°C. DETAILED DESCRIPTION

[0038] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0039] Unless otherwise specified in the present invention, all raw materials used are commercially available. Table 1 below shows preferred sources for purchasing the materials.

[0040]

[0041]

[0042] Table 1 Raw material model and source

[0043] Example 1

[0044] The present invention firstly prepares the material - two-dimensional copper tetracarboxylphenylporphyrin (Cu-TCPP) nanosheets by a solvothermal method. The specific process is as follows:

[0045] (1) Add 3.6mg Cu(NO 3 ) 2 ·3H 2 O and 10 mg of polyvinylpyrrolidone (PVP) were added to a mixed solvent of 12 mL of ethanol and N,N-dimethylformamide (DMF) (ethanol:DMF=1:3) to obtain a mixed solution. Then, 10 μL of 1.0 M trifluoroacetic acid (TFA) was dropped into the mixed solution and ultrasonicated for 15 min to uniformly disperse the solution to obtain solution 1.

[0046] (2) 4 mg of tetrakis(4-carboxyphenyl)porphine (TCPP) was dissolved in 4 mL of a mixed solvent of DMF and ethanol (ethanol:DMF=1:3), and ultrasonically dispersed for 10 min to obtain Solution 2.

[0047] (3) Solution 2 was slowly dripped into solution 1. After complete mixing, the resulting mixed solution was transferred to a 50 mL hydrothermal reactor lined with polytetrafluoroethylene, and the reactor was placed in an oven at 80° C. for reaction for 3 h.

[0048] (4) After the reaction is completed, the reactor is cooled to room temperature naturally, and the reaction solution is transferred to a centrifuge tube. At room temperature, the tube is washed once with DMF for 10 min at a rotation speed of 11,000 rpm, and then washed at least twice with ethanol for 10 min at a rotation speed of 11,000 rpm.

[0049] (5) The purple-red nanosheets obtained by centrifugation are placed in a 50° C. vacuum drying oven and collected for later use after drying.

[0050] Embodiment 2 to Embodiment 7

[0051] After the Cu-TCPP nanosheets were prepared, a photothermal pervaporation membrane was further prepared according to the following method. The difference between the examples mainly lies in the amount of raw materials used (see Table 2):

[0052] Dissolve 0.5g PVA and nanomaterial Cu-TCPP in 100g deionized water in a certain proportion, stir at high temperature in a 95°C oil bath to obtain a uniform and stable PVA solution. When the solution cools to room temperature, add a certain mass of P(AA / AMPS) as a cross-linking agent, the mass ratio of PVA to the cross-linking agent is 7:3, and stir magnetically at room temperature for 2 hours to obtain a uniform PVA casting solution. After standing and degassing, use a 10μm wire rod to coat it on a PMIA substrate, and the PMIA substrate is prepared according to the method of patent 202211588036.7. Finally, the composite film is irradiated with a xenon lamp light source for a cross-linking reaction instead of the traditional blast drying oven heating, where the xenon lamp light source light power is set to 0.4~0.8W·cm -2 , the distance between the light source and the film is 5 to 30 cm, and the preferred condition is that the light source power is 0.6 W·cm -2 , the distance between the light source and the film is 20 cm.

[0053] Serial number PVA (wt%) PVA:P(AA / AMPS) PVA:Cu-TCPP Membrane Product Code Example 2 0.5 7:3 5:1 NM1 Example 3 0.5 7:3 5:2 NM2 Example 4 0.5 7:3 5:3 NM3 Example 5 0.5 7:3 5:4 NM4 Example 6 0.5 7:3 1:1 NM5 Example 7 0.5 7:3 4:5 NM6 Comparative Example 0.5 7:3 1:0 NM0

[0054] Table 2 Raw material values ​​and membrane product codes of Examples 2 to 7 and Comparative Examples

[0055] Structure and performance characterization

[0056] (I) Structural characterization of two-dimensional copper tetracarboxyphenylporphyrin (Cu-TCPP) nanosheets

[0057] (1) Crystal structure of Cu-TCPP

[0058] The results were characterized by X-ray diffractometer (D / max-2550, Rigaku Smart Lab, Japan). Figure 1 The XRD diffraction curve is basically close to the theoretical curve of Cu-TCPP, and has several characteristic peaks of the Cu-TCPP nanosheet tetragonal unit cell structure, indicating that the present invention successfully synthesized the Cu-TCPP nanosheet. The peaks at 2θ=7.4°, 11.6°, 19.2° and 30.3° are attributed to the (110)(210), (400) and (440) crystal planes, indicating that the nanosheet is composed of regular binuclear Cu 2 (COO) 4 The paddle-wheel structure consists of Cu atoms located in the center of the structure connecting TCPP monomers along the ab plane, and the (400) crystal plane represents that the nanosheet has a lamellar crystal structure, which indicates that the nanosheet is a two-dimensional structure.

[0059] (2) Chemical structure of Cu-TCPP

[0060] The chemical structure of the nanosheets was analyzed by Fourier transform infrared spectroscopy (FTIR) and ultraviolet-visible spectrophotometry (UV-vis).

[0061] Figure 2 The FTIR spectra of TCPP and Cu-TCPP nanosheets are shown. It can be observed that -1 The NH peak at the porphyrin center disappears, and the 999cm -1 The Cu-N peak at the center of Cu-TCPP appears, indicating that the hydrogen protons are replaced by copper ions. -1 A new peak corresponding to the CO-Cu bond appears at 2+ In addition, the 3315cm -1 The NH peak at 1700 cm-1 almost disappeared, further confirming the substitution effect of copper ions. -1 The intensity of the C=O peak at the nanosheet decreases, confirming the unique Cu 2 (COO) 4 The paddle wheel structure is formed.

[0062] like Figure 3 As shown in the figure, the UV-visible absorption spectra of TCPP and Cu-TCPP nanosheets show that the Soret bandwidth absorption peak of the porphyrin ligand shifts from 415nm to 433nm of Cu-TCPP, and at the same time, the Q band at 548nm is reduced to one, which further proves that the porphyrin ring and Cu 2+ Successfully metallized.

[0063] (3) Elemental composition of Cu-TCPP

[0064] The Cu-TCPP nanosheets were further analyzed by X-ray photoelectron spectroscopy XPS (PHI 5000VersaProbe III, ULVAC-PHI, Japan) to determine their surface elemental composition. Figure 4 As shown in the full spectrum of (a), the peaks at 285, 399, 532, and 935 eV correspond to the binding energy peaks of C, N, O, and Cu elements, indicating the elemental composition of the nanosheets. Further, the bonding forms of the specific constituent elements were analyzed, such as Figure 4 As shown in (e), with the formation of Cu-TCPP nanosheets, binding energy peaks at 935.3 and 957.1 eV corresponding to the Cu2p3 / 2 and 2p1 / 2 spin-orbit states, respectively, and four satellite peaks at 941.1, 944.8, 959.7, and 963.7 eV were observed, indicating the presence of Cu in the Cu-TCPP nanosheets. 2+ Valence. Figure 4 In (c), the peaks at 531.9 and 533.0 eV are attributed to the signals of C=O and C-OH, corresponding to Cu 2 (COO) 4Unit structure. Figure 4 In (b), the peaks at 285.1 and 288.6 eV are attributed to the signal peaks of C=C and C=O. Both chemical bonds belong to the ligand porphyrin TCPP, confirming the existence of porphyrin. Figure 4 In (d), the pyrrolic nitrogen (-NH-) peak at 400.9 eV is low, confirming the formation of metalloporphyrin and the coordination of pyrrolic nitrogen with metal ions, which is consistent with the UV absorption spectrum test results.

[0065] (4) Cu-TCPP microstructure

[0066] The morphology and structure of Cu-TCPP nanosheets were characterized by scanning electron microscopy (SEM, SUPRATM55, ZEISS, Germany). Figure 5 As shown in Figure 1, the surface of Cu-TCPP presents a distinct lamellar structure with a relatively uniform morphology, which is consistent with the lamellar characteristic peaks shown in XRD. The thickness of Cu-TCPP was measured using an atomic force microscope (AFM). Figure 6 As shown. From the test results, it can be seen that the surface of the evenly dispersed nanosheets is relatively flat, the lateral size is 2 to 4 nm, and the thickness of the nanosheets is about 5 nm, which is quite different from the single-layer thickness of Cu-TCPP nanosheets reported in the prior art of about 0.68 nm. This is mainly due to the fact that multiple layers of nanosheets are stacked on each other during the synthesis process to form a nano-deposit. The Cu-TCPP with large lateral size and ultra-thin nanosheet structure prepared by the present invention is conducive to the nanosheets playing a role in light-heat conversion in the composite film and will not cause local defects in the dense layer of the composite film.

[0067] (II) Characterization and performance testing of photothermal pervaporation membranes

[0068] (1) Microstructure of photothermal pervaporation membrane

[0069] The surface morphology of the photothermal film was characterized by SEM. Figure 7As shown in the figure. As can be seen from the figure, the surface of the PVA membrane remains dense. Cu-TCPP nanosheets can be distributed relatively evenly in the membrane and have good stability. This is because the -NH- group in Cu-TCPP can cross-link with the -OH in the hydrophilic polymer chain to form a weak intramolecular hydrogen bond, and the -COOH group can interact with the -OH group in the PVA chain to form a chemical bond (-COOC-) interface, which lays the foundation for the nanosheets to uniformly supply heat at different points on the membrane surface and promote the thermal cross-linking reaction of the separation layer. With the increase of the nanosheet content, some nanosheets aggregated to form clusters on the NM5 and NM6 membranes. This is because the organic-inorganic interface compatibility between the nanosheets and PVA is still limited. This large nanocluster will reduce the adhesion between the nanosheets and the membrane surface, causing the aggregates to fall off during use, which in turn causes defects on the membrane surface, seriously affecting the membrane separation effect. The increase in the content of nanosheets, on the one hand, gradually increases the roughness of the membrane surface, which is conducive to enhancing the hydrophilicity of the membrane surface; on the other hand, the hanging -COOH groups of Cu-TCPP nanosheets will also increase the hydrophilicity of the composite membrane, which is conducive to the permeation of water molecules through the photothermal membrane. Therefore, in the actual preparation and use process, there must be enough Cu-TCPP nanosheets to meet the thermal cross-linking conditions of the PVA membrane, and the separation performance of the composite membrane must not be affected. Choosing the appropriate amount of nanosheets is crucial for the preparation of photothermal membranes.

[0070] (2) Surface chemical properties of photothermal pervaporation membranes

[0071] Energy dispersive X-ray spectrometer (EDS) was used to scan and analyze the elements on the film surface to further characterize the surface chemical properties of the photothermal film. The element contents of C, S, O and Cu were obtained through the EDS element spectrum, such as Figure 8 As shown, all composite membrane surfaces contain S elements, indicating that the crosslinking agent was successfully introduced. The original composite membrane without Cu-TCPP (Comparative Example NM0) only contains C, S and O elements, while NM1 to NM6 composite membranes all contain Cu elements after testing. According to the element scanning results, the Cu element is evenly distributed on the membrane surface, indicating that the Cu-TCPP nanosheets are well combined with the PVA membrane and stably exist in the membrane.

[0072] According to the qualitative analysis of elemental composition, the Cu content increased from 0.229% to 0.496% due to the continuous increase in the content of nanosheets, as shown in Table 3, indicating that the nanosheets were successfully introduced into the membrane matrix to prepare the composite membrane.

[0073]

[0074] Table 3 Statistical table of Cu element content on the surface of photothermal pervaporation membrane

[0075] (3) Photothermal pervaporation membrane photothermal conversion performance test

[0076] The photothermal performance of the photothermal pervaporation membrane was preliminarily tested. -2 Under the irradiation of xenon lamp, the real-time temperature of the film surface is measured by infrared thermal imager, and the formula ΔT = T i -T 0 The temperature difference ΔT of the powder under light is calculated to characterize the heat generation capacity of the photothermal film. i is the real-time temperature displayed by the infrared thermal imager (℃), T 0 The starting temperature (°C) of the test is recorded as follows: Fig. 9 shown.

[0077] Depend on Fig. 9 From the temperature change diagram, it can be observed that within 10 minutes, the surface temperature of all photothermal films quickly rose to above 50°C; within 40 minutes, the temperature of all films rose to above 70°C, and the surface temperature of the NM6 film with a Cu-TCPP addition of 125% rose to 108.7°C; after 40 minutes, the surface temperature of the photothermal film remained basically constant over time. This shows that Cu-TCPP can continuously provide heat for the cross-linking reaction of PVA, thereby obtaining a dense film.

[0078] As the content of Cu-TCPP nanosheets in the film increases, the reaction temperature of the photothermal film increases from 69.6℃ to 108.7℃, which shows that adding a high content of Cu-TCPP helps to enhance the photothermal effect of the film-forming process and increase the reaction temperature and reaction efficiency of the film surface. Cu-TCPP nanosheets have strong absorption characteristics in the ultraviolet-visible light region, with the Soret band absorption peak at 414nm and the Q band absorption peak at around 280nm, covering a wide spectrum range from ultraviolet to visible light. This wide-spectrum absorption characteristic enables it to efficiently utilize the energy of sunlight or other light sources. In addition, the two-dimensional nanosheet structure of Cu-TCPP has a high specific surface area and abundant surface active sites, which can enhance the light capture ability and thus improve the photothermal conversion efficiency. Compared with traditional metal nanoparticles (such as gold and silver) that rely on the surface plasmon resonance (SPR) effect, the photothermal performance of Cu-TCPP is more stable and not easily attenuated by agglomeration, especially not attenuated by agglomeration, thus providing a stable cross-linking reaction temperature for its introduction into the film material.

[0079] In the same time, the ΔT of different membranes changes as follows Fig.10As shown in the figure, as the addition amount of Cu-TCPP increases from 0% to 125%, ΔT increases from 41.7℃ to 90.6℃, further proving that Cu-TCPP has good light-to-heat conversion performance, which is due to the generation and relaxation of MOF electron-hole pairs. Under light irradiation, electrons absorb energy and are excited, are highly unstable, and tend to dissipate additional energy into heat through non-radiative relaxation processes and return to the initial state, thereby generating a thermal effect. At the same time, the thermal insulation performance and uniform distribution of PVA make the heat generated by the nanosheets evenly distributed on the surface of the film, supplying heat for the cross-linking reaction.

[0080] (4) Photothermal pervaporation membrane separation performance

[0081] Using 75℃ 3.5wt.% NaCl solution as feed liquid, the pervaporation desalination performance was tested to investigate the photothermal pervaporation membrane formation effect. The results are as follows: Fig.11 As shown in Figure 2, as the relative content of Cu-TCPP in the membrane increases from 0% to 125%, the pervaporation flux of the photothermal membranes NM1 to NM6 increases from 171.24 L·m -2 ·h -1 Down to 95.26L·m -2 ·h -1 , but the salt retention rate increased from 64.39% to 99.51%.

[0082] In the NM1~NM3 membranes, the relative content of Cu-TCPP is less than 60%, which means that when the distribution amount in the PVA membrane is small, its light absorption ability is poor, and insufficient heat generation leads to a low temperature of the photothermal membrane, which cannot completely cross-link PVA and P(AA / AMPS) to form a dense cross-linked network of PVA, causing large defects in the PVA membrane and making it difficult to obtain a good salt rejection rate. In the NM4~NM6 membranes, the relative addition amount of Cu-TCPP reaches more than 80%, and the heating capacity of the photothermal membrane is significantly improved. Within 20 minutes, the membrane surface temperature has risen to about 90°C, providing sufficient conditions for the PVA cross-linking reaction, and forming a dense PVA layer that meets the desalination standard. Furthermore, when the relative content of Cu-TCPP increases from 80% to 125%, the pervaporation flux increases from 95.26L·m -2 ·h -1 Increased to 103.78L·m -2 ·h -1 The interception rate decreased slightly from 99.51% to 97.95%. The applicant analyzed that this may be attributed to the fact that when the addition amount is greater than 100%, a large number of nanosheets form agglomerates inside the membrane and are difficult to disperse, resulting in the formation of large channels with local defects on the surface of the PVA membrane, which is not conducive to the interception of NaCl.

[0083] (5) Desalination performance of photothermal pervaporation membrane on real Bohai Sea water

[0084] In order to verify the practical applicability of the photothermal pervaporation membrane of the present invention, the photothermal pervaporation membrane was subjected to a pervaporation test at 75°C using real Bohai Sea water, and the contents of various ions in the Bohai Sea water raw material liquid and the permeate were detected. The results are as follows: Fig.12 As shown in the figure: the boron removal rate of the photothermal pervaporation membrane is 93.60%, and the removal rates of the remaining salts are Cl - :99.87%;Mg 2+ :100%;Ca 2+ :100%; SO 4 2- :100%;Na + : 99.87%; K + : 99.94%, which shows that the photothermal pervaporation membrane has a very excellent seawater desalination capacity.

[0085] Based on the above results, in the polymer film-forming process of the present invention, the photothermal effect is used to not only realize the defect-free construction of the pervaporation desalination membrane, but also the prepared pervaporation membrane with photothermal effect further improves the separation performance during the application process. This is mainly because the photothermal pervaporation membrane can produce a photothermal effect under light conditions. When the feed liquid flows through the membrane surface, the heat generated by the photothermal membrane will exchange heat with the feed liquid, which intensifies the molecular thermal motion in the feed liquid, accelerates the diffusion rate of salt ions and water molecules, and after obtaining more energy, the water molecules are more likely to change from liquid to gas, which greatly accelerates the pervaporation water permeation rate.

[0086] In summary, the present invention successfully prepared Cu-TCPP nanosheet materials by solvothermal method, with a lateral size of 2-4 nm and a thickness of 5 nm, and successfully introduced them into PVA composite membranes to successfully prepare photothermal pervaporation composite membranes with good separation performance. When the relative content of Cu-TCPP was 100%, the experimental temperature was 75 ° C, and when treating 3.5 wt.% saline solution, the pervaporation flux of the nanocomposite membrane reached 95.26 L·m -2 ·h -1 At the same time, its salt rejection rate can reach 99.51%, showing excellent pervaporation desalination performance. The photothermal pervaporation desalination membrane prepared by the present invention combines the technical advantages of photothermal conversion and pervaporation, and has the characteristics of high efficiency, energy saving, and environmental protection. In the context of increasingly tight energy and increasing environmental protection requirements, this technology has great development potential and has good application prospects in the fields of seawater desalination, industrial saline wastewater treatment, and brackish water purification.

[0087] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the above embodiments do not limit the present invention in any form, and any technical solution obtained by equivalent replacement or equivalent transformation falls within the protection scope of the present invention.

Claims

1. A method for preparing a two-dimensional tetracarboxylphenylporphyrin copper nanosheet material, characterized in that: The steps include: S1, adding Cu(NO3)2·3H2O and polyvinylpyrrolidone PVP into a mixed solvent to form a mixed solution, then dropping trifluoroacetic acid TFA into the mixed solution, and uniformly dispersing by ultrasonication to obtain solution 1; S2, dissolving tetrakis(4-carboxyphenyl)porphine TCPP in a mixed solvent, and uniformly dispersing by ultrasonication to obtain solution 2; S3, slowly dripping solution 2 into solution 1, after completely mixing, transferring the obtained mixed solution to a hydrothermal reactor lined with polytetrafluoroethylene, and placing the reactor in an oven for heating and reaction for a period of time; S4. After the reaction is completed, the reactor is cooled naturally to room temperature, and the solution after the reaction is transferred to a centrifuge tube for centrifugal washing, and then dried to obtain the product.

2. The method for preparing the two-dimensional tetracarboxylphenylporphyrin copper nanosheet material according to claim 1, characterized in that: The mixed solvent is composed of ethanol and N,N-dimethylformamide (DMF), and the volume ratio of ethanol to DMF is 1:

3.

3. The method for preparing the two-dimensional tetracarboxylphenylporphyrin copper nanosheet material according to claim 1, characterized in that: In step S3, the oven is heated to 70-100° C., and the reaction time is 2-6 hours.

4. The method for preparing the two-dimensional tetracarboxylphenylporphyrin copper nanosheet material according to claim 1, characterized in that: In step S4, the drying method is vacuum drying; the centrifugal washing method is: at room temperature, washing once with DMF, the washing time is 5 to 20 minutes, and the rotation speed is 8000 to 15000 rpm; and then washing at least twice with ethanol, the washing time is 5 to 20 minutes, and the rotation speed is 8000 to 15000 rpm.

5. The method for preparing the two-dimensional tetracarboxylphenylporphyrin copper nanosheet material according to claim 1, characterized in that: The prepared nanosheet material has a flat surface and a lateral size of 2 to 4 nm. Multiple layers of nanosheets are stacked to form a nano-deposit with a thickness of about 5 nm.

6. A photothermal pervaporation desalination membrane modified by two-dimensional tetracarboxylphenylporphyrin copper nanosheets, characterized in that: The preparation method is: (1) dissolving PVA and the tetracarboxylphenylporphyrin copper nanosheet material prepared according to any one of claims 1 to 5 in deionized water in a certain proportion, stirring at high temperature in an oil bath to obtain a uniform and stable PVA solution; (2) After the solution cools to room temperature, P(AA / AMPS) is added as a cross-linking agent, and magnetic stirring is performed at room temperature to obtain a uniform PVA casting solution; (3) After static degassing, the casting solution is coated on a substrate and a photothermal pervaporation desalination membrane is prepared by photothermal crosslinking.

7. The photothermal pervaporation desalination membrane modified by two-dimensional tetracarboxylphenylporphyrin copper nanosheets according to claim 6, characterized in that: The temperature in the oil bath is 80-100° C., and the substrate is a PMIA substrate.

8. The photothermal pervaporation desalination membrane modified by two-dimensional tetracarboxylphenylporphyrin copper nanosheets according to claim 6, characterized in that: The mass ratio of the PVA to the P(AA / AMPS) cross-linking agent is 7:

3.

9. The photothermal pervaporation desalination membrane modified by two-dimensional tetracarboxylphenylporphyrin copper nanosheets according to claim 6, characterized in that: The specific process of photothermal crosslinking is: using xenon lamp light source to irradiate for crosslinking reaction, and the light power of the xenon lamp light source is set to 0.4-0.8W·cm -2 , the distance between the light source and the film is 5 to 30 cm.

10. Use of the photothermal pervaporation desalination membrane according to any one of claims 6 to 9 in seawater desalination, brackish water desalination and saline wastewater treatment.

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