A cellulose-MOF photothermal film and its preparation method and application

Abstract

The present invention provides a cellulose MOF photothermal film and its preparation method and application. The preparation method of the cellulose MOF photothermal film of the present invention, with a fiber textile cloth as a substrate, forms a MOFs coating on the surface of the textile cloth fiber to form a ZIF 8 layer; based on the ZIF 8 layer, a polypyrrole layer is formed on its surface by vapor deposition to form a cellulose MOF photothermal film. The specific steps of the preparation method are as follows: (1) the fiber textile cloth is immersed in an aqueous solution of zinc nitrate, and after taking out the non-woven fabric, it is placed in a 2-methylimidazole solution and allowed to stand; (2) the cellulose textile cloth treated in step (1) is dried and immersed in an ammonium persulfate solution, the cellulose textile cloth modified with ammonium persulfate is taken out and dried and sealed in a container, and vaporized pyrrole is introduced into the container. The cellulose MOF photothermal film prepared by the method of the present invention effectively improves the evaporation performance of the photothermal composite film, and can be better applied to the preparation of solar absorption materials or evaporation systems / devices / equipment, etc.

Description

Technical Field

[0001] The present invention relates to the field of photothermal films, and in particular to a cellulose-MOF photothermal film and a preparation method and application thereof. Background Art

[0002] Through comprehensive research on solar-driven water evaporation and power generation, it can be found that as a new type of solar water evaporation system, solar energy, as a renewable energy source, does not consume additional energy while achieving water evaporation, and is a perfect clean energy source. While obtaining fresh water resources, the generation and utilization of energy brought by water evaporation has also attracted widespread attention from researchers around the world. Whether from the perspective of material selection or device structure design, it leaves a broad space for development in solving energy shortages and water treatment in the future. At present, there are still some problems in related research: (1) From the material aspect, there are many types of materials used for water evaporation, but there are not many materials that can combine evaporation and power generation at the same time; (2) Generators that can achieve efficient solar water evaporation and power generation at the same time are rare, and they still need to be designed from the perspective of materials or structure; (3) Most of the previous research focused on evaporation and power generation, ignoring the additional weak energy that may be brought by temperature in this process. Therefore, based on the above problems, the present invention develops a cellulose-MOF photothermal membrane. Summary of the Invention

[0003] In view of this, the present invention proposes a cellulose-MOF photothermal film and its preparation method and application, which effectively improves the evaporation performance of the photothermal composite film.

[0004] The technical solution of the present invention is achieved as follows:

[0005] A method for preparing a cellulose-MOF photothermal film comprises the following steps: using a fiber textile cloth as a substrate, forming a MOFs coating on the surface of the textile cloth fiber to form a ZIF-8 layer; based on the ZIF-8 layer, forming a polypyrrole layer on its surface by vapor deposition to form a cellulose-MOF photothermal film.

[0006] Furthermore, the specific steps of the preparation method are:

[0007] (1) Immerse the fiber textile fabric in a zinc nitrate aqueous solution, remove the non-woven fabric, and place it in a 2-methylimidazole solution for standing;

[0008] (2) Immersing the cellulose textile fabric treated in step (1) in an ammonium persulfate solution, taking out the ammonium persulfate-modified cellulose textile fabric and sealing it in a container, and introducing vaporized pyrrole into the container.

[0009] Furthermore, in step (1), the mass concentration of the zinc nitrate aqueous solution is 1%-20%, preferably 5-20%, and more preferably 5-10%.

[0010] Furthermore, in step (1), the soaking time is 0.5 to 1.5 hours.

[0011] Furthermore, in step (1), the concentration of the 2-methylimidazole solution is 0.01 to 0.02 mg / ml.

[0012] Furthermore, in step (1), the standing time is 20 to 30 hours.

[0013] Furthermore, the concentration of the ammonium persulfate solution is 0.4-0.6 mol / L.

[0014] A cellulose-MOF photothermal film is prepared by any preparation method described in the present invention.

[0015] A cellulose-MOF photothermal film consists of a cellulose substrate, a ZIF-8 layer and a polypyrrole layer, wherein the ZIF-8 layer is an intermediate water-transmitting layer and the polypyrrole layer is a surface light-absorbing layer.

[0016] The cellulose-MOF photothermal film of the present invention is used in preparing an evaporation system, device or equipment.

[0017] The cellulose-MOF photothermal film of the present invention is used in a solar absorber.

[0018] The cellulose-MOF photothermal film of the present invention is used in preparing a solar water evaporation system.

[0019] The cellulose-MOF photothermal film of the present invention is used in the preparation of solar energy absorption materials.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] (1) The present invention uses a fiber textile fabric as a substrate, a ZIF-8 layer grown by a two-step method as an intermediate water transport layer, and a polypyrrole layer grown by a vapor deposition method as an evaporator of a light absorption layer.

[0022] (2) The present invention controls the growth morphology of ZIF-8 by changing the reaction conditions, and utilizes the outstanding functional properties of MOF materials such as high porosity, large specific surface area, regular pores, and adjustable pore size, as well as the excellent photothermal conversion properties of polypyrrole. Scanning electron microscopy characterization of the ZIF-8 layer and the photothermal layer of the composite membrane shows that the growth of ZIF-8 particles makes the cellulose surface rough, and the nucleation effect is best in a zinc nitrate solution of about 5%.

[0023] (3) The present invention uses DSC measurement to compare the evaporation enthalpy of pure water. Combined with actual water evaporation tests, the evaporation effect of the ZIF-8 layer grown in 5% zinc nitrate solution is the best. The actual test results show that 1.63 kg m can be achieved under standard sunlight.-2 h -1 The stable planar evaporation rate of the cellulose composite membrane grown without ZIF-8 layer is 1.48 kg m-2 h-1. This may be because the coverage of polypyrrole weakens the ability of the intermediate layer to transport water.

[0024] (4) The present invention effectively improves the phase change process of water evaporation through reasonable pore design, thereby improving the evaporation performance of the photothermal composite membrane. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Scanning electron microscope images of ZIF-8 fiber textiles grown under different concentration conditions.

[0026] Figure 2 (a) Scanning electron microscope image of the fiber surface based on 5% zinc nitrate solution; (b) Scanning electron microscope image of the fiber surface after PPy coating.

[0027] Figure 3 (a) DSC curves of phase transition energy changes of different samples; (b) corresponding evaporation enthalpy.

[0028] Figure 4 Mass change curve of cellulose-MOF photothermal film. DETAILED DESCRIPTION

[0029] In order to better understand the technical content of the present invention, specific embodiments are provided below to further illustrate the present invention.

[0030] Unless otherwise specified, the experimental methods used in the examples of the present invention are all conventional methods.

[0031] Unless otherwise specified, the materials, reagents, etc. used in the examples of the present invention can be obtained from commercial sources.

[0032] A method for preparing a cellulose-MOF photothermal film comprises the following steps: using a fiber textile cloth as a substrate, forming a MOFs coating on the surface of the textile cloth fiber to form a ZIF-8 layer; based on the ZIF-8 layer, forming a polypyrrole layer on its surface by vapor deposition to form a cellulose-MOF photothermal film.

[0033] Specific steps:

[0034] (1) Immersing a non-woven fabric in a zinc nitrate aqueous solution (1 wt%-20 wt%) for 0.5-1.5 h, removing the non-woven fabric and placing it in a 2-methylimidazole solution (0.01-0.02 mg / ml) for 20-30 h, resulting in a dense and uniform MOFs coating on the surface of the treated fabric fiber, i.e., forming a ZIF-8 layer on the cellulose substrate;

[0035] (2) Immersing the cellulose textile fabric treated in step (1) in a 0.4-0.6 mol / L ammonium persulfate solution, taking out the ammonium persulfate-modified cellulose textile fabric, drying it, and sealing it in a container, introducing vaporized pyrrole into the container, and allowing polypyrrole to grow and polymerize on the surface of the ammonium persulfate-modified cellulose fabric.

[0036] Example

[0037] 1. Preparation of Cellulose-MOF Photothermal Film

[0038] 1.1 Experimental Materials and Methods

[0039] 1.1.1 Experimental instruments

[0040] Table 1 Experimental instruments

[0041]

[0042] 1.1.2 Experimental Reagents

[0043] Table 2 Experimental reagents

[0044]

[0045] 1.1.3 Experimental steps (1) Growth of ZIF-8

[0046] The growth of ZIF-8 mainly involves two processes: (1) the formation of nucleation sites on the fiber textile; and (2) the nucleation and crystallization process.

[0047] In order to construct in situ grown ZIF-8 fiber textiles,

[0048] In the first stage, the fiber textile was immersed in an aqueous solution of zinc nitrate for 1 h. Without obvious MOF crystals on the surface, metal coordination ions were first introduced, which may form nucleation sites.

[0049] In the second stage, the nonwoven fabric from the first stage was taken out and placed in a 2-methylimidazole solution (0.01315 mg / ml) and allowed to stand for 24 h. Crystals formed on the fibers of the woven fabric, and their size increased with the incubation time.

[0050] A zinc nitrate solution with gradient concentrations of 0%, 1%, 5%, 10%, 15%, and 20% by mass was set to produce nucleation sites of different densities.

[0051] Surface scanning electron microscopy (SEM) images Figure 1 As shown, there is a dense and uniform MOFs coating on the surface of the treated textile fibers.

[0052] (2) Growth of polypyrrole layer

[0053] Based on the successful growth of ZIF-8, the polymerization growth of polypyridine by vapor deposition on the surface of cellulose textile fabric coated with MOFs mainly involves four processes:

[0054] (i) immersing the cellulose textile fabric coated with MOFs in step (1) into an ammonium persulfate solution;

[0055] (ii) adsorption of ammonium persulfate onto the cellulose backbone during drying;

[0056] (iii) vaporized pyrrole (monomer) is introduced into a sealed container of ammonium persulfate-modified cellulose woven cloth;

[0057] Finally (iv) growth and polymerization of polypyrrole on the ammonium persulfate-modified cellulose surface.

[0058] Due to the lack of solvent at this time, the pyrrole monomer vapor has good flow permeability. In addition, the presence of a large number of hydroxyl groups on the cellulose surface also facilitates the adsorption of ammonium persulfate and pyrrole monomers. Therefore, the polymerization vapor phase growth generally has higher continuity and chemical purity than the solution environment synthesis, providing continuous channel electron transport for in-plane synthesis.

[0059] 1.2 Experimental Results

[0060] 1.2.1 Pore Design and Control of Cellulose-MOF Photothermal Membranes

[0061] According to the above ZIF-8 growth mode, a number of composite membranes with nucleation in different environments were prepared, such as Figure 1 Scanning electron microscopy shows that ZIF-8 grows continuously on cellulose. In a low concentration of zinc nitrate solution (1%), the cellulose surface cannot form enough nucleation sites, so the nucleated ZIF-8 particles are relatively sparse. When the concentration of zinc nitrate reaches 5%, the cellulose surface adsorbs enough metal coordination ions, and the dense nucleation sites allow ZIF-8 to wrap around the fiber. As the concentration of zinc nitrate gradually increases, Figure 1 d. Figure 1 e. Figure 1 As shown in (f), ZIF-8 particles accumulate on the cellulose surface.

[0062] 1.2.2 Morphology analysis of cellulose-MOF photothermal film

[0063] like Figure 2 As shown, the scanning electron microscope image of the fiber surface based on 5% zinc nitrate solution shows that the smoothness of the fiber surface is changed due to the growth of ZIF-8, and the fiber surface becomes rough after the growth of ZIF-8. Figure 2Figure b shows the fiber composite membrane after polypyrrole coating. The fiber composite membrane now consists of three layers: a cellulose substrate, a ZIF-8 intermediate water-transmitting layer, and a surface polypyrrole layer that acts as a light-absorbing layer. The polypyrrole coating reduces the roughness of the fiber surface caused by ZIF-8, thereby forming a complete cellulose-MOF photothermal membrane.

[0064] 1.2.3 DSC test of cellulose-MOF photothermal film

[0065] According to the different growth levels of ZIF-8 cellulose membrane (Mx%), the cellulose photothermal membranes prepared by covering polypyrrole again were named C@M 0％ P, C@M 1％ P, C@M 5％ P, C@M 10％ P, C@M 15％ P, C@M 20％ P, where the photothermal film grown without ZIF-8 is named C@M 0％ P. Differential scanning calorimetry (DSC) is a technique used to measure the thermodynamic properties of substances, which can represent the energy changes involved in the evaporation of water. Figure 3 The DSC measurement results of the composite films with different parameters are shown. It can be seen that the lowest evaporation enthalpy is 2190 J g -1 , and the evaporation enthalpy of pure water is about 2227 J g -1 The evaporation enthalpy of water in the cellulose photothermal film without ZIF-8 as the intermediate layer is 2275 J g -1 This shows that the evaporation enthalpy of water on the composite membrane can be reduced by suitable growth conditions, which is of great value for improving the water evaporation rate.

[0066] The water evaporation performance of cellulose-MOF photothermal films with different ZIF-8 growth morphologies is different. A xenon lamp light source is used to simulate the full spectrum of sunlight, and then a full-spectrum intensity light power meter is used to calibrate the intensity of the light source to maintain a sunlight intensity of 100mW cm -2 Before each measurement, the light source needs to be stabilized for 30 minutes to ensure the stability and accuracy of the measurement data. The electronic balance is connected to the software on the computer to record the evaporation process of water in real time and analyze the mass change data. Figure 4 The actual evaporation performance of the system can be evaluated. 5％ P has the best water evaporation performance, which is consistent with the previous DSC test results, indicating that ZIF-8 acts as an intermediate layer for water transmission and increases the evaporation rate of the cellulose-MOF photothermal film by reducing the evaporation enthalpy of water.

[0067] 1.3 Summary

[0068] In the invention, an evaporator is mainly provided with a fiber textile cloth as a substrate, a ZIF-8 layer grown by a two-step method as an intermediate water transport layer, and a polypyrrole layer grown by a vapor deposition method as a light absorption layer. By changing the reaction conditions to control the growth morphology of ZIF-8, and utilizing the functional properties of MOF materials such as high porosity, large specific surface area, regular pores, and adjustable pore size, and the photothermal conversion properties of polypyrrole, the ZIF-8 layer and the photothermal layer of the composite membrane were characterized by scanning electron microscopy, which showed that the growth of ZIF-8 particles made the cellulose surface rough, and the nucleation effect was best in a zinc nitrate solution of about 5%. And by comparing the evaporation enthalpy of pure water through DSC measurement, combined with the actual water evaporation test, the ZIF-8 layer grown in a 5% zinc nitrate solution had the best evaporation effect. The actual test results showed that 1.63 kg m -2 h -1 The evaporation rate of the polypyrrole is significantly reduced, which may be due to the fact that the polypyrrole coating weakens the ability of the intermediate layer to transport water. The present invention effectively improves the phase change process of water evaporation through reasonable pore design, thereby improving the evaporation performance of the photothermal composite membrane.

[0069] In addition, based on the embodiment of the present invention, the immersion time is 0.5-1.5h, the concentration of the 2-methylimidazole solution is 0.01-0.02mg / ml, the standing time is 20-30h, and the concentration of the ammonium persulfate solution is 0.4-0.6mol / L. Adjustments within the above solution concentration range or time range can achieve the purpose of the present invention.

[0070] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A cellulose-MOF photothermal film, characterized in that: The preparation method of the cellulose-MOF photothermal film uses a fiber textile cloth as a substrate, forms a MOFs coating on the surface of the textile cloth fiber to form a ZIF-8 layer; based on the ZIF-8 layer, a polypyrrole layer is formed on its surface by vapor deposition to form a cellulose-MOF photothermal film; The specific steps of the preparation method of the cellulose-MOF photothermal film are as follows: (1) Immerse the fiber textile fabric in a zinc nitrate aqueous solution, take out the non-woven fabric and place it in a 2-methylimidazole solution and let it stand; (2) immersing the cellulose textile fabric treated in step (1) in an ammonium persulfate solution, taking out the ammonium persulfate-modified cellulose textile fabric and sealing it in a container, and introducing the vaporized pyrrole into the container; In step (1), the mass concentration of the zinc nitrate aqueous solution is 1%-20%, and the soaking time is 0.5-1.5 h. The concentration of the 2-methylimidazole solution is 0.01-0.02 mg / ml, and the standing time is 20-30 h; In step (2), the concentration of the ammonium persulfate solution is 0.4-0.6 mol / L; The cellulose-MOF photothermal film consists of a cellulose substrate, a ZIF-8 layer and a polypyrrole layer, wherein the ZIF-8 layer is an intermediate water-transmitting layer and the polypyrrole layer is a surface light-absorbing layer.

2. The cellulose-MOF photothermal film according to claim 1 is used in the preparation of solar energy absorption materials or evaporation systems / devices / equipment.

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