Flexible Cu2O-Cu-C composite nanofiber membrane as well as preparation method and application thereof

Abstract

The invention relates to the technical field of functional materials, in particular to a flexible Cu2O-Cu-C composite nanofiber membrane and a preparation method and application thereof.The preparation method includes the following steps that firstly, copper acetate and PAN are dissolved in a solvent to obtain an electrostatic spinning solution, the mass fraction of the PAN in the spinning solution is 7-9%, and the mass ratio of the copper acetate to the PAN is (1.9-2.5): 7; 2, obtaining a PAN / Cu < 2 + > nanofiber membrane by adopting the electrostatic spinning solution in the step 1 through an electrostatic spinning process; 3, carrying out heat treatment on the PAN / Cu < 2 + > nanofiber membrane; step 4, pre-oxidizing and carbonizing the PAN / Cu < 2 + > nanofiber membrane subjected to heat treatment to prepare a Cu2O-Cu-C nanofiber membrane; and step 5, carrying out hydrophilic treatment on the Cu2O-Cu-coated C nanofiber membrane, so as to obtain the hydrophilic flexible Cu2O-Cu-coated C nanofiber membrane. The preparation method disclosed by the invention is simple, low in energy consumption in the preparation process, low in equipment requirement, low in toxicity and free of potential safety hazards, is sufficient in moisture supplement in the aspect of light-heat water evaporation, can be recycled and has a very good practical application prospect.

Description

Technical Field

[0001] The present invention relates to the technical field of functional materials, and in particular to a flexible Cu2O-Cu@C composite nanofiber membrane and its preparation method and application. Background Art

[0002] Due to the global water shortage, solar-driven clean water production has proven to be one of the most promising strategies to alleviate global fresh water because of its green solar energy, low cost, and simple operating system. So far, plasmonic metals (such as Au, Ag), semiconductors (such as CuO, NiO), polymer materials (such as polypyrrole, polydopamine), and carbon-based materials are the main photothermal materials for solar-driven evaporation to produce clean water from brine and polluted wastewater. Among them, carbon-based materials are widely used as photothermal materials because of their high solar absorption ability in a broad spectrum.

[0003] Carbon nanofiber membranes obtained by carbonizing polyacrylonitrile (PAN) have been prepared in large quantities and used in energy generation, energy storage, and water treatment. Electrospinning nanofibers and then carbonizing them is a low-cost and simple method (Hydrophobic and porous carbon nanofiber membrane for high performance solar-driven interfacial evaporation with excellent salt resistance, J. Colloid. Interf. Sci. 612 (2022) 66-75.). However, when PAN-based carbon nanofiber membranes are used in multiple fields such as clean water carbon nanofiber membrane evaporators for a long time, their poor mechanical properties and brittleness seriously damage the dimensional stability of the materials.

[0004] Currently, the evaporation rate of the prepared membrane materials is low (Janus MXene-based photothermal membrane for efficient and durable water evaporation, Desalination (2023).) Moreover, most flexible carbon nanofibers are used in fields such as electrode capacitors, and there are few applications in the field of solar-driven water evaporation. The carbon nanofiber membranes used in the field of photothermal water evaporation are mostly hydrophobic membranes, with insufficient water replenishment and low photothermal water evaporation rate.

[0005] As in the existing patent, Chinese Patent CN201911007671.X discloses a photothermal conversion thin film and its preparation method and a double-layer evaporation structure for solar steam generation. The evaporation rate of the prepared photothermal conversion thin film is 1.19 kg·m -2·h -1 , the evaporation rate is not high. Chinese Patent CN201910328996.1 discloses a flexible silicon carbide / carbon nanofiber composite fiber membrane material, its preparation method and application. During the preparation of the flexible silicon carbide / carbon nanofiber composite fiber membrane, the reaction temperature is 1400 °C. A reaction temperature of 1400 °C requires high equipment requirements, and the energy consumption and cost are relatively large during use, and there are safety hazards, which also limits the promotion of actual large-scale production.

[0006] Therefore, how to develop carbon nanofiber membranes applied in photothermal water evaporation, making them have characteristics such as good flexibility, good mechanical properties, sufficient water replenishment, and recyclability is an issue that needs attention currently. Summary of the Invention

[0007] In view of this, the purpose of the present invention is to propose a flexible Cu2O-Cu@C composite nanofiber membrane, its preparation method and application, to solve the problems of low evaporation rate and high cost of the membrane materials prepared in the prior art. The preparation method of the nanofiber membrane prepared by the present invention is simple, and it has characteristics such as good flexibility, recyclability, relatively high evaporation rate, and low cost.

[0008] Based on the above purpose, the present invention provides a preparation method of a flexible Cu2O-Cu@C composite nanofiber membrane, including the following steps:

[0009] Step 1: Dissolve copper acetate and PAN in a solvent to obtain an electrospinning solution, wherein the mass fraction of PAN in the spinning solution is 7-9%, and the mass ratio of copper acetate to PAN is 1.9-2.5:7;

[0010] Step 2: Use the electrospinning solution of Step 1 to obtain a PAN / Cu 2+ nanofiber membrane through the electrospinning process;

[0011] Step 3: Heat-treat the PAN / Cu 2+ nanofiber membrane;

[0012] Step 4: Pre-oxidize and carbonize the heat-treated PAN / Cu 2+ nanofiber membrane to prepare a Cu2O-Cu@C nanofiber membrane;

[0013] Step 5: Perform hydrophilic treatment on the Cu2O-Cu@C nanofiber membrane to obtain a hydrophilic flexible Cu2O-Cu@C nanofiber membrane.

[0014] Preferably, the mass fraction of PAN in the spinning solution in Step 1 is 8%. The solvent is N,N-dimethylformamide (DMF) solvent.

[0015] Preferably, the copper acetate described in Step 1 is anhydrous copper acetate, and the mass ratio of anhydrous copper acetate to PAN is 2:7.

[0016] Preferably, the spinning conditions of the electrospinning process described in Step 2 are as follows: the voltage is 16 kV, the spinning flow rate is 1.1 - 1.3 mL / h, the temperature is 23 - 27 °C, the relative humidity is 34 - 40%, the receiving distance is 15 cm, and the spinning disk rotation speed is 10 - 15 r / min.

[0017] Preferably, the heat treatment described in Step 3 is to subject the PAN / Cu 2+ nanofiber membrane obtained in Step 2 to treatment at a temperature of 118 - 125 °C for 15.5 - 16.5 h, and then naturally cooled. The steps of the heat treatment are to eliminate the internal stress and residual solvent in the nanofibers to improve the structural uniformity of the nanofibers.

[0018] Preferably, the pre-oxidation carbonization described in Step 4 is to first heat the heat-treated PAN / Cu 2+ nanofiber membrane at a rate of 3 °C / min to 220 °C and hold for 90 min; then heat it to 300 - 500 °C at a rate of 5 °C / min under the protection of an inert gas and hold for 2 h, and then naturally cool to room temperature.

[0019] Preferably, the method of hydrophilic treatment described in Step 5 includes the following steps:

[0020] S1. Dissolve chitosan and acetic acid in water to prepare Solution D with a chitosan mass fraction of 2% and an acetic acid volume fraction of 2%; mix 2.5% glutaraldehyde by mass and 10% PVA aqueous solution in a volume ratio of 1:10, and stir and dissolve at 100 °C to form Solution E;

[0021] S2. Mix Solution D and Solution E in a volume ratio of 1:1 under normal conditions, then soak the Cu2O-Cu@C nanofiber membrane in the mixed solution at room temperature, and then perform cyclic freezing and thawing.

[0022] Preferably, for the preparation of Solution D: Add 0.1 g of chitosan and 0.1 mL of acetic acid (acetic acid concentration is 99.9%) to 5 mL of deionized water and stir at room temperature for 90 min to form Solution D.

[0023] For the preparation of Solution E: Add 0.5 g of PVA to 5 mL of deionized water, stir at 100 °C for 60 min to obtain a 10% PVA aqueous solution, and then add 0.25 mL of 2.5% glutaraldehyde and continue to stir for 30 min to form Solution E.

[0024] Preferably, the soaking time in S2 is 9.5 - 10.5 h, the number of cycles of freezing and thawing is three, the freezing time each time is 10 h, the freezing temperature is -20 °C, and the thawing time is 2 h.

[0025] The present invention also provides a flexible Cu2O-Cu@C composite nanofiber membrane, which is prepared by using the preparation method of the flexible Cu2O-Cu@C composite nanofiber membrane.

[0026] The present invention also provides the application of the flexible Cu2O-Cu@C composite nanofiber membrane in the production of clean water driven by solar energy.

[0027] Advantages of the present invention: The hydrophilic flexible Cu2O-Cu@C composite nanofiber membrane prepared by the present invention has excellent flexible characteristics and hydrophilicity, and has a high evaporation rate for different dye wastewaters and seawater. The preparation method of the present invention is simple, the energy consumption during the preparation process is low, the requirements for equipment are low, the toxicity is small, there is no safety hazard, and the water supplement is sufficient for solar-thermal water evaporation and can be recycled, having good practical application prospects. Description of the Drawings

[0028] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only those of the present invention. For those of ordinary skill in the art, other drawings can also be obtained based on these drawings without creative efforts.

[0029] Figure 1 It is a schematic diagram of the preparation process of the present invention;

[0030] Figure 2a It is a PAN / Cu 2+ nanofiber membrane;

[0031] Figure 2b It is a PAN / Cu 2+ heat-treated nanofiber membrane;

[0032] Figure 2c It is a Cu2O-Cu@C nanofiber membrane;

[0033] Figure 2d It is a hydrophilic flexible Cu2O-Cu@C composite nanofiber membrane;

[0034] Figure 2e It is a nanofiber membrane with anhydrous copper acetate:PAN = 0:7;

[0035] Figure 2f It is a Cu2O-Cu@C nanofiber membrane with anhydrous copper acetate:PAN = 4:7;

[0036] Figure 2g It is a Cu2O-Cu@C nanofiber membrane with anhydrous copper acetate:PAN = 6:7;

[0037] Figure 3a It is PAN / Cu 2+ SEM image of the nanofiber membrane;

[0038] Figure 3b It is PAN / Cu 2+ SEM image of the heat-treated nanofiber membrane;

[0039] Figure 3c It is the SEM image of the Cu2O-Cu@C nanofiber membrane carbonized at 300 °C;

[0040] Figure 3d It is the SEM image of the Cu2O-Cu@C nanofiber membrane carbonized at 400 °C;

[0041] Figure 3e It is the SEM image of the Cu2O-Cu@C nanofiber membrane carbonized at 500 °C;

[0042] Figure 3f It is the SEM image of the nanofiber membrane with anhydrous copper acetate:PAN = 0:7;

[0043] Figure 3g It is the SEM image of the Cu2O-Cu@C nanofiber membrane with anhydrous copper acetate:PAN = 4:7;

[0044] Figure 3h It is the SEM image of the Cu2O-Cu@C nanofiber membrane with anhydrous copper acetate:PAN = 6:7;

[0045] Figure 4 It is the flexibility display diagram of the Cu2O-Cu@C nanofiber membrane in Example 2 of the present invention;

[0046] Figure 5 It is the schematic diagram of the cyclic photo-thermal water evaporation rate of the Cu2O-Cu@C nanofiber membrane in Example 2 of the present invention;

[0047] Figure 6 It is the cyclic photo-thermal water evaporation rate of the hydrophilic flexible Cu2O-Cu@C composite nanofiber membrane in Example 2 of the present invention.

[0048] Figure 7 It is the stress-strain curve diagram of the Cu2O-Cu@C nanofiber membrane in Example 2 of the present invention and the carbonized membrane without doped copper acetate in Comparative Example 1. Detailed implementation manners

[0049] To make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below in conjunction with specific embodiments.

[0050] It should be noted that, unless otherwise defined, the technical terms or scientific terms used in the present invention should have the ordinary meanings understood by those with ordinary skills in the field to which the present invention belongs. Words such as "including" or "comprising" and the like mean that the elements or objects appearing before this word cover the elements or objects listed after this word and their equivalents, without excluding other elements or objects.

[0051] Example 1

[0052] In this example, 0.2285 grams of anhydrous copper acetate, 0.8 grams of PAN, and 10 grams of DMF were weighed into a 20 ml glass bottle and continuously stirred at 50 °C to obtain a blue transparent spinning solution A.

[0053] The spinning solution A was poured into a syringe ( Figure 1 ). The spinning parameters were adjusted as follows: spinning voltage 16 kV, receiving distance 15 cm. The rotation speed of the needle disk was 12 r / min. The spinning flow rate was 1.2 mL / h. The temperature was 25 ± 2 °C. The relative humidity was 37 ± 3%. PAN / Cu 2+ nano-fiber membrane B ( Figure 2a ) was obtained. It can be seen from SEM Figure 3a that the fiber surface is smooth and the fiber diameters are relatively uniform.

[0054] The PAN / Cu 2+ nano-fiber membrane was placed in an oven at a temperature of 120 °C for 16 h. It was cooled naturally to obtain a heat-treated membrane C of PAN / Cu 2+ nano-fiber membrane ( Figure 2b ). It can be seen from SEM Figure 3b that the fiber diameters are uniform.

[0055] The PAN / Cu 2+ nano-fiber membrane was cut to an appropriate size, clamped between quartz plates, and placed in a tubular carbonization furnace for pre-oxidation. The specific parameters of the pre-oxidation process were set as follows: the initial temperature was 50 °C, the temperature was raised at a rate of 3 °C / min, held at 90 °C for 30 min, then raised to 220 °C and held for 90 min. After the pre-oxidation was completed, it was cooled naturally to room temperature to obtain a pre-oxidized membrane. The pre-oxidized nano-fiber membrane was subjected to a carbonization process to obtain a Cu2O-Cu@C nano-fiber membrane. The specific parameters of the carbonization process were as follows: First, nitrogen was introduced, the temperature was raised to 300 °C at a rate of 5 °C / min, held for 120 min, and then cooled naturally to room temperature and taken out to obtain a carbonized membrane; it can also be seen from its SEM image that the carbon membrane fibers are evenly distributed ( Figure 3c ).

[0056] In the pre-oxidation stage, not only the heat resistance of PAN nanofibers was improved, but also the residual copper acetate was converted into Cu2O; part of the Cu2O was converted into Cu at an appropriate carbonization temperature. The obtained carbon nanofiber membrane has a certain flexibility ( Figure 4 ).

[0057] 0.1 g of chitosan and 0.1 mL of acetic acid (concentration 99.9%) were added to 5 mL of deionized water and stirred at room temperature for 90 min to form solution D. 0.5 g of PVA was added to 5 mL of deionized water, and stirred at 100 °C for 60 min to obtain a 10% PVA aqueous solution. Then, 0.25 mL of 2.5% glutaraldehyde was added and stirred for another 30 min to form solution E. Solution D and solution E were mixed evenly at room temperature to obtain solution F. Then, the Cu2O-Cu@C nanofiber membrane was immersed in the mixed solution at room temperature, and after 10 min, it was put into the refrigerator for freezing (-20 °C)

[0058] for 10 h, and then thawed in deionized water at room temperature for 2 h, and this cycle was repeated three times to obtain a hydrophilic flexible Cu2O-Cu@C composite nanofiber membrane.

[0059] The obtained carbon membrane and the Cu2O-Cu@C nanofiber membrane attached with a hydrogel membrane were respectively subjected to photothermal water evaporation tests. The obtained carbon membrane and the hydrophilic flexible Cu2O-Cu@C composite nanofiber membrane can be reused, and the water evaporation rate of the carbon membrane is 1.3 kg·m -2 ·h -1 , and the water evaporation rate of the Cu2O-Cu@C nanofiber membrane attached with a hydrogel membrane is 1.51 kg·m -2 ·h -1 . The materials prepared in this example show broad application prospects in the field of photothermal water evaporation.

[0060] Example 2

[0061] In this example, 0.2285 g of anhydrous copper acetate, 0.8 g of PAN, and 10 g of DMF were weighed and placed in a 20 ml glass bottle, and continuously stirred at 50 °C to obtain a blue transparent spinning solution A.

[0062] The spinning solution A was poured into a syringe ( Figure 1 ). The spinning parameters were adjusted as follows: spinning voltage 16 kV, receiving distance 15 cm. The rotation speed of the needle disk was 12 r / min. The temperature was 25 ± 2 °C. The relative humidity was 37 ± 3%. PAN / Cu 2+ nanofiber membrane B ( Figure 2a ) was obtained. It can be seen from the SEM Figure 3a that the fiber surface is smooth and the fiber diameter is relatively uniform.

[0063] The PAN / Cu 2+The nanofiber membrane was placed in an oven at a temperature of 120 °C for 16 h. It was cooled naturally to obtain PAN / Cu 2+ Heat-treated nanofiber membrane C( Figure 2b ). It can be seen from SEM Figure 3b that the fiber diameters are uniform.

[0064] The PAN / Cu 2+ nanofiber membrane was cut into an appropriate size, clamped between quartz plates, and placed in a tubular carbonization furnace for pre-oxidation. The specific parameters of the pre-oxidation process were set with an initial temperature of 50 °C, heated at a rate of 3 °C / min, held at 90 °C for 30 min, then heated to 220 °C and held for 90 min. After the pre-oxidation, it was cooled naturally to room temperature to obtain a pre-oxidized membrane. The pre-oxidized nanofiber membrane was subjected to a carbonization process to obtain a Cu2O-Cu@C nanofiber membrane. First, nitrogen was introduced, heated to 400 °C at a rate of 5 °C / min, held for 120 min, and then cooled naturally to room temperature and taken out( Figure 2c , 3d).

[0065] In the pre-oxidation stage, not only the heat resistance of PAN nanofibers was improved, but also the residual copper acetate was converted into Cu2O; part of the Cu2O was converted into Cu at an appropriate carbonization temperature. The obtained carbon nanofiber membrane has a certain flexibility. When bent, the stress is concentrated at the weak interface between C atoms. The doped Cu2O-Cu@C nanofiber membrane forms Cu2O and Cu inside the nanofibers; Cu2O and Cu can form a chain structure through the bridging effect, improving the interfacial interaction between C skeletons. Due to the enhanced interfacial interaction and structural densification, the obtained Cu2O-Cu@C nanofiber membrane can dissipate external energy through stress transfer to prevent the C chains from slipping and structural damage when subjected to pulling and compression, making the obtained Cu2O-Cu@C nanofiber membrane have strong mechanical properties and flexibility.

[0066] 0.1 g of chitosan and 0.1 mL of acetic acid (concentration of 99.9%) were added to 5 mL of deionized water and stirred at room temperature for 90 min to form solution D. 0.5 g of PVA was added to 5 mL of deionized water, stirred at 100 °C for 60 min to obtain a 10% PVA aqueous solution, and then 0.25 mL of 2.5% glutaraldehyde was added and stirred for another 30 min to form solution E. Solution D and solution E were mixed evenly at room temperature to obtain solution F. Then, the Cu2O-Cu@C nanofiber membrane was soaked in the mixed solution at room temperature, and after 10 min, it was placed in a refrigerator and frozen (-20 °C)

[0067] for 10 h, and then thawed in deionized water at room temperature for 2 h, and this cycle was repeated three times to obtain a hydrophilic flexible Cu2O-Cu@C composite nanofiber membrane( Figure 2d ).

[0068] The obtained carbon film and the Cu2O-Cu@C nanofiber film-attached hydrogel film were respectively subjected to photothermal water evaporation tests ( Figure 5 and Figure 6 ). As shown in the figure, both the obtained carbon film and the hydrophilic flexible Cu2O-Cu@C composite nanofiber film can be recycled, and the water evaporation efficiency is greater than 1.5 kg·m -2 ·h -1 . The present invention not only exhibits flexibility but also mentions the mechanism of flexibility. The water evaporation efficiency of the carbon film is 1.57 kg·m -2 ·h -1 , and the evaporation rate of the hydrophilic flexible Cu2O-Cu@C composite nanofiber film reaches 1.76 kg·m -2 ·h -1 , showing broad application prospects.

[0069] Example 3

[0070] In this example, 0.2285 g of anhydrous copper acetate, 0.8 g of PAN, and 10 g of DMF were weighed into a 20 ml glass bottle and continuously stirred at 50 °C to obtain a blue transparent spinning solution A.

[0071] The spinning solution A was poured into a syringe ( Figure 1 ). The spinning parameters were adjusted as follows: spinning voltage 16 kV, receiving distance 15 cm. The needle disk rotation speed was 12 r / min. The temperature was 25 ± 2 °C. The relative humidity was 37 ± 3%. PAN / Cu 2+ nanofiber membrane B ( Figure 2a ) was obtained. It can be seen from SEM Figure 3a that the fiber surface is smooth and the fiber diameters are relatively uniform.

[0072] The PAN / Cu 2+ nanofiber membrane was placed in an oven at a temperature of 120 °C for 16 h. After natural cooling, PAN / Cu 2+ nanofiber membrane heat-treated membrane C ( Figure 2b ) was obtained. It can be seen from SEM Figure 3b that the fiber diameters are uniform.

[0073] The PAN / Cu 2+The nanofiber membrane was cut to an appropriate size, sandwiched between quartz plates, and placed in a tubular carbonization furnace for pre-oxidation. The specific parameters of the pre-oxidation process were set with an initial temperature of 50 °C, heated at a rate of 3 °C / min, held at 90 °C for 30 min, then heated to 220 °C and held for 90 min. After the pre-oxidation, it was naturally cooled to room temperature to obtain the pre-oxidized membrane. The pre-oxidized nanofiber membrane was subjected to a carbonization process to obtain a Cu2O-Cu@C nanofiber membrane. First, nitrogen was introduced, heated to 500 °C at a rate of 5 °C / min, held for 120 min, and then naturally cooled to room temperature and taken out. It can also be seen from its SEM images that the fiber distribution is uniform ( Figure 3e ).

[0074] 0.1 g of chitosan and 0.1 mL of acetic acid (concentration 99.9%) were added to 5 mL of deionized water and stirred at room temperature for 90 min to form solution D. 0.5 g of PVA was added to 5 mL of deionized water, stirred at 100 °C for 60 min to obtain a 10% PVA aqueous solution, and then 0.25 mL of 2.5% glutaraldehyde was added and stirred for another 30 min to form solution E. At room temperature, solution D and solution E were mixed evenly to obtain solution F. Then, the Cu2O-Cu@C nanofiber membrane was immersed in the mixed solution at room temperature. After 10 min, it was placed in a refrigerator and frozen (-20 °C) for 10 h, and then thawed in room temperature deionized water for 2 h. This cycle was repeated three times to obtain a hydrophilic flexible Cu2O-Cu@C composite nanofiber membrane.

[0075] The obtained carbon membrane and Cu2O-Cu@C nanofiber membrane were subjected to a solar-thermal water evaporation test. The solar-thermal water evaporation rate of the obtained carbon membrane was 1.48 kg·m -2 ·h -1 , and the solar-thermal water evaporation rate of the Cu2O-Cu@C nanofiber membrane was 1.61 kg·m -2 ·h -1 . It shows broad application prospects.

[0076] Comparative Example 1

[0077] In this comparative example, 0 g of anhydrous copper acetate, 0.8 g of PAN, and 10 g of DMF were weighed and placed in a 20 ml glass bottle, and continuously stirred at 50 °C to obtain a blue transparent spinning solution A. The spinning solution A was poured into a syringe ( Figure 1 ). The spinning parameters were adjusted as follows: spinning voltage 16 kV, receiving distance 15 cm. The needle plate rotation speed was 12 r / min. The temperature was 25 ± 2 °C. The relative humidity was 37 ± 3%. A nanofiber membrane B was obtained.

[0078] The nanofiber membrane B was placed in an oven at a temperature of 120 °C for 16 h. It was naturally cooled to obtain a heat-treated membrane C of PAN nanofiber membrane.

[0079] Cut the PAN nanofiber membrane into an appropriate size, sandwich it between quartz plates, and place it in a tubular carbonization furnace for pre-oxidation. The specific parameters of the pre-oxidation process are as follows: set the initial temperature at 50 °C, increase the temperature at a rate of 3 °C / min, hold the temperature at 90 °C for 30 min, then increase the temperature to 220 °C and hold for 90 min. After the pre-oxidation is completed, cool it naturally to room temperature to obtain the pre-oxidized membrane. Carry out the carbonization process on the pre-oxidized nanofiber membrane to obtain the carbon nanofiber membrane. First, introduce nitrogen, increase the temperature to 400 °C at a rate of 5 °C / min, hold for 120 min, and then cool it naturally to room temperature and take it out ( Figure 2e ). It can be seen from Figure 2e that the carbon content of the obtained carbon film is very low, which is not conducive to the subsequent photo-thermal water evaporation experiment. Many broken fibers can also be seen in its SEM image ( Figure 3f ).

[0080] Comparative Example 2

[0081] In this comparative example, weigh 0.4571 g of anhydrous copper acetate, 0.8 g of PAN, and 10 g of DMF into a 20 ml glass bottle, and continuously stir at 50 °C to obtain a blue transparent spinning solution A. Pour the spinning solution A into a syringe ( Figure 1 ). Adjust the spinning parameters as follows: spinning voltage 16 kV, receiving distance 15 cm. The needle disk rotation speed is 12 r / min. The temperature is 25 ± 2 °C. The relative humidity is 37 ± 3%. Obtain the PAN / Cu 2+ nanofiber membrane B.

[0082] Put the PAN / Cu 2+ nanofiber membrane into an oven at a temperature of 120 °C for 16 h. Cool it naturally to obtain the heat-treated membrane C of the PAN / Cu 2+ nanofiber membrane. Cut the PAN / Cu 2+ nanofiber membrane into an appropriate size, sandwich it between quartz plates, and place it in a tubular carbonization furnace for pre-oxidation. The specific parameters of the pre-oxidation process are as follows: set the initial temperature at 50 °C, increase the temperature at a rate of 3 °C / min, hold the temperature at 90 °C for 30 min, then increase the temperature to 220 °C and hold for 90 min. After the pre-oxidation is completed, cool it naturally to room temperature to obtain the pre-oxidized membrane. Carry out the carbonization process on the pre-oxidized nanofiber membrane to obtain the Cu2O-Cu@C nanofiber membrane. First, introduce nitrogen, increase the temperature to 400 °C at a rate of 5 °C / min, hold for 120 min, and then cool it naturally to room temperature and take it out ( Figure 2f ). It can be seen from Figure 2f that there are cracks in the Cu2O-Cu@C nanofiber membrane, indicating that its flexibility is insufficient and it is even less conducive to subsequent utilization. Many broken fibers can also be seen in its SEM image ( Figure 3g ).

[0083] Comparative Example 3

[0084] In this comparative example, 0.6857 g of anhydrous copper acetate, 0.8 g of PAN, and 10 g of DMF were weighed and placed in a 20 ml glass bottle, and continuously stirred at 50 °C to obtain a blue transparent spinning solution A. The spinning solution A was poured into a syringe ( Figure 1 ). The spinning parameters were adjusted as follows: spinning voltage 16 kV, receiving distance 15 cm. The needle disk rotation speed was 12 r / min. The temperature was 25 ± 2 °C. The relative humidity was 37 ± 3%. PAN / Cu 2+ nano fiber membrane B was obtained.

[0085] The PAN / Cu 2+ nano fiber membrane was placed in an oven at a temperature of 120 °C for 16 h. It was cooled naturally to obtain the heat-treated membrane C of PAN / Cu 2+ nano fiber membrane. The PAN / Cu 2+ nano fiber membrane was cut to an appropriate size, clamped between quartz plates, and placed in a tubular carbonization furnace for pre-oxidation. The specific parameters of the pre-oxidation process were set as follows: the initial temperature was 50 °C, the temperature was raised at a rate of 3 °C / min, held at 90 °C for 30 min, then raised to 220 °C and held for 90 min. After pre-oxidation, it was cooled naturally to room temperature to obtain a pre-oxidized membrane. The pre-oxidized nano fiber membrane was subjected to a carbonization process to obtain a Cu2O-Cu@C nano fiber membrane. First, nitrogen was introduced, and the temperature was raised to 400 °C at a rate of 5 °C / min and held for 120 min, and then cooled naturally to room temperature and taken out ( Figure 2g ). It can be seen from Figure 2g that the Cu2O-Cu@C nano fiber membrane was almost broken and had great brittleness, which had no value for subsequent applications. It can be seen from the SEM image that there were both broken fibers and beading, and the fiber distribution was uneven ( Figure 3h ).

[0086] Comparative Example 4

[0087] In this comparative example, 0.2285 g of anhydrous copper acetate, 0.8 g of PAN, and 10 g of DMF were weighed and placed in a 20 ml glass bottle, and continuously stirred at 50 °C to obtain a blue transparent spinning solution A.

[0088] The spinning solution A was poured into a syringe ( Figure 1 ). The spinning parameters were adjusted as follows: spinning voltage 16 kV, receiving distance 15 cm. The needle disk rotation speed was 12 r / min. The temperature was 25 ± 2 °C. The relative humidity was 37 ± 3%. PAN / Cu 2+ nano fiber membrane B ( Figure 2a ). It can be seen from the SEM Figure 3a that the fiber surface was smooth and the fiber diameters were relatively uniform.

[0089] The PAN / Cu 2+The nanofiber membrane was cut into an appropriate size, sandwiched between quartz plates, and placed in a tubular carbonization furnace for pre-oxidation. The specific parameters of the pre-oxidation process were set as follows: the initial temperature was 50 °C, the temperature was increased at a rate of 3 °C / min, held at 90 °C for 30 min, then the temperature was increased to 220 °C and held for 90 min. After the pre-oxidation was completed, it was naturally cooled to room temperature to obtain the pre-oxidized membrane. The pre-oxidized nanofiber membrane was subjected to a carbonization process to obtain a Cu2O-Cu@C nanofiber membrane. First, nitrogen was introduced, the temperature was increased to 400 °C at a rate of 5 °C / min, held for 120 min, and then naturally cooled to room temperature and taken out.

[0090] The obtained Cu2O-Cu@C nanofiber membrane was subjected to a photo-thermal water evaporation test. The obtained carbon membrane could be recycled, and the water evaporation rate was 1.49 kg·m -2 ·h -1 , showing certain application prospects. However, compared with the heat-treated carbon membrane (water evaporation rate of 1.57 kg·m -2 ·h -1 ), the water evaporation rate was lower.

[0091] Mechanical property test

[0092] The Cu2O-Cu@C nanofiber membrane obtained in Example 2 and the carbon membrane obtained in Comparative Example 1 were respectively cut into strips of 1 cm × 4 cm, the thickness of the membrane was measured, and then a stress-strain curve test was carried out ( Figure 7 ). It can be seen from the figure that the fracture stress of the carbon membrane without doping copper acetate was 0.27 MPa, and the fracture stress of the Cu2O-Cu@C nanofiber membrane was 3.95 MPa, which was 14.6 times that of the C membrane without doping copper acetate. This indicates that the obtained Cu2O-Cu@C nanofiber membrane can withstand stronger external forces during application and has stronger flexibility than the undoped carbon membrane. Flexibility is very beneficial in subsequent hydrogel treatment and photo-thermal water evaporation tests. Therefore, the Cu2O-Cu@C nanofiber membrane has broad application prospects in photo-thermal water evaporation. Compared with the Cu2O-Cu@C nanofiber membrane prepared in Comparative Document 4, the Cu2O-Cu@C nanofiber membrane prepared in Example 2 has a more uniform structure and can effectively eliminate the internal stress in the nanofibers.

[0093] Those of ordinary skill in the art should understand that the discussion of any above embodiment is only exemplary, and is not intended to imply that the scope of the present invention is limited to these examples; under the concept of the present invention, the technical features in the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations in different aspects of the present invention as described above, which are not provided in detail for the sake of brevity. Any omission, modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A preparation method of a flexible Cu2O-Cu@C composite nanofiber membrane, characterized in that, It includes the following steps: Step 1: Dissolve copper acetate and PAN in a solvent to obtain an electrospinning solution, wherein the mass fraction of PAN in the spinning solution is 7-9%, and the mass ratio of copper acetate to PAN is 1.9-2.5:7; Step 2: Use the electrospinning solution from Step 1 to obtain a PAN / Cu 2+ nano-fiber membrane through the electrospinning process; Step 3. Heat-treat the PAN / Cu 2+ nanofiber membrane; Step 4. Pre-oxidize and carbonize the heat-treated PAN / Cu 2+ nanofiber membrane to prepare a Cu2O-Cu@C nanofiber membrane; Step 5: Perform hydrophilic treatment on the Cu2O-Cu@C nanofiber membrane to obtain a hydrophilic flexible Cu2O-Cu@C nanofiber membrane.

2. The preparation method of the flexible Cu2O-Cu@C composite nanofiber membrane according to claim 1, characterized in that, The mass fraction of PAN in the spinning solution described in Step 1 is 8%.

3. The preparation method of the flexible Cu2O-Cu@C composite nanofiber membrane according to claim 1, characterized in that, The copper acetate described in Step 1 is anhydrous copper acetate, and the mass ratio of anhydrous copper acetate to PAN is 2:

7.

4. The preparation method of the flexible Cu2O-Cu@C composite nanofiber membrane according to claim 1, characterized in that, The spinning conditions of the electrospinning process described in Step 2 are: voltage is 16 kV, spinning flow rate is 1.1-1.3 mL / h, temperature is 23-27 °C, relative humidity is 34-40%, receiving distance is 15 cm, and spinning disk rotation speed is 10-15 r / min.

5. The preparation method of the flexible Cu2O-Cu@C composite nanofiber membrane according to claim 1, wherein The heat treatment described in Step 3 is to subject the PAN / Cu 2+ nanofiber membrane obtained in Step 2 to treatment at a temperature of 118 - 125 °C for 15.5 - 16.5 h, and then naturally cooled.

6. The preparation method of the flexible Cu2O-Cu@C composite nanofiber membrane according to claim 1, characterized in that The pre-oxidation carbonization described in Step 4 is to subject the heat-treated PAN / Cu 2+ nanofiber membrane to a first heating at a rate of 3 °C / min to 220 °C and hold for 90 min; then under the protection of an inert gas, heat it at a rate of 5 °C / min to 300 - 500 °C and hold for 2 h, and then naturally cool to room temperature.

7. The preparation method of the flexible Cu2O-Cu@C composite nanofiber membrane according to claim 1, characterized in that, The method of the hydrophilic treatment described in Step 5 includes the following steps: S1: Add chitosan and acetic acid to water to prepare Solution D with a chitosan mass fraction of 2% and an acetic acid volume fraction of 2%; Mix 2.5% glutaraldehyde by mass and 10% PVA aqueous solution in a volume ratio of 1:10, and stir and dissolve at 100 °C to form Solution E; S2: Mix Solution D and Solution E in a volume ratio of 1:1 under normal conditions, then soak the Cu2O-Cu@C nanofiber membrane in the mixed solution at room temperature, and then perform cyclic freezing and thawing.

8. The preparation method of the flexible Cu2O-Cu@C composite nanofiber membrane according to claim 7, wherein, In S2, the soaking time is 9.5-10.5 h, the number of cyclic freezing and thawing is three times, the freezing time each time is 10 h, the freezing temperature is -20 °C, and the thawing time is 2 h.

9. A flexible Cu2O-Cu@C composite nanofiber membrane, characterized in that, It is prepared by using the preparation method of the flexible Cu2O-Cu@C composite nanofiber membrane according to any one of claims 1-8.

10. Application of the flexible Cu2O-Cu@C composite nanofiber membrane according to claim 9 in the production of clean water driven by solar energy.

Images