3D arch-bridge-shaped carbon nanotube hollow fiber membrane solar interface evaporator and preparation method and application thereof

Abstract

The invention relates to the field of water treatment, and particularly discloses a 3D arch-bridge-shaped carbon nano tube hollow fiber membrane solar interface evaporator and a preparation method and application thereof.The 3D arch-bridge-shaped carbon nano tube hollow fiber membrane solar interface evaporator comprises heat insulation foam used for floating on the sea surface, and the upper surface of the heat insulation foam is provided with an arch-bridge-shaped evaporation component which is used for seawater evaporation and is of a porous and / or multi-gap structure; the arch-bridge-shaped evaporation part is an arch-bridge-shaped carbon nano tube hollow fiber membrane. The solar interface evaporator integrates multiple functions of light absorption, water transmission, salt tolerance and the like, can efficiently utilize solar energy to carry out seawater desalination, has the characteristics of high evaporation speed, high photo-thermal conversion efficiency and high stability, and has a wide application prospect in the field of solar seawater desalination.

Description

Technical Field

[0001] The present invention relates to the field of solar desalination, and particularly to a preparation method and application of a 3D arch-shaped solar interfacial evaporator. Technical Background

[0002] With the rapid development of agriculture and industry, the shortage of fresh water resources has become one of the world-wide crises, forcing the development of efficient technologies for portable and clean water supply. So far, desalination technology is considered as an effective solution. For this, many desalination strategies have been proposed, such as membrane desalination, electrodialysis, reverse osmosis, etc. Among these methods, solar interfacial evaporation has attracted much attention due to its simple operation, sustainable operation and environmental protection. In the past few years, researchers have been committed to developing different structures and materials to optimize the water production efficiency of solar evaporators (especially in the case of high evaporation rate and all-weather water collection). Nowadays, a variety of photothermal conversion materials and structures that can be applied to interfacial evaporation have been reported, but the results show that the optimization of photothermal materials and evaporator structures can only limitedly improve the evaporation rate. In addition, so far, many evaporators pursue high evaporation rate, especially all-weather evaporation, which makes the traditional self-cleaning of the evaporator ineffective, so salt deposition is likely to occur during the desalination process.

[0003] More importantly, compared with the traditional 2D planar evaporator, this evaporator increases its evaporation rate by increasing the evaporation area, but the preparation operation is complex and the stability is poor, which is not suitable for large-scale applications. In contrast, for 3D evaporators, since the side walls cannot absorb solar light, and the side evaporation causes the temperature on the side of the evaporator to be lower than the ambient temperature, which is beneficial for the evaporator to absorb energy from the environment. However, most 3D evaporators do not consider the steam diffusion channels, which causes a large amount of steam to stagnate inside the evaporator and cannot diffuse, thus limiting the evaporation rate. And during the long-term application process, the long-term stability of the evaporator is the key to whether the solar evaporator can be applied on a large scale. Summary of the Invention

[0004] Aiming at the defects of traditional solar evaporators in practical engineering applications, the present invention provides a 3D arch-shaped nanotube hollow fiber membrane solar interfacial evaporator for seawater desalination, its preparation method and application. This evaporator integrates excellent photothermal conversion performance, a porous structure for stable water transmission, and good solar water evaporation performance. It has a high removal rate for saline wastewater, and at the same time inhibits salt deposition on the surface of the evaporator, making the evaporator have the characteristics of strong stability.

[0005] In order to achieve the above invention purpose, the present invention provides the following technical solutions:

[0006] A 3D arch-shaped solar interface evaporator for seawater desalination, comprising a heat-insulating foam for floating on the sea surface, the foam having a lower surface for contacting seawater and an upper surface corresponding to the lower surface, and a plurality of arch-shaped evaporation components with a large specific surface area having a porous and / or multi-gap structure for seawater evaporation are vertically extended upward from the upper surface of the heat-insulating foam, and the evaporation components extend downward through the lower surface of the foam to extend below the seawater surface to form a guiding end for transmitting seawater to the top of the arch evaporation components, and the arch three-dimensional evaporation components have hydrophilicity and a photothermal conversion layer.

[0007] Further, the arch three-dimensional evaporation component is a support and breathable component for enhancing the steam diffusion efficiency extending from the water guiding end to the top end of the evaporation component, and the support and breathable component includes a hollow pipe having a steam diffusion channel, and / or a plurality of air guide holes for quickly diffusing evaporation are opened on the wall of the cylinder along the axial direction of the hollow pipe. The porous structure and the hollow pipe inside the evaporation component will form a number of diversion channels suitable for quickly diffusing steam.

[0008] Further, the arch-shaped three-dimensional evaporation component is an arch-shaped carbon nanotube hollow fiber membrane, and the hollow fiber membrane is distributed in parallel or in an array on the heat-insulating foam.

[0009] Further, the outer wall diameter of the hollow fiber membrane is 1.15 - 1.6 mm, and the inner wall diameter is 0.15 - 0.6 mm.

[0010] Further, the bending angle of the arch three-dimensional evaporation component (arch-shaped carbon nanotube hollow fiber membrane) is 45 - 180°, and the chord length is 2.8 - 3 cm.

[0011] Further, the height of the arch-shaped three-dimensional evaporation component (the distance between the highest point of the arch-shaped three-dimensional evaporation component and the heat-insulating foam) is 0.5 - 2 cm. The length of the arch-shaped evaporation component (the chord length of the arch-shaped carbon nanotube hollow fiber membrane. The width (the length of the arrangement of multiple arch-shaped carbon nanotube hollow fiber membranes) of the arch-shaped evaporation component can be adjusted according to actual situations, such as the arrangement of 10 arch-shaped carbon nanotube hollow fiber membranes.

[0012] Further, the heat-insulating foam is a foam having heat-insulating properties and capable of floating on the water surface, such as melamine foam, polyethylene foam, metal foam (such as open-cell foam, closed-cell foam, and composite foam, etc., and the material can be aluminum) or glass foam, etc.

[0013] Further, the heat-insulating foam can be cut according to actual needs to form a heat-insulating foam support material. Further, the preparation method of the arch-shaped carbon nanotube hollow fiber membrane includes the following steps

[0014] Step a: Mix the carbon nanotube slurry and polyvinyl butyral evenly at a mass ratio of 18 - 21:1 - 3 to obtain mixture A;

[0015] Step b: Pour mixture A into a syringe and place it in a film spinning device to prepare a hollow fiber membrane;

[0016] Step c: Bend the obtained hollow fiber membrane into an arch shape with different bending angles within the range of 45° - 180° and dry it to obtain solid A;

[0017] Step d: Place solid A in a tubular furnace and conduct high-temperature calcination under an argon atmosphere. The calcination temperature is 800 - 900 °C, and the calcination time is 1 - 2 h to obtain an arch-shaped carbon nanotube hollow fiber membrane;

[0018] Step e: Immerse the arch-shaped carbon nanotube hollow fiber membrane obtained in step d into aqueous solutions of polyvinyl alcohol, sodium alginate, and calcium chloride in sequence. The solution concentrations are 1 - 2 g / L, 2 - 5 g / L, and 1 - 3 g / L respectively, and the soaking times are 5 - 8 h, 2 - 5 h, and 2 - 5 h respectively. Finally, obtain an arch-shaped carbon nanotube hollow fiber membrane modified with hydrogel.

[0019] Further, the concentration of the carbon nanotube slurry is 18 - 20 wt.%.

[0020] Further, the solvent of the carbon nanotube slurry is N-methylpyrrolidone (NMP).

[0021] Further, in step a, the way of mixing evenly is stirring. The stirring time is 3 - 5 h, and the stirring speed is 600 - 800 rpm.

[0022] Further, in step b, the film spinning device is two micro-injection pumps, which are respectively used to place deionized water and prepare mixture A. Using mixture A as the shell liquid and deionized water as the core liquid, under the action of the micro-injection pumps, the two are simultaneously extruded from a concentric needle. The outer wall diameter of the concentric needle is 1.15 - 1. mm, and the inner wall diameter is 0.15 - 0.6 mm. Among them, the pump speed of the core liquid is 8 - 10 ml / h, and the pump speed of the shell liquid is 25 - 30 mm / h.

[0023] Further, in step b, the obtained hollow fiber membrane is stored in water.

[0024] Further, in step c, the diameter of the arch-shaped carbon nanotube hollow fiber membrane with different bending angles obtained is 2.8 - 3 cm.

[0025] Further, in step d, the heating rate to the calcination temperature is 5 - 6 °C / min.

[0026] The present invention also provides a method for preparing the above-mentioned 3D arch-shaped solar interface evaporator, which includes the following steps:

[0027] (1) Insert the arch-shaped carbon nanotube hollow fiber membrane into the heat-insulating foam support material in sequence, and extend downward through the heat-insulating support material;

[0028] (2) Adjust the height of the arch-shaped hollow fiber membrane above the heat-insulating foam to make it consistent, and obtain a 3D arch-shaped array solar interface evaporator.

[0029] The present invention also provides the application of the above-mentioned 3D arch-shaped solar interface evaporator in seawater desalination, which is applicable to saline wastewater, especially high-concentration saline wastewater (salt concentration range is 15-25 wt.%), preferably for treating high-concentration saline wastewater within the wind speed range of 1.5-3.5 m / s. -1

[0030] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0031] The present invention provides a solar interface-driven evaporator and its preparation method and application. The solar evaporator is composed of a hollow fiber membrane serving as a substrate and a water supply channel, and carbon nanotubes distributed therein serving as a photothermal material. The carbon nanotubes in the present invention endow the evaporator with efficient light absorption due to their good photothermal conversion performance and wide solar band absorption. In the wavelength range of 200-2500 nm, the solar interface evaporator achieves a light absorption capacity of 92.4%. In addition, the hollow morphology enables the evaporator to have a good water transport channel. Due to the arch shape, there is a difference in energy acquisition between the upper and lower parts of the evaporator, which will form a temperature gradient, thereby inducing Marangoni convection and quickly distributing water on the surface of the evaporator through the water transport channel. This solar interface evaporator integrates functions such as light absorption, water transport, and salt tolerance, and can efficiently utilize solar energy for seawater desalination. It has the characteristics of fast evaporation speed, high photothermal conversion efficiency (it can achieve a photothermal conversion efficiency of 148.17% under 1 sun intensity), and high stability (it can continuously operate for 8 hours in high-salt wastewater without salt crystallization on the surface). After testing, under 1 sun intensity (1 kW m -2 ), the evaporation rate of this solar evaporator in high-salt wastewater with a concentration of 25 wt.% is as high as 2.92 kg m -2 h -1 , and it has broad application prospects in the field of solar seawater desalination. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The following further details the specific embodiments of the present invention with reference to the accompanying drawings.

[0033] Figure 1 is a physical photo of the solar interface evaporator;

[0034] Figure 2 SEM image of the solar interfacial evaporator;

[0035] Figure 3 Evaporation rate of the solar interfacial evaporator for 25 wt.% high-salinity wastewater at different wind speeds;

[0036] Figure 4 Surface schematic diagram of the solar interfacial evaporator continuously operating for 8 h in 25 wt.% high-salinity wastewater;

[0037] Figure 5 Evaporation rate of the solar interfacial evaporator for 25 wt.% high-salinity wastewater at different bending angles;

[0038] Figure 6 Principle diagram of the evaporation of the solar interfacial evaporator. Specific implementation mode

[0039] The following non-limiting examples can enable those of ordinary skill in the art to more comprehensively understand the present invention, but do not limit the present invention in any way.

[0040] Example 1

[0041] A solar interfacial evaporator includes heat-insulating foam for floating on the sea surface. The foam has a lower surface for contacting seawater and an upper surface corresponding to the lower surface, and the heat-insulating foam is melamine foam. A number of arch-shaped evaporation components for seawater evaporation are vertically extended upward from the upper surface of the heat-insulating foam. The evaporation components extend downward through the lower surface of the foam to extend below the seawater surface to form a guiding end for transmitting seawater to the top of the arch-shaped evaporation components. The arch-shaped evaporation components are arch-shaped carbon nanotube hollow fiber membranes, and the hollow fiber membranes are distributed in parallel on the heat-insulating foam.

[0042] The preparation method of the arch-shaped carbon nanotube hollow fiber membrane includes the following steps:

[0043] 10 g of a carbon nanotube NMP slurry with a concentration of 20 wt.% was magnetically stirred with 0.5 g of polyvinyl butyral at a stirring speed of 600 rpm for 5 h to obtain a mixed solution A. Two 25-ml syringes were prepared, filled with the mixed solution A and deionized water respectively, and placed in two micro-injection pumps. Among them, the mixed solution A was used as the shell liquid, and deionized water was used as the core liquid. Under the action of the micro-injection pumps, both were pumped out from the concentric needle at the same time. The outer wall diameter of the concentric needle was 1.15 mm, and the inner wall diameter was 0.22 mm. The pump speeds of the micro-injection pumps for placing the shell liquid and the core liquid were 30 mm / h and 10 ml / h respectively, and a hollow fiber membrane was prepared using a spinning membrane device. Subsequently, the obtained hollow fiber membrane was bent into a semi-circular structure with a diameter of 3 cm and a bending angle of 180°, and dried at room temperature.

[0044] The dried hollow fiber membrane was placed in a tube furnace for calcination. The calcination temperature was 800 °C, the heating rate was 5.3 °C / min, the calcination time was 1 h, and argon was introduced. Then, the calcined carbon nanotube hollow fiber membrane was successively immersed in an aqueous solution of polyvinyl alcohol with a concentration of 1 g / L for 5 h, an aqueous solution of sodium alginate with a concentration of 2 g / L for 3 h, and an aqueous solution of calcium chloride with a concentration of 1.5 g / L for 3 h, and finally a hydrogel-modified arch-shaped carbon nanotube hollow fiber membrane was obtained. In addition, under dry conditions, it was measured that the hydrogel-modified carbon nanotube hollow fiber membrane could achieve 92.4% light absorption in the wavelength range of 200 - 2500 nm.

[0045] A preparation method of a solar interface evaporator includes the following steps:

[0046] The melamine foam was cut into a cube with a length, width, and height of 5 cm, 5 cm, and 2 cm respectively, and two notches with a length of 1.5 cm were drawn parallel above the melamine foam (the distance between the two notches was 3 cm). Then, the hydrogel-modified arch-shaped carbon nanotube hollow fiber membranes were successively inserted parallel into the notches of the melamine foam one by one (10 carbon nanotube hollow fiber membranes), and extended downward through the melamine foam. After adjusting the height of the carbon nanotube hollow fiber membranes above the melamine, an arch-shaped evaporation component with a height of 1.5 cm, a length (chord length) of 3 cm, and a width of 1.5 cm was finally prepared, and a 3D arch-shaped solar interface evaporator was finally formed (see Figure 1 ).

[0047] The prepared solar interface evaporator was placed inside a weighing balance, and the evaporation of the prepared solar evaporator for 25 wt.% high-salt (NaCl) wastewater was tested under the condition of double-sided ventilation (wind speed of 2.5 m / s on both sides of the windshield of the weighing balance) at 1 sun intensity (1 kW m -2 ).

[0048] Figure 1 It is a physical diagram of a carbon nanotube hollow fiber membrane solar interface evaporator;

[0049] Figure 2 It is the scanning electron microscope result of the prepared carbon nanotube hollow fiber membrane. The prepared carbon nanotube hollow fiber membrane has a porous structure and good water transportation performance.

[0050] Example 2

[0051] The difference between this embodiment and Example 1 is that when measuring evaporation, the solar interface evaporator has ventilation on only one side (wind speed is 2.5 m / s), and the others are the same as Example 1, and the evaporation rate of the solar evaporator is obtained.

[0052] Example 3

[0053] The difference between this embodiment and Example 1 is that when measuring evaporation, the solar interface evaporator does not have ventilation, and the others are the same as Example 1, and the evaporation rate of the solar evaporator is measured.

[0054] Example 4

[0055] The difference between this embodiment and Example 1 is that the carbon nanotube hollow fiber membrane is prepared into an arc structure with a bending angle of 135° and a chord length of 3 cm. Finally, the length (chord length) of the prepared arch-shaped evaporation component is adjusted to 3 cm, the width is 1.5 cm, and the height is 1.2 cm, and the others are the same as Example 1.

[0056] Example 5

[0057] The difference between this embodiment and Example 1 is that the carbon nanotube hollow fiber membrane is prepared into an arc structure with a bending angle of 90° and a chord length of 3 cm. Finally, the length (chord length) of the prepared arch-shaped solar evaporator is adjusted to 3 cm, the width is 1.5 cm, and the height is 0.85 cm, and the others are the same as Example 1.

[0058] Example 6

[0059] The difference between this embodiment and Example 1 is that the carbon nanotube hollow fiber is prepared into an arc structure with a bending angle of 45° and a chord length of 3 cm. Finally, the length (chord length) of the prepared arch-shaped solar evaporator is adjusted to 3 cm, the width is 1.5 cm, and the height is 0.5 cm, and the others are the same as Example 1.

[0060] The experimental steps of Example 2 - 3 are the same as those of Example 1, and the difference lies in whether there is ventilation when measuring evaporation. Figure 3 It shows the evaporation effect of a 180° arch solar evaporator on a 25 wt.% NaCl solution under different ventilation conditions. Under ventilation, the evaporation rate is as high as 2.92 kg / m2 h -1 , achieving a photothermal conversion efficiency of 148.17%, while the maximum rate without ventilation was only 1.82kg / m 2 h -1 In addition, the 3D arch bridge solar interface evaporator prepared in Example 1 was tested by inductively coupled plasma spectrometer (ICP) to determine the Na + The concentration is 13200mgL -1 After 12 hours of solar evaporation, the representative metal Na in pure water was collected + The concentration is only 11.50mgL -1 , reaching the drinking water standard of the World Health Organization. The melamine foam of the 3D arch bridge solar interface evaporator prepared in Example 1 was cut into cubes with a length, width and height of 3 cm, 3 cm and 2 cm respectively, and a salt resistance test was carried out. Under the condition of double-sided ventilation, after continuous operation for 8 hours in high-salt wastewater with a concentration of 25wt.%, there was still no salt crystal formation on the surface of the evaporator (see Figure 4 ).

[0061] The steps of Examples 4-6 are basically the same as those of Example 1, except that the bending angles of the carbon nanotube hollow fiber membranes are different. Figure 5 The graph shows the evaporation rate of 25wt.% high-salinity wastewater at different bending angles of the solar evaporator. It can be seen from the figure that the evaporator has the best effect when the bending angle is 180°.

[0062] The schematic diagram of the solar interface evaporator of the present invention is as follows Figure 6 As shown. The prepared 3D arch bridge-shaped solar evaporator floats on the sea surface under the action of melamine foam, and seawater can be transported to the surface of the solar interface evaporator through the porous structure of the carbon nanotube hollow fiber membrane. The evaporator converts the solar energy captured from the environment into thermal energy through the internal photothermal material. When the seawater on the surface of the evaporator absorbs enough heat, a phase change will occur to produce fresh water.

Claims

1. A 3D arch bridge-shaped solar interface evaporator for seawater desalination, characterized by: It comprises a thermal insulation foam for floating on the sea surface, wherein the upper surface of the thermal insulation foam is provided with an arch bridge-shaped evaporation component with a porous and / or multi-gap structure for evaporating seawater, wherein the evaporation component partially passes downward through the lower surface of the thermal insulation foam and extends below the seawater surface to form a guide end for transmitting seawater to the top of the arch bridge evaporation component, and the arch bridge evaporation component has hydrophilicity and a light-to-heat conversion layer.

2. The 3D array solar interface evaporator according to claim 1, characterized in that: The arch bridge evaporation component is a supporting breathable component extending from the water guide end to the top of the evaporation component for enhancing the steam diffusion efficiency. The supporting breathable component includes a hollow pipe with a steam diffusion channel, and / or a plurality of air guide holes for rapid diffusion and evaporation are opened on the wall of the column along the axial direction of the hollow pipe.

3. The 3D arch bridge solar interface evaporator according to claim 1 or 2, characterized in that: The arch bridge evaporation component is an arch bridge carbon nanotube hollow fiber membrane, and the hollow fiber membrane is distributed in parallel or in an array on the insulation foam; the insulation foam is a foam with insulation properties and floating on the water surface, such as melamine foam, polyethylene foam, metal foam or glass foam.

4. The 3D arch bridge solar interface evaporator according to claim 3, characterized in that: The outer wall diameter of the hollow fiber membrane is 1.15-1.6 mm, and the inner wall diameter is 0.15-0.6 mm.

5. The 3D arch bridge solar interface evaporator according to claim 1, characterized in that: The bending angle of the arch bridge-shaped evaporation component is 45 to 180 degrees.

6. The 3D arch bridge solar interface evaporator according to claim 5, characterized in that: The chord length of the arch bridge-shaped evaporation component is 2.8 to 3 cm, and the height is 1 to 3 cm.

7. The 3D arch bridge solar interface evaporator according to claim 3, characterized in that: The method for preparing the arch bridge-shaped carbon nanotube hollow fiber membrane comprises the following steps: Step a: uniformly mixing carbon nanotube slurry and polyvinyl butyral in a mass ratio of 18-21:1-3 to obtain a mixed solution A; Step b: pouring the mixed solution A into a syringe and placing it into a membrane spinning device to prepare a hollow fiber membrane; Step c: bending the obtained hollow fiber membrane into an arch bridge shape and drying it to obtain a solid A; Step d: placing solid A in a tubular furnace for high-temperature calcination, the calcination temperature is 800-900° C., and the calcination time is 1-2 hours to obtain an arch bridge-shaped carbon nanotube hollow fiber membrane; Step e: immersing the arch bridge-shaped carbon nanotube hollow fiber membrane obtained in step d in a polyvinyl alcohol aqueous solution, a sodium alginate aqueous solution, and a calcium chloride aqueous solution in turn, wherein the concentrations of the aqueous solutions are 1-2 g / L, 2-5 g / L, and 1-3 g / L, respectively, and the immersion time is 5-8 h, 2-5 h, and 2-5 h, respectively, to finally obtain an arch bridge-shaped carbon nanotube hollow fiber membrane modified with hydrogel.

8. The 3D arch bridge solar interface evaporator according to claim 7, characterized in that: In step a, the concentration of the carbon nanotube slurry is 18-20 wt.%, and the solvent is N-methylpyrrolidine; the mixing method is stirring, the stirring time is 3-5 hours, and the stirring speed is 600-800 rpm; In step b, the membrane spinning equipment is two micro-injection pumps, which are used to place deionized water and mixed solution A respectively, with mixed solution A as the shell liquid and deionized water as the core liquid. The pumping speed of the core liquid is 8-10 ml / h, and the pumping speed of the shell liquid is 25-30 mm / h; the obtained hollow fiber membrane is placed in water for storage; In step d, the speed of heating to the calcination temperature is 5-6°C / min.

9. The method for preparing the 3D arch bridge solar interface evaporator according to claims 1-8, characterized in that: The steps include: (1) fixing the arch bridge-shaped carbon nanotube hollow fiber membranes on the thermal insulation foam support material in sequence, and extending downward through the thermal insulation foam support material; (2) The height of the arch-shaped hollow fiber membrane above the thermal insulation foam is adjusted to obtain a 3D arch-shaped solar interface evaporator.

10. Application of the 3D arch bridge-shaped solar interface evaporator according to any one of claims 1 to 8 in seawater desalination.

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