A carbonized loofah photothermal evaporator with a city wall structure, its preparation method and application

Abstract

This invention relates to a carbonized loofah photothermal evaporator with a wall-like structure and its preparation method, relating to the field of solar-driven interfacial water evaporation. The invention utilizes freeze-drying technology to dry fresh loofah, obtaining a freeze-dried loofah that retains its porous structure; then, it carbonizes the freeze-dried loofah in a tubular furnace under an inert gas environment. The carbonized loofah retains the anisotropic structure of the inner and outer layers of the fresh loofah. The outer layer, with its dense structure resembling a wall, maintains its shape and provides structural protection. The inner layer, with its loose and porous structure, acts as a channel for directional water transport, facilitating efficient water evaporation. The resulting integrated carbonized loofah photothermal evaporator exhibits excellent water transport rate and good photothermal conversion capability, making it applicable to interfacial water evaporation. This evaporator uses readily available raw materials, has a simple manufacturing process, high photothermal evaporation efficiency, and is environmentally friendly, showing promising applications in seawater desalination.

Description

Technical Field

[0001] This invention belongs to the field of solar-driven interface water evaporation, and particularly relates to a carbonized loofah photothermal evaporator with a wall structure, its preparation method, and its application in seawater desalination and wastewater treatment. Background Technology

[0002] Solar-driven interfacial water evaporation technology is a seawater desalination technology that utilizes solar energy as a power source. Compared to traditional seawater desalination methods, it has advantages such as lower operating costs, no need for large amounts of electricity or fuel, and less environmental impact. The core of realizing solar-driven interfacial water evaporation lies in fabricating an evaporator with good photothermal properties, thermal conductivity, and water transport capacity. Currently, evaporator design focuses on achieving higher water evaporation efficiency, selecting precious metal materials, carbon-based materials, and polymer materials with high photothermal conversion efficiency for the photothermal layer, and then supplementing it with a support layer and a water transport layer to construct the evaporator. Furthermore, pursuing greener and more environmentally friendly evaporators in both the fabrication and application stages is also essential. Therefore, developing evaporators using biomass materials that have abundant raw material sources, simple fabrication processes, low production costs, and are more environmentally friendly has significant research value and broad application prospects.

[0003] As a common vegetable, loofah possesses a loose and porous biological structure. The loofah sponge formed from its mature fruit, besides being used as kitchen cleaning tools such as pot scrubbers, also has rich scientific research value. For example, patent CN102247813B utilizes the hydrophilic and oleophilic properties and porous structure of natural loofah sponge to prepare a composite material that adsorbs common metal ions such as potassium, sodium, and calcium, as well as Rhodamine 6G organic dye, and can recover organic matter after modification with bipyridine and triethylamine. Patent CN113800945B utilizes the porous structure of loofah sponge to fill a carbon source, and after carbonization, reacts with molten silicon to prepare loofah-derived porous silicon carbide skeleton, which is used in the field of high-temperature photothermal storage. Invention CN110844959A discloses a method for preparing hydrothermal evaporation devices by molding, carbonizing, and in-situ depositing carbon nanotubes using loofah sponge as raw material. However, these inventions mostly focus on the modification of dried loofah sponge, and rarely use fresh loofah. Using specific processing techniques, the moisture in fresh loofah is removed while preserving its peel and pulp structure. It is then directly carbonized to prepare a carbon-based material. Compared to dried loofah sponge, the prepared carbon-based material has a richer porous structure, offering greater potential for application in the preparation of natural biomass evaporators. Summary of the Invention

[0004] In view of this, the present invention discloses a carbonized loofah photothermal evaporator with a city wall structure and its preparation method, which is not only simple to prepare and rich in raw materials, but also environmentally friendly and suitable for seawater desalination and wastewater treatment.

[0005] Specifically, this invention uses fresh loofah as raw material and leverages the anisotropic composition of its inner and outer layers to prepare a carbonized loofah photothermal evaporator with a wall-like structure. Fresh loofah is processed through freeze-drying and high-temperature carbonization to obtain the carbonized loofah for solar evaporation. The carbonized loofah retains the anisotropic structure of its inner and outer layers. The outer layer, a dense structure, acts like a wall, maintaining its shape and providing structural protection. The inner layer, the loofah pulp, has a loose and porous structure, serving as a channel for directional water transport and facilitating efficient water evaporation. This invention employs different carbonization temperatures (400℃-800℃) to achieve different morphologies in the porous structure of the resulting carbonized loofah, thereby allowing for the regulation of the evaporator's performance.

[0006] To achieve the above-mentioned technical objectives, the technical solution adopted by the present invention is as follows:

[0007] The primary technical objective of this invention is to claim protection for a method for preparing a carbonized loofah photothermal evaporator with a wall-like structure. This method involves selecting fresh loofahs, retaining the outer wall, and cutting them into uniformly sized cylinders. The loofahs are then treated using vacuum freeze-drying technology to remove moisture while preserving their porous biological framework to the greatest extent possible. The dried loofahs are then placed at room temperature for further air drying. Finally, the dried fresh loofahs are placed in a tube furnace for carbonization at different temperatures to obtain an integrated carbonized loofah photothermal evaporator applicable to seawater desalination.

[0008] Specifically, the steps include the following:

[0009] (1) Select fresh loofahs of similar thickness and size, wash them and cut them into regular cylindrical shapes with a knife;

[0010] (2) Place the cut cylindrical loofah into a freeze dryer and dry it at low temperature in a vacuum environment. After taking it out, let it stand at room temperature to continue drying.

[0011] (3) The dried loofah from step (2) is placed in a tube furnace for high-temperature carbonization treatment to finally obtain the carbonized loofah photothermal evaporator with the wall structure.

[0012] Preferably, in step (1), fresh loofah with few seeds should be used, and the loofah should be cut into cylindrical loofah segments with a diameter of 3-5cm and a height of 8-10cm.

[0013] Preferably, in step (2), the freeze drying is carried out under vacuum conditions at -60°C for 6 hours.

[0014] Preferably, in step (3), the carbonization temperature is 400-800℃, the heating rate is 5℃ / min, and when the required carbonization temperature is reached, the carbonized loofah is taken out after the tube furnace cools down to room temperature.

[0015] Specifically, the dried loofah from step (2) is placed in a tube furnace for high-temperature carbonization treatment at 400℃, 500℃, 600℃, 700℃, and 800℃, with a heating rate of 5℃ / min. During high-temperature carbonization, an inert gas—argon—should be introduced into the tube furnace to prevent the loofah from being damaged by high-temperature oxidation.

[0016] The second technical objective of this invention is to provide a carbonized loofah photothermal evaporator with a city wall structure prepared by the above method. The carbonized loofah retains the characteristic of the anisotropic structure of the inner and outer layers of fresh loofah. The outer layer of loofah skin has a dense structure, similar to a city wall, which plays a role in maintaining shape and structural protection. The inner layer of loofah pulp has a loose and porous structure, which can act as a channel for directional water transport and help water evaporate efficiently.

[0017] The third technical objective of this invention is to provide the application of the above-mentioned carbonized loofah photothermal evaporator with a city wall structure in the fields of seawater desalination and wastewater treatment.

[0018] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0019] This invention selects fresh, seedless loofah, removes moisture using vacuum freeze-drying technology while preserving the biological structural framework of the loofah peel and pulp to the greatest extent possible, and then prepares carbonized loofah with a wall-like structure through high-temperature carbonization technology. The carbonized loofah peel has a dense structure, providing structural protection, while the carbonized loofah pulp has a loose structure, acting as an efficient water transport channel. The carbonized loofah exhibits excellent photothermal conversion capabilities, enabling the evaporation and desalination of seawater and wastewater using solar-driven interfacial water evaporation technology. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0021] Figure 1 This is a schematic cross-sectional view of the carbonized loofah photothermal evaporator with a city wall structure prepared in Examples 1-5.

[0022] Figure 2 These are microscopic morphological images of carbonized loofahs prepared at different carbonization temperatures in Examples 1-5.

[0023] Figure 3 These are Fourier transform infrared spectra of carbonized loofah prepared at different carbonization temperatures in Examples 1-5.

[0024] Figure 4 This is a contact angle diagram of the carbonized loofah water prepared in Example 2.

[0025] Figure 5 This is a diagram showing the salt tolerance effect of the carbonized loofah prepared in Example 2. Detailed Implementation

[0026] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0027] The term "embodiment" used herein, as an example, is not necessarily to be construed as superior to or better than other embodiments. Performance testing in the embodiments of this application, unless otherwise specified, employs conventional testing methods in the art. It should be understood that the terminology used in this application is merely for describing particular implementations and is not intended to limit the scope of this disclosure.

[0028] Unless otherwise stated, the technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; other experimental methods and technical means not specifically mentioned herein refer to experimental methods and technical means commonly used by one of ordinary skill in the art.

[0029] To better illustrate the content of this application, numerous specific details are provided in the following detailed embodiments. Those skilled in the art should understand that this application can be implemented even without certain specific details. In the embodiments, some methods, means, instruments, and devices well-known to those skilled in the art are not described in detail in order to highlight the main points of this application.

[0030] Without conflict, the technical features disclosed in the embodiments of this application can be combined arbitrarily, and the resulting technical solution belongs to the content disclosed in the embodiments of this application.

[0031] This invention discloses a method for preparing a carbonized loofah photothermal evaporator with a city wall structure.

[0032] To better understand the present invention, the following embodiments are provided for further detailed description of the present invention, but they should not be construed as limiting the present invention. Any non-essential improvements and adjustments made by those skilled in the art based on the above-described invention are also considered to fall within the protection scope of the present invention.

[0033] Example 1

[0034] Fresh loofah was selected and cut into cylindrical pieces with a diameter of 5cm and a height of 10cm. The loofah was then freeze-dried at -60℃ for 6 hours using vacuum freeze-drying technology. After that, the loofah was removed and left to air-dry at room temperature for another 24 hours. The dried fresh loofah was then placed in a tube furnace and inert gas - argon was introduced. The temperature was raised to 400℃ at a rate of 5℃ / min to perform high-temperature carbonization of the loofah.

[0035] Examples 2-5

[0036] Examples 2-5 provide a method for preparing a carbonized loofah photothermal evaporator with a city wall structure, as detailed below:

[0037] The specific operation method is the same as in Example 1, the only difference being the carbonization temperature. The carbonization temperature in Example 2 is 500℃, in Example 3 it is 600℃, in Example 4 it is 700℃, and in Example 5 it is 800℃, thus obtaining carbonized loofah photothermal evaporators for city wall structures treated with different carbonization temperatures.

[0038] In addition, to further illustrate the advantages of the present invention compared to the prior art, the inventors conducted the following experiments, the specific operations of which are as follows:

[0039] Experimental Example 1

[0040] The internal pore structure of the carbonized loofah photothermal evaporators with a city wall structure prepared in Examples 1-5 was analyzed using scanning electron microscopy, such as... Figure 2 As shown.

[0041] Figure 2 The results showed that SEM images of loofahs at various carbonization temperatures (400℃ and 500℃) revealed clear pore structures and regular pore sizes. However, the cut surface of the loofah treated at 400℃ contained incompletely carbonized biological debris. As the carbonization temperature increased, irregular pores of varying sizes gradually appeared inside the carbonized loofah, and the structure began to collapse, with more debris blocking the pores, potentially causing a decrease in water absorption at that carbonization temperature. When the carbonization temperature was further increased to 800℃, the pore structure of the carbonized loofah became disordered and irregular. In comparison, the loofah treated at 500℃ retained the most complete structure and had the clearest pore structure. Compared with common photothermal evaporators made from dried loofah sponge, carbonized loofah photothermal evaporators carbonize fresh loofah at different temperatures, and the size of the pores inside the loofah can be changed accordingly, making it easier to select the most suitable temperature. Dried loofah sponge, because of its larger material pores and greater hardness, does not have a regular microporous structure inside.

[0042] Experimental Example 2

[0043] The carbonized loofahs of Examples 1-5 were measured using an infrared spectrometer, such as... Figure 3 As shown.

[0044] Figure 3 The results showed that carbonized loofah treated at different carbonization temperatures all reached a thickness of 3430 cm. -1 and 1064cm -1 Characteristic peaks belonging to NH and CN groups were observed nearby. This is because the hydrophilic functional groups of carbohydrates and proteins contained in fresh loofah remain in the structure of the carbonized loofah after high-temperature carbonization, ensuring the hydrophilicity of the carbonized loofah.

[0045] Experimental Example 3

[0046] The carbonized loofah photothermal evaporator prepared at a carbonization temperature of 500℃ in Example 2 was tested for contact angle. Due to the wall-like structural characteristics of the carbonized loofah, the surface of the loofah is concave, and the water absorption of different parts varies. Therefore, it is necessary to test the contact angle of the edge and center of the carbonized loofah separately to characterize the wetting performance of different parts of the carbonized loofah photothermal evaporator. The results are as follows. Figure 4 As shown.

[0047] Figure 4 The figures show the water contact angles after 0.1 seconds when water droplets are placed on the edge and center of a carbonized loofah. The center of the carbonized loofah exhibits excellent water absorption, with a water contact angle close to 0°. The water absorption of the edge of the loofah skin is significantly lower than that of the center, with a water contact angle of 41.40°. Similar results were observed in carbonized loofahs treated at different temperatures, indicating that the center of the carbonized loofah, regardless of the temperature treatment, possesses good water absorption.

[0048] Test Example 4

[0049] The carbonized loofah photothermal evaporators prepared at different carbonization temperatures in Examples 1-5 were tested to measure the evaporation rate of fresh water, demonstrating their photothermal evaporation effect. The test light intensity was 1 kW·m. -2 The simulated sunlight was subjected to 1 hour of irradiation, and the results are shown in Table 1.

[0050] Table 1. Freshwater evaporation rates of carbonized loofah prepared at different carbonization temperatures in Examples 1-5

[0051]

[0052]

[0053] Table 1 shows that the evaporation rate of carbonized loofah at various temperatures exhibits a stable upward trend within 1 hour, with the highest evaporation rate (1.732 kg·m³) observed at a carbonization temperature of 500℃. -2h -1 The minimum evaporation rate of carbonized loofah treated at 400℃ was 1.304 kg·m³. -2 h -1 After reaching its peak evaporation rate, further increases in carbonization temperature lead to a gradual decrease in the evaporation rate. Based on SEM images, this phenomenon is caused by the fact that at a carbonization temperature of 400℃, the inside of the loofah is not yet fully carbonized. As the carbonization temperature rises, the inside of the loofah is fully carbonized, the water transport channels become unobstructed, and the higher degree of structural carbonization also improves the photothermal conversion capacity of the carbonized loofah, thus increasing the evaporation rate. However, when the carbonization temperature continues to rise, the excessively high temperature damages the internal pore structure of the loofah, causing it to collapse and block the water transport channels. This results in a decrease in the evaporation rate of the loofah treated with excessively high carbonization temperatures.

[0054] Experimental Example 5

[0055] To further simulate the application of carbonized loofah in seawater desalination, a 3.5% NaCl solution was prepared instead of deionized water. The brine evaporation rate of carbonized loofah prepared at different carbonization temperatures was tested under the following conditions: light intensity 1 kW·m². -2 The test results, which simulated 1 hour of sunlight exposure, are shown in Table 2.

[0056] Table 2. Evaporation rates of carbonized loofah brine prepared at different carbonization temperatures in Examples 1-5

[0057]

[0058] As shown in Table 2, seawater evaporation and freshwater evaporation show the same pattern. The carbonized loofah treated at 500℃ still has the best evaporation efficiency, while the carbonized loofah treated at 400℃ has the lowest evaporation rate. The evaporation rate of carbonized loofah treated at 600-800℃ gradually decreases with increasing temperature.

[0059] Experimental Example 6

[0060] The salt tolerance of Example 2 was tested to investigate whether salt deposition would occur on its surface during prolonged brine evaporation, thus affecting its brine evaporation rate. The results are as follows: Figure 5 .

[0061] The results showed that no significant salt accumulation occurred in the center and edges of the carbonized loofah within the first 3 hours. After 3 hours, a small amount of salt deposition appeared on the edge of the loofah peel, while no salt deposition was observed in the central loofah pulp. This is likely because the loofah becomes concave after carbonization, forming a wall-like structure with higher edges and a lower center. The raised areas of the loofah peel have a small contact area, preventing salt particles from dispersing and causing them to accumulate. Due to this natural wall-like structure, salt particles do not accumulate excessively in the center of the carbonized loofah. This indicates that the edge of the carbonized loofah peel not only protects the more brittle central loofah pulp, maintaining structural stability during prolonged carbonization, but also allows salt particles to accumulate without affecting the water evaporation rate of the central loofah pulp.

[0062] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a carbonized loofah photothermal evaporator with a city wall structure, characterized in that, The method specifically includes the following steps: (1) Select fresh loofahs of similar thickness and size, wash them and cut them into regular cylindrical shapes with a knife; (2) Place the cut cylindrical loofah into a freeze dryer and dry it at low temperature in a vacuum environment. After taking it out, let it stand at room temperature to continue drying. (3) The dried loofah from step (2) is placed in a tube furnace for high-temperature carbonization treatment to finally obtain the carbonized loofah photothermal evaporator with the wall structure. The carbonization temperature is 400–800℃, and the heating rate is 5℃ / min.

2. The method for preparing a carbonized loofah photothermal evaporator with a city wall structure according to claim 1, characterized in that, In step (1), fresh loofah with few seeds should be used, and the loofah should be cut into cylindrical loofah segments with a diameter of 3-5cm and a height of 8-10cm.

3. The method for preparing a carbonized loofah photothermal evaporator with a city wall structure according to claim 1, characterized in that, In step (2), the freeze drying is carried out under vacuum conditions at -60°C for 6 hours.

4. A carbonized loofah photothermal evaporator with a city wall structure prepared by the method described in claim 1, characterized in that, The carbonized loofah retains the anisotropic structure of the inner and outer layers of the fresh loofah. The outer layer of the loofah skin is dense, similar to a city wall, which helps maintain its shape and provide structural protection. The inner layer of the loofah pulp is loose and porous, which can act as a channel for directional water transport and help water evaporate efficiently.

5. The application of a carbonized loofah photothermal evaporator prepared by the method described in claim 1 or the carbonized loofah photothermal evaporator described in claim 4 in the fields of seawater desalination and wastewater treatment.

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