A bamboo shoot-based photothermal material for solar desalination and its preparation method

Abstract

The present invention relates to the field of materials technology, and specifically relates to a bamboo shoot-based photothermal material that can be used for solar desalination of seawater and a preparation method thereof; the present invention uses a one-step pyrolysis reduction method to prepare a photothermal layer (porous carbon doped with silver nanoparticles) and a freeze-drying technique to prepare a substrate (porous bamboo shoots), and attaches the porous carbon doped with silver nanoparticles to the porous bamboo shoot substrate through simple coating, and finally prepares a photothermal material that can be used for efficient solar desalination of seawater. This material has the characteristics of high evaporation rate, low thermal conductivity, and high quality of fresh water; the entire preparation process of the present invention has the advantages of economy, efficiency, and environmental friendliness.

Description

Technical Field

[0001] The present invention relates to the technical field of materials, and particularly relates to a bamboo shoot-based photothermal material for solar desalination and a preparation method thereof. Background Art

[0002] In the prior art, solar photothermal conversion materials, such as carbon foam, graphite porous material, carbon aerogel, graphene, porous carbon, etc., have been developed. However, these materials have disadvantages such as high cost, poor biodegradability, and pollution of water bodies by the carrier layer, and it is difficult to optimize and control the material structure and performance. Therefore, developing a new type of high-efficiency photothermal conversion material with low cost, controllable structure, and clean environmental protection has become a key problem to be solved urgently in the field of solar desalination. Summary of the Invention

[0003] The present invention relates to the technical field of materials, and particularly relates to a photothermal material for efficient solar desalination and a preparation method thereof. The present invention uses a one-step pyrolysis reduction method to prepare a photothermal layer - porous carbon doped with silver nanoparticles, and a freeze-drying technique to prepare a substrate - porous bamboo shoots. The porous carbon doped with silver nanoparticles is attached to the porous bamboo shoot substrate by simple coating, and finally a photothermal material for efficient solar desalination is prepared. This material has the characteristics of high evaporation rate, low thermal conductivity, and low salt content. The entire preparation process of the present invention has the advantages of economy, high efficiency, and environmental protection.

[0004] A bamboo shoot-based photothermal material for solar desalination comprises the following steps:

[0005] 1) Pretreatment of the bamboo shoot substrate

[0006] Cut the bamboo shoots into blocks with dimensions of 3 cm × 3 cm × 1.5 cm along the growth direction, wash away the surface impurities with distilled water, place the processed bamboo shoot blocks in a freeze-dryer for directional freeze molding, and then perform freeze-drying to obtain a porous bamboo shoot substrate;

[0007] 2) Preparation of porous carbon doped with silver nanoparticles

[0008] Cut the bamboo shoots into slices and soak them in distilled water to remove impurities. The washed sample is dried at 60 °C for 12 h and then ground into powder; mix the bamboo shoot powder with silver nitrate solution to obtain a mixed solution 1. The mixed solution 1 is oscillated at 25 °C for 3 h, filtered to obtain a precipitate, dried in an oven at 50 °C for 12 hours, and finally the dried bamboo shoot powder is placed in a tubular furnace for high-temperature carbonization to obtain porous carbon doped with silver nanoparticles;

[0009] 3) Preparation of the bamboo shoot-based photothermal material

[0010] Disperse the porous carbon doped with silver nanoparticles prepared in step (2) in an aqueous solution of polyvinyl alcohol and stir evenly to obtain a mixed solution 2. Then, evenly brush the mixed solution 2 on the surface of the porous bamboo shoots prepared in step (1) and bake it in an oven at 50 °C for 2 hours to obtain the bamboo shoot-based photothermal material.

[0011] In some embodiments of the present invention, the time of directional freeze-casting in step (1) is 5-20 h, the temperature of directional freeze-casting is -80 °C to -18 °C, the temperature of freeze-drying is -80 °C to -18 °C, and the time of freeze-drying is 10-50 h.

[0012] In some embodiments of the present invention, the concentration of the silver nitrate solution in step (2) is 1 mg / mL, and the weight-to-volume ratio of the bamboo shoot powder to the silver nitrate solution is 1 g:100 ml.

[0013] In some embodiments of the present invention, the temperature of high-temperature carbonization in step (2) is 750 °C, the heat preservation time of high-temperature carbonization is 2 h, and the heating rate of high-temperature carbonization is 5 °C / min.

[0014] In some embodiments of the present invention, the concentration of the aqueous solution of polyvinyl alcohol in step (3) is 5 wt%, and the weight ratio of the porous carbon doped with silver nanoparticles to the aqueous solution of polyvinyl alcohol is 1:19 - 1:1, preferably 1:3.

[0015] On the other hand, the present invention provides a bamboo shoot-based photothermal material prepared by the above method.

[0016] On yet another aspect, the present invention provides the application of the bamboo shoot-based photothermal material prepared by the above method in solar seawater desalination.

[0017] The present invention uses bamboo shoots as raw materials and prepares a novel bamboo shoot-based photothermal conversion material with controllable structure and biodegradability through freeze-drying and pyrolytic reduction technologies to achieve the efficient utilization of solar energy and efficient water evaporation; the porous bamboo shoot substrate prepared by the freeze-drying technology of the present invention has good and fast water transportation channels and excellent heat management capabilities, which are beneficial to the concentration of heat energy on the surface of the photothermal material; the porous carbon doped with silver nanoparticles of the present invention has a fast thermal response ability and a light absorption rate as high as 96%; based on the above advantages, it meets the needs of solar seawater desalination, improves the interfacial light steam conversion efficiency, and maximizes the seawater desalination efficiency; the raw materials of the present invention are wide, the cost is low, and it has biodegradable properties. Description of the Drawings

[0018] Figure 1 SEM top view of the porous bamboo shoots prepared in Example 3.

[0019] Figure 2 SEM image of the bamboo shoot-based photothermal material prepared in Example 3, showing a side view.

[0020] Figure 3 SEM image of the bamboo shoot-based photothermal material prepared in Example 3, showing a top view.

[0021] Figure 4 TEM image of the porous carbon doped with silver nanoparticles in Example 3.

[0022] Figure 5 Actual object image of the bamboo shoot-based photothermal material prepared in Example 3.

[0023] Figure 6 Simulated light illumination surface temperature change diagram of the bamboo shoot-based photothermal material prepared in Example 3.

[0024] Figure 7 Light absorption rate diagram of the bamboo shoot-based photothermal material prepared in Example 3.

[0025] Figure 8 Diagram of the number of cycles and evaporation rate change of the bamboo shoot-based photothermal material prepared in Example 3 during the cyclic test.

[0026] Figure 9 Effect of porous carbon doped with different contents of silver nanoparticles in Examples 1 - 4 on the evaporation rate.

[0027] Figure 10 Comparison diagram of the thermal conductivity of the bamboo shoot substrate and the bamboo shoot-based photothermal material prepared in Example 3.

[0028] Among them, A is the thermal conductivity of the bamboo shoot substrate, B is the thermal conductivity of the bamboo shoot-based photothermal material, Dry represents the dry state (without moisture), and Wet represents the wet state (moisture-saturated). Detailed implementation manners

[0029] To better understand the present invention, the content of the present invention will be further clarified below in conjunction with embodiments, but the present invention is not limited to the following embodiments.

[0030] The evaporator is wrapped with polystyrene foam and floats on the surface of distilled water. A xenon light source and optical elements (AM1.5) are used to simulate sunlight illumination and correct the spectrum respectively. The light intensity is adjusted by a light power meter. The change of the water mass is tracked in real time by an electronic microbalance (accuracy 0.001 g). At the same time, an infrared camera is used to record the surface temperature of the sample. The temperature and humidity during the experiment are maintained at 25°C and 40% respectively.

[0031] The evaporation rate and evaporation efficiency are calculated as follows:

[0032]

[0033] η = (Δvh LV ) / I

[0034] h LV = h v + CΔT

[0035] where m represents the evaporation rate (g), A represents the interfacial area of the photothermal material (m 2 ), Δv represents the evaporation rate (kg m -2 h -1 ); h v is the enthalpy of phase change (2256.0 kJ kg -1 , C is the specific heat capacity of water (4.2 J g -1 K -1 ), ΔT is the change from the initial temperature to the final temperature (°C), and I is the power density of solar illumination (1 kW m -2 ).

[0036] Example 1

[0037] 1) Pretreatment of bamboo shoot substrate

[0038] Cut the bamboo shoots into blocks of 3 cm × 3 cm × 1.5 cm along the growth direction, wash them with distilled water to remove surface impurities, place the processed bamboo shoot blocks in a freeze dryer for directional freeze forming, where the freeze forming temperature is -80 °C, the freeze forming time is 5 h, the freeze drying temperature is -80 °C, and the freeze drying time is 10 h, and then perform freeze drying to obtain a porous bamboo shoot substrate;

[0039] 2) Preparation of porous carbon doped with silver nanoparticles

[0040] Cut the bamboo shoots into slices, soak them in distilled water to remove impurities, dry the washed bamboo shoot slices at 60 °C for 12 h, and then grind them into powder. Take 1 g of bamboo shoot powder and mix it with 100 ml of silver nitrate solution (1 mg / mL) to obtain a mixed solution 1. Oscillate the mixed solution 1 at 25 °C for 3 h, filter to obtain a precipitate, dry it in an oven at 50 °C for 12 hours, and place it in a tube furnace for high-temperature carbonization. Among them, the high-temperature carbonization temperature is 750 °C, the holding time of the high-temperature carbonization is 2 h, and the heating rate of the high-temperature carbonization is 5 °C / min to obtain porous carbon doped with silver nanoparticles;

[0041] 3) Preparation of bamboo shoot-based photothermal material

[0042] Disperse 1 g of the porous carbon doped with silver nanoparticles prepared in step 2) in 19 g of a polyvinyl alcohol (5 wt%) solution, stir evenly to obtain a mixed solution 2, then evenly apply the mixed solution 2 on the surface of the porous bamboo shoots prepared in step 1), and dry it in an oven at 50 °C for 2 hours to obtain a bamboo shoot-based photothermal material (Sample No. 1).

[0043] Example 2

[0044] 1) Pretreatment of the bamboo shoot substrate

[0045] Cut the bamboo shoots into blocks with dimensions of 3 cm × 3 cm × 1.5 cm along the growth direction, wash them with distilled water to remove surface impurities, place the treated bamboo shoot blocks in a freeze dryer for directional freeze forming, where the temperature of freeze forming is -80 °C, the time of freeze forming is 5 h, the temperature of freeze drying is -80 °C, and the time of freeze drying is 10 h, and then carry out freeze drying to obtain a porous bamboo shoot substrate;

[0046] 2) Preparation of porous carbon doped with silver nanoparticles

[0047] Cut the bamboo shoots into slices, soak them in distilled water to remove impurities, dry the washed bamboo shoot slices at 60 °C for 12 h, and then grind them into powder. Take 1 g of bamboo shoot powder and mix it with 100 ml of silver nitrate solution (1 mg / mL) to obtain a mixed solution 1. Oscillate the mixed solution 1 at 25 °C for 3 h, filter to obtain a precipitate, dry it in an oven at 50 °C for 12 hours, and place it in a tube furnace for high-temperature carbonization. Among them, the temperature of high-temperature carbonization is 750 °C, the holding time of high-temperature carbonization is 2 h, and the heating rate of high-temperature carbonization is 5 °C / min to obtain porous carbon doped with silver nanoparticles;

[0048] 3) Preparation of bamboo shoot-based photothermal material

[0049] Disperse 2.5 g of the porous carbon doped with silver nanoparticles prepared in step 2) in 17.5 g of a polyvinyl alcohol (5 wt%) solution, stir evenly to obtain a mixed solution 2, then evenly apply the mixed solution 2 on the surface of the porous bamboo shoots prepared in step 1), and dry it in an oven at 50 °C for 2 hours to obtain a bamboo shoot-based photothermal material (Sample No. 2).

[0050] Example 3

[0051] 1) Pretreatment of the bamboo shoot substrate

[0052] Cut the bamboo shoots into blocks with dimensions of 3 cm × 3 cm × 1.5 cm along the growth direction, wash them with distilled water to remove surface impurities, place the processed bamboo shoot blocks in a freeze dryer for directional freezing and forming. The temperature for freezing and forming is -80 °C, the time for freezing and forming is 5 h, the temperature for freeze drying is -80 °C, and the time for freeze drying is 10 h. Then, perform freeze drying to obtain a porous bamboo shoot substrate;

[0053] 2) Preparation of porous carbon doped with silver nanoparticles

[0054] Cut the bamboo shoots into slices, soak them in distilled water to remove impurities, dry the washed bamboo shoot slices at 60 °C for 12 h, and then grind them into powder. Take 1 g of bamboo shoot powder and mix it with 100 ml of silver nitrate solution (1 mg / mL) to obtain a mixed solution 1. Oscillate the mixed solution 1 at 25 °C for 3 h, filter to obtain a precipitate, dry it in an oven at 50 °C for 12 h, and place it in a tube furnace for high-temperature carbonization. The temperature for high-temperature carbonization is 750 °C, the holding time for high-temperature carbonization is 2 h, and the heating rate for high-temperature carbonization is 5 °C / min to obtain porous carbon doped with silver nanoparticles;

[0055] 3) Preparation of bamboo shoot-based photothermal materials

[0056] Disperse 5 g of the porous carbon doped with silver nanoparticles prepared in step 2) in 15 g of a polyvinyl alcohol (5 wt%) solution and stir evenly to obtain a mixed solution 2. Then, evenly apply the mixed solution 2 on the surface of the porous bamboo shoots prepared in step 1) and dry it in an oven at 50 °C for 2 h to obtain a bamboo shoot-based photothermal material (Sample No. 3).

[0057] Example 4

[0058] 1) Pretreatment of bamboo shoot substrate

[0059] Cut the bamboo shoots into blocks with dimensions of 3 cm × 3 cm × 1.5 cm along the growth direction, wash them with distilled water to remove surface impurities, place the processed bamboo shoot blocks in a freeze dryer for directional freezing and forming. The temperature for freezing and forming is -80 °C, the time for freezing and forming is 5 h, the temperature for freeze drying is -80 °C, and the time for freeze drying is 10 h. Then, perform freeze drying to obtain a porous bamboo shoot substrate;

[0060] 2) Preparation of porous carbon doped with silver nanoparticles

[0061] Cut the bamboo shoots into slices, soak them in distilled water to remove impurities, dry the washed bamboo shoot slices at 60 °C for 12 h, and then grind them into powder. Take 1 g of bamboo shoot powder and mix it with 100 ml of silver nitrate solution (1 mg / mL) to obtain mixed solution 1. Oscillate mixed solution 1 at 25 °C for 3 h, filter to obtain a precipitate, dry it in an oven at 50 °C for 12 hours, and place it in a tube furnace for high-temperature carbonization. Among them, the high-temperature carbonization temperature is 750 °C, the heat preservation time of the high-temperature carbonization is 2 h, and the heating rate of the high-temperature carbonization is 5 °C / min to obtain porous carbon doped with silver nanoparticles;

[0062] 3) Preparation of bamboo shoot-based photothermal materials

[0063] Disperse 10 g of the porous carbon doped with silver nanoparticles prepared in step 2) in 10 g of a polyvinyl alcohol (5 wt%) solution, stir evenly to obtain mixed solution 2, and then evenly brush mixed solution 2 on the surface of the porous bamboo shoots prepared in step 1), and dry it in an oven at 50 °C for 2 hours to obtain a bamboo shoot-based photothermal material (Sample No. 4).

[0064] Example 5

[0065] The evaporation rate and evaporation amount of the bamboo shoot-based photothermal materials in Examples 1-4 were tested. The results are shown in Table 1 and Figure 9. The bamboo shoot-based photothermal material (Sample No. 3) prepared in Example 3 was subjected to a cycling test, and the results are as follows Figure 8 shown. The thermal conductivity of the bamboo shoot substrate and the bamboo shoot-based photothermal material prepared in Example 3 was tested, and the results are as follows Figure 10 shown.

[0066] Table 1

[0067]

[0068] Example 6

[0069] 1) Pretreatment of bamboo shoot substrate

[0070] Cut the bamboo shoots into blocks of 3 cm × 3 cm × 1.5 cm along the growth direction, wash them with distilled water to remove surface impurities, place the processed bamboo shoot blocks in a freeze dryer for directional freeze molding. Among them, the freeze molding temperature is -40 °C, the freeze molding time is 15 h, the freeze drying temperature is -50 °C, and the freeze drying time is 30 h. Then, perform freeze drying to obtain a porous bamboo shoot substrate;

[0071] 2) Preparation of porous carbon doped with silver nanoparticles

[0072] Cut the bamboo shoots into slices, soak them in distilled water to remove impurities, dry the washed bamboo shoot slices at 60 °C for 12 h, and then grind them into powder. Take 1 g of bamboo shoot powder and mix it with 100 ml of silver nitrate solution (1 mg / mL) to obtain mixed solution 1. Oscillate mixed solution 1 at 25 °C for 3 h, filter to obtain a precipitate, dry it in an oven at 50 °C for 12 hours, and place it in a tube furnace for high-temperature carbonization. Among them, the temperature of the high-temperature carbonization is 750 °C, the heat preservation time of the high-temperature carbonization is 2 h, and the heating rate of the high-temperature carbonization is 5 °C / min to obtain porous carbon doped with silver nanoparticles;

[0073] 3) Preparation of bamboo shoot-based photothermal material

[0074] Disperse 5 g of the porous carbon doped with silver nanoparticles prepared in step 2) in 15 g of polyvinyl alcohol (5 wt%) solution and stir evenly to obtain mixed solution 2. Then evenly brush mixed solution 2 on the surface of the porous bamboo shoots prepared in step 1), and dry it in an oven at 50 °C for 2 hours to obtain the bamboo shoot-based photothermal material, and measure its evaporation rate to be 1.5 kg m -2 h -1 。

[0075] Example 7

[0076] 1) Pretreatment of bamboo shoot substrate

[0077] Cut the bamboo shoots into blocks with dimensions of 3 cm × 3 cm × 1.5 cm along the growth direction, wash them with distilled water to remove surface impurities, place the processed bamboo shoot blocks in a freeze dryer for directional freeze molding. Among them, the temperature of the freeze molding is -18 °C, the time of the freeze molding is 20 h, the temperature of the freeze drying is -18 °C, the time of the freeze drying is 50 h, and then carry out freeze drying to obtain a porous bamboo shoot substrate;

[0078] 2) Preparation of porous carbon doped with silver nanoparticles

[0079] Cut the bamboo shoots into slices, soak them in distilled water to remove impurities, dry the washed bamboo shoot slices at 60 °C for 12 h, and then grind them into powder. Take 1 g of bamboo shoot powder and mix it with 100 ml of silver nitrate solution (1 mg / mL) to obtain mixed solution 1. Oscillate mixed solution 1 at 25 °C for 3 h, filter to obtain a precipitate, dry it in an oven at 50 °C for 12 hours, and place it in a tube furnace for high-temperature carbonization. Among them, the temperature of the high-temperature carbonization is 750 °C, the heat preservation time of the high-temperature carbonization is 2 h, and the heating rate of the high-temperature carbonization is 5 °C / min to obtain porous carbon doped with silver nanoparticles;

[0080] 3) Preparation of bamboo shoot-based photothermal material

[0081] Disperse 5 g of the porous carbon doped with silver nanoparticles prepared in step 2) in 15 g of a polyvinyl alcohol (5 wt%) solution and stir evenly to obtain a mixed solution 2. Then, evenly apply the mixed solution 2 on the surface of the porous bamboo shoots prepared in step 1), and bake it in an oven at 50 °C for 2 hours to obtain a bamboo shoot-based photothermal material. Measure its evaporation rate to be 1.51 kg m -2 h -1 。

[0082] Example 8

[0083] 1) Pretreatment of the bamboo shoot substrate

[0084] Cut the bamboo shoots into blocks with dimensions of 3 cm × 3 cm × 1.5 cm along the growth direction, wash them with distilled water to remove surface impurities, and place the processed bamboo shoot blocks in a freeze dryer for directional freeze molding. The temperature of the freeze molding is -50 °C, the time of the freeze molding is 6 h, the temperature of the freeze drying is -50 °C, and the time of the freeze drying is 20 h. Then, perform freeze drying to obtain a porous bamboo shoot substrate;

[0085] 2) Preparation of porous carbon doped with silver nanoparticles

[0086] Cut the bamboo shoots into slices, soak them in distilled water to remove impurities, dry the washed bamboo shoot slices at 60 °C for 12 h, and then grind them into powder. Take 1 g of the bamboo shoot powder and mix it with 100 ml of a silver nitrate solution (1 mg / mL) to obtain a mixed solution 1. Oscillate the mixed solution 1 at 25 °C for 3 h, filter to obtain a precipitate, bake it in an oven at 50 °C for 12 hours, and place it in a tube furnace for high-temperature carbonization. The temperature of the high-temperature carbonization is 750 °C, the holding time of the high-temperature carbonization is 2 h, and the heating rate of the high-temperature carbonization is 5 °C / min to obtain porous carbon doped with silver nanoparticles;

[0087] 3) Preparation of the bamboo shoot-based photothermal material

[0088] Disperse 5 g of the porous carbon doped with silver nanoparticles prepared in step 2) in 15 g of a polyvinyl alcohol (5 wt%) solution and stir evenly to obtain a mixed solution 2. Then, evenly apply the mixed solution 2 on the surface of the porous bamboo shoots prepared in step 1), and bake it in an oven at 50 °C for 2 hours to obtain a bamboo shoot-based photothermal material. Measure its evaporation rate to be 1.49 kg m -2 h -1 。

[0089] As described above, these are only several specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution and inventive concept of the present invention, makes equivalent substitutions or changes, and should be covered within the protection scope of the present invention.

Claims

1. A preparation method of bamboo shoot-based photothermal materials for solar desalination of seawater, characterized in that It includes the following steps: 1) Pretreatment of bamboo shoot substrate Cut the bamboo shoots into blocks with a size of 3 cm×3 cm×1.5 cm along the growth direction, wash them with distilled water to remove surface impurities, place the processed bamboo shoot blocks in a freeze dryer for directional freezing and forming, and then perform freeze drying to obtain a porous bamboo shoot substrate; 2) Preparation of porous carbon doped with silver nanoparticles Cut the bamboo shoots into slices, soak them in distilled water to remove impurities, dry the washed samples at 60°C for 12 h, and then grind them into powder; mix the bamboo shoot powder with silver nitrate solution to obtain mixed solution 1, shake mixed solution 1 at 25°C for 3 h, filter to obtain a precipitate, dry it in an oven at 50°C for 12 hours, and finally place the dried bamboo shoot powder in a tube furnace for high-temperature carbonization to obtain porous carbon doped with silver nanoparticles; 3) Preparation of bamboo shoot-based photothermal material Disperse the porous carbon doped with silver nanoparticles prepared in step 2) in an aqueous solution of polyvinyl alcohol and stir evenly to obtain mixed solution 2, then evenly coat mixed solution 2 on the surface of the porous bamboo shoots prepared in step 1), and dry it in an oven at 50°C for 2 hours to obtain a bamboo shoot-based photothermal material.

2. The preparation method of the bamboo shoot-based photothermal material for solar desalination according to claim 1, wherein The time for directional freezing and forming in step 1) is 5-20 h, the temperature for directional freezing and forming is -80°C to -18°C, the temperature for freeze drying is -80°C to -18°C, and the time for freeze drying is 10-50 h.

3. The preparation method of a bamboo shoot-based photothermal material for solar desalination according to claim 1, characterized in that In step 2), the concentration of the silver nitrate solution is 1 mg / mL, and the weight-volume ratio of the bamboo shoot powder to the silver nitrate solution is 1 g:100 ml.

4. The preparation method of the bamboo shoot-based photothermal material for solar desalination according to claim 1, wherein In step 2), the temperature for high-temperature carbonization is 750°C, the heat preservation time for high-temperature carbonization is 2 h, and the heating rate for high-temperature carbonization is 5°C / min.

5. The preparation method of the bamboo shoot-based photothermal material for solar desalination according to claim 1, characterized in that In step 3), the concentration of the aqueous solution of polyvinyl alcohol is 5 wt%, and the weight ratio of the porous carbon doped with silver nanoparticles to the aqueous solution of polyvinyl alcohol is 1:19 - 1:

1.

6. The preparation method of a bamboo shoot-based photothermal material for solar desalination according to claim 5, characterized in that The weight ratio of the porous carbon doped with silver nanoparticles to the aqueous solution of polyvinyl alcohol is 1:

3.

7. A bamboo shoot-based photothermal material prepared by the method according to any one of claims 1-5.

8. Application of the bamboo shoot-based photothermal material according to claim 7 in solar seawater desalination.

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