A biomass aerogel-based seawater evaporator with controllable pore size and preparation method thereof

Abstract

The present invention discloses a biomass aerogel-based seawater evaporator with controllable pore size and a preparation method thereof. In the present invention, a wood fiber suspension is mixed with carboxymethyl nanocellulose, and the mixture is sequentially subjected to directional freezing, freeze drying, acetylation, and cleaning, and then a titanium carbide photothermal layer is sprayed on the top to obtain a biomass aerogel-based seawater evaporator. The biomass aerogel-based seawater evaporator prepared by the present invention has low density, high porosity, and high light absorption rate. Compared with other biomass-based seawater evaporators, the evaporator obtained by the present invention can adjust the pore size of the aerogel by controlling the carboxymethyl nanocellulose content, thereby balancing the evaporation enthalpy and water transfer rate of the evaporator to obtain excellent seawater evaporation efficiency, showing great application prospects in the field of seawater desalination.

Description

Technical Field

[0001] The invention relates to the technical field of seawater evaporator material preparation, and in particular to a biomass aerogel-based seawater evaporator with controllable pore size and a preparation method thereof. Background Art

[0002] With the rapid population growth and the increasingly serious water pollution, the shortage of fresh water resources has become one of the major problems facing the world today. About 70% of the earth's surface is covered by seawater, and salt water resources are abundant. Therefore, seawater desalination is considered to be the most promising way to solve the problem of fresh water shortage. Reverse osmosis and thermal distillation are currently common methods of seawater desalination. However, these technologies are limited by high energy consumption and complex equipment. Solar interfacial water evaporation technology has become one of the most promising water treatment technologies at present because it uses clean energy, has low carbon emissions and high treatment efficiency.

[0003] The interior of existing solar interfacial water evaporators is usually disordered, which is not conducive to the rapid transmission of seawater inside the evaporator and easily leads to the accumulation of salt. In addition, most of the existing solar interfacial water evaporators also include multiple components such as photothermal layer, thermal insulation layer and water transmission layer, which are easily destroyed in complex seawater environments. Inspired by the transmission of water and nutrients in wood, researchers prepared a cellulose aerogel-based seawater evaporator with vertical channels through directional freezing technology. Although its vertically arranged porous structure greatly improves the liquid absorption rate of the evaporator, its water evaporation rate is still relatively low, which is related to the high energy demand inherent in water evaporation (i.e., evaporation enthalpy). According to the evaporation enthalpy-related theory, reducing the pore size of the evaporator is conducive to reducing the water evaporation enthalpy and thus accelerating evaporation. However, the reduction in pore size may hinder the absorption of water by the evaporator. Therefore, it is necessary to design a biomass aerogel-based seawater evaporator with controllable pore size to achieve a balance between evaporation enthalpy and water transmission rate, so as to achieve a higher seawater evaporation efficiency (>2kg m 2 / h, 1kW / m 2 ). Summary of the invention

[0004] In order to overcome the deficiencies of the above-mentioned prior art, the present invention provides a biomass aerogel-based seawater evaporator with controllable pore size and a preparation method thereof. The prepared biomass aerogel-based seawater evaporator has low density, high porosity and high light absorption rate. Compared with other biomass-based seawater evaporators, the evaporator obtained by the present invention can adjust the pore size of the aerogel by controlling the content of carboxymethyl nanocellulose (CMNC), thereby balancing the evaporation enthalpy and water transfer rate of the evaporator to obtain excellent seawater evaporation efficiency, showing great application prospects in the field of seawater desalination.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] The invention discloses a biomass aerogel-based seawater evaporator with controllable pore size, comprising wood fiber and carboxymethyl nanocellulose.

[0007] The method for preparing a biomass aerogel-based seawater evaporator with controllable pore size comprises mixing a wood fiber suspension with carboxymethyl nanocellulose, sequentially performing directionally freezing, freeze drying, acetylation, and washing, and then spraying a titanium carbide photothermal layer on the top to obtain the evaporator.

[0008] The mixing of the wood fiber suspension and the carboxymethyl nanocellulose is carried out according to the following steps:

[0009] S1. Prepare a wood fiber suspension with a mass fraction of 4 wt%;

[0010] S2. Add a carboxymethyl nanocellulose suspension with a solid content of 1 wt% to the wood fiber suspension obtained in step S1, and stir at room temperature for 15 to 60 minutes; the amount of carboxymethyl nanocellulose added is 10 to 30 wt% of the absolute dry weight of the wood fiber; and adjust the concentration of the wood fiber suspension to 1 to 3 wt%.

[0011] The diameter of the wood fiber ranges from 5 to 100 nm.

[0012] The diameter of the carboxymethyl nanocellulose is in the range of 4 to 10 nm, and the carboxymethyl content is in the range of 1.2 to 3.0 mmol / g.

[0013] The directional freezing is carried out in a directional freezing device, and the directional freezing conditions are: the directional freezing angle is 0-20 degrees, the freezing source is liquid nitrogen, and the freezing time is 45 minutes.

[0014] The freeze drying is carried out in a freeze dryer under the following conditions: temperature of -98.5 to -60°C, pressure of 14 to 35 Pa, and freezing time of 36 to 72 hours.

[0015] The acetylation is carried out as follows: the freeze-dried product is placed in an 8 wt % acetyl chloride solution at room temperature for reaction for 3 to 7 hours.

[0016] The cleaning is carried out in the following manner: the acetylated product is fully cleaned with tetrahydrofuran, ethanol and deionized water in sequence.

[0017] The titanium carbide photothermal layer is sprayed in the following manner: the titanium carbide photothermal layer is sprayed on the top of the product after thorough cleaning and acetylation, and after the titanium carbide photothermal layer is sprayed, it is freeze-dried in a freeze dryer for 24 to 48 hours.

[0018] The spraying amount of the titanium carbide photothermal layer is 0.5-2.5 mg / cm 2 .

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] (1) The biomass aerogel-based seawater evaporator prepared in the present invention has a highly ordered vertically arranged pore structure, which can quickly transport water and dissolve the salt in seawater in time to improve the stability of seawater evaporation.

[0021] (2) The biomass aerogel-based seawater evaporator prepared by the present invention has a low density (13.50-32.12 mg / cm 3 ), high porosity (92.62~98.60%) and high light absorption (79.60~93.90%).

[0022] (3) The evaporator obtained by the present invention can adjust the pore size of the aerogel (21.6-91.9 μm) by controlling the carboxymethyl nanocellulose (CMNC) content, thereby further regulating the evaporation enthalpy and water transfer rate of the evaporator to obtain excellent seawater evaporation efficiency (1.87-3.36 kg / m 2 / h), showing great application prospects in the field of seawater desalination.

[0023] (4) The present invention can use agricultural and forestry waste as raw materials to prepare wood fiber through mechanical pulping, which is not affected by the source of the raw materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a physical picture of the sample in Example 2.

[0025] Figure 2 These are the corresponding SEM images (ac) of the sample obtained in Example 2 in different directions: top, front and side.

[0026] Figure 3 The top SEM images of the samples obtained in Examples 1, 3, 4 and Comparative Example are shown. DETAILED DESCRIPTION

[0027] The present invention is further described below in conjunction with the examples, but it should not be construed as limiting the present invention. Without departing from the spirit and substance of the present invention, simple modifications or replacements made to the methods, steps or conditions of the present invention are within the scope of the present invention. Unless otherwise specified, the technical means used in the examples are conventional means well known to those skilled in the art.

[0028] Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in the art. Unless otherwise specified, the reagents and materials used in the following examples are commercially available.

[0029] Example 1

[0030] A method for preparing a biomass aerogel-based seawater evaporator with controllable pore size, the specific steps are as follows:

[0031] S1. Prepare a wood fiber suspension having a mass fraction of 4 wt% and a fiber diameter of 20 to 100 nm;

[0032] S2. Add a carboxymethyl nanocellulose suspension with a solid content of 1 wt% to the wood fiber suspension obtained in step S1 and stir at room temperature for 15 minutes; the amount of carboxymethyl nanocellulose added is 10 wt% of the absolute dry weight of the wood fiber, the diameter range is 4 to 10 nm, and the carboxymethyl content is 1.2 to 3.0 mmol / g; adjust the concentration of the wood fiber suspension to 1 wt%.

[0033] S3. Freeze the mixed solution obtained in step S2 in a directional freezing device, the directional freezing conditions are: freezing angle 0°, freezing source is liquid nitrogen, freezing time 45min; after directional freezing, put it into a freeze dryer for freeze drying, the freeze drying conditions are: -60.0℃, 35Pa, freeze drying for 36h;

[0034] S4. The freeze-dried product of step S3 was placed in an acetyl chloride solution (8 wt %) at room temperature for 3 h, and then washed with tetrahydrofuran (THF), ethanol and deionized water in sequence;

[0035] S5. Spray a titanium carbide photothermal layer (0.5 mg / cm 2 ), and freeze-dried in a freeze dryer for 24 hours to obtain a biomass aerogel-based seawater evaporator.

[0036] The biomass aerogel-based seawater evaporator prepared in this example was weighed at room temperature and pressure to measure its density, which was 13.50 mg / cm 3 .

[0037] The porosity of the biomass aerogel-based seawater evaporator prepared in this example was measured by mass density method at room temperature and pressure. The porosity was 98.68% at room temperature and pressure.

[0038] The surface morphology of the biomass aerogel-based seawater evaporator prepared in this example was observed by scanning electron microscopy, and the pore size was 91.9 μm.

[0039] The biomass aerogel-based seawater evaporator prepared in this example was measured by near-infrared spectrometer to determine its light absorption rate at 1 kW / m 2 The light absorption rate under light intensity of is 90.36%.

[0040] The water evaporation mass of the biomass aerogel-based seawater evaporator prepared in this embodiment was measured in a dark environment and compared with deionized water of the same surface area. The evaporation enthalpy of the evaporator was then calculated using the evaporation enthalpy of water (2450 J / g), and the evaporation enthalpy was 1791.60 J / g.

[0041] The water absorption mass per unit time of the biomass aerogel-based seawater evaporator prepared in this example was measured at room temperature and pressure to calculate the water transmission rate, and the water transmission rate was 75.84 g / min.

[0042] The biomass aerogel-based seawater evaporator prepared in this example was placed on an electronic balance, and the mass change of water during the evaporation process was recorded in real time to calculate its seawater evaporation efficiency. 2 The evaporation efficiency of seawater under the light intensity of 1.87 kg / m 2 / h.

[0043] Example 2

[0044] A method for preparing a biomass aerogel-based seawater evaporator with controllable pore size, the specific steps are as follows:

[0045] S1. Prepare a wood fiber suspension having a mass fraction of 4 wt% and a fiber diameter of 6 to 11 nm;

[0046] S2. Add a carboxymethyl nanocellulose suspension having a solid content of 1 wt% to the wood fiber suspension obtained in step S1 and stir at room temperature for 30 min; the amount of carboxymethyl nanocellulose added is 20 wt% of the absolute dry weight of the wood fiber, the diameter range is 4 to 10 nm, and the carboxymethyl content is 1.2 to 3.0 mmol / g; adjust the concentration of the wood fiber suspension to 2 wt%,

[0047] S3. Freeze the mixed solution obtained in step S2 in a directional freezing device, the directional freezing conditions are: freezing angle 10°, freezing source is liquid nitrogen, freezing time 45min; after directional freezing, put it into a freeze dryer for freeze drying, the freeze drying conditions are: -86.5℃, 20Pa, freeze drying for 48h;

[0048] S4. The freeze-dried product of step S3 was placed in an acetyl chloride solution (8 wt %) at room temperature for 5 h, and then washed with tetrahydrofuran (THF), ethanol and deionized water in sequence;

[0049] S5. Spray a titanium carbide photothermal layer (1 mg / cm 2 ), and freeze-dried in a freeze dryer for 36 hours to obtain a biomass aerogel-based seawater evaporator.

[0050] The biomass aerogel-based seawater evaporator prepared in this example was weighed at room temperature and pressure to measure its density, which was 23.38 mg / cm 3 .

[0051] The porosity of the biomass aerogel-based seawater evaporator prepared in this example was measured by mass density method at room temperature and pressure. The porosity was 97.74% at room temperature and pressure.

[0052] The surface morphology of the biomass aerogel-based seawater evaporator prepared in this example was observed by scanning electron microscopy, and the pore size was 73.4 μm.

[0053] The biomass aerogel-based seawater evaporator prepared in this example was measured by near-infrared spectrometer to determine its light absorption rate at 1 kW / m 2 The light absorption rate under light intensity of is 93.10%.

[0054] The water evaporation mass of the biomass aerogel-based seawater evaporator prepared in this embodiment was measured in a dark environment and compared with deionized water of the same surface area. The evaporation enthalpy of the evaporator was then calculated using the evaporation enthalpy of water (2450 J / g), and the evaporation enthalpy was 1434.35 J / g.

[0055] The water absorption mass per unit time of the biomass aerogel-based seawater evaporator prepared in this example was measured at room temperature and pressure to calculate the water transmission rate, and the water transmission rate was 55.61 g / min.

[0056] The biomass aerogel-based seawater evaporator prepared in this example was placed on an electronic balance, and the mass change of water during the evaporation process was recorded in real time to calculate its seawater evaporation efficiency. 2 The evaporation efficiency of seawater under the light intensity is 3.36Kg / m 2 / h.

[0057] Example 3

[0058] A method for preparing a biomass aerogel-based seawater evaporator with controllable pore size, the specific steps are as follows:

[0059] S1. Prepare a wood fiber suspension with a mass fraction of 4 wt% and a fiber diameter of 5 to 8 nm;

[0060] S2. Adding a carboxymethyl nanocellulose suspension having a solid content of 1 wt% to the wood fiber suspension obtained in step S1 and stirring at room temperature for 60 min, wherein the amount of carboxymethyl nanocellulose added is 30 wt% of the absolute dry weight of the wood fiber, the diameter ranges from 4 to 10 nm, and the carboxymethyl content is 1.2 to 3.0 mmol / g; adjusting the concentration of the wood fiber suspension to 3 wt%;

[0061] S3. Freeze the mixed solution obtained in step S2 in a directional freezing device, the directional freezing conditions are: freezing angle 20°, freezing source is liquid nitrogen, freezing time 45min; after directional freezing, put it into a freeze dryer for freeze drying, the freeze drying conditions are: -98.5℃, 14Pa, freeze drying for 72h;

[0062] S4. The freeze-dried product of step S3 was placed in an acetyl chloride solution (8 wt %) at room temperature for 7 h, and then washed with tetrahydrofuran (THF), ethanol and deionized water in sequence;

[0063] S5. Spray a titanium carbide photothermal layer (2 mg / cm 2 ), and freeze-dried in a freeze dryer for 36 hours to obtain a biomass aerogel-based seawater evaporator.

[0064] The biomass aerogel-based seawater evaporator prepared in this example was weighed at room temperature and pressure to measure its density, which was 32.12 mg / cm 3 .

[0065] The porosity of the biomass aerogel-based seawater evaporator prepared in this example was measured by mass density method at room temperature and pressure. The porosity was 96.62% at room temperature and pressure.

[0066] The surface morphology of the biomass aerogel-based seawater evaporator prepared in this example was observed by scanning electron microscopy, and the pore size was 21.6 μm.

[0067] The biomass aerogel-based seawater evaporator prepared in this example was measured by near-infrared spectrometer to determine its light absorption rate at 1 kW / m 2 The light absorption rate under light intensity of is 93.90%.

[0068] The water evaporation mass of the biomass aerogel-based seawater evaporator prepared in this example was measured in a dark environment and compared with deionized water of the same surface area. The evaporation enthalpy of the evaporator was then calculated using the evaporation enthalpy of water (2450 J / g), and the evaporation enthalpy was 1146.53 J / g.

[0069] The water absorption mass per unit time of the biomass aerogel-based seawater evaporator prepared in this example was measured at room temperature and pressure to calculate the water transmission rate, and the water transmission rate was 31.94 g / min.

[0070] The biomass aerogel-based seawater evaporator prepared in this example was placed on an electronic balance, and the mass change of water during the evaporation process was recorded in real time to calculate its seawater evaporation efficiency. 2 The evaporation efficiency of seawater under the light intensity of 2.10kg / m2 / h.

[0071] Example 4

[0072] A method for preparing a biomass aerogel-based seawater evaporator with controllable pore size, the specific steps are as follows:

[0073] S1. Prepare a wood fiber suspension having a mass fraction of 4 wt% and a fiber diameter of 20 to 100 nm;

[0074] S2. Adding a carboxymethyl nanocellulose suspension having a solid content of 1 wt% to the wood fiber suspension obtained in step S1 and stirring at room temperature for 45 min, wherein the amount of carboxymethyl nanocellulose added is 25 wt% of the absolute dry weight of the wood fiber, the diameter ranges from 4 to 10 nm, and the carboxymethyl content is 1.2 to 3.0 mmol / g; adjusting the concentration of the wood fiber suspension to 1.5 wt%;

[0075] S3. Freeze the mixed solution obtained in step S2 in a directional freezing device, the directional freezing conditions are: freezing angle 5°, freezing source is liquid nitrogen, freezing time 45min; after directional freezing, put it into a freeze dryer for freeze drying, the freeze drying conditions are: -86.5℃, 20Pa, freeze drying for 72h;

[0076] S4. The freeze-dried product of step S3 was placed in an acetyl chloride solution (8 wt %) at room temperature for 6 h, and then washed with tetrahydrofuran (THF), ethanol and deionized water in sequence;

[0077] S5. Spray a titanium carbide photothermal layer (1.5 mg / cm 2 ), and freeze-dried in a freeze dryer for 48 hours to obtain the biomass aerogel-based seawater evaporator.

[0078] The biomass aerogel-based seawater evaporator prepared in this example was weighed at room temperature and pressure to measure its density, which was 23.15 mg / cm 3 .

[0079] The porosity of the biomass aerogel-based seawater evaporator prepared in this example was measured by mass density method at room temperature and pressure. The porosity was 97.76% at room temperature and pressure.

[0080] The surface morphology of the biomass aerogel-based seawater evaporator prepared in this example was observed by scanning electron microscopy, and the pore size was 85.6 μm.

[0081] The biomass aerogel-based seawater evaporator prepared in this example was measured by near-infrared spectrometer to determine its light absorption rate at 1 kW / m 2The light absorption rate under light intensity of is 92.10%.

[0082] The water evaporation mass of the biomass aerogel-based seawater evaporator prepared in this example was measured in a dark environment and compared with deionized water of the same surface area. The evaporation enthalpy of the evaporator was then calculated using the evaporation enthalpy of water (2450 J / g), and the evaporation enthalpy was 1206.33 J / g.

[0083] The water absorption mass per unit time of the biomass aerogel-based seawater evaporator prepared in this example was measured at room temperature and pressure to calculate the water transmission rate, and the water transmission rate was 45.36 g / min.

[0084] The biomass aerogel-based seawater evaporator prepared in this example was placed on an electronic balance, and the mass change of water during the evaporation process was recorded in real time to calculate its seawater evaporation efficiency. 2 The evaporation efficiency of seawater under the light intensity of 2.36 kg / m 2 / h.

[0085] Comparative Example 1

[0086] Different from Example 2, step S2 is not performed in this comparative example, and the other step conditions are the same as those in Example 2.

[0087] The biomass aerogel-based seawater evaporator prepared in this comparative example was measured for density by weighing method at room temperature and pressure. The density at room temperature and pressure was 625 mg / cm 3 .

[0088] The porosity of the biomass aerogel-based seawater evaporator prepared in this comparative example was measured by mass density method at room temperature and pressure, and the porosity was 35.80% at room temperature and pressure.

[0089] The surface morphology of the biomass aerogel-based seawater evaporator prepared in this comparative example was observed by scanning electron microscopy, and no obvious void structure was observed.

[0090] The biomass aerogel-based seawater evaporator prepared in this comparative example was measured by near-infrared spectrometer to determine its light absorption rate at 1 kW / m 2 The light absorption rate under light intensity of 85.50% is achieved.

[0091] The water evaporation mass of the biomass aerogel-based seawater evaporator prepared in this embodiment was measured in a dark environment and compared with deionized water of the same surface area. The evaporation enthalpy of the evaporator was then calculated using the evaporation enthalpy of water (2450 J / g), and the evaporation enthalpy was 2030.38 J / g.

[0092] The water absorption mass per unit time of the biomass aerogel-based seawater evaporator prepared in this example was measured at room temperature and pressure to calculate the water transmission rate, and the water transmission rate was 15.21 g / min.

[0093] The biomass aerogel-based seawater evaporator prepared in this example was placed on an electronic balance, and the mass change of water during the evaporation process was recorded in real time to calculate its seawater evaporation efficiency. 2 The evaporation efficiency of seawater under the light intensity of 0.60kg / m 2 / h.

[0094] The following table is a comparison table of density, porosity, pore size, light absorption rate, evaporation enthalpy, water transfer rate and evaporation efficiency of the seawater evaporators prepared in Examples 1 to 4 and Comparative Example 1.

[0095] project Example 1 Example 2 Example 3 Example 4 Comparative Example 1 <![CDATA[Density (mg / cm 3 )]]> 13.50 23.38 32.12 23.15 625 Porosity (%) 98.60 97.74 96.62 97.76 35.80 Pore ​​size (μm) 91.9 73.4 21.6 85.6 - Light absorption rate (%) 90.36 93.10 93.90 92.10 85.50 Enthalpy of evaporation (J / g) 1791.60 1434.35 1146.53 1206.33 2030.38 Water transmission rate (g / min) 75.84 55.61 31.94 45.36 15.21 <![CDATA[Evaporation efficiency (kg / m 2 / h)]]> 1.87 3.36 2.10 2.36 0.60

[0096] The residual lignin in the full-component wood fiber will hinder the hydrogen bonds between carbohydrate polymers, making the biomass aerogel-based seawater evaporator brittle and structurally collapsed. Since carboxymethyl nanocellulose has carboxyl / hydroxyl groups and micro-nano scales, it can not only form hydrogen bonds with the wood cellulose components, but also fill in between the entangled fibers. The CMNC fibers connect the two nearby sheets like a bridge, giving the evaporator a wood-like microstructure and vertically arranged directional channels, while supporting the micro-nano pore structure of the evaporator and maintaining its stability. At the same time, increasing the CMNC and slurry concentrations will strengthen the hydrogen bonding and fiber entanglement inside the evaporator, thereby increasing the density of the evaporator and reducing its porosity and pore size.

[0097] The biomass aerogel-based seawater evaporator (4.5×4.5×1cm 3 ) is placed in a beaker filled with natural seawater (250mL), and the evaporator can float on the surface of natural seawater and allow natural light to illuminate its top. The entire seawater evaporation device is placed on an electronic balance to record the mass change of water during the evaporation process in real time and evaluate its water evaporation efficiency. The excellent evaporation efficiency of the biomass aerogel-based seawater evaporator is the result of the combined effect of water evaporation enthalpy and water transfer rate. At the same volume, the specific surface area of ​​the small-aperture evaporator is larger than that of the large-aperture evaporator. Therefore, in the small-aperture evaporator, the lignocellulosic matrix can form more intermediate water, thereby weakening the hydrogen bonds between water molecules to reduce the evaporation enthalpy during the evaporation process. The large pore size can increase the water transfer rate during the evaporation process. The preparation conditions adopted in Example 2 obtain a suitable pore size, achieving a balance between the water evaporation enthalpy and the water transfer rate of the biomass aerogel-based seawater evaporator during the evaporation process, thereby achieving the highest evaporation efficiency.

[0098] The technical principle of the present invention is: through the physical cross-linking, directional freezing, freeze drying and chemical modification of micro / nanostructured biomass wood fiber and carboxymethyl nanocellulose (CMNC), a biomass aerogel-based seawater evaporator with controllable pore size is rationally designed, and the key parameters are systematically studied. Among them, the micro-nanoscale wood fiber can expose more hydroxyl groups and produce a larger specific surface area, which is conducive to the mutual bonding between fibers, thereby improving the mechanical properties and structural stability of the seawater evaporator. The appropriate freezing angle and slurry concentration help to construct the anisotropic vertical channel structure inside the seawater evaporator, which helps to quickly transfer water and redissolve salt in water. The rich hydroxyl / carboxyl groups of CMNC and its own nanoscale help to enhance the interconnection between cellulose fibers, so the pore size (21.6~91.9μm) of the biomass aerogel-based seawater evaporator can be effectively regulated by adjusting the CMNC content. Regulating the pore size of the evaporator can achieve a balance between the evaporation enthalpy and the water transmission rate to improve the seawater evaporation efficiency of the evaporator. During the freeze-drying process, the freeze-drying temperature and pressure determine the sublimation rate of the liquid phase in the suspension. A moderate sublimation rate can better form a directional channel structure of the evaporator. After acetylation modification at room temperature, some hydroxyl groups on cellulose are replaced by acetyl groups, which not only improves the stability of the fiber in water, but also retains the fully hydrophilic channels of the biomass aerogel without affecting the water absorption and diffusion of the evaporator.

Claims

1. A biomass aerogel-based seawater evaporator with controllable pore size, It is characterized in that The invention comprises wood fiber and carboxymethyl nanocellulose; the wood fiber suspension is mixed with carboxymethyl nanocellulose, and then the mixture is subjected to sequential direction freezing, freeze drying, acetylation, washing, and then a titanium carbide photothermal layer is sprayed on the top to obtain the mixture; The mixing of the wood fiber suspension and the carboxymethyl nanocellulose is carried out according to the following steps: S1. Prepare a wood fiber suspension with a mass fraction of 4 wt%; S2. Add a carboxymethyl nanocellulose suspension having a solid content of 1 wt% to the wood fiber suspension obtained in step S1, and stir at room temperature for 15 to 60 min; the amount of carboxymethyl nanocellulose added is 10 to 30 wt% of the absolute dry weight of the wood fiber; and adjust the concentration of the wood fiber suspension to 1 to 3 wt%; The directional freezing is carried out in a directional freezing device, and the directional freezing conditions are: the directional freezing angle is 0 to 20 degrees, the freezing source is liquid nitrogen, and the freezing time is 45 minutes; the freeze drying is carried out in a freeze dryer, and the conditions are a temperature of -98.5 to -60°C, a pressure of 14 to 35 Pa, and a freezing time of 36 to 72 hours; The acetylation is carried out as follows: the freeze-dried product is placed in an 8 wt % acetyl chloride solution at room temperature for reaction for 3 to 7 hours; The diameter of the wood fiber ranges from 5 to 100 nm; The diameter of the carboxymethyl nanocellulose is in the range of 4 to 10 nm.

2. A method for preparing a biomass aerogel-based seawater evaporator with controllable pore size as claimed in claim 1, It is characterized in that The wood fiber suspension is mixed with carboxymethyl nanocellulose, and then directionally frozen, freeze-dried, acetylated, washed, and then a titanium carbide photothermal layer is sprayed on the top to obtain; The mixing of the wood fiber suspension and the carboxymethyl nanocellulose is carried out according to the following steps: S1. Prepare a wood fiber suspension with a mass fraction of 4 wt%; S2. Add a carboxymethyl nanocellulose suspension having a solid content of 1 wt% to the wood fiber suspension obtained in step S1, and stir at room temperature for 15 to 60 min; the amount of carboxymethyl nanocellulose added is 10 to 30 wt% of the absolute dry weight of the wood fiber; and adjust the concentration of the wood fiber suspension to 1 to 3 wt%; The directional freezing is carried out in a directional freezing device, and the directional freezing conditions are: the directional freezing angle is 0 to 20 degrees, the freezing source is liquid nitrogen, and the freezing time is 45 minutes; the freeze drying is carried out in a freeze dryer, and the conditions are a temperature of -98.5 to -60°C, a pressure of 14 to 35 Pa, and a freezing time of 36 to 72 hours; The acetylation is carried out as follows: the freeze-dried product is placed in an 8 wt % acetyl chloride solution at room temperature for 3 to 7 hours; The diameter of the wood fiber ranges from 5 to 100 nm; The diameter of the carboxymethyl nanocellulose is in the range of 4 to 10 nm.

3. A method for preparing a biomass aerogel-based seawater evaporator with controllable pore size according to claim 2, It is characterized in that The carboxymethyl content is 1.2 to 3.0 mmol / g.

4. A method for preparing a biomass aerogel-based seawater evaporator with controllable pore size according to claim 2, It is characterized in that The cleaning is carried out in the following manner: the acetylated product is fully cleaned with tetrahydrofuran, ethanol and deionized water in sequence.

5. The method for preparing a biomass aerogel-based seawater evaporator with controllable pore size according to claim 2, It is characterized in that The titanium carbide photothermal layer is sprayed in the following manner: the titanium carbide photothermal layer is sprayed on the top of the product after thorough cleaning and acetylation, and after the titanium carbide photothermal layer is sprayed, it is freeze-dried in a freeze dryer for 24 to 48 hours.

6. A method for preparing a biomass aerogel-based seawater evaporator with controllable pore size according to claim 2, It is characterized in that The spraying amount of the titanium carbide photothermal layer is 0.5-2.5 mg / cm 2 .

Images