Carbon-based composite moisture absorption material based on in-situ activation as well as preparation method and application of carbon-based composite moisture absorption material

Abstract

The invention belongs to the technical field of moisture absorption materials, and particularly discloses a carbon-based composite moisture absorption material based on in-situ activation and a preparation method and application thereof.The preparation method comprises the steps that a K-MOF precursor is selected, and the carbonization condition (the inert atmosphere of 600-800 DEG C) is controlled, so that the potassium element is reserved in a carbon skeleton in the potassium salt composite form of K2O / KOH and the like; a chemical bonding interface is constructed through an in-situ chemical reaction; in the carbonization process, K < + > ions and a carbon skeleton form C-O-K bonds, so that the heat conduction of the interface is enhanced; the hierarchical porous structure (micropore-mesopore-macropore synergy) realizes rapid diffusion of water molecules, and solar energy driven desorption without external energy supply is not needed; according to the method, residual potassium salt is directionally converted into KHCO3 through CO2 / H2O mixed gas, high-dispersion K2CO3 active sites are generated through heat treatment, structural damage caused by acid pickling is avoided, and the adsorption performance of the obtained porous carbon loaded potassium carbonate (K2CO3) composite structure is greatly improved; the K2CO3 nanocrystals are fixed by utilizing a carbon skeleton confinement effect, the performance is not reduced after multiple cycles, and the problem of short service life caused by salt deliquescence of a traditional composite material is solved.

Description

Technical Field

[0001] The invention relates to the technical field of hygroscopic materials, in particular to an in-situ activated carbon-based composite hygroscopic material and a preparation method and application thereof. Background Art

[0002] As the global water shortage problem becomes increasingly serious, the development of efficient water collection technology is particularly important. Traditional water desalination technologies such as flash evaporation and distillation require not only complex basic equipment but also high energy consumption, which hinders their popularization. Water resources are abundant in the atmosphere, accounting for about 10% of all fresh water in the earth's lakes. It is a ubiquitous natural resource that helps alleviate the global water crisis. Atmospheric water collection technology is divided into fog collection, dew point collection and adsorption atmospheric water collection technology. The former two require continuous high relative humidity or a large amount of energy input, making them unsuitable for arid areas with low relative humidity and areas with limited infrastructure. Adsorption-based atmospheric water collection has demonstrated unique adaptability and flexibility in recent years. It can capture moisture from the air anytime and anywhere and is considered to be an environmentally friendly and promising water production technology. Its core lies in the development of functional materials with efficient moisture absorption, rapid desorption and cyclic stability. The current mainstream technical routes have the following bottleneck problems: 1. Traditional hygroscopic salts (such as CaCl2, LiCl) are prone to agglomeration of particles, poor recyclability, and the adsorption amount of materials decays after recycling, and the desorption energy consumption is high. 2. Traditional porous materials such as zeolite and molecular sieve have low adsorption capacity, high regeneration temperature and high desorption energy consumption. 3. Metal-organic framework (MOF) is a new type of porous material. It is a framework structure self-assembled by inorganic metal ions and organic ligands through coordination bonds. It has the characteristics of high porosity, large specific surface area, adjustable pore size and diverse topological structures. Therefore, it has great potential in the field of atmospheric water collection. However, most MOF powders are white or light-colored, and their own photothermal conversion capacity is low. They usually need to be mixed with solar absorbers such as carbon black and graphite powder to achieve solar thermal desorption function. In addition, mixing MOF with graphene will also lead to a decrease in specific surface area and water absorption. The long-term stability of MOF in actual environmental applications is still controversial. 4. MOF-derived carbon materials require hydrochloric acid etching process to remove residual metals, which may lead to loss of active sites and low adsorption capacity. In the prior art, the application of potassium-based MOF carbonization products is mostly focused on the field of electrochemistry, and there has been no report on its use in atmospheric water collection. 5. Photothermal-hygroscopic composite materials: The physical mixing of graphene / carbon nanotubes and hygroscopic salts causes the salt particles to be wrapped, reducing the hygroscopic dynamics, and the thermal conductivity between the photothermal layer and the hygroscopic layer is insufficient. The hygroscopic salts usually used contain halogens and are highly corrosive, and there is a risk of leakage if used for a long time.

[0003] Therefore, there is an urgent need for a new type of high-efficiency water collection material and its preparation method to improve the efficiency of atmospheric water collection and reduce energy consumption. Summary of the invention

[0004] In order to solve the above technical problems, the present invention provides a carbon-based composite hygroscopic material based on in-situ activation and a preparation method and application thereof.

[0005] To achieve the above object, the present invention is implemented according to the following technical solutions:

[0006] One of the technical solutions of the present invention is a method for preparing a carbon-based composite hygroscopic material based on in-situ activation, comprising the following steps:

[0007] S1. Preparation of K-MOF precursor;

[0008] S2, uniformly dispersing the K-MOF precursor in a nickel boat, placing the boat in a tube furnace, and then replacing the tube furnace with nitrogen three times; then carbonizing the boat under a nitrogen flow, and then naturally cooling the boat to room temperature to obtain a derived carbon material;

[0009] S3, put the derived carbon powder into a U-shaped tube, and introduce CO 2 / H 2 O mixed gas is subjected to gas activation treatment to obtain an activated derivative carbon material;

[0010] S4. Heat the activated derivative carbon material to 120-150° C. and maintain for 1-2 hours, and cool to room temperature to obtain a composite hygroscopic material.

[0011] Furthermore, the step S1 specifically includes:

[0012] S1-1, dissolve 0.632 g potassium nitrate and 0.074 g ammonium fluoride in 1 ml deionized water to obtain solution A;

[0013] S1-2, dissolving 1.51 g of 1,3,5-trimethylbenzene trimesic acid BTC in 14 mL of N,N′-dimethylformamide under ultrasonic conditions to obtain solution B;

[0014] S1-3. After mixing solution A and solution B, seal and heat to 180° C. and store for 3 days; after cooling to room temperature, filter and discard the filtrate, wash the product three times with DMF and three times with ethanol to obtain a K-MOF precursor.

[0015] Furthermore, in step S2, the carbonization treatment is performed by heating from room temperature to a carbonization temperature of 700°C at a heating rate of 2°C / min and maintaining the temperature for 60 minutes.

[0016] Furthermore, in step S3, CO is introduced 2 / H 2 The process of O mixed gas is:

[0017] The carbon dioxide gas cylinder is used as the gas source. After the carbon dioxide gas is washed with pure water, it carries CO 2 / H 2 The O mixed gas enters the U-shaped tube, and the tail gas pipe is connected to the beaker. The flow rate is adjusted to 80-120 mL / min according to the bubbles in the beaker, and the process continues for 12 h.

[0018] The second technical solution of the present invention is an in-situ activated carbon-based composite hygroscopic material prepared by the above method.

[0019] The third technical solution of the present invention is an application of in-situ activated carbon-based composite hygroscopic material in atmospheric water collection.

[0020] Compared with the prior art, the present invention selects K-MOF precursor and controls the carbonization conditions (600-800℃ inert atmosphere) to make potassium element K 2 O / KOH and other potassium salt composite forms are retained in the carbon skeleton; chemical bonding interface is constructed through in situ chemical reaction: K + The ions form COK bonds with the carbon skeleton to enhance interfacial heat conduction; the hierarchical porous structure (micropore-mesopore-macroporous synergy) enables rapid diffusion of water molecules and solar-driven desorption without external energy supply; CO 2 / H 2 O mixed gas directional conversion of residual potassium salt to KHCO 3 , and then heat treated to generate highly dispersed K 2 CO 3 Active sites, avoiding structural damage caused by acid washing, the obtained porous carbon loaded with potassium carbonate (K 2 CO 3 )'s composite structure has greatly improved its adsorption performance; the carbon skeleton confinement effect is used to fix K 2 CO 3 Nanocrystals have no performance degradation after multiple cycles, solving the problem of short life of traditional composite materials due to salt deliquescence. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Scanning electron microscopy images of K-MOF precursor: (a) scale bar is 50 μm; (b) scale bar is 20 μm.

[0022] Figure 2 It is the composite potassium carbonate (K 2 CO 3 @AC-700) SEM images: (a) scale bar is 50 μm; (b) scale bar is 10 μm.

[0023] Figure 3 K 2 CO 3 @AC-700 transmission electron microscope image.

[0024] Figure 4 K 2 CO 3 @AC-700’s transmission electron microscope-X-ray energy spectrum analysis diagram.

[0025] Figure 5 K 2 CO 3 @AC-700’s X-ray diffraction pattern.

[0026] Figure 6 K 2 CO 3 @Aperture distribution diagram of AC-700.

[0027] Figure 7 K 2 CO 3 @AC-700 water adsorption performance diagram.

[0028] Figure 8 K 2 CO 3 @AC-700 UV-visible-near-infrared absorption spectrum.

[0029] Fig. 9 K 2 CO 3 @AC-700 water adsorption cycle 30 times.

[0030] Fig.10 K 2 CO 3 @Water quality test chart collected by AC-700. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with embodiments. The specific embodiments described herein are only used to explain the present invention and are not used to limit the invention.

[0032] Unless otherwise specified, the raw materials and reagents used in the following examples were commercially available.

[0033] Example 1: Preparation of carbon-based composite hygroscopic material based on in-situ activation

[0034] 1) K-MOF precursor synthesis: Using the solvothermal method, 0.632 g potassium nitrate (KNO 3 ) and 0.074 g ammonium fluoride (NH 4F) dissolved in 1ml deionized water; take a 20mL glass vial, dissolve 1.51g of 1,3,5-benzene trimesic acid BTC in 14mL N,N′-dimethylformamide (DMF) under ultrasound, wait until it is completely dissolved, and then pour it into the initial 50mL Teflon liner; then seal the reactor and heat it to 180°C and store it for 3 days; after cooling to room temperature, filter, wash the product three times with DMF, wash it three times with ethanol, and dry it to obtain the K-MOF precursor. Using potassium as the raw material, the yield of colorless rod-shaped crystals of K-MOF is ≥90%. The electron microscope image of the K-MOF precursor is as follows Figure 1 As shown by Figure 1 It can be seen that the metal organic framework compound was successfully synthesized, which is a rod-shaped crystal with high crystallinity.

[0035] 2) In-situ carbonization activation: Disperse about 1g of the dried K-MOF precursor evenly in a nickel boat, place it in a tube furnace, and then replace the tube furnace with nitrogen three times at room temperature, with each ventilation time of about 0.5h to 1h. Then, slowly increase the temperature from room temperature to the carbonization temperature of 700℃ under nitrogen flow, with a heating rate of 2℃ / min, and maintain for 60min; then cool naturally to room temperature to obtain a derived carbon material. The derived carbon material retains the K element to form K 2 O / KOH and other potassium salt complexes.

[0036] 3) Gas activation treatment: The obtained derived carbon material is placed in a U-shaped tube and CO is introduced into the tube. 2 / H 2 O mixed gas (Specific operation: Carbon dioxide cylinder is used as the gas source, and the carbon dioxide gas is washed with pure water and then carries CO 2 / H 2 O mixed gas enters the U-shaped tube, and the tail gas pipe is connected to the beaker. The flow rate is adjusted to 100mL / min according to the bubbles in the beaker, which is roughly uniform and continuous bubbles). This process continues for 12 hours, so that K 2 O / KOH and other potassium salt complexes fully react to form KHCO 3 .

[0037] 4) Thermally induced phase change: The activated carbon derivative material is heated to 120-150°C and maintained for 2 hours to make the KHCO 3 Decompose into K 2 CO 3 , cooled to room temperature to obtain a composite hygroscopic material of porous carbon loaded with potassium carbonate, denoted as K 2 CO 3 @AC-700.K 2 CO 3 @AC-700 electron microscope image Figure 2 As shown by Figure 2It can be seen that the generated carbon material can better maintain the morphology of the original precursor. Figure 3 K 2 CO 3 @AC-700 transmission electron microscope image, we can see that the carbon material is wrapped with dark substances. Further analysis using transmission electron microscope-X-ray energy spectrum, such as Figure 4 As shown in the figure, the three elements C, O, and K are evenly distributed. Then, the X-ray diffractometer is used for analysis, as shown in the figure. Figure 5 As shown, XRD shows that there is K on the amorphous peak of carbon. 2 CO 3 The sharp peak is consistent with the crystal standard card, which confirms that the composite hygroscopic material of porous carbon loaded with potassium carbonate is successfully synthesized. Figure 6 K 2 CO 3 @AC-700 pore size distribution diagram, by Figure 6 It can be seen that the hierarchical porous structure (micropore-mesopore-macroporous synergy) is conducive to the rapid diffusion of water molecules.

[0038] Example 2: Application of in-situ activated carbon-based composite hygroscopic materials in atmospheric water collection

[0039] The volumetric method was used to measure the gas adsorption using a BELSORP MAX II gas adsorption analyzer. Approximately 0.1 g of dry K 2 CO 3 @AC-700 was placed in the analysis tube of the vapor sorption analyzer and activated by in-situ degassing at 160°C for 12 hours to ensure complete removal of residual water, and then the test was started.

[0040] K 2 CO 3 @AC-700 water adsorption performance Figure 7 As shown, the adsorption process is mainly divided into three steps. The first step is chemical adsorption, K 2 CO 3 Adsorbed water molecules become K 2 CO 3 1.5H 2 O; the second step is deliquescent adsorption, hydrated potassium carbonate crystals continue to adsorb water molecules deliquescing; the third step is solution adsorption, concentrated potassium carbonate solution adsorbs water molecules to become a dilute solution. The adsorption capacity is 1.05g / g under 25℃ / 60%RH conditions. The metal ion concentration in the collected aqueous solution is detected by inductively coupled plasma optical emission spectroscopy (ICP-OES), such as Fig.10 As shown, K of this embodiment 2 CO 3 @AC-700 collected K in water + The content is <10ppm, and the heavy metal content in the collected water meets the WHO standard.

[0041] As a comparison, the above K 2 CO 3 @AC-700 replaced with MAF-4 (aka ZIF-8) derived carbon NPC MAF-4 -800 or Steam-80, MAF-4 adsorbs less than 350 mg / g at 25°C / 60% RH; Steam-80 adsorbs about 0.3 g / g at 25°C / 60% RH. 2 CO 3 @AC-700 has a 3-fold improvement in water adsorption compared to conventional dilution materials.

[0042] K was detected using UV-vis-NIR spectroscopy (Lambda 950, PerkinElmer). 2 CO 3 @AC-700 UV-visible-near-infrared absorption spectrum, K 2 CO 3 @AC-700 UV-visible near-infrared absorption spectrum Figure 8 As shown by Figure 8 It can be seen that the solar light absorption rate is about 97%, 1kW / m 2 The surface temperature under illumination rose to 70°C within 10 min, and the desorption efficiency was improved.

[0043] Furthermore, K 2 CO 3 @AC-700 capacity after 30 cycles Fig. 9 As shown by Fig. 9 It can be seen that K 2 CO 3 @AC-700 has a capacity retention rate of >95% after 30 cycles. 2 CO 3 @AC-700's performance does not decrease after multiple cycles, solving the problem of short life of traditional composite materials due to salt deliquescence (traditional composite materials <20 cycles).

[0044] The technical solution of the present invention is not limited to the above-mentioned specific embodiments. All technical variations made according to the technical solution of the present invention fall within the protection scope of the present invention.

Claims

1. A method for preparing a carbon-based composite hygroscopic material based on in-situ activation, characterized in that: The following steps are involved: S1. Preparation of K-MOF precursor; S2, uniformly dispersing the K-MOF precursor in a nickel boat, placing the boat in a tube furnace, and then replacing the tube furnace with nitrogen three times; then carbonizing the boat under a nitrogen flow, and then naturally cooling the boat to room temperature to obtain a derived carbon material; S3, placing the obtained derived carbon powder into a U-shaped tube, introducing a CO2 / H2O mixed gas for gas activation treatment, and obtaining an activated derived carbon material; S4. Heat the activated derivative carbon material to 120-150° C. and maintain for 1-2 hours, and cool to room temperature to obtain a composite hygroscopic material.

2. The method for preparing a carbon-based composite hygroscopic material based on in-situ activation according to claim 1, characterized in that: The step S1 specifically includes: S1-1, dissolve 0.632 g potassium nitrate and 0.074 g ammonium fluoride in 1 ml deionized water to obtain solution A; S1-2, dissolving 1.51 g of 1,3,5-trimethylbenzene trimesic acid BTC in 14 mL of N,N'-dimethylformamide under ultrasonic conditions to obtain solution B; S1-3. After mixing solution A and solution B, seal and heat to 180° C. and store for 3 days; after cooling to room temperature, filter and discard the filtrate, wash the product three times with DMF and three times with ethanol to obtain a K-MOF precursor.

3. The method for preparing a carbon-based composite hygroscopic material based on in-situ activation according to claim 1, characterized in that: In the step S2, the carbonization treatment is performed by heating from room temperature to a carbonization temperature of 700°C at a heating rate of 2°C / min and maintaining the temperature for 60 minutes.

4. The method for preparing a carbon-based composite hygroscopic material based on in-situ activation according to claim 1, characterized in that: In step S3, the process of introducing the CO2 / H2O mixed gas is as follows: Using a carbon dioxide cylinder as the gas source, the carbon dioxide gas enters the U-shaped tube with a CO2 / H2OO mixture after washing the bottle with pure water. The tail pipe is then connected to a beaker. The flow rate is adjusted to 80-120 mL / min according to the bubbles in the beaker and continued for 12 hours.

5. A carbon-based composite hygroscopic material based on in-situ activation prepared by the method according to any one of claims 1 to 4.

6. An application of the in-situ activated carbon-based composite hygroscopic material as claimed in claim 5 in atmospheric water collection.

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