Mxene-mof biomimetic porous material and preparation method and application thereof

Abstract

This invention provides an MXene-MOF biomimetic porous material, its preparation method, and its applications. The biomimetic porous material has directional honeycomb or layered porous channels arranged along the freezing direction, with characteristic pore sizes ranging from 20 to 200 μm. This invention uses MXene two-dimensional sheets as the framework reinforcing phase, CALF-20 as the main CO2 adsorption functional phase, and CMC as the connecting and shaping binder phase. A biomimetic hierarchical porous channel arrangement along the freezing direction is constructed through directional freeze-drying, thus balancing bulk formability, gas mass transfer efficiency, and utilization of adsorption active sites. The biomimetic porous material sample prepared by this invention achieves an efficiency of 9.89% in passive direct air capture tests, higher than the CALF-20 sample (48 h) without MXene (4.56%). The resulting bulk sample exhibits directional pores, lightweight, self-supporting properties, hydrophobicity, and a certain degree of elastic recovery.

Description

Technical Field

[0001] This invention relates to the fields of environmental governance, direct air capture, and carbon capture materials, and specifically to an MXene-MOF biomimetic porous material, its preparation method, and its application. The biomimetic porous material is used for efficient CO2 capture and is applied to direct air capture (DAC). Background Technology

[0002] Carbon dioxide capture, utilization, and storage (CCUS) is a key technological pathway for addressing global climate change, among which DAC technology has attracted widespread attention due to its ability to directly capture ultra-low concentrations of CO2 from the atmosphere. Adsorbent materials, as the core of this technology, directly determine the efficiency and economic feasibility of the carbon capture process.

[0003] While the liquid amine method is widely used for CO2 capture, it suffers from problems such as high regeneration energy consumption, equipment corrosion, solvent evaporation, and degradation. In contrast, solid adsorbents offer advantages in reducing corrosion and simplifying processes, but traditional activated carbon, zeolite, and conventional polymer adsorbents are still often limited by insufficient capacity under low partial pressure, difficulty in powder forming, and poor mass transfer efficiency under complex operating conditions.

[0004] MOF materials possess tunable pore structures and high CO2 affinity, showing great potential in adsorption and separation applications; however, their mechanical stability and engineering adaptability in powder form remain limited. MXenes exhibit two-dimensional layered structures, abundant surface functional groups, and ease of constructing continuous networks; however, when used alone, they also suffer from issues such as interlayer stacking and insufficient self-support.

[0005] Existing technologies, such as CN118450940A, use electrochemical fiber adsorbents formed by porous carriers composed of adsorbents and conductive materials. A conductive layer is formed on the surface or inside the pores of the carrier through spinning technology. Combined with resistance heating or induction heating methods, carbon dioxide adsorption and desorption are achieved. However, the preparation process involves many steps and the low-concentration carbon dioxide capture capacity is insufficient.

[0006] Therefore, this invention proposes an MXene-MOF biomimetic porous material suitable for industrial production and its preparation method. Summary of the Invention

[0007] To achieve the above-mentioned technical objectives, this invention provides an MXene-MOF biomimetic porous material and its preparation method, addressing the shortcomings of existing solid adsorbents in bulk formation, directional mass transfer, and low-concentration CO2 capture. This invention uses MXene two-dimensional sheets as the framework reinforcing phase, CALF-20 as the main CO2 adsorption functional phase, and carboxymethyl cellulose (CMC) as the connecting and shaping binder. A biomimetic hierarchical porous channel arranged along the freezing direction is constructed through directional freeze-drying, thus balancing bulk formability, gas mass transfer efficiency, and utilization of adsorption active sites. The biomimetic porous material sample prepared by this invention achieves an efficiency of 9.89% in passive direct air capture tests, higher than the Calf-20 sample (48 h) without MXene (4.56%). The resulting bulk sample possesses directional pores, is lightweight, self-supporting, hydrophobic, and has a certain elastic recovery capability.

[0008] To achieve the above objectives, the technical solution of the present invention is as follows: In a first aspect, an MXene-MOF biomimetic porous material is provided, wherein the MXene-MOF biomimetic porous material is prepared by using MXene two-dimensional sheets as the skeleton reinforcement phase, CALF-20 as the CO2 adsorption functional phase and carboxymethyl cellulose as the connecting and molding bonding phase, and has directional honeycomb or layered porous channels arranged along the freezing direction, with characteristic pore size of 20~200 μm.

[0009] In some embodiments, the static water contact angle of the MXene-MOF biomimetic porous material is 110~118°, preferably about 114°.

[0010] In some embodiments, the MXene-MOF biomimetic porous material exhibits higher trapping efficiency than the CALF-20 sample without MXene under the same passive direct air trapping test conditions.

[0011] In some embodiments, the MXene-MOF biomimetic porous material is a composite block or an aerogel.

[0012] Secondly, a method for preparing MXene-MOF biomimetic porous materials is provided, including: S1. Mix MXene dispersion, MOF and binder to form a slurry; or grow MOF in situ on the surface of MXene dispersion and then mix it with binder to form a slurry; S2. The slurry is subjected to directional freezing and freeze-drying to obtain MXene-MOF biomimetic porous material.

[0013] In some embodiments, the adhesive is carboxymethyl cellulose.

[0014] In some embodiments, the concentration of MXene in the MXene dispersion is 10-15 mg / mL, preferably 10 mg / mL, 11 mg / mL, 12 mg / mL, 13 mg / mL, 14 mg / mL, 15 mg / mL, or any two of the above values ​​forming any range.

[0015] In some embodiments, the method for preparing the MXene dispersion includes: adding the MAX precursor to an etching system for etching and purifying it to prepare the MXene dispersion.

[0016] In some embodiments, the MAX precursor is selected from at least one of Ti3AlC2, Ti2AlC, Ti3AlCN, Ta4AlC3, V2AlC, V3AlC2, Mo2AlC, and Mo2TiAlC2.

[0017] In some embodiments, the MXene is selected from Ti3C2T x Ti2CT x Ti3CNT x Ta4C3T x V2CT x V3C2T x Mo2CT x and Mo2TiC2T x At least one of the following, T includes one or more of -OH, -F, and -O, x represents the number of T, and x>0. Preferably, MXene is Ti3C2T. x .

[0018] In some embodiments, the etching system is an aqueous HF solution or a LiF / HCl mixed etching system. In some embodiments, the concentration of the aqueous HF solution is 40-50 wt%, preferably 40 wt%, 41 wt%, 42 wt%, 43 wt%, 44 wt%, 45 wt%, 46 wt%, 47 wt%, 48 wt%, 49 wt%, 50 wt%, or any two of the above values ​​forming any range. In some embodiments, in the LiF / HCl mixed etching system, the HCl concentration is 6~9 mol / L, and the amount of LiF added is 1.0~1.6 g LiF per 20 mL of hydrochloric acid. Preferably, the HCl concentration is any one of the ranges consisting of any two values ​​from 6 mol / L, 7 mol / L, 8 mol / L, 9 mol / L, etc.; preferably, the amount of LiF added is any one of the ranges consisting of any two values ​​from 1.0 g LiF, 1.1 g LiF, 1.2 g LiF, 1.3 g LiF, 1.4 g LiF, 1.5 g LiF, 1.6 g LiF per 20 mL of hydrochloric acid, etc. In some embodiments, when using an HF aqueous solution as the etching system, the etching temperature is 20-25 °C and the etching time is 18-24 h; when using a LiF / HCl mixed etching system, the etching temperature is 35-40 °C and the etching time is 20-24 h; the etching time can be 20 °C, 22 °C, 25 °C, or 35 °C, 38 °C, 39 °C, or 40 °C. In some embodiments, the purification process includes: repeatedly centrifuging and washing the reaction solution after the etching reaction with deionized water to obtain a washing product; dispersing the washing product in deionized water and sonicating it under an inert gas atmosphere to obtain a dispersion; then centrifuging the dispersion at high speed and freeze-drying it to obtain MXene; dispersing the MXene material in an organic solvent to obtain an MXene dispersion. In some embodiments, the organic solvent is selected from at least one of DMF, DMAc, NMP, and DMSO.

[0019] In some embodiments, the MOF is at least one selected from HKUST-1, ZIF-8, MOF-808, ZU-301, UiO-66, UTSA-16, CALF-20, TIFSIX-3-Ni, NbOFFIVE-1-Ni, UiO-66-NH2, MOF-74 / CPO-27, MOF-74-Mg / CPO-27-Mg, SIFSIX, and aluminum fumarate.

[0020] In some embodiments, the preparation process of the MOF includes: Zn... 2+The concentration of Zn is 1.5~2.5 mol / L, the concentration of oxalic acid or oxalate is 0.8~1.2 mol / L, and the concentration of 1,2,4-triazole is 1.6~2.5 mol / L; the solvent is a water / methanol mixture with a water to methanol volume ratio of 1:1~1:10; the reaction temperature is 20~30 °C, and the reaction time is 12~48 h. In some embodiments, the Zn 2+ The source substance is selected from at least one of zinc oxide, zinc hydroxide, or zinc nitrate. In some embodiments, the oxalate is selected from at least one of sodium oxalate, potassium oxalate, ammonium hydrogen oxalate, or ammonium oxalate.

[0021] In some embodiments, the mass ratio of the MXene dispersion, MOF, and binder is (1~5):(1~5):(1~5) based on the mass of the feed materials; preferably, the mass ratio of the MXene dispersion, MOF, and binder is 3:2:2.

[0022] In some embodiments, the adhesive is present in the form of an aqueous solution of carboxymethyl cellulose at a concentration of 0.1 to 0.5 g / mL, preferably 0.1 g / mL, 0.2 g / mL, 0.3 g / mL, 0.4 g / mL, 0.5 g / mL, or any two of the above values ​​forming any range.

[0023] In some embodiments, in S1, Zn is added sequentially to the MXene dispersion. 2+ MOFs were prepared by in-situ growth of source substances, oxalic acid or oxalate and 1,2,4-triazole.

[0024] In some embodiments, the directional freezing temperature in S2 is 70~80 K, preferably 70K, 71K, 72K, 73K, 74K, 75K, 76K, 77K, 78K, 79K, or 80K; the directional freezing time is 20~40 min; the freeze-drying temperature is -100~20℃, preferably -100℃, -90℃, -80℃, -70℃, -60℃, -50℃, -40℃, -30℃, -20℃, -10℃, 0℃, 10℃, or 20℃; and the freeze-drying time is 24~36 h.

[0025] Thirdly, an application of the MXene-MOF biomimetic porous material described in this invention is provided for CO2 capture.

[0026] In this invention, "room temperature" refers to room temperature of 10~40℃, preferably 10~35℃, 20~30℃, or 25℃. "Atmospheric pressure" refers to 1 atm (101.3 kPa), and "CO2 in gas" refers to the concentration of gaseous CO2 in the gas of 300~500 ppm.

[0027] Compared with the prior art, one of the above technical solutions has the following advantages or beneficial effects: This invention provides an MXene-MOF biomimetic porous material and its preparation method, which has at least the following effects: 1) CMC can promote the interfacial connection between CALF-20 and MXene, improving the processability and bulk molding properties of the slurry; 2) Directional freezing introduces a channel structure continuously arranged along the freezing direction inside the material, which is beneficial to gas diffusion and mass transfer; 3) The obtained sample is lightweight, self-supporting, hydrophobic, and has a certain elastic recovery ability; 4) The existing figures show that the CALF-20 system exhibits good capture response in scenarios such as 100 vol% CO2, 400ppm CO2, simulated flue gas, and passive air adsorption; 5) Although the final equilibrium adsorption capacity is affected by the sample composition and test conditions, the bulk sample with MXene introduction has better passive direct air capture efficiency than the control sample without MXene introduction, indicating that it has advantages in air-side mass transfer and engineering application. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the process for preparing biomimetic porous materials. Figure 1 As shown, under the promotion of CMC, CALF-20 and MXene samples are linked by polymerization or in-situ growth, and after directional freezing, freeze drying or annealing, they form a block or aerogel-like biomimetic porous material.

[0029] Figure 2 SEM images of the cross-section and longitudinal section of the CALF-20 (48 h) / MXene sample prepared in Example 2.

[0030] Figure 3 This is a sample performance characterization diagram of a biomimetic porous material. Figure 3 (a) embodies ultra-lightweight, Figure 3 (b) Detection of hydrophobic contact angle, Figure 3 (c) represents elastic recovery. Figure 3 The middle (d) represents the load-bearing structure.

[0031] Figure 4 A comparison of the adsorption capacities of CALF-20 samples with different synthesis times and CMC-CALF-20 (48 h) samples under conditions of 100 vol% CO2 and 400 ppm CO2. Figure 4 (a) is the CALF-20 (12 h) sample. Figure 4 (b) is the CALF-20 (24 h) sample. Figure 4 (c) is the CALF-20 (48 h) sample. Figure 4 The middle (d) sample is CMC-CALF-20 (48 h).

[0032] Figure 5 Comparison of dynamic adsorption curves for CALF-20 (24 h), CALF-20 (48 h), blank MXene, CALF-20 (24 h) / MXene, and CALF-20 (48 h) / MXene samples.

[0033] Figure 6 The desorption curves of CALF-20 (24 h), CALF-20 (48 h), and CALF-20 (48 h) / MXene samples at different temperatures are shown. Figure 6 (a) is CALF-20 (24 h). Figure 6 (b) is CALF-20 (48 h) / MXene. Figure 6 (c) represents blank MXene. Figure 6 In the middle (d), the sample desorption rate is represented.

[0034] Figure 7 The graph shows the change in the absorption capacity of the sample after 8 cycles in flue gas.

[0035] Figure 8 This is a comparison of the high-temperature adsorption behavior of the sample under different CO2 concentrations as a function of temperature. Figure 8 (a) is 20 vol% CO2. Figure 8 (b) represents the condition of 1 vol% CO2.

[0036] Figure 9 This is a comparison chart showing the efficiency of passive adsorption of carbon dioxide in real air for the samples. Detailed Implementation

[0037] The present invention will be further illustrated below with reference to specific embodiments. These embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0038] Preparation methods, materials, structures, or composition ratios not explicitly described in the technical solutions of this invention are all considered as conventional technical features disclosed in the prior art.

[0039] Example 1: Preparation of CALF-20 (1) Dissolve zinc acetate, sodium oxalate and 1,2,4-triazole in a methanol-water mixture with a volume ratio of 1:1, so that the concentration of zinc acetate in the solution is 2.5 mol / L, the concentration of sodium oxalate is 1 mol / L and the concentration of 1,2,4-triazole is 2 mol / L. Control the reaction time at 25℃ for 12 h, 24 h and 48 h to obtain CALF-20 (12 h), CALF-20 (24 h) and CALF-20 (48 h) respectively.

[0040] (2) Dissolve zinc acetate, sodium oxalate and 1,2,4-triazole in a methanol-water mixture with a volume ratio of 1:1 to prepare a reaction solution with a zinc acetate concentration of 2.5 mol / L, a sodium oxalate concentration of 1.0 mol / L and a 1,2,4-triazole concentration of 2.0 mol / L. Add carboxymethyl cellulose to the reaction solution under stirring. The amount of carboxymethyl cellulose added is 0.20 g / mL of the reaction solution, that is, 2.0 g of carboxymethyl cellulose (0.2 g / mL) is added for every 10 mL of the reaction solution. Continue to react at 25 °C for 48 h. After the reaction is completed, CMC-CALF-20 (48 h) is obtained by solid-liquid separation, washing and drying.

[0041] Example 2: Preparation of MXene-MOF biomimetic porous materials (1) The MAX precursor Ti3AlC2 was added to an HF aqueous etching system with a mass concentration of 45% and etched at 25°C for 20h. The etched material was repeatedly centrifuged and washed with deionized water. The washing product was obtained after centrifugation. The washing product was dispersed in deionized water and ultrasonically exfoliated under an inert gas atmosphere to obtain a dispersion. The dispersion was then centrifuged at high speed and freeze-dried to obtain MXene. The MXene material was dispersed in DMF to obtain an MXene dispersion with a concentration of 12 mg / mL.

[0042] (2) Add carboxymethyl cellulose to 10 mL of deionized water. The amount of carboxymethyl cellulose added is 0.20 g / mL of water, that is, 2.0 g of carboxymethyl cellulose is added to every 10 mL of water. Stir until the carboxymethyl cellulose is fully swollen and forms a uniform adhesive phase.

[0043] (3) Under stirring conditions, 3 g of MXene dispersion with a concentration of 12 mg / mL and 2 g of CALF-20 powder prepared in Example 1 are added to the binder phase obtained in step (2) in sequence. Stirring and ultrasonic dispersion are continued to make MXene, CALF-20 and carboxymethyl cellulose uniformly mixed to obtain a uniform slurry. The slurry is degassed and then injected into a mold. The amount of carboxymethyl cellulose added is 0.20 g / mL water, that is, 2.0 g of carboxymethyl cellulose is added for every 10 mL of water in step (2).

[0044] (4) The slurry was directionally frozen at 77 K for 20 min, and then freeze-dried for 24 h at a cold trap temperature of -60 ℃ and a vacuum degree of no more than 50 Pa to obtain CALF-20 / MXene biomimetic porous material, as shown in Table 1 below.

[0045] Table 1 Figure 2 Used to characterize the morphology of oriented porous channels in biomimetic porous materials. For example... Figure 2 As shown, honeycomb-like or layered pores arranged along the freezing direction can be observed in both the cross-section and longitudinal section of the CALF-20 (48 h) / MXene biomimetic porous material sample. The characteristic pore size is about 20~200 μm, indicating that the directional freezing process successfully constructed a continuous mass transfer channel.

[0046] Figure 3 This is a sample performance characterization diagram of a biomimetic porous material. (Example:) Figure 3 As shown, the CALF-20 (48 h) / MXene biomimetic porous material sample has ultra-lightweight ( Figure 3 (a) The hydrophobic contact angle is approximately 114°. Figure 3 (b) and elastic recovery ( Figure 3 (c) and load-bearing objects ( Figure 3 It exhibits good strength and plasticity, with properties such as (d) and medium strength. The sample obtained in this embodiment can exist stably in block form, showing obvious characteristics of being lightweight, self-supporting, hydrophobic, and compressive.

[0047] Example 3 The difference from Example 2 is that in step (3), CALF-20 is first grown in situ in the MXene dispersion. Specifically, zinc acetate, sodium oxalate, and 1,2,4-triazole are dissolved in a methanol-water mixture with a volume ratio of 1:1 to prepare a precursor solution with a zinc acetate concentration of 2.5 mol / L, a sodium oxalate concentration of 1.0 mol / L, and a 1,2,4-triazole concentration of 2.0 mol / L. Under stirring conditions, 3 g of MXene dispersion is added to the precursor solution, and the reaction is carried out at 25 °C for 48 h to allow CALF-20 to grow in situ on the surface of the MXene sheets, thus obtaining a CALF-20 / MXene composite dispersion system. Subsequently, 2 g of carboxymethyl cellulose is added, and stirring and ultrasonic dispersion are continued to obtain a uniform slurry. The remaining preparation process is the same as in Example 2.

[0048] Example 4 The difference from Example 2 is that the etching system of the MXene dispersion is a LiF / HCl mixed etching system, the HCl concentration is 7 mol / L, the LiF addition is 1.3 g LiF per 20 mL of hydrochloric acid, the etching temperature is 35 ℃, and the etching time is 24 h. The rest of the preparation process is the same as in Example 2.

[0049] Example 5 The difference from Example 2 is that the concentration of the MXene dispersion prepared in step (1) is 15 mg / mL. The rest of the preparation process is the same as in Example 2.

[0050] Comparative Example 1 The difference from Example 2 is that carboxymethyl cellulose is not added. Specifically, the addition of carboxymethyl cellulose in step (2) of Example 2 is omitted, and only 10 mL of deionized water is used as the dispersion medium; then 3 g of MXene dispersion and 2 g of CALF-20 powder prepared in Example 1 are added to the dispersion medium, stirred and ultrasonically dispersed, and then injected into the mold. The rest of the preparation process is the same as in Example 2.

[0051] The obtained samples failed to form complete and stable self-supporting blocks, and it was difficult to maintain the oriented porous structure aligned along the freezing direction. This demonstrates that carboxymethyl cellulose can promote the interfacial bonding between CALF-20 and MXene, and improve the slurry formability and block structure stability; without the addition of carboxymethyl cellulose, it is difficult to obtain stable CALF-20 / MXene biomimetic porous materials.

[0052] Comparative Example 2 The difference from Example 2 is that: in step (4), directional freezing is not performed, but the slurry obtained in step (3) is directly pre-frozen and then freeze-dried for 24 hours. The rest of the preparation process is the same as in Example 2.

[0053] The resulting product lacked a continuously arranged directional mass transfer channel along the freezing direction, exhibited a disordered pore structure, and displayed poor CO2 adsorption performance with an adsorption capacity of 0.0107 mmol / g. This indicates that the directional freezing process plays a crucial role in constructing continuous mass transfer channels and improving the gas diffusion and adsorption performance of the material.

[0054] Example 1 The CALF-20 (12 h), CALF-20 (24 h), CALF-20 (48 h), and CMC-CALF-20 (48 h) samples prepared in Example 1 were subjected to CO2 adsorption tests under the following two conditions: Condition 1: 100 vol% CO2, 1 bar; Condition 2: 400 ppm CO2. The test results are as follows: Figure 4 As shown in Table 2.

[0055] Table 2 Adsorption capacity of samples at different CO2 concentrations The results above indicate that extending the synthesis time of CALF-20 is beneficial to improving the adsorption capacity of the material under high CO2 concentration conditions, while the sample after CMC molding still maintains a good capture response under low CO2 concentration conditions.

[0056] Example 2 CALF-20 (24 h), CALF-20 (48 h), blank MXene, CALF-20 (24 h) / MXene, and CALF-20 (48 h) / MXene samples were loaded into fixed-bed adsorption devices, with a sample loading of approximately 100 mg. Dynamic CO2 adsorption tests were conducted at atmospheric pressure and 298 K. The test gas was a CO2 / N2 mixture, with a CO2 volume fraction of 20 vol% and N2 as the equilibrium gas, and a total gas flow rate of 20 mL / min. Before the test, the samples were pretreated by purging under an N2 atmosphere to remove residual gas and weakly adsorbed components from the sample channels. Subsequently, the CO2 / N2 mixture was switched to the adsorption test, and the change in CO2 concentration in the outlet gas over time was recorded to obtain the dynamic adsorption curves. The dynamic CO2 adsorption capacity of each sample was calculated based on the integral of the breakthrough curve, and the results are shown in Table 3.

[0057] CALF-20 is the main active component for CO2 adsorption. For CALF-20 powder samples, the adsorption capacity is calculated based on the sample mass; for CALF-20 / MXene composite samples, the adsorption capacity is calculated based on the mass of CALF-20 added to the composite sample; for blank MXene samples, the adsorption capacity is calculated based on the mass of the MXene sample.

[0058] Table 3 Dynamic adsorption capacity of each sample Depend on Figure 5 As shown in Table 3, the adsorption capacity of blank MXene itself is relatively low; however, after introducing MXene into the bulk structure, the adsorption capacity of the blank MXene sample in the dynamic adsorption test is significantly lower than that of the CALF-20 (24 h) / MXene and CALF-20 (48 h) / MXene samples. CALF-20 is still the main active phase for CO2 adsorption, and the material obtains better shaping and air-side mass transfer basis while maintaining a certain adsorption capacity.

[0059] Example 3 CALF-20 (48 h), blank MXene, and CALF-20 (48 h) / MXene samples were subjected to dynamic adsorption under a 20 vol% CO2 / N2 mixed gas environment at an adsorption temperature of 298 K and a total gas flow rate of 20 mL / min. After the samples reached adsorption saturation, dry N2 gas was used for thermal desorption and regeneration. The desorption temperatures were set at 323 K, 333 K, 353 K, 373 K, and 393 K, respectively, and the N2 flow rate was 20 mL / min. The CO2 concentration in the outlet gas was recorded over time, and the CO2 desorption amount and desorption efficiency were calculated based on the desorption curves.

[0060] Depend onFigure 6 The results show that as the desorption temperature increases, CALF-20 (48 h) ( Figure 6 (a)), CALF-20 (48 h) / MXene ( Figure 6 (b) and blank MXene ( Figure 6 In sample (c), both the endpoint desorption amount and desorption rate showed an increasing trend. The sample desorption rate was compared to that of sample (c). Figure 6 As shown in (d), when the desorption temperature is increased to 353 K and above, the desorption efficiency of most groups reaches or exceeds 90%. This result indicates that the material of the present invention has good thermal regeneration potential.

[0061] Example 4 The CALF-20 (48 h) / MXene sample was loaded into a fixed-bed adsorption device, and adsorption tests were conducted at 373 K by introducing simulated flue gas, which was a 20 vol% CO2 / N2 mixture with N2 as the equilibrium gas, and a total gas flow rate of 20 mL / min. After the sample reached adsorption saturation, desorption and regeneration were performed at 90 °C using dry N2 gas at a flow rate of 20 mL / min. The adsorption-desorption process was repeated 8 times, and the CO2 adsorption capacity after each cycle was recorded to evaluate the cycle stability and regeneration performance of the sample.

[0062] like Figure 7 As shown, the sample under simulated flue gas underwent 8 cycles without significant performance degradation, indicating that the biomimetic porous material prepared by this invention has good regeneration capability.

[0063] Example 5 The high-temperature adsorption performance of CALF-20 (48 h) and CALF-20 (48 h) / MXene samples was tested under 20 vol% CO2 (simulated flue gas) and 1 vol% CO2 (simulated indoor conditions).

[0064] Table 4 High-temperature adsorption performance of CALF-20 (48 h) / MXene samples Figure 8 The results in Table 4 show that as the temperature increases, the equilibrium adsorption capacity of the material gradually decreases, but it still maintains a certain capture capacity at higher temperatures.

[0065] Example 6 The CALF-20 (48 h) and CALF-20 (48 h) / MXene samples were subjected to passive direct air trapping tests in real air.

[0066] Figure 9The results show that in the passive direct air capture test, the efficiency of the Calf-20 48 h / MXene sample was 9.89%, significantly higher than that of the Calf-20 48 h sample without MXene (4.56%). This result indicates that although the introduction of MXene may not lead to a higher equilibrium adsorption capacity under all test conditions, it has a positive effect on bulk structure construction, air-side mass transfer, and the passive air capture process.

[0067] Example 7: Estimated raw material cost and unit CO2 adsorption material cost of the present invention To evaluate the engineering application potential of the material of this invention, the raw material preparation cost and the unit CO2 adsorption material cost were estimated. This estimation is based on existing formulations and test data from existing embodiments, only including the raw material cost of the adsorbent itself, excluding equipment depreciation, labor, freezing / freeze-drying power consumption, solvent recovery, auxiliary systems, and plant costs. Therefore, the results can be considered conservative estimates for the material side. In existing embodiments, the formulation of the molding slurry is as follows: 2 g of carboxymethyl cellulose (CMC) is added to 10 mL of water, followed by 2 g of CALF-20 powder, and then approximately 3 g of MXene dispersion with a concentration of 10-15 mg / mL. Based on the dry weight of MXene, 3 g of dispersion corresponds to approximately 0.03-0.045 g of MXene solids. Therefore, the dry weight content of MXene in the resulting composite adsorbent is approximately 0.74-1.11 wt%, and CALF-20 and CMC each account for approximately 49.4-49.6 wt%.

[0068] In this embodiment, the price of MXene is calculated at 400 yuan / kg. CALF-20 is calculated based on its publicly disclosed composition [Zn2(1,2,4-triazolate)2(oxalate)]. Literature indicates that CALF-20 consists of a zinc source, 1,2,4-triazole, and oxalic acid, and its synthesis exhibits good scalability and high yield. Based on 1 kg of CALF-20, theoretically, approximately 0.389 kg of 1,2,4-triazole, 0.355 kg of oxalic acid dihydrate, and 0.459 kg of ZnO are required according to stoichiometry. Based on publicly available bulk pricing, 1,2,4-triazole is approximately USD 3.4–6.0 / kg, CMC is approximately USD 2.42–2.95 / kg, oxalic acid dihydrate is approximately USD 0.4–1.6 / kg, and ZnO is approximately USD 2.11–3.10 / kg. Using a conversion of 1 USD = 6.8864 CNY, the theoretical raw material cost for CALF-20 is approximately RMB 16.8–29.8 / kg. If we further consider the 85–90% yield correction commonly used in the industrial preparation of CALF-20, its raw material cost is approximately RMB 18.6–35.0 / kg.

[0069] Based on the aforementioned raw material prices and the formulation of the current embodiment, the raw material cost of the composite adsorbent of the present invention can be further estimated. With CALF-20 costing 18.6~35.0 yuan / kg, CMC costing approximately 16.7~20.3 yuan / kg, and MXene costing 400 yuan / kg, the raw material cost of the resulting composite adsorbent is approximately 20.5~31.8 yuan / kg. This shows that although the unit price of MXene is higher than that of CALF-20 and CMC, its contribution to the final material cost is limited because its dry basis proportion in the current formulation is only about 0.74~1.11 wt%. The material cost of the current system is mainly determined by the CALF-20 active phase and the CMC molding phase. This result indicates that further cost reduction of the material of the present invention does not primarily rely on continuing to lower the unit price of MXene, but rather on improving the utilization efficiency of the active phase, reducing the proportion of inactive molding components, and improving the adsorption capacity per unit mass through formulation optimization.

[0070] Regarding the unit cost of CO2 adsorbent material, existing test data were used to predict and estimate the cost based on the assumption that "the adsorption performance will reach 1.5 times the current value after subsequent proportional optimization." Existing data show that the CMC-CALF-20 (48 h) sample has an adsorption capacity of 1.94057 mmol / g under 100 vol% CO2 conditions and 0.09714 mmol / g under 400 ppm CO2 conditions; the CALF-20 (48 h) / MXene sample has an adsorption capacity of approximately 6.515 mmol / gCalf-20 under 20 vol% CO2 conditions; furthermore, the CALF-20 (48 h) / MXene sample has an efficiency of 9.89% in real-world passive direct air capture tests, higher than the 4.56% of the CALF-20 (48 h) sample without MXene. Based on this, if the above adsorption capacity is scaled up by 1.5 times, the predicted adsorption capacities of the material under the conditions of 100 vol% CO2, 20 vol% CO2 and 400 ppm CO2 are approximately 14.5 mmol / g Calf-20, 9.51 mmol / g Calf-20 and 0.7287 mmol / g, respectively.

[0071] Based on the above capacity, the theoretical CO2 loading per kilogram of adsorbent under different operating conditions is approximately 0.128 kg / kg, 0.0860 kg / kg, and 0.00641 kg / kg, respectively. Therefore, to capture 1 ton of CO2 in a single adsorption process, the required adsorbent inventory is approximately 7.81 tons, 11.63 tons, and 155.94 tons, respectively. If estimated solely from the perspective of adsorbent raw material inventory, the corresponding material costs are approximately RMB 159.9–248.4 / kg CO2, RMB 238.2–369.9 / kg CO2, and RMB 3195.2–4962.0 / kg CO2, respectively, which translates to approximately RMB 159,900–248,400 / ton CO2, RMB 238,200–369,900 / ton CO2, and RMB 3,195,000–4,962,000 / ton CO2. The results indicate that under low partial pressure air capture conditions, the material inventory required for a unit CO2 adsorption increases significantly. Therefore, the economics of air capture scenarios are highly dependent on multiple regeneration cycles and efficient contactor design, and cannot be determined solely by the single-cycle balancing capacity.

[0072] Considering that solid adsorbents typically operate in multi-cycle mode in engineering, the material cost is further amortized using 1000 and 5000 adsorption-desorption cycles. Based on 1000 cycles, the amortized cost per unit CO2 of the material of this invention under conditions of 100 vol% CO2, 20 vol% CO2, and 400 ppm CO2 is approximately RMB 159.9~248.4 / ton CO2, RMB 238.2~369.9 / ton CO2, and RMB 3195.2~4962.0 / ton CO2, respectively; based on 5000 cycles, the costs are approximately RMB 32.0~49.7 / ton CO2, RMB 47.6~74.0 / ton CO2, and RMB 639.0~992.4 / ton CO2, respectively. The above results indicate that for high-concentration CO2 or simulated flue gas conditions, the material of this invention, after achieving multi-cycle regeneration, already demonstrates good potential for engineering applications in terms of material cost. For direct air capture conditions, although the material cost is still significantly higher than that for high-concentration conditions, considering the directional pore structure, good bulk formability, and high passive direct air capture efficiency of the material of this invention, there is still considerable room for improvement in material economy under air capture scenarios if the MXene / CALF-20 / CMC ratio is further optimized, the proportion of inactive binder components is reduced, and the low partial pressure adsorption capacity is increased.

[0073] In summary, the raw material cost of the composite adsorbent of this invention under current, incompletely optimized conditions is approximately RMB 20.5–31.8 / kg. Based on existing performance and a 1.5-fold capacity increase, the amortized cost per unit of CO2 material under 100 vol% CO2 and 20 vol% CO2 conditions can be reduced to approximately RMB 32.0–9.7 / ton CO2 and RMB 47.6–74.0 / ton CO2, respectively (based on 5000 cycles). This indicates that the material of this invention possesses both a low raw material cost base and the potential for cost reduction after further capacity enhancement, making it particularly suitable for CO2 capture scenarios requiring bulk molding, rapid mass transfer, and low-energy regeneration.

[0074] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An MXene-MOF biomimetic porous material, characterized in that, The MXene-MOF biomimetic porous material is prepared by using MXene two-dimensional sheets as the skeleton reinforcement phase, CALF-20 as the CO2 adsorption functional phase, and carboxymethyl cellulose as the connecting and molding bonding phase. It has directional honeycomb or layered porous channels arranged along the freezing direction, with characteristic pore sizes of 20~200μm.

2. The biomimetic porous material according to claim 1, characterized in that, Its static water contact angle is 110~118°.

3. A method for preparing an MXene-MOF biomimetic porous material, characterized in that, include: S1. Mix MXene dispersion, MOF and binder to form a slurry; or grow MOF in situ on the surface of MXene dispersion and then mix it with binder to form a slurry; S2. The slurry is subjected to directional freezing and freeze-drying to obtain MXene-MOF biomimetic porous material; The adhesive is carboxymethyl cellulose; The MOF is CALF-20.

4. The preparation method according to claim 3, characterized in that, The concentration of MXene in the MXene dispersion is 10~15 mg / mL; Alternatively, the method for preparing the MXene dispersion includes: adding the MAX precursor to an etching system for etching, and then purifying it to prepare the MXene dispersion.

5. The preparation method according to claim 4, characterized in that, The MAX precursor is selected from at least one of Ti3AlC2, Ti2AlC, Ti3AlCN, Ta4AlC3, V2AlC, V3AlC2, Mo2AlC and Mo2TiAlC2; Alternatively, the MXene is selected from Ti3C2T. x Ti2CT x Ti3CNT x Ta4C3T x V2CT x V3C2T x Mo2CT x and Mo2TiC2T x At least one of them, T includes one or more of -OH, -F and -O, x represents the number of T, x>0; Alternatively, the etching system may be an aqueous HF solution or a LiF / HCl mixed etching system.

6. The preparation method according to claim 4, characterized in that, The purification process includes: repeatedly centrifuging and washing the reaction solution after the etching reaction with deionized water to obtain a washing product after centrifugation; dispersing the washing product in deionized water and sonicating it under an inert gas atmosphere to obtain a dispersion; then centrifuging the dispersion at high speed and freeze-drying it to obtain MXene; dispersing the MXene material in an organic solvent to obtain an MXene dispersion; or, the organic solvent is selected from at least one of DMF, DMAc, NMP and DMSO.

7. The preparation method according to claim 4, characterized in that, The preparation process of the MOF includes: based on the total reaction liquid volume, Zn 2+ The concentration of the active ingredient was 1.5–2.5 mol / L, the concentration of oxalic acid or oxalate was 0.8–1.2 mol / L, and the concentration of 1,2,4-triazole was 1.6–2.5 mol / L; the solvent was a water / methanol mixture with a water to methanol volume ratio of 1:1 to 1:10; the reaction temperature was 20–30 °C, and the reaction time was 12–48 h. Or, the Zn 2+ The source substance is selected from at least one of zinc oxide, zinc hydroxide, or zinc nitrate; Alternatively, the oxalate is selected from at least one of sodium oxalate, potassium oxalate, ammonium hydrogen oxalate, or ammonium oxalate.

8. The preparation method according to claim 4, characterized in that, In S1, Zn is added sequentially to the MXene dispersion. 2+ MOFs were prepared by in-situ growth of source substances, oxalic acid or oxalate and 1,2,4-triazole.

9. The preparation method according to claim 4, characterized in that, In S2, the directional freezing temperature is 70~80 K, the directional freezing time is 20~40 min, the freeze-drying temperature is -40~20 ℃, and the freeze-drying time is 24~36 h.

10. An application of the MXene-MOF biomimetic porous material according to claim 1, characterized in that, Used for CO2 capture.

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