An intercalated MXene separation membrane, a preparation method and application in H2 / CO2 separation

Abstract

The application discloses a kind of MOF-801@MXene nanosheet as construction unit by in-situ synthesis at room temperature, thereby constructing MOF@MXene membrane with significantly enhanced permeability and selectivity.The method can be anchored Zr metal ions by electrostatic interaction from the surrounding through negative MXene nanosheet, then coordinate with ligand at room temperature, thereby growing MOF-801 crystal on MXene nanosheet uniformly.Then the synthesized MOF-801@MXene nanosheet is vacuum suction filtration on the surface of porous organic substrate to prepare membrane.Due to the fact that MOF-801 crystal can provide more transmission channels for H2 molecules, and has high adsorption capacity for CO2 molecules to prevent diffusion, the prepared membrane shows excellent gas separation performance, and H2 / CO2 selectivity is 26.6.

Description

Technical Field

[0001] This invention relates to an intercalated MXene separation membrane, its preparation method, and its application in H2 / CO2 separation, belonging to the field of gas separation membrane technology. Background Technology

[0002] Compared to other two-dimensional materials such as graphene oxide, MXene membranes have robust separation channels that can maintain structural integrity for more than a month even when immersed in aqueous solutions[1], while GO membranes are damaged due to strong hydration between GO nanosheets and water molecules[2,3].

[0003] To date, the most studied MXene is Ti3C2T. x It has been widely prepared as a separation membrane for water purification. However, there are few reports on MXene membranes for gas separation. The prior art has reported the construction of layered MXene membranes with neat and regular channels to achieve high H2 / CO2 separation performance, which opens the door to gas separation using MXene-based membranes [4]. The prior art has also given an tunable MXene film with a thickness as low as 20 nm, whose stacking behavior and interlayer spacing can be precisely controlled by functionalizing borate and PEI molecules, thereby realizing the transformation from H2 selective channels to CO2 selective channels [5]. In addition, a simple heat treatment process has been given to prepare self-crosslinked MXene hollow fiber membranes. The synthesized membrane with effective interlayer space regulation exhibits excellent H2 / CO2 gas separation performance and good operational stability. However, these studies focus on using cross-linking strategies or utilizing the inherent nanochannels within MXene membranes to manipulate interlayer space. Traditional intercalation methods involve physical blending [6-8], which requires the synthesis of porous crystals first, followed by mixing with membrane building blocks. This method is complex, time-consuming, and results in poor uniformity of the mixed crystals, thus failing to effectively improve the separation properties of MXene membranes.

[0004] References:

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[0011] [7]C.Xu,A.Cui,Y.Xu,X.Fu,Graphene oxide–TiO2 composite filtration membranes and their potential application for water purification,Carbon,62(2013)465-471.

[0012] [8] K. Goh, W. Jiang, HE Karahan, S. Zhai, L. Wei, D. Yu, AGFane, R. Wang, Y. Chen, All carbon nanoarchitectures as high-performance separation membranes with superior stability, Adv. Funct. Mater., 25 (2015) 7348-7359. Summary of the Invention

[0013] The technical problem this invention aims to solve is that in the preparation of MXene membranes for gas separation, traditional methods use direct mixing of crystals for intercalation in two-dimensional sheets, which suffers from poor mixing uniformity, complex steps, and low separation performance. This invention proposes a method using MOF-801@MXene nanosheets synthesized in situ at room temperature as building blocks to construct MOF@MXene membranes with significantly enhanced permeability and selectivity. Specifically, negatively charged MXene nanosheets can anchor Zr metal ions from their surroundings through electrostatic interactions, and then coordinate with ligands at room temperature, thereby uniformly growing MOF-801 crystals on the MXene nanosheets.

[0014] The technical solution is:

[0015] An intercalated MXene separation membrane includes MXene two-dimensional nanosheets and MOF-801 crystals distributed in layers between the nanosheets, wherein the MOF-801 crystals are attached to the surface of at least one layer of MXene two-dimensional nanosheets.

[0016] The MOF-801 crystals are attached to the surface of MXene two-dimensional nanosheets through in-situ synthesis; the interlayer channel spacing is 0.35-0.40 nm.

[0017] MOF-801 crystals account for 5-15% of the weight of MXene two-dimensional nanosheets.

[0018] The MXene two-dimensional nanosheets mentioned are Ti3C2T x .

[0019] The method for preparing the intercalated MXene separation membrane includes the following steps:

[0020] Step 1: Prepare a mixed solution containing fumaric acid, ZrOCl2 and MXene nanosheets, stir the reaction to generate MOF-801 crystals on the surface of MXene nanosheets, and obtain the film-forming solution.

[0021] Step 2: The membrane-forming solution is applied to the substrate by suction to load MXene nanosheets loaded with MOF-801 crystals, followed by drying to obtain the intercalated MXene separation membrane.

[0022] In step 1, the concentration of fumaric acid in the solution is 0.01-0.15 mmol / L, and the molar ratio of fumaric acid to ZrOCl2 is 1:0.8-1.2.

[0023] The stirring reaction time is 0.5-5 hours.

[0024] The substrate is a porous polymer material.

[0025] The drying process involves treating the product at 10-40℃ for 5-30 hours.

[0026] The above-mentioned intercalated MXene separation membrane is used in H2 / CO2 separation.

[0027] The volume ratio of H2 / CO2 is (0.1-0.9):(0.9-0.1).

[0028] Beneficial effects

[0029] This invention utilizes in-situ synthesized MOF-801@MXene nanosheets as building blocks to construct MOF@MXene membranes with significantly enhanced permeability and selectivity. Negatively charged MXene nanosheets anchor Zr metal ions from their surroundings via electrostatic interactions, then coordinate with ligands at room temperature, resulting in the uniform growth of MOF-801 crystals with a particle size of approximately 20 nm on the MXene nanosheets. The synthesized MOF-801@MXene nanosheets were then vacuum-filtered onto a porous organic substrate to form a membrane. The physicochemical properties of the synthesized MOF-801@MXene nanosheets and the resulting membrane were observed using XPS, AFM, SEM, IR, XRD, and gas adsorption methods. Because the MOF-801 crystals provide more transport channels for H2 molecules and have a high adsorption capacity for CO2 molecules to prevent their diffusion, the prepared membrane exhibits excellent gas separation performance, with an H2 permeability of 2200 GPU and an H2 / CO2 selectivity of 26.6. Attached Figure Description

[0030] Figure 1 Schematic diagram of the preparation process of gas separation membrane.

[0031] Figure 2 (a) Zeta potentials of MXene, ZrOCl2 and MXene-ZrOCl2 solutions; concentrations of 0.01, 0.16, 0.11, 0.17 and 0.49 mg / mL, respectively; (b) AFM plot, (c) STEMHAADF image, (d) EDX mapping and (e) XRD pattern of MOF-801@MXene nanosheets.

[0032] Figure 3 (a) SEM surface of MOF-801@MXene membrane, (b) AFM image and (c) cross section, (d) SEM image of MOF-801@MXene membrane and (e) EDX mapping.

[0033] Figure 4 (a) SEM image of the MXene film, (b) cross-sectional image with a thickness of 350 nm, (c) AFM image, (d) SEM image, and (e) EDX mapping.

[0034] Figure 5 AFM images of (a) MXene and (b) MOF-801@MXene membranes.

[0035] Figure 6 SEM surface images and EDX mappings of (a) MXene films with (b) Ti, (c) C and (d) O elements.

[0036] Figure 7SEM surface images and EDX mappings of (a) (b) Ti, (c) Zr, (d) C and (d) O elements in MOF-801@MXene film.

[0037] Figure 8 (a) FTIR spectrum of MOF-801@MXene film; (b) XPS survey scan; (c) Zr3d and (d) C1s spectra.

[0038] Figure 9 Effect of MOF reactant concentration on single gas separation performance of MOF-801@MXene membrane (25℃, 1 bar).

[0039] Figure 10 SEM surface and cross-sectional images of MOF-801@MXene membranes with different MOF reactant concentrations: (a) and (a1) 0.375 mmol / L; (b) and (b1) 0.5 mmol / L; (c) and (c1) 0.75 mmol / L; (d) and (d1) 1.5 mmol / L.

[0040] Figure 11 (a) TEM image of MOF-801 crystal and (b) XRD pattern; (c) SEM surface image of MOF-801-MXene membrane produced by physical mixing of nanosheets and crystals; (d) pure gas separation performance of H2 / CO2 of pristine MXene, MOF-801-MXene and MOF-801@MXene membranes (25℃, 1 bar).

[0041] Figure 12 (a) XRD patterns of pristine MXene and MOF-801@MXene films; (b) Gas adsorption of pristine MXene, MOF-801 and MOF-801@MXene at 25 °C; (c) Schematic diagram of the role of MOF-801 crystals in molecular transport. Detailed Implementation

[0042] Example 1 Synthesis of Ti3C2Tx MXene Nanosheets

[0043] 0.67 g of LiF powder was dissolved in 10 mL of HCl solution (6 M). After stirring for approximately 40 minutes, 1 g of Ti3AlC2 was added to the mixture, and the mixture was stirred at 35 °C for 1 day. The synthesized product was centrifuged multiple times, washed with water and ethanol after each centrifugation, until the pH of the supernatant was approximately 7. The precipitate was dispersed in water and sonicated under a nitrogen atmosphere for 1 hour to separate MXene powders. Unexfoliated MXene powder was then removed by centrifugation at 3500 rpm for 1 hour. Finally, the concentration of the resulting MXene solution was approximately 0.2 mg / mL.-1 .

[0044] Example 2 Synthesis of MOF-801 crystal

[0045] Fumaric acid (87 mg, 0.75 mmol) and ZrOCl₂·8H₂O (242 mg, 0.75 mmol) were dissolved in 10 mL of an aqueous solution containing a measured amount of acetic acid, and the solution was heated at 60 °C for 12 h. The resulting white crystals were collected and washed several times with 100 mL of water. Finally, the solid was dried under vacuum at 80 °C for 12 h.

[0046] Example 3: In-situ synthesis of MXene@MOF-801 nanosheets

[0047] MXene@MOF-801 nanosheets were synthesized in situ in a one-step manner at room temperature. Specifically, fumaric acid (0.0375, 0.05, 0.075, or 0.15 mmol), equimolar amounts of ZrOCl2, and a specific amount of MXene nanosheets were dispersed in a 250-mL polytetrafluoroethylene beaker containing 100 mL of aqueous acetic acid solution, and then magnetically stirred at room temperature for one hour to form a homogeneous solution for film formation.

[0048] Example 4: Preparation of MXene@MOF-801 membrane

[0049] MXene-based membranes were prepared by vacuum filtration. The synthesized MXene@MOF-801 nanosheets were deposited on the surface of a porous PTFE substrate, a separation layer was formed under a pressure of 1 bar, and then the membrane was vacuum dried at 30 °C for 12 h.

[0050] Preparation of MXene@MOF-801 membrane (Comparative Example 1)

[0051] The method is the same as in Example 4, except that Ti3C2T is used directly. x MXene nanosheets are deposited on the surface of a porous PTFE substrate.

[0052] MOF-801 intercalated MXene membranes were prepared using the physical intercalation strategy described in Example 2.

[0053] To highlight the potential advantages of our MOF-801@MXene membrane via room-temperature in-situ synthesis, a well-known physical intercalation strategy was employed to prepare the MOF-801-intercalated MXene membrane (denoted as MOF-801-MXene). The preparation method involved mixing pre-synthesized MOF-801 crystals with an MXene dispersion used as a filtration solution. The crystals were introduced into the MXene membrane via physical mixing, and gas transport behavior was evaluated (the mass fraction of MOF was approximately 13.7%, consistent with the mass fraction of the optimized MOF-801@MXene membrane calculated from XPS results). The MOF-801 crystals were synthesized via a low-temperature hydrothermal method [G. Wiβmann, A. Schaate, S. Lilienthal, I. Bremer, AMSchneider, P. Behrens, Modulated synthesis of Zr-fumarate MOF, Microporous Mesoporous Mater., 152(2012)64-70.].

[0054] Synthesis and characterization of MOF-801@MXene nanosheets

[0055] MOF crystals with regular and highly tunable pore structures are selected to create nanochannels in two-dimensional films to facilitate molecular transport. The water-stable MOF material MOF-801 can be obtained via a green synthesis method at low temperatures using water as a solvent. This invention employs a simple one-step method to grow MOF-801 in situ on MXene nanosheets by stirring a mixture containing nanosheets, a metal source (ZrOCl2), and a ligand (fumaric acid) at room temperature.

[0056] from Figure 2 As can be seen in region (a), the zeta potential of the MXene dispersion is approximately -33.2 mV, indicating that the nanosheets are negatively charged, while the Zr metal source is positively charged. Therefore, during the room temperature reaction, the positive Zr... 4+ MOF-801 crystals can first be attached to the surface of negatively charged MXene nanosheets via electrostatic interactions, and then coordinated with a ligand (fumaric acid) to form MOF-801 crystals in situ on the surface of the MXene nanosheets. Furthermore, with Zr... 4+ With the increase of the nanosheet ratio, the zeta potential of the solution almost becomes zero after MXene is mixed with the metal source. This indicates that the negatively charged groups on the MXene nanosheets gradually pair with metal cations, and there are no excess metal ions in the solution. This allows MOF crystals to grow in situ on the nanosheets rather than in the solution. Notably, when there are too many metal ions, the zeta potential of the mixed solution becomes positive, indicating the presence of residual metal ions in the solution that may generate MOF crystals and potentially disrupt the layered film structure.

[0057] Figure 2 (b) is an AFM image of the obtained MOF-801@MXene nanosheets. The results show that the nanosheets exhibit a sheet-like structure with a thickness of approximately 20 nm, indicating successful growth of MOF-801 crystals. Furthermore, the nanosheets were characterized by TEM. Although small dark spots were detected by EDX mapping (…),… Figure 2 Regions (c) and (d) confirm that MOF-801 crystals are uniformly dispersed on the nanosheet surface, but the signal is weak, possibly due to the poor resistance of MOF materials to electron beam irradiation. Furthermore, the diffraction peaks of MOF-801@MXene nanosheets in the 2θ range of 8–10° are consistent with the simulated diffraction peaks of MOF-801. These results further demonstrate the successful synthesis of MOF-801 crystals on MXene nanosheets via a room-temperature in-situ synthesis method.

[0058] Characterization of MOF-801@MXene membrane

[0059] The resulting nanosheets were deposited on the surface of a porous substrate, and a layered membrane was assembled using a simple vacuum filtration method. For example... Figure 3 As shown in (a), compared with the MXene film prepared in Control Example 1, the synthesized dark black MOF-801@MXene film exhibits a flat surface morphology with fewer wrinkles. Figure 4 (Region a). Meanwhile, due to the intercalation of MOF crystals between MXene nanosheets, the average surface roughness of the MOF-801@MXene film is approximately 62.2 nm, significantly greater than that of the MXene nanosheets (29.6 nm). Figure 3 area b Figure 4 region c and Figure 5 ).also, Figure 3 The SEM cross-sectional image in region c shows an undamaged laminate with a considerable thickness. EDS mapping results indicate that the new Zr element is uniformly distributed along with Ti, C, and O elements. Figure 3 The d and e regions Figure 4 d region and Figure 6 , Figure 7 This further demonstrates that MOF-801 crystals were successfully and uniformly distributed on the surface of MXene nanosheets on the MOF-801@MXene film.

[0060] The chemical properties of the membrane were further investigated using FTIR. Figure 8 As shown in region a, in the FTIR spectrum of the MOF-801@MXene film, ~1724 cm⁻¹ -1 ~1652.7cm -1 and ~1524cm -1The peak at this point is considered to be a -C=OO bond, ~1068 cm⁻¹ -1 and ~661cm -1 The peaks at that point represent -CO and Zr-O bonds, which are generated by the functional groups of fumaric acid and metal clusters in MOF-801. XPS can reveal more information about the chemical structure and elemental composition. Figure 8 As can be seen in region b, Zr element was detected in MOF-801@MXene compared to pure MXene nanosheets. Furthermore, Figure 8 The Zr3d spectrum of MOF-801@MXene, shown in region c, reveals the binding energies of the Zr3d3 / 2 and Zr3d5 / 2 states, located at 185.1 eV and 182.8 eV, respectively. The C1s spectrum of MOF-801@MXene shows enhanced intensities of OC=O and CC compared to MXene, further confirming the presence of MOF-801 crystals on the surface of the MXene nanosheets.

[0061] Effect of MOF reactant concentration on gas separation performance

[0062] The effect of reactant amount on the gas transport performance of the MOF-801@MXene membrane was further observed. Figure 9 As can be seen, the original MXene membrane exhibits a low H2 permeability of approximately 773 GPUs and an H2 / CO2 selectivity of approximately 17. However, after introducing MOF-801 crystals, the H2 permeability increased to over 1000 GPUs, and the selectivity improved to ~30. The MOF-801 crystals uniformly grown on the MXene nanosheets not only expanded the transport channels within the membrane but also provided additional molecular sieving channels conferred by the inherent pore structure of MOF-801, thereby achieving rapid and efficient H2 sieving higher than that for CO2. Furthermore, it is worth noting that when the amount of reactants is excessive, free MOF nanocrystals tend to appear in the bulk solution, which may disrupt the initial structure during membrane assembly. Figure 10 This significantly sacrifices molecular sieving ability. Therefore, the MOF-801@MXene membrane with an optimized reactant amount of 0.05 mmol exhibits an H2 / CO2 selectivity of up to 29.4 and an H2 permeability of 2334 GPU.

[0063] Gas separation performance test method

[0064] Gas permeation tests were conducted using self-made equipment. Gas transport behavior was evaluated using the constant pressure / variable volume method. Single-gas permeability coefficients were measured at 1 bar and 25°C using a bubble flow meter. The test was repeated at least three times once the system reached a steady state.

[0065] Where P is the gas permeability (1 GPU = 10⁻⁶). -6cm 3 (STP)cm-2s-1cm Hg), Δp represents the transmembrane pressure (atm), p atm The pressure is represented by atmospheric pressure (atm), T is the permeation temperature (°C), and A is the effective membrane area (m²). 2 ), where dV / dt is the volumetric displacement rate in the bubble flowmeter. For mixed gas testing, H2 / CO2 (50 / 50, V / V) is used as the feed gas, and argon is used as the purge gas.

[0066] like Figure 11 As shown in Figure d, the H2 permeability of the MOF-801-MXene membrane prepared in Comparative Example 2 increased to ~1824 GPU, nearly 2.5 times higher than the original MXene membrane. However, the H2 / CO2 selectivity decreased significantly to ~5.1. This is attributed to the fact that the free MOF crystals dispersed in the solution altered the stacking behavior of the nanosheets, leading to local aggregation of crystals within the membrane, which was also... Figure 11 The true morphology of the membrane shown in Figure c is confirmed. In contrast, the MOF-801@MXene membrane exhibits enhanced H2 permeability of 2334 GPU and selectivity of 29.4, which are significantly better than the original MXene and MOF-801-MXene membranes. This is attributed to the uniform distribution of MOF-801 crystals on the MXene nanosheets, which expands the interlayer transport channels and endows the inherent MOF structure with abundant additional sieving channels.

[0067] Transmission mechanism analysis

[0068] To further understand the role of MOF crystals in gas separation within MXene membranes, a series of experiments were conducted. First, the interlayer spacing of the membrane was observed. For example... Figure 12 As shown in region a, the pristine MXene film exhibits a diffraction peak at 2θ = 6.72°, corresponding to a d-interval of 1.31 nm according to Bragg's law. After in-situ growth of MOF-801 crystals on the MXene nanosheets at room temperature, the characteristic peak shifts slightly to a lower theta value, corresponding to a d-interval of 1.35 nm. Considering the thickness of the monolayer MXene nanosheets is approximately 0.98 nm, the interlayer channel spacing increases from 0.33 nm to 0.37 nm. The results indicate that the embedded MOF-801 crystals effectively expand the transport channels within the MXene film, such as… Figure 10 As shown in c. Meanwhile, the MOF-801 crystal exhibits a face-centered cubic (fcu) topology, with interconnected tetrahedral and octahedral cages whose faces form triangular windows—the sole entry point for molecular sieving, providing additional molecular transport channels. Figure 12 c). During the permeation of H2 or CO2 molecules through the MOF-801@MXene membrane, CO2 (kinetic diameter, k) d : Compared to the molecular dynamics diameter k, d Smaller H2 molecules encounter less transport resistance, resulting in a significant increase in the H2 permeability of the MOF-801@MXene membrane. Simultaneously, MOF-801 crystals exhibit superior adsorption capacity for CO2 molecules compared to H2 molecules. Figure 12 (b) The crystals in the MOF-801@MXene membrane can inhibit CO2 permeation through the membrane and significantly improve H2 / CO2 selectivity. These results confirm that the MOF-801 crystals expand the laminar transport channels while providing additional molecular sieving channels, which helps to improve H2 permeability and H2 / CO2 selectivity.

Claims

1. An application of an intercalated MXene separation membrane in H2 / CO2 separation, the intercalated MXene separation membrane comprising MXene two-dimensional nanosheets, characterized in that, It also includes MOF-801 crystals distributed in the layers between the nanosheets, and the MOF-801 crystals are attached to the surface of at least one layer of MXene two-dimensional nanosheets; the MOF-801 crystals are attached to the surface of the MXene two-dimensional nanosheets by in-situ synthesis; the interlayer channel spacing is 0.35-0.40 nm; A method for preparing an intercalated MXene separation membrane, characterized by comprising the following steps: Step 1: Prepare a mixed solution containing fumaric acid, ZrOCl2 and MXene nanosheets, stir the reaction to generate MOF-801 crystals on the surface of MXene nanosheets, and obtain the film-forming solution. Step 2: The membrane-forming solution is applied to the substrate by suction to load MXene nanosheets loaded with MOF-801 crystals, followed by drying to obtain the intercalated MXene separation membrane.

2. Use according to claim 1, characterized in that, MOF-801 crystals account for 5-15% of the weight of MXene two-dimensional nanosheets.

3. Use according to claim 1, characterized in that, The MXene two-dimensional nanosheet is Ti3C2T x .

4. Use according to claim 1, characterized in that, In step 1, the concentration of fumaric acid in the solution is 0.01-0.15 mmol / L, and the molar ratio of fumaric acid to ZrOCl2 is 1:0.8-1.

2.

5. The use according to claim 1, characterized in that, The stirring reaction time is 0.5-5 hours.

6. Use according to claim 1, characterized in that, The substrate is a porous polymer material.

7. Use according to claim 1, characterized in that, The drying process involves treating the product at 10-40℃ for 5-30 hours.

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