A metal organic framework composite, a preparation method thereof and application thereof in carbon dioxide cycloaddition reaction

Abstract

This invention provides a method for preparing a metal-organic framework complex, comprising the following steps: (1) thoroughly mixing a hexadecyltrimethylammonium bromide solution and a terephthalic acid solution, adding copper acetate, and washing by centrifugation to obtain a Cu(BDC)(DMF) / CTAB precursor; (2) immersing the Cu(BDC)(DMF) / CTAB precursor in pure ethanol or an aqueous ethanol solution, and maintaining the temperature at 50-70 °C for 6-24 h to obtain the metal-organic framework complex. This invention also provides the application of the metal-organic framework complex in the CO₂ cycloaddition reaction, whereby the metal-organic framework complex exhibits excellent catalytic performance. This research opens up new avenues for designing and preparing compositionally optimized metal-organic framework complexes and highlights their enormous potential in energy-related applications.

Description

Technical Field

[0001] This invention relates to the field of metal-organic framework technology, specifically to a metal-organic framework composite and its preparation method and its application in carbon dioxide cycloaddition reactions, and more specifically to the preparation methods of CuO@Cu(BDC)(DMF) nanosheets and CuO@CuBDC-R nanorods and their application in carbon dioxide cycloaddition reactions. Background Technology

[0002] Metal-organic frameworks (MOFs) are materials formed by connecting metal centers / nodes with organic ligands. They possess significant advantages such as high specific surface area, regular pore structure, and diverse topologies, thus attracting widespread research attention and finding extensive applications in catalysis, gas storage and separation, drug release, and sensing. By controlling and optimizing the basic parameters of MOFs, such as chemical composition, size, and morphology, their physicochemical properties can be customized and multifunctionality endowed, which has become a current research hotspot.

[0003] Metal-based nanoparticles occupy a core position in many catalytic fields such as energy, chemical engineering, and environmental protection due to their excellent catalytic activity. Metal-based nanoparticles supported on MOFs exhibit enhanced synergistic effects in multiple fields (especially catalysis). By rationally selecting the metal center and organic ligand type of the MOF support, controlling the pore size, surface functional groups, and morphology of the MOFs, and optimizing the loading method, loading amount, and particle size of the metal-based nanoparticles, synergistic effects of both functions can be achieved. This not only fully utilizes the intrinsic activity of metal-based nanoparticles but also leverages the structural tunability and porous properties of MOFs to expand their application scenarios in heterogeneous catalysis, electrocatalysis, photocatalysis, biosensing, and other fields. This breaks through the performance limitations of single metal-based nanoparticles or single MOF materials, meeting the multifunctional needs of complex application scenarios, and has become a research hotspot and important development direction in the field of materials science. Summary of the Invention

[0004] The purpose of this invention is to provide a metal-organic framework composite, its preparation method and application. A Cu(BDC)(DMF) / CTAB precursor is obtained by adding CTAB, and then the precursor is immersed in two different solvent systems to obtain CuO@Cu(BDC)(DMF) nanosheets and CuO@CuBDC-R nanorods, respectively.

[0005] According to one aspect of this application, a method for preparing a metal-organic framework complex is provided, comprising the following steps: (1) thoroughly mixing a hexadecyltrimethylammonium bromide solution and a terephthalic acid solution, adding copper acetate, and washing by centrifugation to obtain a Cu(BDC)(DMF) / CTAB precursor; (2) immersing the Cu(BDC)(DMF) / CTAB precursor in pure ethanol or an aqueous ethanol solution, and keeping it at 50~70 ℃ for 6~24 h to obtain the metal-organic framework complex.

[0006] In some specific implementations, in step (1), the molar ratio of hexadecyltrimethylammonium bromide to terephthalic acid is 0.04 to 0.23.

[0007] In some specific implementations, in step (1), the molar ratio of copper acetate to terephthalic acid is 0.5 to 1.5.

[0008] In some specific implementations, in step (2), the Cu(BDC)(DMF) / CTAB precursor is immersed in pure ethanol and kept at 50~70 ℃ for 6~24 h to obtain CuO@Cu(BDC)(DMF) nanosheets; or the Cu(BDC)(DMF) / CTAB precursor is immersed in an aqueous ethanol solution and kept at 50~70 ℃ for 6~24 h to obtain CuO@CuBDC-R nanorods.

[0009] In some specific implementations, the volume ratio of ethanol to water in the aqueous ethanol solution is 1:1.

[0010] On the other hand, this application also provides metal-organic framework composites prepared by the aforementioned method. Specifically, the metal-organic framework composites are CuO@Cu(BDC)(DMF) nanosheets or CuO@CuBDC-R nanorods.

[0011] In some specific embodiments, the application of the aforementioned metal-organic framework composites as catalysts in CO2 cycloaddition reactions is provided. Specifically, CuO@Cu(BDC)(DMF) nanosheets and CuO@CuBDC-R nanorods are used as catalysts in CO2 cycloaddition reactions.

[0012] In some specific embodiments, the substrate in the CO2 cycloaddition reaction includes 1,2-epoxyhexane, styrene oxide, or 1-bromo-2,3-epoxypropane.

[0013] The beneficial effects of this invention are as follows: This invention obtains a Cu(BDC)(DMF) / CTAB precursor by adding CTAB, and then impregnates the precursor in two different solvent systems to obtain CuO@Cu(BDC)(DMF) nanosheets and CuO@CuBDC-R nanorods, respectively. By controlling the amount of CTAB, the CuO loading in CuO@Cu(BDC)(DMF) nanosheets and CuO@CuBDC-R nanorods can be precisely controlled. Both CuO@Cu(BDC)(DMF) nanosheets and CuO@CuBDC-R nanorods exhibit excellent catalytic performance in the CO2 cycloaddition reaction. This research opens up new avenues for designing and preparing compositionally optimized MOF-based composites and highlights their great potential in energy-related applications. Attached Figure Description

[0014] Figure 1 Images of the metal-organic framework composites are shown in the scanning electron microscope (SEM), X-ray diffraction (XRD), and Fourier transform infrared (FT-IR) spectra. Among them, a is the SEM image of CuO@Cu(BDC)(DMF) nanosheets, b is the SEM image of CuO@CuBDC-R nanorods, c is the XRD pattern of CuO@Cu(BDC)(DMF) nanosheets and CuO@CuBDC-R nanorods, and d is the FT-IR pattern of CuO@Cu(BDC)(DMF) nanosheets and CuO@CuBDC-R nanorods. Figure 2 Images are transmission electron microscopy (TEM) images of metal-organic framework composites; where a is a TEM image of CuO@Cu(BDC)(DMF) nanosheets, b is the size distribution of CuO particles in CuO@Cu(BDC)(DMF) nanosheets, c is a TEM image of CuO@CuBDC-R nanorods, d is the size distribution of CuO particles in CuO@CuBDC-R nanorods, e is an HR-TEM image of CuO@Cu(BDC)(DMF) nanosheets, and f is an HR-TEM image of CuO@CuBDC-R nanorods. Figure 3 TGA image of CuO@CuBDC-R nanorods with a CuO loading of 32.5%; Figure 4 TGA image of CuO@CuBDC-R nanorods with a CuO loading of 16.5%; Figure 5The images show the isothermal adsorption-desorption curves and XPS spectra of metal-organic framework composites; where a is the N2 adsorption-desorption isotherm and pore size distribution of CuO@Cu(BDC)(DMF) nanosheets, b is the N2 adsorption-desorption isotherm and pore size distribution of CuO@CuBDC-R nanorods, c is the Cu 2p high-resolution XPS spectrum of CuO@CuBDC-R nanorods, and d is the Cu 2p high-resolution XPS spectrum of CuO@Cu(BDC)(DMF) nanosheets. Figure 6 This diagram illustrates the performance of metal-organic framework (MOF) composites in the carbon dioxide cycloaddition reaction. Specifically, a) is a schematic diagram of CuO@Cu(BDC)(DMF) nanosheets and CuO@CuBDC-R nanorods as catalysts for the cycloaddition of carbon dioxide with epoxides to form cyclic carbonates; b) compares the conversion rates of 1,2-epoxyhexane using CuO@Cu(BDC)(DMF) nanosheets and CuO@CuBDC-R nanorods as catalysts over time; c) compares the conversion rates of carbon dioxide with epoxides using CuO@Cu(BDC)(DMF) nanosheets and CuO@CuBDC-R nanorods as catalysts; d) shows the retention of 1,2-epoxyhexane conversion rate using CuO@Cu(BDC)(DMF) nanosheets in four consecutive cycles; and e) shows the content of 16.5... wt. % and 32.5 wt. The conversion rate of CuO@CuBDC-R nanorods catalyzing the reaction of carbon dioxide with 1,2-epoxyhexane; Figure 7 The conversion rate of 1,2-epoxyhexane catalyzed by CuO@Cu(BDC)(DMF) nanosheets and CuO@CuBDC-R nanorods varies with CTAB / BDC. 2- The curve showing the change in molar ratio. Detailed Implementation

[0015] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0016] Unless otherwise specified, all materials and reagents used in the following examples are commercially available. Copper acetate (Cu(OAc)2), terephthalic acid (H2BDC), hexadecyltrimethylammonium bromide (CTAB), tetrabutylammonium bromide (TBAB), styrene oxide, 1-bromo-2,3-epoxypropane, and 1,2-epoxyhexane were purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.; N,N-dimethylformamide (DMF) and ethanol (CH3CH2OH) were purchased from Sinopharm Chemical Reagent Co., Ltd.; deionized water (H2O) and the above solvents were all of analytical grade.

[0017] Experimental Example 1: Preparation of Metal-Organic Framework Composites Preparation of Cu(BDC)(DMF) / CTAB precursor The preparation method includes the following steps: (1) Dissolve 90 mg of copper acetate (Cu(OAc)2) and terephthalic acid (H2BDC) in 45 mL of mixed solvent (volume ratio DMF / water / ethanol = 5:2:2) to obtain Cu(OAc)2 solution and H2BDC solution respectively; (2) Dissolve 0.1044 g CTAB in 45 mL of a mixed solvent of ethanol and water (volume ratio of ethanol to water 1:1) to obtain a CTAB solution; (3) Subsequently, at room temperature, 10 mL of CTAB solution was added to 45 mL of H2BDC solution and stirred thoroughly for 5 min. Then, 45 mL of Cu(OAc)2 solution was added to the above mixed solution and allowed to stand for 30 min. After washing with DMF and ethanol by centrifugation at 6000 r / min, Cu(BDC)(DMF) / CTAB precursor was obtained.

[0018] Preparation of CuO@Cu(BDC)(DMF) nanosheets Cu(BDC)(DMF) / CTAB precursor was immersed in 10 mL of pure ethanol and kept at 60 °C for 12 h in air to obtain CuO@Cu(BDC)(DMF) nanosheets.

[0019] Preparation of CuO@CuBDC-R nanorods Cu(BDC)(DMF) / CTAB precursor was immersed in 10 mL of ethanol-water mixed solvent (ethanol to water volume ratio of 1:1) and kept at 60 ℃ for 12 h in air atmosphere to obtain CuO@CuBDC-R nanorods.

[0020] Example 2: Characterization of Metal-Organic Framework Complexes The two metal-organic framework composites CuO@Cu(BDC)(DMF) nanosheets and CuO@CuBDC-R nanorods obtained in Example 1 above were characterized and their performance was tested.

[0021] The morphology of the samples was characterized using field emission scanning electron microscopy (FE-SEM, Hitachi SU8010) and transmission electron microscopy (TEM, JEOL JEM-2100F); such as Figure 1 As shown in Figure a, CuO@Cu(BDC)(DMF) is in the form of nanosheets with a side length of approximately 200 nm; CuO@CuBDC-R is in the form of rods with a length of approximately 2 μm and a width of approximately 200 nm. Figure 1 b).

[0022] Using Cu Kα Crystal structure information was obtained using an X-ray diffractometer (XRD, PANalytical Empyrean) with a radiation source (λ=1.5406 Å). For example... Figure 1 As shown in Figure c, the diffraction peaks of CuO@Cu(BDC)(DMF) nanosheets are consistent with those of simulated Cu(BDC)(DMF), indicating that they have the same crystal structure as Cu(BDC)(DMF). In this structure, the secondary structural units (SBUs) are composed of Cu 2+ The dimer is generated by terephthalate (BDC) 2- Ligand bridging occurs, with DMF molecules occupying axial coordination sites. No diffraction peaks were detected for CuO, attributed to its low content. In contrast, the XRD pattern of CuO@CuBDC-R nanorods showed characteristic peaks different from Cu(BDC)(DMF) but matching those of CuBDC, indicating a structural transformation where the Cu center only aligns with the BDC ligands. 2- The ligands are coordinated, and no DMF molecules are coordinated. In addition, due to the relatively high CuO content, CuO diffraction peaks can be clearly detected.

[0023] The organic functional groups in the complex were characterized using Fourier transform infrared spectroscopy (FT-IR, Bruker VERTEX 70). Figure 1 As shown in d, CuO@Cu(BDC)(DMF) nanosheets exhibit a typical characteristic peak: 1110 cm⁻¹ - The CO-Cu stretching vibration peak at ¹, 1591 cm⁻¹ - ¹ and 1395 cm - ¹BDC 2- The asymmetric and symmetric stretching vibration peaks of the COO⁻ group, 1510 cm⁻¹ - The benzene ring vibration peak at ¹ and the C=O stretching vibration peak of coordinated DMF at 1667 cm⁻¹; in addition, at 473 cm⁻¹ - The presence of a characteristic absorption peak at ¹, attributed to the Cu-O stretching vibration, confirms the formation of CuO. For CuO@CuBDC-R nanorods, no characteristic peak of coordinated DMF was observed, and the COO⁻ asymmetric stretching peak red-shifted from 1591 cm⁻¹ to 1585 cm⁻¹.

[0024] High-resolution transmission electron microscopy (HRTEM) was used to further investigate the lattice fringes and internal microstructure. For example... Figure 2As shown in Figures 2a and 2f, monodisperse and non-agglomerated nanoparticles are uniformly distributed on their respective MOF supports. Statistical analysis shows that the average particle sizes of CuO nanoparticles in CuO@Cu(BDC)(DMF) nanosheets and CuO@CuBDC-R nanorods are 4.61 nm and 5.07 nm, respectively. As shown in Figures 2e and 2f, the interplanar spacings are 0.234 nm and 0.149 nm, respectively, corresponding to the (111) and (11-3) crystal planes of monoclinic CuO in CuO@Cu(BDC)(DMF) nanosheets and CuO@CuBDC-R nanorods, confirming the successful formation of CuO in both parent MOFs.

[0025] The thermal stability of the composite was evaluated using a thermogravimetric analyzer (TGA, TA Instruments Q500), and the CuO loading was further verified. Figure 3 and Figure 4 As shown, the CuO loading of CuO@CuBDC-R nanorods was 32.5% and 16.5%, respectively. This was achieved by adjusting the ratio of CTAB to BDC... 2- The molar ratio (from 0.04 to 0.23) can also, to some extent, regulate the content of CuO nanoparticles in each composite system. When CTAB / BDC 2- When the molar ratio decreased from 0.12 to 0.04, the CuO nanoparticle content in CuO@CuBDC-R nanorods decreased significantly from 32.5% to 16.5%.

[0026] The isothermal adsorption-desorption curves of the samples were determined using a liquid nitrogen adsorption-desorption isotherm (77 K, Micromeritics ASAP 2020 system). The nitrogen adsorption-desorption isotherm of CuO@Cu(BDC)(DMF) nanosheets showed a significant increase in adsorption in the low-pressure region (Figure 5a), confirming the microporous structure of the material. Significant hysteresis loops were observed in the high relative pressure region (P / P0>0.8), a phenomenon likely originating from the interlayer pores between the nanosheets. This type of structural feature is not typically present in bulk materials. The CuO@CuBDC-R rod-shaped material exhibited a similar adsorption-desorption isotherm profile, but lacked the rapid adsorption process in the low-pressure region, which may be related to its relatively low specific surface area. Figure 5 b). Analysis using Brunauer-Emmett-Teller (BET) and density functional theory (DFT) methods revealed that the specific surface area of ​​CuO@Cu(BDC)(DMF) nanosheets was significantly higher than that of CuO@CuBDC-R rods (84.8 m²). 2 ・g -1 vs 45.5 m 2 ・g -1The corresponding pore sizes are 0.6 nm and 0.8 nm, respectively. Figure 5 (Illustration 5a and illustration 5b).

[0027] X-ray photoelectron spectroscopy (XPS, THERMO VG ESCALAB 250) was used to analyze the material composition and investigate the surface electronic states of the constituent elements. For example... Figure 5 As shown in Figure c, for CuO@CuBDC-R nanorods, the Cu 2p XPS spectrum of CuO nanoparticles exhibits typical peaks: a Cu 2p3 / 2 peak at 933.2 eV, a Cu 2p1 / 2 peak at 953.0 eV, and characteristic satellite peaks at 941.2 eV and 963.0 eV. For the CuBDC component in CuO@CuBDC-R nanorods, a characteristic Cu 2p3 / 2 peak was observed at 935.0 eV, accompanied by two previously reported "satellite peaks," indicating that all Cu species in CuO@CuBDC-R nanorods are in the Cu(II) state. Figure 5 As shown in Figure d, in CuO@Cu(BDC)(DMF) nanosheets, the Cu 2p XPS spectra of CuO nanoparticles show typical Cu 2p3 / 2 and Cu 2p1 / 2 peaks at 934.7 eV and 954.4 eV, respectively.

[0028] Experimental Example 3: Application of Metal-Organic Framework Complexes in CO2 Cycloaddition Reactions like Figure 6 As shown in Figure a, a cycloaddition reaction of CO2 (approximately 5 L of saturated bulb filled with CO2) with 1,2-epoxyhexane (4 mmol) was carried out for 6 h at ambient pressure and 60 °C using 5 mg CuO@Cu(BDC)(DMF) nanosheets or CuO@CuBDC-R nanorods as catalysts and 64 mg tetrabutylammonium bromide (TBAB) as a co-catalyst. Figure 6 As shown in b, CuO@Cu(BDC)(DMF) nanosheets achieved a conversion rate of 90.6% for 1,2-epoxyhexane, while CuO@CuBDC-R nanorods achieved a conversion rate of 52.8%. In addition, the substrate universality of CuO@Cu(BDC)(DMF) nanosheets or CuO@CuBDC-R nanorods as catalysts for the oxidation of styrene and 1-bromo-2,3-epoxypropane was investigated. Figure 6c). The experimental procedure is as follows: Using 5 mg CuO@Cu(BDC)(DMF) nanosheets or CuO@CuBDC-R nanorods as catalysts and 64 mg TBAB as co-catalysts, CO2 (approximately 5 L) reacted with styrene oxide (4 mmol) for 24 h and CO2 (approximately 5 L) reacted with 1-bromo-2,3-epoxypropane (4 mmol) for 18 h under normal pressure and 80 °C. The results are as follows. Figure 6 As shown in Figure c, CuO@Cu(BDC)(DMF) nanosheets achieved a styrene oxide conversion rate of 55.0%, while CuO@CuBDC-R nanorods achieved a conversion rate of 46.1%. CuO@Cu(BDC)(DMF) nanosheets also achieved a conversion rate of 82.5% for 1-bromo-2,3-epoxypropane, while CuO@CuBDC-R nanorods achieved a conversion rate of 68.4%. This demonstrates the excellent applicability of this composite in the efficient conversion of various epoxides to cyclic carbonates.

[0029] Four consecutive cyclic catalytic reactions were conducted to convert 1,2-epoxyhexane. The experimental procedure was consistent with the CO2 cycloaddition experiment with 1,2-epoxyhexane described above. After each catalytic reaction, the catalyst was washed with ethanol by centrifugation and then vacuum-dried at 80 °C for 6 h before use to evaluate the catalytic stability of CuO@Cu(BDC)(DMF) nanosheets. The results showed that the catalytic activity did not decrease significantly after four cycles. Figure 6 (d) indicates that the composite has excellent structural stability.

[0030] To elucidate the effect of component ratios in the complex on catalytic performance, a systematic study was conducted on control samples. For example... Figure 7 As shown, the epoxide conversion rate of CuO@Cu(BDC)(DMF) nanosheets varies with CTAB / BDC. 2- The molar ratio (which determines the CuO content) exhibits a volcanic change with increasing molar ratio; in contrast, the conversion rate of the CuO@CuBDC-R nanorod catalyst increases with increasing CTAB / BDC ratio. 2- The increase in the molar ratio exhibits an approximately inverted volcano-like change, when CTAB / BDC 2- The peak efficiency of 86.0% was reached at a molar ratio of 0.23. For example, the conversion of 1,2-epoxyhexane catalyzed by CuO@CuBDC-R nanorods with different CuO contents showed that the conversion rate at a CuO content of 32.5% (52.8%) was lower than that at a CuO content of 16.5% (62.1%). Figure 6e). This indicates that the synergistic effect between the MOF support and CuO nanoparticles is highly dependent on their relative ratio. Only when the ratio is within the optimal range can the two complexes exert the maximum synergistic effect and achieve optimal catalytic performance; an imbalance in the ratio will disrupt this synergy, leading to a decrease in catalytic activity. Specifically, the optimal MOF / CuO ratio (CTAB / BDC²) is... - CuO@Cu(BDC)(DMF) nanosheets (molar ratio 0.12) catalyzed a higher 1,2-epoxyhexane conversion rate (90.6%) than CuO@CuBDC-R nanorods at their optimal ratio (CTAB / BDC²). - The conversion rate (86.0%) catalyzed at a molar ratio of 0.23 was attributed to the nanosheet morphology providing more accessible active sites (verified by N2 adsorption measurements) and the ideal synergistic effect between CuO and Cu(BDC)(DMF) substrates.

[0031] The preparation method and application of a metal-organic framework composite provided by the present invention have been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention. It should be noted that those skilled in the art can make several improvements and modifications to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims

1. A method of preparing a metal organic framework composite, characterized in that, The process includes the following steps: (1) After thoroughly mixing hexadecyltrimethylammonium bromide solution and terephthalic acid solution, copper acetate is added, and after centrifugation and washing, Cu(BDC)(DMF) / CTAB precursor is obtained; (2) The Cu(BDC)(DMF) / CTAB precursor is immersed in pure ethanol or an aqueous ethanol solution and kept at 50~70℃ for 8~24 h to obtain the metal-organic framework complex.

2. The method for preparing the metal-organic framework composite according to claim 1, characterized in that, In step (1), the molar ratio of hexadecyltrimethylammonium bromide to terephthalic acid is 0.04~0.

23.

3. The method for preparing the metal-organic framework composite according to claim 1, characterized in that, In step (1), the molar ratio of copper acetate to terephthalic acid is 0.5 to 1.

5.

4. The method for preparing the metal-organic framework composite according to claim 1, characterized in that, In step (2), the Cu(BDC)(DMF) / CTAB precursor is immersed in pure ethanol and kept at 50~70 ℃ for 6~24 h to obtain CuO@Cu(BDC)(DMF) nanosheets. Alternatively, Cu(BDC)(DMF) / CTAB precursors can be immersed in an aqueous ethanol solution and kept at 50-70 °C for 6-24 h to obtain CuO@CuBDC-R nanorods.

5. The method for preparing the metal-organic framework composite according to claim 4, characterized in that... The volume ratio of ethanol to water in an aqueous ethanol solution is 1:

1.

6. The metal-organic framework composite prepared by the method according to claims 1 to 5.

7. The metal-organic framework composite according to claim 6, characterized in that, The metal-organic framework composite is CuO@Cu(BDC)(DMF) nanosheets or CuO@CuBDC-R nanorods.

8. The application of the metal-organic framework complex according to claim 6 or 7 as a catalyst in the CO2 cycloaddition reaction.

9. The application according to claim 8, characterized in that, In the CO2 cycloaddition reaction, the substrates include 1,2-epoxyhexane, styrene oxide, or 1-bromo-2,3-epoxypropane.

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