Supercritical carbon dioxide assisted derived MIL-125-NH2 / TiO2 heterojunction and preparation method and application thereof

Abstract

The application discloses a kind of supercritical carbon dioxide assisted derivatization MIL-125-NH2 / TiO2 heterojunction and its preparation method and application, preparation method is: MIL-125-NH2 with cosolvent is added to reactor, high-pressure CO2 is added, and heated to reaction temperature, cooling, obtains MIL-125-NH2 / TiO2 heterojunction.The application is successfully induced metal oxide in-situ generation in MOFs framework by the synergistic effect of supercritical carbon dioxide and cosolvent, while the surface realizes the modification of triazine functional group, and realizes the in-situ conversion of MIL-125-NH2 to TiO2 nanorod, while retaining part of the MIL-125-NH2 framework, finally constructs MIL-125-NH2 / TiO2 heterojunction, and its visible light catalytic hydrogen production performance is 47.3 times of unmodified MIL-125-NH2.

Description

Technical Field

[0001] This invention belongs to the field of photocatalytic water splitting for hydrogen production technology, specifically relating to a supercritical carbon dioxide-assisted derived MIL-125-NH2 / TiO2 heterojunction, its preparation method, and its application. Background Technology

[0002] MIL-125-NH2 is a titanium-based metal-organic framework (MOF) with excellent visible light absorption and reactant adsorption capabilities. It also features a tunable metal-organic ligand coordination structure and a highly ordered porous structure, making it an ideal precursor for advanced photocatalysts. By converting it to TiO2, a strongly coupled MIL-125-NH2 / TiO2 heterojunction structure can be constructed. This structure exhibits both high interfacial compatibility and strong charge transfer capabilities, significantly improving photocatalytic hydrogen production performance.

[0003] However, current in-situ reconstruction strategies for MIL-125-NH2 mainly rely on hydrothermal or solvothermal treatment, which limits their controllability. This is primarily due to: ① The high specific heat capacity and latent heat of phase change of water / organic solvents result in a slow heating rate, while their low thermal conductivity leads to a slow heat transfer rate, resulting in a long post-treatment time (approximately 12-24 h) and almost complete decomposition of the organic ligands; ② Mass transfer in hydrothermal / solvothermal systems is achieved through free diffusion, and the high surface tension of water / organic solvents makes it difficult for them to penetrate the microporous structure of MIL-125-NH2, hindering the construction of strongly coupled MIL-125-NH2 / TiO2 heterostructures. Furthermore, in-situ conversion of MIL-125-NH2 to TiO2 can also be achieved through calcination, but the resulting TiO2 typically retains the morphology of the original organic framework, making it difficult to construct unique morphologies. Therefore, exploring in-situ reconstruction methods for MIL-125-NH2 with strong heat and mass transfer capabilities, scalability, and high controllability is of great research significance and practical demand. Summary of the Invention

[0004] To overcome the problems of poor controllability, long processing time, and difficulty in scaling up the in-situ conversion of MIL-125-NH2 in existing technologies, the present invention proposes a supercritical carbon dioxide-assisted derivatized MIL-125-NH2 / TiO2 heterojunction, its preparation method, and its application. This MIL-125-NH2 / TiO2 heterojunction has a hollow structure and can be applied to the field of photocatalytic hydrogen production. Its photocatalytic hydrogen production performance is 47.3 times that of unmodified MIL-125-NH2.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for preparing a supercritical carbon dioxide-derived MIL-125-NH2 / TiO2 heterojunction includes the following steps: MIL-125-NH2 and a co-solvent were added to a reactor, high-pressure CO2 was added, and the mixture was heated to the reaction temperature and then cooled to obtain a MIL-125-NH2 / TiO2 heterojunction.

[0006] Furthermore, the co-solvent is acetonitrile.

[0007] Furthermore, the ratio of MIL-125-NH2 to the co-solvent is 100~500 mg: 100~500 μL.

[0008] Furthermore, the temperature after adding high-pressure CO2 is 40~65℃, and the pressure is 5~10 MPa.

[0009] Furthermore, the temperature after adding high-pressure CO2 is 65℃ and the pressure is 8 MPa.

[0010] Furthermore, the reaction temperature is 280~350℃.

[0011] Furthermore, the reaction temperature is 320℃.

[0012] Furthermore, the cooling system is water-cooled.

[0013] A MIL-125-NH2 / TiO2 heterojunction.

[0014] Application of a MIL-125-NH2 / TiO2 heterojunction in photocatalytic hydrogen production.

[0015] Compared with the prior art, the present invention has the following beneficial effects: This invention utilizes supercritical carbon dioxide and a co-solvent to assist in the in-situ conversion of MIL-125-NH2 to TiO2, and to construct a MIL-125-NH2 / TiO2 heterojunction. Supercritical carbon dioxide possesses excellent heat and mass transfer capabilities, resulting in a rapid heating rate. Compared to the traditional hydrothermal / solvothermal methods with a post-treatment time of approximately 12-24 hours, the method used in this invention reduces the post-treatment time to less than 180 seconds, making it more efficient. Simultaneously, supercritical carbon dioxide has extremely low viscosity and almost zero surface tension, allowing it to more easily penetrate the numerous microporous structures of MIL-125-NH2 compared to water / organic solvents, thus efficiently achieving the in-situ conversion of the bulk structure of MIL-125-NH2. In this invention, supercritical carbon dioxide serves not only as a solvent but also as a reactant, penetrating into the pores of MIL-125-NH2 and dissociating into... O undergoes an oxidation reaction with the Ti-O cluster, thus achieving the in-situ conversion of MIL-125-NH2 to TiO2.

[0016] Furthermore, in this invention, acetonitrile, besides being polymerized at high temperature into a triazine derivative and covalently functionalized and grafted onto the catalyst surface, also adsorbs around the organic ligands on the surface of MIL-125-NH2, thus protecting the outer framework of MIL-125-NH2. Therefore, MIL-125-NH2 is in situ converted to TiO2 internally, while retaining the MOF framework externally, ultimately forming a MIL-125-NH2 / TiO2 heterojunction. The formation of the MIL-125-NH2 / TiO2 heterojunction in this invention effectively enhances the separation and migration of photogenerated carriers, while the surface-grafted triazine functional groups strengthen the adsorption and activation of reactant water, thereby significantly improving the photocatalytic hydrogen production performance. Simultaneously, the extremely strong organic solubility of supercritical carbon dioxide ensures uniform dispersion of acetonitrile in the system, thus requiring a lower amount of acetonitrile and reducing organic pollution. Attached Figure Description

[0017] Figure 1 Bar charts showing the visible light photocatalytic hydrogen production activity of MIL-125-NH2, Example 1, and Comparative Example 1; Figure 2 Bar charts showing the UV photocatalytic hydrogen production activity of MIL-125, Comparative Example 2, and Comparative Example 3; Figure 3 The XRD patterns are for MIL-125-NH2, Example 1, and Comparative Example 1. Figure 4 The XRD patterns of MIL-125, Comparative Example 2, and Comparative Example 3 are shown. Figure 5 TGA curves for MIL-125-NH2, Example 1, and Comparative Example 1; where a is the TGA curve and b is a partial enlarged view of Example 1 and Comparative Example 1 in a. Figure 6 The compositional analysis of the liquid and gaseous products obtained in Example 1 and Comparative Example 1 is as follows: where a is the liquid product and b is the gaseous product.

[0018] Figure 7 The adsorption energy curves of acetonitrile and carbon dioxide molecules in MIL-125-NH2 and MIL-125 are shown, respectively. Among them, a is the adsorption energy curve in MIL-125-NH2 and b is the adsorption energy curve in MIL-125. Figure 8 The PL spectra of MIL-125-NH2, Example 1, and Comparative Example 1 are shown; where a is the steady-state PL spectrum and b is the transient PL spectrum. Figure 9 The photoelectrochemical properties of MIL-125-NH2, Example 1, and Comparative Example 1 are shown; where a is the EIS impedance spectrum and b is the photocurrent-time curve. Figure 10 The bar charts show the visible light photocatalytic hydrogen production activity of Examples 1-8; Figure 11 The heating curves are for Example 1 and Comparative Example 1. Figure 12 The XRD pattern is shown in Comparative Example 4. Figure 13 The images are TEM images of MIL-125-NH2, Example 1, Comparative Example 1, and Comparative Example 4, where a is MIL-125-NH2, b is Example 1, c is Comparative Example 1, and d is Comparative Example 4. Detailed Implementation

[0019] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. The preferred embodiments of the present invention are shown in the accompanying drawings. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure of the present invention.

[0020] Supercritical carbon dioxide (ScCO2) combines the strong diffusivity of gases with the strong heat transfer capacity of liquids. Its surface tension is almost zero, giving it excellent permeability and mass transfer efficiency. At the same time, it has a strong ability to dissolve organic matter, making it scalable, green, and efficient. It is widely used in the field of green synthesis of materials.

[0021] Thanks to the extremely strong heat and mass transfer capabilities of supercritical carbon dioxide, the in-situ conversion of MIL-125-NH2 can be completed in a very short time, demonstrating the high efficiency of the supercritical carbon dioxide-assisted conversion strategy. Simultaneously, the strong organic solubility and microporous permeability of supercritical carbon dioxide significantly reduce the amount of acetonitrile used, resulting in a uniform reaction while also offering the advantages of being environmentally friendly. Based on this, this invention utilizes a supercritical carbon dioxide / acetonitrile co-solvent system to assist in the in-situ conversion of MIL-125-NH2 and the construction of the MIL-125-NH2 / TiO2 heterostructure.

[0022] The present invention discloses a method for preparing a supercritical carbon dioxide-assisted derived MIL-125-NH2 / TiO2 heterojunction, comprising the following steps: First, MIL-125-NH2 was prepared using a solvothermal method. The obtained MIL-125-NH2 was placed in a high-temperature, high-pressure reactor, and a certain amount of co-solvent (acetonitrile) was added. CO2 was injected into the reactor to fully displace the internal atmosphere. Then, high-pressure CO2 was pumped in using a gas compressor to control the initial temperature and pressure, and the reactor was rapidly heated. Once the target temperature was reached, the reactor was immediately placed in room temperature (25°C) water for cooling. The resulting solid product was collected, washed, and dried to obtain the supercritical carbon dioxide-assisted derived MIL-125-NH2 / TiO2 heterojunction. The specific steps are as follows: 1) Add 100~500 mg MIL-125-NH2 to a high-temperature and high-pressure reactor, and add 100~500 μL of acetonitrile. Then seal the reactor.

[0023] 2) Inject CO2 into the reactor three times to replace the internal atmosphere of the reactor, and then pump in high-pressure CO2 through a gas compressor. To prevent CO2 from liquefying, the initial temperature can be controlled at 40~65℃ and the initial pressure can be controlled at 5~10 MPa.

[0024] 3) Place the reactor in the electric furnace and heat it. Once the thermocouple in the reactor detects that the temperature has reached 280~350℃, immediately remove the reactor from the electric furnace and immerse it in a room temperature water bath to cool it down.

[0025] 4) Collect the gaseous, liquid and solid products respectively. Wash the obtained solid products with methanol and N,N-dimethylformamide in sequence, repeat 3 times, and dry at 60℃ for 12 h to obtain the supercritical carbon dioxide-assisted derivatized MIL-125-NH2 / TiO2 heterojunction, i.e., photocatalyst, to realize the metal-organic framework derivatization transformation.

[0026] This invention also provides an application of a supercritical carbon dioxide-assisted derived MIL-125-NH2 / TiO2 heterojunction in photocatalytic hydrogen production. Specifically, 20 mg of photocatalyst is dispersed in a mixed solution of 2 mL triethanolamine, 30 mL acetonitrile, and 500 μL deionized water. A chloroplatinic acid solution containing 0.2 mg Pt is added, wherein Pt is used as a co-catalyst and the mass of Pt is 1 wt% of the photocatalyst. A 300 W xenon lamp equipped with a 400 nm cutoff filter is used as the light source for hydrogen production.

[0027] Supercritical carbon dioxide rapidly permeates into the hierarchical porous structure of MIL-125-NH2 during the reaction, inducing the detachment of ligands within MIL-125-NH2 and transforming Ti-O clusters in situ into TiO2 nanorods. A small number of acetonitrile molecules adsorb onto the polar sites of the MIL-125-NH2 framework, inhibiting the decomposition of the organic framework and preserving the MIL-125-NH2 shell, thus forming a MIL-125-NH2 / TiO2 heterojunction, which significantly promotes the separation and transfer of photogenerated carriers. Simultaneously, acetonitrile molecules polymerize into triazine derivatives under high temperature and pressure and graft them onto the surface of the MIL-125-NH2 / TiO2 heterojunction, providing a large number of active sites for the photocatalytic hydrogen production reaction, which is beneficial for the adsorption of reactants. The two synergistically enhance the photocatalytic hydrogen production performance of the supercritical carbon dioxide-assisted derived MIL-125-NH2 / TiO2 heterojunction under visible light.

[0028] The following description, in conjunction with specific embodiments, illustrates the content of the present invention. However, the following description is not intended to limit the scope of the present invention.

[0029] In this invention, MIL-125-NH2 is prepared by a solvothermal method and is denoted as MIL-NH2.

[0030] Example 1 1) Add 500 mg MIL-125-NH2 to a high-temperature and high-pressure reactor, and add 500 μL acetonitrile. Then seal the reactor.

[0031] 2) Inject CO2 into the reactor to fully replace the internal atmosphere, and then pump in high-pressure CO2 through a gas compressor. The initial temperature is controlled at 65℃ and the initial pressure is controlled at 8 MPa.

[0032] 3) Place the reactor in the electric furnace and heat it to 320°C. Once the thermocouple in the reactor detects that the temperature has reached 320°C, immediately remove the reactor from the electric furnace and immerse it in a room temperature water bath to cool it down.

[0033] 4) Collect the gaseous, liquid and solid products respectively. Wash the obtained solid products with methanol and N,N-dimethylformamide in sequence, repeat 3 times, and dry at 60℃ for 12 h to obtain the supercritical carbon dioxide-assisted derivatized MIL-125-NH2 / TiO2 heterojunction, denoted as SCM-MIL-NH2.

[0034] Example 2 The difference between this embodiment and Embodiment 1 is that after the reactor is heated to 280°C in an electric furnace, it is immediately removed from the furnace and immersed in a room temperature water bath to cool, thereby obtaining a supercritical carbon dioxide-assisted derived MIL-125-NH2 / TiO2 heterojunction, denoted as SCM-MIL-NH2-280.

[0035] Example 3 The difference between this embodiment and Embodiment 1 is that after the reactor is heated to 290°C in an electric furnace, it is immediately removed from the furnace and immersed in a room temperature water bath to cool, thereby obtaining a supercritical carbon dioxide-assisted derived MIL-125-NH2 / TiO2 heterojunction, denoted as SCM-MIL-NH2-290.

[0036] Example 4 The difference between this embodiment and Embodiment 1 is that after the reactor is heated to 300°C in an electric furnace, it is immediately removed from the furnace and immersed in a room temperature water bath to cool, thereby obtaining a supercritical carbon dioxide-assisted derived MIL-125-NH2 / TiO2 heterojunction, denoted as SCM-MIL-NH2-300.

[0037] Example 5 The difference between this embodiment and Embodiment 1 is that after the reactor is heated to 310°C in an electric furnace, it is immediately removed from the furnace and immersed in a room temperature water bath to cool, thereby obtaining a supercritical carbon dioxide-assisted derived MIL-125-NH2 / TiO2 heterojunction, denoted as SCM-MIL-NH2-310.

[0038] Example 6 The difference between this embodiment and Embodiment 1 is that after the reactor is heated to 330°C in an electric furnace, it is immediately removed from the furnace and immersed in a room temperature water bath to cool, thus obtaining a supercritical carbon dioxide-assisted derived MIL-125-NH2 / TiO2 heterojunction, denoted as SCM-MIL-NH2-330.

[0039] Example 7 The difference between this embodiment and Embodiment 1 is that after the reactor is heated to 340°C in an electric furnace, it is immediately removed from the furnace and immersed in a room temperature water bath to cool, thereby obtaining a supercritical carbon dioxide-assisted derived MIL-125-NH2 / TiO2 heterojunction, denoted as SCM-MIL-NH2-340.

[0040] Example 8 The difference between this embodiment and Embodiment 1 is that after the reaction vessel is heated to 350°C in an electric furnace, it is immediately removed from the furnace and immersed in a room temperature water bath to cool, and the resulting solid sample is denoted as SCM-MIL-NH2-350.

[0041] Example 9 1) Add 100 mg of MIL-125-NH2 to a high-temperature and high-pressure reactor, and add 100 μL of acetonitrile. Then seal the reactor.

[0042] 2) Inject CO2 into the reactor to fully replace the internal atmosphere, and then pump in high-pressure CO2 through a gas compressor. The initial temperature is controlled at 40℃ and the initial pressure is controlled at 5.0 MPa.

[0043] 3) Place the reactor in the electric furnace and heat it to 320°C. Once the thermocouple in the reactor detects that the temperature has reached 320°C, immediately remove the reactor from the electric furnace and immerse it in a room temperature water bath to cool it down.

[0044] 4) Collect the gaseous, liquid and solid products respectively. Wash the obtained solid products with methanol and N,N-dimethylformamide in sequence, repeat 3 times, and dry at 60℃ for 12 h to obtain the supercritical carbon dioxide-assisted derivatized MIL-125-NH2 / TiO2 heterojunction.

[0045] Example 10 1) Add 500 mg MIL-125-NH2 to a high-temperature and high-pressure reactor, and add 400 μL of acetonitrile. Then seal the reactor.

[0046] 2) Inject CO2 into the reactor to fully replace the internal atmosphere, and then pump in high-pressure CO2 through a gas compressor. The initial temperature is controlled at 40℃ and the initial pressure is controlled at 10.0 MPa.

[0047] 3) Place the reactor in the electric furnace and heat it to 320°C. Once the thermocouple in the reactor detects that the temperature has reached 320°C, immediately remove the reactor from the electric furnace and immerse it in a room temperature water bath to cool it down.

[0048] 4) Collect the gaseous, liquid and solid products respectively. Wash the obtained solid products with methanol and N,N-dimethylformamide in sequence, repeat 3 times, and dry at 60℃ for 12 h to obtain the supercritical carbon dioxide-assisted derivatized MIL-125-NH2 / TiO2 heterojunction.

[0049] Example 11 1) Add 300 mg MIL-125-NH2 to a high-temperature and high-pressure reactor, and add 500 μL of acetonitrile. Then seal the reactor.

[0050] 2) Inject CO2 into the reactor to fully replace the internal atmosphere, and then pump in high-pressure CO2 through a gas compressor. The initial temperature is controlled at 60℃ and the initial pressure is controlled at 7.0 MPa.

[0051] 3) Place the reactor in the electric furnace and heat it to 320°C. Once the thermocouple in the reactor detects that the temperature has reached 320°C, immediately remove the reactor from the electric furnace and immerse it in a room temperature water bath to cool it down.

[0052] 4) Collect the gaseous, liquid and solid products respectively. Wash the obtained solid products with methanol and N,N-dimethylformamide in sequence, repeat 3 times, and dry at 60℃ for 12 h to obtain the supercritical carbon dioxide-assisted derivatized MIL-125-NH2 / TiO2 heterojunction.

[0053] The method of this invention is also applicable to other MOF materials, such as UiO-66-NH2.

[0054] To investigate the mechanism of MIL-125-NH2 conversion to TiO2 in the supercritical carbon dioxide / acetonitrile co-solvent system, the following comparative examples were analyzed: Comparative Example 1 1) Add 500 mg of MIL-125-NH2 to a high-temperature and high-pressure reactor without adding acetonitrile, and then seal the reactor.

[0055] 2) Inject CO2 into the reactor to fully replace the internal atmosphere, and then pump in high-pressure CO2 through a gas compressor. The initial temperature is controlled at 65℃ and the initial pressure is controlled at 8.0 MPa.

[0056] 3) Place the reactor in the electric furnace and heat it to 320°C. Once the thermocouple in the reactor detects that the temperature has reached 320°C, immediately remove the reactor from the electric furnace and immerse it in a room temperature water bath to cool it down.

[0057] 4) Collect the solid product and wash it with methanol and N,N-dimethylformamide in sequence, repeating the process 3 times. Then dry it at 60°C for 12 h. The resulting sample is denoted as SC-MIL-NH2.

[0058] Comparative Example 2 1) Add 500 mg of MIL-125 to a high-temperature and high-pressure reactor, and then add 500 μL of acetonitrile. The reactor is then sealed. MIL-125 is a MOF with the same structure as MIL-125-NH2 but without NH2, and is prepared by a solvothermal method. It is denoted as MIL.

[0059] 2) Inject CO2 into the reactor to fully replace the internal atmosphere, and then pump in high-pressure CO2 through a gas compressor. The initial temperature is controlled at 65℃ and the initial pressure is controlled at 8.0 MPa.

[0060] 3) Place the reactor in the electric furnace and heat it to 320°C. Once the thermocouple in the reactor detects that the temperature has reached 320°C, immediately remove the reactor from the electric furnace and immerse it in a room temperature water bath to cool it down.

[0061] 4) Collect the solid product and wash it with methanol and N,N-dimethylformamide in sequence, repeating the process 3 times. Then dry it at 60°C for 12 h. The resulting sample is denoted as SCM-MIL.

[0062] Comparative Example 3 1) Add 500 mg of MIL-125 to a high-temperature and high-pressure reactor without adding acetonitrile, and then seal the reactor.

[0063] 2) Inject CO2 into the reactor to fully replace the internal atmosphere, and then pump in high-pressure CO2 through a gas compressor. The initial temperature is controlled at 65℃ and the initial pressure is controlled at 8.0 MPa.

[0064] 3) Place the reactor in the electric furnace and heat it to 320°C. Once the thermocouple in the reactor detects that the temperature has reached 320°C, immediately remove the reactor from the electric furnace and immerse it in a room temperature water bath to cool it down.

[0065] 4) Collect the solid product and wash it with methanol and N,N-dimethylformamide in sequence, repeating the process 3 times. Then dry it at 60°C for 12 h. The resulting sample is denoted as SC-MIL.

[0066] Comparative Example 4 1) Add 500 mg of MIL-125-NH2 to an alumina crucible, and then seal the crucible with aluminum foil.

[0067] 2) Place the crucible in a muffle furnace and heat it in an air atmosphere at 10°C. o C min -1 The heating rate from 20 o C rises to 400 o C, and keep warm for 12 hours.

[0068] 3) Collect the obtained solid and denote it as C-TiO2.

[0069] Comparative Example 5 The difference between this comparative example and Example 1 is that 500 μL of benzyl alcohol was added as a co-solvent, and the resulting solid sample was designated as SCBnOH-MIL-NH2-320.

[0070] Comparative Example 6 The difference between this comparative example and Example 1 is that 500 μL of benzaldehyde was added as a co-solvent, and the resulting solid sample was designated SCPhCHO-MIL-NH2-320.

[0071] Comparative Example 7 The difference between this comparative example and Example 1 is that 500 μL of methanol was added as a co-solvent, and the resulting solid sample was denoted as SCMeOH-MIL-NH2-320.

[0072] Benzyl alcohol in Comparative Example 5, benzaldehyde in Comparative Example 6, and methanol in Comparative Example 7 could not achieve the preparation of the MIL-125-NH2 / TiO2 heterojunction in this invention. In contrast, acetonitrile in this invention can selectively adsorb onto the amino group of the MOF, protecting part of the MOF structure from supercritical CO2 oxidation. Benzyl alcohol and benzaldehyde cannot achieve the same effect as acetonitrile.

[0073] Performance evaluation: Figure 1 The bar charts show the visible light photocatalytic hydrogen production activity of MIL-125-NH2, Example 1, and Comparative Example 1. The photocatalytic hydrogen production test method was as follows: 20 mg of photocatalyst was dispersed in a mixed solution of 2 mL triethanolamine, 30 mL acetonitrile, and 500 μL deionized water. Pt (1 wt% of the photocatalyst) was added as a co-catalyst. A 300W xenon lamp equipped with a 400 nm cutoff filter was used as the light source to detect the amount of hydrogen produced in the photocatalytic system. According to... Figure 1 It can be seen that the photocatalytic hydrogen production activity of the sample SCM-MIL-NH2 obtained in Example 1 is 47.3 times and 5.0 times that of MIL-125-NH2 and the sample SC-MIL-NH2 obtained in Comparative Example 1, respectively, indicating that supercritical carbon dioxide and acetonitrile play a synergistic role in the conversion process of MIL-125-NH2.

[0074] Figure 2 The bar charts show the UV photocatalytic hydrogen production activity of MIL-125, Comparative Example 2, and Comparative Example 3. The photocatalytic hydrogen production test methods are basically the same as those used for the photocatalyst in Example 1, except that a 400 nm cutoff filter is not used, and a 300W xenon lamp with full-spectrum irradiation is employed. According to... Figure 2 It can be seen that the photocatalytic hydrogen production activities of the samples obtained in Comparative Example 2 and Comparative Example 3 are similar, indicating that the presence of acetonitrile in the reaction system has little impact on the conversion process of MIL-125. This is further supported by the similar framework structure of MIL-125 and MIL-125-NH2. Figure 1 The results show that acetonitrile mainly acts on the NH2 active site in MIL-125-NH2.

[0075] Figure 3 The XRD patterns of MIL-125-NH2, Example 1, and Comparative Example 1 are shown below. Figure 3It can be seen that both Example 1 and Comparative Example 1 exhibited diffraction peaks at 25.3°, 38.0°, and 48.4°, which are attributed to TiO2 (PDF-01-0562), indicating that MIL-125-NH2 was converted to TiO2 during the supercritical carbon dioxide post-treatment process. Meanwhile, the obtained sample SCM-MIL-NH2 still retained some of the diffraction peaks of MIL-125-NH2 (6.8°, 9.7°, and 11.6°), indicating that acetonitrile, as a co-solvent, can partially protect the framework structure of MIL-125-NH2, ultimately forming a MIL-125-NH2 / TiO2 heterojunction with the in-situ converted TiO2.

[0076] Figure 4 The XRD patterns of MIL-125, Comparative Example 2, and Comparative Example 3 are shown below. Figure 4 It can be seen that in Comparative Examples 2 and 3, MIL-125-NH2 was eventually completely converted to TiO2, and... Figure 3 In contrast, acetonitrile directly acts on the amino site of MIL-125-NH2, thereby protecting the organic framework structure.

[0077] Figure 5 Figures a and b show the TGA curves for MIL-125-NH2, Example 1, and Comparative Example 1, respectively, with oxygen as the test atmosphere. As the temperature increases, physically adsorbed and residual species (including methanol, water, N,N-dimethylformamide, and acetic acid) are gradually removed from the pores of the sample. Subsequently, the organic ligands begin to decompose at approximately 340°C, and the sample is eventually completely oxidized to TiO2. For ease of comparison, the residual TiO2 content in the sample (…) is… W TiO2 Normalized to 100%. Figure 5 The ligand content in SCM-MIL-NH2 can be calculated from b. W Ligand The concentration of acetonitrile was approximately 21.9%, slightly higher than the 19.5% of SC-MIL-NH2, indicating that the presence of acetonitrile partially inhibited the decomposition of the organic ligands. Figure 3 It can be seen that even after the framework structure is almost completely decomposed, a certain amount of organic ligands in SC-MIL-NH2 are still retained on the surface of the in-situ transformed TiO2.

[0078] Figure 6 This refers to the component analysis of the liquid and gaseous products obtained in Example 1 and Comparative Example 1, where BR-SCM and BR-SC refer to the liquid and gaseous products collected in Example 1 and Comparative Example 1, respectively, without the addition of MOF. According to... Figure 6From a, we can see that both SCM-MIL-NH2 and SC-MIL-NH2 show peaks corresponding to the ligand H2BDC-NH2 of MIL-125-NH2 (approximately located at...). Figure 6 The peak intensity of H2BDC-NH2 was 9.953 min (in the range of a), and the correlation peak intensity of SCM-MIL-NH2 was significantly higher than that of SC-MIL-NH2. This can be attributed to the protective effect of acetonitrile on H2BDC-NH2, reducing the decomposition of H2BDC-NH2. According to Figure 6 As shown in step b, the reaction produces reducing gaseous products H2 and CO. H2 originates from the dehydrogenation of H2BDC-NH2 at high temperature, while CO originates from the dissociation of supercritical carbon dioxide. CO further proves that supercritical carbon dioxide participated in the reaction as a reactant.

[0079] Figure 7 Acetonitrile and carbon dioxide molecules are respectively in MIL-125-NH2 ( Figure 7 a) and MIL-125 ( Figure 7 The adsorption energy curve in (b) is obtained by GCMS under simulated reaction conditions. Figure 7 The adsorption energy curve of acetonitrile (a) can be decomposed into six Gaussian components, corresponding to different adsorption microenvironments and molecular orientations, with an average adsorption energy of -2.04 eV; while the adsorption energy curve of CO2 can only be decomposed into two Gaussian components, with an average adsorption energy of only -0.78 eV. The significant difference in adsorption energy distribution and intensity indicates that acetonitrile has a much stronger affinity for MIL-125-NH2 than CO2 and can occupy more types of adsorption sites. Figure 7 In Figure b, the adsorption energy curve of acetonitrile on MIL-125 can only be decomposed into two Gaussian components, with an average adsorption energy of -0.70 eV; while the adsorption energy curve of CO2 only has a single Gaussian component, with an average adsorption energy of -0.30 eV. Compared with MIL-125, acetonitrile has a significantly stronger adsorption affinity in MIL-125-NH2, and the adsorption energy difference between acetonitrile and CO2 molecules is also greater, indicating that the amino group is the preferential adsorption site for acetonitrile, further demonstrating the effective protection of the organic ligands of MIL-125-NH2 by acetonitrile.

[0080] Figure 8 The PL spectra are for MIL-125-NH2, Example 1, and Comparative Example 1, where a is the steady-state PL spectrum and b is the transient PL spectrum. According to... Figure 8 As shown in section a, compared to SC-MIL-NH2, the steady-state PL emission peak of SCM-MIL-NH2 is significantly red-shifted to 550 nm. This red-shift phenomenon is attributed to the triazine group introduced during the treatment process. According to Figure 8As shown in Figure b, SCM-MIL-NH2 exhibits the longest average photogenerated carrier lifetime, indicating its higher efficiency in separating photogenerated electron-hole pairs. The formation of the MIL-125-NH2 / TiO2 heterojunction and the surface triazine functionalization synergistically suppress charge recombination and promote charge transport.

[0081] Figure 9 The photoelectrochemical performance of SCM-125-NH2, Example 1, and Comparative Example 1 is shown, where a is the EIS impedance spectrum and b is the photocurrent-time curve. SCM-MIL-NH2 exhibits the smallest Nyquist circle diameter in the EIS impedance spectrum, indicating that the supercritical carbon dioxide-assisted derivatization strategy significantly reduces the interfacial charge transfer resistance of the catalyst. Simultaneously, SCM-MIL-NH2 exhibits the highest photocurrent density (…). Figure 9 Figure b) shows that more charge carriers migrate to the catalyst surface under light irradiation. Therefore, the synergistic modification of the supercritical carbon dioxide and acetonitrile co-solvent significantly optimizes the photogenerated carrier dynamics of the photocatalyst.

[0082] Figure 10 The bar charts show the visible light photocatalytic hydrogen production activity of Examples 1-8, based on... Figure 10 It can be seen that 320℃ (i.e. Example 1) is the optimal post-processing temperature, and the resulting sample has the highest photocatalytic hydrogen production activity.

[0083] Figure 11 The figures show the temperature rise curves for Example 1 and Comparative Example 1, where BR-SCM and BR-SC refer to the temperature rise curves measured in Example 1 and Comparative Example 1 respectively without the addition of MOF. According to... Figure 11 It can be seen that the post-processing of Example 1 and Comparative Example 1 was completed within 180 s, indicating that the supercritical carbon dioxide-assisted derivatization strategy has the characteristics of being fast and efficient.

[0084] Figure 12 The XRD spectrum of Comparative Example 4 shows typical anatase TiO2 characteristic peaks, indicating that the calcination method can convert MIL-125-NH2 into TiO2, which is different from the in-situ conversion of MIL-125-NH2 into TiO2 in this invention, while retaining the MOF framework on the outside, and finally forming a MIL-125-NH2 / TiO2 heterojunction.

[0085] Figure 13 TEM images of MIL-125-NH2, Example 1, Comparative Example 1, and Comparative Example 4. MIL-125-NH2 exhibits a typical octahedral configuration, while obvious nanorod structures are observed in Example 1 and Comparative Example 1. Figure 3 and Figure 4The results indicate that the nanorods are anatase TiO2. In Example 1, the partially retained MIL-125-NH2 organic framework structure is clearly observed. According to... Figure 13 As can be seen from the above, Comparative Example 4 is also anatase TiO2, but its morphology and structure are significantly different from those of Example 1 and Comparative Example 1. It presents a bulk with a porous structure. This structural difference is caused by supercritical carbon dioxide as a reactant destroying the organic ligand of MIL-125-NH2.

[0086] Unlike existing patents (CN118341482B, CN121715201A), in this invention, supercritical carbon dioxide not only acts as a solvent but also as a reactant, permeating into the pores of MIL-125-NH2 and dissociating to release... O undergoes an oxidation reaction with the Ti-O cluster, thus achieving the in-situ conversion of MIL-125-NH2 to TiO2.

[0087] Unlike the existing patent (CN118341482B), in this invention, acetonitrile, in addition to being polymerized at high temperature into a triazine derivative and covalently functionalized and grafted onto the catalyst surface, also adsorbs around the organic ligands on the surface of MIL-125-NH2, thus protecting the outer framework of MIL-125-NH2. Therefore, MIL-125-NH2 is in situ converted to TiO2 internally, while the MOF framework is retained externally, ultimately forming a MIL-125-NH2 / TiO2 heterojunction. The formation of the MIL-125-NH2 / TiO2 heterojunction in this invention effectively enhances the separation and migration of photogenerated carriers, while the surface-grafted triazine functional groups enhance the adsorption and activation of the reactant water, thereby significantly improving the photocatalytic hydrogen production performance. Furthermore, the extremely strong organic solubility of supercritical carbon dioxide ensures uniform dispersion of acetonitrile in the system, thus requiring a lower amount of acetonitrile and reducing organic pollution.

[0088] The above description only illustrates the preferred embodiments of the present invention and should not be construed as limiting the scope of the claims. The present invention is not limited to the above embodiments, and variations in its specific structure are permitted. All modifications made within the scope of the independent claims of this invention are also within the scope of protection of this invention.

[0089] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

Claims

1. A method for preparing a supercritical carbon dioxide-assisted derived MIL-125-NH2 / TiO2 heterojunction, characterized in that, Includes the following steps: MIL-125-NH2 and a co-solvent were added to a reactor, high-pressure CO2 was added, and the mixture was heated to the reaction temperature and then cooled to obtain a MIL-125-NH2 / TiO2 heterojunction.

2. The method for preparing the supercritical carbon dioxide-assisted derived MIL-125-NH2 / TiO2 heterojunction according to claim 1, characterized in that, The co-solvent is acetonitrile.

3. The method for preparing the supercritical carbon dioxide-assisted derived MIL-125-NH2 / TiO2 heterojunction according to claim 1, characterized in that, The ratio of MIL-125-NH2 to co-solvent is 100~500 mg: 100~500 μL.

4. The method for preparing the supercritical carbon dioxide-assisted derived MIL-125-NH2 / TiO2 heterojunction according to claim 1, characterized in that, The temperature after adding high-pressure CO2 is 40~65℃ and the pressure is 5~10 MPa.

5. The method for preparing the supercritical carbon dioxide-assisted derived MIL-125-NH2 / TiO2 heterojunction according to claim 1 or 4, characterized in that, The temperature after adding high-pressure CO2 is 65℃ and the pressure is 8 MPa.

6. The method for preparing the supercritical carbon dioxide-assisted derived MIL-125-NH2 / TiO2 heterojunction according to claim 1, characterized in that, The reaction temperature is 280~350℃.

7. The method for preparing the supercritical carbon dioxide-assisted derived MIL-125-NH2 / TiO2 heterojunction according to claim 1 or 6, characterized in that, The reaction temperature is 320℃.

8. The method for preparing the supercritical carbon dioxide-assisted derived MIL-125-NH2 / TiO2 heterojunction according to claim 1, characterized in that, The cooling system is water-cooled.

9. A MIL-125-NH2 / TiO2 heterojunction prepared by the method according to any one of claims 1-8.

10. The application of a MIL-125-NH2 / TiO2 heterojunction prepared by any one of claims 1-8 in photocatalytic hydrogen production.

Images