A core-shell structured indium-based metal-organic framework heterojunction catalyst and its preparation method

Abstract

The application discloses a preparation method of a core-shell structure indium-based metal organic framework heterojunction catalyst, which comprises the following steps: simultaneously adding carboxylic acid ligands and tetrakis(4-carboxyphenyl)porphyrin ligands into an organic solvent, and then uniformly mixing with a metal indium salt solution under ultrasonic waves to obtain a purple mixed solution of the metal indium salt and the ligands; performing a solvothermal reaction on the purple mixed solution at 100-150 DEG C for 4-8 hours, and then separating a red wet solid, which is washed and dried, and the obtained red powder is a core-shell structure indium-based metal organic framework material, namely, NH2-MIL-68(In)@In-TCPP heterostructure. The NH2-MIL-68(In)@In-TCPP heterostructure with the core-shell structure is constructed by the shared indium metal nodes, meanwhile, the excellent electron transmission performance and the higher CO2 adsorption and wide spectral response capacity of the tetrakis(4-carboxyphenyl)porphyrin unit are combined, so that the utilization rate of sunlight and the CO2 photocatalytic conversion efficiency are significantly improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of metal catalysis, and particularly relates to a core-shell structure indium-based metal organic framework heterojunction catalyst and a preparation method and application thereof. BACKGROUND

[0002] Metal organic framework (MOFs) materials are widely concerned in the fields of gas separation, catalysis, environmental purification, etc. due to their wide monomer sources, adjustable structure units, excellent specific surface area and pore structure. However, most single MOFs materials have weak conductivity, low electron transport efficiency, weak light absorption capacity and poor stability due to the mismatch between metal orbit and ligand orbit, which greatly limits their application in the fields of photoelectricity, heat, etc.

[0003] Compared with single MOFs materials, the photo-induced charge transfer efficiency can be improved and the interface interaction can be enhanced to improve the stability by constructing multi-component MOFs heterostructure. The current methods for preparing MOFs heterojunction mainly include heteroepitaxial growth, surfactant template assistance and metal ion exchange. However, the above strategies have high requirements for the matching between metal and ligand units, and the different metal and ligand units need to be screened, which makes the steps complex and the success rate low. In addition, the mismatch between the energy band structure of different MOFs materials and the metal orbit is not conducive to the stability of the heterostructure, the light absorption capacity and the carrier separation efficiency. SUMMARY

[0004] The technical problem to be solved by the application is to provide a core-shell structure indium-based metal organic framework heterojunction catalyst and a preparation method thereof to solve the problems of weak conductivity, low electron transport efficiency, weak light absorption capacity and poor stability in the existing MOFs-based catalysts.

[0005] The technical scheme adopted by the application to solve the above problems is as follows:

[0006] A core-shell structure indium-based metal organic framework heterojunction catalyst, which comprises a two-dimensional layered indium tetracarboxyphenyl porphyrin (In-TCPP) nanosheet as a shell layer and a metal organic framework NH2-MIL-68(In) with a spindle structure as a core, and the shell layer wraps the inner core with the spindle structure to form a core-shell structure, wherein the length of the spindle is in the range of 1-2.0 μm.

[0007] The preparation method of the core-shell structure indium-based metal organic framework heterojunction catalyst comprises the following steps:

[0008] (1) adding 2-aminoterephthalic acid and tetrakis(4-carboxyphenyl)porphyrin as ligands into an organic solvent and mixing them uniformly to obtain a ligand solution; dissolving a metal indium salt into the organic solvent to obtain a metal indium salt solution;

[0009] (2) uniformly mixing the ligand solution obtained in step (1) with the metal indium salt solution to obtain a purple solution of a mixture of the metal indium salt and the ligand;

[0010] (3) The purple solution in step (2) is subjected to a solvothermal reaction at 100-150° C. for 4-8 hours, and then the red wet solid is separated. After washing and drying, the resulting red powder is an indium-based metal-organic framework heterojunction catalyst with a core-shell structure, that is, an NH2-MIL-68(In)@In-TCPP heterostructure with a core-shell structure.

[0011] According to the above scheme, in step (1), in the ligand solution, the concentration of 2-aminoterephthalic acid is in the range of 10 to 100 mmol / L, the concentration of tetrakis(4-carboxyphenyl)porphyrin is in the range of 1 to 10 mmol / L, and the molar ratio of 2-aminoterephthalic acid to tetrakis(4-carboxyphenyl)porphyrin is (4 to 20):1. Preferably, in the ligand solution, the concentration of 2-aminoterephthalic acid is in the range of 10 to 30 mmol / L, the concentration of tetrakis(4-carboxyphenyl)porphyrin is in the range of 1 to 4 mmol / L, and the molar ratio of 2-aminoterephthalic acid to tetrakis(4-carboxyphenyl)porphyrin is (7.5 to 15):1.

[0012] According to the above scheme, in step (1), the metal indium salt solution In 3+ The theoretical concentration (based on In in indium salts) 3+ (calculated based on complete ionization) is in the range of 0.05 to 0.25 mol / L.

[0013] According to the above scheme, in step (1), the organic solvent is a mixture of one or more of N-N-dimethylformamide, methanol, etc.; the metal indium salt is a mixture of one or more of indium nitrate, indium chloride, etc.

[0014] According to the above scheme, in step (1), 2-aminoterephthalic acid can also be replaced by one or more carboxylic acid ligands such as terephthalic acid, 2,2'-bipyridine-5,5'-dicarboxylic acid, and 1,3,5-benzenetricarboxylic acid.

[0015] According to the above scheme, in step (2), when the ligand solution is mixed with the metal indium salt solution, tetrakis(4-carboxyphenyl)porphyrin and In 3+ The molar ratio is calculated in the range of (0.01 to 0.05):1.

[0016] According to the above scheme, the mixing in step (1) and step (2) is both ultrasonically treated, and the ultrasonic time does not exceed 0.5h.

[0017] According to the above scheme, in step (3), the temperature of the solvothermal reaction is 100-150°C, and the solvothermal reaction time is 4-8 hours. Preferably, the temperature of the solvothermal reaction is 120-140°C, and the solvothermal reaction time is 4.5-6 hours.

[0018] The core-shell indium-based metal-organic framework heterojunction catalyst of the present invention can be used for the CO2 reduction reaction coupled with water oxidation to prepare formic acid and H2O2.

[0019] The technical concept of the present invention is as follows:

[0020] The present invention adopts a one-pot method for the first time to control the nucleation kinetics of two indium-based MOFs materials to construct a NH2-MIL-68(In)@In-TCPP heterostructure with a core-shell structure, so that it has both a stable heterogeneous interface and efficient carrier separation efficiency. The present invention first adjusts the nucleation kinetics of the two MOFs materials to form a metal indium-based node with defect sites under the action of competitive coordination, and then forms an efficient and stable heterogeneous interface through the shared metal indium-based node. Among them, due to the rapid reaction nucleation of 2-aminoterephthalic acid and indium salt, NH2-MIL-68(In) forms an inner core platform, and the indium metal sites developed on the surface will coordinate with the porphyrin ligand with slower nucleation kinetics to form In-TCPP nanosheets on the surface, thereby obtaining a NH2-MIL-68(In)@In-TCPP heterostructure with a stable core-shell structure.

[0021] Taking the photocatalytic CO2 reduction coupled with H2O oxidation as an example, the core-shell NH2-MIL-68(In)@In-TCPP heterostructure of the present invention demonstrated excellent sunlight utilization, carrier mobility, and CO2 reduction coupled with water oxidation conversion efficiency. The In-O bond in the indium metal node of the core NH2-MIL-68(In) serves as a water oxidation site, while the In-N site in In-TCPP serves as a CO2 RR site. The resulting defective indium metal node further optimizes interfacial electron transfer and enhances catalyst activity. Moreover, the spindle-shaped NH2-MIL-68(In) is completely wrapped by two-dimensional In-TCPP nanosheets. This heterogeneous structure not only ensures the separation of the redox sites of CO2 and H2O, but also avoids the recombination of photogenerated carriers, further enhances the absorption capacity of sunlight, and realizes the effective separation of photogenerated electrons and holes. At the same time, combined with the excellent electron transport performance of the porphyrin unit and the high CO2 adsorption and wide spectrum response capabilities, it significantly improves the utilization rate of solar energy and the CO2 photocatalytic conversion efficiency.

[0022] The preparation method provided by the present invention can construct a variety of MOFs heterojunction catalysts with core-shell structures, such as replacing metal In with transition metals such as Fe and Al to form MOF cores of NH2-MIL-68(Al) and MIL-88B(Fe), and in situ growing MOFs materials such as Fe-TCPP and Al-TCPP to synthesize different MOFs-based heterojunction metal catalysts. According to the characteristics of each metal, they can be applied to different types of catalytic reactions, greatly improving the catalytic activity.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] First, through a unique synthetic strategy, the present invention successfully synthesized a core-shell NH2-MIL-68(In)@In-TCPP heterojunction, forming a novel metal-organic framework composite material. This structure not only provides a stable heterojunction interface for interfacial electron-hole transport, but also effectively inhibits the recombination of photogenerated electrons and holes, accelerating carrier transfer, thereby enhancing its light absorption capacity and exhibiting excellent catalytic activity and stability.

[0025] Second, compared with the traditional bottom-up synthesis method of dual MOF heterojunction catalysts, the present invention is the first to use a one-pot method to regulate the reaction kinetics to form a core-shell structure heterojunction without adding any template agent, reducing the tedious steps of the heterojunction catalyst and greatly reducing the preparation cost. The preparation method is green and simple, and does not produce polluting gases, which will help promote the large-scale and widespread application of heterojunction catalysts in the fields of light, electricity, and thermal catalysis. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a scanning electron microscope image of the metal indium frame material NH2-MIL-68 (In) prepared in Comparative Example 1.

[0027] Figure 2 This is a scanning electron microscope image of the metal indium frame material In-TCPP prepared in Comparative Example 2.

[0028] Figure 3 This is a scanning electron microscope image of the core-shell indium-based metal-organic framework heterojunction catalyst (NH2-MIL-68(In)@In-TCPP) prepared in Example 1.

[0029] Figure 4 These are transmission electron microscope images of the core-shell indium-based metal-organic framework heterojunction catalyst (NH2-MIL-68(In)@In-TCPP) prepared in Example 1 at different growth times (i.e., the solvent thermal time in step (3) of Example 1 is 0.5h, 1h, 3h, and 5h, respectively).

[0030] Figure 5 a is the X-ray diffraction spectrum of the final products prepared in Comparative Example 1, Comparative Example 2 and Example 1; Figure 5 b is the X-ray diffraction spectrum of the product when the solvent thermal time in step (3) of Example 1 is 0.5h, 1h, 3h and 5h respectively.

[0031] Figure 6 This is the activity diagram of the core-shell indium-based metal organic framework heterojunction catalyst (NH2-MIL-68(In)@In-TCPP) prepared in Example 1 under sunlight conditions driving CO2 reduction and H2O oxidation. Note: Figure 6 The vertical axis is the total output for 4 hours.

[0032] Figure 7 1 is a performance diagram of the catalysts prepared in Example 1, the blank control, and Comparative Examples 1 to 3 for photocatalytic CO2 reduction and H2O oxidation.

[0033] Figure 8 This is a stability test chart of CO2 reduction and H2O oxidation of the core-shell structured indium-based metal-organic framework heterojunction catalyst (NH2-MIL-68(In)@In-TCPP) prepared in Example 1.

[0034] Figure 9 This is a cyclic performance diagram of the core-shell indium-based metal-organic framework heterojunction catalyst (NH2-MIL-68(In)@In-TCPP) prepared in Example 1 for CO2 reduction and H2O oxidation.

[0035] In the accompanying drawings, M68N represents NH2-MIL-68(In), and M68N@In-TCPP represents NH2-MIL-68(In)@In-TCPP. DETAILED DESCRIPTION

[0036] In order to better understand the present invention, the content of the present invention is further described below in conjunction with the examples, but the present invention is not limited to the following examples.

[0037] Example 1

[0038] A method for preparing a core-shell structured indium-based metal-organic framework heterojunction catalyst, the specific steps are as follows

[0039] (1) Weigh 0.09 mmol of 2-aminoterephthalic acid and 0.01 mmol of tetrakis(4-carboxyphenyl)porphyrin into a round-bottom flask, then add 5 mL of NN dimethylformamide and sonicate for 0.5 h to obtain a ligand solution (wherein the concentration of 2-aminoterephthalic acid is within the range of 18 mmol / L and the concentration of tetrakis(4-carboxyphenyl)porphyrin is 2 mmol / L); add indium nitrate salt into NN dimethylformamide to prepare a 0.1 mol / L indium nitrate solution. 3+ The theoretical concentration is 0.1 mol / L;

[0040] (2) The ligand solution described in step (1) and indium nitrate are mixed uniformly in a volume ratio of 1:1 to obtain a purple mixed solution; wherein, tetrakis(4-carboxyphenyl)porphyrin and In 3+ The molar ratio is 0.02:1;

[0041] (3) The purple mixed solution was transferred to a sealed reactor and reacted at 130 °C for 5 h. After the reaction was completed, it was washed with N-dimethylformamide solution and centrifuged. After drying, it was ground into powder. The resulting red powder was an indium-based metal-organic framework heterojunction catalyst with a core-shell structure, that is, NH2-MIL-68(In)@In-TCPP heterojunction with a core-shell structure.

[0042] The scanning electron microscopy of the core-shell indium-based metal organic framework heterojunction catalyst prepared in Example 1 is as follows: Figure 3 As shown, it can be seen that the morphology and structure of NH2-MIL-68(In)@In-TCPP are uniform, the surface is rough, and the overall structure is a spindle. The length is mainly concentrated between 1 and 1.5 μm, and the outer layer of the spindle structure is wrapped with two-dimensional layered nanosheets. This is because the nucleation kinetics of tetrakis(4-carboxyphenyl)porphyrin and indium salt are slow, and they will compete with 2-aminoterephthalic acid ligands for coordination at the same time, thereby acting as a capping agent to inhibit the growth of NH2-MIL-68(In) and shorten the length.

[0043] The transmission electron microscopy images of the core-shell indium-based metal organic framework heterojunction catalyst prepared in Example 1 at different growth time periods are as follows: Figure 4 As shown in the figure, the inner core spindle NH2-MIL-68(In) was synthesized within 0.5h. As time went on, a two-dimensional lamellar structure gradually formed on the surface, which became thicker as the reaction time progressed. It was preliminarily inferred that this was due to the growth and wrapping of In-TCPP on the surface.

[0044] The X-ray diffraction of the core-shell indium-based metal organic framework heterojunction catalyst prepared in Example 1 (the final product after the solvent thermal reaction for 5 hours) is as follows: Figure 5As shown in a, 4.9° and 9.8° are characteristic peaks of spindle NH2-MIL-68 (In), corresponding to the (110) and (220) crystal planes, respectively; 7.5° belongs to the characteristic peak of In-TCPP (021) crystal plane. Figure 5 b is the X-ray diffraction spectrum of the product when the solvent thermal time in step (3) of Example 1 is 0.5h, 1h, 3h and 5h respectively, showing that the characteristic peak of spindle NH2-MIL-68(In) appears within 10min of the reaction, proving that the NH2-MIL-68(In)@In-TCPP heterostructure is based on NH2-MIL-68(In) as the core. As the reaction time proceeds, the characteristic peak at 7.5° belonging to the In-TCPP(021) crystal plane gradually increases, proving that the In-TCPP framework material is wrapped on the surface with two-dimensional nanosheets.

[0045] Comparative Example 1

[0046] The only difference between Comparative Example 1 and Example 1 is that tetrakis(4-carboxyphenyl)porphyrin is not added, and the final product is the metal indium framework material NH2-MIL-68(In).

[0047] The scanning electron microscopy of the single NH2-MIL-68(In) prepared in Comparative Example 1 is as follows: Figure 1 As shown, the rods are similar to spindle structures with relatively uniform sizes, and the rod lengths are mainly between 7 and 10 μm.

[0048] Comparative Example 2

[0049] The only difference between Comparative Example 2 and Example 1 is that no 2-aminoterephthalic acid is added, and the final product is a metal indium frame material In-TCPP. The scanning electron microscope shows Figure 2 As shown, it is a bulk amorphous structure.

[0050] Comparative Example 3

[0051] The products of Comparative Example 1 and Comparative Example 2 were mixed at a mass ratio of 10:1 to obtain a physical mixture of metal indium framework materials (NH2-MIL-68(In)+In-TCPP).

[0052] Application Examples

[0053] The catalysts prepared in Example 1 and Comparative Examples 1 to 3 were used in the CO2 reduction reaction coupled with water oxidation to produce formic acid and H2O2. Outdoor tests and laboratory tests were conducted.

[0054] The specific process of outdoor testing is as follows: 5 mg of each catalyst is added to 10 mL of pure water to prepare a catalyst solution with a concentration of 0.5 mg / mL, and then sunlight (with a light intensity of 1.0 to 1.3 W / cm 2) is directly used to drive the photocatalytic reaction, and the concentrated sunlight intensity is 1.0-1.33W / cm 2 After the reaction, the CO2 conversion products are mainly HCOOH and CO, and the H2O oxidation product is mainly H2O2. No additional sacrificial agent or photosensitizer is required. Continuous illumination and timely collection and detection of gaseous and liquid phase products are required.

[0055] like Figure 6 As shown in Figure 1, the HCOOH yield of the NH2-MIL-68(In)@In-TCPP catalyst prepared in Example 1 is as high as 397.5 μmol g -1 h -1 The CO yield was 61.2 μmol g -1 h -1 Meanwhile, the activity of water oxidation product H2O2 was 312 μmol g -1 h -1 The calculated solar energy conversion efficiency (STC) was 0.04%. This result demonstrates that the synthesized NH2-MIL-68(In)@In-TCPP heterojunction catalyst has excellent practical application potential and can achieve efficient CO2 reduction to HCOOH and H2O oxidation to H2O2 under sunlight.

[0056] Unlike outdoor testing, the test process under laboratory conditions is as follows: 5 mg of each catalyst was added to 10 mL of pure water to prepare a catalyst solution with a concentration of 0.5 mg / mL. A 300 W xenon lamp was used as the light source, and a 400 nm visible light cutoff filter was configured. The light source intensity was adjusted to 0.3 W / cm 2 . Continuous illumination and timely collection and detection of gas and liquid products. Stability test is to test the reaction under continuous illumination for 25 hours, and take gas and liquid products for testing every 5 hours. Cyclic test is to test the above catalyst for 5 hours. After each 5 hours of testing, the catalyst is centrifuged and washed with pure water and dried. The test is repeated 5 times, and the catalyst activity is recorded each time. The results are as follows Figures 7-9 shown.

[0057] like Figure 7 As shown in the figure, the HCOOH activity of the core-shell indium-based metal organic framework heterojunction catalyst (NH2-MIL-68(In)@In-TCPP) prepared in Example 1 is 121.1 μmol g -1 h -1 The yield of H2O2 was 119.3 μmol g -1 h -1 In Comparative Example 1, the HCOOH yield of NH2-MIL-68(In) as the catalyst was 16.7 μmol g -1 h-1 The yield of H2O2 was 21.3 μmol g -1 h -1 In comparative example 2, the HCOOH activity of In-TCPP as a catalyst was 15.8 μmol g -1 h -1 No H2O2 was produced, O2 was the main product, and the yield was 4.3 μmol g -1 h -1 In Comparative Example 3, the catalytic activity of NH2-MIL-68(In)+In-TCPP as a catalyst was 12.4 μmol g -1 h -1 The yield of H2O2 was 22.5 μmol g -1 h -1 . It can be seen that compared with NH2-MIL-68(In) and In-TCPP prepared in Comparative Examples 1 and 2, the activity of the NH2-MIL-68(In)@In-TCPP catalyst prepared in the present invention is significantly improved, and it is also 10 times the activity of Comparative Example 3. This result proves that the heterogeneous interface in the NH2-MIL-68(In)@In-TCPP catalyst significantly promotes the migration of photogenerated carriers, so that the separated electrons and holes participate in the CO2 reduction and H2O oxidation reactions, respectively.

[0058] like Figure 8 and Figure 9 As shown, after 5 cycles and a total of 25 hours of photocatalytic experiments, the chemical skeleton and crystal structure of the core-shell indium-based metal-organic framework heterojunction catalyst (NH2-MIL-68(In)@In-TCPP) prepared in Example 1 are also very stable, and the activity can be maintained at more than 91%.

[0059] It can be seen that the core-shell structure indium-based metal-organic framework heterojunction catalyst described in the present invention outperforms conventional inorganic semiconductor catalysts in the prior art in key indicators such as sunlight absorption energy, catalytic activity and stability in solar-driven photocatalytic CO2 reduction and H2O oxidation reactions. In particular, in long-term stability tests, the NH2-MIL-68(In)@In-TCPP catalyst demonstrated excellent chemical skeleton and crystal structure stability.

[0060] Example 2

[0061] A method for preparing a core-shell structured indium-based metal-organic framework heterojunction catalyst, the specific steps are as follows

[0062] (1) Take 0.12 mmol of 2-amino terephthalic acid and 0.01 mmol of tetra(4-carboxyphenyl) porphyrin into a round-bottom flask, then add 5 mL of N-N dimethylformamide, and ultrasonic for 0.5 h to obtain a ligand solution (wherein the concentration of 2-amino terephthalic acid is in the range of 25 mmol / L, and the concentration of tetra(4-carboxyphenyl) porphyrin is 2 mmol / L); add indium nitrate salt into N-N dimethylformamide to configure a 0.1 mol / L indium nitrate solution, and the theoretical concentration of In 3+ is 0.1 mol / L;

[0063] (2) Mix the ligand solution and indium nitrate of step (1) uniformly in a volume ratio of 1:1 to obtain a purple mixed solution; wherein the molar ratio of tetra(4-carboxyphenyl) porphyrin to In 3+ is 0.02:1;

[0064] (3) Transfer the above-mentioned purple mixed solution to a reaction kettle for sealing, and react at 130℃ for 5 h; after the reaction is completed, wash with N-N dimethylformamide solution, centrifuge, dry, and grind into a powder to obtain a red powder, which is a core-shell structured indium-based metal organic framework heterojunction catalyst, i.e. NH2-MIL-68(In)@In-TCPP heterostructure with core-shell structure.

[0065] Under the same laboratory conditions as in Example 1, the yield of HCOOH of the NH2-MIL-68(In)@In-TCPP catalyst obtained in Example 2 is 42.4 μmol g -1 h -1 , and the yield of H2O2 is 50.6 μmol g -1 h -1 .

[0066] Example 3

[0067] A preparation method of a core-shell structured indium-based metal organic framework heterojunction catalyst, the specific steps are as follows

[0068] (1) Take 0.075 mmol of 2-amino terephthalic acid and 0.01 mmol of tetra(4-carboxyphenyl) porphyrin into a round-bottom flask, then add 5 mL of N-N dimethylformamide, and ultrasonic for 0.5 h to obtain a ligand solution (wherein the concentration of 2-amino terephthalic acid is in the range of 15 mmol / L, and the concentration of tetra(4-carboxyphenyl) porphyrin is 2 mmol / L); add indium nitrate salt into N-N dimethylformamide to configure a 0.1 mol / L indium nitrate solution, and the theoretical concentration of In 3+ is 0.1 mol / L;

[0069] (2) The ligand solution and indium nitrate described in step (1) are mixed uniformly at a volume ratio of 1:1 to obtain a purple mixed solution; wherein the molar ratio of tetrakis(4-carboxyphenyl)porphyrin and In 3+ is 0.02:1;

[0070] (3) The above-mentioned purple mixed solution is transferred to a reaction kettle and sealed, and reacted at 130℃ for 5h. After the reaction is completed, the product is washed with N-N dimethylformamide solution, centrifuged, dried and ground into powder. The obtained red powder is the core-shell structured indium-based metal organic framework heterojunction catalyst, i.e. NH2-MIL-68(In)@In-TCPP heterostructure with core-shell structure.

[0071] Under the same laboratory conditions as in Example 1, the yield of HCOOH catalyzed by the NH2-MIL-68(In)@In-TCPP catalyst obtained in Example 3 is 45.4μmol g -1 h -1 , and the yield of H2O2 is 53.2μmol g -1 h -1 .

[0072] In summary, compared with the traditional catalyst, the core-shell structured indium-based metal organic framework heterojunction catalyst (NH2-MIL-68(In)@In-TCPP) provided by the present application exhibits excellent catalytic activity and stability in the technology of solar-driven CO2 reduction for preparing formic acid coupled with H2O oxidation for preparing H2O2, has low cost, and has wide application range.

[0073] The above only describes the preferred embodiments of the present application, and it should be pointed out that for ordinary skilled persons in the art, several improvements and changes can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application.

Claims

1. A method for preparing a core-shell indium-based metal-organic framework heterojunction catalyst, characterized in that: The steps include: (1) Adding 2-aminoterephthalic acid ligand and tetrakis(4-carboxyphenyl)porphyrin ligand into an organic solvent and mixing them uniformly to obtain a ligand solution; dissolving metal indium salt into the organic solvent to obtain a metal indium salt solution; wherein the molar ratio of 2-aminoterephthalic acid and tetrakis(4-carboxyphenyl)porphyrin is (4-20):1; (2) The ligand solution obtained in step (1) is mixed evenly with the metal indium salt solution to obtain a purple solution of the metal indium salt and the ligand; wherein, when the ligand solution is mixed with the metal indium salt solution, tetrakis(4-carboxyphenyl)porphyrin and In 3+ The molar ratio is (0.01~0.05):1; (3) The purple solution in step (2) is subjected to a solvent thermal reaction, and then a red wet solid is separated. After washing and drying, the resulting red powder is an indium-based metal-organic framework heterojunction catalyst with a core-shell structure.

2. The method for preparing a core-shell indium-based metal-organic framework heterojunction catalyst according to claim 1, characterized in that: In step (1), the concentration of 2-aminoterephthalic acid in the ligand solution is in the range of 10 to 100 mmol / L, and the concentration of tetrakis(4-carboxyphenyl)porphyrin is in the range of 1 to 10 mmol / L.

3. The method for preparing a core-shell indium-based metal-organic framework heterojunction catalyst according to claim 1, characterized in that: In step (1), the metal indium salt solution In 3+ The theoretical concentration is in the range of 0.05~0.25 mol / L.

4. The method for preparing a core-shell indium-based metal-organic framework heterojunction catalyst according to claim 1, characterized in that: The organic solvent in step (1) includes one or both of N-dimethylformamide and methanol; the metal indium salt includes one or both of indium nitrate and indium chloride.

5. The method for preparing a core-shell indium-based metal-organic framework heterojunction catalyst according to claim 1, characterized in that: In step (3), the temperature of the solvent thermal reaction is 100-150°C, and the time of the solvent thermal reaction is 4-8 h.

6. The method for preparing a core-shell indium-based metal-organic framework heterojunction catalyst according to claim 1, characterized in that: In step (3), the temperature of the solvothermal reaction is 120-140°C, and the time of the solvothermal reaction is 4.5-6 h.

7. A core-shell indium-based metal-organic framework heterojunction catalyst prepared by the method of claim 1, characterized in that: It uses two-dimensional layered tetracarboxyphenylporphyrin indium nanosheets as the shell and a spindle-structured metal-organic framework NH2-MIL-68(In) as the core. The shell wraps the core of the spindle structure to form a core-shell structure; the length of the spindle is in the range of 1~2.0 μm.

8. Use of the core-shell indium-based metal-organic framework heterojunction photocatalyst according to claim 7 in the production of formic acid and H2O2 by coupling CO2 reduction reaction with water oxidation.

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