Preparation method and application of a hierarchical pore ZIF-67 / biochar composite thermo-optical catalyst

Abstract

The present invention discloses a preparation method and application of a multi-level porous ZIF-67 / biochar composite thermal photocatalyst, and the specific steps include: pre-treatment of peanut shells, preparation of peanut shell carbon PC, preparation of ZIF-67 / PC and preparation of ZIF-67. In order to achieve the design requirements of catalysts for efficient thermal photocatalytic CO2 conversion and C-C coupling under a continuous process, the present invention composites MOF materials with biochar, makes full use of the high CO2 adsorption activation ability and excellent photoelectric properties of biochar and MOF materials, and obtains a thermal photocatalyst that can efficiently convert CO2 and H2O into C2H4 products using a continuous process in a fixed bed reactor. The present invention not only has a simple synthesis method and easy-to-control reaction conditions, but also enriches the catalyst types for the thermal photocatalytic conversion of CO2, and also provides an important scientific basis for establishing an efficient and high-throughput catalytic conversion technology of CO2.

Description

Technical Field

[0001] The present invention relates to the technical field of catalysts, and particularly to a preparation method and application of a hierarchical pore ZIF-67 / biochar composite thermophotocatalyst. Background Art

[0002] Currently, reducing the emissions of the main greenhouse gas CO2 and providing fuel for the growing global population remain one of the greatest technological challenges of our time. Utilizing thermophotocatalysis to achieve the high-value utilization of CO2 provides a promising solution for establishing a sustainable economy and has now become one of the research hotspots in the global chemical and chemical engineering fields.

[0003] Compared with metal-based catalysts and other carbon-based catalysts, biochar is derived from nature, has adjustable morphology and pore structure, a large specific surface area, abundant surface groups (such as C-O, C=O, COOH, and OH), various heteroatom dopants (such as O, N, P, and S), and diverse inorganic components (such as Ca, K, Na, Si, and Mg). These characteristics endow biochar with good catalytic performance and can provide a cost-effective and sustainable platform for the development of new-generation functional materials. Moreover, the application of biochar functional materials is considered a sustainable process because it can not only capture and catalyze the conversion of CO2, but also convert waste biomass into biochar, reducing anthropogenic CO2 emissions. Co-based metal-organic framework materials (Co-MOFs) are used in photocatalytic CO2 conversion due to their advantages such as simple preparation, high photoactivity, and good stability. The composite of MOFs and biochar materials for thermophotocatalytic CO2 conversion, using the strong light response, carrier generation and transfer ability, and CO2 capture and activation ability of the materials to realize the continuous thermophotocatalytic CO2 of the catalyst with H2O as the proton source, is of great significance for promoting the development of the thermophotocatalytic CO2 conversion field. However, currently, the thermophotocatalytic CO2 conversion catalysts have problems such as low catalytic performance, cumbersome preparation, and being unfavorable for mass production.

[0004] Therefore, it is an urgent problem for those skilled in the art to provide a method for simply and greenly preparing a MOF / biochar composite material using biomass with a green economy and MOF materials with a high specific surface area as raw materials, and obtaining a high-performance thermophotocatalytic CO2 conversion catalyst by utilizing the characteristics of the natural biomass element composition and rich pore structure to realize the composite of carbon materials and MOF materials. Summary of the Invention

[0005] In view of this, the present invention provides a preparation method and application of a hierarchical pore ZIF-67 / biochar composite thermophotocatalyst.

[0006] To solve the above technical problems, the present invention adopts the following technical solutions:

[0007] A preparation method of a hierarchical porous ZIF-67 / biochar composite thermophotocatalyst, characterized by comprising the following steps:

[0008] Step 1: Pretreatment of peanut shells: First, grind the peanut shells and perform a pretreatment operation, and then dry them for later use;

[0009] Step 2: Preparation method of peanut shell carbon PC: Place the pretreated peanut shells in a tubular furnace for roasting, grind them, wash them three times with water, and then PC is obtained;

[0010] Step 3: Preparation method of ZIF-67 / PC: First, mix PC with 40 mL of absolute ethanol and ultrasonicate for 30 min, then add cobalt nitrate hexahydrate and continue to ultrasonically disperse for 1 h. Then, slowly add a 40 mL absolute ethanol solution containing 2-methylimidazole to the PS mixture, stir for 30 min, let it stand for 24 h, and finally centrifuge and wash three times with absolute ethanol, vacuum dry overnight, and then grind to obtain ZIF-67 / PC;

[0011] Step 4: Preparation method of ZIF-67: First, mix a 150 mL absolute ethanol solution containing 2-methylimidazole with a 75 mL absolute ethanol solution containing cobalt nitrate hexahydrate and stir for 3 h, then centrifuge and wash three times with absolute ethanol, vacuum dry overnight, and then grind to obtain ZIF-67.

[0012] Preferably, the specific method of the pretreatment operation in Step 1 is: Place 15 g of peanut shells in 150 mL of absolute ethanol and ultrasonicate for 30 min, then replace the ethanol solution and stir at room temperature for 1 h.

[0013] Preferably, the drying temperature in Step 1 is 60 °C.

[0014] Preferably, the roasting conditions in Step 2 are: Roast in an inert argon atmosphere, the roasting temperature is 800 °C, the roasting time is 3 h, and the heating rate is 6 °C / min.

[0015] Preferably, the mass of PC added in Step 3 is 0.1 g, the mass of cobalt nitrate hexahydrate added is 0.146 g, and the mass of 2-methylimidazole added is 0.164 g.

[0016] Preferably, the vacuum drying temperature in both Step 3 and Step 4 is 80 °C.

[0017] Preferably, the mass of 2-methylimidazole added in Step 4 is 7.5 g, and the mass of cobalt nitrate hexahydrate added is 0.5 g.

[0018] Preferably, the application of the ZIF-67 / PC composite thermophotocatalyst obtained by a preparation method of a hierarchical porous ZIF-67 / biochar composite thermophotocatalyst in the CO2 conversion process.

[0019] The present invention has achieved the following technical effects compared with the prior art:

[0020] The present invention uses peanut shells as the source of biochar. After simply mixing the precursors and drying, it can synthesize the required powder thermophotocatalytic / photoelectrocatalytic materials on a large scale. The results of X-ray powder diffraction combined with X-ray photoelectron spectroscopy, scanning electron microscopy, and N2 adsorption-desorption tests show that in the present invention, ZIF-67 is loaded on the surface of peanut shell carbon in the form of dodecahedra. Due to the reducibility of peanut shell carbon, Co in ZIF-67 / PC mainly exists in the divalent form. The obtained material ZIF-67 / PC mainly presents a hierarchical pore structure with the coexistence of micropores and mesopores. Moreover, the combination of the two materials improves the generation and separation efficiency of carriers, and overall enhances the thermophotocatalytic CO2 conversion performance. Description of the Drawings

[0021] Figure 1 SEM and EDS mapping diagrams of ZIF-67 / PC for the preparation method and application of a hierarchical pore ZIF-67 / biochar composite thermophotocatalyst of the present invention.

[0022] Figure 2 XRD diagrams of PC, ZIF-67, and ZIF-67 / PC for the preparation method and application of a hierarchical pore ZIF-67 / biochar composite thermophotocatalyst of the present invention.

[0023] Figure 3 Fine spectra of Co in ZIF-67 and ZIF-67 / PC for the preparation method and application of a hierarchical pore ZIF-67 / biochar composite thermophotocatalyst of the present invention.

[0024] Figure 4 N2 adsorption-desorption test diagram of ZIF-67 / PC for the preparation method and application of a hierarchical pore ZIF-67 / biochar composite thermophotocatalyst of the present invention.

[0025] Figure 5 Results diagrams of the thermophotocatalytic CO2 conversion performance of PC, ZIF-67, and ZIF-67 / PC for the preparation method and application of a hierarchical pore ZIF-67 / biochar composite thermophotocatalyst of the present invention.

[0026] Figure 6 Photocurrent density diagrams of materials under monochromatic light of PC, ZIF-67, and ZIF-67 / PC for the preparation method and application of a hierarchical pore ZIF-67 / biochar composite thermophotocatalyst of the present invention.

[0027] Figure 7PC of the preparation method and application of a hierarchical pore ZIF-67 / biochar composite thermophotocatalyst of the present invention, impedance diagrams of ZIF-67 and ZIF-67 / PC.

[0028] Figure 8 PC of the preparation method and application of a hierarchical pore ZIF-67 / biochar composite thermophotocatalyst of the present invention, XPS valence band diagrams of ZIF-67 and ZIF-67 / PC.

[0029] Figure 9 PC of the preparation method and application of a hierarchical pore ZIF-67 / biochar composite thermophotocatalyst of the present invention, band gap diagrams of ZIF-67 and ZIF-67 / PC obtained from IPCE.

[0030] Figure 10 PC of the preparation method and application of a hierarchical pore ZIF-67 / biochar composite thermophotocatalyst of the present invention, photocurrent diagrams of ZIF-67 and ZIF-67 / PC.

[0031] Figure 11 PC of the preparation method and application of a hierarchical pore ZIF-67 / biochar composite thermophotocatalyst of the present invention, photoelectric conversion efficiency diagrams of ZIF-67 and ZIF-67 / PC. Detailed implementation manners

[0032] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0033] Example 1

[0034] Refer to Figures 1-11 The present invention discloses a preparation method and application of a hierarchical pore ZIF-67 / biochar composite thermophotocatalyst, including the following steps:

[0035] Step 1: Pretreatment of peanut shells: First, grind the peanut shells, perform pretreatment operations, and then dry for later use;

[0036] Step 2: Preparation method of peanut shell carbon PC: Place the pretreated peanut shells in a tubular furnace for roasting, grind and wash three times with water to obtain PC;

[0037] Step 3: Preparation method of ZIF-67 / PC: First, mix PC with 40 mL of absolute ethanol and ultrasonicate for 30 min, then add cobalt nitrate hexahydrate and continue to ultrasonically disperse for 1 h. Next, slowly add a 40 mL absolute ethanol solution containing 2-methylimidazole to the PS mixture, stir for 30 min, let it stand for 24 h, and finally wash three times by centrifugation with absolute ethanol, dry overnight under vacuum and then grind to obtain ZIF-67 / PC;

[0038] Step 4: Preparation method of ZIF-67: First, mix a 150 mL absolute ethanol solution containing 2-methylimidazole with a 75 mL absolute ethanol solution containing cobalt nitrate hexahydrate and stir for 3 h, then wash three times by centrifugation with absolute ethanol, dry overnight under vacuum and then grind to obtain ZIF-67.

[0039] The specific method of the pretreatment operation in Step 1 is: Place 15 g of peanut shells in 150 mL of absolute ethanol and ultrasonicate for 30 min, then replace the ethanol solution and stir at room temperature for 1 h.

[0040] The drying temperature in Step 1 is 60 °C.

[0041] The calcination conditions in Step 2 are: Calcination is carried out in an inert argon atmosphere, the calcination temperature is 800 °C, the calcination time is 3 h, and the heating rate is 6 °C / min.

[0042] In Step 3, the mass of PC added is 0.1 g, the mass of cobalt nitrate hexahydrate added is 0.146 g, and the mass of 2-methylimidazole added is 0.164 g.

[0043] The vacuum drying temperature in both Step 3 and Step 4 is 80 °C.

[0044] In Step 4, the mass of 2-methylimidazole added is 7.5 g, and the mass of cobalt nitrate hexahydrate added is 0.5 g.

[0045] Example 2

[0046] Thermal photocatalytic CO2 conversion performance evaluation of PC: Accurately weigh 15 mg of PC in Step 2. Under the reaction conditions of a reaction pressure of 0.2 MPa, a reaction gas flow rate of 10 mL / min, a reaction set temperature of 350 °C, a catalyst surface temperature of 280 °C, and a light source of a 300 W xenon lamp with a power of 450 mW·cm -2 Perform performance tests on the CO2 photothermal catalysis of PC in a fixed-bed reactor using a continuous process under the above conditions.

[0047] Example 3

[0048] Performance Evaluation of Thermal Photocatalytic CO₂ Conversion of ZIF-67: Accurately weigh 15 mg of ZIF-67 obtained in Step 3. Under the reaction conditions of a reaction pressure of 0.2 MPa, a reaction gas flow rate of 10 mL / min, a reaction set temperature of 350 °C, a catalyst surface temperature of 280 °C, and a 300 W xenon lamp with a power of 450 mW·cm -2 perform a performance test on the CO₂ photothermal catalysis of ZIF-67 in a fixed-bed reactor using a continuous process.

[0049] Example 4

[0050] Performance Evaluation of Thermal Photocatalytic CO₂ Conversion of ZIF-67 / PC: Accurately weigh 15 mg of ZIF-67 / PC obtained in Step 4. Under the reaction conditions of a reaction pressure of 0.2 MPa, a reaction gas flow rate of 10 mL / min, a reaction set temperature of 350 °C, a catalyst surface temperature of 280 °C, and a 300 W xenon lamp with a power of 450 mW·cm -2 perform a performance test on the CO₂ photothermal catalysis of ZIF-67 / PC in a fixed-bed reactor using a continuous process.

[0051] Example 5

[0052] Photocurrent Response Test of PC Prepared in Step 2, ZIF-67 Prepared in Step 3, and ZIF-67 / PC Prepared in Step 4. Use a xenon lamp corrected by the solar spectrum to simulate sunlight with a light intensity of 100 mW / cm 2 , and perform the test using a standard three-electrode photoelectrochemical cell system with a side quartz glass incident window. Use a platinum sheet as the counter electrode, an Ag / AgCl electrode as the reference electrode, and the working electrode is a 1×1 cm 2 thin film electrode of the sample made on FTO conductive glass, and use 0.1 mol / L Na₂SO₄ as the electrolyte. In a typical test process, use a Shanghai Chenhua electrochemical workstation to monitor and record the generated photocurrent / voltage curve. In summary, through the above examples and Figure 1 the results show that: after compounding, ZIF-67 is relatively uniformly distributed on peanut shell carbon in a dodecahedron configuration with a size of about less than 100 nm, and the main elements of the composite material are C, N, O, and Co; through the above examples and Figure 2 the results show that: ZIF-67 and PC are successfully compounded; through the above examples and Figure 3 the results show that: ZIF-67 / PC has a high Co 2+ proportion, which is beneficial to improving the catalytic performance of the catalyst; through the above examples and Figure 4 the results show that: ZIF-67 / PC has a hierarchical pore structure with coexisting mesopores and micropores; through the above examples and Figure 5The results show that after combining ZIF-67 with PC, the catalyst has high catalytic performance; through the above embodiments and Figure 6 The results show that the composite material has strong light absorption ability at 400 - 600 nm; through the above embodiments and Figure 7 The results show that the conductivity of ZIF-67 can be improved after material combination; through the above embodiments and Figure 8 The results show that the valence band top positions of PC, ZIF-67, and ZIF-67 / PC are 2.13, 1.10, and 1.31 eV respectively; through the above embodiments and Figure 9 The results show that the band gaps of PC, ZIF-67, and ZIF-67 / PC are 2.16, 2.07, and 2.14 eV respectively; through the above embodiments and Figure 10 The results show that the composite material ZIF-67 / PC has strong photocurrent; through the above embodiments and Figure 11 The results show that the composite material ZIF-67 / PC has strong photoelectric conversion efficiency.

[0053] The above are only the preferred embodiments of the present invention, and do not limit the technical scope of the present invention. Therefore, any minor modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. Application of a hierarchical pore ZIF-67 / biochar composite thermo-optical catalyst in the process of CO2 conversion, characterized in that, This application is for the preparation of CO, methane, C2H4, and C2H6 products through thermophotocatalytic CO2 conversion; The preparation method of the hierarchical porous ZIF-67 / biochar composite thermophotocatalyst includes the following steps: Step 1: Pretreatment of peanut shells: First, grind the peanut shells and perform pretreatment operations, and then dry them for later use; Step 2: Preparation method of peanut shell carbon PC: Place the pretreated peanut shells in a tube furnace for roasting, grind and wash them three times with water to obtain PC; Step 3: Preparation method of ZIF-67 / PC: First, mix PC with 40 mL of absolute ethanol and ultrasonicate for 30 min, then add cobalt nitrate hexahydrate and continue to ultrasonically disperse for 1 h. Then, slowly add a 40 mL absolute ethanol solution containing 2-methylimidazole to the PC mixture, stir for 30 min, let it stand for 24 h, and finally wash it three times by centrifugation with absolute ethanol and grind it after vacuum drying overnight to obtain ZIF-67 / PC.

2. The application according to claim 1, wherein The specific method of the pretreatment operation in Step 1 is: Place 15 g of peanut shells in 150 mL of absolute ethanol and ultrasonicate for 30 min, then replace the ethanol solution and stir at room temperature for 1 h.

3. The application according to claim 1, characterized in that, The drying temperature in Step 1 is 60 °C.

4. The application according to claim 1, wherein The roasting conditions in Step 2 are: Roast in an inert argon atmosphere, the roasting temperature is 800 °C, the roasting time is 3 h, and the heating rate is 6 °C / min.

5. The application according to claim 1, characterized in that, In Step 3, the mass of PC added is 0.1 g, the mass of cobalt nitrate hexahydrate added is 0.146 g, and the mass of 2-methylimidazole added is 0.164 g.

6. The application according to claim 1, wherein The temperature of vacuum drying in Step 3 is 80 °C.

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