A double-mofs-derived composite photocatalyst and a preparation method and application thereof

Abstract

The application belongs to the technical field of photocatalysts, and particularly discloses a kind of double MOFs derived composite photocatalyst and its preparation method and application.The composite photocatalyst is carbon layer coated ZnFe2O4 / Fe2O3 heterojunction composite material, which is prepared by calcining two kinds of metal organic framework materials ZIF-8 and MIL-101 after mixing.The preparation method comprises mixing and grinding two kinds of MOF materials, and then calcining at 400-1000 DEG C.The composite material has full-spectrum response characteristics and excellent light-heat conversion performance.The composite material is used for photocatalytic reduction of carbon dioxide, and under intermittent pulse near-infrared irradiation, the selectivity of methane is improved, and the composite material has good cycle stability.

Description

Technical Field

[0001] This invention belongs to the field of photocatalyst technology, specifically relating to a composite photocatalyst derived from dual MOFs, its preparation method, and its application. Background Technology

[0002] With the escalating global energy crisis and the continued worsening of the greenhouse effect, the resource-based conversion and utilization of carbon dioxide has become an important research direction for energy conservation, emission reduction, and alleviating environmental pressure. Currently, the mainstream technological approach in the industry is to catalytically convert carbon dioxide into high-value-added carbon-based chemicals such as carbon monoxide and methane, thereby achieving the recycling of carbon resources. Among numerous conversion technologies, photocatalytic carbon dioxide reduction technology, with its advantages of being solar-powered and pollution-free, has become one of the core technologies for the resource-based utilization of carbon dioxide.

[0003] However, existing traditional photocatalysis technologies suffer from inherent technical bottlenecks, resulting in extremely low solar energy utilization efficiency, which severely restricts the catalytic conversion efficiency of carbon dioxide. Sunlight comprises ultraviolet, visible, and infrared light, with ultraviolet and visible light accounting for only 48% of the total solar energy. Traditional photocatalytic materials can only be excited by light in these wavelengths to achieve catalytic reactions. Infrared light, which accounts for 52% of the total solar energy, cannot be directly utilized and cannot participate in the photocatalytic excitation process, significantly reducing solar energy utilization and carbon dioxide reduction catalytic efficiency, and greatly limiting the industrial application of photocatalysis technology.

[0004] To overcome the limitations of traditional photocatalysis, such as its inability to utilize infrared light and low spectral utilization, full-spectrum photothermal catalysis technology has been gradually developed in this field. This technology abandons the traditional principle of directly exciting catalysts with infrared light, and instead utilizes the photothermal effect of infrared light to increase the surface temperature of the catalyst, achieving comprehensive utilization of the entire solar spectrum. This effectively breaks through the technical limitations of single photocatalysis and has now become a research hotspot in the fields of carbon dioxide emission reduction and resource utilization.

[0005] Zinc ferrite (ZnFe2O4) is a photothermal catalytic material with excellent comprehensive performance, possessing advantages such as high catalytic activity, good basic thermal stability, and low preparation cost. It also exhibits unique photothermal properties and is widely used in photothermal catalysis research. However, pure-phase ZnFe2O4 catalytic materials have significant technical drawbacks: firstly, poor selectivity in catalytic reactions and low precision in target product yield; secondly, catalytic performance is easily affected by reaction conditions such as temperature and atmosphere, resulting in poor adaptability to various operating conditions; and thirdly, high-temperature reaction environments easily lead to phase transformation and structural degradation, resulting in catalyst activity decay and shortened lifespan, making it difficult to meet the requirements of high-performance, long-cycle photothermal catalysis applications.

[0006] In summary, existing carbon dioxide photothermal catalytic materials generally suffer from technical drawbacks such as limited spectral utilization range, low catalytic selectivity, poor thermal stability, and susceptibility to structural damage at high temperatures, which severely restrict the efficiency and stability of carbon dioxide catalytic conversion. Therefore, there is an urgent need to develop a novel composite catalytic material with stable structure, high full-spectrum utilization, and excellent catalytic selectivity to overcome the many shortcomings of existing technologies. Summary of the Invention

[0007] The purpose of this invention is to provide a composite photocatalyst derived from dual MOFs, its preparation method, and its application, which solves the problems of limited spectral utilization range, low catalytic selectivity, poor thermal stability, and easy damage to the structure at high temperatures that are common in existing carbon dioxide photothermal catalytic materials.

[0008] This invention is achieved through the following technical solution: This invention discloses a dual MOF-derived composite photocatalyst, wherein the composite photocatalyst is a carbon-coated ZnFe2O4 / Fe2O3 heterojunction composite material, denoted as ZnFe2O4 / Fe2O3@C, wherein: ZnFe2O4 and Fe2O3 form a heterojunction structure; The composite photocatalyst was prepared by calcining a mixture of two metal-organic framework materials, ZIF-8 (Zn) and MIL-101 (Fe).

[0009] Furthermore, the carbon layer is a graphitic carbon layer, which appears at 1317 cm⁻¹ in Raman spectroscopy. -1 The place has sp 2 Characteristic peaks of the D band in carbon-type structures.

[0010] Furthermore, in the X-ray diffraction pattern, characteristic peaks belonging to ZnFe2O4 are present at 2θ = 18.38°, 30.24°, 35.63°, 37.27°, 43.30°, 53.73°, 57.28°, 62.91°, 74.44° and 75.45°; Furthermore, it exhibits characteristic peaks at 2θ = 24.20°, 33.21°, 35.72°, 39.31°, 40.95°, 49.57°, 54.16°, 57.60°, 62.59°, 64.18°, 69.71°, 72.03°, and 75.68°, which are attributed to Fe2O3.

[0011] This invention also discloses a method for preparing a dual MOF-derived composite photocatalyst, comprising the following steps: Step 1: Mix ZIF-8 (Zn) and MIL-101 (Fe), and grind them thoroughly to obtain the composite material precursor; Step 2: The composite precursor is calcined at high temperature and then naturally cooled to obtain the composite photocatalyst, which is a ZnFe2O4 / Fe2O3@C composite material; The conditions for high-temperature calcination are: heating to 400-1000℃ and maintaining it for 4-6 hours.

[0012] Furthermore, in step 1, ZIF-8 (Zn) accounts for 15% of the total mass of MIL-101 (Fe).

[0013] Furthermore, in step 2, the temperature is increased from room temperature to 400-1000℃ at a heating rate of 3~5℃ / min.

[0014] The present invention also discloses the application of the composite photocatalyst in the photocatalytic reduction of CO2.

[0015] Furthermore, the photocatalytic reduction of CO2 uses near-infrared light as the light source.

[0016] Furthermore, the near-infrared light adopts an intermittent pulsed illumination mode.

[0017] Furthermore, the intermittent pulsed light mode includes: using a single-wavelength LED pulsed light source, after the reactor is heated to the temperature required for the photothermal reaction and maintained at a constant temperature, the pulsed light source is activated to carry out the photocatalytic reaction.

[0018] Compared with the prior art, the present invention has the following beneficial technical effects: This invention discloses a dual MOF-derived composite photocatalyst, which is a carbon-coated ZnFe2O4 / Fe2O3 heterojunction composite material. It is prepared by calcining a mixture of two metal-organic framework materials, ZIF-8 (Zn) and MIL-101 (Fe). The heterojunction interface between ZnFe2O4 and Fe2O3 generated in situ through co-calcination of the dual MOFs can effectively promote the separation and transport of photogenerated carriers, significantly improving photocatalytic efficiency. At the same time, the presence of the carbon layer not only enhances the conductivity of the composite material, which is beneficial to electron transfer, but also plays a structural protection role, improving the stability of the catalyst. This provides a structural basis for solving the problems of low catalytic efficiency and poor stability of existing photocatalytic materials.

[0019] Furthermore, the carbon layer is specified as a graphite carbon layer. The presence of the graphite carbon layer can effectively reduce heat loss under near-infrared light irradiation, providing good thermal insulation and thus reducing heat loss. At the same time, the sp² carbon structure has good electrical conductivity, which helps to improve electron transfer in the photocatalytic process and further enhance the overall catalytic efficiency of the composite material.

[0020] Furthermore, the composite material was identified as having characteristic peaks belonging to ZnFe2O4 and Fe2O3 in the X-ray diffraction pattern. The clear assignment of the XRD characteristic peaks confirmed the successful coexistence of the two phases ZnFe2O4 and Fe2O3, forming an effective heterojunction structure. This structure can generate a strong electron transfer effect, thereby enhancing the efficiency of photocatalytic reduction of carbon dioxide, which is consistent with the XPS test results.

[0021] This invention also discloses a method for preparing a composite photocatalyst derived from two MOFs. The method involves mixing and grinding ZIF-8 (Zn) and MIL-101 (Fe), followed by calcination at 400-1000℃ for 4-6 hours. This one-step calcination method is simple and convenient to operate, and can simultaneously decompose the two MOFs during the calcination process. ZIF-8 provides the zinc source, and MIL-101 (Fe) provides the iron and carbon sources, generating ZnFe2O4 / Fe2O3 heterojunctions in situ and forming a carbon coating layer. This avoids the complex operation of multi-step synthesis, reduces the preparation cost, and has good reproducibility.

[0022] Furthermore, the ZIF-8 (Zn) content was limited to 15% of the total mass of the two MOFs. This specific ratio ensures that the proportion of ZnFe2O4 and Fe2O3 phases in the composite material is moderate, forming the optimal heterojunction interface contact area, thereby obtaining the best photogenerated carrier separation effect. If the ZIF-8 ratio is too low, the heterojunction effect will not be obvious, and if the ratio is too high, it may mask the main catalytic effect of Fe2O3. The 15% mass ratio is the key parameter for achieving the best catalytic performance.

[0023] Furthermore, the heating rate is limited to 3-5℃ / min from room temperature to 400-1000℃. The technical effect is that this heating rate can ensure that the two MOFs decompose uniformly during calcination, avoid structural collapse due to excessive heating or increased energy consumption due to excessively slow heating, and at the same time, it is conducive to the uniform formation of carbon layers and the stable construction of heterojunction interfaces, ensuring that the composite material has good crystallinity and structural integrity.

[0024] The composite photocatalyst described in this invention is applied to the photocatalytic reduction of CO2. This composite material can effectively utilize solar energy to drive the carbon dioxide reduction reaction, converting greenhouse gases into high-value-added carbon-based chemicals such as carbon monoxide and methane, thereby realizing the recycling of carbon resources.

[0025] Furthermore, traditional photocatalysts struggle to utilize near-infrared light, which accounts for 52% of the total solar energy. However, the composite material of this invention, due to its carbon coating and ZnFe2O4 / Fe2O3 heterojunction structure, can generate a photothermal effect in the near-infrared region. This heat raises the surface temperature of the catalyst to drive the catalytic reaction, thereby achieving efficient utilization of the entire solar spectrum and overcoming the technical bottleneck of traditional photocatalysis, which can only utilize ultraviolet-visible light.

[0026] Furthermore, compared to continuous non-pulsed light irradiation, intermittent pulsed light irradiation enables timely desorption of intermediate products adsorbed on the active sites of the catalyst, releasing more active sites for subsequent reactions, thereby significantly improving product selectivity. Experimental data show that under intermittent pulsed light irradiation, the selectivity of CH4 increased dramatically from 16.1% under continuous light irradiation to 74.0%, and the yield increased from 11.0 μmol g / L. -1 h -1 Increased to 50.3 μmol g -1 h -1 This achieved unexpected technical results.

[0027] Furthermore, specific parameters for the intermittent pulsed illumination mode were defined, including the use of a single-wavelength LED pulsed light source and the activation of the pulsed light source after the reactor is heated to 200°C. The technical advantages are: the single-wavelength LED light source can provide stable and controllable near-infrared light output; the reaction temperature of 200°C matches the photothermal properties of the composite material, ensuring that the catalyst can fully exert its photothermal synergistic catalytic effect at this temperature, thereby obtaining the best catalytic efficiency and product selectivity, and providing specific process parameter guidance for industrial applications. Attached Figure Description

[0028] Figure 1 XRD patterns for all samples; Figure 2 Raman plots for all samples; Figure 3 Figure 1 shows the SEM images of all samples; Figure 2 shows the SEM image of the sample prepared in Example 1; Figure 3 shows the SEM image of the sample prepared in Example 2; Figure 4 shows the SEM image of the sample prepared in Example 3; and Figure 5 shows the SEM image of the sample prepared in Example 4. Figure 4 The images shown are TEM images of the samples prepared in Example 3; where Figure (a) is a TEM image of ZFO / FO@C-800, Figures (b) and (c) are HR-TEM images; Figures (d)-(g) are elemental mapping images of C, Fe, O, and Zn, respectively. Figure 5 The images show infrared thermographic images of the photothermal performance of the samples prepared in Example 3; where, Figure (a) is before illumination (0 seconds, 25.5℃); Figure (b) is after 30 seconds of illumination (45.7℃); Figure (c) is after 60 seconds of illumination (57.5℃); Figure (d) is after 90 seconds of illumination (62.8℃); Figure (e) is after 120 seconds of illumination (72.8℃); and Figure (f) is after 300 seconds of illumination (79.7℃). Figure 6 UV-Vis spectra of different catalysts; Figure 7 The yield graphs of CO2 products catalytically reduced by intermittent pulsed near-infrared irradiation for all samples; Figure 8 The yield graphs of CO2 products under intermittent pulsed near-infrared irradiation and continuous non-pulsed near-infrared irradiation are shown for the samples prepared in Example 3. Figure 9 The image shows the cyclic stability of the sample prepared in Example 3. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of the present invention clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention; that is, the described embodiments are only a part of the embodiments of the present invention, and not all of them.

[0030] The detailed description of the embodiments of the present invention provided in the following figures is not intended to limit the scope of the claimed invention, but merely to illustrate one selected embodiment of the invention. All other embodiments obtained by those skilled in the art based on the figures and embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0031] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0032] Example 1 This embodiment discloses a method for preparing a composite photocatalyst derived from two MOFs, including the following steps: 1) The prepared ZIF-8 (Zn) and MIL-101 (Fe) were precisely proportioned and thoroughly ground and mixed to obtain composite material A. ZIF-8 (Zn) accounted for 15% of the mass of MIL-101 (Fe).

[0033] 2) Place composite material A in a muffle furnace for heating. The heating process starts at 25 °C and continues at 3 °C min. -1 The temperature was steadily increased at a rate until it reached 400 °C and held at that temperature for 4 hours. After natural cooling, the ZnFe2O4 / Fe2O3@C-400 composite material was obtained, which is a composite photocatalyst derived from dual MOFs.

[0034] The ZIF-8(Zn) preparation method is as follows: 3.95 mmol (approximately 1.176 g) of Zn(NO3)2·6H2O and 0.2 mol (approximately 16.43 g) of 2-methylimidazole are dissolved in 85 mL of deionized water and stirred thoroughly for 45 min to obtain a mixed solution. The mixed solution is ultrasonically treated for 10 min, and then the resulting suspension is allowed to stand for 12 h. The solution is then washed three times alternately with methanol and ethanol, and the solid product is obtained by centrifugation (5000 rpm). The obtained solid product is dried in an oven at 60 °C for 24 h to obtain ZIF-8(Zn) powder.

[0035] The preparation method of MIL-101(Fe) is as follows: 2.45 mmol (approximately 0.662 g) of FeCl3·6H2O and 1.25 mmol (approximately 0.263 g) of trimesic acid were dissolved in 15 mL of a mixed solvent of DMF and methanol (volume ratio 1:1) to obtain mixture A. Mixture A was sonicated for 30 minutes until completely dissolved, then transferred to a hydrothermal reactor and heated in an oven at 110 °C for 20 h. After the reaction was complete, the mixture was cooled to room temperature, and the product was obtained by washing three times alternately with 20 mL of DMF and 20 mL of methanol by centrifugation. The product was dried in a vacuum drying oven at 70 °C for 12 h to obtain MIL-101(Fe) powder.

[0036] In the following examples, the preparation methods of ZIF-8 (Zn) and MIL-101 (Fe) are the same as in Example 1.

[0037] Example 2 This embodiment discloses a method for preparing a composite photocatalyst derived from two MOFs, including the following steps: 1) The prepared ZIF-8 (Zn) and MIL-101 (Fe) were precisely mixed at a mass ratio of 15%, and the resulting composite material A was obtained after thorough grinding and mixing.

[0038] 2) Place composite material A in a muffle furnace for heating. The heating process starts at 25 °C and continues at 4 °C min. -1 The temperature was steadily increased at a rate until it reached 600 °C and held at that temperature for 5 hours. After natural cooling, the ZnFe2O4 / Fe2O3@C-600 composite material was obtained, which is a composite photocatalyst derived from dual MOFs.

[0039] Example 3 This embodiment discloses a method for preparing a composite photocatalyst derived from two MOFs, including the following steps: 1) The prepared ZIF-8 (Zn) and MIL-101 (Fe) were precisely mixed at a mass ratio of 15%, and the resulting composite material A was obtained after thorough grinding and mixing.

[0040] 2) Place composite material A in a muffle furnace for heating. The heating process starts at 25 °C and continues at 5 °C for 5 min. -1 The temperature was steadily increased at a rate until it reached 800 °C and held at that temperature for 6 h. After natural cooling, the ZnFe2O4 / Fe2O3@C-800 composite material was obtained, which is a composite photocatalyst derived from dual MOFs.

[0041] Example 4 This embodiment discloses a method for preparing a composite photocatalyst derived from two MOFs, including the following steps: 1) The prepared ZIF-8 (Zn) and MIL-101 (Fe) were precisely mixed at a mass ratio of 15%, and the resulting composite material A was obtained after thorough grinding and mixing.

[0042] 2) Place composite material A in a muffle furnace for heating. The heating process starts at 25 °C and continues at 5 °C for 5 min. -1 The temperature was steadily increased at a rate until it reached 1000 °C and held at that temperature for 6 h. After natural cooling, the ZnFe2O4 / Fe2O3@C-1000 composite material was obtained, which is a composite photocatalyst derived from dual MOFs.

[0043] Comparative Example 1 1) Dissolve 2.45 mmol FeCl3·6H2O and 1.25 mmol trimesic acid in 15 mL DMF solution (methanol, 1:1 methanol-DMF) to obtain mixture A.

[0044] 2) After ultrasonic treatment of the above mixture A until it is transparent, it is transferred to a hydrothermal reactor and heated in an oven at 105°C for 20 hours to obtain mixture B.

[0045] 3) After the reaction was cooled to room temperature, product D was obtained by centrifugation three times, alternating between 20 mL DMF and 20 mL methanol. The product was recovered by centrifugation and further dried under vacuum at 60 °C for 12 h.

[0046] 4) Place the vacuum-dried product D in a muffle furnace and heat it. Start at 25°C and heat at 5°C for 5 min. -1 The temperature steadily increased until it reached 400℃, and was maintained at that temperature for 4 hours to obtain Fe2O3 material.

[0047] Comparative Example 2 1) Dissolve 3.95 mmol of Zn(NO3)2·6H2O and 0.20 mol of 2-methylimidazole in 85 mL of deionized water and stir thoroughly for 30 min to obtain mixture A.

[0048] 2) The above mixture A was ultrasonically treated, and the resulting suspension was allowed to stand for 10 h. Then, it was washed three times alternately with methanol and ethanol, and the mixture B was obtained by centrifugation (500 rpm). The mixture C was then heated in an oven at 60°C for 24 h to obtain product C.

[0049] 3) Place the vacuum-dried product C in a muffle furnace and heat it. Start at 25°C and heat at 5°C for 5 min. -1 The temperature steadily increased until it reached 400℃, and was maintained at this temperature for 4 h to obtain ZnFe2O4 material.

[0050] Figure 1 The images show the XRD patterns of the composite materials prepared under different embodiment conditions. Figure 1 We can conclude that at 2θ = 24.20 ° 33.21 ° 35.72 ° 39.31 ° 40.95 ° 49.57 ° 54.16 ° 57.60 ° 62.59 ° 64.18 ° 69.71 ° 72.03 ° and 75.68 ° Characteristic peaks can be observed at this point. According to the standard crystal diffraction file (PDF # 85-0987), these peaks belong to the (110), (121), (-110), (222), (120), (220), (132), (-121), (130), (-211), (242), (343), and (-220) crystal planes of Fe2O3. Furthermore, at 2θ = 18.38... ° 30.24 ° 35.63 ° 37.27 ° 43.30 ° 53.73 ° 57.28 ° 62.91 ° 74.44 ° and 75.45 °The characteristic peaks at the point are attributed to the (111), (220), (311), (222), (400), (422), (511), (440), (533) and (622) crystal planes of ZnFe2O4 (PDF # 73-1963). XRD test results show that the composite material was successfully prepared.

[0051] Figure 2 The Raman plots of the composite materials prepared under different embodiment conditions are shown below. Figure 2 We can conclude that the values ​​are 223, 241, and 290 cm. -1 The characteristic peak at that location is attributed to Fe2O3 A. 1g Pattern, and 404 cm -1 and 611 cm -1 The characteristic peak corresponds to the E of Fe2O3. g Pattern. Furthermore, at 504 cm -1 The characteristic peak at that location is attributed to the E of ZnFe2O4. g Pattern, and at 657 cm -1 The weaker characteristic peak is attributed to the A of ZnFe2O4. 1g Pattern, 1317 cm -1 The peak at that location belongs to the D band of graphitic carbon, indicating the presence of sp in the sample. 2 The carbon-type structure helps improve electron transfer during photocatalysis and protects the stability of the catalyst structure. XRD and Raman tests show that the ZFO / FO@C composite material was successfully prepared, and the higher the calcination temperature in the range of 400-1000℃, the higher the degree of crystallinity of the composite material. Studies have shown that higher crystallinity leads to stronger photocatalytic activity.

[0052] Figure 3 SEM images of samples prepared under different embodiment conditions. Figure 3 Figure (a) in the figure is a SEM image of Example 1. Figure 3 Figure (b) in the figure is the SEM image of Example 2. Figure 3 Figure (c) in the figure is the SEM image of Example 3. Figure 3 Figure (d) in the figure is a SEM image of Example 4. The composites prepared at different annealing temperatures exhibit irregular shapes with rough surfaces.

[0053] Figure 4 This is a TEM image of the sample prepared in Example 3. Figure 4 In Figure (a), a thin carbon layer is clearly observed on the surface of the composite material, consistent with the Raman results. Figure 4In the HR-TEM image shown in Figure (b), a lattice spacing of 0.269 nm is observed to correspond to the (121) crystal plane of Fe2O3, while a lattice spacing of 0.295 nm is associated with the (220) crystal plane of ZnFe2O4. Furthermore, as... Figure 4 In the HR-TEM image shown in Figure (c), 0.269 nm corresponds to the (121) crystal plane of Fe2O3, while the 0.241 nm lattice spacing corresponds to the (241) crystal plane of ZnFe2O4. This indicates that a tight bond is formed between the Fe2O3 nanoparticles and ZnFe2O4, and this tight bond interface is beneficial for the efficient transport of electrons during the catalytic process. Furthermore, as shown in Figures (d)-(g), the energy dispersive spectroscopy (EDS) results show that the prepared photocatalyst contains only C, O, Fe, and Zn elements, and the four elements are uniformly distributed in the catalyst, which is beneficial for the rapid transport of electrons, thereby improving the catalytic efficiency.

[0054] Figure 5 The image shows the photothermal properties of the sample prepared in Example 3. To verify the effect of thermal effect on the near-infrared light-driven photocatalytic CO2 activity of the composite material, the macroscopic change in the center temperature of Example 3 within 5 minutes was recorded using an infrared thermal imaging camera. Figure 5 As shown in Figures (a) to (f), the core temperature of the composite material rapidly increased from 25.5 °C to 79.7 °C within 5 minutes, indicating that the heterojunction catalyst ZFO / FO@C-800 possesses the superior photothermal conversion capability. This superiority is attributed to the strong absorption capacity of ZnFe2O4 and its outer carbon shell in the near-infrared region. The outer carbon shell effectively reduces heat loss under near-infrared irradiation and provides good thermal insulation, thereby reducing heat loss.

[0055] Figure 6 The UV-Vis spectra of the composite materials prepared in Examples 1-4 and the ZnFe2O4 and Fe2O3 prepared in two comparative examples are shown. The test results indicate that ZnFe2O4 and Fe2O3 are excellent photoresponsive materials with broad light absorption bands. In the composite material ZFO / FO@CX, its response to visible light and even infrared light gradually increases with increasing calcination temperature, which is beneficial to the catalytic reduction of carbon dioxide in the infrared region.

[0056] Figure 7 The graphs show the yields of CO2 products from intermittent pulsed near-infrared irradiation catalytic reduction of single-phase Fe2O3, ZnFe2O4, and composite materials prepared under different conditions in two comparative examples. The CO formation rate of single-phase Fe2O3 is 25 μmol / g. -1 h -1The CO and CH4 formation rates of ZnFe2O4 were 2.4 μmol g, respectively. -1 h -1 and 8.1 μmol g -1 h -1 Notably, the ZFO / FO@CX composite exhibits significantly improved photocatalytic reduction efficiency, particularly ZFO / FO@C-800, which demonstrates the highest CH4 and CO generation efficiencies. The CH4 generation rate is 6.2 times higher than that of single-phase ZnFe2O4. This enhanced photocatalytic performance can be attributed to the inclusion of Fe2O3, indicating a strong electron transfer between ZnFe2O4 and Fe2O3. This is consistent with XRD and XPS results, suggesting that the construction of the heterojunction is beneficial for the photocatalytic reaction.

[0057] Figure 8 The graph shows the CO2 product yields under intermittent pulsed near-infrared irradiation and continuous non-pulsed near-infrared irradiation in Example 3. Under continuous non-pulsed irradiation, the CH4 yield and selectivity of the ZFO / FO@C-800 complex were 11.0 μmol g. -1 h -1 And 16.1%. In stark contrast, under intermittent pulsed light irradiation, the CH4 yield and selectivity of ZFO / FO@C-800 were significantly improved, reaching 50.3 μmol g, respectively. -1 h -1 The improved product selectivity is mainly attributed to the fact that during continuous non-pulsed processes, many intermediate products adsorb onto the active sites of the photocatalyst, reducing the number of active sites available for photocatalytic reactions, inhibiting the separation of photogenerated carriers, and further decreasing the efficiency of photocatalytic CO2 reduction. However, under intermittent pulsed light irradiation, these intermediate products are desorbed from the photocatalyst surface, releasing more photocatalytic active sites, thereby enhancing the selectivity of the product CH4.

[0058] The performance testing process for the intermittent pulsed near-infrared illumination mode is as follows: The photocatalytic CO2 reduction performance was tested using a steel reactor equipped with a quartz window at the top. The temperature inside the reactor was precisely controlled by a heating element. A single-wavelength LED lamp was used as the light source for top illumination. First, 20 mg of catalyst was uniformly dispersed in a beaker at the bottom of the reactor (its surface area is approximately 9.0 cm²). 2Subsequently, argon gas was introduced for at least 30 minutes to remove air from the reactor. Next, a certain amount of deionized water (0.2 mL) was injected into the reactor, and the reactor was heated to 200 °C in the dark. After maintaining a constant temperature, the light source was started in a pulsed manner with a duty cycle of 1:1 (e.g., 30 seconds of illumination followed by 30 seconds of shutdown), with a total pulse cycle duration of 1 minute, and the reaction was continued for 5 hours. To detect the gases produced during the photocatalysis process, the post-reaction gases were analyzed using an Agilent GC-7890B gas chromatograph equipped with two thermal conductivity detectors (TCDs). One detection line used argon as the carrier gas for hydrogen detection, while the other detection line used helium for CO, CO2, and CH4 detection.

[0059] In contrast, the continuous non-pulsed illumination mode keeps the light source constantly on, with all other conditions remaining exactly the same.

[0060] Figure 9 The cyclic stability graph for the sample prepared in Example 3 is shown, where the red line represents CO and the blue line represents CH4. Each cycle lasted 5 h to assess its stability. The results show that ZFO / FO@C-800 exhibits good cyclic stability, which is crucial for sustained photocatalytic reactions. Even after 20 h of cycling, the photocatalytic performance of this catalyst remained unchanged, demonstrating its superior durability and stability.

[0061] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the protection scope of the present invention.

Claims

1. A composite photocatalyst derived from two MOFs, characterized in that, The composite photocatalyst is a carbon-coated ZnFe2O4 / Fe2O3 heterojunction composite material, denoted as ZnFe2O4 / Fe2O3@C, wherein: ZnFe2O4 and Fe2O3 form a heterojunction structure; The composite photocatalyst was prepared by calcining a mixture of two metal-organic framework materials, ZIF-8 (Zn) and MIL-101 (Fe).

2. The dual MOF-derived composite photocatalyst according to claim 1, characterized in that, The carbon layer is a graphitic carbon layer, which appears at 1317 cm⁻¹ in Raman spectroscopy. -1 The place has sp 2 Characteristic peaks of the D band in carbon-type structures.

3. The composite photocatalyst derived from dual MOFs according to claim 1, characterized in that, In the X-ray diffraction pattern, characteristic peaks belonging to ZnFe2O4 are present at 2θ = 18.38°, 30.24°, 35.63°, 37.27°, 43.30°, 53.73°, 57.28°, 62.91°, 74.44° and 75.45°. Furthermore, it exhibits characteristic peaks at 2θ = 24.20°, 33.21°, 35.72°, 39.31°, 40.95°, 49.57°, 54.16°, 57.60°, 62.59°, 64.18°, 69.71°, 72.03°, and 75.68°, which are attributed to Fe2O3.

4. A method for preparing a composite photocatalyst derived from two MOFs, characterized in that, Includes the following steps: Step 1: Mix ZIF-8 (Zn) and MIL-101 (Fe), and grind them thoroughly to obtain the composite material precursor; Step 2: The composite precursor is calcined at high temperature and then naturally cooled to obtain the composite photocatalyst, which is a ZnFe2O4 / Fe2O3@C composite material; The conditions for high-temperature calcination are: heating to 400-1000℃ and maintaining it for 4-6 hours.

5. The method for preparing a dual MOF-derived composite photocatalyst according to claim 4, characterized in that, In step 1, ZIF-8 (Zn) accounts for 15% of the total mass of MIL-101 (Fe).

6. The method for preparing a dual MOF-derived composite photocatalyst according to claim 4, characterized in that, In step 2, the temperature is increased from room temperature to 400-1000℃ at a heating rate of 3~5℃ / min.

7. The application of the composite photocatalyst according to any one of claims 1-3 in the photocatalytic reduction of CO2.

8. The application according to claim 7, characterized in that, The photocatalytic reduction of CO2 uses near-infrared light as the light source.

9. The application according to claim 8, characterized in that, The near-infrared light adopts an intermittent pulsed illumination mode.

10. The application according to claim 9, characterized in that, The intermittent pulsed light mode includes: using a single-wavelength LED pulsed light source, after the reactor is heated to the temperature required for the photothermal reaction and maintained at a constant temperature, the pulsed light source is activated to carry out the photocatalytic reaction.

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