In-situ growth covalent organic framework composite monatomic platinum photocatalyst based on g-C3N4 as well as preparation and application of in-situ growth covalent organic framework composite monatomic platinum photocatalyst

Abstract

The invention relates to a g-C3N4-based in-situ growth covalent organic framework composite monatomic platinum photocatalyst as well as preparation and application thereof, and the catalyst is prepared from the following main raw materials: 2, 2 '-bipyridine-5, 5'-diamine, 1, 3, 5-tricarboxaldehyde phenol, Pt and g-C3N4. The expression of the obtained catalyst is Pt / xTPBPY-CN, x is the mass percent of TP-BPY-COF in the obtained catalyst to TPBPY-CN, and the numerical range of x is 10-60%; according to the scheme, the catalyst prepared through the in-situ growth method can achieve the technical effects that the catalytic performance can be improved, the cost can be reduced, and NO photocatalytic oxidation can be efficiently achieved.

Description

Technical Field

[0001] The present invention belongs to the field of photocatalytic materials, and particularly relates to a TP-BPY-COF / g-C prepared by an in-situ growth method 3 N 4 composite photocatalyst and its application in the oxidation of low-concentration nitrogen oxides (NO). This technology is widely used in the fields of air pollution control, environmental purification, photocatalytic oxidation reaction, etc. Background Art

[0002] With the accelerating development of urbanization and industrialization, nitrogen oxides (NOx) have become one of the important pollutants threatening human health and environmental quality. Low-concentration NO (in the ppb range) widely exists in indoor and outdoor air, but its toxicity and contribution to the formation of ozone and particulate matter cannot be ignored. Although physical adsorption and chemical washing technologies have been applied to NO removal, these methods usually have problems such as high energy consumption, low efficiency, and secondary pollution.

[0003] Photocatalytic technology has become a research hotspot in air pollution control due to its green and economic characteristics. In recent years, graphitic carbon nitride (g-C 3 N 4 ) has attracted extensive attention due to its excellent chemical stability, moderate bandgap, and low cost. However, its performance is limited by problems such as high photogenerated carrier recombination rate, low specific surface area, and limited light absorption range. Therefore, how to improve the photocatalytic performance of g-C 3 N 4 is the key to current research.

[0004] Studies have shown that constructing a Z-scheme heterojunction can effectively improve the photocatalytic performance of g-C 3 N 4 . The heterojunction improves the photocatalytic reaction efficiency by accelerating the separation of photogenerated electrons and holes. Wu et al. developed a BiOIO 3 / g-C 3 N 4 heterostructure, which improved the separation efficiency of photogenerated carriers and achieved a NO removal rate of 46.9%. However, the interfacial connection of such binary heterostructures is usually dominated by van der Waals forces, with weak interfacial driving force and poor electron communication ability. In addition, such heterostructures are prone to deactivate during the reaction process and have poor stability.

[0005] Covalent organic framework materials (COF) show great potential in the field of photocatalysis due to their high specific surface area and tunable electronic structure. For example, Zhang et al. prepared by depositing on TiO 2The in-situ growth of hydrophobic COF on the surface significantly improves the light absorption capacity and carrier separation efficiency. In recent years, the preparation of COF composites through in-situ growth technology has significantly optimized the heterojunction interface and enhanced the separation and transfer performance of photo-generated carriers. In addition, the porous structure of COF can compensate for the defects of g-C 3 N 4 with low porosity and provide more NO adsorption sites. However, there are still problems such as insufficient interface connection stability in the application of current COF composites.

[0006] Platinum single atoms have great potential in photocatalysis due to their high activity and high atomic utilization rate. For example, Yang et al. developed a Pt@TpBpy-NS catalyst, achieving a solar energy conversion efficiency of 0.23% for water splitting. However, the specific mechanism of action of platinum-based single atoms in the photocatalytic degradation of nitrogen oxides is still unclear. In addition, the high cost of platinum limits its large-scale application, and it is necessary to further optimize the loading method and dosage of platinum to reduce costs and improve performance.

[0007] In summary, how to improve the performance of g-C 3 N 4 -based catalysts through reasonable design of the catalyst structure and optimization of the preparation process, and achieve low-cost and efficient photocatalytic oxidation of NO is an urgent problem to be solved in the current technical field. Summary of the Invention

[0008] In view of the above deficiencies of the prior art, the present application provides an in-situ growth covalent organic framework composite single-atom platinum photocatalyst based on g-C 3 N 4 prepared by an in-situ growth method, which can improve the catalytic performance, reduce costs and efficiently achieve photocatalytic oxidation of NO.

[0009] To solve the above technical problems, the technical solution adopted in the present application is: an in-situ growth covalent organic framework composite single-atom platinum photocatalyst based on g-C 3 N 4 . The main raw materials for preparing the catalyst include: 2,2'-bipyridine-5,5'-diamine (BPY), 1,3,5-triformylphenol (TP), Pt and g-C 3 N 4 (CN). The obtained catalyst is expressed as: Pt / xTPBPY-CN, where x is the mass percentage of TP-BPY-COF in TPBPY-CN in the obtained catalyst, and the value range of x is 10-60%.

[0010] Further, the value range of x is 40-50%.

[0011] Further, the value of x is 40%.

[0012] Further, the TPBPY-CN is in-situ grown TPBPY-CN.

[0013] Further, the Pt is from 50 - 100 mg of a platinum nitrate solution with a mass percentage of 18%.

[0014] This application also provides a preparation method of the above-mentioned in-situ grown covalent organic framework composite single-atom platinum photocatalyst based on g-C 3 N 4 which includes:

[0015] (1) Preparation of g-C 3 N 4 (CN): Put melamine into an aluminum oxide crucible, heat it to 500 - 600 °C and keep it for 3 - 5 hours;

[0016] (2) Preparation of TPBPY-CN: Put 2,2'-bipyridine-5,5'-diamine (5,5'-diamino-2,2'-bipyridine, BPY, CAS: 52382 - 48 - 6), 1,3,5-triformylphenol (triformylphloroglucinol, Tp, CAS: 34374 - 88 - 4) and a specified amount of g-C 3 N 4 into a Pyrex tube, so that TP-BPY-COF can be in-situ grown on CN during the reaction, and use N,N-dimethylacetamide (DMAc) and o-dichlorobenzene (o-DCB) as a mixed solvent; ultrasonically treat the mixture at room temperature for 20 - 40 minutes, then freeze it in a liquid nitrogen bath (77K) and perform three freeze-pump-thaw cycles to obtain a homogeneous solution; transfer the homogeneous solution to an oven, heat it at 110 - 130 °C for 60 - 80 hours to form a precipitate; separate the obtained precipitate by filtration and wash it with tetrahydrofuran; finally, perform Soxhlet extraction on the product with tetrahydrofuran and then dry it under vacuum to obtain TPBPY-CN with different mass fractions, denoted as XTPBPY-CN, where X represents the mass fraction of TP-BPY-COF in TPBPY-CN, and the range of X is 10 - 60%;

[0017] (3) Preparation of Pt / TPBPY-CN: Mix the synthesized TPBPY-CN with a platinum nitrate solution; then add a mixed solution of ethanol and methanol to obtain a mixture, ultrasonically treat the mixture at room temperature for 10 - 20 minutes, and then stir it at room temperature to obtain the final composite, denoted as Pt-XTPBPY-CN, where x is the mass percentage content of TP-BPY-COF in the obtained catalyst in TPBPY-CN, and the value range of x is 10 - 60%.

[0018] Further, the platinum nitrate solution described in step (1) is a platinum nitrate solution with a mass percentage of 18% and a mass of 50 - 100 mg.

[0019] Further, it is heated to 540 - 560 °C and maintained for 3 - 4 hours in step (1).

[0020] Further, the molar ratio of 2,2'-bipyridine-5,5'-diamine to 1,3,5-triformylphenol described in step (2) is: 1.5:1.

[0021] Further, the specified amount of g-C 3 N 4 is 20 - 100 mg.

[0022] Further, the mixture described in step (2) is ultrasonically treated at room temperature for 25 - 35 minutes.

[0023] Further, the homogeneous solution described in step (2) is heated in an oven at 115 - 125 °C for 65 - 75 hours.

[0024] Further, the Soxhlet extraction described in step (2) is carried out for 20 - 25 hours.

[0025] Further, the volume ratio of ethanol to methanol described in step (3) is 1:1.

[0026] Further, the mixture described in step (3) is ultrasonically treated at room temperature for 12 - 16 minutes, and then stirred at room temperature for 20 - 25 hours.

[0027] This application also provides an application of the in-situ growth covalent organic framework composite single-atom platinum photocatalyst based on g-C 3 N 4 obtained above in the photocatalytic oxidation of NO.

[0028] Advantages and beneficial effects of this application:

[0029] 1. The present invention solves the key problems in the prior art through the following technical means: constructing a stable Z-scheme heterojunction photocatalyst to improve the separation efficiency of photo-generated carriers and significantly reduce the electron-hole recombination rate; improving the overall material's light absorption range and the adsorption capacity for NO by compositing a porous and high specific surface area COF material on the surface of g-C 3 N 4 ; realizing efficient NO oxidation and reduction by coordinating platinum single atoms to the porous COF structure as high-active sites and introducing new photocatalytic oxidation and reduction paths; through the Schiff base reaction principle, -NH on g-C 3 N 4 ​2 Condense with -CHO on the COF to form a -H-C=N-H chemical bond, thereby constructing a stable chemically bonded heterostructure and enhancing the interfacial driving force and electron communication ability; in the present invention, by in-situ growing TP-BPY-COF on the surface of g-C 3 N 4 A Z-type heterojunction connected by chemical bonds is constructed. In addition, platinum single atoms are coordinated on the porous TP-BPY-COF, introducing a new reaction path and further improving the photocatalytic degradation efficiency of NO.

[0030] 2. The catalyst with this specific composition and structure in this application has significantly improved photocatalytic performance. The NO oxidation efficiency can reach 65.3%, which is significantly higher than that of the traditional g-C 3 N 4 -based catalyst (about 35%); the NO 3 - selectivity is close to 100%, effectively reducing the generation of NO 2 by-products; the catalyst performance retention rate exceeds 95% after cyclic experiments, showing excellent stability.

[0031] 3. The in-situ grown catalyst of single-atom Pt / TP-BPY-COF / g-C 3 N 4 has good oxidation efficiency for NO, mainly due to the efficient catalytic effect of single-atom Pt and its ability to adsorb and activate NO. At the same time, TP-BPY-COF provides a highly ordered pore structure and N coordination groups, forming a stable coordination with Pt and enhancing its stability and activity; g-C 3 N 4 As a photocatalytic material, it absorbs visible light and generates photoinduced charges. By constructing a chemically bonded heterostructure with TP-BPY-COF, the separation and migration of photoinduced electrons and holes are promoted, reducing recombination. At the same time, single-atom Pt captures photoinduced electrons, enhancing the generation efficiency of reactive oxygen species, and these reactive oxygen species further promote the oxidation reaction of NO, thus achieving high photocatalytic performance.

[0032] 4. The in-situ grown catalyst of single-atom Pt / TP-BPY-COF / g-C 3 N 4 has an optimized heterojunction interface. Among them, the Z-type heterojunction design effectively improves the separation efficiency of photoinduced carriers and reduces the recombination rate of electron-hole pairs; chemically bonded heterojunction: during the photocatalytic process, electrons are transmitted through the -H-C=N-H- bond, making the electron transmission more accurate and fast, and further strengthening the electron communication ability between composite materials. Interface growth: The porous COF material grows in-situ on g-C 3 N 4On the one hand, it makes up for the deficiencies of g-C 3 N 4 and enhances the light / NO absorption capacity of the composite material.

[0033] 5. The single-atom Pt / TP-BPY-COF / g-C 3 N 4 in-situ growth catalyst of the present application realizes the precise coordination of platinum single atoms: the platinum single atoms are precisely coordinated on TP-BPY-COF through chelation reaction, further enhancing the catalytic activity with TP-BPY-COF as the reaction site. Redox reaction: the addition of platinum single atoms introduces a new NO reduction reaction through a new reduction reaction mechanism. In this mechanism, NO molecules are initially adsorbed on Pt 2+ , promoting the transfer of electrons from platinum to the nitrogen atom of NO. However, the inherent redox potential is proven to be insufficient to overcome the energy barrier associated with NO reduction. The activation of the light source causes the simultaneous photoactivation of platinum and NO, prompting the transfer of photoelectrons from TP-BPY-COF to platinum. Then, the activated Pt 2+ catalyzes the reduction of NO, where the photo-generated electrons transfer from platinum to NO, forming Pt 4+ and N 2 . The third stage is that the electron-rich Pt 4+ hinders the desorption of N 2 and promotes the further reduction of N 2 to N-NH. The electrons on TP-BPY-COF finally transition to N-NH for further reduction. During the whole reduction process, N 2 is converted into NH 3 or NH 4 + , and Pt 4+ is reduced to Pt 2+ due to the electron transfer of TP-BPY-COF, thus establishing a redox cycle of Pt 2+ →Pt 4+ →Pt 2+ , further improving the catalytic activity of photocatalytic degradation of NO. Description of the Drawings

[0034] Figure 1 (a) Schematic diagram detailing the synthesis process of TPBPY-CN, (b) XRD patterns of the crystal structures of CN, TP-BPY-COF, TPBPY-CN, and Pt / TPBPY-CN; (c) molecular structure of TP-BPY-COF.

[0035] Figure 2 (a, b) High-resolution transmission electron microscope (HRTEM) images of CoCe-CN, (c - g) energy-dispersive X-ray spectroscopy (EDS) mappings of CoCe-CN.

[0036] Figure 3 (a) NO conversion rates of 10 / 30 / 50 / 70CoCe-CN and CN, (b) NO 2 concentration and selectivity of CN and 50CoCe-CN, (c) NO conversion rates of 50Co-CN, 50Ce-CN and 50CoCe-CN, (d) Trapping experiments for photocatalytic NO removal by CoCe-CN.

[0037] Figure 4 (a) Ultraviolet-visible spectra (UV-vis spectra) of photocatalysts, (b) Photoluminescence spectra (PL spectra) of photocatalysts, (c) Electrochemical impedance spectra (EIS plots) of photocatalysts, (d) Transient photocurrent responses of photocatalysts. Detailed implementation manners

[0038] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the embodiments and the accompanying drawings. Obviously, the described embodiments are only preferred embodiments, rather than all embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present application without creative efforts shall fall within the protection scope of the present application.

[0039] The g-C 3 N 4 (CN) used in the following examples of the present application can be obtained by the following method: Put 4 grams of melamine into a 30-ml aluminum oxide crucible (alumina crucible) with a lid, then heat it to 550 °C and keep it for 4 hours to obtain the final sample; heat it during use, and the obtained powder is ground for standby.

[0040] Example 1:

[0041] Preparation of 50TPBPY-CN: 27.9 mg of 2,2'-bipyridine-5,5'-diamine (0.15 mmol), 21 mg of 1,3,5-triformylphenol (Tp) (0.1 mmol) and 48.9 mg of g-C 3 N 4Add it to a 10 mL Pyrex tube. Use a mixed solvent of 1.5 mL of N,N-dimethylacetamide (DMAc) and 0.5 mL of o-dichlorobenzene (o-DCB). Mix it with the above in the Pyrex tube. Ultrasonically treat the mixture at room temperature for 30 minutes, then freeze it in a liquid nitrogen bath (77 K) and perform three freeze-pump-thaw cycles (this process is to freeze the mixed solution and raw materials, then pump the vacuum to reduce the pressure in the Pyrex tube, and then thaw; when thawing, the gas dissolved in the solution will bubble out, and then freeze, pump the vacuum, and thaw again. Three operations can suck out those gases to ensure that there is no oxygen in the whole synthesis process), to obtain a homogeneous solution; transfer the homogeneous solution to an oven and heat it at 120 °C for 72 hours. The obtained precipitate is separated by filtration and washed three times with tetrahydrofuran; finally, the product is Soxhlet extracted with tetrahydrofuran for 24 hours, and then dried under vacuum at 60 °C to obtain TPBPY-CN with a mass fraction of 50%.

[0042] Preparation of Pt-50TPBPY-CN: Mix 200 mg of the synthesized 50TPBPY-CN with 0.1 g of 18% platinum nitrate solution; then, add 80 mL of a mixed solution of ethanol and methanol (1:1 volume ratio). The mixture is ultrasonically treated at room temperature for 15 minutes, and then stirred at room temperature for 24 hours. The final complex is collected and labeled as Pt-XTPBPY-CN.

[0043] Subsequently, the photocatalytic oxidation NO activity test is carried out according to the activity detection process.

[0044] Example 2:

[0045] Preparation of 40TPBPY-CN: Add 27.9 mg of 2,2'-bipyridine-5,5'-diamine (0.15 mmol) and 21 mg of 1,3,5-triformylphenol (Tp) (0.1 mmol) and 73.35 mg of g-C 3 N 4 Add it to a 10 mL Pyrex tube. Use a mixed solvent of 1.5 mL of N,N-dimethylacetamide (DMAc) and 0.5 mL of o-dichlorobenzene (o-DCB). Ultrasonically treat the mixture at room temperature for 30 minutes, then freeze it in a liquid nitrogen bath (77 K) and perform three freeze-pump-thaw cycles. Transfer the homogeneous solution to an oven and heat it at 120 °C for 72 hours. The obtained precipitate is separated by filtration and washed three times with tetrahydrofuran. Finally, the product is Soxhlet extracted with tetrahydrofuran for 24 hours, and then dried under vacuum at 60 °C to obtain TPBPY-CN with a mass fraction of 40%.

[0046] Preparation of Pt-40TPBPY-CN: Mix 200 mg of the synthesized 40TPBPY-CN with 0.1 g of 18% platinum nitrate solution. Then, add 80 mL of a mixed solution of ethanol and methanol (1:1 volume ratio). The mixture is sonicated for 15 minutes at room temperature and then stirred for 24 hours at room temperature. The final complex is collected and labeled as Pt-XTPBPY-CN.

[0047] Subsequently, the photocatalytic oxidation NO activity test is carried out according to the activity detection process.

[0048] Example 3:

[0049] Preparation of 60TPBPY-CN: Add 27.9 mg of 2,2'-bipyridine-5,5'-diamine (0.15 mmol), 21 mg of 1,3,5-triformylphenol (Tp) (0.1 mmol), and 32.6 mg of g-C 3 N 4 to a 10 mL Pyrex tube. Use a mixed solvent of 1.5 mL of N,N-dimethylacetamide (DMAc) and 0.5 mL of ortho-dichlorobenzene (o-DCB). The mixture is sonicated for 30 minutes at room temperature and then frozen in a liquid nitrogen bath (77 K) and subjected to three freeze-pump-thaw cycles. The homogeneous solution is transferred to an oven and heated at 120 °C for 72 hours. The resulting precipitate is separated by filtration and washed three times with tetrahydrofuran. Finally, the product is Soxhlet extracted with tetrahydrofuran for 24 hours and then dried under vacuum at 60 °C to obtain TPBPY-CN with a mass fraction of 60%.

[0050] Preparation of Pt-60TPBPY-CN: Mix 200 mg of the synthesized 60TPBPY-CN with 50 mg of 18% platinum nitrate solution. Then, add 80 mL of a mixed solution of ethanol and methanol (1:1 volume ratio). The mixture is sonicated for 15 minutes at room temperature and then stirred for 24 hours at room temperature. The final complex is collected and labeled as Pt-XTPBPY-CN.

[0051] Subsequently, the photocatalytic oxidation NO activity test is carried out according to the activity detection process.

[0052] Comparative Example 1

[0053] Preparation of TP-BPY-COF: 27.9 mg of 2,2'-bipyridine-5,5'-diamine (0.15 mmol) and 21 mg of 1,3,5-triformylphenol (Tp) (0.1 mmol) were added into a 10 mL Pyrex tube; a mixed solvent of 1.5 mL of N,N-dimethylacetamide (DMAc) and 0.5 mL of o-dichlorobenzene (o-DCB) was used; the mixture was sonicated at room temperature for 30 minutes, then frozen in a liquid nitrogen bath (77 K) and subjected to three freeze-pump-thaw cycles; the homogeneous solution was transferred to an oven and heated at 120 °C for 72 hours; the obtained precipitate was separated by filtration and washed three times with tetrahydrofuran. Finally, the product was subjected to Soxhlet extraction with tetrahydrofuran for 24 hours and then dried under vacuum at 60 °C to obtain TP-BPY-COF.

[0054] Preparation of 40TPBPY-CN-AF: The TP-BPY-COF obtained in step (1) and 73.35 mg of g-C 3 N 4 were added into a 10 mL Pyrex tube; a mixed solvent of 1.5 mL of N,N-dimethylacetamide (DMAc) and 0.5 mL of o-dichlorobenzene (o-DCB) was used; the mixture was sonicated at room temperature for 30 minutes, then frozen in a liquid nitrogen bath (77 K) and subjected to three freeze-pump-thaw cycles. The homogeneous solution was transferred to an oven and heated at 120 °C for 72 hours. The obtained precipitate was separated by filtration and washed three times with tetrahydrofuran. Finally, the product was subjected to Soxhlet extraction with tetrahydrofuran for 24 hours and then dried under vacuum at 60 °C to obtain 40% by mass of TPBPY-CN-AF.

[0055] The TPBPY-CN-AF obtained in this comparative example, where AF represents non-in-situ growth, and the optimal catalyst product is to add g-C 3 N 4 during the COF synthesis to enable in-situ growth; here, in the comparative example, the synthesized COF and g-C 3 N 4 were directly mixed to obtain a product of non-in-situ growth TPBPY-CN; this comparative example was compared with the in-situ growth catalysts in Examples 1-3 of this application. This comparative example synthesized TPBPY-CN-AF by a non-in-situ growth method, where AF represents that this sample is a simple mixture of TP-BPY-COF and g-C3N4; while the TPBPY-CN prepared in Examples 1-3 was added with CN during the synthesis of TP-BPY-COF, such that during the COF synthesis, it grew on g-C 3 N 4 above.

[0056] Product activity detection method:

[0057] The activity of the catalyst for the photocatalytic oxidation of NO was evaluated in a continuous-flow cubic reactor. The reactor was made of quartz (20×15×10 cm) and covered with aluminum foil on all sides except the top. Before each experiment, 0.2 g of the prepared catalyst was mixed with 15 mL of deionized water and sonicated for 15 minutes. Then, the mixture was placed in a glass dish with a diameter of 12 cm and vacuum-dried at 60 °C for 6 hours. After that, the glass dish was placed at the center of the cubic reactor. The light source was a 300 W xenon lamp equipped with a 420 nm cut-off filter, which was vertically placed 20 cm above the catalyst surface. During the photocatalytic reaction, 50 ppm NO provided from a compressed gas cylinder (N 2 equilibrium) was diluted to 800 ppb by a pure air stream and flowed through the sample surface, and the total flow rate in the reactor was 2 L / min. When the adsorption-desorption equilibrium between NO and the catalyst was reached, the xenon lamp was turned on to start the photocatalytic NO oxidation reaction. The light intensity measured by a light power meter vertically placed 20 cm below the lamp was 1.516 W. During the whole reaction process, the concentrations of NO and NO 2 were measured and recorded by a NOx analyzer, and the photocatalytic efficiency of NO was calculated according to the following formula: where, C 0 (ppb) is the NO concentration at the start of the reaction, and C (ppb) is the NO concentration at a given time.

[0058] For the test results of the embodiments and comparative examples of this application, refer to the attached Figures 1-4 .

[0059] Figure 1 (a) Schematic diagram detailing the synthesis process of TPBPY-CN, (b) XRD patterns of the crystal structures of CN, TP-BPY-COF, TPBPY-CN, and Pt / TPBPY-CN; (c) molecular structure of TP-BPY-COF; The phase structures of the synthesized CN, TP-BPY-COF, TPBPY-CN, and Pt / TPBPY-CN catalysts were systematically characterized by powder X-ray diffraction (PXRD). As Figure 1 (b) shows, the PXRD pattern of CN is very close to the reference pattern of CN (PDF87-1526#), clearly confirming the successful synthesis of g-C 3 N 4 . A new peak appears at 3.6° in the PXRD pattern of TPBPY-CN, corresponding to the (100) plane of TP-BPY-COF, indicating the formation of TP-BPY-COF during the synthesis process. The structure of TP-BPY-COF was also confirmed, as Figure 1(c). In the Pt-40TPBPY-CN composite, the absence of identifiable platinum diffraction peaks indicates that platinum is highly dispersed in the catalyst system, possibly indicating the formation of single-atom platinum on the surface of TP-BPY-COF; therefore, these PXRD results conclusively verify the successful synthesis of Pt-TPBPY-CN without affecting the structural integrity of the constituent materials.

[0060] Figure 2 (a) Molecular structure of Pt-40TPBPY-CN, (b) TP-BPY-COF, (c) CN, (d) SEM image of TPBPY-CN, (e) EDS spectrum of Pt-40TPBPY-CN (f-g) TEM images. The morphological structure and elemental composition of the prepared photocatalyst were confirmed by scanning electron microscopy and elemental analysis. Figure 2 (b) Highlights the unique bar-shaped morphology of TP-BPY-COF. Meanwhile, the SEM image of TPBPY-CN ( Figure 2 (d)) shows that strip-like structures grow on the surface of the nanosheet CN structure ( Figure 2 (c)), which provides clear evidence for the in-situ growth of TP-BPY-COF on the surface of CN during the synthesis process. In Figure 2 (e), the EDS spectrum of Pt-TPBPY-CN shows that platinum is mainly concentrated on the strip-like structure of TP-BPY-COF, thus confirming the coordination of platinum on TP-BPY-COF. In addition, the TEM results can also clearly show that TP-BPY-COF grows in-situ on the nanosheet CN, as shown in Figure 2 (f). After further investigation of the TP-BPY-COF shown in Figure 2 (g), we observed that single-atom platinum exists on the ribbon-like TP-BPY-COF, which is consistent with the consistent results of the EDS spectrum. According to the results of XRD, SEM, and TEM, the morphology and molecular structure of Pt / TP-BPY-CN are as shown in Figure 2 (a).

[0061] Figure 3 (a) Photocatalytic removal efficiency of NO for 0 / 10 / 20 / 30 / 40 / 50 / 100TPBPY-CN; (b) Photocatalytic removal efficiency of NO for CN, TP-BPY-COF, 40TPBPY-CN, Pt / 40TPBPY-CN, and 40TPBPY-CN-AF; (c) Selectivity of NO for CN, 40TPBPY-CN, and Pt / 40TPBPY-CN; (d) Results of the 600-min cycle experiment of Pt / 40TPBPY-CN; We used the prepared samples to conduct catalytic activity tests to evaluate the efficiency of photocatalytic removal of NO. Figure 3(a) shows the photocatalytic efficiency of TPBPY-CN with different mass fractions, indicating that the efficiency increases with the increase of the mass fraction ratio of TP-BPY-COF. It is worth noting that when the mass fraction of TP-BPY-COF exceeds 40%, the photocatalytic performance gradually decreases, and when the mass fraction is 40%, the photocatalytic efficiency reaches 44.8%. This result emphasizes the synergistic relationship between CN and TP-BPY-COF, which is consistent with their optoelectrochemical properties. In addition, the synergistic effect is mainly induced by in-situ growth, because we found that the photocatalytic efficiency of 40TPBPY-CN-AF (Comparative Example 1) is only 31.8%, which is lower than that of 40TPBPY-CN. To evaluate the effect of single atoms on the photocatalytic performance of Pt / 40TPBPY-CN, its photocatalytic efficiency was also analyzed simultaneously. Figure 3 (b) gives the efficiency comparison between Pt / 40TPBPY-CN and 40TPBPY-CN. The results clearly show that after adding platinum, the photocatalytic efficiency is greatly improved, and the efficiency reaches 65%, confirming the superior photocatalytic composite material with single-atom doping of TPBPY-CN. In addition, Pt / 40TPBPY-CN shows a NO 3 - oxidation selectivity of nearly 100% ( Figure 3 (c)), while 40TPBPY-CN and CN reach NO 3 - oxidation selectivities of 97.9% and 89% respectively, confirming the superior selectivity of the Pt / 40TPBPY-CN sample. The formation of the chemical-bonded heterostructure promotes the photo transfer of e - / h + and weakens their recombination. In addition, due to the surface plasmon resonance (SPR) providing additional electrons, single-atom Pt also plays a key role in the photocatalytic reaction. In addition, through the results of the 600-minute cyclic experiment ( Figure 3 (d)), it was found that after 5 cyclic experiments, the efficiency of Pt / 40TPBPY-CN decreased from 63% to 59%, indicating its good stability in the photocatalytic reaction.

[0062] Figure 4 (a) UV-vis DRS spectra, (b) fluorescence spectra, (c) resistance diagrams, (d) transient photocurrent response curves of CN, TP-BPY-COF, TPBPY-CN, Pt-40TPBPY-CN, and 40TPBPY-CN-AF photocatalysts. Through the analysis of UV-vis DRS and PL spectra, the electronic structure and optoelectrochemical characteristics of the prepared samples were further elucidated. In the UV-vis DRS spectra ( Figure 4(a)) TP-BPY-COF exhibits considerable light absorption intensity in the visible light spectrum, significantly enhancing the light absorption of 40TPBPY-CN in the ultraviolet and visible ranges. In addition, the introduction of platinum further enhances the visible light absorption, making the visible light absorption intensity of the synthesized sample the highest. Figure 4 (b) shows the PL spectra of the synthesized photocatalysts at an emission wavelength of 370 nm under room temperature conditions. Notably, the peaks associated with the CN and 40TPBPY-CN-AF photocatalysts show relatively high peak intensities, indicating a relatively high recombination rate between photo-generated electrons and holes. For the TP-BPY-COF and 40TPBPY-CN samples, there is an almost negligible peak intensity at 460 nm, which confirms that TP-BPY-COF has strong performance in suppressing the recombination of photo-electrons and holes. In summary, in-situ growth of TP-BPY-COF on the surface of CN can effectively inhibit the carrier recombination of the 40TPBPY-CN photocatalyst. The transfer efficiency of photo-generated electrons and holes is a key factor affecting photocatalytic performance, which was evaluated by photocurrent response and EIS. As Figure 4 (c) shows, the EIS Nyquist plot of the Pt / 40TPBPY-COF sample shows the lowest electrochemical impedance, indicating rapid charge transfer during the photocatalytic reaction. In addition, the transient photocurrent response curve ( Figure 4 (d)) shows that Pt-40TPBPY-CN has the highest photocurrent density, which is about 5 times and 3 times that of CN and TP-BPY-COF, respectively. Therefore, the combination of TP-BPY-COF and CN significantly improves the photoelectrochemical performance by accelerating the transfer rate of electrons and holes while suppressing their recombination. In addition, the coordination of platinum to TP-BPY-COF further enhances these capabilities. To study the effect of in-situ growth on the catalytic performance, we conducted a comparative analysis of the photoelectrochemical performance of in-situ growth catalysts and non-in-situ synthesized catalysts. Compared with 40TPBPY-CN-AF, 40TPBPY-CN shows a lower electron / hole pair recombination rate, lower electrochemical impedance, and higher photocurrent density. These results confirm that chemically bonded photocatalytic materials can significantly improve photocatalytic performance.

Claims

1. An in-situ grown covalent organic framework composite single-atom platinum photocatalyst based on g-C3N4, characterized by: The main raw materials of the catalyst include: 2,2'-bipyridine-5,5'-diamine, 1,3,5-triformaldehyde phenol, Pt and g-C3N4; the expression of the obtained catalyst is: Pt / xTPBPY-CN, wherein x is the mass percentage of TP-BPY-COF in the obtained catalyst to TPBPY-CN, and the numerical range of x is 10-60%.

2. The in-situ grown covalent organic framework composite single-atom platinum photocatalyst based on g-C3N4 according to claim 1, characterized in that: The value range of x is 40-50%.

3. The in-situ grown covalent organic framework composite single-atom platinum photocatalyst based on g-C3N4 according to claim 2, characterized in that: The value of x is 40%.

4. The in-situ grown covalent organic framework composite single-atom platinum photocatalyst based on g-C3N4 according to claim 1, characterized in that: The TPBPY-CN is in-situ grown TPBPY-CN; the Pt comes from 50-100 mg of 18% by mass platinum nitrate solution.

5. A method for preparing an in-situ grown covalent organic framework composite single-atom platinum photocatalyst based on g-C3N4 according to any one of claims 1 to 4, characterized in that: include: (1) Preparation of g-C3N4(CN): Melamine was placed in an aluminum oxide crucible, heated to 500-600°C and maintained for 3-5 hours; (2) Preparation of TPBPY-CN: 2,2'-bipyridine-5,5'-diamine, 1,3,5-triformaldehyde phenol and a specified amount of g-C3N4 were added to a Pyrex tube so that TP-BPY-COF could grow in situ on CN during the reaction, and N,N-dimethylacetamide and o-dichlorobenzene were used as mixed solvents; the mixture was ultrasonically treated at room temperature for 20-40 minutes, then frozen in a liquid nitrogen bath and subjected to three freeze-pump-thaw cycles to obtain a uniform solution; the uniform solution was transferred to an oven and heated at 110-130°C for 60-80 hours to produce a precipitate; the obtained precipitate was separated by filtration and washed with tetrahydrofuran; finally, the product was subjected to Soxhlet extraction with tetrahydrofuran and then dried under vacuum to obtain TPBPY-CN of different mass fractions, which were represented by XTPBPY-CN, wherein x is the mass percentage of TP-BPY-COF in the catalyst to TPBPY-CN, and the numerical range of x is 10-60%; (3) Preparation of Pt / TPBPY-CN: The TPBPY-CN synthesized in step (2) was mixed with a platinum nitrate solution; then a mixed solution of ethanol and methanol was added to obtain a mixture, the mixture was ultrasonically treated at room temperature for 10-20 minutes, and then stirred at room temperature to obtain a final composite and labeled as Pt-XTPBPY-CN, wherein X represents the mass fraction of TP-BPY-COF, ranging from 10-60%.

6. The method for preparing the in-situ grown covalent organic framework composite single-atom platinum photocatalyst based on g-C3N4 according to claim 5, characterized in that: The platinum nitrate solution described in step (1) is 50 mg of a platinum nitrate solution with a mass percentage of 18%; the heating to 540-560° C. described in step (1) is maintained for 3-4 hours.

7. The method for preparing the in-situ grown covalent organic framework composite single-atom platinum photocatalyst based on g-C3N4 according to claim 5, characterized in that: The molar ratio of 2,2'-bipyridine-5,5'-diamine to 1,3,5-triformaldehyde phenol in step (2) is 1-2:1; the mixture in step (2) is ultrasonically treated at room temperature for 25-35 minutes.

8. The method for preparing the in-situ grown covalent organic framework composite single-atom platinum photocatalyst based on g-C3N4 according to claim 7, characterized in that: The homogeneous solution in step (2) is heated in an oven at 115-125° C. for 65-75 hours; and the Soxhlet extraction in step (2) is performed for 20-25 hours.

9. The method for preparing the in-situ grown covalent organic framework composite single-atom platinum photocatalyst based on g-C3N4 according to claim 5, characterized in that: The volume ratio of ethanol to methanol in step (3) is 1:1; the mixture in step (3) is ultrasonically treated at room temperature for 12-16 minutes, and then stirred at room temperature for 20-25 hours.

10. Use of the in-situ grown covalent organic framework composite single-atom platinum photocatalyst based on g-C3N4 according to any one of claims 1 to 4 in the photocatalytic oxidation of NO.

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