Preparation method and application of Co-COF / CdS composite material

Abstract

The invention belongs to the technical field of photocatalytic materials, and discloses a preparation method and application of a Co-COF / CdS composite material. The composite material is prepared from Salphen-based Co-COF anchored by monatomic Co and CdS NRs through an electrostatic self-assembly method, and Co monatomic is coordinated and combined with O and N elements in a COF framework and is uniformly dispersed. The preparation method comprises the following steps: performing hydrothermal synthesis on CdS and NRs, preparing Co-COF by a three-step method, and performing electrostatic self-assembly compounding on the CdS and the NRs. The separation efficiency of traditional CdS photo-generated charges is improved, the photo-corrosion phenomenon of the traditional CdS photo-generated charges is reduced, precious metal is replaced with non-precious metal Co, the process is mild, operation is easy and convenient, the obtained composite material is stable in structure and good in uniformity, the photocatalytic activity is remarkably improved, and the composite material can be efficiently used for producing synthesis gas through photocatalytic formic acid decomposition.

Description

Technical Field

[0001] This invention belongs to the field of photocatalytic materials technology, specifically relating to a method for preparing Co-COF / CdS composite materials and their applications. Background Technology

[0002] Cadmium sulfide (CdS) has become a research hotspot in photocatalysis, photoelectric conversion, and other fields due to its suitable redox band position and narrow band gap characteristics, and has broad application prospects in energy conversion and environmental remediation. Among them, CdS nanorods (CdS NRs) have attracted widespread attention from researchers because of their unique one-dimensional structure, which can effectively promote charge transport and further improve material performance.

[0003] However, blank CdS NRs prepared by traditional methods have significant drawbacks: First, the high recombination rate of photogenerated electrons and holes on the CdS NRs surface limits the material's performance; second, CdS NRs are prone to photocorrosion, exhibit poor structural stability, and the powder itself is prone to agglomeration, affecting the material's uniformity and application performance. To address these issues, the conventional strategy is to load noble metals and their oxides onto the CdS surface as modifiers. While this can improve charge separation efficiency to some extent, it suffers from drawbacks such as high cost, insufficient reserves, and limited modification effects, making it difficult to meet the demands of large-scale applications.

[0004] Two-dimensional covalent organic frameworks (COFs) possess characteristics such as controllable structure, porosity, customizable function, excellent light absorption performance, and good physicochemical stability. They can serve as ideal carriers for metal single atoms, providing periodic coordination sites for non-noble metal atoms such as Fe, Co, and Ni, thus achieving stable dispersion of metal single atoms. Among them, Salphen-based COFs have an extended π-conjugated structure, which can effectively mediate electron transport. After anchoring metal single atoms, they can form highly efficient active sites, effectively solving the problems of aggregation, high charge recombination rate, and poor stability of CdS-based materials.

[0005] Based on this, a composite preparation method based on CdS NRs and Salphen-based COFs anchored by metal single atoms was developed to overcome the inherent defects of traditional CdS-based materials and obtain composite materials with uniform composition, stable structure and excellent performance, which has important theoretical significance and practical application value. Summary of the Invention

[0006] This invention provides a method for preparing and applying a single-atom Co-anchored covalent organic framework / cadmium sulfide (Co-COF / CdS) composite material, which improves the charge separation efficiency and structural stability of traditional CdS, and finally obtains a composite material with uniform composition, uniform Co single-atom dispersion, and stable structure. Moreover, the preparation process is simple, mild, and highly reproducible.

[0007] To achieve the above objectives, the present invention provides the following technical solution: A Co-COF / CdS composite material is formed by electrostatic self-assembly of a Salphen-based covalent organic framework Co-COF anchored by single-atom Co and CdS NRs. In the Co-COF, Co is uniformly dispersed in single-atom form within the Salphen-based covalent organic framework network, and Co is coordinated with O and N elements in the polymer. The composite material is prepared through the following steps: Preparation of S1 and CdS NRs: Cadmium nitrate (Cd(NO3)2·4H2O) and thiourea (CH4N2S) were added to ethylenediamine for hydrothermal reaction. After cooling to room temperature, the precipitate was collected, washed, and vacuum dried to obtain CdS NRs. Preparation of S2 and Co-COF: A three-step method was used, the specific steps of which are as follows: S2-1, Solvent degassing and pre-coordination: The NMP solvent was degassed. Under nitrogen protection, cobalt acetylacetonate and 2,3,5,6-tetraamino-2,5-cyclohexadiene-1,4-dione (TABQ) were added to a three-necked flask and the degassed NMP was added. The mixture was stirred at room temperature for 1-2 h to pre-coordination to form an intermediate. S2-2, Ultrasonic-assisted and solvothermal reaction: 2,5-dihydroxy-1,4-benzenedicarboxaldehyde (DHTA) and the remaining degassed NMP are added to the pre-coordination system. The solid is stirred until completely dissolved. After ultrasonic-assisted pre-assembly, an oil bath solvothermal reaction is carried out under nitrogen protection at 180-200 °C. S2-3, Washing and Drying: After the reaction is complete, the precipitate is collected, washed and purified, and then dried under vacuum to obtain Co-COF; S3. Preparation of Co-COF / CdS composite material: The CdS NRs prepared in step S1 and the Co-COF prepared in step S2 were ultrasonically dispersed in anhydrous ethanol, and the solvent was evaporated by stirring in a water bath and then vacuum dried to obtain the Co-COF / CdS composite material.

[0008] Preferably, the amount of Cd(NO3)2·4H2O used in step S1 is 4.0-5.0 g, and the amount of CH4N2S used is 4.0-5.0 g.

[0009] Preferably, in step S1, the amount of ethylenediamine used is 50-70 mL, the hydrothermal reaction temperature is 150-170 ℃, the reaction time is 40-50 h, the washing is performed by alternating washing with deionized water and ethanol 3-5 times, the vacuum drying temperature is 60-80 ℃, and the drying time is 18-24 h.

[0010] Preferably, the molar ratio of 2,5-dihydroxy-1,4-benzenedicarboxaldehyde, 2,3,5,6-tetraamino-2,5-cyclohexadiene-1,4-dione and cobalt acetylacetonate in step S2-1 is 1.6-1.8:1:3.6-3.8.

[0011] Preferably, the volume of the three-necked flask in step S2-1 is 20-30 mL, the amount of degassed NMP added for the first time is 4-5 mL, and the total volume of NMP is 8-10 mL.

[0012] Preferably, the stirring time under nitrogen atmosphere in step S2-2 is 30 min, the ultrasonic-assisted pre-assembly uses high-power ultrasound with an ultrasonic power of 300 W and an ultrasonic time of 25-35 min, and the oil bath solvothermal reaction time is 70-74 h.

[0013] Preferably, the washing and purification in steps S2-3 involves dispersing the product in methanol and soaking it at 70-80 °C for 36-48 h, and the vacuum drying temperature is 60-80 °C for 12-24 h.

[0014] Preferably, in step S3, the amount of CdS NRs used is 70-90 mg, the amount of anhydrous ethanol used is 50-70 mL, the ultrasonic power is 100 W, the ultrasonic time is 25-35 min, the water bath stirring temperature is 55-65 ℃, the stirring speed is 200-300 r / min, the vacuum drying temperature is 60-80 ℃, and the drying time is 12-24 h.

[0015] Preferably, the content of Co-COF relative to CdS is 0.5 wt.%-2.0 wt.%.

[0016] Preferably, the application of the Co-COF / CdS composite material in the photocatalytic decomposition of formic acid to produce syngas (CO / H2).

[0017] The advantages of this invention compared to the prior art are as follows: (1) This invention combines a single-atom Co-anchored Salphen-based Co-COF with CdS NRs via electrostatic self-assembly. The extended π-conjugated structure of the Salphen-based COF constructs a highly efficient electron transport channel, where the Co single atom forms stable coordination with the O and N elements in the COF framework, creating high-density active sites. The π-conjugated structure rapidly transfers photogenerated electrons from CdS NRs, inhibiting electron-hole recombination. The single-atom Co precisely catalyzes the formic acid decomposition rate-determining step, resulting in a significantly improved photocatalytic activity compared to blank CdS NRs.

[0018] (2) The excellent stability of the Co-COF of the present invention can inhibit the photocorrosion of CdS NRs and extend the material life. At the same time, it disperses CdS NRs through electrostatic interaction, avoids agglomeration, and ensures the uniformity of the material. The present invention uses non-noble metal Co single atoms to replace noble metal modification, and achieves uniform dispersion of Co single atoms through coordination, which not only reduces the preparation cost and solves the problem of insufficient noble metal reserves, but also improves catalytic stability.

[0019] (3) In the Co-COF preparation stage, this invention employs a pre-coordination strategy to lay the foundation for single-atom anchoring, combined with ultrasound-assisted assembly to promote uniform dispersion and nucleation of monomers. Subsequently, impurities are removed through washing and purification to ensure product purity. The entire process uses mild reaction conditions such as hydrothermal and solvothermal, requiring no harsh processes, and is simple to operate and highly reproducible. Attached Figure Description

[0020] Figure 1 This is a high-angle annular dark-field scanning transmission electron microscope (HAADF-STEM) image of the Co-COF material prepared in Comparative Example 2. Figure 2 The images shown are transmission electron microscope (TEM) images (a) and energy dispersive spectroscopy (EDS) spectra (b) of the Co-COF material prepared in Comparative Example 2. Figure 3 The diagram shows the structure (a) and infrared spectrum (b) of the Co-COF material prepared in Comparative Example 2. Figure 4 The X-ray photoelectron spectroscopy (XPS) of the Co-COF material prepared in Comparative Example 2 is shown in (a) as the full spectrum, (b) as the N 1s spectrum, (c) as the O 1s spectrum, and (d) as the Co 2p spectrum. Figure 5 The image shows a TEM image of CdS prepared in Comparative Example 1. Figure 6 The zeta potential spectra of the CdS prepared in Comparative Example 1 and the Co-COF materials prepared in Comparative Example 2 are shown. Figure 7 These are TEM images (a) and corresponding EDS distribution maps (b) of the Co-COF / CdS composite material prepared in Example 1. Figure 8 The X-ray diffraction (XRD) patterns are those of the Co-COF / CdS composite material prepared in Example 1 and the CdS prepared in Comparative Example 1. Figure 9 The high-resolution Cd 3d (a) and S 2p (b) comparison spectra of the Co-COF / CdS composite material prepared in Example 1 and the CdS prepared in Comparative Example 1 are shown. Figure 10The images show the temperature change curves (a) and corresponding infrared photographs (b) of the Co-COF / CdS composite material prepared in Example 1 and the CdS prepared in Comparative Example 1 during irradiation. Figure 11 These are single-particle concentrated light images (a) and single-particle concentrated light spectra (c) of the Co-COF / CdS composite material prepared in Example 1, and single-particle concentrated light images (b) and single-particle concentrated light spectra (d) of CdS prepared in Comparative Example 1. Figure 12 The images show the electrochemical impedance spectroscopy (EIS) spectra of the Co-COF / CdS composite material prepared in Example 1 and the CdS prepared in Comparative Example 1. Figure 13 The formic acid decomposition performance of the Co-COF / CdS composite material prepared in Example 1, the CdS prepared in Comparative Example 1, the Co-COF prepared in Comparative Example 2, and the CoCl2 / CdS prepared in Comparative Example 3 under visible light (λ ≥ 420 nm) irradiation is shown. Figure 14 This is a long-term test spectrum of the photocatalytic formic acid decomposition of the Co-COF / CdS composite material prepared in Example 1; Figure 15 This is a photocatalytic formic acid decomposition cycle experiment of the Co-COF / CdS composite material prepared in Example 1; Figure 16 The images show the XRD patterns of the Co-COF / CdS composite material prepared in Example 1 before and after photocatalytic formic acid decomposition under light irradiation. Detailed Implementation

[0021] To make the above-mentioned objectives, features, and advantages of the present invention more readily understood, the specific embodiments of the present invention will be described in detail below with reference to examples. The following content is only for illustrative purposes and explanation of the inventive concept. Those skilled in the art can make various modifications, additions, or similar substitutions to the specific embodiments described, as long as they do not deviate from the core concept of the present invention or exceed the scope defined by the claims, they should all be included in the protection scope of the present invention.

[0022] The preparation method of the present invention will be described in detail below through specific embodiments and comparative examples.

[0023] Example 1 A Co-COF / CdS composite material is prepared by the following steps: Preparation of S1 and CdS NRs: 4.5 g Cd(NO3)2·4H2O and 4.5 g CH4N2S were added to a 100 mL polytetrafluoroethylene reactor liner, and 60 mL ethylenediamine was added to completely dissolve them. The reactor was placed in a 160 ℃ oven for hydrothermal treatment for 45 h. After cooling to room temperature, the precipitate was collected and washed 4 times alternately with deionized water and ethanol. Then it was dried in a vacuum environment at 70 ℃ for 21 h to obtain CdS NRs. Preparation of S2 and Co-COF: S2-1, Solvent Degassing and Pre-coordination: 282.2 mg (1.7 mmol) of 2,5-dihydroxy-1,4-benzenedicarboxaldehyde, 168 mg (1 mmol) of 2,3,5,6-tetraamino-2,5-cyclohexadiene-1,4-dione, and 951.5 mg (3.7 mmol) of cobalt acetylacetonate were prepared for use. First, the NMP solvent was degassed. Under continuous nitrogen purging, cobalt acetylacetonate and 2,3,5,6-tetraamino-2,5-cyclohexadiene-1,4-dione were added to a 25 mL three-necked flask, followed by 4.5 mL of degassed NMP. The mixture was stirred at room temperature for 1.5 h to allow for complete pre-coordination and formation of the intermediate. S2-2, Ultrasonic-Assisted and Solvothermal Reaction: 2,5-Dihydroxy-1,4-benzenedicarboxaldehyde and the remaining degassed NMP (total NMP volume 9 mL) were added to the above pre-coordination system, and stirring was continued for 30 min under a nitrogen atmosphere to ensure complete dissolution and homogeneity of the solids. The mixture was then placed in an ultrasonic instrument for high-power ultrasonic-assisted pre-assembly (ultrasonic power 300 W, ultrasonic time 30 min). The ultrasonically treated mixture was then placed in a 190 ℃ oil bath and reacted for 72 h under nitrogen protection. S2-3, Washing and Drying: After the reaction, the black precipitate was collected, and the product was then dispersed in methanol solvent and soaked at 75 °C for 42 h to remove impurities. After the reaction, the product was centrifuged, and the collected black solid was dried under vacuum at 70 °C for 18 h to obtain Co-COF; S3. Preparation of Co-COF / CdS composite material: Weigh 80 mg of CdS NRs prepared in step S1 and 0.8 mg of Co-COF prepared in step S2 into a beaker, add 60 mL of anhydrous ethanol, and sonicate at 100 W for 30 min to disperse the two evenly. Then transfer to a 60 ℃ water bath and stir at 250 r / min until the ethanol is completely evaporated. Place the formed composite catalyst in a vacuum environment at 70 ℃ and dry for 18 h to obtain a Co-COF / CdS composite material with a Co-COF content of 1.0 wt.% relative to CdS.

[0024] Example 2 A Co-COF / CdS composite material is prepared by the following steps: Preparation of S1 and CdS NRs: 4.0 g Cd(NO3)2·4H2O and 4.0 g CH4N2S were added to a 100 mL polytetrafluoroethylene reactor liner, and 50 mL ethylenediamine was added to completely dissolve them. The reactor was placed in a 150 ℃ oven for hydrothermal treatment for 40 h. After cooling to room temperature, the precipitate was collected, washed three times alternately with deionized water and ethanol, and then dried in a vacuum environment at 60 ℃ for 18 h to obtain CdS NRs. Preparation of S2 and Co-COF: A three-step method was used, the specific steps of which are as follows: S2-1, Solvent Degassing and Pre-coordination: 265.6 mg (1.6 mmol) of 2,5-dihydroxy-1,4-benzenedicarboxaldehyde, 168 mg (1 mmol) of 2,3,5,6-tetraamino-2,5-cyclohexadiene-1,4-dione, and 925.7 mg (3.6 mmol) of cobalt acetylacetonate were prepared. First, the NMP solvent was degassed. Under continuous nitrogen purging, cobalt acetylacetonate and 2,3,5,6-tetraamino-2,5-cyclohexadiene-1,4-dione were added to a 20 mL three-necked flask, followed by 4 mL of degassed NMP. The mixture was stirred at room temperature for 1 h to allow for complete pre-coordination and formation of an intermediate. S2-2, Ultrasonic-Assisted and Solvothermal Reaction: 2,5-Dihydroxy-1,4-benzenedicarboxaldehyde and the remaining degassed NMP (total NMP volume 8 mL) were added to the above pre-coordination system, and stirring was continued for 30 min under a nitrogen atmosphere to ensure complete dissolution and homogeneity of the solids. The mixture was then placed in an ultrasonic instrument for high-power ultrasonic-assisted pre-assembly (ultrasonic power 300 W, ultrasonic time 25 min). The ultrasonically treated mixture was then placed in an oil bath at 180 ℃ and reacted for 70 h under nitrogen protection. S2-3, Washing and Drying: After the reaction, the black precipitate was collected. The product was then dispersed in methanol solvent and soaked at 70 °C for 36 h to remove impurities. After the reaction, the product was centrifuged, and the collected black solid was dried under vacuum at 60 °C for 12 h to obtain Co-COF. S3. Preparation of Co-COF / CdS composite material: Weigh 90 mg of CdS NRs prepared in step S1 and 0.45 mg of Co-COF prepared in step S2 into a beaker, add 50 mL of anhydrous ethanol, and sonicate at 100 W for 25 min to disperse the two evenly. Then transfer to a 55 ℃ water bath and stir at 200 r / min until the ethanol is completely evaporated. Place the formed composite catalyst in a vacuum environment at 60 ℃ and dry for 12 h to obtain a Co-COF / CdS composite material with a Co-COF content of 0.5 wt.% relative to CdS.

[0025] Example 3 A Co-COF / CdS composite material is prepared by the following steps: Preparation of S1 and CdS NRs: 5.0 g Cd(NO3)2·4H2O and 5.0 g CH4N2S were added to a 100 mL polytetrafluoroethylene reactor liner, and 70 mL ethylenediamine was added to completely dissolve them. The reactor was placed in a 170 ℃ oven for hydrothermal treatment for 50 h. After cooling to room temperature, the precipitate was collected and washed 5 times alternately with deionized water and ethanol. Then it was dried in a vacuum environment at 80 ℃ for 24 h to obtain CdS NRs. Preparation of S2 and Co-COF: A three-step method was used, the specific steps of which are as follows: S2-1, Solvent Degassing and Pre-coordination: 298.8 mg (1.8 mmol) of 2,5-dihydroxy-1,4-benzenedicarboxaldehyde, 168 mg (1 mmol) of 2,3,5,6-tetraamino-2,5-cyclohexadiene-1,4-dione, and 977.2 mg (3.8 mmol) of cobalt acetylacetonate were prepared. First, the NMP solvent was degassed. Under continuous nitrogen purging, cobalt acetylacetonate and 2,3,5,6-tetraamino-2,5-cyclohexadiene-1,4-dione were added to a 30 mL three-necked flask, followed by 5 mL of degassed NMP. The mixture was stirred at room temperature for 2 h to allow for complete pre-coordination and formation of an intermediate. S2-2, Ultrasonic-Assisted and Solvothermal Reaction: 2,5-Dihydroxy-1,4-benzenedicarboxaldehyde and the remaining degassed NMP (total NMP volume 10 mL) were added to the above pre-coordination system. Stirring was continued for 30 min under a nitrogen atmosphere until the solids were completely dissolved and homogeneous. The mixture was then placed in an ultrasonic instrument for high-power ultrasonic-assisted pre-assembly (ultrasonic power 300 W, ultrasonic time 35 min). The ultrasonically treated mixture was then placed in a 200 ℃ oil bath and reacted for 74 h under nitrogen protection. S2-3, Washing and Drying: After the reaction, the black precipitate was collected. The product was then dispersed in methanol solvent and soaked at 80 °C for 48 h to remove impurities. After the reaction, the product was centrifuged, and the collected black solid was dried under vacuum at 80 °C for 24 h to obtain Co-COF. S3. Preparation of Co-COF / CdS composite material: Weigh 70 mg of CdS NRs prepared in step S1 and 1.4 mg of Co-COF prepared in step S2 into a beaker, add 70 mL of anhydrous ethanol, and sonicate at 100 W for 35 min to disperse the two evenly. Then transfer to a 65 ℃ water bath and stir at 300 r / min until the ethanol is completely evaporated. Place the formed composite catalyst in a vacuum environment at 80 ℃ and dry for 24 h to obtain a Co-COF / CdS composite material with a Co-COF content of 2.0 wt.% relative to CdS.

[0026] Comparative Example 1 (Blank CdS NRs) Only CdS NRs were prepared without combining them with Co-COF, and the steps were the same as step S1 in Example 1.

[0027] Comparative Example 2 (Blank Co-COF) Only Co-COF was prepared, without combining it with CdS NRs, and the steps were the same as step S2 in Example 1.

[0028] Comparative Example 3 (CoCl2 / CdS) Preparation of S1 and CdS NRs: Same as step S1 in Example 1; S2, Preparation of CoCl2 / CdS composite material: Weigh 80 mg of CdS NRs prepared in step S1 and CoCl2 with the corresponding Co content (consistent with the Co content of Co-COF in Example 1) into a beaker, add 60 mL of anhydrous ethanol, and sonicate at 100 W for 30 min to disperse the two evenly. Then transfer to a 60 ℃ water bath and stir at 250 r / min until the ethanol is completely evaporated. Place the formed composite material in a vacuum environment at 70 ℃ for 18 h to obtain the CoCl2 / CdS composite material.

[0029] Figure 1 This is a HAADF-STEM image of the Co-COF material prepared in Comparative Example 2. It shows numerous discrete, dense bright spots, representing Co single atoms, confirming that the Co single atoms are uniformly dispersed in the COF network, rather than forming clusters or nanoparticles.

[0030] Figure 2The images shown are TEM (a) and EDS (b) images of the Co-COF material prepared in Comparative Example 2. These confirm that the Co-COF material has a granular morphology and that the constituent elements (C, N, O, and Co) are highly uniformly distributed.

[0031] Figure 3 This shows a schematic diagram (a) and an infrared spectrum (b) of the Co-COF material prepared in Comparative Example 2. The infrared spectrum is centered at 1660 cm⁻¹. -1 The signal at this location corresponds to the stretching vibration of the C=N double bond in Co-COF, and is located at 1045 cm⁻¹. -1 The vibrational peak at the point proves that a carbonyl group was successfully introduced into the organic framework, confirming the structure in Figure (a).

[0032] Figure 4 This is the XPS of the Co-COF material prepared in Comparative Example 2. The full spectrum shows that the sample is composed of four elements: C, N, O, and Co. In the N 1s high-resolution spectrum, two characteristic peaks belonging to C-NH2 (399.3 eV) and C=N (400.3 eV) are observed, with the formation of the C=N bond confirming the successful occurrence of the reaction. In the O 1s spectrum, two characteristic peaks appear at binding energies of 531.6 and 533.1 eV, corresponding to CO and C=O, respectively. The peak fitting results of the Co 2p high-resolution XPS spectrum show that Co 2p... 3 / 2 (781.7 eV) and Co 2p 1 / 2 The characteristic peak at 789.9 eV indicates the successful introduction of a single Co atom into the COF structure. Combining these results, we can conclude the successful introduction of a single-atom Co and the successful preparation of COF.

[0033] Figure 5 This is a TEM image of the CdS prepared in Comparative Example 1, showing the structure of nanorods.

[0034] Figure 6 The images show the Zeta potential spectra of the CdS prepared in Comparative Example 1 and the Co-COF prepared in Comparative Example 2. The Zeta potentials of CdS and Co-COF are in opposite directions, indicating that there is an electrostatic interaction between them, which is the basis for their ability to be combined together through electrostatic self-assembly.

[0035] Figure 7The images show a TEM image (a) and a corresponding EDS distribution map (b) of the Co-COF / CdS composite material prepared in Example 1. It can be seen that a tight interfacial contact is formed between the CdS NRs and the Co-COF nanoparticles. The EDS spectrum shows a uniform distribution of Cd, S, C, N, O, and Co elements, indicating a good interfacial bond between Co-COF and CdS NRs. This provides favorable conditions for the transfer of photogenerated electrons from CdS NRs to Co-COF.

[0036] Figure 8 The XRD patterns are of the Co-COF / CdS composite material prepared in Example 1 and the CdS prepared in Comparative Example 1. Since the relative content of Co-COF in the composite sample is low, no diffraction peaks were observed.

[0037] Figure 9 The high-resolution Cd 3d (a) and S 2p (b) comparison spectra of the Co-COF / CdS composite material prepared in Example 1 and the CdS prepared in Comparative Example 1 confirm that there is an interaction between CdS and Co-COF, which affects the electronic distribution of CdS.

[0038] Figure 10 Figure (a) shows the temperature change curves (and corresponding infrared images) of the Co-COF / CdS composite material prepared in Example 1 and the CdS prepared in Comparative Example 1 during irradiation, along with their corresponding infrared images (b). The initial temperature of the formic acid decomposition reaction system was approximately 30 °C. The system temperature rose rapidly in the initial stage and reached a steady state within 1 h. The final reaction temperature of the Co-COF / CdS composite sample reached 50.7 °C, significantly higher than that of the blank CdS NRs (44.5 °C). Infrared imaging of the final reaction temperatures of the blank CdS NRs and the Co-COF / CdS composite sample confirmed this result (Figure b). The results clearly demonstrate that the introduction of Co-COF helps to increase the reaction temperature, thereby accelerating the photocatalytic formic acid decomposition process.

[0039] Figure 11Figures (a) and (c) show the single-particle focused fluorescence images (a) and (c) of the Co-COF / CdS composite material prepared in Example 1, and the single-particle focused fluorescence images (b) and (d) of CdS prepared in Comparative Example 1. Points 1, 2, 3, and 4 in Figures (a) and (b) are the locations selected for testing the fluorescence intensity of Co-COF / CdS and CdS, respectively; Figures (c) and (d) show the corresponding fluorescence intensity curves of Co-COF / CdS and CdS at these four points, respectively. The blank CdS NRs show bright single-particle fluorescence images and strong emission peaks (Figures b and d). In contrast, the Co-COF / CdS composite material shows darker single-particle fluorescence images (Figures a and c), confirming the efficient transfer of photogenerated electrons from CdS to Co-COF.

[0040] Figure 12 The images show the EIS spectra of the Co-COF / CdS composite material prepared in Example 1 and the CdS prepared in Comparative Example 1. The Co-COF / CdS composite material has a smaller charge transfer resistance, indicating that Co-COF effectively promotes charge separation in the composite material.

[0041] Figure 13 The formic acid decomposition performance of the Co-COF / CdS composite material prepared in Example 1, CdS prepared in Comparative Example 1, Co-COF prepared in Comparative Example 2, and CoCl2 / CdS prepared in Comparative Example 3 under visible light (λ ≥ 420 nm) irradiation is described. The specific experimental procedures for photocatalytic formic acid decomposition to syngas using the Co-COF / CdS composite material, CdS, Co-COF, and CoCl2 / CdS as photocatalysts are as follows: The photocatalytic formic acid decomposition experiment was conducted in a sealed 50 mL round-bottom flask (total volume approximately 82 mL). The experimental light source was a 300 W Xe lamp equipped with a cutoff filter of λ ≥ 420 nm, approximately 9 cm from the reaction apparatus, with an average light intensity of 520 mW cm⁻¹. -2First, 20 mL of H2O and 1 mL of anhydrous formic acid were added to a round-bottom flask. The pH of the solution was slowly adjusted to 3.5 using solid NaOH. 2.5 mg of photocatalyst was weighed and added to the solution, and the mixture was sonicated to obtain a uniformly dispersed solution. The flask was sealed, and then high-purity Ar gas was passed through the solution for 30 min to purge air from the flask. The gaseous products CO and H2 obtained from the reaction were detected and quantified using a gas chromatograph (GC-1690) equipped with flame ionization (FID) and a thermal conductivity detector (TCD), respectively. The photocatalytic performance of the blank Co-COF was negligible. Compared with the blank CdS NRs in Comparative Example 1, the photocatalytic activity of Co-COF / CdS for formic acid decomposition was significantly improved, with H2 yield increasing by 4.05 times and CO yield increasing by 2.95 times, and was also significantly higher than CoCl2 / CdS.

[0042] Figure 14 This is a long-term photocatalytic decomposition spectrum of the Co-COF / CdS composite material prepared in Example 1. Under 420 nm monochromatic light irradiation, the composite sample maintained its durable photocatalytic performance for 30 h, confirming its excellent stability.

[0043] Figure 15 This is a cyclic experiment of photocatalytic formic acid decomposition using the Co-COF / CdS composite material prepared in Example 1. After four cycles, the performance did not show a significant decrease, further confirming its stability.

[0044] Figure 16 The images show the XRD patterns of the Co-COF / CdS composite material prepared in Example 1 before and after photocatalytic formic acid decomposition. No significant changes were observed in the spectra before and after irradiation, confirming its stability. Furthermore, Co-COF effectively inhibits the photocorrosion of CdS and enhances the photocatalytic formic acid decomposition performance of CdS.

Claims

1. A method for preparing a Co-COF / CdS composite material, characterized in that, Includes the following steps: Preparation of S1 and CdS NRs: Cd(NO3)2·4H2O and CH4N2S were added to ethylenediamine for hydrothermal reaction. After cooling to room temperature, the precipitate was collected, washed, and vacuum dried to obtain CdS NRs. Preparation of S2 and Co-COF: A three-step method was used, the specific steps of which are as follows: S2-1, Solvent degassing and pre-coordination: The NMP solvent was degassed. Under nitrogen protection, cobalt acetylacetone and TABQ were added to a three-necked flask and the degassed NMP was added. The mixture was stirred at room temperature for 1-2 h to pre-coordination to form an intermediate. S2-2, Ultrasonic-assisted and solvothermal reaction: DHTA and the remaining degassed NMP are added to the pre-coordinated system, and the solid is stirred until it is completely dissolved. After ultrasonic-assisted pre-assembly, an oil bath solvothermal reaction is carried out under nitrogen protection at 180-200 °C. S2-3, Washing and Drying: After the reaction is complete, the precipitate is collected, washed and purified, and then dried under vacuum to obtain Co-COF; S3. Preparation of Co-COF / CdS composite material: The CdS NRs prepared in step S1 and the Co-COF prepared in step S2 were ultrasonically dispersed in anhydrous ethanol, and the solvent was evaporated by stirring in a water bath and then vacuum dried to obtain the Co-COF / CdS composite material.

2. The method for preparing the Co-COF / CdS composite material according to claim 1, characterized in that, In step S1, the amount of Cd(NO3)2·4H2O used is 4.0-5.0 g, and the amount of CH4N2S used is 4.0-5.0 g.

3. The method for preparing the Co-COF / CdS composite material according to claim 1, characterized in that, In step S1, the amount of ethylenediamine used is 50-70 mL, the hydrothermal reaction temperature is 150-170 ℃, the reaction time is 40-50 h, the washing is performed by alternating washing with deionized water and ethanol 3-5 times, the vacuum drying temperature is 60-80 ℃, and the drying time is 18-24 h.

4. The method for preparing the Co-COF / CdS composite material according to claim 1, characterized in that, In step S2-1, the molar ratio of DHTA, TABQ and cobalt acetylacetonate is 1.6-1.8:1:3.6-3.

8.

5. The method for preparing the Co-COF / CdS composite material according to claim 1, characterized in that, In step S2-1, the volume of the three-necked flask is 20-30 mL, the amount of degassed NMP added for the first time is 4-5 mL, and the total volume of NMP is 8-10 mL.

6. The method for preparing the Co-COF / CdS composite material according to claim 1, characterized in that, In step S2-2, the stirring time under nitrogen atmosphere is 30 min, the ultrasonic-assisted pre-assembly uses high-power ultrasound with an ultrasonic power of 300 W and an ultrasonic time of 25-35 min, and the oil bath solvothermal reaction time is 70-74 h.

7. The method for preparing the Co-COF / CdS composite material according to claim 1, characterized in that, In steps S2-3, the washing and purification involves dispersing the product in methanol and soaking it at 70-80 ℃ for 36-48 h, and the vacuum drying temperature is 60-80 ℃ for 12-24 h.

8. The method for preparing the Co-COF / CdS composite material according to claim 1, characterized in that, In step S3, the amount of CdS NRs used is 70-90 mg, the amount of anhydrous ethanol used is 50-70 mL, the ultrasonic power is 100 W, the ultrasonic time is 25-35 min, the water bath stirring temperature is 55-65 ℃, the stirring speed is 200-300 r / min, the vacuum drying temperature is 60-80 ℃, and the drying time is 12-24 h.

9. The method for preparing the Co-COF / CdS composite material according to claim 1, characterized in that, The content of Co-COF relative to CdS is 0.5 wt.%-2.0 wt.%.

10. The application of a Co-COF / CdS composite material prepared by the method according to any one of claims 1-9 in the photocatalytic decomposition of formic acid to produce syngas.

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