Co3O4 / TiO2-coated C-N composite photocatalytic material as well as preparation method and application thereof

Abstract

The invention discloses a Co3O4 / TiO2 C-N composite photocatalytic material as well as a preparation method and application thereof. The preparation method comprises the following steps: adding an organic ligand and a titanium source into a solvent, carrying out solvothermal reaction to synthesize NH2-MIL-125 (Ti), adding the NH2-MIL-125 (Ti), the organic ligand and a cobalt source into the solvent, growing a ZIF-67 nanocage on the surface of the NH2-MIL-125 (Ti) at normal temperature to obtain ZIF-67 / NH2-MIL-125 (Ti), and carrying out pyrolysis to obtain the Co3O4 / TiO2 (at) C-N composite photocatalytic material. The Co3O4 / TiO2 C-N composite photocatalytic material prepared by the invention is black powder, is simple in preparation method, large in specific surface area, small in particle size, uniform in dispersion and relatively high in photocatalytic activity, and still has a certain photocatalytic effect under a visible light condition.

Description

Technical Field

[0001] This invention belongs to the field of photocatalyst preparation technology, specifically relating to a Co3O4 / TiO2@CN composite photocatalytic material, its preparation method, and its application. Background Technology

[0002] Since the beginning of the new century, with the rapid development of science and technology and industry, human society has undergone tremendous changes. The vigorous development of modern urban construction has brought tremendous impetus to economic prosperity and the improvement of people's living standards. At the same time, air pollution has become a serious challenge, with large amounts of factory emissions, traffic exhaust, coal-fired emissions, and indoor pollution sources all becoming major sources of air pollution. The continuous increase in harmful substances such as particulate matter, sulfur dioxide, nitrogen oxides, and volatile organic compounds in the atmosphere has led to serious air pollution phenomena such as smog and photochemical smog, posing a huge threat to human health and the environment.

[0003] With the improvement of indoor living environments in modern society, research on indoor air quality and the degradation of indoor pollutants has received much attention. Indoor air pollutants include volatile organic compounds (VOCs), benzene, xylene, toluene, etc. These pollutants come from furniture, decoration materials, cleaning agents, fragrances, etc. Among them, formaldehyde is one of the most common indoor air pollutants, often used in the production of adhesives, paints, furniture, building materials, and home appliances. It easily volatilizes into indoor air, and long-term exposure to high concentrations of formaldehyde may harm human health, such as respiratory problems, eye irritation, and potential carcinogenic risks. Therefore, developing a simple, pollution-free photocatalytic degradation material for gaseous formaldehyde is crucial.

[0004] Following Akira Fujishima's discovery of photo-induced catalytic water splitting in 1972, photocatalysis technology made groundbreaking progress. Titanium dioxide (TiO2) has become the most widely studied material in this field due to its advantages, including abundant reserves, low cost, chemical stability, non-toxicity, and strong photocatalytic oxidation ability. Despite the broad application prospects of TiO2, its inherent defects limit its practical application: firstly, its band gap is approximately 3.2 eV, responding only to ultraviolet light, which accounts for less than 5% of the solar spectrum, resulting in low solar energy utilization; secondly, its high photogenerated electron-hole recombination rate significantly weakens photocatalytic activity; and thirdly, its weak adsorption performance limits its degradation effect on volatile organic pollutants such as formaldehyde. These defects are even more pronounced in the degradation of gaseous pollutants such as formaldehyde. The mass transfer process of pollutants migrating from the gas phase to the TiO2 solid surface becomes a key bottleneck in the reaction rate, directly determining the contact probability between pollutants and active sites and the overall removal efficiency.

[0005] To address the issues of wide bandgap, limited ultraviolet light response, high electron-hole recombination rate, and poor adsorption capacity of TiO2, the following strategies can be employed for modification and optimization: First, non-metallic doping can broaden the light absorption spectrum range of TiO2; second, semiconductor heterojunctions can be constructed to promote the effective separation of photogenerated electrons and holes; and third, TiO2 can be prepared using metal-organic frameworks (MOFs) as sacrificial templates to increase the highly active exposed surface area of ​​the material, thereby enhancing its adsorption capacity for pollutants.

[0006] Cobalt (Co), as a 3d transition metal with multiple oxidation states, has seen its oxides become a research hotspot due to their structural tunability, with cobalt tetroxide (Co3O4) being particularly prominent. Co3O4 has a spinel structure, with Co in the crystal lattice... 2+ (Tetrahedral interstitial space) and Co 3+ The coexistence of octahedral interstices provides a channel for charge transfer. As a typical p-type semiconductor, Co3O4 possesses several core advantages suitable for photocatalysis: Firstly, its band gap is approximately 2.0-2.4 eV, effectively responding to visible light, which constitutes a significant portion of the solar spectrum, thus greatly improving solar energy utilization; secondly, Co... 2+ / Co 3+ The presence of redox pairs can accelerate the separation of photogenerated charges and enhance the kinetics of catalytic reactions.

[0007] Porous metal-organic frameworks (MOFs) with coordination structures are ideal templates for preparing functional materials, and can be transformed into metal oxides or metal nanoparticles through one-step pyrolysis in air or nitrogen atmosphere. This route is simple and efficient, and the derived materials can be precisely controlled by leveraging the structural characteristics of MOFs. Crucially, the unique MOF-on-MOF structure enables high-quality contact at the pn heterojunction interface of the derived metal oxide heterostructure, significantly improving light utilization and achieving adaptive band alignment, ensuring efficient charge separation. MOF-derived Co3O4 / TiO2 heterojunctions can significantly enhance the photocatalytic performance of formaldehyde through interfacial synergy. Furthermore, pyrolysis optimizes the pore structure: reducing the original specific surface area while transforming micropores into mesopores and retaining open diffusion channels, facilitating mass transfer between reactants and products, and further improving catalytic performance.

[0008] Yi Ke et al. (In Situ Self-Assembled ZIF-67 / MIL-125-Derived Co3O4 / TiO2 p (Yi Ke, Qian Liang,* Shuang Zhao, Zhihui Zhang, Xiazhang Li, and Zhongyu Li) synthesized a Co3O4 / TiO2 p-n heterojunction photocatalyst by preparing a ZIF-67 / MIL-125 composite precursor followed by one-step air-atmosphere calcination. The prepared Co3O4 / TiO2 material had a low specific surface area. For the degradation of gaseous pollutants, this limited surface area leads to insufficient adsorption sites and restricted mass transfer, making it difficult to meet the requirements for efficient migration of gases such as formaldehyde from the gas phase to the solid surface. In this paper, the TiO2 was derived from the pyrolysis of MIL-125(Ti) without nitrogen doping modification, and its band gap remained relatively wide (2.85 eV). The introduction of nitrogen can effectively improve the absorption of visible light. Summary of the Invention

[0009] To address the problems of poor visible light absorption and high recombination rate of photogenerated electrons and holes in existing TiO2 photocatalysts, the present invention aims to provide a Co3O4 / TiO2@CN composite photocatalyst, its preparation method, and its application in the photocatalytic degradation of gaseous formaldehyde. The preparation method of this invention is simple and easy to operate. The photocatalyst derived from MOF has a large specific surface area and good adsorption properties. The doping of C and N elements shortens the band gap of the synthesized TiO2, forming a heterojunction with ZIF-derived Co3O4, promoting the separation of photogenerated charges, and exhibiting good photocatalytic activity.

[0010] To achieve the above objectives, the present invention provides the following technical solution: A method for preparing a Co3O4 / TiO2@CN composite photocatalytic material includes the following steps: (1) Dissolve the organic ligand in a solvent, add the titanium source, stir and mix to obtain a precursor solution; perform a hydrothermal reaction on the precursor solution, centrifuge to separate the solid after the reaction, wash, dry and grind to obtain NH2-MIL-125 (Ti); (2) NH2-MIL-125 (Ti) was ultrasonically dispersed in methanol, and a soluble cobalt salt was added under stirring to obtain solution A; 2-methylimidazole was added to methanol to obtain solution B; solution A was poured into solution B under vigorous stirring, and the mixture was allowed to stand for aging reaction. After the reaction was completed, the solid was separated by centrifugation, washed, and dried to obtain ZIF-67 / NH2-MIL-125 (Ti) composite powder; (3) The ZIF-67 / NH2-MIL-125 (Ti) composite powder was calcined at high temperature and cooled to room temperature to obtain Co3O4 / TiO2@CN composite photocatalytic material.

[0011] Furthermore, in step (1), the organic ligand is 2-aminoterephthalic acid.

[0012] Furthermore, in step (1), the titanium source is isopropyl titanate or tetrabutyl titanate.

[0013] Furthermore, in step (1), the solvent is a mixed solution of N,N-dimethylformamide (DMF) and methanol, and the volume ratio of N,N-dimethylformamide to methanol is 1:1-9:1.

[0014] More preferably, the volume ratio of DMF to methanol is 1:1 to 1.5:1.

[0015] Furthermore, in step (1), the molar ratio of the solvent to the organic ligand is 150:1-200:1, and the molar ratio of the organic ligand to the titanium source is 2:1-6:1. More preferably, the molar ratio of the solvent to the organic ligand is 154.95:1-155.05:1, and the molar ratio of the organic ligand to the titanium source is 2:1-2.5:1.

[0016] Furthermore, in step (1), the stirring time is 15-30 min.

[0017] Furthermore, in step (1), the temperature of the hydrothermal reaction is 150℃~180℃, and the time is 15h~24h; More preferably, the temperature of the solvothermal reaction is 150~155°C and the time is 15~16 hours.

[0018] Furthermore, in step (2), the ultrasound time is 15-30 min.

[0019] Furthermore, in step (2), the soluble cobalt salt is Co(NO3)2·6H2O, CoCl2·6H2O or Co(CH3COO)2·4H2O.

[0020] Furthermore, in step (2), the molar ratio of 2-methylimidazole to soluble cobalt salt is 4:1-9:1; More preferably, the molar ratio of 2-methylimidazole to cobalt source is 8.05:1-8.15:1.

[0021] Furthermore, in step (2), the mass ratio of NH2-MIL-125 (Ti) to soluble cobalt salt is 1:1 to 1:5.

[0022] Furthermore, in step (2), the stirring time is 15 min to 40 min, and the precipitation aging time is 20 h to 24 h.

[0023] Furthermore, in step (3), the calcination conditions are to heat the air to 400℃~550℃ and calcination time is 2h~3h.

[0024] This invention provides a Co3O4 / TiO2@CN composite photocatalytic material, which is prepared by the above-described preparation method.

[0025] This invention provides an application of a Co3O4 / TiO2@CN composite photocatalytic material in the photocatalytic degradation of gaseous formaldehyde.

[0026] Compared with the prior art, the present invention has the following advantages: (1) The TiO2@CN prepared by the method of the present invention has a unique disc-shaped morphology, which increases its specific surface area, has good adsorption of formaldehyde, and enhances the photocatalytic reaction sites.

[0027] (2) The TiO2@CN prepared by the method of the present invention effectively shortens the band gap of the synthesized TiO2 by doping with C and N elements, thereby improving its absorption of visible light.

[0028] (3) In this invention, ZIF-67 is grown on the surface of NH2-MIL-125 (Ti) by in-situ growth method. After calcination, TiO2 and Co3O4 form a heterojunction, which promotes the separation efficiency of photogenerated charge and has good photocatalytic activity and a high degradation rate of formaldehyde.

[0029] (4) The preparation method of the present invention is simple to operate and has low cost. Attached Figure Description

[0030] Figure 1 The XRD patterns are of the ZIF-67 / NH2-MIL-125 (Ti) composites prepared in Examples 1-4 and the ZIF-67 and NH2-MIL-125 (Ti) of Comparative Example 1.

[0031] Figure 2 The images show the XRD patterns of Co3O4 / TiO2@CN-2 (CoTCN-2), Co3O4, and TCN prepared in Example 2 and Comparative Example 1.

[0032] Figure 3SEM images of ZIF-67, NH2-MIL-125 (Ti), ZIF-67 / NH2-MIL-125 (Ti)-1, ZIF-67 / NH2-MIL-125 (Ti)-2, ZIF-67 / NH2-MIL-125 (Ti)-3, ZIF-67 / NH2-MIL-125 (Ti)-4, Co3O4, TCN, and CoTCN-1, CoTCN-2, CoTCN-3, and CoTCN-4 prepared in Examples 1-4 and Comparative Example 1.

[0033] Figure 4 The graphs show the degradation effects of photocatalysts TiO2, TCN, Co3O4, CoTCN-1, CoTCN-2, CoTCN-3, and CoTCN-4 on gaseous formaldehyde in Examples 1-4 and Comparative Example 1.

[0034] Figure 5 The UV-Vis absorption spectra of TiO2, TCN, Co3O4, CoTCN-1, CoTCN-2, CoTCN-3, and CoTCN-4 in Examples 1-4 and Comparative Example 1 are shown. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Modifications or equivalent substitutions made by those skilled in the art based on their understanding of the technical solutions of this invention, without departing from the spirit and scope of the invention, should be covered within the protection scope of this invention. Unless otherwise stated, the raw materials and reagents used in the embodiments of this invention are conventionally purchased raw materials and reagents.

[0036] Example 1 A method for preparing a Co3O4 / TiO2@CN composite photocatalytic material includes the following steps: (1) Dissolve 0.66g of 2-aminoterephthalic acid in 30ml of a mixed solution of DMF and methanol with a volume ratio of 1:1. After stirring and dissolving, add 0.54mL of isopropyl titanate under rapid stirring and stir for 15min to obtain the precursor solution.

[0037] (2) The precursor solution was placed in a reactor for hydrothermal reaction at a temperature of 150°C for 15 hours. After the reaction, the solid was separated by centrifugation, washed three times with DMF and methanol respectively, dried, and ground to obtain NH2-MIL-125(Ti).

[0038] (3) Add 0.57g of NH2-MIL-125 (Ti) to 100mL of methanol and sonicate for 10min. Then add 1.43g of Co(NO3)2·6H2O and stir to dissolve to obtain solution A. Add 3.24g of 2-methylimidazole to 100mL of methanol and stir to dissolve to obtain solution B. Pour solution A into solution B under vigorous stirring and stir for 15min. After standing for 20h, centrifuge to separate the solid. Wash with methanol 3 times, dry and grind to obtain ZIF-67 / NH2-MIL-125 (Ti)-1 (Z / M-1) composite powder.

[0039] (4) The composite powder is heated to 400℃ in a muffle furnace and calcined for 2h (heating rate is 2℃ / min). After cooling to room temperature, Co3O4 / TiO2@CN-1 is obtained, which is called CoTCN-1.

[0040] Example 2 A method for preparing a Co3O4 / TiO2@CN composite photocatalytic material includes the following steps: (1) Dissolve 0.66g of 2-aminoterephthalic acid in 30ml of a mixed solution of DMF and methanol with a volume ratio of 1:1. After stirring and dissolving, add 0.54mL of isopropyl titanate under rapid stirring and stir for 15min to obtain the precursor solution.

[0041] (2) The precursor solution was placed in a reactor for hydrothermal reaction at a temperature of 150°C for 15 hours. After the reaction, the solid was separated by centrifugation, washed three times with DMF and methanol respectively, dried, and ground to obtain NH2-MIL-125(Ti).

[0042] (3) Add 0.86g of NH2-MIL-125 (Ti) to 100mL of methanol and sonicate for 10min. Then add 1.43g of Co(NO3)2·6H2O and stir to dissolve to obtain solution A. Add 3.24g of 2-methylimidazole to 100mL of methanol and stir to dissolve to obtain solution B. Pour solution A into solution B under vigorous stirring and stir for 15min. After standing for 20h, centrifuge to separate the solid. Wash with methanol 3 times, dry and grind to obtain ZIF-67 / NH2-MIL-125 (Ti)-2 (Z / M-2) composite powder.

[0043] (4) The composite powder is heated to 400℃ in a muffle furnace and calcined for 2 hours (heating rate is 2℃ / min). After cooling to room temperature, Co3O4 / TiO2@CN-2 is obtained, which is called CoTCN-2.

[0044] Example 3 A method for preparing a Co3O4 / TiO2@CN composite photocatalytic material includes the following steps: (1) Dissolve 0.66g of 2-aminoterephthalic acid in 30ml of a mixed solution of DMF and methanol with a volume ratio of 1:1. After stirring and dissolving, add 0.54mL of isopropyl titanate under rapid stirring and stir for 15min to obtain the precursor solution.

[0045] (2) The precursor solution was placed in a reactor for hydrothermal reaction at a temperature of 150°C for 15 hours. After the reaction, the solid was separated by centrifugation, washed three times with DMF and methanol respectively, dried, and ground to obtain NH2-MIL-125(Ti).

[0046] (3) Add 1.14g of NH2-MIL-125 (Ti) to 100mL of methanol and sonicate for 10min. Then add 1.43g of Co(NO3)2·6H2O and stir to dissolve to obtain solution A. Add 3.24g of 2-methylimidazole to 100mL of methanol and stir to dissolve to obtain solution B. Pour solution A into solution B under vigorous stirring and stir for 15min. After standing for 20h, centrifuge to separate the solid. Wash with methanol 3 times, dry and grind to obtain ZIF-67 / NH2-MIL-125 (Ti)-3 (Z / M-3) composite powder.

[0047] (4) The composite powder is heated to 400℃ in a muffle furnace and calcined for 2 hours (heating rate is 2℃ / min). After cooling to room temperature, Co3O4 / TiO2@CN-3 is obtained, which is called CoTCN-3.

[0048] Example 4 A method for preparing a Co3O4 / TiO2@CN composite photocatalytic material includes the following steps: (1) Dissolve 0.66g of 2-aminoterephthalic acid in 30ml of a mixed solution of DMF and methanol with a volume ratio of 1:1. After stirring and dissolving, add 0.54mL of isopropyl titanate under rapid stirring and stir for 15min to obtain the precursor solution.

[0049] (2) The precursor solution was placed in a reactor for hydrothermal reaction at a temperature of 150°C for 15 hours. After the reaction, the solid was separated by centrifugation, washed three times with DMF and methanol respectively, dried, and ground to obtain NH2-MIL-125(Ti).

[0050] (3) Add 1.43g of NH2-MIL-125 (Ti) to 100mL of methanol and sonicate for 10min. Then add 1.43g of Co(NO3)2·6H2O and stir to dissolve to obtain solution A. Add 3.24g of 2-methylimidazole to 100mL of methanol and stir to dissolve to obtain solution B. Pour solution A into solution B under vigorous stirring and stir for 15min. After standing for 20h, centrifuge to separate the solid. Wash with methanol 3 times, dry and grind to obtain ZIF-67 / NH2-MIL-125 (Ti)-4 (Z / M-4) composite powder.

[0051] (4) The composite powder is heated to 400℃ in a muffle furnace and calcined for 2 hours (heating rate is 2℃ / min). After cooling to room temperature, Co3O4 / TiO2@CN-4 is obtained, which is called CoTCN-4.

[0052] Comparative Example 1 A method for preparing a disc-shaped TiO2@CN photocatalytic material includes the following steps: (1) Dissolve 0.66g of 2-aminoterephthalic acid in 30ml of a mixed solution of DMF and methanol with a volume ratio of 1:1. After stirring and dissolving, add 0.54mL of isopropyl titanate under rapid stirring and stir for 15min to obtain the precursor solution.

[0053] (2) The precursor solution was placed in a reactor for hydrothermal reaction at a temperature of 150°C for 15 hours. After the reaction, the solid was separated by centrifugation, washed three times with DMF and methanol respectively, dried, and ground to obtain NH2-MIL-125(Ti).

[0054] (3) NH2-MIL-125 (Ti) is heated to 400℃ in a muffle furnace and calcined for 2h (heating rate is 2℃ / min). After cooling to room temperature, TiO2@CN can be obtained, which is called TCN.

[0055] Comparative Example 2 A method for preparing Co3O4 material includes the following steps: (1) Add 1.43g Co(NO3)2·6H2O to 100mL methanol, stir and dissolve to obtain solution A. Add 3.24g 2-methylimidazole to 100mL methanol, stir and dissolve to obtain solution B. Pour solution A into solution B under vigorous stirring, stir for 15min, let stand for 20h, centrifuge to separate the solid, wash with methanol 3 times, dry, grind to obtain ZIF-67 powder.

[0056] (2) Heat ZIF-67 powder to 400℃ in a muffle furnace for 2 hours (heating rate is 2℃ / min), and cool to room temperature to obtain Co3O4.

[0057] Performance testing 1. X-ray diffraction (XRD) test The composition and crystal structure of the sample were determined using a Cu-target Kα radiation source on a Bruker D8 Advance. The test results are shown in [Figure number missing]. Figure 1 .

[0058] like Figure 1 The XRD patterns of composite materials Z / M-1, Z / M-2, Z / M-3, Z / M-4, NH2-MIL-125 (Ti) and ZIF-67 are shown.

[0059] The characteristic peaks of NH2-MIL-125 and its composites Z / M-1, Z / M-2, Z / M-3, and Z / M-4 at 6.5°, 9.5°, 11.2°, 16.2°, and 17.3° correspond to the (101), (200), (211), (222), and (312) crystal planes of NH2-MIL-125, respectively. These peaks are consistent with the standard peaks of NH2–MIL-125 and show strong diffraction, indicating that NH2-MIL-125 has good crystallinity and high purity. Pure ZIF-67 and its composite materials Z / M-1, Z / M-2, Z / M-3, and Z / M-4 exhibit diffraction peaks at 7.3°, 10.3°, 12.7°, 14.6°, 16.3°, 17.9°, 22.1°, 24.5°, 26.6°, and 29.5°, respectively. These peaks correspond to the (011), (002), (112), (022), (013), (222), (114), (233), (134), and (044) crystal planes of ZIF-67. The peak values ​​decrease, and the Z / M-3 composite material has the lowest content and exhibits characteristic peaks belonging to ZIF-67, confirming the successful composite material formation.

[0060] like Figure 2The XRD patterns of the calcined composite materials CoTCN-2, Co3O4, and TiO2@CN are shown. The diffraction peaks of NH2-MIL-125(Ti)-derived TiO2 appear at 25.4°, 38.1°, 48.2°, 52.2°, and 62.9°, corresponding to the (101), (004), (200), (202), and (204) crystal planes of anatase TiO2 (PDF#97-009-2363), respectively. The diffraction peaks of ZIF-67-derived Co3O4 appeared at 19.0°, 31.3°, 36.9°, 38.6°, 44.8°, 55.7°, 59.4°, and 65.3°, corresponding to the (111), (220), (311), (222), (400), (422), (511), and (440) crystal planes of Co3O4 (PDF#97-003-6256), respectively. CoTCN-2 exhibited diffraction peaks of both Co3O4 and TiO2. The successful preparation of the composite material was verified by increasing the Co3O4 loading.

[0061] 2. Scanning electron microscopy (SEM) testing The microstructure of the samples was observed using a scanning electron microscope (SU8220), and the results are shown in [Figure number missing]. Figure 3 , Figure 3 In the above, (a), (c), (e), (g), (i), and (k) represent ZIF-67, NH2–MIL-125(Ti), Z / M-1, Z / M-2, Z / M-3, and Z / M-4, respectively. Figure 3 In the figure, (b), (d), (f), (h), (j), and (l) are Co3O4, TCN, CoTCN-1, CoTCN-2, CoTCN-3, and CoTCN-4 obtained by calcination, respectively.

[0062] Figure 3 In (a), the original ZIF-67 has a regular rhombic dodecahedral shape with a particle size of about 300 nm. The morphology of the Co3O4 obtained after calcination has changed significantly: the polyhedral structure of the original ZIF-67 has basically collapsed, and its originally regular porous framework structure has collapsed, eventually transforming into a spherical or irregular blocky Co3O4 particle aggregate with a rough surface and reduced porosity; some particles have slight depressions or cracks due to framework shrinkage, and there is a certain degree of agglomeration between particles. The overall morphology retains the general outline of the ZIF-67 precursor, but the crystal form and pore structure have been completely transformed. Figure 3 In (c), NH2-MIL125 (Ti) has a disc-like structure with an average diameter of approximately 1 μm. Figure 3(d) represents TCN obtained after calcination, which well retains the disc-shaped morphology of MOF, and its surface becomes rough, providing ample reaction sites and adsorption activity for the degradation reaction. Figure 3 It can be seen that ZIF-67 was grown on the NH2-MIL-125(Ti) surface through in-situ synthesis. With the increase of MOF content, the size and content of ZIF-67 grown on its surface decreased. The Co3O4 obtained after calcination was well dispersed and tightly contacted on the TCN surface, which is consistent with the XRD results.

[0063] 3. Photocatalytic formaldehyde degradation performance test CoTCN composite photocatalyst material was used for the degradation of gaseous formaldehyde. The application method was as follows: 0.15g of CoTCN composite photocatalyst material was evenly distributed in a petri dish, placed in a Tedlar gas bag, and 3μL of formaldehyde solution was injected. 4L of fresh air was then introduced, and the gas bag was placed in a 60℃ oven for 20 minutes to ensure complete vaporization. The entire degradation process was first carried out under dark conditions for 1.5 hours of dark adsorption. A xenon lamp equipped with a 420nm cutoff filter was used for photocatalytic reaction. 5mL of gas was collected from the gas bag every 30 minutes, and the formaldehyde concentration was detected using phenol reagent spectrophotometry. The formaldehyde removal rate was calculated using the following formula, indicating the formaldehyde degradation performance of the reaction catalyst material.

[0064] Removal efficiency(%)=(C0-C) / C0×100% Where C0 represents the concentration of gaseous pollutants at adsorption equilibrium, in ppm; C represents the concentration of gaseous pollutants at each sampling point, in ppm. Test results are shown in Table 1 and... Figure 4 .

[0065] As shown in Table 1, formaldehyde hardly degraded under blank conditions and under pure TiO2 conditions. The formaldehyde degradation rate of the TCN photocatalyst was 39% after 8 hours of illumination. This indicates that the MOF-derived TiO2@CN, due to the doping of C and N elements, effectively shortened the band gap of TiO2, improving its absorption of visible light and thus enhancing photocatalytic efficiency. After being combined with Co3O4, the formaldehyde degradation rate was significantly improved, with CoTCN-2 showing the best effect at 83%. This indicates that Co3O4 was attached to the surface of the disc-shaped TCN, forming a pn heterojunction at the contact surface, promoting the effective separation of photogenerated electrons and holes, and effectively improving photocatalytic efficiency. CoTCN-1 had a lower formaldehyde degradation rate compared to CoTCN-2 because of excessive Co3O4 attachment on its surface, which affected the adsorption of formaldehyde molecules on the composite material surface. With the decrease in the amount of Co3O4 attached, the degradation capacity of CoTCN-3 and CoTCN-4 gradually decreased.

[0066] Table 1

[0067] 4. Ultraviolet-vis diffuse reflectance spectra (UV-vis DRS) test UV-Vis diffuse reflectance spectroscopy was used to measure the catalyst's absorption capacity for light in different wavelengths within the UV-Vis range, and its band gap was calculated accordingly. A Hitachi U-3900 spectrophotometer was used to characterize the sample's absorption of UV and visible light using UV-Vis diffuse reflectance spectroscopy (with BaSO4 as the reflectance standard). The test results are shown below. Figure 5 .

[0068] Depend on Figure 5 As can be seen, compared with pure TiO2, MOF-derived TCN exhibits higher absorbance and a redshift, indicating that C and N doping enhances the absorption capacity of TCN for visible light. Non-metallic doping effectively broadens the absorption range of titanium dioxide for visible light, enhances absorption in the visible light region, and effectively shortens the band gap of titanium dioxide. The CoTCN series composites show high absorbance across the overall spectral band, indicating better photocatalytic activity; and the longer cutoff wavelength means it can absorb more visible light. The combination of TiO2 and Co3O4 broadens the absorption spectrum, increases visible light utilization, and improves photocatalytic efficiency. The absorbance of CoTCN-3 and CoTCN-4 in the ultraviolet band is slightly lower than that of CoTCN1-2, possibly due to the lower amount of Co3O4 on the surface. Figure 3 This can be verified.

[0069] Contents not described in detail in this specification are prior art known to those skilled in the art. Although specific embodiments of this invention have been described above, it should be understood that this invention is not limited to the scope of those embodiments. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this invention should be included within the scope of protection of the claims.

Claims

1. A method for preparing a Co3O4 / TiO2@CN composite photocatalytic material, characterized in that, Includes the following steps: (1) Dissolve the organic ligand in a solvent, add the titanium source, and stir to mix to obtain a precursor solution; The precursor solution underwent a hydrothermal reaction, and the solid was separated by centrifugation after the reaction. The solid was then washed, dried, and ground to obtain NH2-MIL-125 (Ti). (2) NH2-MIL-125 (Ti) was ultrasonically dispersed in methanol, and a soluble cobalt salt was added under stirring to obtain solution A; 2-methylimidazole was added to methanol to obtain solution B; solution A was poured into solution B under vigorous stirring, and the mixture was allowed to stand for aging reaction. After the reaction was completed, the solid was separated by centrifugation, washed, and dried to obtain ZIF-67 / NH2-MIL-125 (Ti) composite powder; (3) The ZIF-67 / NH2-MIL-125 (Ti) composite powder was calcined at high temperature and cooled to room temperature to obtain Co3O4 / TiO2@CN composite photocatalytic material.

2. The preparation method of the Co3O4 / TiO2@CN composite photocatalytic material according to claim 1, characterized in that, In step (1), the organic ligand is 2-aminoterephthalic acid; the titanium source is isopropyl titanate or tetrabutyl titanate; and the molar ratio of the organic ligand to the titanium source is 2:1-6:

1.

3. The preparation method of the Co3O4 / TiO2@CN composite photocatalytic material according to claim 1, characterized in that, In step (1), the solvent is a mixed solution of N,N-dimethylformamide and methanol, and the volume ratio of N,N-dimethylformamide to methanol is 1:1-9:

1.

4. The preparation method of the Co3O4 / TiO2@CN composite photocatalytic material according to claim 1, characterized in that, In step (1), the stirring time is 15-30 min; the temperature of the hydrothermal reaction is 150℃~180℃, and the time is 15h~24h.

5. The preparation method of the Co3O4 / TiO2@CN composite photocatalytic material according to claim 1, characterized in that, In step (2), the soluble cobalt salt is Co(NO3)2·6H2O, CoCl2·6H2O or Co(CH3COO)2·4H2O; the molar ratio of 2-methylimidazole to the soluble cobalt salt is 4:1-9:

1.

6. The preparation method of the Co3O4 / TiO2@CN composite photocatalytic material according to claim 1, characterized in that, In step (2), the mass ratio of NH2-MIL-125 (Ti) to soluble cobalt salt is 1:1 to 1:

5.

7. The preparation method of the Co3O4 / TiO2@CN composite photocatalytic material according to claim 1, characterized in that, In step (2), the stirring time is 15 min to 40 min, and the sedimentation aging time is 20 h to 24 h.

8. The preparation method of the Co3O4 / TiO2@CN composite photocatalytic material according to claim 1, characterized in that, In step (3), the calcination conditions are: heating in air to 400℃~550℃, and calcination time is 2h~3h.

9. The Co3O4 / TiO2@CN composite photocatalytic material prepared by the preparation method according to any one of claims 1-8.

10. The application of the Co3O4 / TiO2@CN composite photocatalytic material according to claim 9 in the photocatalytic degradation of gaseous formaldehyde.

Images