A porous nanocomposite Co / TiO2@CN catalyst and its preparation and application

Abstract

This invention belongs to the field of catalyst preparation technology and discloses a porous nanocomposite Co / TiO2@CN catalyst, its preparation, and application. The invention utilizes a MOFs epitaxial growth strategy to synthesize a ZIF-67@NH2-MIL-125 composite structure. Using this as a sacrificial template, a metal / titanium dioxide / carbon-nitrogen composite (Co / TiO2@CN) is further prepared through high-temperature pyrolysis. This method offers the advantages of a simple preparation process and low cost. The resulting composite material exhibits excellent photocatalytic activity, effectively addressing the low photocatalytic efficiency of single semiconductor materials.

Description

Technical Field

[0001] The present invention belongs to the technical field of catalyst preparation, and in particular relates to a porous nano-composite Co / TiO2@CN catalyst and its preparation and application. Background Art

[0002] Photocatalytic technology, due to its ability to completely degrade organic pollutants into harmless small molecules (such as CO2 and H2O) under illumination, shows great potential for application in dye wastewater treatment. Semiconductor photocatalytic materials are at the core of photocatalytic dye degradation. These materials possess a unique electronic structure that, when exposed to light, produces photogenerated electrons and holes. These active charge carriers participate in redox reactions, generating highly oxidizing active species (such as OH radicals and O2⁻ superoxides), thereby decomposing complex organic dyes into harmless small molecules. Therefore, semiconductor materials, due to their excellent photogenerated electron-hole generation capacity, chemical stability, and environmental friendliness, are ideal for photocatalytic dye degradation.

[0003] Titanium dioxide (TiO2), a typical photocatalytic material, has been widely used in environmental purification due to its excellent photocatalytic activity, chemical stability, non-toxicity, and low cost. However, TiO2's photoresponse range is primarily confined to the ultraviolet region (wavelength <387 nm), which accounts for only approximately 5% of the solar spectrum, significantly limiting its application under visible light. Furthermore, photogenerated electron-hole pairs in TiO2 readily recombine, further reducing its photocatalytic efficiency. To overcome these shortcomings, researchers have explored various approaches, such as metal ion doping, non-metallic doping, heterojunction construction, and noble metal deposition, to extend the photoresponse range of TiO2 and enhance its photocatalytic activity. Despite these improvements, TiO2-based composites still face challenges in terms of photoresponse range, suppression of photogenerated electron-hole recombination, and material stability.

[0004] Therefore, how to improve the photocatalytic performance of materials by optimizing the preparation method and how to achieve efficient degradation of dyes in actual environments are issues that need to be urgently addressed in current research. Summary of the Invention

[0005] In order to overcome the above-mentioned shortcomings and deficiencies of the prior art, the primary purpose of the present invention is to provide a method for preparing a porous nanocomposite Co / TiO2@CN catalyst.

[0006] This invention innovatively utilizes a MOFs epitaxial growth strategy to synthesize a ZIF-67@NH2-MIL-125 composite structure. Using this as a sacrificial template, a metal / titanium dioxide / carbon-nitrogen composite (Co / TiO2@CN) is further prepared through high-temperature pyrolysis. This technology offers the advantages of simple preparation and low cost. The composite material prepared by this method exhibits excellent photocatalytic activity, effectively addressing the low photocatalytic efficiency of single semiconductor materials.

[0007] Another object of the present invention is to provide a porous nanocomposite Co / TiO2@CN catalyst prepared by the above method.

[0008] Another object of the present invention is to provide the use of the above-mentioned porous nanocomposite Co / TiO2@CN catalyst in photocatalytic degradation of dyes.

[0009] The purpose of the present invention is achieved through the following solutions:

[0010] A method for preparing a nanocomposite Co / TiO2@CN catalyst comprises the following steps:

[0011] (1) 2-aminoterephthalic acid, titanium source, methanol and solvent are mixed uniformly, heated for reaction, washed and dried to obtain NH2-MIL-125 powder;

[0012] (2) Evenly mix NH2-MIL-125 powder, 2-methylimidazole, cobalt salt and solvent, stir to react, wash and dry to obtain ZIF-67@NH2-MIL-125 powder;

[0013] (3) Under an inert atmosphere, the ZIF-67@NH2-MIL-125 powder was pyrolyzed and cooled to obtain a nanocomposite Co / TiO2@CN catalyst.

[0014] The titanium source in step (1) is at least one of isopropyl titanate and tetra-n-butoxytitanium (Ti(OBu)4).

[0015] The solvent in step (1) is at least one of N,N-dimethylformamide (DMF) and dimethylacetamide (DMAc).

[0016] The molar ratio of the 2-aminoterephthalic acid to the titanium in the titanium source in step (1) is 1-4:1.

[0017] The molar ratio of 2-aminoterephthalic acid to methanol in step (1) is 1:100-200.

[0018] The volume ratio of the solvent to methanol in step (1) is 1-5:1.

[0019] The temperature of the heating reaction in step (1) is 120°C-180°C, preferably 150°C.

[0020] The heating reaction time in step (1) is 10-72 hours, preferably 15-24 hours.

[0021] The washing in step (1) is centrifugal washing, wherein the reagent for centrifugal washing is at least one of methanol, ethanol, and acetone.

[0022] The drying in step (1) and step (2) is performed by vacuum drying or oven drying; the drying temperature is 60° C.-120° C., and the drying time is 6-24 h.

[0023] The cobalt salt in step (2) is at least one of Co(NO3)2·6H2O, (CH3COO)2Co·6H2O, and CoCl2·6H2O.

[0024] The solvent in step (2) is at least one of methanol and water.

[0025] The amount of the solvent used in step (2) is such that the concentration of the cobalt salt in the mixed solution is 5-100 mM.

[0026] The mass ratio of the NH2-MIL-125 powder to 2-methylimidazole in step (2) is 1:5-10.

[0027] The molar ratio of cobalt to 2-methylimidazole in the cobalt salt in step (2) is 1:1-8.

[0028] The stirring reaction in step (2) is carried out at room temperature for 1-10 hours, preferably 2-4 hours.

[0029] The inert atmosphere in step (3) is argon or nitrogen, preferably nitrogen.

[0030] The heating rate of the pyrolysis in step (3) is 1-20°C / min, more preferably 10°C / min.

[0031] The pyrolysis temperature in step (3) is 600-900°C, preferably 700-800°C.

[0032] The holding time of the pyrolysis in step (3) is 1-10 hours, preferably 2 hours.

[0033] The cooling in step (3) is cooling to room temperature.

[0034] Nanocomposite Co / TiO2@CN catalyst prepared by the above method.

[0035] Application of the above-mentioned nanocomposite Co / TiO2@CN catalyst in photocatalytic degradation of dyes.

[0036] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0037] (1) The present invention provides a simple and efficient method for preparing a porous nanocomposite Co / TiO2@CN catalyst. This method can synthesize a catalyst with excellent performance through only basic operations such as solution mixing, stirring, and pyrolysis. The entire preparation process does not require complex equipment or the use of expensive precious metal materials, making it suitable for large-scale production and having significant economic advantages. In addition, the preparation process adheres to the principles of green environmental protection and meets the requirements of modern industry for sustainable development.

[0038] (2) The present invention utilizes MOF materials as precursors, so that the resulting catalyst has a porous structure, which provides abundant pores and channels, thereby improving the mass transfer capacity and obtaining excellent catalytic performance.

[0039] (3) During the catalyst preparation process of the present invention, Co and TiO2 form an effective heterojunction structure through thermal decomposition. This heterojunction can effectively promote the transfer of photogenerated electrons from TiO2 to Co, thereby reducing the recombination probability of electron-hole pairs, extending the lifetime of photogenerated carriers, and further improving the photocatalytic efficiency. At the same time, the presence of the heterojunction also improves the electron transmission path, reduces the loss during charge transfer, and makes the photocatalytic reaction more efficient. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 This is the scanning electron microscope (SEM) image of ZIF-67@NH2-MIL-125 in Example 1.

[0041] Figure 2 This is the scanning electron microscope (SEM) image of Co / TiO2@CN-700 in Example 1.

[0042] Figure 3 X-ray diffraction (XRD) patterns of the catalysts prepared in Example 1, Comparative Example 1 and Comparative Example 2.

[0043] Figure 4 This is a graph showing the photocatalytic reaction performance test results of the catalysts of Example 1, Comparative Example 1 and Comparative Example 2. DETAILED DESCRIPTION

[0044] The present invention will be described in further detail below with reference to the Examples and accompanying drawings, but the embodiments of the present invention are not limited thereto. Where specific conditions are not specified in the Examples, conventional conditions or conditions recommended by the manufacturer were followed. Reagents or instruments used, where the manufacturer is not specified, are commercially available conventional products.

[0045] Unless otherwise specified, all reagents used in the examples can be purchased from the market.

[0046] Example 1

[0047] (1) Preparation of NH2-MIL-125

[0048] 217 mg of 2-aminoterephthalic acid, 0.14 mL (0.47 mmol) of isopropyl titanate, 5 mL of N,N-dimethylformamide (DMF), and 5 mL (0.124 mol) of methanol were mixed and added to a reactor. Ultrasonication was then performed to uniformly disperse the mixture. The reactor was sealed and placed in an oven, heated to 150°C, and maintained at this temperature for 15 hours. After the reaction, the product was washed several times with methanol to remove unreacted products and then dried in an oven at 100°C for 10 hours to obtain NH2-MIL-125 nanocrystals. These crystals were regular discs with diameters of approximately 700-1000 nm.

[0049] (2) Preparation of ZIF-67@NH2-MIL-125

[0050] 4 mg of NH2-MIL-125 was placed in a round-bottom flask, 1 mL of methanol was added, and the mixture was uniformly dispersed by sonication. 30 mg of 2-methylimidazole and 52 mg of Co(NO3)2·6H2O were dissolved in 3 mL and 5 mL of methanol, respectively, and dispersed by sonication until uniform. Under continuous stirring, the two methanol solutions were slowly added dropwise to the NH2-MIL-125 suspension and allowed to react at room temperature for 4 h. After the reaction, the product was washed several times with methanol to remove unreacted products and impurities, and then dried in an oven at 100°C for 10 h to obtain ZIF-67@NH2-MIL-125 powder.

[0051] (3) Preparation of Co / TiO2@CN-700 materials

[0052] 50 mg of ZIF-67@NH2-MIL-125 powder was placed in a tube furnace and heated to 700°C at a rate of 10°C / min under nitrogen. The temperature was maintained for 2 hours for thermal decomposition. After the reaction, the furnace was cooled to room temperature and the Co / TiO2@CN-700 catalyst was collected.

[0053] The Co / TiO2@CN-700 catalyst was used in the photocatalytic degradation of dye (Rhodamine B). The specific reaction steps are as follows:

[0054] Weigh 15 mg of the Co / TiO2@CN-700 catalyst and add it to a beaker containing 50 mL of a rhodamine B solution (initial concentration 2.5 mg / L). Stir in the dark for 30 minutes to allow the catalyst and solution to reach adsorption equilibrium. Place the beaker under a xenon lamp for a 1-hour photocatalytic reaction. After the reaction, sample the solution and measure the absorbance of the rhodamine B at 554 nm using a UV-visible spectrophotometer. The degradation rate of the dye is calculated based on the change in absorbance.

[0055] The performance index of the obtained catalyst in the photocatalytic degradation reaction of Rhodamine B is: the degradation rate of Rhodamine B reaches 98.2%.

[0056] Example 2

[0057] The difference from Example 1 is that the amount of isopropyl titanate added in step (1) is 0.18 ml (0.60 mmol), and NH2-MIL-125 crystals with larger particle size are prepared, with a diameter of about 1.5-2.5 μm.

[0058] The performance index of the obtained catalyst in the photocatalytic degradation reaction of Rhodamine B is: the degradation rate of Rhodamine B reaches 93.1%.

[0059] Example 3

[0060] The difference from Example 1 is that the amount of isopropyl titanate added in step (1) is 0.10 ml (0.34 mmol), and NH2-MIL-125 crystals with smaller particle size are prepared, with a diameter of about 300-500 nm.

[0061] The performance index of the obtained catalyst in the photocatalytic degradation reaction of Rhodamine B is: the degradation rate of Rhodamine B reaches 88.7%.

[0062] Example 4

[0063] The difference from Example 1 is that in step (2), after adding 2-methylimidazole and Co(NO3)2·6H2O methanol solution and reacting at room temperature for 2 h, the surface of the obtained ZIF-67@NH2-MIL-125 exhibits an uneven structure, and ZIF-67 is less distributed on the surface of NH2-MIL-125.

[0064] The performance index of the obtained catalyst in the photocatalytic degradation reaction of Rhodamine B is: the degradation rate of Rhodamine B reaches 70.3%.

[0065] Example 5

[0066] The difference from Example 1 is that in step (3), 50 mg of ZIF-67@NH2-MIL-125 powder was placed in a tube furnace, heated to 800°C at a heating rate of 10°C / min under a nitrogen atmosphere, and maintained at this temperature for pyrolysis for 2 h to produce a Co / TiO2@CN-800 catalyst. The Co / TiO2@CN-800 material prepared at this pyrolysis temperature had a significantly increased particle size of the Co nanoparticles on its surface.

[0067] The performance index of the obtained catalyst in the photocatalytic degradation of Rhodamine B is: the degradation rate of Rhodamine B is 97.8%.

[0068] Example 6

[0069] Weigh 15 mg of the Co / TiO2@CN-700 catalyst prepared in Example 1 and add it to a beaker containing 50 mL of a rhodamine B solution (initial concentration 5 mg / L). Stir in the dark for 30 minutes to allow the catalyst and solution to reach adsorption equilibrium. Place the beaker under a xenon lamp for a 1-hour photocatalytic reaction. After the reaction, sample the solution and measure the absorbance of the rhodamine B at 554 nm using a UV-visible spectrophotometer. Calculate the dye degradation rate based on the change in absorbance.

[0070] The performance index of the obtained catalyst in the photocatalytic degradation of Rhodamine B is: the degradation rate of Rhodamine B reaches 60.3%.

[0071] Comparative Example 1

[0072] The difference from Example 1 is that the Co@CN catalyst is prepared by pyrolysis of ZIF-67. The specific steps are as follows:

[0073] (1) Preparation of ZIF-67

[0074] Dissolve 30 mg of 2-methylimidazole and 52 mg of cobalt nitrate hexahydrate in 3 mL and 5 mL of methanol, respectively. Add the 2-methylimidazole methanol solution to the cobalt nitrate hexahydrate methanol solution under stirring, mix thoroughly, and allow to react for 24 hours. After completion of the reaction, centrifuge to obtain ZIF-67 crystals.

[0075] (2) Preparation of Co@CN catalyst

[0076] 50 mg of ZIF-67 powder was placed in a tube furnace and heated to 700°C at 10°C / min under nitrogen. This temperature was maintained for 2 hours. After the furnace temperature naturally cooled to room temperature, the Co@CN catalyst was collected.

[0077] The performance index of the obtained catalyst in the photocatalytic degradation reaction of Rhodamine B is: the degradation rate of Rhodamine B is 11.3%.

[0078] Comparative Example 2

[0079] The difference from Example 1 is that the TiO2@CN catalyst is prepared directly by pyrolysis of NH2-MIL-125. The specific steps are as follows:

[0080] (1) Preparation of NH2-MIL-125

[0081] 217 mg of 2-aminoterephthalic acid, 0.14 mL of isopropyl titanate, 5 mL of N,N-dimethylformamide (DMF), and 5 mL of methanol were mixed and added to a reactor. Ultrasonication was then performed to uniformly disperse the mixture. The reactor was sealed and placed in an oven, heated to 150°C, and maintained at this temperature for 15 hours. After the reaction, the product was washed several times with methanol to remove unreacted products and then dried in an oven at 100°C for 10 hours to obtain NH2-MIL-125 powder.

[0082] (2) Preparation of Co / TiO2@CN catalyst

[0083] 50 mg of NH2-MIL-125 powder was placed in a tube furnace and heated to 700°C at a rate of 10°C / min under nitrogen. This temperature was maintained for 2 hours. After the furnace temperature naturally cooled to room temperature, the TiO2@CN catalyst was collected.

[0084] The performance index of the obtained catalyst in the photocatalytic degradation reaction of Rhodamine B is: the degradation rate of Rhodamine B is 93.2%.

[0085] Analysis of attached figures:

[0086] Figure 1 This is a scanning electron microscope (SEM) image of ZIF-67@NH2-MIL-125, which shows that the material is disc-shaped as a whole and the surface is evenly covered with ZIF-67 particles.

[0087] Figure 2 This is the SEM image of Co / TiO2@CN-700 obtained in Example 1. The image shows that the material still has a disc-shaped structure after pyrolysis, and the surface is evenly covered with Co particles.

[0088] Figure 3The X-ray diffraction (XRD) spectrum shows that Co@CN has diffraction peaks at 44.2°, 51.5°, and 75.8°, corresponding to the (111), (200), and (220) crystal planes of face-centered cubic Co. TiO2@CN has diffraction peaks at 27.4°, 36.1°, 41.2°, and 54.3°, corresponding to the (110), (101), (111), and (211) crystal planes of rutile phase TiO2. Co / TiO2@CN-700 also has diffraction peaks at the above positions. This indicates that a composite structure in which Co and TiO2 crystal phases coexist has been formed, and Co and TiO2 particles are evenly distributed in the carbon nitrogen (CN) carrier.

[0089] Figure 4 The results of the photocatalytic performance test of the catalysts are shown in the figure. As shown in the figure, the Co@CN and TiO2@CN catalysts have low activity, with Rhodamine B degradation rates of 11.3% and 93.2%, respectively, after one hour of reaction. However, the Co / TiO2@CN-700 catalyst, a composite of Co and TiO2, has enhanced activity, with a Rhodamine B degradation rate of 98.9% after one hour of reaction. This shows that the Co / TiO2@CN catalyst of the present invention exhibits superior performance in the photocatalytic degradation of dyes.

[0090] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be considered as equivalent replacement methods and are included in the scope of protection of the present invention.

Claims

1. A method for preparing a nanocomposite Co / TiO2@CN catalyst, characterized in that: The following steps are involved: (1) 2-aminoterephthalic acid, titanium source, methanol and solvent are mixed uniformly, heated for reaction, washed and dried to obtain NH2-MIL-125 powder; (2) Evenly mix NH2-MIL-125 powder, 2-methylimidazole, cobalt salt and solvent, stir to react, wash and dry to obtain ZIF-67@NH2-MIL-125 powder; (3) Under an inert atmosphere, the ZIF-67@NH2-MIL-125 powder was pyrolyzed and cooled to obtain a nanocomposite Co / TiO2@CN catalyst; The molar ratio of 2-aminoterephthalic acid to methanol in step (1) is 1:100-200; The mass ratio of the NH2-MIL-125 powder to 2-methylimidazole in step (2) is 1:5-10; The pyrolysis temperature in step (3) is 700-800°C; the pyrolysis holding time is 1-10h.

2. The method for preparing the nanocomposite Co / TiO2@CN catalyst according to claim 1, characterized in that: The titanium source in step (1) is at least one of isopropyl titanate and tetra-n-butoxy titanium; The solvent in step (1) is at least one of N,N-dimethylformamide and dimethylacetamide.

3. The method for preparing the nanocomposite Co / TiO2@CN catalyst according to claim 1, characterized in that: The molar ratio of the 2-aminoterephthalic acid to the titanium in the titanium source in step (1) is 1-4:1; The volume ratio of the solvent to methanol in step (1) is 1-5:

1.

4. The method for preparing the nanocomposite Co / TiO2@CN catalyst according to claim 1, characterized in that: The temperature of the heating reaction in step (1) is 120°C-180°C; The heating reaction time in step (1) is 10-72 hours; The drying in step (1) and step (2) is performed by vacuum drying or oven drying; the drying temperature is 60° C.-120° C., and the drying time is 6-24 h.

5. The method for preparing the nanocomposite Co / TiO2@CN catalyst according to claim 1, characterized in that: The cobalt salt in step (2) is at least one of Co(NO3)2·6H2O, (CH3COO)2Co·6H2O, and CoCl2·6H2O; The solvent in step (2) is at least one of methanol and water.

6. The method for preparing the nanocomposite Co / TiO2@CN catalyst according to claim 1, characterized in that: The amount of the solvent in step (2) is such that the concentration of the cobalt salt in the mixed solution is 5-100 mM; The molar ratio of cobalt to 2-methylimidazole in the cobalt salt in step (2) is 1:1-8.

7. The method for preparing the nanocomposite Co / TiO2@CN catalyst according to claim 1, characterized in that: The stirring reaction in step (2) is carried out at room temperature for 1-10 hours.

8. The method for preparing the nanocomposite Co / TiO2@CN catalyst according to claim 1, characterized in that: The inert atmosphere in step (3) is argon or nitrogen; The heating rate of the pyrolysis in step (3) is 1-20°C / min.

9. A nanocomposite Co / TiO2@CN catalyst prepared by the method according to any one of claims 1 to 8.

10. Use of the nanocomposite Co / TiO2@CN catalyst according to claim 9 in the photocatalytic degradation of Rhodamine B.

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