A MOF-confined noble metal composite material, its preparation method and application

Abstract

The present invention discloses a MOF-confined noble metal composite material, a preparation method thereof and an application thereof. In this preparation method, a zirconium salt and / or a hafnium salt are dispersed in a mixed solvent of N,N-dimethylformamide and ethanol to obtain a metal salt solution; a noble metal precursor powder is dispersed in ethanol to obtain a noble metal precursor solution; then the metal salt solution and the noble metal solution are uniformly mixed, a monobasic organic acid and 2-aminoterephthalic acid are added, and after stirring and reacting, the MOF-confined noble metal material is obtained. The catalyst preparation reaction of the present invention has mild conditions, a simple process and a high yield, is suitable for efficiently catalytically purifying formaldehyde pollutants in air at normal temperature, and has broad application prospects.

Description

Technical Field

[0001] The present invention belongs to the technical field of the development of MOF nano-catalysts, and relates to a MOF-confined noble metal composite material, a preparation method thereof and an application thereof. Background Art

[0002] Formaldehyde in the air is one of the typical toxic gaseous pollutants, which is widely sourced from primary emissions such as home building materials, decoration materials, daily necessities, etc., as well as secondary reactions of volatile organic compounds generated by combustion activities such as cooking and smoking with strong oxidants such as ozone. Its release period is as long as three to five years, and it has the risk of causing diseases such as nasopharyngeal carcinoma and leukemia. Severe formaldehyde pollution has become an important current public environmental health problem, accelerating the urgent need for powerful formaldehyde removal agents.

[0003] The room-temperature catalytic formaldehyde remover can in-situ activate O2 in the air, spontaneously generate reactive oxygen species to catalytically convert formaldehyde into CO2, and is applicable to the treatment of formaldehyde in indoor low-light or non-illuminated environments. Metal-organic frameworks (MOFs) are porous compounds formed by the coordination of metal ions / ion clusters with organic ligands. They have a large specific surface area, flexible structures, and adjustable metal valence states, and have become a class of potential formaldehyde-removing catalysts. However, at present, most single MOFs have poor charge transfer ability due to the change of their own metal ion valence states, resulting in low oxygen activation ability, and can only show good formaldehyde-removing performance in static tests ("Synergetic Molecular Oxygen Activation and Catalytic Oxidation of Formaldehyde over Defective MIL-88B(Fe) Nanorods at Room Temperature", Shuping Zhang, Yifan Zhuo, Chizoba I. Ezugwu, Chong-chen Wang, Chuanhao Li, Shengwei Liu, Environ. Sci. Technol., Vol. 55, No. 12, pp. 8341-8350, June 2021), or act as formaldehyde adsorbents (Patent CN201711091658.8), and cannot achieve the complete removal of formaldehyde. MOFs can be used as carriers to load noble metals, providing more metal sites for oxygen activation and promoting the catalytic oxidation of formaldehyde. In addition, the current preparation technology of MOF-supported noble metals is complex, usually requiring a complex two-step method, that is, after preparing the MOF material, the noble metal is loaded by sodium borohydride or hydrogen reduction method ("Synergetic modulation of molecular oxygen activation and surface acidity / basicity on defective M / UiO-66m (M=Pt, Pd) for advanced oxidation of gaseous formaldehyde at room temperature", Yifan Zhuo, Xiuling Guo, Wei Cai, Tao Shao, Dehua Xia, Chuanhao Li, Shengwei Liu, Appl. Catal. B-Environ Energy., Vol. 333, No. 15, pp. 122789-122801, September 2023; Patent CN201911370310.1). Summary of the Invention

[0004] In view of the problems existing in the prior art, the present invention provides a MOF-confined noble metal composite material, a preparation method and an application thereof, so as to solve the technical problem that the oxygen activation ability of MOF in the prior art is relatively low and the complete removal of formaldehyde cannot be achieved, and at the same time solve the technical problem that the preparation technology of MOF loaded with noble metals in the prior art is complicated.

[0005] The present invention is realized through the following technical solutions:

[0006] A preparation method of a MOF-confined noble metal composite material includes the following steps:

[0007] S1: Dispersing zirconium salt and / or hafnium salt in a mixed solvent of N,N-dimethylformamide and ethanol to obtain a metal salt solution; the ratio of the zirconium salt and / or hafnium salt to the mixed solvent of N,N-dimethylformamide and ethanol is (0.5~1.6) g:50 mL; dispersing noble metal precursor powder in ethanol to obtain a noble metal precursor solution;

[0008] S2: Mixing the metal salt solution and the noble metal solution evenly, wherein the mass ratio of the metal salt to the noble metal precursor is (0.5~1.6) g:(3~12) mg, then adding a monobasic organic acid and 2-aminoterephthalic acid, and after stirring and reacting, obtaining the MOF-confined noble metal material.

[0009] Preferably, in the mixed solvent of N,N-dimethylformamide and ethanol, the volume ratio of N,N-dimethylformamide to ethanol is 1:(5~1); the zirconium salt is any one of zirconium tetrachloride, zirconium nitrate and zirconyl nitrate; the hafnium salt is hafnium tetrachloride or hafnium oxynitrate; the concentration of the metal salt solution is 0.04~0.1 mol / L.

[0010] Preferably, the noble metal precursor is any one of chloroplatinic acid, chloroiridic acid and sodium chloropalladate; the concentration of the noble metal precursor solution is 0.12~0.48 mg / mL.

[0011] Preferably, when dispersing zirconium salt and hafnium salt in the mixed solvent of N,N-dimethylformamide and ethanol, the molar ratio of the zirconium salt to the hafnium salt is (0.8~0.2):(0.2~0.8).

[0012] Preferably, the monobasic organic acid is any one of formic acid, glacial acetic acid and propionic acid, and the volume ratio of the monobasic organic acid to the mixed solvent of N,N-dimethylformamide and ethanol in step S1 is (3~8):(20~50); the concentration of 2-aminoterephthalic acid is the same as the molar concentration of the metal salt solution.

[0013] Preferably, in step S2, the temperature of the stirring reaction is 120~140 °C and the time is 5~12 h.

[0014] Preferably, in step S2, after the stirring reaction, it further includes centrifugally washing the product and drying it at 100-160 °C for 12-20 h to obtain the MOF-confined noble metal material.

[0015] A MOF-confined noble metal composite material is prepared by the above method; the particle size of the noble metal in the composite material is 2-3 nm.

[0016] Application of the above-mentioned MOF-confined noble metal composite material in the field of formaldehyde purification.

[0017] Compared with the prior art, the present invention has the following beneficial technical effects:

[0018] The present invention discloses a preparation method of a MOF-confined noble metal composite material. This method selects zirconium salt or hafnium salt (or a mixture of both), disperses it in a mixed solvent composed of N,N-dimethylformamide (DMF) and ethanol. On the one hand, DMF serves as a solvent to dissolve zirconium salt or hafnium salt, and on the other hand, it can act as a noble metal reducing agent. Ethanol reduces the overall viscosity of the solvent and improves volatility, saving costs. This solvent combination helps the uniform dispersion of metal salts, providing a good basis for subsequent reactions. And the noble metal precursor powder is dispersed in ethanol to form a uniform solution. This step is the key to ensuring the uniform distribution of noble metals in the MOF structure. Then the metal salt solution and the noble metal precursor solution are mixed, and then a monobasic organic acid is added as a regulator and 2-aminoterephthalic acid is added as a ligand. The introduction of the monobasic organic acid not only helps to adjust the reaction environment to make the pH value between 3 and 5, but also can produce a competitive coordination effect with 2-aminoterephthalic acid, thereby introducing defects in the MOF structure. Because the monobasic organic acid contains one carboxyl group and 2-aminoterephthalic acid contains two carboxyl groups, defects can be formed during the coordination process to improve the catalytic performance. This method in-situ uses DMF to replace the Pt of chloroplatinic acid 4+ with the six-coordinate configuration of Cl - to form Pt(CO)2Cl2, and Pt 2+ can be coordinated with the -NH2 of 2-aminoterephthalic acid and atomized, and Pt 0It is further reduced by DMF and aggregated into nanoparticles, thus avoiding the subsequent secondary reduction process, and the preparation process is simple. In addition, through the competitive coordination of organic acids and ligands, defects are introduced into the MOF structure, and these defects can confine metal sites and improve the performance of the catalyst. In addition, during the formation of MOF, the in-situ generation and confinement of noble metal nanoparticles are realized, avoiding the subsequent complex loading process, and improving the stability and activity of the catalyst. By utilizing the high specific surface area and pore structure of MOF and combining with the catalytic activity of noble metals, the efficient adsorption and catalytic conversion of formaldehyde are achieved. At the same time, the in-situ confinement of the in-situ reduced noble metals by MOF is realized, avoiding the aggregation of noble metals during the conventional reduction process and affecting the catalytic performance of noble metals. This method has a simple process and a reasonable design. By using MOF, the in-situ confinement of noble metals is realized, avoiding the aggregation of noble metals during the conventional reduction process, and effectively improving the adsorption and catalytic performance of the material for formaldehyde.

[0019] Furthermore, another inventive point of the present invention lies in dispersing zirconium salts and / or hafnium salts in a mixed solvent of N,N-dimethylformamide and ethanol, where the volume ratio of DMF to ethanol is 1:(5 - 1); the concentration of the metal salt solution is 0.04 - 0.1 mol / L. DMF is a strongly polar solvent and has good solubility for many inorganic salts and organic compounds, while ethanol is a relatively mild solvent. The addition of ethanol can reduce the toxicity of the entire solvent system and improve the volatility of the solvent, which is beneficial for subsequent treatment. The combined use of the two can integrate the advantages of both, ensuring the full dissolution of the solute and improving the properties of the solvent. The volume ratio of 1:(5 - 1), the design of this ratio range makes the solvent system neither too viscous (too high a proportion of DMF leads to an increase in solution viscosity, which is not conducive to the diffusion and mixing of reactants), nor too diluted (too high a proportion of ethanol may reduce the solubility of the solute). The appropriate ratio helps to form a homogeneous solution and promote the progress of the reaction. The concentration of the metal salt solution is 0.04 - 0.1 mol / L. Too low a concentration leads to too slow a reaction rate and affects production efficiency, while too high a concentration increases the viscosity of the solution and even causes the solute to precipitate, which is not conducive to the uniform progress of the reaction. The appropriate concentration range can ensure that the reaction proceeds at a relatively fast rate while ensuring the quality and purity of the product. The mixed solvent of DMF and ethanol and the appropriate concentration setting help to uniformly disperse the metal salts and noble metal precursors, thereby increasing the contact opportunities between the reactants and accelerating the reaction process. The homogeneous solution system helps to form homogeneous MOF crystals and noble metal nanoparticles, avoiding the quality differences of the products caused by uneven distribution of the reactants.

[0020] Furthermore, another inventive point of the present invention lies in that the concentration of the noble metal precursor solution is 0.12 - 0.48 mg / mL. By precisely adjusting the concentration of the noble metal precursor solution, precise control of the noble metal loading amount in the MOF material can be achieved, which is crucial for optimizing the performance of the catalyst because the noble metal loading amount directly affects its catalytic activity and selectivity. Within an appropriate concentration range, the noble metal precursor can be more effectively dispersed in the solvent, and thus can be more uniformly embedded into the MOF structure during the subsequent reaction process. This avoids the agglomeration of the noble metal and improves the utilization rate of the noble metal. The catalytic performance of the noble metal is closely related to its particle size, dispersion degree, and interaction with the carrier. By controlling the concentration of the noble metal precursor solution, the particle size and dispersion degree of the noble metal nanoparticles can be indirectly regulated, thereby optimizing the catalytic performance of the catalyst. Smaller particle size and uniform dispersion degree generally mean higher catalytic activity and better stability. Within an appropriate concentration range, the noble metal precursor solution can be more easily mixed uniformly with the metal salt solution, simplifying the preparation process. In addition, due to the moderate concentration, precipitation or stratification phenomena are not likely to occur during the reaction process, which is beneficial to the formation of a uniform MOF-confined noble metal material.

[0021] Furthermore, another inventive point of the present invention lies in that when the zirconium salt and hafnium salt are dispersed in a mixed solvent of N,N-dimethylformamide and ethanol, the molar ratio of the zirconium salt to the hafnium salt is (0.8 - 0.2):(0.2 - 0.8). Zirconium and hafnium, as metal centers, play different roles in the MOF structure. By adjusting the molar ratio of the two, properties such as the pore size, specific surface area, stability, and catalytic activity of the MOF material can be regulated. This regulation helps to optimize the catalytic effect of the catalyst for formaldehyde purification. Zirconium and hafnium produce a synergistic effect during the catalytic process, that is, the catalytic effect when the two act together is better than that of a single metal. By adjusting the molar ratio, the optimal synergistic effect point can be found, enabling further improvement of the catalyst performance. At the same time, the addition of hafnium can improve the thermal stability and chemical stability of the MOF material. Therefore, by adjusting the molar ratio of zirconium and hafnium, while maintaining the catalytic activity, the stability and service life of the catalyst can be improved. When the noble metal precursor solution is mixed with the metal salt solution, different ratios of zirconium and hafnium will affect the distribution and particle size of the noble metal nanoparticles in the MOF structure. By optimizing the molar ratio, uniform distribution and particle size control of the noble metal nanoparticles can be achieved, thereby improving the catalytic activity and selectivity of the catalyst.

[0022] Furthermore, another inventive point of the present invention lies in that the zirconium salt is any one of zirconium tetrachloride, zirconium nitrate and zirconyl nitrate; the hafnium salt is hafnium tetrachloride or hafnium oxynitrate; the noble metal precursor is any one of chloroplatinic acid, chloroiridic acid and sodium chloropalladate. These selected salts and precursors are common and easily obtainable chemicals in the market, which helps to reduce the procurement difficulty and cost of raw materials, and is also beneficial to the industrial production of the catalyst. These salts and precursors have good solubility in a mixed solvent of N,N-dimethylformamide (DMF) and ethanol, and can form a homogeneous solution. In addition, they also have high reaction activity and can undergo a coordination reaction with ligands (such as 2-aminoterephthalic acid) under appropriate conditions to form a stable MOF structure. Different zirconium salts, hafnium salts and noble metal precursors have different catalytic performances and selectivities. By selecting specific salts and precursors, precise regulation of the catalyst performance can be achieved. Noble metal precursors such as chloroplatinic acid, chloroiridic acid and sodium chloropalladate can be in-situ reduced to form noble metal nanoparticles during the reaction and be uniformly embedded in the MOF structure. This in-situ confinement method not only simplifies the preparation process, but also helps to improve the utilization rate of noble metals and the stability of the catalyst.

[0023] Furthermore, another inventive point of the present invention lies in that the monobasic organic acid is any one of formic acid, glacial acetic acid and propionic acid; the volume ratio of the monobasic organic acid to the mixed solvent of N,N-dimethylformamide and ethanol in step S1 is (3-8):(20-50); the concentration of 2-aminoterephthalic acid is the same as the molar concentration of the metal salt solution. The addition of the monobasic organic acid is used to adjust the pH value of the reaction system on the one hand. During the synthesis of MOF, the pH value is a key parameter, which affects the coordination reaction rate between the ligand and the metal ion and the structure of the product. By selecting the appropriate monobasic organic acid and its dosage, the pH value of the reaction system can be precisely controlled, thereby optimizing the crystal structure and performance of MOF. In addition, the carboxyl group in the monobasic organic acid can coordinate with the metal ion, and this coordination helps the dispersion and stabilization of the metal ion in the solution, thereby promoting the progress of the coordination reaction. In addition, the organic acid can also be used as a template or structure-directing agent to guide the growth of MOF crystals and form MOF materials with specific structures and properties. By controlling the concentration of 2-aminoterephthalic acid to be the same as the concentration of the metal salt solution, the molar ratio between the ligand and the metal ion can be ensured to be close to the ideal value, which is conducive to the formation of MOF materials with complete structures and excellent properties. The addition of the monobasic organic acid and the precise control of the ligand dosage help to optimize the properties such as the pore size, specific surface area and catalytic activity of the MOF material. The improvement of these properties helps to enhance the catalytic effect of the catalyst on a specific reaction, increase the reaction rate and conversion rate, and reduce the generation of by-products at the same time. By optimizing the structure and performance of the MOF material, the stability and service life of the catalyst can also be improved. A stable catalyst structure helps to reduce the inactivation and degradation of the catalyst during the reaction, thereby maintaining long-term catalytic activity.

[0024] Furthermore, another inventive aspect of the present invention lies in that in step S2, the temperature of the stirring reaction is 120-140 °C and the time is 5-12 h. At a relatively high temperature, the molecular motion intensifies, and the collision frequency between metal ions and ligands (such as 2-aminoterephthalic acid) increases, thereby promoting the coordination reaction between them. This coordination reaction is a key step in forming the MOF structure. Therefore, increasing the temperature helps to accelerate the reaction rate and shorten the reaction time. An appropriate temperature range is conducive to forming an MOF material with a regular crystal structure and good performance. Excessively high temperature leads to the destruction of the crystal structure or the formation of unstable phases, while excessively low temperature makes the reaction rate too slow to form a complete crystal structure. Therefore, the temperature range of 120-140 °C is a relatively optimized choice. In addition, the noble metal precursor is reduced to metal nanoparticles during the reaction and embedded in the MOF structure. Temperature is crucial. High temperature helps to promote the reduction reaction and ensure the uniform distribution and stable existence of noble metal nanoparticles in the MOF structure. The optimized MOF structure and the distribution of noble metal nanoparticles can significantly improve the catalytic performance of the catalyst. This improvement in performance may be manifested as higher catalytic activity, better selectivity, and longer service life.

[0025] Furthermore, another inventive aspect of the present invention lies in that after the stirring reaction, it further includes centrifugally washing the product and drying it at 100-160 °C for 12-20 h to obtain the MOF-confined noble metal material. Centrifugal washing is an effective method to remove unreacted raw materials, solvents, by-products, and other impurities in the product. These impurities will affect the purity and performance of the MOF material. Therefore, washing can significantly improve the quality of the product. During the washing process, the crystal structure of the MOF can be further stabilized, and factors that may damage or affect the stability of the MOF can be removed. At the same time, washing also helps to remove excess ligands or solvent molecules adsorbed on the surface of the MOF, making the pores of the MOF more unobstructed, which is beneficial for subsequent applications. During the drying process, residual solvent molecules in the product can be completely removed through high-temperature treatment. If these solvent molecules remain in the MOF, they may affect its stability and catalytic performance. Therefore, drying is an important step in preparing high-quality MOF materials. Appropriate drying temperature and time help to enhance the thermal stability and chemical stability of the MOF material. High-temperature treatment can promote the further solidification of the MOF crystal structure, making it more stable, which is of great significance for the long-term use and storage of the catalyst. Brief Description of the Drawings

[0026] To more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the attached drawings required for the embodiments. It should be understood that the following attached drawings only show some embodiments of the present invention, and thus should not be regarded as a limitation of the scope. For those of ordinary skill in the art, without creative efforts, other related attached drawings can also be obtained based on these attached drawings.

[0027] Figure 1 XRD spectra of Pt@Zr-MOF prepared in Example 1 of the present invention and Pt@ZH-MOF prepared in Example 2.

[0028] Figure 2 SEM image of Pt@Zr-MOF prepared in Example 1 of the present invention;

[0029] Figure 3 HADDF-STEM of Pt@Zr-MOF prepared in Example 1 of the present invention;

[0030] Figure 4 ESR detection of superoxide radical generation diagrams of Pt@Zr-MOF prepared in Example 1 of the present invention and Pt@ZH-MOF prepared in Example 2;

[0031] Figure 5 Room-temperature catalytic formaldehyde removal performance of Pt@Zr-MOF prepared in Example 1 of the present invention, where (A) is the formaldehyde removal rate and (B) is the carbon dioxide production;

[0032] Figure 6 Room-temperature catalytic formaldehyde removal performance of Pt@ZH-MOF-3 prepared in Example 3 of the present invention, where (A) is the formaldehyde removal rate and (B) is the carbon dioxide production;

[0033] Figure 7 Room-temperature catalytic formaldehyde removal performance of Ir@ZH-MOF prepared in Example 4 of the present invention, where (A) is the formaldehyde removal rate and (B) is the carbon dioxide production;

[0034] Figure 8 Room-temperature catalytic formaldehyde removal performance of Pd@ZH-MOF prepared in Example 5 of the present invention, where (A) is the formaldehyde removal rate and (B) is the carbon dioxide production;

[0035] Figure 9 Room-temperature catalytic formaldehyde removal performance of Pt@Hf-MOF prepared in Example 6 of the present invention, where (A) is the formaldehyde removal rate and (B) is the carbon dioxide production;

[0036] Figure 10For the performance of the Ir@Zr-MOF prepared in Example 7 of the present invention for catalytic formaldehyde removal at room temperature, where (A) is the formaldehyde removal rate and (B) is the carbon dioxide production amount. Detailed implementation manners

[0037] To enable those skilled in the art to understand the features and effects of the present invention, the following provides a general description and definition of the terms and expressions mentioned in the specification and claims. Unless otherwise specified, all technical and scientific terms used herein shall have the ordinary meaning understood by those skilled in the art for the present invention. In case of conflict, the definition in this specification shall prevail.

[0038] The theories or mechanisms described and disclosed herein, whether correct or incorrect, shall not limit the scope of the present invention in any way, that is, the content of the present invention can be implemented without being limited by any specific theory or mechanism.

[0039] In this article, all features defined in the form of numerical ranges or percentage ranges, such as numerical values, quantities, contents, and concentrations, are only for the sake of simplicity and convenience. Accordingly, the description of numerical ranges or percentage ranges should be regarded as having covered and specifically disclosed all possible sub-ranges and individual numerical values within the ranges (including integers and fractions).

[0040] In this article, unless otherwise specified, "comprising", "including", "containing", "having" or similar expressions cover the meanings of "consisting of" and "mainly consisting of". For example, "A comprises a" covers the meanings of "A comprises a and others" and "A only comprises a".

[0041] In this article, for the sake of concise description, all possible combinations of all technical features in each embodiment or example are not described. Therefore, as long as there is no contradiction in the combination of these technical features, the technical features in each embodiment or example can be combined arbitrarily, and all possible combinations should be considered as the scope described in this specification.

[0042] The present invention provides a preparation method of a MOF-confined noble metal composite at room temperature, comprising the following steps:

[0043] (1) Disperse metal zirconium salt and / or hafnium salt in a mixed solvent of N,N-dimethylformamide (DMF) and ethanol with a volume ratio of 1:(5~1) to obtain a metal salt solution with a concentration of 0.04~0.1 mol / L; wherein, the ratio of the zirconium salt and / or hafnium salt to the mixed solvent of N,N-dimethylformamide and ethanol is (0.5~1.6) g:50 mL;

[0044] The zirconium salt is any one of zirconium tetrachloride, zirconium nitrate, and zirconyl nitrate; the hafnium salt is hafnium tetrachloride or hafnium oxynitrate; the noble metal precursor is any one of chloroplatinic acid, chloroiridic acid, and sodium chloropalladate;

[0045] When the zirconium salt and the hafnium salt are dispersed in a mixed solvent of N,N-dimethylformamide and ethanol, the molar ratio of the zirconium salt to the hafnium salt is (0.8~0.2):(0.2~0.8). In a preferred embodiment, the molar ratio of the zirconium salt to the hafnium salt is 0.8:0.2, 0.6:0.4, 0.4:0.6, or 0.2:0.8. In a preferred embodiment, the volume ratio of DMF to ethanol is 1:5, 1:4, 1:3, 1:2, or 1:1.

[0046] (2)Disperse the noble metal precursor powder in ethanol to prepare a noble metal precursor solution with a concentration of 0.12~0.48 mg / mL;

[0047] The noble metal precursor is any one of chloroplatinic acid, chloroiridic acid, and sodium chloropalladate.

[0048] (3)Mix the metal salt solution and the noble metal solution evenly. Among them, the mass ratio of the metal salt to the noble metal precursor is (0.5~1.6) g:(3~12) mg. Then add a monobasic organic acid and a 2-aminoterephthalic acid ligand, and stir and react at a temperature of 120~140 °C for 5~12 h. After the reaction is completed, centrifuge and separate, wash the precipitate with ethanol, and perform vacuum drying at 100~160 °C for 12~20 h to obtain the MOF-confined noble metal material. The volume ratio of the monobasic organic acid to the mixed solvent of N,N-dimethylformamide and ethanol in step S1 is (3~8):(20~50), so that while the MOF forms defects, the in-situ confined noble metal nanoparticles are generated, that is, the synchronous regulation of the MOF crystal growth rate and the noble metal particle size is realized.

[0049] The monobasic organic acid is any one of formic acid, glacial acetic acid, and propionic acid; the concentration of 2-aminoterephthalic acid is the same as the molar concentration of the metal salt solution.

[0050] The present invention aims at the deficiencies of the existing preparation technologies of MOF-based formaldehyde removal catalysts, and provides a highly efficient MOF-based catalyst for formaldehyde adsorption-catalytic conversion. The zirconium-based and / or hafnium-based MOF-confined noble metal catalyst prepared by the one-step oil bath method in the present invention constructs defective MOFs by adjusting the volume of monobasic organic acid, reaction time and temperature, and utilizing the competitive coordination effect between monobasic organic acid and 2-aminoterephthalic acid; meanwhile, the noble metal nanoparticles in-situ confined by the reduction of organic acid or DMF are realized, that is, the synchronous regulation of the MOF crystal growth rate and the noble metal particle size is achieved. Compared with the method for preparing zirconium-based or hafnium-based MOF by traditional hydrothermal reaction, the oil bath method has mild preparation conditions, simple and safe process, reduces the dosage of organic solvent DMF, and is easy for large-scale production. The zirconium-based and / or hafnium-based MOF-confined noble metal catalyst prepared in the present invention can rapidly convert the formaldehyde and oxygen gas molecules adsorbed by MOF into carbon dioxide and water after activation on the surface of noble metal nanoparticles. It has the advantages of less catalyst dosage and stable and persistent catalytic performance. That is, the present invention adopts the one-step oil bath method to react zirconium ions or hafnium ions with 2-aminoterephthalic acid to generate zirconium-based or hafnium-based MOF, and at the same time adds a noble metal precursor solution during the in-situ self-assembly process of MOF, and synchronously controls the MOF crystal growth rate and the particle size of noble metal by adjusting the volume of monobasic organic acid, reaction time and temperature. Finally, the particle size of noble metal in the synthesized product is 2-3 nm, and a MOF-confined noble metal nanoparticle catalyst with a specific particle size is prepared. If the volume of monobasic organic acid is too large (small), the defects formed in MOF will be too many or too large (too few or too small), and the particle size of noble metal nanoparticles will be too large (small), resulting in poor catalytic performance; the reaction time and temperature affect the formation of MOF defects and the formation rate of confined noble metal nanoparticles. High (low) reaction time and temperature usually lead to a faster (slower) reaction rate, and the particle size of noble metal nanoparticles is too large (small), resulting in poor catalytic performance. The catalyst preparation reaction in the present invention has mild conditions, simple process, high yield, can be recycled, is suitable for efficiently catalyzing and purifying formaldehyde pollutants in air at normal temperature, and has broad application prospects.

[0051] In the present invention, the formaldehyde catalytic performance of the catalyst is evaluated by a fixed-bed mobile phase test system. Test conditions: the catalyst dosage is 0.1 g, the formaldehyde concentration is 100 ppm, the mass space velocity is 60,000 mL⋅h -1 ⋅g cat -1 , the relative humidity is 30%, and the temperature is 20±2 °C.

[0052] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of this application.

[0053] The following embodiments use conventional instrument equipment in the art. For the experimental methods without specific conditions noted in the following embodiments, they are usually carried out under conventional conditions or according to the conditions recommended by the manufacturer. Various raw materials are used in the following embodiments. Unless otherwise stated, commercially available products are used, and their specifications are conventional specifications in the art. In the specification of the present invention and the following embodiments, unless otherwise specified, "%" represents weight percentage, "parts" represents weight parts, and the ratio represents weight ratio.

[0054] Example 1

[0055] A preparation method of a MOF-confined noble metal composite material, comprising the following steps:

[0056] (1) Disperse 0.5 g of zirconium tetrachloride in a mixed solution of 10 mL of DMF and 40 mL of ethanol, stir until completely dissolved, and prepare a 0.04 mol / L zirconium tetrachloride solution;

[0057] (2) Disperse 3 mg of chloroplatinic acid in 25 mL of ethanol, stir evenly, and prepare a 0.12 mg / mL chloroplatinic acid precursor solution;

[0058] (3) Mix the zirconium tetrachloride solution and the chloroplatinic acid precursor solution evenly, wherein the mass ratio of the metal salt to the noble metal precursor is 0.5 g:3 mg, add 3 mL of glacial acetic acid and a 0.04 mol / L 2-aminoterephthalic acid ligand, stir until a clear solution is obtained, place it in an oil bath at 120 °C and stir and react for 5 h. After completion, centrifuge and separate, wash the precipitate with ethanol 3 times and place it in a vacuum drying oven at 100 °C for drying for 16 h. Finally, a zirconium-based MOF-confined Pt nanocatalyst is prepared, and the sample is labeled as Pt@Zr-MOF.

[0059] Example 2

[0060] A preparation method of a MOF-confined noble metal composite material, comprising the following steps:

[0061] (1) Disperse 0.35 g of zirconium tetrachloride and 0.12 g of hafnium tetrachloride in a mixed solution of 15 mL of DMF and 35 mL of ethanol, stir until completely dissolved, and prepare a mixed solution of zirconium tetrachloride and hafnium tetrachloride, wherein the concentration of zirconium tetrachloride is 0.03 mol / L and the concentration of hafnium tetrachloride is 0.01 mol / L;

[0062] (2) Disperse 5 mg of chloroplatinic acid in 25 mL of ethanol, stir evenly to obtain a chloroplatinic acid precursor solution with a concentration of 0.20 mg / mL.

[0063] (3) Mix the zirconium tetrachloride solution and the chloroplatinic acid precursor evenly. Among them, the mass ratio of the metal salt to the noble metal precursor is 0.5 g:5 mg. Add 6 mL of glacial acetic acid and a 2-aminoterephthalic acid ligand with a concentration of 0.04 mol / L, stir until a clear solution is obtained, place it in an oil bath at 140 °C and stir for 8 h. After completion, centrifuge and separate, wash the precipitate with ethanol 3 times and dry it in a vacuum drying oven at 120 °C for 20 h. Finally, a zirconium / hafnium-based MOF-confined Pt nanocatalyst is prepared, and the sample is labeled as Pt@ZH-MOF. Under normal temperature conditions, when the initial concentration of formaldehyde is 100 ppm for the Pt@ZH-MOF prepared in this example, the removal rate and conversion rate of formaldehyde are 97.7% and 96.3% respectively.

[0064] Figure 1 XRD patterns of Pt@Zr-MOF prepared in Example 1 of the present invention and Pt@ZH-MOF prepared in Example 2. As can be seen from the figure, the XRD diffraction peaks of Pt@Zr-MOF and Pt@ZH-MOF are similar to the standard spectrum of UiO-66-NH2, and the diffraction peak intensities are relatively high, indicating that the catalyst has high crystallinity. The diffraction peaks of Pt nanoparticles are not detected, proving that Pt particles are highly dispersed on Zr-MOF or ZH-MOF.

[0065] Figures 2 - 3 SEM and High Angle Annular Dark Field-Scanning Transmission Electron Microscopy (HAADF-STEM) images of Pt@Zr-MOF prepared in Example 1 of the present invention. As can be seen from the figure, Pt@Zr-MOF presents an octahedral morphology, Pt is highly dispersed on the Zr-MOF support, and the particle size of Pt is 2-3 nm. Similar sample structures are obtained in other examples as in this example.

[0066] Figure 4ESR detection of superoxide radical generation in Pt@Zr-MOF prepared in Example 1 and Pt@ZH-MOF prepared in Example 2 of the present invention. As can be seen from the figure, the ESR spectra of Pt@Zr-MOF and Pt@ZH-MOF show sextet characteristic peaks of DMPO / superoxide radical, indicating that O2 can be activated on the surfaces of Pt@Zr-MOF and Pt@ZH-MOF to generate superoxide radicals. Among them, DMPO is 5,5-dimethyl-1-pyrroline N-oxide, which is a commonly used radical scavenger.

[0067] Figure 5 Room-temperature catalytic aldehyde removal performance of Pt@Zr-MOF prepared in Example 1 of the present invention. Among them, (A) is the formaldehyde removal rate, and (B) is the carbon dioxide generation amount. As can be seen from the figure, under room-temperature conditions, when the initial concentration of formaldehyde is 100 ppm, the formaldehyde removal rate and formaldehyde conversion rate of Pt@Zr-MOF prepared in Example 1 of the present invention are 98.7% and 98.3% respectively.

[0068] Example 3

[0069] A preparation method of an MOF-confined noble metal room-temperature composite material, comprising the following steps:

[0070] (1) Disperse 0.38 g of zirconium tetrachloride and 0.1 g of hafnium tetrachloride in a mixed solvent of N,N-dimethylformamide and ethanol with a volume ratio of 1:5. The total volume of the mixed solvent of N,N-dimethylformamide and ethanol is 50 mL to obtain a metal salt solution with a concentration of 0.04 mol / L; the molar ratio of the zirconium salt to the hafnium salt is 0.8:0.2;

[0071] (2) Disperse 3 mg of chloroplatinic acid powder in 25 mL of ethanol to obtain a chloroplatinic acid solution with a concentration of 0.12 mg / mL;

[0072] (3) Mix the metal salt solution and the chloroplatinic acid solution evenly. Among them, the mass ratio of the metal salt to the noble metal precursor is 0.5 g:5 mg. Add formic acid and a 0.04 mol / L 2-aminoterephthalic acid ligand, and stir and react at 120 °C for 12 h. After the reaction, centrifuge and separate, wash the precipitate with ethanol, and perform vacuum drying at 100 °C for 20 h to obtain an MOF-confined noble metal material, denoted as Pt@ZH-MOF-3. The ratio of formic acid to the mixed solvent of N,N-dimethylformamide and ethanol in step (1) is 3:50. In the Pt@ZH-MOF prepared in this example, the average particle size of Pt is 2.2 nm.

[0073] Figure 6This is the performance of Pt@ZH-MOF-3 prepared in Example 3 of the present invention for catalytic removal of formaldehyde at room temperature. Among them, (A) is the formaldehyde removal rate, and (B) is the carbon dioxide generation amount. As can be seen from the figure, under room temperature conditions, when the initial concentration of formaldehyde is 100 ppm, the formaldehyde removal rate and formaldehyde conversion rate of Pt@ZH-MOF-3 prepared in Example 3 of the present invention are 90.3% and 89.9% respectively.

[0074] Example 4

[0075] A preparation method of an MOF-confined noble metal composite material at room temperature includes the following steps:

[0076] (1) 0.17 g of zirconium nitrate and 0.59 g of hafnium oxynitrate are dispersed in a mixed solvent of N,N-dimethylformamide and ethanol with a volume ratio of 1:4. The total volume of the mixed solvent of N,N-dimethylformamide and ethanol is 50 mL, and a metal salt solution with a concentration of 0.05 mol / L is prepared; the molar ratio of the zirconium salt to the hafnium salt is 0.2:0.8;

[0077] (2) 12 mg of iridium chloride acid powder is dispersed in 25 mL of ethanol to prepare an iridium chloride acid solution with a concentration of 0.48 mg / mL;

[0078] (3) The metal salt solution and the iridium chloride acid solution are mixed evenly. Among them, the mass ratio of the metal salt to the noble metal precursor is 0.8 g:12 mg. Glacial acetic acid and a 0.05 mol / L 2-aminoterephthalic acid ligand are added, and the mixture is stirred and reacted at 140 °C for 5 h. After the reaction, centrifugal separation is carried out, the precipitate is washed with ethanol, and vacuum drying is carried out at 160 °C for 12 h to obtain an MOF-confined noble metal material, denoted as Ir@ZH-MOF. The ratio of the monobasic organic acid to the mixed solvent of N,N-dimethylformamide and ethanol in step (1) is 8:50. In the Ir@ZH-MOF prepared in this example, the average particle size of Ir is 2.5 nm.

[0079] Figure 7 This is the performance of Ir@ZH-MOF prepared in Example 4 of the present invention for catalytic removal of formaldehyde at room temperature. Among them, (A) is the formaldehyde removal rate, and (B) is the carbon dioxide generation amount. As can be seen from the figure, under room temperature conditions, when the initial concentration of formaldehyde is 100 ppm, the formaldehyde removal rate and formaldehyde conversion rate of Ir@ZH-MOF prepared in Example 4 of the present invention are 93.3% and 93.1% respectively.

[0080] Example 5

[0081] A preparation method of an MOF-confined noble metal composite material at room temperature includes the following steps:

[0082] (1) 0.62 g of zirconium oxynitrate and 0.4 g of hafnium oxynitrate were dispersed in a mixed solvent of N,N-dimethylformamide and ethanol with a volume ratio of 1:3. The total volume of the mixed solvent of N,N-dimethylformamide and ethanol was 50 mL, and a metal salt solution with a concentration of 0.07 mol / L was prepared; the molar ratio of the zirconium salt to the hafnium salt was 0.6:0.4,

[0083] (2) 7.5 mg of sodium tetrachloropalladate powder was dispersed in 25 mL of ethanol to prepare a sodium tetrachloropalladate solution with a concentration of 0.3 mg / mL;

[0084] (3) The metal salt solution and the sodium tetrachloropalladate solution were mixed evenly. Among them, the mass ratio of the metal salt to the noble metal precursor was 1.0 g:8.5 mg. Propionic acid and a 0.07 mol / L 2-aminoterephthalic acid ligand were added, and the mixture was stirred and reacted at 130 °C for 8 h. After the reaction, centrifugal separation was carried out, the precipitate was washed with ethanol, and vacuum drying was carried out at 140 °C for 18 h to obtain the MOF-confined noble metal material, denoted as Pd@ZH-MOF. The ratio of propionic acid to the mixed solvent of N,N-dimethylformamide and ethanol in step (1) was 5:50. In the Pd@ZH-MOF prepared in this example, the average particle size of Pd was 3 nm.

[0085] Figure 8 This is the performance of the Pd@ZH-MOF prepared in Example 5 of the present invention for catalytic removal of aldehydes at room temperature. Among them, (A) is the formaldehyde removal rate, and (B) is the carbon dioxide generation amount. It can be seen from the figure that under room temperature conditions, when the initial concentration of formaldehyde is 100 ppm, the formaldehyde removal rate and formaldehyde conversion rate of the Pd@ZH-MOF prepared in Example 5 of the present invention are 94.5% and 91.9% respectively.

[0086] Example 6

[0087] A preparation method of a MOF-confined noble metal composite material at room temperature, comprising the following steps:

[0088] (1) 1.32 g of hafnium tetrachloride was dispersed in a mixed solvent of N,N-dimethylformamide and ethanol with a volume ratio of 1:2. The total volume of the mixed solvent of N,N-dimethylformamide and ethanol was 50 mL, and a metal salt solution with a concentration of 0.08 mol / L was prepared;

[0089] (2) 11.25 mg of chloroplatinic acid powder was dispersed in 25 mL of ethanol to prepare a chloroplatinic acid solution with a concentration of 0.45 mg / mL;

[0090] (3) Mix the metal salt solution and the chloroplatinic acid solution evenly. Among them, the mass ratio of the metal salt to the noble metal precursor is 1.3 g: 11.3 mg. Add formic acid and 0.08 mol / L of 2-aminoterephthalic acid ligand, stir and react at 130 °C for 10 h. After the reaction, centrifuge and separate, wash the precipitate with ethanol, and conduct vacuum drying at 150 °C for 14 h to obtain the MOF-confined noble metal material, denoted as Pt@Hf-MOF. The ratio of the formic acid to the N,N-dimethylformamide and ethanol mixed solvent in step (1) is 7:50. In the Pt@Hf-MOF prepared in this example, the average particle size of Pt is 3 nm.

[0091] Figure 9 The room-temperature catalytic formaldehyde removal performance of the Pt@Hf-MOF prepared in Example 6 of the present invention is as follows. Among them, (A) is the formaldehyde removal rate, and (B) is the carbon dioxide generation amount. It can be seen from the figure that under room-temperature conditions, when the initial concentration of formaldehyde is 100 ppm, the formaldehyde removal rate and formaldehyde conversion rate of the Pt@Hf-MOF prepared in Example 6 of the present invention are 96.4% and 96.1% respectively.

[0092] Example 7

[0093] A preparation method of a MOF-confined noble metal room-temperature composite material includes the following steps:

[0094] (1) Disperse 1.6 g of zirconium nitrate in a mixed solvent of N,N-dimethylformamide and ethanol with a volume ratio of 1:1. The total volume of the N,N-dimethylformamide and ethanol mixed solvent is 50 mL to obtain a metal salt solution with a concentration of 0.1 mol / L;

[0095] (2) Disperse 8.75 mg of chloroiridic acid powder in 25 mL of ethanol to obtain a chloroiridic acid solution with a concentration of 0.35 mg / mL;

[0096] (3) Mix the metal salt solution and the chloroiridic acid solution evenly. Among them, the mass ratio of the metal salt to the noble metal precursor is 1.6 g: 8.8 mg. Add propionic acid and 0.1 mol / L of 2-aminoterephthalic acid ligand, stir and react at 125 °C for 11 h. After the reaction, centrifuge and separate, wash the precipitate with ethanol, and conduct vacuum drying at 110 °C for 19 h to obtain the MOF-confined noble metal material, denoted as Ir@Zr-MOF. The ratio of the propionic acid to the N,N-dimethylformamide and ethanol mixed solvent in step S1 is 4:50. In the Ir@Zr-MOF prepared in this example, the average particle size of Ir is 2.6 nm.

[0097] Figure 10The room-temperature catalytic formaldehyde removal performance of the Ir@Zr-MOF prepared in Example 7 of the present invention. Among them, (A) is the formaldehyde removal rate, and (B) is the carbon dioxide production amount. It can be seen from the figure that under room-temperature conditions, when the initial concentration of formaldehyde is 100 ppm, the formaldehyde removal rate and formaldehyde conversion rate of the Ir@Zr-MOF prepared in Example 7 of the present invention are 97.5% and 96.2% respectively.

[0098] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and modifications can be made, and these improvements and modifications should also be regarded as the protection scope of the present invention.

[0099] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit the protection scope of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a MOF confined noble metal composite material, characterized in that: The following steps are involved: S1: Dispersing zirconium salt and / or hafnium salt in a mixed solvent of N,N-dimethylformamide and ethanol to obtain a metal salt solution; the ratio of the zirconium salt and / or hafnium salt to the mixed solvent of N,N-dimethylformamide and ethanol is (0.5-1.6) g:50 mL; dispersing a noble metal precursor powder in ethanol to obtain a noble metal precursor solution; S2: uniformly mixing the metal salt solution and the noble metal precursor solution, wherein the mass ratio of the metal salt to the noble metal precursor is (0.5-1.6) g:(3-12) mg, and then adding a monobasic organic acid and 2-aminoterephthalic acid, stirring and reacting to obtain a MOF confined noble metal material; The volume ratio of the monobasic organic acid to the N,N-dimethylformamide and ethanol mixed solvent in step S1 is (3-8):(20-50); the concentration of the 2-aminoterephthalic acid is the same as the molar concentration of the metal salt solution; In step S2, the stirring reaction temperature is 120-140° C. and the time is 5-12 h; In the mixed solvent of N,N-dimethylformamide and ethanol, the volume ratio of N,N-dimethylformamide to ethanol is 1:(5-1); The zirconium salt is any one of zirconium tetrachloride, zirconium nitrate and zirconium oxynitrate; the hafnium salt is hafnium tetrachloride or hafnium oxynitrate; the concentration of the metal salt solution is 0.04-0.1 mol / L; The noble metal precursor is any one of chloroplatinic acid, chloroiridic acid and sodium chloropalladate; the concentration of the noble metal precursor solution is 0.12-0.48 mg / mL.

2. The method for preparing a MOF confined noble metal composite material according to claim 1, characterized in that: When the zirconium salt and the hafnium salt are dispersed in a mixed solvent of N,N-dimethylformamide and ethanol, the molar ratio of the zirconium salt to the hafnium salt is (0.8-0.2):(0.2-0.8).

3. The method for preparing a MOF confined noble metal composite material according to claim 1, characterized in that: The monobasic organic acid is any one of formic acid, glacial acetic acid and propionic acid.

4. The method for preparing a MOF confined noble metal composite material according to claim 1, characterized in that: In step S2, after stirring the reaction, the product is centrifugally washed and dried at 100-160° C. for 12-20 hours to obtain the MOF confined precious metal material.

5. A MOF confined precious metal composite material, characterized in that: It is prepared by the method according to any one of claims 1 to 4; the particle size of the precious metal in the composite material is 2 to 3 nm.

6. Application of the MOF confined precious metal composite material described in claim 5 in the field of formaldehyde purification.

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