Method for synthesizing Fe-BDC microwave catalyst by microwave solvothermal method and application thereof

Abstract

The application belongs to the field of microwave catalysis technology, and particularly relates to a method for synthesizing Fe-BDC microwave catalyst by a microwave solvothermal method and application. The method comprises the following steps: (1) dissolving terephthalic acid in a NaAc aqueous solution to obtain liquid A; (2) dissolving an iron salt in a NaAc aqueous solution to obtain liquid B; (3) under stirring, adding liquid B dropwise into liquid A; (4) under stirring, performing microwave irradiation treatment on the mixed liquid obtained in step (3); and (5) filtering and collecting the precipitate, washing, drying, and obtaining the Fe-BDC microwave catalyst. The application uses sodium acetate (NaAc) to regulate the complexation of H2BDC and iron, thereby improving the coordination efficiency, promoting the regulation and synthesis of Fe-BDC with a high content of catalytic sites, improving the catalytic activity, and using non-corrosive and non-toxic substances as solvents in the synthesis process, which is green, energy-saving, and environment-friendly.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of microwave catalysis, and particularly relates to a method for synthesizing Fe-BDC microwave catalyst by a microwave solvothermal method and application thereof. BACKGROUND

[0002] Metal-organic frameworks (MOFs) are a new type of porous material, and metal centers separated by organic ligands can be regarded as quantum dots, which have unique electronic, optical and catalytic properties. MOFs materials mainly promote redox reactions by means of a large number of active sites. Iron-based MOFs contain iron and organic carbon, and have basic elements and structures required by microwave catalysts. Due to the characteristics of low cost, easy preparation and green environmental protection, the iron-based MOFs become a feasible catalyst. Fe-BDC, as a typical iron-based MOF, is a crystal structure formed by combining Fe3-μ3-oxo clusters and terephthalic acid (H2BDC).

[0003] So far, many different methods have been developed for preparing iron-based MOF materials, including solvothermal method, normal temperature stirring co-precipitation method, microwave solvothermal synthesis method, electrochemical synthesis method, mechanical chemical synthesis method grinding, dry gel transformation, template orientation, etc. The most commonly used method is the solvothermal method.

[0004] The microwave solvothermal synthesis method is a green chemical synthesis method, which uses microwave characteristics to accelerate chemical reactions. Compared with the traditional solvothermal method, the microwave can realize rapid and uniform heating, improve the uniformity and crystal quality of the synthesized product, reduce the occurrence of side reactions, and the product has high purity. Due to the improvement of the reaction rate, the synthesis process is accelerated, and the microwave solvothermal synthesis method can thus improve the overall yield of the product. Compared with the traditional solvothermal method, the microwave solvothermal synthesis method significantly reduces the large use of solvents, thereby effectively avoiding the problems of environmental pollution and resource waste that may be caused. Therefore, the microwave solvothermal synthesis technology has significant advantages in time, energy efficiency and selectivity. In addition, the product has the advantages of high specific surface area, small size, large pore volume, strong adsorption capacity, low cost and simple process, and becomes the preferred method for realizing large-scale material synthesis in a short time. SUMMARY

[0005] The purpose of the present application is to provide a method for synthesizing Fe-BDC microwave catalyst by a microwave solvothermal method and application thereof. In the present application, NaAc is used as a solvent, and acetate ions (Ac - ) are used to adjust the reaction environment of the precursor during the synthesis process, so as to promote the formation of defects in the structure of the product and improve the catalytic activity of the product. Under microwave irradiation, the Fe-BDC with defects is beneficial to expose the catalytically active sites and effective mass transfer, and can solve the problem of insufficient microwave catalytic performance in the prior art.

[0006] In order to achieve the above object, the technical scheme of the present application is as follows:

[0007] The present application provides a preparation method of a microwave solvent thermal synthesis Fe-BDC microwave catalyst, which comprises the following steps:

[0008] (1) Dissolve terephthalic acid in NaAc aqueous solution, and ultrasonic to obtain A liquid;

[0009] (2) Dissolve iron salt in NaAc aqueous solution, and stir until completely dissolved to obtain B liquid;

[0010] (3) Under stirring, drop B liquid into A liquid;

[0011] (4) Under stirring, microwave irradiation treatment is carried out on the mixed liquid obtained in step (3);

[0012] (5) Collect the precipitate by filtration, wash, dry, and obtain Fe-BDC microwave catalyst.

[0013] In the above technical scheme, preferably, in step (1), the concentration of the NaAc aqueous solution is 1-5 mol / L.

[0014] In the above technical scheme, preferably, in step (2), the iron salt is any one of ferric chloride, ferric nitrate and ferric sulfate.

[0015] In the above technical scheme, preferably, in step (3), the molar ratio of iron element in the iron salt to terephthalic acid is 1:1-2:1.

[0016] In the above technical scheme, preferably, in step (4), the power of microwave irradiation is 320-640 W, and the time of microwave irradiation is 1-60 min.

[0017] In the above technical scheme, preferably, in step (5), deionized water and ethanol are used for washing; the drying temperature is 40-90 DEG C, and the drying time is 10-20 h.

[0018] The present application further provides an application of the Fe-BDC microwave catalyst prepared by the above method in microwave irradiation degradation of organic pollutants in wastewater.

[0019] In the above technical scheme, preferably, the application conditions are as follows: the microwave power is 80-800 W.

[0020] The present application has the following beneficial effects:

[0021] Another aspect of the present application provides a microwave solvent thermal synthesis Fe-BDC microwave catalyst obtained by the above preparation method, characterized in that the solvent thermal reaction system is heated by microwave irradiation, and the synthesis method is efficient and low in energy consumption.

[0022] 1、The synthesis method of the Fe-BDC microwave catalyst provided by the present application uses NaAc as a solvent, and Ac - The interaction between the reactant and the metal center can be changed, thereby affecting the crystal structure of the product, and hydrogen bonds can also be formed in the synthesis, which helps the formation of defects, Ac - The targeted adjustment can change the growth rate of the crystal, cause the generation of defects, and thus affect the final catalytic performance. Moreover, acetic acid and acetate are non-corrosive and non-toxic substances, and are green, energy-saving and environmentally friendly when used in reactions.

[0023] 2、The synthesis method of the Fe-BDC microwave catalyst provided by the present application uses NaAc as a solvent, and Ac

[0024] 4、The preparation method of the present application is simple to operate, high in safety, low in cost, and green and environmentally friendly. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 Activity comparison of Fe-BDC microwave catalyst samples prepared in Example 1 and Comparative Examples 1-2 in microwave degradation of tetracycline;

[0026] Figure 2 Activity comparison of Fe-BDC microwave catalyst samples prepared in Example 1 and Comparative Examples 3-5 in microwave degradation of tetracycline;

[0027] Figure 3 XRD pattern of the Fe-BDC microwave catalyst sample prepared in Example 1 and Comparative Example 1;

[0028] Figure 4 FT-IR pattern of the Fe-BDC microwave catalyst sample prepared in Example 1 and Comparative Example 1;

[0029] Figure 5 Activity comparison of Fe-BDC microwave catalyst samples prepared in Example 1-3 in microwave degradation of tetracycline;

[0030] Figure 6Comparison of the activities of the Fe-BDC microwave catalyst samples prepared for Example 1, 4 and Comparative Example 6 in microwave degradation of tetracycline;

[0031] Figure 7 Comparison of the activities of the Fe-BDC microwave catalyst samples prepared for Example 1, 5, 6 and Comparative Example 7 in microwave degradation of tetracycline;

[0032] Figure 8 Comparison of the activities of the Fe-BDC microwave catalyst samples prepared for Example 1, 7, 8 and Comparative Example 8 in microwave degradation of tetracycline;

[0033] Figure 9 Activity of the sample prepared for Example 1 in microwave catalytic degradation of tetracycline after repeated use. DETAILED DESCRIPTION

[0034] The technical solutions of the present application will be described clearly and completely below in combination with the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all the other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0035] Unless otherwise specified, the materials used in the embodiments of the present application can be obtained by commercial channels or prepared according to the conventional methods well known to those skilled in the art.

[0036] Example 1

[0037] (1) 0.824 g of terephthalic acid (H2BDC) was weighed into 20 mL of 1 mol / L NaAc, and ultrasonic treatment was performed for 10 min to obtain solution A;

[0038] (2) 1.35 g of iron chloride hexahydrate was weighed into 10 mL of 1 mol / L NaAc, and ultrasonic treatment was performed for 10 min to obtain solution B;

[0039] (3) Solution B was added dropwise to solution A under stirring, and the stirring was continued;

[0040] (4) The mixture was placed in a microwave chemical reactor under stirring, and microwave irradiation treatment was performed at 480 W for 8 min;

[0041] (5) The precipitate was collected by filtration, washed with deionized water and ethanol, and dried at 70°C for 18 h to obtain Fe-BDC.

[0042] Example 2

[0043] Fe-BDC samples were prepared by a method similar to that of Example 1, and the iron salt was 2.02 g of iron nitrate nonahydrate.

[0044] Example 3

[0045] A Fe-BDC sample was prepared in a similar manner as in Example 1, except that the iron salt was 1.99 g of iron sulfate.

[0046] Example 4

[0047] A Fe-BDC sample was prepared in a similar manner as in Example 1, except that the ligand terephthalic acid was 0.412 g.

[0048] Example 5

[0049] A Fe-BDC sample was prepared in a similar manner as in Example 1, except that the concentration of the aqueous NaAc solution was 3 mol / L.

[0050] Example 6

[0051] A Fe-BDC sample was prepared in a similar manner as in Example 1, except that the concentration of the aqueous NaAc solution was 5 mol / L.

[0052] Example 7

[0053] A Fe-BDC sample was prepared in a similar manner as in Example 1, except that the microwave power was 320 W.

[0054] Example 8

[0055] A Fe-BDC sample was prepared in a similar manner as in Example 1, except that the microwave power was 640 W.

[0056] Comparative Example 1

[0057] A Fe-BDC sample was prepared in a similar manner as in Example 1, except that the microwave power was 320 W.

[0058] (1) 0.824 g of terephthalic acid (H2BDC) was weighed into 20 mL of 1 mol / L NaAc solution, and ultrasonic treatment was performed for 10 min to obtain solution A;

[0059] (2) 1.35 g of iron chloride hexahydrate was weighed into 10 mL of 1 mol / L NaAc solution, and ultrasonic treatment was performed for 10 min to obtain solution B;

[0060] (3) Solution B was slowly added dropwise to solution A under stirring, and stirring was continued for 30 min;

[0061] (4) The mixture was transferred to a stainless steel reactor, and reaction was performed at 120°C for 15 h;

[0062] (5) After cooling to room temperature, the precipitate was collected by suction filtration, washed with deionized water and ethanol, and dried at 70°C for 18 h to obtain Fe-BDC.

[0063] Comparative Example 2

[0064] Fe-BDC was prepared by normal temperature stirring co-precipitation method, and the specific steps were as follows:

[0065] (1) 0.824 g of terephthalic acid (H2BDC) was weighed and dissolved in 20 mL of 1 mol / L NaAc reaction solvent, and ultrasonic treatment was performed for 30 min to obtain solution A;

[0066] (2) 1.35 g of iron chloride hexahydrate was weighed and dissolved in 10 mL of 1 mol / L NaAc, and stirring was performed until complete dissolution to obtain mixed solution B;

[0067] (3) Under stirring conditions, solution B was slowly added dropwise to solution A, and stirring was continued for 12 h;

[0068] (4) The precipitate was collected by suction filtration, and the precipitate was washed with distilled water and anhydrous ethanol, and dried in an oven at 70°C for 18 h to obtain Fe-BDC.

[0069] Comparative Example 3

[0070] Fe-BDC was prepared by microwave DMF solvothermal method:

[0071] (1) 0.824 g of terephthalic acid (H2BDC) was weighed and dissolved in 20 mL of DMF (content 99.5%) reaction solvent, and ultrasonic treatment was performed for 30 min to obtain solution A;

[0072] (2) 1.35 g of iron chloride was weighed and dissolved in 10 mL of DMF (content 99.5%), and stirring was performed until complete dissolution to obtain mixed solution B;

[0073] (3) Under stirring conditions, solution B was added dropwise to solution A, and stirring was continued;

[0074] (4) Under stirring conditions, the above mixed solution was placed in a microwave oven chemical reactor and subjected to continuous stirring under microwave power 480 W irradiation conditions for 8 min;

[0075] (5) The precipitate was collected by suction filtration, and the precipitate was washed with distilled water and anhydrous ethanol, and dried in an oven at 70°C for 18 h to obtain Fe-BDC.

[0076] Comparative Example 4

[0077] Fe-BDC sample was prepared by microwave solvothermal method, and the preparation method was similar to that of Example 1, except that the reaction solvent was NaOH aqueous solution.

[0078] Comparative Example 5

[0079] The Fe-BDC sample was prepared by a microwave solvothermal method, and the preparation method was similar to that of Example 1, except that the reaction solvent was a Na2CO3 aqueous solution.

[0080] Comparative Example 6

[0081] The Fe-BDC sample was prepared by a method similar to that of Example 1, except that the iron salt was 1.01 g of iron chloride hexahydrate.

[0082] Comparative Example 7

[0083] The Fe-BDC sample was prepared by a method similar to that of Example 1, except that the concentration of the NaAc aqueous solution was 0.1 mol / L.

[0084] Comparative Example 8

[0085] The Fe-BDC sample was prepared by a method similar to that of Example 1, except that the microwave power was 160 W.

[0086] Application Example 1

[0087] 0.04 g of the sample prepared in Example 1-8 or Comparative Example 1-8 was added to 100 mL of a tetracycline solution with a concentration of 50 mg / L, and after adsorption equilibrium was reached, the solution mixed with the sample was placed in a microwave reactor, the microwave power was set to 480 W, and microwave reaction was performed for 10 min.

[0088] The tetracycline wastewater removal rates of the samples in Example 1-8 are shown in Table 1.

[0089] Table 1

[0090]

[0091] Figure 1 The tetracycline wastewater removal rates of the samples obtained in Example 1, Comparative Example 1, and Comparative Example 2 are shown in the time change curve, which reflects the removal effects of the catalysts obtained by different preparation methods on tetracycline. As can be seen from the figure, the tetracycline removal rates of Example 1 and Comparative Example 2 can both reach more than 80%, and Example 1 has more adsorption sites and better tetracycline removal effect. It is shown that using NaAc as the reaction solvent, the microwave solvothermal method is simple and efficient.

[0092] Figure 2The tetracycline removal rate-time curves of the samples obtained from Example 1, Comparative Example 3, Comparative Example 4 and Comparative Example 5 reflect the removal effect of the catalysts prepared by different solvents on tetracycline. As can be seen from the figure, Example 1 has a faster tetracycline removal rate and a better removal effect than Comparative Examples 3, 4 and 5. It is indicated that the targeted adjustment of acetate ions leads to the generation of defects, the increase in the number of active sites, and thus the improvement in the catalytic performance. Moreover, NaAc is non-toxic, non-corrosive and low in cost. Therefore, the microwave catalytic performance of the Fe-BDC prepared by using NaAc as the reaction solvent is superior to that of the catalysts prepared by using other reaction solvents.

[0093] Figure 3 The XRD pattern of the sample obtained from Example 1 and Comparative Example 1 shows that Example 1 has strong and sharp diffraction peaks at 2θ = 17.8°, 25.6° and 28.3°, and no other impurity peaks are found. The sharp diffraction peaks prove that the prepared catalyst sample has good crystallinity.

[0094] Figure 4 The FT-IR pattern of the sample obtained from Example 1 and Comparative Example 1 shows that the samples have similar structural vibrations because they are both constructed by the same trivalent metal center and carboxylate bridging ligand. The characteristic diffraction peaks at 1393 cm -1 and 1557 cm -1 may mainly come from the vibration of the carboxylate group, representing the asymmetric and symmetric stretching vibrations of the carboxylate part, respectively. The characteristic peak at 1393 cm -1 may also come from the -COO- in terephthalic acid. The wide band near 3390 cm -1 is attributed to O-H. The absorption bands at 744 cm -1 and 525 cm -1 are caused by the C-H vibration bending of the terephthalic acid linker on the aromatic ring and the Fe-O vibration band. The presence of the characteristic functional groups indicates that the microwave solvothermal method successfully synthesizes Fe-BDC. Compared with Comparative Example 4, the hydroxyl peak near 3390 cm -1 and the absorption peak at 525 cm -1 of Example 1 are wider and stronger, indicating that there are more free hydroxyl groups and Fe-O bonds in the structure. The absorption peak at 1557 cm -1 is blue-shifted, the stretching vibration is shifted to a lower frequency, the spectrum band is widened, and the intensity is increased, indicating the formation of hydrogen bonds, which helps to form defects.

[0095] Figure 5The samples obtained from Example 1, Example 2 and Example 3 were subjected to tetracycline wastewater removal rate-time curve. As can be seen from the figure, compared with Example 2-3, the adsorption sites of Example 1 are increased, and the removal rate of 50 mg / L tetracycline reaches 92.70% after microwave treatment for 10 min. According to the hard / soft acid-base theory of Pearson, the metal-organic framework constructed by ferric chloride (hard Lewis acid) and carboxylic acid ligand (hard Lewis base) is more stable.

[0096] Figure 6 The samples obtained from Example 1, Example 4 and Comparative Example 6 were subjected to tetracycline wastewater removal rate-time curve. As can be seen from the figure, compared with Comparative Example 6, the adsorption sites of Example 1 and Example 4 are increased, and compared with Example 4, the adsorption sites of Example 1 are more, and the removal effect of tetracycline is better. Therefore, the molar ratio of iron salt to terephthalic acid is selected to be 1:1-2:1.

[0097] Figure 7 The samples obtained from Example 1, Example 5, Example 6 and Comparative Example 7 were subjected to tetracycline wastewater removal rate-time curve. Ac - If the concentration is too low, the degradation rate of tetracycline is less than 40%. Therefore, the concentration of NaAc is selected to be 1-5 mol / L.

[0098] Figure 8 The samples obtained from Example 1, Example 7, Example 8 and Comparative Example 8 were subjected to tetracycline wastewater removal rate-time curve. If the microwave power is too low, it may lead to incomplete reaction; if the microwave power is too high, it may lead to structure collapse. Therefore, the microwave power is selected to be 320-640 W.

[0099] Application Example 2

[0100] 0.04 g of Fe-BDC catalyst prepared in Example 1 was added into 100 mL tetracycline solution with a concentration of 50 mg / L, and after adsorption reached equilibrium, it was placed into a microwave reactor, and the microwave power was set to be 480 W, and microwave treatment was performed for 10 min. After microwave treatment, the catalyst was recovered, washed with deionized water and ethanol for three times respectively, placed into an oven for drying, and then 100 mL tetracycline solution with a concentration of 50 mg / L was subjected to microwave treatment again, and the catalyst was reused for two times. The results are shown in Table 2. Figure 9 The removal rates of tetracycline after microwave treatment for 10 min in three experiments were 92.70%, 83.64% and 74.56% respectively, which indicates that the catalyst has good stability.

[0101] It should be noted that the above examples are only the preferred examples of the present application, and are not limited to the implementation. The protection scope of the present application should be limited by the scope defined by the claims. Other different forms of changes or variations can also be made on the basis of the above description. The obvious changes or variations derived therefrom are still within the protection scope of the present application.

Claims

1. A method for synthesizing Fe-BDC microwave catalyst by microwave solvothermal method, characterized in that, The method comprises the following steps: (1) dissolving terephthalic acid in NaAc aqueous solution to obtain A liquid; (2) dissolving iron salt in NaAc aqueous solution to obtain B liquid; (3) under stirring, adding B liquid into A liquid drop by drop; (4) under stirring, treating the mixed liquid obtained in step (3) by microwave irradiation; (5) collecting the precipitate by filtration, washing, drying to obtain Fe-BDC microwave catalyst; In step (1), the concentration of NaAc aqueous solution is 1-3 mol / L; In step (2), the iron salt is ferric chloride hexahydrate; In step (3), the molar ratio of iron salt to terephthalic acid is 1:1-2:1; In step (4), the power of microwave irradiation is 320-640 W, and the time of microwave irradiation is 1-60 min.

2. The method of synthesizing Fe-BDC microwave catalyst according to claim 1, wherein, In step (5), washing with deionized water and ethanol; The drying temperature is 40-90 ℃, and the drying time is 10-20 h.

3. Application of Fe-BDC microwave catalyst prepared by the method of any one of claims 1-2 in microwave irradiation degradation of organic pollutants in wastewater.

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