A double built-in electric field photocatalyst for degrading fluorine-containing organic pollutants and a preparation method and application thereof

Abstract

This invention discloses a method for preparing a dual-built-in electric field photocatalyst for degrading fluorine-containing organic pollutants: (1) a certain amount of aldehyde monomer and amine monomer are dissolved in an organic solvent and stirred to obtain solution A; (2) a certain amount of Lewis acid-type metal salt is added to solution A, stirred, and allowed to stand at room temperature for a period of time to generate a precipitate, which is then centrifuged and dried to obtain a fused-ring pyrimidine covalent organic framework material (BTT-COF); (3) BTT-COF is placed in a cadmium sulfide precursor solution for hydrothermal reaction, and after the reaction is completed, it is washed and dried to obtain a dual-built-in electric field fused-ring pyrimidine covalent organic framework / cadmium sulfide photocatalyst (BTT-COF / CdS). This invention also includes the BTT-COF / CdS catalyst prepared by the above method and its application in the photocatalytic degradation of organic pollutants in water. By constructing a dual built-in electric field to synergistically drive the dissociation and directional migration of photogenerated excitons inside BTT-COF, as well as the redistribution and directional transport of interfacial charges, the degradation efficiency and defluorination rate of the catalyst are significantly improved. It has good stability and reusability and can be used for the treatment of recalcitrant organic pollutants, especially fluorine-containing organic pollutants.

Description

Technical Field

[0001] This invention relates to the fields of environmental functional materials and water pollution control agents, specifically to a dual-built-in electric field photocatalyst for degrading fluorinated organic pollutants, its preparation method, and its application. Background Technology

[0002] With the rapid development of the pharmaceutical industry and medical activities, antibiotic pollutants are constantly entering the environment through pharmaceutical wastewater and hospital sewage. The overuse and discharge of antibiotics have caused serious water pollution, directly threatening ecosystem security and human health. Traditional water treatment technologies are ineffective in removing these recalcitrant organic pollutants, which possess strong chemical stability and low biodegradability. Their long-term residues in the aquatic environment not only have toxic effects on aquatic organisms but may also promote the spread of antibiotic-resistant bacteria and resistance genes. Therefore, developing efficient and green wastewater treatment technologies is of great significance.

[0003] Traditional methods such as adsorption, coagulation, and membrane separation mainly achieve the enrichment or phase transfer of pollutants, but are difficult to completely destroy their molecular structure. Conventional biological treatment is also easily affected by the antibacterial effects of antibiotics and changes in water quality conditions. Advanced oxidation technologies can break the stable chemical bonds in recalcitrant organic pollutants by generating highly reactive species such as hydroxyl radicals, superoxide radicals, singlet oxygen, and photogenerated holes, making it an important research direction for the advanced treatment of antibiotic wastewater. Among these technologies, visible light photocatalysis has advantages such as mild reaction conditions, utilization of solar energy, no need for large-scale addition of chemical oxidants, and relatively less secondary pollution. However, single photocatalysts usually suffer from insufficient visible light utilization, rapid recombination of photogenerated electrons and holes, and low interfacial reaction efficiency.

[0004] Covalent organic frameworks (COFs) are a class of porous organic materials formed by organic monomers linked by covalent bonds. They possess characteristics such as designable framework structures, tunable pore sizes, large specific surface areas, and abundant functional sites. By introducing electron donors and acceptors into the molecular framework, donor-acceptor conjugated structures can be constructed, promoting the directional migration of photogenerated carriers. However, single covalent organic frameworks may still suffer from problems such as strong exciton binding, limited carrier separation efficiency, carrier recombination, photocorrosion, and insufficient oxygen activation capabilities. Therefore, developing COF catalytic materials that combine high catalytic activity with excellent structural stability has become a key technical challenge that urgently needs to be overcome in this field. Summary of the Invention

[0005] This invention provides a dual-built-in electric field photocatalyst for degrading fluorinated organic pollutants and its preparation method, achieving efficient degradation of fluorinated organic pollutants and effectively solving the technical problems of limited carrier separation, fast carrier recombination rate, and insufficient degradation efficiency of fluorinated pollutants in existing single COF catalysts.

[0006] A method for preparing a dual-built-in electric field photocatalyst for degrading fluorinated organic pollutants includes the following steps: (1) Dissolve a certain amount of aldehyde monomer and amine monomer in an organic solvent and stir to obtain solution A; (2) A certain amount of Lewis acid type metal salt was added to solution A, stirred, and allowed to stand at room temperature for a period of time to generate a precipitate. Then, the precipitate was centrifuged and dried to obtain a fused cyclic pyrimidine type covalent organic framework material (BTT-COF). (3) BTT-COF was placed in a cadmium sulfide precursor solution for hydrothermal reaction. After the reaction was completed, it was washed and dried to obtain a dual-built-in electric field fused-ring pyrimidine covalent organic framework / cadmium sulfide photocatalyst (BTT-COF / CdS).

[0007] The specific process conditions for each step in the above preparation route are as follows: (a) In step (1): The aldehyde monomer is at least one of terephthalaldehyde, trialdehyde phloroglucinol, 2,2'-bithiophene-5,5'-dicarboxaldehyde, or benzo[1,2-b:3,4-b':5,6-b]trithiophene-2,5,8-trialdehyde; the amine monomer is at least one of p-phenylenediamine, [2,2'-bipyridine]-5,5'-diamine, 4,4(pyrimidin-2,5-diyl)diphenylamine, or tetrafluorop-phenylenediamine; the organic solvent is at least one of N,N-dimethylacetamide, mesitylene, 1,4-dioxane, or a mixture of 1,4-dioxane / mesitylene in any ratio. Preferably, the aldehyde monomer is benzo[1,2-b:3,4-b':5,6-b]trithiophene-2,5,8-trialdehyde, the amine monomer is 4,4(pyrimidin-2,5-diyl)diphenylamine, and the organic solvent is a mixture of 1,4-dioxane and mesitylene.

[0008] The amount of the aldehyde monomer is 0.01-0.5 mmol, the amount of the amine monomer is 0.02-0.7 mmol, and the amount of organic solvent is 10-60 mL. Preferably, 0.2 mmol of benzo[1,2-b:3,4-b':5,6-b]trithiophene-2,5,8-trialdehyde and 0.3 mmol of 4,4-(pyrimidin-2,5-diyl)diphenylamine are dissolved in 25 mL of a 4:1 mixture of 1,4-dioxane and mesitylene.

[0009] (ii) In step (2): The Lewis acid-type metal salt is at least one selected from scandium trifluoromethanesulfonate, lanthanum trifluoromethanesulfonate, cadmium trifluoromethanesulfonate, or copper trifluoromethanesulfonate. Preferably, the Lewis acid-type metal salt is scandium trifluoromethanesulfonate.

[0010] The amount of the Lewis acid-type metal salt is 0-50 mg, and the reaction time is 6-72 h. Preferably, 6 mg of scandium trifluoromethanesulfonate is added to solution A, stirred until homogeneous, and allowed to stand at room temperature for 48 h.

[0011] (iii) In step (3): The CdS precursor is composed of a cadmium salt, a sulfur source, ethanol, and water. The cadmium salt is one or more of cadmium sulfate, cadmium chloride hemihydrate, and cadmium acetate; the sulfur source is one or more of thioacetamide, thiourea, and sodium sulfide. Preferably, the cadmium salt is cadmium chloride hemihydrate, and the sulfur source is thiourea.

[0012] The amount of cadmium salt and sulfur source is 0-100 mg, the amount of deionized water and ethanol is 10-60 mL, and the amount of BTT-COF is 0-100 mg. Preferably, 50 mg of BTT-COF, 8.8 mg of cadmium chloride hemipentahydrate, and 4 mg of thiourea are added to a mixed solution of 30 mL of ethanol and water at a volume ratio of 1:2.

[0013] The hydrothermal reaction is carried out at a temperature of 60-120 °C for 2-12 h. Preferably, the hydrothermal reaction temperature is 90 °C and the reaction time is 10 h.

[0014] This invention also includes an application of the prepared dual-built-in electric field BTT-COF / CdS catalyst for photocatalytic degradation of organic pollutants in water. Specifically, it includes the following steps: adding the BTT-COF / CdS photocatalyst to wastewater containing organic pollutants and continuously stirring; under light irradiation, active species are generated, thereby rapidly degrading the organic matter in the water. The organic pollutants include, but are not limited to, one or more of ofloxacin, florfenicol, quinolone antibiotics, and perfluorinated compounds; the pH of the wastewater is 3-10; and the concentration of the organic pollutants is 1-100 mg / L.

[0015] Compared with existing technologies, the beneficial effects of this invention are as follows: (1) This invention prepares a BTT-COF / CdS photocatalyst for degrading fluorinated organic pollutants. A dual-built-in electric field-driven S-scheme charge migration system is constructed by coupling the molecular built-in electric field generated by the BTT-COF DA structure with the interfacial built-in electric field generated by the Cd-N atomic bridge. The dual built-in electric fields promote the dissociation and directional charge migration of photogenerated excitons within the BTT-COF, as well as the redistribution and directional transport of interfacial charges. The connection effect of the Cd-N atomic bridge promotes the effective separation of photogenerated electrons and holes, reduces ineffective recombination of charge carriers, retains photogenerated charge carriers with strong redox capabilities, and improves light energy utilization efficiency and interfacial reaction efficiency.

[0016] (2) The BTT-COF / CdS photocatalyst prepared in this invention utilizes the Cd-N interface channel and dual built-in electric field to retain highly reducing electrons, thereby enhancing the degradation of fluorine-containing organic pollutants and promoting defluorination, thus reducing the toxicity of pollutants.

[0017] (3) The prepared photocatalyst exhibits high photocatalytic activity, good structural stability and recyclability. The preparation process is mild and simple, with good repeatability, and is suitable for the photocatalytic removal of organic pollutants such as antibiotics in water. Attached Figure Description

[0018] Figure 1 X-ray spectra of three samples BC-0, CdS, and BC-10 (BTT-COF / CdS is abbreviated as BC); Figure 2 Degradation curves of ofloxacin by BC-0, BC-5, BC-10, and BC-15; Figure 3 The effect of pH on the degradation of ofloxacin by BC-10 under light conditions; Figure 4 The effect of ionic strength of BC-10 on the degradation of ofloxacin under light conditions; Figure 5 The effect of ionic strength of BC-0 on the degradation of ofloxacin under light conditions; Figure 6 The effect of humic acid dosage on the degradation of ofloxacin under light conditions was investigated for BC-10. Figure 7 The effect of humic acid dosage on the degradation of ofloxacin under light conditions in BC-0; Figure 8 The defluorination rates of ofloxacin for BC-0 and BC-10 are shown in the graph. Figure 9 This is a cyclic experimental diagram of the degradation of ofloxacin in the BC-10 system. Detailed Implementation

[0019] The present invention will now be described in detail with reference to the accompanying drawings and specific examples. Example

[0020] The preparation method of a dual-built-in electric field photocatalyst for degrading fluorinated organic pollutants in this embodiment includes the following steps: (1) Add 0.2 mmol of benzo[1,2-b:3,4-b':5,6-b'']trithiophene-2,5,8-tricarboxaldehyde and 0.3 mmol of 4,4'-(pyrimidin-2,5-diyl)diphenylamine to 25 mL of a 4:1 mixture of 1,4-dioxane and mesitylene, stir to dissolve, and obtain solution A; (2) Add 6 mg of scandium trifluoromethanesulfonate to solution A, stir evenly, let stand at room temperature for 48 h, and then centrifuge and dry to obtain fused cyclic pyrimidine covalent organic framework material (BTT-COF). (3) 50 mg BTT-COF, 8.8 mg cadmium chloride hemipentahydrate and 4 mg thiourea were added to 30 mL of a mixed solution of ethanol and water with a volume ratio of 1:2. The mixture was hydrothermally reacted at 90 °C for 10 h. After washing and drying, a dual-built-in electric field fused-ring pyrimidine covalent organic framework / cadmium sulfide photocatalyst (denoted as BC-10) was obtained.

[0021] Example 2 To facilitate performance comparison, the operation steps of Example 1 were repeated, except that in step (3), 50 mg of BTT-COF was added to 30 mL of a mixed solution of ethanol and water with a volume ratio of 1:2, and the mixture was hydrothermally reacted at 90 °C for 10 h. The resulting catalyst was denoted as BC-0.

[0022] Example 3 To facilitate performance comparison, the operation steps of Example 1 were repeated, except that in step (3), 50 mg BTT-COF, 4.4 mg cadmium chloride hemipentahydrate and 2 mg thiourea were added to a 30 mL mixed solution of ethanol and water with a volume ratio of 1:2, and the mixture was hydrothermally reacted at 90 °C for 10 h. The resulting catalyst was designated as BC-5.

[0023] Example 4 To facilitate performance comparison, the operation steps of Example 1 were repeated, except that in step (3), 50 mg BTT-COF, 13.2 mg cadmium chloride hemipentahydrate and 6 mg thiourea were added to a 30 mL mixed solution of ethanol and water with a volume ratio of 1:2, and the mixture was hydrothermally reacted at 90 °C for 10 h. The resulting catalyst was designated as BC-15.

[0024] Figure 1 The images show the XRD patterns of BC-0 and BC-10 prepared in Examples 1 and 2, respectively. Figure 1It can be seen that the characteristic peaks at 3.34°, 4.26°, and 26.66° correspond to the (110), (200), and (001) planes of BC-0, showing certain crystallinity and long-range order. The characteristic peaks at 24.84°, 26.53°, 28.22°, 36.66°, 43.74°, 47.89°, 51.89°, 58.35°, 60.91°, 66.86°, 70.96°, and 75.69° correspond to the (100), (002), (101), (102), (110), (103), (112), (202), (104), (203), (211), and (105) planes of CdS with hexagonal wurtzite structure, showing high crystallinity. Characteristic peaks corresponding to BC-0 and CdS were detected simultaneously in the XRD pattern of the BC-10 composite material, proving the successful synthesis of the composite material.

[0025] Application Example 1 BC-10 from Example 1, BC-0 from Example 2, BC-5 from Example 3, and BC-15 from Example 4 were used as heterogeneous catalysts for treating organic pollutants. Specifically, 10 mg each of BC-10 from Example 1, BC-0 from Example 2, BC-5 from Example 3, and BC-15 from Example 4 were weighed and uniformly dispersed in 100 mL of an aqueous solution of ofloxacin with a concentration of 10 mg / L. The reaction was carried out at 600 rpm for 60 min, and 1 mL of the solution was sampled every 10 min to determine the pollutant concentration.

[0026] Under the conditions of this application example, by Figure 2 It can be seen that BC-0 has a weak ability to degrade ofloxacin. After combining with CdS, the resulting dual-built-in electric field catalyst exhibits significant performance under light irradiation. BC-10 shows the best performance in photodegradation of ofloxacin, achieving a removal efficiency of approximately 99% within 30 minutes, with a degradation rate constant (k value) as high as 0.15 minutes. -1 .

[0027] Application Example 2 Repeat the steps of Example 1, except that the pH of the solution used in Example 1 to treat organic pollutants with BC-10 as a heterogeneous catalyst is adjusted: the pH is set to 3, 5, 7, 9, and 11, respectively. The concentration of pollutants at each time point is measured.

[0028] Under the conditions of this application example, by Figure 3 It can be seen that the change of pH value from 3 to 11 has almost no effect on the degradation of pollutants in the reaction system, which proves that the BC-10 system has high reaction stability and a wide range of pH values ​​for application, and is also conducive to its application in practical engineering.

[0029] Application Example 3 Repeat the steps of Example 1, except that, in the solution where BC-10 and BC-0 are used as heterogeneous catalysts to treat organic pollutants in Example 1, different concentrations of Cl are added respectively. - This creates a concentration gradient of 10, 20, and 30 mM ions in the solution. The concentration of pollutants at each time point is measured.

[0030] Under the conditions of this application example, by Figure 4 and Figure 5 It can be seen that there is a significant difference in salt tolerance between BC-10 and BC-0. Even under high salt content, BC-10 can still promote photogenerated carrier separation and O2 activation, and maintain a high capacity for generating active species. Figure 4 Therefore, the Cl- ionization can be overcome by extending the reaction time. - The inhibition showed that it was significantly better than BC-0 in terms of salt tolerance.

[0031] Application Example 4 Repeat the steps of Example 1, except that, in the solution where BC-10 and BC-0 are used as heterogeneous catalysts to treat organic pollutants in Example 1, different concentrations of humic acid are added to create a concentration gradient of 3, 5, and 10 mg / L of humic acid. The concentration of pollutants at each time point is measured.

[0032] Under the conditions of this application example, by Figure 6 and Figure 7 It can be seen that the concentration of humic acid has a relatively small inhibitory effect on the degradation of ofloxacin, and the difference between different concentrations is small, indicating that the catalyst has a strong ability to resist interference from organic matter.

[0033] Application Example 5 Repeat the steps of Example 1, under the conditions of this application example, by Figure 8 It can be seen that the defluorination rate of BC-10 can reach about 60%, which is significantly higher than that of BC-0. This proves that the BTT-COF / CdS interface coupling in BC-10 can promote the directional separation and migration of photogenerated carriers, retain strong oxidizing holes and reducing electrons, and continuously enhance O2 activation and the generation of reactive oxygen species, thereby promoting the deep degradation of fluorine-containing intermediates and the breaking of CF bonds.

[0034] Application Example 6 The reusability of the BC-10 catalyst from Example 1 for treating ofloxacin contaminants was tested. Specifically, 10 mg of the BC-10 catalyst from Example 1 was weighed and uniformly dispersed in 100 mL of an aqueous solution of ofloxacin with a concentration of 10 mg / L. The reaction was carried out at 600 rpm for 60 min, with 1 mL samples taken every 10 min to determine the contaminant concentration. The reacted catalyst was then centrifuged, washed, and dried. This process was repeated five times.

[0035] Under the conditions of this application example, by Figure 9 It can be seen that after 5 cycles of the experiment, BC-10 still showed satisfactory performance in degrading of ofloxacin, indicating that it has good reusability.

[0036] Example 5 Repeat the steps of Example 1, except that in step (1), the amount of organic solvent is 12.5 mL.

[0037] The BTT-COF / CdS catalyst prepared under the conditions of this embodiment has inferior performance to the catalyst prepared under the conditions of Example 1. Under the same conditions as Application Example 1, the degradation rate of ofloxacin pollutant is 71% within 30 min and the defluorination rate is 20%.

[0038] Example 6 Repeat the steps of Example 1, except that in step (2), the amount of Lewis acid metal salt is 3 mg.

[0039] The BTT-COF / CdS catalyst prepared under the conditions of this embodiment has inferior performance to the catalyst prepared under the conditions of Example 1. Under the same conditions as Application Example 1, the degradation rate of ofloxacin pollutants is 81% within 30 min and the defluorination rate is 23%.

[0040] Example 7 Repeat the steps of Example 1, except that in step (3), the hydrothermal reaction temperature is 60 °C.

[0041] The BTT-COF / CdS catalyst prepared under the conditions of this embodiment has inferior performance to the catalyst prepared under the conditions of Example 1. Under the same conditions as Application Example 1, the degradation rate of ofloxacin pollutant is 49% within 30 min and the defluorination rate is 14%.

[0042] Example 8 Repeat the steps of Example 1, except that in step (3), the hydrothermal reaction time is 3 h.

[0043] The BTT-COF / CdS catalyst prepared under the conditions of this embodiment has inferior performance to the catalyst prepared under the conditions of Example 1. Under the same conditions as Application Example 1, the degradation rate of ofloxacin pollutants is 64% within 30 min and the defluorination rate is 19%.

[0044] The specific embodiments described above illustrate the technical solution and beneficial effects of the present invention in detail. It should be understood that the above description is only the most preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, additions, and equivalent substitutions made within the scope of the principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a dual-built-in electric field photocatalyst for degrading fluorinated organic pollutants, characterized in that, Includes the following steps: (1) Dissolve a certain amount of aldehyde monomer and amine monomer in an organic solvent and stir to obtain solution A; (2) A certain amount of Lewis acid type metal salt was added to solution A, stirred, and allowed to stand at room temperature for a period of time to generate a precipitate. Then, the precipitate was centrifuged and dried to obtain a fused cyclic pyrimidine type covalent organic framework material (BTT-COF). (3) BTT-COF was placed in a cadmium sulfide precursor solution for hydrothermal reaction. After the reaction was completed, it was washed and dried to obtain a dual-built-in electric field fused-ring pyrimidine covalent organic framework / cadmium sulfide photocatalyst (BTT-COF / CdS).

2. The method for preparing a dual-built-in electric field photocatalyst for degrading fluorinated organic pollutants according to claim 1, characterized in that, In step (1), the aldehyde monomer is at least one of terephthalaldehyde, trialdehyde phloroglucinol, 2,2'-bithiophene-5,5'-dicarboxaldehyde, or benzo[1,2-b:3,4-b':5,6-b]trithiophene-2,5,8-trialdehyde; the amine monomer is at least one of p-phenylenediamine, [2,2'-bipyridine]-5,5'-diamine, 4,4(pyrimidin-2,5-diyl)diphenylamine, or tetrafluorop-phenylenediamine; and the organic solvent is at least one of N,N-dimethylacetamide, mesitylene, 1,4-dioxane, or a mixture of 1,4-dioxane / mesitylene in any ratio.

3. The method for preparing a dual-built-in electric field photocatalyst for degrading fluorinated organic pollutants according to claim 1, characterized in that, In step (1), the amount of aldehyde monomer is 0.01-0.5 mmol, the amount of amine monomer is 0.02-0.7 mmol, and the amount of organic solvent is 10-60 mL.

4. The method for preparing a dual-built-in electric field photocatalyst for degrading fluorinated organic pollutants according to claim 1, characterized in that, In step (2), the Lewis acid type metal salt is at least one of scandium trifluoromethanesulfonate, lanthanum trifluoromethanesulfonate, cadmium trifluoromethanesulfonate, or copper trifluoromethanesulfonate.

5. The method for preparing a dual-built-in electric field photocatalyst for degrading fluorinated organic pollutants according to claim 1, characterized in that, In step (2), the amount of the Lewis acid type metal salt is 0-50 mg, and the reaction time is 6-72 h.

6. The method for preparing a dual-built-in electric field photocatalyst for degrading fluorinated organic pollutants according to claim 1, characterized in that, In step (3), the CdS precursor is composed of cadmium salt, sulfur source, ethanol and water; wherein the cadmium salt is one or more of cadmium sulfate, cadmium chloride hemipentahydrate, and cadmium acetate, and the sulfur source is one or more of thioacetamide, thiourea, and sodium sulfide.

7. The method for preparing a dual-built-in electric field photocatalyst for degrading fluorinated organic pollutants according to claim 1, characterized in that, In step (3), the amount of cadmium salt and sulfur source is 0-100 mg, the amount of deionized water and ethanol is 10-60 mL, and the amount of BTT-COF is 0-100 mg.

8. The method for preparing a dual-built-in electric field photocatalyst for degrading fluorinated organic pollutants according to claim 1, characterized in that, In step (3), the temperature of the hydrothermal reaction is 60~120 ℃ and the reaction time is 2~12 h.

9. A dual-built-in electric field fused-ring pyrimidine covalent organic framework / cadmium sulfide photocatalyst prepared by the method according to any one of claims 1 to 8, characterized in that, The catalyst has the ability to degrade organic pollutants in a visible light-driven manner.

10. An application of the dual-built-in electric field BTT-COF / CdS catalyst as described in claim 9 for the photocatalytic degradation of organic pollutants in water, characterized in that, Includes the following steps: Adding BTT-COF / CdS photocatalyst to wastewater containing organic pollutants and continuously stirring it will generate active species under light conditions, thereby rapidly degrading organic matter in the water.

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