Preparation of MnO2 (at) Co (II)-MOF composite material and application of MnO2 (at) Co (II)-MOF composite material in visible light degradation of chrome black T

Abstract

The invention discloses preparation of a MnO2 (at) Co (II)-MOF composite material and application of the MnO2 (at) Co (II)-MOF composite material in visible light degradation of chrome black T. The preparation method comprises the following steps: step 1, preparing a red bulk crystal Co (II)-MOF through a water / solvothermal method; and 2, grinding the red bulk crystal Co (II)-MOF into powder, introducing a potassium permanganate aqueous solution into a reaction system, converting potassium permanganate into manganese dioxide through an illumination reaction, and compounding the manganese dioxide with Co (II)-MOF to generate the MnO2 (at) Co (II)-MOF composite material. The MnO2 (at) Co (II)-MOF composite material is obtained by degrading a potassium permanganate aqueous solution through Co (II)-MOF, and the MnO2 (at) Co (II)-MOF composite material not only can effectively improve the catalytic efficiency, but also has excellent stability and cyclic utilization performance. And the chrome black T solution is subjected to photocatalytic degradation by utilizing the excellent photocatalytic performance.

Description

Technical Field

[0001] The invention relates to the technical field of MnO2@Co(II)-MOF composite materials, and in particular to the preparation of a MnO2@Co(II)-MOF composite material and the application of the visible light-degradable chrome black T. Background Art

[0002] Due to rapid industrialization, water pollution has expanded dramatically and environmental problems have become increasingly prominent. In particular, industrial wastewater usually contains a large amount of organic matter, which poses a serious threat to health and water safety. Photocatalysis, as a clean, green and sustainable technology, has been used to address the challenges of water pollution. When treating complex wastewater, existing photocatalytic technology uses natural light energy to excite oxygen or water molecules in the environment into active free radicals with strong oxidizing ability, thereby oxidizing and degrading organic pollutants. In the photocatalytic degradation of wastewater technology, although a variety of photocatalysts have been developed, the existing photocatalytic technology still has some defects and challenges. At present, photocatalytic technology faces problems such as low sunlight utilization and high recombination rate of photogenerated carriers. For example: many traditional photocatalysts, such as TiO2, only work effectively in the ultraviolet light region, which limits their practical application under sunlight. Some photocatalysts have poor stability under long-term use or extreme environmental conditions (such as high temperature, strong acid or strong base), resulting in catalyst collapse or reduced activity, thereby affecting their long-term use effect. Therefore, strengthening the light-harvesting performance of materials and improving the efficiency of photogenerated charge transfer and utilization are effective means to solve these problems.

[0003] In recent years, metal-organic frameworks (MOFs) as photocatalysts have attracted more and more attention from researchers due to their advantages such as high specific surface area, crystalline porosity, designable and modified structure, special electron transport pathways, and customizable band gap structure. However, despite the unique advantages of MOF photocatalysts in photocatalysis, their development is constrained by bottlenecks such as the rapid recombination of photogenerated carriers, low light utilization efficiency, and poor stability. Therefore, it is difficult for a single photocatalytic material to meet the above requirements at the same time, and the construction of heterojunctions has become inevitable. By utilizing the light absorption characteristics and synergistic effects of different semiconductor materials, photocatalytic materials that can simultaneously improve the solar light absorption utilization rate and the separation and transfer efficiency of photogenerated carriers can be obtained, thereby improving the efficiency of solar photocatalytic degradation of organic pollutants. In addition, efficient photocatalysts and their preparation processes are often costly, which limits their application on an industrial scale. Photocatalytic wastewater treatment systems have high requirements for equipment, light sources, and catalysts, and require reasonable design and maintenance, which increases the complexity and operating costs of the system. Although photocatalytic wastewater degradation technology shows good potential, it still needs to be improved and optimized to address the above defects. This may involve solutions such as the development of new photocatalysts, optimization of reaction conditions, simplification of system design, and adoption of more efficient light sources to improve process efficiency and economy.

[0004] In summary, based on the existing technical background and challenges of chrome black T wastewater treatment, the development of a new high-performance photocatalytic material MnO2@Co(II)-MOF will be of great significance to improving water pollution and enhancing environmental governance capabilities. Summary of the invention

[0005] In order to overcome the defects of the above prior art, the purpose of the present invention is to provide a preparation of a MnO2@Co(II)-MOF composite material and its application in visible light degradation of chrome black T. The MnO2@Co(II)-MOF composite material is obtained by degrading potassium permanganate aqueous solution by Co(II)-MOF. The material can not only effectively improve the catalytic efficiency, but also has excellent stability and recyclability. Utilizing its excellent photocatalytic performance, the chrome black T solution is photocatalytically degraded.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is:

[0007] A MnO2@Co(II)-MOF composite material is produced by reacting Co(II)-MOF with potassium permanganate (KMnO4) under photocatalytic conditions. The photocatalytic activity of Co(II)-MOF excites electrons to the conduction band, generates electron-hole pairs, and then promotes the reduction reaction of KMnO4 to generate MnO2 and attach to the surface or inside of Co(II)-MOF.

[0008] The introduction of MnO2 increases the light absorption capacity of the material in the visible light region. MnO2 promotes the transfer of electrons from MnO2 to Co(II) ions to form Co(I) and positively charged MnO2, which improves the separation efficiency of electron-hole pairs and thus enhances the photocatalytic activity.

[0009] MnO2@Co(II)-MOF is used as a photocatalyst to generate active oxygen species (such as ·OH, ·O2 - ) is used to effectively degrade chrome black T.

[0010] The results of 195K CO2 isothermal adsorption test showed that Co(II)-MOF has a high specific surface area (163.64m 2 ·g -1 ) and high porosity It not only provides a large number of active sites for photocatalytic reactions, but also increases the contact area with pollutants and improves degradation efficiency.

[0011] A method for preparing a MnO2@Co(II)-MOF composite material comprises the following steps:

[0012] Step 1: Preparation of red bulk crystalline Co(II)-MOF by water / solvothermal method;

[0013] Step 2: Grind the red block crystal Co(II)-MOF into powder, add it to a potassium permanganate aqueous solution, convert the potassium permanganate into manganese dioxide through a light reaction, and combine it with Co(II)-MOF to form a MnO2@Co(II)-MOF composite material.

[0014] The operation steps of step 1 are:

[0015] First, Co(NO3)2·6H2O (19-21.8 mg), 3,6-di(pyridin-4-yl)-1,2,4,5-tetrazine (L) (15-17.7 mg), trimesic acid (H3btc) (9-10.5 mg), N,N-dimethylformamide (2-4 mL), and methanol (3-5 mL) were mixed, and the resulting mixture was placed in a transparent glass bottle, the bottle cap was sealed with tin foil, and ultrasonically treated for 10-15 min. The bottle was kept in an oven at 100-120°C for 66-85 h, and then slowly cooled to room temperature within 5-8 h to obtain red block crystals of Co(II)-MOF with a yield of 80-86% (based on L ligand).

[0016] The molar mass ratio of the raw materials is Co(NO3)2·6H2O:L:H3btc:N,N-dimethylformamide:methanol=1:1:1:2:2-2:1:1:2:2.

[0018] The operation steps of step 2 are:

[0019] After the red block crystal Co(II)-MOF is ground into powder, an aqueous potassium permanganate solution is introduced into the reaction system, and the potassium permanganate is converted into manganese dioxide through a light reaction, and then combined with Co(II)-MOF to form a MnO2@Co(II)-MOF composite material.

[0020] Further, 9-15 mg of Co(II)-MOF powder sample was dispersed in 5-9 mL, 80-300 mg / L potassium permanganate aqueous solution, and was placed under visible light for 1-4 hours during stirring. After the reaction, the sample color changed from red to black, and was washed and filtered with a mixed solution of N,N-dimethylformamide, distilled water, and ethanol (volume ratio of 1:3:1-1:5:1). The filtered sample was placed at room temperature and dried naturally to obtain a MnO2@Co(II)-MOF composite material.

[0021] The MnO2@Co(II)-MOF composite material synthesized above is used to degrade chrome black T pollutants in aqueous solution, and the specific steps are as follows:

[0022] Take 20-40 mL of 200 mg / L chrome black T aqueous solution and place it in a quartz tube, record the initial absorbance with a UV-visible spectrometer, and add 10-60 mg of MnO2@Co(II)-MOF composite material as a catalyst to the chrome black T aqueous solution; at room temperature, place the reactor under visible light irradiation, stir the reaction, and during the reaction, take samples at regular intervals, and use a UV-visible spectrophotometer to measure the concentration change of chrome black T in the solution.

[0023] (1) Condition optimization: changing the concentration of chrome black T solution

[0024] The other degradation conditions were kept unchanged, and only the concentration of chrome black T solution was changed: 30, 50, 70, 90, 120, 150, 200, 300 mg / L;

[0025] (2) Condition optimization: changing the loading amount of MnO2@Co(II)-MOF composites

[0026] The other degradation conditions were controlled to remain unchanged, and only the loading amount of MnO2@Co(II)-MOF composite material was changed: 10, 15, 20, 30, 40, 50, 60 mg;

[0027] (3) Effect of aqueous solution pH on the degradation efficiency of chrome black T

[0028] Take 20-40mL of 200mg / L chrome black T aqueous solution of a certain concentration and place it in a quartz tube, and record the initial absorbance with a UV-visible spectrometer. Add 10-60mg of MnO2@Co(II)-MOF catalyst to the chrome black T aqueous solution. Use hydrochloric acid and sodium hydroxide solution to adjust the pH value of the chrome black T aqueous solution to 1, 3, 5, 8, 10, and 12. At room temperature, place the reactor under visible light irradiation and stir the reaction. During the reaction process, samples are taken at regular intervals, and the concentration change of chrome black T in the solution is measured using a UV-visible spectrophotometer.

[0029] (4) Anion and cation anti-interference test

[0030] In order to test the anti-interference ability of MnO2@Co(II)-MOF composite materials in the degradation of chrome black T, the interfering ions were consistent with the mass of chrome black T in 40mL of chrome black T solution, and the mass ratio of the two was 1:1. The anions were potassium phosphate, potassium carbonate, potassium iodide, and potassium sulfite; the cations were magnesium nitrate, nickel nitrate, zinc nitrate, calcium nitrate, sodium nitrate, and cadmium nitrate.

[0031] Take 20-40mL 200mg / L chrome black T aqueous solution of a certain concentration and place it in a quartz tube, add anions and cations of equal mass, and record the initial absorbance with a UV-visible spectrometer. Add 10-60mg of MnO2@Co(II)-MOF catalyst to a mixed aqueous solution of chrome black T and interfering ions. At room temperature, place the reactor under visible light irradiation and stir the reaction. During the reaction, samples are taken at regular intervals, and the concentration change of chrome black T in the solution is measured using a UV-visible spectrophotometer. The MnO2@Co(II)-MOF composite material is used to degrade chrome black T pollutants in aqueous solutions.

[0032] Beneficial effects of the present invention:

[0033] Transformation of catalytic reaction: Co(II)-MOF degrades potassium permanganate to generate MnO2 loaded on Co(II)-MOF to obtain MnO2@Co(II)-MOF composite material. This composite material can also be used as a visible light photocatalyst to degrade organic pollutant chrome black T, demonstrating the application potential of the material in degrading organic pollutants.

[0034] Multiple catalytic applications: The same Co(II)-MOF material was used to achieve effective catalytic degradation of different pollutants (potassium permanganate and chrome black T), demonstrating the versatility and universality of the material.

[0035] The use of photocatalytic methods to degrade the organic pollutant Chrome Black T, especially when the reaction is carried out at room temperature and normal pressure, complies with the principles of green chemistry and overcomes the problems of harsh experimental conditions and secondary pollution faced by traditional chemical degradation methods (such as chemical oxidants or high-temperature treatment).

[0036] The structure of the MnO2@Co(II)-MOF composite material is conducive to the separation and transmission of photogenerated carriers. Its porous structure and high specific surface area can provide more catalytic active reaction sites, increase the contact area with chrome black T, and thus improve the photocatalytic degradation efficiency.

[0037] During the degradation process of chrome black T, the study of the photocatalytic reaction mechanism can further guide the optimization and application of materials.

[0038] Since this material can efficiently degrade pollutants, its application in environmental governance can be studied in the future, such as in the treatment systems of sewage treatment plants. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 This is a schematic diagram of the two-dimensional structure of Co(II)-MOF.

[0040] Figure 2 Schematic diagram of the color change of Co(II)-MOF and MnO2@Co(II)-MOF.

[0041] Figure 3 This is the PXRD pattern of MnO2@Co(II)-MOF composite material.

[0042] Figure 4 This is the IR graph of MnO2@Co(II)-MOF composite material.

[0043] Figure 5 This is the UV-vis image of MnO2@Co(II)-MOF composite material.

[0044] Figure 6 This is the XPS graph of MnO2@Co(II)-MOF composite material.

[0045] Figure 7 This is the UV graph of 30 mg MnO2@Co(II)-MOF composite material degrading different concentrations of chrome black T.

[0046] Figure 8 This is the UV graph of the degradation of 200 mg / L chrome black T by MnO2@Co(II)-MOF composites with different loading amounts.

[0047] Fig. 9 The purpose of this study is to study the effect of aqueous solution pH on the degradation efficiency of chrome black T.

[0048] Fig.10 The effect of anions and cations on the degradation efficiency of 200 mg / L chrome black T by 15 mg MnO2@Co(II)-MOF composite material.

[0049] Fig.11EPR detection of O2 in the process of degradation of chrome black T by MnO2@Co(II)-MOF composites - formation.

[0050] Fig.12 It is the synthesis route of MnO2@Co(II)-MOF composite materials and the route for the degradation of chrome black T. DETAILED DESCRIPTION

[0051] The present invention will be further described in detail below in conjunction with the accompanying drawings.

[0052] like Figure 1-Figure 12 As shown in the figure, a MnO2@Co(II)-MOF composite material is prepared by reacting Co(II)-MOF with potassium permanganate (KMnO4) under photocatalytic conditions. This process involves the photocatalytic activity of Co(II)-MOF, which can excite electrons to the conduction band, generate electron-hole pairs, and then promote the reduction reaction of KMnO4 to generate MnO2 and attach to the surface or inside of Co(II)-MOF. Figure 2 The left image shows the powder morphology of Co(II)-MOF, which is red in color. Figure 2 The right figure shows the powder morphology of MnO2@Co(II)-MOF, whose color changes to dark brown. The introduction of MnO2 increases the light absorption capacity of the material. The presence of MnO2 promotes the transfer of electrons from MnO2 to Co(II) ions, which helps to improve the separation efficiency of electron-hole pairs, thereby improving the photocatalytic activity. The introduction of MnO2 increases the photocatalytic activity of the material because MnO2 itself is a photocatalyst that can produce active oxygen species (such as ·OH, ·O2 - ), these species can effectively degrade the organic pollutant chromium black T. The combination of MnO2 and Co(II)-MOF may improve the stability of the composite material, allowing it to maintain high catalytic activity after multiple uses.

[0053] XRD analysis shows that after Co(II)-MOF is loaded with MnO2, the framework integrity is still maintained. The IR peaks of MnO2@Co(II)-MOF composites are similar to those of Co(II)-MOF, except for the peak at 350cm -1A new IR absorption peak appears at the irradiation point, which can be attributed to the MnO2 peak. UV-visible spectroscopy analysis shows that MnO2@Co(II)-MOF has a strong light absorption capacity in the visible light region, which helps to improve the photocatalytic light absorption efficiency. The enhanced light absorption capacity of MnO2@Co(II)-MOF enables the effective generation of electron-hole pairs under visible light irradiation, thereby improving the degradation efficiency of chrome black T. The introduction of MnO2 may promote the transfer of electrons from MnO2 to Co(II) ions, forming positively charged MnO2 and Co(I). This electron transfer process promotes the generation of catalyst active sites and improves the catalytic efficiency. The presence of MnO2 not only promotes the transfer of electrons, but also decomposes chrome black T into simpler and harmless substances through its oxidizing property.

[0054] Study on the synthesis mechanism of MnO2@Co(II)-MOF composite materials:

[0055] As a photocatalyst, Co(II)-MOF is excited under light to generate photogenerated electrons (e-) and photogenerated holes (h + ). This process can be expressed as: Co(II)-MOF+hv→Co(II)-MOF→e - +h +

[0056] The photogenerated holes (h + ) has a high oxidizing ability and can oxidize the Mn(VII) ions in potassium permanganate (KMnO4) and reduce them to low-valent manganese (such as Mn(II) or Mn(IV)):

[0057] MnO4 - +8h + +4e - →Mn 2+ +4H2O

[0058] During the reaction, the structure of Co(II)-MOF may cause the reduction product of manganese to precipitate as manganese dioxide (MnO2) and combine with MOF to form MnO2@Co(II)-MOF. Through the above reaction, the MnO2@Co(II)-MOF composite material is formed. This material combines the structural characteristics of Co(II)-MOF and the catalytic activity of MnO2, and has the potential for further photocatalysis.

[0059] Study on the degradation reaction mechanism of chrome black T:

[0060] MnO2@Co(II)-MOF can generate photogenerated electrons and holes under light, and superoxide radicals (·O2 - ) and the generation of hydroxyl radicals (·OH):

[0061] O2+e - → O2 -

[0062] H2O+h + → OH+H +

[0063] Generated O2 - and ·OH can effectively degrade chrome black T dye, the process is as follows:

[0064] C n H m +·OH→intermediate product→degradation product

[0065] Through a series of oxidation reactions, the molecular structure of Chrome Black T is destroyed, eventually forming harmless degradation products.

[0066] The invention involves the photocatalytic degradation of potassium permanganate by Co(II)-MOF to generate MnO2@Co(II)-MOF, and then using the generated composite material to photocatalytically degrade chrome black T solution. The overall process has good application prospects and environmental benefits.

[0067] Embodiment 1:

[0068] Step 1: Synthesis of Co(II)-MOF

[0069] First, Co(NO3)2·6H2O (21.8 mg), 3,6-di(pyridin-4-yl)-1,2,4,5-tetrazine (L) (17.7 mg), trimesic acid (H3btc) (10.5 mg), N,N-dimethylformamide (3 mL), and methanol (5 mL) were mixed, and all the mixtures were put into a transparent glass bottle, the bottle cap was sealed with tin foil, ultrasonically treated for 5 min, and kept in an oven at 120°C for 72 h, and then slowly cooled to room temperature within 12 h. After filtering and washing (mixed solution of N,N-dimethylformamide and methanol), red block crystals of Co(II)-MOF were obtained, with a yield of 86% (based on L ligand).

[0070] Step 2: Preparation of MnO2@Co(II)-MOF

[0071] 10 mg Co(II)-MOF powder sample was dispersed in 5 mL, 96 mg / L potassium permanganate aqueous solution, and irradiated under a light source with a wavelength of 465 nm for 4 hours during stirring. After the reaction, the sample color changed from red to black, and was washed and filtered with a mixed solution of N,N-dimethylformamide, distilled water, and ethanol. The filtered sample was placed at room temperature and dried naturally to obtain a MnO2@Co(II)-MOF composite material.

[0072] Embodiment 2:

[0073] Step 1: Synthesis of Co(II)-MOF

[0074] First, Co(NO3)2·6H2O (21.8 mg), 3,6-di(pyridin-4-yl)-1,2,4,5-tetrazine (L) (20.0 mg), trimesic acid (H3btc) (15.5 mg), N,N-dimethylformamide (2 mL), and methanol (7 mL) were mixed, and all the mixtures were put into a polytetrafluoroethylene hydrothermal tank, ultrasonically treated for 10 min, and kept in an oven at 120°C for 72 h, and then slowly cooled to room temperature within 12 h. After filtering and washing, red block crystals of Co(II)-MOF were obtained.

[0075] Step 2: Preparation of MnO2@Co(II)-MOF

[0076] 20 mg Co(II)-MOF powder sample was dispersed in 10 mL, 96 mg / L potassium permanganate aqueous solution and irradiated under visible light for 6 hours during stirring. After the reaction, the sample color changed from red to black, and was washed and filtered with a mixed solution of N,N-dimethylformamide, distilled water, and ethanol. The filtered sample was placed at room temperature and dried naturally to obtain the MnO2@Co(II)-MOF composite material.

[0077] Embodiment 3:

[0078] Step 1: Synthesis of Co(II)-MOF

[0079] First, Co(NO3)2·6H2O (43.6 mg), 3,6-di(pyridin-4-yl)-1,2,4,5-tetrazine (L) (35.4 mg), trimesic acid (H3btc) (21.0 mg), N,N-dimethylformamide (6 mL), and methanol (10 mL) were mixed, and all the mixtures were placed in a polytetrafluoroethylene hydrothermal tank, ultrasonically treated for 10 min, and kept in an oven at 120°C for 72 h, and then slowly cooled to room temperature within 12 h. Filter and wash (mixed solution of N,N-dimethylformamide and methanol) to obtain red block crystals of Co(II)-MOF.

[0080] Step 2: Preparation of MnO2@Co(II)-MOF

[0081] 30mg Co(II)-MOF powder sample was dispersed in 20mL, 96mg / L potassium permanganate aqueous solution, and irradiated under a light source with a wavelength of 465nm for 8 hours during stirring. After the reaction, the sample color changed from red to black, and was washed and filtered with a mixed solution of N,N-dimethylformamide, distilled water, and ethanol. The filtered sample was placed at room temperature and dried naturally to obtain the MnO2@Co(II)-MOF composite material.

[0082] Photocatalytic degradation experimental steps

[0083] Take 40mL of 200mg / L chrome black T aqueous solution of a certain concentration and place it in a quartz tube, and record the initial absorbance with a UV-visible spectrometer. Add 30mg of MnO2@Co(II)-MOF catalyst to the chrome black T aqueous solution. At room temperature, place the reactor under visible light irradiation and stir the reaction. During the reaction, samples are taken at regular intervals, and the concentration change of chrome black T in the solution is measured using a UV-visible spectrophotometer.

[0084] Condition optimization: changing the concentration of chrome black T solution

[0085] The other degradation conditions were kept unchanged, and only the concentration of chrome black T solution was changed: 30, 50, 70, 90, 120, 150, 200, 300 mg / L;

[0086] Condition optimization: changing the loading amount of MnO2@Co(II)-MOF composites

[0087] The other degradation conditions were controlled to remain unchanged, and only the loading amount of MnO2@Co(II)-MOF composite material was changed: 10, 15, 20, 30, 40, 50, 60 mg;

[0088] Effect of pH of aqueous solution on degradation efficiency of chrome black T

[0089] Take 40mL of 200mg / L chrome black T aqueous solution of a certain concentration and place it in a quartz tube, and record the initial absorbance with a UV-visible spectrometer. Add 15mg of MnO2@Co(II)-MOF catalyst to the chrome black T aqueous solution. Use hydrochloric acid and sodium hydroxide solution to adjust the pH value of the chrome black T aqueous solution: 1, 3, 5, 8, 10, 12. At room temperature, place the reactor under visible light irradiation and stir the reaction. During the reaction process, samples are taken at regular intervals, and the concentration change of chrome black T in the solution is measured using a UV-visible spectrophotometer.

[0090] Anion and cation anti-interference test

[0091] In order to test the anti-interference ability of MnO2@Co(II)-MOF composite materials in the degradation of chrome black T, the interfering ions were consistent with the mass of chrome black T in 40mL of chrome black T solution, and the mass ratio of the two was 1:1. The anions were potassium phosphate, potassium carbonate, potassium iodide, and potassium sulfite; the cations were magnesium nitrate, nickel nitrate, zinc nitrate, calcium nitrate, sodium nitrate, and cadmium nitrate.

[0092] Take 40mL of 200mg / L chrome black T aqueous solution of a certain concentration and place it in a quartz tube, add anions and cations of equal mass, and record the initial absorbance with a UV-visible spectrometer. Add 15mg of MnO2@Co(II)-MOF catalyst to the mixed aqueous solution of chrome black T and interfering ions. At room temperature, place the reactor under visible light irradiation and stir the reaction. During the reaction, samples are taken at regular intervals, and the concentration change of chrome black T in the solution is measured using a UV-visible spectrophotometer.

[0093] Study on the mechanism of photocatalytic degradation of chrome black T

[0094] In order to further study the photodegradation mechanism of chrome black T by MnO2@Co(II)-MOF composites, free radical capture experiments and electron spin resonance (EPR) experiments were carried out. - quencher), ethylenediaminetetraacetic acid (EDTA, h + quencher), isopropyl alcohol (IPA, ·OH quencher) and benzoquinone (BQ, ·O2 - The degradation efficiency of chrome black T was studied by using MnO2@Co(II)-MOF composite material as photocatalyst in aqueous solution of chrome black T. The free radical scavenging agent 5,5'-dimethyl-1-pyrroline N-oxide (DMPO) was added to perform EPR test to study whether O2 - .like Figure 3 As shown, Co(II)-MOF still maintains the integrity of the framework after loading MnO2.

[0095] like Figure 4 As shown in Figure 2, the IR peaks of the MnO2@Co(II)-MOF composite are similar to those of Co(II)-MOF, except for the peak at 350 cm -1 The IR absorption peak at , this peak can be attributed to the MnO2 peak.

[0096] like Figure 5 As shown, the spectral results prove that MnO2 was successfully loaded on Co(II)-MOF.

[0097] like Figure 6 As shown, the spectral results prove that MnO2 was successfully loaded on Co(II)-MOF.

[0098] like Figure 7 As shown, the degradation rate of 30 mg MnO2@Co(II)-MOF composite material for 40 mL 200 mg / L chrome black T was over 99% within 10 min.

[0099] like Figure 8 As shown, the degradation rate of 15 mg MnO2@Co(II)-MOF composite material for 40 mL 200 mg / L chrome black T was over 99% within 10 min.

[0100] like Fig. 9 As shown in the figure, the MnO2@Co(II)-MOF composite material has the best degradation effect on chrome black T under acidic conditions.

[0101] like Fig.10 As shown in the figure, the degradation efficiency of MnO2@Co(II)-MOF composites on chrome black T is not affected by the coexistence of I - 、SO3 2- 、CO3 2- 、Cd 2+ 、Na + , Ca 2+ Mg 2+ 、Ni 2+ 、Zn 2+ The influence of ions.

[0102] like Fig.11 As shown in the figure, O2 was formed during the degradation of chrome black T by MnO2@Co(II)-MOF composites. - .

[0103] The photocatalytic degradation performance of the MnO2@Co(II)-MOF obtained by the present invention on chrome black T solution includes degradation of chrome black T of different concentrations in aqueous solution, degradation of chrome black T in solutions of different pH values, degradation of chrome black T under the condition of the presence of competitive ions, etc. The results show that the composite material exhibits high selectivity, high stability, high degradation efficiency, and high recyclability in the degradation of chrome black T solution.

[0104] The MnO2@Co(II)-MOF composite material of the present invention has broad application prospects, especially in the fields of wastewater treatment and environmental protection. Its efficient photocatalytic degradation ability can not only solve the pollution problem of dyes such as chrome black T, but also be applicable to the removal of other organic pollutants, with good economic benefits and social value. The present invention provides a novel photocatalytic MnO2@Co(II)-MOF composite material, which can be used to efficiently degrade chrome black T pollutants in wastewater, provides an efficient and sustainable solution for environmental governance, and has important theoretical significance and practical application prospects.

Claims

1. A MnO2@Co(II)-MOF composite material, characterized in that: The photocatalytic activity of Co(II)-MOF excites electrons to the conduction band, generates electron-hole pairs, and then promotes the reduction reaction of KMnO4 to generate MnO2 and attach to the surface or inside of Co(II)-MOF. Co(II)-MOF has a high specific surface area and high porosity, which provides a large number of active sites for photocatalytic reactions, increases the contact area with pollutants, and improves the degradation efficiency.

2. A method for preparing a MnO2@Co(II)-MOF composite material, characterized in that: The following steps are involved: Step 1: Preparation of red bulk crystalline Co(II)-MOF by water / solvothermal method; Step 2: Grind the red block crystal Co(II)-MOF into powder, add it to a potassium permanganate aqueous solution, convert the potassium permanganate into manganese dioxide through a light reaction, and combine it with Co(II)-MOF to form a MnO2@Co(II)-MOF composite material.

3. The method for preparing a MnO2@Co(II)-MOF composite material according to claim 2, characterized in that: The operation steps of step 1 are: First, Co(NO3)2·6H2O, 3,6-di(pyridin-4-yl)-1,2,4,5-tetrazine (L), trimesic acid (H3btc), N,N-dimethylformamide, and methanol were mixed, and the resulting mixture was placed in a transparent glass bottle, the bottle cap was sealed with tin foil, and ultrasonically treated for 10-15 minutes. The mixture was kept in an oven at 100-120°C for 66-85 hours, and then slowly cooled to room temperature within 5-8 hours to obtain red block crystals of Co(II)-MOF.

4. The method for preparing a MnO2@Co(II)-MOF composite material according to claim 3, characterized in that: In the step 1, the molar mass ratio of the raw materials is Co(NO3)2·6H2O:3,6-di(pyridin-4-yl)-1,2,4,5-tetrazine (L):H3btc:N,N-dimethylformamide:methanol=1:1:1:2:2-2:1:1:2:

2.

5. The method for preparing a MnO2@Co(II)-MOF composite material according to claim 2, characterized in that: The operation steps of step 2 are: 9-15 mg Co(II)-MOF powder sample was dispersed in 5-9 mL of 80-300 mg / L potassium permanganate aqueous solution and irradiated under visible light for 1-4 hours during stirring; After the reaction, the color of the sample changed from red to black, and it was washed and filtered with a mixed solution of N,N-dimethylformamide, distilled water, and ethanol. The filtered sample was placed at room temperature and dried naturally to obtain the MnO2@Co(II)-MOF composite material.

6. The method for preparing a MnO2@Co(II)-MOF composite material according to claim 5, characterized in that: The volume ratio of N,N-dimethylformamide, distilled water and ethanol is 1:3:1-1:5:

1.

7. Use of the MnO2@Co(II)-MOF composite material according to any one of claims 1 to 6, characterized in that: The MnO2@Co(II)-MOF composite material is used to degrade chromium black T pollutants in aqueous solution.

8. The use of the MnO2@Co(II)-MOF composite material according to claim 7, characterized in that: The specific steps are as follows: Take 20-40 mL of 200 mg / L chrome black T aqueous solution and place it in a quartz tube, record the initial absorbance with a UV-visible spectrometer, and add 10-60 mg of MnO2@Co(II)-MOF composite material as a catalyst to the chrome black T aqueous solution; at room temperature, place the reactor under visible light irradiation, stir the reaction, and during the reaction, take samples at regular intervals, and use a UV-visible spectrophotometer to measure the concentration change of chrome black T in the solution.

Images