A core-shell structured MOF@porous carbon-based heterogeneous catalyst and its preparation method and application

Abstract

The invention discloses a MOF@porous carbon-based heterogeneous catalyst with a core-shell structure, and a preparation method and application thereof; the invention modifies the catalyst by introducing groups such as hydroxyl groups and amine groups to increase the catalytic activity of the catalyst, and the catalyst is suitable for catalytic oxidation reactions; the preparation method of the catalyst of the invention is simple to operate, the raw materials are cheap and easily available, the reaction conditions are mild, the applicable pH range is wide, the obtained heterogeneous catalyst is easy to separate from dye wastewater and organic pollution wastewater, and has broad development prospects.

Description

Technical Field

[0001] The invention relates to a MOF@porous carbon-based heterogeneous catalyst with a core-shell structure and a preparation method and application thereof, and belongs to the field of organic wastewater treatment. Background Art

[0002] At present, the treatment of high-concentration refractory organic wastewater pollution has become an important strategic goal for the sustainable use of global water resources and the sustainable development of the national economy. Refractory wastewater mainly refers to wastewater discharged in the process of chemical, printing and dyeing, coking and other industries. This wastewater has carcinogenic and teratogenic effects, leading to various genetic diseases. At present, there are three main methods for the treatment of organic wastewater: 1) anaerobic biological treatment, that is, under anaerobic conditions, anaerobic microorganisms decompose organic matter in wastewater to produce methane and carbon dioxide; 2) aerobic biological treatment, which is generally only used to treat low-concentration organic wastewater; 3) oxidation method, that is, a water treatment method that oxidizes oxides in high-concentration organic wastewater under the action of a strong oxidizing chemical reagent under the action of a catalyst. Fenton oxidation is one of them, and its application is also the most extensive. It mainly uses the powerful oxidizing effect of hydroxyl radicals produced by a mixture of hydroxyl radicals and divalent iron ions to oxidize organic matter in wastewater to achieve the purpose of removing organic matter.

[0003] Metal-organic frameworks (MOFs) are a class of porous crystalline materials with periodic multidimensional network structures formed by self-assembly of metal ions or metal cluster units and organic ligands through ligand interaction. Due to the flexibility of their structural geometry, size and function, MOFs have received increasing attention and have led to a dramatic increase in their types and functions in recent years. The structure, topology, pores and functions of MOFs can be easily designed and adjusted by changing the metal nodes and ligands and post-synthesis modifications. Metal frameworks have broad application prospects in chemistry and materials science due to their highly ordered and tunable composition and structure. They are widely used in applications such as gas adsorption separation, heterogeneous catalysis, proton conduction, and drug transport. Since the possible composition and structure of MOFs are almost unlimited and can be used to make a large number of metal nodes and functional ligands, the application of MOFs in organic catalysis, asymmetric catalysis and photocatalysis has attracted widespread attention. Therefore, the combination of different types of MOF active sites (such as metal nodes, functional groups and guests in pores) makes MOF a promising multifunctional catalytic material. Catalysis, as one of the earliest applications of MOFs, has become the most promising direction after 20 years of development. Summary of the invention

[0004] The present invention aims to provide a MOF@porous carbon-based heterogeneous catalyst with a core-shell structure and a preparation method and application thereof.

[0005] The catalyst of the present invention uses a carbon-based porous material prepared from a polymer as a precursor as a carrier, and MOF or the metal on the MOF as an active substance. The porous carbon-based material plays a role in supporting and dispersing the active substance, so that the active substance is evenly dispersed, which is convenient for MOF to contact and adhere. The porous structure provides a large specific surface area, and the obtained core-shell structure catalyst with uniform distribution of active sites is further modified with sodium hydroxide or hydroxylamine hydrochloride to increase the surface groups that improve the reaction efficiency, so as to obtain the desired catalyst.

[0006] The technical solution of the present invention is as follows:

[0007] A method for preparing a core-shell structured MOF@porous carbon-based heterogeneous catalyst comprises the following steps:

[0008] (1) adding polyvinylpyrrolidone (PVP) to N,N-dimethylformamide (DMF) to obtain solution a;

[0009] Preferably, the concentration of polyvinyl pyrrolidone in solution a is 0.005 g / mL;

[0010] (2) adding a polymer to solution a and stirring uniformly to obtain solution b;

[0011] The polymer is PAN, PSF or PVDF, preferably PAN; the volume ratio of the polymer mass to the N,N-dimethylformamide in step (1) is 1:5-15, g / mL, preferably 1:10, g / mL;

[0012] (3) adding MOF material to solution b, stirring evenly, and adding tetraethyl orthosilicate (TEOS) dropwise during stirring to obtain solution c;

[0013] The MOF material is an iron-based MOF. In addition to the iron-based MOF, other transition metal-related MOFs may be added to prepare a catalyst containing two or more MOFs. The preferred MOF material is Fe-BTC or MIL-101 (Fe). The preferred mass ratio of the MOF material to the polymer in step (2) is 1:10.

[0014] The volume ratio of the ethyl orthosilicate to the N,N-dimethylformamide in step (1) is 1:3-10, preferably 1:5;

[0015] (4) adding solution c dropwise into the ethanol-water solution, solidifying and forming the solution by phase inversion method to obtain formed small balls, taking out the formed small balls, and drying them at room temperature to obtain dry small balls;

[0016] The volume ratio of ethanol to water in the ethanol-water solution is 1:4;

[0017] (5) Sodium hydroxide modification: Add the dried pellets into a sodium hydroxide solution, react at 60-80°C for 15 min, then take them out for washing, dry them at room temperature, put them into a crucible, isolate them from oxygen, and calcine them at 500°C in a muffle furnace for 2-4 h to obtain a hydroxyl-modified MOF@carbon-based core-shell structure catalyst;

[0018] The mass fraction of the sodium hydroxide solution is 5-7%; the mass ratio of sodium hydroxide to dry balls is 1:1-5, preferably 1:3.25.

[0019] Alternatively, step (5) can also be replaced by hydroxylamine hydrochloride modification: add the dried pellets to a hydroxylamine hydrochloride solution, adjust the pH to 6 with sodium carbonate, react at 70°C for 1 hour, then take out and wash, dry at room temperature, put into a crucible, isolate oxygen, and calcine at 500°C in a muffle furnace for 2 to 4 hours to obtain an amine-modified MOF@carbon-based core-shell structure catalyst;

[0020] The mass fraction of the hydroxylamine hydrochloride solution is 3-5%; the mass ratio of hydroxylamine hydrochloride to the dry pellets is 1:1-5, preferably 1:3.25.

[0021] In the present invention, "solution a", "solution b" and "solution c" have no special meanings, and are marked as "a", "b" and "c" only to distinguish solutions prepared in different operation steps.

[0022] The present invention modifies the catalyst by introducing groups such as hydroxyl groups and amine groups to increase the catalytic activity of the catalyst. The present invention relates to the catalyst prepared by the above preparation method.

[0023] The catalyst of the invention can be applied to the reaction of oxidizing and degrading active dyes, organic pollutants and the like in waste water by hydrogen peroxide.

[0024] The beneficial effects of the present invention are:

[0025] The present invention provides a MOF@ porous carbon-based heterogeneous catalyst with a core-shell structure, which is suitable for catalytic oxidation reactions. The preparation method of the catalyst of the present invention is simple to operate, the raw materials are cheap and readily available, the reaction conditions are mild, the applicable pH range is wide, and the obtained heterogeneous catalyst is easy to separate from dye wastewater and organic pollution wastewater, and has broad development prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a TEM image of the catalyst of Example 3 of the present invention.

[0027] Figure 2 This is the EDS mapping diagram of the catalyst of Example 3 of the present invention.

[0028] Figure 3This is a performance test of the catalyst catalytic oxidation X-3B under different modification conditions in Examples 1, 2 and 3 of the present invention.

[0029] Figure 4 This is a performance test of the catalyst catalytic oxidation X-3B of different polymers in Example 2 of the present invention and Comparative Example 2.

[0030] Figure 5 This is a performance test of the catalytic oxidation of the catalyst X-3B prepared at different calcination temperatures in Example 2 of the present invention and Comparative Example 3. DETAILED DESCRIPTION

[0031] The present invention is described in detail below in conjunction with specific embodiments, but the present invention is not limited to the following embodiments. Without departing from the content and scope of the present invention, changes in implementation should be included in the technical scope of the present invention.

[0032] Reagents used in the examples: polyvinyl pyrrolidone (AR) Shanghai Aladdin Biochemical Co., Ltd., NN dimethylformamide (AR) Yonghua Chemical Technology Co., Ltd., sodium hydroxide (AR) Shanghai Aladdin Biochemical Co., Ltd., hydroxylamine hydrochloride (AR) Shanghai Aladdin Biochemical Co., Ltd., anhydrous ethanol (AR) Shanghai Aladdin Reagent Co., Ltd., polyacrylonitrile (PAN) Shanghai Huitong Plastic Co., Ltd., tetraethyl orthosilicate (AR) Shanghai Aladdin Biochemical Co., Ltd., X-3B Shanghai San'ai'en Reagent Co., Ltd., hydrogen peroxide (≥30%, AR) Shanghai Aladdin Reagent Co., Ltd., deionized water EDI water production device.

[0033] Example 1: MOF@carbon-based core-shell structure catalyst (polymer is PAN)

[0034] Add 0.05g PVP to 10mL DMF, stir the mixture evenly, then slowly add 1g PAN (stirring and adding) until completely dissolved, add 0.1g Fe-BTC, and continue stirring until completely uniform. Then use a pipette to transfer 2ml of positive TEOS, stirring while adding. Use a syringe to take the prepared solution, add it dropwise to the ethanol aqueous solution, prepare it into small balls, stir, solidify and dry. Then calcine at 500℃ in a muffle furnace for 3h to obtain the MOF@carbon-based core-shell structure catalyst.

[0035] Example 2: Sodium hydroxide modified MOF@carbon-based core-shell catalyst

[0036] Add 0.05g PVP to 10mL DMF, stir the mixture evenly, then slowly add 1g PAN (stirring while adding) until completely dissolved, add 0.1g Fe-BTC, and continue stirring until completely uniform. Then use a pipette to transfer 2ml of normal TEOS, stirring while adding. Use a syringe to take the prepared solution, add it dropwise into the ethanol-water solution, prepare into small balls, stir, solidify and dry.

[0037] Add 60 mL of water and 4.8 g of sodium hydroxide to a round-bottom flask. After cooling, add 15.6 g of dry pellets and react in an 80 °C oil bath for 15 min. After the reaction is completed, take out, wash with deionized water, and dry at room temperature. After drying, put it in a crucible to isolate oxygen and calcine it at 500 °C in a muffle furnace for 3 h to obtain a MOF@carbon-based core-shell structure catalyst modified with sodium hydroxide.

[0038] Example 3: MOF@carbon-based core-shell structure catalyst modified by hydroxylamine hydrochloride

[0039] Add 0.05g PVP to 10mL DMF, stir the mixture evenly, then slowly add 1g PAN (stirring while adding) until completely dissolved, add 0.1g Fe-BTC, and continue stirring until completely uniform. Then use a pipette to transfer 2ml of normal TEOS, stirring while adding. Use a syringe to take the prepared solution, add it dropwise into the ethanol-water solution, prepare into small balls, stir, solidify and dry.

[0040] 100 mL of water and 3.474 g of hydroxylamine hydrochloride were added to the flask, the pH was adjusted to 6 with sodium carbonate, 11.3 g of dry pellets were added, and an oil bath of 70 ° C was placed for 1 hour. After the reaction was completed, the pellets were taken out, washed with deionized water, and dried at room temperature. After drying, they were placed in a crucible to isolate oxygen and calcined at 500 ° C in a muffle furnace for 3 hours to obtain a MOF@carbon-based core-shell structure catalyst modified with hydroxylamine hydrochloride.

[0041] Comparative Example 1: MOF@carbon-based core-shell structure catalyst modified by sodium hydroxide (changing MOF type)

[0042] Add 0.05g PVP to 10mL DMF, stir the mixture evenly, then slowly add 1g PAN (stirring while adding) until completely dissolved, add 0.1g MIL-101(Fe) to it, and continue stirring until completely uniform. Then use a pipette to transfer 2ml of normal TEOS, stirring while adding. Use a syringe to take the prepared solution, add it dropwise to the ethanol aqueous solution, prepare it into small balls, stir, solidify and shape, and dry.

[0043] Add 60 mL of water and 4.8 g of sodium hydroxide to a round-bottom flask. After cooling, add 15.6 g of dry pellets and react in an 80°C oil bath for 15 min. After the reaction is completed, take out the pellets, wash with deionized water, and dry at room temperature. After drying, place them in a crucible to isolate them from oxygen and calcine them in a muffle furnace at 500°C for 3 h to obtain the prepared catalyst.

[0044] Comparative Example 2: MOF@carbon-based core-shell structure catalyst modified by sodium hydroxide (PSF, PVDF, etc. for changing polymer)

[0045] Add 0.05g PVP to 10mL DMF, stir the mixture evenly, then slowly add 1g PSF or PVDF (stirring while adding) until completely dissolved, add 0.1g Fe-BTC, and continue stirring until completely uniform. Then use a pipette to transfer 2ml of normal TEOS, stirring while adding. Use a syringe to take the prepared solution, add it dropwise into the ethanol-water solution, prepare into small balls, stir, solidify and dry.

[0046] Add 60 mL of water and 4.8 g of sodium hydroxide to a round-bottom flask. After cooling, add 15.6 g of dry pellets and react in an 80°C oil bath for 15 min. After the reaction is completed, take out the pellets, wash with deionized water, and dry at room temperature. After drying, place them in a crucible to isolate them from oxygen and calcine them in a muffle furnace at 500°C for 3 h to obtain the prepared catalyst.

[0047] Comparative Example 3: MOF@carbon-based core-shell structure catalyst modified by sodium hydroxide (calcination temperature changed to 350°C, 750°C)

[0048] Add 0.05g PVP to 10mL DMF, stir the mixture evenly, then slowly add 1g PAN (stirring while adding) until completely dissolved, add 0.1g Fe-BTC, and continue stirring until completely uniform. Then use a pipette to transfer 2ml of normal TEOS, stirring while adding. Use a syringe to take the prepared solution, add it dropwise into the ethanol-water solution, prepare into small balls, stir, solidify and dry.

[0049] Add 60 mL of water and 4.8 g of sodium hydroxide to a round-bottom flask. After cooling, add 15.6 g of dry pellets and react in an 80°C oil bath for 15 min. After the reaction is completed, take out, wash with deionized water, and dry at room temperature. After drying, put it in a crucible to isolate it from oxygen, and calcine it in a muffle furnace at 350°C, 500°C, and 750°C for 3 h, respectively, to obtain the prepared catalyst.

[0050] Example 4: Catalyst performance test

[0051] The catalysts prepared in Examples 1, 2, 3 and Comparative Examples 2 and 3 were tested for their catalytic performance in the oxidative degradation of X-3B active brilliant red dye by hydrogen peroxide. The catalytic performance of the catalysts was analyzed by calculating the decolorization rate of dye wastewater.

[0052] The experimental steps of photodegradation of active dyes by catalytic H2O2 are as follows: first, 100mL of X-3B dye solution with a concentration of 100mg / L is prepared, then 0.05g of catalyst is weighed and added to the dye solution, and the solution is placed in a 25℃ constant temperature oscillation box. Before the photocatalytic degradation experiment, the reaction solution is first oscillated for 60min under light-proof conditions to achieve the adsorption equilibrium of the catalyst; the light source is placed above the solution, the visible light lamp is turned on (the light source is a 200W halogen lamp), 100μL of H2O2 with a mass concentration of 30% is added, and the degradation experiment is started under visible light conditions. The degradation time is 120min. During the oxidative degradation process, the reaction solution is drawn at certain time intervals to analyze the absorbance of the test solution.

[0053] Table 1 Comparison of performance of catalysts prepared in Examples and Comparative Examples

[0054]

Claims

1. A method for preparing a core-shell structured MOF@porous carbon-based heterogeneous catalyst, characterized in that: The steps include: (1) adding polyvinyl pyrrolidone to N,N-dimethylformamide to obtain solution a; (2) adding a polymer to solution a and stirring evenly to obtain solution b; The polymer is PAN or PSF; (3) adding MOF material to solution b, stirring evenly, and adding tetraethyl orthosilicate dropwise during stirring to obtain solution c; The MOF material is an iron-based MOF, or a mixture of an iron-based MOF and other transition metal MOFs; (4) adding solution c dropwise into the ethanol-water solution, solidifying and forming the solution by phase inversion method to obtain formed small balls, taking out the formed small balls, and drying them at room temperature to obtain dry small balls; (5) Sodium hydroxide modification: The dried pellets were added to a sodium hydroxide solution and reacted at 60-80°C for 15 min. The pellets were then taken out for washing, dried at room temperature, placed in a crucible, isolated from oxygen, and calcined in a muffle furnace at 500°C for 2-4 h to obtain a hydroxyl-modified MOF@carbon-based core-shell structure catalyst.

2. The method for preparing the MOF@porous carbon-based heterogeneous catalyst with a core-shell structure as claimed in claim 1, characterized in that: The concentration of polyvinyl pyrrolidone in the solution a obtained in step (1) is 0.005 g / mL.

3. The method for preparing the MOF@porous carbon-based heterogeneous catalyst with a core-shell structure as claimed in claim 1, characterized in that: In step (2), the volume ratio of the polymer mass to the N,N-dimethylformamide in step (1) is 1:5-15, g / mL.

4. The method for preparing the MOF@porous carbon-based heterogeneous catalyst with a core-shell structure as claimed in claim 1, characterized in that: In step (3), the mass ratio of the MOF material to the polymer in step (2) is 1:

10.

5. The method for preparing the MOF@porous carbon-based heterogeneous catalyst with a core-shell structure as claimed in claim 1, characterized in that: In step (3), the volume ratio of ethyl orthosilicate to N,N-dimethylformamide in step (1) is 1:3-10.

6. The method for preparing the MOF@porous carbon-based heterogeneous catalyst with a core-shell structure according to claim 1, characterized in that: In step (5), the mass ratio of sodium hydroxide to dried pellets is 1:1-5.

7. The method for preparing the MOF@porous carbon-based heterogeneous catalyst with a core-shell structure as claimed in claim 1, characterized in that: Step (5) is replaced by hydroxylamine hydrochloride modification: the dried pellets are added to a hydroxylamine hydrochloride solution, the pH is adjusted to 6 with sodium carbonate, and the reaction is carried out at 70°C for 1 hour. Then, the pellets are taken out for washing, dried at room temperature, placed in a crucible, isolated from oxygen, and calcined at 500°C in a muffle furnace for 2 to 4 hours to obtain an amine-modified MOF@carbon-based core-shell structure catalyst.

8. The method for preparing the MOF@porous carbon-based heterogeneous catalyst with a core-shell structure as claimed in claim 7, characterized in that: The mass ratio of hydroxylamine hydrochloride to dry pellets is 1:1-5.

9. The catalyst obtained by the preparation method according to any one of claims 1 to 8.

10. Use of the catalyst as claimed in claim 9 in the reaction of oxidative degradation of organic pollutants in wastewater by hydrogen peroxide.

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