Mnfe2o4@cm composite material, and preparation method and use thereof

Abstract

The application provides a MnFe2O4@CM composite material, which is obtained by loading MnFe2O4 on a double-face isomerous net carbon film, and the double-face isomerous net carbon film is obtained by acid washing, water washing, high-temperature pyrolysis and alkali activation of an industrial dust filtration film; the application also provides a preparation method of the MnFe2O4@CM composite material and application of the MnFe2O4@CM composite material in municipal sludge treatment; the MnFe2O4@CM composite material is used in combination with a persulfate when treating municipal sludge, and can efficiently remove perfluorinated compounds in the sludge.

Description

TECHNICAL FIELD

[0001] The application relates to the field of solid waste treatment, in particular to a MnFe2O4@CM composite material and a preparation method and application thereof. BACKGROUND

[0002] With the continuous development of the national urbanization level, the amount of sewage is increasing, and the sludge generated in the treatment process is growing explosively, so finding a reasonable sludge disposal approach has become a research hotspot. Land use is one of the most effective ways of sludge resource utilization, but a large amount of organic pollutants exist in sludge, which will cause secondary pollution of land in the process of resource utilization.

[0003] Perfluorinated compounds (PFCs) are widely used in antifouling agents, cosmetics, medicines, electrical and electronic parts, photo imaging processing, hydraulic oil, textiles, flame retardants and pesticides, etc. due to their stable chemical properties, low surface activity, hydrophobicity and lipophilicity. In addition, perfluorinated compounds are extremely persistent, have high biological accumulation and biological amplification, and can migrate over long distances. In 2009, the Stockholm Convention listed nine substances such as perfluorooctane sulfonate (PFOS) and its salts and perfluorooctyl sulfonyl fluoride as persistent organic pollutants. Due to their hydrophobic and oleophobic properties, conventional wastewater treatment processes cannot effectively remove them, and they will eventually accumulate in large amounts in sludge and are difficult to handle. How to deeply remove them from sludge has become a problem in the industry.

[0004] The degradation effect of traditional advanced oxidation technology in removing perfluorinated compounds mainly depends on the action of hydroxyl radicals, but it has the disadvantages of short cycle and low oxidation potential. The activated persulfate method is a new type of perfluorinated compound treatment technology with good development prospects. In recent years, AOPs technology based on sulfate radicals (SO4 ·- ) has also received more and more attention. It is an innovative treatment technology based on oxidized persulfate, which has the advantages of long cycle, high oxidation potential and wide applicable pH range compared with Fenton technology based on hydroxyl radicals. Persulfate mainly includes peroxodisulfate (PS) and persulfate (PMS), and its oxidation-reduction potential is 2.01V and 1.82V respectively. However, in the degradation experiment, the direct reaction of persulfate with organic pollutants has the problems of low reaction rate and long time consumption, so a technology for rapidly activating PS and PMS is needed. Common physical activation methods such as ultraviolet irradiation, heating and ultrasonic can effectively activate persulfate, but they all need additional energy input.

[0005] Meanwhile, the industrial dust removal film as an important component of bag dust removal in the field of industrial sludge incineration, after retirement, occupies land resources due to its stacking, and the toxic and harmful substances such as dust and heavy metals contained therein can cause pollution to surface water, groundwater, soil and the like through rainwater scouring, migration and transformation, and also have an impact on the air under the action of wind, thereby causing harm to humans and animals and plants, and thus how to harmless and resource the same has become a hot issue in the environmental field. SUMMARY

[0006] In view of the above-mentioned shortcomings of the prior art, the purpose of the present application is to provide a MnFe2O4@CM composite material and a preparation method and use thereof, for solving the problem that the perfluorinated compound pollution in sludge is difficult to treat in the prior art, and harmless and resource the industrial dust removal film.

[0007] To achieve the above-mentioned purpose and other related purposes, the present application provides a MnFe2O4@CM composite material, which is obtained by loading MnFe2O4 on a double-face isomerous net carbon film, and the double-face isomerous net carbon film is obtained by pretreatment, high-temperature pyrolysis and alkali activation of an industrial dust filtration film.

[0008] The present application also provides a preparation method of the MnFe2O4@CM composite material as described above, comprising the following steps:

[0009] 1) pretreating the industrial dust filtration film, then performing high-temperature pyrolysis and alkali activation to obtain a double-face isomerous net carbon film;

[0010] 2) mixing MnFe2O4 with the double-face isomerous net carbon film to obtain a MnFe2O4@CM composite material.

[0011] In some embodiments of the present application, the high-temperature pyrolysis and alkali activation process in step 1) is a stepwise high-temperature pyrolysis method assisted by alkali activation, specifically comprising the following steps: heating the industrial dust filtration film to 85-105℃ at a rate of 2-5℃ / min under air atmosphere, and constant temperature calcination for 30-60min; heating to 120-180℃ at a rate of 1-4℃ / min under air atmosphere, and constant temperature calcination for 30-60min; heating to 220-300℃ at a rate of 1-4℃ / min under vacuum, and constant temperature calcination for 2-5h to obtain a pre-carbonized sample; after cooling the pre-carbonized sample to room temperature, alkali activation treatment; heating to 650-800℃ at a rate of 1-4℃ / min under vacuum, and constant temperature calcination for 2-5h for recarbonization to obtain the double-face isomerous net carbon film CM.

[0012] In some embodiments of the present application, in step 2), the MnFe2O4 is obtained by mixing a solution containing trivalent iron ions with a solution containing divalent manganese ions, and then adding an alkali solution to react.

[0013] In some embodiments of the present application, in step 2), the mass ratio of the MnFe2O4 and the double-faced isomerous net carbon film is 1:1-1:10.

[0014] In some embodiments of the present application, in step 2), the mixing time is 1-14 h.

[0015] The present application also provides an application of the MnFe2O4@CM composite material as described above in municipal sludge treatment, wherein the MnFe2O4@CM composite material is used in combination with a persulfate salt in treating municipal sludge, and is used for treating organic pollutants in the municipal sludge.

[0016] As described above, the MnFe2O4@CM composite material, the preparation method and the application thereof according to the present application have the following beneficial effects:

[0017] The MnFe2O4@CM composite material provided by the present application has magnetism, high oxygen vacancy abundance and surface hydroxyl groups, and when used in combination with a persulfate salt in treating municipal sludge, the two transition metals Mn 2+ and Fe 3+ in the structure of the composite material can transfer electrons to the persulfate salt through valence state conversion to produce active substances, thereby achieving a good pollutant treatment effect, and the MnFe2O4@CM composite material has very high catalytic activity, and by introducing the CM into the spinel MnFe2O4, the electron transfer between the MnFe2O4 and the persulfate salt can be strengthened by virtue of the π-electron affinity of the highly aromatic structure surface of the biochar, and at the same time, the composite material can realize efficient removal of pollutants by virtue of electrostatic adsorption, surface functional group combination and other effects, and at the same time, the composite material is convenient to separate and recycle, resistant to high temperature and high pressure, and has good recycling performance.

[0018] The preparation method of the MnFe2O4@CM composite material according to the present application has simple process, mild conditions, uniform heating, energy saving, high efficiency, easy control, general preparation conditions and materials, stable product morphology, high purity, and convenient and simple product processing, and is suitable for medium-scale industrial production.

[0019] The MnFe2O4@CM composite material prepared by the present application can act on perfluorinated compounds which are difficult to remove in sludge by virtue of electrostatic adsorption and surface functional group combination of the CM, and Π-Π stacking effect of the CM and the organic pollutants, and can catalytically oxidize the perfluorinated compounds into small molecules of CO2 and H2O to realize efficient removal of the perfluorinated compounds.

[0020] The MnFe2O4@CM composite material according to the present application has the following advantages: firstly, the industrial dust removal film raw material is easy to obtain, and the manganese source and the iron source are abundant in nature and cheap and easy to obtain, and the manganese source and the iron source can be obtained from industrial manganese slag and iron slag; secondly, the Mn 2+ and Fe 3+When dissolved in water, it has low toxicity to the natural environment. Furthermore, iron and manganese salts are commonly used in wastewater and sludge treatment processes, making them better suited to treatment systems. This provides possibilities for the practical application of advanced oxidation technologies based on MnFe2O4. Finally, Mn and Fe are located close to each other on the periodic table and have similar ionic radii, resulting in MnFe2O4 exhibiting higher stability in the system, which is beneficial for material recycling and practical application. Attached Figure Description

[0021] Figure 1 The image shown is a SEM image of the double-sided heterogeneous carbon film CM prepared in Example 1 of the present invention at a magnification of 5 μm.

[0022] Figure 2 The image shown is a SEM image of the double-sided heterogeneous carbon film CM prepared in Example 1 of the present invention at a magnification of 1 μm.

[0023] Figure 3 The image shown is a SEM image of MnFe2O4 prepared in Example 1 of the present invention at a magnification of 100 nm.

[0024] Figure 4 The image shown is a SEM image of the MnFe2O4@CM composite material prepared in Example 1 of the present invention at a magnification of 1 μm.

[0025] Figure 5 The image shown is the XRD pattern of the MnFe2O4@CM composite material prepared in Example 1 of the present invention. Detailed Implementation

[0026] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0027] Before further describing specific embodiments of the present invention, it should be understood that the scope of protection of the present invention is not limited to the specific embodiments described below; it should also be understood that the terminology used in the embodiments of the present invention is for describing specific embodiments and not for limiting the scope of protection of the present invention; in the specification and claims of the present invention, unless otherwise expressly stated in the text, the singular forms "a", "an" and "this" include the plural forms.

[0028] When the embodiments give numerical ranges, it is understood that, unless the application indicates otherwise, every numerical range's two endpoints, and any number between the two endpoints, are optional. Unless otherwise defined, all technical and scientific terms used in the application have the same meaning as commonly understood by one of ordinary skill in the art. Except in the Examples, or where otherwise explicitly indicated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The materials, methods, and examples provided herein are illustrative only and, in no way, limit the scope of the application. Other embodiments will be apparent to those skilled in the art from consideration of the specification and practice of the application disclosed herein.

[0029] Reference will now be made to the drawings, which depict only exemplary embodiments of the application. The drawings are schematic illustrations of the basic concepts of the present application and as such are not drawn to scale. In the drawings, like reference numerals refer to like parts throughout the several views, and the illustrations are presented for the purposes of simplicity and ease of understanding only, and are not intended to limit the scope of the application.

[0030] The first aspect of the present application provides a MnFe2O4@CM composite material, the composite material is obtained by loading MnFe2O4 on a double-face isomerous net carbon film (CM), and the double-face isomerous net carbon film is obtained by pretreatment, high-temperature pyrolysis and alkali activation of an industrial dust filter film.

[0031] The double-face isomerous net carbon film has a double-face isomerous net hierarchical porous structure, and the hierarchical porous structure includes mesopores with a pore size of 5-50 nm, 5-10 nm, 10-15 nm, 15-20 nm, 20-25 nm, 25-30 nm, 30-35 nm, 35-40 nm, 40-45 nm or 45-50 nm, and macropores with a pore size of 50-600 nm, 50-100 nm, 100-150 nm, 150-200 nm, 200-250 nm, 250-300 nm, 300-350 nm, 350-400 nm, 400-450 nm, 450-500 nm, 500-550 nm or 550-600 nm.

[0032] The MnFe2O4 is an octahedron with a diameter of 50-250 nm. For example, the diameter is 50-70 nm, 70-90 nm, 90-110 nm, 110-130 nm, 130-150 nm, 150-170 nm, 170-190 nm, 190-210 nm, 210-230 nm or 230-250 nm.

[0033] The industrial dust filter film is a PET / PTFE double-face composite film. PET is a polyterephthalic acid plastic, and PTFE is polytetrafluoroethylene.

[0034] The pretreatment is acid pickling and water washing.

[0035] The second aspect of the present application provides a preparation method of the MnFe2O4@CM composite material, comprising the following steps:

[0036] 1) The industrial dust filter membrane is pretreated and then pyrolyzed at high temperature, and is activated by alkali to obtain a double-sided isomerous net carbon membrane;

[0037] 2) The MnFe2O4 is mixed with the double-sided isomerous net carbon membrane to obtain the MnFe2O4@CM composite material.

[0038] In the preparation method of the MnFe2O4@CM composite material, in step 1), the pretreatment is acid pickling and water washing. The pretreatment specifically comprises alternating immersion and washing with acid and water.

[0039] The acid pickling adopts sulfuric acid with a concentration of 0.005-0.3 mol / L. For example, the concentration of sulfuric acid is 0.005-0.01 mol / L, 0.01-0.05 mol / L, 0.05-0.10 mol / L, 0.10-0.15 mol / L, 0.15-0.20 mol / L, 0.20-0.25 mol / L or 0.25-0.3 mol / L.

[0040] In the preparation method of the MnFe2O4@CM composite material, in step 1), the process of pyrolysis at high temperature and activation by alkali is a process of adopting a stepwise pyrolysis method and activation by alkali, and specifically comprises the following steps: the industrial dust filter membrane is heated to 85-105℃ at a rate of 2-5℃ / min under an air atmosphere, and is calcined at constant temperature for 30-60 min; the industrial dust filter membrane is heated to 120-180℃ at a rate of 1-4℃ / min under an air atmosphere, and is calcined at constant temperature for 30-60 min; the industrial dust filter membrane is heated to 220-300℃ at a rate of 1-4℃ / min under vacuum, and is calcined at constant temperature for 2-5 h to obtain a pre-carbonized sample; the pre-carbonized sample is cooled to room temperature and then is activated by alkali; the pre-carbonized sample is heated to 650-800℃ at a rate of 1-4℃ / min under vacuum, and is calcined at constant temperature for 2-5 h to perform recarbonization, and a double-sided isomerous net carbon membrane CM is obtained.

[0041] In a preferred embodiment of the present application, the industrial dust filter membrane is heated to 105℃ at a rate of 3℃ / min under an air atmosphere, and is calcined at constant temperature for 40 min; the industrial dust filter membrane is heated to 170℃ at a rate of 2℃ / min under an air atmosphere, and is calcined at constant temperature for 30 min; the industrial dust filter membrane is heated to 230℃ at a rate of 1℃ / min under vacuum, and is calcined at constant temperature for 3 h to perform alkali activation, and a pre-carbonized activated sample is obtained; the pre-carbonized activated sample is heated to 750℃ at a rate of 2℃ / min under vacuum, and is calcined at constant temperature for 2 h.

[0042] The alkali used in the alkali activation treatment is KOH or NaOH.

[0043] The molar ratio of the alkali to the pre-carbonized sample in the alkali activation treatment is 1:1 to 5:1. In a preferred embodiment of the present application, the molar ratio of the alkali to the pre-carbonized sample is 3:1. In the present application, the molar amount of the pre-carbonized sample is calculated by taking the mass of the pre-carbonized sample as pure carbon and then calculating the molar amount.

[0044] The time of the alkali activation treatment is 10 to 60 minutes. For example, it is 10 to 15 minutes, 15 to 20 minutes, 20 to 25 minutes, 25 to 30 minutes, 30 to 35 minutes, 35 to 40 minutes, 40 to 45 minutes, 45 to 50 minutes, 50 to 55 minutes, or 55 to 60 minutes.

[0045] The alkali activation process in the present application is also assisted by ultrasonic treatment. The ultrasonic treatment is performed at room temperature using an intelligent ultrasonic cleaner DL-120D (Shanghai Zhixin Instrument and Equipment Co., Ltd.). The ultrasonic treatment allows the pre-carbonized sample and the alkali to be fully mixed and reacted.

[0046] In the preparation method of the MnFe2O4@CM composite material of the present application, in step 2), the MnFe2O4 is obtained by mixing a solution containing trivalent iron ions and a solution containing divalent manganese ions, and then adding an alkali solution.

[0047] The solution containing trivalent iron ions is selected from one or more of FeCl3 solution, Fe2(SO4)3 solution, or Fe(NO3)3 solution.

[0048] The solution containing divalent manganese ions is selected from one or more of MnCl2 solution or MnSO4 solution.

[0049] The alkali solution is selected from one or more of NaOH solution, KOH solution, or ammonia solution.

[0050] The concentration of hydroxide ions in the alkali solution is 0.01 to 7 mol / L. For example, it is 0.01 to 0.05 mol / L, 0.05 to 1 mol / L, 1 to 2 mol / L, 2 to 3 mol / L, 3 to 4 mol / L, 4 to 5 mol / L, 5 to 6 mol / L, or 6 to 7 mol / L. In a preferred embodiment of the present application, the concentration of hydroxide ions in the alkali solution is 0.05 to 5 mol / L. In a preferred embodiment of the present application, the concentration of hydroxide ions in the alkali solution is 3 to 5 mol / L.

[0051] The ratio of the amount of substance of the ferric ions in the solution containing ferric ions to the amount of substance of the manganese ions in the solution containing divalent manganese ions is 6:1-1:1. The ratio of the amount of substance of the ferric ions to the amount of substance of the divalent manganese ions in the mixed solution is 6:1-1:1. For example, 6:1-5:1, 5:1-4:1, 4:1-3:1, 3:1-2:1, or 2:1-1:1. In a preferred embodiment of the application, the ratio of the amount of substance of the ferric ions to the amount of substance of the divalent manganese ions is 5:1.

[0052] The temperature of the reaction is 40-100℃. For example, 40-50℃, 50-55℃, 55-65℃, 65-75℃, 75-85℃, 85-95℃, or 95-100℃. In a preferred embodiment of the application, the temperature of the reaction is 55-95℃.

[0053] The pH of the reaction is 8-12. For example, 8-9, 9-10, 10-11, or 11-12. In a preferred embodiment of the application, the pH of the reaction is 9-11.

[0054] The time of the reaction is 15-120min. For example, 15-30min, 30-45min, 45-60min, 60-75min, 75-90min, 90-105min, or 105-120min. In a preferred embodiment of the application, the time of the reaction is 30-90min.

[0055] In the preparation method of the MnFe2O4@CM composite material of the application, in step 2), the mass ratio of the MnFe2O4 and the double-face isomerous net carbon film is 1:1-1:10. For example, 1:1-1:3, 1:3-1:5, 1:5-1:7, 1:7-1:9, or 1:9-1:10. In a preferred embodiment of the application, the mass ratio of the MnFe2O4 and the double-face isomerous net carbon film is 1:1-1:7.

[0056] In the preparation method of the MnFe2O4@CM composite material of the application, in step 2), the mixing time is 1-14h. For example, 1-2h, 2-3h, 3-4h, 4-6h, 6-8h, 8-10h, 10-12h, or 12-14h. In a preferred embodiment of the application, the mixing time is 2-4h.

[0057] The preparation method of the MnFe2O4@CM composite material of the application further comprises one or more of the following steps:

[0058] (1) separating the MnFe2O4@CM composite material; and / or,

[0059] (2) washing the MnFe2O4@CM composite material; and / or,

[0060] (3) drying the MnFe2O4@CM composite material; and / or,

[0061] (4) grinding the MnFe2O4@CM composite material

[0062] The MnFe2O4@CM composite material of the application takes an industrial dust filtration membrane as a precursor, and performs pre-carbonization-alkali activation on a PET / PTFE double-sided composite membrane through stepwise high-temperature pyrolysis assisted by alkali activation, and then obtains CM through high-temperature pyrolysis and recarbonization. Meanwhile, the spinel MnFe2O4 is prepared through a coprecipitation method under the action of an alkaline precipitant, and finally, the MnFe2O4 is loaded on the surface of the CM through an impregnation method with the help of the rich hydroxyl groups of the CM and the MnFe2O4 under the action of hydrogen bonds, so as to obtain a MnFe2O4 / CM material which is magnetically recyclable, has high oxygen vacancy abundance and surface hydroxyl groups, has high catalytic performance, and has a stable structure.

[0063] The third aspect of the application provides application of the MnFe2O4@CM composite material as described above in municipal sludge treatment. The MnFe2O4@CM composite material is used in combination with persulfate in the treatment of municipal sludge, and is used for treating organic pollutants in the municipal sludge.

[0064] In the application, the "municipal sludge" is sludge containing more than 80% of water after municipal sewage treatment. The municipal sludge is usually obtained after the sewage in the sewer is treated by adding chemicals, concentrated, and then treated by a plate and frame machine or a centrifugal machine. Further, the municipal sludge is dewatered sludge in the drying process after anaerobic digestion, i.e., sludge in the drying process.

[0065] In the application of the MnFe2O4@CM composite material in municipal sludge treatment, the MnFe2O4@CM composite material mainly treats organic pollutants and / or heavy metals in the municipal sludge treatment.

[0066] The organic pollutants include perfluorinated compounds. In a preferred embodiment of the application, the perfluorinated compounds are one or more of perfluorocarboxylic acids (PFCAs), perfluorooctanoic acids (PFOAs), or perfluorooctane sulfonates (PFOSs). The MnFe2O4@CM composite material adsorbs and fixes the persistent organic pollutants such as perfluorinated compounds through Π-Π stacking and functional group complexation, and realizes efficient removal of perfluorinated compounds in the municipal sludge through combination with persulfate.

[0067] In the application of the MnFe2O4@CM composite material in the treatment of municipal sludge, the mass ratio of the municipal sludge, the MnFe2O4@CM composite material and the persulfate is (250-350):(1-2):(14-20). For example, (250-270):(1-2):(14-20), (270-290):(1-2):(14-20), (290-310):(1-2):(14-20), (310-330):(1-2):(14-20), (330-350):(1-2):(14-20), (250-350):(1-1.5):(14-20), (250-350):(1.5-2):(14-20), (250-350):(1-2):(14-16), (250-350):(1-1.5):(16-18) or (250-350):(1-1.5):(18-20).

[0068] The mass ratio of the MnFe2O4@CM composite material and the persulfate is 1:7-1:10, based on the total mass of the reaction substances. For example, 1:7-1:8, 1:8-1:9 or 1:9-1:10.

[0069] The persulfate is selected from sodium persulfate or potassium persulfate.

[0070] In the application of the MnFe2O4@CM composite material in the treatment of municipal sludge, the treatment occurs in the solar drying process or the low-temperature drying process of the municipal sludge.

[0071] In the present application, the "solar drying" can also be referred to as "solar sludge drying", which refers to the drying treatment of sludge using solar energy as the main energy. The principle is as follows: 1) radiation drying, when the sludge in the greenhouse receives effective radiation of external sunlight, the temperature rises, so that the internal moisture can evaporate to the surrounding air, thereby increasing the air humidity on the surface of the sludge, and even reaching saturation; 2) through natural circulation or ventilation, the wet air in the greenhouse is discharged, so that the humidity on the surface of the sludge changes from the original saturated state to the unsaturated state, thereby promoting the further evaporation of the internal moisture of the sludge to the surrounding air.

[0072] When the MnFe2O4@CM composite material removes organic matter in the municipal sludge, it is in the drying process of the municipal sludge, and the drying process is selected from solar drying or low-temperature drying. The above drying process can provide more heat energy for the catalytic process, so that the activation effect of the composite material is better, the catalytic performance is better, the heat loss of the whole reaction is smaller, the energy utilization rate is better, and the quality and efficiency of the process flow are improved.

[0073] The application of the MnFe2O4@CM composite material in the municipal sludge treatment is mixed treatment.

[0074] The application of the MnFe2O4@CM composite material in the municipal sludge treatment is mixed treatment.

[0075] The application of the MnFe2O4@CM composite material in the municipal sludge treatment is mixed treatment.

[0076] In the MnFe2O4@CM composite material, the iron manganese spinel MnFe2O4 is a metal oxide with magnetism, and one unit cell contains 8 MnFe2O4 molecules, that is, 8 Mn 2+ , 16 Fe 3+ and 32 oxygen ions, wherein Mn and Fe will occupy the octahedral and tetrahedral centers of the single crystal, respectively. 2+ 3+ The two transition metals Mnand Fe in the MnFe2O4 structure can convert the valence state and transfer electrons to persulfate, thereby producing active substances and achieving good pollutant treatment effect, and have high catalytic activity.

[0077] Example 1

[0078] Preparation of MnFe2O4@CM composite material

[0079] 1) After the industrial dust filtration membrane (PET / PTFE double-sided composite membrane) was washed alternately with 0.1 mol / L sulfuric acid and deionized water, it was placed in a nickel crucible, heated to 105°C at a rate of 3°C / min under an air atmosphere, and then kept at a constant temperature for 40 min; heated to 170°C at a rate of 2°C / min under an air atmosphere, and then kept at a constant temperature for 30 min; heated to 270°C at a rate of 1°C / min under a vacuum atmosphere, and then kept at a constant temperature for 3 h to obtain a pre-carbonized sample; after the pre-carbonized sample was cooled to room temperature, it was mixed with NaOH at a molar ratio of 3:1 for alkali activation for 30 min, and ultrasonic treatment was performed simultaneously during the alkali activation process (room temperature ultrasonic treatment); after the activation, the sample was heated to 750°C at a rate of 2°C / min under a vacuum, and then kept at a constant temperature for 2 h to obtain a double-sided isomorphic carbon membrane CM, and the SEM characterization results of the CM product are shown in FIG. 1. Figures 1-2

[0080] 2) FeCl3·6H2O and MnCl2·4H2O were weighed at a molar ratio of 5:1 in 40 mL ultrapure water, the mixed solution was placed in a water bath, the water bath temperature was 90°C, 4 mol / L NaOH was slowly added under strong mechanical stirring, the pH of the system was controlled at 10.5, and the reaction was performed for 60 min to prepare a MnFe2O4 solution, and the SEM characterization results of the MnFe2O4 crystal are shown in FIG. 2. Figure 3

[0081] 3) The prepared CM was added to the above MnFe2O4 solution at a mass ratio of CM to MnFe2O4 of 4:1, and immersed for 3 h, the product was separated by a magnetic plate, and washed alternately with deionized water and anhydrous ethanol to obtain a MnFe2O4@CM composite material, and the SEM characterization results of the composite material are shown in FIG. 3. Figure 4

[0082] As shown in FIG. 1, the structure of the PET membrane end of the CM membrane prepared in the present application contains regular micropores. Figures 1-2 As shown in FIG. 2, the pores of the PTFE membrane end are larger, but part of the pores are collapsed, which may be because the PET has stronger thermal stability due to the presence of benzene rings. Figure 1 Figure 2 As shown in FIG. 3, the MnFe2O4 synthesized in the present application is an octahedron with a diameter of about 100-200 nm.

[0083] As shown in FIG. 1, the structure of the PET membrane end of the CM membrane prepared in the present application contains regular micropores. Figure 3 As shown in FIG. 2, the pores of the PTFE membrane end are larger, but part of the pores are collapsed, which may be because the PET has stronger thermal stability due to the presence of benzene rings.

[0084] As shown in FIG. 3, the MnFe2O4 synthesized in the present application is an octahedron with a diameter of about 100-200 nm. Figure 4 ​​​​It can be seen that the product MnFe2O4@CM is a composite material of MnFe2O4 and CM.

[0085] The Figure 5 In the composite material, the peaks appearing at 2θ = 18.0°, 29.7°, 34.9°, 42.5°, 52.6°, 56.1° and 61.6° are characteristic peaks of MnFe2O4 (JCPDS card No. 75-0035), which correspond to the (111), (220), (311), (400) and (440) crystal planes of face-centered cubic structure MnFe2O4, respectively; the two humps appearing at about 2θ = 26° and 44° are characteristic peaks of carbon material after graphitization.

[0086] Example 2

[0087] Preparation of MnFe2O4@CM composite material

[0088] 1) After the industrial dust filter membrane (PET / PTFE double-sided composite membrane) was washed alternately with 0.2 mol / L sulfuric acid and deionized water, it was placed in a nickel crucible and heated to 100°C at a rate of 2°C / min under air atmosphere, and then kept at constant temperature for 30 min; heated to 170°C at a rate of 1°C / min under air atmosphere, and then kept at constant temperature for 20 min; heated to 270°C at a rate of 1°C / min under vacuum atmosphere, and then kept at constant temperature for 3 h to obtain a pre-carbonized sample; after the pre-carbonized sample was cooled to room temperature, it was subjected to alkali activation with KOH and the pre-carbonized sample at a molar ratio of 2:1, and at the same time, ultrasonic treatment was performed (room temperature ultrasonic treatment); after activation, the sample was heated to 800°C at a rate of 2°C / min under vacuum, and then kept at constant temperature for 2 h to obtain a double-sided hetero-network carbon membrane CM.

[0089] 2) Fe2(SO4)3 and MnSO4·H2O were weighed at a molar ratio of 4:1 in 40 mL ultrapure water, the mixed solution was stirred uniformly and placed in a water bath, the water bath temperature was 95°C, under strong mechanical stirring, 3 mol / L KOH was slowly added dropwise, the pH was controlled at 11, and the reaction was carried out for 45 min to prepare a MnFe2O4 solution.

[0090] 3) According to the mass ratio of CM to MnFe2O4 of 5:1, the prepared CM was added to the above MnFe2O4 solution, and immersed for 6 h, then the product was separated by a magnetic plate, and then washed alternately with deionized water and anhydrous ethanol to obtain a MnFe2O4@CM composite material.

[0091] Example 3

[0092] Preparation of MnFe2O4@CM composite material

[0093] 1) The industrial dust filtration membrane (PET / PTFE double-sided composite membrane) is washed alternately with 0.25 mol / L sulfuric acid and deionized water, then placed in a nickel crucible, heated to 95°C at 2°C / min in an air atmosphere, and held at constant temperature for 40 min; heated to 170°C at 1°C / min in an air atmosphere, and held at constant temperature for 20 min; heated to 250°C at 2°C / min in a vacuum atmosphere, and held at constant temperature for 2 h to obtain a pre-carbonized sample; after the pre-carbonized sample cools to room temperature, it is alkali-activated with NaOH and the pre-carbonized sample at a molar ratio of 1.5:1, and simultaneously ultrasonic treated (room temperature ultrasonic treatment) during the alkali treatment; after activation, the sample is heated to 700°C at 2°C / min under vacuum, and held at constant temperature for 2 h to obtain a double-sided isomorphic net carbon membrane CM.

[0094] 2) Fe(NO3)3 and MnSO4·H2O are weighed at a molar ratio of 5:1 in 40 mL ultrapure water, the mixed solution is stirred uniformly and placed in a water bath, the water bath temperature is 90°C, under strong mechanical stirring, 20% ammonia water is slowly added dropwise, the pH of the system is controlled at 10, and the reaction is carried out for 45 min to prepare a MnFe2O4 solution.

[0095] 3) The prepared CM is added to the above MnFe2O4 solution at a mass ratio of CM to MnFe2O4 of 4:1, immersed for 5 h, the product is separated by a magnetic plate, and then washed alternately with deionized water and anhydrous ethanol to obtain a MnFe2O4@CM composite material.

[0096] Example 4

[0097] Application of MnFe2O4@CM composite material in removing perfluorinated compounds

[0098] The MnFe2O4@CM composite material prepared in Example 1 and peroxodisulfate are applied to remove perfluorinated compounds and heavy metals in municipal sludge (taken from a sludge disposal plant in Liu'an) in the drying process. The specific process is as follows: 100 mL of municipal sludge sample (mass about 90 g) containing various perfluorinated compounds at a concentration of 10 ug / kg (calculated on the dry basis of sludge) is poured into a 250 mL conical flask, the pH is adjusted to 7±0.5 with diluted H2SO4 and NaOH, 0.3 g of MnFe2O4@CM composite material is added, then peroxodisulfate is added, the mixture is stirred uniformly, the amount of peroxodisulfate added is 25 kg per ton of sludge (calculated on the basis of 80% moisture content), and the mixture is placed in a drying machine, the drying temperature is 75°C, and the reaction time is 3 h.

[0099] Comparative Example 1 is the dewatered sludge without drying, Comparative Example 2 is the peroxodisulfate system alone, and Comparative Example 3 is the MnFe2O4@CM composite material alone. The results are shown in Table 1.

[0100] Table 1

[0101]

[0102]

[0103] From the above table 1, for 10 μg / kg (dry basis) of perfluorinated carboxylic acid (PFCAs), perfluorooctanoic acid (PFOAs) or perfluorooctane sulfonate (PFOS), the removal rate of the sodium persulfate system alone in the comparative example 2 is 1.4%, 0.6% and 2.1% respectively; the removal rate of the MnFe2O4@CM composite material and the sodium persulfate composite system of the comparative example 1 is 2.8%, 2.6% and 3.1% respectively; this is because the two transition metals Mn 2+ and Fe 3+ in the structure of MnFe2O4 can convert the valence state to transfer electrons to persulfate to produce active substances, thereby achieving good pollutant treatment effect and having high catalytic activity, and the CM is introduced into the spinel MnFe2O4, on the one hand, the CM serves as an electron transport channel in the catalytic reaction to shorten the ion diffusion distance, and can also strengthen the electron transfer between MnFe2O4 and persulfate by the π electron affinity of the highly aromatic structure surface of the biochar, and on the other hand, the CM can also be used for hydrophobic and oleophobic perfluorinated compounds by using the electrostatic adsorption, surface functional group combination, Π-Π stacking and other effects, and the CM can catalytically oxidize the perfluorinated compounds into small molecules of CO2 and H2O; after the introduction of solar drying in the example 4, the removal rates of the three are increased by 1.8%, 1.7% and 2.3% respectively, which indicates that the drying process provides heat energy for the catalytic process, so that the activation effect of the composite material is better and the catalytic performance is better.

[0104] In summary, the MnFe2O4@CM of the application loads MnFe2O4 on the CM prepared from the industrial dust filtration membrane, reasonably recycles and harmlessly disposes the industrial dust filtration membrane, and the preparation process of the composite material of the application is simple, the conditions are mild, the heating is uniform, the energy is efficient, the control is easy, the preparation conditions and materials are universal, the product morphology is stable, the purity is high, the product processing is convenient and simple, and the application is suitable for medium-scale industrial production; the prepared MnFe2O4@CM composite material can activate the persulfate system and efficiently remove the perfluorinated compounds which are difficult to remove in sludge. Therefore, the application effectively overcomes the various shortcomings in the prior art and has high industrial utilization value.

[0105] The above embodiments are only illustrative of the principles of the present application and its efficacy, and are not intended to limit the present application. Any modification or change made by any person skilled in the art without departing from the spirit and scope of the present application shall be covered by the claims of the present application.

Claims

1. Use of MnFe2O4@CM composite material in the treatment of municipal sludge, characterized in that, The MnFe2O4@CM composite material is used in combination with persulfate when treating municipal sludge, and is used for treating organic pollutants in municipal sludge; the organic pollutants are selected from perfluorinated compounds; the composite material is obtained by loading MnFe2O4 on a double-face isomorphic network carbon film, and the double-face isomorphic network carbon film is obtained by pretreatment, high-temperature pyrolysis and alkali activation of an industrial dust filtration film; the pretreatment is acid pickling and water washing; the high-temperature pyrolysis and alkali activation process is a step-by-step high-temperature pyrolysis method supplemented by alkali activation, and specifically includes the following steps: the industrial dust filtration film is heated to 85-105 DEG C at a rate of 2-5 DEG C / min in an air atmosphere, and is kept at constant temperature for 30-60 min; the temperature is raised to 120-180 DEG C at a rate of 1-4 DEG C / min in an air atmosphere, and is kept at constant temperature for 30-60 min; the temperature is raised to 220-300 DEG C at a rate of 1-4 DEG C / min under vacuum, and is kept at constant temperature for 2-5 h to obtain a pre-carbonized sample; after the pre-carbonized sample is cooled to room temperature, alkali activation treatment is performed; recarbonization is performed by heating to 650-800 DEG C at a rate of 1-4 DEG C / min under vacuum, and keeping at constant temperature for 2-5 h to obtain the double-face isomorphic network carbon film CM; the double-face isomorphic network carbon film has a double-face isomorphic network hierarchical porous structure, and the hierarchical porous structure includes mesopores with a pore size of 5-50 nm and macropores with a pore size of 50-600 nm; the MnFe2O4 is an octahedron with a diameter of 50-250 nm; and the industrial dust filtration film is a PET / PTFE double-face composite film.

2. Use according to claim 1, characterized in that, The method comprises the following steps: 1) pretreating an industrial dust filtration film, then performing high-temperature pyrolysis supplemented by alkali activation to obtain a double-face isomorphic network carbon film; 2) mixing MnFe2O4 with the double-face isomorphic network carbon film to obtain a MnFe2O4@CM composite material.

3. Use according to claim 2, characterized in that, The acid pickling uses 0.005-0.3 mol / L sulfuric acid; And / or, the alkali used in the alkali activation treatment is KOH or NaOH; And / or, the molar ratio of alkali to pre-carbonized sample in the alkali activation treatment is 1:1-5:1; And / or, the time of the alkali activation treatment is 10-60 min; And / or, the alkali activation process is further supplemented by ultrasonic treatment.

4. Use according to claim 2, characterized in that, In step 2), the MnFe2O4 is obtained by mixing a solution containing trivalent iron ions with a solution containing divalent manganese ions, and then adding an alkali solution to react.

5. Use according to claim 4, characterized in that, The solution containing trivalent iron ions is selected from one or more of FeCl3 solution, Fe2(SO4)3 solution or Fe(NO3)3 solution; And / or, the solution containing divalent manganese ions is selected from one or more of MnCl2 solution or MnSO4 solution; And / or, the alkali solution is selected from one or more of NaOH solution, KOH solution or ammonia solution; And / or, the concentration of hydroxide in the alkali solution is 0.01-7 mol / L; And / or, the molar ratio of trivalent iron ions in the solution containing trivalent iron ions to manganese ions in the solution containing divalent manganese ions is 6:1-1:1; And / or, the temperature of the reaction is 40-100 DEG C; And / or, the pH of the reaction is 8-12; And / or, the reaction time is 15-120 min.

6. Use according to claim 2, characterized in that, In step 2), the mass ratio of the MnFe2O4 and the double-faced isomerous net carbon film is 1:1-1:10; And / or, in step 2), the mixing time is 1-14 h; And / or, in step 2), the mixing is impregnation mixing.

7. Use according to claim 1, characterized in that, The mass ratio of the municipal sludge, the MnFe2O4@CM composite material and the persulfate is (250-350):(1-2):(14-20); And / or, the treatment occurs in a solar drying process or a low-temperature drying process of the municipal sludge; And / or, the treatment temperature is 25-75℃; And / or, the treatment time is 1-6 h; And / or, the treatment is mixing treatment.

Images