CN113058431A - Method for preparing ZIF-8 composite membrane through electrodeposition and application thereof - Google Patents

Method for preparing ZIF-8 composite membrane through electrodeposition and application thereof Download PDF

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CN113058431A
CN113058431A CN202110441800.7A CN202110441800A CN113058431A CN 113058431 A CN113058431 A CN 113058431A CN 202110441800 A CN202110441800 A CN 202110441800A CN 113058431 A CN113058431 A CN 113058431A
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zif
electrodeposition
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马军
吕东伟
孙雪瑾
蒋海成
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Harbin Institute of Technology
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D67/00—Processes specially adapted for manufacturing semi-permeable membranes for separation processes or apparatus
    • B01D67/0002—Organic membrane manufacture
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D61/00—Processes of separation using semi-permeable membranes, e.g. dialysis, osmosis or ultrafiltration; Apparatus, accessories or auxiliary operations specially adapted therefor
    • B01D61/02—Reverse osmosis; Hyperfiltration ; Nanofiltration
    • B01D61/027—Nanofiltration
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D69/00—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor
    • B01D69/12—Composite membranes; Ultra-thin membranes
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D71/00—Semi-permeable membranes for separation processes or apparatus characterised by the material; Manufacturing processes specially adapted therefor
    • B01D71/02—Inorganic material
    • B01D71/024—Oxides
    • B01D71/025—Aluminium oxide
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D71/00—Semi-permeable membranes for separation processes or apparatus characterised by the material; Manufacturing processes specially adapted therefor
    • B01D71/06—Organic material
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D71/00—Semi-permeable membranes for separation processes or apparatus characterised by the material; Manufacturing processes specially adapted therefor
    • B01D71/06—Organic material
    • B01D71/30—Polyalkenyl halides
    • B01D71/32—Polyalkenyl halides containing fluorine atoms
    • B01D71/34—Polyvinylidene fluoride
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F1/44—Treatment of water, waste water, or sewage by dialysis, osmosis or reverse osmosis
    • C02F1/442—Treatment of water, waste water, or sewage by dialysis, osmosis or reverse osmosis by nanofiltration
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2101/00—Nature of the contaminant
    • C02F2101/30—Organic compounds
    • C02F2101/308—Dyes; Colorants; Fluorescent agents

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Abstract

The invention discloses a method for preparing a ZIF-8 composite membrane by electrodeposition and application thereof, and relates to a method for preparing a ZIF-8 composite membrane by electrodeposition and application thereof. The invention aims to solve the problems of uneven thickness and difficult control of defects in the existing preparation method. The film is composed of a basement membrane and a ZIF-8 separation layer; the separating layer is a compact ZIF-8 crystal separating layer with uniform thickness, and has small and uniform membrane pores, uniform and thin membrane layer thickness and strong separating capability for small molecular pollutants in water. The method comprises the following steps: after noble metal is sputtered on the basement membrane for conduction, the basement membrane and graphite paper are respectively used as a working electrode and a counter electrode, immersed into an electrolytic cell containing precursor solution, and the basement membrane is used as a cathode and synthesized by a one-step electrodeposition method at normal temperature and normal pressure. The composite membrane prepared by the invention has excellent interception performance to smaller dye molecules, and the flux is larger than that of the MOFs composite membrane prepared by the traditional method. The invention is used for intercepting dye wastewater.

Description

Method for preparing ZIF-8 composite membrane through electrodeposition and application thereof
Technical Field
The invention relates to a method for preparing a ZIF-8 composite membrane by electrodeposition and application thereof.
Background
At present, due to the fact that industrial water is inappropriately discharged into the environment, the utilization rate of chemical fertilizers in the agricultural field is high, the discharge of domestic water is increased due to population growth, and the like, the problem of water pollution is one of the main problems of global environmental pollution, and serious freshwater resource deficiency and ecological environment damage are caused. As industry develops, more and more synthetic dyes are used on a large scale in industry instead of natural dyes. There are currently over 10 and over ten thousand commercial dyes (of which the azo dyes are about 70% by weight) and not all dyes adhere to the surface during industrial dyeing processes, the lost dyes generating dye waste. Over 100 million tons of dye are produced worldwide each year, 50% of which are textile dyes.
Among the water treatment technologies, the membrane technology has attracted much attention, and is a method for effectively removing contaminants from water due to its high efficiency, no secondary pollution, simple operation, and small space requirement, compared to other purification technologies. In recent years, more and more membrane separation techniques have been studied for the treatment of dye wastewater. The dye wastewater with a plurality of small molecules has the characteristics of difficult biodegradation and difficult interception, wherein the nanofiltration membrane has better application prospect aiming at the dye molecules with small molecular diameters in the water.
Different types of organic polymer membranes, porous composite membranes (TFCs), inorganic membranes, etc., can be used for wastewater treatment. The organic film has various pore sizes but poor tolerance and is easy to be polluted; in addition, inorganic membranes are not effective in treating wastewater containing small-molecule contaminants. Among emerging materials, organic-inorganic hybrid microporous crystalline Materials (MOFs) have been extensively studied in the last decade, gaining widespread attention and acceptance throughout the world due to their high specific surface area, unique structure and chemical tunability. Zeolitic Imidazolate Frameworks (ZIFs) are a subset of metal-organic frameworks and are novel crystalline porous materials that combine the excellent properties of zeolites and MOFs, such as crystallinity, microporosity, high specific surface area, and excellent thermal and chemical stability.
Electrochemical methods have many advantages over other methods, such as shorter synthesis times and milder synthesis conditions, it also offers the possibility of directly influencing the reaction in real time, it offers more control capability and the ability to carry out the synthesis in a continuous manner, furthermore the local nature of the electrochemical method allows the formation of oriented films without the need for pretreatment of the surface as is often the case. Can have good application prospect for micromolecular dye wastewater which is difficult to treat, uniform and stable membrane pores of a ZIF-8 membrane and smaller pore diameter.
Disclosure of Invention
The invention provides a method for preparing a composite membrane with a ZIF-8 separating layer by electrodeposition and application thereof, aiming at solving the problems of uneven thickness and difficulty in controlling defects of the existing preparation method.
The invention relates to a method for preparing a ZIF-8 composite membrane by electrodeposition, which is used for carrying out electrodeposition synthesis at normal temperature and normal pressure by taking analytically pure zinc acetate dihydrate and 2-methylimidazole dissolved in deionized water as raw materials, and specifically comprises the following steps:
firstly, preparing an electrodeposition precursor solution: respectively and completely dissolving 2-methylimidazole and zinc nitrate dihydrate in deionized water to obtain a 2-methylimidazole solution and a zinc nitrate dihydrate solution, and mixing and stirring the two solutions to obtain a ZIF-8 precursor solution;
secondly, pretreatment of a base film: washing a base film in deionized water, drying, and sputtering and depositing noble metal on the base film to obtain a conductive base film;
thirdly, electro-deposition: fixing a conductive base film and graphite paper by using an electrode clamp and separating the conductive base film and the graphite paper in parallel by 2.0cm by adopting a two-electrode deposition system, immersing the conductive base film and the graphite paper into a ZIF-8 precursor solution, and carrying out electrodeposition by using the conductive base film as a working electrode and the graphite paper as a counter electrode to obtain a composite film;
and fourthly, after the electrodeposition is finished, repeatedly washing the composite membrane by deionized water until no ZIF-8 large particles are left on the surface of the composite membrane, and drying to obtain the ZIF-8 composite membrane.
The ZIF-8 composite membrane prepared by the method is applied to water treatment, and is used for intercepting dye wastewater.
The invention has the advantages that:
1. the ZIF-8 modified material used in the invention has high crystallinity and stable structure, and the pressure filtration is required in the nanofiltration membrane filtration process, and is generally 0.2-0.5 MPa. The stable crystal structure of ZIF-8 makes it difficult to compress under pressure filtration and causes problems such as small porosity and flux reduction.
2. The ZIF-8 separation layer synthesized by the method has good self-limitation, the thickness of the separation layer can be controlled, and the thickness of the ZIF-8 separation layer is increased very slowly when the thickness reaches a certain thickness.
3. The method has the advantages of mild synthesis conditions, simple preparation process and short preparation time, and compared with the traditional preparation methods, such as a hydrothermal method, in-situ growth and the like, the method has the advantages of short synthesis time, compact and uniform thickness of the synthesized ZIF-8 film and fewer defects.
4. The ZIF-8 crystal has better physical and chemical stability and thermal stability, the high porosity ensures that the filtering flux of the crystal is larger than that of the traditional nanofiltration membrane material, and the microporous structure can intercept smaller pollutants in water, thereby having better interception effect on micromolecular dye wastewater.
5. The method can be carried out in a water solution at normal temperature and normal pressure, the preparation time is short, the prepared separation layer has few defects, the film layer is compact and uniform in thickness, and ZIF-8 is used as a microporous crystal material, has small pore diameter, high porosity and stable structure and is suitable for intercepting treatment of small molecular pollutants in water. The preparation method has the advantages that the ZIF-8 separation layer and the base film are tightly combined and are not easy to fall off due to the action of an electric field.
Drawings
FIG. 1 is a schematic diagram of an electrochemical cathodic deposition process of the present invention;
FIG. 2 is a plan view of a scanning electron microscope of a ZIF-8/AAO composite film prepared in example 1;
FIG. 3 is a sectional view of a scanning electron microscope of a ZIF-8/AAO composite film prepared in example 1;
FIG. 4 is a scanning electron microscope plan view of a ZIF-8/PVDF composite film prepared in example 2;
FIG. 5 is a scanning electron microscope cross-sectional view of a ZIF-8/PVDF composite film prepared in example 2;
FIG. 6 is a Fourier infrared spectrum of a ZIF-8/AAO composite membrane prepared in example 1;
FIG. 7 is a Fourier transform infrared spectrum of the ZIF-8/PVDF composite membrane prepared in example 2;
FIG. 8 is an X-ray diffraction pattern of the ZIF-8/AAO composite membrane prepared in example 1; wherein 1 represents a ZIF-8 membrane, and 2 represents a ZIF-8/AAO composite membrane;
FIG. 9 is an X-ray diffraction pattern of the ZIF-8/PVDF composite membrane prepared in example 2; wherein 1 represents a ZIF-8 membrane, and 2 represents a ZIF-8// PVDF composite membrane;
FIG. 10 is XPS spectra of Zn element of two composite films of example 1 and example 2; wherein 1 represents example 1 and 2 represents example 2;
FIG. 11 is XPS spectra of N element of the composite membranes of example 1 and example 2;
FIG. 12 is a bar graph comparing the flux and rejection rates of dye wastewater performance tests for the ZIF-8/AAO composite membrane prepared in example 1 and the ZIF-8/PVDF composite membrane prepared in example 2; where A represents flux and B represents rejection.
Detailed Description
The first embodiment is as follows: the method for preparing the ZIF-8 composite membrane by electrodeposition takes analytically pure zinc acetate dihydrate and 2-methylimidazole dissolved in deionized water as raw materials, and carries out electrodeposition synthesis at normal temperature and normal pressure, and specifically comprises the following steps:
firstly, preparing an electrodeposition precursor solution: respectively and completely dissolving 2-methylimidazole and zinc nitrate dihydrate in deionized water to obtain a 2-methylimidazole solution and a zinc nitrate dihydrate solution, and mixing and stirring the two solutions to obtain a ZIF-8 precursor solution;
secondly, pretreatment of a base film: washing a base film in deionized water, drying, and sputtering and depositing noble metal on the base film to obtain a conductive base film;
thirdly, electro-deposition: fixing a conductive base film and graphite paper by using an electrode clamp and separating the conductive base film and the graphite paper in parallel by 2.0cm by adopting a two-electrode deposition system, immersing the conductive base film and the graphite paper into a ZIF-8 precursor solution, and carrying out electrodeposition by using the conductive base film as a working electrode and the graphite paper as a counter electrode to obtain a composite film;
and fourthly, after the electrodeposition is finished, repeatedly washing the composite membrane by deionized water until no ZIF-8 large particles are left on the surface of the composite membrane, and drying to obtain the ZIF-8 composite membrane.
In the embodiment, an electrochemical method is adopted, a base membrane to be modified is taken as the cathode of an electrolytic cell, zinc ions in a precursor solution move to the surface of the cathode membrane after electrification and are loaded, and react with 2-methylimidazole in the solution to generate ZIF-8 crystals on the surface of the membrane and continuously grow. When the preparation is started, more and uniform ZIF-8 growth sites are uniformly generated on the conductive base membrane under the action of an electric field, so that ZIF-8 crystals can uniformly grow on a porous anodic aluminum oxide membrane or a polyvinylidene fluoride membrane with larger pore diameter, and the modification is realized. As ZIF-8 grows on the surface of the basement membrane, crystal particles become large and are connected densely, the conductive surface of the basement membrane is covered, and the conductivity is weakened. After a ZIF-8 thin layer is formed, the growth of crystals is basically stopped, which is beneficial to the growth control of a separation layer on the surface of the modified composite film.
The second embodiment is as follows: the first difference between the present embodiment and the specific embodiment is: in the first step, the molar ratio of the 2-methylimidazole to the zinc nitrate dihydrate is (60-70): 1. The rest is the same as the first embodiment.
The third concrete implementation mode: the present embodiment is different from the first to the second embodiments in that: and dissolving the 2-methylimidazole in the step two in deionized water, wherein the concentration is 0.8-1.2 mol/L. The rest is the same as one of the first to second embodiments.
The fourth concrete implementation mode: the difference between this embodiment mode and one of the first to third embodiment modes is: and in the second step, the base film is an inorganic film, in particular a porous anodic aluminum oxide film. The others are the same as in one of the first to third embodiments.
The fifth concrete implementation mode: the difference between this embodiment and one of the first to fourth embodiments is: and in the second step, the base film is an organic film, in particular a polyvinylidene fluoride film. The other is the same as one of the first to fourth embodiments.
In this embodiment, when an organic film is selected, the drying in step four is not suitable for being put into an oven for drying, because the ZIF-8 separation layer may be peeled off when the organic film is excessively bent and the temperature is severely changed due to the difference in young's modulus and the difference in coefficient of thermal expansion between the base film and the ZIF-8 crystal layer; therefore, normal air drying should be selected to avoid cracking of the ZIF-8 separation layer.
The PVDF film in this embodiment needs to be longer in sputtering conduction time than the AAO-based film.
The sixth specific implementation mode: the difference between this embodiment and one of the first to fifth embodiments is: the noble metal deposited in the second step is Pt; the sputtering time was 60 s. The other is the same as one of the first to fifth embodiments.
The seventh embodiment: the difference between this embodiment and one of the first to sixth embodiments is: and in the third step, the conductive base film has the same size as the graphite paper. The other is the same as one of the first to sixth embodiments.
The specific implementation mode is eight: the present embodiment differs from one of the first to seventh embodiments in that: the parameters of electrodeposition in the third step are as follows: the constant potential mode is 0.16-0.25 mA. The other is the same as one of the first to seventh embodiments.
The method is characterized in that different deposition time and deposition current density are adopted according to different requirements of water treatment in the electrodeposition process, the electrodeposition time is required to enable the ZIF-8 crystal to be layered without defects but not too thick, a proper current density range is determined according to a cyclic voltammetry curve of a base membrane in a precursor solution, and the current density is 0.12-0.16 mA/cm2And the problems of excessive film defects and uneven film thickness caused by bubbles generated by violent hydrolysis of water in the precursor liquid are avoided.
The specific implementation method nine: the present embodiment differs from the first to eighth embodiments in that: the deposition time of the electrodeposition in the step three is 30min to 90 min. The rest is the same as the first to eighth embodiments.
Along with the increase of the electrodeposition time, the ZIF-8 crystal gradually grows to form a film, the morphology of the surface of the composite film is different due to different electrodeposition time, the surface of the composite film needs to be compact, the defects are few, and the separation layer is not too thick.
The detailed implementation mode is ten: the application of the ZIF-8 composite membrane in water treatment in the embodiment is to use the ZIF-8 composite membrane for dye wastewater interception.
The beneficial effects of the present invention are demonstrated by the following examples:
example 1: the method for preparing the ZIF-8 composite membrane by electrodeposition specifically comprises the following steps:
firstly, preparing an electrodeposition precursor solution: 4.105g of 2-methylimidazole is dissolved in 50mL of deionized water to obtain a 2-methylimidazole solution, 0.183g of zinc nitrate dihydrate is dissolved in 10mL of deionized water to obtain a zinc nitrate dihydrate solution, and the two solutions are mixed and stirred to obtain a ZIF-8 precursor solution;
secondly, pretreatment of a base film: ultrasonically cleaning a porous anodic alumina membrane with the diameter of 13mm and the pore diameter of 200nm for 5min, drying, and sputtering Pt on the base membrane for 60s by using a sputtering instrument to obtain a conductive base membrane;
thirdly, electro-deposition: fixing the conductive base film and graphite paper by an electrode clamp by adopting a two-electrode deposition system, separating the conductive base film and the graphite paper in parallel by 2.0cm, immersing the conductive base film and the graphite paper into a ZIF-8 precursor solution, taking the conductive base film as a working electrode and the graphite paper as a counter electrode, and taking the current density of 0.15mA/cm2Performing cathode electrodeposition for 60min under constant current to obtain a composite membrane;
and fourthly, after the electrodeposition is finished, repeatedly washing the composite membrane by deionized water until no ZIF-8 large particles are left on the surface of the composite membrane, and drying to obtain the ZIF-8/AAO composite membrane.
Example 2: the method for preparing the ZIF-8 composite membrane by electrodeposition specifically comprises the following steps:
firstly, preparing an electrodeposition precursor solution: 4.105g of 2-methylimidazole is dissolved in 50mL of deionized water to obtain a 2-methylimidazole solution, 0.183g of zinc nitrate dihydrate is dissolved in 10mL of deionized water to obtain a zinc nitrate dihydrate solution, and the two solutions are mixed and stirred to obtain a ZIF-8 precursor solution;
secondly, pretreatment of a base film: cleaning a polyvinylidene fluoride membrane with the diameter of 15mm and the molecular weight cutoff of 100KD, drying the polyvinylidene fluoride membrane at room temperature, and sputtering Pt on the base membrane for 60s by using a sputtering instrument to obtain a conductive base membrane;
thirdly, electro-deposition: fixing the conductive base film and graphite paper by an electrode clamp by adopting a two-electrode deposition system, separating the conductive base film and the graphite paper in parallel by 2.0cm, immersing the conductive base film and the graphite paper into a ZIF-8 precursor solution, taking the conductive base film as a working electrode and the graphite paper as a counter electrode, and taking the current density of 0.15mA/cm2Performing cathode electrodeposition for 60min under constant current to obtain a composite membrane;
and fourthly, after the electrodeposition is finished, repeatedly washing the composite membrane by using deionized water until no ZIF-8 large particles are left on the surface of the composite membrane, and drying to obtain the ZIF-8/PVDF composite membrane.
FIG. 1 is a schematic diagram of an electrochemical cathode deposition process, in which a base membrane to be modified is used as an electrolytic cell cathode, zinc ions in a precursor solution move to the surface of the cathode membrane after electrification and are loaded, and react with 2-methylimidazole in the solution to generate ZIF-8 crystals on the surface of the membrane and continuously grow. When a compact film layer is formed, the cathode resistance is increased, the growth of the ZIF-8 crystal is basically stopped, the thickness of a separation layer is about the grain size of the formed crystal, and the screenshot shows that compared with the traditional method, the crystal layer with the thickness of more than 1 mu m is synthesized and grown for a longer time.
FIG. 2 is a plan view of a scanning electron microscope of a ZIF-8/AAO composite film prepared in example 1; FIG. 3 is a sectional view of a scanning electron microscope of a ZIF-8/AAO composite film prepared in example 1; as can be seen from the figure, the AAO surface was covered with a uniform and dense ZIF-8 crystal layer with few defects, and the separation layer was uniform in thickness and free from large undulations.
FIG. 4 is a scanning electron microscope plan view of a ZIF-8/PVDF composite film prepared in example 2; FIG. 5 is a scanning electron microscope cross-sectional view of a ZIF-8/PVDF composite film prepared in example 2; as can be seen from the figure, the surface of PVDF was covered with a uniform and dense ZIF-8 crystal layer with few defects, and the thickness of the separation layer was uniform without large undulations.
FIG. 6 is a Fourier infrared spectrum of a ZIF-8/AAO composite membrane prepared in example 1; as can be seen by comparing the peaks of the original film and the ZIF-8 crystal particles, the modified composite film was found to be 997 cm and 1145cm-1The characteristic peak of ZIF-8 is obvious, the absorption band of the area is related to C-N stretching in imidazole ring, and compared with the original film, the characteristic peak or peak value is increased to 1571cm-1The peak is C-N characteristic peak. 2920cm-1The absorption band at (d) is due to the aromatic C-H stretching of imidazole.
FIG. 7 is a Fourier transform infrared spectrum of the ZIF-8/PVDF composite membrane prepared in example 2; as can be seen from the comparison of the peaks of the PVDF raw film and the ZIF-8 crystal particles in the figure, the modified composite film was found to be 997 and 1145cm-1The characteristic peak of ZIF-8 is obvious, the absorption band of the area is related to C-N stretching in imidazole ring, and compared with the original film, the characteristic peak or peak value is larger, 2920cm-1The absorption band at (d) is due to the aromatic C-H stretching of imidazole. 1571cm-1The peak is C-N characteristic peak. The PVDF membrane has more characteristic peaks, and the successful ZIF-8 loading needs to be analyzed by comparing the composite membrane with the original membrane.
FIG. 8 is an X-ray diffraction pattern of the ZIF-8/AAO composite membrane prepared in example 1; wherein 1 represents a ZIF-8 membrane, and 2 represents a ZIF-8/AAO composite membrane; as can be seen by comparing ZIF-8, several ZIF-8 crystal peaks at (001) (002) (012) (022) (112) (222), especially the highest characteristic peak at an angle of 7 DEG 2theta, were apparent in the image of the ZIF-8/AAO composite film, and the characteristic peaks appeared on the modified AAO film, demonstrating that ZIF-8 was firmly supported to the AAO surface.
FIG. 9 is an X-ray diffraction pattern of the ZIF-8/PVDF composite membrane prepared in example 2; wherein 1 represents a ZIF-8 membrane, and 2 represents a ZIF-8// PVDF composite membrane; as can be seen by comparing ZIF-8, several ZIF-8 crystal characteristic peaks at (001) (002) (012) (022) (112) (222) also appeared on the modified PVDF film, demonstrating that ZIF-8 is firmly supported to the PVDF film surface.
FIG. 10 is XPS spectra of Zn element of two composite films of example 1 and example 2;
FIG. 11 shows two embodiments of example 1 and example 2XPS spectrum of composite film N element; for the Zn element peak, Zn 2p at the binding energy of 1022eV3/2Zn 2p at binding energy 1045eV1/2Both characteristic peaks are narrow peak type, meaning that most of Zn element is in ZIF-8 crystal tetrahedral coordination. The PVDF original film, namely the polyvinylidene fluoride, does not contain N element in the components, and the existence of the characteristic peak of the N element also shows that ZIF-8 is successfully grown and loaded on the surfaces of two base films.
FIG. 12 is a bar graph comparing the flux and rejection rates of dye wastewater performance tests for the ZIF-8/AAO composite membrane prepared in example 1 and the ZIF-8/PVDF composite membrane prepared in example 2; wherein A represents flux and B represents rejection; comparing the data graphs of the filtration experiment of 10mg/L methylene blue solution, wherein an orange column body is the filtration flux comparison of the modified composite membrane, and a blue column body is the membrane retention rate comparison; the microfiltration membrane with an AAO of 200nm used in this example does not need to have flux under pressure and has substantially no filtering effect on methylene blue dye molecules. It can be seen that the ZIF-8/AAO composite membrane prepared in the embodiment 1 of the invention has a good filtering effect on methylene blue solution, the rejection rate is more than 98%, the membrane flux is larger than that of a traditional nanofiltration membrane and a ZIF-8 membrane prepared by a traditional method, and the water treatment efficiency is high, so that the ZIF-8 microporous crystal material has the advantage of being used as a nanofiltration membrane modification material. The rejection rate of the ZIF-8/PVDF composite membrane subjected to electro-deposition for 60min to methylene blue can reach 97%, and the composite membrane prepared in the embodiment 2 of the invention has a good filtering effect on methylene blue solution.

Claims (10)

1. A method for preparing a ZIF-8 composite membrane by electrodeposition is characterized in that the ZIF-8 composite membrane is prepared by electrodeposition synthesis at normal temperature and normal pressure by taking analytically pure zinc acetate dihydrate and 2-methylimidazole dissolved in deionized water as raw materials and specifically comprises the following steps:
firstly, preparing an electrodeposition precursor solution: respectively and completely dissolving 2-methylimidazole and zinc nitrate dihydrate in deionized water to obtain a 2-methylimidazole solution and a zinc nitrate dihydrate solution, and mixing and stirring the two solutions to obtain a ZIF-8 precursor solution;
secondly, pretreatment of a base film: washing a base film in deionized water, drying, and sputtering and depositing noble metal on the base film to obtain a conductive base film;
thirdly, electro-deposition: fixing a conductive base film and graphite paper by using an electrode clamp and separating the conductive base film and the graphite paper in parallel by 2.0cm by adopting a two-electrode deposition system, immersing the conductive base film and the graphite paper into a ZIF-8 precursor solution, and carrying out electrodeposition by using the conductive base film as a working electrode and the graphite paper as a counter electrode to obtain a composite film;
and fourthly, after the electrodeposition is finished, repeatedly washing the composite membrane by deionized water until no ZIF-8 large particles are left on the surface of the composite membrane, and drying to obtain the ZIF-8 composite membrane.
2. The method for preparing the ZIF-8 composite membrane through electrodeposition as claimed in claim 1, wherein the molar ratio of 2-methylimidazole to zinc nitrate dihydrate in the first step is (60-70): 1.
3. The method for preparing the ZIF-8 composite membrane by electrodeposition as claimed in claim 1, wherein the 2-methylimidazole in step two is dissolved in deionized water at a concentration of 0.8 to 1.2 mol/L.
4. The method for preparing the ZIF-8 composite membrane by electrodeposition as claimed in claim 1, wherein the base membrane in step two is an inorganic membrane, specifically a porous anodic aluminum oxide membrane.
5. The method for preparing the ZIF-8 composite membrane by electrodeposition as claimed in claim 1, wherein the base membrane in the second step is an organic membrane, specifically a polyvinylidene fluoride membrane.
6. The method of electrowinning a ZIF-8 composite membrane as claimed in claim 1, wherein the noble metal deposited in step two is Pt; the sputtering time was 60 s.
7. The method of electrodepositing a ZIF-8 composite film according to claim 1, wherein the conductive base film is the same size as graphite paper in step three.
8. The method for preparing the ZIF-8 composite film by electrodeposition as claimed in claim 1, wherein the parameters of electrodeposition in step three are: the constant potential mode is 0.16-0.25 mA.
9. The method for preparing the ZIF-8 composite membrane by electrodeposition as claimed in claim 1, wherein the deposition time of the electrodeposition in step three is 30 to 90 min.
10. The use of the ZIF-8 composite membrane prepared by the method of claim 1, in water treatment, wherein the ZIF-8 composite membrane is used for dye wastewater rejection.
CN202110441800.7A 2021-04-23 2021-04-23 Method for preparing ZIF-8 composite membrane through electrodeposition and application thereof Pending CN113058431A (en)

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