CN113087944B

CN113087944B - MOFs composite electro-catalytic membrane and preparation method and application thereof

Info

Publication number: CN113087944B
Application number: CN202110363117.6A
Authority: CN
Inventors: 李益华; 韩加祥; 宋奇
Original assignee: Southwest Minzu University
Current assignee: Southwest Minzu University
Priority date: 2021-04-02
Filing date: 2021-04-02
Publication date: 2022-01-07
Anticipated expiration: 2041-04-02
Also published as: CN113087944A

Abstract

The invention provides an MOFs composite electro-catalytic membrane and a preparation method and application thereof, and relates to the technical field of electro-catalytic membranes. The preparation method comprises the following steps: s1: dissolving polyvinylidene fluoride in an organic solvent according to a ratio, and fully dissolving to obtain a polyvinylidene fluoride solution; s2: adding carbon powder and a metal organic frame material into the prepared polyvinylidene fluoride solution in proportion, fully dissolving to prepare a membrane casting solution, and performing ultrasonic defoaming treatment; s3: and preparing the membrane casting solution into the MOFs composite electro-catalytic membrane. The invention also provides the MOFs composite electro-catalytic membrane prepared by the method, and the MOFs composite electro-catalytic membrane is applied as a cathode material in a biofuel cell. The invention can prepare the composite electro-catalytic membrane with higher pollution resistance and degradation efficiency on pollutants in sewage. The application of the composite material as a cathode material of a biofuel cell can further improve the degradation efficiency and the pollution resistance of the composite material to pollutants in sewage.

Description

MOFs composite electro-catalytic membrane and preparation method and application thereof

Technical Field

The invention relates to the technical field of electrocatalysis membranes, in particular to an MOFs composite electrocatalysis membrane and a preparation method and application thereof.

Background

In recent decades, with the rapid development of industries such as aquatic products, cultivation, medicines and the like, the water body environmental pollution condition of China is getting more and more serious; the polluted water is derived from the original domestic sewage and industrial wastewater and is changed into surface water, underground water and the like which are polluted nationwide. In the water pollution treatment technology, the membrane technology is widely applied due to the characteristics of high efficiency and environmental protection. However, the membrane pollution problem is one of bottlenecks which limit the wide application of membrane technology, the membrane pollution causes the service cycle of the membrane to be shortened, the cleaning frequency is increased, and the operation cost of the membrane in wastewater treatment is greatly increased.

A Microbial Fuel Cell (MFC) is a novel water treatment technology, and a typical MFC is composed of electrogenesis microbes, an anode chamber, a cathode chamber, a proton exchange membrane, an anode material, a cathode material, and the like, and the reaction principle is as follows: at the anode, the electrogenic bacteria oxidize the organic matter into CO₂Electrons and protons are released and reach the cathode through the external circuit connection, the protons pass through the cation exchange membrane to reach the cathode, and then an Oxygen Reduction Reaction (ORR) occurs at the cathode, namely, oxygen is reduced as an electron acceptor to generate water molecules, so that a stable electronic loop is formed, and the conversion of organic chemical energy in the sewage to electric energy is realized. However, since the reduction of oxygen is an irreversible reaction, the reaction kinetics is slow, which results in a loss of 0.3-0.4V of the cathode potential; the wide application of the MFC has certain limitation; in order to improve the applicability of MFC, the prior art uses a platinum-series catalyst for the cathode material of MFC to improve the electrocatalytic activity of cathode oxygen reduction, thereby improving the applicability of MFC.

In order to improve the effect and efficiency of water treatment, the prior art combines MFC and membrane technology, and membrane filtration can improve the quality of effluent after sewage treatment by MFC and improve the overall efficiency of sewage treatment; the directional movement of electrons and protons in the MFC can generate a micro electric field, can slow down the attachment of bacterial metabolites and the like to the surface of the membrane, and can alleviate membrane pollution.

At present, the manufacturing cost of improving the electrocatalytic activity of cathode oxygen reduction of an MFC cathode material by using a platinum catalyst is high; the membrane used in combination with MFC is generally a carbon membrane, which is generally used as an anode material of MFC, and its anti-pollution performance and degradation efficiency of pollutants in sewage are low.

Disclosure of Invention

The invention aims to provide a preparation method of an MOFs composite electro-catalytic membrane, which can be used for preparing the composite electro-catalytic membrane with higher pollution resistance and higher degradation efficiency on pollutants in sewage.

The second purpose of the invention is to provide the MOFs composite electro-catalytic membrane which is prepared by the preparation method and has higher anti-pollution performance and degradation efficiency on organic matters.

The third purpose of the invention is to provide the application of the MOFs composite electrocatalytic membrane, which can be effectively applied to the cathode material of a biofuel cell.

The embodiment of the invention is realized by the following technical scheme:

a preparation method of MOFs composite electrocatalytic membrane comprises the following steps:

s1: dissolving polyvinylidene fluoride in an organic solvent according to a ratio, and fully dissolving to obtain a polyvinylidene fluoride solution;

s2: adding carbon powder and a metal organic frame material into the prepared polyvinylidene fluoride solution in proportion, fully dissolving to prepare a membrane casting solution, and performing ultrasonic defoaming treatment;

s3: and preparing the membrane casting solution into the MOFs composite electro-catalytic membrane.

Metal Organic Framework (MOF) is an inorganic-organic hybrid porous material with a more stable crystal structure and a larger specific surface area. MOFs result from coordination reactions between metal ions/clusters (e.g., transition metals and lanthanides) and organic ligands.

According to the invention, MOFs is added into the carbon film to form the MOFs composite electro-catalytic film, and the MOFs has higher catalytic reaction activity through adsorption, acid-base neutralization, hydrophobicity, pi-pi interaction, hydrogen bond acting force and electrostatic interaction, so that the anti-pollution performance of the MOFs composite electro-catalytic film and the degradation efficiency of organic matters are higher.

Further, in the step S1, 2-4 g of polyvinylidene fluoride is dissolved in 18-22 mL of organic solvent.

Further, in the step S2, 0.4-0.8 g of carbon powder and 0.3-0.7 g of metal organic framework material are added into 18-22 mL of polyvinylidene fluoride solution.

The addition amount of the carbon fibers and the addition amount of the MOFs can influence the specific surface area, the porosity and the pore size of the membrane, so that the degradation efficiency of the electro-catalytic membrane on pollutants in sewage is influenced; according to the invention, the addition amount of the carbon fibers and the addition amount of the MOFs are controlled within the range, so that the electrocatalytic membrane with small pore diameter and large specific surface area is prepared, and the degradation efficiency of the electrocatalytic membrane on pollutants in sewage is high.

Further, the metal-organic framework material in the step S2 is MIL-101(Fe) or Fe-MOF crystal.

Among the MOFs, the pore size and shape of the MOFs are determined by the kind and properties of metal ions and organic ligands. The invention adopts MIL-101(Fe) and Fe-MOF crystals, which not only has small aperture and higher catalytic activity, but also has simple synthetic route and lower cost.

Further, the preparation method of MIL-101(Fe) comprises the following steps: a. weighing metal salt FeCl according to the molar ratio of iron to nickel of 1-9: 1₃·6H₂O and NiCl₂·6H₂O, taking organic ligand terephthalic acid according to the molar ratio of 1: 1-3 to the total metal salt, respectively adding the organic ligand terephthalic acid to N, N dimethylformamide solvent, stirring and reacting at 60-150 ℃ for 6-48 h, and cooling to room temperature; b. carrying out suction filtration on the cooled reaction solution to obtain solid powder, washing the solid powder by using an N, N-dimethylformamide solvent, then heating and refluxing the solid powder in a methanol solvent, and cooling and carrying out suction filtration; c. and roasting the solid powder obtained after suction filtration at 500-800 ℃, and then carrying out acid washing by using a 5% dilute hydrochloric acid solution to obtain the MIL-101(Fe) metal organic framework material.

When the MIL-101(Fe) produced by the general production method is tested for catalytic activity, the intermolecular connection mode is an ionic bond, so that partial hydrolysis can be generated in an aqueous solution, and therefore, the intermolecular force of the MIL-101(Fe) is changed by adopting a high-temperature roasting treatment mode, so that the structure of the MIL-101(Fe) is more stable; and 5% diluted hydrochloric acid solution is added for acid cleaning after high-temperature roasting to remove impurities, so that the structure is more stable, and hydrolysis is not easy to generate.

The MOFs composite electro-catalytic membrane prepared by the preparation method has the thickness of 180-500 microns.

The thickness of the membrane also affects the specific surface area, porosity and pore size of the membrane, thereby affecting the degradation efficiency of the electrocatalytic membrane; the invention controls the thickness of the MOFs composite electro-catalytic membrane within the range to prepare the electro-catalytic membrane with small aperture and larger specific surface area, so that the degradation efficiency of the electro-catalytic membrane on pollutants in sewage is higher.

The MOFs composite electro-catalytic membrane prepared by the method is applied as a cathode material in a biofuel cell.

The MOFs composite electro-catalytic membrane is applied to the cathode material of the biofuel cell, so that the electro-catalytic activity of cathode oxygen reduction can be effectively improved; the MOFs composite electrocatalytic membrane is coupled with the MFC to treat sewage, the MOFs composite electrocatalytic membrane has both electric conduction and filtration functions as a cathode material of the MFC, and the anode anaerobic bacteria of the MFC can release electrons generated when organic matters in the sewage are oxidized, the electrons are transferred to the cathode through an external circuit, and the electrons and an electron acceptor O are arranged at the cathode₂The water is generated in a combined manner to form a continuous electronic loop, so that the chemical energy of organic matters in the sewage is converted into electric energy; pollutants in the sewage are decomposed by the MFC and then filtered by the electrocatalytic membrane, so that the high-efficiency pollutant treatment efficiency is realized; in addition, in the process, micro electric fields can be generated by the directional movement of electrons and protons in the MFC, so that the adhesion of bacterial metabolites and the like to the surface of the electrocatalytic membrane can be effectively slowed down, and the pollution of the electrocatalytic membrane can be relieved; the MOFs composite electro-catalytic membrane is used as the cathode material of the MFC and is coupled with the MFC to treat sewage, the cathode material with poor original performance of the MFC is replaced, and the degradation efficiency of pollutants in the sewage and the anti-pollution performance of the electro-catalytic membrane can be effectively improved.

The technical scheme of the embodiment of the invention at least has the following advantages and beneficial effects:

1. according to the invention, the MOFs is added into the carbon film in a compounding manner, and the adding proportion and the thickness of the finally prepared MOFs compound electrocatalysis film are controlled, so that the electrocatalysis film with small aperture and large specific surface area can be prepared; the composite material can be effectively applied to cathode materials in a biofuel cell, and has higher degradation efficiency on pollutants in sewage.

2. The MOFs composite electro-catalytic membrane prepared by the method is applied as a cathode material in a biofuel cell, so that the degradation efficiency of pollutants in sewage can be further improved, and the anti-pollution performance of the MOFs composite electro-catalytic membrane can be effectively improved.

Drawings

FIG. 1 is a graph showing the results provided in Experimental example 2 of the present invention;

FIG. 2 is a graph showing the results of Experimental example 2 of the present invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. The examples, in which specific conditions are not specified, were conducted under conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products available commercially.

The following specifically describes an MOFs composite electrocatalytic film provided by the embodiment of the present invention, and a preparation method and an application thereof.

Example 1

The embodiment provides a preparation method of an MOFs composite electrocatalytic membrane, which comprises the following steps:

s1: dissolving 2g of polyvinylidene fluoride in 18mL of N, N-dimethylformamide, and fully dissolving to obtain a polyvinylidene fluoride solution;

s2: adding 0.4g of carbon powder and 0.3g of MIL-101(Fe) into the prepared polyvinylidene fluoride solution, fully dissolving to prepare a casting solution, and performing ultrasonic defoaming treatment and ultrasonic defoaming treatment;

s3: and casting and scraping the membrane on the surface of the carbon fiber cloth by adopting a four-side preparation device, then adding the membrane into deionized water, and soaking for 12 hours for phase conversion treatment to obtain the MOFs composite electro-catalytic membrane.

The embodiment also provides the MOFs composite electro-catalytic membrane prepared by the preparation method, and the thickness of the MOFs composite electro-catalytic membrane is 200 microns.

Example 2

s1: dissolving 4g of polyvinylidene fluoride in 20mL of N, N-dimethylformamide, and fully dissolving to obtain a polyvinylidene fluoride solution;

s2: adding 0.8g of carbon powder and 0.7g of MIL-101(Fe) into the prepared polyvinylidene fluoride solution, fully dissolving to prepare a casting solution, and performing ultrasonic defoaming treatment and ultrasonic defoaming treatment;

s3: and casting and scraping the membrane on the surface of the carbon fiber cloth by adopting a four-side preparation device, then adding the membrane into deionized water, and soaking for 18 hours for phase conversion treatment to obtain the MOFs composite electro-catalytic membrane.

The embodiment also provides the MOFs composite electro-catalytic membrane prepared by the preparation method, and the thickness of the MOFs composite electro-catalytic membrane is 500 microns.

Example 3

s2: adding 0.4g of carbon powder and 0.3g of Fe-MOF crystal into the prepared polyvinylidene fluoride solution, fully dissolving to prepare a membrane casting solution, performing ultrasonic defoaming treatment, and performing ultrasonic defoaming treatment;

The embodiment also provides the MOFs composite electro-catalytic membrane prepared by the preparation method, and the thickness of the MOFs composite electro-catalytic membrane is 300 microns.

Example 4

s1: dissolving 3g of polyvinylidene fluoride in 22mL of N, N-dimethylformamide, and fully dissolving to obtain a polyvinylidene fluoride solution;

s2: adding 0.6g of carbon powder and 0.5g of Fe-MOF crystal into the prepared polyvinylidene fluoride solution, fully dissolving to prepare a membrane casting solution, performing ultrasonic defoaming treatment, and performing ultrasonic defoaming treatment;

s3: and casting and scraping the membrane on the surface of the carbon fiber cloth by adopting a four-side preparation device, then adding the membrane into deionized water, and soaking for 24 hours for phase conversion treatment to obtain the MOFs composite electro-catalytic membrane.

The embodiment also provides the MOFs composite electro-catalytic membrane prepared by the preparation method, and the thickness of the MOFs composite electro-catalytic membrane is 180 micrometers.

Comparative example

The embodiment provides a preparation method of an electrocatalytic membrane, which comprises the following steps:

s2: adding 2g of carbon powder into the prepared polyvinylidene fluoride solution, fully dissolving to prepare a casting solution, and performing ultrasonic defoaming treatment and ultrasonic defoaming treatment;

s3: and casting and scraping the membrane on the surface of the carbon fiber cloth by adopting a four-side preparation device, then adding the membrane into deionized water, and soaking for 12 hours for phase conversion treatment to obtain the electro-catalytic membrane.

The embodiment also provides the electrocatalytic film prepared by the preparation method, wherein the thickness of the electrocatalytic film is 200 microns.

Experimental example 1

The MOFs composite electrocatalytic membranes prepared in examples 1 to 4 and the electrocatalytic membranes prepared in comparative examples were respectively tested by a multipoint BET method and specific surface area and pore size distribution were calculated, and the results are shown in Table 1.

TABLE 1 electrocatalytic film Properties Table

As can be seen from Table 1, the MOFs composite electro-catalytic membrane prepared by the invention has large specific surface area and small pore size, thereby having higher degradation efficiency on pollutants in sewage.

Experimental apparatus:

in the sewage treatment process of the MFC-electrocatalytic membrane reactor, the anode chamber and the cathode chamber are horizontally arranged in an H shape, and the anode chamber and the cathode chamber are separated by a cation exchange membrane. The volumes of the anode chamber and the cathode chamber are both 400 mL; 200 mL of nutrient solution and 200 mL of domesticated bacteria solution are added into the anode chamber, and 400mL of nutrient solution is added into the cathode chamber. In the reactor, carbon brushes for microorganism attachment during acclimation were placed in the anode chamber, the electrocatalytic membrane prepared in any of examples 1 to 4 and comparative examples was placed in the cathode chamber, and the bottom was aerated with air stones. During operation, nutrient solution is pumped into the anode chamber through a peristaltic pump (frequency is set to be 3), then a water outlet of the anode chamber is connected with a water inlet of the cathode chamber through a conduit, the anode chamber solution is pumped into the cathode chamber through the peristaltic pump, then an overflow port of the cathode chamber is opened to prevent the cathode chamber from overflowing due to overhigh water level, and finally an air pump is connected with an air inlet of the cathode chamber to continuously pump air.

In the current output loop, the carbon brush is placed in the anode chamber to lead out electrons, the carbon brush is connected with a 500 omega resistor through a copper wire, and the other end of the resistor is connected with the cathode electro-catalytic membrane through the copper wire to form a complete electronic loop.

Experimental example 2

The electrocatalytic membranes prepared in example 1 and comparative example were separately subjected to an anti-pollution performance test. The electrocatalytic membranes prepared in example 1 and comparative example were respectively assembled in the cathode chamber of the MFC-electrocatalytic membrane reactor as the cathode, the carbon brush assembled in the anode chamber as the anode, the anode and the cathode were connected to the dc power supply, and the output voltage was controlled at 0.4V. Meanwhile, a group of devices without increasing electric field is set as a comparative test group, and the anti-pollution flux of the MOFs composite electro-catalytic membrane prepared in example 1 and the anti-pollution flux of the electro-catalytic membrane prepared in the comparative example are respectively tested, wherein the result of the comparative example is shown in FIG. 1, and the result of the example 1 is shown in FIG. 2.

As can be seen from FIGS. 1 and 2, the stable anti-pollution flux of the electrocatalytic membrane prepared by the comparative example after 50min under the conditions of no increase of electric field and 0.4V voltage addition is 18L (m)²·h)^-1The influence of the micro-electric field environment on the anti-pollution flux is small; the stable anti-pollution flux of the MOFs composite electro-catalytic membrane prepared in example 1 is 33L (m) after 50min under the condition of not increasing the electric field²·h)^-1Compared with the electrocatalytic membrane prepared by a comparative example, the anti-pollution performance of the electrocatalytic membrane is improved by 83 percent; when 0.4V voltage is added, the stable anti-pollution flux of the MOFs composite electro-catalytic membrane prepared in example 1 is 45L (m) after 50min²·h)^-1Compared with the situation without increasing the electric field, the anti-pollution performance is improved by 36 percent;

the electrocatalytic film prepared by the comparative example is a simple carbon film, and the MOFs composite electrocatalytic film prepared by the example 1 is formed by compounding and adding MOFs in the carbon film; the MOFs composite electrocatalytic membrane prepared by the invention has higher anti-pollution performance, and the MOFs composite electrocatalytic membrane prepared by the invention is applied to a cathode material of an MFC and is coupled with the MFC for use, so that a micro electric field generated by the MFC can also effectively improve the anti-pollution performance of the MOFs composite electrocatalytic membrane.

Experimental example 3

The MOFs composite electro-catalytic membrane prepared in the embodiment 1 is assembled in a cathode chamber of an MFC-electro-catalytic membrane reactor to serve as a cathode, a carbon brush assembled in an anode chamber serves as an anode, the anode and the cathode are connected with a direct-current power supply, and the output voltage is controlled to be 0.4V. Taking 20mL of water inlet samples and water outlet samples in the MFC-electrocatalytic membrane reactor every 1d, measuring corresponding COD values and calculating the removal rate of the COD values; the results are shown in Table 2.

TABLE 2 COD removal Rate Table

As can be seen from Table 2, on day 4, the MOFs composite electrocatalytic film prepared in example 1 can reach 80% degradation rate of organic matters in sewage in MFC; the MOFs composite electro-catalytic membrane prepared by the invention is proved to be applied to the cathode material of the MFC, has higher degradation performance on organic matters in sewage when being coupled with the MFC for sewage treatment, and can efficiently treat the sewage.

Experimental example 4

The MOFs composite electro-catalytic membrane assembly prepared in the example 3 is used for electrochemical work, the electro-catalytic activity of the assembly is tested by using STEp, the output voltage is controlled to be 0.6V and 0.8V, 1mol/L NaCl is used for electrolyte, and the PH =2,3 and 4 are respectively adjusted; in the experiment, rhodamine B is used for simulating pollutants in sewage, and the concentration is set to be 0.04 mg/L; testing the absorbance of the electrolyzed rhodamine B solution, calculating the concentration of the electrolyzed rhodamine B solution, and then calculating the degradation rate of the rhodamine B; the results are shown in Table 3.

TABLE 3 rhodamine B degradation Rate Table

As can be seen from Table 3, the MOFs composite electrocatalytic film prepared in example 3 has a degradation rate of rhodamine B approaching one hundred percent, and has no requirement on PH; the MOFs composite electro-catalytic membrane prepared by the method is proved to have higher electro-catalytic activity in electrochemical application and higher degradation rate on pollutants in sewage; the MOFs composite electrocatalytic membrane prepared by the invention can be effectively applied to the cathode material of the MFC, so that the electrocatalytic activity of the cathode oxygen reduction of the MFC is higher.

In conclusion, the MOFs composite electro-catalytic membrane provided by the application can be effectively applied to the cathode material of the MFC, and has higher electro-catalytic activity when being applied to the cathode material of the MFC; the MOFs composite electro-catalytic membrane prepared by the method has high degradation performance on pollutants in sewage and has high pollution resistance; when the composite material is applied to a cathode material of an MFC and is coupled with the MFC for use, the pollution resistance can be further improved.

The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A preparation method of an MOFs composite electrocatalytic film is characterized by comprising the following steps:

s2: adding carbon powder and a metal organic frame material into the prepared polyvinylidene fluoride solution in proportion, fully dissolving to prepare a membrane casting solution, and performing ultrasonic defoaming treatment; the metal organic framework material is MIL-101(Fe) or Fe-MOF crystal; the preparation method of the MIL-101(Fe) comprises the following steps: a. weighing metal salt FeCl according to the molar ratio of iron to nickel of 1-9: 1₃·6H₂O and NiCl₂·6H₂O, taking organic ligand terephthalic acid according to the molar ratio of 1: 1-3 to the total metal salt, respectively adding the organic ligand terephthalic acid to N, N dimethylformamide solvent, stirring and reacting at 60-150 ℃ for 6-48 h, and cooling to room temperature; b. carrying out suction filtration on the cooled reaction solution to obtain solid powder, washing the solid powder by using an N, N-dimethylformamide solvent, then heating and refluxing the solid powder in a methanol solvent, and cooling and carrying out suction filtration; c. roasting the solid powder obtained after suction filtration at 500-800 ℃, and then carrying out acid washing by using 5% dilute hydrochloric acid solution to obtain an MIL-101(Fe) metal organic framework material;

2. The method of claim 1, wherein the organic solvent in step S1 is N, N-dimethylformamide.

3. The method of preparing the MOFs composite electrocatalytic film according to claim 1, wherein in the step S1, 2 to 4g of polyvinylidene fluoride is dissolved in 18 to 22mL of organic solvent.

4. The method of claim 1, wherein 0.4-0.8 g of carbon powder and 0.3-0.7 g of metal-organic framework material are added to 18-22 mL of polyvinylidene fluoride solution in the step S2.

5. The method for preparing the MOFs composite electrocatalytic membrane according to claim 1, wherein in the step S3, the membrane casting solution is cast and scraped on the surface of the carbon fiber cloth by a four-side preparation device, and then the carbon fiber cloth is added into deionized water and soaked for 12-24 h for phase inversion treatment.

6. The MOFs composite electrocatalytic film prepared by the preparation method according to any one of claims 1 to 5, wherein the thickness is 180 to 500 μm.

7. Use of a MOFs composite electrocatalytic membrane according to claim 6 as cathode material in a biofuel cell.