CN113943488A

CN113943488A - Composite material based on polytetrafluoroethylene-coated MOFs material and preparation method thereof

Info

Publication number: CN113943488A
Application number: CN202111014781.6A
Authority: CN
Inventors: 周小平; 李丹; 黄燕丽
Original assignee: Jinan University
Current assignee: Jinan University
Priority date: 2021-08-31
Filing date: 2021-08-31
Publication date: 2022-01-18
Anticipated expiration: 2041-08-31
Also published as: CN113943488B

Abstract

The invention discloses a composite material based on polytetrafluoroethylene-coated MOFs material and a preparation method thereof. The composite material is formed by wrapping MOFs material by polytetrafluoroethylene. The preparation method of the composite material comprises the following steps: and dripping the polytetrafluoroethylene emulsion into the MOFs material suspension in an ultrasonic state, then placing the MOFs material suspension in liquid nitrogen for freezing, removing moisture after thawing, and drying to obtain the composite material based on the MOFs material wrapped by the polytetrafluoroethylene. The method also comprises the step of placing the composite material in an inert atmosphere to carry out annealing treatment so as to remove moisture and nonionic surfactants in the composite material. According to the invention, the PTFE/ZIF-8-370 composite material is obtained by combining the high polymer material polytetrafluoroethylene and ZIF-8 for the first time, and has excellent performances of water stability, high pressure resistance, less loss under catalytic reaction and the like, so that a new building block is provided for an unstable metal organic frame, and a new idea is provided for the design of a metal organic frame material.

Description

Composite material based on polytetrafluoroethylene-coated MOFs material and preparation method thereof

Technical Field

The invention relates to the technical field of metal organic frameworks protected by high molecular polymers, in particular to a composite material based on a polytetrafluoroethylene-coated MOFs material and a preparation method thereof.

Background

Because Metal Organic Frameworks (MOFs) have the structural characteristics of large specific surface area, high porosity and the like, the MOFs is widely applied to the fields of gas storage and separation, biosensors, catalysis, biological medicine release and the like. The zeolite imidazolate framework material ZIF-8 shows a special pore structure and high hydrothermal stability and chemical stability, so that the ZIF-8 becomes a research hotspot in multiple fields. The use of ZIF-8 has been extended to aqueous solutions (removal of heavy metal ions from water, photocatalytic degradation of dyes).

Nevertheless, it has been reported in the literature that ZIF-8 crystallites are unstable in water and also produce new species. Therefore, it is a problem to be solved in the art to protect ZIF-8 from decomposition in aqueous solution applications or other reactions.

The high molecular polymer Polytetrafluoroethylene (PTFE) has excellent mechanical toughness, chemical stability, corrosion resistance, high temperature resistance, high lubrication non-adhesiveness, electric insulation, good ageing resistance and high endurance capacity, and is also a super-hydrophobic material.

Different from the traditional metal organic framework material, the metal organic framework material is combined with a high molecular polymer, so that the metal organic framework material not only retains the characteristics of the metal organic framework material, but also has the characteristics of the high molecular material. The composite material combining polytetrafluoroethylene and ZIF-8 can improve the characteristics of ZIF-8 such as water stability, high pressure resistance, hydrophobicity and the like, so that the composite material has wide application prospect in more fields.

Disclosure of Invention

The invention aims to solve the problems in the prior art and provides a composite material based on a polytetrafluoroethylene-coated MOFs material and a preparation method thereof, wherein the composite material can prevent ZIF-8 from being decomposed in aqueous solution application or other reactions.

In order to achieve the above object, the present invention adopts the following technical solutions.

A composite material based on polytetrafluoroethylene-coated MOFs materials is formed by coating the MOFs materials with polytetrafluoroethylene.

Preferably, the polytetrafluoroethylene accounts for 20 wt% -70 wt% of the composite material, and the MOFs material accounts for 30 wt% -80 wt% of the composite material.

Preferably, the polytetrafluoroethylene accounts for 20 wt% -50 wt% of the composite material, and the MOFs material accounts for 50 wt% -80 wt% of the composite material.

Preferably, the MOFs material is ZIF-8.

The preparation method of the composite material based on the polytetrafluoroethylene-coated MOFs material comprises the following steps:

and (3) dripping the polytetrafluoroethylene emulsion into the MOFs material suspension in the ultrasonic state, continuously carrying out ultrasonic treatment, then placing the MOFs material suspension in liquid nitrogen for freezing, removing moisture after thawing, and drying to obtain the composite material based on the MOFs material wrapped by the polytetrafluoroethylene.

Preferably, the composite material based on the polytetrafluoroethylene-coated MOFs material is subjected to an annealing treatment in an inert atmosphere to remove moisture and nonionic surfactants in the composite material.

Preferably, the annealing treatment is to place the composite material based on the polytetrafluoroethylene-coated MOFs material in a tube furnace with argon flow, heat to 120 ℃ for 20min, and then heat to 370 ℃ for 30 min.

Preferably, the polytetrafluoroethylene emulsion comprises 60 wt% polytetrafluoroethylene, 30 wt% nonionic surfactant and 10 wt% water. The nonionic surfactant is.

Preferably, the concentration of the MOFs material suspension is 11 mg/ml.

Preferably, the time of the ultrasound is 2 min.

Preferably, the temperature of the drying is 100 ℃.

Because the polytetrafluoroethylene has excellent mechanical toughness, chemical stability, corrosion resistance, hydrophobicity and other properties, the problem that the ZIF-8 is decomposed in an aqueous solution can be effectively solved, and the original characteristics of the ZIF-8 are kept.

Compared with the prior art, the invention has the following beneficial effects:

(1) the composite material disclosed by the invention has excellent performances of high pressure resistance, good water stability, less loss under catalytic reaction and the like, so that a new building block is provided for an unstable metal organic frame, and a new idea is provided for the design of a metal organic frame material.

(2) The composite material has higher hydrophobicity than ZIF-8, and the hydrophobicity of the composite material is further improved after annealing treatment.

Drawings

FIG. 1a is a scanning electron micrograph (left) and a transmission electron micrograph (right) of 80% PTFE/ZIF-8 according to example 2 of the present invention.

FIG. 1b is a scanning electron micrograph (left) and a transmission electron micrograph (right) of 80% PTFE/ZIF-8-370 of example 3 of the present invention.

FIG. 1c is a scanning electron micrograph (left) and a transmission electron micrograph (right) of 50% PTFE/ZIF-8 of example 2 of the present invention.

FIG. 1d is a scanning electron micrograph (left) and a transmission electron micrograph (right) of 50% PTFE/ZIF-8-370 of example 3 of the present invention.

FIG. 2 is a graph showing the results of water stability tests on the ZIF-8 of example 1 and the PTFE/ZIF-8-370 composite of example 3 of the present invention.

FIG. 3 is a graph showing the results of the high pressure stability tests of the ZIF-8 of example 1, the PTFE/ZIF-8 composite of example 2 and the PTFE/ZIF-8-370 composite of example 3 in accordance with the present invention.

FIG. 4 is a graph showing the results of recovery of the catalyst used as the ZIF-8 of example 1, the PTFE/ZIF-8 composite of example 2, and the PTFE/ZIF-8-370 composite of example 3 in accordance with the present invention.

FIG. 5 is a graph of the water contact angle of the ZIF-8 of example 1 of the present invention, the PTFE/ZIF-8 composite of example 2, and the PTFE/ZIF-8-370 composite of example 3.

Detailed Description

The following examples further illustrate the practice of the present invention, but the practice of the present invention is not limited thereto.

The experimental methods in the following examples are all conventional methods unless otherwise specified; the chemical reagents and raw materials used are all conventional raw materials in the field and are all commercially available unless otherwise specified.

The main reagent sources are as follows:

zinc nitrate hexahydrate: CAS registry number 10196-18-6;

2-methylimidazole: CAS registry number 693-98-1;

polytetrafluoroethylene emulsion: CAS registry number 9002-84-0;

tetrahydrofuran (CAS registry number: 109-99-9), benzaldehyde (CAS registry number: 100-52-7), malononitrile (CAS registry number: 109-77-3), acetonitrile (CAS registry number 75-05-8), ethanol (CAS registry number 64-17-5);

EXAMPLE 1 preparation of ZIF-8

(1) Weighing 1.17g of zinc nitrate hexahydrate in a 20mL glass bottle, adding 8mL of deionized water, adding 20.27g of 2-methylimidazole in a 250mL conical bottle, and adding 80mL of deionized water;

(2) performing ultrasonic treatment on the glass bottle and the conical bottle in the step (1) until the solid is dissolved;

(3) slowly dripping the solution in the glass bottle in the step (2) into the solution of 2-methylimidazole, and then stirring for 5 min;

(4) and (4) centrifuging the turbid liquid obtained in the step (3) to obtain a white solid product, washing the white solid product with ethanol for three times, and drying the white solid product in a vacuum drying oven at 100 ℃ for 12 hours to obtain ZIF-8 powder.

EXAMPLE 2 preparation of PTFE/ZIF-8 composites

Preparation of 80% PTFE/ZIF-8 composite material

(1) Dispersing the ZIF-8 prepared in the example 1 in deionized water, performing ultrasonic treatment to obtain 5ml of suspension with the concentration of 11mg/ml, taking 20% of PTFE/ZIF-8 composite material in polytetrafluoroethylene emulsion according to the mass ratio of PTFE to ZIF-8, slowly dropping the obtained polytetrafluoroethylene emulsion into the ZIF-8 suspension in an ultrasonic state, and performing ultrasonic treatment (with the power of 100%) for 2min to obtain a mixture of the polytetrafluoroethylene and the ZIF-8.

(2) And (2) completely freezing the mixture obtained in the step (1) in liquid nitrogen, taking out, placing at normal temperature for thawing, and removing water after thawing.

(3) And (3) drying the mixture subjected to moisture removal in the step (2) in a vacuum drying oven at 100 ℃ for 6 hours to obtain a white and fluffy product with the touch of the cotton candy, namely the 80% PTFE/ZIF-8 composite material.

Preparation of two, 50% PTFE/ZIF-8 composite material

(1) Dispersing the ZIF-8 prepared in the example 1 in deionized water, performing ultrasonic treatment to obtain 5ml of suspension with the concentration of 11mg/ml, taking 50% of PTFE/ZIF-8 composite material in polytetrafluoroethylene emulsion according to the mass ratio of PTFE to ZIF-8 of 5:5, slowly dropping the obtained polytetrafluoroethylene emulsion into the ZIF-8 suspension in an ultrasonic state, and performing ultrasonic treatment (with the power of 100%) for 2min to obtain a mixture of polytetrafluoroethylene and ZIF-8.

(3) And (3) drying the mixture subjected to moisture removal in the step (2) in a vacuum drying oven at 100 ℃ for 6 hours to obtain a white and fluffy product with the touch of the cotton candy, namely the 50% PTFE/ZIF-8 composite material.

EXAMPLE 3 preparation of PTFE/ZIF-8-370 composite

And (3) putting the PTFE/ZIF-8 composite material obtained in the step (a) into a tubular furnace, and annealing by using argon flow.

(1) The sample was placed in a tube furnace and heated to 120 ℃ for 20 min.

(2) After the step (1) is finished, the temperature is raised to 370 ℃ and kept for 30 min.

(3) Finally obtaining brown solid which is the PTFE/ZIF-8-370 composite material.

TABLE 1

As can be seen from the SEM image (left) of FIG. 1a, when the mass fraction ratio of PTFE to ZIF-8 is 2:8 and 80% of the synthesized PTFE/ZIF-8 is not annealed, the PTFE is not uniformly wrapped in the ZIF-8 and cannot be wrapped in a spherical shape.

From the SEM image (left) of FIG. 1c, it can be seen that when the mass fraction ratio of PTFE to ZIF-8 is 5:5, and 50% PTFE/ZIF-8 is synthesized without annealing, the PTFE can uniformly wrap the ZIF-8 to form spherical shapes.

Example 4 PTFE/ZIF-8 and PTFE/ZIF-8-370 composite Performance testing

The PTFE/ZIF-8 and PTFE/ZIF-8-370 composite materials prepared in the embodiments 2 and 3 are subjected to stability tests under the following test conditions:

1. and (3) testing the water stability: deionized water was 3ml and the number of stirring revolutions was 750 rpm.

FIG. 2 is a graph showing the stability in water of ZIF-8 and PTFE/ZIF-8-370 composites of examples 1 and 3. As can be seen from FIG. 2, after 24h of stirring, the ZIF-8 framework had collapsed, but the PTFE/ZIF-8-370 retained essentially the original diffraction peak and the framework remained stable. The result shows that the PTFE/ZIF-8-70 composite material has better stability when stirred in water for 24 hours under the same condition compared with ZIF-8 microcrystal. Encapsulation of the teflon coating was shown to protect ZIF-8.

2. Stability test under high pressure: 10mg sample, 10Mpa, hold for 2min

FIG. 3 is a graph showing stability test of ZIF-8 and its composite material in examples 1, 2 and 3 maintained at 10MPa for 2 min. As can be seen from FIG. 3, the framework of ZIF-8 had completely collapsed under a pressure of 10MPa, but the original diffraction peak was still retained in the composite materials of PTFE/ZIF-8 and PTFE/ZIF-8-370, and the framework was stable. The PTFE/ZIF-8 and PTFE/ZIF-8-370 composite material prepared by the invention has high pressure resistance.

3. And (3) testing the recovery rate of the catalyst: 20mg of ZIF-8 and composite materials PTFE/ZIF-8 and PTFE/ZIF-8-370 thereof are used as catalysts, and benzaldehyde and malononitrile are subjected to catalytic test at normal temperature.

FIG. 4 is a graph showing recovery of ZIF-8 and its composite catalyzed in example 2. As can be seen from FIG. 4, ZIF-8 and composite materials thereof, namely PTFE/ZIF-8 and PTFE/ZIF-8-370, are used as catalysts, and after catalytic reaction, ethanol is used for cleaning the catalysts and drying at 60 ℃, the recovery rate of ZIF-8 is less than 50%, the recovery rate of 80% PTFE/ZIF-8 is about 65%, the recovery rate of 50% PTFE/ZIF-8 is 75%, the recovery rate of 80% PTFE/ZIF-8-370 is 92.75%, and the recovery rate of 50% PTFE/ZIF-8-370 is more 96.5%. The recovery rate of ZIF-8 is the lowest in the catalytic stirring process, and the recovery rate of the annealed composite material PTFE/ZIF-8-370 is higher.

Example 5, ZIF-8 and composite hydrophobicity testing thereof

And (3) testing the hydrophobicity of the ZIF-8 and the composite material thereof: and (3) placing the ZIF-8 and the composite material thereof on a glass sheet, flattening, and testing by a contact angle tester.

TABLE 2

FIG. 5 is a graph of water contact angles of ZIF-8 and its composites in examples 1, 2, and 3. It can be seen that ZIF-8 does not exhibit hydrophobicity. The PTFE/ZIF-8 water contact angle is 150 ℃ at 140 DEG, the PTFE/ZIF-8-370 water contact angle is 160 ℃ at 150 DEG, and the ultrahigh hydrophobicity is shown.

Claims

1. The composite material based on the polytetrafluoroethylene-coated MOFs material is characterized by being formed by coating the MOFs material with the polytetrafluoroethylene.

2. The composite material of claim 1, wherein the polytetrafluoroethylene constitutes 20 wt% -70 wt% of the composite material, and the MOFs material constitutes 30 wt% -80 wt% of the composite material.

3. The composite material of claim 2, wherein said polytetrafluoroethylene constitutes 20 wt% -50 wt% of the composite material, and said MOFs constitutes 50 wt% -80 wt% of the composite material.

4. Composite material based on polytetrafluoroethylene-coated MOFs according to any of claims 1 to 3, wherein said MOFs is ZIF-8.

5. Method for preparing a composite material based on polytetrafluoroethylene-coated MOFs according to any of the claims 1 to 4, comprising the following steps:

6. The method according to claim 5, wherein the composite material based on the polytetrafluoroethylene-coated MOFs is subjected to an annealing treatment under an inert atmosphere to remove moisture and nonionic surfactants from the composite material.

7. The method according to claim 6, characterized in that the annealing treatment consists in placing the composite material based on polytetrafluoroethylene-coated MOFs in a tube furnace with argon flow, heating to 120 ℃ for 20min, and then raising the temperature to 370 ℃ for 30 min.

8. The method of claim 5, wherein the polytetrafluoroethylene emulsion comprises 60 wt% polytetrafluoroethylene, 30 wt% nonionic surfactant, and 10 wt% water.

9. The method according to claim 5, characterized in that the concentration of said MOFs material suspension is 11 mg/ml.

10. The method of claim 5, wherein the ultrasound is performed for a period of 2 min.