阅读说明：本技术 一种利用羟基双金属盐自转化制备双金属mof膜的方法与渗透蒸发分离应用 (Method for preparing bimetallic MOF (Metal organic framework) membrane by utilizing self-transformation of hydroxyl bimetallic salt and pervaporation separation application ) 是由 张雄福 马畅畅 刘海鸥 于 2020-06-15 设计创作，主要内容包括：本发明提供了一种利用羟基双金属盐自转化制备双金属MOF膜的方法与渗透蒸发分离应用,即先在多孔载体表面引入一层ZnO纳米活性层,然后通过硝酸钴溶液对引入的ZnO纳米活性层进行原位处理得到锌/钴羟基双金属盐层,作为连接膜层与载体的连接层和MOF膜层生长的生长点；最后将该载体置于无金属源的成膜液中,经溶剂热转化生长获得连续完整的锌/钴双金属MOF膜层。该制备方法有效解决了目前双金属MOF膜制备存在的困难问题,具有简便高效并易于大规模制备的特点。该膜对甲醇/甲基叔丁基醚共沸物分离性能展现了优异的分离性能和良好的操作稳定性,具有潜在的实际应用价值。(The invention provides a method for preparing a bimetallic MOF (Metal-organic framework) membrane by utilizing self-transformation of hydroxyl bimetallic salt and application of pervaporation separation, which comprises the steps of introducing a ZnO nano active layer on the surface of a porous carrier, and then carrying out in-situ treatment on the introduced ZnO nano active layer by using a cobalt nitrate solution to obtain a zinc/cobalt hydroxyl bimetallic salt layer serving as a connecting layer for connecting a membrane layer and the carrier and a growth point for growth of the MOF membrane layer; finally, the carrier is placed in a film forming solution without a metal source, and a continuous and complete zinc/cobalt bimetallic MOF film layer is obtained through solvent thermal conversion growth. The preparation method effectively solves the problem of difficulty in the existing preparation of the bimetallic MOF film, and has the characteristics of simplicity, convenience, high efficiency and easiness in large-scale preparation. The membrane shows excellent separation performance and good operation stability to the separation performance of the methanol/methyl tert-butyl ether azeotrope, and has potential practical application value.)

1. A method for preparing a zinc/cobalt bimetallic MOF membrane by utilizing self-transformation of hydroxyl bimetallic salt is characterized by comprising the following steps:

(1) introducing ZnO nanoparticles or ZnO nano-array active layer on the surface of a carrier

Mixing ethylene glycol monomethyl ether and zinc acetate according to the weight ratio of (15-30): 1, stirring the mixture for 20-60 min in water bath at 70 ℃, and then slowly dropwise adding a small amount of ethanolamine, wherein the molar ratio of the ethanolamine to the zinc acetate is 2: 1, stirring at room temperature for 12-24 hours to obtain zinc sol; introducing a zinc sol layer to the surface of the carrier by means of lifting or spin coating, and roasting at 400-500 ℃ for 200min to obtain a ZnO nanoparticle active layer;

on the basis of the ZnO nano particle active layer, putting the ZnO nano particle active layer into hexamethylenetetramine, zinc nitrate hexahydrate and a mixture of water in a molar ratio of 1: 1: reacting for 3-6 h at 100 ℃ in 500 ZnO nano-array synthetic solution to obtain a ZnO nano-array active layer;

(2) preparation of hydroxyl double metal salt layer on carrier

Placing the carrier introduced with the ZnO nano particles or the ZnO nano array active layer into a cobalt nitrate solution, and reacting for 2-24 hours at 25-100 ℃ to obtain a zinc/cobalt hydroxyl double-metal salt layer; the cobalt nitrate solution in the step (2) is composed of hexahydrate and a cobalt nitrate aqueous solution, wherein the molar ratio of cobalt nitrate hexahydrate to water is (1-5): 500, a step of;

(3) and (3) placing the carrier introduced with the zinc/cobalt hydroxyl double-metal salt layer into the zinc/cobalt double-metal MOFs membrane layer synthetic solution, and carrying out high-temperature reaction in a polytetrafluoroethylene stainless steel reaction kettle to obtain the zinc/cobalt double-metal MOFs membrane layer.

2. The method according to claim 1, wherein the zinc/cobalt bimetallic MOFs membrane layer prepared in the step (3) is a bimetallic ZIF-8 or ZIF-67 membrane layer which is composed of zinc ions and cobalt ions which are simultaneously used as metal centers and dimethyl imidazole which is used as an organic ligand; or a bimetallic ZIF-7 or ZIF-9 film layer which is composed of zinc ions and cobalt ions as metal centers and benzimidazole as organic ligands.

3. The method as claimed in claim 1, wherein in the step (3), when the bimetallic ZIF-8 or ZIF-67 membrane layer is prepared, the molar ratio of the dimethylimidazole, the sodium formate and the water in the synthetic solution is 10: 1: (800-1200), the reaction temperature is 100-150 ℃, and the reaction time is 5-12 h; when the bimetallic ZIF-7 or ZIF-9 film layer is prepared, the molar ratio of benzimidazole, sodium formate, water and DMF in the synthetic liquid is 10: 1: (250-350): (150-250) the reaction temperature is 100-150 ℃, and the reaction time is 12-24 h.

4. The method of claim 1, further comprising the step of pre-processing: selecting a porous ceramic tube or ceramic plate with the average pore diameter of 200 nm-2 mu m as a carrier, respectively ultrasonically cleaning by deionized water and absolute ethyl alcohol before use, and drying in a vacuum oven.

5. Use of a zinc/cobalt bimetallic MOF membrane prepared by the method of claim 1 for pervaporation separation.

6. The use according to claim 5, wherein the zinc/cobalt bimetallic MOFs membrane is placed in a pervaporation unit to separate the mixture at a pressure of 0.1MPa for permeation measurement and at a temperature of 50 ℃ and at a flow rate of 500mL/h, and the products of permeation measurement are collected by a cold trap and analyzed by gas chromatography.

7. Use according to claim 6, wherein the mixture is methanol/methyl tert-butyl ether.

Technical Field

The invention provides a method for preparing a bimetallic MOF (Metal organic framework) membrane by utilizing self-transformation of hydroxyl bimetallic salt and a pervaporation separation technology, and opens up a new way for preparing a high-performance bimetallic MOF membrane.

Background

In recent years, due to the great increase of energy consumption and the enhancement of environmental awareness of people, compared with separation technologies such as evaporation, rectification and the like with high energy consumption and high pollution, a membrane separation technology is paid attention to by scientific researchers due to the advantages of energy conservation, high efficiency, simplicity in operation, low energy consumption, environmental friendliness and the like. Membrane separation performance is generally limited by the upper robertson limit, and separation performance depends on the physical and chemical properties of the membrane material, and thus, it is urgently required to find a new membrane material with high performance.

Metal Organic Frameworks (MOFs) are porous crystalline materials formed by coordination and combination of metal ions or ion clusters and organic ligands, have the advantages of high specific surface area, designability of framework structure composition, good post-modification property, pore size adjustability, high stability and the like, and have wide attention on potential applications in the aspects of separation, catalysis, drug transportation, electronic sensing and the like. The bimetallic MOFs refers to that a single MOFs crystal skeleton structure simultaneously contains two metal ions, although the research on the bimetallic MOFs is still in a starting stage, the bimetallic MOFs has a more excellent effect in some application aspects compared with the traditional single-metal MOFs, for example, in the field of gas adsorption and storage, the stability and the affinity to a target gas can be greatly improved by introducing the second metal ions into the MOFs crystal; generally, due to the rotation of the organic ligand, the channel of the MOFs may generate a "gate opening effect" to change the channel size, and the channel size of the MOFs may be precisely adjusted and controlled by introducing a second metal ion. For example, Jeong et al replace some Zn ions in ZIF-8 with Co ions, the crystal structure is not damaged, and the Co-N bond is more rigid than the Zn-N bond, thus inhibiting the ligand from rotating and reducing the effective pore diameter of the crystal; in addition, the addition of Co enhances the intercrystalline structure of the film and improves the separation performance of the film [ Hillman F, Zimmerman J M, Paek S M, ethyl. Rapid microwave-induced synthesis of hybrid-ionic-membranes metals and hybrid linkers [ J ]. Journal of materials chemistry A,2017,5(13): 6090-.

At present, the preparation of the bimetallic MOFs mostly adopts a one-pot method or a post-synthesis ion exchange method, wherein the one-pot method means that the MOFs synthetic solution contains two metal ions at the same time, but the two metal ions are difficult to ensure to react at the same time, so that the formation of physically mixed single-metal MOFs is avoided. For example, Serre et al used a one-pot process with the addition of Fe³⁺And Cr³⁺To produce bimetallic MIL-53(Cr/Fe) material, but due to Cr³⁺Compared with Fe³⁺More inert, cannot ensure that two metal ions react simultaneously, and inert Fe is selected⁰To replace Fe³⁺Can ensure that two metal ions react simultaneously, namely the introduction of two metals is controlled by controlling the reactivity of the metal ions [ Nouar F, Devic T, Chevreau H, et al].Chemical Communications,2012,48(82):10237-10239]. Post-synthesis ion exchange refers to the process of immersing a single metal MOFs in a synthetic solution containing another metal ion for several days to achieve the purpose of ion exchange, but the process is time-consuming and energy-consuming. Therefore, it is of great significance to develop a simple and efficient synthesis method for preparing the bimetallic MOFs film, but still has great challenges.

Hydroxy bimetallic salts (HDSs) are called anion-exchanging layered compounds, which consist of cationic sheets and interlayer anions and are prepared by reacting a divalent metal oxide with another divalent metal cation. HDSs have high ion exchange rates, and HDSs are used as intermediates to rapidly prepare MOFs, such as HKUST-1, ZIF-8, Cu-BDC and IRMOF-3, which are synthesized by Zhao et al at room temperature, and the versatility of the synthesis method is demonstrated [ ZHao J, Nunn W T, Lemaire P C, et al. Zhang et al also rapidly prepared hierarchical pore containing ZIF-8, ZIF-61 and ZIF-90[ Zhang H, Huo J, Yang H, et al. Green and Rapid preparation of hierarchical pore with HDSs ] 2019,7(3):1022-1029 ]. Although the synthesis of MOFs by taking HDSs as intermediates is very advantageous, the MOFs crystals synthesized by using HDSs are all monometallic MOFs, and the subsequent application is limited because no report of preparing MOFs films by means of HDSs is provided. In view of the fact that HDSs can promote the synthesis of ultrafast MOFs and have two metal ions at the same time, the invention provides a technology for preparing bimetallic MOFs membranes by providing metal salts for intermediates by using HDSs.

Disclosure of Invention

Aiming at the problem of difficulty in preparation of the existing bimetallic MOF film, the invention provides a method for preparing a zinc/cobalt bimetallic MOF film by self-transformation by using hydroxyl bimetallic salt (HDS) as an activity induction intermediate.

The invention has the following inventive concept: firstly, introducing a ZnO nano active layer on the surface of a porous carrier, namely introducing a ZnO nano particle layer by a sol-gel pulling method or growing a ZnO nano array layer by a hydrothermal synthesis method; then reacting with cobalt nitrate aqueous solution to obtain a zinc/cobalt hydroxyl double metal salt layer (HDS layer); and finally, placing the carrier introduced with the HDS layer in an organic ligand synthetic solution without a metal source, and forming a continuous and complete zinc/cobalt bimetallic MOFs film layer through solvothermal growth. The synthesis method can effectively solve the problem of preparation of the existing bimetallic MOF film layer, is simple and efficient, is green and pollution-free, and has good novelty and great application prospect.

The technical scheme of the invention is as follows:

a method for preparing zinc/cobalt bimetallic MOFs membrane by utilizing self-transformation of hydroxyl bimetallic salt is disclosed, wherein the zinc/cobalt bimetallic MOFs is a bimetallic MOF structure formed by coordination of taking zinc and cobalt as metal sources and taking dimethyl imidazole or benzimidazole as organic ligands, and a carrier is a porous ceramic tube or ceramic wafer with the average pore diameter of 200 nm-2 mu m, and the method comprises the following specific steps:

(1) introducing ZnO nanoparticles or ZnO nano-array active layer on the surface of a carrier

Mixing ethylene glycol monomethyl ether and zinc acetate according to the weight ratio of (15-30): 1, stirring the mixture for 20-60 min in water bath at 70 ℃, and then slowly dropwise adding a small amount of ethanolamine, wherein the molar ratio of the ethanolamine to the zinc acetate is 2: 1, stirring at room temperature for 12-24 hours to obtain zinc sol; introducing a zinc sol layer to the surface of the carrier by means of lifting or spin coating, and roasting at 400-500 ℃ for 200min to obtain a ZnO nanoparticle active layer;

on the basis of the ZnO nano particle active layer, putting the ZnO nano particle active layer into hexamethylenetetramine, zinc nitrate hexahydrate and a mixture of water in a molar ratio of 1: 1: and reacting for 3-6 h at 100 ℃ in 500 ZnO nano-array synthetic solution to obtain the ZnO nano-array active layer.

(2) Preparation of hydroxyl double metal salt layer on carrier

Placing the carrier introduced with the ZnO nano particles or the ZnO nano array active layer into a cobalt nitrate solution, and reacting for 2-24 hours at 25-100 ℃ to obtain a zinc/cobalt hydroxyl double-metal salt layer; the cobalt nitrate solution in the step (2) is composed of hexahydrate and a cobalt nitrate aqueous solution, wherein the molar ratio of cobalt nitrate hexahydrate to water is (1-5): 500.

(3) and (3) placing the carrier introduced with the zinc/cobalt hydroxyl double-metal salt layer into the zinc/cobalt double-metal MOFs membrane layer synthetic solution, and carrying out high-temperature reaction in a polytetrafluoroethylene stainless steel reaction kettle to obtain the zinc/cobalt double-metal MOFs membrane layer.

Further, the zinc/cobalt bimetallic MOFs membrane layer prepared in the step (3) refers to a zinc/cobalt bimetallic ZIF membrane layer, namely a bimetallic ZIF-8 or ZIF-67 membrane layer which takes zinc ions and cobalt ions as metal centers at the same time and dimethyl imidazole as an organic ligand; or a bimetallic ZIF-7 or ZIF-9 film layer which is composed of zinc ions and cobalt ions as metal centers and benzimidazole as organic ligands.

When the bimetallic ZIF-8 or ZIF-67 film layer is prepared in the step (3), the molar ratio of the dimethyl imidazole, the sodium formate and the water in the synthetic liquid is 10: 1: (800-1200), the reaction temperature is 100-150 ℃, and the reaction time is 5-12 h; when the bimetallic ZIF-7 or ZIF-9 film layer is prepared, the molar ratio of benzimidazole, sodium formate, water and DMF in the synthetic liquid is 10: 1: (250-350): (150-250) the reaction temperature is 100-150 ℃, and the reaction time is 12-24 h.

The method also comprises the following pretreatment steps: selecting a porous ceramic tube or ceramic plate with the average pore diameter of 200 nm-2 mu m as a carrier, respectively ultrasonically cleaning by deionized water and absolute ethyl alcohol before use, and drying in a vacuum oven.

The invention also aims to protect the application of the zinc/cobalt bimetallic MOFs membrane prepared by the method in pervaporation separation. The specific application method comprises the following steps: bimetallic zinc/cobaltThe MOFs membrane is placed in a pervaporation device to separate a mixture, wherein the mixture is preferably methanol/methyl tert-butyl ether, the pressure for measuring the permeation is 0.1MPa, the temperature is 50 ℃, the flow rate is 500mL/h, a cold trap is used for collecting products for measuring the permeation, the products are analyzed by gas chromatography, and the permeation flux is up to 1.5 kg-m^-2·h^-1Above, the separation factor of methanol/methyl t-butyl ether exceeds 6000.

The invention has the beneficial effects that:

the method for preparing the zinc/cobalt bimetallic MOFs film by utilizing the self-transformation of the hydroxyl bimetallic salt solves the preparation problem of the existing bimetallic MOFs film, has the advantages of simplicity, convenience, high efficiency, easiness in synthesis and the like, has certain universality for the preparation of other kinds of bimetallic MOFs films, and has wide application prospect and potential.

Drawings

FIG. 1a is a SEM image of the surface of the ZnO nano-array prepared in example 2.

FIG. 1b is a SEM image of the cross section of the ZnO nano-array prepared in example 2.

Fig. 2a is a SEM image of the surface of the zinc-cobalt hydroxy double metal salt layer prepared in example 2.

Fig. 2b is a cross-sectional SEM image of the zinc-cobalt hydroxy double metal salt layer prepared in example 2.

FIG. 3a is a SEM image of the surface of a layer of a bimetallic ZIF-8-67 film prepared in example 2.

FIG. 3b is a SEM image of a cross-section of a dual metal ZIF-8-67 film prepared in example 2.

FIG. 4a is a SEM image of the surface of a bimetallic ZIF-7-9 film prepared in example 3.

FIG. 4b is a SEM image of a cross-section of a dual metal ZIF-7-9 film prepared in example 3.

Detailed Description

The invention is described in more detail below with reference to specific examples, without limiting the scope of the invention. Unless otherwise specified, the experimental methods adopted by the invention are all conventional methods, and experimental equipment, materials, reagents and the like used in the experimental method can be obtained from commercial sources.