A three-dimensional metal organic framework single crystal and its preparation method and application

Abstract

The present invention belongs to the technical field of metal-organic framework materials, and specifically relates to a three-dimensional metal-organic framework single crystal, a preparation method thereof, and an application. The present invention provides a three-dimensional metal-organic framework single crystal, in which Cd ions are combined with the oxygen coordination atoms of a rigid carboxylic acid ligand and the nitrogen coordination atoms of a flexible bipyridine ligand to form a three-dimensional metal-organic framework single crystal [Cd2(adc)2(bpp)3·4H2O] containing crystal water with a flexible layer structure by mixing. n After heating to remove water molecules, a three-dimensional metal-organic framework single crystal [Cd2(adc)2(bpp)3] with a stable structure is obtained. n It has good water stability, and its water absorption rate is greater than that of silica gel desiccant, and it has potential application value in the field of detecting water molecules in the environment.

Description

Technical Field

[0001] The present invention belongs to the technical field of metal organic framework materials, and in particular relates to a three-dimensional metal organic framework single crystal and a preparation method and application thereof. Background Art

[0002] Metal-organic framework materials are hybrid materials formed by the coordination and connection of inorganic metal ions or ion clusters with organic ligands. They have the advantages of adjustable pore morphology and modifiable physical and chemical properties, and show potential application value in the fields of selective adsorption separation, sensing, drug delivery, etc. In the field of selective adsorption, some metal-organic framework materials can use their inherent regular pore structure to accommodate the adsorption of small guest molecules such as carbon monoxide and methane. Other metal-organic framework materials, although they are non-porous structures, can undergo adaptive flexible structural changes under the stimulation of guest molecules to achieve selective adsorption and separation of guest molecules. However, the water stability of metal framework materials is generally poor, which greatly limits their application in aquatic environments or humid environments. Research scholars have [2] (Chemical Industry Progress, 2022, 41(08), 4254-4267) The water stability of MOF was studied from multiple perspectives, including the basic composition of metal organic framework materials, structural design principles, and factors affecting water adsorption behavior. In addition, the researchers [3] (J.Am.Chem.Soc., 2014, 136(49), 16978-16981) It was found that by using the vapor deposition polydimethylsiloxane technology, a polydimethylsiloxane protective layer of about 10 nm thick can be formed on the surface of the metal organic framework crystal, so that the originally hydrophilic metal organic framework material is transformed into a highly hydrophobic property, thereby blocking the invasion of water molecules. The study found that the formation of this surface protective layer does not affect the original structure, porosity and accessibility of the catalytic active sites of the metal organic framework crystal, so that the modified MOFs can maintain their existing gas adsorption and catalytic capabilities very well.

[0003] However, the above preparation method is complicated and has a long preparation cycle. If the water stability can be improved by changing the skeleton structure, it will be an important breakthrough in this field.

[0004] Therefore, the synthesis of water-stable metal-organic framework materials is a key issue that needs to be urgently addressed in this field.

[0005] [1] Liu Xueting. Design, synthesis and performance study of a series of MOF-5-like structures with moisture resistance[D]. Liaoning Normal University.

[0006] [2] Zu Mei, Xu Haitao, Xie Wei, et al. Progress in water stability and water absorption applications of metal organic framework materials[J]. Chemical Industry Progress, 2022(008):041.

[0007] [3] Zhang W, Hu Y, Ge J, et al. A Facile and General Coating Approach to Moisture / Water-Resistant Metal–Organic Frameworks with Intact Porosity[J]. American Chemical Society, 2014(49). Summary of the invention

[0008] In order to solve the above technical problems, the present invention provides a three-dimensional metal organic framework single crystal, wherein Cd ions are combined with oxygen coordination atoms of rigid carboxylic acid ligands and nitrogen coordination atoms of flexible bipyridine ligands to mix and construct a three-dimensional metal organic framework single crystal containing crystal water with a flexible layer structure [Cd 2 (adc) 2 (bpp) 3 ·4H 2 O] n After heating and removing water molecules, a stable three-dimensional [Cd 2 (adc) 2 (bpp) 3 ] n Metal-organic framework single crystal. The three-dimensional structure consists of a rigid 4,4'-azophthalic acid (ADC) ligand supporting a two-dimensional flexible layer of 1,3-di(4-pyridyl)propane (BPP) coordinated Cd ions [Cd 2 (bpp) 3 ] n It can absorb water quickly in a humid environment and its crystal structure is stable. The crystal structure after water absorption is different from the crystal structure before dehydration [Cd 2 (adc) 2 (bpp) 3 ·4H 2 O] n The in-situ single crystal X-ray diffraction test shows that the three-dimensional metal organic framework single crystal [Cd 2 (adc) 2 (bpp) 3 ] n The water absorption-dehydration process is a reversible process, which relies on the two-dimensional flexible layer [Cd 2 (bpp) 3 ] n The expansion and contraction of the crystal skeleton structure realizes the hydrogen bonding and release of water molecules. After the crystal absorbs water, the structure is compact and has no pores, which effectively improves the structural stability of the crystal after water absorption.

[0009] Specifically, the technical solution of the present invention is as follows:

[0010] A three-dimensional metal organic framework single crystal [Cd 2 (adc) 2 (bpp) 3 ] n The single crystal is a three-dimensional structure composed of 4,4'-azophthalic acid supported 1,3-di(4-pyridyl)propane coordinated Cd two-dimensional layer. The two-dimensional layer structure is flexible, which enables the single crystal material to undergo dynamic expansion and contraction along the two-dimensional layer direction under the stimulation of water molecules. After the material undergoes a water absorption-dehydration cycle, the structure has good stability and the water absorption rate is greater than that of silica gel desiccant.

[0011] Furthermore, the [Cd 2 (adc) 2 (bpp) 3 ] n It is a three-dimensional block structure.

[0012] Furthermore, the [Cd 2 (adc) 2 (bpp) 3 ] n Each asymmetric unit in the crystal structure contains two Cd(Ⅱ), three 4,4'-azophthalic acid (adc 2- ) and two 1,3-di(4-pyridyl)propane (bpp), three flexible bpp ligands coordinated with Cd(Ⅱ) with different degrees of twist to form a flexible two-dimensional layer [Cd 2 (bpp) 3 ] n .

[0013] Furthermore, the three-dimensional metal-organic framework single crystal is a red and transparent millimeter-scale single crystal.

[0014] The second aspect of the present invention provides a three-dimensional metal organic framework single crystal [Cd 2 (adc) 2 (bpp) 3 ] n A preparation method is provided, wherein the method uses a hydrothermal method to produce millimeter-scale single crystals with a three-dimensional block structure, red transparency, and excellent crystallinity.

[0015] A metal organic framework single crystal [Cd 2 (adc) 2 (bpp) 3 ·4H 2 O] n The preparation method comprises the following steps:

[0016] Cadmium nitrate tetrahydrate, 4,4'-azophthalic acid, 1,3-di(4-pyridyl)propane, and distilled water were added to a polytetrafluoroethylene liner, and an organic amine was added to adjust the pH value of the mixed solution. The polytetrafluoroethylene liner was then placed in a stainless steel reactor, screwed tightly, and heated in an oven at 100°C. After being kept constant at this temperature for five days, it was naturally cooled to room temperature. The system after the reaction was phase separated, and the non-liquid phase product obtained was washed, dried, and heated at 95°C for 2h to obtain the three-dimensional metal organic framework single crystal [Cd 2 (adc) 2 (bpp) 3 ] n .

[0017] In the preparation method, preferably, the molar ratio of cadmium nitrate tetrahydrate, 4,4'-azophthalic acid, and 1,3-di(4-pyridyl)propane is 1:1:1.

[0018] In the preparation method, preferably, the organic amine is ethylenediamine.

[0019] In the preparation method, preferably, the ratio of distilled water, ethylenediamine, cadmium nitrate tetrahydrate, 4,4'-azophthalic acid, and 1,3-di(4-pyridyl)propane is 4 mL: 0.1 mL: 0.25 mmol: 0.25 mmol: 0.25 mmol.

[0020] In the preparation method, distilled water is used for washing and natural drying is used for drying.

[0021] The three-dimensional metal organic framework single crystal [Cd 2 (adc) 2 (bpp) 3 ] n Dynamic expansion and contraction behavior occurs along the two-dimensional layer direction. After the water absorption-dehydration cycle, the single crystal structure has good stability, and the water absorption rate is greater than that of silica gel desiccant.

[0022] The three-dimensional metal organic framework single crystal [Cd 2 (adc) 2 (bpp) 3 ] n A three-dimensional metal organic framework single crystal [Cd 2 (adc) 2 (bpp) 3 ] n The three-dimensional metal organic framework single crystal [Cd 2 (adc) 2 (bpp) 3 ] n .

[0023] The dynamic behavior of expansion and contraction is verified by in-situ testing of single crystal X-ray diffraction.

[0024] The dehydration-absorption cycle is 2 (adc) 2 (bpp) 3 ·4H 2 O] n In situ testing of metal-organic framework single crystals.

[0025] The water absorption speed is verified by infrared spectroscopy testing of characteristic absorption peaks of water molecules.

[0026] The beneficial effects of the present application include: providing a three-dimensional [Cd 2 (adc) 2 (bpp) 3 ] n Metal-organic framework single crystals have good water stability. The three-dimensional structure of the two-dimensional flexible layer constructed by a mixture of rigid and flexible organic ligands has a water absorption rate greater than that of silica gel desiccant and has potential application value in the field of water molecule detection in the environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The accompanying drawings in the specification, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0028] Figure 1 For three-dimensional metal organic framework single crystals [Cd 2 (adc) 2 (bpp) 3 ] n The crystal structure after water absorption [Cd 2 (adc) 2 (bpp) 3 ·4H 2 O] n Matching diagram.

[0029] Figure 2 For three-dimensional metal organic framework single crystals [Cd 2 (adc) 2 (bpp) 3 ] n Three-dimensional structure diagram along the b-axis.

[0030] Figure 3 For three-dimensional metal organic framework single crystals [Cd 2 (adc) 2 (bpp) 3 ] n After water absorption, the crystals [Cd 2 (adc)2 (bpp) 3 ·4H 2 O] n Thermogravimetric and differential thermal analysis diagrams.

[0031] Figure 4 For three-dimensional metal organic framework single crystals [Cd 2 (adc) 2 (bpp) 3 ] n Water absorption-dehydration and structural test procedure diagram.

[0032] Figure 5 For three-dimensional metal organic framework single crystals [Cd 2 (adc) 2 (bpp) 3 ] n Expansion and contraction diagram of the crystal structure.

[0033] Figure 6 For three-dimensional metal organic framework single crystals [Cd 2 (adc) 2 (bpp) 3 ·4H 2 O] n Powder diffraction pattern of .

[0034] Figure 7 For three-dimensional metal organic framework single crystals [Cd 2 (adc) 2 (bpp) 3 ] n Fitting curve of infrared test data of water absorption rate. DETAILED DESCRIPTION

[0035] The present invention is described below by specific embodiments. Unless otherwise specified, the technical means used in the present invention are methods known to those skilled in the art. In addition, the embodiments should be understood as illustrative rather than limiting the scope of the present invention, and the essence and scope of the present invention are limited only by the claims. For those skilled in the art, various changes or modifications to the material composition and dosage in these embodiments, without departing from the essence and scope of the present invention, also belong to the protection scope of the present invention.

[0036] The analysis method in the examples of this application is as follows:

[0037] Single crystal X-ray diffraction analysis was performed using a Rigaku MicroMax-007 diffractometer.

[0038] Example 1

[0039] This embodiment provides a three-dimensional metal organic framework single crystal [Cd 2(adc) 2 (bpp) 3 ] n The preparation method comprises the following specific steps:

[0040] (a) 77 mg of cadmium nitrate tetrahydrate, 67 mg of 4,4'-azophthalic acid and 99 mg of 1,3-di(4-pyridyl)propane were mixed.

[0041] (b) The mixture in step (a) was added into a polytetrafluoroethylene liner containing 4 mL of distilled water, 0.1 mL of ethylenediamine was added, and the polytetrafluoroethylene liner was placed into a stainless steel reactor, which was then screwed tightly.

[0042] (c) The stainless steel reactor in step (b) was placed in an oven, which was set to maintain a constant temperature of 100° C. for 5 days, and then naturally cooled to room temperature.

[0043] (d) The reaction mixture was filtered, the non-liquid phase product was washed with distilled water, dried naturally, and heated at 95°C for 2 h to obtain a millimeter-scale three-dimensional metal organic framework single crystal [Cd 2 (adc) 2 (bpp) 3 ] n .

[0044] Example 2

[0045] Due to the wide variety of organic ligands and the various coordination forms, even the same ligand and the same coordination functional group will have different coordination modes under different reaction conditions.

[0046] In the preparation process of this example, it was found that in step (c) of Example 1, after heating at 100°C for 2 days, the generated product was cooled, the pH was adjusted to below 2, acidified for 2 hours, and then the pH was adjusted to 10, and the heating at 100°C for 3 days was continued, so that the ligand coordination process experienced three flexible bpp ligands with different degrees of distortion coordinated with Cd(II) to form a flexible two-dimensional layer [Cd 2 (bpp) 3 ] n , a three-dimensional structure consisting of a two-dimensional layer of Cd coordinated by 1,3-di(4-pyridyl)propane supported by 4,4'-azophthalic acid, and the obtained [Cd 2 (adc) 2 (bpp) 3 ] n Has better water absorption effect.

[0047] Taking the water absorption effect of Example 1 as 100%, the water absorption effect of Example 2 is as follows:

[0048] sample Water absorption effect Test 1 132％ Test 2 136％ Test 3 135％

[0049] Example 3

[0050] This embodiment provides the three-dimensional [Cd 2 (adc) 2 (bpp) 3 ] n Performance test of single crystal.

[0051] (1)Flexibility test

[0052] Select 3D [Cd 2 (adc) 2 (bpp) 3 ·4H 2 O] n Single crystal in situ testing of the single crystal structure during the dehydration-water absorption cycle process.

[0053] Figure 3 It is three-dimensional [Cd 2 (adc) 2 (bpp) 3 ·4H 2 O] n Thermogravimetric and differential thermal analysis diagrams of the single crystal show that the crystal can lose crystalline water at 95°C, and in the temperature range of 95°C to 150°C, the material has no weight loss and the structure remains stable.

[0054] Figure 4 It is three-dimensional [Cd 2 (adc) 2 (bpp) 3 ·4H 2 O] n A processing procedure diagram of a single crystal, wherein the processing procedure is low temperature structure test (1) - high temperature dehydration - high temperature structure test (1a) - low temperature structure test (1b) - high temperature water absorption - low temperature structure test (1c).

[0055] Figure 5 It is three-dimensional [Cd 2 (adc) 2 (bpp) 3 ·4H 2 O] n Single crystal Figure 4 Schematic diagram of the crystal structure changes during the processing procedure shown. The unit cell parameters are obtained from single crystal X-ray diffraction tests, which show that the crystal can shrink and expand under the stimulation of water molecules. The shrinkage and expansion are dynamic behaviors along the two-dimensional layer, and the layer spacing does not change significantly.

[0056] Figure 6 It is three-dimensional [Cd 2 (adc) 2(bpp) 3 ·4H 2 O] n The X-ray powder diffraction patterns of the single crystal before and after the dehydration-water absorption cycle show that the single crystal is of good quality and the structure has not changed.

[0057] (2) Water absorption speed test

[0058] The water absorption process of the dehydrated crystals was monitored semi-quantitatively in situ by KBr tablet infrared spectroscopy, and compared with the relative water absorption rate of silica gel desiccant. 0.0040g of dehydrated crystals and 0.0040g of silica gel were mixed with 0.0920g of KBr and ground and pressed into tablets to prepare two samples. 0.0920g of KBr alone was ground and pressed into tablets as a blank sample. Then the three samples were placed in an oven and kept at a constant temperature of 100℃ for 3h. The sample was placed in an air environment and the stretching vibration peak of water molecules (3434cm -1 ) changes.

[0059] Figure 7 The rate of change of the peak intensity of the stretching vibration of water molecules detected during the water absorption process shows that the water absorption speed of the crystal is greater than that of silica gel.

Claims

1. A three-dimensional metal organic framework single crystal, It is characterized in that The invention is composed of a plurality of asymmetric units, wherein the asymmetric units include Cd(II) and 4,4'-azophthalic acid and 1,3-di(4-pyridyl)propane coordinated thereto; the structural formula of the three-dimensional metal organic framework single crystal is [Cd 2 (adc) 2 (bpp) 3 ]n; Three 1,3-di(4-pyridyl)propanes coordinated with Cd(Ⅱ) with different twists to obtain a flexible two-dimensional layer, and two 4,4'-azobenzenedicarboxylic acids supported 1,3-di(4-pyridyl)propanes coordinated with Cd(Ⅱ) to form a three-dimensional metal-organic framework single crystal; The three-dimensional metal organic framework single crystal is a red and transparent millimeter-scale single crystal; The method for preparing the three-dimensional metal organic framework single crystal comprises the following steps: (1) mixing cadmium nitrate tetrahydrate, 4,4'-azophthalic acid and 1,3-di(4-pyridyl)propane in water; (2) adding an organic amine to adjust the pH value of the solution; (3) heating the solution in an oven at 100°C, reacting at a constant temperature for 5 days, and then cooling the solution to room temperature; (4) filtering the product, washing the non-liquid phase product, drying it, and heating it at 95°C for 2 hours to obtain a three-dimensional metal organic framework single crystal; (1), the molar ratio of cadmium nitrate tetrahydrate, 4,4'-azophthalic acid, and 1,3-di(4-pyridyl)propane is 1:1:1; (2), wherein the organic amine is ethylenediamine; The ratio of water, ethylenediamine, cadmium nitrate tetrahydrate, 4,4'-azophthalic acid, and 1,3-di(4-pyridyl)propane is 4 mL:0.1 mL:0.25 mmol:0.25 mmol:0.25 mmol.

2. Use of the three-dimensional metal organic framework single crystal according to claim 1 in gas dehydration or solution water molecule adsorption.

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