CN111763331B - An alkaline earth metal [ Mg (lna) ]2]nSingle crystal adsorbing material and preparation method and application thereof - Google Patents

Abstract

The present invention provides an alkaline earth metal [ Mg (lna) ]₂]_nA single crystal adsorbing material and a preparation method and application thereof belong to the technical field of preparation of VOCs gas adsorbing materials, and the method comprises the following steps: s1, mixing isonicotinic acid and magnesium chloride in a molar ratio of 1: 0.2-2, adding an absolute ethyl alcohol solution, and uniformly stirring to obtain a mixed solution; s2, sealing the mixed solution of S1 in an inner container of a reaction kettle, placing the reaction kettle in an electric heating blowing dry box, heating to 90-180 ℃ at the speed of 5-40 ℃/h, and preserving heat for 30-45 h; then cooling to 15-35 ℃ at the speed of 0.5-5.0 ℃/h; s3, purifying the reaction product obtained in the S2 to obtain alkaline earth metal [ Mg (lna)₂]_nA single crystal adsorbent material. The method mainly adopts a solvent synthesis method, is prepared by one-step reaction, has simple preparation process, lower cost and low energy consumption, and the prepared adsorbing material has high purification efficiency on VOCs gas in the wood drying industry.

Description

An alkaline earth metal [ Mg (lna) ]2]nSingle crystal adsorbing material and preparation method and application thereof

Technical Field

The invention belongs to the technical field of preparation of VOCs (volatile organic compounds) gas adsorption materials, and particularly relates to an alkaline earth metal [ Mg (lna) ] targeted for intelligent adsorption₂]_nA single crystal adsorption material and a preparation method and application thereof.

Background

Volatile Organic Compounds (VOCs) refer to volatile organic compounds with boiling points lower than 260 ℃ and saturated vapor pressures higher than 133.322Pa at normal temperature and normal pressure, have the characteristics of strong volatility, irritation, toxic harmfulness and the like, and are a main induction factor of human carcinogenesis at present.

During the drying process of the wood at normal temperature or high temperature, specific VOCs gas pollutants such as terpenoids (alpha-pinene, beta-pinene, myrcene, camphene and the like), non-terpenoids (carbon tetrachloride, aromatic hydrocarbon, carboxylic acid, formaldehyde, acetaldehyde and the like) and the like are often released. Such as alpha-pinene, is harmful to the body by inhalation, ingestion or percutaneous absorption. Beta-pinene, an isomer of alpha-pinene, has similar chemical properties to alpha-pinene. Benzene (Benzene, C)₆H₆) It is a colorless transparent liquid with combustion, carcinogenic toxicity and strong aromatic smell at normal temperature. Carbon tetrachloride (carbon tetrachloride), a colorless transparent volatile liquid, has a special aromatic odor, and its toxicity causes chemical organ damage and accelerates the decomposition of the ozone layer.

Currently, the methods for treating VOCs mainly include: recovery techniques such as a condensation recovery method, a membrane separation method, an adsorption method, and a solution absorption method; catalytic combustion, thermal combustion, plasma and biodegradation. These methods all achieve different degrees of effect in industry, but also have certain disadvantages. For example, the condensation recovery method is suitable for treating medium-concentration organic waste gas, but has high treatment cost, poor absorption effect and possibility of causing secondary pollution in the absorption process. The combustion process has high requirements for temperature and the catalyst used in combustion is costly. The photocatalysis method is mainly used for low-concentration treatment, the yield is low, the catalyst has strict requirements on the characteristic wavelength of an excitation source, and the photocatalysis method is not suitable for large-area treatment. The adsorption method is a treatment method widely applied at present due to simple operation, low energy consumption, high purification efficiency and high recovery rate, and the key point is the selection of the adsorption material.

In the adsorption materials reported in the literature at present, the preparation process of the activated carbon and the modified materials thereof is complicated, the adsorption performance of the activated carbon and the modified materials thereof is greatly influenced by the carbonization time, and in the long-time carbonization process at high temperature, the amorphous fixed carbon is easily graphitized to cause difficult activation, the internal pore structure, the surface active sites, the surface chemical properties and the like of the activated carbon material are damaged, and the adsorption capacity is reduced. The molecular sieve has the problems of energy loss and environmental pollution in the preparation process, the required cost is expensive, and the molecular sieve cannot be used for adsorption under the strong acid/strong alkali condition, so that the purification efficiency is low.

Therefore, a new VOCs gas adsorbing material with simple preparation process, low cost, low energy consumption and high purification efficiency needs to be found.

Disclosure of Invention

To solve the above problems, it is an object of the present invention to provide an alkaline earth metal [ Mg (lna) ] targeted for smart adsorption₂]_nThe method mainly adopts a solvent synthesis method and is formed by one-step reaction, the preparation process is simple, the cost is low, the energy consumption is low, and the prepared adsorbing material has high purification efficiency on VOCs gas.

In order to achieve the above object, the present invention has the following technical means.

An alkaline earth metal [ Mg (lna) ]₂]_nA single crystal adsorbent material having a structural formula of [ Mg (lna) ]₂]_n(ii) a Wherein n is a natural number and is more than or equal to 1;

said [ Mg (lna)₂]_nThe single crystal is crystallized in monoclinic system, and each asymmetric unit has a central ion Mg²⁺Each central ion Mg²⁺Are all in octahedral coordination environment;

wherein, the central ion Mg²⁺The coordination number of (2) is 6, and the coordination numbers are respectively coordinated with carboxyl O atoms in four ligands and N atoms on pyridine rings in two ligands to form an octahedral coordination configuration;

each ligand is bridged with three Mg respectively²⁺One end of which is bonded to Mg by an N atom²⁺Coordinated and two O atoms in the other carboxyl group respectively correspond to Mg²⁺And (4) coordination.

Further, O (1), O (3), O (5) and O (7) in the four ligands occupy the position of the equatorial plane of the octahedron, the relevant bond angles O (1) -Mg-O (3), O (3) Mg-O (7), O (5) -Mg-O (7) and O (1) -Mg-O (5) are respectively 91.74(15) °, 88.12(16) °, 92.25(16) ° and the sum of 87.89(16) ° is 360.00 °, and the four coordinated O atoms are completely coplanar;

mg off the equatorial plane

N (1) and N (2) in the two ligands are in axial bonding position, and the axial bond angle N (1) -Mg-N (2) is 178.0(2) °.

Further, the complex [ Mg (Ina)₂]_nA pore channel with a quadrangular prism structure in a bc plane, wherein the pore channel is Mg²⁺As a vertex, linked by isonicotinic acid.

An alkaline earth metal [ Mg (lna) ]₂]_nThe preparation method of the single crystal adsorbing material comprises the following steps:

s1, mixing isonicotinic acid and magnesium chloride in a molar ratio of 1: 0.2-2, adding an absolute ethyl alcohol solution, and uniformly stirring to obtain a mixed solution;

s2, sealing the mixed solution of S1 in an inner container of a reaction kettle, placing the reaction kettle in an electric heating blowing dry box, heating to 90-180 ℃ at the speed of 5-40 ℃/h, and preserving heat for 30-45 h; then cooling to 15-35 ℃ at the speed of 0.5-5.0 ℃/h;

s3, purifying the reaction product obtained in the S2 to obtain alkaline earth metal [ Mg (lna)₂]_nA single crystal adsorbent material.

Further, in S1, the ratio of the volume usage of the absolute ethyl alcohol solution to the amount of the isonicotinic acid is 1-15: 1 mL/mmol.

Further, in S3, the purification process is as follows:

washing the reaction product of S2 with absolute ethanol for 3-5 times, and observing and screening alkaline earth metals of specific structure under a microscope [ Mg (lna)₂]_nWashing the single crystal adsorbing material with absolute ethyl alcohol for 3-5 times, and then placing the material at 60 ℃ for vacuum drying to constant weight to obtain the product.

Further, the alkaline earth metal of the specific structure [ Mg (lna) ]₂]_nThe screening process of the single crystal adsorbing material is as follows:

and (4) picking crystals with regular shapes and clear edges, and collecting the generated crystals independently.

Using the above alkaline earth metal [ Mg (lna)₂]_nThe single crystal adsorbing material is applied to the adsorption of VOCs gas in the wood drying industry.

Further, the VOCs gas is at least one of alpha-pinene, beta-pinene, benzene and carbon tetrachloride.

The invention has the beneficial effects that:

1. the method mainly adopts a solvent synthesis method, selects alkaline earth metal Mg as an ion center, takes isonicotinic acid (namely 4-picolinic acid) as an organic ligand for constructing MOFs, carries out molecular rearrangement and coordination self-assembly in an absolute ethanol solution, and synthesizes a series of targeted intelligently adsorbed alkaline earth metals [ Mg (lna) ]by one-step reaction₂]_nThe series of single crystal adsorbing materials have excellent adsorbing effect on VOCs gases such as alpha-pinene, beta-pinene, benzene, carbon tetrachloride and the like released in the high-temperature/normal-temperature drying process of the domestic pinus sylvestris wood.

2. The 4-picolinic acid used in the present invention has a basic structure such as pyridine ring or carboxyl group, and the resulting coordination polymer contains sp²The hybridized delocalized pi bond increases the stability of the adsorbing material and the activity of electrons through the actions of pi-pi accumulation and the like. The compound contains N, O donors, so that abundant coordination modes can be formed to construct multifunctional structural units. And the lone pair on the coordination atom in the 4-picolinic acid ligand and the alkaline earth metal Mg²⁺Hollow 3s orbits can be combined into a three-dimensional network structure through coordination bonds and electrostatic attraction and other forces, thereby forming [ Mg (lna)₂]_nThe single crystal adsorbing material structural unit comprises the following coordination processes:

having a similar coordination to the oxygen atomProcedure

3. In the present invention, Mg²⁺And 4-picolinic acid are combined with each other to form a three-dimensional network structure which is a special three-dimensional skeleton structure of a chain hole type, wherein Mg²⁺A one-dimensional chain structure is formed by chelation with carboxyl oxygen atoms; and the coordination between the octahedron vertex position and the N atom in the pyridine ring forms a three-dimensional pore channel structure with a quadrangular configuration. With four Mg²⁺The vertex of the bottom surface of the quadrangular prism is provided with the length of the bottom edge

In between, its void size and skeleton are large and there is a typical topology rich in a large number of porous pores.

The volume size of the alpha-pinene and beta-pinene gas is close to the pore size of the adsorbing material, and the structure contains sp²C-C double bonds, bonded in a hybrid manner, in which readily mobile pi electrons are present, can be filled [ Mg (lna) ]₂]_nMg in single crystal adsorbing material²⁺Further, specific coordinate bonding occurs in the empty 3s orbital, resulting in [ Mg (lna)₂]_nThe single crystal adsorbing material has good adsorption effect on alpha-pinene and beta-pinene gas.

The volume size of benzene vapor gas is smaller than the void size of the adsorbing material, and 6 carbon atoms in the benzene structure are all sp²Hybridization, the p orbitals of each carbon atom are overlapped to form delocalized big pi bonds, easily flowing pi electrons exist, and the pi electrons are filled into Mg through specific coordination bond bonding action²⁺Hollow 3s orbit, resulting in [ Mg (lna)₂]_nThe single crystal has an adsorption effect on the benzene vapor.

The volume size of carbon tetrachloride gas is smaller than the pore size of the adsorbing material, and carbon of the carbon tetrachloride gas is sp³Mode of hybridization and chlorination in s-sp³The sigma bond mode connection leads to a plurality of Cl in the carbon tetrachloride due to the existence of lone pair electrons in the Cl^-Homoenergetic with Mg²⁺By binding to the metal site of [ Mg (lna) ]₂]_nAnd (3) adsorbing carbon tetrachloride by using the single crystal.

4. The adsorbing material obtained by the method of the invention basically has no corrosion, has little pollution degree to the environment, belongs to an environment-friendly treating agent, obtains excellent adsorption effect in the adsorption treatment of VOCs gases such as alpha-pinene, beta-pinene, benzene, carbon tetrachloride and the like, and the [ Mg (lna) ]₂]_nThe single crystal adsorption material is proved to be capable of being repeatedly recycled for a plurality of times after desorption experiments, and the adsorption quantity of the single crystal adsorption material is not obviously reduced after the single crystal adsorption material is used for a plurality of times.

Drawings

FIG. 1 shows [ Mg (lna) ] in example 1 of the present invention₂]_nAnd (4) a topography under a microscope of the single crystal adsorption material.

FIG. 2 shows [ Mg (lna) ] in example 1 of the present invention₂]_nAnd (5) a photo of the single crystal adsorbing material under an ultraviolet lamp.

FIG. 3 shows [ Mg (lna) ] in example 1 of the present invention₂]_nThe molecular structure diagram and the coordination structure diagram of the single crystal adsorbent.

a)[Mg(lna)₂]_nA molecular structure diagram of the single crystal adsorbent material;

b)[Mg(lna)₂]_nthe coordination structure of the single crystal adsorbent.

FIG. 4 shows [ Mg (lna) ] in example 1 of the present invention₂]_nA pore structure diagram and a partial pore structure diagram of the single crystal adsorbing material.

a)[Mg(lna)₂]_nA pore structure diagram of the single crystal adsorbing material;

b) and c) is [ Mg (lna) ]₂]_nPartial pore structure diagram of single crystal adsorption material.

FIG. 5 shows [ Mg (lna) ] in example 1 of the present invention₂]_nA three-dimensional structure diagram of a single crystal adsorbent.

a)[Mg(lna)₂]_nA-axis structural view of (1);

b)[Mg(lna)₂]_nb-axis structural drawing of (1);

c)[Mg(lna)₂]_nc-axis knot ofAnd (6) patterning.

FIG. 6 shows [ Mg (lna) ] in example 1 of the present invention₂]_nThe single crystal adsorption material adsorbs infrared spectra before and after the alpha-pinene gas.

FIG. 7 shows [ Mg (lna) ] in example 1 of the present invention₂]_nTEM images of single crystal adsorbent material.

a. b and c are enlarged partial views respectively.

FIG. 8 shows [ Mg (lna) ] in example 1 of the present invention₂]_nThermogravimetric plot (TGA) of single crystal adsorbent material.

FIG. 9 shows [ Mg (lna) ] in example 1 of the present invention₂]_nNitrogen adsorption/desorption profile of the single crystal adsorbent material.

FIG. 10 shows [ Mg (lna) ] in example 1 of the present invention₂]_nPore size distribution curve of single crystal adsorbent material.

FIG. 11 shows [ Mg (lna) ] in example 1 of the present invention₂]_nThe single crystal adsorbing material has an adsorption/desorption curve for alpha-pinene.

FIG. 12 shows [ Mg (lna) ] in example 1 of the present invention₂]_nThe single crystal adsorption material has an adsorption/desorption curve for beta-pinene.

FIG. 13 shows [ Mg (lna) ] in example 1 of the present invention₂]_nThe adsorption/desorption curve of the single crystal adsorption material to carbon tetrachloride.

FIG. 14 shows [ Mg (lna) ] in example 1 of the present invention₂]_nAnd (3) the adsorption/desorption curve of the single crystal adsorption material to benzene.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail with reference to the following embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

The experimental methods described in the following examples are all conventional methods unless otherwise specified; the reagents and materials are commercially available, unless otherwise specified.

Example 1

An alkaline earth metal [ Mg (lna) ]₂]_nThe preparation method of the single crystal adsorbing material comprises the following steps:

s1, mixing isonicotinic acid and magnesium chloride in a molar ratio of 1:0.5, adding an absolute ethyl alcohol solution, and uniformly stirring to obtain a mixed solution; wherein the ratio of the volume usage of the absolute ethyl alcohol solution to the amount of the isonicotinic acid substance is 10:1 mL/mmol.

S2, sealing the mixed liquid of S1 in the inner container of a reaction kettle, putting the reaction kettle in an electric heating blowing dry box (SY101BS-0D-C-CX), heating to 120 ℃ at the speed of 20 ℃/h, and preserving heat for 36 h; then cooling to 30 ℃ at the speed of 2.0 ℃/h;

s3, washing the reaction product of S2 with absolute ethyl alcohol for 3-5 times, and observing and screening the alkaline earth metal with a specific structure under a microscope [ Mg (lna) ]₂]_nSingle crystal adsorbing material, collecting crystal with regular shape and clear edge, collecting the crystal, washing with anhydrous ethanol for 3-5 times, and vacuum drying at 60 deg.C to constant weight to obtain alkaline earth metal [ Mg (lna)₂]_nA single crystal adsorbent material. Wherein Ina is Isonicotinic (Isonicotinic).

Example 2

An alkaline earth metal [ Mg (lna) ]₂]_nA method for producing a single crystal adsorbing material was the same as in example 1, except that,

in S1, mixing isonicotinic acid and magnesium chloride in a molar ratio of 1:2, adding an absolute ethanol solution, and uniformly stirring to obtain a mixed solution; wherein the ratio of the volume usage of the absolute ethyl alcohol solution to the amount of the isonicotinic acid substance is 10:1 mL/mmol.

Example 3

An alkaline earth metal [ Mg (lna) ]₂]_nA method for producing a single crystal adsorbing material was the same as in example 1, except that,

in the S, mixing isonicotinic acid and magnesium chloride according to a molar ratio of 1:0.2, adding an absolute ethyl alcohol solution, and uniformly stirring to obtain a mixed solution; wherein the ratio of the volume usage of the absolute ethyl alcohol solution to the amount of the isonicotinic acid substance is 10:1 mL/mmol.

Example 4

An alkaline earth metal [ Mg (lna) ]₂]_nA method for producing a single crystal adsorbing material was the same as in example 1, except that,

in S1, mixing isonicotinic acid and magnesium chloride in a molar ratio of 1:0.5, adding an absolute ethanol solution, and uniformly stirring to obtain a mixed solution; wherein the ratio of the volume usage of the absolute ethyl alcohol solution to the amount of the isonicotinic acid substance is 1:1 mL/mmol.

Example 5

An alkaline earth metal [ Mg (lna) ]₂]_nA method for producing a single crystal adsorbing material was the same as in example 1, except that,

in S1, mixing isonicotinic acid and magnesium chloride in a molar ratio of 1:0.5, adding 2mL of absolute ethanol solution, and uniformly stirring to obtain a mixed solution; wherein the ratio of the volume usage of the absolute ethyl alcohol solution to the amount of the isonicotinic acid substance is 5:1 mL/mmol.

Example 6

An alkaline earth metal [ Mg (lna) ]₂]_nA method for producing a single crystal adsorbing material was the same as in example 1, except that,

in S1, mixing isonicotinic acid and magnesium chloride in a molar ratio of 1:0.5, adding 2mL of absolute ethanol solution, and uniformly stirring to obtain a mixed solution; wherein the ratio of the volume usage of the absolute ethyl alcohol solution to the amount of the isonicotinic acid substance is 15:1 mL/mmol.

Example 7

An alkaline earth metal [ Mg (lna) ]₂]_nA method for producing a single crystal adsorbing material was the same as in example 1, except that,

in S2, sealing the mixed solution of S1 in the inner container of a reaction kettle, placing the reaction kettle in an electrothermal blowing dry box (SY101BS-0D-C-CX), heating to 180 ℃ at 40 ℃/h, and preserving heat for 45 h; then the temperature is reduced to 15 ℃ at the speed of 5.0 ℃/h.

Example 8

An alkaline earth metal [ Mg (lna) ]₂]_nA method for producing a single crystal adsorbing material was the same as in example 1, except that,

in S2, sealing the mixed solution of S1 in the inner container of a reaction kettle, placing the reaction kettle in an electrothermal blowing dry box (SY101BS-0D-C-CX), heating to 90 ℃ at a speed of 5 ℃/h, and preserving heat for 30 h; then the temperature is reduced to 35 ℃ at the speed of 0.5 ℃/h.

Application example 1

The alkaline earth metal [ Mg (lna) ] obtained in example 1 was added₂]_nThe application of the single crystal adsorbing material 107.049mg in the adsorption of alpha-pinene.

1. Adsorption experiments

[ Mg (lna) obtained in example 1 was weighed₂]_n107.049mg of a test sample of a single-crystal adsorbing material was placed in a sample tube of a test chamber of an adsorption apparatus (3H-2000PW, Multi-station gravimetric vapor adsorption apparatus, Betsbed instruments science and technology Co., Ltd., Beijing) [ Mg (lna)₂]_nHeating and vacuum degassing single crystal adsorbent material, maintaining the sample chamber in vacuum, evaporating vapor adsorbate from liquid state in the reagent tube to the sample chamber to form vapor, [ Mg (lna)₂]_nAfter the single crystal material adsorbs alpha-pinene gas, it is weighed out by a microbalance under a certain relative pressure [ Mg (lna)₂]_nThe change of the weight of the single crystal sample before and after adsorption is used for measuring the adsorption and desorption amount of the sample to the specific gas. The adsorbate is the same gas, at most four samples can be tested in parallel in one adsorption experiment, and the average value of the results is taken. The temperature was constant at 25 ℃ during the test.

2. Desorption experiments

The desorption process is the reverse of the adsorption process, and is the relative partial pressure (P/P) of gas in the adsorption process₀) After reaching 0.95, the gas in the adsorption container is partially pumped out by a vacuum pump to reduce the partial pressure in the container, and the adsorption quantity is reduced along with the partial pressure, and the desorption quantity is correspondingly increased. At this time, the relative gas partial pressure gradually decreases from the optimum value of 0.95 to 0. When the partial pressure of gas is reduced to a certain degree, the gas is weighedAnd testing the adsorption quantity at the moment by a heavy method, namely the desorption quantity of the material to the alpha-pinene gas.

Application example 2

The alkaline earth metal [ Mg (lna) ] obtained in example 1 was added₂]_nThe application of the single crystal adsorbing material 120.907mg in beta-pinene adsorption, and the adsorption experiment and the desorption experiment are the same as the method of application example 1.

Application example 3

The alkaline earth metal [ Mg (lna) ] obtained in example 1 was added₂]_nThe application of 121.440mg of the single crystal adsorbent to benzene adsorption was carried out in the same manner as in application example 1.

Application example 4

The alkaline earth metal [ Mg (lna) ] obtained in example 1 was added₂]_nThe application of 106.942mg of single crystal adsorbing material to carbon tetrachloride adsorption was carried out in the same manner as in application example 1.

Alkaline earth Metal [ Mg (lna) ] obtained in example 1 of the present invention₂]_nThe structure characterization results of the single crystal adsorbing material are shown in figures 1-10.

FIG. 1 shows [ Mg (Ina) ]₂]_nMicroscopic topography of single crystal adsorbent material.

As can be seen from a) and b) in FIG. 1, [ Mg (Ina)₂]_nThe appearance with regular shape and clear edge is presented. But the size and morphology of different crystals are significantly different. The growth environment of the crystal is complex and various, and influences on the appearance of the crystal are generated to different degrees. Under a microscope, it can be seen that the individual crystals form a structure enclosing impurities during the growth process. When the crystals are screened as the adsorbing material, the crystals need to be removed.

FIG. 2 shows [ Mg (Ina) ]₂]_nAnd (5) a photo of the single crystal adsorbing material under an ultraviolet lamp.

Under the irradiation of an ultraviolet lamp, the single crystal shows bright fluorescence, and the intensity of the fluorescence has obvious identification degree. The crystal is near colorless crystal under visible light, and shows extremely light purple, but under an ultraviolet lamp, purple bright light is generated.

FIG. 3 shows [ Mg (Ina) ]₂]_nThe molecular structure diagram and the coordination structure diagram of the single crystal adsorbent.

[Mg(Ina)₂]_nThe molecular structure of (Ina ═ Isonicotinic, Isonicotinic) belongs to the monoclinic system. As can be seen from a) in FIG. 3, the central ion Mg²⁺Has a coordination number of 6, and coordinates to carboxyl O atoms (2O1, 2O2) in four different ligands and N atoms (2N1) on pyridine rings in two other ligands, respectively, thereby forming an octahedral coordination configuration. The central ion Mg ion is coordinated with N atoms in two ligands along the direction of the vertex of the octahedron, and O atoms in four ligands form the vertex of the equatorial plane of the octahedron and are combined with the Mg ion in a monodentate coordination mode. Each ligand is respectively bridged with three Mg ions, one end of each ligand is combined by an N atom to be coordinated with the Mg ions, and two O atoms in the carboxyl group at the other end of each ligand are respectively coordinated with different Mg ions.

As can be seen from b) in FIG. 3, the Mg ions are in an octahedral coordination environment, in which O (1), O (3), O (5) and O (7) occupy the equatorial plane position of the octahedron, and the associated bond angles O (1) -Mg-O (3), O (3) Mg-O (7), O (5) -Mg-O (7) and O (1) -Mg-O (5) are 91.74(15), 88.12(16), 92.25(16) and 87.89(16) respectively, and the sum of which is 360.00 degrees, indicating that four coordinated oxygen atoms are completely coplanar, and Mg is deviated from the equatorial plane by 360.00 degrees

N1 and N2 are in an axially keyed position, and the axial key angle N (1) -Mg-N (2) is 178.0(2) °.

FIG. 4 shows [ Mg (Ina) ]₂]_nA pore structure diagram and a partial pore structure diagram of the single crystal adsorbing material.

As can be seen from a) in FIG. 4, [ Mg (Ina))₂]_nThe crystal structure has quadrangular prism-shaped pore canals, the vertex of the quadrilateral is an octahedral structure of Mg ions, and different octahedrons are connected by isonicotinic acid ligands. The pore channel structure is formed, and powerful structural support is provided for the coordination polymer to adsorb guest molecules.

In FIG. 4b) and c) are [ Mg (Ina ]₂]_nStructural diagram of pore unit of crystal, canThe distance between different Mg ions can be accurately obtained. In FIG. 4b) it can be seen that four different Mg ions together form a quadrangular base of a quadrangular prism, the distances of the vertices of which are Mg1-Mg2 long, respectively

Mg1-Mg3 is long

Mg2-Mg4 is long

Mg3-Mg4 is long

From FIG. 4 c), it can be seen that Mg ions in the quadrilateral structural units are respectively coordinated with monodentate oxygen atoms in the same carboxyl group to link different structural units into a three-dimensional pore channel structure, and the distance between the Mg ions in the units is respectively Mg1-Mg2 long

Mg2-Mg1 is long

FIG. 5 is [ Mg (Ina) ]₂]_nA three-dimensional structure diagram of a single crystal adsorbent.

In FIG. 5a) is a complex [ Mg (Ina))₂]_nA-axis structural view of (1); b) is a complex [ Mg (Ina)₂]_nB-axis structural drawing of (1); c) is a complex [ Mg (Ina)₂]_nC-axis structure of (1). As can be seen from FIGS. a) to c), in [ Mg (Ina)₂]_nIn the three-dimensional structure of (2), the complexes are in a stable state and are arranged orderly. The appearance is relatively regular in appearance, uniform in distribution and relatively uniform in pore structure. In FIG. 5a), the complex [ Mg (Ina) ] is viewed from the a-axis direction₂]_nAnd a pore canal with a quadrangular prism structure is formed in a bc plane, and Mg ions are used as vertexes and are connected through isonicotinic acid. While the b-axis and c-axis directions show that the complex [ Mg (Ina)₂]_nIn the method, an eight-membered ring structure is formed by two Mg ions and carboxyl O atoms in two isonicotinic acids and is arranged into a one-dimensional chain structure along the direction of a coordinate axis, isonicotinic acid ligands are bridged among the chain structures, and the N atoms and the carboxyl O atoms are respectively connected with the Mg ions in different chains to form a two-dimensional plane structure. In contrast, it can be seen from FIGS. 5b) and c) that the pyridine ring structures in isonicotinic acid bridging different Mg ion chain structures form different dihedral angles between the chain structures. This structural feature produces different pi electron densities, which in turn affects the adsorption performance of different gases.

FIG. 6 shows [ Mg (Ina) ]₂]_nThe single crystal material absorbs the infrared spectrum before and after the alpha-pinene gas.

FIG. 6a is [ Mg (Ina)₂]_nFor the infrared curve before the adsorption of alpha-pinene gas, FIG. 6b is [ Mg (Ina)₂]_nInfrared curve after adsorption of alpha-pinene gas. As can be seen in FIG. 6a, 3380cm^-1The broad peak is the characteristic absorption peak of hydrogen bond associated in the molecule, and after the alpha-pinene is absorbed (figure 6b), the broad peak moves to 3400cm in the high wave number direction^-1The absorption peak becomes weak; 1680cm^-1-1740cm^-1No obvious absorption peak appeared in between (FIG. 6a), indicating [ Mg (Ina)₂]_nThe carboxyl group in the pair has been deprotonated; 1642cm^-1And 1580cm^-1(FIG. 6a) is assigned to the O-C ═ O asymmetric stretching vibration absorption peak and the vibration stretching vibration absorption peak, respectively, and for the carboxylate group-containing complex, the asymmetric stretching vibration absorption peak γ according to O-C ═ O_asAnd symmetric telescopic vibration absorption peak gamma_sThe difference between the two is delta gamma_as-γ_sThe size of the complex can be determined by the coordination mode of O-C ═ O and the metal ion, and the data in FIG. 6a shows that Δ γ is<160cm^-1Description of [ Mg (Ina)₂]_nMainly in a bidentate chelate coordination mode, which is consistent with the results in fig. 3, fig. 4 and fig. 5, the two absorption peaks are obviously weakened after the alpha-pinene is adsorbed (fig. 6 b); 1440cm^-1The absorption peak at (fig. 6a) is attributed to the C-O stretching vibration absorption peak, and the peak attenuation almost disappears after the absorption of the adsorbed alpha-pinene gas; 1362cm^-1Where (FIG. 6a) belongs to O-H in-plane bending vibrationA dynamic absorption peak, which is significantly weakened after the absorption of alpha-pinene (fig. 6 a); 1175cm^-1The C-H bending vibration absorption peak in the attributive pyridine ring (figure 6a) is weakened after the alpha-pinene is absorbed (figure 6 a); 938cm^-1、882cm^-1、728cm^-1And 664cm^-1(FIG. 6a) are respectively assigned to the adjacent 5C-H in-plane and out-plane bending vibration, C-H asymmetric stretching vibration absorption peak and aromatic heterocycle substitution region absorption peak of aromatic heterocycle, and after the alpha-pinene is absorbed, the absorption peaks at the four positions are shifted and weakened (FIG. 6 b); the above analysis shows that after adsorption of alpha-pinene, [ Mg (Ina)₂]_nIn the structure, partial hydrogen bond action is formed between oxygen atoms in C ═ O and C-O and alpha-pinene, pi-pi stacking action between pyridine aromatic heterocycle and alpha-pinene and indirect coordination action with aromatic heterocycle, coordination chelation action between alpha-pinene pi electron and metal Mg and the like, so that the absorption intensity of the absorption vibration peak of the corresponding active functional group is slightly changed, and the absorption peak value is shifted. Accordingly, [ Mg (Ina) ]₂]_nThe adsorption process of the single crystal material to the alpha-pinene gas comprises physical adsorption of the material with the porous structure and has a certain chemical adsorption effect.

FIG. 7 shows [ Mg (Ina) ]₂]_nTEM images of single crystal adsorbent material.

The micron-sized three-dimensional [ Mg (Ina) is synthesized for the first time by a temperature programming method₂]_nThe single crystal material is subjected to a high-resolution transmission electron microscope atlas (figure 7), and the crystal lattice stripes of the whole crystal are continuous, so that no obvious crystal boundary exists. Description [ Mg (Ina)₂]_nIs a complete single crystal. Randomly selecting regions on the crystal to observe the lattice structure, and finding that the patterns of the regions are the same, the stacking mode exists, and the layers are zigzag staggered, so that the whole crystal is further proved to be the same in all parts, a large number of porous and pore channels exist in the structure, and the Mg (Ina) is added₂]_nThe specific surface area and the porosity of the composite adsorbent are favorable for adsorbing VOCs gas molecules such as alpha-pinene, beta-pinene, benzene, carbon tetrachloride and the like.

FIG. 8 shows [ Mg (Ina) ]₂]_nSingle crystal adsorbing materialThermogravimetric curve (TGA) of (a).

[Mg(Ina)₂]_nThe single crystal adsorbing material has excellent thermal stability. Before heating to 500 deg.c, the weight loss rate is only 4.4%, and the crystal is adsorbed water and other small molecules. [ Mg (Ina)₂]_nThe single crystal structure analysis shows that no coordination water molecule exists in the framework, and the ligand is chelated with the central ion of the metal Mg by a carboxyl O atom to form a bond, so that the framework stability is very good. At about 480 ℃, [ Mg (Ina)₂]_nThe single crystal adsorbent material undergoes a weight loss corresponding to a collapse of the framework of the material, indicating [ Mg (Ina)₂]_nThe single crystal framework can keep good thermal stability at 480 ℃.

FIG. 9 shows [ Mg (Ina) ]₂]_nNitrogen adsorption/desorption profile of the single crystal adsorbent material.

[Mg(Ina)₂]_nN of single crystal adsorbing material under 77K₂The adsorption/desorption isotherms are shown in FIG. 9, and it can be seen that when P/P is present₀Less than 0.7, with P/P₀Increase, material only shows to N₂A small amount of adsorption; when P/P is present₀Between 0.7 and 0.9, with P/P₀Enlargement of material pair N₂The adsorption amount of (b) increases rapidly; when P/P is present₀Greater than 0.9, N₂The adsorption amount increases slowly and reaches saturation. The major adsorption ramp phase occurs on the isotherm due to the occurrence of N in the pores of the structure₂Adsorption phenomena. In N₂In the desorption stage, the desorption curve and the adsorption curve can be basically overlapped, and only when the desorption isotherm is 0.8 relative pressure, an H4 type hysteresis loop is slightly shown, which indicates that [ Mg (Ina)₂]_nThere were also very few mesopores in the single crystal material, which was concluded to match the pore structure parameters of table 1.

FIG. 10 shows [ Mg (Ina) ]₂]_nPore size distribution curve of single crystal adsorbent material.

[Mg(Ina)₂]_nThe pore size distribution curve of the single crystal adsorbent material is shown in FIG. 10, and it can be seen that the pore size of the material is mainly concentrated on

And

description of [ Mg (Ina) ]₂]_nThe material had permanent microporous channels at 77K, which is a microporous material, and this conclusion is essentially consistent with the channel dimensions (pore size) measured in the crystallographic data of Table 2

). The maximum pore volume can reach 2.810cm³Per g, mean micropore volume of 2.702cm³In terms of/g, corresponds to the porosity parameters in Table 1.

TABLE 1 is [ Mg (Ina)₂]_nSpecific surface area of single crystal adsorbent material and related parameters.

Table 2 lists [ Mg (Ina)₂]_nCrystallographic data and structure refinement data of the single crystal adsorbent material.

As can be seen from Table 1, [ Mg (Ina)₂]_nThe BET specific surface area of the single crystal adsorbing material is 573.5382m²G, Langmuir specific surface area 745.0791m²(iv)/g, indicates that the material has a porosity, and the average micropore pore volume of the material measured is 2.702cm³G, average pore diameter 10.4818 nm. Pore Volume and mean pore diameter in Table 1 and pore Volume and pore size (Volume/mm) in Table 2³2719.1, respectively; pore size

) Basic agreement, Explanation [ Mg (Ina)₂]_nThe structure of the single crystal adsorption material can keep good skeleton integrity, and the permanent microporous pore channel has good adsorption capacity for specific adsorbed gas.

TABLE 1[ Mg (Ina)₂]_nSpecific surface area of single crystal adsorbent material and related parameters

TABLE 2[ Mg (Ina)₂]_nCrystallographic and structural refinement data of single crystal adsorbent materials

Alkaline earth Metal [ Mg (Ina) ] obtained in example 1 of the present invention₂]_nThe results of adsorption/desorption isotherms of the single crystal adsorbent material for the four wood-dried VOCs gases are shown in fig. 11-14.

FIG. 11 shows [ Mg (Ina) ]₂]_nAnd (3) the adsorption/desorption isotherm of the single crystal adsorption material on the alpha-pinene.

[Mg(Ina)₂]_nIsotherm of the single crystal adsorbing material to alpha-pinene along with the relative pressure P/P₀When the adsorption quantity of the material to alpha-pinene is gradually increased from 0 to 0.9, the maximum adsorption quantity is 10.85mg/g, which indicates that [ Mg (Ina)₂]_nThe adsorption capacity of the single crystal adsorption material to alpha-pinene is the same as P/P₀And (4) positively correlating. In the desorption stage, with P/P₀And the absorption amount is correspondingly reduced, and the reduction trend is slow and stable. But as can be seen from FIG. 11, [ Mg (Ina)₂]_nThe desorption isotherm and the adsorption isotherm of the single crystal adsorbing material to the alpha-pinene are not coincident completely, and according to the trend of a desorption curve, when P/P is adopted₀When the molecular weight is close to 0, partial alpha-pinene molecules cannot be desorbed from pores, which shows that the adsorption of the material on the alpha-pinene is not only a physical adsorption effect, but also other acting forces (pi bonds in the alpha-pinene may generate a coordination reaction with metal central ions Mg, and pi bonds in the alpha-pinene may also generate a pi-pi stacking effect with an organic framework ligand pyridine ring), so that the adsorption process is irreversible.

FIG. 12 shows [ Mg (Ina) ]₂]_nAnd (3) an adsorption/desorption isotherm of the single crystal adsorption material on beta-pinene.

[Mg(Ina)₂]_nIsotherm of the single crystal adsorbing material to beta-pinene along with the relative pressure P/P₀When the adsorption quantity of the material is gradually increased from 0.04 to 0.95, the adsorption quantity of the material to beta-pinene shows a slight rising trend, and the adsorption quantity is slowly increased. In the desorption stage, with P/P₀The reduction is only carried out by a small amount of beta-pinene, the degree of the reduction of the adsorption quantity is weak, the desorption curve is not coincident with the adsorption curve, and when P/P is reached₀At approximately 0.08 relative pressures, some amount of beta-pinene remains unreleased, and therefore [ Mg (Ina)₂]_nThe single crystal material also has physical adsorption and chemical bonding acting force on the beta-pinene, and the adsorption process is irreversible.

FIG. 13 shows [ Mg (Ina) ]₂]_nThe adsorption/desorption isotherm of the carbon tetrachloride by the single crystal adsorption material.

[Mg(Ina)₂]_nThe adsorption/desorption isotherm of carbon tetrachloride by the single-crystal adsorbent material is shown in fig. 13, and can be divided into three stages according to the change of the adsorption amount. When P/P is present₀When the adsorption quantity of the material to carbon tetrachloride is less than 0.1, the adsorption quantity of the material to carbon tetrachloride is along with P/P₀Increase in size and increase rapidly; when P/P is present₀When the adsorption quantity is between 0.1 and 0.80, the increase trend of the adsorption quantity is slowed down; when P/P is present₀Above 0.80, there was only a slight increase in the amount of adsorption. Desorption phase, with P/P₀And the carbon tetrachloride is reduced, and only a small amount of carbon tetrachloride is desorbed. The degree of decrease in the amount of adsorption was weak. The adsorption and desorption curves are not coincident, and hysteresis exists; when P/P is present₀Between 0 and 0.1, the degree of decrease in the amount of adsorption slightly increases, but a part of carbon tetrachloride is not desorbed from the voids, similarly stated [ Mg (Ina) ]₂]_nThe adsorption of the single crystal material to carbon tetrachloride has physical adsorption and may also have chemical coordination acting force, so that the adsorption process is irreversible.

FIG. 14 shows [ Mg (Ina) ]₂]_nAnd (3) an adsorption/desorption isotherm of the single crystal adsorption material on benzene.

[Mg(Ina)₂]_nThe adsorption/desorption isotherms of the single-crystal adsorbent material for benzene are shown in FIG. 14, which is a function of the relative pressure P/P₀When the molecular weight of benzene is increased from 0 to 0.95, the adsorption capacity of the material to benzene is also increased rapidly, which shows that when a small amount of benzene molecules enter the pore channels of the material, the benzene molecules have pi-pi acting force ([ Mg (Ina))₂]_nOrganic skeleton ligand pyridine ring and benzene ring to form pi-pi acting force) to be adsorbed on the inner wall surface of the pore channel.

According to [ Mg (Ina) ] in Table 2₂]_nThe diameter of a pore channel window of the crystallography data and the structure refinement data of the single crystal adsorption material is 0.991nm, the diameter of an inner cavity of the pore channel reaches 2.6382nm, when a large number of benzene molecules enter the pore channel of the material, the benzene molecules are condensed and gradually reach single-layer saturated adsorption, and the maximum adsorption capacity is 8.285 mg/g; the benzene desorption isotherm is divided into two stages according to the desorption condition. P/P₀In the range of 0.1-0.95, the desorption phenomenon is slow, and when P/P is in₀When decreasing from 0.1 to 0, the desorption curve rapidly decreases. In the benzene desorption process, the key for determining whether benzene is desorbed or not is whether benzene molecules at the window are desorbed or not. Upon desorption, [ Mg (Ina)₂]_nThe pores are equivalent to micropores with a diameter of 0.991nm, so that when P/P is₀When the temperature is reduced to a sufficient level, the benzene molecules at the window can be desorbed, and then the benzene molecules in the pore canal can be desorbed. However, the adsorption isotherm and the desorption isotherm of benzene cannot coincide, which indicates that physical adsorption and chemical action force exist at the same time in the adsorption stage, and the adsorption shows an irreversible process.

TABLE 3[ Mg (Ina)₂]_nAdsorption capacity of single crystal adsorption material to four kinds of wood drying VOCs gas

Table 4 shows the structural characteristics of four wood-dried VOCs gases.

As can be seen from tables 3-4, the molar volumes and molecular volumes of α -pinene, β -pinene, carbon tetrachloride, benzene decrease in this order, [ Mg (Ina) ]₂]_nThe single crystal material has the adsorption capacity of alpha-pinene > carbon tetrachloride > benzene > beta-pinene to four kinds of gas.

The average micropore pore volume of the material obtained in combination with Table 1 was 2.702cm³(ii)/g, average pore diameter 10.4818nm, [ Mg (Ina) in Table 2₂]_nThe diameter of the pore channel window is 0.991nm, the diameter of the pore channel inner cavity reaches 2.6382nm, and then the molecular structure of the adsorbed four gases is analyzed.

Can find that [ Mg (Ina)₂]_nThe single crystal material is in a smaller P/P ratio in the process of adsorbing different gases₀When the range (0-0.1) is continuously increased, the adsorption capacity shows a rapid increase tendency, because the molecular volumes of the four gases are smaller than the pore size

When a small amount of VOCs gas molecules enter a material pore channel, the VOCs gas molecules are adsorbed on the surface of the inner wall of the pore channel under the guide of pi-pi acting force, chlorine atom lone-pair electron coordination and indirect acting force of a six-membered ring and the gas molecules; following P/P₀The gas molecules enter the material structure continuously and are adsorbed on the inner wall of the pore channel continuously, and the single-layer saturated adsorption is gradually achieved; when P/P is present₀When the adsorption capacity is higher (more than 0.8), molecules in the pore channel are condensed, a large number of gas molecules are gathered in a cavity formed by single-layer adsorption, and the adsorption capacity is slowly increased under the enhancement of chemical acting force until the maximum saturated adsorption capacity is reached. It is worth noting that the carbon-carbon double bond in the molecular structure of beta-pinene is outside the six-membered ring, thus generating great steric hindrance effect, resulting in [ Mg (Ina)₂]_nThe number of molecules that can be accommodated in the pores and pore structure of the single crystal material is reduced, so that the adsorption amount is minimized compared with the other three gases.

The present invention is not limited to the above preferred embodiments, and any modifications, equivalent substitutions and improvements made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (7)

1. An alkaline earth metal [ Mg (lna) ]₂]_nThe application of the single crystal adsorption material in the adsorption of VOCs gas in the wood drying industry is characterized in that the VOCs gas is at least one of alpha-pinene, beta-pinene, benzene and carbon tetrachloride;

the structural formula of the adsorbing material is [ Mg (lna) ]₂]_n(ii) a Wherein n is a natural number and is more than or equal to 1;

said [ Mg (lna)₂]_nThe single crystal is crystallized in monoclinic system, and each asymmetric unit has a central ion Mg²⁺Each central ion Mg²⁺Are all in octahedral coordination environment;

wherein, the central ion Mg²⁺The coordination number of (2) is 6, and the coordination numbers are respectively coordinated with carboxyl O atoms in four ligands and N atoms on pyridine rings in two ligands to form an octahedral coordination configuration;

each ligand is bridged with three Mg respectively²⁺One end of which is bonded to Mg by an N atom²⁺Coordinated and two O atoms in the other carboxyl group respectively correspond to Mg²⁺And (4) coordination.

2. Use according to claim 1, characterized in that O (1), O (3), O (5), O (7) of the four ligands occupy the equatorial plane position of the octahedron with the associated bond angles O (1) -Mg-O (3), O (3) Mg-O (7), O (5) -Mg-O (7), O (1) -Mg-O (5) respectively of 91.74(15) ° 88.12(16) ° 92.25(16) ° 87.89(16) ° plus 360.00 °, and the four coordinated O atoms are perfectly coplanar;

mg off the equatorial plane

N (1) and N (2) of the two ligands being in axial bonding position, the axes of whichThe bond angle N (1) -Mg-N (2) was 178.0(2) °.

3. Use according to claim 2, characterized in that the complex [ Mg (Ina)₂]_nA pore channel with a quadrangular prism structure in a bc plane, wherein the pore channel is Mg²⁺As a vertex, linked by isonicotinic acid.

4. Use according to claim 1, characterized in that said alkaline earth metal [ Mg (lna) ]₂]_nThe single crystal adsorbing material is prepared by the following method:

s1, mixing isonicotinic acid and magnesium chloride in a molar ratio of 1: 0.2-2, adding an absolute ethyl alcohol solution, and uniformly stirring to obtain a mixed solution;

s2, sealing the mixed solution of S1 in an inner container of a reaction kettle, placing the reaction kettle in an electric heating blowing dry box, heating to 90-180 ℃ at the speed of 5-40 ℃/h, and preserving heat for 30-45 h; then cooling to 15-35 ℃ at the speed of 0.5-5.0 ℃/h;

s3, purifying the reaction product obtained in the S2 to obtain alkaline earth metal [ Mg (lna)₂]_nA single crystal adsorbent material.

5. The use according to claim 4, wherein in S1, the ratio of the volume usage amount of the absolute ethanol solution to the amount of the isonicotinic acid substance is 1-15 mL: 1 mmol.

6. The use of claim 4, wherein in S3, the purification treatment method comprises:

washing the reaction product of S2 with absolute ethanol for 3-5 times, and observing and screening alkaline earth metals of specific structure under a microscope [ Mg (lna)₂]_nWashing the single crystal adsorbing material with absolute ethyl alcohol for 3-5 times, and then placing the material at 60 ℃ for vacuum drying to constant weight to obtain the product.

7. Use according to claim 6, characterized in that the alkaline earth metal [ M ] of specific structureg(lna)₂]_nThe screening process of the single crystal adsorbing material is as follows:

and (4) picking crystals with regular shapes and clear edges, and collecting the generated crystals independently.

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