Application of zinc-based microporous metal-organic frameworks in formaldehyde removal

Abstract

The application belongs to the technical field of formaldehyde adsorption, and particularly relates to application of a zinc-based microporous metal organic framework (BUT-236) material in formaldehyde removal. The zinc-based microporous metal organic framework (BUT-236) material is synthesized and prepared in pure water by using an environmentally-friendly zinc element as a metal node and using 1,2,4-triazole amino and isophthalic acid as organic ligands. The zinc-based microporous metal organic framework material and a binder are mixed, and granulation by a granulator can form spherical formaldehyde adsorption particles. The zinc-based MOFs have pore sizes matched with formaldehyde, rich amino functional groups, and good formaldehyde adsorption performance, and thus can be suitable for indoor formaldehyde purification.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of formaldehyde adsorption, and particularly relates to application of a zinc-based microporous metal organic framework material in formaldehyde removal. TECHNICAL BACKGROUND

[0002] Formaldehyde (HCHO) is a typical volatile organic pollutant, and its release sources mainly include urea-formaldehyde resin-based composite materials such as plywood, shaving board and wallpaper adhesive widely used in indoor decoration materials. Long-term exposure to HCHO polluted environment can induce various pathological reactions, including conjunctival and upper respiratory mucosa irritation symptoms, and is significantly positively correlated with nasopharyngeal carcinoma, pregnancy complications, glioma and hematopoietic system malignancies. Therefore, developing efficient indoor formaldehyde purification technology has become an important research direction in the field of environmental functional materials.

[0003] Among numerous pollutant treatment technologies, adsorption separation method is considered as the most potential formaldehyde elimination strategy in practical application scenarios due to practical advantages such as simple operation and low energy consumption. Although traditional adsorbents such as activated alumina and activated carbon have realized large-scale application, they generally have inherent defects such as insufficient specificity of adsorption sites, weak binding energy and limited dynamic adsorption capacity. Metal-Organic Frameworks (MOFs) are a new type of porous material, which are formed by self-assembly of metal nodes and organic ligands through coordination bonds. Due to its adjustable pore structure and rich surface functional groups, it shows a breakthrough application prospect in the field of volatile organic pollutant capture. However, most MOFs are synthesized by solvothermal method. The synthesis process needs a large amount of toxic and harmful organic solvents, resulting in high production cost and serious pollution, which is difficult to popularize to commercial application. The greatest advantage of the present application is to report a green and large-scale preparation of zinc-based MOFs and its formaldehyde adsorption performance, which promotes the commercialization of MOF adsorbents in the field of formaldehyde. SUMMARY

[0004] The application aims to provide application of a zinc-based microporous metal organic framework material in formaldehyde removal.

[0005] Further, the zinc-based organic framework material is named BUT-236, and the organic ligand is 3-amino 1,2,4-triazole and isophthalic acid.

[0006] Further, the preparation method of the zinc-based organic framework material comprises the following steps:

[0007] Zn(OAC)2·2H2O aqueous solution is prepared; 3-amino-1,2,4-triazole aqueous solution is prepared; NaOH and isophthalic acid are mixed, water is added, and sodium isophthalate solution is prepared; first, sodium isophthalate solution and 3-amino-1,2,4-triazole aqueous solution are mixed, Zn(OAC)2·2H2O aqueous solution is added, then stirring reaction is carried out at 60℃ for 2 hours, filtration is carried out, deionized water washing is carried out, and vacuum drying is carried out at 120℃ for 12 hours, so that the zinc-based organic framework material is obtained.

[0008] A formaldehyde adsorption particle, the adsorption particle comprising a zinc-based organic framework material and hydroxyethyl cellulose, the mass ratio of the zinc-based organic framework material and hydroxyethyl cellulose being 97:3. Hydroxyethyl cellulose is used as a binder, and after being mixed with BUT-236 at a mass ratio of 97:3, uniform spherical particles are formed by granulation. This combination enhances the mechanical strength of the MOF material, prevents the pulverous MOF from being dispersed due to air flow or vibration during use, and ensures long-term stable use of the material. The addition amount of hydroxyethyl cellulose is low (3%), and does not significantly block the microporous structure of the MOF (the pore size matches that of the formaldehyde molecule), but instead can optimize the pore distribution of the particle and promote the diffusion of formaldehyde molecules in the material.

[0009] Further, the zinc-based organic framework material is regenerated and recycled after formaldehyde adsorption and removal.

[0010] The application also provides a method for adsorbing and removing formaldehyde by the zinc-based organic framework material, comprising the following steps: adding the zinc-based organic framework material into formaldehyde-air mixed gas, and separating the zinc-based organic framework material after the formaldehyde gas concentration is stable and unchanged.

[0011] The application also provides a method for regenerating the zinc-based organic framework material after adsorbing and removing formaldehyde, comprising the following steps: placing the zinc-based organic framework material after adsorbing and removing formaldehyde under the sun for 24 h to realize regeneration and recycling.

[0012] The application also provides a method for regenerating the zinc-based organic framework material after adsorbing and removing formaldehyde, comprising the following steps: vacuum drying and desorption of the zinc-based organic framework material after adsorbing and removing formaldehyde to realize regeneration and recycling.

[0013] Further, the drying temperature is 120-150℃.

[0014] Compared with the prior art, the application has the following technical effects:

[0015] The application successfully synthesizes a Zn-MOF (BUT-236) in pure water, which has a porous structure, rich amino (-NH2) functional groups, and good water stability, and is easy to form. The synthesis of the zinc-based organic framework material is green and low in cost, and exhibits excellent performance in the field of formaldehyde removal, and can be desorbed and recycled, and is a potential formaldehyde adsorbent.

[0016] (2) BUT-236 itself has water stability (synthesized in pure water), and the hydrophobicity of hydroxyethyl cellulose can further reduce the competitive adsorption of water molecules in the MOF channel in a humid environment, thereby maintaining the formaldehyde adsorption efficiency.

[0017] (3) The synthesis of BUT-236 uses water as a solvent, and hydroxyethyl cellulose as a non-toxic and degradable binder, which meets the green chemistry concept and reduces the environmental burden in the production process. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 The synthesis raw material of BUT-236 and its structural diagram.

[0019] Figure 2 The adsorption curve of formaldehyde after the static adsorption experiment of examples 1 and 2 at room temperature.

[0020] Figure 3 The size of the formaldehyde molecule and the intermolecular distance between the two N atoms in the -NH2 of the BUT-236 channel.

[0021] Figure 4 The scanning electron microscope images of example 1 before (a) and after (b) adsorbing formaldehyde.

[0022] Figure 5 The adsorption curve of formaldehyde after the static adsorption experiment of the regenerated material of example 1. DETAILED DESCRIPTION

[0023] Example 1

[0024] (1) Zn(OAc)2·2H2O (34.38 g; 0.157 mol) was placed in a 100 ml volumetric flask, water was added, and a zinc salt solution of 1.57 mol / L was prepared;

[0025] (2) 3-amino-1,2,4-triazole (22.428 g, 0.267 mol) was placed in a 100 ml volumetric flask, water was added, and a 3-amino-1,2,4-triazole solution of 2.67 mol / L was prepared;

[0026] (3) NaOH (31.208 g, 0.188 mol) and isophthalic acid (15.04 g, 0.376 mol) were placed in a 100 ml volumetric flask, water was added, and a 1.88 mmol / L 100 mL isophthalic acid sodium solution was prepared;

[0027] 7.5 ml of 3-amino-1,2,4-triazole solution was first mixed with 5.35 ml of isophthalic acid sodium solution, then 12.75 ml of zinc salt solution was added, and then the reaction was stirred at 60°C for 2 hours, filtered, washed with deionized water, and vacuum dried at 120°C for 12 hours. The MOF product obtained is named as BUT-236.

[0028] The raw material composition and the three-dimensional space structure of BUT-236 are shown in Figure 1 The structure of the BUT-236 has one-dimensional channels, and the intermolecular distance between the two N atoms on the -NH2 in the channel is 4.32 Å.

[0029] The sample obtained in Example 1 was post-processed and dried to obtain an adsorption sample for testing of formaldehyde static adsorption.

[0030] Example 2

[0031] 19.4 g of the product obtained in Example 1 and 0.6 g of hydroxyethyl cellulose were weighed into a mortar, and deionized water was added dropwise while grinding until the two were mixed uniformly to form a paste, which was processed into 3.00 mm spherical particles by a semi-automatic granulator.

[0032] The sample obtained in Example 2 was post-processed and dried to obtain an adsorption sample for testing of formaldehyde static adsorption

[0033] Example 3

[0034] First step: 0.2944 g of the sample obtained in Example 1 was weighed into a 25 L container containing 1 mg / m 3 formaldehyde air mixture.

[0035] Second step: after the formaldehyde gas concentration was stable, the measurement was started.

[0036] Third step: the change of formaldehyde concentration in the container was determined by a formaldehyde detector.

[0037] Example 4

[0038] First step: 20 g of the sample of Example 2 was weighed into a container containing 1 mg / m 3 formaldehyde air mixture.

[0039] Second step: after the formaldehyde gas concentration was stable, the measurement was started.

[0040] Third step: The concentration change of formaldehyde in the container was determined by the formaldehyde detector.

[0041] The adsorption curves obtained after static adsorption experiments of Examples 1 and 2 are shown in FIG. 1. Figure 2 It is shown that the BUT-236 and the material after processing and molding can remove 0.64 mg / m 3 , 0.69 mg / m 3 of formaldehyde in 3 hours, respectively, and have good trace static adsorption performance. The above shows that the material has good application prospect in the field of adsorbing and removing formaldehyde in air.

[0042] Figure 3 The size of the formaldehyde molecule and the intermolecular distance between the two N atoms on the -NH2 in the pore of BUT-236. As can be seen from the figure, the size of the formaldehyde molecule is just matched with the size of the pore.

[0043] BUT-236 has strong adsorption force on formaldehyde molecules, which is due to:

[0044] (1) The presence of ammonia sites

[0045] Characteristics of ammonia sites: For example, the amino group -NH2 has a lone pair of electrons, which can act as a Lewis base and interact with the carbonyl group (C=O) in the formaldehyde molecule.

[0046] Hydrogen bonding: The hydrogen atom (H) in the formaldehyde molecule can form a hydrogen bond with the nitrogen atom (N) in the ammonia site, which enhances the adsorption force.

[0047] The hydroxyl group (-OH) and ether bond (-O-) in the hydroxyethyl cellulose molecule interact with the formaldehyde molecule through weak hydrogen bonds or van der Waals forces, which assist the amino group (-NH2) of the MOF to capture formaldehyde and form a multi-level adsorption mechanism.

[0048] (2) The polarity of the formaldehyde molecule

[0049] Formaldehyde (HCHO) is a polar molecule, and its carbonyl group (C=O) has high electronegativity, resulting in the presence of partial positive charge (δ+) and partial negative charge (δ-) in the molecule. This polarity makes the formaldehyde molecule easily attracted by the polar sites (such as ammonia sites) in the pore, and the adsorption is enhanced by electrostatic interaction.

[0050] (3) The confinement effect of the pore structure

[0051] Because the size of formaldehyde molecule matches the size of the pore of BUT-236, the pore structure of BUT-236 provides a confined space for formaldehyde molecules, making it easier for formaldehyde molecules to contact with ammonia sites in the pore, further enhancing the adsorption effect.

[0052] (4) Coordination effect

[0053] The oxygen atom (O) in the formaldehyde molecule has a lone pair of electrons, which can act as a ligand to coordinate with the metal center (such as Zn²⁺), further enhancing the adsorption stability of formaldehyde molecules in the pore.

[0054] (5) π-π interaction

[0055] There are aromatic rings in the structure of BUT-236 (such as benzene rings in the phthalic acid ligand), and formaldehyde molecules may have π-π interactions with aromatic rings, further enhancing the adsorption force.

[0056] Figure 4 SEM images of the sample before and after adsorbing formaldehyde in Example 1 are compared. As can be seen from the figure, the morphology of BUT-236 does not change before and after adsorbing formaldehyde, proving its good stability.

[0057] The sample after adsorption test in Example 1 was placed in the sun for 24 h, or vacuum dried for desorption, with a drying temperature of 120-150 degrees Celsius, to regenerate the material and repeat the formaldehyde adsorption test. During the regeneration of the material (such as sunning or vacuum drying), the hydroxyethyl cellulose maintains the integrity of the particle structure, avoiding the pulverization or structural collapse of the MOF due to repeated desorption-adsorption cycles, thereby supporting the recycling of the material. The test conditions are the same as in Example 2, and the above operation is repeated twice. The results obtained are shown in Figure 5 , 0.58 mg / m 3 , 0.58 mg / m 3 , indicating that the regenerated material can adsorb and remove 0.57 mg / m 3 , 0.58 mg / m 3 , 0.58 mg / m 3 of formaldehyde in 3 hours, still having good trace static adsorption performance, proving its good recycling ability.

Claims

1. Use of a zinc-based microporous metal organic framework material in formaldehyde removal, characterized in that: The preparation method of the zinc-based organic framework material comprises the following steps: An aqueous solution of Zn(OAC)2·2H2O is prepared; an aqueous solution of 3-amino-1,2,4-triazole is prepared; NaOH and isophthalic acid are mixed, water is added, and a sodium isophthalate solution is prepared; the sodium isophthalate solution and the aqueous solution of 3-amino-1,2,4-triazole are first mixed, the aqueous solution of Zn(OAC)2·2H2O is then added, and then stirring reaction is carried out at 60 DEG C for 2 hours, filtration, deionized water washing, and vacuum drying at 120 DEG C for 12 hours are carried out, so that the zinc-based organic framework material is obtained.

2. Use of the zinc-based microporous metal organic framework material according to claim 1 for formaldehyde removal, characterized in that: The zinc-based organic framework material can be regenerated and recycled after formaldehyde adsorption and removal.

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