Preparation method of MOF toluene adsorbent

Abstract

The invention discloses a preparation method of an MOF (Metal Organic Framework) toluene adsorbent, relates to a preparation method of a toluene adsorbent, and aims to solve the technical problems of poor selectivity and poor adsorption effect of the existing activated carbon adsorbent for removing indoor toluene. The preparation method of the MOF type toluene adsorbent comprises the following steps: mixing ferric nitrate nonahydrate, 1, 3, 5-benzene tricarboxylic acid and formic acid, transferring the mixture into a high-pressure kettle with a polytetrafluoroethylene lining, keeping for 10-12 hours at the temperature of 120-130 DEG C for hydrothermal reaction, and then washing and drying to obtain the MOF type toluene adsorbent. The methylbenzene removal rate reaches 80% or above, and the catalyst can be repeatedly used for at least five times and can be used in the field of environmental monitoring.

Description

Technical Field

[0001] The invention relates to a preparation method of a toluene adsorbent, and belongs to the technical field of environmental protection and material science. Background Art

[0002] As people pay more and more attention to the quality of the living environment, the issue of indoor air quality has gradually become a focus. Toluene, as a common organic solvent, is widely used in building materials and home decoration, but its excessive content may pose a threat to the health of residents. Existing adsorbents for removing indoor toluene include activated carbon, but the structure of activated carbon is disordered and it is often not selective when removing volatile organic compounds from the indoor environment. In addition, the characteristics of toluene as a polar pollutant lead to limited removal effect of activated carbon on toluene. At the same time, the specific surface area of ​​activated carbon is limited, which leads to poor removal effect of the adsorbent. Summary of the invention

[0003] The present invention aims to solve the technical problems of poor selectivity and adsorption effect of existing activated carbon adsorbents for removing indoor toluene, and provides a method for preparing a MOF-based toluene adsorbent.

[0004] The preparation method of the MOF-based toluene adsorbent of the present invention is carried out according to the following steps:

[0005] 1. Weigh ferric nitrate nonahydrate (Fe(NO3)3·9H2O), 1,3,5-benzenetricarboxylic acid (H3BTC), and formic acid according to the molar ratio of (1-1.5):1:(0.15-0.33); dissolve ferric nitrate in deionized water to obtain a ferric nitrate solution; dissolve 1,3,5-benzenetricarboxylic acid and formic acid in water to obtain a 1,3,5-benzenetricarboxylic acid solution; add the ferric nitrate solution to the 1,3,5-benzenetricarboxylic acid solution, and stir magnetically for 1.5-2 hours to obtain a mixed solution;

[0006] 2. Transfer the mixed solution to a polytetrafluoroethylene-lined autoclave, place the autoclave in a high-temperature furnace, and maintain it at a temperature of 120-130°C for 10-12 hours. Then wash the reaction product with water and ethanol, and then dry it to obtain a MOF-based toluene adsorbent.

[0007] Furthermore, the concentration of the ferric nitrate solution in step 1 is 0.167 mol / L to 0.25 mol / L.

[0008] Furthermore, the drying in step 2 is carried out at a temperature of 80 to 90° C. for 2 to 3 hours.

[0009] The MOF-type toluene adsorbent prepared by the present invention is a new type of porous material with a periodic network structure formed by self-assembly of metal ions and organic ligands, that is, a metal organic framework (MOF) material. The MOF material has a structural basis for further adjustment and modification, and can be adjusted and modified for specific pollutants to improve the adsorption capacity of the MOF material.

[0010] The MOF-based toluene adsorbent prepared by the present invention has a high specific surface area. At the same time, formic acid is involved in the synthesis, and the specific surface area reaches 1015m 2 / g-1117.4m 2 / g, and defects are formed inside the adsorbent to improve its specific surface area and pore structure, thereby enhancing its adsorption capacity for low-concentration toluene, and can effectively adsorb toluene in indoor environments.

[0011] The MOF toluene adsorbent prepared by the present invention is synthesized using an organic ligand such as trimesic acid, so there are a large number of benzene ring structures in the adsorbent, which can form π-π bonds with toluene in the air, thereby increasing the adsorption capacity of selectively adsorbing toluene, and the toluene removal rate reaches more than 80%.

[0012] The structural stability of the MOF structure itself means that it can be recycled many times. The adsorbent should be able to maintain ≥75% adsorption performance after at least 5 cycles, reducing the cost of use and extending the service life. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 It is a N2 gas adsorption-desorption curve diagram of MIL-100(Fe)-FA prepared in Example 1 and MIL-100(Fe) prepared in the comparative example;

[0014] Figure 2 is a scanning electron microscope photograph of MIL-100 (Fe) prepared in Comparative Example 1;

[0015] Figure 3 is a scanning electron microscope photograph of MIL-100(Fe)-FA prepared in Example 1;

[0016] Figure 4 This is a schematic diagram of the adsorption test equipment for adsorbent materials;

[0017] Figure 5 It is a comparison chart of the adsorption results of MIL-100(Fe)-FA prepared in Example 1, MIL-100(Fe) prepared in the comparative example, and activated carbon;

[0018] Figure 6This is a diagram showing the adsorption effect of the repeated use of MIL-100(Fe)-FA prepared in Example 1, MIL-100(Fe) prepared in the comparative example, and activated carbon. DETAILED DESCRIPTION

[0019] Example 1: The preparation method of the MOF toluene adsorbent of this example is carried out according to the following steps:

[0020] 1. Weigh 6.06 g of ferric nitrate nonahydrate (Fe(NO3)3·9H2O), 2.1 g of 1,3,5-benzenetricarboxylic acid and 0.152 g of formic acid with a mass percentage concentration of 96%; dissolve ferric nitrate in 30 mL of deionized water to obtain a ferric nitrate solution; dissolve 1,3,5-benzenetricarboxylic acid and formic acid in 30 mL of deionized water to obtain a 1,3,5-benzenetricarboxylic acid solution; add the ferric nitrate solution to the 1,3,5-benzenetricarboxylic acid solution, and stir magnetically for 2 hours to obtain a mixed solution;

[0021] 2. The mixed solution was transferred to a polytetrafluoroethylene-lined autoclave, and the autoclave was placed in a high-temperature furnace and maintained at 130°C for 12 hours. The reaction product was then washed with water and ethanol, and then dried at 80°C for 2 hours to obtain a MOF-based toluene adsorbent, recorded as MIL-100(Fe)-FA.

[0022] Comparative Example 1: This comparative example differs from Example 1 in that formic acid is omitted in step 1, and the rest is the same as Example 1. The obtained adsorbent is recorded as MIL-100(Fe).

[0023] The MIL-100(Fe)-FA prepared in Example 1 and the MIL-100(Fe) prepared in the comparative example were subjected to N2 gas adsorption-desorption curve tests. The obtained nitrogen adsorption-desorption curves are shown in FIG. Figure 1 As shown, from Figure 1 It can be seen that the N2 adsorption-analysis curves of MIL-100(Fe) and MIL-100(Fe)-FA belong to type I adsorption curves. The nitrogen adsorption amount increases at the low-pressure end of the adsorption curve, indicating that the material interacts strongly with nitrogen and that there are many microporous structures inside the material. The pore size distribution of the adsorbent was analyzed using the non-local density functional theory analytical model (NLDFT), and the pore volume of the adsorbent was calculated using the NLDFT and t-plot models. The results are shown in Table 1. It can be seen from Table 1 that the specific surface area and pore volume of MIL-100(Fe)-FA are increased by 57.09% and 34% respectively compared with MIL-100(Fe). This shows that the specific surface area of ​​the material can be increased by adjusting with formic acid.

[0024] Table 1 Specific surface area and pore volume of MIL-100(Fe)-FA and MIL-100(Fe)

[0025] sample <![CDATA[S BET (m 2 / g)]]> <![CDATA[V NLDFT cm 3 / g)]]> MIL-100(Fe) 711.28 0.4241 MIL-100(Fe)-FA 1117.4 0.5683

[0026] The scanning electron microscopy of MIL-100 (Fe) prepared in Comparative Example 1 is as follows: Figure 2 As shown, the scanning electron microscopy of MIL-100(Fe)-FA prepared in Example 1 is as follows Figure 3 As shown, from Figure 2 It can be seen that MIL-100(Fe) has a distinct octagonal pyramid morphology, which is consistent with previous cognition. Figure 3 It can be seen that the surface morphology of the adsorbent MIL-100(Fe)-FA prepared in Example 1 under the condition of adding formic acid changes significantly, and many small-particle crystal structures appear. These structures have irregular polyhedral morphology and are obviously agglomerated with each other, which indicates that the addition of formic acid has a significant effect on the structure of MIL-100(Fe).

[0027] Combined with the actual application requirements of the indoor environment, the toluene concentration is recorded as 500ug / m 3 Under the conditions of , the average concentration of toluene in the environmental chamber after different adsorption times was used to evaluate the adsorption performance of the adsorbent. MIL-100 (Fe) prepared in the comparative example, MIL-100 (Fe) -FA prepared in Example 1 and traditional adsorbent activated carbon were selected as adsorption materials. Test equipment such as Figure 4 As shown, the nitrogen bottle 1 is connected to the air inlet of the environmental chamber 4 through the first gas flow meter 2 and the first gas control valve 3; the air outlet of the environmental chamber 4 is connected to the sampling pump 8 through the second gas control valve 5, the second gas flow meter 6, and the multi-filler adsorption tube 7; the environmental chamber 4 is placed in a constant temperature water bath 9; a fan is provided in the environmental chamber 4 to mix the toluene evenly in the environmental chamber; a thermometer and hygrometer is also provided in the environmental chamber 4 to detect the ambient temperature and humidity; the gas sample collected by the sampling pump 8 is detected by a gas chromatograph-mass spectrometer 10. According to GB / T 29899-2013 "Test method for release of volatile organic compounds in artificial boards and their products - small release chamber method", the adsorption effect of MIL-100(Fe)-FA, MIL-100(Fe) and activated carbon on toluene is shown in the figure below. Figure 5 As shown, from Figure 5 It can be seen that the initial concentration of toluene in the environmental chamber is 500ug / m 3 Under the condition of , the three adsorbents reached adsorption equilibrium after 50 minutes of adsorption. When the adsorption equilibrium was reached, MIL-100(Fe)-FA reduced the toluene content in the environment by 420ug / m 3The adsorption efficiency reached 84%. MIL-100 (Fe) reduced the toluene content in the environment by 354ug / m 3 The adsorption efficiency reached 70.8%, and the activated carbon reduced the toluene in the environment by 180ug / m 3 The adsorption efficiency is only 36%. Comparison shows that the adsorption effect of MIL-100(Fe)-FA prepared in Example 1 is better than that of MIL-100(Fe) and activated carbon.

[0028] After the adsorption test was completed, the three adsorption materials, MIL-100(Fe)-FA prepared in Example 1, MIL-100(Fe) prepared in the comparative example, and the traditional adsorbent activated carbon, were subjected to adsorption-desorption cycle test. From the toluene adsorption experiment, it can be seen that the adsorbent reaches adsorption equilibrium in 50 minutes. Therefore, when conducting the adsorption-desorption cycle test, the adsorption time is 50 minutes and the toluene concentration is 500ug / m 3 After the adsorption is completed, the adsorbent is desorbed at 80°C for 60 minutes. The toluene adsorption rate P is used to represent the results of each experiment. Figure 6 The figure is a diagram showing the repeated use of the MIL-100(Fe)-FA prepared in Example 1, the MIL-100(Fe)-FA prepared in the comparative example, and the activated carbon. Through the adsorption-desorption cycle experiment, after repeated reuse for five times, the adsorption efficiency of the MIL-100(Fe)-FA prepared in Example 1 for toluene is still 80.6%, and the MIL-100(Fe) prepared in the comparative example decreases from 70.8% to 64% after five cycles, and the toluene adsorption efficiency of the activated carbon decreases from 36.6% to 23%. It shows that the MIL-100(Fe)-FA prepared in Example 1 has good reusability.

Claims

1. A method for preparing a MOF-based toluene adsorbent, characterized in that The method proceeds as follows:

1. Weigh ferric nitrate nonahydrate, 1,3,5-benzenetricarboxylic acid and formic acid according to the molar ratio of ferric nitrate nonahydrate, 1,3,5-benzenetricarboxylic acid and formic acid of (1-1.5):1:(0.15-0.33); dissolve ferric nitrate in deionized water to obtain a ferric nitrate solution; dissolve 1,3,5-benzenetricarboxylic acid and formic acid in water to obtain a 1,3,5-benzenetricarboxylic acid solution; add the ferric nitrate solution to the 1,3,5-benzenetricarboxylic acid solution, and stir magnetically for 1.5-2 hours to obtain a mixed solution; 2. Transfer the mixed solution to a polytetrafluoroethylene-lined autoclave, place the autoclave in a high-temperature furnace, and maintain it at a temperature of 120-130°C for 10-12 hours. Then wash the reaction product with water and ethanol, and then dry it to obtain a MOF-based toluene adsorbent.

2. The method for preparing a MOF-based toluene adsorbent according to claim 1, characterized in that The concentration of the ferric nitrate solution in step 1 is 0.167 mol / L to 0.25 mol / L.

3. The method for preparing a MOF-based toluene adsorbent according to claim 1, characterized in that: The drying in step 2 is carried out at a temperature of 80 to 90° C. for 2 to 3 hours.

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