Copper-based metal organic framework adsorbent for adsorbing aniline in wastewater

Abstract

The invention discloses a copper-based metal organic framework adsorbent for adsorbing aniline in wastewater and a preparation method of the copper-based metal organic framework adsorbent. The molecular formula of the adsorbent is {[Cu3 (5-OH-m-C6H3-(COO) 2) 3 (H2O) 2 (CH3CN)] 4 (H2O) (CH3OH)} n, and in the formula, 5-OH-m-C6H3-(COOH) 2 is 5-hydroxyisophthalic acid and belongs to a P21 / n space group of a monoclinic system. The adsorbent is formed through coordinate bonds, a large number of hydrogen bonds exist in the structure, and the adsorbent can keep the structure stable in a solution with the pH being 5.00-9.00. The method can effectively enrich aniline in wastewater and can be recycled by a centrifugal separation method.

Description

Technical Field

[0001] The invention relates to the research and development field of metal organic framework materials, and in particular to a copper-based metal organic framework adsorbent for adsorbing aniline in waste water and a preparation method thereof. Background Art

[0002] Aniline is a toxic organic substance that will harm aquatic life and destroy the ecological balance when it enters the water. At present, there are many methods to remove aniline from wastewater, mainly including physical, chemical and biological methods. These methods have their own advantages and disadvantages. Adsorption is a method of removing aniline using adsorption materials such as activated carbon, zeolite, and resin, which has the advantages of low cost and simple operation. However, traditional adsorbents (such as activated carbon, zeolite) have many disadvantages in terms of adsorption capacity, selectivity, regeneration, mechanical strength, environmental friendliness, cost and applicability. Therefore, the development of new, efficient, environmentally friendly and economical adsorbents is an important research direction in the current wastewater treatment field.

[0003] Metal-organic frameworks (MOFs) are a new type of porous material composed of metal ions and organic ligands. They have high specific surface area, adjustable pore structure and chemical functionality, and have attracted much attention in the field of adsorption in recent years. Copper and its compounds have the advantages of abundant resource reserves, low cost and eco-friendliness, so they have begun to attract attention and research. Therefore, copper-based metal-organic framework adsorbents have shown broad application prospects in the field of wastewater treatment due to their advantages such as high specific surface area, adjustable pores, chemical stability, high adsorption capacity, selectivity, easy functionalization, environmental friendliness and regeneration performance. If some modified groups (such as hydroxyl, amino), coordinated water molecules or free water molecules are introduced into the copper-based metal-organic framework adsorbent, the adsorbent will be able to adsorb organic pollutants in wastewater through a large number of hydrogen bonds. Summary of the invention

[0004] In order to solve the technical problem that the adsorbent has low adsorption efficiency for aniline, the present invention develops a hydroxyl-modified copper-based (II) metal organic framework adsorbent capable of enriching aniline pollutants in wastewater.

[0005] The invention discloses a copper-based metal organic framework adsorbent for adsorbing aniline from wastewater, and the molecular formula is {[Cu3(5-OH-m-C6H3-(COO)2)3(H2O)2(CH3CN)]4(H2O)(CH3OH)} n , where 5-OH-m-C6H3-(COOH)2 is 5-hydroxyisophthalic acid.

[0006] The copper-based metal organic framework adsorbent crystal belongs to the monoclinic system, P21 / n space group, and the unit cell parameters are: α=90.00°, β=103.0620(10)°, γ=90.00°,

[0007] The preparation method of the copper-based metal organic framework adsorbent of the present invention is as follows: first, 0.0364 g (0.2 mmol) of 2-hydroxyisophthalic acid and 0.0198 g (0.2 mmol) of cuprous chloride are weighed and mixed in a 20-25 mL polytetrafluoroethylene reactor liner, and then 5 mL of analytically pure acetonitrile and 5 mL of deionized water are added to the mixture;

[0008] After the inner tank of the reactor was sealed with a stainless steel sleeve, it was heated in a forced air drying oven at 100°C for 24 hours, and then cooled to room temperature at a rate of 5°C / hour;

[0009] After cooling to room temperature, the inner container of the reactor was opened to obtain blue block crystals, that is, the adsorbent was obtained.

[0010] During preparation, each raw material can be added in multiples of the amount of the raw material used in the preparation method.

[0011] Compared with the prior art, the copper-based metal organic framework adsorbent of the present invention, specifically 5-hydroxyisophthalic acid copper (II) metal organic framework adsorbent, has three copper ions, three 5-hydroxyisophthalic acid anions, two coordinated water molecules, one coordinated acetonitrile molecule, four free water molecules and one free methanol molecule in the independent molecular structure of the adsorbent. There are two types of coordinated copper ions in the independent molecular structure. One is that the copper ion is coordinated with five oxygen atoms; the other is that the copper ion is coordinated with four oxygen atoms and one nitrogen atom. The 5-hydroxyisophthalic acid anion takes μ4-η 1 :η 1 :η 1 :η 1 The copper-based metal organic framework adsorbent can effectively enrich aniline in wastewater and can be recycled by centrifugal separation. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 Schematic diagram of the minimum molecular structure of the copper-based metal organic framework adsorbent of the present invention;

[0013] Figure 2 A schematic diagram of a two-dimensional structure of the copper-based metal organic framework adsorbent of the present invention formed by ligand bridging;

[0014] Figure 3 A schematic diagram of hydrogen bonds existing in the two-dimensional structure of the copper-based metal organic framework adsorbent of the present invention;

[0015] Figure 4 Schematic diagram of X-ray photoelectron spectrum of the copper-based metal organic framework adsorbent of the present invention;

[0016] Figure 4 a is a schematic diagram of the full spectrum of X-ray photoelectron spectrum of the adsorbent;

[0017] Figure 4 b is a schematic diagram of the Cu(2p) spectrum in the adsorbent;

[0018] Figure 5 is a theoretically simulated X-ray powder diffraction pattern of the copper-based metal organic framework adsorbent of the present invention;

[0019] Figure 6 The X-ray powder diffraction diagram of the copper-based metal organic framework adsorbent of the present invention after being soaked in solutions of different pH (5.00-9.00) and after desorption;

[0020] Figure 7 The figure is a curve diagram showing the effect of the dosage of the copper-based metal organic framework adsorbent of the present invention on the adsorption of aniline at 25° C. and pH=7.00;

[0021] in, Figure 7 a is the removal curve of the effect of adsorbent dosage on the adsorption performance of aniline;

[0022] Figure 7 b is the adsorption amount curve of the effect of adsorbent dosage on the adsorption performance of aniline;

[0023] Figure 8 It is a curve diagram of the effect of pH on the adsorption of aniline under the conditions of 25° C. and a dosage of 0.0150 g of the copper-based metal organic framework of the present invention;

[0024] in, Figure 8 a is the removal curve of the effect of pH on the adsorption performance of aniline;

[0025] Figure 8 b is the adsorption amount curve of the effect of pH on the adsorption performance of aniline;

[0026] Fig. 9 The graph is a graph showing the effect of temperature on the adsorption of aniline by the copper-based metal organic framework of the present invention when pH=6.00 and the dosage is 0.0150g; wherein, Fig. 9 a is the removal curve of the effect of temperature on the adsorption performance of aniline;

[0027] Fig. 9 b is the adsorption amount curve of the effect of temperature on the adsorption performance of aniline;

[0028] Fig.10The graph is a cyclic experimental result of the adsorption of aniline by the copper-based metal organic framework of the present invention at 20°C and pH=6.00. DETAILED DESCRIPTION

[0029] The present invention is further described below with reference to the embodiments and drawings, but is not intended to limit the present invention.

[0030] Example

[0031] The copper-based metal organic framework adsorbent of the present invention, specifically 5-hydroxyisophthalic acid copper (II) metal organic framework adsorbent, is prepared by first weighing 0.0364 g (0.2 mmol) of 2-hydroxyisophthalic acid and 0.0198 g (0.2 mmol) of cuprous chloride in a 23 mL polytetrafluoroethylene reactor liner, and then adding 5 mL of analytically pure acetonitrile and 5 mL of ionized water to the mixture;

[0032] After the inner tank of the reactor was sealed with a stainless steel sleeve, it was heated in a forced air drying oven at 100°C for 24 hours, and then cooled to room temperature at a rate of 5°C / hour;

[0033] After cooling to room temperature, the inner tank of the reactor is opened to obtain blue block crystals, that is, the adsorbent is obtained.

[0034] Table 1 shows the crystallographic parameters of the copper (II) metal organic framework adsorbent of the present invention:

[0035]

[0036] Table 2 shows some bond lengths and bond angles of the copper (II) metal organic framework of the present invention;

[0037]

[0038] Symmetry codes: (A)-x+1,-y+1,-z+1; (B)x+3 / 2,-y+3 / 2,z+1 / 2; (C)-x+5 / 2,y+1 / 2,-z+3 / 2; (D)x-3 / 2,-y+3 / 2,z-1 / 2; (E)-x+5 / 2,y-1 / 2,-z+3 / 2.

[0039] Table 3 shows the hydrogen bonds present in the copper (II) metal organic framework structure of the present invention:

[0040]

[0041] The adsorbent prepared in the embodiment was analyzed by X-ray diffraction. Figure 1As shown, the molecular formula of the blue block crystal is {[Cu3(5-OH-m-C6H3-(COO)2)3(H2O)2(CH3CN)]4(H2O)(CH3OH)} n (where 5-OH-m-C6H3-(COOH)2 is 5-hydroxyisophthalic acid), there are three copper ions, three 5-hydroxyisophthalic acid anions, two coordinated water molecules, one coordinated acetonitrile molecule, four free water molecules and one free methanol molecule in the independent molecular structure. 1 :η 1 :η 1 :η 1 The adjacent copper ions are bridged in the form of to form a two-dimensional structure, such as Figure 2 In this two-dimensional structure, the 5-hydroxyisophthalic acid anion has an uncoordinated hydroxyl functional group and a large number of OH···O hydrogen bonds, such as Figure 3 shown.

[0042] X-ray photoelectron spectroscopy, such as Figure 4 shown. Figure 4 a is the full spectrum of the copper (II) metal organic framework of the present invention, indicating that the adsorbent is mainly composed of C, O and Cu elements; Figure 4 b is a schematic diagram of the Cu(2p) spectrum of the copper-based metal organic framework adsorbent of the present invention, indicating that the copper ions in the adsorbent are copper(II).

[0043] The copper (II) metal organic framework adsorbent after adsorbing aniline was recovered and reused by centrifugation at 10000 rpm in a high-speed centrifuge. X-ray powder diffraction analysis showed that the main diffraction peak position of the powder diffraction pattern of the copper (II) metal organic framework adsorbed was perfectly matched with the main diffraction peak position of the single crystal simulation map, such as Figure 5 As shown, this indicates that the copper (II) metal organic framework after adsorption of aniline is adsorbed as a pure phase with a purity of not less than 99%. This proves that the copper (II) metal organic framework after adsorption of aniline can be recovered and reused by centrifugal separation.

[0044] Example The blue crystals were ground into powder and soaked in solutions with pH values ​​of 5.00, 6.00, 7.00, 8.00, and 9.00, respectively. The solid powders were collected by centrifugation, dried naturally at room temperature, and their structures were tested by X-ray powder diffraction. The test results, such as Figure 6As shown, the diffraction peak position of the sample after immersion is consistent with the theoretical simulation of 5-hydroxyisophthalic acid copper (II) metal organic framework adsorbent, which indicates that the 5-hydroxyisophthalic acid copper (II) metal organic framework adsorbent can maintain its structure unchanged in a solution with a pH of 5.00-9.00. Therefore, the effects of adsorbent dosage and temperature on the adsorption performance of aniline can be explored in a solution with a pH of 5.00-9.00.

[0045] Weigh 0.0100-0.0250 g of the adsorbent prepared in the example into a 250 mL beaker with a circulating water device, add 100 mL of 5 mg / L aniline aqueous solution into the beaker, turn on the magnetic stirrer, and after reacting for a certain time (30 min, 60 min, 90 min, 120 min, 150 min), take samples and analyze the concentration of aniline in the solution. Figure 7 The removal curve of the effect of adsorbent dosage on the adsorption performance of aniline is shown in ( Figure 7 a) and adsorption curve ( Figure 7 b). The experimental results show that the dosage of the copper (II) metal organic framework has a significant effect on the adsorption of aniline at 25°C. Through calculation, it is found that the optimal dosage is 0.0150g, and the maximum equilibrium adsorption capacity at this time is 17.93mg / g.

[0046] The experiment explored the effect of pH (5.00-9.00) on the adsorption of aniline at 25°C. During the experiment, 100 mL of 5 mg / L aniline aqueous solution was added to a 250 mL beaker with a circulating water device, and the magnetic stirrer was turned on. The pH of the solution was adjusted with 0.01 mol / L HCl and NaOH, respectively. After the required pH aniline solution was obtained, 0.0150 g of copper (II) metal organic framework adsorbent was added. After the reaction was carried out for a certain period of time (30 min, 60 min, 90 min, 120 min, 150 min), the concentration of aniline in the solution was sampled and analyzed. Figure 7 The removal curve of the effect of pH on the adsorption performance of aniline is shown in ( Figure 8 a) and adsorption curve ( Figure 8 b) By Figure 7 It can be seen that the pH of the copper-based metal organic framework has a significant effect on the adsorption of aniline at 25°C and a dosage of 0.0150g. Calculation shows that the optimal solution pH is 6.00, and the maximum equilibrium adsorption capacity at this time is 20.23mg / g.

[0047] Experiments were conducted to explore the effect of temperature (20-40°C) on the adsorption of aniline by copper-based metal organic frameworks at 25°C and pH = 6.00. During the experiment, a 250mL beaker containing 100mL of 5mg / L aniline aqueous solution was placed in a constant temperature water bath, the magnetic stirrer was turned on, and 0.01mol / L HCl was used to adjust the pH of the solution to 6.00. The temperature of the constant temperature water bath was then adjusted to 20°C, 25°C, 30°C, 35°C, and 40°C. Then, 0.0150g of copper (II) metal organic framework adsorbent was added to beakers at different temperatures, and the reaction was carried out for a certain period of time (30min, 60min, 90min, 120min, 150min), and then samples were taken to analyze the concentration of aniline in the solution. Figure 8 The removal curves showing the effect of temperature on the adsorption performance of aniline ( Fig. 9 a) and adsorption curve ( Fig. 9 b) By Figure 8 It can be seen that the temperature of the copper-based metal organic framework adsorbent has a significant effect on the adsorption of aniline when pH = 6.00 and the dosage is 0.0150g. Calculation shows that the optimal solution temperature within the studied temperature range is 20°C, and the maximum equilibrium adsorption capacity at this time is 22.23mg / g.

[0048] A cyclic experiment of adsorption of aniline on copper-based metal organic framework was carried out at 20°C and pH = 6.00. During the experiment, a 250mL beaker containing 100mL of 5mg / L aniline aqueous solution was placed in a constant temperature water bath at 20°C, the magnetic stirrer was turned on, and the pH of the solution was adjusted to 6.00 using 0.01mol / L HCl, and then 0.0150g of the desorbed copper (II) metal organic framework adsorbent was added to the beaker. After the reaction was carried out for a certain period of time (30min, 60min, 90min, 120min, 150min), the concentration of aniline in the solution was sampled and analyzed.

[0049] Reference Fig.10 The experimental results show that the first cycle of the copper-based metal organic framework adsorbing aniline has an equilibrium adsorption capacity of 22.23 mg / g, and the efficiency can be maintained at 100%; after five cycles, the equilibrium adsorption capacity of aniline is 21.89 mg / g, and the efficiency is 98.47%.

Claims

1. A copper-based metal organic framework adsorbent for adsorbing aniline in wastewater, characterized in that: The molecular formula of the adsorbent is {[Cu3(5-OH-m-C6H3-(COO)2)3(H2O)2(CH3CN)]4(H2O)(CH3OH)} n , where 5-OH-m-C6H3-(COOH)2 is 5-hydroxyisophthalic acid.

2. The copper-based metal organic framework adsorbent according to claim 1, characterized in that: The adsorbent belongs to the monoclinic system, P21 / n space group, and the unit cell parameters are: α=90.00°, β=103.0620(10)°, γ=90.00°, 3. The copper-based metal organic framework adsorbent according to any one of claims 1 to 2, characterized in that: The adsorbent has a large number of OH···O hydrogen bonds, can maintain a stable structure in a solution with a pH value of 5.00-9.00, can effectively enrich aniline in wastewater, and can be recovered and reused by a centrifugal separation method.

4. The copper-based metal organic framework adsorbent according to claim 3, characterized in that: The copper-based metal organic framework adsorbent has the best adsorption capacity for aniline in wastewater when pH=6.00, dosage is 0.0150g, and solution temperature is 20℃.

5. The method for preparing the copper-based metal organic framework adsorbent according to any one of claims 1 to 2, characterized in that: First, weigh 0.0364 g or 0.2 mmol of 2-hydroxyisophthalic acid and 0.0198 g or 0.2 mmol of cuprous chloride and mix them in a 20-25 mL polytetrafluoroethylene reactor liner, then add 5 mL of analytical grade acetonitrile and 5 mL of deionized water to the mixture; After the inner tank of the reactor was sealed with a stainless steel sleeve, it was heated in a forced air drying oven at 100°C for 24 hours, and then cooled to room temperature at a rate of 5°C / hour; After cooling to room temperature, the inner container of the reactor was opened to obtain blue block crystals, that is, the adsorbent was obtained.

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