A citric acid modified MOF-808 heavy metal adsorbent, a preparation method thereof and application thereof in removing chromium in a complex state in water

Abstract

The application provides a kind of citric acid modified MOF-808 heavy metal adsorbent and its preparation method and application in removing complex chromium in water, the preparation method of the obtained citric acid modified heavy metal adsorbent MOF-808-CA, comprising: citric acid is dissolved in water, and MOF-808 powder is added, mixed, heated and reacted, and the solid is separated after the reaction is completed, the solid is washed and dried to obtain MOF-808-CA material.The obtained citric acid modified heavy metal adsorbent MOF-808-CA has many adsorption sites, can be used for adsorbing complex chromium in water, and has excellent adsorption performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of heavy metal adsorbent materials, in particular to a citric acid modified MOFs heavy metal adsorbent, a preparation method thereof and application thereof in removing complex chromium in water. BACKGROUND

[0002] Under the current social background of rapid development of industrial production, due to the inconsistency of production process requirements of different industrial departments, various types of heavy metal wastewater will be produced. At the same time, a large amount of complexing agents such as EDTA, citric acid, humic acid, etc. will be added in the production process. Organic acids are easy to combine with heavy metals to form stable heavy metal complexes, which greatly increases the content of complex heavy metals in effluent, and also increases the difficulty of heavy metal treatment. At present, a variety of treatment technologies including chemical precipitation method, coagulation-flocculation method, ion exchange method, electrochemical method and adsorption method have been developed to remove complex heavy metals in wastewater. The adsorption method has the advantages of high removal rate, low energy consumption, simple operation and low cost, and therefore the adsorption method is considered to be an effective technology for removing complex heavy metals in water.

[0003] Metal organic framework (MOFs) is a unique three-dimensional organic-inorganic composite material with a porous nanostructure, which is usually assembled by metal ion groups and organic ligands. Metal organic framework material has the characteristics of large specific surface area, high porosity, easy chemical functionalization and designable pore channel, and is considered to be an ideal material for developing heavy metal adsorbents. Zirconium-based MOFs material not only has large specific surface area and porosity, but also has good thermal stability, chemical stability and structural stability, which can cope with complex and variable water environment. However, the space steric hindrance and insufficient coordination sites of MOFs material lead to the decrease of the adsorption capacity of MOFs material for heavy metal ions.

[0004] The Chinese patent document with publication number CN111187417A discloses a modification method and application of metal organic framework material. The patent improves the hydrophobicity and water vapor interference resistance of MOFs material by in-situ modification of metal nodes of the metal organic framework material through one-step synthesis method, and is suitable for adsorption separation in water-containing or water vapor interference environment. However, the one-step synthesis modification method may have adverse effects on the preparation of metal organic framework material, thereby affecting the performance of the final material, and the modified material has not been used for adsorption of complex metals. SUMMARY

[0005] In view of the problems existing in the prior art, the present application provides a citric acid modified MOF-808 heavy metal adsorbent, a preparation method thereof and application thereof in removing complex chromium in water. The obtained citric acid modified heavy metal adsorbent MOF-808-CA has many adsorption sites and can be used for adsorbing complex chromium in water, and has excellent adsorption performance.

[0006] The application is realized by the following technical solutions.

[0007] The application discloses a preparation method of a citric acid modified MOF-808 heavy metal adsorbent.

[0008] The citric acid is dissolved in water, and the MOF-808 powder is added and mixed, and then heated for reaction.

[0009] Preferably, the mass ratio of the citric acid to the MOF-808 powder is (2-10) g:(1-5) g.

[0010] Preferably, the reaction temperature is 15-80 DEG C, and the reaction time is 8-48 h.

[0011] Preferably, the washing is specifically: first washing with water, and then washing with acetone.

[0012] Preferably, the drying is carried out under vacuum conditions, the drying temperature is 50-80 DEG C, and the drying time is 8-24 h.

[0013] Preferably, the preparation method of the MOF-808 powder comprises the following steps: dissolving zirconium oxychloride octahydrate and trimesic acid in a mixed solution of N,N-dimethylformamide and formic acid, and heating for reaction to obtain a suspension; centrifuging the obtained suspension, discarding the supernatant to obtain a solid, and then washing and drying the solid to obtain the MOF-808 powder.

[0014] Further, in the preparation method of the MOF-808 powder, the reaction temperature is 100-180 DEG C, and the reaction time is 8-72 h.

[0015] The citric acid modified MOF-808 heavy metal adsorbent is obtained by using the preparation method.

[0016] The application of the citric acid modified heavy metal adsorbent in adsorbing complex chromium in water bodies.

[0017] Compared with the prior art, the application has the following beneficial effects:

[0018] The application adopts a heavy metal adsorbent MOF-808 modified by citric acid (CA), and the specific surface area and pore volume of the material obtained by the post-modification method are larger than those of the material obtained by one-step synthesis reaction, and the problems of few adsorption sites of MOF-808 and low adsorption capacity of the complex state of chromium are solved. The citric acid replaces the formic acid group on the Zr cluster of MOF-808 as a heavy metal ion chelating agent with free-COOH groups, and the free carboxyl group of the citric acid can provide a synergistic double-COOH site, enrich the adsorption site, and improve the adsorption potential of the complex state of chromium. The adsorption mechanism of the obtained MOF-808-CA for the complex state of chromium is as follows: (1) the ligand exchange between the complex state of chromium and Zr-OH on the MOF-808-CA, so that the Lewis acid / base interaction between the unsaturated central ligand Zr 4+ and the carboxyl group on the complex state of chromium occurs, and then a stable Zr-EDTA-Cr ternary complex is formed, which is the main adsorption mechanism; (2) the complexation between the carboxyl group of MOF-808-CA and the complex state of chromium. Therefore, the introduction of the citric acid molecule improves the adsorption capacity of the material for the complex state of chromium, and the adsorption of the material for the complex state of chromium also has good selectivity, the material is easy to separate after adsorption, there is no secondary pollution, and the material has wide market prospects and significant environmental benefits. The modified MOF-808-CA heavy metal adsorbent material prepared in the application contains a strong Zr-O bond in the material structure, so that the material has unique super-stability in an acidic aqueous solution, and the material has a high specific surface area and a regular pore structure.

[0019] The application adopts the MOF-808-CA modified by citric acid to adsorb the complex state of chromium, has good adsorption effect, high removal efficiency, and has wide application prospects and application value. DETAILED DESCRIPTION

[0020] In order to further understand the application, the application is described below in combination with examples, and these descriptions are only used to further explain the features and advantages of the application, and are not used to limit the claims of the application.

[0021] The preparation method of the citric acid modified MOF-808 heavy metal adsorbent described in the application comprises:

[0022] (1) zirconium oxychloride octahydrate and trimesic acid are dissolved in a mixed solution of N,N-dimethylformamide and formic acid, ultrasonic dissolution is performed, and then the solution is added to a reaction container and heated to obtain a suspension; the obtained suspension is centrifuged, the supernatant is discarded, and then the obtained solid is dispersed in an acetone solution, washed, and dried to obtain MOF-808 powder;

[0023] (2) Dissolve citric acid in water, then mix the MOF-808 powder obtained in step (1) in water, centrifuge to obtain a solid after heating reaction, and then wash the solid, disperse the obtained solid in an acetone solution, wash, and dry to obtain the MOF-808-CA material.

[0024] In the embodiment of the present application, in step (1), the molar ratio of zirconium oxychloride octahydrate to trimesic acid is (1-6):(1-3), the molar volume ratio of the mixed solution of N,N-dimethylformamide and formic acid to zirconium oxychloride octahydrate and trimesic acid is (50-100)mL:(0.5-5)mmol:(0.5-5)mmol, and the molar volume ratio of acetone to zirconium oxychloride octahydrate and trimesic acid is (10-100)mL:(1-3)mmol:(1-3)mmol.

[0025] In the embodiment of the present application, in step (1), the heating reaction temperature is 100-180℃, and the heating reaction time is 8-72h.

[0026] In the embodiment of the present application, in step (2), the mass-volume ratio of citric acid, MOF-808 and water is (2-10)g:(1-5)g:(500-1000)mL.

[0027] In the embodiment of the present application, in step (2), the heating reaction temperature is 15-80℃, and the heating reaction time is 8-48h.

[0028] The citric acid modified MOFs heavy metal adsorbent MOF-808-CA material prepared by the present application can be used for selective adsorption and removal of complex chromium in an aqueous solution.

[0029] Example 1

[0030] 1) 2.425g of zirconium oxychloride octahydrate (ZrOCl2·8H2O) and 0.525g of trimesic acid (H3BTC) were dissolved in 220mL of a DMF and formic acid mixture (VDMF:formic acid = 1:1), and ultrasonic treatment was performed for 30min until dissolution. The mixture was transferred to a 100mL PTFE-lined reaction kettle, and reaction was performed at 130℃ for 48h. After the reaction was completed, natural cooling was performed to room temperature, and a white solid was collected by centrifugation. Then, the white solid was washed with DMF for 6 times, and then transferred to a 100mL acetone solution for soaking for three days. After centrifugation, the solid was activated in a vacuum drying oven at 60℃ for 12h to obtain MOF-808.

[0031] 2) 2.882 g of citric acid was stirred in 300 mL of ultrapure water for 1 h to dissolve, then 0.5 g of MOF-808 was added, and stirring was continued at 25 °C for 24 h, and the white precipitate obtained was collected by centrifugation. Then, the unreacted CA was removed by washing several times with ultrapure water, and then transferred to a 50 mL acetone solution for three days to replace the water in the pores, and after centrifugation, it was activated in a vacuum drying oven at 60 °C for 12 h to obtain MOF-808-CA.

[0032] The specific surface area of the MOF-808-CA synthesized in this example was 653.59 m 2 / g, and the pore volume was 0.467 cm 3 / g, which was higher than the specific surface area and pore volume of the modified zirconium-based MOF material obtained in Example 1 of document CN111187417A.

[0033] Example 2

[0034] Adsorption experiments were carried out on the MOF-808-CA adsorbent prepared in Example 1 for complex chromium wastewater. The mass ratio of adsorbent to wastewater was 0.0004:1, the initial concentration of complex chromium was 5 mg / L, the temperature was 25 °C, the pH was 4, the rotation speed was 150 r / min, and the adsorption time was 12 h. The saturated adsorption capacity of complex chromium was 4.52 mg / g.

[0035] Example 3

[0036] The initial concentration of complex chromium was 10 mg / L, and the other conditions were the same as in Example 2. The measured saturated adsorption capacity of complex chromium was 8.83 mg / g.

[0037] Example 4

[0038] The initial concentration of complex chromium was 20 mg / L, and the other conditions were the same as in Example 2. The measured saturated adsorption capacity of complex chromium was 13.47 mg / g.

[0039] Example 5

[0040] The initial concentration of complex chromium was 40 mg / L, and the other conditions were the same as in Example 2. The measured saturated adsorption capacity of complex chromium was 16.25 mg / g.

[0041] Example 6

[0042] The initial concentration of complex chromium was 50 mg / L, and the other conditions were the same as in Example 2. The measured saturated adsorption capacity of complex chromium was 17 mg / g.

[0043] It can be seen that within a certain concentration range, the adsorption capacity of the MOF-808-CA adsorbent for complex chromium increases with the increase of the concentration of complex chromium in the water body.

[0044] Example 7

[0045] The same as Example 2, the adsorption time is 5 min, and other conditions remain unchanged. The measured saturated adsorption capacity of complex chromium is 1.77 mg / g.

[0046] Example 8

[0047] The same as Example 2, the adsorption time is 60 min, and other conditions remain unchanged. The measured saturated adsorption capacity of complex chromium is 2.74 mg / g.

[0048] Example 9

[0049] The same as Example 2, the adsorption time is 270 min, and other conditions remain unchanged. The measured saturated adsorption capacity of complex chromium is 3.76 mg / g.

[0050] Example 10

[0051] The same as Example 2, the adsorption time is 570 min, and other conditions remain unchanged. The measured saturated adsorption capacity of complex chromium is 4.12 mg / g.

[0052] It can be seen that before the adsorption reaches equilibrium, the longer the adsorption time, the higher the adsorption capacity of MOF-808-CA adsorbent for complex chromium.

[0053] Example 11

[0054] The same as Example 2, the solution pH is 2.0, and other conditions remain unchanged. The measured saturated adsorption capacity of complex chromium is 3.20 mg / g.

[0055] Example 12

[0056] The same as Example 2, the solution pH is 3.0, and other conditions remain unchanged. The measured saturated adsorption capacity of complex chromium is 4.62 mg / g.

[0057] Example 13

[0058] The same as Example 2, the solution pH is 5.0, and other conditions remain unchanged. The measured saturated adsorption capacity of complex chromium is 4.32 mg / g.

[0059] Example 14

[0060] The same as Example 2, the solution pH is 7.0, and other conditions remain unchanged. The measured saturated adsorption capacity of complex chromium is 4.01 mg / g.

[0061] Example 15

[0062] The same as Example 2, the solution pH is 9.0, and other conditions remain unchanged. The measured saturated adsorption capacity of complex chromium is 3.81 mg / g.

[0063] It can be seen that the maximum adsorption amount appears at pH = 3.0, and the slightly acidic condition is more conducive to the adsorption of the MOF-808-CA adsorbent to the complex chromium, and the adsorption amount of the MOF-808-CA adsorbent to the complex chromium decreases with the increase of pH value when pH is greater than 3.

[0064] Comparative Example 1

[0065] In Example 6, the MOF-808 adsorbent prepared in Example 1 was used, and other conditions were unchanged, and the measured saturated adsorption amount of complex chromium was 12.9 mg / g.

[0066] It can be seen that the MOF-808-CA adsorbent modified by citric acid has significantly improved the adsorption amount of complex chromium compared with MOF-808.

[0067] Comparative Example 2

[0068] In Example 2, the molar ratio of Cr(III):EDTA-Na2 / sodium citrate in water was 1:0.5, and other conditions were unchanged, and the measured saturated adsorption amount of complex chromium was 4.28 mg / g.

[0069] Comparative Example 3

[0070] In Example 2, the molar ratio of Cr(III):EDTA-Na2 / sodium citrate in water was 1:5, and other conditions were unchanged, and the measured saturated adsorption amount of complex chromium was 3.91 mg / g.

[0071] Comparative Example 4

[0072] In Example 2, the molar ratio of Cr(III):EDTA-Na2 / sodium citrate in water was 1:30, and other conditions were unchanged, and the measured saturated adsorption amount of complex chromium was 3.63 mg / g.

[0073] As can be seen from the above, the addition of organic complexing agent has an inhibitory effect on the adsorption of MOF-808-CA adsorbent to complex chromium, and the adsorption amount of MOF-808-CA adsorbent to complex chromium decreases with the increase of ionic strength.

Claims

1. Use of a citric acid modified MOF-808 heavy metal adsorbent for adsorbing complexed chromium in water bodies, characterized in that, The preparation method of the citric acid modified MOF-808 heavy metal adsorbent comprises the following steps: dissolving citric acid in water, adding MOF-808 powder, mixing, heating reaction, separating the solid after the reaction is completed, and washing and drying the solid to obtain the MOF-808-CA material.

2. Use according to claim 1, characterized in that, The mass ratio of citric acid to MOF-808 powder is (2-10) g:(1-5) g.

3. Use according to claim 1, characterized in that, The reaction temperature is 15-80 DEG C, and the reaction time is 8-48 h.

4. Use according to claim 1, characterized in that, The washing specifically comprises the following steps: firstly washing with water, and then washing with acetone.

5. The use according to claim 1, characterized in that, The drying is carried out under vacuum, the drying temperature is 50-80 DEG C, and the drying time is 8-24 h.

6. Use according to claim 1, characterized in that, The preparation method of the MOF-808 powder comprises the following steps: dissolving zirconium oxychloride octahydrate and trimesic acid in a mixed solution of N,N-dimethylformamide and formic acid, heating reaction to obtain a suspension, centrifuging the obtained suspension, discarding the supernatant to obtain a solid, and washing and drying the solid to obtain the MOF-808 powder.

7. Use according to claim 6, characterized in that, In the preparation method of the MOF-808 powder, the reaction temperature is 100-180 DEG C, and the reaction time is 8-72 h.