Preparation and application of water system ZIF-8, EY/ZIF-8/PAA composite aerogel
阅读说明：本技术 水系zif-8、ey/zif-8/paa复合气凝胶的制备及应用 (Preparation and application of water system ZIF-8, EY/ZIF-8/PAA composite aerogel ) 是由 陈志军 王青青 杨清香 王芳草 赵俊红 谢云鹏 王聪 雷李玲 于 2020-11-24 设计创作，主要内容包括：本发明提供了一种水系ZIF-8、EY/ZIF-8/PAA复合气凝胶的制备及应用,对ZIF-8的制备方法进行了优化和改进,采用水系法制备了水系的ZIF-8,采用鸡蛋蛋黄(EY)做为生物质基材,ZIF-8为原料,采用原位聚合的方法制备了EY/ZIF-8/PAA复合气凝胶,该复合气凝胶表面粗糙,内部存在不规则多孔结构,具有较低的密度,良好的热稳定性和水稳定性,解决了ZIF-8应用中回收困难的难题,且该气凝胶对重金属离子(Pb～(2+),Cd～(2+))有良好的吸附性能。(The invention provides a preparation method and application of a water system ZIF-8 and EY/ZIF-8/PAA composite aerogel, wherein the preparation method of the ZIF-8 is optimized and improved, the water system ZIF-8 is prepared by adopting a water system method, Egg Yolk (EY) is adopted as a biomass base material, the ZIF-8 is adopted as a raw material, the EY/ZIF-8/PAA composite aerogel is prepared by adopting an in-situ polymerization method, and the composite gas isThe gel has rough surface, irregular porous structure inside, lower density, good thermal stability and water stability, solves the difficult problem of difficult recovery in ZIF-8 application, and the aerogel is used for preparing heavy metal ions (Pb) 2+ ，Cd 2+ ) Has good adsorption performance.)
1. The preparation method of the water system ZIF-8 is characterized by comprising the following steps:
(1) respectively preparing a zinc nitrate solution and a 2-methylimidazole solution;
(2) slowly dripping a zinc nitrate solution into the 2-methylimidazole solution under the condition of stirring at room temperature, continuously stirring for 5min after dripping is finished, centrifuging to obtain a precipitate, washing and centrifuging the precipitate for a plurality of times, and drying in vacuum to obtain ZIF-8.
2. The method for producing an aqueous ZIF-8 as set forth in claim 1, wherein: the concentration of the zinc nitrate solution in the step (1) is 0.496mol/L, and the concentration of the 2-methylimidazole solution is 3.47 mol/L.
3. The method for producing an aqueous ZIF-8 as set forth in claim 1, wherein: the volume ratio of the zinc nitrate solution to the 2-methylimidazole solution in the step (2) is 1: 10.
4. method for preparing EY/ZIF-8/PAA composite aerogels using aqueous ZIF-8 prepared according to any of claims 1 to 3, characterized by the following steps: adding deionized water into the yolk, uniformly stirring, adding ZIF-8, continuously stirring until the mixture is uniformly dispersed, sequentially adding acrylic acid, alcohol and persulfate, stirring for 10-30min, removing froth, heating in a water bath to form gel, taking out, cooling to room temperature, freezing and crystallizing, and freeze-drying to obtain the EY/ZIF-8/PAA composite aerogel.
5. The method of claim 4, wherein: the egg yolk is fresh egg yolk, and the mass ratio of the egg yolk to the ZIF-8 to the acrylic acid to the alcohol to the persulfate is (5-8): (2.5-4.0): (0.5-1.5): (0.2-0.6): (0.01-0.02).
6. The method of claim 4, wherein: the water bath heating temperature is 80-100 ℃, the freezing crystallization temperature is-18 ℃ to-20 ℃, the freezing drying temperature is-45 ℃ to-55 ℃, and the freezing drying time is 1-36 h.
7. The method of claim 4, wherein: the alcohol is 1, 4-butanediol, propylene glycol, hexanediol, polyethylene glycol 200 or polyethylene glycol 400, and the persulfate is potassium persulfate or ammonium persulfate.
8. Use of the EY/ZIF-8/PAA composite aerogel prepared by the method of any one of claims 5 to 7 for adsorbing heavy metal ions.
9. Use according to claim 8, characterized in that: the heavy metal ion is Pb2+Or Cd2+。
10. Use according to claim 9, characterized in that: the EY/ZIF-8/PAA composite aerogel Pb2+The adsorption capacity reaches 370mg/g, and the adsorption capacity is high for Cd2+The adsorption capacity reaches 100 mg/g.
Technical Field
The invention relates to the field of heavy metal adsorption, and particularly relates to preparation and application of a water system ZIF-8 and EY/ZIF-8/PAA composite aerogel.
Background
The rapid development of industry produces large amounts of wastewater, and the treatment of wastewater has been a hot topic because of the negative effects of wastewater on the environment and human health. After being taken by human body, the heavy metal ions in the waste water can cause damage to the kidney, nervous system, cardiovascular and cerebrovascular systems and the like of the human body. In order to protect the environment and human health, a method for removing heavy metals from wastewater to meet the increasing environmental quality requirements is urgently needed. Common methods for treating pollutants in wastewater include chemical precipitation, extraction, membrane separation, ion exchange, electrochemical methods, adsorption and the like, and the adsorption method gradually enters the sight of researchers due to the characteristics of simple operation, safety, simple equipment and the like.
ZIFs are a new subfamily of crystalline porous Metal Organic Frameworks (MOFs) which are formed by linking organic imidazolate to metal ions, such as Zn, Co and the like, to form tetrahedral frameworks, and ZIF-8 is widely used as an adsorbent for removing heavy metal ions in wastewater.
At present, most of ZIF-8 preparation methods are methanol solvent methods. The specific process is as follows: 2.933 g of zinc nitrate hexahydrate (Zn (NO) was weighed3)2·6H2O) dissolved in 200 mL of methanol and placed in 500 mL of methanolIn a mouth bottle, stir for 40 minutes. 6.489 g of 2-methylimidazole were weighed out and dissolved in 200 mL of methanol, and the solution was added dropwise to a three-necked flask and mechanically stirred for 1 hour. And standing to remove the solvent on the upper layer, centrifugally separating the substance on the lower layer, washing for 3 times by using methanol, and drying for 12 hours in vacuum to obtain white powdered ZIF-8.
The ZIF-8 is prepared by a methanol method, the preparation method is relatively simple, but a large amount of methanol solvent is used in the preparation process, the cost is high, and the pollution to the environment is caused. In addition, ZIF-8, when used as a heavy metal adsorbent, has poor dispersibility in an aqueous solution and is difficult to recover, and it causes secondary pollution to the water environment while removing heavy metal ions.
Disclosure of Invention
The invention provides preparation and application of a water system ZIF-8, EY/ZIF-8/PAA composite aerogel, which optimizes and improves the preparation method of the ZIF-8, adopts a water system method to prepare the water system ZIF-8, has low cost and does not generate a large amount of organic solvent waste liquid. Aiming at the defect of difficult recovery of ZIF-8, the invention adopts Egg Yolk (EY) as a biomass base material, ZIF-8 as a raw material, and adopts a water-bath in-situ polymerization method to prepare the EY/ZIF-8/PAA composite aerogel, the composite aerogel has a rough surface, an irregular porous structure in the interior, lower density, good thermal stability and water stability, solves the defect of difficult recovery of ZIF-8, and can be used for preparing heavy metal ions (Pb)2+，Cd2+) Has good adsorption performance.
The technical scheme for realizing the invention is as follows:
the preparation method of the water system ZIF-8 comprises the following steps:
(1) respectively preparing a zinc nitrate solution and a 2-methylimidazole solution;
(2) slowly dripping a zinc nitrate solution into the 2-methylimidazole solution under the condition of stirring at room temperature, continuously stirring for 5min after dripping is finished, centrifuging to obtain a precipitate, washing and centrifuging the precipitate for a plurality of times, and drying in vacuum to obtain ZIF-8.
The concentration of the zinc nitrate solution in the step (1) is 0.496mol/L, and the concentration of the 2-methylimidazole solution is 3.74 mol/L.
The volume ratio of the zinc nitrate solution to the 2-methylimidazole solution in the step (2) is 1: 10.
The method for preparing the EY/ZIF-8/PAA composite aerogel by using the water system ZIF-8 comprises the following steps: adding deionized water into the yolk, uniformly stirring, adding ZIF-8, continuously stirring until the mixture is uniformly dispersed, sequentially adding acrylic acid, alcohol and persulfate, stirring for 10-30min, removing froth, heating in a water bath to form gel, taking out, cooling to room temperature, freezing and crystallizing, and freeze-drying to obtain the EY/ZIF-8/PAA composite aerogel.
The egg yolk is fresh egg yolk, and the mass ratio of the egg yolk to the ZIF-8 to the acrylic acid to the alcohol to the persulfate is (5-8): (2.5-4.0): (0.5-1.5): (0.2-0.6): (0.01-0.02).
The water bath heating temperature is 80-100 ℃, the freezing crystallization temperature is-18 ℃ to-20 ℃, the freezing drying temperature is-45 ℃ to-55 ℃, and the freezing drying time is 1-36 h.
The alcohol is 1, 4-butanediol, propylene glycol, hexanediol, polyethylene glycol 200 or polyethylene glycol 400, and the persulfate is potassium persulfate or ammonium persulfate.
Preferably, the invention also provides application of the EY/ZIF-8/PAA composite aerogel in adsorption of heavy metal ions.
The heavy metal ion is Pb2+Or Cd2+。
The EY/ZIF-8/PAA composite aerogel Pb2+The adsorption capacity reaches 370mg/g, and the adsorption capacity is high for Cd2+The adsorption capacity reaches 100 mg/g.
The invention has the beneficial effects that: the invention adopts deionized water as the solvent to prepare the water system ZIF-8, thereby reducing the cost and avoiding the pollution of organic solvent to the environment; the egg yolk is adopted as the biological base material, the characteristics of protein gelatinization and the advantages of low toxicity and low cost of the biomass base material are utilized, and the acrylic acid is adopted as the cross-linking agent, because the amino acid residue of the protein and the carboxyl of the acrylic acid can be chemically cross-linked to form gel in the water bath process. EY/ZIF-8/PAA composite aerogel for heavy metal ions (Pb)2+，Cd2+) The good adsorption performance is attributed to the fact that the porous structure of the composite aerogel is heavy in adsorptionThe metal ions provide a large number of adsorption sites.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.
FIG. 1 is an SEM image of an EY/ZIF-8/PAA composite aerogel of the present invention.
FIG. 2 is an XRD pattern of an EY/ZIF-8/PAA composite aerogel.
Detailed Description
The technical solutions of the present invention will be described clearly and completely with reference to the following embodiments of the present invention, and it should be understood that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be obtained by a person skilled in the art without inventive effort based on the embodiments of the present invention, are within the scope of the present invention.
Example 1
The preparation method comprises the following steps:
(1) preparation of ZIF-8: 1.17g of zinc nitrate was added to 8.0g of deionized water, and the mixture was dissolved by ultrasonic waves. Secondly, adding 22.74g of 2-methylimidazole into 80g of deionized water, ultrasonically dissolving, finally, slowly dripping a zinc nitrate solution into the 2-methylimidazole solution under the condition of room-temperature magnetic stirring, continuing stirring for five minutes after dripping is finished, centrifuging at 8000r/min to obtain a precipitate, washing the precipitate with deionized water, centrifuging for several times, and performing vacuum drying at 65 ℃ for 12 hours to obtain ZIF-8.
(2) Preparation of gel: taking about 5.0g of Egg Yolk (EY) from fresh eggs, placing the egg yolk in a beaker, adding 5.0 mL of deionized water, magnetically stirring until the egg yolk is uniformly dispersed, then adding about 2.5g of ZIF-8, continuously stirring until the egg yolk is uniformly dispersed, then adding 0.5 g of acrylic acid, 0.2g of 1, 4-butanediol and 0.01g of potassium persulfate, stirring for 10min, removing floating foam, and heating the mixed solution in a water bath at 80 ℃ for 2 hours to form gel.
(3) Preparing aerogel: and taking out the aerogel from the water bath, cooling the aerogel to room temperature in the air, transferring the aerogel to a freezing layer of a refrigerator to freeze and crystallize at the temperature of 18 ℃ below zero for 12 hours, removing the aerogel from the freezing layer, and freeze-drying the aerogel in a freeze dryer at the temperature of 45 ℃ below zero for more than 24 hours to obtain the EY/ZIF-8/PAA composite aerogel.
Example 2
The preparation method comprises the following steps:
(1) preparation of ZIF-8: to 80.0g of deionized water was added 11.7g of zinc nitrate, and the mixture was dissolved by ultrasonic waves. Secondly, 227.94g of 2-methylimidazole is added into 800g of deionized water, ultrasonic dissolution is carried out, finally, under the condition of room-temperature magnetic stirring, zinc nitrate solution is slowly dripped into the 2-methylimidazole solution, stirring is carried out for ten minutes after dripping is finished, standing is carried out for 1 hour, supernatant is discarded, bottom solution is centrifuged under the condition of 10000r/min to obtain precipitate, the precipitate is washed and centrifuged by deionized water for a plurality of times, vacuum drying is carried out at 65 ℃ for more than 12 hours, and ZIF-8 is obtained after grinding.
(2) Preparation of gel: about 8.0g of Egg Yolk (EY) is taken from fresh eggs and placed in a beaker, 8.0 mL of deionized water is added, magnetic stirring is carried out until the mixture is uniformly dispersed, about 4.0g of ZIF-8 is added, stirring is continued until the mixture is uniformly dispersed, then 1.0 g of acrylic acid, 0.4g of 1, 4-butanediol and 0.02g of potassium persulfate are added, stirring is carried out for 10min, floating foam is removed, and the mixed solution is heated in a water bath at 95 ℃ for 2 hours to form gel.
(3) Preparing aerogel: and taking out the aerogel from the water bath, cooling the aerogel to room temperature in the air, transferring the aerogel to a freezing layer of a refrigerator to freeze and crystallize at the temperature of 18 ℃ below zero for 12 hours, removing the aerogel from the freezing layer, and freeze-drying the aerogel in a freeze dryer at the temperature of 50 ℃ below zero for more than 36 hours to obtain the EY/ZIF-8/PAA composite aerogel.
Adsorption experiment:
（1）Pb2+and Cd2+Determination of the standard curve: preparing HNO with the concentration of 1%3Taking 5 volumetric flasks for Pb2+Preparing standard solution with concentration of 0.5 mg/L, 1 mg/L, 2 mg/L, 4 mg/L, 8 mg/L5 concentration gradients. Cd [ Cd ]2+Preparation of Standard Curve and Pb2+The preparation method of the standard curve is the same, the lead single element standard solution and the cadmium single element standard solution used in the experiment are measured by a micro liquid transfer gun and diluted in a volumetric flask, and the water used in the whole process is pure water.
(2) Contact time to Pb2+And Cd2+The adsorption influence of (c): 1mg of the adsorbent was added to 10ml of a 500mg/L lead nitrate (or cadmium nitrate) solution, and the mixture was placed in a constant temperature shaker at 25 ℃ and 30 rpm. Sampling at regular intervals, standing for a while, diluting the supernatant by a certain factor, and taking the diluted supernatant as Pb in the atomic absorption test solution2+(or Cd)2+) And (4) concentration.
(3) pH value to Pb2+And Cd2+The adsorption influence of (c): lead nitrate (or cadmium nitrate) solution is in the pH range of 3.0-7.0 (adjusted by 0.1M HCl and NaOH solution), the same experimental conditions are used, the dosage of the fixed adsorbent is unchanged, samples are taken at fixed time intervals, and after standing for a while, the supernatant is diluted by a certain multiple to be used as Pb in the atomic absorption test solution2+(or Cd)2+) And (4) concentration.
(4) Initial concentration vs. Pb2+And Cd2+The adsorption influence of (c): lead nitrate (or cadmium nitrate) solution (150-2+(or Cd)2+) And (4) concentration.
(5) Adsorbent dosage to Pb2+And Cd2+The adsorption influence of (c): taking a lead nitrate (or cadmium nitrate) solution at 500mg/L and an adsorbent at 2-11mg under the same experimental conditions at fixed time intervals, taking a sample, standing for a moment, taking a supernatant, diluting by a certain multiple, and taking the supernatant as Pb in an atomic absorption test solution2+(or Cd)2+) And (4) concentration.
The adsorption capacity is calculated by the following formula:
wherein in the formula, Q: adsorption amount, mg/g, C0: initial concentration of adsorption solution, mg/L, Ct: equilibrium concentration of the solution after adsorption, time, mg/L, V: volume of adsorption solution, L, m: mass of adsorbent, g.
The experimental results are as follows:
FIG. 1 is an SEM image of an EY/ZIF-8/PAA composite aerogel, wherein (a) X950, (b) X1100, and (c) X200. FIG. 1 shows that the composite aerogel has a rough surface and an irregular porous structure inside, and ZIF-8 exists on the surface, the inner wall of the pores, the edges and the like of the composite aerogel in a single or small part of agglomerated form. ZIF-8 in the composite aerogel improves the Pb content2+(or Cd)2 +) The internal porous structure increases the composite aerogel and Pb2+(or Cd)2+) Provides more adsorption sites.
FIG. 2 is an XRD pattern of EY/ZIF-8/PAA composite aerogel, wherein the XRD pattern of the synthesized ZIF-8 is consistent with that of standard card. In an XRD pattern of the external composite aerogel, amorphous diffraction peaks of about 2 theta =20 degrees and characteristic crystal faces of ZIF-8 of (002), (013) and (222) indicate that the EY/ZIF-8/PAA composite aerogel is successfully prepared.
The adsorption experiment result shows that the EY/ZIF-8/PAA composite aerogel has Pb-free performance2+(or Cd)2+) Has good adsorption property to Pb2+The adsorption capacity reaches 370mg/g, and the adsorption capacity is high for Cd2+The adsorption capacity reaches 100 mg/g.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.