Method for preparing post-modified amino-functionalized zif-8 and cellulose composite aerogel and application thereof

Abstract

The present invention discloses a method for preparing a composite aerogel of post-modified amino ZIF-8 and cellulose, comprising the following steps: 1) preparing amino ZIF-8; 2) preparing a cellulose suspension; 3) adding amino ZIF-8 to the cellulose suspension and mixing evenly, then adding polyethyleneimine for mechanical stirring to obtain a mixed solution; 4) dropping a cross-linking agent into the mixed solution for a cross-linking reaction to obtain a composite hydrogel; 5) sealing, heating, and baking the composite hydrogel, washing it with deionized water, and drying it to obtain a composite aerogel. The present invention also discloses the application of the composite aerogel in the field of platinum ion adsorption. The composite aerogel prepared by the method of the present invention has a three-dimensional network structure composed of interconnected skeleton structures. The specific surface area of ​​the final sample of the composite aerogel measured by nitrogen adsorption is as high as 499.5 cm 2 / g, and the adsorption capacity for molybdenum ions is 407 mg / g, showing excellent adsorption performance.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of composite material preparation, and particularly relates to a preparation method and application of a post-modified amino ZIF-8 and cellulose composite aerogel. BACKGROUND

[0002] Molybdenum is a trace element present in plants and animals; it is harmful to plants at a concentration higher than 5 μg / g and to ruminants at a concentration higher than 10 μg / g. Molybdenum is a second-row transition element, which has various industrial applications, such as an ingredient of electronic and vacuum tubes, fire-resistant materials and hardness steel alloys; the pollution of molybdenum in water bodies and underground water poses a serious threat to the human population; if the concentration of water-soluble molybdenum-derived anions exceeds 5 mg / L, it will also cause serious environmental pollution. Therefore, it is very important and concerned to recover or remove molybdenum from various industrial waste liquids from the perspectives of resource utilization and environmental protection.

[0003] In the prior art, various methods for removing molybdenum from wastewater, such as chemical precipitation, adsorption process, ion exchange, electrochemical technology and biological treatment. So far, among various wastewater treatment methods, the adsorption method occupies an important position due to its high efficiency, low energy consumption, simple operation and recyclable conditions.

[0004] The development of adsorbent materials should focus on their ecological environmental friendliness. Biomass is an easily available and environmentally friendly material; MOFs material is a porous crystalline material composed of metal ions or metal clusters and organic ligands; MOFs material has very high specific surface area and adjustable pore size, making it have wide application prospects in gas storage, gas separation, adsorption and drug release fields. The pore size and structure of MOFs material can be designed and controlled, so that it can selectively adsorb specific substances. This makes MOFs material have high selectivity for adsorption and separation, and can realize efficient separation of different gases, liquids or ions.

[0005] Aerogel is a general term for dry gel materials, which has high porosity, large specific surface area, low density and other superior characteristics; its structure contains a large number of hydrophilic functional groups -OH and -COOH. Through methods such as grafting, crosslinking and surface functionalization of other active groups, the activity of heavy metal ions can be realized to improve the adsorption performance. SUMMARY

[0006] The present invention aims to address, at least to some extent, one of the technical problems in the related art. To this end, the present invention primarily provides a method for preparing and applying a composite aerogel of post-modified amino-modified ZIF-8 and cellulose. This composite aerogel exhibits advantages such as environmental friendliness, strong hydrophilicity, high mechanical properties and thermal stability, large specific surface area, good selective adsorption, high adsorption capacity, easy recycling, and high repeated adsorption efficiency. Furthermore, this composite aerogel can recover molybdenum from aqueous environments, which is of great significance for reducing ecological risks.

[0007] The purpose of the present invention is achieved through the following technical solutions:

[0008] A method for preparing a composite aerogel of post-modified amino-modified ZIF-8 and cellulose comprises the following steps:

[0009] 1) adding ZIF-8 powder and 3-aminopropyltriethoxysilane to anhydrous ethanol, stirring the mixture thoroughly, centrifuging, washing, and drying the mixture to obtain amino-modified ZIF-8;

[0010] 2) adding orange peel powder to an alkaline solution, heating and mechanically stirring, washing and drying to obtain cellulose powder, then adding the cellulose powder to a mixed solution of TEMPO (2,2,6,6-tetramethylpiperidinyloxide), NaBr, and NaClO, mechanically stirring, washing and drying to obtain pretreated cellulose powder, and then adding the pretreated cellulose powder to deionized water to obtain a cellulose suspension;

[0011] 3) adding the amino-modified ZIF-8 to the cellulose suspension and mixing uniformly, then adding polyethyleneimine and mechanically stirring to obtain a mixed solution;

[0012] 4) adding a crosslinking agent dropwise into the mixed solution to perform a crosslinking reaction to obtain a composite hydrogel;

[0013] 5) The composite hydrogel is sealed, heated, and baked, and then washed with deionized water and dried to obtain the composite aerogel.

[0014] Wherein ZIF-8 powder is prepared by the following method:

[0015] 2-Methylimidazole and zinc salt are dissolved in deionized water respectively, mechanically stirred at room temperature, centrifuged, washed, and dried to obtain ZIF-8 powder; and the molar ratio of 2-methylimidazole, zinc salt and deionized water is 1:(1-3):(4-8).

[0016] In a specific embodiment, the mass ratio of the ZIF-8 powder, 3-aminopropyltriethoxysilane and anhydrous ethanol in step 1) is 1:(5-15):(20-40).

[0017] In a specific embodiment, in step 2), the mass ratio of the orange peel powder to the alkaline solution is 1:(10-20), and the molar concentration of the alkaline solution is 0.1-0.5 mol / L.

[0018] In a specific embodiment, in step 2), based on the preparation of 15 ml of cellulose suspension, it includes the following components: cellulose powder, TEMPO (2,2,6,6-tetramethylpiperidinyl oxide), NaBr and NaClO in a mass ratio of 1: (0.1-0.3): (0.1-0.2): (0.5-1.5).

[0019] In a specific embodiment, the ratio of the amino-modified ZIF-8, polyethyleneimine and cellulose suspension is 1g:(5-15)g:(30-50)ml; and the mass ratio of the cellulose suspension to deionized water is (1-3):(97-99), and the polyethyleneimine is a branched polyethyleneimine.

[0020] In a specific embodiment, the cross-linking agent is a 10 wt % epichlorohydrin solution.

[0021] In a specific embodiment, in step 5), the heating conditions are: the heating temperature is 50-70°C and the time is 10-15 hours; the drying includes pre-freezing and freeze-drying performed in sequence: the pre-freezing temperature is -20°C to -196°C, and the pre-freezing time is 0.5 to 6 hours; the freeze-drying temperature is -50°C to -40°C, the freeze-drying pressure is 2 to 50 Pa, and the freeze-drying time is 6 to 48 hours.

[0022] In a specific embodiment, the mechanical stirring in step 3) is performed at a speed of 1000-2000 r / min for 25-35 min.

[0023] A composite aerogel prepared by the above-mentioned preparation method of a composite aerogel of post-modified amino-modified ZIF-8 and cellulose, wherein the amount of amino-modified ZIF-8 contained in the composite aerogel is 100-600 mg, and the interior of the composite aerogel is a three-dimensional network structure composed of interconnected skeleton structures, and the specific surface area of ​​the three-dimensional network structure is 400-550 cm 2 / g.

[0024] An application of the composite aerogel of the above-mentioned post-modified amino-modified ZIF-8 and cellulose in the field of molybdenum ion adsorption.

[0025] Compared with the prior art, the present invention has at least the following advantages:

[0026] 1) The present invention utilizes the advantages of the MOFs material ZIF-8, such as large specific surface area, multiple pore sizes, and adjustable pore size, to amino-modify it. The amino-modified ZIF-8 not only enables the composite aerogel of the present application to maintain a good three-dimensional cross-linked network morphology during the freeze-drying process, but also builds a double-structured network with branched polyethyleneimine to enhance mechanical strength, avoiding collapse during freeze-drying and overly dense structures during cross-linking. This extends the adsorption temperature range of the composite aerogel and reduces its storage requirements. The composite aerogel has reduced losses during desorption and reuse, reducing investment costs and significantly increasing the service life of the composite aerogel.

[0027] 2) The post-modified amino-modified ZIF-8 and cellulose composite aerogel prepared by the present invention has higher hydrophilicity and provides more active sites due to the -NH2 groups attached to the surface of ZIF-8 and the -COOH, -OH, and -CO groups on the branched polyethyleneimine and cellulose (orange peel contains a large amount of cellulose and a small amount of lignin, hemicellulose, pectin, pigments and other natural polymers). The introduced functional groups greatly increase the contact probability between the adsorption material and the aqueous solution, thereby significantly improving its adsorption performance for molybdenum;

[0028] 3) The present invention prepares a composite aerogel with a high specific surface area by mixing and reacting aminated ZIF-8, polyethyleneimine, and a cellulose suspension. The active sites provided by the ZIF-8-NH2 and cellulose further enhance the aerogel's adsorption of platinum ions. The results of the examples show that the prepared composite aerogel adsorbs 407 mg / g of platinum ions, demonstrating excellent adsorption performance and effective absorption of platinum ions. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the specific embodiments of the present invention, the following briefly introduces the drawings required for the specific embodiments or the description of the prior art.

[0030] Figure 1 This is a graph showing the adsorption relationship of the composite aerogel prepared in Example 1 of the present invention under different pH values ​​of molybdenum ion solutions;

[0031] Figure 2 The adsorption of platinum ion solution by composite aerogels with different contents of ZIF-8-NH2 prepared in Example 1 of the present invention;

[0032] Figure 3 The adsorption of platinum ion solution by composite aerogels with different contents of polyethyleneimine prepared in Example 2 of the present invention is shown;

[0033] Figure 4This is a morphology and microstructure diagram of the composite aerogel (when the ZIF-8-NH2 content is 500 mg) prepared in Example 1 of the present invention under electron microscope scanning. DETAILED DESCRIPTION

[0034] The present invention will be further described in detail below with reference to the accompanying drawings and examples. The following examples are merely illustrative and non-restrictive, and should not be used to limit the scope of protection of the present invention.

[0035] When expressing a certain amount, concentration or other value or parameter in the form of a range, preferred range, or preferred upper and lower numerical limits, it should be understood that it is equivalent to specifically disclosing any range by combining any pair of upper range limits or preferred numerical values ​​with any lower range limit or preferred numerical value, without considering whether the range is specifically disclosed. Unless otherwise indicated, the numerical range values ​​listed herein include the endpoints of the range and all integers and fractions within the range.

[0036] Unless otherwise indicated, all percentages, parts, ratios, etc. herein are by weight.

[0037] The materials, methods, and examples herein are illustrative and, unless otherwise indicated, are not to be construed as limiting.

[0038] In the following examples, the orange pith powder, orange peel powder, and grapefruit peel powder used are all commercially available, with a particle size of less than or equal to 200 mesh; the 3-aminopropyltriethoxysilane used is purchased from J&K Technologies Co., Ltd. with a purity of 98%; the polyethyleneimine (branched) used is purchased from MacLean Reagent Co., Ltd. with a purity of 98%; the ammonium molybdate used is purchased from MacLean Reagent Co., Ltd. with a purity of 98%; the epichlorohydrin used is purchased from MacLean Co., Ltd. with a purity of 99%; and the ZnCl2, 2-methylimidazole used is purchased from Aladdin Chemical Reagent Co., Ltd. with a purity of 98%.

[0039] In the following implementation, ZIF-8 powder was prepared by the following method: 2-methylimidazole and zinc salt were dissolved in deionized water, mechanically stirred at room temperature for 10 minutes, centrifuged, washed, and dried to obtain ZIF-8 powder; and the molar ratio of 2-methylimidazole, zinc salt, and deionized water was 1:2:6.

[0040] In the following examples, the adsorption capacity of the composite aerogel was tested at room temperature (25±3° C.) and a rotation speed of 800 rpm using an electromagnetic stirrer; and the specific surface area of ​​the composite aerogel was tested using a nitrogen adsorption method.

[0041] Example 1

[0042] The preparation method of the composite aerogel of post-modified amino-modified ZIF-8 and cellulose provided by the present invention comprises the following steps:

[0043] 1) 1 g of ZIF-8 powder and 10 g of 3-aminopropyltriethoxysilane were added to 30 g of anhydrous ethanol and mechanically stirred at 30°C for 24 h. The mixture was then centrifuged and washed twice with anhydrous ethanol and then with deionized water, and then dried for 12 h to obtain amino-modified ZIF-8 (abbreviated as ZIF-8-NH2).

[0044] 2) adding 10 g of orange peel powder to 150 g of an alkaline solution (0.2 mol / L NaOH solution) and heating and mechanically stirring the mixture. The mixture was washed and dried to obtain a cellulose powder. Subsequently, 2 g of the cellulose powder was added to a mixed solution (mass concentration: 12%) of 0.4 g of TEMPO (2,2,6,6-tetramethylpiperidinyl oxide), 0.25 g of NaBr, and 15 mL of NaClO and mechanically stirred. After washing and drying, a pretreated cellulose powder was obtained. Subsequently, 2 g of the pretreated cellulose powder was added to 98 g of deionized water to obtain a cellulose suspension (2 wt %).

[0045] 3) Different masses (100 mg, 200 mg, 300 mg, 400 mg, 500 mg, and 600 mg) of amino-modified ZIF-8 were added to 20 ml of the cellulose suspension and mixed uniformly. Then, 5 g of polyethyleneimine (branched) was added and mechanically stirred at 1500 rpm for 30 min to obtain a mixed solution.

[0046] 4) adding a crosslinking agent (10 wt % epichlorohydrin solution) dropwise into the mixed solution to carry out a crosslinking reaction, accompanied by mechanical stirring for 30 minutes to obtain a composite hydrogel;

[0047] 5) The composite hydrogel was sealed and baked at 60°C for 12 hours, washed twice with deionized water, and finally pre-frozen at -20°C for 3 hours, and then freeze-dried at -40°C and a freeze-drying pressure of 25 Pa for 15 hours to obtain a composite aerogel.

[0048] The composite aerogels of post-modified amino-modified ZIF-8 and cellulose with different mass contents (100 mg, 200 mg, 300 mg, 400 mg, 500 mg, and 600 mg) prepared in Example 1 were subjected to adsorption experiments in the laboratory. The experimental temperature was 25±3°C, the solution pH was 3, the amount of composite aerogel was 20 mg, and the adsorption solution was a 250 mg / L platinum ion solution. The test results are as follows: Figure 2 As shown in Table 1:

[0049] Table 1: Performance test of composite aerogel as adsorbent in Example 1

[0050] ZIF-8-NH2content (mg) 100 200 300 400 5000 600 Adsorption capacity (mg / g) 261.9 289.9 304.8 323.1 407.1 335.4

[0051] The performance test data in Table 1 show that the adsorption capacity of Mo ions by the composite aerogel slowly increases with increasing the amount of amino-modified ZIF-8 (ZIF-8-NH2). When the content exceeds 500 mg, the adsorption capacity decreases due to ZIF-8-NH2 aggregation. At 500 mg, the adsorption capacity reaches 407.1 mg / g.

[0052] Example 2

[0053] The preparation method of the composite aerogel of post-modified amino-modified ZIF-8 and cellulose provided in this embodiment comprises the following steps:

[0054] 1) 1 g of ZIF-8 powder and 10 g of 3-aminopropyltriethoxysilane were added to 30 g of anhydrous ethanol and mechanically stirred at 30°C for 24 h. The mixture was then centrifuged and washed twice with anhydrous ethanol and then with deionized water, and then dried for 12 h to obtain amino-modified ZIF-8 (abbreviated as ZIF-8-NH2).

[0055] 2) adding 10 g of orange peel powder to 150 g of an alkaline solution (0.2 mol / L NaOH solution), heating and mechanically stirring the solution, and then washing and drying the solution to obtain a cellulose powder; then adding 2 g of the cellulose powder to a mixed solution (mass concentration: 12%) of 0.4 g of TEMPO (2,2,6,6-tetramethylpiperidinyl oxide), 0.25 g of NaBr, and 15 mL of NaClO, mechanically stirring the solution, washing, and drying the solution to obtain a pretreated cellulose powder; then adding 2 g of the pretreated cellulose powder to 98 g of deionized water to obtain a cellulose suspension (2 wt%);

[0056] 3) 500 mg of amino-modified ZIF-8 was added to 20 ml of cellulose suspension and mixed uniformly. Then, different weights (0 g, 0.5 g, 2.5 g, 5 g, 7.5 g, and 10 g) of polyethyleneimine (branched) were added and mechanically stirred at 1500 rpm for 30 min to obtain a mixed solution.

[0057] 4) adding a crosslinking agent (10 wt % epichlorohydrin solution) dropwise into the mixed solution to carry out a crosslinking reaction, accompanied by mechanical stirring for 30 minutes to obtain a composite hydrogel;

[0058] 5) The composite hydrogel was sealed and baked at 60°C for 12 hours, washed twice with deionized water, and finally pre-frozen at -20°C for 3 hours, and then freeze-dried at -40°C and a freeze-drying pressure of 25 Pa for 15 hours to obtain a composite aerogel.

[0059] The composite aerogels of post-modified amino-modified ZIF-8 and cellulose with different contents of polyethyleneimine prepared in Example 2 were subjected to adsorption experiments in the laboratory; the experimental temperature was 25±3°C, the solution pH was 3, the amount of composite aerogel was 20 mg, and the adsorption solution was a 250 mg / L molybdenum ion solution. The test results were as follows: Figure 3 As shown in Table 2:

[0060] Table 2: Performance test of composite aerogel as adsorbent in Example 2

[0061] Polyethyleneimine dosage (g) 0 0.5 2.5 5 7.5 10 Adsorption capacity (mg / g) 49.8 177.4 336.5 407.1 384.2 382.3

[0062] Table 2 shows that the adsorption capacity increases steadily as the amount of polyethyleneimine increases from 0g to 5g. When no polyethyleneimine is added, the adsorption capacity is extremely low, and the composite aerogel has a low degree of crosslinking and easily collapses. When the polyethyleneimine dosage is 5g, the adsorption capacity reaches a maximum of 407.1mg / g. However, when the polyethyleneimine dosage exceeds 5g, the excessive polyethyleneimine causes the composite aerogel to aggregate severely, covering the pores within the composite aerogel and causing a decrease in adsorption capacity.

[0063] Example 3

[0064] The preparation method of the composite aerogel of post-modified amino-modified ZIF-8 and cellulose provided in this embodiment comprises the following steps:

[0065] 1) 1 g of ZIF-8 powder and 10 g of 3-aminopropyltriethoxysilane were added to 30 g of anhydrous ethanol and mechanically stirred at 30°C for 24 h. The mixture was then centrifuged and washed twice with anhydrous ethanol and then with deionized water, and then dried for 12 h to obtain amino-modified ZIF-8.

[0066] 2) adding 10 g of orange peel powder to 150 g of an alkaline solution (0.2 mol / L NaOH solution), heating and mechanically stirring the solution, and then washing and drying the solution to obtain a cellulose powder; then adding 2 g of the cellulose powder to a mixed solution (mass concentration: 12%) of 0.4 g of TEMPO (2,2,6,6-tetramethylpiperidinyl oxide), 0.25 g of NaBr, and 15 mL of NaClO, mechanically stirring the solution, washing, and drying the solution to obtain a pretreated cellulose powder; then adding 2 g of the pretreated cellulose powder to 98 g of deionized water to obtain a cellulose suspension (2 wt%);

[0067] 3) 500 mg of ZIF-8 powder or 500 mg of ZIF-8-NH2 powder was added to 20 ml of cellulose suspension and mixed evenly, followed by adding 5 g of polyethyleneimine and mechanically stirring at a speed of 1500 / min for 30 min to obtain a mixed solution;

[0068] 4) adding a crosslinking agent (10 wt % epichlorohydrin solution) dropwise into the mixed solution to carry out a crosslinking reaction, accompanied by mechanical stirring for 30 minutes to obtain a composite hydrogel;

[0069] 5) The composite hydrogel was sealed and baked at 60°C for 12 hours, washed twice with deionized water, and finally pre-frozen at -20°C for 3 hours, and then freeze-dried at -40°C and a freeze-drying pressure of 25 Pa for 15 hours to obtain a composite aerogel.

[0070] The composite aerogel (CPZ) containing ZIF-8 and the composite aerogel (CPZN) containing ZIF-8-NH2 prepared in this example were subjected to adsorption experiments in the laboratory. At the same time, aerogel (CP) without ZIF-8, as well as ZIF-8 powder and ZIF-8-NH2 powder were introduced into the laboratory for adsorption experiments. The experimental temperature was 25±3°C, the solution pH was 3, the amount of adsorbent (composite aerogel) was 20 mg, and the adsorption solution was a 250 mg / L platinum ion solution. The test structure is shown in Table 3:

[0071] Table 3: Performance test of composite aerogel as adsorbent in Example 3

[0072] Sample type ZIF-8 <![CDATA[ZIF-8-NH2]]> CP CPZ CPZN Adsorption capacity (mg / g) 11.32 21.32 57.32 143 470.8

[0073] It can be seen from the performance test data in Table 3 that when only ZIF-8 and ZIF-8-NH2 materials are used for adsorption, the adsorption capacity is extremely low; when no MOF is added and only cellulose is cross-linked, the adsorption capacity is improved to a certain extent compared with the MOF material; when ZIF-8 is added, the adsorption capacity is further improved, but the adsorption capacity is still very low; when ZIF-8 is aminated and then cross-linked with cellulose, the adsorption capacity is greatly improved; this shows that by adopting the amination treatment of ZIF, a synergistic effect can be produced with cellulose, thereby effectively improving the adsorption capacity of the composite aerogel.

[0074] Example 4

[0075] The preparation method of the composite aerogel of post-modified amino-modified ZIF-8 and cellulose provided in this embodiment comprises the following steps:

[0076] 1) 1 g of ZIF-8 powder and 10 g of 3-aminopropyltriethoxysilane were added to 30 g of anhydrous ethanol and mechanically stirred at 30° C. for 24 h. The mixture was then centrifuged and washed twice with anhydrous ethanol and then with deionized water, and then dried for 12 h to obtain amino-modified ZIF-8.

[0077] 2) adding 10 g of orange peel powder or grapefruit peel powder to 150 g of an alkaline solution (0.2 mol / L NaOH solution), heating and mechanically stirring, and then washing and drying to obtain a cellulose powder; then taking 2 g of the cellulose powder and adding it to a mixed solution (mass concentration: 12%) of 0.4 g of TEMPO (2,2,6,6-tetramethylpiperidinyl oxide), 0.25 g of NaBr, and 15 mL of NaClO, mechanically stirring, washing and drying to obtain a pretreated cellulose powder; then taking 2 g of the pretreated cellulose powder and adding it to 98 g of deionized water to obtain a cellulose suspension (2 wt %);

[0078] 3) 500 mg of amino-modified ZIF-8 was added to 20 ml of cellulose suspension and mixed evenly, followed by addition of 5 g of polyethyleneimine and mechanical stirring at 1500 rpm for 30 min to obtain a mixed solution;

[0079] 4) adding a crosslinking agent (10 wt % epichlorohydrin solution) dropwise into the mixed solution to carry out a crosslinking reaction, accompanied by mechanical stirring for 30 minutes to obtain a composite hydrogel;

[0080] 5) The composite hydrogel was sealed and baked at 60°C for 12 hours, washed twice with deionized water, and finally pre-frozen at -20°C for 3 hours, and then freeze-dried at -40°C and a freeze-drying pressure of 25 Pa for 15 hours to obtain a composite aerogel.

[0081] The composite aerogels prepared in this example, including grapefruit peel powder and ZIF-8, the composite aerogels prepared by adding grapefruit peel powder (YPZ) and ZIF-8-NH2 (YPZN), the composite aerogels prepared by adding orange peel powder and ZIF-8 (JPZ), and the composite aerogels prepared by adding orange peel powder and ZIF-8-NH2 (JPZN), were compared with the composite aerogels (CPZ and CPZN) in Example 3 and subjected to adsorption experiments in the laboratory. The experimental temperature was 25±3°C, the solution pH was 3, the amount of adsorbent (composite aerogel) was 20 mg, and the adsorption solution was a 250 mg / L molybdenum ion solution. The test results are shown in Table 4:

[0082] Table 4 Performance test results of composite aerogel in Example 4

[0083] Sample type YPZ YPZN JPZ JPZN CPZ CPZN Adsorption capacity (mg / g) 91.4 268.4 87.3 221.5 143 470.8

[0084] The performance test data in Table 4 show that when ZIF-8 is added, the adsorption capacities of orange peel powder, grapefruit peel powder, and tangerine peel powder are similar. However, when amino-modified ZIF-8 is added, the differences between the three become significant. Compared with grapefruit peel powder or tangerine peel powder, the composite aerogel prepared using tangerine peel powder in this application exhibits superior adsorption performance. This may be because the majority of tangerine peel is cellulose, while grapefruit peel and tangerine peel also contain significant amounts of pectin, lignin, and other substances. The high degree of crosslinking between cellulose and epichlorohydrin forms a stable three-dimensional crosslinked network, which improves the adsorption performance of the crosslinked product.

[0085] Example 5: Application of composite aerogel in adsorbing molybdenum ion solution

[0086] This embodiment takes Example 1 (when the mass of ZIF-8-NH2 is 500 mg) as an example, by changing the pH value of the platinum ion solution; changing the adsorption capacity of the platinum ion solution on the composite aerogel, specifically as follows Figure 1 As shown, from Figure 1 It can be seen that the adsorption of molybdenum is greatly affected by the pH of the solution. The adsorption amount increases with increasing pH and then decreases rapidly, reaching a maximum of 470.8 mg / g at pH = 3. In summary, the pH value of the molybdenum ion solution is an important parameter in the adsorption process, because pH not only affects the chemical properties and existence form of molybdenum in the aqueous solution, but also affects the charge and active sites on the surface of the composite aerogel.

[0087] In addition, this application takes Example 1 (when the mass of ZIF-8-NH2 is 500 mg) as an example, and the morphology and microstructure of the composite aerogel prepared in Example 1 (when the mass of ZIF-8-NH2 is 500 mg) are described and tested using a scanning electron microscope. The distribution diagram of the composite aerogel under electron microscope scanning is as follows: Figure 4 As shown in the figure, it can be seen that the sample presents a three-dimensional network structure, and the interconnected skeleton structure forms countless pores. The specific surface area test shows that its specific surface area is 499.5cm 2 / g, that is, the composite aerogel in this application is conducive to exposing more binding sites through the physical and chemical cross-linking network, which is beneficial to the mass transfer of molybdenum and promotes the removal process. The high concentration of N element in the sample further indicates that the composite material containing a large amount of amino groups is successfully introduced into the aerogel.

[0088] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some or all of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present invention, and they should all be included in the scope of the claims and description of the present invention.

Claims

1. A method for preparing a composite aerogel of post-modified amino-modified ZIF-8 and cellulose, characterized in that: The steps include: 1) adding ZIF-8 powder and 3-aminopropyltriethoxysilane to anhydrous ethanol, stirring the mixture thoroughly, centrifuging, washing, and drying the mixture to obtain amino-modified ZIF-8; 2) adding orange peel powder to an alkaline solution, heating and mechanically stirring, washing and drying to obtain cellulose powder, then adding the cellulose powder to a mixed solution of 2,2,6,6-tetramethylpiperidinyl oxide, NaBr, and NaClO, mechanically stirring, washing and drying to obtain pretreated cellulose powder, and then adding the pretreated cellulose powder to deionized water to obtain a cellulose suspension; 3) adding the amino-modified ZIF-8 to the cellulose suspension and mixing uniformly, and then adding polyethyleneimine and mechanically stirring to obtain a mixed solution; 4) adding a crosslinking agent dropwise into the mixed solution to perform a crosslinking reaction to obtain a composite hydrogel; 5) The composite hydrogel is sealed, heated, and baked, and then washed with deionized water and dried to obtain the composite aerogel.

2. The method for preparing the composite aerogel of post-modified amino ZIF-8 and cellulose according to claim 1, characterized in that: The mass ratio of the ZIF-8 powder, 3-aminopropyltriethoxysilane and anhydrous ethanol in step 1) is 1:(5-15):(20-40).

3. The method for preparing the composite aerogel of post-modified amino ZIF-8 and cellulose according to claim 1, characterized in that: In step 2), the mass ratio of the orange peel powder to the alkaline solution is 1:(10-20), and the molar concentration of the alkaline solution is 0.1-0.5 mol / L.

4. The method for preparing the composite aerogel of post-modified amino ZIF-8 and cellulose according to claim 1, characterized in that: In step 2), based on the preparation of 15 ml of cellulose suspension, the cellulose suspension includes the following components: cellulose powder, 2,2,6,6-tetramethylpiperidinyl oxide, NaBr and NaClO in a mass ratio of 1: (0.1-0.3): (0.1-0.2): (0.5-1.5).

5. The method for preparing the composite aerogel of post-modified amino ZIF-8 and cellulose according to claim 4, characterized in that: The ratio of the amino-ZIF-8, polyethyleneimine and cellulose suspension is 1g:(5-15)g:(30-50)ml; and the mass ratio of the cellulose suspension to deionized water is (1-3):(97-99); the polyethyleneimine is a branched polyethyleneimine.

6. The method for preparing the composite aerogel of post-modified amino ZIF-8 and cellulose according to claim 4, characterized in that: The cross-linking agent is a 10 wt% epichlorohydrin solution.

7. The method for preparing the composite aerogel of post-modified amino ZIF-8 and cellulose according to claim 4, characterized in that: In step 5), the heating conditions are: the heating temperature is 50-70°C and the time is 10-15 hours; the drying includes pre-freezing and freeze-drying performed in sequence: the pre-freezing temperature is -20°C to -196°C and the pre-freezing time is 0.5 to 6 hours; the freeze-drying temperature is -50°C to -40°C, the freeze-drying pressure is 2 to 50 Pa, and the freeze-drying time is 6 to 48 hours.

8. The method for preparing the composite aerogel of post-modified amino ZIF-8 and cellulose according to claim 4, characterized in that: The mechanical stirring speed in step 3) is 1000-2000 r / min, and the time is 25-35 min.

9. A composite aerogel prepared by the method for preparing a composite aerogel of post-modified amino-modified ZIF-8 and cellulose according to claims 1 to 8, wherein the amount of amino-modified ZIF-8 contained in the composite aerogel is 100-600 mg, and the interior of the composite aerogel is a three-dimensional network structure composed of interconnected skeleton structures, and the specific surface area of ​​the three-dimensional network structure is 400-550 cm 2 / g.

10. Use of the composite aerogel of post-modified amino-modified ZIF-8 and cellulose according to claim 9 in the field of molybdenum ion adsorption.

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