Biomass composite aerogel for in-situ growth of ZIF-8, preparation of biomass composite aerogel and application of biomass composite aerogel in oil-water separation

Abstract

The invention discloses a biomass composite aerogel for in-situ growth of ZIF-8 and preparation and application of the biomass composite aerogel in oil-water separation. The preparation method comprises the following steps: dissolving cellulose, lignin and inorganic zinc salt into an alkali solution, adding a cross-linking agent, and standing to form chemically cross-linked inorganic zinc salt / lignin / cellulose composite hydrogel; and soaking the composite hydrogel in a 2-methylimidazole aqueous solution to obtain the ZIF-8 (at) lignin / cellulose biomass composite aerogel. According to the invention, lignin is introduced into an aerogel skeleton constructed by cellulose, so that a large number of chelation sites are provided for growth of ZIF-8, and the mechanical strength and surface roughness of the composite aerogel are improved; through the ZIF-8 mineralized coating grown in situ, the problems of poor water stability of a biomass aerogel matrix and reusability of MOF nanoparticles are solved; the composite aerogel with a uniform porous structure is obtained by the method and is endowed with excellent oil-water separation performance.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of environmental protection materials, and particularly relates to a biomass composite aerogel in-situ grown with ZIF-8 and a preparation method and application thereof in oil-water separation. BACKGROUND

[0002] With the acceleration of industrialization and the extensive use of oil resources, oil pollution has become one of the global environmental problems. Oily sewage has a great impact on our life, production and ecological environment, and oil leakage accidents have caused great damage and influence on our social and economic activities, fisheries, marine environment, etc. Therefore, efficient oil-water separation technology is crucial for protecting water resources and the ecological environment. Although the traditional oil-water separation method can achieve a certain degree of separation, it often has problems such as low efficiency, high energy consumption and easy clogging when facing complex working conditions. Aerogel is a potential high-efficiency water pollution remediation material due to its low density, high specific surface area, high pore volume and easy surface modification. Especially biomass aerogel has the advantages of wide raw material sources, environmental friendliness and biodegradability. Therefore, finding a green, biodegradable, efficient and environmentally friendly method with a simple preparation process has attracted people's attention.

[0003] Cellulose is the most widely used and most abundant polysaccharide in nature. It has many active functional groups such as hydroxyl and epoxy groups, thereby providing active sites for forming a special wettable surface in cellulose-based oil-water separation materials. Cellulose aerogel is a three-dimensional porous material with the characteristics of large specific surface area, rich porosity, low mass density and high adsorption capacity, and has great application potential in the field of oil-water separation and will not cause secondary environmental pollution.

[0004] Lignin is the second largest biomass resource in the world after cellulose. Unlike the molecular structure of cellulose, lignin is a natural three-dimensional polyphenylpropane rigid structure with abundant oxygen-containing functional groups in nature. It can be cross-linked with cellulose under certain conditions to form a higher cross-linking density skeleton structure and improve the application performance, so it is an ideal modifier of cellulose aerogel. As a typical metal-organic framework material, ZIF-8 (zeolitic imidazolate framework-8) has great potential in wastewater purification due to its unique physical and chemical properties. However, as a powdery crystal material, ZIF-8 is easy to agglomerate after adsorption and difficult to recover, which greatly limits its practical application. Fixing ZIF-8 on polysaccharide material matrix (such as cellulose, chitosan, algae, etc.) is an effective strategy to solve the problems of small particle size, difficult recovery and easy agglomeration of ZIF-8. However, the active sites on the surface of these biomasses may not be able to effectively induce or control the nucleation of ZIF-8, resulting in a large number of ZIF-8 crystals nucleating and growing in the solution homogeneously rather than preferentially on the surface of biomasses heterogeneously. Therefore, how to prepare biomass / ZIF-8 composite materials, make ZIF-8 crystals nucleate and grow on the surface of biomasses heterogeneously, and improve the oil-water separation performance of the composite materials needs to be solved. SUMMARY

[0005] In order to solve the shortcomings and deficiencies of the prior art, the primary purpose of the present application is to provide a preparation method of biomass composite aerogel with in-situ growth of ZIF-8, which is economical and environmentally friendly in raw materials, simple in preparation process and excellent in product performance.

[0006] Another purpose of the present application is to provide a biomass composite aerogel with in-situ growth of ZIF-8 prepared by the above preparation method.

[0007] Still another purpose of the present application is to provide the application of the above biomass composite aerogel with in-situ growth of ZIF-8 in oil-water separation.

[0008] In order to achieve the purpose of the present application, the following technical solutions are adopted:

[0009] In the first aspect, the present application provides a preparation method of biomass composite aerogel with in-situ growth of ZIF-8, comprising the following steps:

[0010] (1) Dissolve cellulose, lignin and inorganic zinc salt into an alkaline solution and stir to obtain a uniform mixed solution;

[0011] (2) Add a cross-linking agent to the uniform mixed solution and stir, and then form a chemically cross-linked inorganic zinc salt / lignin / cellulose composite hydrogel after standing;

[0012] (3) soaking the inorganic zinc salt / lignin / cellulose composite hydrogel in 2-methylimidazole aqueous solution for 12-24 h, washing, freeze-drying to obtain biomass composite aerogel of ZIF-8@lignin / cellulose.

[0013] Preferably, the lignin in step (1) is alkali lignin.

[0014] Preferably, the cellulose in step (1) is hydroxyethyl cellulose.

[0015] Preferably, the alkali in the alkali solution in step (1) is at least one of potassium hydroxide and sodium hydroxide.

[0016] Preferably, the concentration of the alkali solution in step (1) is 5-10 wt%, which can be 5 wt%, 5.5 wt%, 6 wt%, 6.5 wt%, 7 wt%, 7.5 wt%, 8 wt%, 8.5 wt%, 9 wt%, 9.5 wt%, 10 wt%, etc., and any other specific point value in the numerical range can be selected, which will not be repeated here.

[0017] Preferably, the mass ratio of lignin to cellulose in step (1) is (3-5):2 (for example, 3:2, 3.5:2, 4:2, 4.5:2, 5:2, etc.), and any other specific point value in the numerical range can be selected, which will not be repeated here.

[0018] Preferably, the inorganic zinc salt in step (1) is at least one of anhydrous zinc acetate, dihydrate zinc acetate, zinc chloride and zinc nitrate, and more preferably anhydrous zinc acetate.

[0019] Preferably, the ratio of the molar amount of the inorganic zinc salt to the mass of cellulose in step (1) is 0.5-2 mmol:0.2 g (for example, 0.5 mmol:0.2 g, 0.6 mmol:0.2 g, 0.7 mmol:0.2 g, 0.8 mmol:0.2 g, 0.9 mmol:0.2 g, 1.0 mmol:0.2 g, 1.1 mmol:0.2 g, 1.2 mmol:0.2 g, 1.3 mmol:0.2 g, 1.4 mmol:0.2 g, 1.5 mmol:0.2 g, 1.6 mmol:0.2 g, 1.7 mmol:0.2 g, 1.8 mmol:0.2 g, 1.9 mmol:0.2 g, 2.0 mmol:0.2 g, etc.), and any other specific point value in the numerical range can be selected, which will not be repeated here.

[0020] Preferably, the ratio of the mass of the cellulose and the volume of the alkali solution in step (1) is (0.15-0.3) g: 10 mL (e.g. 0.15 g: 10 mL, 0.2 g: 10 mL, 0.25 g: 10 mL, 0.3 g: 10 mL, etc.), and any other specific point value within the numerical range can be selected, which is not convenient to repeat here.

[0021] Preferably, the crosslinking agent in step (2) is at least one of epichlorohydrin, N,N'-methylenebisacrylamide and glutaraldehyde, and more preferably epichlorohydrin.

[0022] Preferably, the ratio of the volume of the crosslinking agent and the mass of the cellulose in step (2) is (0.3-1.2) mL: 0.2 g (e.g. 0.3 mL: 0.2 g, 0.4 mL: 0.2 g, 0.5 mL: 0.2 g, 0.6 mL: 0.2 g, 0.7 mL: 0.2 g, 0.8 mL: 0.2 g, 0.9 mL: 0.2 g, 1.0 mL: 0.2 g, 1.1 mL: 0.2 g, 1.2 mL: 0.2 g, etc.), and any other specific point value within the numerical range can be selected, which is not convenient to repeat here.

[0023] Preferably, the standing time in step (2) is 12-36 h (e.g. 12 h, 13 h, 14 h, 15 h, 16 h, 17 h, 18 h, 19 h, 20 h, 21 h, 22 h, 23 h, 24 h, 25 h, 26 h, 27 h, 28 h, 29 h, 30 h, 31 h, 32 h, 33 h, 34 h, 35 h, 36 h, etc.), and any other specific point value within the numerical range can be selected, which is not convenient to repeat here.

[0024] Preferably, the ratio of the amount of the inorganic zinc salt / lignin / cellulose composite hydrogel and 2-methylimidazole in step (3) is 12 g: (20-30) mL (e.g. 12 g: 20 mL, 12 g: 22 mL, 12 g: 24 mL, 12 g: 25 mL, 12 g: 28 mL, 12 g: 30 mL, etc.), and any other specific point value within the numerical range can be selected, which is not convenient to repeat here.

[0025] Preferably, the aqueous solution of 2-methylimidazole in step (3), wherein the ratio of the mass of 2-methylimidazole and the volume of water is (1-2) g: 25 mL (e.g. 1 g: 25 mL, 1.1 g: 25 mL, 1.2 g: 25 mL, 1.3 g: 25 mL, 1.4 g: 25 mL, 1.5 g: 25 mL, 1.6 g: 25 mL, 1.7 g: 25 mL, 1.8 g: 25 mL, 1.9 g: 25 mL, 2 g: 25 mL, etc.), and any other specific point value within the numerical range can be selected, which is not convenient to repeat here.

[0026] Preferably, the inorganic zinc salt / lignin / cellulose composite hydrogel of step (3) is soaked in the aqueous 2-methylimidazole solution for 12 h, 13 h, 14 h, 15 h, 16 h, 17 h, 18 h, 19 h, 20 h, 21 h, 22 h, 23 h, 24 h, or any other specific point value within the range of 12-24 h, which is not listed here again.

[0027] Preferably, the washing of step (3) is water washing, the freeze-drying temperature is -30 to -60℃ (for example, -30℃, -33℃, -35℃, -38℃, -40℃, -43℃, -45℃, -48℃, -50℃, -53℃, -55℃, -58℃, -60℃, etc.), and the time is 36-60 h (for example, 36 h, 37 h, 38 h, 39 h, 40 h, 41 h, 42 h, 43 h, 44 h, 45 h, 46 h, 47 h, 48 h, 49 h, 50 h, 51 h, 52 h, 53 h, 54 h, 55 h, 56 h, 57 h, 58 h, 59 h, 60 h, etc.), and any other specific point value within the above numerical range can be selected, which is not listed here again.

[0028] In a second aspect, the present application provides a biomass composite aerogel with in-situ grown ZIF-8 prepared by the above method.

[0029] In a third aspect, the present application provides an application of the above biomass composite aerogel with in-situ grown ZIF-8 in the field of oil-water separation.

[0030] The mechanism of the present application is as follows:

[0031] The inorganic zinc salt, cellulose and lignin are dissolved in an alkaline solution, which can effectively break the hydrogen bonds between lignin and lignin, between cellulose and cellulose, and between cellulose and lignin, so that they are completely dissolved. The reaction mechanism of lignin and cellulose can be described as follows: the C-Cl bond in epichlorohydrin is broken to form a carbon cation, which reacts with the hydroxyl group of cellulose or lignin to form an aliphatic ether or an aromatic ether, thereby forming a dense cross-linked network. For the growth of ZIF-8, the lignin / cellulose matrix has abundant functional groups, and Zn 2+ which is anchored in the aerogel network through coordination and electrostatic interaction. Subsequently, the ZIF-8 crystals grow in-situ on the lignin / cellulose matrix by reacting with the 2-methylimidazole solution. The abundant growth points on the surface of the lignin / cellulose matrix can guide the formation of nanoparticles, limit the aggregation of the formed nanoparticles, and promote the formation of well-dispersed, small-sized ZIF-8 crystals on the surface. Finally, the prepared composite hydrogel is freeze-dried, and the pores become larger due to the sublimation of ice crystals to obtain a composite aerogel.

[0032] Compared with the prior art, the present application has the following advantages and beneficial effects:

[0033] (1) The present application introduces lignin into the aerogel skeleton constructed by cellulose, provides a large number of chelating sites for the growth of ZIF-8, improves the mechanical strength and surface roughness of the composite aerogel, thereby constructing a super-wetting surface for separating oil-water mixtures.

[0034] (2) The present application solves the problems of poor water stability of the biomass aerogel matrix and poor reusability of MOF nanoparticles through the in-situ grown ZIF-8 mineralized coating.

[0035] (3) The present application optimizes the pore structure of the composite aerogel by adjusting the ratio of ZIF-8 and lignin, obtains a uniform pore structure, and thereby endows the composite aerogel with excellent oil-water separation performance. BRIEF DESCRIPTION OF DRAWINGS

[0036] Figure 1 For the performance diagram of the composite aerogel prepared in Examples 1-9, Comparative Examples 1-2 and 6 for separating liquid paraffin / water mixtures, it can be observed that the aerogel has excellent oil-water separation capacity.

[0037] Figure 2 For the performance diagram of the composite aerogel prepared in Example 2 for separating different types of oil (liquid paraffin, cyclohexane, n-hexane, soybean oil) / water mixtures, excellent separation flux (>15500 L·m -2 ·h -1 ) and separation efficiency (>99.9%) are exhibited.

[0038] Figure 3 The separation performance of the composite aerogel prepared in Example 2 for separating paraffin / water mixtures for 10 cycles.

[0039] Figure 4 The internal scanning electron microscope image and the pore size distribution graph of the composite aerogel prepared in Example 2.(Cross-section (a), high-magnification graph of cross-section (b), cross-section pore size analysis graph (c); longitudinal section (d)).

[0040] Figure 5 The infrared spectrum of the composite aerogel prepared in Examples 1, 2, 3, Comparative Examples 1, 2, 5, 6.

[0041] Figure 6 The XRD spectrum of Example 2, Comparative Example 6, as can be seen from the figure, the characteristic diffraction peak of ZIF-8 crystal can be clearly detected in Gel4, confirming that the ZIF-8 with high crystal structure is successfully incorporated into the aerogel matrix.

[0042] Figure 7The water contact angle test figure of the composite aerogel prepared in Example 2 can be observed to require 2 milliseconds for the aerogel to completely absorb a 5 μL water droplet, and the WCA is approximately 0°, indicating that the material surface has superhydrophilicity.

[0043] Figure 8 The underwater oil contact angle of the composite aerogel prepared in Example 2 is greater than 152.2°, and the material surface exhibits underwater superoleophobicity (UOCA > 150°).

[0044] Figure 9 The compressive stress-strain curve (a) and the compression modulus (b) of the composite aerogel prepared in Example 2 and Comparative Example 5 indicate that the composite aerogel has excellent mechanical properties.

[0045] Figure 10 The actual figure of the composite aerogel prepared in Example 2 indicates that the composite aerogel has an ultralow density. DETAILED DESCRIPTION

[0046] The application will be described in further detail below with reference to the embodiments and the accompanying drawings, but the embodiments of the application are not limited thereto.

[0047] In the embodiments of the application, specific conditions not specified are carried out according to conventional conditions or the conditions recommended by the manufacturer. The raw materials, reagents and the like used, for which the manufacturer is not specified, are all conventional products that can be obtained by purchase on the market.

[0048] The lignin used in the following examples and comparative examples is alkali lignin; the cellulose is hydroxyethyl cellulose.

[0049] Comparative Example 1

[0050] 0.2 g of cellulose, 0.1 g of lignin and 1 mmol of anhydrous zinc acetate were dissolved in 10 mL of a 10 wt% sodium hydroxide solution, stirred uniformly, 0.6 mL of epichlorohydrin was added, and then it was transferred into a mold and left to stand for 24 h to completely gel to obtain an inorganic zinc salt / lignin / cellulose composite hydrogel. 12 g of the composite hydrogel was soaked in 25 mL of a 2-methylimidazole solution (the ratio of the mass of 2-methylimidazole to the volume of water is 1.5:25 (g / mL)), and soaked for 24 h to obtain a ZIF-8@lignin / cellulose composite hydrogel, which was washed with water for 3 times, and freeze-dried at -30 °C for 36 h to obtain a biomass composite aerogel of ZIF-8@lignin / cellulose, which was named as Gel1.

[0051] Comparative Example 2

[0052] Dissolve 0.2 g cellulose, 0.2 g lignin, 1 mmol zinc acetate into 10 mL 10 wt% sodium hydroxide solution, stir uniformly, add 0.6 mL epichlorohydrin, then transfer it into a mold and stand for 24 h to completely gel to obtain inorganic zinc salt / lignin / cellulose composite hydrogel. Soak 12 g of composite hydrogel in 25 mL 2-methylimidazole solution (the ratio of the mass of 2-methylimidazole and the volume of water is 1.5:25 (g / mL)), soak for 24 h to obtain ZIF-8@lignin / cellulose composite hydrogel, rinse with water for 3 times, freeze-dry at -30 °C for 36 h to obtain biomass composite aerogel of ZIF-8@lignin / cellulose, named as Gel2.

[0053] Example 1

[0054] Dissolve 0.2 g cellulose, 0.3 g lignin, 1 mmol zinc acetate into 10 mL 10 wt% sodium hydroxide solution, stir uniformly, add 0.6 mL epichlorohydrin, then transfer it into a mold and stand for 24 h to completely gel to obtain inorganic zinc salt / lignin / cellulose composite hydrogel. Soak 12 g of composite hydrogel in 25 mL 2-methylimidazole solution (the ratio of the mass of 2-methylimidazole and the volume of water is 1.5:25 (g / mL)), soak for 24 h to obtain ZIF-8@lignin / cellulose composite hydrogel, rinse with water for 3 times, freeze-dry at -30 °C for 36 h to obtain biomass composite aerogel of ZIF-8@lignin / cellulose, named as Gel3.

[0055] Example 2

[0056] Dissolve 0.2 g cellulose, 0.4 g lignin, 1 mmol zinc acetate into 10 mL 10 wt% sodium hydroxide solution, stir uniformly, add 0.6 mL epichlorohydrin, then transfer it into a mold and stand for 24 h to completely gel to obtain inorganic zinc salt / lignin / cellulose composite hydrogel. Soak 12 g of composite hydrogel in 25 mL 2-methylimidazole solution (the ratio of the mass of 2-methylimidazole and the volume of water is 1.5:25 (g / mL)), soak for 24 h to obtain ZIF-8@lignin / cellulose composite hydrogel, rinse with water for 3 times, freeze-dry at -30 °C for 36 h to obtain biomass composite aerogel of ZIF-8@lignin / cellulose, named as Gel4.

[0057] Example 3

[0058] Dissolve 0.2 g cellulose, 0.5 g lignin, 1 mmol zinc acetate in 10 mL 10 wt% sodium hydroxide solution, stir uniformly, add 0.6 mL epichlorohydrin, then transfer it to a mold and stand for 24 h to completely gel to obtain inorganic zinc salt / lignin / cellulose composite hydrogel. Soak 12 g of composite hydrogel in 25 mL of 2-methylimidazole solution (the ratio of the mass of 2-methylimidazole to the volume of water is 1.5:25 (g / mL)), soak for 24 h to obtain ZIF-8@lignin / cellulose composite hydrogel, rinse with water for 3 times, freeze-dry at -30 °C for 36 h to obtain biomass composite aerogel of ZIF-8@lignin / cellulose, named as Gel5.

[0059] Example 4

[0060] Dissolve 0.2 g cellulose, 0.5 g lignin, 1 mmol zinc acetate in 10 mL 10 wt% sodium hydroxide solution, stir uniformly, add 0.6 mL epichlorohydrin, then transfer it to a mold and stand for 24 h to completely gel to obtain inorganic zinc salt / lignin / cellulose composite hydrogel. Soak 12 g of composite hydrogel in 25 mL of 2-methylimidazole solution (the ratio of the mass of 2-methylimidazole to the volume of water is 1.5:25 (g / mL)), soak for 24 h to obtain ZIF-8@lignin / cellulose composite hydrogel, rinse with water for 3 times, freeze-dry at -30 °C for 36 h to obtain biomass composite aerogel of ZIF-8@lignin / cellulose, named as Gel5.

[0061] Example 5

[0062] Dissolve 0.2 g cellulose, 0.5 g lignin, 1 mmol zinc acetate in 10 mL 10 wt% sodium hydroxide solution, stir uniformly, add 0.6 mL epichlorohydrin, then transfer it to a mold and stand for 24 h to completely gel to obtain inorganic zinc salt / lignin / cellulose composite hydrogel. Soak 12 g of composite hydrogel in 25 mL of 2-methylimidazole solution (the ratio of the mass of 2-methylimidazole to the volume of water is 1.5:25 (g / mL)), soak for 24 h to obtain ZIF-8@lignin / cellulose composite hydrogel, rinse with water for 3 times, freeze-dry at -30 °C for 36 h to obtain biomass composite aerogel of ZIF-8@lignin / cellulose, named as Gel5.

[0063] Example 6

[0064] Dissolve 0.2 g cellulose, 0.4 g lignin, 1 mmol zinc acetate dihydrate into 10 mL of 10 wt% sodium hydroxide solution, stir uniformly, add 0.6 mL of epichlorohydrin, then transfer it into a mold and stand for 24 h to completely gel to obtain inorganic zinc salt / lignin / cellulose composite hydrogel. Soak 12 g of composite hydrogel in 25 mL of 2-methylimidazole solution (the ratio of the mass of 2-methylimidazole to the volume of water is 1.5:25 (g / mL)), soak for 24 h to obtain ZIF-8@lignin / cellulose composite hydrogel, rinse with water for 3 times, freeze-dry at -30 °C for 36 h to obtain biomass composite aerogel of ZIF-8@lignin / cellulose, named as Gel8.

[0065] Example 7

[0066] Dissolve 0.2 g cellulose, 0.4 g lignin, 1 mmol zinc acetate dihydrate into 10 mL of 10 wt% sodium hydroxide solution, stir uniformly, add 0.6 mL of epichlorohydrin, then transfer it into a mold and stand for 24 h to completely gel to obtain inorganic zinc salt / lignin / cellulose composite hydrogel. Soak 12 g of composite hydrogel in 25 mL of 2-methylimidazole solution (the ratio of the mass of 2-methylimidazole to the volume of water is 1.5:25 (g / mL)), soak for 24 h to obtain ZIF-8@lignin / cellulose composite hydrogel, rinse with water for 3 times, freeze-dry at -30 °C for 36 h to obtain biomass composite aerogel of ZIF-8@lignin / cellulose, named as Gel9.

[0067] Example 8

[0068] Dissolve 0.2 g cellulose, 0.4 g lignin, 1 mmol zinc acetate dihydrate into 10 mL of 10 wt% sodium hydroxide solution, stir uniformly, add 0.6 mL of epichlorohydrin, then transfer it into a mold and stand for 24 h to completely gel to obtain inorganic zinc salt / lignin / cellulose composite hydrogel. Soak 12 g of composite hydrogel in 25 mL of 2-methylimidazole solution (the ratio of the mass of 2-methylimidazole to the volume of water is 1.5:25 (g / mL)), soak for 24 h to obtain ZIF-8@lignin / cellulose composite hydrogel, rinse with water for 3 times, freeze-dry at -30 °C for 36 h to obtain biomass composite aerogel of ZIF-8@lignin / cellulose, named as Gel10.

[0069] Example 9

[0070] Dissolve 0.2 g cellulose, 0.4 g lignin, 1 mmol zinc acetate into 10 mL 10 wt% sodium hydroxide solution, stir uniformly, add 0.6 mL glutaraldehyde, then transfer it into a mold and stand for 24 h to completely gel to obtain inorganic zinc salt / lignin / cellulose composite hydrogel. Soak 12 g of the composite hydrogel in 25 mL 2-methylimidazole solution (the ratio of the mass of 2-methylimidazole to the volume of water is 1.5:25 (g / mL)), soak for 24 h to obtain ZIF-8@lignin / cellulose composite hydrogel, rinse with water for 3 times, freeze-dry at -30 °C for 36 h to obtain biomass composite aerogel of ZIF-8@lignin / cellulose, named as Gel11.

[0071] Comparative Example 3

[0072] Dissolve 0.2 g cellulose, 0.4 g lignin into 10 mL 10 wt% sodium hydroxide solution, stir uniformly, add 0.6 mL epichlorohydrin, then transfer it into a mold and stand for 24 h to completely gel to obtain lignin / cellulose hydrogel. Soak 12 g of the composite hydrogel in 10 mL 0.1 mol / L zinc acetate aqueous solution for 24 h, then soak in 2-methylimidazole solution (the ratio of the mass of 2-methylimidazole to the volume of water is 1.5:25 (g / mL)), soak for 24 h to obtain ZIF-8@lignin / cellulose composite hydrogel, rinse with water for 3 times, freeze-dry at -30 °C for 36 h to obtain biomass composite aerogel of ZIF-8@lignin / cellulose, named as Gel12.

[0073] Comparative Example 4

[0074] Dissolve 0.2 g cellulose, 0.4 g lignin into 10 mL 10 wt% sodium hydroxide solution, stir uniformly, add 0.6 mL epichlorohydrin, then transfer it into a mold and stand for 24 h to completely gel to obtain lignin / cellulose hydrogel, rinse with water for 3 times, freeze-dry at -30 °C for 36 h to obtain lignin / cellulose aerogel. Soak 12 g of the composite aerogel in 10 mL 0.1 mol / L zinc acetate aqueous solution for 24 h, then soak in 2-methylimidazole solution (the ratio of the mass of 2-methylimidazole to the volume of water is 1.5:25 (g / mL)), soak for 24 h, rinse with water for 3 times, freeze-dry at -30 °C for 36 h to obtain biomass composite aerogel of ZIF-8@lignin / cellulose, named as Gel13.

[0075] Comparative Example 5

[0076] 0.2 g of cellulose was dissolved in 10 mL of 10 wt% sodium hydroxide solution and stirred until homogeneous. 0.6 mL of epichlorohydrin was added, and the mixture was then transferred to a mold and allowed to stand for 24 h to completely gel, yielding a pure cellulose hydrogel. 12 g of the composite hydrogel was soaked in water for 24 h and then freeze-dried at -30℃ for 36 h to obtain a pure cellulose aerogel, named Gel14.

[0077] Comparative Example 6

[0078] 0.2 g of cellulose and 0.4 g of lignin were dissolved in 10 mL of 10 wt% sodium hydroxide solution and stirred until homogeneous. 0.6 mL of epichlorohydrin was then added, and the mixture was transferred to a mold and allowed to stand for 24 h to completely gel, yielding a lignin / cellulose hydrogel. 12 g of the composite hydrogel was immersed in water for 24 h and then freeze-dried at -30℃ for 36 h to obtain a lignin / cellulose aerogel, named Gel15.

[0079] Effect verification:

[0080] Separation performance test: At room temperature, the prepared composite aerogel was placed in the middle of the filtration device as a filter layer, and then 20 mL of a mixture of Sudan III stained oil and water (1:1 v / v) was poured into the separation device to test the oil-water separation performance.

[0081] The oil-water separation flux F(L·m) is calculated using the following formula. -2 ·h -1 ):

[0082]

[0083] Where V represents the volume of the filtrate (L), and A represents the filtration area of ​​the aerogel (m²). 2 ), where t represents the filtering time (h).

[0084] The separation efficiency E (%) is calculated according to the following formula:

[0085]

[0086] Where C0 and C f The concentrations of oil in the raw feed and filtrate are respectively measured by a total organic carbon analyzer.

[0087] The results are as follows Figure 1 As shown in Table 1, the separation flux and separation efficiency of oil-water separation (liquid paraffin / water mixture) of Gel1-Gel15 under gravity only are related values.

[0088] Table 1

[0089]

[0090] Figure 2 The performance chart of the composite aerogel prepared in Example 2 for separating different kinds of oil (liquid paraffin, cyclohexane, n-hexane, soybean oil) / water mixture shows excellent separation flux (>15500 L·m -2 ·h -1 ) and separation efficiency (>99.9%).

[0091] Figure 3 The separation performance of the composite aerogel prepared in Example 2 for separating paraffin / water mixture for 10 cycles, as can be seen from the figure, can reach 12000 L·m -2 ·h -1 The above, the separation of cyclohexane can reach 19498.2 L·m -2 ·h -1 , the separation efficiency is more than 99.9%.

[0092] The composite aerogel was characterized and analyzed by scanning electron microscopy, contact angle and compression test.

[0093] Figure 4 The internal scanning electron micrograph and pore size distribution chart of the composite aerogel prepared in Example 2 are shown in the figure. (Cross section (a), high magnification of cross section (b), cross section pore size analysis chart (c); longitudinal section (d)). As can be seen from the figure, the composite aerogel has a three-dimensional uniform pore structure (a), and a rough surface morphology, a large number of ZIF-8 particles grow uniformly and densely on the skeleton (b), indicating that ZIF-8 is successfully fixed on the biomass aerogel matrix; the pore size is analyzed, and the average ZIF-8@LCA-0.4 is 81.42±13.77 μm (c); element analysis further confirms that the ZIF-8 particles are uniformly distributed in the whole aerogel (e).

[0094] Figure 5 The infrared spectrum of the composite aerogel prepared in Examples 1, 2, 3, Comparative Examples 1, 2, 5, 6 is shown in the figure. The characteristic peaks of ZIF-8 are observed at 756 and 690 cm -1 , which are attributed to Zn-O and Zn-N bonds, respectively, while the peaks at 1310 and 1145 cm -1 are attributed to the C-N bond in the imidazole ring in the organic linker of Zn-MOF. The composite aerogel shows characteristic peaks of Zn-O, Zn-N and C-N bonds, and moves to different wave numbers, indicating that ZIF-8 has certain interaction with biomass aerogel.

[0095] Figure 6 The XRD spectrum of Example 2, Comparative Example 6 is shown in the figure. As can be seen from the figure, the characteristic diffraction peaks of ZIF-8 crystals can be clearly detected in Gel4, which confirms that the ZIF-8 with high crystal structure is successfully incorporated into the aerogel matrix.

[0096] Figure 7 The water contact angle test graph of the composite aerogel prepared in Example 2 can be observed that the time required for the aerogel to completely absorb a 5 μL water droplet is 2 milliseconds, and the WCA is approximately 0°, indicating that the surface of the material has superhydrophilicity.

[0097] Figure 8 The underwater oil contact angle of the composite aerogel prepared in Example 2 is greater than 152.2°, and the surface of the material exhibits underwater superoleophobicity (UOCA > 150°).

[0098] Figure 9 The compressive stress-strain curve (a) and the compressive modulus (b) of the composite aerogel prepared in Example 2 and Comparative Example 5, the compressive modulus of Gel4 is 1.946 MPa, and the specific compressive modulus is 22.347 MPa·g -1 ·cm -3 , which is about 3.5 times higher than the compressive modulus of Gel14, indicating that the composite aerogel has excellent mechanical properties.

[0099] Figure 10 The physical map of the composite aerogel prepared in Example 2 indicates that the composite aerogel has an ultra-low density.

[0100] The above examples are the preferred embodiments of the present application, but the embodiments of the present application are not limited by the above examples, and any changes, modifications, substitutions, combinations, simplifications made without departing from the spirit and principles of the present application are equivalent replacement methods and are included in the protection scope of the present application.

Claims

1. A method for preparing a biomass composite aerogel with in-situ grown ZIF-8, characterized in that, The method comprises the following steps: (1) dissolving cellulose, lignin and inorganic zinc salt into an alkali solution to obtain a mixed solution; (2) adding a crosslinking agent into the mixed solution and uniformly mixing, and then standing to form a chemically crosslinked inorganic zinc salt / lignin / cellulose composite hydrogel; (3) soaking the inorganic zinc salt / lignin / cellulose composite hydrogel in a 2-methylimidazole aqueous solution, washing, and freeze-drying to obtain a biomass composite aerogel of ZIF-8@lignin / cellulose.

2. The method according to claim 1, wherein the biomass composite aerogel is prepared by in-situ growth of ZIF-8. The mass ratio of the lignin to the cellulose in step (1) is (3-5):

2.

3. The method for preparing an in-situ grown ZIF-8 biomass composite aerogel according to claim 1 or 2, characterized in that, The molar amount of the inorganic zinc salt to the mass of the cellulose in step (1) is 0.5-2 mmol:0.2 g. And / or, the inorganic zinc salt in step (1) is at least one of anhydrous zinc acetate, zinc acetate dihydrate, zinc chloride and zinc nitrate.

4. The method according to claim 1 or 2, wherein the biomass composite aerogel is prepared by in-situ growth of ZIF-8. The usage ratio of the inorganic zinc salt / lignin / cellulose composite hydrogel to 2-methylimidazole in step (3) is 12 g:(20-30) mL. And / or, the 2-methylimidazole aqueous solution in step (3) has a ratio of the mass of 2-methylimidazole to the volume of water of (1-2) g:25 mL. And / or, the soaking time in step (3) is 12-24 h.

5. The method according to claim 1 or 2, wherein the biomass composite aerogel is prepared by in-situ growth of ZIF-8. The volume of the crosslinking agent to the mass of the cellulose in step (2) is (0.3-1.2) mL:0.2 g. And / or, the crosslinking agent in step (2) is at least one of epichlorohydrin, N,N'-methylenebisacrylamide and glutaraldehyde.

6. The method according to claim 1 or 2, wherein the biomass composite aerogel is prepared by in-situ growth of ZIF-8. The standing time in step (2) is 12-36 h.

7. The method according to claim 1 or 2, wherein the biomass composite aerogel is prepared by in-situ growth of ZIF-8. The alkali in the alkali solution in step (1) is at least one of potassium hydroxide and sodium hydroxide. And / or, the concentration of the alkali solution in step (1) is 5-10 wt%. And / or, the mass of the cellulose to the volume of the alkali solution in step (1) is (0.15-0.3) g:10 mL.

8. The method according to claim 1 or 2, wherein the biomass composite aerogel is prepared by in-situ growth of ZIF-8. The washing in step (3) is water washing, the freeze-drying temperature is -30 to -60℃, and the time is 36-60 h.

9. A biomass composite aerogel of in-situ grown ZIF-8 prepared by the method of any one of claims 1-8.

10. Application of the biomass composite aerogel of in-situ grown ZIF-8 of claim 9 in oil-water separation.

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