Functionalized magnetic cellulose aerogel as well as preparation method and application thereof

Abstract

The invention discloses functionalized magnetic cellulose aerogel as well as a preparation method and application thereof, and belongs to the technical field of aerogel materials. The functionalized magnetic cellulose aerogel is prepared by the following preparation method: extracting cellulose from agricultural wastes, adding the cellulose into an alkali urea solution, freezing, unfreezing, and uniformly mixing with modified iron cobalt oxygen powder to obtain a mixture; adding polyethyleneimine and a cross-linking agent to form hydrogel, and freeze-drying to obtain the functionalized magnetic cellulose aerogel, the modified Fe-Co-O is obtained by mixing Fe-Co-O nano-powder and a tannic acid aqueous solution for reaction. The aerogel is doped with the modified Fe-Co-O, the material is endowed with the magnetic response characteristic, the tannic acid attached to the surface of the Fe-Co-O can form hydrogen bond interaction with the micro / nano plastic, and benzene rings contained in the tannic acid are beneficial to form pi-pi interaction with aromatic rings in the micro / nano plastic, so that the magnetic response property of the material is improved. The rapid adsorption between the aerogel and the micro / nano plastic is promoted.

Description

Technical Field

[0001] The present invention relates to the technical field of aerogel materials, and more particularly to a functionalized magnetic cellulose aerogel and a preparation method and application thereof. Background Art

[0002] In recent years, with the large-scale production and use of plastic products, the global annual plastic production has exceeded 390 million tons, of which my country's production is 125 million tons, accounting for as high as 32%, ranking first in the world. However, the uncontrolled emission of plastics and the slow degradation process have caused a large amount of waste plastics to break into microplastics (MPs) with a particle size of less than 5 mm or even nanoplastics (NPs) less than 1 micron in the environment. These micro / nanoplastics are easy to adsorb toxic pollutants and accumulate through the food chain due to their small size, large specific surface area and strong mobility, posing a serious threat to aquatic ecosystems and human health. Therefore, how to quickly and efficiently remove micro / nanoplastics from water is of vital importance to protecting the ecological environment and human health.

[0003] In recent years, the use of biomass materials (e.g., cellulose, chitosan, and protein) to prepare novel adsorbents with excellent performance has attracted widespread research attention due to their remarkable non-toxicity, biodegradability, and modifiable properties. Biomass-based aerogel materials are considered ideal candidates for a new generation of high-efficiency adsorbents due to their high porosity, tunable surface functional groups, and environmental friendliness. Cellulose, as nature's most abundant renewable resource, can be extracted at low cost from agricultural waste (e.g., straw, pine sawdust), combining biodegradability with resource sustainability.

[0004] Chinese patent CN119161626A discloses a method for preparing a cellulose hybrid aerogel for adsorbing microplastics. The method comprises the following steps: extracting cellulose from agricultural solid waste, adding it to an alkaline urea solution, stirring and dispersing it, and freezing it at a temperature not exceeding -12°C. After thawing, vermiculite is added and stirred to obtain a mixture; adding an organic amine and a cross-linking agent to the mixture, stirring it to obtain a hydrogel, and freeze-drying it to obtain the cellulose hybrid aerogel. This cellulose hybrid aerogel exhibits an adsorption equilibrium time of 3 hours for polystyrene. However, this long adsorption equilibrium time prevents rapid adsorption, and further shortening the adsorption time is desirable. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the defects and shortcomings of the existing cellulose aerogels used for adsorbing microplastics, such as the long adsorption equilibrium time for micro / nano plastics, the inability to achieve rapid adsorption, and the need to further shorten the adsorption time. A functionalized magnetic cellulose aerogel is provided, which can achieve rapid adsorption of micro / nano plastics and shorten the adsorption time.

[0006] Another object of the present invention is to provide the use of the functionalized magnetic cellulose aerogel in adsorbing micro / nano plastics in water.

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

[0008] A functionalized magnetic cellulose aerogel, wherein the preparation method of the functionalized magnetic cellulose aerogel comprises the following steps:

[0009] Step S1. Extracting cellulose from agricultural waste, adding the cellulose to an alkaline urea solution, stirring and dispersing the cellulose, freezing the solution at a temperature not higher than -12°C, and then thawing the solution and uniformly mixing the solution with a modified iron cobalt oxide powder to obtain a mixture;

[0010] Step S2. adding polyethyleneimine and a cross-linking agent to the mixture, stirring evenly, allowing to stand to form a hydrogel, and freeze-drying to obtain the functionalized magnetic cellulose aerogel;

[0011] In step S1, the preparation method of the modified iron cobalt oxide comprises the following steps: mixing iron cobalt oxide nanopowder and tannic acid aqueous solution at 40-60° C. for 1-3 hours to obtain modified iron cobalt oxide powder;

[0012] In the iron-cobalt oxide, the molar ratio of cobalt to iron is (0.5-1):1;

[0013] The mass ratio of the cellulose, the modified iron cobalt oxide powder and the polyethyleneimine is 10:(1-3):(8-12).

[0014] The functionalized magnetic cellulose aerogel of the present invention is doped with tannic acid-modified iron cobalt oxide powder with a spinel structure. The modified iron cobalt oxide has a large specific surface area, and the tannic acid attached to the surface contains abundant hydroxyl groups, which can form hydrogen bond interactions with micro / nano plastics. At the same time, the benzene rings contained in the tannic acid are conducive to forming π-π interactions with the aromatic rings in the micro / nano plastics, promoting rapid adsorption between the material and the micro / nano plastics and shortening the adsorption time.

[0015] In the preparation method of modified iron cobalt oxide, metal chelation can occur between tannic acid and iron cobalt oxide nanopowder, so that tannic acid can be fixed to the iron cobalt oxide nanopowder. At the same time, due to the presence of tannic acid, the agglomeration between iron cobalt oxides is reduced, and they are better dispersed and fixed in the gel material.

[0016] In the modified iron cobalt oxide, the Co and Fe elements on the surface of the iron cobalt oxide can combine with tannic acid functional molecules and polyethyleneimine functional molecules through chelation, coordination and other effects, thereby improving the structural stability of the aerogel by uniformly dispersing it in the cellulose aerogel. In addition, the modified iron cobalt oxide also adds surface functional groups such as hydroxyl groups, which enhances the adsorption selectivity of micro / nano plastics through hydrogen bonds.

[0017] Modified iron cobalt oxide powder is a type of magnetic nanoparticle. By doping the functionalized magnetic cellulose aerogel of the present invention with modified iron cobalt oxide powder, the aerogel material possesses magnetic responsive properties while retaining high porosity and adsorption capacity. After adsorbing micro / nanoplastics, the aerogel can be rapidly separated and recovered using an external magnetic field, avoiding the risk of secondary contamination associated with traditional filtration or centrifugation methods. Magnetic separation technology simplifies the regeneration process of aerogel materials as adsorbents, and the magnetic aerogel can be reused after desorption, significantly reducing costs and improving sustainability.

[0018] At low temperatures, an alkaline urea solution disrupts hydrogen bonds within and between cellulose molecules, dissolving the cellulose. Polyethyleneimine (PEI) is a water-soluble, strongly positively charged organic polymer. Its backbone and side chains contain numerous amine groups, resulting in a high positive charge density. This makes it a cellulose modifier, effectively improving the adsorption properties of cellulose aerogels. Finally, cross-linking forms a stable three-dimensional network structure.

[0019] The aerogel of the present invention can be used to adsorb and remove micro / nano plastics in water. The aerogel of the present invention can form hydrogen bonds, π-π interactions and electrostatic interactions with micro / nano plastics, and has the characteristics of high adsorption capacity, green environmental protection, and rapid recycling and reuse.

[0020] The invention controls the ratio of cellulose and modified iron cobalt oxide powder, which is beneficial to the uniform dispersion of system components and improves the formability and structural stability of the aerogel.

[0021] When the amount of polyethyleneimine added is insufficient, the adsorption performance needs to be improved; when the amount of polyethyleneimine added is too large, due to the relatively large molecular weight of polyethyleneimine, it will cause the material to agglomerate in water, thereby affecting the adsorption performance of the material.

[0022] The functionalized magnetic cellulose aerogel of the present invention uses agricultural waste and modified iron cobalt oxide powder as raw materials, has a wide source, low cost and is green and environmentally friendly, and realizes the resource utilization of agricultural waste and magnetic nanoparticles.

[0023] The functionalized magnetic cellulose aerogel of the present invention has a simple preparation process, good stability and integrity, and is not prone to secondary pollution.

[0024] In step S1, in the preparation method of the modified iron cobalt oxide, after the mixing reaction is completed, the impurity removal and drying step is also included.

[0025] Preferably, the mass ratio of the cellulose, the modified iron cobalt oxide powder and the polyethyleneimine is 10:(2-3):(8-9), which has a more excellent adsorption performance.

[0026] Preferably, in step S1, the method for extracting cellulose from agricultural waste comprises the following steps: crushing the agricultural waste and placing it in a mixed aqueous dispersion containing hydrogen peroxide and iron oxide, reacting at 70-90°C for 1-2 hours to obtain cellulose powder.

[0027] Agricultural waste contains cellulose, hemicellulose, lignin, and some small molecules. The present method for extracting cellulose from agricultural waste uses hydroxyl radicals (·OH) produced by the Fenton reaction between hydrogen peroxide and iron oxide to selectively degrade most of the lignin, hemicellulose, and small molecules while preserving the integrity of the cellulose skeleton. This fully exposes the hydroxyl groups, significantly improving the purity and reactivity of the cellulose, resulting in a higher-purity cellulose. This lays the foundation for subsequent functional modification.

[0028] Preferably, in step S1, the method for extracting cellulose from agricultural waste comprises the following steps:

[0029] The agricultural waste is crushed, dispersed in an acid solution, and heated for reaction. The cellulose powder is then dispersed in an alkaline solution and heated for reaction. The cellulose powder is dried to obtain the cellulose powder. The acid solution may be a mixed solution of sodium chlorite and glacial acetic acid. The heating time in the acid solution may be 70-80°C for reaction for 4-6 hours. The alkaline solution may be a sodium hydroxide solution. The heating time in the alkaline solution may be 60-80°C for reaction for 2-4 hours.

[0030] The method for extracting cellulose from agricultural waste according to the present invention uses a Fenton method, which consumes fewer chemicals than an acid-base method and is environmentally friendly.

[0031] Moreover, when extracting cellulose using the acid-base method, strong acid / base treatment can easily destroy the structure of the cellulose itself, which can reduce the mechanical properties compared to cellulose extracted using the Fenton method.

[0032] The solid-to-liquid ratio of the agricultural waste and the mixed aqueous solution can be 1: (25-35) g / mL.

[0033] After the reaction is completed, the reaction mixture may be washed with water until the pH value is neutral and then dried in an oven.

[0034] The reagent residue and ash were removed by thorough washing with water and ethanol.

[0035] Preferably, in step S1, in the method for extracting cellulose from agricultural waste: in the mixed aqueous dispersion, the mass content of hydrogen peroxide is 27 wt% to 30 wt%, and the mass content of iron oxide is 2.5 wt% to 5 wt%.

[0036] Preferably, in step S1, the agricultural waste is crushed to 80-300 mesh.

[0037] Preferably, in step S1, the method for preparing the iron cobalt oxide nanopowder comprises the following steps: mixing iron salt, cobalt salt, sodium acetate and ethylene glycol for reaction, and drying to obtain the iron cobalt oxide nanopowder.

[0038] The temperature of the mixing reaction is 180 to 220° C., and the time of the mixing reaction is 6 to 8 hours.

[0039] The molar ratio of the iron salt to the sodium acetate is (0.002-0.004 mol): (0.088-0.176 mol).

[0040] The ratio of iron salt to ethylene glycol is (0.002-0.004 mol): (100-120) ml.

[0041] In step S1, in the method for preparing the iron cobalt oxide nanopowder, after the mixing reaction is completed, the method further includes an impurity removal and drying step.

[0042] Preferably, in step S1, the mass ratio of the iron cobalt oxide nanopowder to tannic acid is (2-6):(1-3), and the mass concentration of the tannic acid aqueous solution is 0.025 g / mL to 0.075 g / mL.

[0043] Preferably, in step S1, the agricultural waste is any one of pine wood powder, rice straw, stalks, corn cobs or sugarcane bagasse.

[0044] Preferably, in step S1, the components of the alkaline urea solution include: 5-10 wt% of sodium hydroxide and 10-14 wt% of urea.

[0045] Preferably, in step S1, the solid-to-liquid ratio of the cellulose and the alkaline urea solution is 0.020-0.032 g / mL.

[0046] Preferably, in step S1, the freezing temperature is -18 to -12°C, and the freezing time is 12 to 15 hours.

[0047] In some embodiments, the cross-linking agent may be a cross-linking agent commonly used in the art, such as an alkylene oxide cross-linking agent or an aldehyde cross-linking agent.

[0048] Preferably, in step S2, the cross-linking agent is epichlorohydrin or glutaraldehyde.

[0049] More preferably, the cross-linking agent is epichlorohydrin.

[0050] When epichlorohydrin is used as a cross-linking agent in the present invention, epichlorohydrin undergoes a ring-opening reaction in an alkaline environment, opening the epoxy group. The chloromethyl group at one end reacts with the hydroxyl group on the cellulose, and the epoxy group at the other end reacts with the amine group on the polyethyleneimine, thereby cross-linking the material to form a stable three-dimensional network structure.

[0051] Preferably, in step S2, the freezing temperature is -18 to -12°C, and the freezing time is 12 to 15 hours.

[0052] The present invention also protects the use of any of the functionalized magnetic cellulose aerogels described above in adsorbing micro / nano plastics in water.

[0053] Preferably, the micro / nano plastic is polystyrene microplastic or polystyrene nanoplastic.

[0054] The particle size of polystyrene microplastics is less than 5 mm. The particle size of polystyrene nanoplastics is less than 1 micron.

[0055] Compared with the prior art, the present invention has the following beneficial effects:

[0056] The present invention discloses a functionalized magnetic cellulose aerogel, in which modified iron cobalt oxide powder modified with tannic acid is doped. The tannic acid attached to the surface of the modified iron cobalt oxide contains abundant hydroxyl groups, which can form hydrogen bond interactions with micro / nano plastics. At the same time, the benzene rings contained in the tannic acid are conducive to forming π-π interactions with the aromatic rings in the micro / nano plastics, thereby promoting rapid adsorption between the material and the micro / nano plastics and shortening the adsorption time. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] Figure 1 These are physical pictures of the cellulose (FPC) aerogel of Comparative Example 1 and the functionalized magnetic cellulose aerogel (PEI-MFPC) material of Example 1; the left picture is the cellulose aerogel (FPC) of Comparative Example 1, and the right picture is the functionalized magnetic cellulose aerogel (PEI-MFPC) of Example 1.

[0058] Figure 2 These are the VSM diagrams of the functionalized magnetic cellulose aerogel (PEI-MFPC) material sample of Example 1 before and after adsorption.

[0059] Figure 3 FTIR spectra of each sample, wherein FPC is the cellulose aerogel of Comparative Example 1, MFPC is the cellulose aerogel doped with modified iron cobalt oxide of Comparative Example 2, and PEI-MFPC is the functionalized magnetic cellulose aerogel of Experimental Example 1.

[0060] Figure 4 This is the XRD pattern of Example 1; PEI-MFPC is the functionalized magnetic cellulose aerogel of Experimental Example 1.

[0061] Figure 5 Graph showing the adsorption data of PS at different initial concentrations by the functionalized magnetic cellulose aerogel (PEI-MFPC) of Example 1 and the cellulose aerogel (FPC) of Comparative Example 1.

[0062] Figure 6 This is the adsorption data of the functionalized magnetic cellulose aerogel (PEI-MFPC) of Example 1 for PS at different contact times.

[0063] Figure 7 This is the recycled adsorption data of the functionalized magnetic cellulose aerogel (PEI-MFPC) in Example 1. DETAILED DESCRIPTION

[0064] In order to more clearly and completely describe the technical solution of the present invention, the present invention is further described in detail through specific embodiments below. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. Various changes can be made within the scope of the rights of the present invention.

[0065] The present invention will be further described below in conjunction with specific embodiments. Experimental methods in the following examples where specific conditions are not specified are generally carried out in accordance with conventional conditions in the art or conditions recommended by the manufacturer. Raw materials, reagents, etc. used, unless otherwise specified, are all available on the market.

[0066] Example 1

[0067] A functionalized magnetic cellulose aerogel is prepared by the following preparation method:

[0068] Step S1.

[0069] 1) Extracting cellulose from agricultural solid waste, comprising the following steps:

[0070] The purchased pine powder was passed through an 80-mesh sieve, and 6 g of pine powder was evenly dispersed in 300 mL of a mixed aqueous dispersion containing 30 wt% hydrogen peroxide and 5 wt% iron oxide. The mixture was heated and stirred at 75°C for 1 hour. After the reaction, it was cooled to room temperature, and the unreacted impurities were removed by deionizing water. The mixture was washed with deionized water until the pH was neutral, and then transferred to an oven for drying to obtain pine cellulose (FPC) powder.

[0071] 2) The preparation method of modified iron cobalt oxide nanopowder is as follows:

[0072] Cobalt chloride (0.476g), ferric chloride (1.081g), and sodium acetate (7.2g) were mixed uniformly with 100ml of ethylene glycol at a molar ratio of 1:2:44 and reacted at 180°C for 8 hours. The mixture was then deionized with ethanol and dried to obtain a FeCoO nanopowder. The resulting FeCoO nanopowder was then mixed uniformly with tannic acid (0.5g) at a mass ratio of 2:1 with 20ml of deionized water. The mixture was then reacted at 50°C for 2 hours. The mixture was deionized and dried to obtain a tannic acid-modified FeCoO nanopowder. The average particle size of the modified FeCoO nanopowder was calculated to be 17nm using the Scherrer equation.

[0073] 3) Add cellulose to the alkaline urea solution, stir and disperse, and then pre-cool; after thawing, add the modified iron cobalt oxide powder and stir evenly to obtain a mixture:

[0074] Take 1.0g of the above-mentioned pine cellulose powder and disperse it in 25mL of alkaline urea (including 1.75g of sodium hydroxide, 3g of urea, and 20.25mL of deionized water). After stirring evenly, ultrasonically disperse it for 30min, and then transfer it to a -18°C refrigerator for precooling for 12h; after precooling, take it out and let it stand, thaw it to room temperature and stir it evenly to obtain dissolved pine cellulose; add 0.2g of the above-mentioned modified iron cobalt oxide powder while stirring, continue stirring until the modified iron cobalt oxide powder is evenly dispersed, and then ultrasonically disperse it for 30min to obtain a uniform pine cellulose / modified iron cobalt oxide mixture.

[0075] Step S2.

[0076] 4) adding polyethyleneimine and a cross-linking agent to the mixture in sequence, stirring evenly, and allowing the mixture to stand to form a hydrogel, washing and removing impurities, and freeze-drying the mixture to obtain the functionalized magnetic cellulose aerogel (PEI-MFPC) that can be used for rapid adsorption of micro / nano plastics.

[0077] 0.9 g of polyethyleneimine was dissolved in 2 mL of deionized water and added dropwise to the mixture of step S3. After stirring at room temperature for 1 hour, the mixture was ultrasonically dispersed for 10 minutes to obtain a uniform mixture. 3 mL of a cross-linking agent was slowly added under stirring, and the cross-linking agent was epichlorohydrin. After continuing to stir for 30 minutes, the mixture was transferred to a silica gel mold and allowed to stand for 12 hours to cross-link and form a hydrogel. The formed hydrogel was fully soaked and washed with deionized water to remove the reagent residue. It was then transferred to a refrigerator at -18°C and frozen for 12 hours, and then dried in a vacuum freeze dryer for 24 hours to obtain the functionalized magnetic cellulose aerogel.

[0078] In this embodiment, the mass ratio of pine cellulose powder, modified iron cobalt oxide powder and polyethyleneimine is 10:2:9.

[0079] Example 2

[0080] A functionalized magnetic cellulose aerogel prepared by a method different from that in Example 1 is prepared by using a mass ratio of pine cellulose powder, modified iron cobalt oxide powder, and polyethyleneimine of 10:3:9. Specifically, the mass of the pine cellulose powder is 1.0 g, the mass of the modified iron cobalt oxide powder is 0.3 g, and the mass of the polyethyleneimine is 0.9 g.

[0081] Example 3

[0082] A functionalized magnetic cellulose aerogel prepared by a method different from that of Example 1 is prepared by using a mass ratio of pine cellulose powder, modified iron cobalt oxide powder, and polyethyleneimine of 10:2:8. Specifically, the mass of the pine cellulose powder is 1.0 g, the mass of the modified iron cobalt oxide powder is 0.2 g, and the mass of the polyethyleneimine is 0.8 g.

[0083] Example 4

[0084] A functionalized magnetic cellulose aerogel prepared by a method different from that of Example 1 is prepared by using a mass ratio of pine cellulose powder, modified iron cobalt oxide powder, and polyethyleneimine of 8:2:9. Specifically, the mass of the pine cellulose powder is 0.8 g, the mass of the modified iron cobalt oxide powder is 0.2 g, and the mass of the polyethyleneimine is 0.9 g.

[0085] Example 5

[0086] A method for preparing an aerogel, which differs from Example 1 in that: the method for extracting cellulose from agricultural solid waste is as follows: 10 g of pine wood powder is uniformly dispersed in 300 mL of a mixed solution containing 4 wt% sodium chlorite and 3 wt% glacial acetic acid, heated and stirred at 75°C for 5 hours, cooled to room temperature after the reaction, and washed with deionized water until the pH is neutral; then the above product is dispersed in 200 mL of a 6 wt% sodium hydroxide solution, heated and stirred at 70°C for 3 hours, cooled to room temperature after the reaction, washed with deionized water until the pH is neutral, and then transferred to an oven for drying to obtain pine wood cellulose powder.

[0087] Example 6

[0088] A functionalized magnetic cellulose aerogel, the preparation method of which differs from that of Example 1 in that:

[0089] In the preparation method of modified iron cobalt oxide nanopowder, cobalt chloride (0.952 g) and ferric chloride (1.081 g) are used, that is, the molar ratio of cobalt to iron is 1:1.

[0090] Example 7

[0091] A functionalized magnetic cellulose aerogel, the preparation method of which differs from that of Example 1 in that: in the preparation method of the modified iron cobalt oxide nanopowder: the obtained iron cobalt oxide nanopowder and tannic acid (0.5 g) are mixed uniformly with 20 ml of deionized water in a mass ratio of 2:1, reacted at 40°C for 3 hours, and after impurities are removed and dried, tannic acid-modified iron cobalt oxide nanopowder is obtained.

[0092] Example 8

[0093] A functionalized magnetic cellulose aerogel, the preparation method of which differs from that of Example 1 in that: in the preparation method of the modified iron cobalt oxide nanopowder: the obtained iron cobalt oxide nanopowder and tannic acid (0.5 g) are mixed uniformly with 20 ml of deionized water in a mass ratio of 2:1, reacted at 60°C for 1 hour, and after impurities are removed and dried, tannic acid-modified iron cobalt oxide nanopowder is obtained.

[0094] Comparative Example 1

[0095] A method for preparing an aerogel is provided, which differs from Example 1 in that modified iron cobalt oxide and polyethyleneimine are not added during the preparation process of this comparative example. The prepared cellulose aerogel is referred to as FPC.

[0096] Comparative Example 2

[0097] A method for preparing an aerogel is provided, which differs from Example 1 in that no polyethyleneimine is added during the preparation process of this comparative example. The prepared aerogel is referred to as MFPC.

[0098] Comparative Example 3

[0099] A method for preparing an aerogel is different from Example 1 in that no crosslinking agent (epichlorohydrin) is added during the preparation process of this comparative example.

[0100] Comparative Example 4

[0101] A method for preparing an aerogel differs from Example 1 in that the method for preparing modified iron cobalt oxide nanopowder is modified as follows: 0.199 g of ferrous chloride, 1.081 g of ferric chloride, and 7.2 g of sodium acetate are uniformly mixed with 100 ml of ethylene glycol in a molar ratio of 1:2:44, reacted at 180°C for 8 hours, and then removed with deionized water and ethanol before drying to obtain ferroferric oxide nanopowder. The obtained ferroferric oxide nanopowder is uniformly mixed with 20-50 ml of deionized water in a mass ratio of 2:1 of tannic acid (0.5 g), reacted at 40-60°C for 1-3 hours, removed from impurities, and dried to obtain tannic acid-modified ferroferric oxide nanopowder.

[0102] Comparative Example 5

[0103] A method for preparing an aerogel, which differs from Example 1 in that the method for preparing modified iron cobalt oxide nanopowder is modified as follows: cobalt chloride (0.476 g), ferric chloride (1.081 g), and sodium acetate (7.2 g) are uniformly mixed with 100 ml of ethylene glycol in a molar ratio of 1:2:44, reacted at 180° C. for 8 hours, and then removed from impurities with deionized water and ethanol and dried to obtain the iron cobalt oxide nanopowder without being modified with tannic acid.

[0104] Result detection

[0105] 1. Material forming test

[0106] The forming state of the aerogels of Examples 1 to 4 and Comparative Examples 1 to 3 in the silica gel mold was observed; except for Comparative Example 3 which was still in a fluid state and did not form a hydrogel, the other hydrogels were in a good state, indicating that the addition of the crosslinking agent has a great influence on whether the material can be formed. Figure 1 As shown, the surface of the aerogel in Comparative Example 1 has many wrinkles and poor shaping; the surface of the aerogel in Example 1 is smooth and the overall shaping is good.

[0107] 2. VSM analysis

[0108] The vibrating sample magnetometer (VSM) was used to characterize the saturation magnetic field strength of the functionalized magnetic cellulose aerogel (PEI-MFPC) in Example 1 before and after the adsorption of PS.

[0109] The test results are as follows Figure 2 As shown, the magnetization curve of the functionalized magnetic cellulose aerogel (PEI-MFPC) is an S-shaped curve, and the saturation magnetization intensity of PEI-MFPC is 3.91emu / g, indicating that the material has soft magnetic properties and excellent magnetic properties. In the presence of a strong external magnetic field, PEI-MFPC can be quickly separated from water; when the external magnetic field is removed, PEI-MFPC still retains some magnetism, indicating that PEI-MFPC meets the characteristics of a soft magnetic material. When PEI-MFPC adsorbs PS, the saturation magnetization intensity increases slightly, demonstrating that after PEI-MFPC adsorbs PS, it can still be quickly separated in the presence of an external magnetic field.

[0110] 3. FTIR test

[0111] The functionalized magnetic cellulose aerogel (PEI-MFPC) of Example 1, the aerogel of Comparative Example 1 (FPC), the aerogel of Comparative Example 2 (MFPC), and the material after adsorption of PS in Example 1 were characterized and tested using Fourier transform infrared spectrometer (FTIR).

[0112] The test results are as follows Figure 3 As shown, the aerogel (FPC) prepared by extracting cellulose from Fenton reaction has a wavelength of 561 cm -1There are Fe-O bonds in iron oxide at 561 cm-1. The Co / Fe-O bonds of the iron cobalt oxide in the magnetic aerogel doped with modified iron cobalt oxide (MFPC) are similar to those at 561 cm-1. -1 coincides with the Fe-O bond, 1636 cm -1 、1507cm -1 The stretching and asymmetric vibration of the CO and CC bonds in the benzene ring of tannic acid appeared, indicating that tannic acid was successfully combined with iron cobalt oxide.

[0113] In the FTIR spectrum of the aerogel (PEI-MFPC) of Example 1, 1588 cm -1 、1462cm -1 、1320cm -1 They correspond to the -NH2 bond, CN bond, and -NH- bond in polyethyleneimine, respectively. -1 The -NH2 stretching peak in the region overlaps with the -OH peak of cellulose, indicating that polyethyleneimine was successfully introduced into the cellulose aerogel.

[0114] In the FTIR image of the aerogel of Example 1 (PEI-MFPC) after adsorption of PS, at 3023 cm -1 Corresponding to aromatic C-H bond stretching vibration, 697 cm -1 The peaks at correspond to the CC bonds in the benzene ring. These peaks are typical peaks of PS, which proves that PS is successfully adsorbed onto the aerogel material.

[0115] 4. XRD analysis

[0116] The three aerogels of Comparative Example 1 (FPC), Comparative Example 2 (MFPC) and Example 1 (MEI-MFPC) were characterized by X-ray diffractometer. Figure 4 shown.

[0117] As can be seen in Figure 4, all three aerogels exhibit a broad diffraction peak near 20.0°, corresponding to the cellulose II crystal plane, indicating that the Fenton reaction successfully extracts cellulose. However, the aerogel (FPC) prepared from cellulose extracted via the Fenton reaction exhibits typical peaks of Fe2O3 at 24.2° and 33.2°, corresponding to the (012) and (104) crystal planes of Fe2O3. Since no other chemical treatments were used during the cellulose extraction process, some Fe2O3 residues were present on the extracted cellulose.

[0118] In the XRD pattern of comparative example 2 (MFPC) aerogel, compared with comparative example 1, typical characteristic peaks of CoFe2O4 appeared at 30.1°, 35.4°, 43.1°, 56.9° and 62.5°, corresponding to the (104), (113), (024), (125) and (208) crystal planes of CoFe2O4, indicating that the modified iron cobalt oxide was successfully introduced into the aerogel.

[0119] In the XRD pattern of Example 1 (PEI-MFPC) aerogel, it has characteristic peaks in both FPC and MFPC aerogels, and the diffraction peak at 20° is broader than that in Comparative Example 1; the diffraction peak intensity at 35.4° (113) is weakened compared with Comparative Example 2, indicating that it is caused by the addition of polyethyleneimine.

[0120] 5. Adsorption experiment

[0121] Adsorption tests were performed on the aerogel materials prepared in Examples 1 to 8 and Comparative Examples 1 to 5.

[0122] The test method is as follows: 50 nm PS is used as a typical pollutant object, the initial PS concentration is set to 100 mg / L, the solution volume is 30 mL, 10 mg of the aerogel materials of Examples 1 to 6 and Comparative Examples 1 to 5 are respectively weighed and added to the above solution, the oscillation frequency is set to 250 rpm, and the oscillation reaction is carried out at 25°C for 2 hours. After the reaction is completed, the supernatant is taken, and the absorbance of the solution before and after adsorption is measured using a UV-visible spectrophotometer. The solution concentration and adsorption capacity are calculated using the standard curve. The results are shown in Table 1.

[0123] Table 1

[0124] Sample name Adsorption capacity (mg / g) Example 1 271.34 Example 2 265.09 Example 3 252.12 Example 4 202.28 Example 5 258.51 Example 6 240.25 Example 7 268.68 Example 8 213.38 Comparative Example 1 21.65 Comparative Example 2 81.46 Comparative Example 3 Unable to form Comparative Example 4 178.86 Comparative Example 5 151.01

[0125] The results show that the functionalized magnetic cellulose aerogel prepared in the embodiment of the present invention can achieve rapid adsorption of micro / nano plastics, and can achieve a high adsorption capacity of more than 200 mg / g within an adsorption time of less than 30 minutes.

[0126] Increasing the amount of polyethyleneimine modifier can improve the adsorption performance of the aerogel material, but when the amount is higher, polyethyleneimine may agglomerate in water, resulting in uneven dispersion and a decrease in adsorption performance.

[0127] In Comparative Example 1, when modified iron cobalt oxide and polyethylene imine are not added, the adsorption capacity for micro / nano plastics in water is extremely low; in Comparative Example 2, when polyethylene imine is not added, the adsorption capacity for micro / nano plastics in water is also low; and in Comparative Example 3, when no cross-linking agent is added, aerogel cannot be formed.

[0128] 6. Adsorption test at different initial concentrations

[0129] Adsorption tests at different initial concentrations were performed on the aerogel of Example 1 (PEI-MFPC) and the aerogel of Comparative Example 1 (FPC).

[0130] The test method is as follows: 50nm PS is used as a typical pollutant object, the initial PS concentration is set to 50-300mg / L, the solution volume is 30mL, 10mg of the aerogel material of Example 1 and Comparative Example 1 are weighed and added to the above solution, the oscillation frequency is set to 250rpm, and the oscillation reaction is carried out at 25℃ for 2h. After the reaction is completed, the supernatant is taken and the absorbance of the solution before and after adsorption is measured by UV-visible spectrophotometer. The solution concentration and adsorption capacity are calculated by the standard curve. The test results are shown as follows: Figure 5 and as shown in Table 2.

[0131] Table 2

[0132]

[0133] from Figure 5 It can be seen that under different initial concentration conditions, the adsorption capacity of PEI-MFPC aerogel is much higher than that of FPC aerogel, indicating that the prepared functionalized magnetic cellulose aerogel material has good adsorption performance for PS.

[0134] 7. Adsorption test at different contact times

[0135] Adsorption tests were performed on the aerogel of Example 1 (PEI-MFPC) at different contact times.

[0136] The test method is as follows: 50nm PS is used as a typical pollutant object, the initial PS concentration is set to 100mg / L, the solution volume is 30mL, 10mg of the aerogel material of Example 1 is weighed and added to the above solution, the oscillation frequency is set to 250rpm, the oscillation reaction is carried out at 25℃, and the time is set from 0 to 120min. After the reaction is completed, the supernatant is taken, and the absorbance of the solution before and after adsorption is measured by UV-visible spectrophotometer. The solution concentration and adsorption capacity are calculated by the standard curve. The test results are shown as follows: Figure 6 shown.

[0137] from Figure 6It can be seen that within the first 10 minutes, the adsorption of PS by PEI-MFPC aerogel showed a rapid upward trend. The main reason is that in the initial stage, there are a large number of active sites on the surface of the aerogel, which can adsorb PS in the solution. Therefore, the adsorption amount of PS in this stage is the fastest growing. At 30 minutes, the adsorption amount has reached 272.71 mg / g. At this time, the aerogel is basically in an adsorption equilibrium state, indicating that PEI-MFPC aerogel has the potential for rapid adsorption of PS. As time goes by, the adsorption amount of the aerogel decreases slightly. The possible reason for this phenomenon is that the combination of PS and aerogel materials mainly relies on some physical effects, such as electrostatic interaction. The binding force of these physical effects is weak, which causes the adsorption saturated material to desorb during the vibration process.

[0138] 8. Recycling test

[0139] The aerogel material of Example 1 (PEI-MFPC) was subjected to a recycling test.

[0140] The test method is as follows: 50nm PS is used as a typical pollutant object, the initial concentration of PS is set to 100mg / L, the solution volume is 30mL, 10mg of the aerogel material of Example 1 is weighed and added to the above solution, the oscillation frequency is set to 250rpm, and the oscillation reaction is carried out at 25℃ for 2h. After the reaction, the supernatant is taken, and the absorbance of the solution before and after adsorption is measured by ultraviolet-visible spectrophotometer. The solution concentration and adsorption capacity are calculated by the standard curve. The measured adsorption capacity is the first utilization; then the aerogel material and PS are separated by solid-liquid separation, collected and regenerated with anhydrous ethanol, and after freeze-drying, the regenerated aerogel material is used for the next round of adsorption test under the same adsorption test conditions. Similarly, this test examines the four-time recycling performance; the test results are as follows Figure 7 shown.

[0141] from Figure 7 It can be seen that the PEI-MFPC aerogel has an adsorption capacity of 272.71 mg / g for PS during its first use. This capacity decreases slightly to 255.47 mg / g after one cycle, and to 230.44 mg / g after the second cycle. The adsorption capacity gradually decreases with increasing use. After four cycles, the adsorption capacity reaches 179.14 mg / g, reaching over 66% of the initial capacity. This indicates that the cellulose hybrid aerogel material prepared by the present invention has good structural stability and good recyclability.

[0142] Obviously, the above embodiments of the present invention are merely examples for the purpose of clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. Those skilled in the art will appreciate that other variations or modifications can be made based on the above description. It is not necessary and impossible to enumerate all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the claims of the present invention.

Claims

1. A functionalized magnetic cellulose aerogel, characterized in that: The preparation method of the functionalized magnetic cellulose aerogel comprises the following steps: Step S1. Extracting cellulose from agricultural waste, adding the cellulose to an alkaline urea solution, stirring and dispersing the cellulose, freezing the solution at a temperature not higher than -12°C, and then thawing the solution and uniformly mixing the solution with a modified iron cobalt oxide powder to obtain a mixture; Step S2. adding polyethyleneimine and a cross-linking agent to the mixture, stirring evenly, allowing to stand to form a hydrogel, and freeze-drying to obtain the functionalized magnetic cellulose aerogel; In step S1, the preparation method of the modified iron cobalt oxide comprises the following steps: mixing iron cobalt oxide nanopowder and tannic acid aqueous solution at 40-60° C. for 1-3 hours to obtain modified iron cobalt oxide powder; In the iron-cobalt oxide, the molar ratio of cobalt to iron is (0.5-1):1; The mass ratio of the cellulose, the modified iron cobalt oxide powder and the polyethyleneimine is 10:(1-3):(8-12).

2. The functionalized magnetic cellulose aerogel according to claim 1, wherein The mass ratio of the cellulose, the modified iron cobalt oxide powder and the polyethylene imine is 10:(2-3):(8-9).

3. The functionalized magnetic cellulose aerogel according to claim 1, wherein In step S1, the method for extracting cellulose from agricultural waste includes the following steps: crushing the agricultural waste and placing it in a mixed aqueous dispersion containing hydrogen peroxide and iron oxide, reacting at 70-90° C. for 1-2 hours to obtain cellulose powder.

4. The functionalized magnetic cellulose aerogel according to claim 3, characterized in that In step S1, in the method for extracting cellulose from agricultural waste: in the mixed aqueous dispersion, the mass content of hydrogen peroxide is 27 wt% to 30 wt%, and the mass content of iron oxide is 2.5 wt% to 5 wt%.

5. The functionalized magnetic cellulose aerogel according to claim 3, wherein: In step S1, agricultural waste is crushed to 80-300 mesh.

6. The functionalized magnetic cellulose aerogel according to claim 1, wherein In step S1, the method for preparing the iron cobalt oxide nanopowder comprises the following steps: mixing iron salt, cobalt salt, sodium acetate and ethylene glycol for reaction, and drying to obtain the iron cobalt oxide nanopowder.

7. The functionalized magnetic cellulose aerogel according to claim 1, wherein: In step S1, the mass ratio of the iron cobalt oxide nanopowder to tannic acid is (2-6):(1-3), and the mass concentration of the tannic acid aqueous solution is 0.025 g / mL to 0.075 g / mL.

8. The functionalized magnetic cellulose aerogel according to claim 1, wherein In step S1, the agricultural waste is any one of pine wood powder, rice straw, stalks, corn cobs or sugarcane bagasse.

9. The functionalized magnetic cellulose aerogel according to claim 1, wherein: In step S2, the cross-linking agent is epichlorohydrin or glutaraldehyde.

10. Use of the functionalized magnetic cellulose aerogel according to any one of claims 1 to 9 in adsorbing micro / nano plastics in water.

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