Superhydrophobic esterified corn stalk aerogel oil-absorbing material and its preparation method

Abstract

This invention relates to the field of adsorption functional polymer materials technology, specifically a superhydrophobic esterified modified corn stalk aerogel oil-absorbing material and its preparation method. The method includes the following steps: adding corn stalk cellulose pretreated with alkaline hydrogen peroxide to an acetic acid-formic acid mixed solution and reacting under microwave assistance; washing and drying after the reaction to obtain esterified modified corn stalks; mixing chitosan polycarboxylic acid aqueous solution and polyvinyl alcohol aqueous solution, then adding the esterified modified corn stalks and alkaline hydrogen peroxide pretreated corn stalk lignin aqueous dispersion to obtain an aerogel precursor solution; soaking and freeze-drying the aerogel precursor solution to obtain a composite aerogel; and hydrophobically modifying the composite aerogel and drying it to obtain the superhydrophobic esterified modified corn stalk aerogel oil-absorbing material. The method of this invention is green, simple, and energy-saving. The obtained aerogel oil-absorbing material exhibits high oil absorption rate, superhydrophobicity, and good thermal stability.

Description

Technical Field

[0001] This invention relates to the field of adsorption functional polymer materials technology, and in particular to superhydrophobic esterified modified corn stalk aerogel oil-absorbing material and its preparation method. Background Technology

[0002] Oily wastewater, formed from crude oil spills, industrial waste oil, kitchen waste oil, and water-insoluble chemical reagents, not only forms an oil film on the water surface, hindering carbon dioxide and oxygen from entering the water and affecting the survival of aquatic plants and animals, but also contains harmful components such as aromatic hydrocarbons that can harm human health through these organisms. Therefore, efficient, rapid, and environmentally friendly treatment of oily wastewater has become a major concern.

[0003] Oil absorption using adsorbent materials is a common method for treating oily wastewater due to its simplicity, low energy consumption, and reusability. Natural organic oil-absorbing materials based on agricultural and forestry waste such as straw, fruit peels, and sawdust offer advantages such as wide availability, low cost, eco-friendliness, and efficient waste utilization, making them a superior choice for treating oily wastewater. Corn stalks, a typical agricultural waste, are mainly composed of cellulose, lignin, and hemicellulose. Their porous structure, wide availability, renewability, and biodegradability provide a foundation for the preparation of oil-absorbing materials. Various aerogel materials prepared from corn stalks and other raw materials have been used for oil absorption and pollution removal, but their oil absorption rate is low, the oil absorption effect is unsatisfactory, and they exhibit water absorption and poor buoyancy, making them unsuitable for oil absorption in oil-water mixtures, thus limiting their application.

[0004] Therefore, there is an urgent need for a new aerogel oil-absorbing material to solve the above-mentioned technical problems. Summary of the Invention

[0005] The purpose of this invention is to provide an esterified modified corn stalk aerogel with high oil absorption capacity, superhydrophobicity, and good thermal stability, as well as its preparation method. To achieve the above objective, this invention uses corn stalk cellulose pretreated with alkaline hydrogen peroxide, followed by esterification modification of corn stalks using formic acid as a catalyst and acetic acid as an esterifying agent under microwave assistance. The esterified modified corn stalks, corn stalk lignin aqueous dispersion pretreated with alkaline hydrogen peroxide, chitosan polycarboxylic acid aqueous solution, and polyvinyl alcohol as a reinforcing agent are mixed and stirred evenly, and placed in an oven to accelerate the reaction. Subsequently, unreacted polycarboxylic acids and polyvinyl alcohol are removed by displacement in deionized water. After directional pre-freezing, the aerogel is freeze-dried in a freeze dryer to obtain the aerogel. Finally, the aerogel is hydrophobically modified to obtain a superhydrophobic esterified modified corn stalk aerogel oil-absorbing material.

[0006] The present invention is specifically implemented according to the following technical solution:

[0007] A method for preparing superhydrophobic esterified modified corn stalk aerogel oil-absorbing material includes the following steps:

[0008] S1, Preparation of esterified modified corn stalks:

[0009] Corn stalk cellulose pretreated with alkaline hydrogen peroxide was added to an acetic acid-formic acid mixed solution and reacted under microwave assistance. After the reaction was completed, the corn stalks were washed and dried to obtain esterified modified corn stalks.

[0010] S2, Preparation of superhydrophobic esterified modified corn stalk aerogel oil-absorbing material:

[0011] A mixture of chitosan polycarboxylic acid aqueous solution and polyvinyl alcohol aqueous solution was added to esterified modified corn stalks and corn stalk lignin aqueous dispersion pretreated with alkaline hydrogen peroxide to obtain an aerogel precursor solution; the aerogel precursor solution was soaked and freeze-dried to obtain a composite aerogel.

[0012] The composite aerogel was modified by hydrophobicity and then dried to obtain a superhydrophobic esterified corn stalk aerogel oil-absorbing material.

[0013] Preferably, in step S1, the preparation process of corn stalk cellulose after alkaline hydrogen peroxide pretreatment is as follows: corn stalks are washed, dried, and crushed, then added to an aqueous hydrogen peroxide solution, followed by the addition of alkali to adjust the pH to 11.5, and the reaction is stirred; after the reaction is completed, acid is added to adjust the pH to neutral, and then the mixture is filtered to obtain filter residue and filtrate; the filter residue is washed and dried to obtain corn stalk cellulose after alkaline hydrogen peroxide pretreatment.

[0014] Preferably, the hydrogen peroxide aqueous solution contains 1% hydrogen peroxide by volume; the base is sodium hydroxide; and the acid is acetic acid.

[0015] Specifically, in step S1, the preparation process of corn stalk cellulose after alkaline hydrogen peroxide pretreatment is as follows: Corn stalks are repeatedly washed with deionized water and anhydrous ethanol and vacuum dried at 60°C to constant weight. After being pulverized by a high-speed multi-functional pulverizer and passed through a 60-80 mesh sieve, they are added to a 1% (v / v) hydrogen peroxide aqueous solution. The pH of the solution is adjusted to 11.5 with sodium hydroxide. After magnetic stirring for 12 hours at room temperature, the pH of the solution is adjusted to neutral with acetic acid. Then, the solution is filtered to obtain filter residue and filtrate. The filter residue is repeatedly washed with distilled water and anhydrous ethanol and vacuum dried at 60°C to constant weight to obtain corn stalk cellulose after alkaline hydrogen peroxide pretreatment.

[0016] Preferably, in step S1, the mass ratio of the corn stalk cellulose pretreated with alkaline hydrogen peroxide to the acetic acid-formic acid mixed solution is 1:30-50.

[0017] Preferably, in step S1, the acetic acid-formic acid mixed solution is obtained by mixing acetic acid and formic acid, wherein the mass percentage of formic acid is 1-9%.

[0018] Preferably, in step S1, the microwave power is 100-500W, the reaction temperature is 70-110℃, and the reaction time is 5-25min.

[0019] Specifically, the process of step S1 is as follows:

[0020] One part by weight of corn stalk cellulose pretreated with 60-80 mesh alkaline hydrogen peroxide was added to 30-50 times its weight of an acetic acid-formic acid mixed solution (in which the mass percentage of formic acid was 1-9%). The mixture was reacted for 5-25 minutes under microwave power of 100-500W and reaction temperature of 70-110℃. After washing with deionized water and anhydrous ethanol until neutral, the mixture was vacuum dried at 50-60℃ for 12 hours to obtain esterified modified corn stalks.

[0021] Preferably, in step S2, the preparation process of the corn straw lignin aqueous dispersion after alkaline hydrogen peroxide pretreatment is as follows:

[0022] Acetic acid solution was added to the filtrate obtained during the preparation of corn stalk cellulose after alkaline hydrogen peroxide pretreatment, and the pH value was adjusted to 5.5. The precipitate was obtained by vacuum concentration and centrifugation. The precipitate was washed and dried to obtain corn stalk lignin pretreated with alkaline hydrogen peroxide.

[0023] The corn stalk lignin pretreated with alkaline hydrogen peroxide was mixed evenly with an aqueous acetic acid solution to obtain an aqueous dispersion of corn stalk lignin pretreated with alkaline hydrogen peroxide.

[0024] Furthermore, acetic acid solution is added to water to prepare an acetic acid aqueous solution with a pH of 2-5. The acetic acid aqueous solution is then mixed evenly with corn stalk lignin pretreated with alkaline hydrogen peroxide to obtain an aqueous dispersion of corn stalk lignin pretreated with alkaline hydrogen peroxide. The mass ratio of corn stalk lignin pretreated with alkaline hydrogen peroxide to acetic acid aqueous solution is 25-75:100.

[0025] Specifically, in step S2, the preparation process of the corn straw lignin aqueous dispersion after alkaline hydrogen peroxide pretreatment is as follows:

[0026] Add 36wt% acetic acid solution to the filtrate obtained during the preparation of corn stalk cellulose after alkaline hydrogen peroxide pretreatment, adjust the pH value to 5.5, concentrate under reduced pressure and separate by centrifugation to obtain a precipitate, wash the precipitate three times with anhydrous ethanol and water respectively, and dry it in a drying oven at 60℃ to constant weight to obtain corn stalk lignin after alkaline hydrogen peroxide pretreatment.

[0027] Prepare an acetic acid aqueous solution with a pH of 2-5 by adding a 36% acetic acid solution to water. Add the corn stalk lignin pretreated with alkaline hydrogen peroxide to the aforementioned acetic acid aqueous solution at room temperature and stir to form an aqueous dispersion of corn stalk lignin pretreated with alkaline hydrogen peroxide. The mass ratio of corn stalk lignin pretreated with alkaline hydrogen peroxide to the aforementioned acetic acid aqueous solution is 25-75:100.

[0028] Preferably, in step S2, the mass ratio of chitosan, polycarboxylic acid, polyvinyl alcohol, esterified modified corn stalks, and corn stalk lignin pretreated with alkaline hydrogen peroxide is (0.15~0.35):0.21:(0.07~0.35):(0.1~0.3):0.1.

[0029] Preferably, in step S2, the mass percentage of the polycarboxylic acid in the aqueous solution is 2%; and the mass ratio of polyvinyl alcohol to water in the aqueous solution is (0.07-0.35):3.5.

[0030] Preferably, the polycarboxylic acid is at least one selected from citric acid, oxalic acid, maleic acid, succinic acid, adipic acid, malic acid, and tartaric acid.

[0031] Preferably, in step S2, the process of hydrophobic modification of the composite aerogel is as follows: the composite aerogel is immersed in a mixed solution of silane, silane coupling agent and n-hexane; the mass ratio of silane, silane coupling agent and n-hexane is (2-5):(1-2):(93-97).

[0032] Preferably, the silane is at least one of hexadecyltrimethoxysilane, perfluorooctyltriethoxysilane, perfluorooctyltrichlorosilane, methyltrimethoxysilane, trichlorovinylsilane, and polydimethylsiloxane; and the silane coupling agent is at least one of KH-570, KH-550, KH-560, and KH-792.

[0033] Preferably, in step S2, the freeze-drying process is as follows: the aerogel precursor solution after soaking is pre-frozen at -18°C in a directional manner, and then placed in a freeze dryer to dry and obtain the composite aerogel. The directional pre-freezing lasts for 24 hours, and the drying in the freeze dryer lasts for 48 hours.

[0034] Specifically, the process of step S2 is as follows:

[0035] Take 0.15 to 0.35 parts by weight of chitosan and add it to 10.5 parts by weight of 2% polycarboxylic acid aqueous solution (the polycarboxylic acid in the aqueous solution is 2% by weight). Seal and let stand overnight to completely dissolve it to obtain chitosan polycarboxylic acid aqueous solution.

[0036] Take 0.07 to 0.35 parts by weight of polyvinyl alcohol and add it to 3.5 parts by weight of deionized water. Stir mechanically in an oil bath at 90°C for 2 hours until it is completely dissolved. Cool and store at room temperature for later use to obtain a polyvinyl alcohol aqueous solution.

[0037] After mixing chitosan polycarboxylic acid aqueous solution and polyvinyl alcohol aqueous solution and stirring for 3 hours, ultrasonic degassing was performed. Then, 0.1-0.3 parts by weight of esterified modified corn straw and 0.1 parts by weight of corn straw lignin aqueous dispersion pretreated with alkaline hydrogen peroxide were added. The mixture was poured into a mold and reacted at 55-75℃ for 1-5 hours. After the reaction was completed, aerogel precursor liquid was obtained.

[0038] The aerogel precursor solution was soaked in deionized water for 48 hours to remove unreacted polycarboxylic acids and polyvinyl alcohol. After soaking, the aerogel precursor solution was pre-frozen at -18°C for 24 hours and then placed in a freeze dryer to dry for 48 hours to obtain composite aerogel.

[0039] The composite aerogel was immersed in a hexane solution of silane and silane coupling agent (mass ratio of silane, silane coupling agent and hexane was 2-5:1-2:93-97) for hydrophobic modification for 6 hours, and then dried in a vacuum drying oven at 60℃ to constant weight to obtain a superhydrophobic esterified modified corn straw aerogel oil-absorbing material.

[0040] The superhydrophobic esterified modified corn stalk aerogel oil-absorbing material obtained by this invention can be repeatedly squeezed to remove oil after oil absorption and can be recycled.

[0041] Mechanism of action:

[0042] This invention introduces homologous lignin (a water dispersion of corn straw lignin pretreated with alkaline hydrogen peroxide) as a structural reinforcing agent into the aerogel, which supports the network skeleton of the composite aerogel, forming a robust three-dimensional interconnected porous network, thereby enhancing the mechanical properties and oil absorption capacity of the aerogel.

[0043] Chitosan, as a crosslinking agent, enables crosslinking between corn stalks and chitosan through hydrogen bonding between chitosan molecules and electrostatic interaction between corn stalks and chitosan; at the same time, the introduction of chitosan gives the aerogel higher mechanical properties.

[0044] Using polycarboxylic acids (citric acid, oxalic acid, maleic acid, succinic acid, adipic acid, malic acid, tartaric acid, etc.) as covalent crosslinking agents can not only undergo esterification with the hydroxyl groups on esterified corn stalks to achieve crosslinking between corn stalk cellulose, but also undergo amidation with the amino groups on chitosan to achieve crosslinking between chitosan, thereby improving its hydrophobic properties.

[0045] Polyvinyl alcohol, as a reinforcing agent, can reduce the strength damage caused by crosslinking, effectively improve the problem of reduced pore size caused by hydrogen bonding between chitosan molecules and electrostatic interaction between corn stalks and chitosan, enhance the strength stability of the gel, and maintain its anisotropic hierarchical porous structure. At the same time, the hydroxyl groups of polyvinyl alcohol and corn stalks can be physically crosslinked through electrostatic interaction.

[0046] The mixed silane-modified composite aerogel, using silanes (such as hexadecyltrimethoxysilane, perfluorooctyltriethoxysilane, perfluorooctyltrichlorosilane, methyltrimethoxysilane, trichlorovinylsilane, and polydimethylsiloxane) and silane coupling agents (such as KH-570, KH-550, KH-560, and KH-792), improves hydrophobicity from general to superhydrophobic. Furthermore, the introduction of homologous lignin supports the network framework of the esterified corn stalk aerogel, significantly increasing its porosity and exhibiting high thermal stability, making it suitable for the adsorption of hot oils. This indicates that the use of silane coupling agents enhances the covalent bonding between the hydroxyl groups and siloxanes on the aerogel framework.

[0047] This invention employs directional pre-freezing followed by freeze-drying to prepare an aerogel that retains its gel network structure and possesses a layered assembly structure with aligned channels. The introduction of homologous lignin and the directional pre-freezing technique jointly enhance the mechanical strength and elasticity of the esterified corn stalk aerogel. The polygonal structure of the aerogel, combined with silane chains, gives it unique porosity and surface morphology. The resulting superhydrophobic esterified corn stalk aerogel oil-absorbing material is not only superhydrophobic but can also be recycled through repeated extrusion to remove oil.

[0048] This invention employs a one-step pretreatment of corn stalks with alkaline hydrogen peroxide. The process is simple, the conditions are mild, and it allows for the removal of homologous lignin in the preparation of aerogels. This not only improves the mechanical properties of the aerogels but also makes more complete use of the corn stalks. Esterified modified corn stalks are obtained by reacting with formic acid as a catalyst and acetic acid as an esterifying agent under microwave assistance at a temperature of 70–110°C for 5–25 minutes using 100–500W microwave power. The chemicals used are safe and readily available. Esterified corn stalks, corn stalk lignin aqueous dispersion pretreated with alkaline hydrogen peroxide, chitosan polycarboxylic acid aqueous solution, and polyvinyl alcohol (PEA) reinforcing agent were mixed and stirred evenly to obtain an aerogel precursor solution. The aerogel precursor solution was reacted at 55–75°C for 1–5 h, then replaced with deionized water for 48 h, directionally pre-frozen at -18°C for 24 h, and then freeze-dried for 48 h to obtain an aerogel that maintains its gel network structure. The obtained aerogel was then hydrophobically modified to obtain a superhydrophobic esterified corn stalk aerogel oil-absorbing material. In this invention, corn stalks pretreated with alkaline hydrogen peroxide are first esterified to give them good hydrophobic properties. Then, together with pretreated homologous lignin, an aerogel precursor solution is formed through composite cross-linking with biodegradable chitosan and citric acid, and reinforcement and cross-linking with PVA. After pre-freezing and freeze-drying, a superhydrophobic esterified corn stalk aerogel oil-absorbing material is obtained. This not only avoids the impact of repeated freezing and thawing on the strength of the aerogel, but also introduces homologous lignin as a structural reinforcing agent into the aerogel, supporting the network skeleton of the esterified modified corn stalk aerogel, forming a robust three-dimensional interconnected porous network, and enhancing the mechanical properties and oil absorption capacity of the aerogel.

[0049] This invention utilizes low-cost corn stalk fiber, homologous lignin, chitosan, citric acid, and polyvinyl alcohol to develop a fully biodegradable aerogel through a simple and scalable method. The invention employs bio-based raw materials—corn stalk, citric acid, chitosan, and biocompatible polyvinyl alcohol—while the other components are general chemicals. Hydrogen peroxide is a daily-use disinfectant with a concentration of <10%. The preparation conditions are mild, and the process is relatively simple.

[0050] The superhydrophobic esterified modified corn stalk aerogel oil-absorbing material prepared in this invention has a water contact angle of 153.6°, indicating that it has superhydrophobicity, making the hydrophobic modified aerogel more suitable for oil-water separation in oil-water mixed systems.

[0051] The method for preparing superhydrophobic esterified modified corn stalk aerogel oil-absorbing material according to the present invention is green, simple and energy-saving.

[0052] This invention provides an environmentally friendly, green, and low-cost method for preparing aerogels with high oil absorption capacity, superhydrophobicity, and good thermal stability, using corn stalks, chitosan, and polyvinyl alcohol as raw materials. Microwave-assisted modification rapidly yields esterified corn stalks. The composite aerogel is modified by mixing hexadecyltrimethoxysilane and the silane coupling agent KH-570 to achieve superhydrophobicity. The resulting superhydrophobic esterified corn stalk aerogel oil-absorbing material exhibits high oil absorption capacity, superhydrophobicity, and good thermal stability.

[0053] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0054] This invention first pretreats corn stalks with alkaline hydrogen peroxide, then performs esterification modification with microwave assistance, and then obtains superhydrophobic esterified modified corn stalk aerogel oil-absorbing material through reinforcement, crosslinking, freezing, impregnation and other means. It has the advantages of high oil absorption ratio, superhydrophobicity, good thermal stability and recyclability. Attached Figure Description

[0055] Figure 1 This is a photograph of the composite aerogel prepared in Example 1;

[0056] Figure 2 Water contact angle (WCA) diagram of the composite aerogel prepared in Example 1;

[0057] Figure 3 This is a photograph of the superhydrophobic esterified modified corn stalk aerogel oil-absorbing material prepared in Example 1;

[0058] Figure 4 Water contact angle (WCA) diagram of the superhydrophobic esterified modified corn stalk aerogel oil-absorbing material prepared in Example 1;

[0059] Figure 5 Thermogravimetric analysis (DTG) curves of chitosan, polyvinyl alcohol, esterified corn stalks, composite aerogel, and superhydrophobic esterified corn stalk aerogel oil-absorbing material in Example 1 are shown. Detailed Implementation

[0060] The present invention will be further described below with reference to specific embodiments. The illustrative embodiments and descriptions herein are used to explain the present invention, but are not intended to limit the present invention.

[0061] All raw materials used in this invention are not particularly restricted in their source and can be purchased from the market or prepared using conventional methods known to those skilled in the art.

[0062] The devices involved in this invention are not particularly limited to those commonly used in the field, and their operation and usage are well known to those skilled in the art.

[0063] The present invention will be further described below with reference to specific embodiments. The illustrative embodiments and descriptions herein are used to explain the present invention, but are not intended to limit the present invention.

[0064] In the following embodiments, the preparation process of corn stalk cellulose pretreated with alkaline hydrogen peroxide is as follows: Corn stalks are repeatedly washed with deionized water and anhydrous ethanol and vacuum dried at 60°C to constant weight. After being pulverized by a high-speed multi-functional pulverizer and passed through a 60-80 mesh sieve, the pulverized stalks are added to a 1% (v / v) hydrogen peroxide aqueous solution. The pH of the solution is adjusted to 11.5 with sodium hydroxide. After magnetic stirring at room temperature for 12 hours, the pH of the solution is adjusted to neutral with acetic acid. The solution is then filtered to obtain filtrate and filter residue. The filter residue is repeatedly washed with distilled water and anhydrous ethanol and vacuum dried at 60°C to constant weight to obtain corn stalk cellulose pretreated with alkaline hydrogen peroxide.

[0065] The preparation process of the corn stalk lignin aqueous dispersion after alkaline hydrogen peroxide pretreatment in the following embodiments is as follows: 36 wt% acetic acid solution is added to the filtrate obtained in the preparation process of corn stalk cellulose after alkaline hydrogen peroxide pretreatment, the pH value is adjusted to 5.5, and the precipitate is obtained by vacuum concentration and centrifugation; the precipitate is washed three times with anhydrous ethanol and water in turn, and dried in a drying oven at 60°C to constant weight to obtain corn stalk lignin after alkaline hydrogen peroxide pretreatment;

[0066] 16.7 g of 36 wt% acetic acid solution was added to 83.3 g of water to prepare 100 g of acetic acid aqueous solution with pH 2.4. Corn lignin pretreated with alkaline hydrogen peroxide was added to the aforementioned acetic acid aqueous solution at room temperature and stirred until an aqueous dispersion of corn lignin pretreated with alkaline hydrogen peroxide was formed. The mass ratio of corn lignin pretreated with alkaline hydrogen peroxide to the aforementioned acetic acid aqueous solution was 1:2.

[0067] Example 1:

[0068] A method for preparing superhydrophobic esterified modified corn stalk aerogel oil-absorbing material includes the following steps:

[0069] S1, Preparation of esterified modified corn stalks:

[0070] Corn stalk cellulose pretreated with alkaline hydrogen peroxide (60-80 mesh) was added to a 40-fold mass of acetic acid-formic acid mixed solution (the mass ratio of corn stalk cellulose pretreated with alkaline hydrogen peroxide to the acetic acid-formic acid mixed solution was 1:40; the mass percentage of formic acid in the acetic acid-formic acid mixed solution was 7 wt%). The reaction was carried out for 20 min at a microwave power of 400 W and a reaction temperature of 100 °C. After the reaction was completed, the mixture was removed and allowed to stand at room temperature. It was then washed with deionized water and anhydrous ethanol until neutral and dried under vacuum at 60 °C for 12 h to obtain esterified modified corn stalks.

[0071] S2, Preparation of superhydrophobic esterified modified corn stalk aerogel oil-absorbing material:

[0072] 0.2g of chitosan was added to 10.5g of a 2% citric acid aqueous solution (citric acid content was 2% by mass), sealed, and left to stand overnight to dissolve completely. 0.14g of polyvinyl alcohol was added to 3.5g of deionized water, and mechanically stirred in a 90℃ oil bath for 2 hours until completely dissolved. The solution was then cooled to room temperature and stored for later use. The chitosan-citric acid aqueous solution and the polyvinyl alcohol aqueous solution were mixed and magnetically stirred for 3 hours. After stirring, the mixture was ultrasonically degassed. Then, 0.15g of esterified modified corn stalks and 0.3g of corn stalk lignin aqueous dispersion pretreated with alkaline hydrogen peroxide (the mass of the corn stalk lignin pretreated with alkaline hydrogen peroxide was 0.1g) were added to the mixed solution, and the mixture was reacted in a 70℃ oven for 2 hours. After the reaction, the mixture was soaked in deionized water for 48 hours to remove unreacted citric acid. The soaked hydrogel was then pre-frozen at -18℃ for 24 hours and then dried in a freeze dryer for 48 hours to obtain a composite aerogel. The composite aerogel was immersed in a hexane solution of hexadecyltrimethoxysilane and silane coupling agent KH-570 (mass ratio of hexadecyltrimethoxysilane, silane coupling agent KH-570 and hexane was 3:1:96) for hydrophobic modification for 6 hours. After modification, it was washed multiple times with hexane and finally placed in a vacuum drying oven at 60℃ to dry to constant weight, thus obtaining a superhydrophobic esterified modified corn straw aerogel oil-absorbing material.

[0073] A certain mass of the superhydrophobic esterified corn stalk aerogel oil-absorbing material prepared in Example 1 was weighed and adsorbed for 5 hours in a pure engine oil system, an engine oil-water mixture system, and an organic solvent (xylene) system, respectively. The oil on the surface of the aerogel was wiped off with oil-absorbing paper, and then weighed to obtain an oil absorption ratio of 47.8 g·g in each of the three systems. -1 46.1 g·g -1 43.3g·g -1 .

[0074] Sudan III was used to stain the engine oil, and Rhodamine B was used to stain the water to make it easier to observe the oil and water droplets on the surface of the composite aerogel and the superhydrophobic esterified corn stalk aerogel oil-absorbing material.

[0075] Depend on Figure 1 , Figure 2 It can be seen that oil droplets and water droplets can be rapidly adsorbed on the surface of the composite aerogel in this embodiment, with a contact angle of 0° for water. Figure 3 , Figure 4 It can be seen that oil droplets can be rapidly adsorbed on the surface of the superhydrophobic esterified modified corn stalk aerogel oil-absorbing material in this embodiment, while water droplets can maintain a spherical shape for a long time on the surface of the superhydrophobic esterified modified corn stalk aerogel oil-absorbing material, with a contact angle of 153.6° to water, which demonstrates the effectiveness of hydrophobic modification, thereby making the superhydrophobic esterified modified corn stalk aerogel oil-absorbing material more suitable for oil-water separation in oil-water mixed systems.

[0076] Figure 5 As shown, the composite aerogel before hydrophobic modification and the hydrophobic esterified corn stalk aerogel oil-absorbing material after hydrophobic modification both have higher thermal stability than their constituent raw materials (chitosan, polyvinyl alcohol, and esterified corn stalk), making them more suitable for the adsorption of hot oil.

[0077] Example 2:

[0078] A method for preparing superhydrophobic esterified modified corn stalk aerogel oil-absorbing material includes the following steps:

[0079] S1, Preparation of esterified modified corn stalks:

[0080] Corn stalk cellulose pretreated with alkaline hydrogen peroxide (60-80 mesh) was added to a 40-fold mass of acetic acid-formic acid mixed solution (the mass ratio of corn stalk cellulose pretreated with alkaline hydrogen peroxide to the acetic acid-formic acid mixed solution was 1:40; the mass percentage of formic acid in the acetic acid-formic acid mixed solution was 7 wt%). The reaction was carried out for 20 min at a microwave power of 400 W and a reaction temperature of 100 °C. After the reaction was completed, the mixture was removed and allowed to stand at room temperature. It was then washed with deionized water and anhydrous ethanol until neutral and dried under vacuum at 60 °C for 12 h to obtain esterified modified corn stalks.

[0081] S2, Preparation of superhydrophobic esterified modified corn stalk aerogel oil-absorbing material:

[0082] 0.2g of chitosan was added to 10.5g of a 2% citric acid aqueous solution (citric acid content was 2% by mass), sealed, and left to stand overnight to dissolve completely. 0.14g of polyvinyl alcohol was added to 3.5g of deionized water and mechanically stirred in a 90℃ oil bath for 2 hours to dissolve completely. The solution was then cooled to room temperature and stored for later use. The chitosan-citric acid aqueous solution and the polyvinyl alcohol aqueous solution were mixed and magnetically stirred for 3 hours. After stirring, the mixture was ultrasonically degassed. Then, 0.1g of esterified modified corn stalks and 0.3g of corn stalk lignin aqueous dispersion pretreated with alkaline hydrogen peroxide (the mass of the corn stalk lignin pretreated with alkaline hydrogen peroxide was 0.1g) were added to the mixed solution and reacted in an oven at 60℃ for 4 hours. After the reaction, the mixture was soaked in deionized water for 48 hours to remove unreacted citric acid. The soaked hydrogel was then pre-frozen at -18℃ for 24 hours and then dried in a freeze dryer for 48 hours to obtain a composite aerogel. The composite aerogel was immersed in a hexane solution of hexadecyltrimethoxysilane and silane coupling agent KH-570 (mass ratio of hexadecyltrimethoxysilane, silane coupling agent KH-570 and hexane was 2.5:1.5:96) for hydrophobic modification for 6 hours. After modification, it was washed multiple times with hexane and finally dried in a vacuum drying oven at 60℃ to constant weight to obtain a superhydrophobic esterified modified corn straw aerogel oil-absorbing material.

[0083] A certain mass of the superhydrophobic esterified corn stalk aerogel oil-absorbing material prepared in Example 2 was weighed and adsorbed for 5 hours in a pure engine oil system, an engine oil-water mixture system, and an organic solvent (xylene) system, respectively. The oil on the surface of the aerogel was wiped off with oil-absorbing paper, and then weighed to obtain an oil absorption ratio of 32.65 g·g in each of the three systems. -1 31.33g·g -1 31.23 g·g -1 .

[0084] Example 3:

[0085] A method for preparing superhydrophobic esterified modified corn stalk aerogel oil-absorbing material includes the following steps:

[0086] S1, Preparation of esterified modified corn stalks:

[0087] Corn stalk cellulose pretreated with alkaline hydrogen peroxide (60-80 mesh) was added to a 40-fold mass of acetic acid-formic acid mixed solution (the mass ratio of corn stalk cellulose pretreated with alkaline hydrogen peroxide to the acetic acid-formic acid mixed solution was 1:40; the mass percentage of formic acid in the acetic acid-formic acid mixed solution was 7 wt%). The reaction was carried out for 20 min at a microwave power of 400 W and a reaction temperature of 100 °C. After the reaction was completed, the mixture was removed and allowed to stand at room temperature. It was then washed with deionized water and anhydrous ethanol until neutral and dried under vacuum at 60 °C for 12 h to obtain esterified modified corn stalks.

[0088] S2, Preparation of superhydrophobic esterified modified corn stalk aerogel oil-absorbing material:

[0089] 0.2g of chitosan was added to 10.5g of a 2% citric acid aqueous solution (citric acid content was 2% by mass), sealed, and left to stand overnight to dissolve completely. 0.14g of polyvinyl alcohol was added to 3.5g of deionized water and mechanically stirred in a 90℃ oil bath for 2 hours to dissolve completely. The solution was then cooled to room temperature and stored for later use. The chitosan-citric acid aqueous solution and the polyvinyl alcohol aqueous solution were mixed and magnetically stirred for 3 hours. After stirring, the mixture was ultrasonically degassed. Then, 0.2g of esterified modified corn stalks and 0.3g of corn stalk lignin aqueous dispersion pretreated with alkaline hydrogen peroxide (the mass of the corn stalk lignin pretreated with alkaline hydrogen peroxide was 0.1g) were added to the mixed solution and reacted in an oven at 75℃ for 2 hours. After the reaction, the mixture was soaked in deionized water for 48 hours to remove unreacted citric acid. The soaked hydrogel was then pre-frozen at -18℃ for 24 hours and then dried in a freeze dryer for 48 hours to obtain a composite aerogel. The composite aerogel was immersed in a hexane solution of hexadecyltrimethoxysilane and silane coupling agent KH-570 (mass ratio of hexadecyltrimethoxysilane, silane coupling agent KH-570, and hexane was 3.5:1.5:95) for hydrophobic modification for 6 hours. After modification, it was washed multiple times with hexane and finally dried in a vacuum drying oven at 60℃ to constant weight to obtain a superhydrophobic esterified modified corn stalk aerogel oil-absorbing material.

[0090] A certain mass of the superhydrophobic esterified corn stalk aerogel oil-absorbing material prepared in Example 3 was weighed and adsorbed for 5 hours in a pure engine oil system, an engine oil-water mixture system, and an organic solvent (xylene) system, respectively. The oil on the surface of the aerogel was wiped off with oil-absorbing paper, and then weighed to obtain an oil absorption ratio of 35.8 g·g in each of the three systems. -1 34.6 g·g -1 33.3g·g -1 .

[0091] The technical solutions of the present invention are not limited to the specific embodiments described above. Any technical modifications made in accordance with the technical solutions of the present invention fall within the protection scope of the present invention.

Claims

1. A method for preparing superhydrophobic esterified modified corn stalk aerogel oil-absorbing material, characterized in that: Includes the following steps: S1, Preparation of esterified modified corn stalks: Corn stalk cellulose pretreated with alkaline hydrogen peroxide was added to an acetic acid-formic acid mixed solution and reacted under microwave assistance. After the reaction was completed, the corn stalks were washed and dried to obtain esterified modified corn stalks. S2, Preparation of superhydrophobic esterified modified corn stalk aerogel oil-absorbing material: A mixture of chitosan polycarboxylic acid aqueous solution and polyvinyl alcohol aqueous solution was added to esterified modified corn stalks and corn stalk lignin aqueous dispersion pretreated with alkaline hydrogen peroxide to obtain an aerogel precursor solution; the aerogel precursor solution was soaked and freeze-dried to obtain a composite aerogel. The composite aerogel was modified by hydrophobicity and then dried to obtain a superhydrophobic esterified corn stalk aerogel oil-absorbing material.

2. The preparation method of the superhydrophobic esterified modified corn stalk aerogel oil-absorbing material according to claim 1, characterized in that: In step S1, the preparation process of corn stalk cellulose after alkaline hydrogen peroxide pretreatment is as follows: corn stalks are washed, dried, and crushed, then added to a hydrogen peroxide aqueous solution, followed by the addition of alkali to adjust the pH to 11.5, and the reaction is stirred; after the reaction is completed, acid is added to adjust the pH to neutral, and then the mixture is filtered to obtain filter residue and filtrate; the filter residue is washed and dried to obtain corn stalk cellulose after alkaline hydrogen peroxide pretreatment.

3. The preparation method of the superhydrophobic esterified modified corn stalk aerogel oil-absorbing material according to claim 1, characterized in that: In step S1, the mass ratio of the corn stalk cellulose pretreated with alkaline hydrogen peroxide to the acetic acid-formic acid mixed solution is 1:30-50. The acetic acid-formic acid mixed solution is obtained by mixing acetic acid and formic acid, and the mass percentage of formic acid in the acetic acid-formic acid mixed solution is 1% to 9%.

4. The preparation method of the superhydrophobic esterified modified corn stalk aerogel oil-absorbing material according to claim 1, characterized in that: In step S1, the microwave power is 100-500W, the reaction temperature is 70-110℃, and the reaction time is 5-25min.

5. The preparation method of the superhydrophobic esterified modified corn stalk aerogel oil-absorbing material according to claim 2, characterized in that: In step S2, the preparation process of the corn straw lignin aqueous dispersion after alkaline hydrogen peroxide pretreatment is as follows: Acetic acid solution was added to the filtrate obtained during the preparation of corn stalk cellulose after alkaline hydrogen peroxide pretreatment, and the pH value was adjusted to 5.

5. The precipitate was obtained by vacuum concentration and centrifugation. The precipitate was washed and dried to obtain corn stalk lignin pretreated with alkaline hydrogen peroxide. The corn stalk lignin pretreated with alkaline hydrogen peroxide was mixed evenly with an aqueous acetic acid solution to obtain an aqueous dispersion of corn stalk lignin pretreated with alkaline hydrogen peroxide.

6. The method for preparing the superhydrophobic esterified modified corn stalk aerogel oil-absorbing material according to claim 5, characterized in that: In step S2 The mass ratio of chitosan, polycarboxylic acid, polyvinyl alcohol, esterified modified corn stalks, and corn stalk lignin pretreated with alkaline hydrogen peroxide was (0.15~0.35):0.21:(0.07~0.35):(0.1~0.3):0.

1.

7. The preparation method of the superhydrophobic esterified modified corn stalk aerogel oil-absorbing material according to claim 1, characterized in that: In step S2, the polycarboxylic acid aqueous solution contains 2% polycarboxylic acid by mass; the polyvinyl alcohol aqueous solution contains polyvinyl alcohol by mass ratio of (0.07-0.35):3.5 by water. The polycarboxylic acid is at least one of citric acid, oxalic acid, maleic acid, succinic acid, adipic acid, malic acid, and tartaric acid.

8. The method for preparing the superhydrophobic esterified modified corn stalk aerogel oil-absorbing material according to claim 1, characterized in that: In step S2, the process of hydrophobic modification of the composite aerogel is as follows: the composite aerogel is immersed in a mixed solution of silane, silane coupling agent and n-hexane; the mass ratio of silane, silane coupling agent and n-hexane is (2-5):(1-2):(93-97).

9. The preparation method of the superhydrophobic esterified modified corn stalk aerogel oil-absorbing material according to claim 8, characterized in that: The silane is at least one of hexadecyltrimethoxysilane, perfluorooctyltriethoxysilane, perfluorooctyltrichlorosilane, methyltrimethoxysilane, trichlorovinylsilane, and polydimethylsiloxane; the silane coupling agent is at least one of KH-570, KH-550, KH-560, and KH-792.

10. A superhydrophobic esterified corn stalk aerogel oil-absorbing material, characterized in that, It is prepared by the preparation method described in any one of claims 1 to 9.

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