A method for preparing collagen fiber / ZnO composite aerogel using chromium-containing waste leather scraps as raw material and its application

Abstract

This invention discloses a method for preparing collagen fiber / ZnO composite aerogel using chromium-containing waste leather scraps as raw material and its application. The preparation method includes placing the chromium-containing waste leather scraps in a mixture of oxalic acid and sulfuric acid for chromium removal treatment, purifying the resulting collagen fiber suspension, adjusting the pH of the suspension, and freeze-drying to obtain collagen aerogel; immersing the suspension in a zinc precursor solution to obtain a collagen aerogel adsorbed with the zinc precursor, followed by hydrolysis and condensation in a sodium hydroxide hydrolysate; and immersing the obtained product in n-hexane to obtain the collagen fiber / ZnO composite aerogel. The composite aerogel prepared by this method realizes the transformation of hazardous waste into valuable resources, endows collagen fibers with photocatalytic properties and improves their stability, exhibits excellent photocatalytic degradation effect and recyclability of organic dyes in wastewater, and simultaneously solves the problem of difficult recovery of nano-ZnO.

Description

Technical Field

[0001] This invention belongs to the field of chromium-containing waste leather scrap treatment technology, and relates to a method for preparing collagen fiber / ZnO composite aerogel using chromium-containing waste leather scrap as raw material and its application. Background Technology

[0002] With social and economic development, environmental pollution has become increasingly serious. In the leather industry, only 20% of raw hides are converted into leather during the tanning process, generating 450 kg of solid waste per metric ton of hide, including 250 kg of non-tanned leather scraps and 200 kg of tanned leather scraps. Chrome tanning agents are commonly used, with over 90% of leather production worldwide employing chrome tanning, generating chrome sludge and chromium-containing waste leather scraps during the process. Statistics show that approximately 800,000 tons of chromium-containing waste leather scraps are generated globally each year, with China producing approximately 250,000 tons annually. Chromium-containing waste leather scraps contain large amounts of the heavy metal chromium, which, if not treated promptly, will cause serious harm to the environment and human health; therefore, chromium-containing waste leather scraps are classified as hazardous waste. Furthermore, the main component of chromium-containing waste leather scraps is collagen, and its incomplete utilization represents a huge waste of resources. Collagen is rich in various active groups such as -COOH, -NH2, and -OH, and possesses excellent renewability and biodegradability. Preparing it into a highly porous aerogel would be an excellent adsorbent material. However, pure collagen aerogels suffer from poor stability when used as adsorbents for organic matter in wastewater. Therefore, modification is often employed to enhance their stability. Furthermore, achieving recyclability requires subsequent analysis, a cumbersome process. Summary of the Invention

[0003] To address the problems existing in the prior art, this invention provides a method for preparing collagen fiber / ZnO composite aerogel using chromium-containing waste leather scraps as raw material and its application, thereby solving the technical problems in the prior art where the use of pure collagen aerogel as an adsorbent material for adsorbing organic matter in wastewater is characterized by poor stability and the need for desorption treatment, leading to a cumbersome application process.

[0004] This invention is achieved through the following technical solution:

[0005] A method for preparing collagen fiber / ZnO composite aerogel using chromium-containing waste leather scraps as raw material includes the following steps:

[0006] S1: Chromium-containing waste leather scraps are placed in a mixture of oxalic acid and sulfuric acid for chromium removal treatment. The collagen fiber suspension is purified by filtration, water washing, sodium chloride salting out, and ultrapure water dialysis, and then obtained by freeze drying to obtain collagen aerogel.

[0007] S2: The collagen aerogel is immersed in a zinc precursor solution to obtain a collagen aerogel adsorbed with zinc precursor.

[0008] S3: The collagen aerogel with adsorbed zinc precursor is placed in sodium hydroxide hydrolysate to cause the zinc precursor to undergo hydrolysis and condensation.

[0009] S4: The product obtained in S3 is immersed in n-hexane and naturally dried at room temperature to obtain the collagen fiber / ZnO composite aerogel.

[0010] Preferably, in step S1, the pH value of the collagen fiber suspension is adjusted to 3-12 before freeze-drying; and the freeze-drying time is 24-72 hours.

[0011] Preferably, in step S2, the zinc precursor solution is prepared by placing zinc acetate dihydrate in anhydrous ethanol at 80-95°C and stirring until completely dissolved to obtain the zinc precursor solution.

[0012] Preferably, the concentration of zinc acetate dihydrate is 10–150 mmol / L.

[0013] Preferably, in step S3, the preparation process of the sodium hydroxide hydrolysate is as follows: sodium hydroxide is placed in anhydrous ethanol and ultrasonically dissolved for 30-60 minutes to obtain the sodium hydroxide hydrolysate; the molar ratio of sodium hydroxide to zinc acetate dihydrate is (5-10):1.

[0014] Preferably, in step S2, the mass ratio of the collagen aerogel to the volume of the zinc precursor solution is 10 mg:(1.5-5) mL; the immersion temperature of the collagen aerogel in the zinc precursor solution is 50-90°C, and the immersion time is 4-8 h.

[0015] Preferably, in step S3, the mass ratio of the collagen aerogel to the volume of the sodium hydroxide hydrolysate is 10 mg:(1.5-5) mL; the reaction temperature of the collagen aerogel adsorbed with zinc precursor in the sodium hydroxide hydrolysate is 50-90°C, and the reaction time is 3-6 h.

[0016] Preferably, in step S4, the mass ratio of the collagen aerogel to the volume of n-hexane is 10 mg: (2-8) mL; the soaking time of the product of the collagen aerogel adsorbed with zinc precursor after hydrolysis and condensation in n-hexane is 2-5 h; and the natural drying time is 24-48 h.

[0017] A method for preparing collagen fiber / ZnO composite aerogel using chromium-containing waste leather scraps as raw material is described above.

[0018] The above-mentioned application of collagen fiber / ZnO composite aerogel prepared from chromium-containing waste leather scraps in the field of organic dye wastewater treatment.

[0019] Compared with the prior art, the present invention has the following beneficial technical effects:

[0020] A method for preparing collagen fiber / ZnO composite aerogel using chromium-containing waste leather scraps as raw material is disclosed. This method utilizes chromium-containing waste leather scraps, a hazardous waste generated during leather processing, as raw material. Collagen fibers are extracted and prepared using an acid-based dechromiuming process, thus turning waste into a valuable resource. Furthermore, a photocatalytic material, nano-ZnO, is loaded onto the collagen fibers in situ to prepare the composite aerogel, endowing the collagen fibers with photocatalytic properties. This allows the adsorbed pollutants to be photocatalytically degraded, achieving a dual process of adsorption and degradation. This effectively solves the complex process of post-adsorption desorption required when using collagen aerogel alone as the adsorbent material. In addition, some zinc ions coordinate with the carboxyl and amino groups of collagen, improving the structural strength of the collagen fibers. Simultaneously, the hydroxyl groups on the ZnO surface are linked to the amino groups of collagen through hydrogen bonds, allowing ZnO to firmly adhere to the surface of the collagen fibers. This avoids the three-dimensional structural collapse and poor stability problems caused by swelling when the collagen aerogel is in the liquid phase.

[0021] Furthermore, adjusting the pH of the collagen fiber suspension to 3–12 before freeze-drying can effectively broaden the application range of collagen fibers, enabling efficient adsorption of organic pollutants with different charges. If the organic matter is negatively charged, adjusting the pH of the collagen to acidic will make the collagen fiber surface positively charged, resulting in a higher adsorption rate through positive-negative attraction. Conversely, adjusting the pH of the collagen to alkaline will improve its adsorption efficiency. Additionally, the freeze-drying time should be 24–72 hours; a shorter time will prevent the formation of collagen aerogels.

[0022] Furthermore, the preparation process of the zinc precursor solution is as follows: zinc acetate dihydrate is placed in anhydrous ethanol at 80-95°C and stirred until completely dissolved to obtain the zinc precursor solution. This process allows zinc acetate dihydrate to be fully dissolved in anhydrous ethanol.

[0023] Furthermore, the concentration of zinc acetate dihydrate is 10–150 mmol / L; the molar ratio of zinc acetate dihydrate to sodium hydroxide hydrolysate is 1:(5–10), in which sodium hydroxide is in excess, which can effectively cause the zinc precursor to undergo hydrolysis and condensation reaction.

[0024] Furthermore, the preparation process of the sodium hydroxide hydrolysate is as follows: sodium hydroxide is placed in anhydrous ethanol and ultrasonically dissolved for 30-60 minutes to obtain the sodium hydroxide hydrolysate. This ultrasonic treatment process can achieve complete dissolution of sodium hydroxide, which cannot be achieved by conventional stirring.

[0025] Furthermore, the ratio of the mass of the collagen aerogel to the volume of the zinc precursor solution is 10 mg: (1.5–5) mL, which allows the collagen aerogel to be fully immersed in the zinc precursor solution for reaction. The immersion temperature is 50–90°C, which can effectively prevent the zinc precursor solution from precipitating out. The immersion time is 4–8 h, which allows the zinc precursor solution to fully penetrate into the collagen aerogel.

[0026] Furthermore, the mass ratio of collagen aerogel to sodium hydroxide hydrolysate is 10 mg:(1.5-5) mL, and the reaction temperature of the collagen aerogel adsorbed with zinc precursor in sodium hydroxide hydrolysate is 50-90°C, and the reaction time is 3-6 h, which effectively allows the zinc precursor solution to undergo hydrolysis and be loaded into the collagen aerogel.

[0027] Furthermore, the mass ratio of collagen aerogel to hexane volume is 10 mg:(2-8) mL, and hexane can accelerate the reaction of Zn(OH)4. 2- Water molecules are removed to generate nano-zinc oxide. If the amount of n-hexane added is too small, the zinc oxide will precipitate less or very slowly, affecting the reaction rate. Excessive n-hexane will waste organic solvent. The ratio of the mass of collagen aerogel to the volume of n-hexane is 10 mg: (2-8) mL, which ensures the reaction efficiency and controls the experimental cost. In addition, the product after the zinc precursor undergoes hydrolysis and condensation is soaked in n-hexane for 2-5 hours to ensure the amount of zinc oxide generated. Attached Figure Description

[0028] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1 This is a schematic diagram of the process for producing collagen fiber / ZnO composite aerogel using chromium-containing waste leather scraps as raw material in this invention.

[0030] Figure 2 SEM images of the collagen fiber / ZnO composite aerogel in Example 1 (a, ZnO, b, collagen aerogel, c, collagen fiber / ZnO composite aerogel);

[0031] Figure 3 The adsorption curves and photocatalytic degradation curves of methylene blue for the collagen fiber / ZnO composite aerogel in Example 2 are shown.

[0032] Figure 4This refers to the stability of the photocatalytic degradation of methylene blue by the collagen fiber / ZnO composite aerogel in Example 3. Detailed Implementation

[0033] To enable those skilled in the art to understand the features and effects of the present invention, the terms and expressions used in the specification and claims are explained and defined in general below. Unless otherwise specified, all technical and scientific terms used herein have the ordinary meaning understood by those skilled in the art regarding the present invention, and in case of conflict, the definitions in this specification shall prevail.

[0034] The theories or mechanisms described and disclosed herein, whether right or wrong, should not in any way limit the scope of the invention, that is, the contents of the invention can be implemented without being limited by any particular theory or mechanism.

[0035] In this document, all features defined by numerical ranges or percentage ranges, such as numerical values, quantities, contents, and concentrations, are for the sake of brevity and convenience only. Accordingly, descriptions of numerical ranges or percentage ranges should be considered as covering and specifically disclosing all possible sub-ranges and individual numerical values ​​(including integers and fractions) within those ranges.

[0036] In this article, unless otherwise specified, “contains,” “includes,” “containing,” “has,” or similar terms cover the meanings of “composed of” and “mainly composed of,” for example, “A contains a” covers the meanings of “A contains a and others” and “A contains only a.”

[0037] For the sake of brevity, not all possible combinations of the technical features in each implementation scheme or embodiment are described herein. Therefore, as long as there is no contradiction in the combination of these technical features, the technical features in each implementation scheme or embodiment can be combined arbitrarily, and all possible combinations should be considered within the scope of this specification.

[0038] like Figure 1 As shown, this invention provides a method for preparing collagen fiber / ZnO composite aerogel using chromium-containing waste leather scraps as raw material, comprising the following steps:

[0039] S1: Chromium-containing waste leather scraps are placed in a mixture of oxalic acid and sulfuric acid for chromium removal treatment. The collagen fiber suspension is purified by filtration, water washing, sodium chloride salting out, and ultrapure water dialysis. The collagen fibers are then freeze-dried to obtain collagen aerogel.

[0040] Specifically, 10 parts oxalic acid and 5 parts sulfuric acid were dissolved in 105 parts deionized water to obtain a mixed acid solution. 10 parts chromium-containing waste leather scraps were placed in 35 parts of the mixed acid solution and stirred at 40°C for 4 hours, then filtered and washed with water. This process was repeated three times, and the coarse precipitate was collected by centrifugation. After washing twice with water at room temperature (~25°C), the precipitate was centrifuged and dispersed in a 0.5 mol / L acetic acid solution. Then, 0.7–3.0 mol / L sodium chloride was added for salting out and purification. The purified precipitate was then dissolved again in a 0.1 mol / L acetic acid solution, and dialyzed with ultrapure water to obtain a collagen fiber dispersion. The pH of the dispersion was adjusted to 3–12, with a more preferred pH of 6–9. Finally, the dispersion was freeze-dried at -50°C for 48–72 hours to obtain collagen aerogel.

[0041] S2: The collagen aerogel is immersed in a zinc precursor solution to obtain a collagen aerogel adsorbed with zinc precursor.

[0042] The preparation process of the zinc precursor solution is as follows: zinc acetate dihydrate is placed in anhydrous ethanol at 80-95°C and stirred until completely dissolved to obtain the zinc precursor solution. Since the temperature of the anhydrous ethanol is relatively high and it evaporates quickly, the dissolution process is carried out in a glass bottle with a lid.

[0043] The concentration of zinc acetate dihydrate is 10–150 mmol / L, more preferably 40–120 mmol / L; the mass ratio of the collagen aerogel to the volume of the zinc precursor solution is 10 mg:(1.5–5) mL, more preferably 10 mg:(2–4) mL. Controlling this mass ratio ensures the collagen aerogel is fully submerged in the zinc precursor solution, allowing the zinc precursor to penetrate the interior of the collagen aerogel. The immersion temperature of the collagen aerogel in the zinc precursor solution is 50–90°C, more preferably 60–80°C, and the immersion time is 4–8 h.

[0044] S3: The collagen aerogel with adsorbed zinc precursor is placed in sodium hydroxide hydrolysate to cause the zinc precursor to undergo hydrolysis and condensation. The resulting product is then soaked in n-hexane to obtain the collagen fiber / ZnO composite aerogel.

[0045] The preparation process of the sodium hydroxide hydrolysate is as follows: sodium hydroxide is placed in anhydrous ethanol and ultrasonically dissolved for 30-60 minutes to obtain the sodium hydroxide hydrolysate. The molar ratio of sodium hydroxide to zinc acetate dihydrate is (5-10):1, more preferably (7-9):1.

[0046] The mass ratio of the collagen aerogel to the volume of the sodium hydroxide hydrolysate is 10 mg:(1.5-5) mL, more preferably 10 mg:(2-4) mL. The reaction temperature of the collagen aerogel adsorbed with zinc precursor in the sodium hydroxide hydrolysate is 50-90°C, more preferably 60-80°C, and the reaction time is 3-6 h.

[0047] The mass ratio of collagen aerogel to hexane is 10 mg:(2-8) mL, more preferably 10 mg:(3-6) mL. The product of the zinc precursor after hydrolysis and condensation is soaked in hexane for 2-5 hours. Hexane can promote the polymerization of Zn(OH)4. 2- Water molecules are removed to generate nano-zinc oxide.

[0048] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0049] The following examples use instruments and equipment conventional in the art. Experimental methods in the following examples, unless otherwise specified, are generally performed under conventional conditions or as recommended by the manufacturer. All raw materials used in the following examples are conventional commercially available products with specifications conventional in the art. In this specification and the following examples, unless otherwise specified, "%" refers to weight percentage, "parts" refers to parts by weight, and "ratio" refers to weight proportion.

[0050] Comparative Example 1

[0051] 0.0198 g of zinc acetate dihydrate was dissolved in 9.0 mL of ethanol solution and stirred at 80 °C until completely dissolved to obtain a zinc precursor solution with a concentration of 10 mmol / L. Then, 0.0288 g of sodium hydroxide was dissolved in 9.0 mL of ethanol solution and sonicated for 30 min to prepare a hydrolysate with a sodium hydroxide concentration of 50 mmol / L. Subsequently, the zinc precursor solution was added dropwise to the hydrolysate, and the reaction was carried out at 60 °C for 3 h. After that, 9.0 mL of n-hexane was added, and the mixture was allowed to stand for 2 h. Finally, the mixture was naturally dried at room temperature for 24 h to obtain ZnO.

[0052] Comparative Example 2

[0053] Ten parts oxalic acid and five parts sulfuric acid were dissolved in 105 parts deionized water to obtain a mixed acid solution. Ten parts chromium-containing waste leather scraps were placed in 35 parts of the mixed acid solution and stirred at 40°C for 4 hours, then filtered and washed with water. The above operation was repeated three times, and the coarse precipitate was collected by centrifugation. After washing twice with water at room temperature (~25°C), the precipitate was centrifuged and dispersed in 0.5 mol / L acetic acid solution. Then, 0.7-3.0 mol / L sodium chloride was added for salting out and purification. The purified precipitate was dissolved again in 0.1 mol / L acetic acid solution and dialyzed with ultrapure water to obtain a collagen fiber dispersion. 1.5 g of the collagen fiber dispersion was taken, the pH was adjusted to 9, and then freeze-dried at -50°C for 48 hours to obtain collagen aerogel.

[0054] Example 1

[0055] 10 parts oxalic acid and 5 parts sulfuric acid were dissolved in 105 parts deionized water to obtain a mixed acid solution. 10 parts chromium-containing waste leather scraps were placed in 35 parts of the mixed acid solution and stirred at 40°C for 4 hours, then filtered and washed with water. The above operation was repeated 3 times, and the coarse precipitate was collected by centrifugation. After washing twice with water at room temperature (~25°C), the precipitate was centrifuged and dispersed in 0.5 mol / L acetic acid solution. Subsequently, 0.7-3.0 mol / L sodium chloride was added for salting out and purification. The purified precipitate was dissolved again in 0.1 mol / L acetic acid solution, and dialyzed with ultrapure water to obtain a collagen fiber dispersion. Take 1.5g of collagen fiber dispersion, adjust the pH to 9, and freeze-dry at -50℃ for 48h to obtain collagen aerogel with a mass of approximately 45mg. Dissolve 0.0198g of zinc acetate dihydrate in 9.0mL of ethanol solution and stir at 80℃ until completely dissolved to obtain a zinc precursor solution with a concentration of 10mmol / L. Place the above collagen aerogel in the zinc precursor solution and soak at 80℃ for 6h to allow the precursor solution to fully penetrate the collagen aerogel. Then, dissolve 0.0288g of sodium hydroxide in 9.0mL of ethanol solution and sonicate for 30min to prepare a hydrolysate with a sodium hydroxide concentration of 80mmol / L. Subsequently, transfer the aerogel to the hydrolysate, let it stand at 70℃ for 4h, remove it, soak it in 9.0mL of n-hexane for 3h, and then air-dry it at room temperature for 36h to obtain collagen fiber / ZnO aerogel.

[0056] Example 2

[0057] 10 parts oxalic acid and 5 parts sulfuric acid were dissolved in 105 parts deionized water to obtain a mixed acid solution. 10 parts chromium-containing waste leather scraps were placed in 35 parts of the mixed acid solution and stirred at 40°C for 4 hours, then filtered and washed with water. The above operation was repeated 3 times, and the coarse precipitate was collected by centrifugation. After washing twice with water at room temperature (~25°C), the precipitate was centrifuged and dispersed in 0.5 mol / L acetic acid solution. Subsequently, 0.7-3.0 mol / L sodium chloride was added for salting out and purification. The purified precipitate was dissolved again in 0.1 mol / L acetic acid solution, and dialyzed with ultrapure water to obtain a collagen fiber dispersion. Take 2.0 g of collagen fiber dispersion, adjust the pH to 7, and freeze-dry at -50℃ for 72 h to obtain collagen aerogel with a mass of about 60 mg; dissolve 0.9878 g of zinc acetate dihydrate in 30 mL of ethanol solution and stir at 95℃ until completely dissolved to obtain a zinc precursor solution with a concentration of 150 mmol / L. Place the above collagen aerogel in the zinc precursor solution and soak at 65℃ for 7 h to allow the precursor solution to fully penetrate the collagen aerogel; then dissolve 0.9 g of sodium hydroxide in 30 mL of ethanol solution and sonicate for 60 min to prepare a hydrolysate with a sodium hydroxide concentration of 750 mmol / L; then transfer the aerogel to the hydrolysate, let it stand at 60℃ for 5 h, remove it, soak it in 48 mL of n-hexane for 5 h, and then air-dry it at room temperature for 42 h to obtain collagen fiber / ZnO aerogel.

[0058] Example 3

[0059] 10 parts oxalic acid and 5 parts sulfuric acid were dissolved in 105 parts deionized water to obtain a mixed acid solution. 10 parts chromium-containing waste leather scraps were placed in 35 parts of the mixed acid solution and stirred at 40°C for 4 hours, then filtered and washed with water. The above operation was repeated 3 times, and the coarse precipitate was collected by centrifugation. After washing twice with water at room temperature (~25°C), the precipitate was centrifuged and dispersed in 0.5 mol / L acetic acid solution. Subsequently, 0.7-3.0 mol / L sodium chloride was added for salting out and purification. The purified precipitate was dissolved again in 0.1 mol / L acetic acid solution, and dialyzed with ultrapure water to obtain a collagen fiber dispersion. Take 2.5 g of collagen fiber dispersion, adjust the pH to 5, and freeze-dry at -50℃ for 72 h to obtain collagen aerogel with a mass of approximately 75 mg. Dissolve 0.3564 g of zinc acetate dihydrate in 13.5 mL of ethanol solution and stir at 90℃ until completely dissolved to obtain a zinc precursor solution with a concentration of 120 mmol / L. Place the above collagen aerogel in the zinc precursor solution and soak at 70℃ for 8 h to allow the precursor solution to fully penetrate the collagen aerogel. Then, dissolve 0.745 g of sodium hydroxide in 27.0 mL of ethanol solution and sonicate for 40 min to prepare a hydrolysate with a sodium hydroxide concentration of 690 mmol / L. Transfer the aerogel to the hydrolysate and react at 90℃ for 6 h. After that, remove it and soak it in 22.5 mL of n-hexane for 4.5 h. Dry naturally at room temperature for 48 h to obtain collagen fiber / ZnO aerogel.

[0060] Example 4:

[0061] 10 parts oxalic acid and 5 parts sulfuric acid were dissolved in 105 parts deionized water to obtain a mixed acid solution. 10 parts chromium-containing waste leather scraps were placed in 35 parts of the mixed acid solution and stirred at 40°C for 4 hours, then filtered and washed with water. The above operation was repeated 3 times, and the coarse precipitate was collected by centrifugation. After washing twice with water at room temperature (~25°C), the precipitate was centrifuged and dispersed in 0.5 mol / L acetic acid solution. Subsequently, 0.7-3.0 mol / L sodium chloride was added for salting out and purification. The purified precipitate was dissolved again in 0.1 mol / L acetic acid solution, and dialyzed with ultrapure water to obtain a collagen fiber dispersion. Take 0.7 g of collagen fiber dispersion, adjust the pH to 12, and freeze-dry at -50℃ for 48 h to obtain collagen aerogel with a mass of about 20 mg; dissolve 0.1405 g of zinc acetate dihydrate in 8.0 mL of ethanol solution and stir at 85℃ until completely dissolved to obtain a zinc precursor solution with a concentration of 80 mmol / L. Place the above collagen aerogel in the zinc precursor solution and soak at 50℃ for 4 h to allow the precursor solution to fully penetrate the collagen aerogel; then dissolve 0.144 g of sodium hydroxide in 6.0 mL of ethanol solution and sonicate for 50 min to prepare a hydrolysate with a sodium hydroxide concentration of 600 mmol / L; then transfer the aerogel to the hydrolysate and react at 50℃ for 3 h, then remove and soak in 10.5 mL of n-hexane for 2 h; and air-dry at room temperature for 24 h to obtain collagen fiber / ZnO aerogel.

[0062] Example 5

[0063] 10 parts oxalic acid and 5 parts sulfuric acid were dissolved in 105 parts deionized water to obtain a mixed acid solution. 10 parts chromium-containing waste leather scraps were placed in 35 parts of the mixed acid solution and stirred at 40°C for 4 hours, then filtered and washed with water. The above operation was repeated 3 times, and the coarse precipitate was collected by centrifugation. After washing twice with water at room temperature (~25°C), the precipitate was centrifuged and dispersed in 0.5 mol / L acetic acid solution. Subsequently, 0.7-3.0 mol / L sodium chloride was added for salting out and purification. The purified precipitate was dissolved again in 0.1 mol / L acetic acid solution, and dialyzed with ultrapure water to obtain a collagen fiber dispersion. Take 1.0 g of collagen fiber dispersion, adjust the pH to 3, and freeze-dry at -50℃ for 24 h to obtain collagen aerogel with a mass of about 30 mg; dissolve 0.0988 g of zinc acetate dihydrate in 9 mL of ethanol solution and stir at 87℃ until completely dissolved to obtain a zinc precursor solution with a concentration of 50 mmol / L. Place the above collagen aerogel in the zinc precursor solution and soak at 60℃ for 5 h to allow the precursor solution to fully penetrate the collagen aerogel; then dissolve 0.204 g of sodium hydroxide in 12 mL of ethanol solution and sonicate for 35 min to prepare a hydrolysate with a sodium hydroxide concentration of 425 mmol / L; then transfer the aerogel to the hydrolysate and react at 80℃ for 4.5 h, then remove and soak in 18 mL of n-hexane for 4 h; and air-dry at room temperature for 30 h to obtain collagen fiber / ZnO aerogel.

[0064] Example 6

[0065] 10 parts oxalic acid and 5 parts sulfuric acid were dissolved in 105 parts deionized water to obtain a mixed acid solution. 10 parts chromium-containing waste leather scraps were placed in 35 parts of the mixed acid solution and stirred at 40°C for 4 hours, then filtered and washed with water. The above operation was repeated 3 times, and the coarse precipitate was collected by centrifugation. After washing twice with water at room temperature (~25°C), the precipitate was centrifuged and dispersed in 0.5 mol / L acetic acid solution. Subsequently, 0.7-3.0 mol / L sodium chloride was added for salting out and purification. The purified precipitate was dissolved again in 0.1 mol / L acetic acid solution, and dialyzed with ultrapure water to obtain a collagen fiber dispersion. Take 1.65 g of collagen fiber dispersion, adjust the pH to 3, and freeze-dry at -50℃ for 24 h to obtain collagen aerogel with a mass of approximately 50 mg. Dissolve 0.0494 g of zinc acetate dihydrate in 7.5 mL of ethanol solution and stir at 83℃ until completely dissolved to obtain a zinc precursor solution with a concentration of 30 mmol / L. Place the above collagen aerogel in the zinc precursor solution and soak at 90℃ for 4 h to allow the precursor solution to fully penetrate the collagen aerogel. Then, dissolve 0.09 g of sodium hydroxide in 7.5 mL of ethanol solution and sonicate for 45 min to prepare a hydrolysate with a sodium hydroxide concentration of 300 mmol / L. Subsequently, transfer the aerogel to the hydrolysate and react at 75℃ for 5.5 h. After that, remove it and soak it in 12 mL of n-hexane for 3.5 h. Dry it naturally at room temperature for 40 h to obtain collagen fiber / ZnO aerogel.

[0066] The microstructure of ZnO in Comparative Example 1, collagen aerogel in Comparative Example 2, and collagen fiber / ZnO composite aerogel in Example 1 was observed using field emission scanning electron microscopy. Figure 2 As can be seen, the prepared ZnO mainly exhibits a nanosheet structure. Before the introduction of ZnO, the surface of the collagen aerogel is smooth and has a porous structure; after the introduction of ZnO, the pore structure becomes smaller and the fiber surface becomes rougher due to the deposition of ZnO on the fiber surface, indicating that zinc oxide was successfully deposited on the surface of the collagen fibers.

[0067] The collagen fiber / ZnO composite aerogel prepared in Example 2 was placed in 80 mL of 10 mg / L methylene blue solution and stirred in the dark for 60 min to reach adsorption-desorption equilibrium. Then, a photocatalytic degradation experiment was conducted under 300 W xenon lamp illumination for 160 min, with samples taken every 20 min. Figure 3 As can be seen, the adsorption rate of the composite aerogel increases rapidly in the first 10 minutes and tends to reach adsorption equilibrium at 60 minutes, with an adsorption rate of about 27.7%; its photocatalytic degradation rate increases significantly in the first 40 minutes and finally reaches 94.5% after 160 minutes.

[0068] Figure 4This demonstrates the stability of the adsorption-photocatalytic degradation of methylene blue by collagen fiber / ZnO aerogel in Example 3. The aerogel degraded 94.3% of the methylene blue within 160 minutes, and after 5 cycles, the degradation rate still reached 83.7%, indicating a significant enhancement in stability after composite processing.

[0069] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

[0070] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for preparing collagen fiber / ZnO composite aerogel using chromium-containing waste leather scraps as raw material, characterized in that, Includes the following steps: S1: Chromium-containing waste leather scraps are placed in a mixture of oxalic acid and sulfuric acid for chromium removal treatment. The collagen fiber suspension is purified by filtration, water washing, sodium chloride salting-out, and ultrapure water dialysis, and then obtained by freeze drying to obtain collagen aerogel. The ratio of oxalic acid to sulfuric acid is 10 parts by mass: 5 parts. S2: The collagen aerogel is immersed in a zinc precursor solution to obtain a collagen aerogel adsorbed with zinc precursor; the zinc precursor solution is prepared by placing zinc acetate dihydrate in anhydrous ethanol at 80~95 °C and stirring until completely dissolved to obtain the zinc precursor solution. S3: The collagen aerogel with adsorbed zinc precursor is placed in sodium hydroxide hydrolysate to cause the zinc precursor to undergo hydrolysis and condensation. S4: The product obtained in S3 is immersed in n-hexane and naturally dried at room temperature to obtain the collagen fiber / ZnO composite aerogel.

2. The method for preparing collagen fiber / ZnO composite aerogel using chromium-containing waste leather scraps as raw material according to claim 1, characterized in that, In step S1, before freeze-drying the collagen fiber suspension, the pH value of the collagen fiber suspension is adjusted to 3~12; at the same time, the freeze-drying time is 24~72 h.

3. The method for preparing collagen fiber / ZnO composite aerogel using chromium-containing waste leather scraps as raw material according to claim 1, characterized in that, The concentration of zinc acetate dihydrate is 10~150 mmol / L.

4. The method for preparing collagen fiber / ZnO composite aerogel using chromium-containing waste leather scraps as raw material according to claim 1, characterized in that, In step S3, the preparation process of sodium hydroxide hydrolysate is as follows: sodium hydroxide is placed in anhydrous ethanol and ultrasonically dissolved for 30-60 min to obtain the sodium hydroxide hydrolysate; the molar ratio of sodium hydroxide to zinc acetate dihydrate is (5-10):

1.

5. A method for preparing collagen fiber / ZnO composite aerogel using chromium-containing waste leather scraps as raw material according to claim 1, characterized in that, In step S2, the mass ratio of the collagen aerogel to the volume of the zinc precursor solution is 10 mg:(1.5~5) mL; the immersion temperature of the collagen aerogel in the zinc precursor solution is 50~90 ℃, and the immersion time is 4~8 h.

6. A method for preparing collagen fiber / ZnO composite aerogel using chromium-containing waste leather scraps as raw material according to claim 1, characterized in that, In step S3, the mass ratio of the collagen aerogel to the volume of the sodium hydroxide hydrolysate is 10 mg:(1.5~5) mL; the reaction temperature of the collagen aerogel adsorbed with zinc precursor in the sodium hydroxide hydrolysate is 50~90 ℃, and the reaction time is 3~6 h.

7. A method for preparing collagen fiber / ZnO composite aerogel using chromium-containing waste leather scraps as raw material according to claim 1, characterized in that, In step S4, the mass ratio of the collagen aerogel to the volume of n-hexane is 10 mg:(2~8) mL; the product of the collagen aerogel adsorbed with zinc precursor after hydrolysis and condensation is soaked in n-hexane for 2~5 h; and the natural drying time is 24~48 h.

8. A method for preparing collagen fiber / ZnO composite aerogel using chromium-containing waste leather scraps as raw material, characterized in that, It is prepared by the method described in any one of claims 1 to 7.

9. The application of the collagen fiber / ZnO composite aerogel prepared from chromium-containing waste leather scraps as described in claim 8 in the field of organic dye wastewater treatment.

Images