Preparation method and application of starch-based super-hydrophobic oleophilic aerogel
By preparing a multi-layered interpenetrating porous structure through the acetal reaction of natural starch and glutaraldehyde and gradient casting, combined with nanoscale calcium carbonate deposition, the stability and environmental problems of traditional superhydrophilic-underwater superoleophobic systems are solved, achieving efficient oil-water separation and self-cleaning properties.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-04-30
- Publication Date
- 2026-07-03
AI Technical Summary
Existing superhydrophilic-underwater superoleophobic systems rely on synthetic polymers and inorganic ions, which involve complex processes and poor long-term stability of the substrate materials, making it difficult to achieve efficient oil-water separation and posing environmental and health threats.
A three-dimensional cross-linked network is formed by the acetal reaction of natural starch and glutaraldehyde. Combined with gradient casting and hydrophobic modification, a multi-layered interpenetrating porous structure is prepared, and nano-sized calcium carbonate particles are deposited on the gel surface to form a superhydrophobic and oleophilic aerogel.
The prepared starch-based superhydrophobic and oleophilic aerogel has high oil-water separation efficiency, anti-swelling and self-cleaning properties. The process is simple, low-cost and environmentally friendly, making it suitable for industrial applications.
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Figure CN122325836A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of oil-water separation and recovery technology, specifically to a method for preparing starch-based superhydrophobic and oleophilic aerogel and its application. Background Technology
[0002] Food wastewater contains large amounts of dispersed and floating oil. Direct discharge or improper treatment can cause environmental pollution and serious resource waste. In principle, oil-water mixtures can be separated using traditional methods such as air buoyancy, electrochemical polymerization, and centrifugation. However, these methods have significant drawbacks, including complex control, the need for skilled operators, high operating costs, and a noticeable environmental footprint. Currently, superwetting systems for oil-water separation are divided into superhydrophilic-underwater superoleophobic and superhydrophobic-superoleophilic systems, with drastically different separation principles and application scenarios. The development of superhydrophilic-underwater superoleophobic systems largely focuses on using synthetic polymers (such as polyvinyl alcohol, polyacrylic acid, and polyimide) or hydrophilically modified polymers as substrates. While these materials can achieve some oil-water separation, they have inherent defects that cannot be ignored. Starch and cellulose, on the other hand, are natural hydrophilic polymers with good biocompatibility, easy degradation, and environmental friendliness. Starch retrogradation can form a three-dimensional skeletal network, making it an advantageous substrate material for constructing superwetting systems. However, superhydrophilic-underwater superoleophobic systems based on starch or cellulose strongly "lock in" water molecules due to the presence of numerous hydroxyl groups, making oil-water separation difficult through gravity. Furthermore, the swelling from water absorption easily clogs micron-sized pores, affecting oil-water separation flux. In addition, the nanoscale rough surfaces are typically constructed from inorganic ions such as silica, which not only easily detach in practical applications but also pose threats to the environment and human health. Therefore, improvements are urgently needed. Summary of the Invention
[0003] The purpose of this invention is to provide a method for preparing starch-based superhydrophobic and oleophilic aerogels and their applications, which solves the problems of traditional techniques for preparing superhydrophobic and oleophilic systems, which rely on synthetic polymers and inorganic ions, have complex processes, and have poor long-term stability of the substrate material.
[0004] This invention is achieved through the following technical solutions:
[0005] A method for preparing a starch-based superhydrophobic and oleophilic aerogel, the method comprising the following steps:
[0006] 1) Starch gelatinization: Add deionized water to natural corn starch, stir, and then gelatinize the natural corn starch suspension. The gelatinization temperature is 85℃~95℃, the gelatinization time is 25~35min, and then cool to 60℃-65℃.
[0007] 2) Acetal reaction; glutaraldehyde is added to the starch paste obtained in step 1), the reaction is completed, and the mixture is cooled for long-term retrogradation. After vacuum freeze-drying, the first starch aerogel is obtained.
[0008] 3) Gradient casting: A starch suspension with a lower concentration is gelatinized using the same method as in step 1) and reacted with glutaraldehyde to obtain a pre-formed liquid. The pre-formed liquid is then cast into the first starch aerogel. After long-term retrogradation, it is freeze-dried under vacuum. This gradient casting process is repeated, and the retrogradation and vacuum freeze-drying process is repeated to obtain the second starch aerogel.
[0009] 4) Hydrophobic modification: The second starch aerogel is reacted with palmitoyl chloride by impregnation to obtain the third starch aerogel;
[0010] 5) Calcium carbonate deposition: The third starch aerogel is first soaked in calcium chloride solution, dried by air drying, then soaked in sodium carbonate solution, washed with anhydrous ethanol, and dried again to obtain superhydrophobic and oleophilic starch aerogel.
[0011] Preferably, the mass concentration of the natural corn starch suspension in step 1) is 2%~10% (w / w).
[0012] Preferably, in step 2), the glutaraldehyde concentration is 15%~35% (w / w, starch-based), the crosslinking reaction temperature of starch paste and glutaraldehyde is 60-65℃, the reaction time is 20~40min, the setback temperature is 3℃-5℃, and the setback time is 3~5 days.
[0013] Preferably, the glutaraldehyde concentration, reaction temperature, time, and retrogradation time in step 3) are consistent with the preparation process of the first starch aerogel.
[0014] Preferably, the starch suspension concentration gradient in step 3) of gradient casting is 0.1%~2% (w / w).
[0015] Preferably, the gradient pouring number is 1 to 9 times.
[0016] Preferably, step 4) is as follows: first, the second starch aerogel is immersed in ethyl acetate, then triethylamine and palmitoyl chloride are added dropwise, and after stirring for 1.5 to 3 hours, it is washed with anhydrous ethanol and dried at 40°C to obtain the third starch aerogel.
[0017] Preferably, the mass ratio of triethylamine to the second starch aerogel is 10:1 to 13:1.
[0018] Preferably, the mass ratio of palmitoyl chloride to the second starch aerogel is 2:1 to 4:1.
[0019] Preferably, in step 5), the concentration of the calcium chloride solution is 0.5 mol / L to 1.5 mol / L, and the soaking time is 6 to 8 hours; the concentration of the sodium carbonate solution is 0.5 mol / L to 1.5 mol / L, and the soaking time is 6 to 8 hours.
[0020] This invention utilizes the acetal reaction between the hydroxyl groups of natural starch and the aldehyde groups of glutaraldehyde to form a robust three-dimensional cross-linked network, effectively maintaining the stability of the starch gel as a substrate. Following repeated casting at gradient concentrations, a multi-layered, interpenetrating three-dimensional network structure containing micron-sized pores is obtained. Surface energy is reduced through long-chain palmitoyl chloride modification, and a rough surface of nano-sized calcium carbonate particles is left on the gel surface through a single impregnation method (calcium chloride and sodium carbonate solution). The prepared starch aerogel exhibits superhydrophobic and oleophilic properties, strong underwater oil absorption capacity, high mechanical and chemical stability, high oil-water separation efficiency, anti-swelling, strong wear resistance, good self-cleaning properties, and strong antifouling ability, showing promising prospects for industrial application.
[0021] Therefore, this invention also protects the application of starch-based superhydrophobic and oleophilic aerogels obtained by the above preparation method for oil-water separation.
[0022] The beneficial effects of this invention are as follows: This invention forms a strong three-dimensional cross-linked network through the acetal reaction between the hydroxyl groups of natural starch and the aldehyde groups of glutaraldehyde, effectively maintaining the firmness of the starch gel as a substrate. Then, after repeated casting under gradient concentration, a multi-layered interpenetrating three-dimensional network structure containing micron-sized pores is obtained. The surface energy is reduced by modifying with long-chain palmitoyl chloride, and a rough surface of nano-sized calcium carbonate particles is left on the gel surface by a one-time impregnation method (calcium chloride and sodium carbonate solution). This technology is simple, low-cost, and environmentally friendly. It avoids the reliance of traditional preparation techniques on synthetic polymers to provide the material skeleton and avoids the reliance of traditional superwetting systems on silica prepared by the TEOS (tetraethoxysilane) method to construct the nano-sized rough surface. The raw materials are widely available and environmentally friendly. The starch aerogel prepared in this way has superhydrophobic and oleophilic properties, strong underwater oil absorption capacity, high oil-water separation efficiency, anti-swelling, and good self-cleaning properties, and has good prospects for industrial application. Attached Figure Description
[0023] Figure 1 These are scanning electron microscope (SEM) images of starch aerogels prepared by different methods in Examples 1-3 and Comparative Examples 1-5, where the red arrows indicate calcium carbonate deposited on the gel network.
[0024] Figure 2 The contact angle and roll-off angle of starch aerogels prepared by different methods in Examples 1-3 and Comparative Examples 1-5 are shown.
[0025] Figure 3This refers to the water-oil affinity and self-cleaning ability of the starch aerogels prepared in Example 2 and Comparative Example 5.
[0026] Figure 4 The underwater oil absorption capacity of starch aerogels prepared by different methods in Examples 1-3 and Comparative Examples 1-5 is shown. Detailed Implementation
[0027] The following is a further description of the invention, but not a limitation thereof.
[0028] Example 1:
[0029] (1) Starch gelatinization: Add deionized water to natural corn starch and stir to obtain a uniform natural corn starch suspension with a concentration of 2% (w / w). Gelatinize the suspension in a water bath at 85°C for 25 min and then cool it to 60°C.
[0030] (2) Acetal reaction: Glutaraldehyde was added to starch paste at 60℃ and reacted for 20 min to ensure its concentration was 15% (w / w, starch base). After the reaction was completed, it was poured into a mold and regenerated at 4℃ for 3 days. After vacuum freeze-drying, the first starch aerogel was obtained.
[0031] (3) Gradient casting: After gelatinizing a natural starch suspension with a lower concentration of 0.5% (w / w), it reacts with glutaraldehyde to obtain a pre-formed liquid. The pre-formed liquid is cast into the first starch aerogel, and after long-term retrogradation at 4°C, it is vacuum freeze-dried. The same gradient casting method is used once to obtain the second starch aerogel.
[0032] The glutaraldehyde concentration, reaction temperature and time, and reversion temperature and time are consistent with those in step (2);
[0033] (4) Hydrophobic modification: The second starch aerogel was completely soaked with 200 mL of ethyl acetate, and triethylamine and palmitoyl chloride were added dropwise and stirred for 1.5 h. The ratio of triethylamine: palmitoyl chloride: second starch aerogel was 10:2:1 (mass ratio). The aerogel was washed with anhydrous ethanol at least three times and dried at 40 °C to obtain the third starch aerogel.
[0034] (5) Calcium carbonate deposition: The third starch aerogel was first soaked in 0.5 mol / L calcium chloride solution for 6 h at room temperature, then air-dried and then soaked in 0.5 mol / L sodium carbonate solution for 6 h. It was washed with anhydrous ethanol more than three times and then air-dried again to obtain starch-based superhydrophobic and oleophilic aerogel.
[0035] Example 2
[0036] (1) Starch gelatinization: Same as in Example 1 (1), except that the concentration of natural corn starch suspension is 6% (w / w), and the gelatinization temperature and time are 90℃ and 30min respectively; then cooled to 62℃;
[0037] (2) Acetal reaction: Same as in Example 1 (2), except that the glutaraldehyde concentration is 25% (w / w), the crosslinking reaction temperature and time are 62℃ and 30min respectively, and the settling time is 4 days;
[0038] (3) Gradient casting: Same as (3) in Example 1, except that the concentration gradient is 1% (w / w) and the number of castings is 4.
[0039] (4) Hydrophobic modification: Same as in Example 1 (4), except that the ethyl acetate is 250 mL, the reaction time is 2.5 h, and the ratio of triethylamine: palmitoyl chloride: second starch aerogel is 12:3:1 (mass ratio).
[0040] (5) Calcium carbonate deposition: Same as in Example 1 (5), except that the concentrations of calcium chloride and sodium carbonate are 1 mol / L and the soaking time is 7 h.
[0041] Example 3
[0042] (1) Starch gelatinization: Same as in Example 1 (1), except that the concentration of natural corn starch suspension is 10% (w / w), and the gelatinization temperature and time are 95℃ and 35min respectively; then cooled to 65℃;
[0043] (2) Acetal reaction: Same as in Example 1 (2), except that the glutaraldehyde concentration is 35% (w / w), the crosslinking reaction temperature and time are 65℃ and 40min respectively, and the settling time is 5 days;
[0044] (3) Gradient casting: Same as (3) in Example 1, except that the concentration gradient is 1% (w / w) and the number of castings is 9;
[0045] (4) Hydrophobic modification: Same as in Example 1 (4), except that the ethyl acetate is 300 mL, the reaction time is 3 h, and the ratio of triethylamine: palmitoyl chloride: second starch aerogel is 13:4:1 (mass ratio).
[0046] (5) Calcium carbonate deposition: Same as in Example 1 (5), except that the concentrations of calcium chloride and sodium carbonate are 1.5 mol / L and the soaking time is 8 h.
[0047] Comparative Example 1
[0048] Same as Example 2, except that it did not undergo gradient pouring.
[0049] Comparative Example 2
[0050] Same as Example 2, except that it did not undergo the glutaraldehyde crosslinking reaction.
[0051] Comparative Example 3
[0052] Same as Example 2, except that it was not modified to be hydrophobic.
[0053] Comparative Example 4
[0054] Same as Example 2, except that calcium carbonate deposition was not performed.
[0055] Comparative Example 5
[0056] Natural freeze-dried aerogel: Deionized water is added to natural corn starch and stirred to obtain a uniform natural corn starch suspension with a concentration of 6% (w / w). The suspension is gelatinized in a water bath at 90°C for 30 minutes and then freeze-dried after cooling to room temperature.
[0057] To further illustrate the technical effects of the present invention, measurements were performed on the relevant samples obtained from Examples 1-3 and Comparative Examples 1-5.
[0058] I. Effects of different preparation methods on the microstructure of starch aerogel
[0059] Starch aerogels prepared by different methods in Examples 1-3 and Comparative Examples 1-5 were fixed onto an aluminum substrate using double-sided tape and then plated with a gold-palladium alloy layer. The effects of different preparation methods on the microstructure of the gels were observed using scanning electron microscopy at 5000x magnification and 2.0kV accelerating voltage. Results are shown below. Figure 1 .
[0060] II. Determination of contact angle and roll-off angle of starch aerogel
[0061] The water contact angle and roll-off angle of starch aerogel in air were determined using a fully automated contact angle measuring instrument. See results below. Figure 2 .
[0062] III. Underwater oil absorption capacity of starch aerogels
[0063] Starch aerogels prepared by different methods were immersed in chloroform for 45 min, and the gel mass before and after absorption was measured. (See results below.) Figure 4 The oil absorption capacity is calculated using the following formula:
[0064] In the formula, m0 and m1 represent the mass of starch gel before and after absorption, respectively.
[0065] IV. Self-cleaning ability test
[0066] See Figure 3 Sediment taken from the natural environment was scattered on the surface of the starch aerogels prepared in Example 2 and Comparative Example 5, and water was continuously used to rinse them. The retention of sediment on the gel surface was observed. See the results below. Figure 3 .
[0067] Depend on Figure 1 The results show that different preparation methods have a significant impact on starch aerogels. The ordered porous structure in Comparative Example 5 was obtained by freeze-drying natural starch gel. Gradient repeated casting resulted in multi-layered interpenetrating networks in Examples 1, 2, and 3, leading to more small and denser micron-sized pores compared to Comparative Examples 1 and 5, implying a stronger capillary effect and providing a basis for the gel's higher oil absorption capacity. Nanoscale hydrophobic calcium carbonate particles (indicated by red arrows) adhere to the gel network, forming the protruding structure of the superhydrophobic gel. Figure 2 It can be seen that the natural starch aerogel in Comparative Example 5 has strong hydrophilicity, while the improved gels in Examples 1-3 have significantly enhanced hydrophobicity. Compared with Comparative Example 3, the long fatty chains in Examples 1-3 reduce the surface energy of the gel, transforming it from a highly wettable surface conforming to the Wenzel model to a superhydrophobic surface conforming to the Cassie-Baxter model (contact angle > 150°, roll-off angle < 10°). Figure 3 The underwater oil absorption and self-cleaning processes of natural gels and modified gels were further demonstrated. Example 2 showed significant hydrophobicity and oil absorption capacity, good self-cleaning properties in the environment, and stable gel structure after oil absorption. In contrast, Comparative Example 5 showed oil repellency underwater and significant swelling, material disintegration, and contamination. Figure 4 The underwater oil absorption capacity of starch aerogels prepared by different methods corresponds to their hydrophobicity. Due to the hydrophilicity of natural starch, the underwater oil absorption capacity of Comparative Example 5 is almost 0, while the high hydrophobicity and micro / nano hierarchical structure of Examples 1-3 endow the gels with higher oil absorption capacity, among which Example 2 has the best oil absorption effect.
[0068] As can be seen from the comparison between Example 2 and Comparative Example 1, gradient casting gives the gel a multi-layered interpenetrating network, forming more small and dense micron-sized pores, which provides a basis for higher oil absorption capacity. At the same time, gradient casting makes the resulting gel have a larger contact angle and a lower roll-off angle, which is more in line with the superhydrophobic interface.
[0069] As can be seen from the comparison between Example 2 and Comparative Example 2, the glutaraldehyde crosslinking reaction is beneficial to the formation of a strong three-dimensional crosslinking network, which effectively maintains the firmness of the starch gel as a substrate, provides a basis for higher oil absorption capacity, and at the same time makes the resulting gel have a larger contact angle and a lower roll-off angle, which is more in line with the superhydrophobic interface.
[0070] A comparison of Example 2 and Comparative Example 4 shows that leaving a rough surface of nano-sized calcium carbonate particles on the gel surface results in a larger contact angle and a lower roll-off angle, which is more in line with the superhydrophobic interface and also increases the oil absorption capacity.
[0071] In summary, glutaraldehyde crosslinking and gradient repeated casting can obtain a stable multilayer interpenetrating network structure, forming more small and dense micron-sized pores. Moreover, long aliphatic chains endow the gel with a low surface energy interface to achieve superhydrophobicity, and calcium carbonate deposition further improves the hydrophobicity of the gel. This avoids the micro / nano hierarchical structure of superwetting materials that is traditionally prepared using non-renewable organic solvents (TEOS, tetraethoxysilane) to prepare SiO2 particles.
[0072] Although the invention has been described with reference to illustrative embodiments, those skilled in the art will understand that various other changes, omissions, and / or additions can be made without departing from the spirit and scope of the invention, and that elements of the embodiments can be substituted with substantially equivalents. Furthermore, many modifications can be made without departing from the scope of the invention to adapt particular situations or materials to the teachings of the invention.
Claims
1. A method for preparing a starch-based superhydrophobic oleophilic aerogel, characterized in that, The method includes the following steps: 1) Starch gelatinization: Add deionized water to natural corn starch, stir, and then gelatinize the natural corn starch suspension. The gelatinization temperature is 85℃~95℃, the gelatinization time is 25~35min, and then cool to 60℃-65℃. 2) Acetal reaction; glutaraldehyde is added to the starch paste obtained in step 1), the reaction is completed, and the mixture is cooled for long-term retrogradation. After vacuum freeze-drying, the first starch aerogel is obtained. 3) Gradient casting: A starch suspension with a lower concentration is gelatinized using the same method as in step 1) and reacted with glutaraldehyde to obtain a pre-formed liquid. The pre-formed liquid is then cast into the first starch aerogel. After long-term retrogradation, it is freeze-dried under vacuum. This gradient casting process is repeated, and the retrogradation and vacuum freeze-drying process is repeated to obtain the second starch aerogel. 4) Hydrophobic modification: The second starch aerogel is reacted with palmitoyl chloride by impregnation to obtain the third starch aerogel; 5) Calcium carbonate deposition: The third starch aerogel is first soaked in calcium chloride solution, dried by air drying, then soaked in sodium carbonate solution, washed with anhydrous ethanol, and dried again to obtain superhydrophobic and oleophilic starch aerogel.
2. The production method according to claim 1, characterized by, Step 1) The mass concentration of the natural corn starch suspension is 2%~10%.
3. The preparation method according to claim 1, characterized in that, Step 2) The glutaraldehyde concentration is 15wt%~35wt% of starch-based starch, the cross-linking reaction temperature of starch paste and glutaraldehyde is 60-65℃, the reaction time is 20-40min, the setback temperature is 3℃-5℃, and the setback time is 3-5 days.
4. The preparation method according to claim 1, characterized in that, Step 3) The glutaraldehyde concentration, reaction temperature, time, and retrogradation time are consistent with the preparation process of the first starch aerogel.
5. The preparation method according to claim 1, characterized in that, Step 3) The starch suspension concentration gradient in the gradient casting is 0.1wt%~2wt%.
6. The preparation method according to claim 1, characterized in that, The gradient pouring process is repeated 1 to 9 times.
7. The preparation method according to claim 1, characterized in that, Step 4) The specific steps are as follows: First, the second starch aerogel is immersed in ethyl acetate, and then triethylamine and palmitoyl chloride are added dropwise. After stirring for 1.5 to 3 hours, it is washed with anhydrous ethanol and dried at 40°C to obtain the third starch aerogel.
8. The preparation method according to claim 7, characterized in that, The mass ratio of triethylamine to the second starch aerogel is 10:1 to 13:1; the mass ratio of palmitoyl chloride to the second starch aerogel is 2:1 to 4:
1.
9. The preparation method according to claim 1, characterized in that, In step 5), the concentration of the calcium chloride solution is 0.5 mol / L to 1.5 mol / L, and the soaking time is 6 to 8 hours; the concentration of the sodium carbonate solution is 0.5 mol / L to 1.5 mol / L, and the soaking time is 6 to 8 hours.
10. The application of the starch-based superhydrophobic and oleophilic aerogel obtained by the preparation method according to claim 1, characterized in that, Used for oil-water separation.