Anisotropic superhydrophobic / superoleophilic composite aerogel material and a preparation method thereof

Abstract

The application discloses an anisotropic super-hydrophobic / super-oleophilic composite aerogel material and a preparation method thereof, takes natural seaweed as a carrier, grows MOFs in situ on the surface of the seaweed, then performs directional composite of the MOFs@seaweed and PVDF through directional freeze drying, and further removes DMF solvent by using a phase transfer method. The introduction of the MOFs@seaweed can establish nanoscale roughness and enhance the hydrophobic oleophilic capacity of the aerogel; the directional freeze drying can significantly enhance the oil absorption capacity of the aerogel in the radial direction; the removal of the DMF solvent can significantly improve the porosity of the aerogel; and the PVDF aerogel prepared by the directional freeze drying method has excellent mechanical properties, and can greatly improve the reusability of the MOFs@seaweed powder as a matrix.

Description

Technical Field

[0001] This invention belongs to the field of adsorption materials technology, specifically relating to an anisotropic superhydrophobic / superoleophilic metal-organic framework (MOFs) modified natural seaweed / polyvinylidene fluoride composite aerogel material and its preparation method. Background Technology

[0002] Crude oil spills are mainly divided into land-based and offshore tanker spills, both causing irreversible and widespread damage. Land-based spills are more hazardous but can be recovered and treated through methods such as combustion. However, offshore tanker spills can lead to highly toxic substances in the oil entering the food chain, posing a significant threat to ecological security. For example, floating oil can adhere to the feathers of seabirds, causing their death. The resulting aromatic hydrocarbons can pollute marine life, indirectly affecting human health. When an offshore spill occurs, the common approach is to collect the spill, pump it out, and then proceed with further treatment, such as bioremediation, filtration, and absorption, to remove the oil. There are three main methods for cleaning up oil spills: chemical methods, bioremediation methods, and physical methods. Chemical methods include on-site combustion, but they have significant drawbacks, including high costs, residual substances after treatment, and even the generation of byproducts. Bioremediation methods use microorganisms to degrade the leaked oil, but the treatment cycle is too long and is greatly affected by external factors. Physical methods include absorption, sedimentation, and filtration. Among these, adsorption is the simplest and most convenient. Therefore, the simple method of physical adsorption can effectively deal with oil spills and achieve oil-water separation.

[0003] Ideal oil-water separation materials should meet the following conditions: excellent adsorption performance, environmental friendliness, strong recyclability, and strong environmental adaptability. However, most existing oil adsorbents do not possess superhydrophobic properties and inevitably absorb water during use, reducing their oil / water selectivity, and their oil absorption performance is not ideal. Furthermore, many existing superhydrophobic oil-absorbing materials lack elasticity, leading to high recycling costs or non-recyclability. Therefore, there is an urgent need for an adsorbent material that is superhydrophobic, superoleophilic, has excellent recycling performance, is inexpensive, and environmentally friendly. Summary of the Invention

[0004] The purpose of this invention is to provide an anisotropic superhydrophobic / superoleophilic composite aerogel material and its preparation method.

[0005] The objective of this invention is achieved through the following technical solutions.

[0006] An anisotropic superhydrophobic / superoleophilic composite aerogel material and its preparation method are disclosed, comprising the following steps:

[0007] (1) Disperse the seaweed with MOFs on its surface (MOFs@seaweed) in a polyvinylidene fluoride (PVDF) N,N-dimethylformamide (DMF) solution and ultrasonically disperse for 10-30 min to promote uniform dispersion of MOFs@seaweed.

[0008] (2) Place the dispersion obtained in step (1) into a directional freezing mold and perform directional freezing;

[0009] (3) Using a phase transfer method, the DMF solvent in the sample obtained in step (2) is removed, thereby forming a porous structure;

[0010] (4) The porous structure obtained in step (3) is freeze-dried to obtain anisotropic superhydrophobic / superoleophilic composite aerogel material.

[0011] Preferably, in step (1), the PVDF DMF solution is obtained by dissolving PVDF in DMF at 40–100°C.

[0012] Preferably, in step (1), MOFs@algae is prepared by in-situ growth: Algae powder is dispersed in a zinc nitrate hexahydrate solution with a concentration of 0.01-0.05 g / ml, ultrasonically dispersed for 5-15 min, stirred at room temperature for 2-10 h, filtered, washed with deionized water 3-5 times, and dried at 50-100℃ for 5-10 h to obtain solid powder; the obtained solid powder is dispersed in a dimethylimidazole solution with a concentration of 0.01-0.05 g / ml, ultrasonically dispersed for 5-15 min, and stirred at room temperature for 2-10 h, filtered, washed with deionized water 3-5 times, and dried at 50-100℃ for 5-10 h to obtain solid powder; the obtained solid powder is dispersed in a dimethylimidazole solution with a concentration of 0.01-0.05 g / ml, ultrasonically dispersed for 5-15 min, and stirred at room temperature for 2-10 h to obtain solid powder. After growing in place for 5–15 hours, the mixture was filtered, washed 3–5 times with deionized water, and dried at 50–100℃ for 5–10 hours to obtain MOFs@algae powder. The solvent of the zinc nitrate hexahydrate solution was a mixture of deionized water and methanol, with a volume ratio of 1:6–12; the mass ratio of algae powder to zinc nitrate hexahydrate was 1:(0.5–3); the solvent of the dimethylimidazole solution was a mixture of deionized water and methanol, with a volume ratio of 1:6–12; the mass ratio of algae to dimethylimidazole was 1:(0.5–3).

[0013] Preferably, in step (1), the mass ratio of PVDF, DMF, and MOFs@algae is 1:(5-20):(0.05-0.6).

[0014] Preferably, in step (2), the directional freezing temperature is -60℃ to -30℃; and the directional freezing time is 0.5 to 1h.

[0015] Preferably, in step (3), the DMF solvent is removed by the following steps: the sample is placed in a water bath at 2 to 10°C for phase separation for 5 to 15 hours, and the water is changed every 1 to 3 hours.

[0016] Preferably, in step (4), the freeze-drying temperature is -60℃ to -30℃ and the freeze-drying time is 20 to 50 hours.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] (1) This invention uses seaweed, which has advantages such as large specific surface area, wide availability and low cost, and successfully applies it to oil-water separation aerogel. This effectively improves the oil absorption capacity of the adsorbent, reduces the cost of the adsorbent, and realizes the resource utilization of seaweed. This is of great significance for resource recycling and environmental protection.

[0019] (2) This invention uses seaweed as a carrier to grow MOFs in situ on its surface, which effectively improves the hydrophobic properties of seaweed.

[0020] (3) The aerogel prepared by the present invention has an oriented structure and can achieve rapid adsorption in the radial direction.

[0021] (4) The aerogel prepared by the present invention not only has the advantages of high porosity and low density, but also has excellent circulating oil-water separation performance. Attached Figure Description

[0022] Figure 1 Scanning electron microscope (SEM) images of natural seaweed (a, b) and MOFs@seaweed prepared in Example 1 (c, d) at different magnifications.

[0023] Figure 2 The image shows the compression rebound of the MOFs@algae / PVDF composite aerogel prepared in Example 4.

[0024] Figure 3 The XRD patterns are of pure MOFs prepared in Comparative Example 1, MOFs@algae prepared in Example 1, and pure algae. Detailed Implementation

[0025] The principle of this invention is as follows: Using natural seaweed as a carrier, MOFs are grown in situ on its surface. Then, MOFs@seaweed are directionally composited with PVDF through directional freeze-drying, and DMF solvent is further removed using a phase transfer method. The introduction of MOFs@seaweed can establish nanoscale roughness, enhancing the hydrophobic and oleophilic properties of the aerogel; directional freeze-drying can significantly enhance the radial oil absorption capacity of the aerogel; the removal of DMF solvent can significantly increase the porosity of the aerogel; the PVDF aerogel prepared by directional freeze-drying has excellent mechanical properties, and as a matrix for MOFs@seaweed powder, it can greatly improve its reusability.

[0026] This invention is illustrated by the following examples, but these examples are for illustrative purposes only and should not be construed as limiting the scope or application of the invention. Unless otherwise specified, all raw materials used in this invention are commercially available; it should be noted that the natural seaweed used is spirulina powder.

[0027] Example 1

[0028] 4g of zinc nitrate hexahydrate was dissolved in a 220ml mixture of methanol and deionized water (volume ratio 10:1). 2g of spirulina powder was added under stirring, and the mixture was ultrasonically dispersed for 10min, stirred for 6h, filtered, washed 5 times with deionized water, and dried at 70℃ for 5h to obtain a solid powder. The obtained solid powder was dispersed in 330ml of dimethylimidazole solution (4g dimethylimidazole, 30ml deionized water, 300ml methanol), ultrasonically dispersed for 15min, grown in situ under stirring for 6h, filtered, washed 5 times with deionized water, and dried at 60℃ for 6h to obtain MOFs@seaweed powder. Figure 1 In the image, a and b are scanning electron microscope images of natural seaweed at different magnifications. Figure 1 In Figures c and d, we see scanning electron microscope (SEM) images of MOFs@algae prepared in Example 1. The natural algae exhibit a certain spiral shape, and after in-situ growth of MOFs, many spherical structures were observed to be loaded. These spherical structures can increase the specific surface area and roughen the surface, which is beneficial for improving the adsorption rate and adsorption capacity of the composite aerogel.

[0029] Example 2

[0030] 1 g of PVDF was dissolved in 10 g of DMF at 60 °C with stirring. Then, 0.1 g of MOFs@algae prepared in Example 1 was weighed and dispersed in the PVDF-DMF solution, and ultrasonically dispersed for 15 min to promote uniform dispersion of MOFs@algae. The dispersion was placed in a directional freeze-drying mold and directionally freeze-dried at -40 °C for 35 min. The directionally frozen sample was placed in a 6 °C water bath for phase separation for 8 h, with the water changed every 3 h to remove the DMF solvent from the sample. Finally, the obtained solid was freeze-dried at -45 °C for 30 h to obtain anisotropic MOFs@algae / PVDF composite aerogel with a water contact angle of 134 °C and an adsorption capacity for pump oil in the radial direction (adsorption capacity is the mass ratio of oil adsorbed to the mass of the aerogel itself when the aerogel is saturated with oil) of 4.17 g / g.

[0031] Example 3

[0032] Anisotropic superhydrophobic / superoleophilic composite aerogel materials were prepared according to the steps of Example 2, with the only difference being the addition of 0.2 g of MOFs@algae powder prepared in Example 1 during the experiment. The composite aerogel material obtained in this example has a water contact angle of 139° and an adsorption capacity for pump oil in the radial direction of 4.78 g / g.

[0033] Example 4

[0034] Anisotropic superhydrophobic / superoleophilic composite aerogel materials were prepared according to the steps of Example 2, with the only difference being the addition of 0.3g of MOFs@algae powder prepared in Example 1 during the experiment. The composite aerogel material obtained in this example has a water contact angle of 145° and an adsorption capacity for pump oil in the radial direction of 5.69g / g. Figure 2 The image shows the compression rebound of the prepared MOFs@algae / PVDF composite aerogel. It can be seen that the sample has excellent compression rebound performance, which allows it to quickly expel the absorbed oil through compression and then quickly absorb it again. In other words, repeated oil absorption can be achieved through a simple compression method.

[0035] Example 5

[0036] Anisotropic superhydrophobic / superoleophilic composite aerogel materials were prepared according to the steps of Example 2, with the only difference being the addition of 0.4 g of MOFs@algae powder prepared in Example 1 during the experiment. The composite aerogel material obtained in this example has a water contact angle of 140°C and an adsorption capacity for pump oil in the radial direction of 5.07 g / g.

[0037] Comparing Examples 2-5, it can be seen that with a fixed PVDF to DMF ratio of 1:10, when the mass ratio of MOFs@algae to PVDF increases from 0.1:1 to 0.4:1, the water contact angle and the adsorption capacity for pump oil of the composite aerogel first gradually increase and then gradually decrease. When the mass ratio of MOFs@bamboo charcoal to PVDF is 0.3:1, the water contact angle of the composite aerogel reaches 145°, and the adsorption capacity for pump oil is as high as 5.69 g / g.

[0038] Comparative Example 1

[0039] The steps are the same as in Example 1, but no spirulina powder is added during the experiment to obtain pure MOF powder. Figure 3 The XRD patterns of pure MOFs prepared in Comparative Example 1, MOFs@algae prepared in Example 1, and pure algae further demonstrate that MOF particles were successfully loaded onto the surface of algae in Example 1.

[0040] Comparative Example 2

[0041] The preparation process of the aerogel was the same as in Example 4, but MOFs@algae were not added during the experiment. The resulting anisotropic polyvinylidene fluoride aerogel material had a water contact angle of 119° and an adsorption capacity for pump oil of 3.12 g / g in the radial method. Compared with the results of Examples 2-5, it can be seen that the addition of MOFs@algae can effectively improve the hydrophobicity of the aerogel and its adsorption capacity for pump oil.

[0042] Comparative Example 3

[0043] The preparation process of the aerogel was the same as in Example 4, but 0.3g of natural spirulina powder was added during the experiment instead of MOFs@algae. The water contact angle of the anisotropic algae / PVDF composite aerogel was 114°, and the adsorption capacity of pump oil in the radial method was 3.31g / g.

[0044] Comparative Example 4

[0045] The preparation process of the aerogel was the same as in Example 4, but 0.3g of pure MOFs prepared in Comparative Example 1 was added during the experiment instead of MOFs@algae. The water contact angle of the anisotropic MOFs / PVDF composite aerogel was 122°, and the adsorption capacity of pump oil in the radial method was 3.44g / g.

Claims

1. A method for preparing an anisotropic superhydrophobic / superoleophilic composite aerogel material, characterized in that, Comprising the following steps: (1) dispersing MOFs@seaweed in a DMF solution of PVDF, and ultrasonic dispersion for 10-30 min to promote uniform dispersion of MOFs@seaweed; (2) placing the dispersion obtained in step (1) in a directional freezing mold, and performing directional freezing; (3) removing the DMF solvent in the sample obtained in step (2) by phase transfer method, thereby forming a porous structure; (4) freeze-drying the porous structure obtained in step (3) to obtain an anisotropic superhydrophobic / superoleophilic composite aerogel material; In step (1), the mass ratio of PVDF, DMF, and MOFs@seaweed is 1:(5-20):(0.05-0.6); The MOFs@seaweed is prepared by in-situ growth method: seaweed powder is dispersed in zinc nitrate hexahydrate solution with a concentration of 0.01-0.05 g / ml, ultrasonic dispersion for 5-15 min, stirring at room temperature for 2-10 h, filtration, deionized water washing for 3-5 times, 50-100 o C drying for 5-10 h to obtain solid powder; the obtained solid powder is dispersed in dimethyl imidazole solution with a concentration of 0.01-0.05 g / ml, ultrasonic dispersion for 5-15 min, in-situ growth under stirring for 5-15 h, filtration, deionized water washing for 3-5 times, 50-100 o C drying for 5-10 h to obtain MOFs@seaweed powder; wherein the solvent of zinc nitrate hexahydrate solution is a mixture of deionized water and methanol with a volume ratio of 1:6-12; the mass ratio of seaweed powder to zinc nitrate hexahydrate is 1:(0.5-3); the solvent of dimethyl imidazole solution is a mixture of deionized water and methanol with a volume ratio of 1:6-12; the mass ratio of seaweed to dimethyl imidazole is 1:(0.5-3).

2. The method of claim 1, wherein, In step (1), the DMF solution of PVDF is obtained by dissolving PVDF in 40-100 o C in DMF.

3. The method of claim 1, wherein, In step (2), the temperature of directional freezing is -60 o C ~ -30 o C; the time of directional freezing is 0.5 ~ 1 h.

4. The method of claim 1, wherein, In step (3), the DMF solvent is removed by placing the sample in a 2-10 o C water bath for phase separation for 5-15 h, with water changes every 1-3 h.

5. The method of claim 1, wherein, In step (4), the freeze-drying temperature is -60 o C ~ -30 o C; the freeze-drying time is 20 ~ 50 h.

6. The anisotropic superhydrophobic / superoleophilic composite aerogel material prepared by the method of any one of claims 1-5.

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