Magnetic responsive superhydrophobic chitosan aerogel and application thereof in adsorption of MPs and oil-water separation

Abstract

The present application relates to a kind of magnetic response superhydrophobic chitosan aerogel and its application in adsorption MPs and oil-water separation.The multifunctional aerogel is prepared by non-fluorinated coating technology, and the adsorbent is prepared by polydimethylsiloxane, CZIF-67 and chitosan as raw material, wherein chitosan is used as support skeleton, CZIF-67 is used to give aerogel with magnetism, and PDMS is used to give aerogel with chemical stable superhydrophobicity, so that aerogel has high adsorption capacity for MPs and oil, and removal efficiency is close to 100%, and the adsorption capacity for MPs reaches 34.5mg / g.In addition, it also has good removal effect on other new pollutants.In addition, it also has excellent magnetic and photo-thermal conversion performance, and can realize magnetic driving oil absorption and removal of high viscosity oil.This multifunctional aerogel provides a new strategy for removing MPs, oil and other new pollutants in complex and harsh water environment.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of super-hydrophobic materials, and particularly relates to a magnetic response super-hydrophobic chitosan aerogel and multifunctional application thereof in removal of microplastics (MPs) and oil-water separation. BACKGROUND

[0002] With the rapid development of society, water pollution is a growing problem. It will seriously affect the ecosystem and human health, leading to environmental degradation and the occurrence of diseases around the world. These pollutants mainly include heavy metals, leaked oil, industrial oily wastewater and microplastics, especially leaked oil wastewater and oily wastewater have the greatest impact on the environment. In addition, microplastics (MPs) are ubiquitous in aquatic and terrestrial environments, and MPs are prone to aging in aquatic environments, resulting in rough surface morphology and negatively charged surface properties, which are easy to serve as mobile platforms for many organic pollutants and harmful microorganisms. Current studies have shown that various types of MPs are easily ingested by organisms, affecting human health. In order to solve these problems, various physical and chemical methods such as in-situ incineration, biodegradation, membrane separation, chemical dispersion or coagulation, photocatalysis and electrochemistry have been widely used. For example, coagulation-flocculation-sedimentation technology can remove MPs by 75.6-85.2%, and membrane bioreactors can significantly remove more than 95% of MPs (>20 μm), but their operation cost is expensive, and they have limitations such as low separation efficiency, high energy consumption and secondary pollution, which hinder their application in practice. Therefore, people hope to develop a fast and effective method to remove oily wastewater and microplastics.

[0003] Zhuang et al. prepared a cellulose nanofiber aerogel with a directional structure by liquid nitrogen freezing method for adsorption of small size MPs in water. Sun et al. prepared a chitin-based sponge with graphene oxide (GO) and oxygen-doped carbon nitride (O-C3N4), and the adsorption rate of MPs reached 92.1%. In the above adsorption methods, adsorption method is one of the most concerned strategies by the public due to its low cost, simple operation, high efficiency and time saving. In recent years, porous materials with excellent oil-water separation efficiency such as aerogels, porous membranes and sponges have attracted widespread attention, especially chitosan aerogel, which has been widely used in oil-water separation and MP adsorption due to its high porosity, open cell structure, good mechanical properties, good elasticity, low cost and other advantages. However, pure chitosan aerogel shows hydrophilicity, which means that they will simultaneously adsorb water and MPs, thereby greatly reducing their adsorption capacity for MPs and even destroying their mechanical behavior. Therefore, it is necessary to modify the aerogel so that it can selectively absorb oil or water, thereby realizing oil-water separation and hopefully achieving better absorption performance and higher recyclability in removing MPs, and further realizing multifunctional application of adsorbing MPs and oil-water separation. SUMMARY

[0004] The multifunctional aerogel is prepared by using a non-fluorinated coating technology, chitosan is used as a carrier to support CZIF-67, and polydimethylsiloxane is subjected to hydrophobic treatment, so that the obtained aerogel has high adsorption capacity for MPs and oil, and the removal efficiency is close to 100%.

[0005] To achieve the above object, the technical scheme adopted by the present application is as follows: a magnetic response super-hydrophobic chitosan aerogel, and a preparation method thereof, comprising the following steps:

[0006] 1) Dissolve cobalt nitrate hexahydrate in methanol to form solution A, and dissolve 2-methylimidazole in methanol to form solution B, then mix and stir solution A and solution B, centrifuge and wash, dry, and calcine to obtain CZIF-67.

[0007] 2) Add CZIF-67 to deionized water, add chitosan (CS) and acetic acid, stir to form a chitosan hydrogel, and freeze-dry to obtain a CZIF-67 / CS aerogel.

[0008] 3) Take a hydrophobic material, add or do not add a curing agent, dissolve in an organic solvent, stir to obtain a uniform suspension, immerse the CZIF-67 / CS aerogel in the suspension, and then vacuum dry the mixed system to obtain a magnetic response super-hydrophobic chitosan aerogel PDMS@CZIF-67 / CS.

[0009] Preferably, in step 1), the molar ratio of cobalt nitrate hexahydrate to 2-methylimidazole is 1:1.

[0010] Preferably, in step 1), the calcination is carried out at 600℃ for 1h.

[0011] Preferably, in step 2), the mass ratio of chitosan to CZIF-67 is 5-10:1. More preferably, the mass ratio of chitosan to CZIF-67 is 10:1.

[0012] Preferably, in step 3), the hydrophobic material is selected from stearic acid, lauric acid, PFTEOS or polydimethylsiloxane (PDMS). More preferably, the hydrophobic material is PDMS.

[0013] Preferably, in step 3), the curing agent is butyl diphenyl urethane.

[0014] Preferably, in step 3), the organic solvent is selected from ethanol or n-hexane.

[0015] The application provides an application of the magnetic response super-hydrophobic chitosan aerogel as an adsorbent in removing organic pollutants.

[0016] Preferably, the method is as follows: the pH of the aqueous solution containing organic pollutants is adjusted to 6-12, then the magnetic response super-hydrophobic chitosan aerogel PDMS@CZIF-67 / CS is added, oscillation adsorption is carried out by using an oscillation box, and then separation is carried out by using a magnet. More preferably, the pH of the aqueous solution containing organic pollutants is adjusted to 8.

[0017] Preferably, the organic pollutants are antibiotics, microplastic derivatives, anionic dyes or cationic dyes.

[0018] More preferably, the antibiotics are selected from levofloxacin and tetracycline.

[0019] More preferably, the microplastic derivatives are selected from microplastics or dimethyl phthalate.

[0020] More preferably, the anionic dyes are selected from Congo red or methyl orange.

[0021] More preferably, the cationic dyes are selected from rhodamine B and methylene blue.

[0022] The application provides an application of a magnetic response super-hydrophobic chitosan aerogel as an adsorbent in oil-water separation.

[0023] Preferably, the method is as follows: the magnetic response super-hydrophobic chitosan aerogel PDMS@CZIF-67 / CS is added in an oil-water mixture, and static adsorption is carried out.

[0024] More preferably, the oil includes n-hexane, n-pentane, dichloromethane, ethyl acetate, DMF, chloroform, engine oil, peanut oil and olive oil.

[0025] The application has the following beneficial effects:

[0026] 1. Compared with pure chitosan aerogel, the PDMS@CZIF-67 / CS has a higher specific surface area, provides more active sites in the adsorption process, and has a larger internal pore volume after freeze-drying, which is more conducive to adsorption. The main adsorption mechanism of the negatively charged microplastics is hydrophobic interaction, electrostatic interaction, π-π interaction and hydrogen bonding.

[0027] 2. The PDMS@CZIF-67 / CS can simultaneously adsorb MPs and separate oil and water, and has a good removal effect on other novel pollutants (antibiotics, microplastic derivatives, anionic dyes, etc.), and still has excellent adsorption effect in harsh environments such as strong acid and strong salt.

[0028] 3, The PDMS@CZIF-67 / CS of the application has excellent magnetic properties and photothermal conversion performance, and can realize magnetic driving oil absorption and removal of high viscosity oil. This multifunctional aerogel provides a new strategy for removing MPs, oil and other new pollutants in complex and harsh water environments.

[0029] 4, The super-hydrophobic modifier used in the application is an environmentally friendly reagent without fluorine. The entire preparation method is very simple, does not require the use of expensive reagents, equipment and harsh experimental conditions, the raw materials are easy to obtain, the production cost is low, the synthesized material has good stability, high separation efficiency and strong recycling performance, and solves the problem of high production cost in the existing preparation method of super-hydrophobic material. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 is a synthesis diagram of PDMS@CZIF-67 / CS aerogel.

[0031] Figure 2 is a scanning electron microscope image of chitosan CS (a, d), CZIF-67 / CS aerogel (b, e) and PDMS@CZIF-67 / CS aerogel (c, f).

[0032] Figure 3 is a photo of PDMS@CZIF-67 / CS aerogel on the flower core and pine branch (a), and a digital photo of PDMS@CZIF-67 / CS aerogel (b).

[0033] Figure 4 is the (a) XRD spectrum, (b) FT-IR spectrum, and (c-f) XPS diagram of PDMS@CZIF-67 / CS.

[0034] Figure 5 is (a) the effect of CZIF-67 loading on adsorption efficiency, (b) the effect of different hydrophobic materials on contact angle, (c) the effect of pH value on aerogel, and (d) the Zeta potential diagram of aerogel.

[0035] Figure 6 is (a) the change of PDMS@CZIF-67 / CS adsorption time with MP adsorption amount; (b-c) the corresponding simulation diagram obtained by three kinds of models.

[0036] Figure 7 is (a) the adsorption capacity of PDMS@CZIF-67 / CS for MPs; (b-d) Freundlich, Langmuir isotherm.

[0037] Figure 8 is the adsorption efficiency of PDMS@CZIF-67 / CS for different pollutants.

[0038] Figure 9 are (a) the photo of water droplets on PDMS@CZIF-67 / CS, (b) PDMS@CZIF-67 / CS exhibits perfect waterproof performance under the action of water flux, (c) silver mirror phenomenon of PDMS@CZIF-67 / CS in water immersion.

[0039] Figure 10 are the absorption capacity of PDMS@CZIF-67 / CS in different organic solvents.

[0040] Figure 11 are the photos of (a) n-hexane absorption process and (b) dichloromethane absorption process.

[0041] Figure 12 are PDMS@CZIF-67 / CS used for gravity separation of oil-water mixture.

[0042] Figure 13 are the photos of PDMS@CZIF-67 / CS for dynamic oil-water separation (pump separation) of different density oils.

[0043] Figure 14 are the optical images of the clockwise spiral oil absorption movement of PDMS@CZIF-67 / CS.

[0044] Figure 15 are the wetting behaviors of high viscosity oil on the top of the surface of PDMS@CZIF-67 / CS under light conditions.

[0045] Figure 16 are the hydrophobicities of PDMS@CZIF-67 / CS in different harsh environments. DETAILED DESCRIPTION

[0046] Example 1 Magnetically responsive superhydrophobic chitosan aerogel (PDMS@CZIF-67 / CS)

[0047] (I) The preparation method is as follows:

[0048] The synthesis route of PDMS@CZIF-67 / CS is as Figure 1 .

[0049] 1. Preparation of CZIF-67:

[0050] 10 mmol of cobalt nitrate hexahydrate was dissolved in 100 mL of methanol to form solution A. 10 mmol of 2-methylimidazole was dissolved in 100 mL of methanol to form solution B. Solution A was added to solution B, and after stirring at room temperature for 24 h, the precipitate was collected by centrifugation, washed, and dried. The obtained product was calcined at 600 ℃ for 1 h to obtain CZIF-67.

[0051] 2. Preparation of CZIF-67 / CS aerogel:

[0052] Add 0.2g of CZIF-67 to 20mL of deionized water, then add 2.0g of chitosan (CS) to the above mixed solution, slowly add 0.8mL of acetic acid solution, stir vigorously to form a high-viscosity chitosan hydrogel, freeze-dry for 24 hours to obtain CZIF-67 / CS aerogel.

[0053] 3. Preparation of PDMS@CZIF-67 / CS:

[0054] 0.847 g of PDMS (polydimethylsiloxane) and 0.0847 g of curing agent (butyl diphenylcarbamate) were dissolved in 50 mL of n-hexane and stirred for 5 min to obtain a homogeneous suspension. CZIF-67 / CS aerogel was immersed in the suspension and vacuum dried to obtain magnetically responsive superhydrophobic chitosan aerogel PDMS@CZIF-67 / CS.

[0055] (II) Testing

[0056] 1. The microstructure of chitosan (CS), CZIF-67 / CS aerogel, and PDMS@CZIF-67 / CS aerogel was observed using a scanning electron microscope (test voltage 10.0 kV, scale bar 100 μm). The results are as follows: Figure 2 .

[0057] like Figure 2 As shown, chitosan has a highly interconnected porous network structure. Figure 2 a); The skeleton surface is smooth ( Figure 2 (d). CZIF-67 / CS aerogel deposited clumps of CZIF-67 on the smooth CS framework surface, but the distribution was uneven. Figure 2 (b) Figure 2 The inserted image in the image shows the crystal structure of CZIF-67 in aerogel. CZIF-67 has a uniform dodecahedral rhombic structure. After PDMS treatment, CZIF-67 is covered by a PDMS film, forming a non-uniform, rough structure, which improves agglomeration. Figure 2 c, f).

[0058] 2. PDMS@CZIF-67 / CS aerogel is ultralight, such as... Figure 3 As shown in Figure a, aerogels can be placed on relatively light substrates (such as flower centers and pine branches) without deformation. Furthermore, the simple and controllable method ensures that aerogels can be easily designed and manufactured into ideal shapes for a variety of applications, such as cubes, solid polygons, and other complex three-dimensional shapes. Figure 3 (b)

[0059] 3. For example Figure 4As shown in Figure a, the chemical composition of the PDMS@CZIF-67 / CS aerogel was analyzed by XRD. Typical peaks of the synthesized CZIF-67 appeared at 2θ = 44.24, 51.52, and 75.74°. Identifiable CZIF-67 peaks were present in the CZIF-67 / CS spectrum. After hydrophobic modification, the crystal structure of the aerogel did not change significantly. The XRD results indicate that the aerogel was successfully prepared.

[0060] 4. For example Figure 4 As shown in b, in the FTIR spectrum, in the range of 600-1500 cm⁻¹ -1 The peak observed at 802 cm⁻¹ is due to the stretching vibration of the imidazole ring in CZIF-67. CZIF-67 / CS contains characteristic peaks of both CS and CZIF-67, which are rich in nitrogen-containing functional groups. After superhydrophobic modification, the peak at 802 cm⁻¹ is observed. -1 1091cm -1 and 1260cm -1 The broad peaks represent the tensile vibrations of Si-C, Si-O-Si, and Si-CH3, indicating that PDMS was successfully deposited on the sample.

[0061] 5. For example Figure 4 As shown in Figure cf, XPS spectroscopy reveals that the sample is mainly composed of C, N, O, and Si atoms. Figure 4 In (c), peaks of Si 2s and Si 2p were detected, corresponding to Si-O and Si-C bonds, respectively. These phenomena confirm that PDMS was successfully modified. Figure 4 In the middle d, the N1s peak of PDMS@CZIF-67 / CS aerogel was assigned to NC, NH, pyridine N, and amino at 398.3, 399.4, 398.8, and 401.0 eV, respectively. Figure 4 As shown in Figure e, the high-resolution C 1s peak of the aerogel consists of three peaks located at 284.7, 286.8, and 288.6 eV, corresponding to C-C, CN, and C=O bonds, respectively. Figure 4 In the study, the O1s peak of the aerogel consisted of three peaks located at 531.18, 531.98, and 532.88 eV, corresponding to C=O, COC, and C-OH bonds, respectively. The XPS analysis results further confirmed the successful synthesis of the aerogel.

[0062] Example 2: Application of magnetically responsive superhydrophobic chitosan aerogel PDMS@CZIF-67 / CS in microplastic removal

[0063] Method: A single aerogel PDMS@CZIF-67 / CS was added to 10 mL of 10 mg·L⁻¹ aerogel. -1The microplastics (MPs) solution was subjected to oscillation adsorption, and the residual MPs in the suspension were detected by a fluorescence spectrophotometer.

[0064] The adsorption rate (η) was calculated by the following formula:

[0065]

[0066] In the formula, C0 (mg / L) is the initial concentration of MPs; C t (mg / L) is the concentration of MPs in the solution after adsorption.

[0067] (I) The influence of CZIF-67 loading on the removal of microplastics

[0068] In order to obtain the best aerogel, the influence of the loading of CZIF-67 on the adsorption performance was studied.

[0069] Method: 0.000 g, 0.200 g and 0.400 g of CZIF-67 were respectively added into 20 mL of deionized water. Then 2.0 g of CS was added into the above mixed solution, 0.8 mL of acetic acid solution was slowly added, and the high-viscosity chitosan gel was formed by vigorous stirring, and was freeze-dried for 24 h to form CZIF-67 / CS aerogels with different CZIF-67 loadings.

[0070] The three kinds of aerogels were respectively added into 10 mL of 10 mg·L -1 The microplastics solution was subjected to oscillation adsorption at 25℃ for 1 h, and after the adsorption was completed, the material and the sample solution were separated under the action of an external magnetic field, and the residual MPs in the sample solution were detected by a fluorescence spectrophotometer. The results are shown in Figure 5 a.

[0071] From Figure 5 a, it can be seen that the removal rate of MPs increases with the increase of the loading of CZIF-67, which is due to the electrostatic attraction and π-π interaction between MPs and CZIF-67. However, when the amount of CZIF-67 added increases to 0.4 g, the removal rate decreases, the mechanical property decreases, and the structure becomes loose and easy to collapse. Therefore, the preferred optimal loading of CZIF-67 is that, according to the mass ratio, chitosan:CZIF-67=10:1.

[0072] (II) The influence of hydrophobic materials on the removal of microplastics

[0073] In order to obtain the best hydrophobic performance, different hydrophobic materials were selected to modify the aerogel.

[0074] 1. 3.556 g of stearic acid was dissolved in 50 mL of ethanol solution, stirred for 5 min to obtain a uniform suspension, and the CZIF-67 / CS aerogel was immersed in the suspension for 3 h for hydrophobic treatment to obtain a stearic acid modified aerogel.

[0075] 2. 2.504 g of lauric acid was dissolved in 50 mL of ethanol solution, stirred for 5 min to obtain a uniform suspension, and the CZIF-67 / CS aerogel was immersed in the suspension for 3 h for hydrophobic treatment to obtain a lauric acid modified aerogel.

[0076] 3. 1.694 g of perfluorooctyltrichlorosilane (PFTEOS) was dissolved in 50 mL of ethanol solution, stirred for 5 min to obtain a uniform suspension, and the CZIF-67 / CS aerogel was immersed in the suspension for 1 h for hydrophobic treatment to obtain a PFTEOS modified aerogel.

[0077] 4. 0.847 g of polydimethylsiloxane (PDMS) and 0.0847 g of curing agent (diphenyl butyl carbamate) were dissolved in 50 mL of n-hexane, stirred for 5 min to obtain a uniform suspension, and the CZIF-67 / CS aerogel was immersed in the suspension for 20 min for hydrophobic treatment to obtain a PDMS@CZIF-67 / CS aerogel.

[0078] The four different hydrophobic material aerogels were added to 10 mL of 10 mg·L -1 MPs solution, and oscillated for 1 h at 25°C for adsorption. After adsorption, the material was separated from the sample solution under the action of an external magnetic field, and the residual MPs in the sample solution were detected by a fluorescence spectrophotometer. The results are shown in Figure 5 b.

[0079] From Figure 5 b, it can be seen that when PDMS is used for hydrophobic modification, the hydrophobic angle is the largest, reaching 151.7°, and the removal rate reaches 98%. Therefore, the hydrophobic material is preferably PDMS.

[0080] (Three) Effect of solution pH on microplastic removal

[0081] The pH value affects the surface charge of the adsorbent and the MPs in the aqueous solution, and is one of the key factors affecting the removal process.

[0082] Method: The PDMS@CZIF-67 / CS aerogel prepared in Example 1 was added to 10 mL of 10 mg·L -1MPs solution, change the pH value of the solution to 2, 4, 6, 8, 10, 12, oscillate and adsorb at 25 DEG C for 1h, separate the material from the sample solution under the action of an external magnetic field, and detect the residual MPs in the sample solution by a fluorescence spectrophotometer. The results are as follows Figure 5 c and d in the formula.

[0083] From Figure 5 c, it can be seen that when the pH value is 8, the adsorption efficiency is the highest, and the adsorption capacity gradually decreases with the increase of the pH value. From Figure 5 d, it can be seen that under alkaline conditions, the hydroxyl ions in the solution compete with the negatively charged MPs for the adsorption sites on the positively charged aerogel, which indicates that the electrostatic interaction is an important mechanism for the adsorption of MPs on the PDMS@CZIF-67 / CS aerogel. Therefore, the pH of the aqueous solution containing microplastics is preferably adjusted to 8.

[0084] (Four) Adsorption kinetics

[0085] The adsorption rate is an important indicator for evaluating the performance of the adsorbent and understanding the adsorption process. In order to investigate the rate and mechanism of the adsorption of microplastics on the PDMS@CZIF-67 / CS aerogel, experiments at different time points were carried out. Two kinds of kinetic models (pseudo-first-order kinetic model, pseudo-second-order kinetic model) were used to fit the experimental results. From Figure 6 , it can be seen that in a multi-component system, the adsorption capacity of PDMS@CZIF-67 / CS for MPs increases sharply within the first 10min, and reaches adsorption equilibrium within 40min. The pseudo-first-order kinetic equation and the pseudo-second-order kinetic equation were used to study the adsorption kinetics of MPs on PDMS@CZIF-67 / CS.

[0086] Pseudo-first-order kinetics:

[0087]

[0088] Pseudo-second-order kinetics:

[0089]

[0090] q e (mg·g -1 ) is the amount of adsorbed MPs at equilibrium, q t (mg·g -1 ) is the amount of adsorbed MPs at t. k1 is the rate constant of pseudo-first-order adsorption kinetics, and k2 is the rate constant of pseudo-second-order adsorption kinetics. From the kinetic parameters, it can be seen that the R 2 (0.9977) value of the pseudo-second-order model is greater than the R 2 (0.8390) of the pseudo-first-order model, and the q eThe calculated value is closer to the experimental result. Therefore, the adsorption of aerogel to MPs can be effectively fitted with the pseudo-second-order model, indicating that the adsorption process is chemical adsorption (electrostatic interaction).

[0091] (v) Adsorption isotherm

[0092] The saturated adsorption capacity was evaluated by the removal performance of PDMS@CZIF-67 / CS for MPs in 10 mL standard solution. The adsorption performance of PDMS@CZIF-67 / CS for MPs was estimated by Freundlich and Langmuir isotherm models. Figure 7 Adsorption isotherm of PDMS@CZIF-67 / CS.

[0093] Freundlich model:

[0094]

[0095] Langmuir model:

[0096]

[0097] where q e and q m (mg·g -1 ) are the equilibrium adsorption capacity and the maximum adsorption capacity, respectively, Ce(mg·L -1 ) is the concentration of the single solution, k L (L·mg -1 ) is the Langmuir constant. K f (mg·L -1 ) is the Freundlich constant, and 1 / n represents the adsorption strength. Langmuir and Freundlich models were used to describe the adsorption process of MPs. Figure 7 Data analysis showed that the Langmuir model had a higher correlation coefficient R 2 value than the Freundlich model. Therefore, the Langmuir model is more suitable for describing this adsorption process. The above analysis results show that the adsorption of MPs is a uniform monolayer adsorption process. In addition, the theoretical maximum adsorption capacity of PDMS@CZIF-67 / CS fitted by the Langmuir model is 34.5 mg / g.

[0098] (vi) Mechanism between PDMS@CZIF-67 / CS and MPs

[0099] The mechanism of PDMS@CZIF-67 / CS adsorbing MPs was studied. Because PDMS@CZIF-67 / CS and MPs have strong hydrophobicity, and based on the principle of similar dissolution, microplastics can be adsorbed by hydrophobic interaction. Electrostatic interaction plays an important role in the absorption of MP particles, which can be confirmed by zeta potential (ζ) Figure 5 d). In addition, the imidazole ring (in CZIF-67) can be regarded as an aromatic compound, which can interact with MPs through π-π stacking. From the perspective of molecular structure, it is easy to form hydrogen bonds between the hydroxyl groups of chitosan and the hydrogen atoms of MPs. In addition, slight van der Waals forces also promote the absorption process. In summary, the main adsorption mechanisms for negatively charged microplastics are hydrophobic interaction, electrostatic interaction, π-π interaction and hydrogen bonding.

[0100] (VII) Removal of other pollutants

[0101] In order to prove that PDMS@CZIF-67 / CS has different adsorption capacity for different pollutants, the present application selects representative pollutants, including antibiotics (levofloxacin, tetracycline), microplastic derivatives (dimethyl phthalate), anionic dyes (congo red, methyl orange) and cationic dyes (rhodamine B, methylene blue), all with an initial concentration of 10 mg / L, for independent adsorption studies. From Figure 8 It can be seen from Table 6 that the removal rates of PDMS@CZIF-67 / CS for levofloxacin and tetracycline are 63.7% and 85.6%, respectively, because there is electrostatic attraction, π-π interaction and hydrogen bonding between them. The removal rate of dimethyl phthalate is 73.8%, which can be adsorbed by hydrophobic interaction, electrostatic attraction and π-π interaction. In addition, due to the electrostatic attraction between anionic dyes and aerogels, the removal rates of congo red and methyl orange are 94%. However, due to the electrostatic repulsion between cationic dyes and aerogels, the adsorption effect of rhodamine B and methylene blue is relatively poor, with removal rates of 44.9% and 50.2%, respectively.

[0102] Example 3 Application of magnetically responsive superhydrophobic chitosan aerogel PDMS@CZIF-67 / CS in oil-water separation

[0103] The application of aerogel as adsorbent material in oil-water separation was investigated.

[0104] Adsorption capacity is the standard for evaluating the performance of oil-absorbing materials, which can be measured by the following procedure. Weigh a single aerogel, then put it into different types of oils and organic solvents for adsorption test, take it out after adsorption saturation, wipe off the surface of oils and organic solvents with filter paper, then weigh the aerogel after oil absorption. The adsorption capacity (Q) is calculated by the following formula:

[0105]

[0106] Where m0 and m1 are the weights of the aerogel before and after adsorption, respectively.

[0107] (a) Wetting ability of PDMS@CZIF-67 / CS

[0108] like Figure 9 As shown, water droplets maintain a stable spherical shape on the PDMS@CZIF-67 / CS surface. Figure 9 (a). PDMS@CZIF-67 / CS also exhibits strong repulsion against impacting water flows. Figure 9 (b) Numerous bubbles appeared around the surface of PDMS@CZIF-67 / CS in water, producing a specular reflection phenomenon. Figure 9 (c)

[0109] (II) Saturated adsorption of different oils and organic solvents by PDMS@CZIF-67 / CS

[0110] The saturated adsorption capacity of PDMS@CZIF-67 / CS for three types of oil (engine oil, peanut oil, olive oil) or organic solvents (ethanol, n-hexane, n-pentane, N,N-dimethylformamide, dichloromethane, chloroform, ethyl acetate) was investigated.

[0111] Depend on Figure 10 It is evident that the adsorption capacity depends on the density and viscosity of the oil and organic solvent. The adsorption capacity is lowest when the organic solvent is n-hexane. The adsorption capacity is highest when the oil is peanut oil, reaching 10 times its own weight. The recyclability of these oils and organic solvents was evaluated; after 12 cycles of adsorption and desorption, the adsorption capacity did not decrease significantly. This excellent recyclability is mainly due to the chemical durability, porous structure, and high layer roughness of the PDMS layer.

[0112] (III) Practical Application

[0113] The practical application of PDMS@CZIF-67 / CS oil spill cleanup was investigated, simulating the separation of mixed oil from a mixture under natural conditions. Selective adsorption experiments were conducted using Sudan III-stained n-hexane (light oil) and dichloromethane (heavy oil) mixed with water.

[0114] Depend on Figure 11 As shown in Figure a, PDMS@CZIF-67 / CS can selectively adsorb n-hexane and dichloromethane. When the material comes into contact with n-hexane in the water layer, the n-hexane can be rapidly adsorbed into the material within seconds, achieving static separation of n-hexane and water, with no red contaminants observed in the water. Figure 11As can be seen from Fig. b, when the material is in contact with dichloromethane in the underwater layer, dichloromethane can be quickly absorbed into the material in a few seconds, and static separation of water and dichloromethane can be achieved, and no red contaminants are observed in the water. In summary, it can be shown that the material has high separation efficiency and no pollution.

[0115] (Four) Continuous oil-water separation ability of PDMS@CZIF-67 / CS

[0116] The continuous oil-water separation ability of PDMS@CZIF-67 / CS was investigated, and the results are shown in Fig. Figure 12 .

[0117] As shown in Fig. Figure 12 , the PDMS@CZIF-67 / CS was inserted into the funnel, and the light oil / water (heavy oil / water) mixture was poured into the funnel. Due to the superhydrophobic-superoleophilic property of PDMS@CZIF-67 / CS, the organic phase flowed down, and the water phase was trapped in the funnel.

[0118] Figure 13 In the experiment, one end of the peristaltic pump conduit was inserted into PDMS@CZIF-67 / CS, and this end was placed in the light oil / water (heavy oil / water) mixture. Under the drive of the peristaltic pump, the organic phase was gradually transferred to the beaker at the other end of the conduit. After the separation was completed, there was no residue in the water phase and the organic phase.

[0119] (Five) Magnetic response characteristics of PDMS@CZIF-67 / CS

[0120] The magnetic response characteristics of PDMS@CZIF-67 / CS were investigated. Since CZIF-67 has magnetism, PDMS@CZIF-67 / CS floating on the water surface can be easily controlled, and under the influence of an external magnetic field, it can be controlled to move to a designated pollution area, thereby realizing self-driven oil absorption. Based on the above driving principle and structural design.

[0121] Figure 14 The optical image of the aerogel in the clockwise spiral motion is shown. Under the action of the magnet, PDMS@CZIF-67 / CS accurately and quickly absorbs oil on the water surface according to the spiral trajectory, which also indicates that PDMS@CZIF-67 / CS indeed has the characteristics of magnetic stimulation response.

[0122] (Six) Photothermal conversion performance of PDMS@CZIF-67 / CS

[0123] The photothermal conversion performance of PDMS@CZIF-67 / CS was investigated.

[0124] Figure 15The penetration behavior of high viscosity oil (peanut oil) on the surface of PDMS@CZIF-67 / CS with or without simulated sunlight was shown. Without simulated sunlight irradiation, it took about 10 seconds for the oil droplet to be completely absorbed Figure 15 in the middle a). In contrast, under 1 simulated sunlight irradiation, it only took 3 seconds to completely absorb the same oil droplet Figure 15 in the middle b), making the penetration rate nearly 3 times higher. In addition, the peanut oil exposed to light has a low temperature response, indicating that the peanut oil is heated in situ by collecting solar energy through PDMS@CZIF-67 / CS. It is further verified that PDMS@CZIF-67 / CS has good lipophilicity and self-heating performance, which can improve the flow of high viscosity oil and accelerate oil absorption.

[0125] (VII) Investigation of the mechanical stability of magnetically responsive superhydrophobic PDMS@CZIF-67 / CS

[0126] The chemical stability of PDMS@CZIF-67 / CS was investigated. The surface stability and durability of PDMS@CZIF-67 / CS play a crucial role in practical applications.

[0127] As shown in Figure 16 , when exposed to various harsh environments such as strong acid, strong salt, high temperature, and freezing, PDMS@CZIF-67 / CS will not lose its superhydrophobicity, and will maintain good water resistance, with the contact angle still able to maintain above 150°, proving that they have good chemical stability.

Claims

1. A magnetically responsive superhydrophobic chitosan aerogel, characterized in that, The preparation method of the magnetic response super-hydrophobic chitosan aerogel comprises the following steps: 1) Dissolve cobalt nitrate hexahydrate in methanol to form solution A, and dissolve 2-methylimidazole in methanol to form solution B; after mixing and stirring the solution A and the solution B, centrifugal washing, drying, calcination and carbonization, CZIF-67 is obtained; 2) Add the CZIF-67 into deionized water, and add chitosan CS and acetic acid to form a chitosan hydrogel by stirring; freeze-drying to obtain a CZIF-67 / CS aerogel; the mass ratio of chitosan to CZIF-67 is 5-10:1; 3) Take the hydrophobic material polydimethylsiloxane (PDMS), add or do not add a curing agent, dissolve in an organic solvent, and stir to obtain a uniform suspension; then immerse the CZIF-67 / CS aerogel in the suspension, and then vacuum dry the mixed system to obtain a magnetic response super-hydrophobic chitosan aerogel PDMS@CZIF-67 / CS.

2. The magnetically responsive superhydrophobic chitosan aerogel according to claim 1, characterized in that, In step 1), the molar ratio of cobalt nitrate hexahydrate to 2-methylimidazole is 1:1; the calcination is carried out at 600 DEG C for 1 h.

3. The magnetically responsive superhydrophobic chitosan aerogel according to claim 1, wherein, In step 3), the curing agent is butyl diphenyl carbamate; and the organic solvent is selected from ethanol or n-hexane.

4. The application of the magnetic response super-hydrophobic chitosan aerogel in removing organic pollutants as an adsorbent according to any one of claims 1-3.

5. Use according to claim 4, characterized in that, The method is as follows: adjust the pH of the aqueous solution containing the organic pollutants to 6-12, then add the magnetic response super-hydrophobic chitosan aerogel PDMS@CZIF-67 / CS, and use a shaking box for oscillation adsorption, and then use a magnet for separation.

6. Use according to claim 5, characterized in that, The organic pollutants are antibiotics, microplastics, dimethyl phthalate, anionic dyes or cationic dyes; the antibiotics are selected from levofloxacin or tetracycline; the anionic dyes are selected from Congo red or methyl orange; and the cationic dyes are selected from rhodamine B or methylene blue.

7. The application of the magnetic response super-hydrophobic chitosan aerogel in oil-water separation as an adsorbent according to any one of claims 1-3.

8. Use according to claim 7, characterized in that, The method is as follows: add the magnetic response super-hydrophobic chitosan aerogel PDMS@CZIF-67 / CS in an oil-water mixture, and stand for adsorption.

9. Use according to claim 8, characterized in that, The oil includes n-hexane, n-pentane, dichloromethane, ethyl acetate, N, N-dimethylformamide (DMF), chloroform, engine oil, peanut oil and olive oil.

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