ZIF-90-biochar-MF composite foam as well as preparation method and application thereof

Abstract

The invention relates to the technical field of adsorption materials, in particular to ZIF-90-biochar-MF composite foam as well as a preparation method and application thereof. The preparation method comprises the following steps: by taking melamine foam as a matrix, carrying out coordination on a methanol solution of zinc nitrate hexahydrate and imidazole-2-formaldehyde to form a ZIF-90 precursor; the preparation method comprises the following steps: adding a ZIF-67 precursor into biochar to form a load liquid, then adding the load liquid into melamine foam, and then adding hexadecylamine for hydrophobic modification to obtain the ZIF-90-biochar (at) MF composite foam. According to the preparation method, cetylamine is used as a hydrophobic modifier, ZIF-90 is loaded on a melamine foam skeleton by an in-situ growth method, and charcoal is added, so that the prepared material can construct a micron-scale rough layer on the surface of a microporous membrane, the roughness of the surface of the MF skeleton is increased, and due to the fact that the surfaces of ZIF-90 and charcoal are rich in hydrophobic functional groups, the surface of the MF skeleton can be effectively improved. The surface hydrophobicity is improved, and the oil absorption performance of the composite material is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of adsorption materials, and in particular to a ZIF-90-biochar@MF composite foam and a preparation method and application thereof. Background Art

[0002] Oil and organic solvent spills pose a significant threat to human health and the environment. Oil spills not only pose a significant challenge in environmental cleanup, but also present significant economic value in resource recovery.

[0003] Currently, mainstream technologies for oil-water separation encompass a variety of approaches, including physical methods utilizing gravity-induced settling, chemical methods using chemical reagents to promote separation, incineration treatment performed directly on the contaminated site, electrochemical separation techniques, and biodegradation methods leveraging microbial activity. While these technologies can achieve initial oil-water separation to some extent, they generally suffer from low selective separation efficiency or limited absorption capacity, resulting in the recovered oil often failing to meet reuse standards. Summary of the Invention

[0004] The purpose of the present invention is to overcome the deficiencies of the prior art and provide a ZIF-90-biochar@MF composite foam and a preparation method thereof, which solves the technical problems of low selective separation efficiency or limited absorption capacity of the existing oil-water separation technology.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions: The first object of the present invention is to provide a method for preparing a ZIF-90-biochar@MF composite foam, comprising the following steps: S1. Add a soluble zinc salt to a solvent, mix well to obtain a zinc salt solution, and add an organic ligand solution to the zinc salt solution to obtain a ZIF-90 precursor.

[0006] S2. The ZIF-90 precursor was added to the biochar by the room temperature impregnation method for in-situ loading and soaking to form a loading liquid. Then, melamine foam was added to the loading liquid to allow ZIF-67 and biochar to grow in situ and be loaded on the melamine foam to obtain ZIF-90-biochar loaded MF composite foam.

[0007] S3. Using hexadecylamine as a modifier, the ZIF-90-biochar-loaded MF composite foam was hydrophobically modified to obtain the ZIF-90-biochar@MF composite foam.

[0008] Furthermore, the soluble zinc salt is zinc nitrate hexahydrate, and the concentration of the soluble cobalt salt solution is 0.01 g·mL -1 ~0.02 g·mL -1The mass ratio of soluble zinc salt to organic ligand is 1:1.3-1.6, the organic ligand is imidazole-2-carboxaldehyde, and the concentration of the organic ligand solution is 0.013 g·mL -1 ~0.015g·mL -1 .

[0009] Furthermore, during the loading process, 30 mL to 40 mL of loading liquid was added to the 1 cm×1 cm×1 cm melamine foam.

[0010] Furthermore, the biochar is alkali-activated biochar, which is obtained by soaking durian peel biochar in a solution with a concentration of 1 mol·L -1 ~2 mol·L -1 The alkali-activated biochar was obtained by alkali modification in a NaOH solution under stirring for 2 h to 3 h.

[0011] Furthermore, the in-situ loading immersion time is 9 h to 15 h.

[0012] Furthermore, 60 mL to 70 mL of hexadecylamine solution was added to the 1 cm × 1 cm × 1 cm ZIF-90-biochar-loaded MF composite foam. The mass concentration of the hexadecylamine solution was 10%. The hydrophobic modification temperature was 65 ° C to 75 ° C, and the time was 8 h to 12 h.

[0013] The second object of the present invention is to provide a ZIF-90-biochar@MF composite foam, which is prepared by the above-mentioned preparation method of the ZIF-67-biochar@MF composite foam.

[0014] The third object of the present invention is to provide the use of the above-mentioned ZIF-90-biochar@MF composite foam as an adsorption material in oil-water separation.

[0015] The present invention has the beneficial effect of using hexadecylamine as a hydrophobic modifier to load ZIF-90 onto a melamine foam (MF) framework using a simple in situ growth method. Alkali-activated durian peel biochar is then added to the resulting material, which builds a micrometer-scale roughness layer on the surface of the microporous membrane, increasing the roughness of the MF framework. Furthermore, the abundant hydrophobic functional groups on the surfaces of ZIF-90 and biochar enhance their surface hydrophobicity, which in turn improves the oil absorption performance of the composite material. The use of hexadecylamine as a modifier securely anchors ZIF-67 and biochar particles to the MF surface, enhancing the material's hydrophobicity while also improving its recyclability and stability in complex environments. This addresses the technical issues of low selective separation efficiency and limited absorption capacity in existing oil-water separation technologies. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1This is a scanning electron microscope image of the ZIF-90-biochar@MF composite foam prepared in Example 1 of the present invention.

[0017] Figure 2 This is a diagram of the hydrophobic properties of the ZIF-90-biochar@MF composite foams prepared in Examples 1 to 3 of the present invention. Figure 2 Wherein a is embodiment 1, b is embodiment 2, and c is embodiment 3.

[0018] Figure 3 This is a comparison chart of the adsorption capacity of the ZIF-90-biochar@MF composite foam of the present invention for different organic solvents.

[0019] Figure 4 This is a comparison chart of the oil-water separation efficiency of the ZIF-90-biochar@MF composite foam of the present invention for different organic solvents.

[0020] Figure 5 This is a graph showing the recycling performance of the ZIF-90-biochar@MF composite foam of the present invention. DETAILED DESCRIPTION

[0021] The following will provide a clear and complete description of the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0022] It should be noted that the professional terms used in the present invention are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention. Unless otherwise specified, the various raw materials, reagents, instruments and equipment used in the following embodiments of the present invention can be purchased from the market or prepared by existing methods.

[0023] In one aspect, the present invention provides a method for preparing a ZIF-90-biochar@MF composite foam, comprising the following steps: S1. Add a soluble zinc salt to a solvent, mix well to obtain a zinc salt solution, and add an organic ligand solution to the zinc salt solution to obtain a ZIF-90 precursor.

[0024] S2. The ZIF-90 precursor was added to the biochar by the room temperature impregnation method for in-situ loading and soaking to form a loading liquid. Then, melamine foam was added to the loading liquid to allow ZIF-67 and biochar to grow in situ and be loaded on the melamine foam to obtain ZIF-90-biochar loaded MF composite foam.

[0025] S2. Using hexadecylamine as a modifier, the ZIF-90-biochar-loaded MF composite foam was hydrophobically modified to obtain the ZIF-90-biochar@MF composite foam.

[0026] This invention uses octadecylamine as a hydrophobic modifier, loading ZIF-90 onto a melamine foam (MF) framework via a simple in situ growth method. Biochar is then added to the resulting material, which builds a micrometer-scale roughness layer on the surface of the microporous membrane, increasing the roughness of the MF framework. Furthermore, the abundant hydrophobic functional groups on the surfaces of ZIF-90 and biochar enhance their surface hydrophobicity, which in turn improves the composite's oil absorption performance. Using octadecylamine as a modifier securely anchors ZIF-67 and biochar particles to the MF surface, improving the material's recyclability and stability in complex environments. This addresses the technical issues of low selective separation efficiency and limited absorption capacity in existing oil-water separation technologies.

[0027] In some embodiments, the soluble cobalt salt is zinc nitrate hexahydrate, and the concentration of the soluble cobalt salt solution is 0.01 g·mL -1 ~0.02 g·mL -1 The solvent is methanol, the mass ratio of soluble zinc salt to organic ligand is 1:1.3-1.6, the organic ligand is imidazole-2-carboxaldehyde, and the concentration of the organic ligand solution is 0.013 g·mL -1 ~0.015 g·mL -1 .

[0028] In some embodiments, the concentration of biochar in the loading solution is 0.0007 g·mL -1 ~0.0036 g·mL -1 .

[0029] In some embodiments, during the loading process, 30 mL to 40 mL of loading liquid is added to a 1 cm×1 cm×1 cm melamine foam.

[0030] It should be noted that in order to further improve the performance of biochar-modified melamine foam materials, the melamine foam needs to be pretreated before use. The melamine foam is ultrasonically cleaned with anhydrous ethanol and deionized water for 3 h in sequence, and then dried in an oven at 40°C.

[0031] In some embodiments, the biochar is alkali-activated biochar, which is obtained by soaking durian peel biochar in a solution with a concentration of 1 mol·L -1 ~2 mol·L -1 The alkali-activated biochar was obtained by alkali modification in a NaOH solution under stirring for 2 h to 3 h.

[0032] It should be noted that durian peel biochar is prepared using durian peel powder as the raw material through a hydrothermal reaction at 200°C for 8 hours. The durian peel powder is obtained by grinding durian peels and passing them through a 100-mesh sieve. Before grinding, the durian peels are rinsed three times with distilled water to remove impurities and then dried in a 50°C oven until the interior is moisture-free. After the alkaline modification is completed, the modified solution is subjected to solid-liquid separation to obtain a solid product. The solid product is filtered and washed until the solution is neutral, then dried in an oven at 105°C until the interior is moisture-free, and further ground in a mortar.

[0033] In some embodiments, the in-situ loading soaking time is 9 h to 15 h.

[0034] In some embodiments, 60 mL to 70 mL of hexadecylamine solution was added to a 1 cm × 1 cm × 1 cm ZIF-90-biochar-loaded MF composite foam, the mass concentration of the hexadecylamine solution was 10%, the temperature of the hydrophobic modification was 65° C. to 75° C., and the time was 8 h to 12 h.

[0035] On the other hand, the present invention also provides a ZIF-90-biochar@MF composite foam, which is prepared by the above-mentioned preparation method of the ZIF-90-biochar@MF composite foam.

[0036] The present invention also provides the use of ZIF-90-biochar@MF composite foam as an adsorption material in oil-water separation.

[0037] The following is further described through specific examples.

[0038] Example 1 A method for preparing a ZIF-90-biochar@MF composite foam comprises the following steps: S1. Preparation of alkali-activated biochar: durian peel was used as raw material, rinsed three times with distilled water to remove impurities, dried in a 50°C oven for 4 h, dried until there was no moisture inside, and then crushed and passed through a 100-mesh sieve to obtain durian peel powder; 5.0 g of durian peel powder was weighed and added to a beaker filled with 50 mL of deionized water, and ultrasonically stirred for 30 min; 40 mL of the mixture was poured into a hydrothermal synthesis reactor with a polytetrafluoroethylene liner, the hydrothermal reactor was sealed, and a hydrothermal reaction was carried out at 200°C for 8 h; after the hydrothermal reaction was completed, a reaction solution was obtained, the reaction solution was centrifuged to separate the solid product, and washed with distilled water; the solid product was placed in an oven and dried to constant weight, and the oven temperature was set to 105°C to obtain durian peel biochar.

[0039] The durian peel biochar was soaked in 1 mol·L -1The product was placed in a NaOH solution and stirred at a constant temperature for 2 h to obtain an alkali-modified solution. The alkali-modified solution was subjected to solid-liquid separation to obtain a solid product. The solid product was filtered and washed until the solution was neutral, and then dried in an oven at 105°C until there was no moisture inside. The solid product was then further ground in a mortar to obtain alkali-activated biochar.

[0040] S2. Preparation of ZIF-90 / MF composite foam: Add 0.37 g zinc nitrate hexahydrate to 35 mL methanol solvent and sonicate for 5 minutes to obtain a zinc source solution. Then add 0.37 g imidazole-2-carboxaldehyde to the above solution and sonicate for 10 minutes to obtain a mixed solution. Weigh 0.1 g alkali-activated biochar and add it to the above mixed solution. Stir evenly and let the mixed solution stand for 20 minutes to obtain a loading solution.

[0041] S3. Cut the melamine foam into 1 cm × 1 cm × 1 cm, ultrasonically clean it with anhydrous ethanol and deionized water for 3 h, and then dry it in an oven at 40 °C to obtain the treated melamine foam. Add 35 mL of the loading liquid to the treated melamine foam and soak it at room temperature for 15 h to separate the ZIF-90-biochar-loaded MF composite foam. Wash the ZIF-90-biochar-loaded MF composite foam with methanol until there is no powder precipitation, and place it in a vacuum drying oven at 65 °C for 24 h.

[0042] S4. Modification of ZIF-90 / MF composite foam: The ZIF-90-biochar-loaded MF composite foam was placed in 65 mL of 10% hexadecylamine methanol solution, and then the mixed solution was refluxed in an oil bath at 70°C for 10 h. After the reflux, it was washed several times with methanol and placed in a drying oven at 50°C for 12 h to obtain ZIF-90-biochar@MF composite foam.

[0043] Example 2 A method for preparing a ZIF-90-biochar@MF composite foam comprises the following steps: S1. Preparation of alkali-activated biochar: durian peel was used as raw material, rinsed three times with distilled water to remove impurities, dried in a 50°C oven for 4 h, dried until there was no moisture inside, and then crushed and passed through a 100-mesh sieve to obtain durian peel powder; 5.0 g of durian peel powder was weighed and added to a beaker filled with 50 mL of deionized water, and ultrasonically stirred for 30 min; 40 mL of the mixture was poured into a hydrothermal synthesis reactor with a polytetrafluoroethylene liner, the hydrothermal reactor was sealed, and a hydrothermal reaction was carried out at 200°C for 8 h; after the hydrothermal reaction was completed, a reaction solution was obtained, the reaction solution was centrifuged to separate the solid product, and washed with distilled water; the solid product was placed in an oven and dried to constant weight, and the oven temperature was set to 105°C to obtain durian peel biochar.

[0044] The durian peel biochar was soaked in 1 mol·L -1 The product was placed in a NaOH solution and stirred at a constant temperature for 2 h to obtain an alkali-modified solution. The alkali-modified solution was subjected to solid-liquid separation to obtain a solid product. The solid product was filtered and washed until the solution was neutral, and then dried in an oven at 105°C until there was no moisture inside. The solid product was then further ground in a mortar to obtain alkali-activated biochar.

[0045] S2. Preparation of ZIF-90 / MF composite foam: Add 0.37 g of zinc nitrate hexahydrate to 35 mL of methanol solvent and sonicate for 5 minutes to obtain a zinc source solution. Then add 0.48 g of imidazole-2-carboxaldehyde to the above solution and sonicate for 10 minutes to obtain a mixed solution. Weigh 0.1 g of alkali-activated biochar and add it to the above mixed solution. Stir evenly and let the mixed solution stand for 20 minutes to obtain a loading solution.

[0046] S3. Cut the melamine foam into 1 cm × 1 cm × 1 cm, ultrasonically clean it with anhydrous ethanol and deionized water for 3 h, and then dry it in an oven at 40 °C to obtain the treated melamine foam. Add 35 mL of the loading liquid to the treated melamine foam and soak it at room temperature for 15 h to separate the ZIF-90-biochar-loaded MF composite foam. Wash the ZIF-90-biochar-loaded MF composite foam with methanol until there is no powder precipitation, and place it in a vacuum drying oven at 65 °C for 24 h.

[0047] S4. Modification of ZIF-90 / MF composite foam: The ZIF-90-biochar-loaded MF composite foam was placed in 65 mL of 10% hexadecylamine methanol solution, and then the mixed solution was refluxed in an oil bath at 70 °C for 10 h. After the reflux, it was washed several times with methanol and placed in a drying oven at 50 °C for 12 h to obtain ZIF-90-biochar@MF composite foam.

[0048] Example 3 A method for preparing a ZIF-90-biochar@MF composite foam comprises the following steps: S1. Preparation of alkali-activated biochar: durian peel was used as raw material, rinsed three times with distilled water to remove impurities, dried in a 50°C oven for 4 h, dried until there was no moisture inside, and then crushed and passed through a 100-mesh sieve to obtain durian peel powder; 5.0 g of durian peel powder was weighed and added to a beaker filled with 50 mL of deionized water, and ultrasonically stirred for 30 min; 40 mL of the mixture was poured into a hydrothermal synthesis reactor with a polytetrafluoroethylene liner, the hydrothermal reactor was sealed, and a hydrothermal reaction was carried out at 200°C for 8 h; after the hydrothermal reaction was completed, a reaction solution was obtained, the reaction solution was centrifuged to separate the solid product, and washed with distilled water; the solid product was placed in an oven and dried to constant weight, and the oven temperature was set to 105°C to obtain durian peel biochar.

[0049] The durian peel biochar was soaked in 1 mol·L -1 The product was placed in a NaOH solution and stirred at a constant temperature for 2 h to obtain an alkali-modified solution. The alkali-modified solution was subjected to solid-liquid separation to obtain a solid product. The solid product was filtered and washed until the solution was neutral, and then dried in an oven at 105°C until there was no moisture inside. The solid product was then further ground in a mortar to obtain alkali-activated biochar.

[0050] S2. Preparation of ZIF-90 / MF composite foam: Add 0.37 g zinc nitrate hexahydrate to 35 ml methanol solvent and sonicate for 5 minutes to obtain a zinc source solution. Then add 0.59 g imidazole-2-carboxaldehyde to the above solution and sonicate for 10 minutes to obtain a mixed solution. Weigh 0.1 g alkali-activated biochar and add it to the above mixed solution. Stir evenly and let the mixed solution stand for 20 minutes to obtain a loading solution.

[0051] S3. Cut the melamine foam into 1 cm × 1 cm × 1 cm, ultrasonically clean it with anhydrous ethanol and deionized water for 3 h, and then dry it in an oven at 40 °C to obtain the treated melamine foam. Add 35 mL of the loading liquid to the treated melamine foam and soak it at room temperature for 15 h to separate the ZIF-90-biochar-loaded MF composite foam. Wash the ZIF-90-biochar-loaded MF composite foam with methanol until there is no powder precipitation, and place it in a vacuum drying oven at 65 °C for 24 h.

[0052] S3. Modification of ZIF-90 / MF composite foam: ZIF-90-biochar-loaded MF composite foam was placed in 65 mL of 10% hexadecylamine methanol solution, and then the mixed solution was refluxed in an oil bath at 70 °C for 10 h. The drug was removed, washed several times with methanol, and placed in a drying oven at 50 °C for 12 h to obtain ZIF-90-biochar@MF composite foam.

[0053] The properties of the composite foam prepared in the example were tested. The results are as follows:

[0054] Figure 1 This is a scanning electron microscope image of the ZIF-90-biochar@MF composite foam prepared in Example 1 of the present invention. Figure 1 As shown in the figure, the skeleton of the composite MF is relatively rough. This is because ZIF-90 and biochar are successfully attached to the surface of MF. The formation of these rough structures improves the adsorption capacity of ZIF-90-biochar@MF composite foam.

[0055] Figure 2 This is a diagram of the hydrophobic properties of the ZIF-90-biochar@MF composite foams prepared in Examples 1 to 3 of the present invention. Figure 2The horizontal and vertical table 1:1 is Example 1, the horizontal and vertical table 1:1.3 is Example 2, and the horizontal and vertical table 1:1.6 is Example 3. Figure 2 As shown, the contact angles of the ZIF-90-biochar@MF composite foams prepared in Examples 1 to 3 were 150.12°, 157.89°, and 147.3°, respectively, which showed excellent hydrophobicity and increased the oil absorption performance of the composite material.

[0056] The biochar-modified melamine foam prepared in Example 2 was used as an adsorption material in oil-water separation. The process specifically includes the following steps:

[0057] The maximum adsorption capacity of ZIF-90-biochar@composite foam for different oils and organic solvents was measured by weighing method.

[0058] The specific testing protocol is as follows: Measure the initial mass of a 1 cm × 1 cm × 1 cm ZIF-90-biochar@composite foam. Then, use tweezers to pick up the sponge and soak it in dimethyl sulfoxide (DMSO), dimethylformamide (DMF), isopropyl alcohol (IPA), epichlorohydrin (ECH), triethylamine (TEA), tetraethyl orthosilicate (TEOS), xylene, gasoline, vegetable oil, glycerol, or carbon tetrachloride for 10 minutes until adsorption saturation is reached. The foam is then removed and weighed. The specific calculation formula is as follows:

[0059] (1).

[0060] In the formula, m1 is the mass of melamine foam after oil absorption, g; m0 is the initial mass of melamine foam, g.

[0061] To investigate the oil-water separation performance of ZIF-90-biochar@composite foam, 1 g of different oils and organic solvents were weighed and 40 mL of deionized water was added. The formula for calculating the oil-water separation efficiency is:

[0062] (2).

[0063] Where: E is the separation efficiency, %; C is the total mass of the composite foam and beaker, g; C1 is the total mass of the separated oil, foam, and beaker, g; C2 is the mass of the oil before separation, g.

[0064] Figure 3 This is a comparison chart of the adsorption capacity of ZIF-90-biochar@MF composite foam prepared in Example 2 of the present invention for different organic solvents. Figure 3As shown in the figure, the adsorption capacity of ZIF-90-biochar@MF composite foam for 11 different organic solvents including DMSO, DMF, IPA, ECH, TEA, TEOS, xylene, gasoline, vegetable oil, glycerol, and carbon tetrachloride is 59.75 g·g -1 ~147.64 g·g -1 The adsorption capacity of CCl4 reached a maximum of 147.64 g·g -1 .

[0065] Figure 4 This is a diagram showing the oil-water separation efficiency of the ZIF-90-biochar@MF composite foam prepared in Example 2 of the present invention for different organic solvents. Figure 4 As shown in the figure, the oil-water separation efficiency of ZIF-90-biochar@MF composite foam for eleven oils and organic solvents including DMSO, DMF, IPA, ECH, TEA, TEOS, xylene, gasoline, vegetable oil, glycerol, and carbon tetrachloride is higher than 90%.

[0066] For oil-absorbing foam, recycling performance is very important. Therefore, the total mass of ZIF-90-biochar@MF composite foam after oil absorption at different recycling times was measured. The adsorption capacity of ZIF-90-biochar@MF composite foam at different recycling times was calculated according to the adsorption capacity calculation formula (1), and a relationship diagram was drawn.

[0067] Figure 4 This is a comparison chart of the adsorption capacity of ZIF-90-biochar@MF composite foam prepared in Example 2 of the present invention for three oil products: vegetable oil, ECH, and CCl4 under different cycle times. Figure 4 As shown in the figure, under constant experimental conditions, the material's recycling performance exhibits an initial increase followed by a decrease. After 20 cycles, the adsorption capacity of the ZIF-90-biochar@MF composite foam for vegetable oil, ECH, and CCl4 remained at 89.4%, 88.6%, and 77.8% of the initial capacity, respectively, demonstrating excellent reuse potential.

[0068] In summary, ZIF-90-biochar@MF composite foam has a wide range of applications, including oil-water separation, environmental treatment, and building sound and thermal insulation. Its broad application has brought more business opportunities and economic benefits to related industries. The research and development and production of this foam material has also promoted the upgrading and development of related industries, driving the coordinated development of upstream and downstream enterprises in the industry chain. ZIF-90-biochar@MF composite foam is characterized by its simple preparation, recyclability, and reusability, meeting current societal requirements for environmental protection and sustainable development. Its application not only helps reduce environmental pollution but also promotes the development of a circular economy, bringing long-term economic and social benefits.

[0069] The above description is merely a preferred embodiment of the present invention, and the above specific embodiment is not intended to limit the present invention. Various variations and modifications are possible within the technical scope of the present invention. Any modifications, alterations, or equivalent substitutions made by a person skilled in the art based on the above description are within the scope of protection of the present invention.

Claims

1. A method for preparing ZIF-90-biochar@MF composite foam, characterized in that: The following steps are involved: A soluble zinc salt is added to a solvent, mixed evenly to obtain a zinc salt solution, and an organic ligand solution is added to the zinc salt solution to obtain a ZIF-90 precursor; The ZIF-90 precursor was added to biochar by room temperature impregnation method for in-situ loading and soaking to form a loading solution. Then, melamine foam was added to the loading solution to allow ZIF-67 and biochar to grow in situ and load on the melamine foam, thus obtaining ZIF-90-biochar loaded MF composite foam. Hexadecylamine was used as a modifier to hydrophobically modify the ZIF-90-biochar-loaded MF composite foam to obtain the ZIF-90-biochar@MF composite foam.

2. The method for preparing the ZIF-90-biochar@MF composite foam according to claim 1, wherein The concentration of soluble zinc salt solution is 0.01 g·mL -1 ~0.02g·mL -1 The soluble zinc salt is zinc nitrate hexahydrate, the mass ratio of the soluble zinc salt to the organic ligand is 1:1.3-1.6, the organic ligand is imidazole-2-carboxaldehyde, and the concentration of the organic ligand solution is 0.013 g·mL -1 ~0.015g·mL -1 .

3. The method for preparing the ZIF-90-biochar@MF composite foam according to claim 1, wherein The concentration of biochar in the loading solution was 0.0007 g·mL -1 ~0.0036 g·mL -1 .

4. The method for preparing the ZIF-90-biochar@MF composite foam according to claim 1, wherein During the loading process, 30 mL to 40 mL of loading liquid was added to 1 cm × 1 cm × 1 cm melamine foam.

5. The method for preparing the ZIF-90-biochar@MF composite foam according to claim 1, wherein The biochar is alkali-activated biochar, which is obtained by soaking durian peel biochar in a solution with a concentration of 1 mol·L -1 ~2 mol·L -1 The alkali-activated biochar was obtained by alkali modification in a NaOH solution under stirring for 2 h to 3 h.

6. The method for preparing the ZIF-90-biochar@MF composite foam according to claim 1, wherein: The in-situ loading immersion time is 9 h to 15 h.

7. The method for preparing the ZIF-90-biochar@MF composite foam according to claim 1, wherein: 60 mL to 70 mL of hexadecylamine solution was added to a 1 cm × 1 cm × 1 cm ZIF-90-biochar-loaded MF composite foam. The mass concentration of the hexadecylamine solution was 10%. The hydrophobic modification temperature was 65°C to 75°C, and the time was 8 h to 12 h.

8. A ZIF-90-biochar@MF composite foam, characterized in that: The composite foam is prepared by the method for preparing the ZIF-90-biochar@MF composite foam according to any one of claims 1 to 7.

9. Use of the ZIF-90-biochar@MF composite foam according to claim 8 as an adsorption material in oil-water separation.

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