Long alkyl chain super-hydrophobic covalent organic polymer, preparation method thereof and application of long alkyl chain super-hydrophobic covalent organic polymer in oil-water separation

Abstract

The invention belongs to the technical field of functional material preparation and application, and particularly relates to a long alkyl chain covalent organic polymer as well as a preparation method and application thereof in oil-water separation. The chemical structure of the long alkyl chain covalent organic polymer is shown as a formula (I), the long alkyl chain covalent organic polymer is successfully loaded on melamine sponge through an impregnation method, and the prepared modified sponge LNU-33 at MS has good hydrophobic and oleophylic characteristics and can be used for separating a mixture of an organic solvent and water. The synthetic process is simple, the oil-water separation efficiency is higher, and the oil-water separation catalyst has a good application prospect in the field of oil-water separation. # imgabs0 #

Description

Technical Field

[0001] The invention belongs to the technical field of functional material preparation and application, and specifically relates to a long alkyl chain covalent organic polymer and a preparation method thereof and application in oil-water separation. Background Art

[0002] With the rapid development of industrialization and the improvement of oilfield production technology, the discharge of oily wastewater and toxic organic solvents in industry has caused serious environmental pollution and threatened human health. Some conventional methods, such as chemical dispersion, flotation, skimming, gravity separation, etc., have disadvantages such as complex manufacturing process, low chemical stability, and insufficient buoyancy. The adsorbent method has received continuous attention in the field of oil-water separation due to its advantages such as simple operation, significant effect, and no secondary pollution. Therefore, it is urgent to develop oil-water separation materials with a wide range of sources, low cost, and high adsorption capacity.

[0003] As an emerging lightweight ordered extended organic network, covalent organic polymers have an ordered framework structure, rich pore structure and high specific surface area. Atoms are connected by strong covalent bonds. Compared with metal organic frameworks, they have better chemical and thermal stability. By designing the skeleton structure and selecting effective building units, they can be endowed with superhydrophobic properties. As a new type of adsorption and separation material, they exhibit special wettability and have broad application prospects in the field of oil-water separation.

[0004] Porous materials (fabric, film and sponge) are ideal substrates for preparing super-hydrophobic materials due to their wide sources, low cost and high adsorption capacity. Melamine sponge is a kind of three-dimensional porous foam material as a kind of melamine-formaldehyde polymer. Although it has both hydrophilicity and lipophilicity, it has the advantages of high porosity, low density, good mechanical properties and strong adsorption capacity. It is considered to be an ideal substrate for preparing novel oil-water separation materials. Therefore, it becomes a practical method to realize oil-water selective separation by carrying out super-hydrophobic modification to melamine sponge. The present invention can cope with complex and changeable oil-water mixture separation by loading super-hydrophobic covalent organic polymer on melamine sponge and modifying it. Summary of the invention

[0005] The present invention provides a method for preparing a long alkyl chain covalent organic polymer and its application in oil-water separation. Since the alkyl group is hydrophobic, the present invention introduces a long alkyl chain into the polymer monomer, which improves the surface roughness while reducing the surface free energy. Under the synergistic effect of the two, while giving the sponge super-hydrophobic properties, it is ensured that it has high stability. Compared with traditional fluorinated materials, long alkyl chain covalent organic polymers are environmentally friendly and low-priced while creating super-hydrophobic surfaces.

[0006] The technical solution adopted by the present invention is as follows: a long alkyl chain covalent organic polymer, the chemical structure of which is shown in formula (I),

[0007]

[0008] The above-mentioned method for preparing a long alkyl chain covalent organic polymer comprises the following steps: placing 2,7-dibromo-9,9-didocosylfluorene and 1,3,5-triethynylbenzene in a reaction container, adding a catalyst, pumping air through an oil pump, then introducing nitrogen, repeating degassing and then ventilating, adding an organic solvent after three cycles, heating the reaction system to 80°C, reflux reaction for 72 hours, cooling to room temperature after the reaction is completed, filtering and washing the crude product, Soxhlet extraction, and vacuum drying to obtain a long alkyl chain covalent organic polymer LNU-33.

[0009] The above-mentioned method for preparing a long alkyl chain covalent organic polymer comprises the following steps: the molar ratio of 2,7-dibromo-9,9-docosylfluorene:1,3,5-triethynylbenzene=3:2.

[0010] In the above-mentioned method for preparing a long alkyl chain covalent organic polymer, the catalyst is tetrakis(triphenylphosphine)palladium and cuprous iodide, and the mass ratio is tetrakis(triphenylphosphine)palladium: cuprous iodide=4:1.

[0011] In the above-mentioned method for preparing a long alkyl chain covalent organic polymer, the organic solvent is anhydrous and oxygen-free N,N-dimethylformamide and anhydrous and oxygen-free triethylamine, and the volume ratio of anhydrous and oxygen-free N,N-dimethylformamide: anhydrous and oxygen-free triethylamine is 2.5:1.

[0012] The above-mentioned method for preparing a long alkyl chain covalent organic polymer, wherein the crude product is filtered, washed, and Soxhlet extracted. The specific steps are to filter and wash the solids with tetrahydrofuran, dichloromethane and acetone for multiple times, and then Soxhlet extract the crude product with tetrahydrofuran, dichloromethane and chloroform for 24 hours.

[0013] A modified sponge LNU-33@MS is prepared by dispersing the long alkyl chain covalent organic polymer LNU-33 in a suspension of methyltrimethoxysilane and tetrahydrofuran, then adding a pretreated melamine sponge for ultrasonic treatment, and drying to form the modified sponge LNU-33@MS.

[0014] The modified sponge LNU-33@MS is prepared by ultrasonically cleaning the melamine sponge with deionized water, acetone and anhydrous ethanol for three times, and then drying it in a drying oven at 70° C. for 5 hours.

[0015] The above-mentioned modified sponge LNU-33@MS, long alkyl chain covalent organic polymer LNU-33: methyltrimethoxysilane: tetrahydrofuran = 1-2 mg: 3-5 mg: 2-4 mL.

[0016] Application of the modified sponge LNU-33@MS in oil-water separation.

[0017] The beneficial effects of the present invention are:

[0018] The long alkyl chain covalent organic polymer prepared by the present invention requires a simple preparation device, has low operation difficulty, and can be adapted to large-scale production.

[0019] The covalent organic polymer prepared by the present invention has high roughness and low surface energy without using fluorine-containing substances due to the introduction of hydrophobic long alkyl chains, and can form a super-hydrophobic surface with a hydrophobic angle greater than 150°. The application is not limited by size and shape and can be loaded on a variety of substrates.

[0020] Compared with the prior art, the long alkyl chain covalent organic polymer prepared by the present invention has a simple synthesis process, low cost, and is commercially available. In addition, the material contains no fluorine-containing substances, meets green environmental protection requirements, has good stability, and its excellent oil absorption properties make this type of material have good application prospects in the field of oily wastewater treatment. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is the infrared spectrum of the covalent organic polymer LNU-33 prepared in the present invention;

[0022] Figure 2 This is a scanning electron microscope image of the covalent organic polymer LNU-33 prepared in the present invention;

[0023] Figure 3 This is a transmission electron microscopy image of the covalent organic polymer LNU-33 prepared in the present invention;

[0024] Figure 4 The powder X-ray diffraction pattern of the covalent organic polymer LNU-33 prepared in the present invention;

[0025] Figure 5 Thermogravimetric diagram of the covalent organic polymer LNU-33 prepared in the present invention;

[0026] Figure 6 The water contact angle diagram of the covalent organic polymer LNU-33 prepared in the present invention;

[0027] Figure 7 The oil contact angle diagram of the covalent organic polymer LNU-33 prepared in the present invention;

[0028] Figure 8Comparison of contact angles of water (methylene blue staining) and chloroform (Sudan III staining) on ​​the original sponge MS (a) and the modified sponge LNU-33@MS (b);

[0029] Fig. 9 Schematic diagram of the original sponge MS immersed in water (a), the modified sponge LNU-33@MS floating on the water surface (b), and the silver mirror phenomenon immersed in water (c);

[0030] Fig.10 Schematic diagram of the hydrophobic and lipophilic properties of the modified sponge LNU-33@MS prepared in the present invention (water is dyed with methylene blue, and chloroform (a) and toluene (b) are both colorless);

[0031] Fig.11 The modified sponge LNU-33@MS prepared by the present invention selectively adsorbs light oil in toluene simulated water stained with Sudan III (a) and selectively adsorbs heavy oil in chloroform simulated water stained with Sudan III (b);

[0032] Fig.12 Schematic diagram of the process of separating a mixture of water (methylene blue staining) and chloroform (Sudan III staining) by the modified sponge LNU-33@MS prepared by the present invention under the action of gravity;

[0033] Fig.13 This is a diagram of the continuous separation process of water (colorless) and toluene (Sudan III dyed) by the modified sponge LNU-33@MS prepared in the present invention with the assistance of a vacuum pump. DETAILED DESCRIPTION

[0034] The following specific embodiments further illustrate the present invention. The specific process of the preparation steps of LNU-33 and LNU-33@MS is as follows:

[0035] Example 1 Preparation of a long alkyl chain covalent organic polymer LNU-33

[0036] 1. Synthesis of LNU-33

[0037] Under nitrogen conditions, 989 mg (1.50 mmoL) of 2,7-dibromo-9,9-dioctylfluorene and 150 mg (0.99 mmoL) of 1,3,5-triethynylbenzene were added to a round-bottom flask, and then 10 mg of cuprous iodide and 40 mg of tetrakis(triphenylphosphine)palladium were added as catalysts. The gas was pumped through an oil pump, and then nitrogen was introduced, and degassing and ventilation were repeated three times. Then, 20 mL of purified N,N-dimethylformamide and 8 mL of anhydrous and oxygen-free triethylamine were added to the round-bottom flask using a disposable syringe. Finally, the reaction system was heated to 80°C and refluxed for 72 hours.

[0038] 2. Post-processing of LNU-33

[0039] After the reaction is completed and cooled to room temperature, the reactant is filtered, and then the solid is filtered and washed multiple times with tetrahydrofuran, dichloromethane and acetone to wash away the unreacted monomers and possible residual catalysts. The crude product is then Soxhlet extracted with tetrahydrofuran, dichloromethane and chloroform for 24 hours to further purify the product. Finally, it is dried in a vacuum drying oven at 90°C for 10 hours, and the obtained brown powder solid is the covalent organic polymer LNU-33.

[0040] The synthetic route of long alkyl chain covalent organic polymer LNU-33 is as follows:

[0041]

[0042] Example 2 Preparation of a super hydrophobic sponge LNU-33@MS

[0043] The mold-cut melamine sponge (10mm×10mm×10mm) was ultrasonically cleaned 3 times with deionized water, acetone, and anhydrous ethanol, and then dried in a drying oven at 70°C for 5 hours before use. In a sample bottle (20mL), 30mg of methyltrimethoxysilane was dispersed in 10mL of tetrahydrofuran and ultrasonically dispersed to form a suspension. Then LNU-33 (10mg) and the pretreated melamine sponge were added, and then ultrasonically treated for 3 minutes. Finally, the formed LNU-33@MS was dried in an oven at 120°C for 3 hours.

[0044] Example 3 Basic Characterization

[0045] Infrared spectroscopy is used to characterize the chemical structure of covalent organic polymers, such as Figure 1 As shown in the figure, the top curve a is LNU-33, curve b is 2,7-dibromo-9,9-dioctylfluorene monomer, and curve c is 1,3,5-triethynylbenzene monomer. It can be seen from the figure that the polymer LNU-33 has a -1 No C-Br stretching vibration peak was found at 3300 cm -1 No stretching vibration peak of CH connected to the alkynyl group was found at 2200cm -1 The newly generated absorption peak is the stretching vibration peak of -C≡C-, which proves the success of the Sonogashira-Hagihara coupling reaction. The product is polymerized as expected and the degree of polymerization is complete.

[0046] In order to study the surface morphology and internal structure of the material, a scanning electron microscope (SEM) was used. Figure 2 ) and transmission electron microscopy ( Figure 3) It can be observed from the scanning electron microscopy that LNU-33 is composed of spherical particles with a diameter of about 5 microns, while the transmission electron microscopy image shows that the material has a worm-like porous structure, proving the amorphous structure of the material.

[0047] The crystallinity of the materials was characterized by powder X-ray diffraction. Figure 4 : is the powder X-ray diffraction spectrum of polymer LNU-33. From the spectrum, it can be observed that the wide-angle XRD spectrum of covalent organic polymer LNU-33 shows only one broad peak, which further confirms that polymer LNU-33 is an amorphous material.

[0048] Figure 5 The polymer is heated at 10℃min under air condition. -1 The thermal stability of LNU-33 was tested by the heating rate. From the thermogravimetric spectrum, we can see that the material begins to decompose at around 300°C, indicating that the material has good thermal stability. At the same time, when we tested the solubility of the material, we found that LNU-33 would not dissolve or decompose in common organic solvents (methanol, ethanol, tetrahydrofuran, acetone, dichloromethane, chloroform, N,N-dimethylformamide, triethylamine, etc.), proving that the polymer has good chemical stability.

[0049] The water contact angle and oil contact angle of the polymer were tested by contact angle tester. Figure 6 and Figure 7 The water contact angle diagram and oil contact angle diagram of the long alkyl chain covalent organic polymer LNU-33 prepared by the present invention are shown in FIG. The long alkyl chain functional groups in the skeleton make the polymer have super hydrophobic properties. Figure 6 As can be seen from the figure, the water contact angle of LNU-33 is 152.9°, while its oil contact angle is almost 0° ( Figure 7 ), further indicating that LNU-33 can be applied to the separation of water and organic solvents.

[0050] Example 4 Application Performance Test

[0051] Figure 8 This is a comparison of the water and chloroform contact angles of the original sponge MS (a) and the modified sponge LNU-33@MS (b). The water is stained with methylene blue and the chloroform is stained with Sudan III. Figure 8 As can be seen in (a), on the original sponge MS, the contact angles of water and chloroform are close to 0°, and the absorption of water and chloroform does not show selectivity. Figure 8 As can be seen in (b), the water droplet on the modified sponge LNU-33@MS is spherical, while the contact angle of chloroform on the modified sponge LNU-33@MS is 0°, indicating that LNU-33@MS has the ability to selectively adsorb organic solvents.

[0052] Fig. 9 Schematic diagram of the original sponge MS immersed in water (a), the modified sponge LNU-33@MS floating on the water surface (b), and the silver mirror phenomenon immersed in water (c). Fig. 9 As can be seen in (a), the unmodified original sponge MS can absorb water and sink to the bottom of the water; Fig. 9 In (b), it can be seen that the modified sponge LNU-33@MS can float on the water surface without external force. Fig. 9 As can be seen in (c), under the action of external force, the surface of the modified sponge is densely covered with small bubbles and a silver mirror phenomenon occurs, indicating that LNU-33@MS has excellent hydrophobicity.

[0053] Fig.10 Schematic diagram of the hydrophobic and oleophilic properties of the modified sponge LNU-33@MS prepared by the present invention. Fig.10 In (a), we can see that in the heavy oil system composed of water (methylene blue dye) / chloroform, LNU-33@MS completely floats on the water surface; Fig.10 As can be seen in (b), in the light oil system composed of toluene / water (dyed with methylene blue), LNU-33@MS sinks to the bottom of toluene and floats on the water surface, indicating that LNU-33@MS has good hydrophobic and lipophilic properties and can be used for the separation of water and organic solvents.

[0054] Fig.11 The modified sponge LNU-33@MS prepared in the present invention selectively adsorbs light oil in water (a) and heavy oil in water (b) by toluene (a). The aqueous phase was not dyed, and toluene and chloroform were both dyed with Sudan III. Fig.11 (a) and Fig.11 As can be seen in (b), in the simulated offshore light oil (toluene) and heavy oil (chloroform) leakage conditions, toluene and chloroform can be quickly absorbed by the modified sponge LNU-33@MS, while water is completely rejected by LNU-33@MS, indicating that LNU-33@MS can be used to treat light oil and heavy oil leakage pollution.

[0055] Fig.12 Schematic diagram of the process of separating a mixture of water and chloroform under gravity using the modified sponge LNU-33@MS prepared in the present invention. A gravity-driven separation device was constructed using common glass instruments to separate a mixed solvent of water (methylene blue dye) and chloroform (Sudan III dye). Fig.12 (a) and Fig.12As can be seen in (b), due to the superhydrophobic properties of LNU-33@MS, the water in the mixed liquid is retained in the upper funnel, while the chloroform can fall into the collection device through the sponge under the action of gravity, thus achieving effective separation of the water phase and the oil phase, indicating that the modified sponge LNU-33@MS can achieve efficient oil-water separation under the action of gravity alone.

[0056] Fig.13 The modified sponge LNU-33@MS prepared in the present invention is used to continuously separate water and toluene with the assistance of a vacuum pump. Undyed distilled water is used as the aqueous phase, and toluene (Sudan III dyed) is used as the organic phase. Fig.13 It can be seen that after the vacuum pump is turned on, the organic solvent adsorbed by the sponge at the water-oil interface can be sucked into the receiving bottle through the catheter. However, due to the superhydrophobic properties of LNU-33@MS, water cannot be adsorbed by the modified sponge LNU-33@MS and is retained in the beaker, which fully proves the possibility that the modified sponge LNU-33@MS can be used on a large scale for continuous oil-water separation.

Claims

1. A long alkyl chain covalent organic polymer, characterized in that The chemical structure of the long alkyl chain covalent organic polymer is shown in formula (I), 2. The method for preparing a long alkyl chain covalent organic polymer according to claim 1, characterized in that: The method comprises the following steps: placing 2,7-dibromo-9,9-didocosylfluorene and 1,3,5-triethynylbenzene in a reaction container, adding a catalyst, pumping air through an oil pump, then introducing nitrogen, repeating degassing and then ventilating, adding an organic solvent after three cycles, heating the reaction system to 80°C, reflux reaction for 72 hours, cooling to room temperature after the reaction is completed, filtering and washing the crude product, performing Soxhlet extraction, and vacuum drying to obtain a long alkyl chain covalent organic polymer LNU-33.

3. A method for preparing a long alkyl chain covalent organic polymer according to claim 2, characterized in that: In terms of molar ratio, 2,7-dibromo-9,9-docosylfluorene:1,3,5-triethynylbenzene=3:

2.

4. A method for preparing a long alkyl chain covalent organic polymer according to claim 2, characterized in that: The catalyst is tetrakis(triphenylphosphine)palladium and cuprous iodide, and the mass ratio is tetrakis(triphenylphosphine)palladium: cuprous iodide=4:

1.

5. The method for preparing a long alkyl chain covalent organic polymer according to claim 2, characterized in that: The organic solvent is anhydrous and oxygen-free N,N-dimethylformamide and anhydrous and oxygen-free triethylamine, and the volume ratio of anhydrous and oxygen-free N,N-dimethylformamide to anhydrous and oxygen-free triethylamine is 2.5:

1.

6. A method for preparing a long alkyl chain covalent organic polymer according to claim 2, characterized in that: The crude product is filtered, washed and extracted by Soxhlet, and the specific steps are to filter and wash the solid matter with tetrahydrofuran, dichloromethane and acetone for multiple times, and then extract the crude product by Soxhlet for 24 hours with tetrahydrofuran, dichloromethane and chloroform respectively.

7. A modified sponge LNU-33@MS, characterized in that: The long alkyl chain covalent organic polymer LNU-33 described in claim 1 is dispersed in a suspension of methyltrimethoxysilane and tetrahydrofuran, and then a pretreated melamine sponge is added for ultrasonic treatment and dried to form a modified sponge LNU-33@MS.

8. The modified sponge LNU-33@MS according to claim 7, characterized in that: The pretreated melamine sponge is prepared by ultrasonically cleaning the melamine sponge with deionized water, acetone and anhydrous ethanol for three times respectively, and then drying the melamine sponge in a drying oven at 70° C. for 5 hours.

9. The modified sponge LNU-33@MS according to claim 7, characterized in that: Long alkyl chain covalent organic polymer LNU-33: methyltrimethoxysilane: tetrahydrofuran = 1-2 mg: 3-5 mg: 2-4 mL.

10. Use of the modified sponge LNU-33@MS according to claim 7 in oil-water separation.

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