A regenerated cationic cellulose-based composite filter membrane, a preparation method thereof and application thereof in nano-plastic removal

Abstract

The application discloses a regenerated cationic cellulose-based composite filter membrane and a preparation method and nanometer plastic removal application thereof, and belongs to the technical field of regenerated cellulose water treatment filter materials. In the application, a sodium hydroxide-urea-thiourea ternary system is used to fully dissolve cellulose, the cellulose is modified by 2,3-epoxypropyl trimethylammonium chloride cation, a PVDF membrane is used as a base, and a hydrophilic composite filter membrane is prepared by vacuum filtration and loading of a cationized cellulose layer. The preparation process is mild, and the defects of the traditional cellulose membrane, such as insufficient dissolution, uneven pore size and poor screening precision, are solved. The filter membrane surface is positively charged, the hydrophilicity is greatly improved, the water contact angle is only 39°, the particle size of 50-500 nm carboxylated nanometer plastics can be efficiently intercepted, the removal efficiency of 100 nm polystyrene nanometer plastics reaches 97.01%, and the water flux is excellent. The process is green and low-cost, can remove polystyrene, polymethyl methacrylate and polyvinyl chloride nanometer plastics in a wide range, and has a good engineering application prospect in the field of deep treatment of water body nanometer plastic pollution.

Description

Technical Field

[0001] This invention belongs to the field of regenerated cellulose technology, specifically relating to a method for preparing a regenerated cationized cellulose-based composite filter membrane material for filtering nanoplastics and its application. Background Technology

[0002] Plastic pollution in water bodies has become a prominent global environmental problem. Plastic waste in water bodies, after natural weathering, physical fragmentation, and biodegradation, generates large amounts of microplastics and nanoplastic particles. Nanoplastics, in particular, are extremely small and highly mobile, capable of penetrating conventional water treatment barriers. They easily accumulate in the aquatic environment over long periods and, through bioaccumulation in the food chain, harm aquatic ecosystems and human health.

[0003] Current technologies for treating micro / nanoplastics in water bodies mainly include coagulation and sedimentation, sludge adsorption, traditional membrane filtration, and advanced oxidation processes. Among these, conventional processes such as coagulation and sedimentation are only effective for large-particle microplastics, with extremely low removal efficiency for nanoplastics, failing to meet the requirements for advanced water purification. While advanced oxidation and electrochemical technologies can degrade ultrafine plastic particles, they suffer from drawbacks such as high energy consumption, complex processes, susceptibility to secondary pollution, and high operating costs, making large-scale application difficult. Membrane filtration technology, with its superior sieving performance, possesses significant technological advantages in the removal of micro / nanoplastics and is currently a key research direction in the field of water treatment.

[0004] Cellulose possesses advantages such as wide availability of raw materials, low cost, excellent hydrophilicity, and complete biodegradability, making it a high-quality substrate for preparing green water purification filter membranes. Currently, most regenerated cellulose filter membranes are prepared using a single alkali-urea dissolution system, which suffers from problems such as insufficient cellulose dissolution, uneven membrane structure, and poor pore size control. The resulting filter membranes exhibit disordered pore size distribution and insufficient sieving precision, making it difficult to efficiently retain nanoplastics. Furthermore, traditional preparation processes often rely on harsh conditions such as high temperatures and strong acids / alkalis, resulting in high energy consumption and easily damaging the cellulose molecular structure. This leads to poor hydrophilicity, mechanical stability, and service life of the filter membrane, significantly limiting the engineering application of cellulose filter membranes in the field of deep nanoplastic processing. Summary of the Invention

[0005] The purpose of this invention is to solve the above-mentioned problems and provide a method for preparing a regenerated cationized cellulose-based hydrophilic composite filter membrane material for filtering nanoplastics. This method has the advantages of simple preparation process, low cost, and green environmental protection.

[0006] The present invention also aims to provide an application of composite filter membrane material in nanoplastic filtration, which improves the hydrophilic and hydrophobic properties of the substrate membrane, increases the filtration efficiency and flux of nanoplastics in water, and expands its application scenarios.

[0007] To achieve the above objectives, the present invention provides the following technologies:

[0008] A method for preparing a regenerated cationized cellulose-based hydrophilic composite filter membrane material for filtering nanoplastics, the specific steps of which are as follows:

[0009] (1) Mix sodium hydroxide, urea, thiourea and deionized water in a specific ratio and stir at room temperature until completely dissolved to obtain a uniform and transparent composite solution. Place the mixed solution in a refrigerator at -10℃ for 10 minutes to pre-freeze.

[0010] (2) Slowly add 200μm cellulose powder to the mixture obtained in step (1), let stand for 15 minutes to allow the cellulose to fully swell, dissolve by magnetic stirring at room temperature, and centrifuge to obtain cellulose solution after the reaction is complete.

[0011] (3) Add the cellulose solution obtained in step (2) to an aqueous solution of 2,3-epoxypropyltrimethylammonium chloride and let it stand to regenerate the cellulose;

[0012] (4) Centrifuge the cellulose suspension collected in step (3), remove the supernatant, add a large amount of deionized water and centrifuge and wash until electrically neutral to obtain a cationic cellulose dispersion.

[0013] (5) The cationized cellulose obtained in step (4) was loaded onto the surface of a 0.45 μm polyvinylidene fluoride membrane by vacuum filtration to prepare a composite filter membrane material, which was then air-dried at room temperature for 24 hours.

[0014] As a preferred technical solution, in step (1), the mass ratio of sodium hydroxide, urea, thiourea, and deionized water is 7:12:7:73.

[0015] As a preferred technical solution, in step (2), the mass ratio of cellulose powder to the solution is 1 wt%.

[0016] As a preferred technical solution, in step (3), the molar concentration of the 2,3-epoxypropyltrimethylammonium chloride aqueous solution is 20%, and the standing time is 24h.

[0017] As a preferred technical solution, in step (4), the centrifugation speed is 10000 r / min for 8 min, and the washing operation is repeated 5-8 times.

[0018] As a preferred technical solution, in step (5), the cationized cellulose loading is 0.1 wt%, and the vacuum filtration pressure is 0.09 bar.

[0019] The regenerated cationized cellulose-based hydrophilic composite filter membrane described in this invention can achieve efficient filtration of nanoplastic pollutants in water.

[0020] The specific filtration process described is as follows: a cationized regenerated cellulose-based hydrophilic composite filter membrane material is laid on the filter element of the filtration device as a filter membrane, the filter tube is tightly connected to the filter element pad, and water containing nanoplastics is poured in from the top of the filter tube along the tube wall. The separation of nanoplastics can be achieved under a pressure of 0.09 bar.

[0021] The applications described herein include nanoplastics of various sizes and types, such as 50nm-500nm carboxylated polystyrene nanoplastics, 100nm carboxylated polymethyl methacrylate nanoplastics, and 100nm carboxylated polyvinyl chloride nanoplastics.

[0022] In the aforementioned applications, the filtration concentration of nanoplastics is 10ppm to 90ppm.

[0023] Compared with the prior art, the advantages and beneficial effects of the present invention are as follows:

[0024] (1) The present invention adopts an alkali-urea-thiourea ternary composite dissolution system, which can more efficiently destroy the hydrogen bonds between cellulose molecules compared with the traditional single alkali-urea system, so that the cellulose is dissolved more fully. The entire process adopts mild preparation conditions, without the need for harsh treatment processes such as high temperature, strong acid and strong alkali, and will not destroy the inherent structure of cellulose molecules. It improves the defects of traditional cellulose filter membranes such as disordered structure, uneven pore size and low sieving accuracy, and greatly improves the retention capacity of nanoplastics.

[0025] (2) This invention uses polyvinylidene fluoride membrane as substrate and cationic regenerated cellulose material as load layer. It adopts vacuum filtration molding process, which has fast molding speed, high membrane flatness, regular pore structure and stable water flux of filter membrane.

[0026] (3) The composite filter membrane prepared by the present invention has excellent screening and retention effect on nano-sized plastic particles in water. It can achieve deep removal of nano-plastics of different types, sizes and concentrations. It has a wide range of applications and stable operation. It has extremely high application value in the field of water microplastic pollution control.

[0027] (4) The cationized cellulose composite filter membrane prepared in this invention can achieve a filtration efficiency of 97.01% for 50 ppm, 100 nm carboxylated polystyrene nanoplastics, and a filtration flux of 1890 L·m -2 ·h -1 ·bar -1.

[0028] (5) The regenerated cationized cellulose-based hydrophilic composite filter membrane material prepared by the present invention can become a green, efficient, environmentally friendly and economical water pollution filter membrane. Attached Figure Description

[0029] Figure 1Infrared spectra of the regenerated cationized cellulose material, cellulose powder, and PVDF membrane of Example 1.

[0030] Figure 2 The Zeta potential characterization diagram of the regenerated cationized cellulose-based composite filter membrane material of this invention is shown in the figure.

[0031] Figure 3 The graph shows the filtration efficiency and filtration flux of the regenerated cationized cellulose-based composite filter membrane material in Example 2 for 50nm polystyrene nanoplastics.

[0032] Figure 4 The graph shows the filtration efficiency and filtration flux of the regenerated cationized cellulose-based composite filter membrane material in Example 2 for 100nm polystyrene nanoplastics.

[0033] Figure 5 The graph shows the filtration efficiency and filtration flux of the regenerated cationized cellulose-based composite filter membrane material in Example 2 for 200nm polystyrene nanoplastics.

[0034] Figure 6 The graph shows the filtration efficiency and filtration flux of the regenerated cationized cellulose-based composite filter membrane material in Example 2 for 500nm polystyrene nanoplastics.

[0035] Figure 7 The graph shows the filtration efficiency and filtration flux of the regenerated cationized cellulose-based composite filter membrane material in Example 4 for different types of carboxylated nanoplastics.

[0036] Figure 8 This is a water contact angle test analysis diagram of the regenerated cationized cellulose-based composite filter membrane material in Example 5. Detailed Implementation

[0037] The present invention will be further described in detail below through embodiments. These embodiments are only used to illustrate the present invention and do not limit the scope of protection of the present invention.

[0038] In the following examples, PVDF is polyvinylidene fluoride, EPTAC is 2,3-epoxypropyltrimethylammonium chloride, NPs are nanoplastics, PS-COOH-NPs are carboxylated polystyrene nanoplastics, PMMA-COOH-NPs are carboxylated polymethyl methacrylate nanoplastics, and PVC-COOH-NPs are carboxylated polyvinyl chloride nanoplastics.

[0039] Example 1

[0040] The preparation method of cationized regenerated cellulose composite filter membrane is as follows:

[0041] Step 1

[0042] Sodium hydroxide, urea, thiourea, and deionized water in a mass ratio of 7:12:7:73 were stirred at room temperature until completely dissolved to obtain a homogeneous and transparent composite solution. This mixture was pre-frozen at -10°C for 10 minutes. 1 wt% of 200 μm cellulose powder was slowly added to the mixture, and the mixture was allowed to stand for 15 minutes to allow the cellulose to fully swell. The mixture was then dissolved by magnetic stirring at room temperature. After the reaction was completed, the cellulose solution was obtained by centrifugation.

[0043] Step Two

[0044] Add 3% EPTAC aqueous solution to the solution in step one and let it stand to regenerate cellulose; centrifuge the collected cellulose suspension, remove the supernatant, add a large amount of deionized water and centrifuge to wash until electrically neutral to obtain a cationic cellulose dispersion.

[0045] Step 3

[0046] The cationized cellulose dispersion obtained in step one was further diluted to prepare a 0.1 wt% dispersion.

[0047] Step Four

[0048] The composite filter material was prepared by loading 10 mL of the dispersion obtained in step 3 onto the surface of a PVDF membrane using a vacuum filtration method, and then air-dried at room temperature for 24 hours to obtain a cationic regenerated cellulose-based hydrophilic composite filter material.

[0049] Example 2

[0050] Experiment on filtration of NPs using regenerated cationized cellulose-based composite filter membrane material: The regenerated cationized cellulose-based composite filter membrane material prepared in Example 1 was laid on the sand core of the filtration device, and the filter cup was tightly connected to the sand core with iron clamps. 10 mL of NP dispersion of the corresponding size, concentration, and type was poured from above the filter cup along the tube wall, and timing was started. Timing began when liquid flowed out from the lower surface of the sand core. NP separation was achieved at 0.09 bar. The filtration efficiency (R) and filtration flux (F) were calculated by combining the NP dispersion volume, separation time, effective filtration area, pressure, and the concentration of the NP dispersion before and after filtration.

[0051]

[0052]

[0053] Where C0 is the concentration of the NPs dispersion before filtration (ppm); C1 is the concentration of the NPs dispersion after filtration (ppm); V is the volume of the NPs dispersion (L); and S is the effective filtration area (m²). 2 T is the filtration time (h); ΔP is the negative pressure (bar) applied to the filtration device during the filtration process.

[0054] Example 3

[0055] To investigate the filtration performance and flux of regenerated cationized cellulose-based composite filter membrane material for PS-COOH-NPs with different particle sizes, PS-COOH-NPs with particle sizes of 50nm, 100nm, 200nm, and 500nm were selected for filtration experiments. The filtration method was the same as in Example 2.

[0056] Example 4

[0057] To investigate the filtration performance and flux of regenerated cationized cellulose-based composite filter membrane materials for different types of NPs, PMMA-COOH-NPs and PVC-COOH-NPs were selected for filtration experiments, and the filtration method was the same as in Example 2.

[0058] Example 5

[0059] To investigate how regenerated cationized cellulose-based composite filter membrane materials can effectively improve the hydrophilicity and hydrophobicity of PVDF membrane surfaces and further confirm that the material has a good hydrophilic surface, a surface water contact angle test was conducted. Specifically, the composite filter membrane sample obtained in Example 1 was placed on a glass slide, and the droplet volume was controlled at 3 μL to record the surface contact angle. Results Analysis

[0060] Infrared characterization analysis was performed on the cationized regenerated cellulose composite filter membrane and PVDF substrate membrane prepared in Example 1 of the present invention.

[0061] Figure 1 The infrared spectrum of the cationized regenerated cellulose material shows that the PVDF curve is only in the 1000-1300 cm⁻¹ range. -1 Numerous sharp characteristic absorption peaks attributable to CF bonds appear in the 3200-3600 cm⁻¹ range. -1 hydroxyl region, 1480cm -1 No significant absorption was observed at any point, indicating that the substrate does not contain hydroxyl or nitrogen-containing groups and will not interfere with the characteristic peaks of cellulose modification; the cellulose powder curve was 3200-3600 cm⁻¹. -1 A broad and strong -OH stretching vibration peak appears, at 1000-1200 cm⁻¹. -1 The characteristic fingerprint peaks of the COC glycosidic bond in the polysaccharide backbone are visible, and the peak at 1480 cm⁻¹ is also present. -1 The position curve is smooth with no absorption depressions, indicating that natural cellulose lacks CN bonds and therefore has no corresponding characteristic peaks; the cationic regenerated cellulose curve completely retains all the characteristic peaks of the cellulose skeleton, indicating that the modification process did not destroy the cellulose polysaccharide backbone structure, and the 3300 cm⁻¹ peak is also present. -1The absorption intensity of the hydroxyl region was significantly weaker compared to pure cellulose, indicating that the hydroxyl groups on the cellulose surface were partially consumed in the etherification grafting reaction. Most importantly, the absorption intensity at 1480 cm⁻¹ was significantly reduced. -1 A faint but clearly distinguishable absorption valley appears at 2900 cm⁻¹, which is attributed to the CN stretching vibration of the quaternary ammonium cation group. -1 The absorption of nearby alkyl CH also increased slightly, corresponding to the alkyl side chain introduced by the grafting cationic reagent. The above spectral changes confirm that the nitrogen-containing cationic group was successfully grafted onto the cellulose molecular chain, and the cellulose cationization modification reaction was successfully completed.

[0062] The cationized regenerated cellulose composite filter membrane prepared in Example 1 of this invention was subjected to nPS filtration analysis and testing.

[0063] like Figures 3-6 As shown, the regenerated cationized cellulose-based composite filter membrane material exhibits good filtration efficiency and flux for PS-COOH-NPs of different sizes. For PS-COOH-NPs with a concentration of 50 ppm, the removal efficiencies for 50 nm, 100 nm, 200 nm, and 500 nm PS-COOH-NPs are 87.3%, 97%, 98.5%, and 98.5%, respectively, with fluxes of 2341 L·m⁻¹. -2 ·bar 1 1575 L·m -2 ·bar -1 1478 L·m -2 ·bar -1 and 1354 L·m -2 ·bar -1 .

[0064] As the size of PS-COOH-NPs increases, the filtration efficiency improves, but the filtration flux gradually decreases: when the size of PS-COOH-NPs with a concentration of 50 ppm increases from 50 nm to 500 nm, the flux decreases by 42.16%.

[0065] Different types of nPS filtering analysis tests.

[0066] Figure 7 To investigate the effect of the cationized regenerated cellulose composite filter membrane prepared in Example 1 on the filtration performance of different types of nanoplastics, filtration experiments were conducted on PMMA-COOH-NPs and PVC-COOH-NPs with a concentration of 50 ppm and a size of 100 nm, respectively. The filtration method was the same as in Example 2. The cationized regenerated cellulose composite filter membrane showed excellent removal effects on both PMMA-COOH-NPs and PVC-COOH-NPs, with filtration efficiencies of over 92%, demonstrating a broad-spectrum effect on different types of nanoplastics.

[0067] Application Example 5

[0068] Figure 8 The water contact angle test analysis of the regenerated cationized cellulose-based composite filter membrane material prepared in Example 1 specifically demonstrates the difference in water contact angle between the two materials: PVDF and cationized regenerated cellulose composite filter membrane. The contact angle of PVDF is about 96.7°, and the water droplets are highly bead-shaped, exhibiting hydrophobicity; while the contact angle of the cationized regenerated cellulose composite filter membrane is only about 33.2°, and the water droplets are flatter, showing significantly stronger hydrophilicity.

Claims

1. A method for preparing a cationized regenerated cellulose composite filter membrane material, characterized in that, Includes the following steps: (1) Mix sodium hydroxide, urea, thiourea and deionized water in a specific ratio and stir at room temperature until completely dissolved to obtain a uniform and transparent composite solution. Place the mixed solution in a refrigerator at -10℃ for 10 minutes to pre-freeze. (2) Slowly add 200μm cellulose powder to the mixture obtained in step (1), let stand for 15 minutes to allow the cellulose to fully swell, dissolve by magnetic stirring at room temperature, and centrifuge to obtain cellulose solution after the reaction is complete. (3) Add the cellulose solution obtained in step (2) to an aqueous solution of 2,3-epoxypropyltrimethylammonium chloride and let it stand to regenerate the cellulose; (4) Centrifuge the cellulose suspension collected in step (3), remove the supernatant, add a large amount of deionized water and centrifuge and wash until electrically neutral to obtain a cationic cellulose dispersion. (5) The cationized cellulose obtained in step (4) was loaded onto the surface of a 0.45 μm polyvinylidene fluoride membrane by vacuum filtration to prepare a composite filter membrane material.

2. The method for preparing the cationized regenerated cellulose composite filter membrane according to claim 1, characterized in that, In step (1), the mass ratio of sodium hydroxide, urea, thiourea and deionized water is 7:12:7:

73.

3. The method for preparing the cationized regenerated cellulose composite filter membrane according to claim 1, characterized in that, In step (2), the cellulose powder accounts for 1 wt% of the solution.

4. The method for preparing the cationized regenerated cellulose composite filter membrane according to claim 1, characterized in that, In step (3), the molar concentration of the aqueous solution of 2,3-epoxypropyltrimethylammonium chloride is 20%, and the standing time is 24h.

5. The method for preparing the cationized regenerated cellulose composite filter membrane according to claim 1, characterized in that, In step (4), the centrifugation speed is 10000 r / min for 8 min, and the washing operation is repeated 5-8 times.

6. The method for preparing the cationized regenerated cellulose composite filter membrane according to claim 1, characterized in that, In step (5), the cationized cellulose loading is 0.1 wt%, and the vacuum filtration pressure is 0.09 bar.

7. The cationic regenerated cellulose composite filter membrane material prepared by the method of any one of claims 1-6, and its application as a filter membrane for filtering nanoplastics in water.

8. The application according to claim 7, characterized in that, The filtration process is as follows: a cationized regenerated cellulose composite filter membrane is laid as a filter layer on the filter element of the filtration device, the filter tube is tightly connected to the filter element pad, and water containing nanoplastics is poured in from the top of the filter tube along the tube wall. The separation of nanoplastics can be achieved under a pressure of 0.09 bar.

9. The application according to claim 7, characterized in that... The types of nanoplastics are: 50nm-500nm carboxylated polystyrene nanoplastics, 100nm carboxylated polymethyl methacrylate nanoplastics, and 100nm carboxylated polyvinyl chloride nanoplastics. The filtration concentration of nanoplastics is 10ppm-90ppm.

10. The application according to claim 7, characterized in that... The filter volume for nanoplastics is 10 mL.

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