Preparation method and application of cationized composite paper-based material for filtering nano plastic

Abstract

The invention discloses a preparation method and application of a cationized composite paper-based material for filtering nano plastic, and belongs to the technical field of nano cellulose. The preparation method comprises the following steps: preparing cationized lignocellulose nanofibers through DES treatment, dissolving out lignin through DES treatment, fully mixing the lignin with a silane coupling agent KH-560 to obtain silanized lignocellulose nanofibers, and then loading a layer of nano lignocellulose material on the surface of a polyvinylidene fluoride filter membrane by adopting a vacuum suction filtration method, and finally, cross-linking polyethyleneimine to obtain the cationized composite paper-based material. The cationized composite paper-based material prepared by the invention is green and environment-friendly, has excellent hydrophilic, antibacterial and recycling performances, and has broad-spectrum effects on the size, concentration and type of carboxylated nano-plastics in efficient capture. The cationized composite paper-based material has the advantages that the carboxylated polystyrene nano-plastic filtering efficiency reaches 97.56%, the filtering flux reaches 1889.99 L.m <-2 >. H <-1 >. Bar <-1 >, the practical application performance of lignocellulose is further widened, and the cationized composite paper-based material has a good application prospect.

Description

Technical Field

[0001] The invention belongs to the technical field of nanocellulose, and in particular relates to a preparation method and application of a cationic composite paper-based material for filtering nanoplastics. Background Art

[0002] With the advancement of science and technology and the development of industry, plastic products have been widely used due to their low cost, high stability, and easy processing. However, the excessive use of plastics, their difficulty in degradation and low recycling rate, as well as inadequate plastic waste management measures, have led to a serious plastic pollution problem.

[0003] Discarded plastic products slowly break down into smaller plastic particles, namely secondary microplastics (MPs) and nanoplastics (NPs), through physical decomposition (such as mechanical wear), chemical induction (such as ultraviolet radiation), and biodegradation. Studies have shown that MPs undergo continuous cleavage and degradation, leading to the formation of NPs (particles with a diameter of less than 1000 nm). NPs are ubiquitous throughout the natural environment, particularly in aquatic environments. Due to their large surface area and low surface polarity, NPs can act as carriers of various harmful substances (such as heavy metals and organic pollutants), posing a potential threat to human health through transmission and bioaccumulation within the food chain.

[0004] Membrane separation technology has been widely used in the field of water treatment due to its significant advantages such as high efficiency, economy, environmental protection and easy operation. Polyvinylidene fluoride (PVDF) is the most commonly used membrane material with high chemical stability and excellent mechanical properties. However, ordinary polyvinylidene fluoride membranes have exposed many problems during actual use, such as hydrophobicity of the membrane surface, poor recycling performance, serious membrane fouling and lack of functional adsorption sites, resulting in poor filtration effect. These problems greatly limit its application scope and effect in water treatment. Therefore, it is of great significance to explore low-cost, environmentally friendly and multifunctional membrane coatings. Summary of the Invention

[0005] The purpose of the present invention is to solve the above-mentioned problems and provide a method for preparing a cationic composite paper-based material, which has the advantages of simple preparation process, low cost, and environmental protection.

[0006] The purpose of the present invention is also to provide an application of a cationic composite paper-based material in the filtration of nanoplastics, enhance its hydrophilic and antibacterial properties, improve the filtration efficiency of nanoplastics in water and increase the number of recycling uses, so as to achieve the purpose of expanding its application scenarios.

[0007] The present invention is achieved through the following technical solutions:

[0008] A method for preparing a cationic composite paper-based material for filtering nanoplastics, comprising the following specific steps:

[0009] (1) Choline chloride and imidazole are mixed to prepare a uniform and transparent DES, and sugarcane bagasse is added for pretreatment to obtain a pretreated sugarcane bagasse mixed solution;

[0010] (2) adding p-toluenesulfonyl chloride and betaine hydrochloride to the mixed solution obtained in step (1) to carry out a cationization reaction, and quenching the reaction with ethanol after the reaction is completed to obtain a cationized sugarcane bagasse mixed solution;

[0011] (3) separating the mixed solution obtained in step (2) by vacuum filtration, washing the cationized sugarcane bagasse with ethanol until it becomes colorless, collecting the washing liquid, and then washing it with deionized water until it becomes neutral, and mechanically grinding it to obtain cationized lignocellulose nanofibers;

[0012] (4) adding a large amount of ionized water to the washing liquid collected in step (3), allowing it to settle, and then centrifuging and freeze-drying to obtain lignin;

[0013] (5) fully mixing the cationized lignocellulose nanofibers obtained in step (3) and the lignin obtained in step (4) with a silane coupling agent KH-560 to react to obtain silanized lignocellulose nanofibers;

[0014] (6) loading the silanized lignocellulose nanofibers obtained in step (5) on the surface of a polyvinylidene fluoride membrane by a vacuum filtration method to prepare a composite paper-based material;

[0015] (7) Soaking the composite paper-based material obtained in step (6) in a polyethyleneimine aqueous solution, washing with deionized water, and naturally air-drying to obtain a cationic composite paper-based material.

[0016] As a preferred technical solution, in step (1), the molar ratio of choline chloride to imidazole is 3:7, the mass ratio of bagasse to DES is 1:25, the pretreatment reaction temperature is 80° C., and the pretreatment time is 19 h.

[0017] As a preferred technical solution, in step (2), the molar ratio of p-toluenesulfonyl chloride and betaine hydrochloride is 1:1, the mass ratio of bagasse to p-toluenesulfonyl chloride is 7:10, the cationization reaction temperature is 80°C, the cationization reaction time is 5h, and the amount of ethanol added is 600mL.

[0018] As a preferred technical solution, in step (3), the ethanol washing times are 8 to 10 times, and the deionized water washing times are 10 to 12 times.

[0019] As a preferred technical solution, in step (4), the static sedimentation time is 24 hours, the centrifugal speed is 5000 rpm, and the freeze-drying time is 48 hours.

[0020] As a preferred technical solution, in step (5), the amount of the cationic lignocellulose nanofibers is 0.006wt% to 0.014wt%, the amount of lignin is 0.002wt% to 0.01wt%, the amount of silane coupling agent KH-560 is 0.006wt%, and the reaction time is 2h.

[0021] As a preferred technical solution, in step (6), the loading amount of the silanized lignocellulose nanofibers is 10 mL.

[0022] As a preferred technical solution, in step (7), the amount of polyethyleneimine in the polyethyleneimine aqueous solution is 1 wt%, the molecular weight of polyethyleneimine is 25000 g / mol, the soaking time is 3 h, and the washing times are 3 times.

[0023] The cationic composite paper-based material of the present invention can be used to efficiently filter nano-plastic pollutants in water bodies.

[0024] The specific filtration process of the application is as follows: the cationic composite paper-based material is laid as a filter membrane 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 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.

[0025] The sizes and types of the nano plastics include: 50nm-500nm carboxylated polystyrene nano plastics, 100nm-500nm amino polystyrene nano plastics, 100nm carboxylated polymethyl methacrylate nano plastics, and 100nm carboxylated polyvinyl chloride nano plastics.

[0026] In the application, the filtration concentration of nano plastics is 10ppm to 90ppm.

[0027] Compared with the prior art, the advantages and beneficial effects of the present invention are:

[0028] (1) The lignocellulose used in the present invention is a biomass material that is low-cost, environmentally friendly, and widely available. Lignocellulose is modified by cationization to introduce charged groups, which promotes the microfibrillation process of the fibers and imparts fiber functionalization.

[0029] (2) The present invention uses polyvinylidene fluoride membrane as the substrate and nano-lignocellulose material as the loading layer, adopts vacuum filtration to achieve loading, and forms a stable cross-linked coating on the surface of the polyvinylidene fluoride membrane by immersion, giving the polyvinylidene fluoride membrane hydrophilic properties, antibacterial properties and a large number of functional adsorption sites.

[0030] (3) The cationic composite paper-based material prepared by the present invention exhibits excellent filtration performance for nanoplastics of different types, sizes and concentrations, and is reusable, which greatly reduces the filtration cost and further broadens the scope of application in the field of filtration and treatment of plastic pollution in water bodies.

[0031] (4) The cationized composite paper-based material prepared by the present invention can achieve a filtration efficiency of 97.56% for 100nm carboxylated polystyrene nanoplastics, and a filtration flux of 1890L·m -2. h -1 .bar -1 After 10 cycles, it still has a good filtration effect, with a filtration efficiency of 88.58% and a filtration flux of 100.79 L·m -2 ·h -1 bar -1 .

[0032] (5) The cationic composite paper-based material prepared by the present invention can become a green, efficient, environmentally friendly and economical water pollution filtration membrane. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 Schematic diagram of the preparation process of the cationic composite paper-based material of the present invention.

[0034] Figure 2 This is a field emission scanning electron microscope image of the cationic composite paper-based material of Example 1.

[0035] Figure 3 This is the infrared spectrum of the cationic composite paper-based material of Example 1.

[0036] Figure 4 This is an analysis chart of the filtration performance of the cationic composite paper-based materials of Examples 3, 4 and 5 on polystyrene nanoplastics;

[0037] Among them, (a) is an analysis diagram of the filtration efficiency and filtration flux of the cationic composite paper-based material for carboxylated polystyrene nanoplastics of different sizes, (b) is an analysis diagram of the filtration efficiency and filtration flux of the cationic composite paper-based material for carboxylated polystyrene nanoplastics of different concentrations, and (c) is an analysis diagram of the filtration efficiency and filtration flux of the cationic composite paper-based material for amino polystyrene nanoplastics.

[0038] Figure 5This is an analysis chart of the circulating filtration efficiency and circulating filtration flux of the cationic composite paper-based material of Example 6 for carboxylated polystyrene nanoplastics.

[0039] Figure 6 Filtration performance analysis chart of the cationized composite paper-based materials of Examples 7 and 8;

[0040] Among them, (a) is an analysis diagram of the filtration efficiency and filtration flux of cationic composite paper-based materials for carboxylated polystyrene nanoplastics in the presence of other coexisting factors, and (b) is an analysis diagram of the filtration efficiency and filtration flux of cationic composite paper-based materials for different types of carboxylated nanoplastics.

[0041] Figure 7 This is a diagram showing the antibacterial effect of the cationic composite paper-based material of Example 9 on Escherichia coli and Staphylococcus aureus;

[0042] Among them, (a) is a diagram showing the antibacterial effect of the cationic composite paper-based material on Escherichia coli, and (b) is a diagram showing the antibacterial effect of the cationic composite paper-based material on Staphylococcus aureus. DETAILED DESCRIPTION

[0043] The present invention is further described in detail below through examples. These examples are only used to illustrate the present invention and do not limit the scope of protection of the present invention.

[0044] In the following examples, DES is a deep eutectic solvent, LCNF is a cationized lignocellulose nanofiber, GLCNF is a silanized lignocellulose nanofiber, PVDF is polyvinylidene fluoride, PEI is polyethyleneimine, NPs is a nanoplastic, PS-COOH-NPs is a carboxylated polystyrene nanoplastic, PS-NH2-NPs is an amino polystyrene nanoplastic, PMMA-COOH-NPs is a carboxylated polymethyl methacrylate nanoplastic, PVC-COOH-NPs is a carboxylated polyvinyl chloride nanoplastic, Ethanol is ethanol, SiO2 is a silica particle, CR is Congo red, MB is methylene blue, Cu 2+ For copper ions.

[0045] Example 1

[0046] The preparation method of the cationic composite paper-based material comprises the following specific steps:

[0047] (1) Choline chloride and imidazole in a molar ratio of 3:7 were used to synthesize a uniform and transparent DES at 80°C. Sugarcane bagasse in a mass ratio of 1:25 to DES was added and mechanical stirring was performed for 19 hours for pretreatment. Then, p-toluenesulfonyl chloride in a mass ratio of 7:10 to sugarcane bagasse and betaine hydrochloride in a molar ratio of 1:1 to p-toluenesulfonyl chloride were added and reacted for 5 hours for cationic modification. The reaction was then quenched with 600 mL of ethanol. After the reaction was completed, the solid was separated by vacuum filtration, and the solid portion was repeatedly washed with ethanol until the filtrate was colorless. The filtrate was collected. Deionized water was then added and repeatedly washed until the washing liquid was neutral. LCNF was obtained by mechanical grinding.

[0048] (2) The filtrate in step (1) was added with a large amount of deionized water, allowed to settle for 24 hours, and lignin was obtained by centrifugation at 5000 rpm and freeze-drying for 48 hours.

[0049] (3) The LCNF prepared in step (1) and the lignin obtained in step (2) were prepared into a 0.016 wt% dispersion at a mass ratio of 3:2, 0.006 wt% of silane coupling agent KH-560 was added, and magnetic stirring was performed for 2 h to obtain GLCNF.

[0050] (4) 10 mL of the GLCNF obtained in step (3) was loaded onto the surface of the PVDF membrane by vacuum filtration to prepare a composite paper-based material, which was then immersed in a 1 wt% PEI aqueous solution for crosslinking for 3 h. After washing with deionized water three times and air-drying, the cationic composite paper-based material was obtained. The complete preparation process is as follows: Figure 1 .

[0051] like Figure 2 (ac) Field emission scanning electron micrographs of the cationic composite paper-based material show that the pore structure of the PVDF membrane surface is covered, and nanocellulose and lignin form a layered micro- and nanoporous structure on the membrane surface, enhancing the hydrophilic surface to a super-hydrophilic one and effectively retaining nanoplastics. Figure 3 This is the infrared spectrum of the cationic composite paper-based material. On the cationic composite paper-based material, the epoxy group on the silane coupling agent KH-560 undergoes a ring-opening reaction, which -1 , 909cm -1 , 815cm -1 The characteristic peak at 3355cm -1 Related to the bending vibration of -OH in GLCNF, 3285 cm -1 Corresponding to the NH stretching vibration of the secondary amine on PEI, 2915 cm -1 Corresponding to the stretching vibration of the CH2 single bond on GLCNF, 1954 cm -1 and 1464cm -1Corresponding to the bending vibration of NH of PEI, 1318 cm -1 The presence of the above characteristic peaks indicates that PEI was successfully grafted onto GLCNF via the silane coupling agent KH-560.

[0052] Example 2

[0053] Experiment on filtration of NPs by cationic composite paper-based material: The cationic composite paper-based material prepared in Example 1 was spread on the filter head of the filtration device, and the filter cup and the filter head pad were tightly connected with an iron clamp. 10 mL of NPs dispersion of corresponding size, concentration, and type was poured from the top of the filter cup along the tube wall and the timing was started. When liquid flowed out from the lower surface of the filter head, the timing started. NPs separation was achieved at 0.09 bar. The filtration efficiency (R) and filtration flux (F) were calculated based on the volume of NPs dispersion, separation time, effective filtration area, pressure, and the concentration of NPs dispersion before and after filtration:

[0054]

[0055]

[0056] Wherein, C0 is the concentration of NPs dispersion before filtration (ppm); C1 is the concentration of NPs dispersion after filtration (ppm); V is the volume of NPs dispersion (L); S is the effective filtration area (m 2 ); T is the filtration time (h); ΔP is the negative pressure applied to the filtration device during the filtration process (bar).

[0057] Example 3

[0058] In order to study the effect of PS-COOH-NPs of different sizes on the filtration performance of the cationic composite paper-based material, PS-COOH-NPs with a concentration of 50 ppm and sizes of 50 nm, 100 nm, 200 nm and 500 nm were selected for filtration experiments. The filtration method was the same as in Example 2. The results are shown in FIG. Figure 4 As shown in (a), the filtration efficiency and filtration flux of the cationic composite paper-based material for PS-COOH-NPs of different sizes are not the same. When the size of PS-COOH-NPs is larger than 100 nm, the filtration efficiency exceeds 93%, but as the size of PS-COOH-NPs increases, its filtration flux decreases.

[0059] Example 4

[0060] In order to study the effect of different concentrations of PS-COOH-NPs on the filtration performance of the cationic composite paper-based material, PS-COOH-NPs with a size of 100 nm and concentrations of 10 ppm, 30 ppm, 50 ppm, 70 ppm and 90 ppm were selected for filtration experiments. The filtration method was the same as in Example 2. The results are shown in FIG. Figure 4 As shown in (b), with the increase of PS-COOH-NPs concentration, the filtration efficiency and filtration flux of the cationic composite paper-based material gradually decreased. When the concentration was 90 ppm, the filtration efficiency was 84.48%, and the filtration flux decreased to 884.27 L·m -2 .h -1 bar -1 .

[0061] Example 5

[0062] In order to study the effect of electrostatic repulsion on the filtration performance of cationic composite paper-based materials, PS-NH2-NPs with a concentration of 50 ppm and sizes of 100 nm, 200 nm, and 500 nm were selected for filtration experiments. The filtration method was the same as in Example 2. The results are shown in Figure 2. Figure 4 As shown in (c), the filtration effect of the cationic composite paper-based material on PS-NH2-NPs is greatly affected by electrostatic repulsion. The filtration efficiency of 500 nm PS-NH2-NPs is 87.39%, and its filtration flux is 1264.22 L·m -2 ·h -1 bar -1 .

[0063] Example 6

[0064] In order to study the cyclic filtration performance of the cationic composite paper-based material, PS-COOH-NPs with a concentration of 50ppm and a size of 100nm were selected for filtration experiments. The filtration method was the same as in Example 2. It is worth noting that the cationic composite paper-based material after one cycle needs to be ultrasonically cleaned and naturally air-dried before the next cycle. The results are shown in Figure 2. Figure 5 As shown in the figure, the filtration efficiency of the cationic composite paper-based material for 100 nm PS-COOH-NPs remained above 91% in the first eight cycles and above 88% after ten cycles, showing an excellent cyclic filtration effect. However, as the number of cycles increased, the flux decreased sharply, and the filtration flux at the tenth cycle was 100.79 L·m -2 ·h -1 bar -1 .

[0065] Example 7

[0066] In order to study the effect of other coexisting factors on the filtration performance of the cationized composite paper-based material, PS-COOH-NPs with a concentration of 50 ppm and a size of 100 nm were selected for filtration experiments. The filtration method was the same as in Example 2. The coexisting factors included: Ethanol (50%, v / v), SiO2 (50 mg / mL), CR (25 mg / mL), MB (25 mg / mL), Cu 2+ (10 mg / mL), thus preparing PS-Ethanol, PS-SiO2, PS-CR, PS-MB and PS-Cu 2+ Coexistence suspension / solution. The results are as follows Figure 6 As shown in (a), in the presence of ethanol and CR factors, the filtration efficiency of the cationic composite paper-based material for PS-COOH-NPs was significantly reduced, while in the presence of SiO2, MB and Cu 2+ In the presence of these factors, the filtration efficiency of cationic composite paper-based materials for PS-COOH-NPs was improved, indicating that other pollutants promoted the removal of PS-COOH-NPs.

[0067] Example 8

[0068] In order to study the effect of different types of NPs on the filtration performance of cationic composite paper-based materials, PMMA-COOH-NPs and PVC-COOH-NPs with a concentration of 50 ppm and a size of 100 nm were selected for filtration experiments. The filtration method was the same as in Example 2. The results are shown in Figure 2. Figure 6 As shown in (b), the cationic composite paper-based material has excellent removal effects on both PMMA-COOH-NPs and PVC-COOH-NPs, with filtration efficiencies above 92%, reflecting a broad-spectrum effect on different types of nanoplastics.

[0069] Example 9

[0070] In order to study the antibacterial properties of cationic composite paper-based materials, Escherichia coli and Staphylococcus aureus were selected as representatives of Gram-negative bacteria and Gram-positive bacteria, respectively, and the bacterial solution concentration was 1×10 6 CFU / mL. The results are as follows Figure 7 As shown in the figure, the cationic composite paper-based material has a certain antibacterial effect on Escherichia coli and Staphylococcus aureus, among which the antibacterial effect on Staphylococcus aureus is better, and the diameter of the inhibition zone is 10 mm.

Claims

1. A method for preparing a cationic composite paper-based material, characterized in that: The following steps are involved: (1) Choline chloride and imidazole are mixed to prepare a uniform and transparent DES, and sugarcane bagasse is added for pretreatment to obtain a pretreated sugarcane bagasse mixed solution; (2) adding p-toluenesulfonyl chloride and betaine hydrochloride to the mixed solution obtained in step (1) to carry out a cationization reaction, and quenching the reaction with ethanol after the reaction is completed to obtain a cationized sugarcane bagasse mixed solution; (3) separating the mixed solution obtained in step (2) by vacuum filtration, washing the cationized sugarcane bagasse with ethanol until it becomes colorless, collecting the washing liquid, and then washing it with deionized water until it becomes neutral, and mechanically grinding it to obtain cationized lignocellulose nanofibers; (4) adding a large amount of ionized water to the washing liquid collected in step (3), allowing it to settle, and then centrifuging and freeze-drying to obtain lignin; (5) fully mixing the cationized lignocellulose nanofibers obtained in step (3) and the lignin obtained in step (4) with a silane coupling agent KH-560 to react to obtain silanized lignocellulose nanofibers; (6) loading the silanized lignocellulose nanofibers obtained in step (5) on the surface of a polyvinylidene fluoride membrane by a vacuum filtration method to prepare a composite paper-based material; (7) Soaking the composite paper-based material obtained in step (6) in a polyethyleneimine aqueous solution, washing with deionized water, and naturally air-drying to obtain a cationic composite paper-based material.

2. The method for preparing a cationic composite paper-based material according to claim 1, wherein: In step (1), the molar ratio of choline chloride to imidazole is 3:7, the mass ratio of bagasse to DES is 1:25, the pretreatment reaction temperature is 80° C., and the pretreatment time is 19 h.

3. The method for preparing a cationic composite paper-based material according to claim 1, wherein: In step (2), the molar ratio of p-toluenesulfonyl chloride to betaine hydrochloride is 1:1, the mass ratio of bagasse to p-toluenesulfonyl chloride is 7:10, the cationization reaction temperature is 80° C., the cationization reaction time is 5 h, and the amount of ethanol added is 600 mL.

4. The method for preparing a cationic composite paper-based material according to claim 1, wherein: In step (3), the ethanol washing times are 8 to 10 times, and the deionized water washing times are 10 to 12 times.

5. The method for preparing a cationic composite paper-based material according to claim 1, wherein: In step (4), the static sedimentation time is 24 hours, the centrifugal speed is 5000 rpm, and the freeze-drying time is 48 hours.

6. The method for preparing a cationic composite paper-based material according to claim 1, wherein: In step (5), the amount of the cationized lignocellulose nanofibers is 0.006 wt% to 0.014 wt%, the amount of lignin is 0.002 wt% to 0.01 wt%, the amount of the silane coupling agent KH-560 is 0.006 wt%, and the reaction time is 2 h.

7. The method for preparing a cationic composite paper-based material according to claim 1, wherein: In step (6), the loading amount of the silanized lignocellulose nanofibers is 10 mL.

8. The method for preparing a cationic composite paper-based material according to claim 1, wherein: In step (7), the amount of polyethyleneimine in the polyethyleneimine aqueous solution is 1 wt %, the molecular weight of polyethyleneimine is 25000 g / mol, the soaking time is 3 h, and the washing times are 3 times.

9. Use of the cationic composite paper-based material prepared by the method for preparing the cationic composite paper-based material according to any one of claims 1 to 8 as a filter membrane for filtering nanoplastics in water.

10. The use according to claim 9, characterized in that The filtration process is as follows: a cationic composite paper-based material is laid as a filter membrane 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 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; the types of nanoplastics are: carboxylated polystyrene nanoplastics, amino polystyrene nanoplastics, carboxylated polymethyl methacrylate nanoplastics and carboxylated polyvinyl chloride nanoplastics, the size of the nanoplastics is: 50nm~500nm, the nanoplastic filtration concentration is: 10ppm~90ppm, and the nanoplastic filtration volume is: 10mL.

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