Preparation method of a Janus type micro-nano plastic separation membrane based on nanocellulose

Abstract

A method for preparing a Janus-type micro / nanoplastics separation membrane based on nanocellulose is disclosed, belonging to the field of micro / nanoplastics removal. This invention aims to solve the problem that existing electrospun nanofiber membranes for removing micro / nanoplastics struggle to simultaneously achieve high separation flux and long-term stable operation. The method includes: 1. Preparation of casting solution; 2. Electrospinning; 3. Preparation of cellulose solution; 4. Spraying; 5. Crosslinking reaction. This invention is used for the preparation of Janus-type micro / nanoplastics separation membranes based on nanocellulose.

Description

Technical Field

[0001] This invention belongs to the field of micro / nanoplastics removal. Background Technology

[0002] Generally speaking, microplastics (MPs) refer to plastic debris or microparticles with a particle size of less than 5 mm. Any plastic produced or used in human daily life can be a potential source of microplastics. Nanoplastics (NPs, 1 nm to 1 μm) have even smaller sizes and larger surface areas. In recent years, micro- and nanoplastic pollution has become increasingly serious, found in various aquatic and terrestrial environments, and can enter human tissues through the food chain, causing health risks such as inflammatory responses, cell damage, and nervous system disorders. Therefore, micro- and nanoplastics, as a new type of pollutant, have attracted widespread attention from scientific research and society.

[0003] Currently, common methods for removing micro / nanoplastics (such as adsorption, catalysis, and biodegradation) generally suffer from low efficiency, high cost, difficulty in effectively removing small-sized pollutants, and secondary pollution. In contrast, membrane separation technology is widely used due to its advantages such as high efficiency, ease of operation, and adjustable pore structure. Reported membrane technologies for removing micro / nanoplastics (NPs) include ultrafiltration, microfiltration, reverse osmosis, and dynamic membrane technology. However, these traditional pressure-driven membranes are mostly prepared using non-solvent-induced phase inversion (NIPS) methods, resulting in low permeability, easy fouling, high operating pressures, and difficulty in overcoming the "trade-off" effect between permeability and selectivity, thus limiting their practicality. Electrospun membranes, composed of randomly stacked fibers, possess high porosity (over 80%), good mechanical strength, adjustable wettability, high surface area, and low membrane permeation resistance. They can achieve water purification under very low pressure or gravity-driven conditions, reducing energy consumption. However, due to the instability of the rheological properties of the electrospinning solution, it is difficult to obtain stable and continuous nanofibers with an average diameter of less than 100 nm. This results in the pore size of the electrospinned nanofiber membrane being at the micrometer level, limiting its separation applications to microfiltration, air filtration, etc. The removal of NPs smaller than 1 μm remains a challenge. To improve the ability of electrospun nanofiber membranes to remove nanoplastics, researchers have adopted the following strategies: (1) Mechanical pressing: The simple hot pressing process can significantly reduce the membrane porosity from ~86% to ~34%, thereby greatly increasing the removal rate of 0.2μm particles from 0% to about 100%. Nanofiber membranes composed of small-diameter nanofibers can also achieve ~100% retention of 0.1μm particles under relatively high pressure by hot pressing, but it is difficult to obtain high separation flux; (2) Layer-by-layer self-assembly: Since NPs are usually negatively charged in the water environment, the PAN nanofiber membrane is modified by the layer-by-layer self-assembly method of positive and negative polyelectrolytes. The positively charged membrane can provide electrostatic attraction (or additional selectivity) for NPs, thereby giving the electrospun fiber membrane high retention performance. However, this strategy leads to rapid decay of separation flux, and after the charge adsorption is saturated, the retention performance decreases, which is not conducive to long-term stable operation. Summary of the Invention

[0004] This invention aims to address the problem that existing electrospun nanofiber membranes for removing micro- and nano-plastics cannot simultaneously achieve high separation flux and long-term stable operation, and thus provides a method for preparing a Janus-type micro- and nano-plastic separation membrane based on nanocellulose.

[0005] A method for preparing a Janus-type micro / nanoplastics separation membrane based on nanocellulose, comprising the following steps:

[0006] 1. Dissolve polyvinylpyrrolidone, tannic acid and metal inorganic salt in a mixed solvent, then stir and let stand to remove bubbles in sequence to obtain casting solution;

[0007] II. Electrospinning using casting solution to obtain nanofiber membranes;

[0008] 3. Mix the bacterial cellulose solution and the carboxylated cellulose nanofiber solution to obtain a cellulose solution;

[0009] 4. Spray the cellulose solution onto one side of the nanofiber membrane and then dry it to obtain the sprayed fiber membrane;

[0010] 5. The sprayed fiber membrane is immersed in glutaraldehyde solution for cross-linking reaction, then washed and dried to obtain Janus-type micro / nanoplastics separation membrane based on nanocellulose.

[0011] The beneficial effects of this invention are:

[0012] This invention utilizes a supramolecular electrospun membrane as the base membrane, and a selective layer of carboxylated cellulose nanofibers with a fiber diameter of 4nm~10nm combined with bacterial cellulose with a diameter of 50nm~100nm. By spraying cellulose onto the electrospun base membrane, a Janus-type separation membrane based on nanocellulose was successfully constructed. By precisely controlling the pore size gradient and surface chemical properties of the Janus membrane, an asymmetric membrane material with multi-level retention function was constructed, achieving efficient retention of micro- and nano-plastics of various particle sizes, while maintaining a high permeation flux while maintaining an extremely high retention rate.

[0013] The preparation method of this invention is simple, and the prepared cellulose Janus separation membrane can significantly reduce the pore size (98.33%). Furthermore, by adjusting the coating amount of bacterial cellulose and carboxylated cellulose nanocrystals, the membrane pore size can be adjusted to achieve the retention of micro / nanoplastics of different particle sizes, exhibiting continuous and excellent removal capacity (99%). It can operate stably for a long time and has good application prospects in the field of water treatment. Attached Figure Description

[0014] Figure 1 The PVP / TA / Ca prepared in step two of Example 1 2+ Microscopic morphology of nanofiber membrane;

[0015] Figure 2 Microscopic morphology of the composite membrane prepared by spraying bacterial cellulose in step five of experiment one for comparison;

[0016] Figure 3 The image shows the microstructure of the Janus-type micro / nanoplastics separation membrane based on nanocellulose prepared in step five of Example 1.

[0017] Figure 4 The PVP / TA / Ca prepared in step two of Example 1 2+ Infrared spectrum of nanofiber membrane;

[0018] Figure 5 The PVP / TA / Ca prepared in step two of Example 1 2+ Raman spectra of nanofiber membranes and PVP / TA membranes prepared in step two of the comparative experiment;

[0019] Figure 6 The PVP / TA / Ca prepared in step two of Example 1 2+ Air-water contact angle diagram of nanofiber membrane;

[0020] Figure 7 The PVP / TA / Ca prepared in step two of Example 1 2+ Air-water contact angle diagrams of nanofiber membrane (Original), composite membrane (BC) prepared by spraying bacterial cellulose in step five of Comparative Experiment 1, and Janus-type micro / nanoplastics separation membrane (1:6) based on nanofiber cellulose prepared in step five of Example 1.

[0021] Figure 8 The PVP / TA / Ca prepared in step two of Example 1 2+ Average pore size diagrams of nanofiber membrane (Original), composite membrane (BC) prepared by spraying bacterial cellulose in step five of Comparative Experiment 1, and Janus-type micro / nanoplastics separation membrane (1:6) based on nanofiber prepared in step five of Example 1.

[0022] Figure 9 This is a comparison chart showing the flux of the Janus-type micro / nanoplastics separation membrane based on nanocellulose prepared in step five of Example 1, which retains solutions of micro / nanoplastics with different particle sizes.

[0023] Figure 10 This is a comparison chart showing the retention rates of Janus-type micro / nanoplastics solutions with different particle sizes obtained by the nanocellulose-based micro / nanoplastics separation membrane prepared in step five of Example 1.

[0024] Figure 11 The PVP / TA / Ca prepared in step two of Example 1 2+ Comparison of flux of nanofiber membrane (Original), composite membrane (BC) prepared by spraying bacterial cellulose in step five of Comparative Experiment 1, and Janus-type micro / nanoplastics separation membrane (1:6) based on nanocellulose prepared in step five of Example 1 with a nanoplastic solution with a particle size of 150 nm.

[0025] Figure 12 The PVP / TA / Ca prepared in step two of Example 1 2+Comparison of the retention rates of 150nm nanoplastic solution by nanofiber membrane (Original), composite membrane (BC) prepared by spraying bacterial cellulose in step five of Comparative Experiment 1, and Janus-type micro / nanoplastics separation membrane (1:6) based on nanocellulose prepared in step five of Example 1.

[0026] Figure 13 The circulating separation performance of the Janus-type micro / nanoplastics separation membrane based on nanocellulose prepared in step five of Example 1 is shown. The dark blue dots represent the pure water flux, the light blue dots represent the NPs retention flux, and the red squares represent the retention rate.

[0027] Figure 14 The tensile strength diagram shows the Janus-type micro / nanoplastics separation membrane based on nanocellulose prepared in step five of Example 1. Detailed Implementation

[0028] Specific Implementation Method 1: This implementation method describes a method for preparing a Janus-type micro / nanoplastics separation membrane based on nanocellulose, which is carried out according to the following steps:

[0029] 1. Dissolve polyvinylpyrrolidone, tannic acid and metal inorganic salt in a mixed solvent, then stir and let stand to remove bubbles in sequence to obtain casting solution;

[0030] II. Electrospinning using casting solution to obtain nanofiber membranes;

[0031] 3. Mix the bacterial cellulose solution and the carboxylated cellulose nanofiber solution to obtain a cellulose solution;

[0032] 4. Spray the cellulose solution onto one side of the nanofiber membrane and then dry it to obtain the sprayed fiber membrane;

[0033] 5. The sprayed fiber membrane is immersed in glutaraldehyde solution for cross-linking reaction, then washed and dried to obtain Janus-type micro / nanoplastics separation membrane based on nanocellulose.

[0034] This specific embodiment proposes a method for preparing a Janus-type micro / nanoplastics separation membrane based on nanocellulose. A Janus-type nanomembrane with a multi-level interconnected pore structure is constructed by using ultrafine natural nanocellulose as a microporous selective layer and a highly permeable electrospun membrane as a macroporous support layer. The selective layer traps micro / nanoplastics based on size sieving effect, while the macropores of the support layer reduce water transport resistance. High permeability and high selectivity are simultaneously achieved under low pressure, enabling the economical, continuous, and efficient removal of plastic contaminants with a particle size of at least 150 nm from water.

[0035] The beneficial effects of this embodiment are:

[0036] This specific embodiment utilizes a supramolecular electrospun membrane as the base membrane, and a selective layer of carboxylated cellulose nanofibers with a fiber diameter of 4nm~10nm combined with bacterial cellulose with a diameter of 50nm~100nm. By spraying cellulose onto the electrospun base membrane, a Janus-type separation membrane based on nanocellulose was successfully constructed. By precisely controlling the pore size gradient and surface chemical properties of the Janus membrane, an asymmetric membrane material with multi-level retention function was constructed, achieving efficient retention of various particle size micro-nanoplastics, while maintaining a high retention rate and a high permeation flux.

[0037] The preparation method described in this specific embodiment is simple, and the prepared cellulose Janus separation membrane can significantly reduce the pore size (98.33%). Furthermore, by adjusting the amount of bacterial cellulose and carboxylated cellulose nanocrystals sprayed, the membrane pore size can be adjusted, enabling the retention of micro / nanoplastics of different particle sizes. It exhibits continuous and excellent removal capacity (99%), can operate stably for a long period, and shows promising application prospects in the field of water treatment.

[0038] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that: the inorganic metal salt mentioned in step one is one or a combination of several of calcium chloride, ferric chloride, copper nitrate, and zinc nitrate; the mixed solvent mentioned in step one is a mixture of DMF and DMSO, and the volume ratio of DMF to DMSO is (2~4):1. Everything else is the same as in Specific Implementation Method One.

[0039] Specific Implementation Method Three: This implementation method differs from Specific Implementation Method One or Two in that: in step one, the temperature is 20℃~60℃ and the stirring speed is 200rpm~400rpm, and the mixture is stirred for 12h~24h, followed by standing to degas for 5min~10min. Everything else is the same as in Specific Implementation Method One or Two.

[0040] Specific Implementation Method Four: This implementation method differs from Specific Implementation Methods One to Three in that the mass percentage of polyvinylpyrrolidone, tannic acid, and inorganic metal salt in the casting solution described in step one is 10% to 12%. Everything else is the same as in Specific Implementation Methods One to Three.

[0041] Specific Implementation Method Five: This implementation method differs from Specific Implementation Methods One to Four in that the electrospinning described in step two is specifically carried out according to the following steps: electrospinning is performed under the conditions of a spinning voltage of 8kV~15kV, a feed speed of 0.6mL / h~1.0mL / h, and a receiving distance of 20cm~25cm. Everything else is the same as in Specific Implementation Methods One to Four.

[0042] Specific Implementation Method Six: This implementation method differs from Specific Implementation Methods One to Five in that: the diameter of the bacterial cellulose described in step three is 50nm~100nm; the diameter of the carboxylated cellulose nanocrystals described in step three is 4nm~10nm. Everything else is the same as Specific Implementation Methods One to Five.

[0043] Specific Implementation Method Seven: This implementation method differs from Specific Implementation Methods One to Six in that: the mass percentage of bacterial cellulose in the cellulose solution described in step three is 0.01% to 0.1%; the mass ratio of bacterial cellulose to carboxylated cellulose nanocrystals in the cellulose solution described in step three is 1:(4~8). Everything else is the same as in Specific Implementation Methods One to Six.

[0044] Specific Implementation Method Eight: This implementation method differs from Specific Implementation Methods One to Seven in that: in step four, under the conditions that the distance between the spray gun head and the film is 10cm~15cm and the spray gun pressure is 0.1MPa~0.2MPa, the spraying amount is (0.56~0.72)g:1cm 2 A cellulose solution is sprayed onto one side of the nanofiber membrane and then dried at a temperature of 30°C to 50°C. Other procedures are the same as in embodiments one through seven.

[0045] Specific Implementation Method Nine: This implementation method differs from Specific Implementation Methods One to Eight in that the mass percentage of the glutaraldehyde solution mentioned in step five is 1% to 3%. Everything else is the same as in Specific Implementation Methods One to Eight.

[0046] Specific Implementation Method Ten: This implementation method differs from Specific Implementation Methods One to Nine in that: in step five, the crosslinking reaction is carried out for 2 to 4 hours at a temperature of 20°C to 40°C. Everything else is the same as in Specific Implementation Methods One to Nine.

[0047] The beneficial effects of the present invention are verified using the following embodiments:

[0048] Example 1:

[0049] A method for preparing a Janus-type micro / nanoplastics separation membrane based on nanocellulose, comprising the following steps:

[0050] 1. Dissolve polyvinylpyrrolidone (PVP), tannic acid (TA) and calcium chloride in a mixed solvent, then stir for 12 hours at room temperature and a stirring speed of 300 rpm, and finally let stand for 10 minutes to remove bubbles to obtain the casting solution.

[0051] The mixed solvent is a mixture of DMF and DMSO, and the volume ratio of DMF to DMSO is 3:1.

[0052] The casting solution contains 10% polyvinylpyrrolidone by mass, 10% tannic acid by mass, and 1% calcium chloride by mass.

[0053] 2. The casting solution was drawn into a syringe, and electrospinning was performed under the conditions of a spinning voltage of 15kV, a feed speed of 0.96mL / h, and a receiving distance of 20cm to obtain PVP / TA / Ca. 2+ Nanofiber membrane;

[0054] 3. Mix a bacterial cellulose (BC) solution with a mass percentage of 0.01% and a carboxylated cellulose nanofiber (C-CNC) solution to obtain a cellulose solution;

[0055] The bacterial cellulose is an ultra-high aspect ratio fibrous nanomaterial obtained by bio-fermentation of Bacillus acetic acid, purchased from Guilin Qihong Technology Co., Ltd., model number Bacterial Cellulose BC, with a length >20μm and a diameter of 50nm~100nm; the carboxylated cellulose nanofibers are purchased from Guilin Qihong Technology Co., Ltd., model number C-CNC99F, with a length of 100nm~500nm and a diameter of 4nm~10nm;

[0056] The cellulose solution contains 0.01% bacterial cellulose by mass; the mass ratio of bacterial cellulose to carboxylated cellulose nanocrystals in the cellulose solution is 1:6.

[0057] IV. Under the conditions of a spray gun nozzle distance of 10cm and a spray gun pressure of 0.15MPa, the spraying amount is 0.64 g: 1cm. 2 A cellulose solution was sprayed onto one side of the nanofiber membrane and then dried at 45°C to obtain the sprayed fiber membrane.

[0058] 5. At room temperature, the sprayed fiber membrane was immersed in glutaraldehyde solution for cross-linking reaction for 4 hours, then washed and dried to obtain Janus-type micro-nanoplastics separation membrane based on nanocellulose.

[0059] The glutaraldehyde solution has a mass percentage of 1%.

[0060] The total thickness of the Janus-type micro / nanoplastics separation membrane based on nanocellulose is 0.3 mm.

[0061] Example 2: This example differs from Example 1 in that: the mass percentage of polyvinylpyrrolidone and tannic acid in the casting solution in step 1 is 12%; and the mass ratio of bacterial cellulose to carboxylated cellulose nanocrystals in the cellulose solution in step 3 is 1:4. Everything else is the same as in Example 1.

[0062] Example 3: This example differs from Example 1 in that the mass ratio of bacterial cellulose to carboxylated cellulose nanocrystals in the cellulose solution described in step 3 is 1:8. Everything else is the same as in Example 1.

[0063] Comparative Experiment 1: This embodiment differs from Embodiment 1 in that: in step 3, a bacterial cellulose solution with a mass percentage of 0.01% is directly sprayed in step 4; step 5 yields the composite membrane prepared by spraying bacterial cellulose. Everything else is the same as in Embodiment 1.

[0064] Comparative Experiment 2: This example differs from Example 1 in that calcium chloride in step 1 is omitted, and the PVP / TA membrane is obtained in step 2. Everything else is the same as in Example 1.

[0065] Figure 1 The PVP / TA / Ca prepared in step two of Example 1 2+ Microscopic morphology of nanofiber membrane; as shown in the figure, the nanofiber membrane fibers are randomly stacked to form macroscopic macropores.

[0066] Figure 2 The image shows the microstructure of the composite membrane prepared by spraying bacterial cellulose in step five of the first experiment. As can be seen from the image, after spraying bacterial cellulose, the bacterial cellulose adheres to the surface of the base membrane and forms micron-sized pores.

[0067] Figure 3 The image shows the microstructure of the Janus-type micro / nanoplastics separation membrane based on nanocellulose prepared in step five of Example 1. As can be seen from the image, the gaps between bacterial cellulose fibers are filled with randomly oriented carboxylated cellulose nanocrystals with a diameter of approximately 4 nm to 10 nm, forming nanoscale pores.

[0068] Figure 4 The PVP / TA / Ca prepared in step two of Example 1 2+ Infrared spectrum of nanofiber membrane; as shown in the figure, the stretching vibration peak of C=O changes from 1688 cm⁻¹ in the literature. -1 Shift to a lower wavenumber of 1657cm -1 This is due to the formation of hydrogen bonds between TA and PVP molecules, which averages out the electron cloud density and leads to a decrease in the stretching vibration frequency.

[0069] Figure 5 The PVP / TA / Ca prepared in step two of Example 1 2+ Raman spectra of nanofiber membranes and PVP / TA membranes prepared in step two of Example 1; as shown in the figure, compared with the PVP / TA membrane, the PVP / TA / Ca membrane prepared in step two of Example 1... 2+ Nanofiber membrane 1348cm -1 A new absorption peak appears at this point, which is due to the interaction between the phenolic hydroxyl group on TA and Ca.2+ Direct evidence of coordination reactions.

[0070] Figure 6 The PVP / TA / Ca prepared in step two of Example 1 2+ Air-water contact angle diagram of nanofiber membrane; as shown in the figure, PVP / TA / Ca 2+ The nanofiber membrane has a contact angle of 0°, making it a superhydrophilic membrane with supramolecular wettability.

[0071] Figure 7 The PVP / TA / Ca prepared in step two of Example 1 2+ Air-water contact angle diagrams of the nanofiber membrane (Original), the composite membrane (BC) prepared by spraying bacterial cellulose in step five of Comparative Experiment 1, and the Janus-type micro / nanoplastics separation membrane (1:6) based on nanofiber cellulose prepared in step five of Example 1; as shown in the figure, PVP / TA / Ca 2+ The membrane contact angle was 0°, while the contact angle of the BC-coated membrane was 21.326°. The contact angle of the Janus-type micro / nanoplastics separation membrane based on nanocellulose prepared in step five of Example 1 was 32.512°, indicating that the contact angle gradually increased after coating with BC and C-CNC. This may be because the cellulose layer covering the membrane surface shields the polar groups, while the hydrophobic cellulose skeleton is more easily exposed on the surface, reducing hydrophilicity.

[0072] Figure 8 The PVP / TA / Ca prepared in step two of Example 1 2+ Average pore size diagrams of the nanofiber membrane (Original), the composite membrane (BC) prepared by spraying bacterial cellulose in step five of the comparative experiment, and the Janus-type micro / nanoplastics separation membrane (1:6) based on nanofiber cellulose prepared in step five of Example 1; As shown in the figure, the average pore size of the base membrane is 8.2292 μm. Since the diameters of BC and C-CNC fibers are relatively small, the average pore size of the Janus-type micro / nanoplastics separation membrane based on nanofiber cellulose prepared in step five of Example 1 is only 137 nm (pore size reduction of 98.33%), which is expected to effectively retain micro / nanoplastics with particle sizes of 150 nm and above.

[0073] Microplastic retention performance test:

[0074] (1) Test of microplastic permeation flux: Nanoplastics with particle sizes of 50, 100, 150, 300, 500, and 1000 nm were added to deionized water to form a 20 ppm solution. The permeation flux of the nanoplastic solution was determined using a cross-flow separation device. The micro / nanoplastic solution was pumped onto a membrane fixed in a membrane tank by a peristaltic pump and rapidly permeated under pressure of 0.01 bar. The solution permeability was calculated using the following formula:

[0075] P = V / (A × t × ΔP);

[0076] In the formula, P is the permeability of the liquid (L m). -2 h -1 bar -1 );

[0077] V is the volume (L) of the filtered liquid passing through the membrane.

[0078] A is the effective membrane area (m²) 2 );

[0079] t is the filtering time (h);

[0080] ΔP is the pressure (bar) exerted on the membrane under cross-flow filtration.

[0081] (2) Microplastic Retention Rate Test: The total organic carbon (TOC) content in the microplastic solution before and after retention was measured using a total organic carbon analyzer. The membrane retention efficiency for the microplastic solution was calculated using the following formula:

[0082] R (%) = (1 - C P / C f )×100%;

[0083] In the formula C p and C f The concentrations of nanoplastics in the permeate and feed solutions are respectively.

[0084] Figure 9 This is a comparison of the flux of the Janus-type micro / nanoplastics separation membrane based on nanocellulose prepared in step five of Example 1, which retains solutions of micro / nanoplastics with different particle sizes. The graph shows that the flux for retaining 50nm NPs is approximately 9000 L / m². -2 h -1 bar -1 Approximately; when the microplastic particle size increases to 150 nm, the permeation flux decreases to 5700 L / m. -2 h -1 bar -1 Approximately; as the microplastic particle size continues to increase, the retention permeation flux gradually decreases, with 1μm microplastics retained at 3000 L / m². -2 h -1 bar -1 about.

[0085] Figure 10This is a comparison of the retention rates of the Janus-type micro / nanoplastics separation membrane based on nanocellulose prepared in step five of Example 1 for solutions of micro / nanoplastics with different particle sizes. As shown in the figure, the Janus-type micro / nanoplastics separation membrane based on nanocellulose exhibits a retention rate of over 99% for nanoparticles with a particle size of 150 nm and above. The size of the nanoparticles is significantly larger than the membrane pore size; therefore, pore size sieving is the dominant retention mechanism. Furthermore, both the membrane surface and the polystyrene nanoplastics are negatively charged, so electrostatic repulsion also contributes to the retention.

[0086] Figure 11 The PVP / TA / Ca prepared in step two of Example 1 2+ A comparison of the flux of nanofiber membranes (Original), composite membranes (BC) prepared by spraying bacterial cellulose in step five of Comparative Experiment 1, and Janus-type micro / nanoplastics separation membranes (1:6) based on nanocellulose prepared in step five of Example 1, with a nanoplastic solution retaining a particle size of 150 nm, is shown in the figure. As can be seen from the figure, the first two membranes have higher flux retention due to their pore size being much larger than 150 nm, with the base membrane flux being 4.5 × 10⁻⁶. 5 L m -2 h -1 bar -1 The membrane flux of BC-coated membrane alone is 2.7 × 10⁻⁶. 5 L m -2 h -1 bar -1 However, the flux of Janus-type micro / nanoplastics separation membranes based on nanocellulose is reduced to 5700 L / m² due to the pore size being drastically reduced to the nanoscale. -2 h -1 bar -1 While the throughput is around 100%, compared with existing technologies, it still has a higher throughput while retaining micro- and nano-plastics of the same particle size.

[0087] Figure 12 The PVP / TA / Ca prepared in step two of Example 1 2+ A comparison of the retention rates of nanofiber membranes (Original), composite membranes (BC) prepared by spraying bacterial cellulose in step five of Comparative Experiment 1, and Janus-type micro / nanoplastics separation membranes (1:6) based on nanofibers prepared in step five of Example 1 for 150 nm nanoplastic solutions. As shown in the figure, the Janus-type micro / nanoplastics separation membrane based on nanofibers has a retention rate of 99.2% due to pore size sieving and electrostatic repulsion effects.

[0088] A cycle consists of 10 minutes of pure water flux plus 30 minutes of 150 nm polystyrene nanoplastic permeation flux retention. After one cycle of the test, the device is backwashed with pure water for 1 minute before the next cycle is performed. A total of three cycles are tested. Figure 13 The figure shows the cyclic separation performance of the Janus-type micro / nanoplastics separation membrane based on nanocellulose prepared in step five of Example 1. Dark blue dots represent pure water flux, light blue dots represent NPs retention flux, and red squares represent the rejection rate. As shown in the figure, the initial water flux of the BC-CNC membrane is 7165.6 L / m³. -2 h -1 bar -1 The initial microplastic retention flux was 5732.48 L m. -2 h -1 bar -1 The permeation flux of PS NPs stabilized at 5000 L / m² after 20 minutes. -2 h -1 bar -1 The flux decay is relatively small; the rejection rate of PS NPs is stable at over 99%, the flux recovery rate (FRR) is around 92%, and the anti-fouling performance is good.

[0089] The tensile strength of the membrane samples was tested using an electronic universal testing machine. First, a 10mm × 20mm sample strip was prepared, and the tensile speed was set to 5mm / min. The sample strip was then vertically fixed to the test clamp for testing. Figure 14 The figure shows the tensile strength of the Janus-type micro / nanoplastics separation membrane based on nanocellulose prepared in step five of Example 1. As can be seen from the figure, the tensile strength of the Janus-type micro / nanoplastics separation membrane based on nanocellulose is about 1.1 MPa.

Claims

1. A method for preparing a Janus-type micro / nanoplastics separation membrane based on nanocellulose, characterized in that... It is done in the following steps:

1. Dissolve polyvinylpyrrolidone, tannic acid and metal inorganic salt in a mixed solvent, then stir and let stand to remove bubbles in sequence to obtain casting solution; II. Electrospinning using casting solution to obtain nanofiber membranes; 3. Mix the bacterial cellulose solution and the carboxylated cellulose nanofiber solution to obtain a cellulose solution; 4. Spray the cellulose solution onto one side of the nanofiber membrane and then dry it to obtain the sprayed fiber membrane; 5. The sprayed fiber membrane is immersed in glutaraldehyde solution for cross-linking reaction, then washed and dried to obtain Janus-type micro / nanoplastics separation membrane based on nanocellulose.

2. The method for preparing a Janus-type micro / nanoplastics separation membrane based on nanocellulose according to claim 1, characterized in that... The inorganic metal salt mentioned in step one is one or a combination of several of calcium chloride, ferric chloride, copper nitrate and zinc nitrate; the mixed solvent mentioned in step one is a mixed solvent of DMF and DMSO, and the volume ratio of DMF to DMSO is (2~4):

1.

3. The method for preparing a Janus-type micro / nanoplastics separation membrane based on nanocellulose according to claim 1, characterized in that... In step one, stir for 12 to 24 hours at a temperature of 20℃ to 60℃ and a stirring speed of 200 rpm to 400 rpm, and then let it stand to degas for 5 to 10 minutes.

4. The method for preparing a Janus-type micro / nanoplastics separation membrane based on nanocellulose according to claim 1, characterized in that... The casting solution described in step one contains 10% to 12% polyvinylpyrrolidone by mass, 10% to 12% tannic acid by mass, and 1% to 2% metal inorganic salt by mass.

5. The method for preparing a Janus-type micro / nanoplastics separation membrane based on nanocellulose according to claim 1, characterized in that... The electrospinning described in step two is carried out in the following steps: electrospinning is performed under the conditions of a spinning voltage of 8kV~15kV, a feed speed of 0.6mL / h~1.0mL / h, and a receiving distance of 20cm~25cm.

6. The method for preparing a Janus-type micro / nanoplastics separation membrane based on nanocellulose according to claim 1, characterized in that... The bacterial cellulose in step three has a diameter of 50 nm to 100 nm; the carboxylated cellulose nanocrystals in step three have a diameter of 4 nm to 10 nm.

7. The method for preparing a Janus-type micro / nanoplastics separation membrane based on nanocellulose according to claim 1, characterized in that... The mass percentage of bacterial cellulose in the cellulose solution described in step three is 0.01% to 0.1%; the mass ratio of bacterial cellulose to carboxylated cellulose nanocrystals in the cellulose solution described in step three is 1:(4~8).

8. The method for preparing a Janus-type micro / nanoplastics separation membrane based on nanocellulose according to claim 1, characterized in that... In step four, under the conditions of a spray gun nozzle distance of 10cm~15cm and a spray gun pressure of 0.1MPa~0.2MPa, the spraying amount is (0.56~0.72)g:1cm 2 A cellulose solution is sprayed onto one side of the nanofiber membrane and then dried at a temperature of 30℃~50℃.

9. The method for preparing a Janus-type micro / nanoplastics separation membrane based on nanocellulose according to claim 1, characterized in that... The glutaraldehyde solution mentioned in step five has a mass percentage of 1% to 3%.

10. The method for preparing a Janus-type micro / nanoplastics separation membrane based on nanocellulose according to claim 1, characterized in that... In step five, the cross-linking reaction is carried out at a temperature of 20℃~40℃ for 2h~4h.

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