Organic vermiculite filler for micro-nano plastic filtration and filtration system thereof

Abstract

The invention relates to an organic vermiculite filler for micro-nano plastic filtration and a filtration system thereof. The filler is prepared from natural vermiculite and a modifier of which the addition amount is 2-8 times of the cation exchange capacity of the natural vermiculite; wherein the modifying agent is hexadecyl trimethyl ammonium bromide or polyquaternium-28 or benzyl triethyl ammonium bromide; the filtering system comprises a hollow column type filtering main body; an inner cavity of the hollow column type filtering main body is sequentially provided with a supporting layer, an organic vermiculite functional layer, a protective layer and an air-water buffer layer from bottom to top; the upper end of the hollow column type filtering main body is communicated with the water outlet assembly; according to the invention, natural vermiculite is organically modified by adopting a cationic surfactant, so that the fixing capacity of hydrophobic micro-nano plastic particles is enhanced, micron-scale and nano-scale plastic particles in a water body are efficiently captured and adsorbed, and the removal rate of micro-nano plastic is remarkably improved.

Description

Technical Field

[0001] This invention relates to the field of water treatment technology, specifically to an organic vermiculite filler and its filtration system for micro-nano plastic filtration. Background Technology

[0002] Micro- and nano-plastics, due to their tiny size, large specific surface area, and strong hydrophobicity, are widely distributed in aquatic, atmospheric, and soil environments. Currently, micro- and nano-plastics have been detected in rivers, lakes, oceans, and even drinking water. These particles can accumulate through the food chain and eventually enter the human body, posing a potential threat to ecosystems and human health. Specifically, their harm manifests in two main ways: First, chemical additives such as colorants, plasticizers, and stabilizers are often added during the plastics production process. These substances may be gradually released into the aquatic environment, causing health problems such as intestinal inflammation, chronic toxicity, and endocrine disorders. Second, the surface of micro- and nano-plastics easily adsorbs pollutants such as heavy metals, pesticides, antibiotics, and pathogens, forming a complex pollution system, thereby exacerbating their ecological risks. Wastewater treatment plants are important collection and discharge points for micro- and nano-plastics. Micro- and nano-plastics enter treatment systems through domestic sewage, industrial wastewater, and urban runoff. Although existing processes (such as primary sedimentation, aeration, biological reaction, and filtration) can remove some particles, a large number of microplastics still penetrate the treatment process due to their extremely small size and stable chemical properties. These particles enter the natural environment with the effluent or sludge, becoming a significant source of secondary microplastic pollution. Studies have shown that even after traditional secondary or tertiary treatment, the amount of microplastics in downstream water bodies can still be significantly higher than in upstream river sections, indicating that the overall removal capacity of existing processes remains limited.

[0003] Currently, commonly used technologies for removing micro- and nano-plastics mainly include physical, chemical, and biological methods. Physical methods, such as adsorption, filtration, and sedimentation, have advantages such as simple operation, low cost, and environmental friendliness. Chemical methods, such as ozone oxidation, electrocoagulation, and photocatalytic degradation, can achieve a certain degree of degradation, but have limitations such as high energy consumption and high operating costs. Biological methods, such as biofilm reactors and microbial degradation, are limited by the high stability and low bioavailability of plastics, resulting in generally low removal efficiency. Overall, filtration and adsorption remain the most promising and economically feasible approaches in wastewater treatment plants. However, traditional rapid sand filtration systems are mainly designed for larger particulate pollutants and have limited capacity to retain micro- and nano-plastics with a particle size of less than 1 μm, resulting in a large amount of micro- and nano-plastics remaining in the effluent. Therefore, it is necessary to functionalize the filter media to enhance its adsorption and retention performance for micro- and nano-plastics, thereby improving the overall removal efficiency. Summary of the Invention

[0004] To address the aforementioned problems, this invention provides an organic vermiculite filler and its filtration system for micro / nano plastic filtration.

[0005] The technical solution of the present invention is: an organic vermiculite filler for micro-nano plastic filtration, comprising natural vermiculite and a modifier added at an amount 2 to 8 times the cation exchange capacity of the natural vermiculite; wherein the modifier is any one of hexadecyltrimethylammonium bromide, polyquaternium-28, and benzyltriethylammonium bromide; Note: The organic vermiculite filler prepared in this application retains the advantages of high specific surface area and layered structure of inorganic clay, and also has the tunable surface properties brought about by organic modification. Intercalation modification can not only significantly enhance the hydrophobicity and surface activity of the material, but also expand its interlayer spacing and form a multi-level pore structure, thereby improving the adsorption and fixation capacity of micron- and nano-sized plastic particles.

[0006] Furthermore, the method for preparing the filler is as follows: S1. Weigh natural vermiculite, grind it through a 40-60 mesh sieve, then take 10-30 g and disperse it in 0.8-1.2 L of deionized water, stir and mix well to obtain a vermiculite suspension; S2. Weigh the modifier and dissolve it in 0.1~0.3 L of deionized water to obtain a modified solution; S3. The modified solution obtained in S2 is poured into the vermiculite suspension at a rate of 1-2 mL / min, stirred at a constant temperature of 70-100 °C for 2-4 h, then kept at a water bath temperature of 70-100 °C for 10-16 h, and then allowed to stand at 22-30 °C for 12-20 h to obtain the modified slurry. Finally, after centrifugation / filtration, it is washed with deionized water 3-5 times and dried at 50-80 °C to constant weight to obtain the organic vermiculite packing material for micro-nano plastic filtration. Explanation: After modification, the surface of vermiculite changes from hydrophilic to hydrophobic, the interlayer spacing increases, and a multi-level porous structure is formed. This allows for efficient retention of micro / nanoplastics through the synergistic effect of electrostatic adsorption, hydrophobic interactions, and van der Waals forces. The organic modification of vermiculite is essentially an ion exchange process, where organic cations (such as hexadecyltrimethylammonium bromide, CTAB) replace inorganic cations (such as Na+) between the vermiculite layers. + Ca 2+ Slow dropwise addition provides sufficient time for the reaction, allowing the modifier molecules to diffuse more effectively and insert into the layered structure of vermiculite, thereby increasing its interlayer spacing and improving compatibility with organic polymers. Moderate heating provides the necessary energy for the ion exchange process, while sufficient stirring time ensures the thoroughness of the reaction and the uniformity of the modification effect. Washing is crucial for removing residual modifiers and impurities. Washing continues until no white precipitate (AgBr) is formed in the filtrate when tested with AgNO3 solution, indicating that bromide ions (Br₂) introduced by quaternary ammonium salt modifiers (such as CTAB) have been formed. - The residue has been completely removed, and usually requires 3 to 5 washes. This invention uses natural vermiculite as a base and introduces cationic surfactants to achieve intercalation modification under high temperature conditions. This significantly expands the interlayer spacing of the vermiculite, forming a multi-level pore-multi-active-site synergistic adsorption structure. After treatment with heat preservation, washing, and drying, the resulting organic vermiculite material transforms from a hydrophilic surface to a stable hydrophobic interface, while simultaneously possessing enhanced electrostatic adsorption capacity, hydrophobic adsorption selectivity, and van der Waals forces, thereby achieving a multi-mechanism, highly efficient capture capability for micro / nano plastic particles.

[0007] Further, in S3, the parameters for centrifugal separation / filtration are as follows: the centrifugal speed for centrifugal separation is 3000~5000 rpm, and the centrifugation time is 5~10 min; the vacuum degree for filtration is -0.06 ~ -0.09 MPa, the filter membrane pore size is 0.45 μm, and the filtration time is 20~30 min. Note: The above-mentioned rotation speed range allows vermiculite particles to settle, achieving effective solid-liquid separation. Too low a speed will result in incomplete separation, while too high a speed may cause the particles to become too dense. A suitable vacuum level during filtration ensures filtration efficiency while preventing filter cake cracking or filtration through the filter. The filter membrane pore size ensures that fine vermiculite particles are retained, yielding high-purity solids. A polytetrafluoroethylene (PTFE) filter membrane can be selected.

[0008] The present invention also provides a filtration system for micro-nano plastic filtration. Based on the above-mentioned organic vermiculite packing, the filtration system includes a hollow column filter body and a multi-stage filter bed with gradient structure and flow regulation function constructed in the hollow column filter body. The multi-stage filter bed includes, from bottom to top, a support layer for supporting the packing and realizing primary uniform water flow, an organic vermiculite functional layer with size sieving effect and multi-mechanism synergistic adsorption capacity, a protective layer for suppressing upper disturbance, uniform rectification and preventing interface scaling, and an air-water buffer layer for stabilizing the upper flow state and also having an exhaust function. The lower end of the hollow column filter body is connected to the water inlet component, and the upper end is connected to the water outlet component. Description: This invention features an optimized design of the filtration device structure. By adjusting the height and particle size distribution of the organic vermiculite packing layer, the water flow within the filter column becomes more uniform, and the contact time is longer, thereby improving adsorption efficiency and bed utilization. The optimized device achieves higher filtration throughput and lower operating resistance without increasing energy consumption, effectively solving the problem of low removal rates of small-sized micro- and nano-plastics in traditional sand filtration systems. This invention further constructs a column-type gradient filtration system matched with this functional filler. The system's internal structure, from bottom to top, consists of a support layer, an organic vermiculite functional layer, a protective layer, and an air-water buffer chamber. Through a synergistic design of thickness, particle size, and structural ratio, it achieves stable water flow distribution, inhibits particle migration, and effectively extends the adsorption path. This structure significantly improves the retention efficiency of micro- and nano-plastics (especially nano-plastics with a size <1 μm), solving the industry problem of traditional filter media's inability to stably remove nano-plastics. The gradient structure design of the support layer-organic vermiculite functional layer-protective layer, combined with cationically intercalated multi-level porous organic vermiculite material, achieves size-selective channels, surface charge regulation, and multi-mechanism synergistic adsorption. Under the combined effects of the filter column's height-to-diameter ratio, layer thickness-particle size coupling matching, and the stable flow configuration of the top buffer chamber, a multi-level capture path for efficient retention of nano-scale microplastics is formed, thereby significantly improving filtration efficiency, stability, and applicability.

[0009] Furthermore, the support layer includes a porous support plate and a PP filter screen and a quartz sand layer covering the porous support plate from bottom to top; wherein, the quartz sand layer is laid with quartz sand particles of 20~30 mesh and a filling thickness of 20~45 mm. Explanation: The support layer is located at the bottom and provides basic support for the entire filtration system, ensuring the stability of the filtration system and preventing particulate matter from clogging the system; the support layer is used to achieve uniform diffusion of water flow at the bottom, stable support, and interface control of the functional layers.

[0010] Furthermore, the thickness of the organic vermiculite functional layer is 30~80 mm; Note: The thickness of the organic vermiculite functional layer ensures good adsorption capacity, suitable pressure drop characteristics and stable flow control, so as to establish sufficient adsorption pathways and residence time.

[0011] Furthermore, the height of the air-water buffer layer is 10~20 mm; Note: The above height can achieve a buffering effect at the outlet while ensuring volume utilization, so as to stabilize the flow at the outlet and reduce local disturbances.

[0012] Furthermore, the ratio of the height to the inner diameter of the hollow column filter body is 13:3; Note: The above ratio can maintain a suitable flow rate and residence time, ensuring filtration efficiency.

[0013] Furthermore, the protective layer includes a quartz sand transition layer and a PP filter screen disposed above the quartz sand transition layer. The quartz sand particle size of the quartz sand transition layer is 20-30 mesh, and the filling thickness is 10-35 mm. Note: The protective layer is used to construct a secondary uniform distribution structure above the functional layer, inhibiting particle migration and maintaining the stability of the outlet interface.

[0014] Furthermore, it can be applied to the filtration and purification of domestic sewage, industrial wastewater, municipal reclaimed water, and other water bodies containing micro-nano plastic pollutants. Compared with the prior art, the beneficial effects of the present invention are: (1) This invention uses cationic surfactants to organically modify natural vermiculite, which changes the surface of vermiculite from hydrophilic to hydrophobic, significantly increasing the interlayer spacing and enhancing the ability to fix hydrophobic micro and nano plastic particles. After modification with cationic surfactants, the specific surface area and surface activity of vermiculite are improved. Through the synergistic effect of multiple mechanisms such as electrostatic adsorption, hydrophobic interaction and van der Waals forces, it can achieve efficient capture and adsorption of micron- and nano-sized plastic particles in water, and significantly improve the removal rate of micro and nano plastics.

[0015] (2) The present invention has optimized the structure of the filter device. By adjusting the height and particle size distribution of the organic vermiculite packing layer, the water flow in the filter column is more uniform and the contact time is more sufficient, thereby improving the adsorption efficiency and bed utilization. The optimized device can achieve higher filtration flux and lower operating resistance without increasing energy consumption. It can effectively solve the problem of low removal rate of small-sized micro-nano plastics (<1μm) and nano-plastics in traditional sand filtration systems. It is suitable for the removal of micro-nano plastics in different types of water bodies (tap water, domestic sewage and industrial wastewater). Compared with traditional single-layer sand filtration devices, this system can significantly improve the removal rate of micro-nano plastics and reduce the plastic residue concentration in the effluent under the same operating conditions, and has significant economic and environmental benefits.

[0016] (3) The organic vermiculite filler provided by the present invention has the advantages of wide availability of raw materials, simple preparation process, low cost and recyclability. The modified vermiculite has a stable structure after multiple washing and drying, and can be reused multiple times without affecting its adsorption performance. It is suitable for long-term application under continuous operation conditions such as sewage treatment plants. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the device structure of the filtration system described in Embodiment 2 of the present invention; Figure 2 These are SEM images of the organic vermiculite before filtration in Embodiment 1 / 2 of the present invention; Figure 3 This is a SEM image of the filtered organic vermiculite from Embodiment 1 / 2 of the present invention, magnified 30,000 times. Figure 4 This is a SEM image of the filtered organic vermiculite from Embodiment 1 / 2 of the present invention, magnified 60,000 times. Detailed Implementation

[0018] To further illustrate the methods and effects of this invention, the technical solution of this invention will be clearly and completely described below in conjunction with experiments.

[0019] Example 1: An organic vermiculite filler for micro / nano plastic filtration, which is made from natural vermiculite modified with hexadecyltrimethylammonium bromide; The method for preparing the organic vermiculite filler in this embodiment includes the following steps: (1) Natural vermiculite should be rinsed with clean water first, dried and then ground in a mortar and sieved. Select the sieved vermiculite particles of 40-60 mesh and determine their cation exchange capacity (CEC). Weigh 20 g of washed natural vermiculite and add it to a beaker containing 1 L of deionized water. Stir to form a uniform suspension solution. (2) Select hexadecyltrimethylammonium bromide (CTAB) as a cationic surfactant. Weigh out CTAB at twice the cation exchange capacity of vermiculite and dissolve it in 200 mL of deionized water to prepare a modified solution. (3) Slowly pour the modified solution described in step (2) into the vermiculite suspension and stir at 80°C for 2 h to allow it to fully react with the exchangeable cations between the vermiculite layers; then keep it in a water bath at 80°C for 10 h and let it stand at room temperature for 12 h. (4) After centrifuging the modified slurry obtained in step (3) at a speed of 4000 rpm for 8 min, wash it with deionized water until the supernatant is free of bromide ions to remove unreacted surfactants and impurities; dry the washed sample at 60 ℃ to constant weight. Example 2: This example describes a filtration system for micro / nano plastic filtration, based on an organic vermiculite packing material for micro / nano plastic filtration from Example 1, such as... Figure 1 As shown, the filtration system includes a hollow column filter body 5, which is constructed from bottom to top with a multi-stage filter bed having a gradient structure and flow regulation function. The multi-stage filter bed includes, in sequence, a support layer 1 for supporting the packing material and realizing primary uniform water flow, an organic vermiculite functional layer 2 with size sieving effect and multi-mechanism synergistic adsorption capacity, a protective layer 3 for suppressing upper disturbance, uniform rectification and preventing interface scaling, and an air-water buffer layer 4 for stabilizing the upper flow state and having an exhaust function. The lower end of the hollow column filter body 5 is connected to the water inlet component 6, and the upper end is connected to the water outlet component 7. The support layer 1 includes a porous support plate and a PP filter screen and a quartz sand layer covering the porous support plate from bottom to top; wherein, the quartz sand layer is laid with quartz sand with a particle size of 24~26 mesh and a filling thickness of 45mm; The thickness of the organic vermiculite functional layer 2 is 30 mm; The height of the air-water buffer layer 4 is 10 mm; wherein, the air-water buffer layer 4 is a cavity structure; The ratio of the height to the inner diameter of the hollow column filter body 5 is 13:3; The protective layer 3 includes a quartz sand transition layer and a PP filter screen disposed above the quartz sand transition layer. The quartz sand particle size of the quartz sand transition layer is 24~26 mesh, and the filling thickness is 35 mm. In the filtration system of this embodiment, a wet method is used during filling, that is, quartz sand or functional filler is gradually added while water is added, and the column wall is gently tapped or the air is vented by the upward flow of water at a low speed to make the bed dense and free of air bubbles, and the surface is leveled to ensure uniform water flow distribution.

[0020] Before conducting micro / nanoplastics filtration experiments using quartz sand filter columns, the column needs to be pre-washed and equilibrated. First, the bulk material is flushed upwards or downwards at eight pore capacities (PV) with deionized water or matrix water identical to the experimental system until clear and free of bubbles, removing fine particles and gases to stabilize the bed structure. Subsequently, a background solution consistent with the experimental conditions is continuously introduced at 4 PV to stabilize the packing material's wettability and chemical environment, achieving system equilibration.

[0021] During the filtration experiment, a peristaltic pump was used to continuously pump the prepared micro / nanoplastics suspension from bottom to top into the filter column at a constant flow rate. As the treatment volume increased, water samples were collected periodically under different flux conditions to analyze the penetration behavior and removal efficiency of the micro / nanoplastics. The specific sampling method was as follows: using the PV of the filter column as a reference, segmented sampling was performed during operation, with water samples collected every 0.3 PV. The concentration of micro / nanoplastics particles in the samples was detected using a three-dimensional fluorescence spectrometer, and the removal rate of micron- and nano-sized plastic particles was evaluated based on the breakthrough curve.

[0022] Example 3: The difference between this example and Example 2 is that the filling height of organic vermiculite in the functional layer is 8 cm.

[0023] Example 4: The difference between this example and Example 2 is that the filling height of organic vermiculite in the functional layer is 0 cm.

[0024] Example 5: The difference between this example and Example 1 lies in the preparation method of the filler: S1. Take 10g of ground natural vermiculite and disperse it in 0.8L of deionized water, stir and mix well to obtain vermiculite suspension; S2. Weigh out a modifier with an addition amount of 5 times the cation exchange capacity of natural vermiculite, and dissolve the modifier in 100 mL of deionized water to obtain a modified solution; S3. The modified solution obtained in S2 was poured into the vermiculite suspension at a rate of 1 mL / min. The mixture was stirred at 70℃ for 2 h, then kept at 70℃ in a water bath for 10 h, and then allowed to stand at 22℃ for 12 h to obtain the modified slurry. Finally, the slurry was centrifuged at 3000 rpm for 5 min, washed three times with deionized water, and dried at 50℃ to constant weight to obtain the organic vermiculite packing material for micro-nano plastic filtration.

[0025] Example 6: The difference between this example and Example 1 lies in the preparation method of the filler: S1. Take 30 g of ground natural vermiculite and disperse it in 1.2 L of deionized water, stir and mix well to obtain vermiculite suspension; S2. Weigh out a modifier with an addition amount equal to 8 times the cation exchange capacity of natural vermiculite, and dissolve the modifier in 300 mL of deionized water to obtain a modified solution; S3. The modified solution obtained in S2 was poured into the vermiculite suspension at a rate of 2 mL / min, stirred at 100 °C for 4 h, then kept at 100 °C in a water bath for 16 h, and then allowed to stand at 30 °C for 20 h to obtain the modified slurry. Finally, it was centrifuged at 5000 rpm for 10 min, washed 5 times with deionized water, and dried at 80 °C to constant weight to obtain the organic vermiculite packing material for micro-nano plastic filtration.

[0026] Example 7: The difference between this example and Example 1 is that in S3, the separation method is vacuum filtration; the vacuum degree of the vacuum filtration process is -0.06MPa, and the pore size of the filter membrane is 0.45μm.

[0027] Example 8: The difference between this example and Example 8 is that the vacuum degree of the filtration process is -0.09MPa and the filtration time is 20min.

[0028] Example 9: The difference between this example and Example 8 is that the vacuum degree of the filtration process is -0.08MPa and the filtration time is 30min.

[0029] Example 10: The difference between this example and Example 2 is that the quartz sand in the support layer 1 has a particle size of 20-23 mesh and a filling thickness of 20mm.

[0030] Example 11: The difference between this example and Example 2 is that the quartz sand in the support layer 1 has a particle size of 27~30 mesh and a filling thickness of 30 mm.

[0031] Example 11: The difference between this example and Example 2 is that the height of the air-water buffer layer 4 is 15mm.

[0032] Example 12: The difference between this example and Example 2 is that the height of the air-water buffer layer 4 is 20 mm.

[0033] Example 13: The difference between this example and Example 2 is that the quartz sand particle size of the quartz sand transition layer in the protective layer 3 is 20~23 mesh, and the filling thickness is 10mm.

[0034] Example 14: The difference between this example and Example 2 is that the quartz sand particle size of the quartz sand transition layer in the protective layer 3 is 27~30 mesh, and the filling thickness is 35 mm.

[0035] (ii) Comparative Example Comparative Example 1: The difference between this comparative example and Example 1 is that no surfactant was used to modify the vermiculite.

[0036] Comparative Example 2: The difference between this comparative example and Example 1 is that the cationic surfactant used is the cationic surfactant polyquaternium-28 (PQ-28).

[0037] Comparative Example 3: The difference between this comparative example and Example 1 is that the cationic surfactant used is benzyltriethylammonium bromide (BLB).

[0038] Comparative Example 4: The difference between this comparative example and Example 1 is that the particle size of the organic vermiculite is 10-40 mesh.

[0039] Comparative Example 5: The difference between this comparative example and Example 1 is that the particle size of the organic vermiculite is 60-100 mesh.

[0040] (III) Performance Testing (1) Performance Test 1 To verify the effectiveness of the organic vermiculite packing material described in this invention as a functional layer in a sand filtration system for removing micro- and nano-plastics of different sizes, a micro- and nano-plastic suspension with an influent concentration of 5 mg / L was prepared and filtered using filter columns laid in Examples 1-4. The experiments targeted nano-plastics with particle sizes of 200 nm and micro-plastics with particle sizes of 1 μm as pollutants, and two sets of flow rates were set: 3.0 mL / min and 20.0 mL / min. In each experiment, influent and effluent samples were collected under different volumetric flux conditions at a fixed flow rate. The concentration of micro-plastics in the effluent was measured and the removal rate was calculated. The performance test results of each example are shown in the table below: Table 1. Removal rate of micro / nano plastic particles under different influent flow rates in Examples 1-4

[0041] The experimental results from Examples 1-4 show that the thickness of the organic vermiculite packing layer has a significant impact on the removal performance of micro- and nano-plastics. When no organic vermiculite is filled, the system has virtually no ability to remove micro- and nano-plastics, indicating that the quartz sand support layer can only achieve physical sieving and cannot effectively adsorb small micro- and nano-plastic particles. However, after filling with a certain height of organic vermiculite, the removal effect of the filtration system is significantly improved, especially under low flow rate conditions.

[0042] At an influent flow rate of 3.0 mL / min, Examples 1 / 2 with a functional layer height of 3 cm achieved removal rates of 47.44% and 70.81% for 200 nm and 1 μm plastic particles, respectively, indicating that the organic vermiculite layer can adsorb and retain plastic particles through its layered structure and surface-active groups. When the filling height increased to 8 cm (Example 3), the removal rates further improved to 87.10% and 92.21%, indicating that a thicker packing layer provides more adsorption sites and a longer mass transfer path, thereby enhancing the interaction with pollutants. When the flow rate increased to 20.0 mL / min, the overall removal rate decreased, but the trend remained consistent. The higher flow rate shortened the residence time of water in the packing layer, limiting the contact and adsorption processes, resulting in a slight decrease in removal efficiency. Even so, the 8 cm packing layer still maintained high removal performance, with removal rates of 58.52% and 78.80% for nano-sized and micro-sized particles, respectively, demonstrating good adsorption stability and erosion resistance.

[0043] Figure 2 The changes in surface morphology before and after filtration of organic vermiculite in Examples 1 / 2 are shown. Figure 2 As shown, the organic vermiculite before filtration exhibits a typical layered structure with a relatively smooth surface, loosely arranged layers, and clear interlayer gaps, demonstrating obvious layered stacking characteristics and a large specific surface area, providing favorable binding space for subsequent adsorption reactions. After filtration, a large number of spherical nanoplastic particles (SNPs) were clearly attached to the surface and interlayer of the organic vermiculite. Figure 3 These particles are uniformly distributed in the interlayer gaps and surface grooves, indicating that the plastic particles are effectively trapped and adsorbed within the layered structure of the organic vermiculite. This is based on scanning electron microscope images taken at high magnification (…). Figure 4 The tight bond between the micro-nanoplastics and vermiculite sheets may be due to the synergistic effect of various interactions such as electrostatic adsorption, hydrophobic interaction, and van der Waals forces.

[0044] In summary, the organic vermiculite functional layer not only relies on physical sieving during the filtration process but also achieves the capture and fixation of micro- and nano-plastic particles through multiple mechanisms such as electrostatic adsorption, hydrophobic interactions, and van der Waals forces. After optimizing the packing layer thickness and flow rate conditions, this system can achieve efficient removal of micro- and nano-plastics of different particle sizes under low energy consumption conditions, providing reliable technical support for the end-of-pipe control of micro- and nano-plastic pollution.

[0045] (2) Performance Test 2 To verify the filtration performance of organic vermiculite prepared under different modification conditions, organic vermiculite prepared in Examples 1 / 2 and Comparative Examples 1-3 were used as functional layer packing materials, and their filtration effects were compared. The concentration of the influent micro-nano plastic suspension was 5 mg / L, the micro-nano plastic particle size was 200 nm, and the influent flow rate was controlled at 3.0 mL / min. The performance test results of each comparative example are shown in the table below: Table 2. Removal rates of 200 nm micro / nanoplastics particles in Examples 1 / 2 and Comparative Examples 1-3 at an influent flow rate of 3.0 mL / min.

[0046] The results showed that cationic surfactant modification could effectively increase the positive charge density on the vermiculite surface, thereby enhancing the electrostatic attraction between the vermiculite and the negatively charged micro / nanoplastics particles. However, different cationic structures showed significant differences in their potential regulation effects. Among them, CTAB modification with long chains and high cationic density had the best effect, indicating that surface potential regulation is a key factor affecting the adsorption performance of organic vermiculite.

[0047] (3) Performance test 3 To investigate the effect of organic vermiculite particle size on filtration performance, organic vermiculite prepared in Comparative Examples 4 and 5 was used as the functional layer packing material, and its filtration effect was compared with that of Examples 1 and 2. The concentration of the influent micro-nano plastic suspension was 5 mg / L, the micro-nano plastic particle size was 200 nm, and the influent flow rate was controlled at 3.0 mL / min. The performance test results for each proportion are shown in the table below: Table 3 Comparison of removal rates of micro / nano plastic particles by organic vermiculite fillers in Examples 1 / 2 and Comparative Examples 4-5

[0048] The results show that there is an optimal range for the particle size of organic vermiculite. When the particle size is too large (20-40 mesh), the specific surface area and external surface active sites are insufficient, resulting in a small effective contact area per unit bed volume and a low removal rate. While a particle size that is too small (60-100 mesh) can increase the specific surface area, the bed is prone to compaction and reduced porosity, leading to a higher pressure drop and localized bypass flow in the early stages. This limits the effective contact between the water and the packing material, and the increased local shear is detrimental to particle adhesion, resulting in a less effective overall performance than medium-sized particles. When the particle size is 40-60 mesh, the bed pore structure and specific surface area reach a better balance, with uniform hydraulic distribution and sufficient contact time, thus achieving the highest removal efficiency.

[0049] (4) Performance Test 4 To evaluate the removal performance of organic vermiculite functional packing material for micro- and nano-plastics under complex water quality conditions, common ions and organic components from domestic sewage were introduced into the filtration background solution to simulate interfering substances that may coexist with micro- and nano-plastics in actual influent. This verified the material's adsorption stability, anti-interference ability, and applicability in filtration devices under non-ideal systems. Organic vermiculite prepared in Examples 1-4 was used as the functional layer packing material. The influent micro- and nano-plastic suspension concentration was 5 mg / L, the micro- and nano-plastic particle size was 200 nm, and the influent flow rate was controlled at 3.0 mL / min. The functional layer laying heights were set to 0, 30, and 80 mm, respectively. The performance test results are as follows: Table 4 Comparison of micro / nanoplastics particle removal rates in non-ideal systems under different functional layer layup heights in Examples 1-4

[0050] Compared to the example using deionized water as the background solution, the removal rate of micro / nanoplastics by organic vermiculite was significantly improved in the simulated domestic wastewater system. Taking a functional layer thickness of 30 mm as an example, the removal rate of micro / nanoplastics was 47.44% in the deionized water system, while it increased to 83.16% in the simulated wastewater system. This promoting effect may be related to the regulation of interfacial electrochemical properties by the ionic strength of the solution and the coexisting components. In the simulated wastewater system, the water contained a certain concentration of Na... + Ca 2+ Mg 2+The presence of cations enhances the electrostatic adsorption stability between the positively charged organic vermiculite surface and the negatively charged micro / nanoplastics particles, creating an "ion bridge" effect. Furthermore, dissolved organic molecules in the simulated wastewater system can adsorb onto the vermiculite sheets through hydrophobic interactions or π–π stacking effects, increasing surface hydrophobicity and further promoting the adhesion and fixation of micro / nanoplastics. Due to the high specific surface area and excellent ion exchange performance of the organic vermiculite interlayer structure, the synergistic effect of these multiple mechanisms results in higher adsorption affinity and filtration efficiency in complex systems.

[0051] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. An organic vermiculite packing material for micro / nano plastic filtration, characterized in that, It is composed of natural vermiculite and a modifier added at an amount of 2 to 8 times the cation exchange capacity of the natural vermiculite; wherein the modifier is any one of hexadecyltrimethylammonium bromide, polyquaternium-28, and benzyltriethylammonium bromide.

2. The organic vermiculite packing material for micro / nano plastic filtration as described in claim 1, characterized in that, The method for preparing the filler is as follows: S1. Weigh natural vermiculite, grind it through a 40-60 mesh sieve, then take 10-30 g and disperse it in 0.8-1.2 L of deionized water, stir and mix well to obtain a vermiculite suspension; S2. Weigh the modifier and dissolve it in 0.1~0.3 L of deionized water to obtain a modified solution; S3. The modified solution obtained in S2 is poured into the vermiculite suspension at a rate of 1-2 mL / min, stirred at a constant temperature of 70-100 °C for 2-4 h, then kept at a water bath temperature of 70-100 °C for 10-16 h, and then allowed to stand at 22-30 °C for 12-20 h to obtain the modified slurry. Finally, after centrifugation / filtration, it is washed 3-5 times with deionized water and dried at 50-80 °C to constant weight to obtain the organic vermiculite packing material for micro-nano plastic filtration.

3. The organic vermiculite packing material for micro / nano plastic filtration as described in claim 1, characterized in that, In S3, the parameters for centrifugal separation / filtration are as follows: the centrifugal speed for centrifugal separation is 3000~5000 rpm, and the centrifugation time is 5~10 min; the vacuum degree for filtration is -0.06 ~ -0.09 MPa, the filter membrane pore size is 0.45 μm, and the filtration time is 20~30 min.

4. A filtration system for micro / nanoplastics filtration, based on the organic vermiculite packing material according to any one of claims 1 to 3, characterized in that, The filtration system includes a hollow column filter body (5) and a multi-stage filter bed with gradient structure and flow regulation function built in the hollow column filter body (5). The multi-stage filter bed includes, from bottom to top, a support layer (1) for supporting the packing and realizing primary uniform water flow, an organic vermiculite functional layer (2) with size screening effect and multi-mechanism synergistic adsorption capacity, a protective layer (3) for suppressing upper disturbance, uniform rectification and preventing interface scaling, and an air-water buffer layer (4) for stabilizing the upper flow state and having an exhaust function. The lower end of the hollow column filter body (5) is connected to the water inlet component (6), and the upper end is connected to the water outlet component (7).

5. A filtration system for micro / nanoplastics filtration as described in claim 4, characterized in that, The support layer (1) includes a porous support plate and a PP filter screen and a quartz sand layer covering the porous support plate from bottom to top; wherein the quartz sand layer is laid with quartz sand particles of 20~30 mesh and a filling thickness of 20~45 mm.

6. A filtration system for micro / nanoplastics filtration as described in claim 4, characterized in that, The thickness of the organic vermiculite functional layer (2) is 30~80 mm.

7. A filtration system for micro / nanoplastics filtration as described in claim 4, characterized in that, The height of the air-water buffer layer (4) is 10~20 mm.

8. A filtration system for micro / nanoplastics filtration as described in claim 4, characterized in that, The ratio of the height to the inner diameter of the hollow column filter body (5) is 13:

3.

9. A filtration system for micro / nanoplastics filtration as described in claim 4, characterized in that, The protective layer (3) includes a quartz sand transition layer and a PP filter screen disposed above the quartz sand transition layer. The quartz sand particle size of the quartz sand transition layer is 20~30 mesh, and the filling thickness is 10~35 mm.

10. A filtration system for micro / nanoplastics filtration as described in claim 4, characterized in that, It can be applied to the filtration and purification of domestic sewage, industrial wastewater, municipal reclaimed water and other water bodies containing micro-nano plastic pollutants.

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