Preparation method of CTAB (Cetyltrimethyl Ammonium Bromide) magnetic biochar composite material and application of CTAB magnetic biochar composite material in adsorbing and removing aged nano plastic in water body

Abstract

The invention discloses a preparation method of a CTAB (Cetyltrimethyl Ammonium Bromide) magnetic biochar composite material and application of the CTAB magnetic biochar composite material in adsorption removal of aged nano-plastics in water, and belongs to the technical field of water treatment. The preparation method of the CTAB magnetic biochar composite material comprises the following steps: performing pyrolysis carbonization on biomass in an inert atmosphere to obtain original biochar (BC); mixing a ferric salt solution with the original biochar, and carrying out a co-precipitation reaction under an alkaline condition to obtain magnetic biochar (MBC); and mixing the magnetic biochar with hexadecyl trimethyl ammonium bromide in water, and carrying out surface modification to obtain the CTAB magnetic biochar composite material (CTAB / MBC). The composite material has multiple adsorption mechanisms through surface modification, can efficiently and stably remove nano-plastics generated by different aging paths, and has good magnetic separation performance, cycle performance and environment anti-interference capability.

Description

Technical Field

[0001] This invention belongs to the field of water treatment technology, and more specifically relates to a method for preparing a CTAB magnetic biochar composite material and its application in the adsorption and removal of aged nanoplastics in water. Background Technology

[0002] Currently, methods for removing microplastics (MPs) from aquatic environments mainly include filtration, flocculation, biodegradation, and chemical oxidation. However, these methods generally suffer from limitations such as size constraints, poor selectivity, high costs, or the introduction of new pollutants. Among these, adsorption methods have attracted considerable attention due to their ease of operation and low cost. Biochar, as a porous and low-cost adsorbent material, has been widely used for microplastic removal, but it suffers from difficulties in separation and recovery, and poor regeneration performance. Magnetizing biochar by doping it with iron or iron oxide can enhance the removal of MPs and make it easier to separate and recover from the aquatic environment. However, the performance of magnetic biochar is still limited by insufficient active sites and sensitivity to environmental variables. In real aquatic environments, its adsorption performance is easily affected by factors such as pH, ionic strength, and dissolved organic matter.

[0003] Furthermore, existing research largely focuses on the removal of pristine microplastics. However, environmental microplastics often undergo aging processes such as photoexposure and oxidation, leading to significant changes in their surface properties (e.g., functional group types, charge, and hydrophobicity), which in turn affect their interaction mechanisms with adsorbents. The differentiated changes in microplastic surface properties caused by different aging pathways have not yet been systematically studied, making it difficult for existing adsorbent materials to achieve efficient and stable selective removal of microplastics in different aging states. Therefore, there is a need to develop an adsorbent material that can adapt to the surface characteristics of microplastics with different aging processes, possesses multiple adsorption mechanisms, and exhibits strong environmental adaptability. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing a CTAB (hexadecyltrimethylammonium bromide) magnetic biochar composite material and its application in the adsorption and removal of aged nanoplastics in water, thereby solving the problems of low adsorption efficiency, single mechanism, and poor environmental adaptability of existing adsorption materials for differentially aged nanoplastics. The composite material of this invention, through surface modification, possesses multiple adsorption mechanisms, enabling efficient and stable removal of nanoplastics generated through different aging pathways, and exhibits good magnetic separation performance and environmental resistance.

[0005] To achieve the above objectives, the present invention provides the following solution: One of the technical solutions of this invention is to provide an application of CTAB magnetic biochar composite material in the adsorption and removal of aged nanoplastics in water.

[0006] The second technical solution of this invention provides a method for preparing a CTAB magnetic biochar composite material for adsorbing aged nanoplastics, comprising the following steps: Biomass is pyrolyzed and carbonized under an inert atmosphere to obtain primitive biochar (BC). The iron salt solution was mixed with the original biochar and a co-precipitation reaction was carried out under alkaline conditions to obtain magnetic biochar (MBC). The magnetic biochar was mixed with hexadecyltrimethylammonium bromide in water to perform surface modification, thereby obtaining the CTAB magnetic biochar composite material (CTAB / MBC).

[0007] Preferably, the pyrolysis carbonization conditions are as follows: under a nitrogen atmosphere, the temperature is increased to 480-520°C at a rate of 8-12°C / min and maintained for 1.5-2.5 hours.

[0008] Preferably, the iron salt solution comprises a mixed aqueous solution of FeSO4 and FeCl3 (capable of providing Fe in aqueous solution). 2+ and Fe 3+ Other iron salts that do not affect subsequent reactions can be considered. FeSO4 and FeCl3 have high solubility in water, which is beneficial for forming a homogeneous solution. Furthermore, sulfate and chloride ions are easily removed during subsequent alkaline precipitation and washing, having minimal impact on product purity; therefore, they are preferred options. Among them, Fe... 2+ with Fe 3+ The molar ratio is 1:1.5~2.5 (to ensure that there are enough ferric ions to react with ferrous ions during the co-precipitation process, preferentially forming Fe3O4 with strong magnetism); the mass ratio of iron salt to raw biochar in the iron salt solution is 0.82:1.

[0009] Preferably, the pH of the mixture is adjusted to 11-12 by adding an alkaline solution to provide the alkaline conditions.

[0010] Preferably, the mass ratio of the magnetic biochar to hexadecyltrimethylammonium bromide is 40-60:1.

[0011] Preferably, the coprecipitation reaction takes 2-3 hours.

[0012] Preferably, the surface modification time is 20-28 hours.

[0013] The third technical solution of the present invention provides a method for adsorbing and removing aged nanoplastics from water, comprising: adding the above-mentioned CTAB magnetic biochar composite material at a dosage of 0.5 g / L to water containing aged nanoplastics to carry out an adsorption reaction; and after the reaction is completed, separating the adsorbed composite material from the water and recovering it by means of an external magnetic field.

[0014] This invention utilizes the synergistic effect of multi-level structural design and surface chemical modification to construct a composite adsorption system with "multiple recognition-adaptive adsorption-convenient separation" functions, thereby efficiently solving the differentiated removal challenges of nanoplastics with different aging pathways. Its technical principle is as follows: The first stage involves constructing a magnetic porous support framework, laying the foundation for efficient capture and separation. Using biomass as the carbon source, controlled-temperature pyrolysis is performed in an inert atmosphere to form pristine biochar rich in pores. This process not only realizes the resource utilization of waste but also constructs a physical adsorption substrate with high specific surface area and hierarchical pores. Subsequently, Fe3O4 nanoparticles are generated in situ on the biochar surface via co-precipitation, achieving magnetic functionalization. The loading of Fe3O4 not only endows the material with superparamagnetism, providing the possibility for subsequent magnetic separation and recovery, but its surface ferrite sites can also coordinate and complex with oxygen-containing functional groups on the nanoplastic surface, adding a chemical adsorption pathway.

[0015] The second level: Introducing a CTAB bifunctional modification layer to achieve intelligent control of surface properties. This is the core of the invention. The surface of magnetic biochar is modified using the cationic surfactant hexadecyltrimethylammonium bromide, introducing two key functional groups: 1. a positively charged quaternary ammonium salt hydrophilic head group; 2. a long-chain alkane hydrophobic tail chain. This modification fundamentally changes the surface properties of the material, transforming it from a single-attribute surface into an interface with dual charge-hydrophobic response characteristics.

[0016] The third level: Synergistic and adaptive selection of multiple mechanisms for precise targeting of different aging pollutants. Faced with nanoplastics exhibiting vastly different surface properties due to varying aging pathways, this composite material can initiate different dominant adsorption mechanisms to achieve precise removal: For chemically oxidized nanoplastics: Strong oxidizing conditions (such as persulfate) oxidize the nanoplastic surface, generating numerous negatively charged oxygen-containing functional groups such as carboxyl and hydroxyl groups, resulting in a significant negative shift in the surface zeta potential. At this point, the positively charged CTAB quaternary ammonium salt head groups on the composite material surface generate a strong electrostatic attraction with the pollutants, becoming the dominant adsorption force, efficiently capturing and immobilizing these charged pollutants. For UV-aged nanoplastics: UV radiation mainly induces polymer chain breakage and cross-linking, increasing surface roughness and hydrophobicity, but with relatively small changes in electrical properties. At this point, the long-chain alkane tails of CTAB on the composite material surface play a crucial role, achieving efficient adsorption through strong hydrophobic interactions with the enhanced hydrophobicity of the plastic surface. Synergistic and fallback mechanisms: In addition to the above specific mechanisms, the porous structure of biochar for physical retention and the coordination complexation of Fe3O4 are always present, providing a basic adsorption guarantee. The four mechanisms (electrostatic, hydrophobic, physical, and coordination) are not isolated but synergistic, ensuring reliable removal of nanoplastic mixtures with unknown aging states or complex properties.

[0017] The fourth level: Enhanced environmental resistance and simplified process. The long-chain alkyl groups in the CTAB-modified layer can, to some extent, shield the active sites from competitive adsorption by dissolved organic matter such as humic acid in the solution. Its stable positive charge provides continuous electrostatic adsorption capacity over a wide pH range, thereby improving the material's environmental stability in real, complex aquatic environments. Finally, the embedded Fe3O4 magnetic core ensures rapid solid-liquid separation after adsorption saturation via a simple external magnetic field, avoiding secondary pollution caused by adsorbent loss and facilitating material regeneration and reuse.

[0018] The present invention discloses the following technical effects: 1. High adsorption performance: CTAB / MBC has an adsorption capacity of 329 mg / g for chemically aged microplastics and 309 mg / g for UV-aged microplastics at the optimal pH. At the highest HA concentration, it has an adsorption capacity of 258.5 mg / g for chemically aged microplastics and 241.5 mg / g for UV-aged microplastics. Significantly higher than unmodified MBC (188 mg / g, 170.5 mg / g, 134.5 mg / g and 111 mg / g) 2. Good environmental stability: The CTAB modification layer enhances the material's resistance to interference in complex water environments such as humic acid and different ionic strengths, resulting in a smaller decrease in adsorption performance and exhibiting more stable performance.

[0019] 3. Good cycling performance: The CTAB / MBC composite material exhibits excellent reusability, maintaining adsorption capacities of 242 mg / g and 245 mg / g after five cycles.

[0020] 4. Synergistic effect of multiple mechanisms: The composite material provided by this invention integrates four mechanisms: physical capture, electrostatic attraction, hydrophobic interaction and coordination complexation. It has different dominant forces on different aging states of nanoplastics (strong negative charge or strong hydrophobicity), and realizes efficient removal of microplastics with different aging paths. Attached Figure Description

[0021] Figure 1 This is a flowchart illustrating the preparation process of the CTAB magnetic biochar composite material for adsorbing aged nanoplastics as described in Example 1. Figure 2 The SEM images of BC(a), MBC(b) and CTAB / MBC(c) described in Example 1; Figure 3 The XRD diffraction pattern (a), FTIR spectrum (b), Zeta potential (c), and VSM curve (d) of BC, MBC, and CTAB / MBC described in Example 1 are shown. Figure 4The SEM images of PS (a), 0.1 PS (b), 0.2 PS (c), 24 hPS (d), 48 hPS (e) and 72 hPS (f) described in Example 1; Figure 5 The XRD diffraction patterns (a) and FTIR spectra (b) of PS, 0.1 PS, 0.2 PS, 24 hPS, 48 hPS and 72 hPS described in Example 1 are shown. Figure 6 The figures and kinetic (a)~(b), intraparticle diffusion (c)~(d), and isothermal (e)~(f) models of the removal effect of MBC and CTAB / MBC on aged PS at different times and different initial concentrations as described in Example 1 are fitted. Figure 7 The graphs show the removal effects of CTAB / MBC and MBC on aged PS described in Example 1 at different pH values ​​(a), different HA concentrations (b), and different anion and cation concentrations (c) to (d). Figure 8 The image shows the removal effect of CTAB / MBC on aged PS after 5 cycles. Detailed Implementation

[0022] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0023] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0024] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0025] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0026] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0027] It should be noted that any aspects not described in detail in this invention are conventional practices in the field and are not the focus of this invention.

[0028] The raw materials used in the following embodiments and comparative examples of this invention are as follows: The monodisperse polystyrene nanospheres (PS, particle size approximately 300 nm, initial concentration 25 mg / mL) used were purchased from Jiangsu Zhichuan Technology Co., Ltd. FeSO4·7H2O, FeCl3, NaOH, NaCl, MgCl2, CaCl2, Na2CO3, Na2SO4·10H2O, NaHCO3, Na2S2O8, and hexadecyltrimethylammonium bromide (CTAB) were all analytical grade and purchased from Sinopharm Chemical Reagent Co., Ltd.; the wheat straw used was collected from a farm in Qingtongxia City, Ningxia; and all water used was deionized water.

[0029] The characterization and analysis methods involved in the following performance tests are as follows: The surface morphology of the samples was observed using field emission scanning electron microscopy (SEM, ZEISS Sigma 300, Germany); the phases and crystal structures were analyzed using X-ray diffraction (XRD, D8 Advance, Bruker, Germany); the surface functional groups were determined using Fourier transform infrared spectroscopy (FTIR, Spectrum Two, PerkinElmer, USA); the surface charge was determined using a Zeta potential analyzer (Zetasizer 3000HSA, Marvern, UK); the magnetization saturation intensity was determined using a vibrating sample magnetometer (VSM, Lake Shore 7404, USA); and the elemental composition and valence state of the material surface were analyzed using X-ray photoelectron spectroscopy (XPS, Thermo Scientific K-Alpha, USA).

[0030] Unless otherwise specified, the room temperature involved in this invention is 25±5℃.

[0031] Example 1 This embodiment provides the preparation and performance testing process of the CTAB magnetic biochar composite material used for adsorbing aged nanoplastics: Figure 1 This is a flowchart illustrating the preparation process of the CTAB magnetic biochar composite material for adsorbing aged nanoplastics as described in this invention.

[0032] 1. Preparation of composite materials (1) Original biochar (BC): Wheat straw was washed with tap water and deionized water in sequence, dried naturally and then crushed. An appropriate amount of powder was placed in a tube furnace and heated to 500℃ at a rate of 10℃ / min under N2 atmosphere and held for 2h. The pyrolysis product was ground through a 200-mesh sieve and stored for later use, and labeled as BC.

[0033] (2) Magnetic biochar (MBC): Under N2 atmosphere, add 100 mL of deionized water to a 250 mL four-necked flask and stir for 10 min. Weigh 0.5562 g FeSO4·7H2O and 1.0812 g FeCl3 and add them to the four-necked flask. Stir for 20 min. Weigh 2 g BC and continue stirring for 30 min. Add 2 mol / L NaOH to adjust the pH to 11.5 ± 0.02. Let stand for 2 h to age. Filter, wash with deionized water until neutral, and dry at 70 °C to obtain MBC.

[0034] (3) CTAB modified magnetic biochar (CTAB / MBC): Weigh 1g of the prepared MBC and 0.02g of CTAB into a beaker, add 20mL of deionized water, stir at room temperature for 24h, and then dry at 70℃ to obtain CTAB / MBC.

[0035] Figure 2 The SEM images are those of BC (a), MBC (b), and CTAB / MBC (c) as described in Example 1. Figure 3 The XRD diffraction pattern (a), FTIR spectrum (b), Zeta potential (c), and VSM curve (d) of BC, MBC, and CTAB / MBC described in Example 1 are shown.

[0036] Depend on Figure 2 and Figure 3 It is evident that the BC surface is smooth and exhibits a porous structure. After loading Fe3O4, the MBC surface becomes rough and adheres with particulate matter. After CTAB modification, the CTAB / MBC surface exhibits a thin film coating with a more uniform particle distribution. Peaks of Fe3O4 were observed at 30.18°, 35.56°, 43.2°, 57.2°, and 63.92°, confirming the successful loading of the magnetic component and that CTAB modification did not alter its crystalline structure. FTIR spectra further revealed information on chemical functional groups; after composite modification, due to the presence of more alkane chains in CTAB, the peak at 2925 cm⁻¹... -1 and 698cm -1The presence of more pronounced CH and -CH2 groups indicates successful CTAB loading. At 586cm... -1 and 450cm -1 The presence of Fe-O bond stretching vibrations indicates successful Fe3O4 loading. Zeta potentials show that the zero-point charges of BC, MBC, and CTAB / MBC are 3.82, 6.11, and 7.52, respectively. This means that at pH < 7.52, the CTAB / MBC surface is positively charged, laying the foundation for its electrostatic adsorption of negatively charged pollutants. VSM hysteresis loops show that the saturation magnetization of MBC and CTAB / MBC are 1.176 emu / g and 1.143 emu / g, respectively, indicating that both possess good ferromagnetism and can achieve rapid solid-liquid separation through an external magnetic field.

[0037] 2. Microplastic aging treatment (1) Chemical oxidative aging: A persulfate oxidation system was used to simulate strong oxidizing conditions in the environment. 10 mL and 25 mg / mL PS stock solutions were mixed with 10 mL of 0.1 mol / L and 0.2 mol / L Na₂S₂O₈ solutions, respectively, and stirred in the dark at 25℃ and 200 rpm for 24 h. After the reaction, the mixture was ultrasonically dispersed to obtain the aging products, which were labeled as 0.1 PS and 0.2 PS, respectively. (2) Ultraviolet aging: 25 mg / mL PS stock solution was placed in a quartz petri dish and placed in a xenon lamp aging chamber (PLS-SXE300UV, Beijing Pofilai). The solution was then subjected to simulated sunlight (920 W / m²). 2 The samples were continuously irradiated for 24, 48, and 72 hours, respectively. After irradiation, the samples were labeled as 24 hPS, 48 hPS, and 72 hPS, respectively.

[0038] Figure 4 The SEM images are those of PS (a), 0.1PS (b), 0.2PS (c), 24hPS (d), 48hPS (e) and 72hPS (f) as described in Example 1. Figure 5 The XRD diffraction patterns (a) and FTIR spectra (b) of PS, 0.1PS, 0.2PS, 24hPS, 48hPS and 72hPS described in Example 1 are shown.

[0039] Depend on Figure 4 and Figure 5It is evident that pristine PS exhibits a tightly packed, regularly arranged spherical granular structure with a smooth surface. After aging, PS develops cracks, pores, or fragmentation, with irregular edges or localized collapse, increasing roughness. Chemical oxidation is more destructive to pristine PS. XRD patterns show a broad, diffuse amorphous peak at 19.66° in pristine PS. After UV aging, the intensity of this peak increases, indicating a possible increase in short-range order in PS. Chemical oxidation aging sharpens the amorphous peak and introduces new diffraction peaks attributed to Na₂SO₄, NaHSO₄, and the small-molecule oxidation product C₇H₆O₂, confirming the oxidative degradation reaction. Compared to unaged PS, both aging methods introduce abundant oxygen-containing functional groups. FTIR spectra show that both aging methods lead to a decrease in the 1495 cm⁻¹ peak. -1 and 1451cm -1 The intensity of the C=C peak at 3426 cm⁻¹ weakens or disappears, while the intensity at 3426 cm⁻¹ decreases or disappears. -1 and 3609cm -1 The enhanced vibration of the -OH peak at 1656 cm⁻¹ indicates that the aging process disrupts the benzene ring structure of PS and introduces oxygen-containing groups. The difference lies in the fact that UV aging primarily leads to the increase in the -OH peak vibration at 1656 cm⁻¹. -1 The C=O vibration is enhanced at this point; while chemical aging not only enhances the C=O and CO absorption peaks, but also at 1290 cm⁻¹. -1 A new sulfonic acid group (-SO3H) characteristic absorption peak was introduced at this location.

[0040] 3. Batch adsorption experiment (1) Kinetic experiment: Accurately weigh 0.03 g of adsorbent (CTAB / MBC or MBC) into a beaker, add 60 mL of 300 mg / L PS solution (i.e., PS, 0.1 PS, 0.2 PS, 24 hPS, 48 hPS and 72 hPS), and stir the reaction at 25℃ and 300 rpm. Samples were taken at different time points (10 min, 20 min, 30 min, 60 min, 90 min, 120 min, 150 min, 180 min, 240 min, 300 min and 360 min), centrifuged the samples, filtered them, collected the filtrate, stored it at room temperature in the dark, and determined the concentration of the filtrate by ultraviolet spectrophotometry and calculated the adsorption capacity. The data fitting adopted pseudo-first-order, pseudo-second-order and Elovich models.

[0041] Based on the kinetic results, it can be concluded that all adsorption processes exhibit the characteristics of rapid adsorption in the initial stage, followed by a slowdown to reach equilibrium in the later stage. Figure 6During the rapid adsorption phase, the large concentration difference in the solution leads to high mass transfer kinetics and a relatively fast adsorption reaction. Subsequently, as time increases, the adsorption sites on the material tend to saturate, resulting in a decrease in the adsorption rate and a gradual equilibrium. The adsorption of aged PS by both materials increases rapidly in the first 50 minutes, reaching equilibrium around 120 minutes. CTAB / MBC showed the highest adsorption capacity for chemically aged microplastics (317.7 mg / g) and UV-aged microplastics (272.3 mg / g), while MBC showed the highest adsorption capacity for both chemically aged and UV-aged microplastics (272.7 mg / g). Kinetic data were fitted using pseudo-first-order, pseudo-second-order, and Elovich models. Most systems better fit the pseudo-first-order and pseudo-second-order kinetic models, indicating that both physical and chemical adsorption are involved in this adsorption process.

[0042] (2) Isothermal experiment: Accurately weigh 0.03g of adsorbent (CTAB / MBC or MBC) into a beaker, add 60mL of PS solution of different concentrations (50mg / L, 100mg / L, 150mg / L, 200mg / L, 250mg / L, 300mg / L, 400mg / L, 450mg / L and 500mg / L) (i.e. PS, 0.1PS, 0.2PS, 24hPS, 48hPS and 72hPS), stir the reaction at 25℃ and 300 rpm, and take samples after adsorption for 3h (based on kinetic equilibrium time). The subsequent steps are the same as the kinetic experiment. The Langmuir and Freundlich models are used for data fitting.

[0043] The adsorption capacity of CTAB / MBC and MBC for aged PS increased with increasing initial solution concentration, eventually approaching saturation. Figure 6 The maximum theoretical adsorption capacities of MBC for 0.2 PS and 72 hPS were 313.5 mg / g and 293.7 mg / g, respectively, while those of CTAB / MBC were 422.5 mg / g and 334.1 mg / g, respectively. Compared to MBC, CTAB / MBC exhibited higher adsorption capacities at different concentrations, and even higher adsorption capacities for chemically oxidized PS, further confirming its superior adsorption performance compared to MBC. The RL of the Langmuir model... 2 The results are higher than those of the Freundlich model, indicating that the adsorption process is mainly monolayer adsorption.

[0044] (3) Environmental Factor Influence Experiment: In the experiment to explore environmental influence factors, the concentration of PS (i.e., PS, 0.1PS, 0.2PS, 24hPS, 48hPS and 72hPS) in the solution was 300mg / L. Different initial pH values ​​(1, 3, 5, 7, 9 and 11) were set; the added ion type was Na + Mg 2+ Ca 2+ CO3 2- SO4 2- and HCO3 - Different ion concentrations were set at (0.01 mol / L, 0.1 mol / L, 0.3 mol / L, and 0.5 mol / L); different humic acid (HA) concentrations were set at (10 mg / L, 20 mg / L, 50 mg / L, 80 mg / L, and 100 mg / L). The reaction was carried out with stirring at 25℃ and 300 rpm. Samples were taken after 3 hours of adsorption, and subsequent steps were the same as in the kinetic experiment. The adsorption capacity was then calculated. The results are as follows: Figure 7 As shown.

[0045] Depend on Figure 7 It was found that solution pH significantly affected the adsorption performance of CTAB / MBC on aged PS. For chemically aged PS (0.1 PS, 0.2 PS), the adsorption capacity of both MBC and CTAB / MBC reached its maximum under acidic conditions (pH 3–5); the adsorption capacity decreased significantly as the pH increased to neutral and alkaline conditions (pH 7–11). For photo-aged PS (24 hPS–72 hPS), the adsorption capacity peaked under near-neutral conditions (pH 7–9), and decreased under strong acidic or strong alkaline conditions. Under all pH conditions, the adsorption capacity of CTAB / MBC was consistently higher than that of MBC, confirming the universal and crucial role of CTAB surface modification in improving performance. CTAB / MBC achieved an adsorption capacity of 329 mg / g for chemically aged microplastics and 309 mg / g for UV-aged microplastics at the optimal pH, significantly higher than unmodified MBC (188 mg / g and 170.5 mg / g, respectively). The addition of HA competitively inhibited adsorption. As the HA concentration increased (0~100 mg / L), the adsorption capacity of both materials for the two microplastics generally decreased. At the highest HA concentration, CTAB / MBC adsorbed 258.5 mg / g of chemically aged microplastics and 241.5 mg / g of UV-aged microplastics, which was significantly higher than that of unmodified MBC (134.5 mg / g and 111 mg / g). However, the decrease in adsorption capacity of CTAB / MBC was relatively smaller, indicating stronger anti-interference ability.

[0046] (4) Cyclic Experiment: The reusability of the material is a key indicator for its practical application. Accurately weigh 0.03 g of adsorbent into a beaker, add 60 mL of PS solution, and the concentration of PS (i.e., 0.2 PS and 72 h PS) in the solution is 300 mg / L. After adsorption for 3 h (based on kinetic equilibrium time) at 25 °C and 300 rpm, take a sample. The subsequent steps are the same as in the kinetic experiment, and calculate the adsorption amount. After each cycle, separate the adsorbed material by centrifugation. Shake the recovered material in ethanol solution for 3 h, then filter, wash 3 times with pure water, and finally dry at 70 °C for subsequent experiments.

[0047] like Figure 8 As shown, the CTAB / MBC composite material exhibits excellent reusability, maintaining adsorption capacities of 242 mg / g and 245 mg / g after five cycles.

[0048] Comparative Examples 1 to 10 were set up according to the parameter changes in Table 1 to verify the effect of parameter changes on the properties of the obtained materials. Except for the parameters listed in Table 1, the other processing steps of each comparative example were the same as those in Example 1.

[0049] Table 1. Effects of parameter variations on the properties of the obtained materials. The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0050] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. Application of a CTAB magnetic biochar composite material in the adsorption and removal of aged nanoplastics in water.

2. A method for preparing a CTAB magnetic biochar composite material for adsorbing aged nanoplastics, characterized in that, Includes the following steps: Biomass is pyrolyzed and carbonized under an inert atmosphere to obtain primitive biochar; The iron salt solution was mixed with the original biochar, and a co-precipitation reaction was carried out under alkaline conditions to obtain magnetic biochar. The magnetic biochar was mixed with hexadecyltrimethylammonium bromide in water to perform surface modification, thereby obtaining the CTAB magnetic biochar composite material.

3. The preparation method according to claim 2, characterized in that, The pyrolysis carbonization conditions are as follows: under a nitrogen atmosphere, the temperature is increased to 480-520℃ at a rate of 8-12℃ / min and maintained for 1.5-2.5h.

4. The preparation method according to claim 2, characterized in that, The iron salt solution comprises a mixed aqueous solution of FeSO4 and FeCl3, wherein Fe 2+ with Fe 3+ The molar ratio is 1:1.5~2.5; the mass ratio of iron salt to raw biochar in the iron salt solution is 0.82:

1.

5. The preparation method according to claim 2, characterized in that, The pH of the mixture is adjusted to 11-12 by adding an alkaline solution to provide the alkaline conditions.

6. The preparation method according to claim 2, characterized in that, The mass ratio of the magnetic biochar to hexadecyltrimethylammonium bromide is 40-60:

1.

7. The preparation method according to claim 2, characterized in that, The coprecipitation reaction takes 2-3 hours.

8. The preparation method according to claim 2, characterized in that, The surface modification time is 20~28h.

9. A method for adsorbing and removing aged nanoplastics from water, characterized in that, include: The CTAB magnetic biochar composite material was added to a water body containing aged nanoplastics at a dosage of 0.5 g / L to carry out an adsorption reaction. After the reaction was completed, the adsorbed composite material was separated from the water body and recovered by applying an external magnetic field.

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