Magnetic porous Co-NC material and preparation method and application thereof

Abstract

The invention relates to a magnetic porous Co-NC material and a preparation method and application thereof. The preparation method of the magnetic porous Co-NC material comprises the following steps: (1) slowly adding a cobalt source methanol solution into an imidazole organic ligand methanol solution, and violently stirring the imidazole organic ligand methanol solution at the same time to prevent secondary nucleation of ZIF-67 nanoparticles; after the ZIF-67 nanoparticles are completely added, slowly stirring to prevent secondary nucleation of the ZIF-67 nanoparticles caused by turbulent flow, and centrifuging, washing and drying to obtain the ZIF-67 nanoparticles; and (2) pyrolyzing the ZIF-67 nanoparticles under the condition of being full of N2, and naturally cooling to room temperature to obtain the magnetic porous Co-NC material.

Description

Technical Field

[0001] This invention belongs to the field of water treatment technology, specifically relating to a magnetic porous Co-NC material, its preparation method, and its application. Background Technology

[0002] The widespread use of plastics and inadequate management of plastic waste have led to a massive accumulation of plastic debris in the global aquatic environment. Plastic debris undergoes physical decomposition and chemical reduction, resulting in the formation of microplastic particles. Microplastics (MPs) are defined as plastic particles with a diameter <5 mm, while nanoplastics (NPs), based on their colloidal behavior, are defined as plastic particles with a diameter <1000 nm. NPs can persist in the natural environment for longer periods, while MPs can act as carriers for other pollutants such as heavy metals, antibiotics, and polycyclic aromatic hydrocarbons (PAHs), promoting their translocation throughout the food chain and accumulation in various organisms. Therefore, removing MPs from the aquatic environment is crucial for protecting the ecological environment and human health.

[0003] To address these issues, various methods such as adsorption, filtration, sedimentation, and density flotation are widely used. Filtration typically achieves high removal efficiency but has certain drawbacks, such as high energy consumption and material costs due to membrane fouling; sedimentation and flotation are ineffective for smaller particles (<100μm). Therefore, developing a green, efficient, and universally applicable method to remove NPs from water is crucial. Adsorption, due to its low cost, simple operation, high efficiency, and time-saving advantages, has become one of the most popular strategies.

[0004] Patent CN116850975A discloses a method for preparing iron-based MOFs-modified biochar, which obtains modified biochar by impregnating biochar in an iron salt solution. This modified biochar is used to adsorb microplastic composite pollutants in water. However, the prepared samples have small pore sizes, and the pores of the biochar are not obvious under SEM (scanning electron microscopy), resulting in a low adsorption rate (only 56%) and a slow adsorption rate (>24h). Patent CN117619351A discloses a method for preparing magnetic nano-adsorbents, achieving a microplastic removal efficiency of up to 88%, but the adsorption rate is slow (>12h). Patent CN117839628A discloses a method for preparing magnetically modified biochar, achieving an adsorption rate of up to 94% and an adsorption time of 4h. However, it has high environmental requirements, only achieving a high adsorption capacity at pH=5 and a temperature of 45℃. Summary of the Invention

[0005] To address the aforementioned technical problems, the present invention aims to provide a magnetic porous Co-NC material derived from ZIF-67 nanoparticles for the treatment of nanoplastics in water. The adsorbent provided by this invention possesses a large specific surface area, high mesopore content, strong magnetization, and a positive zeta potential. By utilizing the electrostatic interaction between the adsorbent and the nanoplastics, the green and efficient removal of nanoplastics is achieved.

[0006] In a first aspect, the present invention provides a method for preparing a magnetic porous Co-NC material, the method comprising the following steps: (1) The cobalt source methanol solution was slowly added to the imidazole organic ligand methanol solution while the imidazole organic ligand methanol solution was vigorously stirred to prevent secondary nucleation of ZIF-67 nanoparticles; after the cobalt source methanol solution was completely added, the solution was stirred slowly to prevent turbulence from causing secondary nucleation of ZIF-67 nanoparticles. After centrifugation, washing and drying, ZIF-67 nanoparticles were obtained. (2) The ZIF-67 nanoparticles were pyrolyzed under N2 conditions and naturally cooled to room temperature to obtain the magnetic porous Co-NC material.

[0007] Preferably, in step (1), the cobalt source is at least one of cobalt nitrate, cobalt chloride, cobalt sulfate, cobalt carbonate, cobalt iodide, cobalt bromide, cobalt fluoride and their hydrates, preferably cobalt nitrate hydrate and / or cobalt chloride hydrate; the imidazole organic ligand is at least one of 2-methylimidazole, 4,5-imidazolium dicarboxylic acid and its derivatives, 2-methyl-4,5-imidazolium dicarboxylic acid, 2-ethyl-4,5-imidazolium dicarboxylic acid and 2-propyl-4,5-imidazolium dicarboxylic acid, preferably 2-methylimidazole.

[0008] Preferably, in step (1), the molar ratio of the cobalt source to the imidazole organic ligand is 1:(1-20), more preferably 1:(2-10).

[0009] Preferably, in step (2), the pyrolysis temperature is 800℃; the heating rate is 2-10℃ / min, preferably 5-10℃ / min; the holding time is 30-240min; and the nitrogen flow rate is 300-400mL / min.

[0010] Secondly, the present invention provides a magnetic porous Co-NC material obtained according to the above preparation method.

[0011] Thirdly, the present invention provides an application of the above-mentioned magnetic porous Co-NC material in the adsorption of nanoplastics in water.

[0012] Preferably, the application includes the following steps: First, the magnetic porous Co-NC material is added to polluted water containing nanoplastics to achieve adsorption equilibrium. Then, a magnet was used to separate the magnetic porous Co-NC material with adsorbed nanoplastics from the water. Finally, the magnetic porous Co-NC material adsorbing nanoplastics was desorbed by ultrasonic treatment in an alkaline water environment, thereby regenerating the magnetic porous Co-NC material and completing the adsorption of nanoplastics in polluted water by the magnetic porous Co-NC material.

[0013] Preferably, the pH value of the polluted water containing nanoplastics is 3-11; Controlling Mg in polluted water containing nanoplastics 2+ Concentration ≤15mmol / L, preferably ≤5mmol / L; PO4 3- Concentration ≤10mmol / L, preferably ≤5mmol / L; SO4 2- The concentration is ≤10 mmol / L, preferably ≤5 mmol / L.

[0014] Preferably, the concentration of nanoplastics in the polluted water containing nanoplastics is 0-70 mg / L, and the ratio of the magnetic porous Co-NC material to the polluted water containing nanoplastics is 1-10 mg: 10-100 mL. The time to reach adsorption equilibrium is 8-20 minutes, preferably 10 minutes.

[0015] Preferably, the pH of the ultrasonic treatment in the alkaline water environment is 11-12, the ultrasonic power is 32-40kHz, the duration of a single ultrasonic treatment is 15-30 minutes, and the number of ultrasonic treatments is 3-5.

[0016] Beneficial effects This invention prepares ZIF-67-derived magnetic porous Co-NC. Using ZIF-67 nanoparticles as a template, it inherits the porous and large specific surface area characteristics of ZIF-67 nanoparticles and retains the structure of ZIF-67 nanoparticles to a great extent. The Co-NC is then prepared through pyrolysis. 2+ Restored to Co 0 The magnetic porous Co-NC possesses extremely strong soft magnetism, allowing for separation using a magnet after adsorption, facilitating recycling. The volatilization of N and O atoms during pyrolysis increases the zeta potential of the adsorbent, significantly enhancing the electrostatic interaction between the adsorbent and the microplastics, further increasing its adsorption capacity. The extremely strong stability of the magnetic porous Co-NC enables it to achieve an ultra-high adsorption capacity of over 200 mg / g in water environments with different physicochemical properties and in different water bodies, and it can also be desorbed in alkaline water for reuse. Attached Figure Description

[0017] Figure 1 (a) and (b) are XRD patterns of ZIF-67 nanoparticles and magnetic porous Co-NC materials prepared in Example 1, respectively. Figure 2 (a)-(d) are SEM images of ZIF-67 nanoparticles, magnetic porous Co-NC material, polystyrene nanoplastics, and magnetic porous Co-NC material after adsorption of nanoplastics prepared in Example 1, respectively. Figure 3 (a) and (b) are the water contact angles of the ZIF-67 nanoparticles and the magnetic porous Co-NC material prepared in Example 1, respectively. Figure 4 (a) and (b) show the N2 adsorption-desorption isotherms and pore size distribution of the ZIF-67 nanoparticles and magnetic porous Co-NC materials prepared in Example 1. Figure 5 The magnetic hysteresis loops of the magnetic porous Co-NC material prepared in Example 1 before and after adsorption of nanoplastics are shown. Figure 6 The infrared spectra of the magnetic porous Co-NC material prepared in Example 1 before and after adsorption of nanoplastics are shown. Figure 7 X-ray photoelectron spectra of different elements adsorbed onto nanoplastics in the magnetic porous Co-NC material prepared in Example 1 before and after adsorption. Figure 8 The adsorption efficiency of the magnetic porous Co-NC material prepared in Example 1 for nanoplastics and the zeta potential diagrams of the two materials under different pH conditions. Figure 9 The graph shows the zeta potential-removal efficiency of aggregates formed by the adsorption of magnetic porous Co-NC nanoplastics at different pH levels by the magnetic porous Co-NC nanoplastics prepared in Example 1. Figure 10 Adsorption efficiency of magnetic porous Co-NC material prepared in Example 1 for nanoplastics in the presence of different competing ions; Figure 11 The graph shows the efficiency of the magnetic porous Co-NC adsorbent prepared in Example 1 for multiple cycles of adsorption on nanoplastics. Figure 12 The kinetic adsorption curve of polystyrene nanoplastics on the magnetic porous Co-NC prepared in Example 1 is shown. Figure 13 The isothermal adsorption curve of the magnetic porous Co-NC material prepared in Example 1 on polystyrene nanoplastics is shown. Detailed Implementation

[0018] The present invention will be further illustrated by the following embodiments. It should be understood that the following embodiments are for illustrative purposes only and are not intended to limit the present invention.

[0019] First, an exemplary method for preparing the magnetic porous Co-NC material provided by the present invention is described. The preparation method may include the following steps: (1) The cobalt source methanol solution was slowly added to the imidazole organic ligand methanol solution while the imidazole organic ligand methanol solution was vigorously stirred to prevent secondary nucleation of ZIF-67 nanoparticles; after the cobalt source methanol solution was completely added, the solution was stirred slowly to prevent turbulence from causing secondary nucleation of ZIF-67 nanoparticles. After centrifugation, washing and drying, ZIF-67 nanoparticles were obtained. (2) The ZIF-67 nanoparticles were placed in a tube furnace and pyrolyzed under N2 conditions. The mixture was then naturally cooled to room temperature to obtain the magnetic porous Co-NC material.

[0020] In some embodiments, in step (1), the cobalt source can be at least one of cobalt nitrate, cobalt chloride, cobalt sulfate, cobalt carbonate, cobalt iodide, cobalt bromide, cobalt fluoride and their hydrates, preferably cobalt nitrate hydrate and / or cobalt chloride hydrate; the imidazole organic ligand can be at least one of 2-methylimidazole, 4,5-imidazolium dicarboxylic acid and its derivatives, 2-methyl-4,5-imidazolium dicarboxylic acid, 2-ethyl-4,5-imidazolium dicarboxylic acid and 2-propyl-4,5-imidazolium dicarboxylic acid, preferably 2-methylimidazole.

[0021] In some embodiments, in step (1), the molar ratio of the cobalt source to the imidazole organic ligand can be 1:(1-20), preferably 1:(2-10). Controlling the molar ratio within this range is beneficial for regulating the coordination of the cobalt source and the imidazole ligand, while avoiding waste of both. If the molar ratio is too large, it will cause the ZIF-67 nanoparticles to aggregate, ultimately preventing the prepared magnetic porous Co-NC material from being fully dispersed in an aqueous environment, thus reducing its utilization efficiency. If the molar ratio is too small, it will reduce the nucleation rate during ZIF-67 crystallization, resulting in excessively large sample particles that cannot exist stably in an aqueous environment and will precipitate, thereby reducing the adsorption efficiency.

[0022] In some embodiments, in step (1), the cobalt source methanol solution is slowly added to the imidazole organic ligand methanol solution at a rate of 20-35 mL / min.

[0023] In some embodiments, in step (1), the speed of vigorous stirring can be 2000-2500 rpm, and the stirring time can be 1-24h.

[0024] In some embodiments, in step (1), the slow stirring speed can be 300-700 rpm, preferably 400-600 rpm; the slow stirring time can be 1-48 h, preferably 1-24 h, more preferably 12-24 h. By controlling the slow stirring time and speed, the coordination degree between the cobalt source and the imidazole ligand can be controlled, thereby regulating the amount and morphology of ZIF-67 generated. If the stirring speed is too fast or the stirring time is too long, it will lead to secondary nucleation of ZIF-67 and uneven size distribution; if the stirring speed is too slow or the stirring time is too short, it will lead to a sharp reduction in the particle size of ZIF-67 nanoparticles, making them difficult to separate from water even after pyrolysis.

[0025] In some embodiments, in step (1), the particle size of the ZIF-67 nanoparticles can be controlled to be in the range of 400-800 nm, and the specific surface area to be 1500-2200 m². 2 / g.

[0026] In some embodiments, in step (2), the pyrolysis temperature can be 800℃; the heating rate can be 2-10℃ / min, preferably 5-10℃ / min; the holding time can be 30-240min; and the nitrogen flow rate can be 300-400mL / min.

[0027] Among these, pyrolysis temperatures above 800℃ will further damage the crystal structure of ZIF-67, causing the hexahedral structure to break down and Co to decompose. 0 Evaporation onto the surface leads to aggregation, resulting in reduced adsorption efficiency; pyrolysis temperatures below 800℃ result in higher oxygen content in the material, and Co... 0 The content of Co-NC will decrease accordingly, and its magnetization will further decrease, making it difficult to remove Co-NC from the water environment after adsorbing nanoplastics. Moreover, it cannot generate enough lattice distortion to increase the surface potential of Co-NC, and the adsorption of nanoplastics is mainly contributed by electrostatic interaction.

[0028] The preparation method provided by this invention uses ZIF-67 as a template. Due to the large specific surface area and porous properties of ZIF-67, the magnetic porous Co-NC possesses the porous characteristics and ordered structure of ZIF-67. ZIF-67 is pyrolyzed in an N2 atmosphere. During the pyrolysis process, C atoms release Co atoms... 2+ Reduced to Co 0The magnetic properties imparted to the adsorbent facilitate its recovery and separation from water, preventing environmental pollution. Furthermore, the positive surface potential of ZIF-67 nanoparticles, coupled with the volatilization of N and O elements during pyrolysis, increases internal metal defects and the formation of more acidic sites, further elevating the surface potential. This enhances the adsorption capacity for nanoplastics with negative surface potentials through electrostatic interactions, resulting in rapid adsorption.

[0029] Furthermore, the Co-NC adsorbent mentioned in this invention adsorbs nanoplastics through electrostatic interactions, and simultaneously adsorbs nanoplastics onto Co-NC through π-π stacking and π-π electron donor interactions. After adsorption is complete, the adsorbent can be separated from the water by a magnet, avoiding secondary pollution of the water by the adsorbent. After ultrasonic washing, it can be recycled multiple times.

[0030] The magnetic porous Co-NC material obtained by the preparation method provided in this invention has extremely high specific surface area and multi-level pore structure.

[0031] The microstructures of ZIF-67 and Co-NC were analyzed using scanning electron microscopy. ZIF-67 exhibited a regular dodecahedral structure, while the pyrolyzed Co-NC showed a slightly inward shrinkage at the edges compared to ZIF-67, exhibiting a hexahedral structure. Furthermore, the particle size of Co-NC decreased, and adjacent particles tended to aggregate. This indicates that the dodecahedral structure of ZIF-67 was gradually destroyed during pyrolysis, and lattice distortion may have become severe, making it difficult to maintain the original morphology.

[0032] In some embodiments, the magnetic porous Co-NC material may have a C atom molar content of 80-88%, a Co atom molar content of 1-3%, an O atom molar content of 5-6%, and a N atom molar content of 6-7%.

[0033] In some embodiments, the magnetic porous Co-NC material can have a particle size range of 400–700 nm, an average pore size range of 1–4 nm, and a pore volume of 0.1–0.3 cm³. 3 ·g -1 The specific surface area can be 200–400 m². 2 / g, the zeta potential can be -50 to 30mV, and the magnetization can be 30 to 50 emu / g.

[0034] The magnetic porous Co-NC material provided by this invention can be applied to the adsorption of nanoplastics in water. The raw materials required for the preparation of ZIF-67 are readily available and inexpensive. The preparation of magnetic porous Co-NC is simple, and the ZIF-67 after pyrolysis has good water stability and acid and alkali resistance, which can meet the adsorption requirements of nanoplastics in complex water matrices. It can also be desorbed and reused in alkaline water.

[0035] In some embodiments, the process steps for the magnetic porous Co-NC material to adsorb nanoplastics in water can be as follows: First, the magnetic porous Co-NC material is added to polluted water containing nanoplastics to achieve adsorption equilibrium. Then, a magnet was used to separate the magnetic porous Co-NC material with adsorbed nanoplastics from the water. Finally, the magnetic porous Co-NC material adsorbing nanoplastics was desorbed by ultrasonic treatment in an alkaline water environment, thereby regenerating the magnetic porous Co-NC material and completing the adsorption of nanoplastics in polluted water by the magnetic porous Co-NC material.

[0036] In some embodiments, the pH value of the polluted water containing nanoplastics can be between 3 and 11. An excessively high pH value can cause hydroxide ions in the solution to compete with the negatively charged nanoplastics for adsorption sites on the positively charged magnetic porous Co-NC material, leading to a decrease in the material's adsorption efficiency.

[0037] In some embodiments, the Mg content in the polluted water containing nanoplastics can be controlled. 2+ Concentration ≤15mmol / L, preferably ≤5mmol / L; PO4 3- Concentration ≤10mmol / L, preferably ≤5mmol / L; SO4 2- The concentration is ≤10 mmol / L, preferably ≤5 mmol / L.

[0038] In some embodiments, the concentration of nanoplastics in the polluted water containing nanoplastics can be 0-70 mg / L, and the ratio of the magnetic porous Co-NC material to the polluted water containing nanoplastics can be 1-10 mg: 10-100 mL; preferably, the concentration of nanoplastics in the polluted water containing nanoplastics is 40 mg / L, and the ratio of the magnetic porous Co-NC material to the polluted water containing nanoplastics is 2 mg: 20 mL.

[0039] In some embodiments, the time to reach adsorption equilibrium can be 8-20 minutes, preferably 10 minutes.

[0040] In some embodiments, the pH of the ultrasonic treatment in the alkaline water environment can be 11-12, the ultrasonic power can be 32-40kHz, the duration of a single ultrasonic treatment can be 15-30 minutes, and the number of ultrasonic treatments can be 3-5.

[0041] In some embodiments, the adsorption capacity of the magnetic porous Co-NC material can be 300-400 mg / g, and the adsorption efficiency can be 50-100%.

[0042] In summary, the magnetic porous Co-NC material provided by this invention overcomes the problems of low adsorption efficiency, slow adsorption rate, difficulty in recovery, inability to be reused, and poor versatility of other adsorbents. Under the action of an external magnetic field, it can be rapidly separated from the aqueous phase, facilitating the separation and reuse of adsorbed nanoplastics and solving the problem of difficult separation after adsorption. Furthermore, it enables the recycling and reuse of the adsorbent, offering advantages such as being green, efficient, low-cost, and recyclable, making it an excellent adsorbent for removing microplastics from water.

[0043] The following examples further illustrate the present invention in detail. It should also be understood that the following examples are only for further explanation of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-essential improvements and adjustments made by those skilled in the art based on the above description of the present invention are within the scope of protection of the present invention. The specific process parameters, etc., in the following examples are merely examples within a suitable range; that is, those skilled in the art can make appropriate selections within the range based on the description herein, and are not intended to be limited to the specific values ​​in the examples below. Unless otherwise specified, the technical means used in the examples are conventional means well known to those skilled in the art.

[0044] This invention characterizes the morphology, composition, and crystal structure of materials using scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FTIR); and uses a UV-Vis spectrophotometer to measure the absorbance of the nanoplastic suspension to calculate the adsorption efficiency of magnetic porous Co-NC on nanoplastics.

[0045] Example 1

[0046] The method for preparing magnetic porous Co-NC material provided in this embodiment includes the following steps: (1) 30 mmol of cobalt nitrate hexahydrate and 264 mmol of 2-methylimidazole were added to 100 ml of methanol solvent and stirred until completely dissolved. Then, the methanol solution of cobalt nitrate hexahydrate was added slowly and evenly to the methanol solution of 2-methylimidazole. Stirring was continued for 24 h. After centrifugation, the mixture was washed three times with methanol and dried at 100 °C to obtain ZIF-67 nanoparticles. (2) The ZIF-67 nanoparticles prepared in step (1) were placed in a crucible and placed in a tube furnace. They were then pyrolyzed and reduced at 800°C for 2 hours under N2 atmosphere with a heating rate of 5°C / min. After cooling to room temperature, the magnetic porous Co-NC material (Co-NC-800) was obtained.

[0047] The crystallinity of the ZIF-67 nanoparticles and magnetic porous Co-NC prepared in Example 1 was tested using X-ray diffraction (XRD). Figure 1 (a) and (b) are the XRD patterns of ZIF-67 nanoparticles and magnetic porous Co-NC materials prepared in Example 1, respectively. Figure 1 (a) It can be seen that the ZIF-67 nanoparticles prepared in Example 1 have good crystallinity and correspond to the standard card of ZIF-67, confirming the successful synthesis of ZIF-67; from Figure 1 (b) It can be seen that the peaks of the magnetic porous Co-NC correspond to the standard card of elemental Co, indicating that the soft magnetism of the magnetic porous Co-NC originates from the soft magnetism of elemental Co.

[0048] The microstructures of the ZIF-67 nanoparticles, magnetic porous Co-NC, polystyrene nanoplastics, and magnetic porous Co-NC after adsorption of nanoplastics prepared in Example 1 were observed using scanning electron microscopy (SEM). Figure 2 (a)-(d) are SEM images of ZIF-67 nanoparticles, magnetic porous Co-NC material, polystyrene nanoplastics, and magnetic porous Co-NC material after adsorbing nanoplastics, respectively, prepared in Example 1. As can be seen from the images, ZIF-67 nanoparticles have a regular dodecahedral structure with a particle size of 500-600 nm. Compared to ZIF-67 nanoparticles, the magnetic porous Co-NC material has slightly inward-shrinking edges, basically maintaining the morphological characteristics of ZIF-67 nanoparticles, with a particle size of 400-500 nm. The polystyrene nanoplastics are uniform spherical particles with a particle size of approximately 500 nm. After adsorbing nanoplastics, the magnetic porous Co-NC material exhibits uniform spherical nanoplastic particles bonded to the surface of the magnetic porous Co-NC.

[0049] Figure 3 (a) and (b) show the water contact angles of the ZIF-67 nanoparticles and the magnetic porous Co-NC material prepared in Example 1, respectively. As can be seen from the figures, the ZIF-67 nanoparticles are hydrophobic, while the magnetic porous Co-NC material becomes hydrophilic after pyrolysis, exhibiting better dispersibility in aqueous solution, which is beneficial for the adsorption process.

[0050] Figure 4(a) and (b) show the N2 adsorption-desorption isotherms and pore size distribution of the ZIF-67 nanoparticles and magnetic porous Co-NC materials prepared in Example 1. Table 1 below shows the specific surface area (SBET), pore volume, and average pore size of the ZIF-67 nanoparticles and magnetic porous Co-NC materials prepared in Example 1:

[0051] from Figure 4 As can be seen from Table 1, the ZIF-67 nanoparticles prepared in Example 1 have a specific surface area as high as 1923.890 m². 2 / g, with an average pore size of 1.459nm. The magnetic porous Co-NC structure collapsed after pyrolysis, but still retained 327.469nm. 2 With a large specific surface area of ​​ / g and an average pore size increased to 2.864nm, the mesopore content is increased, resulting in a wider pore size distribution and higher mesopore content, which can provide more active sites and stronger adsorption for the adsorption of nanoplastics.

[0052] Figure 5 The figure shows the hysteresis loops of the magnetic porous Co-NC material prepared in Example 1 before and after adsorbing nanoplastics. As can be seen from the figure, the magnetic porous Co-NC material prepared in Example 1 has a magnetization of 40 emu / g, and still maintains a magnetization of up to 30 emu / g after adsorbing nanoplastics. This provides sufficiently strong magnetism to allow for complete separation in water using a magnet, achieving green adsorption.

[0053] Figure 6 The image shows the infrared spectra of the magnetic porous Co-NC material prepared in Example 1 before and after adsorption of nanoplastics. As can be seen from the figure, the adsorption of nanoplastics at 1515 cm⁻¹ is... -1 -1700cm -1 The broad peak is attributed to the skeletal vibration of the imidazole five-membered ring, 2531 cm⁻¹. -1 The characteristic peak can be attributed to the stretching vibration of -C=N, 3310-3655 cm⁻¹ -1 The broad peaks at these locations represent bending vibrations or intramolecular hydrogen bonds of -NH / -OH. After adsorption of nanoplastics, the spectral peaks changed significantly: firstly, new peaks appeared at 2844, 2916, and 3020 cm⁻¹. -1 The peaks at 1445 cm⁻¹ correspond to the stretching vibrations of -CH with symmetric stretching, asymmetric stretching, and aromatic -CH, respectively. -1 The peak represents the stretching vibration of the benzene ring, 696 cm⁻¹. -1The sharp peak represents the stretching vibration of the -CH group outside the benzene ring, and these newly emerging peaks confirm the successful adsorption of nanoplastics by the magnetic porous Co-NC; secondly, the absorption peak of the imidazole five-membered ring increases from 1624 cm⁻¹. -1 The red shift to the right and the slight decrease in peak intensity can be attributed to two factors: first, the π-π stacking between the five-membered ring in the magnetic porous Co-NC and the benzene ring in the polystyrene nanoplastic causes the red shift; second, the -C=C in the benzene ring acts as an electron donor, interacting with the -C=N in the five-membered ring via a π-π electron donor-acceptor interaction, leading to the change in peak intensity (2351 cm⁻¹). -1 The decrease in peak intensity is mainly due to the π-π electron donor-acceptor interaction between -C=N and -C=C in the benzene ring.

[0054] Figure 7 The X-ray photoelectron spectroscopy (XPS) spectra of the magnetic porous Co-NC material prepared in Example 1 before and after adsorption of different elements onto the nanoplastics are shown in the figures. As can be seen from the figures, the sample is mainly composed of C, N, O, and Co atoms, with Co atoms detected. 2+ and Co 0 The peak once again proves the source of magnetism in magnetic porous Co-NC.

[0055] The following section verifies the application of the magnetic porous Co-NC material prepared in Example 1 in the removal of polystyrene nanoplastics in aqueous solution.

[0056] The basic method is as follows: 2 mg of magnetic porous Co-NC is added to 20 mL of 40 mg / L nanoplastic solution, and the solution is shaken for adsorption. After adsorption is complete, the nanoplastics are separated using a magnet, and the residual nanoplastics in the suspension are detected using a UV-Vis spectrophotometer. Adsorption efficiency (R) e Calculated using the following formula: Adsorption capacity (q) e Calculated using the following formula: Where: C0 and C t V represents the initial concentration of the nanoplastic suspension and the concentration at contact time t, respectively. V (mL) is the volume of the nanoplastic suspension, and m (mg) is the amount of adsorbent used.

[0057] 1. Effect of pyrolysis temperature on the removal of nanoplastics: To obtain the optimal magnetic porous Co-NC, the effect of pyrolysis temperature on adsorption performance was investigated. Methods: Similar to the preparation method described above, the pyrolysis temperatures were changed to 700℃ and 900℃ respectively to obtain Co-NC-700 and Co-NC-900. 2 mg of each of these Co-NCs was added to 20 mL of a 40 mg / L nanoplastic solution, and adsorption was performed by shaking. After adsorption, separation was performed using a magnet, and the residual nanoplastics in the suspension were detected using a UV-Vis spectrophotometer. The adsorption efficiency is shown in Table 2 below.

[0058] 2. The influence of metal elements and adsorbent magnetism on the removal of nanoplastics: To investigate the effects of metallic elements and magnetism on the adsorption of nanoplastics, ZIFs materials were prepared by doping with zinc and cobalt sources and then subjected to pyrolysis reduction at different temperatures. Method: Similar to the preparation method described above, zinc nitrate hexahydrate and cobalt nitrate hexahydrate in molar ratios of 1:1 and 1:2 were used to synthesize ZIFs materials, named Zn:Co=1:1-ZIF and Zn:Co=1:2-ZIF, respectively. These materials were then pyrolyzed at 700℃, 800℃, and 900℃, and the resulting materials were named Zn:Co=1:1-NC-700, Zn:Co=1:1-NC-800, Zn:Co=1:1-NC-900, Zn:Co=1:2-NC-700, Zn:Co=1:2-NC-800, and Zn:Co=1:2-NC-900. Similar to the preparation method described above, cobalt nitrate hexahydrate was replaced with ferrous sulfate heptahydrate and nickel nitrate hexahydrate, respectively, and magnetic porous Fe-NC adsorbent and magnetic porous Ni-NC adsorbent were prepared in the same manner as in Example 1. Two mg of each of the eight NC materials was added to 20 mL of a 40 mg / L nanoplastic suspension, and the mixture was shaken for adsorption. After adsorption, the nanoplastics were separated using a magnet, and the residual nanoplastics in the suspension were detected using a UV-Vis spectrophotometer. The adsorption efficiency is shown in Table 2 below. Table 2 Adsorption efficiency data of different adsorbent materials for polystyrene nanoplastics Sample Name Adsorption time (minutes) Adsorbent concentration (g / L) Nanoplastic concentration (mg / L) Adsorption efficiency Magnetic porous Co-NC 10 0.1 40 95.64％ Magnetic porous Fe-NC 10 0.1 40 53.67％ Magnetic porous Ni-NC 10 0.1 40 47.53％ Co@NC 10 0.1 40 43.68％ Co-NC-700 10 0.1 40 38.30％ Co-NC-900 10 0.1 40 45.45％ Zn:Co = 1:1-NC-700 10 0.1 40 17.88％ Zn:Co = 1:1-NC-800 10 0.1 40 37.97％ Zn:Co = 1:1-NC-900 10 0.1 40 27.45％ Zn:Co = 1:2-NC-700 10 0.1 40 22.83％ Zn:Co = 1:2-NC-800 10 0.1 40 44.22％ Zn:Co = 1:2-NC-900 10 0.1 40 31.53％

[0059] As can be seen from Table 2, Co-NC-900 obtained by pyrolysis at higher temperatures has higher yields due to the presence of Co. 0The aggregation phenomenon caused by evaporation onto the surface leads to a decrease in the adsorption efficiency of nanoplastics to 45.45%, while the adsorption efficiency of Co-NC-700 obtained by pyrolysis at 700℃ is only 38.30% due to its low surface potential. For Zn:Co-NC, the zeta potential may be significantly reduced, even becoming negative, due to the pyrolysis and volatilization of Zn during the pyrolysis process, resulting in electrostatic repulsion with nanoplastics and affecting the adsorption process. The adsorption efficiency of Fe and Ni-CN for nanoplastics is also much lower than that of Co-NC under the same conditions, possibly because Fe and Ni-CN obtained at 800℃ do not exhibit high zeta potential and magnetization.

[0060] 3. The effect of solution pH on the removal of nanoplastics: pH value affects the surface charge of the adsorbent and nanoplastics in the aqueous solution, and is one of the key factors affecting the removal process. Method: 2 mg of magnetic porous Co-NC was added to 20 mL of 40 mg / L nanoplastic solution. The pH value of the solution was changed to 3, 5, 7, 9, and 11, and adsorption was carried out by shaking. After adsorption was completed, separation was performed using a magnet. The residual nanoplastics in the suspension were detected by UV-Vis spectrophotometer.

[0061] Figure 8 The graphs show the adsorption efficiency of the magnetic porous Co-NC material prepared in Example 1 for nanoplastics and their zeta potentials under different pH conditions. PS represents polystyrene. The graphs show that the adsorption efficiency is higher in neutral and weakly acidic environments, and the adsorption capacity decreases to some extent with increasing pH. This is mainly because, under alkaline conditions, hydroxide ions in the solution compete with the negatively charged nanoplastics for adsorption sites on the positively charged magnetic porous Co-NC, indicating that electrostatic interaction is an important mechanism for the adsorption of nanoplastics by the magnetic porous Co-NC.

[0062] Figure 9 The graph shows the correlation between the zeta potential and removal efficiency of the magnetic porous Co-NC nanoplastics prepared in Example 1, which adsorbed onto aggregates formed at different pH values. As can be seen from the graph, the correlation coefficient R... 2 The value of 0.96 further demonstrates that electrostatic interaction is an important mechanism for the adsorption of magnetic porous Co-NC nanoplastics.

[0063] 4. The effect of the types of competing ions in the solution on the removal of nanoplastics: Competing ions significantly affect the adsorption efficiency of magnetic porous Co-NC for nanoplastics, making it necessary to investigate the influence of the types of competing ions on adsorption. Methods: 2 mg of magnetic porous Co-NC was added to 20 mL of a 40 mg / L nanoplastic solution. Calcium chloride, magnesium chloride, sodium chloride, and potassium chloride were added to the aqueous solution to investigate the effect of cations on adsorption, while sodium chloride, sodium nitrate, sodium sulfate, and sodium phosphate were added to investigate the effect of anions on adsorption. The concentration was 5 mmol / L. Adsorption was performed by shaking. After adsorption, separation was performed using a magnet. The residual nanoplastics in the suspension were detected using a UV-Vis spectrophotometer.

[0064] Figure 10 The graph shows the adsorption efficiency of the magnetic porous Co-NC material prepared in Example 1 for nanoplastics in the presence of different competing ions. It can be seen from the graph that for coexisting cations, Mg... 2+ The adsorption efficiency of nanoplastics was significantly affected, causing a 17.60% decrease in the adsorption efficiency of Co-NC for nanoplastics, while Ca... 2+ Na + and K + The presence of [a specific substance] has little and almost the same impact on the removal efficiency of nanoplastics, both remaining around 8.92±1%, which may be due to Cl [a specific substance]. - The effects caused; the degree to which coexisting anions inhibit the adsorption capacity of nanoplastics is: Cl - (9.92%) <NO3 - (19.21%) <PO4 3- (27.14%) <SO4 2- (29.59%), PO4 3- and SO4 2- The presence of [a substance] exhibits a significant antagonistic effect on the removal of NPs, which is due to the relatively high charge density affecting the adsorption caused by electrostatic interactions.

[0065] 5. The recyclability of magnetic porous Co-NC for adsorbing nanoplastics: The reusability of adsorbents can reduce costs in practical applications. Therefore, a series of adsorption-desorption experiments were conducted to evaluate the adsorption effect of the adsorbent on nanoplastics. Method: The adsorbed magnetic porous Co-NC was sonicated in alkaline water at pH 11 for 20 min, washed repeatedly three times, dried, and then the adsorption experiment was repeated.

[0066] Figure 11The graph shows the adsorption efficiency of the magnetic porous Co-NC adsorbent prepared in Example 1 on nanoplastics after multiple cycles. As can be seen from the graph, the adsorption efficiency of the nanoplastics increased from 95.53% to 100% after the first cycle, and the removal capacity of the nanoplastics remained at 100% even after the fourth cycle. This is likely because the unstable carbon and Co elements on the surface of the Co-NC were washed away by the alkali, increasing its specific surface area and the number of adsorption sites.

[0067] 6. Adsorption kinetics Adsorption rate is an important indicator for evaluating adsorbent performance and understanding the adsorption process. To investigate the rate and mechanism of adsorption of nanoplastics by magnetic porous Co-NC, adsorption was carried out at different time points. Two kinetic models (pseudo-first-order kinetic model and pseudo-second-order kinetic model) were used to fit the experimental results.

[0068] Figure 12 The image shows the kinetic adsorption curve of polystyrene nanoplastics on the magnetic porous Co-NC nanoparticles prepared in Example 1. Table 3 shows the kinetic adsorption data of polystyrene nanoplastics on the magnetic porous Co-NC material prepared in Example 1: from Figure 12 As shown in Table 3, the adsorption capacity of the magnetic porous Co-NC for the nanoplastics increases sharply within the first 2 minutes, reaching adsorption equilibrium within 10 minutes. The adsorption kinetic parameters conform to the pseudo-first-order kinetic model, R0. 2 The value >0.9999 indicates that the error between the calculated and actual values ​​is not significant, thus confirming that the reaction is a first-order reaction. Furthermore, the k value is as high as 1.4587, which is consistent with the transient adsorption mechanism of the adsorbent.

[0069] 7. Adsorption isotherm The saturated adsorption capacity of magnetic porous Co-NC was evaluated by its removal capability from a 20 mL nanoplastic suspension. The adsorption performance of magnetic porous Co-NC for nanoplastics was estimated using the Freundlich and Langmuir isotherm models.

[0070] Figure 13 The table below shows the isothermal adsorption curves of the magnetic porous Co-NC material prepared in Example 1 on polystyrene nanoplastics. Table 4 below shows the isothermal adsorption data of the magnetic porous Co-NC material prepared in Example 1 on polystyrene nanoplastics: from Figure 13As shown in Table 4, compared to the Freundlich model, the adsorption of Co-NC is more consistent with the Langmuir adsorption isotherm model, with a correlation coefficient R0. 2 At around 0.84, this suggests that Co-NC adsorption is more likely to be heterogeneous multilayer adsorption than monolayer adsorption as indicated by the Langmuir adsorption isotherm model.

[0071] 8. The interaction mechanism between magnetic porous Co-NC and nanoplastics: This paper investigates the mechanism of adsorption of polystyrene nanoplastics by magnetic porous Co-NC. At different pH values, the aggregates formed after adsorption of the magnetic porous Co-NC and nanoplastics showed a very strong positive correlation between their zeta potential and removal efficiency, with a correlation coefficient R0. 2 The high electrostatic potential (EMP) of 0.96 indicates that electrostatic interaction is the primary force driving the adsorption of both compounds. Furthermore, the significant influence of interfering ions and pH on the adsorption of nanoplastics further confirms the strong electrostatic attraction between them. At pH 11, both compounds exhibit zeta potentials below -40 mV, indicating very strong electrostatic repulsion, yet still possess a high adsorption capacity of 200 mg / g. This confirms that other mechanisms besides electrostatic attraction are involved in the nanoplastic removal process. To further characterize the interaction mechanism between the complex and the nanoplastics, FTIR and XPS spectroscopic analysis of Co-NC before and after nanoplastic adsorption revealed key insights into weak interactions. The results show that the adsorption process also involves weak interactions such as π-π stacking and π-π electron donor-acceptor interactions. Additionally, mild van der Waals forces also promote the adsorption process.

[0072] Comparative Example 1

[0073] The preparation method of the magnetic porous Co-NC material provided in this comparative example includes the following steps: ZIF-67 was synthesized using cobalt nitrate hexahydrate, 2-methylimidazole, and methanol in a molar ratio of 1:4:500, with a stirring speed of 100-200 rpm and a stirring time of 20 h. Then, using ZIF-67 as a template, the mixture was heated to 300 °C in a N2 atmosphere and held for 1 h, followed by further heating to 800 °C and holding for 2 h, and then naturally cooled to obtain Co@NC.

[0074] In this comparative example, the stirring speed of 100-200 rpm resulted in slight agglomeration of ZIF-67 nanoparticles, and the synthesized ZIF-67 nanoparticles were relatively large; furthermore, the holding temperature of 300℃ during pyrolysis caused Co... 0 A certain degree of aggregation occurs on the surface of Co@NC, leading to a more obvious uneven distribution of surface potential. This is observed in 20 ml of 40 mg·L⁻¹ solution. -1The adsorption efficiency of polystyrene nanoplastics was only 43.68%.

[0075] Although the present invention has been described in detail through the preferred embodiments above, it should be understood that the above description should not be considered as a limitation of the present invention. Various modifications and substitutions to the present invention will be apparent to those skilled in the art after reading the above description. Therefore, the scope of protection of the present invention should be defined by the appended claims.

Claims

1. A method for preparing a magnetic porous Co-NC material, characterized in that, The preparation method comprises the following steps: (1) slowly adding a cobalt source methanol solution into an imidazole organic ligand methanol solution, while stirring the imidazole organic ligand methanol solution vigorously to prevent secondary nucleation of ZIF-67 nanoparticles; after complete addition, slowly stirring again to prevent turbulent flow from causing secondary nucleation of ZIF-67 nanoparticles, and then centrifuging, washing, and drying to obtain ZIF-67 nanoparticles; (2) pyrolyzing the ZIF-67 nanoparticles under N2, and naturally cooling to room temperature to obtain the magnetic porous Co-NC material.

2. The production method according to claim 1, characterized by, In step (1), the cobalt source is at least one of cobalt nitrate, cobalt chloride, cobalt sulfate, cobalt carbonate, cobalt iodide, cobalt bromide, cobalt fluoride, and hydrates thereof, preferably cobalt nitrate hydrate and / or cobalt chloride hydrate; and the imidazole organic ligand is at least one of 2-methylimidazole, 4,5-imidazole dicarboxylic acid and derivatives thereof, 2-methyl-4,5-imidazole dicarboxylic acid, 2-ethyl-4,5-imidazole dicarboxylic acid, and 2-propyl-4,5-imidazole dicarboxylic acid, preferably 2-methylimidazole.

3. The production method according to claim 1 or 2, characterized by, In step (1), the molar ratio of the cobalt source to the imidazole organic ligand is 1:(1-20), preferably 1:(2-10).

4. The production method according to any one of claims 1 to 3, characterized by, In step (2), the pyrolysis temperature is 800℃; the heating rate is 2-10℃ / min, preferably 5-10℃ / min; the holding time is 30-240 min; and the nitrogen flow rate is 300-400 mL / min.

5. A magnetic porous Co-NC material obtained by the preparation method according to any one of claims 1-4.

6. Use of the magnetic porous Co-NC material according to claim 5 in adsorption of nano-plastics in a water body.

7. Use according to claim 6, characterized in that, The use comprises the following steps: First, adding the magnetic porous Co-NC material into a contaminated water body containing nano-plastics for adsorption to reach adsorption equilibrium; Then, using a magnet to separate the magnetic porous Co-NC material adsorbed with nano-plastics from the water body; Finally, performing ultrasonic treatment in an alkaline water environment to desorb the magnetic porous Co-NC material adsorbed with nano-plastics, regenerate the magnetic porous Co-NC material, and complete the adsorption of nano-plastics in the contaminated water body by the magnetic porous Co-NC material.

8. Use according to claim 7, characterized in that, The pH value of the contaminated water body containing nano-plastics is 3-11; Controlling Mg in a contaminated water body containing nano-plastic 2+ concentration < 15 mmol / L, preferably < 5 mmol / L; PO4 3- concentration < 10 mmol / L, preferably < 5 mmol / L; SO4 2- concentration < 10 mmol / L, preferably < 5 mmol / L.

9. Use according to claim 7 or 8, characterized in that, The concentration of nano-plastics in the contaminated water body containing nano-plastics is 0-70 mg / L, and the dosage ratio of the magnetic porous Co-NC material to the contaminated water body containing nano-plastics is 1-10 mg:10-100 mL; The time for reaching adsorption equilibrium is 8-20 minutes, preferably 10 minutes.

10. The use according to any one of claims 7-9, wherein the pH value of the alkaline water environment for ultrasonic treatment is 11-12, the ultrasonic power is 32-40 kHz, the time for single ultrasonic treatment is 15-30 minutes, and the number of ultrasonic treatments is 3-5 times.

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