An iron-based nanocomposite material, its preparation method and application

Abstract

This invention provides a method for preparing iron-based nanocomposite materials, comprising the following steps: mixing ferrous salt, solvent, and spirulina, soaking the mixture, and separating the soaked spirulina; then mixing the soaked spirulina sequentially with solvent, dispersant, and reducing agent to carry out a reduction reaction, thereby obtaining the iron-based nanocomposite material. This invention synthesizes spirulina-supported nano-zero-valent iron composite materials using a liquid-phase reduction method after soaking. By utilizing spirulina as a matrix to disperse nano-zero-valent iron, the aggregation of nano-zero-valent iron is avoided, thus further improving the adsorption performance of nano-zero-valent iron for heavy metal ions. In removing heavy metal ions, spirulina can adsorb heavy metal ions in wastewater, and nano-zero-valent iron removes heavy metal pollutants from wastewater through adsorption, chemical complexation, precipitation, and redox reactions, thereby achieving efficient removal of heavy metal ions.

Description

Technical Field

[0001] This invention belongs to the field of bio-iron-based nanomaterials technology, specifically relating to an iron-based nanocomposite material, its preparation method, and its application. Background Technology

[0002] With the increasing severity of heavy metal pollution, the removal and treatment of heavy metals in wastewater has become an urgent matter.

[0003] Nano-zero-valent iron (nZVI), as a novel environmental remediation material, possesses a unique core-shell structure and advantages such as large specific surface area, low toxicity, low cost, and ease of preparation. It can remove heavy metals from water through chemical reduction and adsorption-precipitation, attracting widespread attention in the field of water environment remediation. However, nZVI suffers from problems such as easy aggregation, passivation, and loss in water, as well as poor electron selectivity, limiting its application in in-situ remediation and storage. To address these issues, resins and silica are commonly used to immobilize nZVI to improve its reaction efficiency; however, the resulting composite materials still exhibit poor heavy metal removal capabilities from wastewater, failing to meet practical application requirements. Therefore, improving the adsorption performance of nano-zero-valent iron for heavy metal ions has become a pressing problem in this field. Summary of the Invention

[0004] The purpose of this invention is to provide an iron-based nanocomposite material, its preparation method, and its applications. The iron-based nanocomposite material prepared by the method provided by this invention can rapidly and efficiently remove heavy metals from pesticide wastewater.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0006] This invention provides a method for preparing iron-based nanocomposite materials, comprising the following steps:

[0007] (1) Mix ferrous salt, solvent and spirulina, soak and separate to obtain soaked spirulina;

[0008] (2) The soaked spirulina obtained in step (1) is mixed with solvent, dispersant and reducing agent in sequence to carry out reduction reaction to obtain iron-based nanocomposite material.

[0009] Preferably, the divalent ferric salt in step (1) is ferrous sulfate heptahydrate.

[0010] Preferably, in step (1), the mass ratio of ferrous salt to spirulina is (130-150):1.

[0011] Preferably, the soaking time in step (1) is 12 to 24 hours, and the soaking temperature is 25 to 28°C.

[0012] Preferably, the dispersant in step (2) is polyethylene glycol.

[0013] Preferably, the reducing agent in step (2) is an aqueous solution of NaBH4.

[0014] Preferably, the mass ratio of Spirulina to NaBH4 in step (1) is 1:(3-4).

[0015] Preferably, the molar ratio of the ferrous salt in step (1) to the reducing agent in step (2) is 1:(2-3).

[0016] The present invention also provides an iron-based nanocomposite material prepared by the preparation method described in the above technical solution.

[0017] The present invention also provides the application of the iron-based nanocomposite material described in the above technical solution in wastewater treatment.

[0018] This invention provides a method for preparing iron-based nanocomposite materials, comprising the following steps: mixing ferrous salt, solvent, and spirulina, soaking the mixture, and separating the soaked spirulina; then mixing the soaked spirulina sequentially with solvent, dispersant, and reducing agent to carry out a reduction reaction, thereby obtaining the iron-based nanocomposite material. This invention synthesizes spirulina-supported nano-zero-valent iron composite materials using a liquid-phase reduction method after soaking. By utilizing spirulina as a matrix to disperse nano-zero-valent iron, the aggregation of nano-zero-valent iron is avoided, thus further improving the adsorption performance of nano-zero-valent iron for heavy metal ions. In removing heavy metal ions, spirulina can adsorb heavy metal ions in wastewater, and nano-zero-valent iron removes heavy metal pollutants from wastewater through adsorption, chemical complexation, precipitation, and redox reactions, thereby achieving efficient removal of heavy metal ions. The results of the examples show that the iron-based nanocomposite material prepared by the preparation method of the present invention has a higher removal rate under dynamic conditions than under static conditions (2 to 8 times); the optimal pH for the removal of Cd(II) is 6.5, and the optimal pH for the removal of Zn(II) and Cu(II) is 8; the Sp.@nZVI before and after adsorption was characterized by XPS, and it was found that the material removes Cd(II), Zn(II) and Cu(II) mainly through electrostatic adsorption, complexation, chemical precipitation and reduction. Attached Figure Description

[0019] Figure 1 This is a process flow diagram for preparing iron-based nanocomposites in Example 1;

[0020] Figure 2 These are scanning electron microscope (SEM) images of the iron-based nanocomposite material prepared in Example 1 at different sizes.

[0021] Figure 3The elemental mapping diagram of the iron-based nanocomposite material prepared in Example 1 is shown below.

[0022] Figure 4 The XRD diffraction patterns of Spirulina and the prepared iron-based nanocomposite material are shown in Example 1.

[0023] Figure 5 The FTIR spectra of Spirulina and the prepared iron-based nanocomposite material are shown in Example 1.

[0024] Figure 6 The hysteresis loop of the iron-based nanocomposite material prepared in Example 1;

[0025] Figure 7 The nitrogen adsorption / desorption diagram of the iron-based nanocomposite material prepared in Example 1 is shown.

[0026] Figure 8 This is a schematic diagram of the movement of the iron-based nanocomposite material prepared in Example 1 under a gradient magnetic field;

[0027] Figure 9 This is a schematic diagram of the movement of the iron-based nanocomposite material prepared in Example 1 under a gradient magnetic field;

[0028] Figure 10 The diagram shows the directional motion of the iron-based nanocomposite material prepared in Example 1 in the upward, downward, leftward, and rightward directions.

[0029] Figure 11 To manipulate the iron-based nanocomposite material prepared in Example 1 to move along a predetermined route;

[0030] Figure 12 This is a schematic diagram of the iron-based nanocomposite material prepared in Example 1 being driven by a rotating magnetic field;

[0031] Figure 13 The motion diagrams of the iron-based nanocomposite material prepared in Example 1 are shown, including planar rotation, spiral advance, upright flipping, and conical rotation.

[0032] Figure 14 The bar chart shows the removal rate and adsorption amount of Cd(II), Zn(II) and Cu(II) by Spirulina in Example 1;

[0033] Figure 15 The curves showing the removal rate and adsorption capacity of Cd(II) by the iron-based nanocomposite material prepared in Example 1 are shown.

[0034] Figure 16 The curves showing the removal rate and adsorption capacity of Zn(II) by the iron-based nanocomposite material prepared in Example 1 are shown.

[0035] Figure 17 The curves showing the removal rate and adsorption capacity of Cu(II) by the iron-based nanocomposite material prepared in Example 1 are shown.

[0036] Figure 18 The removal rates of Cd(II), Zn(II) and Cu(II) by the iron-based nanocomposite material prepared in Example 1 under different conditions;

[0037] Figure 19 The adsorption kinetics curves of Cd(II), Zn(II) and Cu(II) for the iron-based nanocomposite material prepared in Example 1 are shown.

[0038] Figure 20 The adsorption isotherms of Cd(II), Zn(II) and Cu(II) on the iron-based nanocomposite material prepared in Example 1 are shown.

[0039] Figure 21 The XPS spectrum of the iron-based nanocomposite material prepared in Example 1 is shown below.

[0040] Figure 22 The XPS spectrum of the iron-based nanocomposite material prepared in Example 1 after adsorption of Cd(II) is shown.

[0041] Figure 23 The image shows a SEM image of the iron-based nanocomposite material prepared in Example 1 after adsorption of Cd(II).

[0042] Figure 24 The XPS spectrum of the iron-based nanocomposite material prepared in Example 1 after adsorption of Zn(II) is shown.

[0043] Figure 25 The image shows the XPS spectrum of the iron-based nanocomposite material prepared in Example 1 after adsorption of Cu(II).

[0044] Figure 26 The diagram shows the removal mechanism of Cd(II), Zn(II) and Cu(II) by the iron-based nanocomposite material prepared in Example 1;

[0045] Figure 27 The removal rates of Cd(II), Zn(II) and Cu(II) by the iron-based nanocomposite material prepared in Example 1 after 4 cycles of recycling;

[0046] Figure 28 The removal rates of Cd(II), Zn(II) and Cu(II) in soil suspension by the iron-based nanocomposite material prepared in Example 1 are shown.

[0047] Figure 29 The images show the effects of treating soil suspension with the iron-based nanocomposite material prepared in Example 1 before and after treatment. Detailed Implementation

[0048] This invention provides a method for preparing iron-based nanocomposite materials, comprising the following steps:

[0049] (1) Mix ferrous salt, solvent and spirulina, soak and separate to obtain soaked spirulina;

[0050] (2) The soaked spirulina obtained in step (1) is mixed with solvent, dispersant and reducing agent in sequence to carry out reduction reaction to obtain iron-based nanocomposite material.

[0051] This invention involves mixing ferrous salts, a solvent, and spirulina, soaking the mixture, and then separating the soaked spirulina. By mixing the ferrous salts with spirulina and removing the solvent, this invention avoids the influence of free ferrous ions and other impurities in the solvent on subsequent operations.

[0052] In this invention, the divalent iron salt is preferably ferrous sulfate heptahydrate. The use of ferrous sulfate heptahydrate in the preparation of nano-zero ferrous iron results in fewer impurities in the synthesized nano-zero ferrous iron.

[0053] In this invention, the solvent is preferably ultrapure water. Using ultrapure water avoids the influence of other impurities on subsequent operations.

[0054] In this invention, the spirulina is preferably Spirulina platensis; the spirulina is preferably produced by Guangzhou Baiyi Biotechnology Co., Ltd.

[0055] In this invention, the spirulina preferably undergoes pretreatment before use. Pretreatment of the spirulina allows it to maintain its fixed helical structure, preventing damage during subsequent loading processes. Simultaneously, acid treatment of the spirulina cells improves their permeability, which is more conducive to the subsequent loading of nano-zero valent iron.

[0056] In this invention, the preferred pretreatment operation is:

[0057] 1) Spirulina was pretreated by mixing it with an aqueous solution of glutaraldehyde, and then centrifuged and washed to obtain pretreated spirulina;

[0058] 2) Mix the pretreated spirulina obtained in step 1) with an acidic solution, soak it, filter it, and then wash and dry it in sequence to obtain the pretreated spirulina.

[0059] In this invention, spirulina is preferably pretreated by mixing it with an aqueous solution of glutaraldehyde, followed by centrifugation and washing to obtain pretreated spirulina. Pretreatment of spirulina with an aqueous solution of glutaraldehyde in this invention allows the spirulina to maintain its fixed helical structure, preventing damage to the helical structure during subsequent loading processes.

[0060] In this invention, the preferred mass concentration of the glutaraldehyde aqueous solution is 2.5%. This invention does not impose any particular limitation on the amount of the glutaraldehyde aqueous solution used; any amount well-known to those skilled in the art can be used. This invention also does not impose any particular limitation on the mixing operation of the spirulina and the glutaraldehyde aqueous solution; any technical solution for preparing the mixture well-known to those skilled in the art can be used.

[0061] In this invention, the pretreatment time is preferably 8 to 12 hours; the pretreatment temperature is preferably 4°C.

[0062] The present invention does not impose any special limitations on the operation of centrifugal washing; any operation known to those skilled in the art can be used.

[0063] After obtaining the pretreated spirulina, the present invention preferably mixes the pretreated spirulina with an acidic solution, soaks it, filters it, and then washes and dries it in sequence to obtain the pretreated spirulina.

[0064] In this invention, the acidic solution is preferably a sulfuric acid solution; the concentration of the acidic solution is preferably 5 mmol / L. This invention does not have a specific limitation on the amount of acidic solution used, as long as it is sufficient to completely soak the spirulina.

[0065] In this invention, the soaking temperature is preferably 25–28°C; the soaking time is preferably 20–30 minutes; and the soaking is preferably carried out under stirring conditions. This invention does not impose any special limitations on the stirring operation; any stirring operation well-known to those skilled in the art can be used.

[0066] The present invention does not impose any special limitations on the filtration and washing operations; operations familiar to those skilled in the art can be used.

[0067] In this invention, the drying is preferably freeze-drying; the drying time is preferably 12 to 24 hours.

[0068] In this invention, the preferred method for mixing the ferrous salt, solvent, and spirulina is to mix the ferrous salt with the solvent and then add the spirulina.

[0069] The present invention does not have a special limitation on the amount of solvent used, as long as the ferrous salt is completely dissolved.

[0070] In this invention, the preferred mass ratio of the ferrous salt to spirulina is (130-150):1, more preferably 139:1. This invention ensures the ferrous salt loading in spirulina by controlling the ratio of ferrous salt to spirulina.

[0071] In this invention, the mixing of the ferrous salt and the solvent is preferably carried out under ultrasonic conditions. The invention does not impose any particular limitations on the ultrasonic operation, as long as the ferrous salt is completely dissolved.

[0072] In this invention, the soaking time is preferably 12 to 24 hours; the soaking temperature is preferably 25 to 28°C.

[0073] The present invention does not impose any special limitations on the separation operation; any separation operation known to those skilled in the art can be used.

[0074] After obtaining the soaked spirulina, the present invention mixes the soaked spirulina with a solvent, a dispersant and a reducing agent in sequence to carry out a reduction reaction, thereby obtaining an iron-based nanocomposite material.

[0075] In this invention, the solvent is preferably an aqueous solution of ethanol; the volume ratio of ethanol to ultrapure water in the aqueous solution is preferably 3:7. This invention does not impose any special limitation on the amount of solvent used; it can be determined based on common sense. The use of ethanol in this invention can slow down the oxidation rate of nano-zero valent iron.

[0076] In this invention, the solvent is preferably aerated with nitrogen before use. The invention does not impose any particular limitation on the operation of aeration with nitrogen; any operation well-known to those skilled in the art can be used. This invention removes oxygen from the solvent, allowing for the preparation of nano-zero-valent iron through a reduction reaction under anaerobic conditions, thus slowing down the oxidation of the nano-zero-valent iron.

[0077] In this invention, the dispersant is preferably polyethylene glycol; the reducing agent is preferably an aqueous solution of NaBH4; the mass ratio of spirulina to NaBH4 is preferably 1:(3-4); and the molar ratio of the ferrous salt to the reducing agent is preferably 1:(2-3). This invention does not impose any particular limitation on the concentration of the NaBH4 aqueous solution, as long as it ensures complete dissolution of NaBH4.

[0078] The present invention does not have any special limitations on the operation of the spirulina with the solvent and dispersant in sequence, as long as the raw materials are mixed evenly.

[0079] In this invention, the reducing agent is preferably added dropwise. There is no particular limitation on the rate of addition; any dropwise addition method well-known to those skilled in the art can be used. The dropwise addition of the reducing agent in this invention allows ferrous sulfate heptahydrate to be slowly reduced to nano-sized zero-valent iron, resulting in a more complete reduction reaction.

[0080] In this invention, the reduction reaction time is preferably 20 to 40 minutes, more preferably 30 minutes; the reduction reaction temperature is preferably room temperature.

[0081] In this invention, the reduction reaction is preferably carried out under stirring conditions. The stirring operation is not particularly limited in this invention; any stirring operation well-known to those skilled in the art can be used.

[0082] After the reduction reaction is completed, the products obtained from the reduction reaction are preferably separated, washed and dried in sequence to obtain iron-based nanocomposite materials.

[0083] In this invention, the separation is preferably performed using a magnet. The present invention does not impose any particular limitation on the separation operation; any operation well-known to those skilled in the art can be used.

[0084] In this invention, the washing is preferably performed quickly with ethanol. This invention does not impose any particular limitations on the number of washes or the operation; common sense can be used to determine the appropriate method. The rapid use of ethanol in this invention can slow down the oxidation rate of nano-zero valent iron in air.

[0085] In this invention, the drying process is preferably freeze-drying. This invention does not impose any particular limitations on the freeze-drying operation; drying until no moisture remains is required.

[0086] The present invention does not have any special limitation on the source of the above-mentioned raw materials. Commercially available products or well-known preparation methods known to those skilled in the art can be used for preparation.

[0087] This invention synthesizes a spirulina-supported nano-zero-valent iron composite material using a liquid-phase reduction method after soaking. By using spirulina as a matrix to disperse nano-zero-valent iron, the aggregation of nano-zero-valent iron is avoided, thereby further improving the adsorption performance of nano-zero-valent iron for heavy metal ions. When removing heavy metal ions, spirulina can adsorb heavy metal ions in wastewater, and nano-zero-valent iron removes heavy metal pollutants in wastewater through adsorption, chemical complexation, precipitation, and redox reactions, thus achieving efficient removal of heavy metal ions.

[0088] This invention uses Spirulina as a biological template to synthesize Spirulina-supported nano-zero-valent iron (Sp.@nZVI) composite material through a liquid-phase reduction method after soaking. It has excellent removal capabilities for three heavy metal ions: Cd(II), Zn(II) and Cu(II), providing theoretical support for the future use of bio-iron-based nanomaterials to remove pesticide wastewater.

[0089] The present invention also provides an iron-based nanocomposite material prepared by the preparation method described in the above technical solution.

[0090] The iron-based nanocomposite material provided by this invention has excellent adsorption properties and can achieve efficient removal of heavy metal ions.

[0091] The present invention also provides the application of the iron-based nanocomposite material described in the above technical solution in wastewater treatment.

[0092] The present invention does not impose any special limitations on the application of the iron-based nanocomposite material in wastewater treatment; any application operation known to those skilled in the art can be used.

[0093] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0094] All reagents used in the experiment were of analytical grade and purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.; Spirulina platensis was purchased from Guangzhou Baiyi Biotechnology Co., Ltd., and is designated as Sp.

[0095] Spirulina was cultured using laboratory-prepared Zarrouk medium. The medium was dispensed into Erlenmeyer flasks (250 mL), and after adding Spirulina, the flasks were placed in an incubator at 28°C for 7 days of growth. The optimal pH for growth was 8–10. Aeration was performed, and the medium was sterilized.

[0096] Zarrouk's medium (g / L) formula is: sodium bicarbonate (16.80g); potassium dihydrogen phosphate (0.50g); sodium nitrate (2.50g); sodium chloride (1.00g); magnesium sulfate (0.20g); ferric sulfate (0.01g); potassium sulfate (1.00g); calcium chloride monohydrate (0.04g); EDTA (0.08g), adjusted to pH between 8 and 10.

[0097] Example 1

[0098] A method for preparing an iron-based nanocomposite material comprises the following steps:

[0099] (1) Spirulina extracted from the culture medium by centrifugation was washed three times with deionized water, pretreated with glutaraldehyde solution at 4℃ for 12h, washed by centrifugation, soaked in 5mM dilute sulfuric acid at room temperature, placed on a magnetic stirrer and stirred vigorously for 30min, then filtered, washed with deionized water, and dried with a freeze dryer for 12h to obtain pretreated spirulina.

[0100] (2) Weigh 6.95g FeSO4·7H2O and dissolve it in 50mL of ultrapure water. After ultrasonic oscillation, add 0.05g of the pretreated spirulina obtained in step (1), place it in a shaker and soak it at room temperature for 24h, then centrifuge to obtain the soaked spirulina.

[0101] (3) Measure 70 mL of ultrapure water and 30 mL of ethanol and add them to a 500 mL three-necked flask. Purge with nitrogen and stir with an electric stirrer for 15 min. Then add the soaked spirulina obtained in step (2) to the three-necked flask, and then add 0.2 g of polyethylene glycol. Stir for 30 min. Then add 10 mL of prepared NaBH4 aqueous solution dropwise with a pipette. Under stirring conditions, carry out the reduction reaction for 30 min. After the reaction is completed, collect the reaction product with a large magnet, and then wash it three times with C2H5OH. Then place it in a freeze dryer and dry for 24 h to obtain a black solid powder iron-based nanocomposite material, denoted as Sp.@nZVI; wherein, the mass of NaBH4 in the NaBH4 aqueous solution is 0.06 g.

[0102] The process flow diagram for preparing iron-based nanocomposites in Example 1 is shown below. Figure 1 As shown.

[0103] from Figure 1 As can be seen, this invention uses Spirulina as a matrix and prepares iron-based nanocomposite materials through liquid-phase reduction.

[0104] Characterization of Sp.@nZVI prepared in Example 1

[0105] The morphology and elemental composition of Sp.@nZVI were characterized by scanning electron microscopy (SEM) using an energy-dispersive spectroscopy (EDS) instrument. The crystal structure was analyzed using X-ray powder diffraction (XRD) with a Cu target radiation source (λ = 0.15418 nm) and a scanning angle of 10–90° (9 kW). The structure and chemical bonds were characterized using Fourier transform infrared spectroscopy (FTIR). Hysteresis loops were measured using a vibrating sample magnetometer (VSM). Analysis was performed using an automated surface area and pore size analyzer (Tristar II 3020M, Micromeritics, USA, Brunauer-Emmett-Teller, BET) under nitrogen physical adsorption and desorption conditions at 77.2 K. The elemental composition and valence state changes before and after the reaction were analyzed using X-ray photoelectron spectroscopy (XPS).

[0106] Figure 2 The images show scanning electron microscope (SEM) images of the iron-based nanocomposite material prepared in Example 1 at different sizes. In the images, A and D are 5 μm, B is 2 μm, and C, E, and F are 1 μm. The inset of image C is a magnified view of the particles loaded on the surface of Spirulina.

[0107] from Figure 2 As can be seen, the material has a spiral structure, an uneven surface, and is covered with round particles.

[0108] Figure 3 The image shows the elemental mapping diagram of the iron-based nanocomposite material prepared in Example 1. A and B are elemental mapping diagrams, and the yellow, green and blue dots represent elements C (C diagram), O (D diagram) and Fe (E diagram), respectively. F is an EDS energy spectrum diagram.

[0109] from Figure 3 It can be seen that the material is composed of carbon, oxygen and iron.

[0110] Figure 4 The XRD diffraction patterns of Spirulina and the prepared iron-based nanocomposite material are shown in Example 1. Figure 5 The FTIR spectra of Spirulina and the prepared iron-based nanocomposite material are shown in Example 1. Figure 6 The hysteresis loop of the iron-based nanocomposite material prepared in Example 1; Figure 7 The image shows the nitrogen adsorption / desorption diagram of the iron-based nanocomposite material prepared in Example 1, with the inset showing the pore size distribution of the iron-based nanocomposite material.

[0111] from Figure 4 It can be seen that the original Spirulina is in an amorphous state, but after loading nZVI, a distinct characteristic peak (44.75) appears, which comes from the body-centered cubic (bcc) lattice structure of the iron nanoparticles, indicating that nZVI was successfully attached to Spirulina; no additional Fe peak was detected in the XRD pattern, indicating that the material did not oxidize in the short term.

[0112] from Figure 5 As can be seen, the functional groups on the material surface were clearly identified by FTIR spectroscopy. Among all materials, due to the presence of natural biological templates, similar -NH2 (1647 cm⁻¹) groups could be observed. -1 and 1542cm -1 ) and -OH (3440cm) -1 Characteristic peak; after loading nZVI, the material's response peak weakens, compared to the original Sp., 619 cm⁻¹ -1 The sharp peak transforms into a broad peak.

[0113] from Figure 6 It can be seen that when the permanent magnet approaches, the material dispersed in the fluid can be collected quickly; its saturation magnetization can reach 69.1 emu / g, indicating that it has good superparamagnetism, can be magnetically actuated and magnetically dispersed in the fluid, and has no serious aggregation phenomenon.

[0114] from Figure 7As can be seen, the composite material exhibits a typical Type V isotherm curve with a distinct H3 hysteresis loop. This is because the material surface exhibits a slit structure induced by mesopores and nanoparticles, and smaller nano-sized zero-valent iron particles are deposited on the surface of Spirulina, which greatly reduces the pore size of the composite material.

[0115] Magnetic drive of Sp.@nZVI prepared in Example 1

[0116] To test the motion performance of Sp.@nZVI, a solution containing the material was added to a chamber formed by a glass slide and a PDMS reservoir. The chamber was then placed under a gradient magnetic field and a rotating magnetic field. The motion of the Sp.@nZVI was observed and recorded in real time using a bright-field optical microscope (Olympus MX51) and a digital camera (Olympus BX51). The strength, frequency, and spatial orientation of the magnetic field could be precisely adjusted to drive the Sp.@nZVI.

[0117] Figure 8 and 9 This is a schematic diagram of the movement of the iron-based nanocomposite material prepared in Example 1 under a gradient magnetic field; Figure 10 The diagram shows the directional motion of the iron-based nanocomposite material prepared in Example 1 in the upward, downward, leftward, and rightward directions. Figure 11 The diagram shows how to manipulate the iron-based nanocomposite material prepared in Example 1 to move along a predetermined route.

[0118] from Figures 8-11 It can be seen that when a gradient magnetic field is applied vertically, the prepared Sp.@nZVI can be helically propelled, which will make it easy to guide and collect the material in polluted wastewater; Figure 8 and 9 This diagram illustrates the motion of a material under a gradient magnetic field. Under a controlled magnetic field (B = 10 mT, f = 15 Hz), the material can be directionally moved upwards, downwards, leftwards, and rightwards by controlling the field strength and frequency. Furthermore, its trajectory can be controlled according to a predetermined path. Figures 10-11 ).

[0119] Figure 12 This is a schematic diagram of the iron-based nanocomposite material prepared in Example 1 being driven by a rotating magnetic field; Figure 13 The images show the motion diagrams of the iron-based nanocomposite material prepared in Example 1, including planar rotation, spiral forward movement, upright flipping, and conical rotation. The upper left corner shows the planar rotation motion diagram, the upper right corner shows the spiral forward movement diagram, the lower left corner shows the upright flipping motion diagram, and the lower right corner shows the conical rotation motion diagram.

[0120] A triaxial Helmholtz coil system is used to generate the required rotating magnetic field for magnetic actuation. The material is dispersed in a solution and statically placed on a matrix. When a rotating magnetic field is applied in the XY plane, the material is driven to perform planar rotation, helical propulsion, vertical flipping, and conical flipping motions. Figure 13 ).

[0121] Removal performance of Sp.@nZVI prepared in Example 1 for cadmium, zinc and copper

[0122] Simulated pesticide wastewater solutions containing Cd(II), Zn(II), and Cu(II) were prepared at 1000 mg / L using CdCl2, ZnSO4·7H2O, and CuSO4·5H2O, respectively. These solutions were stored in a 4℃ refrigerator for later use. The solutions were then diluted with the prepared 1000 mg / L stock solution to the concentration required for each experiment.

[0123] The ability of Sp.,nZVI and Sp.@nZVI to remove Cd(II), Zn(II) and Cu(II) in aqueous solution was studied. Ultrapure water was aerated for 2 h before use. Optimal dosage adsorption experiments were conducted using material dosages of 0.1, 0.2, 0.4, and 0.5 g / L. The initial concentrations of Cd(II), Zn(II), and Cu(II) solutions were 20 mg / L. The reaction system consisted of 20 mL solutions, which were placed in a shaker and reacted at 200 rpm for 180 min. After the reaction was complete, the solution was filtered through a 0.22 μm filter before analysis.

[0124] Under static and dynamic (shaking) conditions, 0.5 g / L Sp.@nZVI was added to 20 mL of Cd(II), Zn(II), and Cu(II) solutions with an initial concentration of 20 mg / L, respectively, to determine the effect of different working conditions on the adsorption efficiency. 0.5 g / L Sp.@nZVI was mixed with 20 mg / L Cd(II), Zn(II), and Cu(II) solutions, respectively, in 20 mL volumes. Three pH values ​​were set: 5, 6.5, and 8. The mixtures were placed in a shaker at 200 rpm for 3 h, and the effect of different pH values ​​on the adsorption efficiency of the three heavy metals was determined.

[0125] The kinetics of the material for the removal of different heavy metals were tested on a constant-temperature shaking table at 200 rpm. 10 mg of Sp.@nZVI was weighed and added to 20 mg / L solutions of Cd(II), Zn(II) and Cu(II), respectively, with a total system volume of 20 mL. Samples were taken at different time points: 5, 10, 20, 30, 60, 90, 120, and 180 min. After filtration, the supernatant was collected for analysis.

[0126] Adsorption isotherms were performed in 50 mL centrifuge tubes. For a 20 mL system, 10 mg of Sp.@nZVI was weighed and mixed with solutions of Cd(II), Zn(II), and Cu(II) at different initial concentrations: 10, 20, 50, 100, 200, 300, and 500 mg / L. The solutions were placed in a constant-temperature shaking incubator at 200 rpm for 3 hours. After filtration, the effect of different initial heavy metal concentrations on the adsorption effect was determined. The contents of Cd(II), Zn(II), and Cu(II) were determined using ICP-OES, with a detection limit of 1.0 μg / L. Each experiment was performed in triplicate. 0.5 g / L of the material was added to 20 mL of Cd(II), Zn(II) and Cu(II) solution (20 mg / L) for recycling. The reaction was carried out on a shaker at 200 rpm for 3 h. Sp.@nZVI was then collected by centrifugation and added back to the 20 mg / L heavy metal solution. The cycle was repeated 4 times, and no desorption was performed after each cycle.

[0127] Removal efficiency (Re, %) and adsorption capacity (q) of Cd(II), Zn(II) and Cu(II) e The concentrations (mg / g) are calculated using formulas (Equation 1) and (Equation 2), respectively. The formulas are expressed as follows:

[0128]

[0129]

[0130] Wherein, C0 (mg / L) is the initial concentration of the Cd(II), Zn(II), and Cu(II) solutions; C e (mg / L) represents the remaining concentration after adsorption; m(g) represents the mass of the adsorbent; and V(mL) represents the volume of the solution.

[0131] The kinetic data of Cd(II), Zn(II) and Cu(II) were fitted using pseudo-first-order (Equation 3) and pseudo-second-order (Equation 4) kinetic models.

[0132]

[0133]

[0134] Where, q e q represents the amount of adsorption at equilibrium. t K1(min) represents the amount of adsorption at time t. -1 K1(mg / min) is a pseudo-first-order rate constant; K2(mg / min) is a pseudo-second-order rate constant.

[0135] The adsorption isotherms were fitted using the Langmuir (Equation 5) and Freundlich (Equation 6) models. The Langmuir isotherm model is typically used to describe monolayer adsorption on a homogeneous adsorbent surface, where adsorption sites are uniformly distributed; the Freundlich isotherm model primarily describes the non-uniform multilayer adsorption process on a material surface. The formulas are expressed as follows:

[0136]

[0137]

[0138] Among them, C e Q represents the concentrations of Cd(II), Zn(II), and Cu(II) in the solution. e Q represents the adsorption amount under equilibrium conditions. m The maximum adsorption capacity; k F and n are the equilibrium constants of the Freundlich adsorption model, determined by adsorption capacity and spontaneity, respectively.

[0139] Microsoft Excel 2021 (Microsoft, USA) was used for data organization; Origin 2022 trial version (Originlab, USA) was used for data visualization.

[0140] 1. Optimal dosage of Sp.@nZVI for adsorption of Cd(II), Zn(II) and Cu(II)

[0141] To investigate the optimal adsorption dosage of Sp.@nZVI for Cd(II), Zn(II) and Cu(II), batch adsorption experiments were conducted at different dosages, and all removal experiments were carried out for 3 hours.

[0142] Figure 14 The bar chart shows the removal rate and adsorption amount of Cd(II), Zn(II) and Cu(II) by Spirulina in Example 1; Figure 15 The curves showing the removal rate and adsorption capacity of Cd(II) by the iron-based nanocomposite material prepared in Example 1 are shown. Figure 16 The curves showing the removal rate and adsorption capacity of Zn(II) by the iron-based nanocomposite material prepared in Example 1 are shown. Figure 17 The curves show the removal rate and adsorption amount of Cu(II) by the iron-based nanocomposite material prepared in Example 1.

[0143] from Figures 14-17It can be seen that the removal rate of the three heavy metals by Spirulina was 16.37-23.68%, and the adsorption capacity was 3.44-4.57 mg / g. The removal rate of Cd(II), Zn(II) and Cu(II) by Sp.@nZVI was directly proportional to the dosage, while the adsorption capacity was inversely proportional to the dosage. At 0.5 g / L, the removal capacity of Sp.@nZVI for Cd(II), Zn(II) and Cu(II) was 78.50%, 68.61% and 82.26%, respectively, and the adsorption capacity was 34.42, 42.54 and 150.04 mg / g, respectively. Based on a comprehensive evaluation of the removal capacity and adsorption capacity, 0.5 g / L Sp.@nZVI was selected as the dosage for subsequent experiments.

[0144] 2. Removal effects of Sp.@nZVI on Cd(II), Zn(II) and Cu(II) under different conditions

[0145] Figure 18 Figure 1 shows the removal rates of Cd(II), Zn(II), and Cu(II) by the iron-based nanocomposite material prepared in Example 1 under different conditions. Figure A shows the removal rate of Cd(II) by the iron-based nanocomposite material under static and dynamic conditions. Figure B shows the removal rate of Zn(II) by the iron-based nanocomposite material under static and dynamic conditions. Figure C shows the removal rate of Cu(II) by the iron-based nanocomposite material under static and dynamic conditions. Figure D shows the removal rate of Cd(II) by the iron-based nanocomposite material under different pH conditions. Figure E shows the removal rate of Zn(II) by the iron-based nanocomposite material under different pH conditions. Figure F shows the removal rate of Cu(II) by the iron-based nanocomposite material under different pH conditions.

[0146] To evaluate the adsorption performance of Sp.@nZVI for Cd(II), Zn(II), and Cu(II), a series of experiments were conducted. First, the adsorption performance of the material was investigated under both static and dynamic conditions, such as... Figure 18 As shown in Figures A through C, the adsorption capacity of the material under dynamic conditions is higher than that under static conditions, ranging from 2 to 8 times. The high adsorption capacity under dynamic conditions is mainly attributed to the interaction of the fluid and the movement of the material in the solution, which increases the contact area with heavy metals.

[0147] In addition, the effect of initial solution pH of 5, 6.5, and 8 on the adsorption of Sp.@nZVI was investigated. Figure 18(D~F). With increasing initial pH, the removal rates of Cd(II), Zn(II), and Cu(II) also increased. Cd(II) showed the best removal capacity at pH 6.5, reaching 97.69%; Zn(II) and Cu(II) showed the best removal effects at pH 8, with removal rates of 100% and 99.7%, respectively. The pH value of the aqueous solution determines the chemical state of heavy metal ions and the surface charge of the adsorbent, which may directly affect the final removal effect. Studies have shown that in acidic solutions, a large amount of H+... + They can compete with heavy metal ions for adsorption sites on the material surface and hinder the adsorption of heavy metal ions through Coulomb repulsion. However, as the pH value increases, the mutual repulsion between Cd(II), Zn(II), and Cu(II) and the material surface gradually decreases, thereby improving the removal capacity.

[0148] 3. Adsorption kinetics of Sp.@nZVI for Cd(II), Zn(II) and Cu(II)

[0149] Figure 19 The figures show the adsorption kinetics curves of Cd(II), Zn(II) and Cu(II) on the iron-based nanocomposite material prepared in Example 1. In the figure, A is the adsorption kinetics curve of Cd(II) on the iron-based nanocomposite material; B is the adsorption kinetics curve of Zn(II) on the iron-based nanocomposite material; and C is the adsorption kinetics curve of Cu(II) on the iron-based nanocomposite material.

[0150] The adsorption kinetics of Sp.@nZVI for Cd(II), Zn(II), and Cu(II) were investigated. In this experiment, the initial concentrations of Cd(II), Zn(II), and Cu(II) were 20 mg / L, and the Sp.@nZVI dosage was 0.5 g / L. The results are as follows: Figure 19 As shown, adsorption occurred rapidly in the first 5 minutes, gradually reaching equilibrium after 2 hours, with adsorption capacities of 26.00, 58.89, and 75.34 mg / g, respectively. This rapid adsorption may be related to the material's surface area, adsorption sites, and numerous functional groups. Pseudo-first-order and second-order kinetic models were used to fit the Cd(II), Zn(II), and Cu(II) kinetic data at 5, 10, 20, 30, 60, 90, 120, and 180 min, as shown in the figure. Figure 19 As shown, the experimental data are in better agreement with the pseudo-second-order dynamic model.

[0151] The kinetic parameters were determined using nonlinear regression analysis, and the results are listed in Table 1.

[0152] Table 1. Adsorption kinetic parameters of Sp.@nZVI for Cd(II), Zn(II) and Cu(II)

[0153]

[0154] Table 1 shows that the pseudo-second-order kinetic model R² values ​​for the three heavy metal ions are 0.9962, 0.9650, and 0.9910, respectively, which are higher than the pseudo-first-order kinetic model R². Therefore, it can be inferred that the removal of Cd(II), Zn(II), and Cu(II) by Sp.@nZVI follows a pseudo-second-order kinetic model. These results indicate that chemisorption in the pseudo-second-order kinetic model determines the adsorption rates of Cd(II), Zn(II), and Cu(II) by the material.

[0155] 4. Adsorption isotherms of Sp.@nZVI for Cd(II), Zn(II) and Cu(II)

[0156] Figure 20 Figure A shows the adsorption isotherms of Cd(II), Zn(II) and Cu(II) on the iron-based nanocomposite material prepared in Example 1. Figure B shows the adsorption isotherm of Cd(II) on the iron-based nanocomposite material, and Figure C shows the adsorption isotherm of Zn(II) on the iron-based nanocomposite material.

[0157] To better describe the interaction between heavy metals and Sp.@nZVI, adsorption isotherms were studied and fitted using Langmuir and Freundlich models, respectively (e.g., ...). Figure 20 The parameters corresponding to the two isotherms can be obtained through linear fitting, as shown in Table 2.

[0158] Table 2. Adsorption isotherm parameters of Sp.@nZVI for Cd(II), Zn(II) and Cu(II)

[0159]

[0160] As can be seen from Table 2, the Langmuir model is more suitable for the adsorption process than the Freundlich model, with a correlation coefficient R0. 2 >0.90.

[0161] Calculations using the Langmuir isotherm showed that the maximum adsorption capacities were 118.66, 132.86, and 355.66 mg / g when the Sp.@nZVI dose was 0.50 g / L. The theoretical results and experimental values ​​agreed well, indicating that the adsorption process was a homogeneous monolayer adsorption process.

[0162] 5. Removal mechanism of Cd(II), Zn(II) and Cu(II) by Sp.@nZVI

[0163] To investigate the removal mechanism of Cd(II), Zn(II) and Cu(II) by Sp.@nZVI, the changes of Sp.@nZVI before and after the reaction with Cd(II), Zn(II) and Cu(II) were analyzed by XPS characterization.

[0164] Figure 21 The above are XPS spectra of the iron-based nanocomposite materials prepared in Example 1. In the above, A is the full spectrum of the iron-based nanocomposite materials, B is the spectrum of C1s of the iron-based nanocomposite materials, C is the spectrum of O1s of the iron-based nanocomposite materials, and D is the spectrum of Fe 2p of the iron-based nanocomposite materials.

[0165] Figure 22 The images shown are XPS spectra of the iron-based nanocomposite material prepared in Example 1 after adsorbing Cd(II). The spectra are, in order, the full spectrum of the iron-based nanocomposite material after adsorbing Cd(II), the C1s spectrum of the iron-based nanocomposite material after adsorbing Cd(II), the O1s spectrum of the iron-based nanocomposite material after adsorbing Cd(II), the Fe 2p spectrum of the iron-based nanocomposite material after adsorbing Cd(II), and the Cd 3d spectrum of the iron-based nanocomposite material after adsorbing Cd(II).

[0166] Figure 23 The image shows the SEM image of the iron-based nanocomposite material prepared in Example 1 after adsorption of Cd(II).

[0167] like Figure 21 As shown, peaks for Fe, O, and C elements can be observed, indicating that Sp. was successfully loaded with nZVI. Regarding the removal of Cd(II), the Sp.@nZVI full spectrum and SEM image after the reaction show that Cd(II) is uniformly adsorbed on the material surface. Figure 21 A, Figure 22 Full spectrum of Cd(II) adsorbed on iron-based nanocomposites and Figure 23 ).

[0168] from Figure 21 B and Figure 22 The C1s spectrum of the iron-based nanocomposite material after Cd(II) adsorption shows a slight shift in the peaks of C, CO, and C=O after Cd(II) adsorption, indicating that carbon-containing groups participated in the adsorption process. This can also be seen from the O1s spectrum. Figure 21 C and Figure 22 The O1s spectra of the iron-based nanocomposite material after Cd(II) adsorption show similar shifts in the peaks at 532.82 and 531.35 eV related to -OH / COC and CO during Cd(II) adsorption, indicating that oxygen-containing groups also participate in the complexation of Cd. The binding energy of Fe 2p is around 720 eV, which can be further divided into Fe 2p1 / 2 and Fe 2p... 3 / 2These belong to Fe(II / III) oxides. The peak at 725 eV is Fe(III); the peak at 711 eV is Fe(II), including Fe₂O₃, Fe₃O₄, Fe(OH)₃, and FeOOH; and the peak at 707 eV is Fe₂O₃. 0 ;Depend on Figure 22 The Fe 2p spectra after Cd(II) adsorption in the iron-based nanocomposite material show that the Fe 2p after the reaction... 0 The peak disappeared, and peaks for FeO, Fe2O3, FeOOH, and Fe3O4 appeared at 711, 718, 725, and 733 eV, indicating that nZVI was oxidized to FeO·Fe2O3, Fe2O3, and FeOOH after the reaction of Sp.@nZVI with Cd(II). The Cd 3d spectrum after the reaction showed two characteristic peaks of Cd(II) at 405 and 412 eV, confirming that Cd(II) was not oxidized during the reaction with Sp.@nZVI and was mainly adsorbed on the material surface in the form of chemical complexes.

[0169] Regarding the mechanism of Sp.@nZVI removing Zn(II):

[0170] Figure 24 The images show the XPS spectra of the iron-based nanocomposite material prepared in Example 1 after adsorbing Zn(II). In the images, A is the full spectrum of the iron-based nanocomposite material after adsorbing Zn(II), B is the C1s spectrum of the iron-based nanocomposite material after adsorbing Zn(II), C is the O1s spectrum of the iron-based nanocomposite material after adsorbing Zn(II), D is the Fe2p spectrum of the iron-based nanocomposite material after adsorbing Zn(II), and E is the Zn 2q spectrum of the iron-based nanocomposite material after adsorbing Zn(II).

[0171] from Figure 24 The full spectrum of A shows that Sp.@nZVI adsorbs Zn after the reaction. The Fe 2p spectrum shows Fe... 0 Most of it was oxidized to iron oxides (γ-FeOOH and Fe3O4). In addition, characteristic peaks of Zn2p appeared at 1022 and 1045 eV after the reaction, indicating that Sp.@nZVI removed Zn(II) through adsorption and precipitation with iron oxides.

[0172] Regarding the mechanism of Cu(II) removal by Sp.@nZVI:

[0173] Figure 25The images show the XPS spectra of the iron-based nanocomposite material prepared in Example 1 after adsorbing Cu(II). In the images, A is the full spectrum of the iron-based nanocomposite material after adsorbing Cu(II), B is the C1s spectrum of the iron-based nanocomposite material after adsorbing Cu(II), C is the O1s spectrum of the iron-based nanocomposite material after adsorbing Cu(II), D is the Fe2p spectrum of the iron-based nanocomposite material after adsorbing Cu(II), and E is the Cu2q spectrum of the iron-based nanocomposite material after adsorbing Cu(II).

[0174] from Figure 25 The full spectrum of A shows that the material contains Cu(II) after the reaction; the Fe 2p spectrum shows a large number of characteristic peaks of iron oxides (γ-FeOOH), indicating that Fe 0 It is oxidized during the reaction. For example... Figure 25 As shown in E, Cu appears at 932 eV after the reaction. 0 and Cu + Characteristic peaks of Cu appear at 934, 935, 940, and 943 eV. 2+ The characteristic peaks of Cu. Therefore, Cu may be present as Cu. 0 and Cu 2+ Cu exists in a mixed manner 0 Reduced by nZVI, Cu 2+ The removal of Cu(II) is ultimately achieved by displacement and complexation with the functional groups on the particle surface (Equations 7 and 8).

[0175] Fe 0 +Cu 2+ →Fe 2+ +Cu 0 Formula 7;

[0176] Fe 0 +2Cu 2+ +H₂O→Fe 2+ +Cu₂O + 2H⁺ + Formula 8.

[0177] Figure 26 The diagram shows the removal mechanism of Cd(II), Zn(II) and Cu(II) by the iron-based nanocomposite material prepared in Example 1.

[0178] In summary, Sp.@nZVI removes Cd(II), Zn(II), and Cu(II) primarily through electrostatic adsorption, complexation, chemical precipitation, and reduction. Figure 26 ).

[0179] 6. Recycling of Sp.@nZVI and its application in soil suspensions

[0180] Figure 27The figures show the removal rates of Cd(II), Zn(II), and Cu(II) by the iron-based nanocomposite material prepared in Example 1 after 4 cycles. Figure A shows the removal rate of Cd(II) by the iron-based nanocomposite material after 4 cycles, Figure B shows the removal rate of Zn(II) by the iron-based nanocomposite material after 4 cycles, and Figure C shows the removal rate of Cu(II) by the iron-based nanocomposite material after 4 cycles.

[0181] The recycling of adsorbents helps reduce material costs and secondary pollution. Figure 27 The effect of Sp.@nZVI on the removal of Cd(II), Zn(II), and Cu(II) after four cycles was shown, with no desorption operation performed after each cycle. The results showed that after four cycles, the removal rate of the material for all three heavy metals was less than 50%, which may be related to material loss and the reduction of adsorption sites during adsorption. Therefore, subsequent use of a desorbent (such as hydrochloric acid) to fully desorb the used material before recycling can significantly improve the removal efficiency and the number of cycles.

[0182] Figure 28 The removal rate of Cd(II), Zn(II) and Cu(II) in soil suspension by the iron-based nanocomposite material prepared in Example 1 is shown.

[0183] Figure 29 The images show the effects of treating soil suspension with the iron-based nanocomposite material prepared in Example 1 before and after treatment.

[0184] from Figure 28 and 29 It can be seen that when Sp.@nZVI was applied to soil suspension, the removal rates of Cd(II), Zn(II), and Cu(II) were 66.05%, 33.93%, and 56.90%, respectively. This indicates that the material has a good removal effect on Cd(II) and Cu(II) in soil suspension. Compared with the turbid solution of the control group, the soil in the treatment group settled at the bottom of the vial after adsorption, while the upper part was a clear solution.

[0185] The above experiments demonstrate that the iron-based nanocomposite material (Sp.@nZVI) prepared by loading nano-zero-valent iron onto the natural biological template Spirulina in this invention is used for the removal of Cd(II), Zn(II), and Cu(II) from pesticide wastewater. Characterization by SEM, XRD, FTIR, VSM, and BET confirmed the successful loading of nZVI onto the surface of Spirulina. Furthermore, due to the magnetic properties of nZVI, its movement direction and velocity can be controlled by an external magnetic field, allowing for magnetic collection of the material in wastewater. Dosage experiments determined that 0.5 g / L is the optimal dosage of Sp.@nZVI. The removal rate under dynamic conditions is higher than that under static conditions (2–8 times). The optimal pH for Cd(II) removal by Sp.@nZVI is 6.5, and the optimal pH for Zn(II) and Cu(II) removal is 8. Adsorption kinetics and isotherm experiments show that the adsorption of Cd(II), Zn(II), and Cu(II) by Sp.@nZVI follows pseudo-second-order kinetics and the Langmuir model, belonging to monolayer chemisorption. XPS analysis of Sp.@nZVI before and after adsorption revealed that the material removes Cd(II), Zn(II), and Cu(II) primarily through electrostatic adsorption, complexation, chemical precipitation, and reduction. Recycling experiments showed that the removal rate decreased after multiple cycles, indicating the need for desorbing agents to improve the recycling rate. Sp.@nZVI can be applied to soil suspensions, demonstrating good removal efficiency for Cd(II) and Cu(II). In conclusion, Sp.@nZVI is a rapid and efficient iron-based material with potential for removing heavy metals from pesticide wastewater.

[0186] 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 principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing an iron-based nanocomposite material, comprising the following steps: (1) Mix ferrous salt, solvent and spirulina, soak and separate to obtain soaked spirulina; (2) The soaked spirulina obtained in step (1) is mixed with solvent, dispersant and reducing agent in sequence to carry out reduction reaction to obtain iron-based nanocomposite material; The spirulina in step (1) also includes pretreatment of the spirulina before use; The preprocessing operation is as follows: 1) Spirulina was pretreated by mixing it with an aqueous solution of glutaraldehyde, and then centrifuged and washed to obtain pretreated spirulina; 2) Mix the pretreated spirulina obtained in step 1) with an acidic solution, soak it, filter it, and then wash and dry it in sequence to obtain the pretreated spirulina.

2. The preparation method according to claim 1, characterized in that, In step (1), the divalent ferric salt is ferrous sulfate heptahydrate.

3. The preparation method according to claim 1, characterized in that, In step (1), the mass ratio of ferrous salt to spirulina is (130~150):

1.

4. The preparation method according to claim 1, characterized in that, The soaking time in step (1) is 12-24 hours, and the soaking temperature is 25-28°C.

5. The preparation method according to claim 1, characterized in that, The dispersant in step (2) is polyethylene glycol.

6. The preparation method according to claim 1, characterized in that, In step (2), the reducing agent is an aqueous solution of NaBH4.

7. The preparation method according to claim 6, characterized in that, The mass ratio of Spirulina to NaBH4 in step (1) is 1:(3~4).

8. The preparation method according to claim 1, characterized in that, The molar ratio of the ferrous salt in step (1) to the reducing agent in step (2) is 1:(2~3).

9. The iron-based nanocomposite material prepared by the preparation method according to any one of claims 1 to 8.

10. The application of the iron-based nanocomposite material according to claim 9 in wastewater treatment.

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