NFB magnetic composite particle and preparation method and application thereof

Abstract

The invention discloses an NFB magnetic composite particle and a preparation method and application thereof, and belongs to the technical field of magnetic composite particle preparation, the preparation method comprises the following steps: S1, preparing modified biochar through a pyrolysis process; s2, NiFe-LDH (layered double hydroxide) is prepared; and S3, preparing NFB through a one-step hydrothermal synthesis method. According to the NFB magnetic composite particle and the preparation method and application thereof, uniform loading of NiFe-LDH on the surface of biochar is achieved through a one-step hydrothermal method, and complexity of traditional multi-step synthesis is avoided; mixing the modified charcoal with NiFe-LDH, and then carrying out a hydrothermal reaction to prepare an NFB composite material; the material has high specific surface area, rich active sites and excellent photocatalytic performance, and the method is simple, low in cost and high in efficiency and has remarkable industrial application value.

Description

Technical Field

[0001] This invention relates to the field of magnetic composite material preparation technology, and in particular to an NFB magnetic composite particle, its preparation method and application. Background Technology

[0002] Ammonia nitrogen is the most common characteristic pollutant in industrial wastewater, agricultural fertilizers, and domestic sewage. High concentrations of ammonia nitrogen not only interfere with normal human metabolism, disrupt nervous system function, and cause respiratory diseases, but also lead to eutrophication of water bodies, causing ecological damage. Therefore, research on ammonia nitrogen pollution remediation technologies in aquatic environments is of great significance for water pollution control.

[0003] Current research on the applications of biochar includes heavy metal remediation, organic pollution remediation, greenhouse gas sequestration, and soil improvement. There are many methods for modifying biochar, including physical modification, chemical modification, ball milling modification, and chitosan modification. Previous studies have used biochar as a substrate, adding functional groups, chemical bonds, and metals to achieve efficient removal of various pollutants. Layered double hydroxides (LDHs) exhibit high catalytic oxidation performance in treating pollutants such as chlorinated aromatics, pyrene, and chrome black T fuel. Layered double hydroxides can serve as a supporting material for nitrogen pollution remediation, utilizing their electron migration properties to remove nitrates and ammonia nitrogen from water. Therefore, NiFe-LDH has significant application potential in the development of inorganic nitrogen pollution remediation technologies. Summary of the Invention

[0004] The purpose of this invention is to provide NFB magnetic composite particles, their preparation method, and applications. A one-step hydrothermal method achieves uniform loading of NiFe-LDH onto the surface of biochar, avoiding the complexity of traditional multi-step synthesis. Modified biochar is mixed with NiFe-LDH, and the NFB composite material is obtained through a hydrothermal reaction. The material possesses high specific surface area, abundant active sites, and excellent photocatalytic performance. This method is simple, low-cost, and highly efficient, possessing significant industrial application value.

[0005] To achieve the above objectives, the present invention provides a method for preparing NFB magnetic composite particles, comprising the following steps: S1. Modified biochar is prepared by pyrolysis process; S2. Preparation of NiFe-LDH; S3. NiFe-LDH@BC, i.e. NFB, is prepared by a one-step hydrothermal synthesis method.

[0006] Preferably, the specific operation of S1 is as follows: the reeds are repeatedly washed, ground and dried, then placed in a tube furnace and pyrolyzed with nitrogen gas, cooled after pyrolysis, and the cooled product is washed alternately with deionized water and ethanol, dried and cooled after washing to obtain modified biochar.

[0007] Preferably, in S1, the pyrolysis temperature is 500-600℃, the pyrolysis time is 3-3.5h, the heating rate is 3-5℃ / min, the washing is performed alternately with deionized water and ethanol 3-5 times, the drying temperature is 80-100℃, and the drying time is 15-20h.

[0008] Preferably, the specific operation of S2 is as follows: S21. Weigh FeCl3·6H2O, NiCl2·6H2O, NaOH, and Na2CO3 and dissolve them in 100mL of deionized water and stir. Mix the FeCl3·6H2O solution and NiCl2·6H2O solution and make up to volume to obtain mixed system A. Mix NaOH and Na2CO3 to obtain mixed system B. S22. Prepare a formamide solution. Add mixture A and mixture B to the reaction vessel under nitrogen protection. Then transfer the reaction vessel to the reaction kettle, seal and heat. After heating, allow it to stand and cool. After cooling, wash the product after the reaction with deionized water and ethanol alternately. After washing, dry to obtain NiFe-LDH.

[0009] Preferably, in S21, the molar ratio of FeCl3·6H2O to NiCl2·6H2O is 1:2, the molar ratio of NaOH to Na2CO3 is 5:1, the stirring time is 1-1.5h, and the total metal ion concentration in the mixed system A is 1-1.5mol / L.

[0010] Preferably, in S22, the volume percentage concentration of the formamide solution is 30%-35%, and the rate at which mixed system A and mixed system B are added to the reaction vessel is 3-5 mL / min; The reaction vessel is heated to 150-200℃ for 12-15 hours. The product after the reaction is washed 3-5 times by alternating centrifugation with deionized water and ethanol.

[0011] Preferably, the biochar prepared by S1 and the NiFe-LDH prepared by S2 are put into a beaker, and deionized water is added. The mixture is stirred and sonicated to obtain a mixture. After sonication, the mixture is placed in a reaction vessel and heated and allowed to cool. The cooled product is washed alternately with deionized water and ethanol, and then dried to obtain NFB.

[0012] Preferably, in S3, the mass ratio of biochar to NiFe-LDH is 1:(4-50), the amount of deionized water is 30-50 mL, the stirring is carried out for 1-1.5 h, the ultrasonication is carried out for 1-1.5 h, the heating temperature in the reactor is 150-200℃, the heating is carried out for 20-30 h, the product is washed with deionized water and ethanol alternately 3-5 times, the drying temperature is 80-100℃, and the drying is carried out for 15-20 h.

[0013] The present invention also provides an NFB magnetic composite particle, which is prepared by the above-described method for preparing an NFB magnetic composite particle.

[0014] This invention also provides an application of NFB magnetic composite particles, which are used to remove ammonia nitrogen from water.

[0015] Working principle: The composite of NiFe-LDH and BC significantly enhances the catalytic performance. The efficient removal of ammonia nitrogen by NFB can be attributed to: (1) the reduction of electronic transition potential by surface CO, Ni-O, and Fe-O functional groups; (2) Ni 2+ / Fe 3+ Redox reactions accelerate charge transfer efficiency; (3) High specific surface area provides abundant active sites; (4) -OH and C=O groups on the material surface attract NH4+ through electrostatic interaction; (5) Oxygen-containing functional groups -OH enhance the hydrophilicity of the material; (6) NFB promotes the separation of photogenerated electron-hole pairs and promotes the generation of O2. - ·OH active free radicals.

[0016] Therefore, this invention utilizes the aforementioned NFB magnetic composite particles, their preparation method, and applications. A one-step hydrothermal method achieves uniform loading of NiFe-LDH onto the surface of biochar, avoiding the complexity of traditional multi-step synthesis. Modified biochar is mixed with NiFe-LDH, and then an NFB composite material is obtained through a hydrothermal reaction. The material possesses high specific surface area, abundant active sites, and excellent photocatalytic performance. This method is simple, low-cost, and highly efficient, possessing significant industrial application value.

[0017] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0018] Figure 1 These are simplified preparation flowcharts for Examples 1-6 of the present invention; Figure 2 These are SEM images of NFB3, NiFe-LDH, and BC, and EDS image of NFB3 from this invention. Figure 3 This is the N2 adsorption-desorption curve and pore volume-pore size distribution diagram of BC and NFB3 of the present invention; Figure 4 This is the infrared spectrum of NFB3 of the present invention; Figure 5 This is the photoluminescence spectrum of NFB3 of the present invention; Figure 6 This is the photocatalytic response spectrum of NFB3 in this invention; Figure 7 These are ammonia nitrogen removal efficiency analysis charts for Examples 1-6 and Comparative Examples 1-2 of the present invention; Figure 8 This invention relates to different initial concentrations of ammonia nitrogen, pH value, and Cl... - HCO3 - PO4 3- SO4 2- K + Na + Ca 2+ Mg 2+ Effect diagram on removal performance; Figure 9 These are the paramagnetic resonance images of NFB3 and NiFe-LDH of the present invention at 0, 10, and 20 min under visible light irradiation. Figure 10 This is a repeatable NFB3 adsorption experiment of the present invention; Figure 11 These are curves of different dynamic fitting models of the present invention. Detailed Implementation

[0019] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0020] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains.

[0021] Material source: The reeds were collected from waste dumped around Erhai Lake in Dali. Chemical reagents used included FeCl3·6H2O, NiCl2·6H2O, CO(NH2)2, HCl, NaOH, and C8H4K2O. 12 Sb2, NaCl, NaHCO3, CaSO4, MgCl2. All of the above reagents were of analytical grade, and the water used in the experiment was deionized water prepared in the laboratory.

[0022] The ammonia nitrogen pollution removal experiment in this invention is as follows: The optimal conditions for ammonia nitrogen removal by the material were determined by setting different types (BC, NiFe-LDH, NFB), composite material ratios, and NFB dosages. Then, the feasibility of the material's application under actual complex water conditions was verified by setting different initial ammonia nitrogen concentrations, pH, and anions / cations. Parallel experimental groups were performed three times for each single variable, and the average value was used as the final result.

[0023] The amount of adsorption q at time T t As shown in equation (1), the equilibrium adsorption amount q e As shown in Equation (2), the removal rate η (%) is shown in Equation (3).

[0024] (1); (2); (3); The initial concentration of ammonia nitrogen is mg / L. Let t be the ammonia nitrogen concentration, in mg / L. V represents the equilibrium concentration of ammonia nitrogen (mg / L); V represents the solution volume (L); and M represents the mass of biochar (g).

[0025] The data were fitted using pseudo-first-order and pseudo-second-order kinetic equations.

[0026] (4); (5); Where: k1(min -1 k1(g / (mg·min)) and k2(g / (mg·min)) are pseudo-first-order and pseudo-second-order rate constants, respectively; q e (mg / g) and q t (mg / g) represents the amount of adsorption at adsorption equilibrium and at time t (min), respectively.

[0027] The experimental data were fitted using the Langmuir (Equation (6)) and Freundlich (Equation (7)) models.

[0028] (6); (7); In the formula: e (mg / g) represents the amount of adsorption at adsorption equilibrium; m (mg / g) represents the saturated adsorption capacity; K L (L / mg) is the Langmuir adsorption equilibrium constant; K F((mg / g)(L / mg) 1 / n ) represents the Freundlich adsorption equilibrium constant; C e (mg / L) represents the NH4+ concentration in the solution at adsorption equilibrium. + -N concentration; 1 / n is the Freundlich exponent.

[0029] In this invention, unless otherwise specified, all other test materials and instruments are conventional test materials in the field and can be purchased through commercial channels.

[0030] Example 1 like Figure 1 As shown, this invention provides an NFB magnetic composite particle, the preparation method of which is as follows: S1. Preparation of modified biochar: Modified biochar was prepared using a pyrolysis process. Reeds were repeatedly washed, ground, and dried. The solid was then placed in a tube furnace under nitrogen gas and pyrolyzed at 500°C for 3 hours at a heating rate of 5°C / min. After pyrolysis and cooling, the cooled product was washed three times alternately with deionized water and ethanol, dried at 80°C for 16 hours, and then cooled to obtain modified biochar.

[0031] S2. Preparation of NiFe-LDH: S21. Weigh out 9g FeCl3·6H2O, 15.85g NiCl2·6H2O, 4g NaOH, and 2.12g Na2CO3 sequentially and dissolve them in 100mL of deionized water, stirring for 60min. Make up the volume of the FeCl3·6H2O and NiCl2·6H2O solutions to prepare a liquid mixture A with a total metal ion concentration of 1mol / L. Mix the NaOH and Na2CO3 solutions to obtain mixture B.

[0032] S22. Prepare a 33% (vol%) formamide solution. Add mixture A and mixture B simultaneously to the reaction vessel at a rate of 3 mL / min under N2 protection. Then transfer the reaction vessel to a reaction kettle, seal and heat at 160°C for 14 h. After standing and cooling, wash the reaction product three times by alternating centrifugation with deionized water and ethanol, and dry to obtain NiFe-LDH.

[0033] S3. Add 1g of biochar prepared by S1 and 0.25g of NiFe-LDH prepared by S2 into a beaker, add 30mL of deionized water, stir for 60min, sonicate for 60min to obtain a mixture, place the mixture in a reaction vessel and heat at 160℃ for 24h, let it stand and cool, wash the cooled product three times with deionized water and ethanol alternately, and dry at 80℃ for 16h to obtain NFB, denoted as NFB1.

[0034] Example 2 The only difference between this embodiment and Example 1 is that the amount of NiFe-LDH used in S3 is 0.1g, and the final product is named NFB2. All other conditions are the same.

[0035] Example 3 The only difference between this embodiment and Example 1 is that the amount of NiFe-LDH used in S3 is 0.05g, and the final product is named NFB3. All other conditions are the same.

[0036] Example 4 The only difference between this embodiment and Example 1 is that the amount of NiFe-LDH used in S3 is 0.033g, and the final product is named NFB4. All other conditions are the same.

[0037] Example 5 The only difference between this embodiment and Example 1 is that the amount of NiFe-LDH used in S3 is 0.025g, and the final product is named NFB5. All other conditions are the same.

[0038] Example 6 The only difference between this embodiment and Example 1 is that the amount of NiFe-LDH used in S3 is 0.02g, and the final product is named NFB6. All other conditions are the same.

[0039] Comparative Example 1 The product of this comparative example is the modified biochar (BC) prepared in Example 1.

[0040] Comparative Example 2 The product in this comparative example is the NiFe-LDH obtained in Example 1.

[0041] I. Structural Characterization The performance of NFB3, BC and NiFe-LDH was characterized, and the characterization results are as follows: Figure 2 As shown, where Figure 2 (a) in the image is a SEM image of NFB3. Figure 2 Image (b) in the image is a SEM image of NiFe-LDH. Figure 2 (c) in the image is the SEM image of NFB3. Figure 2 (d) in the figure is the EDS plot of NFB3; from Figure 2 As can be seen from (a)-(c) in the figure, plate-like NiFe-LDH is clearly observed uniformly dispersed on the BC surface, and the composite material surface is rough. Figure 2 As can be seen from (d) in the figure, the elements Ni, Fe and Cl contained in NiFe-LDH are all present in NFB3, indicating that the material was successfully prepared.

[0042] NFB3 solid contains a large number of microporous structures and has a larger specific surface area than BC, thus providing more adsorption sites. Detailed information on the specific surface area and pore size distribution of BC and NFB3, as well as N2 adsorption curves, were obtained using the BET and BJH methods. Detailed information on the specific surface area and pore size distribution of BC and NFB3 is shown in Table 1, and the N2 adsorption-desorption curves of BC and NFB3 are shown in... Figure 3 As shown, where Figure 3 In the figure, (a) is the N2 adsorption-desorption curve of BC. Figure 3 (b) shows the N2 adsorption-desorption curve of NFB3. The above characterization results indicate that NiFe-LDH refines the pores during the loading process, and Figure 3 The linear shape of the adsorption isotherm of the H4 hysteresis loop in (b) confirms the above conclusion.

[0043] Table 1. Specific surface area, void volume, and average pore size of BC and NFB3

[0044] II. Optical and photoelectric performance characteristics The removal mechanism was studied using characterization techniques including scanning electron microscopy (SEM), pore size analysis (BET), Fourier transform infrared spectroscopy (FTIR), photocatalytic response (EIS), luminescence spectroscopy (PL), and electron paramagnetic resonance (EPR).

[0045] The results of Fourier transform infrared spectroscopy (FTIR), photoluminescence spectroscopy (PL), and EIS analysis of NFB3, BC, and NiFe-LDH are as follows: Figure 4 , Figure 5 , Figure 6 As shown. By Figure 4 It can be seen that NFB3 is at the CO peak (1240 cm⁻¹). -1 The -OH peak of NiFe-LDH forms a broadened superposition with the peak at 1380 cm⁻¹. -1 CO3 2- Antisymmetric stretching vibration, 3450cm -1 This corresponds to the stretching vibration of the interlayer -OH group. The -OH peak of NiFe-LDH is oriented towards the low frequency of 3400 cm⁻¹. -1 The shift indicates that the two have formed an interfacial connection through hydrogen bonding or electrostatic interaction; while the weakening intensity of the C=O peak in BC indicates that C=O and Ni... 2+ / Fe 3+ Coordination occurs. Interlayer CO3 in NiFe-LDH... 2- Peak (1380cm) -1 The intensity decreased, and the structure split into two peaks after recombination, indicating that the oxygen-containing functional groups of BC participated in the reconstruction of the interlayer structure, further confirming the regulatory role of BC in the interlayer chemical environment of NiFe-LDH.

[0046] PL spectroscopy indicates that the absorption and emission of light occur during transitions between energy levels. Generally, a low PL intensity corresponds to a low recombination rate of photogenerated electron-hole pairs, and vice versa. Figure 5 The lowest spectral response intensity was observed in NFB3, confirming the effective separation of photogenerated carriers and indicating that it has a low photoelectron-hole recombination rate. Therefore, its redox ability is relatively high, meaning it has good photocatalytic efficiency for removing ammonia nitrogen from water.

[0047] EIS represents the electron transport process. The smaller the radius of the semicircle in the Nyquist plot, the smaller the charge transfer resistance of the material, which corresponds to an increase in the mobility of photogenerated electron-hole pairs. Figure 6 NFB3 has a smaller semi-circular radius, meaning it exhibits the lowest charge transfer resistance, the highest electron separation efficiency, and the best photocatalytic performance. After BC is loaded with NiFe-LDH, the surface functional groups CO, Fe-O, and Ni-O can serve as electron transport channels, lowering the potential barrier for electron transitions and providing a photocatalytic response for the removal of ammonia nitrogen from water. Therefore, in terms of material stability and absorption rate, NFB3 is more stable and has better photocatalytic efficiency than NiFe-LDH.

[0048] III. Ammonia Nitrogen Removal Efficiency Analysis The ammonia nitrogen removal efficiency of the materials from Examples 1-6 and Comparative Examples 1-2 was analyzed, and the results are as follows: Figure 7 As shown, where, Figure 7 (a) in the text refers to the effects of Examples 1-6 and Comparative Examples 1-2 on NO. 2- and NO3 - Changes in concentration, Figure 7 (b) in the example refers to the effect of NO on Examples 1-6. 2- and NO3 - Changes in concentration, Figure 7 (c) represents the effect of different dosages of NFB3 on NO. 2- and NO3 - Changes in concentration, Figure 7 In the figure, (d) represents NFB3 and the comparison samples 1-2 against NO. 2- and NO3 - Changes in concentration.

[0049] like Figure 7 As shown in (a), all materials reach adsorption-desorption equilibrium at 120 min. BC has a very weak adsorption capacity for ammonia nitrogen, while NFB shows a significantly stronger adsorption capacity. The optimal composite ratio was selected under different conditions, and the results indicate that NFB3 (NiFe-LDH:BC = 1:30) is the best material at 120 min.

[0050] Depend on Figure 7(b) It can be seen that the removal effect of ammonia nitrogen is better with the increase of NiFe-LDH ratio, which is related to the increase of microporous structure after the composite material, which provides more adsorption pore size.

[0051] To determine the optimal dosage of material during the removal process, a comparison was made of different dosages of NFB3. The effect of NFB3 dosage on the adsorption of ammonia nitrogen is as follows: Figure 7 As shown in (c), the adsorption effect on ammonia nitrogen improves with increasing material dosage, and adsorption stability is achieved within 60 minutes. This is because the increased number of active sites on the catalyst surface leads to higher removal efficiency with increasing catalyst dosage, which promotes the activation and generation of ROS (reactive oxygen species).

[0052] The difference in the removal rate of ammonia nitrogen was not significant when the NFB3 dosage was 0.8 g / L and 1 g / L. This is because excessive photocatalyst can cause particle aggregation in the solution, increase the opacity and turbidity of the solution, and affect the ability of the material to transmit photons through the solution.

[0053] Depend on Figure 7 As shown in (d), a small amount of NOx is generated during the removal process, and its concentration gradually decreases with time, indicating that there may be substances with the ability to reduce NOx.

[0054] IV. Environmental Impact Analysis Due to the differences in the occurrence forms and concentration distribution of ammonia nitrogen, different initial concentrations were used for investigation. Under the conditions of 1g NFB3 and pH=8, ammonia nitrogen was removed at initial concentrations of 10mg / L, 30mg / L, 50mg / L, 100mg / L, and 150mg / L, respectively. The results are as follows... Figure 8 As shown, where Figure 8 (a) shows the effect of different initial ammonia nitrogen concentrations on removal performance. Figure 8 (b) shows the effect of different pH values ​​on removal performance. Figure 8 (c) in the text represents Cl. - HCO3 - PO4 3- SO4 2- Impact on removal performance Figure 8 (d) in K + Na + Ca 2+ Mg 2+ Impact on removal performance.

[0055] Depend on Figure 8As shown in (a), the removal rate did not increase continuously with the increase of the initial concentration of ammonia nitrogen, and its maximum adsorption capacity was limited at a fixed amount of NFB3. However, the adsorption capacity gradually increased, indicating that the concentration difference between high concentrations of ammonia nitrogen and the material surface is conducive to the entry of ammonia nitrogen into the material, thereby improving the material's adsorption capacity.

[0056] The removal performance of the material for ammonia nitrogen under different pH conditions was studied using 1g of NFB3. Figure 8 As can be seen from (b), under acidic conditions, the removal rate of ammonia nitrogen gradually increases with increasing pH. This phenomenon is due to the competitive adsorption of H+ ions under strongly acidic conditions. + Will with NH4 + Competition for active sites on the adsorbent surface. However, the situation is different under alkaline conditions because, with increasing alkalinity (10⁻¹¹), free NH₄⁺ in the solution... + The content of NH3·H2O decreases continuously while the amount of NH4 adsorbed by the material increases. + This reduction leads to a decrease in the adsorption rate.

[0057] Natural water and most industrial and agricultural wastewater contain high concentrations of chlorides, sulfates, and carbonates. Eight common anions and cations were selected: Cl... - HCO3 - PO4 3- SO4 2- K + Na + Ca 2+ Mg 2+ The concentrations were all 15 mg / L. The removal performance of these substances on ammonia nitrogen was investigated, and the results are as follows: Figure 8 As shown in (c)-(d) of the figure, K + Na + Cl - HCO3 - The impact is relatively small; the removal efficiency can still reach over 80% after 120 minutes. However, Ca... 2+ PO4 3- The impact is relatively high, Mg 2+ SO4 2- These results, exhibiting a moderate impact, indicate a stronger competitive adsorption between higher valence ions and ammonia nitrogen. Some studies suggest that Ca... 2+ Mg 2+ Compared to K + Na + It has a certain complexing ability for some functional groups, thus occupying some specific adsorption sites, resulting in lower removal efficiency.

[0058] The main oxidation-active species types in the NFB3 photocatalytic process were obtained through quenching experiments, and the results are as follows: Figure 9 As shown, where Figure 9 (a) shows the h values ​​of NFB3 and NiFe-LDH at 0, 10, and 20 min under visible light irradiation. + The paramagnetic resonance image, Figure 9 (b) shows the detection of O2 by NFB3 and NiFe-LDH under visible light irradiation for 0, 10, and 20 min. - The paramagnetic resonance image, Figure 9 (c) shows the paramagnetic resonance diagrams of ·OH detected by NFB3 and NiFe-LDH at 0, 10 and 20 min under visible light irradiation.

[0059] The three quenchers for NFB3 are ethylenediaminetetraacetic acid (EDTA), isopropanol (IPA), and benzoquinone (BQ), which are used to quench holes (h) respectively. + ), hydroxyl radicals (·OH), superoxide radicals (·O2) - The main reactive free radical in this process is h. + O2 - As can be seen from the graph, under illumination, DEMPO exhibits a characteristic peak, indicating that O2 is reduced by photogenerated electrons to generate ·O2. - DMPO exhibits a typical 1:2:2:1 quadruple peak, indicating the formation of ·OH. Furthermore, in NFB3, ·O2 increases with time. - The amount of ·OH generated increases, h + The amount of ·OH and h in NiFe-LDH decreases. + The amount of O2 generated increases. - The gradually decreasing number of electrons indicates that during the transfer, these electrons rapidly form active substances on the surface, reacting quickly with H₂O to generate ·OH. Combined with the above experimental results, these indicate that NFB₃ photocatalyzes the removal of NH₄⁺. + In the -N process, the main active free radicals are ·OH and ·O2. - and a small amount of h + What occurs is a direct oxidation reaction.

[0060] V. Repeatability Experiments Figure 10 A comparative experiment was conducted on NFB3, repeated five times. As shown in the figure, although the removal rate of ammonia nitrogen by the NFB3 sample gradually decreased after each test, the removal rate still reached 82.01% after five cycles. In conclusion, the experimental results demonstrate that NFB3 exhibits high efficiency, persistence, and stability in removing ammonia nitrogen from water.

[0061] VI. Analysis of Ammonia Nitrogen Removal Mechanism The quasi-first and second-order kinetic fits are shown in Table 2, and different kinetic fit models are as follows: Figure 11 As shown, where, Figure 11 (a) in the model represents the quasi-first and second order dynamic fitting model. Figure 11 Figure (b) shows the Freundlich and Langmuir fitting model. As can be seen from the figure, the removal of ammonia nitrogen by NFB3 is biased towards redox reactions, with surface adsorption sites playing a significant role. The adsorption of ammonia nitrogen follows a pseudo-second-order kinetic model (R0). 2 =0.8721) and Freundlich (R 2 =0.9037) model. NFB3 can efficiently remove ammonia nitrogen from water due to the abundance of oxygen-containing functional groups on the surface of the composite material and its high specific surface area (1407.834 m²). 2 The addition of NiFe-LDH ( / g) promotes charge transfer on the material surface, thus attaching metals to biochar can significantly enhance its catalytic activity. After NiFe-LDH is combined with BC, functional groups C=O, Ni / Fe-O, and NH4 are added to the material surface. + Coordination occurs, forming complexes; and oxygen-containing hydrogen bonds -OH and C=O both exhibit electronegativity, reacting with NH4+. + Electrostatic attraction occurs, causing NH4 to... + Adsorption on the material surface further enhances ion exchange. The added oxygen-containing functional group -OH enhances the hydrophilicity of the material, enabling NFB3 to disperse well in the aquatic environment and increasing the contact area with pollutants. Furthermore, the combination of NiFe-LDH and BC effectively separates photogenerated charge carriers, resulting in the release of active free radicals (·O2). - An increase in ·OH groups leads to photocatalytic oxidation, and NH4+... + -N is removed.

[0062] Table 2. Quasi-first and second-order dynamic fitting

[0063] Therefore, this invention utilizes the aforementioned NFB magnetic composite particles, their preparation method, and applications. A one-step hydrothermal method achieves uniform loading of NiFe-LDH onto the surface of biochar, avoiding the complexity of traditional multi-step synthesis. Modified biochar is mixed with NiFe-LDH, and then an NFB composite material is obtained through a hydrothermal reaction. The material possesses high specific surface area, abundant active sites, and excellent photocatalytic performance. This method is simple, low-cost, and highly efficient, possessing significant industrial application value.

[0064] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for preparing NFB magnetic composite particles, characterized in that: Includes the following steps: S1. Modified biochar is prepared by pyrolysis process; S2. Preparation of NiFe-LDH; S3. NiFe-LDH@BC, i.e. NFB, is prepared by a one-step hydrothermal synthesis method.

2. The method for preparing NFB magnetic composite particles according to claim 1, characterized in that: The specific operation of S1 is as follows: the reeds are repeatedly washed, ground and dried, then placed in a tube furnace and pyrolyzed with nitrogen. After pyrolysis, the product is cooled and washed alternately with deionized water and ethanol. After washing, the product is dried and cooled to obtain modified biochar.

3. The method for preparing NFB magnetic composite particles according to claim 1, characterized in that: In S1, the pyrolysis temperature is 500-600℃, the pyrolysis time is 3-3.5h, the heating rate is 3-5℃ / min, the deionized water and ethanol are washed alternately 3-5 times, the drying temperature is 80-100℃, and the drying time is 15-20h.

4. The method for preparing NFB magnetic composite particles according to claim 1, characterized in that: The specific operation of S2 is as follows: S21. Weigh FeCl3·6H2O, NiCl2·6H2O, NaOH, and Na2CO3 and dissolve them in 100mL of deionized water and stir. Mix the FeCl3·6H2O solution and NiCl2·6H2O solution and make up to volume to obtain mixed system A. Mix NaOH and Na2CO3 to obtain mixed system B. S22. Prepare a formamide solution. Add mixture A and mixture B to the reaction vessel under nitrogen protection. Then transfer the reaction vessel to the reaction kettle, seal and heat. After heating, allow it to stand and cool. After cooling, wash the product after the reaction with deionized water and ethanol alternately. After washing, dry to obtain NiFe-LDH.

5. The method for preparing NFB magnetic composite particles according to claim 4, characterized in that: In S21, the molar ratio of FeCl3·6H2O to NiCl2·6H2O is 1:2, the molar ratio of NaOH to Na2CO3 is 5:1, the stirring time is 1-1.5h, and the total metal ion concentration in the mixed system A is 1-1.5mol / L.

6. The method for preparing NFB magnetic composite particles according to claim 4, characterized in that: In S22, the volume percentage concentration of the formamide solution is 30%-35%, and the rate at which mixed system A and mixed system B are added to the reaction vessel is 3-5 mL / min; The reaction vessel is heated to 150-200℃ for 12-15 hours. The product after the reaction is washed 3-5 times by alternating centrifugation with deionized water and ethanol.

7. The method for preparing NFB magnetic composite particles according to claim 1, characterized in that: The specific operation of S3 is as follows: the biochar obtained by S1 and the NiFe-LDH obtained by S2 are put into a beaker, and deionized water is added. The mixture is stirred and sonicated to obtain a mixture. After sonication, the mixture is placed in a reaction vessel and heated and allowed to cool. The cooled product is washed alternately with deionized water and ethanol. After washing, it is dried to obtain NFB.

8. The method for preparing NFB magnetic composite particles according to claim 7, characterized in that: In S3, the mass ratio of biochar to NiFe-LDH is 1:(4-50), the amount of deionized water is 30-50 mL, stirring is performed for 1-1.5 h, sonication is performed for 1-1.5 h, the heating temperature in the reactor is 150-200℃, heating is performed for 20-30 h, the product is washed with deionized water and ethanol alternately 3-5 times, and the drying temperature is 80-100℃, drying is performed for 15-20 h.

9. An NFB magnetic composite particle, characterized in that: The NFB magnetic composite particles were prepared using the preparation method described in any one of claims 1-8.

10. An application of NFB magnetic composite particles, characterized in that: The NFB magnetic composite particles described in claim 9 are used to remove ammonia nitrogen from water.

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