A nitrogen-doped bimetallic biochar adsorbent, and a preparation method and application thereof

Abstract

This invention relates to the field of environmental functional materials technology, specifically to a method for preparing a nitrogen-doped bimetallic biochar adsorbent and its application. The method uses grape pomace as biomass raw material, which is pretreated with HCl via hydrothermal treatment, then mixed with KOH, urea, and a bimetallic source solution. The nitrogen-doped bimetallic biochar adsorbent is prepared by oxygen-limited pyrolysis carbonization. The nitrogen-doped bimetallic biochar adsorbent prepared by this invention possesses high specific surface area, hierarchical porous structure, and magnetic separation characteristics. It exhibits excellent adsorption and removal effects on the carbamate pesticides methomyl and pirimicarb in water, with maximum adsorption capacities reaching 50.97 mg·g⁻¹, respectively. ‑1 and 159.50 mg·g ‑1 It exhibits good anti-interference ability and stability in complex aquatic environments and can be used for the treatment of pesticide-polluted water bodies.

Description

Technical Field

[0001] This invention relates to the field of environmental functional materials technology, specifically to a method for preparing a nitrogen-doped bimetallic biochar adsorbent and its application. Background Technology

[0002] Carbamate pesticides are among the most widely used types of insecticides, offering advantages such as high insecticidal efficacy, broad insecticidal spectrum, and simple synthesis. However, after application, they easily enter water bodies through surface runoff and soil infiltration, disrupting ecosystem stability and posing health risks such as neurotoxicity and endocrine disruption through bioaccumulation in the food chain. Mefenoxam and pirimicarb are representative varieties of this class of pesticides, and developing efficient and economical removal technologies is of significant practical importance.

[0003] Adsorption is one of the effective methods for controlling this type of pesticide pollution. Biochar (BC) is widely used as an adsorbent in water treatment due to its abundant raw materials, low cost, and environmental friendliness. However, raw biochar has an underdeveloped pore structure and limited surface active sites, resulting in poor adsorption performance, requiring modification.

[0004] To address these issues, researchers often modify biochar by doping with inorganic elements or metals. Nitrogen doping, in particular, can introduce functional groups such as pyridine nitrogen and pyrrole nitrogen to regulate the electron distribution on the biochar surface, enhancing the interaction with pollutants and thus increasing adsorption capacity. Meanwhile, doping with metals such as iron and cobalt can not only further optimize the pore structure but also enhance adsorption specificity by forming metal-oxygen bonds and metal coordination sites, while also endowing biochar with good magnetic separation properties.

[0005] Existing methods for preparing nitrogen-doped bimetallic biochar adsorbents mostly employ a one-step pyrolysis method. While this method is simple to operate, it generally faces the bottleneck of balancing yield and adsorption performance. The main reason is that the drastic decomposition and release of volatile components in biomass during high-temperature pyrolysis leads to a reduction in solid residues. Furthermore, the combined hydrothermal carbonization-pyrolysis method often uses pure water or neutral conditions, which has limited effect on disrupting the dense structure of biomass. A relatively high amount of activator is still required in the subsequent pyrolysis stage to obtain an ideal pore structure, and metal ions are prone to agglomeration during pyrolysis, resulting in poor dispersion uniformity. Summary of the Invention

[0006] To address the above problems, this invention provides a method for preparing a nitrogen-doped bimetallic biochar adsorbent and its application.

[0007] To achieve the above objectives, the technical solution of the present invention is as follows.

[0008] This invention provides a method for preparing a nitrogen-doped bimetallic biochar adsorbent, comprising the following steps: Hydrothermal biochar is obtained by reacting grape pomace biomass with hydrochloric acid solution at 180℃~220℃ using hydrothermal reaction.

[0009] Hydrothermal biochar was mixed with KOH, nitrogen source, iron salt, and bimetallic source solution, dried, and then pyrolyzed under limited oxygen conditions to obtain nitrogen-doped bimetallic biochar adsorbent.

[0010] The bimetallic source solution is a first metal salt solution and a second metal salt solution. The first metal salt solution is an iron salt solution, and the second metal salt solution is a cobalt salt solution or a calcium salt solution.

[0011] Preferably, the hydrothermal reaction time is 6h to 10h.

[0012] Preferably, the heating rate of the oxygen-limited pyrolysis is 10℃ / min to 25℃ / min, the pyrolysis temperature is 550℃ to 650℃, and the holding time is 100min to 140min.

[0013] Preferably, the ratio of grape pomace biomass to hydrochloric acid solution is 1g:5mL-15mL; the concentration of hydrochloric acid solution is 2mol·L⁻¹. -1 ~7mol·L -1 .

[0014] Preferably, the nitrogen source is urea; the mass ratio of the hydrothermal biochar, potassium hydroxide and urea is 1~3:2:1.

[0015] Preferably, the ratio of the bimetallic source solution to hydrothermal biochar is 10 mL to 12 mL: 1 g; the iron salt solution is ferric chloride solution, the cobalt salt solution is cobalt chloride solution, and the calcium salt solution is calcium chloride solution; the concentration of the iron salt solution is 0.02 mol·L⁻¹. -1 ~0.06 mol·L -1 The cobalt salt solution concentration is 0.02 mol·L⁻¹. -1 ~0.1mol·L -1 The calcium salt solution concentration is 0.02 mol·L⁻¹. -1 ~0.1mol·L -1 .

[0016] Preferably, the grape pomace biomass is taken from the core grape-producing area on the eastern foothills of Helan Mountain in Ningxia. Every year, a large amount of grape pomace waste is generated during the winemaking process. Utilizing this waste to prepare biochar can not only reduce the pressure of waste disposal for local wineries, but also achieve efficient resource utilization.

[0017] The present invention also provides an application of the nitrogen-doped bimetallic biochar adsorbent prepared by the above method for removing carbamate pesticides from water.

[0018] Preferably, the carbamate pesticide is methomyl and / or pirimicarb.

[0019] Preferably, the application method is as follows: Based on the total volume of the carbamate pesticide aqueous solution, the nitrogen-doped bimetallic biochar adsorbent is added at a concentration of 0.2 g·L⁻¹. -1 ~0.5g·L -1 The dosage was added to an initial concentration of 20 mg·L⁻¹. -1 ~60mg∙L -1 In aqueous solutions of carbamate pesticides.

[0020] Preferably, the FeCo-NBC adsorbent has a maximum adsorption capacity of 50.97 mg·g for both methomyl and pirimicarb. -1 and 147.56 mg∙g -1 Its adsorption kinetics conform to the Elovich model; the maximum adsorption capacity of the FeCa-NBC adsorbent for methomyl and imidacloprid is 46.35 mg∙g. -1 and 159.50 mg∙g -1 The adsorption kinetics follow a pseudo-second-order kinetic model; the adsorption isotherms of the FeCo-NBC adsorbent and the FeCa-NBC adsorbent both conform to the Freundlich model.

[0021] The beneficial effects of this invention are: 1. This invention combines HCl hydrothermal pretreatment with N, Fe, Co (Ca) oxygen-limited pyrolysis. The HCl hydrothermal pretreatment stage disrupts the dense structure of grape pomace biomass under high temperature and pressure, laying the foundation for pore development in the subsequent pyrolysis stage. The N, Fe, Co (Ca) oxygen-limited pyrolysis stage optimizes the material's pores and surface functional groups through high-temperature activation, synergistically achieving nitrogen doping, bimetallic loading, and carbon framework activation. The resulting nitrogen-doped iron-cobalt (calcium) bimetallic biochar adsorbent exhibits both high adsorption capacity and yield.

[0022] 2. The nitrogen-doped bimetallic biochar adsorbent prepared in this invention exhibits excellent adsorption and removal effects on the carbamate pesticides methomyl and pirimicarb in water, with maximum adsorption capacities reaching 50.97 mg·g, respectively. -1 and 159.50 mg∙g -1 The adsorption kinetics of FeCo-NBC conform to the Elovich model, while those of FeCa-NBC conform to the pseudo-second-order kinetic model. The adsorption isotherms of both adsorbents also conform to the Freundlich model. Furthermore, the saturation magnetizations of FeCo-NBC and FeCa-NBC reach 3.78 emu / g and 4.72 emu / g, respectively, enabling rapid magnetic separation of solid-liquid systems, facilitating recycling and reuse, and demonstrating good potential for practical applications. Attached Figure Description

[0023] Figure 1 The flowcharts for the preparation of nitrogen-doped bimetallic biochar adsorbents in Examples 1 to 10 of the present invention are shown.

[0024] Figure 2 X-ray diffraction patterns of the nitrogen-doped bimetallic biochar adsorbents prepared in Examples 1 and 6 of this invention, the BC adsorbent prepared in Comparative Example 1, and the NBC adsorbent prepared in Comparative Example 2.

[0025] Figure 3 Scanning electron microscope images of the nitrogen-doped bimetallic biochar adsorbent prepared in Examples 1 and 6 of this invention, the BC adsorbent prepared in Comparative Example 1, and the NBC adsorbent prepared in Comparative Example 2, wherein (a) is the BC adsorbent; (b) is the NBC adsorbent; (c) is the FeCo-NBC adsorbent; and (d) is the FeCa-NBC adsorbent.

[0026] Figure 4 Infrared spectra of the nitrogen-doped bimetallic biochar adsorbents prepared in Examples 1 and 6 of this invention, the BC adsorbent prepared in Comparative Example 1, and the NBC adsorbent prepared in Comparative Example 2.

[0027] Figures 5 to 7 The X-ray photoelectron spectra of the nitrogen-doped bimetallic biochar adsorbents prepared in Examples 1 and 6 of this invention, the BC adsorbent prepared in Comparative Example 1, and the NBC adsorbent prepared in Comparative Example 2 are shown below. Figure 5 (a) XPS full spectrum of BC, NBC, FeCo-NBC and FeCa-NBC adsorbents; Figure 5 (b) Fine XPS spectra of Fe2p for FeCo-NBC and FeCa-NBC adsorbents; Figure 5 (c) is the fine Co 2p XPS spectrum of the FeCo-NBC adsorbent; Figure 5 (d) is the fine Ca 2p XPS spectrum of the FeCa-NBC adsorbent; Figure 6 (e) is the fine C1s XPS spectrum of the BC adsorbent; Figure 6 (f) is the fine C1s XPS spectrum of the NBC adsorbent; Figure 6 (g) is the fine C1s XPS spectrum of the FeCo-NBC adsorbent; Figure 6 (h) is the fine C1s XPS spectrum of the FeCa-NBC adsorbent; Figure 7 (i) Fine O1s XPS spectrum of BC adsorbent; Figure 7 (j) is the fine XPS spectrum of the NBC adsorbent in O 1s; Figure 7(k) O 1s XPS fine spectrum of FeCo-NBC adsorbent; Figure 7 (l) is the fine XPS spectrum of FeCa-NBC adsorbent O 1s; Figure 7 (m) is the N 1s XPS fine spectrum of the NBC adsorbent; Figure 7 (n) is the fine N 1s XPS spectrum of the FeCo-NBC adsorbent; Figure 7 (o) is the N 1s XPS fine spectrum of the FeCa-NBC adsorbent.

[0028] Figure 8 Raman spectra of the nitrogen-doped bimetallic biochar adsorbents prepared in Examples 1 and 6 of this invention, the BC adsorbent prepared in Comparative Example 1, and the NBC adsorbent prepared in Comparative Example 2.

[0029] Figure 9 The graph shows the magnetic properties of the nitrogen-doped bimetallic biochar adsorbents prepared in Examples 1 and 6 of this invention. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0031] Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0032] The technical solution of the present invention will be further described below through specific embodiments.

[0033] In the following embodiments, unless otherwise specified, the methods described are conventional methods; and unless otherwise specified, the reagents and materials described are commercially available.

[0034] Example 1 A method for preparing a nitrogen-doped bimetallic biochar adsorbent includes the following steps: Grape pomace waste is washed, dried, and ground to obtain grape pomace (GP) biomass.

[0035] Take 6g of pretreated GP and 60mL of 3mol·L⁻¹ -1 The mixture was stirred magnetically for 1 hour and then placed in a stainless steel high-pressure reactor lined with polytetrafluoroethylene. The mixture was then hydrothermally reacted at 200°C for 8 hours. The resulting black particles were washed until neutral and dried in an oven at 90°C to obtain hydrothermal biochar BC.

[0036] Mix BC, KOH, and urea in a mass ratio of 2:2:1, and add 0.04 mol·L⁻¹ -1 FeCl3 and 0.04 mol·L -1 A CoCl2 mixture was prepared, wherein BC:bimetallic mixture = 1 g: 10 mL. After magnetic stirring for 1 h, the mixture was dried in an oven at 100 °C. The solid mixture was then placed in a muffle furnace and heated to 600 °C at a programmed rate of 10 °C / min, and held for 120 min. After cooling, the product was washed until neutral and dried in an oven at 90 °C to obtain a nitrogen-doped iron-cobalt bimetallic biochar adsorbent, denoted as FeCo-NBC.

[0037] Example 2 The difference between this embodiment and Example 1 is that the concentration of CoCl2 is 0.02 mol·L⁻¹. -1 .

[0038] Example 3 The difference between this embodiment and Example 1 is that the concentration of CoCl2 is 0.06 mol·L⁻¹. -1 .

[0039] Example 4 The difference between this embodiment and Example 1 is that the concentration of CoCl2 is 0.08 mol·L⁻¹. -1 .

[0040] Example 5 The difference between this embodiment and Example 1 is that the concentration of CoCl2 is 0.1 mol·L⁻¹. -1 .

[0041] Example 6 The difference between this embodiment and Example 1 is that: 0.04 mol·L -1 The CoCl2 was replaced with 0.06 mol·L⁻¹ -1 The nitrogen-doped iron-calcium bimetallic biochar adsorbent, denoted as FeCa-NBC, was obtained from CaCl2.

[0042] Example 7 The difference between this embodiment and Example 1 is that: 0.04 mol·L -1 The CoCl2 was replaced with 0.02 mol·L⁻¹ -1 CaCl2.

[0043] Example 8 The difference between this embodiment and Example 1 is that: 0.04 mol·L -1 The CoCl2 was replaced with 0.04 mol·L⁻¹ -1 CaCl2.

[0044] Example 9 The difference between this embodiment and Example 1 is that: 0.04 mol·L -1 The CoCl2 was replaced with 0.08 mol·L⁻¹ -1 CaCl2.

[0045] Example 10 The difference between this embodiment and Example 1 is that: 0.04 mol·L -1 The CoCl2 was replaced with 0.1 mol·L⁻¹ -1 CaCl2.

[0046] Comparative Example 1 A method for preparing a BC adsorbent includes the following steps: Grape pomace waste is washed, dried, and ground to obtain grape pomace (GP) biomass.

[0047] Take 6g of pretreated GP and 60mL of 3mol·L⁻¹ -1 The mixture was stirred magnetically for 1 hour and then placed in a stainless steel high-pressure reactor lined with polytetrafluoroethylene. The mixture was then subjected to hydrothermal reaction at 200°C for 8 hours. The resulting black particles were washed until neutral and dried in an oven at 90°C to obtain hydrothermal biochar BC adsorbent.

[0048] Comparative Example 2 A method for preparing an NBC adsorbent includes the following steps: Grape pomace waste is washed, dried, and ground to obtain grape pomace (GP) biomass.

[0049] Take 6g of pretreated GP and 60mL of 3mol·L⁻¹ -1 The mixture was stirred magnetically for 1 hour and then placed in a stainless steel high-pressure reactor lined with polytetrafluoroethylene. The mixture was then hydrothermally reacted at 200°C for 8 hours. The resulting black particles were washed until neutral and dried in an oven at 90°C to obtain hydrothermal biochar BC.

[0050] BC, KOH, and urea were mixed in a mass ratio of 2:2:1 and magnetically stirred for 1 hour. The mixture was then dried in an oven at 100°C. The solid mixture was placed in a muffle furnace and heated to 600°C at a rate of 10°C / min, maintaining the temperature for 120 minutes. After cooling, the product was washed until neutral and dried in an oven at 90°C to obtain the NBC adsorbent.

[0051] The nitrogen-doped bimetallic biochar adsorbents prepared in Examples 1 and 6, the BC adsorbent prepared in Comparative Example 1, and the NBC adsorbent prepared in Comparative Example 2 were characterized by X-ray diffraction (XRD) using a Bruker D8 Advance-A25 X-ray diffractometer (Germany) with a scanning range of 3° to 80°. The results are as follows: Figure 2As shown. The results show that: BC has broadened diffraction peaks near 2θ=23° and 43°, indicating that its graphitization degree is low; the diffraction peak intensity of NBC at the (100) crystal plane is slightly increased, and no new crystal diffraction peaks appear, indicating that the modification process of KOH and urea mainly changes the pore structure of biochar rather than the crystal structure; FeCo-NBC and FeCa-NBC both show characteristic diffraction peaks of spinel-type iron-based oxides, corresponding to crystal planes such as (220), (311), (400), (422), and (511) respectively (JCPDS No. 85–1436), while retaining the (100) crystal plane of biochar, and the degree of graphitization is enhanced, indicating that Fe and Co (Ca) are successfully introduced into biochar.

[0052] The morphology of the nitrogen-doped bimetallic biochar adsorbents prepared in Examples 1 and 6, the BC adsorbent prepared in Comparative Example 1, and the NBC adsorbent prepared in Comparative Example 2 were observed by scanning electron microscopy (SEM) using a ZEISS EV018 scanning electron microscope (Germany). The results are as follows: Figure 3 As shown. The results indicate that the surface of biochar (BC) exhibits a relatively smooth, sheet-like structure with sparse pore development, resulting in a scarcity of adsorption sites. After activation by co-pyrolysis with KOH and urea, a rough, porous network structure forms on the NBC surface, destroying the original dense sheet-like morphology. This is because the etching effect of KOH generates a large number of micropores and mesopores, while nitrogen doping of urea further modulates the pore morphology and introduces Fe. 3+ With Co 2+ or Ca 2+ After co-doping, both FeCo-NBC and FeCa-NBC exhibited obvious nanoparticle loading characteristics on their surfaces, but their microstructures differed significantly: the bimetallic particles loaded on the FeCo-NBC surface were better dispersed, with no obvious agglomerates, and the particles were tightly bound to the carbon matrix; the FeCa-NBC surface showed an irregular, granular aggregate morphology with many uneven sites. This is because the addition of calcium ions caused the metal oxides generated during the high-temperature pyrolysis of the biomass feedstock, grape pomace, to clog some of the pores of the biochar.

[0053] The nitrogen-doped bimetallic biochar adsorbents prepared in Examples 1 and 6, the BC adsorbent prepared in Comparative Example 1, and the NBC adsorbent prepared in Comparative Example 2 were characterized by Fourier transform infrared spectroscopy (FT-IR) using a Spectrum Tow FT-IR spectrometer (USA) with a scanning range of 500 cm⁻¹. -1 Up to 4000cm -1 The result is as follows Figure 4 As shown. The results indicate that BC and NBC are at 3500cm. -1 3000cm -1 1500cm-1 and 1380cm -1 The surrounding area exhibits characteristic absorption peaks, corresponding to the stretching vibrations of -OH, CH, C=C / C=O, and CN, respectively, reflecting the naturally distributed basic functional groups such as hydroxyl, alkyl, and aromatic groups on its surface. The CN characteristic peak intensity of NBC synergistically activated by urea-KOH is significantly enhanced. FeCo-NBC and FeCa-NBC show similar absorption peaks at 600 cm⁻¹. -1 ~700cm -1 Within the wavenumber range, characteristic stretching vibration peaks of Fe / Co-O and Ca-O appear respectively.

[0054] X-ray photoelectron spectroscopy (XPS) analysis was performed on the nitrogen-doped bimetallic biochar adsorbents prepared in Examples 1 and 6, the BC adsorbent prepared in Comparative Example 1, and the NBC adsorbent prepared in Comparative Example 2. A K-Alpha Plus X-ray photoelectron spectrometer (USA) was used. All binding energies were calibrated using the C1 s peak at 284.8 eV. The results are as follows: Figures 5 to 7 As shown in the figure. The results show that the scanning spectra of FeCo-NBC and FeCa-NBC have peaks around 284.75 eV, 531.89 eV, 400.00 eV, 710.16 eV and 781.14 eV (347.14 eV), respectively, which correspond to the binding energies of C1 s, O 1 s, N1 s, Fe 2p and Co 2p (Ca 2p).

[0055] In the Fe 2p spectrum, FeCo-NBC's Fe 2p 3 / 2 The peak at 710.61 eV is attributed to Fe(II), while the characteristic peaks at 713.16 eV and 723.56 eV indicate the presence of Fe(III), in which Fe... 3+ 72.73% Fe 2+ 27.27%; Fe2p of FeCa-NBC 3 / 2 The peak at 710.44 eV corresponds to Fe(II), and the peaks at 713.23 eV and 724.87 eV correspond to Fe(III), where Fe... 3+ 63.81%, Fe 2+ The proportion of 36.19% indicates that Fe exists in multiple valence states in both samples. Co 2p in FeCo-NBC 3 / 2 At 781.14 eV, Co 2p 1 / 2 The peak at 796.93 eV corresponds to Co(II), indicating that Co in FeCo-NBC is expressed as Co. 2+ Price-state stable load. Ca 2p in FeCa-NBC 3 / 2 At 347.14 eV, Ca 2p 1 / 2The peak at 350.66 eV is the characteristic binding energy of Ca(II), indicating that Ca in FeCa-NBC exists as stable Ca. 2+ The valence state exists on the surface of biochar.

[0056] C1s spectral analysis showed that all samples exhibited four characteristic peaks: CC / C=C (284.80 eV), CN (285.50 eV), CO (286.2 eV), and C=O (287.5 eV). In BC, CC / C=C accounted for as high as 76.2%, representing the dominant carbon structure in the original biochar, containing only 18.3% of the original oxygen-containing functional groups (CO). After KOH activation and urea nitrogen doping, the CC / C=C proportion in NBC decreased to 51.7%, because the alkaline etching effect of KOH disrupted the conjugated structure of some carbon skeletons, while introducing 24.8% CN and 23.5% CO functional groups. In FeCo-NBC, the CC / C=C proportion rebounded to 47.9%, and the CN proportion slightly increased to 26.7%, because the coordination of Fe, Co, and N atoms stabilized some of the conjugated carbon structure. In FeCa-NBC, the CO functional group proportion further increased to 25.1%, and Ca... 2+ The alkaline earth metal properties promote the retention of surface hydroxyl and carboxyl groups.

[0057] In the O 1s spectrum, FeCo-NBC and FeCa-NBC show peaks near 533.27 eV, 531.89 eV, and 530.43 eV (530.1 eV), respectively. These peaks are related to CO, C=O, and Fe / Co-O (Ca-O) groups. Nitrogen in the three nitrogen-doped materials mainly exists in the form of pyrrole nitrogen and pyridine nitrogen. The N element is successfully inserted into the carbon material in the form of pyridine-N and pyrrole-N, which can enhance the interfacial affinity of the carbon structure.

[0058] Raman spectroscopy analysis was performed on the nitrogen-doped bimetallic biochar adsorbents prepared in Examples 1 and 6, the BC adsorbent prepared in Comparative Example 1, and the NBC adsorbent prepared in Comparative Example 2. Crystal defects in the materials were determined using a DXR Raman spectrometer (USA). The results are as follows: Figure 8 As shown. The results indicate that: BC's I D / I G The value is 1.27, NBC rises to 2.46, and the I values ​​for FeCa-NBC and FeCo-NBC are... D / I G They reached 2.72 and 2.71 respectively, I D / I GThe continuous increase in Io indicates that metal doping not only introduces a crystalline metallic phase but also disrupts the ordered structure of carbon through doping and recombination, significantly increasing the defect density of carbon materials. This facilitates the entry and fixation of pesticides, thereby improving adsorption performance. Simultaneously, the Io of FeCo-NBC… G The peak intensity is higher than that of FeCa-NBC, indicating that its graphitization degree is slightly higher, which is conducive to π-π conjugated adsorption.

[0059] The magnetic properties of the nitrogen-doped bimetallic biochar adsorbents prepared in Examples 1 and 6 were measured using a LakeShore 7404 vibrating sample magnetometer (USA). The results are as follows: Figure 9 As shown in the figure, the saturation magnetization of FeCo-NBC and FeCa-NBC reached 3.78 emu / g and 4.72 emu / g, respectively. Although the magnetic contribution of Co was evident, the synergistic effect of magnetic dipole moments between Fe-Co oxides was relatively limited. In contrast, the interfacial interaction between Fe oxides and Ca-based components in FeCa-NBC enhanced the magnetic response activity of Fe ions, while the dispersion regulation of Fe oxide particles by the Ca-based components effectively weakened the cancellation effect of magnetic dipole moments between particles, thereby improving the saturation magnetization of the materials. Both methods can achieve rapid separation of solid and liquid systems, effectively avoiding the risk of secondary pollution during adsorbent recovery and demonstrating good potential for practical application.

[0060] The nitrogen-doped bimetallic biochar adsorbents prepared in Examples 1 and 6, the BC adsorbent prepared in Comparative Example 1, and the NBC adsorbent prepared in Comparative Example 2 were analyzed for specific surface area and porosity (BET) using a Micromeritics ASAP 2460 fully automated specific surface area and porosity analyzer (USA). The results are shown in Table 1.

[0061] Table 1. Specific surface area and pore structure parameters of different adsorbents The results showed that BC had a very underdeveloped pore structure with an average pore size of 25.94 nm, dominated by macropores, making it difficult to provide effective adsorption sites. After activation, NBC's pore size was significantly reduced to 2.23 nm, while its specific surface area and pore volume increased by 23.6 times and 2.0 times, respectively. FeCo-NBC had a slightly lower specific surface area and pore volume than NBC, but still significantly higher than BC, with an average pore size (2.26 nm) close to that of NBC. FeCa-NBC had a lower specific surface area and pore volume than FeCo-NBC, but a larger average pore size (2.58 nm). The pore structures of the two target adsorbents formed distinct complementary advantages: FeCo-NBC, with its high specific surface area as its core advantage, could provide more adsorption sites; FeCa-NBC, characterized by its larger pore size, could optimize mass transfer efficiency.

[0062] Kinetic tests were performed on the nitrogen-doped iron-cobalt bimetallic biochar adsorbent prepared in Example 1 using three different initial concentrations of pesticide mixed aqueous solutions (20, 40, and 60 mg·L⁻¹). -1 Samples were taken at 0, 10, 20, 30, 60, 90, 120, 150, and 180 min. 1.5 mL of the supernatant was collected, filtered through a 0.22 μm filter membrane, and then analyzed by high-performance reversed-phase high-performance liquid chromatography (HPLC). Pseudo-first-order, pseudo-second-order, Elovich, and interparticle diffusion models were used. The results are shown in Table 2.

[0063] Table 2 Adsorption kinetic parameters of FeCo-NBC adsorbent for methomyl and pirimicarb The results show that the kinetic properties of FeCo-NBC are better explained by the Elovich model because its fitting correlation coefficient (R²) is higher. 2 The adsorption efficiency (≥0.99) is significantly better than that of pseudo-first-order and pseudo-second-order adsorption equations, indicating that the FeCo-NBC surface has extremely strong heterogeneity and the adsorption process involves electron transfer between the adsorbent and pesticide molecules or dynamic activation of active sites. The intraparticle diffusion curves of FeCo-NBC are divided into three linear segments, named external diffusion, internal diffusion, and equilibrium, respectively.

[0064] Kinetic tests were performed on the nitrogen-doped iron-calcium bimetallic biochar adsorbent prepared in Example 6. The pseudo-first-order, pseudo-second-order, Elovich, and intraparticle diffusion models were used for fitting, and the results are shown in Table 3.

[0065] Table 3 Adsorption kinetic parameters of FeCa-NBC adsorbent for methomyl and imidacloprid The results show that the kinetic properties of FeCa-NBC are better explained by a pseudo-second-order model (R0). 2 The adsorption capacity (qe, cal) was ≥0.99, and the deviation between the calculated adsorption capacity (qe, cal) and the experimental value (qe, exp) was small, indicating that the adsorption of methamidophos and imidacloprid by FeCa-NBC was mainly chemisorption. The interparticle diffusion curves of FeCo-NBC were divided into three linear segments, named external diffusion, internal diffusion, and equilibrium, respectively.

[0066] Adsorption isotherm analysis was performed on the nitrogen-doped bimetallic biochar adsorbents prepared in Examples 1 and 6, and seven concentrations (10 mg·L⁻¹) were selected. -1 -150mg∙L -1At 180 min, 1.5 mL of the supernatant was collected, filtered through a 0.22 μm filter membrane, and then analyzed by high-performance reversed-phase high-performance liquid chromatography (HPLC). Langmuir, Freundlich, and Temkin models were used for fitting, and the results are shown in Table 4.

[0067] Table 4. Fitting parameters of the adsorption isotherms of FeCo-NBC and FeCa-NBC for methomyl and imidacloprid. The results show that the Freundlich model can perfectly fit the isotherm data of FeCo-NBC and FeCa-NBC, with a significantly higher correlation coefficient (R0). 2 The adsorption ratio (≥0.91) indicates that multilayer adsorption is dominant, which may be due to the heterogeneity of the adsorbent surface caused by the addition of Fe and Co (Ca) elements, resulting in local multilayer adsorption on the biochar surface. The 1 / n values ​​(0.22~0.38) are all less than 0.5, indicating that methamidophos and pirimicarb are easily adsorbed by FeCo-NBC and FeCa-NBC. Furthermore, the maximum adsorption capacity of the two adsorbents was calculated using the Langmuir adsorption model. The maximum adsorption capacity of methamidophos was ranked as follows: FeCo-NBC (50.97 mg∙g⁻¹). -1 FeCa-NBC (46.35 mg∙g) -1 The maximum adsorption capacity against aphids was ranked as follows: FeCa-NBC (159.50 mg∙g). -1 FeCo-NBC (147.56 mg∙g) -1 The Temkin model fitting results further supplemented the differences in adsorption interactions between the two adsorbents. It was observed that the Temkin model (R...) for FeCa-NBC... 2 The value ≥0.88 indicates that chemisorption occurs during the adsorption process, which is consistent with the kinetic conclusion.

[0068] Thermodynamic analysis was performed on the nitrogen-doped iron-cobalt bimetallic biochar adsorbent prepared in Example 1. Thermodynamic properties were studied at three experimental temperatures (20, 30, and 40 °C). At 180 min, 1.5 mL of the supernatant was collected, filtered through a 0.22 μm filter membrane, and analyzed by high-performance reversed-phase high-performance liquid chromatography (HPLC). The results are shown in Table 5.

[0069] Table 5. Adsorption thermodynamic parameters of FeCo-NBC for methomyl and imidacloprid The results showed that the absolute value of ΔG for FeCo-NBC increased with increasing temperature, indicating that higher temperatures favored the adsorption of methomyl and pirimicarb. A positive ΔH value indicated that the reaction was endothermic; the smaller ΔH value for FeCo-NBC in removing methomyl suggested that FeCo-NBC required less heat for the removal reaction, indicating that FeCo-NBC was more favorable for methomyl removal. This is consistent with the difference in maximum adsorption capacity calculated by Langmuir. ΔS > 0 indicated that the adsorption interface tended to become disordered over time, and the adsorption was an irreversible process, which was beneficial to the stability of the reaction system.

[0070] Thermodynamic analysis was performed on the nitrogen-doped iron-calcium bimetallic biochar adsorbent prepared in Example 6, and the results are shown in Table 6.

[0071] Table 6. Adsorption thermodynamic parameters of FeCa-NBC for methomyl and imidacloprid The results showed that the absolute value of ΔG for FeCa-NBC increased with increasing temperature, indicating that higher temperatures favored the adsorption of pymetrozine and imidacloprid. A positive ΔH value indicated that the reaction was endothermic; the smaller ΔH value for FeCa-NBC in removing imidacloprid suggested that FeCa-NBC required less heat for its removal, making it more favorable for imidacloprid removal. This is consistent with the difference in maximum adsorption capacity calculated by Langmuir. ΔS > 0 indicated that the adsorption interface tended towards disorder over time, and the adsorption was an irreversible process, which is beneficial to the stability of the reaction system.

[0072] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a nitrogen-doped bimetallic biochar adsorbent, characterized in that, Includes the following steps: Hydrothermal biochar was obtained by reacting grape pomace biomass with hydrochloric acid solution at 180℃~220℃. Hydrothermal biochar was mixed with KOH, nitrogen source and bimetal source solution, dried and then pyrolyzed by oxygen-limited pyrolysis carbonization method to obtain nitrogen-doped bimetallic biochar adsorbent. The bimetallic source solution is a first metal salt solution and a second metal salt solution. The first metal salt solution is an iron salt solution, and the second metal salt solution is a cobalt salt solution or a calcium salt solution.

2. The method for preparing the nitrogen-doped bimetallic biochar adsorbent according to claim 1, characterized in that, The hydrothermal reaction takes 6 to 10 hours.

3. The method for preparing the nitrogen-doped bimetallic biochar adsorbent according to claim 1, characterized in that, The oxygen-limited carbonization pyrolysis temperature is 550℃~650℃, the time is 100min~140min, and the heating rate is 10℃ / min~25℃ / min.

4. The method for preparing the nitrogen-doped bimetallic biochar adsorbent according to claim 1, characterized in that, The ratio of grape pomace biomass to hydrochloric acid solution is 1g:5mL~15mL; the concentration of hydrochloric acid solution is 2mol·L⁻¹. -1 ~7mol·L -1 .

5. The method for preparing the nitrogen-doped bimetallic biochar adsorbent according to claim 1, characterized in that, The nitrogen source is urea; the mass ratio of the hydrothermal biochar, potassium hydroxide and urea is 1-3:2:

1.

6. The method for preparing the nitrogen-doped bimetallic biochar adsorbent according to claim 1, characterized in that, The ratio of the bimetallic source solution to hydrothermal biochar is 10 mL to 12 mL: 1 g; The iron salt solution is an iron chloride solution, the cobalt salt solution is a cobalt chloride solution, and the calcium salt solution is a calcium chloride solution; The concentration of the iron salt solution is 0.02 mol·L⁻¹. -1 ~0.06 mol·L -1 The cobalt salt solution concentration is 0.02 mol·L⁻¹. -1 ~0.1mol·L -1 The calcium salt solution concentration is 0.02 mol·L⁻¹. -1 ~0.1mol·L -1 .

7. The application of a nitrogen-doped bimetallic biochar adsorbent prepared by the method according to any one of claims 1 to 6, characterized in that, Used to remove carbamate pesticides from water bodies.

8. The application of the nitrogen-doped bimetallic biochar adsorbent according to claim 7, characterized in that, The carbamate pesticides mentioned are methomyl and / or pirimicarb.

9. The application of the nitrogen-doped bimetallic biochar adsorbent according to claim 8, characterized in that, The application method is as follows: Based on the total volume of the carbamate pesticide aqueous solution, add nitrogen-doped bimetallic biochar adsorbent at a rate of 0.2 g / L. -1 ~0.5g·L -1 The dosage was added to an initial concentration of 20 mg·L⁻¹. -1 ~60mg∙L -1 In aqueous solutions of carbamate pesticides.

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