Magnetic nitrogen-doped reduced graphene oxide and preparation method and application thereof

Abstract

This invention belongs to the field of graphene materials and discloses a magnetic nitrogen-doped reduced graphene oxide, its preparation method, and its application. The method includes the following steps: (1) preparation of frangipani extract; (2) adding iron salt, sodium acetate, and frangipani extract to an aqueous solution of graphene oxide, ultrasonically mixing until homogeneous, and then carrying out a hydrothermal reaction. After the reaction is complete, the solid is separated using a strong magnet and washed, and then freeze-dried to obtain magnetic nitrogen-doped reduced graphene oxide. The prepared magnetic nitrogen-doped reduced graphene oxide material, used as a glassy carbon electrode modification material, exhibits excellent electrochemical performance and can be applied in the rapid detection of Cd(II). The synthesis method of this invention has the advantages of being simple, easy to implement, and environmentally friendly. The prepared magnetic nitrogen-doped reduced graphene oxide has important application value in sensing, catalysis, optics, and electronics.

Description

Technical Field

[0001] This invention belongs to the field of graphene materials, specifically relating to a magnetic nitrogen-doped reduced graphene oxide, its preparation method, and its application. Background Technology

[0002] Graphene is a two-dimensional nanomaterial with sps arranged in a hexagonal pattern. 2 Graphene is a bonded carbon atom. In recent years, due to its unique and outstanding properties such as high thermal conductivity, high specific surface area, high mechanical strength, and excellent electron transport performance, graphene has been widely used as an electrode modification material to prepare electrochemical sensors for the detection of substances such as heavy metals, pesticides, and pharmaceuticals. However, during the synthesis and processing of graphene, due to van der Waals forces, it is prone to agglomeration and recombination to form graphite. In current developments, reduced graphene oxide (rGO) is used as a substitute for pristine graphene due to its high specific surface area and excellent conductivity, and is used for the rapid detection of various substances. The reduction of graphene oxide (GO) leads to the partial recovery of the graphite network, usually achieved through chemical, thermal, and electrochemical pathways. In terms of chemical reduction, commonly used reducing agents include hydrazine (N2H4) and its derivatives, hydroquinone, and sodium borohydride (NaBH4). However, these chemicals are harmful to human health and the environment. Therefore, an environmentally friendly reduction method is needed to provide a sustainable alternative for the large-scale production of non-toxic rGO.

[0003] Generally, anchoring inorganic particles in graphene can prevent aggregation and significantly improve electrochemical performance. Various semiconductor nanoparticles, metals, and metal oxides have been anchored on rGO. In metal oxide nanoparticles of decorated reduced graphene oxide, Fe... 2+ and Fe 3+ Magnetite nanoparticles (Fe3O4) composed of valence metals have attracted widespread attention due to their unique properties, such as large specific surface area, ease of modification, strong magnetism, and biocompatibility. However, Fe3O4 nanoparticles exhibit certain limitations, such as mechanical instability, poor electrical conductivity, and weak electrocatalytic activity, resulting in poor electrochemical performance, low detection limits, low sensitivity, and narrow linear range. Therefore, anchoring Fe3O4 nanoparticles onto rGO sheets can effectively solve these major problems. To date, various methods have been used to synthesize Fe3O4 / rGO composites, such as microwave methods, hydrothermal methods, low-temperature plasma methods, microwave-assisted hydrothermal methods, template methods, self-assembly, and hydrolysis methods. However, these methods are time-consuming, use toxic chemicals, are costly, and involve complex processes.

[0004] Plumeria alba flower (PAF) is native to Mexico, mainly distributed in the states of Baja, Sonora, and Chihuahua, and is now widely distributed worldwide. Plumeria alba flower extract (PAFE) contains phenols, alkaloids, flavonoids, amino acids, triterpenoids, iridoids, aldehydes, sugars, aliphatic compounds, and iridoid glycosides, and has been successfully used to prepare nanomaterials such as gold and silver nanoparticles. Summary of the Invention

[0005] In order to overcome the shortcomings and deficiencies of the prior art, the primary objective of this invention is to provide a method for the green preparation of magnetic nitrogen-doped reduced graphene oxide (Fe3O4@N-rGO) based on hydrothermal method.

[0006] Another objective of this invention is to provide a method for preparing magnetic nitrogen-doped reduced graphene oxide.

[0007] Another objective of this invention is to provide an application of the electrochemical sensor prepared from the above-mentioned magnetic nitrogen-doped reduced graphene oxide in the rapid detection of Cd(II).

[0008] The objective of this invention is achieved through the following technical solution:

[0009] A method for preparing magnetic nitrogen-doped reduced graphene oxide includes the following steps:

[0010] (1) Preparation of frangipani extract: Frangipani flowers were mixed with water and heated for extraction. After the reaction was completed, the extract was obtained by filtration.

[0011] (2) Preparation of magnetic nitrogen-doped reduced graphene oxide: Iron salt, sodium acetate and frangipani extract were added to the aqueous solution of graphene oxide, and the mixture was ultrasonically mixed. Then, a hydrothermal reaction was carried out. After the reaction was completed, the solid was separated by a strong magnet and washed. The solid was then freeze-dried to obtain magnetic nitrogen-doped reduced graphene oxide.

[0012] Preferably, the preparation of the frangipani extract in step (1) is as follows: frangipani is mixed with water and reacted at 100±20℃ for 30±10 min. After the reaction is completed, the frangipani extract is obtained by filtration.

[0013] Preferably, the mass-to-volume ratio of frangipani to water is 1.0–5.0 g: 50 mL.

[0014] Preferably, the hydrothermal reaction in step (2) is carried out at 160-210°C for 6-12 hours, and more preferably at 180°C for 9 hours.

[0015] Preferably, the concentration of the graphene oxide aqueous solution in step (2) is 0.05–1.0 mg·mL.-1 More preferably 0.4 mg·mL -1 .

[0016] Preferably, the mass-to-volume ratio of graphene oxide, sodium acetate, and frangipani extract in step (2) is 1 mg:(30-300) mg:(0.25-2.5) mL; and the molar ratio of iron salt to sodium acetate is 1:(5-20).

[0017] Preferably, the mass-to-volume ratio of graphene oxide, sodium acetate, and frangipani extract in step (2) is (1.0-1.5) mg:(100-200) mg:1 mL; and the molar ratio of iron salt to sodium acetate is 1:10±5.

[0018] Preferably, the graphene oxide in step (2) is prepared using a modified Marcano method.

[0019] The magnetic nitrogen-doped reduced graphene oxide prepared by the above method can be used in the rapid detection of Cd(II), and has important application value in sensing, catalysis, optics, and electronics.

[0020] Using graphene oxide and iron salts as raw materials, sodium acetate as an electrostatic stabilizer, complexing agent, and alkali source, and frangipani extract as a reducing agent, end-capping agent, and nitrogen source, a one-step hydrothermal method was used to uniformly anchor Fe3O4 nanoparticles in nitrogen-doped reduced graphene oxide (N-rGO). The raw materials used in this invention are abundant, and the preparation method offers strong controllability. This preparation method effectively controls the growth of Fe3O4 nanoparticles; the obtained Fe3O4 nanoparticles are uniformly dispersed in nitrogen-doped reduced graphene oxide.

[0021] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0022] (1) Fe3O4@N-rGO was prepared using frangipani extract as a reducing agent, end-capping agent and nitrogen source. Using frangipani extract as a reducing agent avoids the use of toxic reducing agents, realizes green preparation and is easy to industrialize.

[0023] (2) The good conductivity and large specific surface area of ​​Fe3O4@N-rGO are utilized to improve the conductivity of glassy carbon electrode, which can be used for rapid detection of trace or ultra-trace Cd(II).

[0024] (3) The electrochemical sensor prepared by the Fe3O4@N-rGO composite material of the present invention can adapt to complex actual detection environments, such as rapid detection of Cd(II) in different samples such as tap water, river water and rice, and has a good recovery rate. Attached Figure Description

[0025] Figure 1 This is a schematic diagram illustrating the preparation process of Fe3O4@N-rGO and the construction process of the electrochemical sensor.

[0026] Figure 2 Infrared spectra of GO, N-rGO, Fe3O4, and Fe3O4@N-rGO.

[0027] Figure 3 TGA plots of GO, N-rGO, Fe3O4, and Fe3O4@N-rGO.

[0028] Figure 4 XRD spectra of GO, N-rGO, Fe3O4 and Fe3O4@N-rGO.

[0029] Figure 5 Raman spectra of GO, N-rGO, Fe3O4, and Fe3O4@N-rGO.

[0030] Figure 6 Electron micrographs of GO(a), N-rGO(b), Fe3O4(c) and Fe3O4@N-rGO(d).

[0031] Figure 7 XPS spectra of GO, N-rGO and Fe3O4@N-rGO (a) and high-resolution XPS spectrum of Fe 2p (b).

[0032] Figure 8 CV plots for GO, N-rGO, Fe3O4, Fe3O4@N-rGO, SC1-Fe3O4@rGO / GCE, SC2-Fe3O4@rGO / GCE, Hy-Fe3O4@rGO / GCE and bare glassy carbon electrode (Bare GCE).

[0033] Figure 9 DPSV diagrams of GO, N-rGO, Fe3O4, Fe3O4@N-rGO, SC1-Fe3O4@rGO / GCE, SC2-Fe3O4@rGO / GCE, Hy-Fe3O4@rGO / GCE and Bare GCE.

[0034] Figure 10 The effects of Fe3O4@N-rGO / GCE on different Cd(II) concentrations (a~l represent concentrations of 2.5, 5.0, 7.5, 10.0, 25.0, 50.0, 75.0, 100.0, 125.0, 150.0, 175.0, and 200.0 μmol·L⁻¹) were investigated. -1 The DPSV response of Cd(II) is shown in (a), and the linear relationship between peak current and Cd(II) concentration is shown in (b). Detailed Implementation

[0035] The present invention will be further described in detail below with reference to the embodiments and accompanying drawings, but the implementation of the present invention is not limited thereto.

[0036] Unless otherwise specified, all reagents used in the examples are commercially available.

[0037] Fourier transform infrared spectroscopy (FTIR): Fourier transform infrared spectroscopy is performed using KBr pellets at 400–4000 cm⁻¹. -1 Measurements were performed within the specified range (Spectrum 100, Perkin Elmer Inc., USA).

[0038] Thermogravimetric analysis (TG): Thermogravimetric analysis was performed using a TGA2 thermogravimetric analyzer (Mettler Toledo, Switzerland) at 50 mL / min. -1 Under a nitrogen atmosphere at 10℃·min -1 The thermal stability of the sample was measured within a temperature range of 40–700 °C.

[0039] X-ray diffraction (XRD): The X-ray diffractometer (Miniflex 600, Rigaku, Japan) is used to perform measurements in the range of 5 to 90° using a Cu target (λ = 0.154 nm).

[0040] Raman spectroscopy: Raman spectrometer (DXR2, Thermo Fisher, USA) was used in the range of 50–3400 cm⁻¹. -1 Measurements are taken within the specified range.

[0041] X-ray photoelectron spectroscopy (XPS): The elemental composition of the products was analyzed using an X-ray photoelectron spectroscopy spectrometer (Thermo Scientific K-Alpha, USA).

[0042] Scanning electron microscopy (SEM): The micromorphology of the product was observed using a scanning electron microscope (Zeiss Merlin Compact, Germany).

[0043] Example 1

[0044] (1) Preparation of frangipani extract: 2.5g of frangipani was added to 50mL of water and refluxed at 100℃ for 30min for extraction. After the reaction was completed, the frangipani extract was obtained by filtration.

[0045] (2) Preparation of Fe3O4@N-rGO: 12 mg of graphene oxide was added to 20 mL of deionized water and dissolved by sonication. 0.54 g of FeCl3·6H2O, 1.64 g of sodium acetate and 10 mL of frangipani extract obtained in step (1) were added and mixed by sonication (30 min). The solution was then transferred to a high-pressure reactor lined with polytetrafluoroethylene, sealed and subjected to hydrothermal reaction at 180 °C for 9 h. After the reaction was completed, the solid was separated by a strong magnet and washed multiple times with deionized water and anhydrous ethanol. Fe3O4@N-rGO was obtained by freeze drying for 72 h.

[0046] Figure 2 The FT-IR spectra of the prepared GO, N-rGO, Fe3O4, and Fe3O4@N-rGO are shown. For the GO sample, the FT-IR spectrum is at 3271 cm⁻¹. -1 The broad and strong absorption peak at 1739 cm⁻¹ corresponds to the stretching vibration of -OH; at 1739 cm⁻¹ -1 The vibration is a stretching vibration at C=O; at 1633 cm⁻¹ -1 The absorption peak at 1078 cm⁻¹ corresponds to the stretching vibration of C=C; -1 The peak intensity at this point is the stretching vibration of the epoxy group (COC). When frangipani extract is used as a reducing agent, the peak intensities of various oxygen-containing functional groups decrease significantly, especially at 1739 cm⁻¹. -1 (C=O) and 1078cm -1 The functional group at (COC) almost disappears. The C=C absorption peak redshifts to 1523 cm⁻¹. -1 Furthermore, N-rGO at 1204cm -1 A new peak appears at 583 cm⁻¹, attributed to the stretching vibration of CN, indicating that nitrogen doping occurred simultaneously during the reduction process. In Fe₃O₄, the peak is observed at 583 cm⁻¹. -1 and 437cm -1 Two strong absorption peaks were observed, which are characteristic vibrations of Fe-O, indicating the successful preparation of Fe3O4. In the Fe3O4@N-rGO nanocomposite, C=C(1562cm⁻¹) was also found. -1 ) and CN (1204cm -1 The absorption peak of ) is also observed at 583 cm⁻¹. -1 and 437cm -1 The two strong absorption peaks are attributed to the stretching mode of Fe-O, indicating that Fe3O4@N-rGO was successfully prepared.

[0047] Figure 3The images show the TGA spectra of GO, N-rGO, Fe3O4, and Fe3O4@N-rGO. GO exhibits three weight loss stages at 40–130℃, 135–222℃, and 222–330℃, with weight loss rates of 16.12%, 40.71%, and 6.96%, respectively. N-rGO also shows three weight loss stages at 40–130℃, 135–222℃, and 222–455℃, with weight loss rates of 9.75%, 4.05%, and 22.96%, respectively. Within the temperature range of 40–700℃, Fe3O4 nanoparticles exhibit high thermal stability, with a weight loss of only 7.55%. The Fe3O4@N-rGO sample also shows three weight loss stages at 40–130℃, 164–281℃, and 281–478℃, with weight loss rates of 6.17%, 6.87%, and 11.28%, respectively. Within the temperature range of 40–700℃, the weight loss rates of GO, N-rGO, Fe3O4, and Fe3O4@N-rGO were 59.48%, 46.13%, 7.55%, and 30.45%, respectively. Therefore, the Fe3O4 content in Fe3O4@N-rGO can be calculated to be 40.29%.

[0048] Figure 4 The XRD spectra of the prepared GO, N-rGO, Fe3O4, and Fe3O4@N-rGO are shown. GO exhibits a diffraction peak at 9.6°. N-rGO shows a broad diffraction peak at 24.9°. Fe3O4 exhibits diffraction peaks at 30.2°, 35.5°, 43.1°, 53.7°, 57.1°, and 62.9°, corresponding to the (220), (311), (400), (422), (511), and (440) crystal planes of Fe3O4 (JCPDS:19-0629), respectively. The spectrum of Fe3O4@N-rGO shows the same characteristic diffraction peaks as Fe3O4. In addition, a characteristic diffraction peak of N-rGO appears at 22.9°, indicating that Fe3O4 and N-rGO coexist in the composite material.

[0049] Figure 5 The images show the Raman spectra of GO, N-rGO, Fe3O4, and Fe3O4@N-rGO. GO has two characteristic peaks, located at 1594 cm⁻¹. -1 (G peak) and 1353cm -1 (D peak). N-rGO also shows a similar peak. However, the intensity of the D peak changes due to the increase in defects. The characteristic peak of Fe3O4 is located at 688 cm⁻¹. -1 A with Fe-O 1g The vibration mode is relevant. The other two characteristic peaks are located at 493 and 353 cm⁻¹. -1 E with Fe-O 1gThe vibrational modes are relevant. In the Fe3O4@N-rGO sample, in addition to the G and D peaks, peaks at 688, 493, and 353 cm⁻¹ were also observed. -1 The characteristic peaks indicate that Fe3O4 and rGO coexist in the composite material. Furthermore, A 1g and E 1g The presence of vibrational modes indicates that the product is a magnetite phase. D / I G The Ig value can indicate the degree of defect in graphene-based materials. The Ig values ​​for GO, N-rGO, and Fe3O4@N-rGO are shown. D / I G The values ​​were 0.83, 0.95, and 1.07, respectively. D / I G The increase in the value indicates that there are more defects in the prepared Fe3O4@N-rGO sample, which means that Fe3O4@N-rGO has more active sites.

[0050] Figure 6 SEM images of the prepared GO, N-rGO, Fe3O4, and Fe3O4@N-rGO are shown. GO shows a small number of wrinkled regions. Figure 6 a), but the surface is relatively smooth. After reduction ( Figure 6 (b) This process eliminated some oxygen-containing functional groups on the GO surface, restoring the conjugated structure and resulting in a significant increase in the number of wrinkles. From Figure 6 As shown in (c), the Fe3O4 nanoparticles are rod-shaped, with a width of 175.14±0.29 nm and a length of 791.01±0.55 nm. Figure 6 (c Illustration). In Fe3O4@N-rGO, rod-shaped Fe3O4 nanoparticles are dispersed in N-rGO ( Figure 6 d). These results demonstrate the successful preparation of Fe3O4@N-rGO.

[0051] The chemical composition of GO, N-rGO, and Fe3O4@N-rGO was analyzed using XPS. Figure 7As shown in (a), C and O were found in the XPS spectrum of GO, with a C / O ratio of 1.48. N-rGO contained C, O, and N, with a C / O ratio of 5.65. The increased C / O ratio confirms the effective reduction of GO by PAFE. The presence of N indicates that reduction and nitrogen doping reactions occurred simultaneously in the hydrothermal reaction. Fe3O4@N-rGO contained C, O, N, and Fe. Six peaks could be fitted in the high-resolution Fe 2p spectrum. The diffraction peaks at 710.2 eV and 723.7 eV were attributed to Fe(II)-O, the diffraction peaks at 712.6 eV and 726.2 eV were attributed to Fe(III)-O, and the diffraction peaks at 718.1 eV and 732.7 eV were attributed to companion peaks. The XPS results indicate the presence of Fe3O4 in the composite material.

[0052] Preparation mechanism investigation: Sodium acetate, as an electrostatic stabilizer, can also act as a ligand, reacting with Fe... 3+ An intermediate complex phase, ferric acetate hydrate, is formed. The ferric acetate hydrate then forms a brown precipitate of Fe₂O₃, which is eventually reduced to FeO by the frangipani extract. When the ratio of Fe₂O₃ to FeO in the solution is 1:1, Fe₃O₄ is formed. Furthermore, the hydroxyl and amino groups of the bioactive molecules in the frangipani extract also react with Fe… 3+ The compounds combine to form complexes, which are then partially reduced by other bioactive substances, eventually generating Fe3O4 particles. During nucleation, the frangipani extract also acts as a capping agent, thus limiting the growth space for Fe3O4 nucleation and resulting in a unique rod-shaped structure.

[0053] Comparative Example 1

[0054] The difference between this comparative example and Example 1 is that no reducing agent is added, that is, the frangipani extract in step (2) is replaced with an equal volume of deionized water (W-Fe3O4@rGO).

[0055] Comparative Example 2

[0056] The difference between this comparative example and Example 1 is that a chemical agent is used for reduction, that is, the frangipani extract in step (2) is replaced with an equal volume of hydrazine hydrate (Hy-Fe3O4@rGO).

[0057] Comparative Example 3

[0058] The difference between this comparative example and Example 1 is that the frangipani extract in step (2) is replaced with sodium citrate (SC1-Fe3O4@rGO).

[0059] Comparative Example 4

[0060] The difference between this comparative example and Example 1 is that sodium acetate in step (2) is replaced with sodium citrate (SC2-Fe3O4@rGO).

[0061] Preparation of modified electrodes: Before surface modification, the glassy carbon electrode (GCE) (Φ=3mm) was carefully polished on a polishing cloth with 5μm and 0.05μm alumina suspensions, respectively, and then thoroughly rinsed with deionized water and anhydrous ethanol, and then air-dried at room temperature. 10μL of Fe3O4@N-rGO dispersion (1mg·mL⁻¹) was then added. -1 Fe3O4@N-rGO / GCE modified electrodes were obtained by drop-coating onto the GCE surface and drying under an infrared lamp. Other modified electrodes were prepared using the same method.

[0062] Electrochemical performance testing: at 1 mmol·L -1 K3Fe(CN)6 and 0.1 mol·L -1 KCl (1:1) is used as a supporting electrolyte at 0.1 V·s -1 Cyclic voltammetry (CV) was performed at a scanning speed within a potential range of -0.2 to 0.6 V (CHI660E, Shanghai Chenhua Instrument Co., Ltd., Shanghai).

[0063] The conductivity of Bare GCE, GO / GCE, Fe3O4 / GCE, N-rGO / GCE, Fe3O4@N-rGO / GCE, W-Fe3O4@rGO / GCE, SCl-Fe3O4@rGO / GCE, SCl-Fe3O4@rGO / GCE, and Hy-Fe3O4@rGO / GCE was analyzed using CV technology. The results are as follows: Figure 8As shown, clear redox peaks were observed in all curves. Compared to bare GCE, GO-modified GCE reduced the redox peak current due to the poor conductivity of GO. For the Fe3O4-modified electrode, the CV response was enhanced. After modifying GCE with N-rGO, the redox peak current was enhanced due to the high conductivity of N-rGO. When Fe3O4 was combined with N-rGO, the redox peak current of Fe3O4@N-rGO / GCE was further enhanced. Compared to Fe3O4@N-rGO / GCE, the redox peak current of W-Fe3O4@rGO / GCE decreased significantly. This is because water replacing PAFE lacks reducing power, and GO still contains a large number of oxygen-containing groups, resulting in poor conductivity. When sodium citrate is used instead of sodium acetate, the conductivity is significantly worse than that of Fe3O4@N-rGO / GCE; when hydrazine hydrate is used as the reducing agent, the conductivity is slightly worse than that of Fe3O4@N-rGO / GCE; and when sodium citrate is used as the reducing agent, the conductivity is slightly worse than that of Fe3O4@N-rGO / GCE and Hy-Fe3O4@rGO / GCE. Therefore, PAFE shows promise as a potential alternative to hydrazine hydrate.

[0064] Cd(II) determination: Cd(II) was detected using differential pulse stripping voltammetry (DPSV). At 0.1 mol·L⁻¹ -1 In ABS buffer solution (pH 5.0), the sample was first pre-enriched for 180 s, then deposited at a deposition potential of -0.9 V for 150 s, and finally Cd(II) was measured in a potential range of -1.0 to -0.7 V with a pulse amplitude of 50 mV, a pulse width of 0.05 s, and a pulse period of 0.5 s.

[0065] The effects of different material modifications on the detection performance of GCE were studied using the DPSV method. The results are as follows: Figure 9As shown, GO / GCE exhibits the lowest peak response signal due to its poor conductivity. Compared to bare GCE, Fe3O4 / GCE shows higher sensitivity to Cd(II), likely due to the unique electron transport and high adsorption properties of Fe3O4 nanoparticles. N-rGO, with its excellent electron transport capability, large electroactive surface area, and good adsorption, increases the peak current when modified with N-rGO. The peak response signal of W-Fe3O4@rGO / GCE is worse than that of Fe3O4 / GCE because water, which replaces PAFE, lacks reducing power, and GO contains a large number of oxygen-containing groups, resulting in the lowest peak current. However, the peak response signals of GCE modified with SC1-Fe3O4@rGO, SC2-Fe3O4@rGO, and Hy-Fe3O4@rGO are significantly improved compared to N-rGO / GCE, but still worse than Fe3O4@N-rGO / GCE. Therefore, PAFE shows promise as a potential alternative to hydrazine hydrate.

[0066] The relationship between peak current and Cd(II) concentration was studied using the DPSV method, and the results are as follows: Figure 10 As shown. From Figure 10 As shown in (a), the peak current value increases with increasing Cd(II) concentration. A linear fit was performed between the peak current value and the Cd(II) concentration. Figure 10 (b) It can be seen that when the Cd(II) concentration is between 2.5 and 200 μmol·L⁻¹ -1 Within this range, there is a good linear relationship between the peak current difference and the concentration. The linear equation is I... p = -0.411C Cd(II) +0.331, the correlation coefficient is R. 2 =0.998, detection limit is 0.10 μmol·L -1 This indicates that the established method has a low level of optical displacement (LOD). Therefore, as an electrode material, Fe3O4@N-rGO has broad application prospects in the field of electrochemical detection of heavy metal ions.

[0067] Detection Mechanism Investigation: The N-rGO prepared using frangipani extract in this invention has a wrinkled and uneven surface structure, providing more contact sites with Cd(II). Furthermore, the oxygen-containing groups remaining during the reduction process of N-rGO can form complexes with Cd(II), thereby enhancing the adsorption of Cd(II) on the electrode surface. In addition, the incorporation of nitrogen into the rGO structure provides lone pairs of electrons as electron acceptors, further improving the conductivity of the electrode. When Fe3O4 is grown in situ on N-rGO, the interlayer spacing of N-rGO increases, and Fe3O4 can adsorb Cd(II) through internal spherical adsorption, further enhancing the adsorption of Cd(II) on the electrode surface and laying the foundation for improved detection sensitivity. In summary, due to the synergistic effect of N-rGO and Fe3O4, Fe3O4@N-rGO / GCE exhibits excellent electrochemical performance for Cd(II), thereby improving the sensitivity of the electrochemical sensor and lowering the detection limit.

[0068] Spiked recovery experiments were conducted to verify the potential of the Fe3O4@N-rGO / GCE electrochemical sensor in practical applications. Table 1 shows the spiked recovery results for river water, tap water, and rice samples. At the three spiked levels, the recoveries ranged from 96.5% to 102.8%, with RSDs all less than 3.3%. These results indicate that the sensor can adapt to complex real-world detection environments and can be used to analyze Cd(II) in real samples.

[0069] Table 1 shows the spiked recovery test results of Cd(II) in different actual samples.

[0070]

[0071]

[0072] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for preparing magnetic nitrogen-doped reduced graphene oxide, characterized by, Includes the following steps: (1) Preparation of frangipani extract: Frangipani was subjected to hydrothermal extraction to obtain frangipani extract; (2) Preparation of magnetic nitrogen-doped reduced graphene oxide: Iron salt, sodium acetate and frangipani extract were added to the aqueous solution of graphene oxide, and the mixture was ultrasonically mixed evenly. Then, a hydrothermal reaction was carried out. After the reaction was completed, the solid was separated by a strong magnet and washed. The solid was then freeze-dried to obtain magnetic nitrogen-doped reduced graphene oxide. Preparation of frangipani extract in step (1): Mix frangipani with water and react at 100±20 ℃ for 30±10 min. After the reaction is completed, filter to obtain frangipani extract. The hydrothermal reaction conditions in step (2) are 160~210 ℃ for 6~12 h; The concentration of the graphene oxide aqueous solution in step (2) is 0.05-1.0 mg•mL -1 ; In step (2), the mass-to-volume ratio of graphene oxide to sodium acetate and frangipani extract is 1 mg:(30~300) mg:(0.25~2.5) mL; the molar ratio of iron salt to sodium acetate is 1:(5~20).

2. The production method according to claim 1, characterized by, The mass-to-volume ratio of frangipani to water is 1.0~5.0 g:50 mL.

3. The production method according to claim 1 or 2, characterized by, In step (2), the mass-to-volume ratio of graphene oxide to sodium acetate and frangipani extract is 1 mg:(100~200) mg:1 mL; the molar ratio of iron salt to sodium acetate is 1:10±5.

4. The preparation method according to claim 1 or 2, characterized in that, The graphene oxide in step (2) was prepared using a modified Marcano method; the iron salt was one or more of FeCl3, Fe(NO3)3 and Fe2(SO4)3.

5. Magnetic nitrogen-doped reduced graphene oxide prepared by the method according to any one of claims 1 to 4.

6. The application of the magnetic nitrogen-doped reduced graphene oxide as described in claim 5 in the rapid detection of Cd(II).

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