Preparation and application of a composite material based on ni / co bimetallic doped moc combined with molecular imprinting technology

Abstract

The application discloses a preparation method of a Ni / Co bimetallic doped MoC composite material combined with a molecular imprinting technique as an electrode material of an electrochemical sensor. The application aims to solve the problems of low sensitivity and poor selectivity of tetracycline detection in the electrochemical sensor. The application mainly comprises the following steps: 1, preparation of MoC and monometallic doped MoC (Ni-MoC and Co-MoC); 2, preparation of Ni / Co bimetallic doped MoC (Ni-Co-MoC); and 3, preparation of a molecular imprinting polymer coated Ni-Co-MoC (MIP@Ni-Co-MoC / GCE). The application has the characteristics of simple synthesis process and high selectivity. By introducing two metal heteroatoms of Ni and Co with different atomic radii and valence electron configurations, lattice distortion can be caused in the MoC crystal lattice, the energy band structure can be controlled, the Fermi level can be optimized, a high-efficiency conductive network can be constructed, and then the electronic transmission and electrocatalytic activity can be improved. The application has high sensitivity (5.04 muA muM −1 cm ‑2 , 0~60 muM) and low detection limit (22.7 nM) in the detection of tetracycline.

Description

Technical Field

[0001] This invention relates to the fields of material preparation and sensing, specifically to the study of electrochemical detection of tetracycline using a Ni / Co bimetallic doped MoC structure as a molecularly imprinted sensor. Background Technology

[0002] Tetracycline is one of the most widely used broad-spectrum antibiotics in animal husbandry, but its irrational use and resulting residues pose a serious threat to food safety, the ecological environment, and human health. Traditional detection techniques (such as HPLC and LC-MS / MS), while highly accurate, suffer from drawbacks such as complex operation, long processing times, and reliance on large instruments and specialized personnel, making them unsuitable for rapid on-site detection. Rapid detection methods like enzyme-linked immunosorbent assays (ELISA) suffer from insufficient specificity and susceptibility to matrix interference. Therefore, developing a rapid electrochemical detection technology for tetracycline with high sensitivity, high specificity, and rapid response is a key research focus in the food and public health testing fields. Molecular imprinting (MIP) technology, due to its strong specificity, good stability, and low preparation cost, is currently widely used in environmental monitoring, catalysis, biomedicine, and sensing. However, traditional MIP detection of TC suffers from poor conductivity and deep embedding of active sites, requiring the use of composite functional materials with high conductivity and high catalytic activity to further improve performance.

[0003] Constructing a hollow nanorod-based Ni-Co-MoC composite material can be an effective strategy to solve the above problems. A molecularly imprinted electrochemical sensor (MIP@Ni-Co-MoC / GCE) was prepared on the surface of a Ni-Co-MoC / GCE electrode via electropolymerization, and after elution, it was constructed, achieving high selectivity and high sensitivity for tetracycline detection. By introducing Ni and Co bimetallic heteroatoms with different atomic radii and valence electron configurations, lattice distortion and defect sites can be induced in the MoC lattice, thereby achieving precise control of its band structure, effectively reducing the band gap and optimizing the Fermi level distribution. Simultaneously, the synergistic effect of the Ni-Co bimetallic material can inject a large number of free carriers into the MoC matrix, significantly increasing the electron concentration of the system, constructing a continuous and efficient conductive network, accelerating the electron migration rate within the bulk phase and at the interface, and improving the charge transfer kinetics. This synergistic regulation and optimization of electronic structure and charge transport properties can significantly increase the number of active sites on the electrode surface, enhance the intrinsic catalytic activity of the sites, promote the efficient adsorption and rapid conversion of reaction intermediates, and ultimately achieve a significant improvement in the electrocatalytic performance of the electrode material.

[0004] In summary, this invention synthesizes hollow nanorod-shaped Ni-Co-MoC electrode materials through bimetallic doping, and then prepares MIP@Ni-Co-MoC / GCE electrodes via electropolymerization. This achieves highly selective and sensitive trace detection of tetracycline (TC). The ternary synergistic effect formed between Ni, Co bimetals, and MoC: bimetallic co-doping significantly increases the number of active sites and electrochemical active area on the electrode surface, optimizes the material's electronic structure, accelerates interfacial electron transport rate, and the complementary nature of the active sites of Ni and Co synergistically promotes the electrochemical reaction, further enhancing the electrode's electrocatalytic performance. This results in excellent electrochemical detection performance and stability, making it a promising electrode material for tetracycline detection. Summary of the Invention

[0005] The purpose of this invention is to overcome the problems of traditional detection methods (such as HPLC and LC-MS / MS) that rely on expensive instruments and have poor convenience, and to provide a cost-effective and convenient detection solution. It improves the shortcomings of traditional molecularly imprinted electrochemical sensors, such as low stability, poor conductivity, and insufficient catalytic activity, by constructing a Ni / Co bimetallic doped MoC composite material, thereby enhancing the sensor's sensitivity and stability.

[0006] The present invention discloses the preparation and application of a Ni / Co bimetallic doped MoC composite material based on molecular imprinting technology. The preparation method is carried out according to the following steps:

[0007] I. Preparation of Ni-MoC, Co-MoC and MoC

[0008] 250 mg of ammonium molybdate tetrahydrate was dissolved in 70 mL of deionized water (if ammonium molybdate tetrahydrate is dissolved in deionized water with cobalt nitrate hexahydrate and nickel chloride hexahydrate respectively, Ni-MoC and Co-MoC are obtained respectively). Then, 300 mg of dopamine hydrochloride was added, and the mixture was stirred for 30 min to form a dark solution. Next, 150 mL of ethanol was added, forming a turbid liquid. Then, 0.4 mL of ammonia water was added, and the mixture was magnetically stirred for 3.5 h to finally form a black solution. The solution was then filtered and freeze-dried to obtain Mo-PDA. This was transferred to a ceramic boat and heated to 600–1000 °C (5 °C min) under an Ar atmosphere. -1 Then, keep it for 2 hours to synthesize MoC.

[0009] II. Preparation of Ni-Co-MoC

[0010] First, 250 mg of ammonium molybdate tetrahydrate, 12-60 mg of cobalt nitrate hexahydrate, and 10-50 mg of nickel chloride hexahydrate were dissolved in 70 mL of deionized water. Then, 300 mg of dopamine hydrochloride was added, and the mixture was stirred for 30 min to form a deep red solution. Next, 150 mL of ethanol was added, resulting in an orange turbid liquid. Then, 0.4 mL of ammonia water was added, and the mixture was magnetically stirred for 3.5 h to finally form a black solution. After filtration, Ni-Co-Mo-PDA was obtained by freeze-drying. This was transferred to a ceramic boat and heated to 800 °C (5 °C min) under an Ar atmosphere. -1 Ni-Co-MoC was synthesized by maintaining the process for 2 hours. The resulting product was named Ni-Co-MoC-x (where x is the molar ratio of Ni / Co doping).

[0011] III. Preparation of MIP@Ni-Co-MoC / GCE

[0012] A 3 mm diameter GCE was polished with alumina powder (1.0, 0.3, and 0.05 μm) and cleaned in an ultrasonic bath of anhydrous ethanol and deionized water to remove impurities. 2 mg of Ni-Co-MoC was immersed in 1 mL of a deionized water-anhydrous ethanol mixture, and then 5 μL of 1% Nafion was added. After ultrasonic dispersion, 5 μL of Ni-Co-MoC suspension was dropped onto the GCE surface and dried under an infrared lamp to obtain the Ni-Co-MoC / GCE working electrode.

[0013] A three-electrode system was used to synthesize a MIP film on the surface of Ni-Co-MoC / GCE via electropolymerization. The prepared Ni-Co-MoC / GCE was then immersed in a solution containing 1 mM TC and 5 mM C6H6O2 in 1 M KCl containing 5 mM [Fe(CN)6]. 3- / 4- In solution, electrochemical polymerization was performed 30 times on the electrode surface via CV at a scan rate of 50 mV / s within a potential range of -0.2 V to 0.7 V. The electrode was stirred in a CH3COOH:CH3OH (V1:V2=2:8) solution for 10 min to elute the embedded TC template molecules until the solution contained 5 mM [Fe(CN)6] in 1 M KCl. 3- / 4- A distinct and stable redox peak was observed in the solution. The prepared sensor was named MIP@Ni-Co-MoC / GCE.

[0014] Compared with existing technologies, the present invention has the following advantages:

[0015] (1) The invention innovatively constructs a Ni-Co-MoC composite structure, and the ternary synergistic effect formed between Ni, Co bimetals and MoC: Bimetal co-doping can significantly increase the number of active sites and electrochemical active area on the electrode surface, optimize the electronic structure of the material, accelerate the interfacial electron transport rate, and the active sites of Ni and Co are complementary, which can synergistically promote the electrochemical reaction and further improve the electrocatalytic performance of the electrode.

[0016] (2) This invention integrates the advantages of molecular imprinting technology and heterostructure materials. Using tetracycline as a template molecule and resorcinol as a functional monomer, a specific molecular imprinted cavity is constructed on the surface of the composite structure through electropolymerization. The imprinted cavity is highly compatible with the tetracycline molecule in terms of spatial morphology, size, and functional group arrangement, enabling precise and specific recognition of the target molecule. The prepared sensor can effectively suppress non-specific adsorption interference. In experiments on complex systems where structural analogs such as ofloxacin and norfloxacin coexist with inorganic ions such as K⁺ and Na⁺ and small molecules such as glucose and dopamine commonly found in food matrices, tetracycline can still be detected with high selectivity, successfully overcoming the technical bottleneck of poor selectivity in traditional electrochemical sensors. Attached Figure Description

[0017] Figure 1 This is a microscopic morphology photograph of a hollow carbon nanorod-shaped Ni-Co-MoC composite material.

[0018] Figure 2 This is a morphology diagram of a hollow carbon nanorod-shaped Ni-Co-MoC composite material.

[0019] Figure 3 The crystal structure and phase composition of a hollow carbon nanorod-shaped Ni-Co-MoC composite material are described.

[0020] Figure 4 It is the chemical composition of a hollow carbon nanorod-shaped Ni-Co-MoC composite material prepared;

[0021] Figure 5 The electrochemical performance of a hollow carbon nanorod-shaped Ni-Co-MoC composite electrode is described.

[0022] Figure 6 The TC map was detected by DPV method using a hollow carbon nanorod-shaped Ni-Co-MoC composite electrode.

[0023] Figure 7 These are test results for the electrode's anti-interference performance, reproducibility, repeatability, and stability of a hollow carbon nanorod-shaped Ni-Co-MoC composite material.

[0024] Figure 8These are microscopic images of a hollow carbon nanorod-shaped Ni-Co-MoC composite material. Detailed Implementation

[0025] Specific Implementation Method 1: Preparation and Application of Ni / Co Bimetallic Doped MoC Composite Material Based on Molecular Imprinting Technology. The preparation method is carried out according to the following steps:

[0026] I. Preparation of Ni-MoC, Co-MoC and MoC

[0027] 250 mg of ammonium molybdate tetrahydrate was dissolved in 70 mL of deionized water (if ammonium molybdate tetrahydrate is dissolved in deionized water with cobalt nitrate hexahydrate and nickel chloride hexahydrate respectively, Ni-MoC and Co-MoC are obtained respectively). Then, 300 mg of dopamine hydrochloride was added, and the mixture was stirred for 30 min to form a dark solution. Next, 150 mL of ethanol was added, forming a turbid liquid. Then, 0.4 mL of ammonia water was added, and the mixture was magnetically stirred for 3.5 h to finally form a black solution. The solution was then filtered and freeze-dried to obtain Mo-PDA. This was transferred to a ceramic boat and heated to 600–1000 °C (5 °C min) under an Ar atmosphere. -1 Then, keep it for 2 hours to synthesize MoC.

[0028] II. Preparation of Ni-Co-MoC

[0029] First, 250 mg of ammonium molybdate tetrahydrate, 12-60 mg of cobalt nitrate hexahydrate, and 10-50 mg of nickel chloride hexahydrate were dissolved in 70 mL of deionized water. Then, 300 mg of dopamine hydrochloride was added, and the mixture was stirred for 30 min to form a deep red solution. Next, 150 mL of ethanol was added, resulting in an orange turbid liquid. Then, 0.4 mL of ammonia water was added, and the mixture was magnetically stirred for 3.5 h to finally form a black solution. After filtration, Ni-Co-Mo-PDA was obtained by freeze-drying. This was transferred to a ceramic boat and heated to 800 °C (5 °C min) under an Ar atmosphere. -1 Ni-Co-MoC was synthesized by maintaining the process for 2 hours. The resulting product was named Ni-Co-MoC-x (where x is the molar ratio of Ni / Co doping).

[0030] III. Preparation of MIP@Ni-Co-MoC / GCE

[0031] A 3 mm diameter GCE was polished with alumina powder (1.0, 0.3, and 0.05 μm) and cleaned in an ultrasonic bath of anhydrous ethanol and deionized water to remove impurities. 2 mg of Ni-Co-MoC was immersed in 1 mL of a deionized water-anhydrous ethanol mixture, and then 5 μL of 1% Nafion was added. After ultrasonic dispersion, 5 μL of Ni-Co-MoC suspension was dropped onto the GCE surface and dried under an infrared lamp to obtain the Ni-Co-MoC / GCE working electrode.

[0032] A three-electrode system was used to synthesize a MIP film on the surface of Ni-Co-MoC / GCE via electropolymerization. The prepared Ni-Co-MoC / GCE was then immersed in a solution containing 1 mM TC and 5 mM C6H6O2 in 1 M KCl containing 5 mM [Fe(CN)6]. 3- / 4- In solution, electrochemical polymerization was performed 30 times on the electrode surface via CV at a scan rate of 50 mV / s within a potential range of -0.2 V to 0.7 V. The electrode was stirred in a CH3COOH:CH3OH (V1:V2=2:8) solution for 10 min to elute the embedded TC template molecules until the solution contained 5 mM [Fe(CN)6] in 1 M KCl. 3- / 4- A distinct and stable redox peak was observed in the solution. The prepared sensor was named MIP@Ni-Co-MoC / GCE.

[0033] Specific Implementation Method Two: Preparation and Application of a Ni / Co Bimetallic Doped MoC Composite Material Based on Molecular Imprinting Technology. The preparation method is carried out according to the following steps:

[0034] The difference between this embodiment and Specific Embodiment 1 is that the calcination temperature in step one is 800℃. Everything else is the same as in Specific Embodiment 1.

[0035] Specific Implementation Method 3: Preparation and Application of a Ni / Co Bimetallic Doped MoC Composite Material Based on Molecular Imprinting Technology. The preparation method is carried out according to the following steps:

[0036] The difference between this embodiment and Specific Embodiment 1 is that the content of (Co(NO3)2·6H2O) used in step two is 29.4 mg. Everything else is the same as in Specific Embodiment 1.

[0037] Specific Implementation Method 4: Preparation and Application of a Ni / Co Bimetallic Doped MoC Composite Material Based on Molecular Imprinting Technology. The preparation method is carried out according to the following steps:

[0038] The difference between this embodiment and Specific Embodiment 1 is that the content of NiCl2·6H2O used in step two is 23.95 mg. Everything else is the same as in Specific Embodiment 1.

[0039] The effectiveness of the present invention was verified by the following experiments:

[0040] This experiment describes the preparation and application of a Ni / Co bimetallic doped MoC composite material based on molecular imprinting technology. The preparation method is carried out according to the following steps:

[0041] I. Preparation of Ni-MoC, Co-MoC and MoC

[0042] 250 mg of ammonium molybdate tetrahydrate was dissolved in 70 mL of deionized water (if ammonium molybdate tetrahydrate is dissolved in deionized water with cobalt nitrate hexahydrate and nickel chloride hexahydrate respectively, Ni-MoC and Co-MoC are obtained respectively). Then, 300 mg of dopamine hydrochloride was added, and the mixture was stirred for 30 min to form a dark solution. Next, 150 mL of ethanol was added, forming a turbid liquid. Then, 0.4 mL of ammonia water was added, and the mixture was magnetically stirred for 3.5 h to finally form a black solution. The solution was then filtered and freeze-dried to obtain Mo-PDA. This was transferred to a ceramic boat and heated to 800 °C (5 °C min) under an Ar atmosphere. -1 Then, keep it for 2 hours to synthesize MoC.

[0043] II. Preparation of Ni-Co-MoC

[0044] First, 250 mg of ammonium molybdate tetrahydrate, 29.4 mg of cobalt nitrate hexahydrate, and 23.95 mg of nickel chloride hexahydrate were dissolved in 70 mL of deionized water. Then, 300 mg of dopamine hydrochloride was added, and the mixture was stirred for 30 min to form a deep red solution. Next, 150 mL of ethanol was added, resulting in an orange turbid liquid. Then, 0.4 mL of ammonia water was added, and the mixture was magnetically stirred for 3.5 h to finally form a black solution. After filtration, Ni-Co-Mo-PDA was obtained by freeze-drying. This was transferred to a ceramic boat and heated to 800 °C (5 °C min) under an Ar atmosphere. -1 Ni-Co-MoC was synthesized by maintaining the process for 2 hours. The resulting product was named Ni-Co-MoC-0.5 (0.5 being the Ni / Co doping molar ratio).

[0045] III. Preparation of MIP@Ni-Co-MoC / GCE

[0046] A 3 mm diameter GCE was polished with alumina powder (1.0, 0.3, and 0.05 μm) and cleaned in an ultrasonic bath of anhydrous ethanol and deionized water to remove impurities. 2 mg of Ni-Co-MoC was immersed in 1 mL of a deionized water-anhydrous ethanol mixture, followed by the addition of 5 μL of 1% Nafion. After ultrasonic dispersion, 5 μL of Ni-Co-MoC suspension was dropped onto the GCE surface and dried under an infrared lamp to obtain the Ni-Co-MoC / GCE working electrode.

[0047] A three-electrode system was used to synthesize a MIP film on the surface of Ni-Co-MoC / GCE via electropolymerization. The prepared Ni-Co-MoC / GCE was then immersed in a solution containing 1 mM TC and 5 mM C6H6O2 in 1 M KCl containing 5 mM [Fe(CN)6]. 3- / 4- In solution, electrochemical polymerization was performed 30 times on the electrode surface via CV at a scan rate of 50 mV / s within a potential range of -0.2 V to 0.7 V. The electrode was stirred in a CH3COOH:CH3OH (V1:V2=2:8) solution for 10 min to elute the embedded TC template molecules until the solution contained 5 mM [Fe(CN)6] in 1 M KCl. 3- / 4- A distinct and stable redox peak was observed in the solution. The prepared sensor was named MIP@Ni-Co-MoC / GCE.

[0048] Figure 1 ad represents the SEM morphology of pure MoC, Ni-MoC, Co-MoC, and Ni-Co-MoC-0.5, respectively. Figure 1 a) is a scan morphology image of pure MoC. Pure MoC exhibits a dense, solid spherical particle packing morphology, with active sites confined to the particle surface and limited mass transfer and electron transport channels. Figure 1 b) shows a Ni-MoC morphology with the appearance of short rod-like structures on the surface, but the size is not uniform. Figure 1 c) Co-MoC is a dense, blocky agglomerate with low surface porosity, which reflects the limitations of single-metal doping in controlling the morphology of MoC. Figure 1 d) Ni-Co-MoC-0.5 co-doped with Ni and Co exhibits a regular hollow nanorod structure. The nanorods have a hollow rod-like structure with a size of about 3 μM, which significantly increases the specific surface area of ​​the material.

[0049] Figure 2 a) TEM image of Ni-Co-MoC-0.5. In the HRTEM image, clear lattice fringes at 0.206 nm, 0.201 nm and 0.248 nm correspond to the (111), (111) and (101) lattice planes of Co, Ni and MoC, respectively. Figure 2 b) is the SAED pattern. Ni-Co-MoC-0.5 exhibits clear polycrystalline diffraction rings, which can be identified as the (111) and (220) crystal planes of Ni, the (111) crystal plane of Co, and the (004) crystal plane of MoC, respectively, confirming the coexistence of metallic Ni, Co and MoC phases in the sample. Figure 2(ch) is an EDS image of Ni-Co-MoC-0.5, showing that C, Mo, Co, and Ni elements are uniformly distributed throughout the Ni-Co-MoC material. These results indicate the successful preparation of Ni-Co-MoC-0.5, a Ni-Co co-doped MoC electrode material.

[0050] Figure 3 a) XRD patterns of MoC and Ni-Co-MoC-0.5, with phase composition analysis. Characteristic diffraction peaks at diffraction angles of 32.6°, 35.3°, 36.3°, 43.3°, 62.5°, and 74.7° correspond to the (004), (100), (101), (103), (106), and (200) crystal planes of MoC (PDF#03-065-3494). The characteristic peak at 26.6° corresponds to the (006) crystal plane of C (PDF#00-026-1076). In the XRD pattern of the Ni-Co-MoC-0.5 sample, in addition to the diffraction peaks of MoC, diffraction peaks at 52.5° and 77.5° are found to correspond to the (200) and (220) phases of Ni in (PDF#00-001-1266), and diffraction peaks at 44.2°, 51.5° and 75.8° are found to correspond to the (111), (200) and (220) phases of Co in (PDF#04-007-8519).

[0051] Figure 3 c) Raman spectroscopy for MoC and Ni-Co-MoC-0.5. Both pure MoC and Ni-Co-MoC-0.5 samples exhibit distinct D and G peaks at 1365 and 1586 cm⁻¹, respectively, corresponding to the characteristics of disordered carbon and graphitized carbon in carbon materials. The I₂ of pure MoC... D / I G The ratio is 0.98, and the I content of Ni-Co-MoC-0.5 is... D / I G The ratio increased to 1.05, indicating that Ni and Co doping can introduce more defects into the carbon framework, increasing defect and disordered atomic arrangement. This structural optimization improves the material's conductivity and electron transport efficiency, providing a superior substrate for TC molecularly imprinted electrochemical detection and enhancing the sensor's response sensitivity and selectivity.

[0052] The surface elemental composition and valence state of MoC, Ni-Co-MoC-0.25, Ni-Co-MoC-0.5 and Ni-Co-MoC-1 structures were analyzed by X-ray photoelectron spectroscopy (XPS). Figure 4a) shows the full spectra of the four materials. All samples contain C, N, Mo, and O elements. Ni and Co elements are absent in MoC. Ni-Co-MoC-0.25, Ni-Co-MoC-0.5, and Ni-Co-MoC-1 show peaks corresponding to Ni and Co. Four peak types are present in the pure MoC sample, located at 229.2 eV (Mo). 3+ Mo 3d 5 / 2 ) and 232.6 eV (Mo3d 3 / 2 The double peaks of the material and the observed MoO2 and MoO3 due to slight oxidation of the material surface. 4+ (230.5 / 234.4eV) and Mo 6+ Characteristic peaks (233.1 / 236.0 eV). When the Ni and Co doping ratios are low (Ni-Co-MoC-0.25), Mo appears at 228.9 eV and 232.6 eV. 2+ The characteristic peaks indicate that Mo in the system 2+ with Mo 3+ Coexistence. With increased Ni and Co doping ratios, compared to Ni-Co-MoC-0.25, the Mo content in Ni-Co-MoC-0.5 increases. 2+ A slight shift occurred in the peak towards lower binding energies. This stems from the strong coupling between Ni, Co, and MoC, which promotes electron transfer from Ni and Co sites to MoC sites. When the doping ratio is increased to Ni-Co-MoC-1, Mo... 3+ The complete disappearance of the characteristic peaks indicates that the main valence state of Mo has completely transformed into Mo. 2+ This study confirms that by controlling the amount of Ni and Co doping, the directional transfer of electrons to Mo sites can be achieved, thereby inducing a continuous transition of Mo species from high valence state to low valence active valence state. Figure 4 c) is the high-resolution XPS spectrum of C1s, with characteristic peaks at 284.6 eV, 284.8 eV and 285.8 eV, which correspond to the characteristic signals of Mo-C bond, C=C double bond and CO / CN bond, respectively. Figure 4 d) is the N 1s high-resolution XPS spectrum, which can be divided into three characteristic peaks at 397.6 eV, 398.9 eV and 401.3 eV, corresponding to pyridine-N, pyrrole-N and graphite-N respectively, while the peak at 395.2 eV is attributed to the binding energy signal of Mo 2p.

[0053] Figure 4 e) is the high-resolution XPS spectrum of Co 2p, with the characteristic peaks at 778.6 eV / 793.5 eV attributed to metallic Co. 0This valence state is generated by the reduction reaction of metal ions during annealing; the characteristic peaks at 780.8 eV / 796.6 eV and 782.8 eV / 798.8 eV correspond to the 2p of Co³⁺, respectively. 3 / 2 2p 1 / 2 orbital with 2p of Co²⁺ 3 / 2 2p 1 / 2 The characteristic peaks at 787.3 eV and 803.1 eV in the orbit are satellite peaks of Co 2p. Figure 4 f) shows the high-resolution XPS spectrum of Ni 2p, with characteristic peaks at 853.3 eV / 870.3 eV and 856.6 eV / 874.5 eV, corresponding to Ni... 0 2p 3 / 2 2p 1 / 2 Orbit and Ni 2+ 2p 3 / 2 2p 1 / 2 The peaks at 862.3 eV and 880.3 eV are satellite peaks of Ni 2p. Notably, compared to Ni-Co-MoC-0.25, the binding energies of Ni 2p and Co 2p in Ni-Co-MoC-0.5 show a positive shift of 0.3 eV. This phenomenon originates from the strong electronic coupling effect between Ni, Co, and MoC, leading to a decrease in the electron cloud density of Ni and Co atoms. Since Mo has a higher electronegativity (2.16) than Ni (1.91) and Co (1.88), this electronegativity difference drives the spontaneous transfer of electrons from the less electronegative Ni and Co sites to the more electronegative MoC matrix. Combining the above XRD, TEM, and XPS characterization results, it can be confirmed that the Ni-Co-MoC heteromaterial has been successfully synthesized.

[0054] The electrochemical behavior of electrodes modified with different materials was studied using cyclic voltammetry and electrochemical impedance spectroscopy to investigate the influence of different modification materials on electrode performance. Tests were conducted in an atmosphere containing 5.0 mM [Fe(CN)6]. 3- / 4- The scan was performed in 1 M KCl electrolyte solution, with a scan rate set at 50 mV / s and a scan range of -0.2 V to 0.7 V. The CV curves were used to analyze the results. Figure 5a) It can be seen that compared with the bare GCE, the peak currents of MoC, Co-MoC, and Ni-MoC electrodes are significantly improved. Furthermore, the peak currents of Co-MoC and Ni-MoC electrodes are even higher than those of the single MoC-modified electrode, indicating that Co and MoC, and Ni and MoC, respectively form a good synergistic effect, all of which can enhance the electrocatalytic activity of the electrode. The Ni-Co-MoC-0.5 bimetallic co-doped electrode has the highest peak current, and its electrochemical performance is superior to that of single-metal doping. This excellent performance stems from the fact that Ni and Co bimetallic co-doping of MoC can significantly increase the number of active sites and the electrochemical active area on the electrode surface, optimize the electronic structure of the material, accelerate the interfacial electron transport rate, and the active sites of Ni and Co are complementary, which can synergistically promote the electrochemical reaction and further enhance the electrocatalytic performance of the electrode.

[0055] Using TC as a template and C6H6O2 as a functional monomer, the CV curves of molecularly imprinted polymers were formed by electropolymerization, as shown in the figure. Figure 5 As shown in b), the peak current decreases significantly with increasing polymerization number because the formation of the MIP film creates an electron-blocking layer at the electrode interface, blocking [Fe(CN)6]. 3- / 4- After the probe contacts the electrode surface and the template molecule TC is eluted and removed, a large number of imprinted cavities are formed, which act as electron transport channels, allowing the redox probe [Fe(CN)] to... 6 ] 3- / 4- It can be used on GCE surfaces, resulting in increased peak current. When the electrode is re-immersed in the TC solution, template molecules are re-adsorbed into the imprinted cavity, and some imprinted cavities are occupied, inhibiting the redox probe [Fe(CN)]. 6 ] 3- / 4- The transfer of the probe hinders the redox reaction, and the current decreases again.

[0056] Figure 5 c) shows the Nyquist curves for electrodes modified with different materials, with the inset representing the equivalent circuit diagram of the resistance. By fitting the AC impedance data, the Rct values ​​for GCE, MoC, Co-MoC, Ni-MoC, and Ni-Co-MoC-0.5 are 330Ω, 269.5Ω, 258Ω, 199.1Ω, and 126.6Ω, respectively, showing a clear decreasing trend. The Ni-Co-MoC-0.5 bimetallic co-doped electrode has the smallest Rct value, significantly lower than the other four electrodes. This indicates that the ternary synergistic effect formed between Ni, Co bimetals, and MoC can significantly modulate the crystal structure of MoC, greatly reducing the electron transfer resistance at the electrode interface and maximizing the electron transport rate.

[0057] Figure 5d) The Rct value of MIP after polymerization increased sharply to 532.1 Ω. After washing with the eluent, the Rct of MIP@Ni-Co-MoC-0.5 / GCE decreased significantly to 219.4 Ω. This is because TC was effectively removed from the imprinted site to create an imprinted cavity, thereby reducing the sensor resistance. When the electrode was immersed in the TC solution again, the Rct increased to 391 Ω. This is consistent with the results of CV.

[0058] Figure 5 e) Ni-Co-MoC-0.5 at different scan rates (10-100 mV s) −1 The CV curves were obtained. The results show a good linear relationship between the oxidation peak current and the square root of the scan rate. Figure 5 f) The linear fitting equation for Ni-Co-MoC-0.5 is Ipa = (-0.846 ± 0.428) + (6.945 ± 0.059)V 1 / 2 The value of R² = 0.999 conforms to the Randles-Sevcik equation, indicating that a diffusion-controlled reaction exists on the electrode surface. To verify the enhancement of the electrode's electrochemical performance by the modified material, the electroactive surface area of ​​the Ni-Co-MoC-0.5 electrode was calculated using the Randles-Sevcik equation (Equation (1)):

[0059] (1)

[0060] Where Ipa is the peak current (A), n is the number of transported electrons (n=1), and A is the electroactive surface area (cm²). 2 D is the diffusion coefficient of K3[Fe(CN)6] (5.65 × 10⁻⁶ cm⁻¹). 2 s -1 C represents the concentration of K3[Fe(CN)6] (5.0 × 10⁻⁶). -6 mol cm -3 ), γ 1 / 2 This is the square root of the scan rate. The electroactive surface area of ​​Ni-Co-MoC-0.5 is calculated to be 0.065 cm². 2 This indicates that Ni-Co-MoC-0.5 effectively enhances mass transfer efficiency.

[0061] Under optimal conditions, [Fe(CN)6] 3- / 4- As an electrochemical probe, the adsorption response of DPV in tetracycline solutions ranging from 0 to 60 μM was recorded to achieve trace detection of tetracycline. The DPV response of MIP@Ni-Co-MoC-0.5 / GCE to different concentrations of tetracycline is shown below. Figure 6As shown in a), the peak current of the DPV decreases with increasing TC concentration because TC occupies the binding sites on the MIP film, leading to the redox probe [Fe(CN)6]. 3- / 4- Unable to reach the GCE surface, peak current decreases. Figure 6 (b) The results show that ΔI is linearly related to TC concentration (c) in the range of 0-60 μM, with the linear regression equation being ΔI(μA) = (2.445 ± 0.091) + (0.353 ± 0.008)C. TC , (R 2 =0.998), sensitivity is 5.04 μA μM −1 cm -2 The detection limit of MIP@Ni-Co-MoC-0.5 / GCE was calculated using the equation (Equation (2)):

[0062] (2)

[0063] Where S is the standard deviation of the current signal obtained from 10 repeated tests of the blank sample, and D is the sensitivity of the electrode, in μA to μM. -1 ꞏcm -2 With a signal-to-noise ratio (S / N) of 3 and the limit of detection (LOD), the detection limit was calculated to be 22.7 nM in the range of 10–60 μM.

[0064] Selectivity, reproducibility, repeatability, and stability play crucial roles in the analytical performance of measurement sensors. The most important advantage of molecularly imprinted polymers is their ability to specifically recognize target molecules. Compounds with molecular structures similar to TC, such as OFL, CIP, and NOR, as well as GLU, DA, and common ions (K+) found in food matrices, are examples of this. + Na + Ca 2+ Mg 2+ and Zn 2+ As an interfering substance, the specificity of the sensor to TC was evaluated through a series of interference experiments. Figure 7 a represents the chemical structure of TC and its reference compound. Because MIP@Ni-Co-MoC-0.5 / GCE contains recognition sites that perfectly match the shape, size, and functional groups of TC, its DPV response to TC is higher than its response to other analytes. Figure 7In (b) and (c), the NIP@Ni-Co-MoC-0.5 / GCE exhibits low response intensity due to the lack of specific adsorption for TC. This indicates that the MIP@Ni-Co-MoC-0.5 / GCE sensor performs well in recognizing TC and can selectively detect TC even in the presence of coexisting species. Five parallel MIP@Ni-Co-MoC-0.5 / GCE sensors were prepared under the same conditions and DPV tests were performed in a solution containing 60 μM TC. The relative standard deviation (RSD) of the peak current was 1.84%, indicating that the MIP@Ni-Co-MoC-0.5 / GCE sensor has good reproducibility. Figure 7 d). To assess repeatability, the same MIP@Ni-Co-MoC-0.5 / GCE electrode was tested every 10 minutes in a solution containing 60 μM TC using DPV, for a total of five repetitions. Figure 7 e) The peak currents corresponding to the five tests have a relative standard deviation (RSD) of 2.09%, and the current in the fifth test decreased by only 3.9% compared to the initial current, demonstrating good repeatability. Figure 7 f) The stability of the MIP@Ni-Co-MoC-0.5 / GCE sensor was evaluated. The DPV signal after adsorption of 60 μM TC was evaluated every 2 days. The current remained at 91.2%, a decrease of 9.8% compared to the initial value, indicating that the electrode has good stability in TC detection.

Claims

1. A method for preparing and applying a Ni / Co bimetallic doped MoC composite material based on molecular imprinting technology, characterized in that... A method for preparing and applying Ni / Co bimetallic doped MoC composite materials based on molecular imprinting technology as sensor electrode materials is carried out according to the following steps: I. Preparation of Ni-MoC, Co-MoC and MoC 250 mg of ammonium molybdate tetrahydrate was dissolved in 70 mL of deionized water (if ammonium molybdate tetrahydrate is dissolved in deionized water with cobalt nitrate hexahydrate and nickel chloride hexahydrate respectively, Ni-MoC and Co-MoC are obtained respectively). Then, 300 mg of dopamine hydrochloride was added, and the mixture was stirred for 30 min to form a dark solution. Next, 150 mL of ethanol was added, forming a turbid liquid. Then, 0.4 mL of ammonia water was added, and the mixture was magnetically stirred for 3.5 h to finally form a black solution. The solution was then filtered and freeze-dried to obtain Mo-PDA. This was transferred to a ceramic boat and heated to 600–1000 °C (5 °C min) under an Ar atmosphere. -1 Then, keep it for 2 hours to synthesize MoC. II. Preparation of Ni-Co-MoC First, 250 mg of ammonium molybdate tetrahydrate, 12-60 mg of cobalt nitrate hexahydrate, and 10-50 mg of nickel chloride hexahydrate were dissolved in 70 mL of deionized water. Then, 300 mg of dopamine hydrochloride was added, and the mixture was stirred for 30 min to form a deep red solution. Next, 150 mL of ethanol was added, resulting in an orange turbid liquid. Then, 0.4 mL of ammonia water was added, and the mixture was magnetically stirred for 3.5 h to finally form a black solution. After filtration, Ni-Co-Mo-PDA was obtained by freeze-drying. This was transferred to a ceramic boat and heated to 800 °C (5 °C min) under an Ar atmosphere. -1 Ni-Co-MoC was synthesized by maintaining the process for 2 hours. The resulting product was named Ni-Co-MoC-x (where x is the molar ratio of Ni / Co doping). III. Preparation of MIP@Ni-Co-MoC / GCE A 3 mm diameter GCE was polished with alumina powder (1.0, 0.3, and 0.05 μm) and cleaned in an ultrasonic bath of anhydrous ethanol and deionized water to remove impurities. 2 mg of Ni-Co-MoC was immersed in 1 mL of a deionized water-anhydrous ethanol mixture, and then 5 μL of 1% Nafion was added. After ultrasonic dispersion, 5 μL of Ni-Co-MoC suspension was dropped onto the surface of the GCE and dried under an infrared lamp to obtain the Ni-Co-MoC / GCE working electrode. A three-electrode system was used to synthesize a MIP film on the surface of Ni-Co-MoC / GCE via electropolymerization. The prepared Ni-Co-MoC / GCE was then immersed in a solution containing 1 mM TC and 5 mM C6H6O2 in 1 M KCl containing 5 mM [Fe(CN)6]. 3- / 4- In solution, electrochemical polymerization was performed 30 times on the electrode surface via CV at a scan rate of 50 mV / s within a potential range of -0.2 V to 0.7 V. The electrode was stirred in a CH3COOH:CH3OH (V1:V2=2:8) solution for 10 min to elute the embedded TC template molecules until the solution contained 5 mM [Fe(CN)6] in 1 M KCl. 3- / 4- A distinct and stable redox peak was observed in the solution. The prepared sensor was named MIP@Ni-Co-MoC / GCE.

2. The preparation method according to claim 1, characterized in that, The calcination temperature in step one is 600~1000℃.

3. The preparation method according to claim 1, characterized in that, In step two, the amount of (Co(NO3)2ꞏ6H2O) added is 12~60mg.

4. The preparation method according to claim 1, characterized in that, In step two, the amount of NiCl2·6H2O added is 10~50mg.

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