Znti-lDH@D-UiO-66 nanocomposite modified electrode, preparation method and detection application thereof

Abstract

This invention discloses a ZnTi-LDH-modified defect-rich UiO-66 nanocomposite electrode, its preparation method, and its application in detecting glyphosate pesticides. First, UiO-66 is treated with a surface-controlled decarboxylation defect technique to obtain defect-rich UiO-66. Then, ZnTi-LDH is prepared in situ on its surface using a hydrothermal method, resulting in a ZnTi-LDH@D-UiO-66 heterostructure. This structure provides a large specific surface area, abundant active sites, and contains both Zr and Ti, two metals that can complex with organophosphorus molecules, significantly improving the catalyst's adsorption and capture of analytes and enhancing the sensor's performance in detecting organophosphorus pesticides. An electrochemical sensing platform constructed based on the ZnTi-LDH@D-UiO-66 nanocomposite modified electrode achieves a wide detection range (0.05~50 μmol L⁻¹) for glyphosate detection. −1 The detection limit is relatively low at 0.19 μmol·L⁻¹. ‑1 (S / N=3), high sensitivity (1.220 μA·μmol) ‑1 •L) has good selectivity, reproducibility and stability.

Description

Technical Field

[0001] This invention belongs to the field of electroanalytical chemistry technology, specifically relating to a ZnTi-LDH modified defect-rich UiO-66 nanocomposite electrode, its preparation method, and its application in detecting glyphosate pesticides. Background Technology

[0002] Glyphosate (N-phosphonomethylglycine) is one of the most widely used organophosphorus (OP) herbicides in the world, renowned for its high efficiency and broad spectrum. However, the use of glyphosate can have adverse effects on plant and animal health. Even low concentrations of glyphosate and its metabolites remaining in soil and groundwater can cause environmental pollution and ecological damage. Therefore, there is an urgent need to develop rapid and convenient technologies to detect glyphosate pollution in aquatic environments for effective analysis and control of its presence.

[0003] Chromatography is a robust technique for glyphosate detection, but it requires derivatization of the pesticide or combination with other techniques to improve detection performance, making the entire process complex and time-consuming. Fluorescence spectroscopy offers high sensitivity, but it requires rigorous sample preparation procedures. Capillary electrophoresis and enzyme-linked immunosorbent assay (ELISA) are commonly used alternatives for glyphosate detection. However, both techniques suffer from cumbersome derivatization processes and narrow linear dynamic range windows. Electrochemical methods, on the other hand, offer advantages such as simple operation, rapid response, low cost, good selectivity, high sensitivity, and fast analysis speed, making them a promising approach for highly sensitive and rapid detection of glyphosate.

[0004] Glyphosate exhibits inert electrochemical behavior, making it difficult to detect directly. Furthermore, due to the lone pairs of electrons in its nitrogen and oxygen atoms, glyphosate readily forms thermodynamically stable complexes with metals through chemical bonds. For example, the three donor groups of glyphosate (amine, carboxylate, and phosphate) can form two pentagonal equatorial planes with copper(II). Therefore, researchers have proposed methods to detect glyphosate by modifying electrodes with nanomaterials to construct indirect electrochemical sensors. For instance, using a glassy carbon electrode modified with reduced graphene oxide and copper nanoparticles to detect glyphosate in Cu... 0 Oxidized to Cu 2+ In this process, because copper ions form a stable copper ion complex with glyphosate, the anodic peak current decreases linearly with the increase of glyphosate concentration, thus achieving highly sensitive detection of glyphosate.

[0005] Metal-organic frameworks (MOFs) possess excellent porosity, crystallinity, high specific surface area, and outstanding thermal stability achieved through strong ligand bonds formed by the combination of metal ions and organic ligands. The mesopores and micropores of MOFs make them highly effective in electrochemical detection; mesopores facilitate the doping of functional materials and allow electrolyte solutions to permeate, while micropores fully expose adsorption sites for selective adsorption of organic compounds (OP). Titanium atoms in titanium dioxide (TiO2) and zirconium atoms in zirconium nanoparticles (ZrNPs) have a strong affinity for phosphate groups and are commonly used to enhance the selective adsorption and capture of OP. To improve the selective adsorption of OP by the catalyst, this invention employs surface-controlled decarboxylation defect engineering technology to decarboxylate UiO-66 (a Zr-MOFs) to obtain defect-rich UiO-66 (D-UiO-66). Then, a zinc-titanium layered double hydroxide (ZnTi-LDH) is prepared in situ on its surface using a hydrothermal method, resulting in a ZnTi-LDH@D-UiO-66 heterostructure. This structure provides a large specific surface area, abundant active sites, and contains both Zr and Ti, two metals that can complex with organophosphorus molecules. This significantly improves the catalyst's adsorption and capture of analytes and enhances the sensing and analysis performance of the corresponding sensor for organophosphorus pesticides. Summary of the Invention

[0006] To address the shortcomings of existing technologies and the needs of research and application in this field, one objective of this invention is to provide a ZnTi-LDH@D-UiO-66 nanocomposite material modified electrode. The modified electrode is characterized by using a glassy carbon electrode as the base electrode and a ZnTi-LDH@D-UiO-66 nanocomposite material obtained through controlled surface decarboxylation as the electrode modification material. In the preparation process of the ZnTi-LDH@D-UiO-66 nanocomposite material, UiO-66 is first treated using surface-controlled decarboxylation defect engineering to obtain a defect-rich sample D-UiO-66. Then, ZnTi-LDH is synthesized in situ using a hydrothermal method to obtain the ZnTi-LDH@D-UiO-66 nanocomposite material. The glassy carbon electrode is denoted as GCE.

[0007] The second objective of this invention is to provide a method for preparing a ZnTi-LDH@D-UiO-66 nanocomposite modified electrode, characterized by the following specific steps:

[0008] (a) Preparation of D-UiO-66

[0009] 0.14 g ZrCl4 and 0.10 g terephthalic acid were dissolved in 20 mL N,N-dimethylformamide and stirred until dissolved. Then, 1.2 mL formic acid was added to the mixed solution, and the mixture was transferred to a polytetrafluoroethylene autoclave. After sealing, the mixture was reacted at 120 °C for 12 h. After centrifugation, washing, and drying, UiO-66 sample was obtained. 150 mg UiO-66 powder, 25 mg AgNO3, and 25 mg K2S2O8 were dissolved in 20 mL acetonitrile and sonicated for 10 min. The resulting mixed solution was then placed in an oil bath at 150 °C for 60 min, and then immediately transferred to ice water for quenching. Finally, after centrifugation, washing, and drying, D-UiO-66 was obtained.

[0010] (b) Preparation of ZnTi-LDH@D-UiO-66

[0011] 50 μL TiCl4, 0.36 g Zn(NO3)2·6H2O and 0.45 g urea were dissolved in 20 mL deionized water; then 100 mg D-UiO-66 powder was added to the mixed solution, stirred for 30 min, and the resulting decomposition solution was transferred to a 50 mL polytetrafluoroethylene autoclave. After reacting at 120 ℃ for 24 h, the solution was cooled and crystallized. After washing and drying, ZnTi-LDH@D-UiO-66 was obtained.

[0012] (c) Preparation of ZnTi-LDH@D-UiO-66 modified GCE

[0013] A 3 mm diameter GCE was polished by drawing figure-eight patterns on chamois leather with 0.2 and 0.05 μm alumina paste, and then rinsed with deionized water to obtain a fresh electrode surface. 10 mg of ZnTi-LDH / D-UiO-66 powder was dispersed in 2 mL of an equal volume ratio of ultrapure water, ethanol, and 0.5 wt% Nafion solution, and ultrasonically treated to obtain an electrode-modified dispersion. 2 ~ 10 μL of this dispersion was drop-coated onto the treated GCE surface and allowed to air dry at room temperature to obtain a ZnTi-LDH@D-UiO-66 modified GCE, denoted as ZnTi-LDH@D-UiO-66 / GCE.

[0014] In the ZnTi-LDH@D-UiO-66 nanostructure obtained in step (b), the cubic structure of UiO-66 has been destroyed by etching, and the particle size has been greatly reduced from the original 100~300 nm to less than 50 nm. At the same time, ZnTi-LDH grows in situ on the destroyed UiO-66 surface to form a heterostructure. This structure can provide a large specific surface area, abundant active sites, and contains two metals, Zr and Ti, that can complex with organophosphorus molecules, which greatly improves the adsorption and capture of analytes by the catalyst and improves the sensing and analysis performance of organophosphorus pesticides by the corresponding sensor.

[0015] The third objective of this invention is to provide a ZnTi-LDH@D-UiO-66 nanocomposite modified electrode for detecting the content of the organophosphorus pesticide glyphosate. The electrode is characterized by using a 0.1 mol / L pH 6.0 phosphate buffer as the supporting electrolyte, adding electrolyte solutions containing different amounts of glyphosate to an electrolytic cell, using the modified electrode as the working electrode, and detecting the glyphosate using differential pulse voltammetry to obtain a linear regression equation between the oxidation peak current difference and the concentration of glyphosate. The same method is used to determine the oxidation peak current difference of glyphosate in the test sample, and substituting this into the linear regression equation yields the glyphosate content in the test sample.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] (a) The ZnTi-LDH@D-UiO-66 nanocomposite modified electrode of the present invention consists of ultrathin and ultrasmall ZnTi-LDH nanosheets assembled in situ on defect-rich UiO-66. The resulting heterostructure provides a large specific surface area and abundant active sites. It also contains two metals, Zr and Ti, which can complex with organophosphorus molecules, which greatly improves the adsorption and capture of analytes by the catalyst and enhances the sensing and analysis performance of the corresponding sensor for organophosphorus pesticides.

[0018] (b) The electrochemical sensing platform constructed based on the ZnTi-LDH@D-UiO-66 nanocomposite modified electrode achieved a wide detection range (0.05 ~ 50 μmol L) for glyphosate detection. −1 The detection limit is relatively low at 0.19 μmol·L⁻¹. -1 (S / N = 3), high sensitivity (1.220 μA·μmol) -1 •L) has good selectivity, reproducibility and stability. Attached Figure Description

[0019] Figure 1SEM images of UiO-66 (a,d) prepared in Comparative Example 2, D-UiO-66 (b,e) prepared in Comparative Example 3, and ZnTi-LDH@D-UiO-66 (c,f) prepared in Example 3.

[0020] Figure 2 The following are the FTIR spectra of UiO-66 and D-UiO-66 prepared in Comparative Examples 2 and 3 (a), the XRD spectra of UiO-66 and D-UiO-66 prepared in Comparative Examples 2 and 3 (b), the XPS spectra of D-UiO-66, ZnTi-LDH and ZnTi-LDH@D-UiO-66 prepared in Comparative Examples 3, 4 and Example 3 (c), and the high-resolution XPS spectra of Zr 3d, Ti 2p and O 1s of D-UiO-66 and ZnTi-LDH@D-UiO-66 prepared in Comparative Examples 3 and Example 3 (df).

[0021] Figure 3 Comparative Examples 1, 2, 3, and 3 correspond to the GCE, UiO-66 / GCE, D-UiO-66 / GCE, and ZnTi-LDH@D-UiO-66 / GCE electrodes, respectively, in a solution containing 5.0 mmol·L⁻¹. -1 [Fe(CN)6] 3- / 4- 0.1 mol·L -1 (a) CV curve and (b) Nyquist plot of KCl solution.

[0022] Figure 4 The ZnTi-LDH@D-UiO-66 / GCE, D-UiO-66 / GCE, and UiO-66 / GCE electrodes corresponding to Example 3, Comparative Example 3, and Comparative Example 2 were subjected to 0.1 mol L⁻¹ −1 CV curves (ac) at different scan rates in phosphate buffer at pH 7.0, showing the ZnTi-LDH@D-UiO-66 / GCE, D-UiO-66 / GCE, and UiO-66 / GCE electrodes corresponding to Examples 3, Comparative Examples 3, and Comparative Examples 2 at 30 ~ 110 mV·s. -1 I within the scan rate range pa Linear relationship with scan rate (d).

[0023] Figure 5 For ZnTi-LDH@D-UiO-66 / GCE corresponding to Example 3, at different pH values ​​of 0.05 μmol·L⁻¹ -1 DPV curve of glyphosate (a) and corresponding peak current histogram (b).

[0024] Figure 6The ZnTi-LDH@D-UiO-66 / GCE corresponding to Examples 1, 2, 3, 4, and 5 were in an electrolyte at 0.05 μmol·L⁻¹. -1 DPV peak current (a) of glyphosate; ZnTi-LDH@D-UiO-66 / GCE corresponding to Example 3 in the presence of 0.05 μmol·L⁻¹ -1 Bar chart showing the effect of enrichment potential (b) and enrichment time (c) in the electrolyte of glyphosate on the peak current of glyphosate DPV.

[0025] Figure 7 The current response curves (a and c) of the ZnTi-LDH@D-UiO-66 / GCE and D-UiO-66 / GCE electrodes for DPV detection of glyphosate are shown in Example 3 and Comparative Example 3, respectively, and the corresponding peak current change values ​​are plotted against their concentrations (b and d).

[0026] Figure 8 For Example 3, ZnTi-LDH@D-UiO-66 / GCE was used at 0.05 μmol·L⁻¹. -1 Peak current histograms of DPV in the presence of glyphosate and the same concentration of interfering substances (a). (b) At 0.05 μmol·L -1 The graph shows the peak current of glyphosate over time. The inset shows the peak current of six ZnTi-LDH@D-UiO-66 / GCE electrodes at 0.05 μmol·L⁻¹. -1 Current response of glyphosate. Detailed Implementation

[0027] To further understand the present invention, the following description, in conjunction with the accompanying drawings and embodiments, will further illustrate the present invention, but does not limit the present invention in any way.

[0028] Example 1:

[0029] (a) Preparation of D-UiO-66

[0030] 0.14 g ZrCl4 and 0.10 g terephthalic acid were dissolved in 20 mL N,N-dimethylformamide and stirred until dissolved. Then, 1.2 mL formic acid was added to the mixed solution. The reaction solution was transferred to a polytetrafluoroethylene autoclave, sealed, and reacted at 120 °C for 12 h. After centrifugation, washing, and drying, UiO-66 sample was obtained. 150 mg UiO-66 powder, 25 mg AgNO3, and 25 mg K2S2O8 were dissolved in 20 mL acetonitrile and sonicated for 10 min. The resulting mixed solution was then placed in an oil bath at 150 °C and reacted for 60 min. The reaction solution was then immediately transferred to ice water for quenching. Finally, after centrifugation, washing, and drying, D-UiO-66 was obtained.

[0031] (b) Preparation of ZnTi-LDH@D-UiO-66

[0032] 50 μL TiCl4, 0.36 g Zn(NO3)2·6H2O and 0.45 g urea were dissolved in 20 mL deionized water; then 100 mg D-UiO-66 powder was added to the mixed solution, stirred for 30 min, and the resulting decomposition solution was transferred to a 50 mL polytetrafluoroethylene autoclave. After reacting at 120 ℃ for 24 h, the solution was cooled and crystallized. After washing and drying, ZnTi-LDH@D-UiO-66 was obtained.

[0033] (c) Preparation of ZnTi-LDH@D-UiO-66 modified GCE

[0034] A 3 mm diameter GCE was polished by drawing figure-eight patterns on chamois leather with 0.2 and 0.05 μm alumina paste, respectively. After rinsing with deionized water, a fresh electrode surface was obtained. 10 mg of ZnTi-LDH@D-UiO-66 powder was dispersed in 6 mL of an equal volume ratio of ultrapure water, ethanol, and 0.5 wt% Nafion solution, and ultrasonically treated to obtain an electrode-modified dispersion. 2 μL of this dispersion was drop-coated onto the treated GCE surface and allowed to dry naturally at room temperature to obtain a ZnTi-LDH@D-UiO-66 modified GCE, denoted as ZnTi-LDH@D-UiO-66 / GCE.

[0035] Example 2:

[0036] (a) Preparation of D-UiO-66

[0037] Prepared according to the method and conditions of step (a) in Example 1;

[0038] (b) Preparation of ZnTi-LDH@D-UiO-66

[0039] Prepared according to the method and conditions of step (b) in Example 1;

[0040] (c) Preparation of ZnTi-LDH@D-UiO-66 modified GCE

[0041] Referring to the method and conditions of step (c) in Example 1, 4 μL of a ZnTi-LDH@D-UiO-66 dispersion with a concentration of 5 mg / mL was drop-coated onto the treated GCE surface. After natural drying at room temperature, the ZnTi-LDH@D-UiO-66 nanocomposite material modified GCE was obtained, denoted as ZnTi-LDH@D-UiO-66 / GCE.

[0042] Example 3:

[0043] (a) Preparation of D-UiO-66

[0044] Prepared according to the method and conditions of step (a) in Example 1;

[0045] (b) Preparation of ZnTi-LDH@D-UiO-66

[0046] Prepared according to the method and conditions of step (b) in Example 1;

[0047] (c) Preparation of ZnTi-LDH@D-UiO-66 modified GCE

[0048] Referring to the method and conditions of step (c) in Example 1, 6 μL of a ZnTi-LDH@D-UiO-66 dispersion with a concentration of 5 mg / mL was drop-coated onto the treated GCE surface. After natural drying at room temperature, the ZnTi-LDH@D-UiO-66 nanocomposite material modified GCE was obtained, denoted as ZnTi-LDH@D-UiO-66 / GCE.

[0049] Example 4:

[0050] (a) Preparation of D-UiO-66

[0051] Prepared according to the method and conditions of step (a) in Example 1;

[0052] (b) Preparation of ZnTi-LDH@D-UiO-66

[0053] Prepared according to the method and conditions of step (b) in Example 1;

[0054] (c) Preparation of ZnTi-LDH@D-UiO-66 modified GCE

[0055] Referring to the method and conditions of step (c) in Example 1, 8 μL of a ZnTi-LDH@D-UiO-66 dispersion with a concentration of 5 mg / mL was drop-coated onto the treated GCE surface. After natural drying at room temperature, the ZnTi-LDH@D-UiO-66 nanocomposite material modified GCE was obtained, denoted as ZnTi-LDH@D-UiO-66 / GCE.

[0056] Example 5:

[0057] (a) Preparation of D-UiO-66

[0058] Prepared according to the method and conditions of step (a) in Example 1;

[0059] (b) Preparation of ZnTi-LDH@D-UiO-66

[0060] Prepared according to the method and conditions of step (b) in Example 1;

[0061] (c) Preparation of ZnTi-LDH@D-UiO-66 modified GCE

[0062] Referring to the method and conditions of step (c) in Example 1, 10 μL of a ZnTi-LDH@D-UiO-66 dispersion with a concentration of 5 mg / mL was drop-coated onto the treated GCE surface. After natural drying at room temperature, the ZnTi-LDH@D-UiO-66 nanocomposite material modified GCE was obtained, denoted as ZnTi-LDH@D-UiO-66 / GCE.

[0063] Comparative Example 1:

[0064] The working electrode is a bare GCE.

[0065] Comparative Example 2:

[0066] (a) Preparation of UiO-66

[0067] 0.14 g ZrCl4 and 0.10 g terephthalic acid were dissolved in 20 mL N,N-dimethylformamide and stirred until dissolved. Then, 1.2 mL formic acid was added to the mixed solution. The reaction solution was transferred to a polytetrafluoroethylene autoclave, sealed, and reacted at 120 °C for 12 h. After centrifugation, washing, and drying, the UiO-66 sample was obtained.

[0068] (b) Preparation of UiO-66 / GCE

[0069] The 3 mm diameter GCE was polished by drawing figure-eight patterns on chamois leather with 0.2 and 0.05 μm alumina pastes, respectively. After rinsing with deionized water, a fresh electrode surface was obtained. The UiO-66 prepared in step (a) was ultrasonically dispersed in deionized water solvent to prepare a dispersion with a concentration of 5 mg / mL. 6 μL of the dispersion was drop-coated onto the treated GCE surface and allowed to dry naturally at room temperature to obtain the UiO-66 modified GCE, denoted as UiO-66 / GCE.

[0070] Comparative Example 3:

[0071] (a) Preparation of D-UiO-66

[0072] Prepared according to the method and conditions of step (a) in Example 1;

[0073] (b) Preparation of D-UiO-66 / GCE

[0074] The 3 mm diameter GCE was polished by drawing figure-eight patterns on chamois leather with 0.2 and 0.05 μm alumina pastes, respectively. After rinsing with deionized water, a fresh electrode surface was obtained. The D-UiO-66 prepared in step (b) was ultrasonically dispersed in deionized water solvent to prepare a dispersion with a concentration of 5 mg / mL. 6 μL of the dispersion was drop-coated onto the treated GCE surface and allowed to dry naturally at room temperature to obtain the D-UiO-66 modified GCE, denoted as D-UiO-66 / GCE.

[0075] Figure 1 SEM images of UiO-66 (a,d) prepared in Comparative Example 2, D-UiO-66 (b,e) prepared in Comparative Example 3, and ZnTi-LDH@D-UiO-66 (c,f) prepared in Example 3 are shown. It can be observed that the pristine UiO-66 exhibits a submicron-sized octahedral morphology with sharp crystal edges and a smooth surface arrangement. Figure 1 a and 1d). After surface decarboxylation treatment, defects are formed, and the smooth surface is damaged to some extent, but the octahedral morphology remains unchanged. The destruction of atoms / ions during decarboxylation leads to the formation of heteropores in the UiO-66-D polyhedral crystal, which is beneficial for increasing the specific surface area, increasing adsorption sites, and improving the mass transfer rate and catalytic activity. Figure 1 b and Figure 1 e). D-UiO-66 was added to the precursor solution for preparing ZnTi-LDH. The cubic structure of UiO-66 was destroyed by etching, and the particle size was significantly reduced from the original 100~300 nm to less than 50 nm. At the same time, ZnTi-LDH grew in situ on the destroyed UiO-66 surface to form a heterostructure. This structure can provide a large specific surface area, abundant active sites, and contains two metals, Zr and Ti, which can complex with organophosphorus molecules. This greatly improves the adsorption and capture of analytes by the catalyst and enhances the sensing and analysis performance of organophosphorus pesticides by the corresponding sensor.

[0076] Figure 2 The images show the FTIR spectra of UiO-66 and D-UiO-66 prepared in Comparative Examples 2 and 3 (a), the XRD spectra of UiO-66 and D-UiO-66 prepared in Comparative Examples 2 and 3 (b), the XPS spectra of D-UiO-66, ZnTi-LDH, and ZnTi-LDH@D-UiO-66 prepared in Comparative Examples 3, 4, and Example 3 (c), and the high-resolution XPS spectra of Zr 3d, Ti 2p, and O 1s of D-UiO-66 and ZnTi-LDH@D-UiO-66 prepared in Comparative Examples 3 and Example 3 (df). The FTIR spectra show that the original UiO-66 has a wavelength range from 1400 to 1600 cm⁻¹. -1The vibrational bands are related to the interaction with carboxylates. Specifically, in the range of 1430–1533 cm⁻¹ -1 Within this range, there is clear evidence that the aminocarboxylate molecule is coordinated with the Zr metal core, characterized by -COO asymmetric stretching in the range of 1499–1570 cm⁻¹. -1 Peak values ​​appear at 1584 and 1434 cm. -1 The peak value generated corresponds to the -COO- symmetric stretching vibration. After silver-catalyzed decarboxylation, D-UiO-66 reaches a peak value at 1665 cm⁻¹. -1 The asymmetric tensile vibration at C=O disappears at 1398 cm. -1 The weakening of the -COO- symmetric stretching vibration at the point indicates the formation of a defective D-UiO-66 with a well-preserved structure. To verify whether the presence of structural defects affects the crystal structure, powder XRD was used, and the results are as follows: Figure 2 As shown in b, both UiO-66 and D-UiO-66 exhibit strong Braggs scattering and have almost identical diffraction peaks with no significant decrease in intensity. This further verifies that the decarboxylation defect generation process did not destroy the crystal structure. XPS test results were used to explain the elemental composition and variations of the ZnTi-LDH@D-UiO-66 heterostructure. An appropriate amount of D-UiO-66 powder was added to the precursor solution during ZnTi-LDH preparation, and XPS tests were also performed on ZnTi-LDH and D-UiO-66. Figure 2 As shown in Figure c, the ZnTi-LDH@D-UiO-66 heterostructure clearly displays the spectra of Zn, Ti, and Zr, indicating the successful preparation of the nanocomposite material. High-resolution analyses of Zr 3d, Ti 2p, and O 1s before and after composite formation reveal significant changes, further demonstrating that the composite formation of nanomaterials can promote synergistic effects between the two components, enabling charge transfer between them.

[0077] Figure 3 Comparative Examples 1, 2, 3, and 3 correspond to the GCE, UiO-66 / GCE, D-UiO-66 / GCE, and ZnTi-LDH@D-UiO-66 / GCE electrodes, respectively, in a solution containing 5.0 mmol·L⁻¹. -1 [Fe(CN)6] 3- / 4- 0.1 mol·L -1 The (a) CV curve and (b) Nyquist plot of KCl solution. Figure 3As shown in Figure a, the peak currents of UiO-66 / GCE, GCE, ZnTi-LDH / D-UiO-66 / GCE, and D-UiO-66 / GCE are 59.82, 65.17, 68.68, and 74.46 μA, respectively. Compared with the traditional GCE, the peak current of UiO-66 / GCE is slightly lower. This is because UiO-66 itself has poor conductivity, and the introduction of surface defects after silver-catalyzed decarboxylation significantly increases the peak current of D-UiO-66 / GCE. However, after modification with ZiTi-LDH, the peak current of D-UiO-66 decreases slightly. This may be because ZnTi-LDH itself has poor conductivity, leading to a decrease in the overall conductivity of the ZiTi-LDH / D-UiO-66 / GCE nanocomposite material. In the same system, the EIS diagrams of different electrodes are shown in Figure a. Figure 3 As shown in b. According to the corresponding Randle equivalent circuit, the EIS of UiO-66 / GCE, GCE, ZnTi-LDH / D-UiO-66 / GCE and D-UiO-66 / GCE are 649.7, 385.8, 287.2 and 130.3 Ω, respectively. This result is consistent with the trend of CV.

[0078] Figure 4 The ZnTi-LDH@D-UiO-66 / GCE, D-UiO-66 / GCE, and UiO-66 / GCE electrodes corresponding to Example 3, Comparative Example 3, and Comparative Example 2 were subjected to 0.1 mol L⁻¹ −1 CV curves (ac) at different scan rates in phosphate buffer at pH 7.0, showing the ZnTi-LDH@D-UiO-66 / GCE, D-UiO-66 / GCE, and UiO-66 / GCE electrodes corresponding to Examples 3, Comparative Examples 3, and Comparative Examples 2 at 30 ~ 110 mV·s. -1 I within the scan rate range pa Linear relationship with scan rate (d). Electrochemical active surface area (ECSA) is proportional to the number of electrocatalytic active sites; therefore, the ECSA value of different electrodes is determined by their electrochemical double-layer capacitor (C). dl It is evaluated based on ) . Figure 4 ac, yielding a fitted graph of current density versus scan rate. The corresponding slope ( Figure 4 d) Show the C of ZnTi-LDH / D-UiO-66 / GCE, D-UiO-66 / GCE and UiO-66 / GCE dl The values ​​were 0.0219, 0.0629, and 0.0776 mF·cm, respectively. -2Due to surface defect engineering in silver-catalyzed decarboxylation, the electrochemically active surface area of ​​D-UiO-66 was significantly increased. The electrochemically active surface area was further enhanced after ZnTi-LDH and D-UiO-66 nanomaterials were combined, which can be attributed to the strong electronic interactions between the two and their synergistic effect.

[0079] Figure 5 For ZnTi-LDH@D-UiO-66 / GCE corresponding to Example 3, at different pH values ​​of 0.05 μmol·L⁻¹ -1 The DPV curve (a) and corresponding peak current histogram (b) of glyphosate were used to investigate the effect of pH value of PB solution on glyphosate detection. Figure 5 The results showed that the response current reached its maximum at pH 6.0. Therefore, pH 6.0 was chosen as the optimal pH for detecting glyphosate. This is likely because glyphosate itself is a non-electrochemically active substance. Considering the stability of the materials, ZnTi-LDH and D-UiO-66 are structurally stable under near-neutral pH conditions. Ti and Zr-O may capture the phosphate groups in glyphosate through coordination. If the pH is too low, it may cause the LDH laminations to dissolve (Zn and Ti loss), and if the pH is too high, it may cause the UiO-66 framework to collapse. Therefore, based on the above considerations, pH = 6.0 was chosen as the optimal condition.

[0080] Figure 6 The ZnTi-LDH@D-UiO-66 / GCE corresponding to Examples 1, 2, 3, 4, and 5 were in an electrolyte at 0.05 μmol·L⁻¹. -1 DPV peak current (a) of glyphosate; ZnTi-LDH@D-UiO-66 / GCE corresponding to Example 3 in the presence of 0.05 μmol·L⁻¹ -1 A bar chart showing the effect of enrichment potential (b) and enrichment time (c) in the electrolyte of glyphosate on the DPV peak current of glyphosate. Figure 6 As shown in Figure a, the peak current gradually increases with increasing modification concentration, reaching its maximum at 6 μL. Further increases in modification concentration result in a decrease in peak current, possibly because excessive loading leads to a thicker layer, hindering the transport of glyphosate molecules and electrons. The optimal modification concentration is 6 μL. At this optimal concentration, the enrichment potential and enrichment time were optimized, as shown in Figure a. Figure 6As shown in b, when the enrichment potential ranges from 0.1 V to 0.3 V, the peak current of glyphosate gradually increases with increasing enrichment potential. However, with further increases in the applied potential, the peak current gradually decreases. Therefore, the optimal enrichment potential for glyphosate is 0.3 V. The effect of enrichment time on the peak current was further investigated at each optimal enrichment potential. Within the enrichment time range of 10–50 s, glyphosate showed an increase in peak current with increasing enrichment time (…). Figure 6 (c) The peak current initially increases and then decreases, with 30 s being the optimal enrichment time for glyphosate. After 30 s, the peak current decreases slowly, which may indicate that the adsorption of glyphosate on the ZnTi-LDH / D-UiO-66 / GCE electrode surface has reached saturation.

[0081] Figure 7 The current response curves (a and c) for glyphosate detection by the ZnTi-LDH@D-UiO-66 / GCE and D-UiO-66 / GCE electrodes corresponding to Example 3 and Comparative Example 3, respectively, and the corresponding peak current changes versus their concentrations (b and d), are shown. To further verify the glyphosate detection performance of the single catalytic active site Zr in D-UiO-66 / GCE and the dual catalytic active sites Zr and Ti in ZnTi-LDH / D-UiO-66 / GCE, the glyphosate capture ability of the modified electrodes was determined by the DPV method under optimal experimental conditions. Figure 7 As shown, the peak current response of the DPV is linearly related to the glyphosate concentration, with the ZnTi-LDH / D-UiO-66 / GCE modified electrode showing a linear relationship with the glyphosate concentration increasing from 0.05 μmol·L⁻¹. -1 Increase to 50 μmol·L -1 ΔI pa It increases with increasing concentration, and the two linear components are respectively derived from the equation ΔI pa1 (μA) = -1.220C-1.958 (R 2 = 0.8882) and ΔI pa2 (μA) = -0.029C-3.406 (R 2 = 0.9466), the calculated limit of detection (LOD) is 0.19 μmol·L⁻¹. -1 The sensitivity (S) is 1.220 μA·μmol. -1 ·L. Simultaneously, under the same conditions, DPV detection was performed on the D-UiO-66 / GCE modified electrode, and its two linear components were ΔI pa1 (μA) = -0.559C-0.152 (R 2 = 0.8899) and ΔI pa2(μA) = -0.028C-0.6819 (R 2 = 0.9724), the calculated limit of detection (LOD) is 6.98 μmol·L -1 The sensitivity is 0.559 μA·μmol. -1 The results further demonstrate that dual-catalytic-sites are superior to single-catalytic-sites. Furthermore, due to intense competition among ions on the electrode surface, further addition of glyphosate to the D-UiO-66 / GCE modified electrode resulted in a slower increase in peak current. The potential shift with increasing glyphosate concentration may be due to glyphosate being a non-electrochemically active species, inducing potential shift when it binds to the active sites on the surface.

[0082] Figure 8 For Example 3, ZnTi-LDH@D-UiO-66 / GCE was used at 0.05 μmol·L⁻¹. -1 Peak current histograms of DPV in the presence of glyphosate and the same concentration of interfering substances (a). (b) At 0.05 μmol·L -1 The graph shows the peak current of glyphosate over time. The inset shows the peak current of six ZnTi-LDH@D-UiO-66 / GCE electrodes at 0.05 μmol·L⁻¹. -1 The current response of glyphosate. To investigate the interference of the sensor, glyphosate was added at a concentration of 0.05 μmol·L⁻¹. -1 The anti-interference ability of the sensor was evaluated using glyphosate and equivalent concentrations of cationic, anionic, and other organophosphorus pesticides. Experimental results showed that these interfering substances did not interfere with the electrochemical sensing of glyphosate. Figure 8 a). Six ZnTi-LDH / D-UiO-66 / GCE electrodes were prepared using the same modification method, and glyphosate solutions of the same concentration were tested. Figure 8 As shown in b, the relative standard deviation is calculated to be 2.5%, indicating that the sensor has good reproducibility. After being stored at 4 ℃ for 10 days, the peak current of the sensor is still 86.6% of the original value. Figure 8 (b. Illustration) This demonstrates that the manufactured sensor exhibits acceptable selectivity, stability, and reproducibility for the detection of glyphosate.

Claims

1. A ZnTi-LDH@D-UiO-66 nanocomposite material modified electrode, characterized in that... The modified electrode is composed of a glassy carbon electrode as the base electrode and a ZnTi-LDH@D-UiO-66 nanocomposite material obtained by controlled surface decarboxylation as the electrode modification material. In the preparation of the ZnTi-LDH@D-UiO-66 nanocomposite material, UiO-66 is first treated with controlled surface decarboxylation defect engineering to obtain a defect-rich sample D-UiO-66. Then, ZnTi-LDH is synthesized in situ using a hydrothermal method to obtain the ZnTi-LDH@D-UiO-66 nanocomposite material. The glassy carbon electrode is denoted as GCE. The preparation method of the ZnTi-LDH@D-UiO-66 nanocomposite modified electrode includes the following specific steps: (a) Preparation of D-UiO-66 0.14 g ZrCl4 and 0.10 g terephthalic acid were dissolved in 20 mL N,N-dimethylformamide and stirred until dissolved. Then, 1.2 mL formic acid was added to the mixture, and it was transferred to a polytetrafluoroethylene autoclave. After sealing, it was reacted at 120 °C for 12 h. After centrifugation, washing, and drying, UiO-66 sample was obtained. 150 mg UiO-66 powder, 25 mg AgNO3, and 25 mg K2S2O8 were dissolved in 20 mL acetonitrile and sonicated for 10 min. The resulting mixture was then placed in an oil bath at 150 °C and reacted for 60 min. Afterward, it was immediately transferred to ice water for quenching. Finally, it was centrifuged, washed, and dried to obtain D-UiO-66. (b) Preparation of ZnTi-LDH@D-UiO-66 50 μL TiCl4, 0.36 g Zn(NO3)2·6H2O and 0.45 g urea were dissolved in 20 mL deionized water; then 100 mg D-UiO-66 powder was added to the mixed solution, stirred for 30 min, and the resulting decomposition solution was transferred to a 50 mL polytetrafluoroethylene autoclave. After reacting at 120 ℃ for 24 h, the solution was cooled and crystallized. After washing and drying, ZnTi-LDH@D-UiO-66 was obtained. (c) Preparation of ZnTi-LDH@D-UiO-66 modified GCE A 3 mm diameter GCE was polished by drawing figure-eight patterns on chamois leather with 0.2 and 0.05 μm alumina paste, and then rinsed with deionized water to obtain a fresh electrode surface. 10 mg of ZnTi-LDH / D-UiO-66 powder was dispersed in 2 mL of an equal volume ratio of ultrapure water, ethanol, and 0.5 wt% Nafion solution, and ultrasonically treated to obtain an electrode-modified dispersion. 2 ~ 10 μL of this dispersion was drop-coated onto the treated GCE surface and allowed to air dry at room temperature to obtain a ZnTi-LDH@D-UiO-66 modified GCE, denoted as ZnTi-LDH@D-UiO-66 / GCE. In the ZnTi-LDH@D-UiO-66 nanostructure obtained in step (b), the cubic structure of UiO-66 has been destroyed by etching, and the particle size has been greatly reduced from the original 100~300 nm to less than 50 nm. At the same time, ZnTi-LDH grows in situ on the destroyed UiO-66 surface to form a heterostructure. This structure can provide a large specific surface area, abundant active sites, and contains two metals, Zr and Ti, that can complex with organophosphorus molecules, which greatly improves the adsorption and capture of analytes by the catalyst and improves the sensing and analysis performance of organophosphorus pesticides by the corresponding sensor.

2. The ZnTi-LDH@D-UiO-66 nanocomposite modified electrode of claim 1, used for detecting the content of the organophosphorus pesticide glyphosate, is characterized in that... Using 0.1 mol / L pH 6.0 phosphate buffer as the supporting electrolyte, electrolyte solutions containing different amounts of glyphosate were added to the electrolytic cell. A modified electrode was used as the working electrode, and differential pulse voltammetry was used to detect the glyphosate oxidation peak current difference and its concentration. The linear regression equation was obtained. The oxidation peak current difference of glyphosate in the test sample was measured using the same method. Substituting the glyphosate into the linear regression equation, the glyphosate content in the test sample was obtained.

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