ZnTi-LDH coated D-UiO-66 nano-composite modified electrode as well as preparation method and detection application of ZnTi-LDH coated D-UiO-66 nano-composite modified electrode

Abstract

The invention discloses a ZnTi-LDH modified UiO-66 nano composite material modified electrode rich in defects, a preparation method of the electrode and application of the electrode to detection of glyphosate pesticides. The preparation method comprises the following steps: firstly, treating UiO-66 by adopting a surface controlled decarboxylation defect technology to obtain defect-rich UiO-66, then preparing ZnTi-LDH on the surface of the UiO-66 in situ by adopting a hydrothermal method to obtain the ZnTi-LDH-coated D-UiO-66 heterostructure, and the structure can provide a large specific surface area and rich active sites, simultaneously contains Zr and Ti two metal types capable of complexing with organic phosphine molecules, and can be used for preparing a high-specific-surface-area catalyst. The adsorption and capture of the catalyst on an analyte are greatly improved, and the sensing analysis performance of a corresponding sensor on an organic phosphine pesticide is improved. An electrochemical sensing platform constructed on the basis of the ZnTi-LDH-coated D-UiO-66 nanocomposite modified electrode obtains a wide detection range (0.05-50 [mu] mol L1), a low detection limit of 0.19 [mu] mol / L (S / N = 3) and high sensitivity (1.220 [mu] A.[ mu] mol / L) when glyphosate is detected, and 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) materials have excellent porosity, crystallinity, high specific surface area, and excellent thermal stability achieved by the combination of metal ions and organic ligands to form strong ligand bonds. The mesopores and micropores of MOFs have a significant effect on the electrochemical detection, the mesopores help to dope functional materials and allow electrolyte solution to penetrate, and the micropores can fully expose the adsorption sites to achieve selective adsorption of OP. Titanium atoms in titanium dioxide (TiO2) and zirconium atoms in zirconium nanoparticles (ZrNPs) have strong affinity for phosphate groups, which are often used to improve the selective adsorption and capture of OP. In order to improve the selective adsorption of the catalyst to OP, the present application uses a surface-controlled decarboxylation defect engineering technology to decarboxylate UiO-66 (a kind of Zr-MOFs) to obtain defect-rich UiO-66 (D-UiO-66), and then uses a hydrothermal method to prepare zinc-titanium layered double hydroxide (ZnTi-LDH) in situ on the surface thereof to obtain ZnTi-LDH@D-UiO-66 heterostructure, which can provide a large specific surface area, abundant active sites, and contain two metal species of Zr and Ti that can complex with organic phosphine molecules, greatly improving the adsorption and capture of the catalyst to the analyte and improving the sensing and analysis performance of the corresponding sensor for organic phosphine pesticides. SUMMARY

[0006] In view of the deficiencies of the prior art and the research and application needs in the field, one of the purposes of the present application is to provide a ZnTi-LDH@D-UiO-66 nanocomposite modified electrode, characterized in that the modified electrode is composed of a glassy carbon electrode as a base electrode and a ZnTi-LDH@D-UiO-66 nanocomposite obtained by surface-controlled decarboxylation as an electrode modification material; in the preparation process of the ZnTi-LDH@D-UiO-66 nanocomposite, first, a surface-controlled decarboxylation defect engineering is used to treat UiO-66 to obtain a defect-rich sample D-UiO-66, and then a hydrothermal method is used to synthesize ZnTi-LDH in situ to obtain the ZnTi-LDH@D-UiO-66 nanocomposite; the glassy carbon electrode is denoted as GCE;

[0007] The second purpose of the present application is to provide a preparation method of a ZnTi-LDH@D-UiO-66 nanocomposite modified electrode, characterized by comprising the following specific steps:

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

[0009] Dissolve 0.14 g ZrCl4and 0.10 g terephthalic acid in 20 mL N,N-dimethylformamide, stir until dissolved; then add 1.2 mL formic acid to the mixed solution, transfer the above reaction solution into a polytetrafluoroethylene autoclave, seal and react at 120 ℃ for 12 h, centrifuge, wash and dry to obtain a UiO-66 sample; dissolve 150 mg of UiO-66 powder, 25 mg of AgNO3and 25 mg of K2S2O8in 20 mL of acetonitrile, ultrasonically treat for 10 min, then place the obtained mixed solution in an oil bath at 150 ℃ for reaction for 60 min, then immediately transfer the reaction solution into ice water for quenching, and finally centrifuge, wash and dry to obtain D-UiO-66;

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

[0011] Dissolve 50 μL of TiCl4, 0.36 g of Zn(NO3)2·6H2O and 0.45 g of urea in 20 mL of deionized water; then add 100 mg of D-UiO-66 powder to the mixed solution, stir for 30 min, then transfer the obtained decomposition solution into a 50 mL polytetrafluoroethylene autoclave, react at 120 ℃ for 24 h, then cool and crystallize, wash and dry to obtain ZnTi-LDH@D-UiO-66;

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

[0013] Polish a GCE with a diameter of 3 mm in a "8" shape on a suede using 0.2 and 0.05 μm alumina slurries in turn, wash with deionized water to obtain a fresh electrode surface; disperse 10 mg of ZnTi-LDH / D-UiO-66 powder in 2 mL of an equal-volume ratio of ultrapure water, ethanol and 0.5 wt% Nafion solution, ultrasonically treat to obtain an electrode modification dispersion; take 2 ~ 10 μL of the dispersion and drop coat on the treated GCE surface, and naturally dry at room temperature to obtain a ZnTi-LDH@D-UiO-66 modified GCE, which is recorded as ZnTi-LDH@D-UiO-66 / GCE;

[0014] In the ZnTi-LDH@D-UiO-66 nanostructure obtained in step (b), the UiO-66 cubic structure has been destroyed by etching, and the particle size has been greatly reduced from 100-300 nm to less than 50 nm; meanwhile, ZnTi-LDH is grown in situ on the surface of the destroyed UiO-66 to form a heterostructure; the structure can provide a large specific surface area, abundant active sites, and contains two metal species of Zr and Ti that can complex with organic phosphine molecules, greatly improving the adsorption and capture of the catalyst for the analyte and improving the sensing and analysis performance of the corresponding sensor for organic phosphine pesticides.

[0015] The third object of the present application is to provide a ZnTi-LDH@D-UiO-66 nanocomposite modified electrode for detecting the content of organic phosphine pesticide glyphosate, characterized in that 0.1 mol / L pH 6.0 phosphate buffer is used as a supporting electrolyte, an electrolyte solution containing different amounts of glyphosate is added to an electrolytic cell, the modified electrode is used as a working electrode, differential pulse voltammetry is used for detection, a linear regression equation of the oxidation peak current difference of glyphosate and its concentration is obtained, the oxidation peak current difference of glyphosate in the sample to be tested is determined by the same method, and the content of glyphosate in the sample to be tested is obtained by substituting the linear regression equation.

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

[0017] (a) The ZnTi-LDH@D-UiO-66 nanocomposite modified electrode of the present application, the ultrathin and ultra-small ZnTi-LDH nanosheet is in situ assembled in the defect-rich UiO-66 to form a heterostructure that can provide a large specific surface area, abundant active sites, and contains two metal species of Zr and Ti that can complex with organic phosphine molecules, greatly improving the adsorption and capture of the catalyst for the analyte and improving the sensing and analysis performance of the corresponding sensor for organic phosphine pesticides.

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

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

[0020] Figure 2 FTIR spectra of UiO-66 and D-UiO-66 prepared in Comparative Example 2, Comparative Example 3 (a), XRD patterns of UiO-66, D-UiO-66 and ZnTi-LDH@D-UiO-66 prepared in Comparative Example 2, Comparative Example 3 and Example 3 (b), XPS spectra of D-UiO-66, ZnTi-LDH and ZnTi-LDH@D-UiO-66 prepared in Comparative Example 3, Comparative Example 4 and Example 3 (c), XPS high resolution Zr 3d, Ti2p and O 1s spectra of D-UiO-66 and ZnTi-LDH@D-UiO-66 prepared in Comparative Example 3 and Example 3 (d-f).

[0021] Figure 3 (a) CV plots and (b) Nyquist plots of Comparative Example 1, Comparative Example 2, Comparative Example 3, Example 3 corresponding GCE, UiO-66 / GCE, D-UiO-66 / GCE and ZnTi-LDH@D-UiO-66 / GCE electrodes in a solution containing 5.0 mmol·L -1 [Fe(CN)6] 3- / 4- -1in 0.1 mol·L -1 KCl.

[0022] Figure 4 CV plots of Example 3, Comparative Example 3 and Comparative Example 2 corresponding ZnTi-LDH@D-UiO-66 / GCE, D-UiO-66 / GCE and UiO-66 / GCE electrodes at different scan rates in 0.1 mol·L −1 pH 7.0 phosphate buffer solution (a-c), I -1 -t vs. scan rate plots of Example 3, Comparative Example 3 and Comparative Example 2 corresponding ZnTi-LDH@D-UiO-66 / GCE, D-UiO-66 / GCE and UiO-66 / GCE electrodes in the range of 30 ~ 110 mV·s pa -1(d).

[0023] Figure 5 DPV plots of Example 3 corresponding ZnTi-LDH@D-UiO-66 / GCE in different pH (a) and corresponding peak current histogram (b) of 0.05 μmol·L -1 -1glyphosate.

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

[0025] Figure 7 The current response curves (a and c) of the ZnTi-LDH@D-UiO-66 / GCE and D-UiO-66 / GCE electrodes corresponding to Example 3 and Comparative Example 3, respectively, for the DPV detection of glyphosate, and the corresponding peak current change value-concentration relationship graphs (b and d).

[0026] Figure 8 The ZnTi-LDH@D-UiO-66 / GCE corresponding to Example 3 was 0.05 μmol·L -1 The DPV peak current histogram (a) of glyphosate and the same concentration of interfering substances. (b) The current response of the ZnTi-LDH@D-UiO-66 / GCE corresponding to Example 3 to 0.05 μmol·L -1 The change of glyphosate peak current with time. The inset is the current response of six ZnTi-LDH@D-UiO-66 / GCE electrodes to 0.05 μmol·L -1 The current response of glyphosate. DETAILED DESCRIPTION

[0027] In order to further understand the present application, the present application will be further described below in conjunction with the accompanying drawings and examples, but the present application is not limited in any way by the present application.

[0028] Example 1:

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

[0030] Dissolve 0.14 g ZrCl4and 0.10 g terephthalic acid in 20 mL N,N-dimethylformamide, stir until dissolved; then add 1.2 mL formic acid to the mixed solution, transfer the above reaction solution into a polytetrafluoroethylene autoclave, seal and react at 120 ℃ for 12 h, centrifuge, wash and dry to obtain a UiO-66 sample; dissolve 150 mg UiO-66 powder, 25 mg AgNO3and 25 mg K2S2O8in 20 mL acetonitrile, ultrasonically treat for 10 min, then place the obtained mixed solution in an oil bath at 150 ℃ and react for 60 min, then immediately transfer the reaction solution into ice water for quenching, and finally centrifuge, wash and dry to obtain D-UiO-66;

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

[0032] Dissolve 50 μL TiCl4, 0.36 g Zn(NO3)2·6H2O and 0.45 g urea in 20 mL deionized water; then add 100 mg D-UiO-66 powder to the mixed solution, stir for 30 min, then transfer the obtained decomposition solution into a 50 mL polytetrafluoroethylene autoclave, react at 120 ℃ for 24 h, then cool and crystallize, and wash and dry to obtain ZnTi-LDH@D-UiO-66;

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

[0034] Polish a GCE with a diameter of 3 mm in an "8" shape on a suede using 0.2 and 0.05 μm alumina slurries in turn, wash with deionized water to obtain a fresh electrode surface; disperse 10 mg ZnTi-LDH@D-UiO-66 powder in 6 mL of an equal-volume-ratio ultrapure water, ethanol and 0.5 wt% Nafion solution, and ultrasonically treat to obtain an electrode modification dispersion; take 2 μL of the dispersion and drop coat on the treated GCE surface, and naturally dry at room temperature to obtain a ZnTi-LDH@D-UiO-66 modified GCE, which is recorded 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] According to the method and conditions of step (c) in Example 1, 4 μL of ZnTi-LDH@D-UiO-66 dispersion solution with a concentration of 5 mg / mL was dropped on the surface of the treated GCE, and a ZnTi-LDH@D-UiO-66 nanocomposite modified GCE was obtained after natural drying at room temperature, which was recorded 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] According to the method and conditions of step (c) in Example 1, 6 μL of ZnTi-LDH dispersion solution with a concentration of 5 mg / mL was dropped on the surface of the treated GCE, and a ZnTi-LDH@D-UiO-66 nanocomposite modified GCE was obtained after natural drying at room temperature, which was recorded 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 ZnTi-LDH dispersion solution with a concentration of 5 mg / mL was dropped on the surface of the treated GCE, and a ZnTi-LDH@D-UiO-66 nanocomposite modified GCE was obtained after natural drying at room temperature, which was recorded as ZnTi-LDH@D-UiO-66 / GCE.

[0056] Example 5:

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

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

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

[0060] 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 ZnTi-LDH dispersion solution with a concentration of 5 mg / mL was dropped on the surface of the treated GCE, and a ZnTi-LDH@D-UiO-66 nanocomposite modified GCE was obtained after natural drying at room temperature, which was recorded as ZnTi-LDH@D-UiO-66 / GCE.

[0063] Comparative Example 1:

[0064] The working electrode was a bare GCE.

[0065] Comparative Example 2:

[0066] (a) Preparation of UiO-66

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

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

[0069] A GCE with a diameter of 3 mm was polished with 0.2 and 0.05 μm alumina slurries on a chamois leather in the shape of an "8", and a fresh electrode surface was obtained after rinsing with deionized water; the D-UiO-66 prepared in step (a) was ultrasonically dispersed in a deionized water solvent to prepare a dispersion liquid with a concentration of 5 mg / mL, 6 μL of the dispersion liquid was dropped on the treated GCE surface, and a D-UiO-66 modified GCE was obtained after natural drying at room temperature, which was recorded as D-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] A GCE with a diameter of 3 mm was polished with 0.2 and 0.05 μm alumina slurries on a chamois leather in the shape of an "8", and a fresh electrode surface was obtained after rinsing with deionized water; the D-UiO-66 prepared in step (a) was ultrasonically dispersed in a deionized water solvent to prepare a dispersion liquid with a concentration of 5 mg / mL, 6 μL of the dispersion liquid was dropped on the treated GCE surface, and a D-UiO-66 modified GCE was obtained after natural drying at room temperature, which was recorded 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. It can be observed that the original UiO-66 exhibits a sub-micron size octahedral morphology with sharp crystal edges and smooth surface arrangement (a, b, c). After surface decarboxylation treatment, the smooth surface is damaged to some extent, but the octahedral morphology is not changed (d, e, f). Figure 1 a and 1d). After the formation of defects after surface decarboxylation treatment, the smooth surface is damaged to some extent, but the octahedral morphology is not changed (d, e, f). Figure 1 b and Figure 1e). In the preparation of the precursor solution of ZnTi-LDH, D-UiO-66 is added, the cubic structure of UiO-66 is destroyed by etching, and the particle size is greatly reduced from the original 100-300 nm to less than 50 nm; at the same time, ZnTi-LDH grows in situ on the surface of the destroyed UiO-66 to form a heterostructure; this structure can provide a large specific surface area, abundant active sites, and contains two metal species of Zr and Ti that can complex with organic phosphine molecules, greatly improving the adsorption and capture of analytes by the catalyst and improving the sensing and analysis performance of the corresponding sensor for organic phosphine pesticides.

[0076] Figure 2 FTIR spectra of UiO-66 and D-UiO-66 prepared in Comparative Example 2 and Comparative Example 3 (a), XRD patterns of UiO-66, D-UiO-66 and ZnTi-LDH@D-UiO-66 prepared in Comparative Example 2, Comparative Example 3 and Example 3 (b), XPS spectra of D-UiO-66, ZnTi-LDH and ZnTi-LDH@D-UiO-66 prepared in Comparative Example 3, Comparative Example 4 and Example 3 (c), and XPS high-resolution Zr 3d, Ti 2p and O 1s spectra of D-UiO-66 and ZnTi-LDH@D-UiO-66 prepared in Comparative Example 3 and Example 3 (d-f). -1 FTIR spectra show that the original UiO-66 has a vibration band from 1400 to 1600 cm -1 -1, which is related to the interaction of carboxylate. Specifically, in the range of 1430 ~ 1533 cm -1 -1, there is clear evidence that the amino carboxylate molecule is coordinated with the Zr metal nucleus, which is characterized by the asymmetric stretching of -COO, which appears a peak at 1499 ~ 1570 cm -1 -1. The peaks generated at 1584 and 1434 cm -1 -1 correspond to the symmetric stretching vibration of -COO-. After silver-catalyzed decarboxylation, the asymmetric stretching vibration of C=O of D-UiO-66 at 1665 cm -1 -1 disappears, and the symmetric stretching vibration of -COO- at 1398 cm -1 -1 is weakened, indicating that a defective D-UiO-66 with intact structure is formed. In order to prove whether the existence of structural defects has an impact on the crystal structure, powder XRD was used for verification, and the results are as follows. Figure 2b. Both UiO-66 and D-UiO-66 showed strong Bragg scattering and both had almost similar diffraction peaks without obvious weakening of intensity. Thus, it was further verified that the decarboxylation defect process did not destroy the crystal structure. The elemental composition and changes of ZnTi-LDH@D-UiO-66 heterostructure were explained by XPS test results. The precursor solution when preparing ZnTi-LDH was added with an appropriate amount of D-UiO-66 powder, so XPS test was also conducted on ZnTi-LDH and D-UiO-66. As shown in Figure 2 c, the obvious display of Zn, Ti and Zr in ZnTi-LDH@D-UiO-66 heterostructure indicated the successful preparation of nanocomposites. And high-resolution Zr3d, Ti 2p and O 1s before and after the composite were analyzed, respectively, and obvious changes could be observed, which further indicated that the composite of nanomaterials could promote the synergistic effect between the two and make the electron charge transfer between the two.

[0077] Figure 3 The (a) CV curve and (b) Nyquist diagram of the GCE, UiO-66 / GCE, D-UiO-66 / GCE and ZnTi-LDH@D-UiO-66 / GCE electrodes corresponding to Comparative Example 1, Comparative Example 2, Comparative Example 3 and Example 3 in the solution containing 5.0 mmol·L -1 [Fe(CN)6] 3- / 4- of 0.1 mol·L -1 KCl were shown in FIG. 11. As shown in Figure 3 a, the peak current of UiO-66 / GCE, GCE, ZnTi-LDH / D-UiO-66 / GCE and D-UiO-66 / GCE was 59.82, 65.17, 68.68 and 74.46 μA, respectively. Compared with the traditional GCE, the peak current of UiO-66 / GCE was slightly reduced, which was due to the poor conductivity of UiO-66 itself. The introduction of surface defects by silver catalytic decarboxylation made the peak current of D-UiO-66 / GCE significantly increased. After D-UiO-66 was modified by ZnTi-LDH, the peak current was slightly reduced, which might be because the conductivity of ZnTi-LDH itself was poor, resulting in the decrease of the overall conductivity of the ZnTi-LDH / D-UiO-66 / GCE nanocomposite. The EIS diagrams of different electrodes in the same system were shown in Figure 3 b. According to the corresponding Randles equivalent circuit, the EIS of UiO-66 / GCE, GCE, ZnTi-LDH / D-UiO-66 / GCE and D-UiO-66 / GCE was 649.7, 385.8, 287.2 and 130.3 Ω, respectively. This result was consistent with the change 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. -2 Due 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 Example 1, Example 2, Example 3, Example 4 and Example 5 was used to detect glyphosate in 0.05 μmol·L -1 -1 The effect of enrichment time (b) and enrichment potential (c) on the DPV peak current of glyphosate was investigated. As shown in Figure 6 a, the peak current gradually increased with the increase of the modification amount, and reached the maximum value at 6 μL. When the modification amount continued to increase, the peak current decreased, which might be because the excessive loading would lead to a thicker layer, hindering the transmission of glyphosate molecules and electrons. The optimal modification amount was 6 μL. Under the optimal modification amount, the enrichment potential and enrichment time were optimized, as shown in Figure 6 b, when the enrichment potential increased from 0.1 V to 0.3 V, the peak current of glyphosate gradually increased with the increase of the enrichment potential. When the potential continued to increase, the peak current gradually decreased with the increase of the potential. Therefore, the optimal enrichment potential of glyphosate was 0.3 V. The effect of enrichment time on the peak current was further investigated under the respective optimal enrichment potential. Glyphosate showed a trend of first increasing and then decreasing with the increase of the enrichment time in the range of 10 ~ 50 s (c), and 30 s was selected as the optimal enrichment time of glyphosate. After 30 s, the peak current slowly decreased, which might be because the adsorption of glyphosate on the surface of ZnTi-LDH / D-UiO-66 / GCE electrode reached saturation. Figure 6

[0081] Figure 7 The current response curves (a and c) of the DPV detection of glyphosate 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 change value-concentration relationship diagram (b and d) are shown. In order to further verify the detection performance of the single catalytic active site Zr in D-UiO-66 / GCE and the double catalytic active sites Zr and Ti in ZnTi-LDH / D-UiO-66 / GCE for glyphosate. Under the optimal experimental conditions, the capture capacity of the modified electrode for glyphosate was determined by DPV method, as shown in Figure 7 the peak current response of DPV showed a linear relationship with the concentration of glyphosate. Among them, the ZnTi-LDH / D-UiO-66 / GCE modified electrode showed a linear relationship with the concentration of glyphosate from 0.05 μmol·L -1 to 50 μmol·L​​-1 , ΔI pa increased with the increase of concentration, two linear parts were 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) was 0.19 μmol·L -1 and the sensitivity (S) was 1.220 μA·μmol -1 ·L. Meanwhile, the D-UiO-66 / GCE modified electrode was detected by DPV under the same conditions, and the two linear parts 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) was 6.98 μmol·L -1 and the sensitivity was 0.559 μA·μmol -1 ·L. It was further proved that the double catalytic sites were superior to the single catalytic site. In addition, due to the fierce competition of ions on the electrode surface, the D-UiO-66 / GCE modified electrode further added glyphosate to the solution, which led to a slower increase in peak current. The shift of potential with the increase of glyphosate concentration may be due to the fact that glyphosate is a non-electrochemically active species, which induces the shift of potential when it binds to the active site on the surface.

[0082] Figure 8 Figure 6 is a histogram of the peak current of DPV of the ZnTi-LDH@D-UiO-66 / GCE corresponding to Example 3 in the presence of 0.05 μmol·L -1 glyphosate and the same concentration of interfering substances (a). (b) is a graph of the change of peak current of 0.05 μmol·L -1 glyphosate with time. The inset is the current response of six ZnTi-LDH@D-UiO-66 / GCE electrodes to 0.05 μmol·L -1 glyphosate. In order to study the interference of the sensor, the anti-interference of the sensor was evaluated by adding the concentration of 0.05 μmol·L -1 glyphosate and the same concentration of cations, anions and other organophosphorus pesticides. The experimental results show that these interfering substances do not interfere with the electrochemical sensing of glyphosate Figure 8a). Six ZnTi-LDH / D-UiO-66 / GCE electrodes were prepared using the same modification method, and the same concentration of glyphosate solution was detected. As shown in Fig. Figure 8 b, the relative standard deviation was calculated to be 2.5%, indicating that the sensor had good reproducibility. After being stored at 4 ℃ for 10 days, the peak current of the sensor was still 86.6% of the original value (Fig. Figure 8 b, inset). It was shown that the sensor manufactured had 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: 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 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. 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, overnight 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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