A kind of [Omim] 6 Mo 7 O 24 Preparation method, product and application of [Mo]-CPE modified electrode

Abstract

The present invention discloses a preparation method, product and application of an [Omim]6Mo7O 24 -CPE modified electrode. The [Omim]6Mo7O 24 -CPE modified electrode of the present invention has high sensitivity in the determination of phosphate content, with a detection limit of 8.5×10 ‑8 mol·L ‑1 , a sensitivity of 5.3 (±0.1) μA·μM, and a standard addition recovery rate for tap water samples of 89.7 - 105.1 mol·L ‑1 ; and the [Omim]6Mo7O 24 -CPE modified electrode of the present invention is less affected by interfering substances such as sodium silicate. In the case of phosphate with a sample concentration 10 times that of phosphate, the relative deviation is only 2.27%.

Description

Technical Field

[0001] The present invention relates to a kind of [Omim] 6 Mo 7 O 24 -CPE modified electrode preparation method, its products and applications, belonging to the field of electrochemical sensors. Background Technique

[0002] Existing literature has reported the use of molybdate solutions and molybdate-modified electrodes (by modifying carbon paste electrodes, gold microdisk electrodes and glassy carbon electrodes with nanomaterials such as gold nanoparticles, carbon nanotubes and graphene, and molybdenum phosphate complexes) to determine the phosphate content of the Keggin complex formed by the reaction between phosphate and molybdate electrodes in the sample. The purpose is to improve electrochemical performance, such as obtaining lower sensitive concentrations, wider linear sensing ranges and higher stabilities, etc. There is also literature (Berchmans et al, Glassy carbon electrode modified with hybrid films containing inorganic molybdate anions trapped in organic matrices of chitosan and ionic liquid for the amperometric sensing of phosphate at neutral pH, Sens. Actuat. B, 2011, 160, 1224.) reporting molybdate / 1-ethyl-3-methylimidazolium tetrafluoroborate / polystyrenesulfonate / poly(3,4-ethylenedioxythiophene) / chitosan film electrodes. Among them, the chitosan matrix provides an interfacial acidic microenvironment, which is beneficial to the formation of phosphomolybdenum complexes. At present, the design of flexible, stretchable and moldable sensor electrodes and on-site detection have received great attention. Flexible carbon composite substrates are suitable for molybdate preloading without changing the precursor structure. Several nanomaterials, such as carbon nanotubes, graphene, conductive polymers and metal nanowires, can be used as flexible transparent electrode materials, and batteries, capacitors and sensors have excellent electrochemical properties. Therefore, carbon-based electrode materials are of great interest for manufacturing flexible substrates for use in phosphate sensor electrodes, and different carbon sources can be used to prepare different flexible carbon films such as carbon nanotubes, graphene and activated carbon.

[0003] To make the carbon material-molybdate combination flexible, it must be combined with a polymer film. Polyvinylidene fluoride-co-hexafluoropropylene (PVDF) has high chemical, electrochemical, thermal, and mechanical stability. Wu et al. (Ammonium heptamolybdate preloaded on flexible carbon-matrix film electrode (AHM@PANI / CC / PVDF) for the electrochemical phosphate sensor in a river water sample, Microchemical Journal, 2021, 170, 106639) demonstrated that the conductivity of the PVDF / metal oxide composite film at room temperature is strong (2.1×10 -3 S cm -1 ). Therefore, during the preparation of the composite material, after adding PVDF to the carbon material, it is possible to retain molybdate and prevent it from dissolving in the aqueous solution. PVDF is hydrophobic, so it can prevent the wettability of the electrode surface and limit the phase change of molybdate in the acidic phosphate aqueous solution. To enhance the wettability of the carbon material / PVDF composite conductive polymer, molybdate should be added to the surface to form a phosphomolybdate Keggin complex, creating a favorable microenvironment for the flexible thin-film electrode substrate. Polyaniline (PANI) was used as a conductive additive in this report to enhance wettability, mechanical property stability, and conductivity. The analytical characteristics obtained for the composite film electrode in this report were a linear range of 10–114 μM, a detection limit of (0.6 μM) (-0.131 V vs. Ag / AgCl), a sensitivity of (0.0648 μA·μM -1 ), and a spiked recovery rate range of 101.3%–113.3%.

[0004] The principle of voltammetric or amperometric determination of phosphate is based on the analysis of the electroactive Keggin complex obtained from the reaction of phosphate ions with Mo(VI). The anion PMo 12 O 40 3- in the electroactive Keggin complex is the most well-known phosphomolybdate complex, which often appears in strongly acidic aqueous solutions. Its reduction electrical signal is often used to determine phosphate. In the determination of phosphate so far, PMo 12 O 40 3-It is often fixed on the surface of the bare electrode to generate a voltammogram, and the voltammogram is consistent with the surface-limited redox process of the Mo center. The dissolution and erosion of inorganic molybdate in the electrode easily cause the decline of the analytical characteristics of the electrode. Therefore, the electrode is usually mixed and fixed with matrix materials such as graphite, carbon nanoparticles, poly(vinyl chloride), poly(vinylidene fluoride - hexafluoropropylene), chitosan - ionic liquid hybrid matrix, zirconium dioxide - zinc oxide - carbon nanotubes, etc., so as to be stably fixed on the electrode, thereby improving the analytical characteristics. However, these electrode modification processes are complex and cumbersome, with a large variety of additives and poor stability, and the analytical performance is not prominent. Summary of the Invention

[0005] Object of the Invention: The technical problem to be solved by the present invention is to provide a preparation method of an [Omim] 6 Mo 7 O 24 -CPE modified electrode, the method has low cost and is simple and easy to operate;

[0006] The present invention also provides an [Omim] 6 Mo 7 O 24 -CPE modified electrode with high sensitivity prepared by the method;

[0007] The present invention also provides the application of the [Omim] 6 Mo 7 O 24 -CPE modified electrode in the determination of the phosphate content in a sample.

[0008] The present invention also provides a method for determining the phosphate concentration in a sample.

[0009] Technical Solution: To solve the above technical problems, the present invention provides the following technical solutions:

[0010] The present invention provides a method for preparing an [Omim] 6 Mo 7 O 24 -CPE modified electrode, including the following steps:

[0011] (1) Mix and stir [Omim]Br with an aqueous solution of ammonium molybdate to generate a white suspension;

[0012] (2) Centrifuge the white suspension, wash it with deionized water until there is no Br ion, and grind it to obtain [Omim] 6 Mo 7 O 24 solid ionic powder;

[0013] (3) Mix [Omim] 6 Mo 7 O 24The solid ionic powder is vacuum-dried, mixed with carbon powder and silicone oil, and pressed into shape to obtain [Omim] 6 Mo 7 O 24 -CPE modified electrode.

[0014] Among them, in step (1), the molar ratio of [Omim]Br to the ammonium molybdate aqueous solution is 1:1, the concentration of [Omim]Br is 50 mmol / L, and the concentration of the ammonium molybdate aqueous solution is 40 - 60 mmol / L.

[0015] Among them, in step (2), the centrifugation rate is 3000 - 5000 r / min, and the centrifugation time is 10 - 30 minutes;

[0016] Among them, in step (3), the temperature of vacuum drying is 60 - 80 °C, and the time is 4 - 8 h;

[0017] Among them, in step (1), [Omim] 6 Mo 7 O 24 The mass ratio of the solid ionic powder, the carbon powder and the silicone oil in step (3) is 12.75 - 51:255:50.

[0018] The present invention also provides [Omim] prepared by the above method 6 Mo 7 O 24 -CPE modified electrode.

[0019] The present invention also provides the application of the [Omim] 6 Mo 7 O 24 -CPE modified electrode in the determination of the phosphate content in a sample.

[0020] The present invention also provides a method for determining the phosphate concentration in a sample, comprising the following steps:

[0021] (1) Connect the [Omim] 6 Mo 7 O 24 -CPE modified electrode, the Ag / AgCl reference electrode and the counter electrode platinum wire to an electrochemical analyzer respectively;

[0022] (2) Add the H 2 PO 4 - standard solution to the H 2 SO 4 -KCl mixed solution, and determine the linear relationship between the phosphate concentration and the current intensity through the electrochemical analyzer to obtain the linear relationship equation between the phosphate concentration and the current intensity as y = 5.2657x + 147.212 (R2 = 0.9970); where y represents the current intensity (μA) and x represents the phosphate concentration (mol·L -1 ).

[0023] (3) Add the test sample containing H 2 PO 4 - to the H 2 SO 4 -KCl mixed solution, measure its current intensity through an electrochemical analyzer, and calculate the phosphate concentration through the linear equation in step (2).

[0024] Among them, the working potential of the [Omim] 6 Mo 7 O 24 -CPE modified electrode for measuring the phosphate content in the sample is -400 to 1200 mV vs. Ag / AgCl.

[0025] Among them, the phosphate concentration in step (3) is 85 nM / 0.1 to 10000 μM.

[0026] Beneficial effects: Compared with the prior art, the present invention has the following remarkable advantages:

[0027] 1. The present invention uses [Omim] 6 Mo 7 O 24 -carbon powder-silicone oil to prepare a highly sensitive phosphate determination electrode to measure the phosphate content in tap water;

[0028] 2. The present invention only uses a supporting electrolyte composed of 0.1 mol·L -1 H 2 SO 4 -KCl (volume ratio 1:1) mixed solution. In the cyclic voltammetry working potential range: -400–1200 mV vs. Ag / AgCl, the obtained electrode analysis characteristics are: linear induction range: 1.0×10 -2 ~1.0×10 -7 mol·L -1 , linear correlation coefficient R 2 = 0.9970, detection limit: 8.5×10 -8 mol·L -1 , sensitivity: 5.3 (±0.1) μA·μM, and the spike recovery rate for tap water samples is 89.7 - 105.1 mol·L -1 ;

[0029] 3. In the present invention, the influence of sodium silicate interference substances is small. In the case of phosphate with a sample concentration 10 times that of phosphate, the relative deviation is only 2.27%.

[0030] 4. The determination result of phosphate in the tap water on the Yangzijin Campus of Yangzhou University is 0.29 ± 0.02 μmol·L -1 , which is consistent with the ion chromatography measurement value of 0.28 ± 0.05 μmol·L -1 . Description of the Drawings

[0031] Figure 1 shows the influence of ammonium molybdate solutions with different concentrations on the mass of the synthesized [Omim] 6 Mo 7 O 24 solid ion powder;

[0032] Figure 2 is the SEM image of the [Omim] 6 Mo 7 O 24 -CPE surface;

[0033] Figure 3 is the EDS spectrum of the [Omim] 6 Mo 7 O 24 -CPE surface;

[0034] Figure 4 is the XPS energy state analysis diagram of molybdenum on the [Omim] 6 Mo 7 O 24 -CPE surface before and after cyclic voltammetry;

[0035] Figure 5 A is the cyclic voltammetry redox peak diagram of [Omim] 6 Mo 7 O 24 -CPE, Figure 5 B is the thumbnail of the cyclic voltammetry redox peak of pure CPE in the NaMo 7 O 24 solution;

[0036] Figure 6 shows the cyclic voltammograms of carbon electrodes with different contents of [Omim] 6 Mo 7 O 24 ;

[0037] Figure 7 is the [Omim] 6 Mo 7 O 24-Cyclic voltammetry current change curve of CPE with scanning potential;

[0038] Figure 8 is [Omim] 6 Mo 7 O 24 -Peak current change curves of A2 / C2 and A3 / C3 of CPE with scanning rate;

[0039] Figure 9 is [Omim] 6 Mo 7 O 24 -Peak current change curve of A5 / C5 of CPE with square root of scanning rate;

[0040] Figure 10 is [Omim] 6 Mo 7 O 24 -Schematic diagram of the method for determining phosphate by CPE cyclic voltammetry;

[0041] Figure 11 is [Omim] 6 Mo 7 O 24 -Peak current of C5 of CPE in H 2 PO 4 - Change curve with scanning potential in standard solution;

[0042] Figure 12 is [Omim] 6 Mo 7 O 24 -Situation of CPE in determining phosphate under the interference of silicate. Detailed implementation method

[0043] The technical solution of the present invention will be further described below with reference to the accompanying drawings.

[0044] Example 1 Preparation of different [Omim] 6 Mo 7 O 24 Prepare

[0045] Add 10 mL of 50 mmol / L 1-octyl-3-methylimidazolium tetrafluoroborate solution ([Omim]Br solution) dropwise to 10 mL of 50 mmol / L ammonium molybdate solution, and stir with a magnetic stirrer at room temperature for 30 min. Then, centrifuge the obtained white suspension at a speed of 4000 r·min -1 for 20 min, wash the suspension with water, repeat the above steps 4 times to obtain a milky white solid; then vacuum dry at 60 °C for 8 h, and grind it into powder repeatedly with an agate mortar to obtain [Omim]6 Mo 7 O 24 Solid ionic powder 1.

[0046] According to the same procedure, 10 mL of a 50 mmol / L 1-octyl-3-methylimidazolium tetrafluoroborate solution was added dropwise to 12.5 mL of a 40 mmol / L ammonium molybdate solution, and stirred with a magnetic stirrer at room temperature for 35 min. Then, the obtained white suspension was centrifuged at a speed of 5000 r·min -1 for 10 min, and the suspension was rinsed with water. The above steps were repeated 4 times to obtain a milky white solid; then it was vacuum dried at 80 °C for 4 h and repeatedly ground into powder with an agate mortar to obtain [Omim] 6 Mo 7 O 24 Solid ionic powder 2.

[0047] According to the same procedure, 10 mL of a 50 mmol / L 1-octyl-3-methylimidazolium tetrafluoroborate solution was added dropwise to 8.3 mL of a 60 mmol / L ammonium molybdate solution, and stirred with a magnetic stirrer at room temperature for 40 min. Then, the obtained white suspension was centrifuged at a speed of 3000 r·min -1 for 30 min, and the suspension was rinsed with water. The above steps were repeated 4 times to obtain a milky white solid; then it was vacuum dried at 70 °C for 6 h and repeatedly ground into powder with an agate mortar to obtain [Omim] 6 Mo 7 O 24 Solid ionic powder 3.

[0048] Compare the relationship between the mass of the three [Omim] 6 Mo 7 O 24 solid ionic powders and the concentration of the ammonium molybdate solution. As Figure 1 shown, with the increase in the concentration of the ammonium molybdate solution, the mass of the precipitate ([Omim] 6 Mo 7 O 24 solid ionic powder) also increases; when the concentration of the ammonium molybdate solution is 50 mmol / L, the mass of the precipitate no longer changes.

[0049] Preparation of the electrode in Example 2

[0050] At room temperature, different amounts of [Omim] 6 Mo 7 O 24 solid ionic powder 1 ([Omim] 6 Mo 7 O 24Solid ionic powder 1 accounted for 0%, 5%, 10%, 15% and 20% of the mass of carbon powder respectively) and 50 mg of silicone oil (10 mPa·s, 25 °C). After mixing for 30 minutes, a slurry was obtained; then the slurry was evenly dispersed into a 1 mL plastic syringe. Pressure was applied using the syringe rod to form a shape, and a copper wire with a diameter of 1 mm was used as the conducting wire; then the five groups of electrodes prepared were polished successively with 1000-mesh, 4000-mesh and 8000-mesh SiC sandpaper, and then dried overnight at room temperature to obtain the [Omim] 6 Mo 7 O 24 -CPE electrode.

[0051] For comparison, [NH 4 6 Mo 7 O 24 solid was used to replace [Omim] 6 Mo 7 O 24 . Using the same method as in this example, [NH 4 6 Mo 7 O 24 -CPE ([NH 4 6 Mo 7 O 24 solid powder accounted for 15% of the mass of carbon powder) was prepared.

[0052] Example 3 Research on the characteristics of [Omim] 6 Mo 7 O 24 -CPE

[0053] Scanning electron micrographs (SEM) were collected using an S-4800II field emission scanning electron microscope (Hitachi, Ltd., Japan) equipped with Noran EDS (Thermo electron Corporation) to obtain the morphological characteristics of [Omim] 6 Mo 7 O 24 -CPE ([Omim] 6 Mo 7 O 24 solid ionic powder 1 accounted for 15% of the mass of carbon powder). As Figure 2 shown, [Omim] 6 Mo 7 O 24 showed a flaky cluster morphology on the surface of the CPE. At the same time, Figure 3 the distribution maps of C, N, O, Si, and Mo elements in​​​6 Mo 7 O 24 is well dispersed on the surface of CPE.

[0054] The XPS spectra of the surface layer were obtained using an ESCALAB 250Xi model (Thermo Fisher Scientific, USA) to confirm [Omim] 6 Mo 7 O 24 - molybdenum species on the CPE surface layer, and the measurement results are as Figure 4 shown. [Omim] 6 Mo 7 O 24 - The XPS energy spectrum measurement of the CPE surface layer was carried out on the electrode after 20 cyclic voltammetry operations in the range of -0.4 to 1.2 V at a scanning rate of 100 mV·s -1 -1 in an electrolyte containing phosphate to distinguish the energy state changes of Mo. According to the literature, the XPS spectrum shows a doublet in the binding energy region of Mo 3d electrons. Before reacting with phosphate, peaks i and ii corresponding to Mo 3d appear as a doublet Mo3d5 / 2 at 234.93 eV and Mo3d3 / 2 at 131.85 eV. The binding energies of the peaks (232.5 eV and 235.6 eV) correspond to the Mo(VI) state. In the presence of H 2 PO 4 - - The corresponding peaks after cyclic voltammetry (CV) also show two resolved peaks (peaks i' and ii') at 231.99 eV and 235.15 eV. As Figure 4 shown, the binding energies of these two peaks, 0.65 eV and 0.67 eV, are lower than those of peaks i and ii, respectively. Peaks i and ii are assigned to Mo3d5 / 2 and Mo3d3 / 2 of the Mo(V) state. In addition, there are no signs of Mo(III) and Mo(IV) in the layer deposited on the [Omim] 6 Mo 7 O 24 - CPE surface (if any, they should appear at Mo(IV, 233.09 eV) and Mo(VI, 234.9 eV)). These results indicate that the parent Mo(VI) surface species are converted to Mo(V) during electroreduction.

[0055] Example 4 [Omim] 6 Mo 7 O 24 - Cyclic voltammogram of CPE

[0056] Voltammetric measurements were carried out using a CHI800D electrochemical analyzer (Shanghai Chenhua Instrument Co., Ltd.). Respectively, [Omim]6 Mo 7 O 24 The -CPE working electrode (WE), Ag / AgCl reference electrode (RE, CHI111) and counter electrode platinum wire (CHI115) were connected to a computer. Cyclic voltammetry (CV) was carried out in 10 mL of a supporting electrolyte mixed solution composed of 0.1 mol·L -1 H 2 SO 4 + KCl (volume ratio 1:1), and the applied working potential range was -400 to +1200 mV vs. SCE.

[0057] To investigate the 6 Mo 7 O 24 -CPE ([Omim] 6 Mo 7 O 24 solid ion powder 1 accounting for 15% of the mass of carbon powder) electrochemical performance, in 0.1 mol·L -1 of H 2 SO 4 -KCl mixed solution, with acidified molybdate(VI) (0.1 mol·L -1 sulfuric acid + 1 mmol·L -1 MoO 4 2- ) solution of pure CPE as a control, CV scans (scan rate 100 mV·s 6 Mo 7 O 24 ([Omim] 6 Mo 7 O 24 solid ion powder 1 accounting for 15% of the mass of carbon powder) of CPE were carried out. As can be seen from -1 A, due to the enhanced conductivity of the [Omim] Figure 5 A, the CV diagram has a very large current response from the electroactive polyoxomolybdate substrate; this is because the flaky [Omim] 6 Mo 7 O 24 -CPE is uniformly dispersed, making the overall modification of the electrode, thus improving the conductivity of the electrode. While the 6 Mo 7 O 24 -CPE cannot observe obvious redox peaks due to the weak conductivity after electrode modification. In addition, in [Omim] 4 6 Mo 7 O 24 -CPE 6 Mo​7 O 24 A series of fine redox peaks were also found in - CPE. Obviously, [Omim] 6 Mo 7 O 24 has a much larger substrate current response than pure CPE ( Figure 5 B). Although [Omim] 6 Mo 7 O 24 has accessible capacitance and a thick background response, the resolution of the peak current can be seen after subtracting the background response, and the resolution of its peak current is significantly improved. The three even peaks C2 / A2 (0.383 / 0.433), C3 / A3 (0.254 / 0.259), and C5 / A5 (-0.131 / -0.097) correspond to various forms of Mo(VI) in solution under 1e, H+ (C2 / A2); 1e, H+ (C3 / A3); and 2e, 2H+ (C5 / A5) processes in the potential range (-400~+1200 mV). All redox peaks of C2 / A2, C3 / A3, and C5 / A5 are related to the Mo(VI) redox peak, which may be generated on the surface of [Omim] 6 Mo 7 O 24 The [Omim]H 2 PO 4 is relatively stable.

[0058] In addition, compared with pure CPE, three additional irreversible peaks (A1, A4, and C3) appear on [Omim] 6 Mo 7 O 24 . According to the following hydrogen molybdenum bronze reaction represented by the general formula H x MoO 3 , C3 is related to the reduction of Mo(VI), where 0<x≤2 in acidic solution.

[0059] C3:MoO 4 2- +4H + +2e→(H 2 MoO 3 ) ads +H 2 O

[0060] The anodic peaks of A1, A4, and A6 correspond to the oxidation sequence of hydrogen molybdenum bronze (H 2 MoO 3 ), indicating that the material dissolved in the solution is based on (MoO 3 +H 2 O→MoO 42- +2H + ) Carry out the reaction and the anodic electrooxidation of A1.

[0061] In the electrode of Example 5, [Omim] 6 Mo 7 O 24 Optimization of the mass ratio

[0062] To obtain the best detection sensitivity, in a 0.1 mol·L 2 PO 4 - H -1 H 2 SO 4 -KCl supporting electrolyte solution containing H 6 Mo 7 O 24 -CPE ([Omim] 6 Mo 7 O 24 Solid ion powder 1 accounting for 0%, 5%, 10%, 15% and 20% of the mass of carbon powder respectively) was added, and the effect of the [Omim] -1 Mo 6 Mo 7 O 24 mass ratio on the CV current was investigated under the conditions of a scanning rate of -400~1200 mV, 100 mV·s Figure 6 ) The results showed that ( 6 Mo 7 O 24 The electrode with 0% [Omim] 6 Mo 7 O 24 did not show any specific redox peaks; while new obvious redox peaks appeared in the electrodes with 5%, 10%, 15% and 20% [Omim] 6 Mo 7 O 24 In particular, when the mass ratio of [Omim] 6 Mo 7 O 24 was 15%, the electrode current was the highest. Therefore, a mass ratio of 15% of [Omim]

[0063] Example 6 Effect of scanning rate on the redox current of [Omim] 6 Mo 7 O 24 -CPE electrode

[0064] Using 15% [Omim] 6 Mo7 O 24 -CPE was used to perform cyclic voltammetry (CV) scans on a 0.1 mol·L -1 solution of H -1 SO 2 -KCl mixture within a scan rate range of 45 - 300 mV·s 4 to obtain a 1.0×10 -4 mol·L -1 H 2 PO 4 - solution. Then, according to Figure 7 the Figure 7 plotted Figure 8 the variation curves of the peak currents of A2 / C2 and A3 / C3 with the scan rate as shown in the figure. In the figure, the currents of C2 / A2 and C3 / A3 are proportional to the scan rate, indicating that the redox process is diffusion-controlled, and the surface control involves one electron. According to Figure 7 plotted Figure 9 showed that the current of C5 / A5 is proportional to the square root of the scan rate, suggesting that the redox process is controlled by two-electron diffusion. These observations are consistent with the literature.

[0065] Example 7 [Omim] 6 Mo 7 O 24 Electrode analysis characteristics

[0066] Figure 10 is the schematic diagram of the method for determining phosphate by cyclic voltammetry of [Omim] 6 Mo 7 O 24 -CPE. Standard solutions of 1.0×10 -2 , 1.0×10 -3 , 1.0×10 -4 , 1.0×10 -5 , 1.0×10 -6 , 1.0×10 -7 , 1.0×10 -8 mol·L -1 of H 2 PO 4 - were used to perform the characteristic analysis of [Omim] 6 Mo 7 O 24 -CPE. Under the conditions of a scan rate of 100 mV·s -1 in the range of -400 to 1200 mV, and a mass ratio of [Omim] 6 Mo 7 O 24 to carbon powder of 15%, according toFigure 9 Step, for [Omim] 6 Mo 7 O 24 -CPE was subjected to CV scanning to determine phosphate ( Figure 11 ). The signal of 10 -8 mol.L -1 H 2 PO 4 - was obtained without linearity, that is, 1.0×10 -2 -1.0×10 -7 mol·L -1 , described by the following equation: y = 5.2657x + 147.212 (R2 = 0.9970); here, y is the current intensity (μA), and x is the concentration of H 2 PO 4 - (mol·L -1 ), the sensitivity is 5.3 (±0.1) μA / μM( Figure 11 ), and the detection limit is 8.5×10 -8 mol·L -1 .

[0067] Table 1 compares the analysis conditions, linear range, sensitivity, and LOD of [Omim] 6 Mo 7 O 24 -CPE with the characteristics of several previously reported phosphate sensors.

[0068] Table 1

[0069]

[0070] 1. Y. Lu, Q. Lan, C. Zhang, B. Liu, X. Wang, X. Xu, and X. Liang, Environ. Sci. Technol., 2021, 55, 13093.

[0071] 2. Y. Lu, X. Li, D. Li, and R. G. Compton, ACS Sens. 2021, 6, 3284 - 3294.

[0072] 3. F. Figueredo, F. Girolametti, E. Aneggi, M. Lekka, A. Annibaldi, and S. Susmel, Anal.

[0073] Chim. Acta, 2021, 1161, 338469.

[0074] 4.S.Berchmans,R.Karthikeyan,S.Gupta,G.E.J.Poinern,T.B.Issa,and Pritam Singh,

[0075] Sens.Actuat.B,2011,160,1224.

[0076] 5.M.B.Arvas,O.Gorduk,M.Gencten,and Y.Sahin,Anal.Methods,2019,11,3874.

[0077] 6.Y.Song,C.Bian,J.Tong,Y.Li,and S.Xia,Sensors,2016,05,1.

[0078] As shown in Table 1, [Omim] 6 Mo 7 O 24 -CPE results are equivalent to or significantly better than the analytical performance of existing methods in the literature. The feature of this invention is that the analytical sensitivity can be increased without going through a complex electrode modification process. The final LOD value of the proposed method allows us to quantify the phosphate concentration in actual tap water.

[0079] Table 2

[0080]

[0081] As shown in Table 2, compared with the modified electrode, this invention can be extended to the development of new, simple, and economical phosphate detection electrodes.

[0082] Example 8 Interference of Silicate

[0083] As is well known, silicate is a common interfering substance in phosphate analysis. To study the effect of silicate on [Omim] 6 Mo 7 O 24 -CPE, sodium silicate with a concentration of 0.5 mg / ml was added to the dihydrogen phosphate standard solution; [Omim] 6 Mo 7 O 24 -CPE was subjected to CV detection according to the steps of Example 6, and then the CV current ( Figure 12 ) was recorded. The above mixed solution with sodium silicate has a signal that almost linearly decreases with all phosphate standard solutions. The relative deviation is 2.27%. These data explain that at the selected pH (pH = 1), the phosphomolybdate complex [PMo 12 O 40 3- ​has a higher formation rate constant relative to the silicate molybdate complex [SiMo 12 O 40 4- Therefore, [Omim] 6 Mo 7 O 24 -CPE has anti-silicate performance when the silicate concentration is 10 times greater than the phosphate concentration at the selected pH = 1.

[0084] Determination of tap water samples in Example 9

[0085] The samples were from laboratory tap water at Yangzhou University in Jiangsu. First, 10 mL of tap water samples were collected, and 1000 μL of this sample was added to the supporting electrolyte (0.1 mol·L -1 H 2 SO 4 -KCl mixed solution (pH = 1); CV was carried out at 20 °C. In the absence or presence of phosphate, the current change at the redox peak was recorded as the measured value. The phosphate concentration was determined by the standard addition method, and the accuracy was evaluated by the recovery test of [Omim] 6 Mo 7 O 24 -CPE.

[0086] The analysis results using the method of the present invention and the IC method (Metrohm 883IC + ion chromatograph) are listed in Table 2. The phosphate concentration in the tap water sample was 0.29 ± 0.02 μmol·L -1 . This was basically consistent with the results measured by the IC method. To evaluate the accuracy of the sensor, a spike recovery (10 μmol·L -1 phosphate standard) experiment was carried out on the tap water sample. Its recovery rate (89.7–105.1%) was also comparable to 87.5–108.7% of the IC method.

[0087] The repeatability of [Omim] 2 PO 4 - Mo 6 O 7 O 24 -CPE was detected and evaluated with three groups of H 2 PO 4 - The relative standard deviation (RSD) of the curve slope was 3.5%. The [Omim] 6 Mo 7 O 24 ​- The repeatability of the CPE was 4.1%, obtained from the RSD calibration graph. The storage stability of the electrode was evaluated after 7 days of storage at room temperature, and the result was an RSD of 8.9%. [Omim] 6 Mo 7 O 24 - The CPE allows for the quantification of phosphate in tap water with satisfactory sensitivity and a wide linear range without any modification to increase the detection limit. The electrode is easy to fabricate and does not require any additional modification steps. It is cost-effective and provides relatively high sensitivity and a wide linear dynamic range for phosphate quantification. It can be used for the on-line and high-throughput monitoring of phosphate in environmental water samples.

Claims

1. [Omim] 6 Mo 7 O 24 Application of -CPE modified electrode in determination of phosphate content in sample It is characterized in that The described [Omim] 6 Mo 7 O 24 The preparation method of the -CPE modified electrode comprises the following steps: (1) Mix [Omim]Br with an aqueous solution of ammonium molybdate and stir to form a white suspension; the molar ratio of [Omim]Br to the aqueous solution of ammonium molybdate is 1:

1. When the concentration of [Omim]Br is 50 mmol / L, the concentration of the aqueous solution of ammonium molybdate is 40 - 60 mmol / L; (2) Centrifuge the white suspension, wash it with deionized water until there is no Br ion, and grind it to obtain [Omim] 6 Mo 7 O 24 solid ionic powder; (3) Mix [Omim] 6 Mo 7 O 24 Solid-state ionic powder is vacuum-dried, mixed with carbon powder and silicone oil, and pressed into a mold to obtain [Omim] 6 Mo 7 O 24 -CPE modified electrode; the [Omim] 6 Mo 7 O 24 The mass ratio of the solid-state ionic powder, carbon powder and silicone oil is 38.25:255:

50.

2. The application according to claim 1, It is characterized in that In step (2), the centrifugation rate is 3000 - 5000 r / min and the centrifugation time is 10 - 30 minutes.

3. The application according to claim 1, It is characterized in that In step (3), the temperature of vacuum drying is 60 - 80 °C and the time is 6 - 8 h.

4. The application according to claim 1, It is characterized in that The said application comprises the following steps: (1) Connect [Omim] 6 Mo 7 O 24 -modified electrode, Ag / AgCl reference electrode and counter electrode platinum wire to an electrochemical analyzer respectively; (2) Add the H 2 PO 4 - standard solution to the H 2 SO 4 -KCl mixed solution, and determine the linear relationship between the phosphate concentration and the current intensity through an electrochemical analyzer. The linear relationship equation between the phosphate concentration and the current intensity is y = 5.2657x + 147.212, R 2 = 0.9970; where y represents the current intensity and x represents the phosphate concentration; (3) Add the sample to be tested containing H 2 PO 4 - to the H 2 SO 4 -KCl mixed solution, measure its current intensity through an electrochemical analyzer, and calculate the concentration of phosphate through the linear equation in step (2).

5. The application according to claim 4, It is characterized in that The [Omim] 6 Mo 7 O 24 The working potential of the -CPE modified electrode for the determination of phosphate content in the sample is -400 ~ 1200 mV vs. Ag / AgCl.

6. The application according to claim 4, It is characterized in that In step (3), the concentration of the phosphate radical is 0.1 - 10000 μM.

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