An electrochemiluminescence sensor for detecting fluoride ions in lithium hexafluorophosphate and an electrochemiluminescence analysis method

Abstract

The present invention belongs to the technical field of electrochemiluminescence detection, and relates to an electrochemiluminescence sensor for detecting fluoride ions in lithium hexafluorophosphate and an electrochemiluminescence analysis method. The present invention provides an electrochemiluminescence sensor for detecting fluoride ions in lithium hexafluorophosphate, comprising an electrode substrate, a UiO‑66‑g‑C3N4 composite material modified on the surface of the electrode substrate, and a fluoride ion fluorescent probe modified on the surface of the UiO‑66‑g‑C3N4 composite material, wherein the UiO‑66‑g‑C3N4 composite material is a heterojunction structure formed based on UiO‑66 and g‑C3N4. The electrochemiluminescence sensor provided by the present invention has the advantages of high electrochemiluminescence intensity, good stability and fast response speed, and the achievable detection range is 1.0x10 ‑11 ~5.0x10 ‑6 mol / L, the minimum detection limit is 8.2.0x10 ‑12 mol / L.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrochemiluminescence detection, and relates to a method for effectively controlling the production process of lithium hexafluorophosphate by using an electrochemiluminescence method to detect the concentration of fluoride ions in lithium hexafluorophosphate, and specifically relates to an electrochemiluminescence sensor and an electrochemiluminescence analysis method for detecting fluoride ions in lithium hexafluorophosphate. Background Art

[0002] Lithium hexafluorophosphate is the main material of lithium-ion battery electrolyte, and its impurity content affects the performance of lithium-ion batteries. Since HF is the main raw material in the production process of lithium hexafluorophosphate, the content of fluoride ions in lithium hexafluorophosphate not only affects the charge and discharge performance of lithium-ion batteries, but also seriously affects the safety performance of lithium-ion batteries. Therefore, it is necessary to strictly control the content of fluoride ions in lithium hexafluorophosphate. Currently, the methods reported for detecting fluoride ions in lithium hexafluorophosphate include spectrophotometry and ion chromatography. However, these methods are complicated, time-consuming, costly, and have low detection sensitivity. Summary of the invention

[0003] The technical problem to be solved by the present invention is to provide an electrochemiluminescence sensor and an electrochemiluminescence analysis method for detecting fluoride ions with high sensitivity, simplicity, rapidity and accuracy, in view of the shortcomings of existing fluoride ion detection methods, which mostly rely on large-scale experimental instruments and have harsh experimental operating conditions and long test time.

[0004] In order to solve the above technical problems, the present invention provides an electrochemiluminescent sensor for detecting fluoride ions in lithium hexafluorophosphate, comprising an electrode substrate, a UiO-66-g-C3N4 composite material modified on the surface of the electrode substrate, and a fluoride ion fluorescent probe modified on the surface of the UiO-66-g-C3N4 composite material. The UiO-66-g-C3N4 composite material is a heterojunction structure formed based on UiO-66 and g-C3N4. The structural formula of the fluoride ion fluorescent probe is:

[0005]

[0006] Furthermore, the electrode substrate may be any one of glassy carbon electrode, FTO or ITO.

[0007] Furthermore, the mass ratio of UiO-66 and g-C3N4 in the UiO-66-g-C3N4 composite material is 1:1.

[0008] The above-mentioned sensor is based on the enhanced electroluminescence intensity of the heterojunction of UiO-66 and g-C3N4 to achieve improved sensitivity; due to the specific binding of the fluoride ion probe (B) to fluoride ions, the electroluminescence quenching of the B / UiO-66-g-C3N4 / GCE modified electrode is caused, thereby realizing the detection of fluoride ions by the B / UiO-66-g-C3N4 / GCE modified electrode.

[0009] The present invention also provides a method for preparing the electrochemiluminescence sensor, comprising the following steps:

[0010] (1) Preparation of UiO-66-g-C3N4 composite material: UiO-66 and g-C3N4 were dispersed in DMF to obtain a UiO-66-g-C3N4 composite dispersion.

[0011] Further, UiO-66 was prepared by dispersing zirconium tetrachloride ZrCl4 and 1,4-phthalic acid in DMF, and then transferring the solution to a stainless steel autoclave lined with polytetrafluoroethylene. After the reaction was completed, the solution was naturally cooled, washed with anhydrous ethanol, and dried to obtain the UiO-66 product.

[0012] Furthermore, nano g-C3N4 was prepared by placing urea in a crucible, calcining it in a muffle furnace, and then cooling it to room temperature. The obtained g-C3N4 powder was dispersed in water and ultrasonically treated to remove the unpeeled g-C3N4. The supernatant was dried to obtain nano g-C3N4.

[0013] (2) Preparation of electrochemiluminescence sensor: The UiO-66-g-C3N4 composite dispersion was thoroughly mixed with the DMF solution of the fluoride ion probe, and then drop-coated on the cleaned electrode substrate, and then placed under an infrared lamp for drying to obtain an electrochemiluminescence sensor that can selectively detect fluoride ions in lithium hexafluorophosphate.

[0014] Preferably, the concentration of the DMF solution of the fluoride ion probe is 5.0×10 -3 mol / L, the concentration of UiO-66-g-C3N4 composite dispersion was 1 mg / mL, the volume ratio of the two was 1:10, and the mass ratio of UiO-66 and g-C3N4 was 1:1.

[0015] Further, the preparation of fluoride ion fluorescent probe:

[0016] Dissolve benzil, nitrobenzaldehyde and ammonium acetate in glacial acetic acid, heat under reflux for reaction, cool to room temperature, add water, filter and dry under vacuum to obtain an orange-yellow solid, i.e., a fluoride ion fluorescent probe.

[0017] Finally, the present invention also provides an electrochemiluminescence analysis method for detecting fluoride ions in lithium hexafluorophosphate, including electrochemiluminescence detection based on a three-electrode system consisting of a working electrode, a reference electrode and an auxiliary electrode, wherein the electrochemiluminescence sensor for detecting fluoride ions in lithium hexafluorophosphate as described above is used as the working electrode. The auxiliary electrode and the reference electrode can be materials commonly used in electrochemiluminescence detection, for example, a platinum electrode is used as the auxiliary electrode, and an Ag / AgCl electrode is used as the reference electrode.

[0018] Further, the specific steps are as follows:

[0019] (1) Preparation of fluoride ion standard solutions of different concentrations:

[0020] Take a certain amount of 1000ppm fluoride ion standard solution and add it to 0.1mol / L PBS buffer solution with pH=7.5 containing 0.05mol / L K2S2O8 to obtain a series of fluoride ion standard solutions with different concentrations ranging from 1.0x10 -11 ~5.0x10 -6 mol / L.

[0021] (2) Drawing of standard curve:

[0022] The three-electrode system was immersed in the 0.1 mol / L PBS buffer solution with pH=7.5 containing a series of different concentrations of fluoride ions and 0.05 mol / L K2S2O8 for 10 min. Cyclic voltammetry was performed in the electrochemical window range of -1.6 to 0 V with a photomultiplier tube high voltage of 800 V and a scan rate of 0.1 V / s. The potential-luminescence intensity curve (E-ECL) was recorded. A linear relationship between the difference in luminescence intensity before and after the addition of fluoride ions and the logarithmic value of the fluoride ion concentration was established to obtain the corresponding linear regression equation.

[0023] (3) Actual sample testing:

[0024] The test is carried out under the same electrochemiluminescence test conditions as step (2), the luminescence intensity is recorded, and the concentration of fluoride ions in the actual sample is calculated using the linear regression equation corresponding to the standard curve obtained in step (2).

[0025] Compared with the prior art, the present invention has achieved the following beneficial effects:

[0026] The electrochemiluminescence sensor provided by the present invention, Uio-66 is a kind of MOF. In the present invention, the heterojunction of Uio-66 and g-C3N4 enhances the electroluminescence intensity, and also serves as an adsorption material to adsorb ions in the solution. However, the selectivity of Uio-66 and C3N4 materials for anions in the solution is not high. Through the introduction of the probe, selective binding to fluoride ions is obtained. When fluoride ions are present in the solution, the fluoride ions are preferentially adsorbed on the electrochemiluminescence sensor, causing fluorescence quenching, and the fluorescence quenching increases with the increase of the concentration of fluoride ions. Based on this, the detection of fluoride ion content is realized. The electrochemiluminescence sensor provided by the present invention has the advantages of high electrochemiluminescence intensity, good stability and fast response speed, and the achievable detection range is 1.0x10 -11 ~5.0x10 -6 mol / L, the minimum detection limit is 8.2.0x10 -12 mol / L. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a standard curve of the difference in luminescence intensity of the modified electrode B / UiO-66-g-C3N4 / GCE before and after adding fluoride ions and the logarithm of the fluoride ion concentration in the embodiment. DETAILED DESCRIPTION

[0028] The present invention will be further described below by way of embodiments in conjunction with the accompanying drawings, but the protection scope of the present invention is not limited to the following embodiments.

[0029] Example

[0030] (1) Preparation of UiO-66-g-C3N4 / GC modified electrode:

[0031] 0.233 g of ZrCl4 and 0.166 g of 1,4-phthalic acid were dissolved in 50 mL of DMF, and then the solution was transferred to a 100 mL polytetrafluoroethylene-lined stainless steel autoclave. It was placed in an oven and heated at 120 °C for 24 hours. The resulting product was centrifuged and washed with anhydrous ethanol to obtain the UiO-66 product. 10 g of urea was placed in a crucible and heated in a muffle furnace at 5 °C min -1 The mixture was heated to 550°C at a heating rate of 100 °C and reacted for 4 h. 0.1 g of the obtained g-C3N4 was dispersed in 100 mL of water and ultrasonically treated for 10 h. The mixture was then centrifuged at 10,000 rpm for several times to remove the unpeeled g-C3N4. The supernatant was dried to obtain nano g-C3N4. 1 mg of UiO-66 and g-C3N4 were taken separately, mixed and ground thoroughly, and evenly dispersed in 1 mL of DMF solution.

[0032] (2) Preparation of fluoride ion fluorescent probe B:

[0033] 0.42 g of benzil, 0.31 g of nitrobenzaldehyde and 1.23 g of ammonium acetate were dissolved in 15 mL of glacial acetic acid, heated to reflux for reaction, cooled to room temperature, added with 30 mL of water, filtered and vacuum dried to obtain an orange-yellow solid, i.e., fluoride ion fluorescent probe B. Accurately weigh the fluoride ion probe (B) and dissolve it in 50 mL of de-DMF to a concentration of 5.0 × 10 - 3 mol / L.

[0034] (3) Preparation of B / UiO-66-g-C3N4 / GCE modified electrode:

[0035] Take 1 mL of the DMF solution of UiO-66-g-C3N4 material and 100 μL of the fluoride ion probe (B) solution and mix them for 1 hour, take 5 μL and drop it on the cleaned glassy carbon electrode to obtain the modified electrode B / UiO-66-g-C3N4 / GCE. The B / UiO-66-g-C3N4 / GCE modified electrode is placed under an infrared lamp for drying to obtain an electrochemiluminescent sensor that can selectively detect fluoride ions in lithium hexafluorophosphate.

[0036] (4) Drawing of standard curve

[0037] The three-electrode system was composed of B / UiO-66-g-C3N4 / GCE as the working electrode, platinum electrode as the auxiliary electrode, and Ag / AgCl electrode as the reference electrode. The luminescence intensity was tested using 0.1 mol / L PBS buffer containing 0.05 mol / L potassium persulfate at pH 7.5 as the blank solution. The three-electrode system was placed in a series of fluoride ion concentrations of 1.0x10 -11 mol / L、1.0x10 -10 mol / L、1.0x10 -9 mol / L、1.0x10 -8 mol / L、1.0x10 -7 mol / L、1.0x10 -6 mol / L、5.0x10 -6 The luminescence intensity was detected in 0.1 mol / L PBS buffer solution containing 0.05 mol / L potassium persulfate and pH 7.5. The detection conditions were within the electrochemical window range of -1.6 to 0 V, the photomultiplier tube high voltage was 800 V, the scan rate was 0.1 V / s, and cyclic voltammetry scanning was performed. The E-ECL curve was recorded, and the linear relationship between the difference in luminescence intensity before and after the addition of fluoride ions and the logarithmic value of the fluoride ion concentration was established to obtain the corresponding linear regression equation. The detection range of the linear regression equation is 1.0x10 -11 ~5.0x10 -6mol / L, the minimum detection limit is 8.2.0x10 -12 mol / L.

[0038] (5) Sample testing

[0039] 0.5 g of lithium hexafluorophosphate was accurately weighed and added to 100 mL of 0.1 mol / L PBS buffer solution at pH 7.5 containing 0.05 mol / L K2S2O8 for electrochemiluminescence detection. The concentration of fluoride ions in the lithium hexafluorophosphate sample to be detected was calculated according to the linear regression equation corresponding to the above step (4). The results are listed in Table 1.

[0040] Comparative Example

[0041] (1) Preparation of UiO-66-g-C3N4 / GC modified electrode:

[0042] 0.233 g of ZrCl4 and 0.166 g of 1,4-phthalic acid were dissolved in 50 mL of DMF, and then the solution was transferred to a 100 mL polytetrafluoroethylene-lined stainless steel autoclave. It was placed in an oven and heated at 120 °C for 24 hours. The resulting product was centrifuged and washed with anhydrous ethanol to obtain the UiO-66 product. 10 g of urea was placed in a crucible and heated in a muffle furnace at 5 °C min -1 The mixture was heated to 550°C at a heating rate of 100 °C and reacted for 4 h. 0.1 g of the obtained g-C3N4 was dispersed in 100 mL of water and ultrasonically treated for 10 h. The mixture was then centrifuged at 10,000 rpm for several times to remove the unpeeled g-C3N4. The supernatant was dried to obtain nano g-C3N4. 1 mg of UiO-66 and g-C3N4 were taken separately, mixed and ground thoroughly, and evenly dispersed in 1 mL of DMF solution.

[0043] (2) Preparation of UiO-66-g-C3N4 / GCE modified electrode:

[0044] Take 5 μL of UiO-66-g-C3N4 solution and drop it on the cleaned glassy carbon electrode to obtain the modified electrode UiO-66-g-C3N4 / GCE. Place the UiO-66-g-C3N4 / GCE modified electrode under an infrared lamp for drying to obtain the electrochemiluminescent sensor for detecting fluoride ions in lithium hexafluorophosphate of the comparative example.

[0045] (3) Drawing of standard curve

[0046] A three-electrode system was formed using the UiO-66-g-C3N4 / GCE modified electrode as the working electrode, the platinum electrode as the auxiliary electrode, and the Ag / AgCl electrode as the reference electrode. Other operating conditions were the same as those for drawing the standard curve in the example.

[0047] (4) Sample testing

[0048] A three-electrode system was formed with the UiO-66-g-C3N4 / GCE modified electrode as the working electrode, the platinum electrode as the auxiliary electrode, and the Ag / AgCl electrode as the reference electrode. Its operating conditions were the same as those for the detection of the samples in the embodiment. The results are listed in Table 1.

[0049] Table 1 Determination results of fluoride ions in lithium hexafluorophosphate (n=3)

[0050]

[0051] Note: 1#, 2# and 3# are different batches of lithium hexafluorophosphate, and the measurement results are the average value of 3 parallel tests.

[0052] As shown in Table 1, the recovery rate of spiked addition is in the range of 97% to 102%. The analysis results of the present invention are very similar to those of the ion chromatography method, which proves the feasibility of the analysis method. When the B / UiO-66-g-C3N4 / GCE modified electrode is not used, but UiO-66-g-C3N4 / GCE is used as the working electrode, the fluoride ions in lithium hexafluorophosphate cannot be detected due to the low sensitivity, which further verifies that the B / UiO-66-g-C3N4 / GCE modified electrode of the present invention can detect fluoride ions very well.

[0053] The above embodiments are only used to illustrate the present invention, not to limit the present invention. Those skilled in the art may make various corresponding changes without departing from the scope of the present invention. Therefore, all technical solutions formed by equivalent replacement or equivalent modification belong to the protection scope of the present invention.

Claims

1. An electrochemiluminescence analysis method for detecting fluoride ions in lithium hexafluorophosphate, characterized in that: The invention comprises an electrochemiluminescence detection based on a three-electrode system consisting of a working electrode, a reference electrode and an auxiliary electrode, wherein an electrochemiluminescence sensor for detecting fluoride ions in lithium hexafluorophosphate is used as the working electrode; The electrochemiluminescent sensor for detecting fluoride ions in lithium hexafluorophosphate, The invention comprises an electrode substrate, a UiO-66-g-C3N4 composite material modified on the surface of the electrode substrate, and a fluoride ion fluorescent probe modified on the surface of the UiO-66-g-C3N4 composite material. The UiO-66-g-C3N4 composite material is a heterojunction structure formed based on UiO-66 and g-C3N4. The structural formula of the fluoride ion fluorescent probe is: ； The mass ratio of UiO-66 and g-C3N4 in the UiO-66-g-C3N4 composite is 1:1; The preparation method of the electrochemiluminescent sensor for detecting fluoride ions in lithium hexafluorophosphate comprises the following steps: (1) Preparation of UiO-66-g-C3N4 composite material: UiO-66 and g-C3N4 were dispersed in DMF to obtain a UiO-66-g-C3N4 composite dispersion; (2) Preparation of electrochemiluminescent sensor: The UiO-66-g-C3N4 composite dispersion was fully mixed with the DMF solution of the fluoride ion probe, and then drop-coated on the cleaned electrode substrate, and then placed under an infrared lamp for drying to obtain an electrochemiluminescent sensor that can selectively detect fluoride ions in lithium hexafluorophosphate; The concentration of the DMF solution of the fluoride ion probe was 5.0×10 -3 mol / L, the concentration of UiO-66-g-C3N4 composite dispersion was 1 mg / mL, and the volume ratio of the two was 1:

10.

2. The electrochemiluminescence analysis method for detecting fluoride ions in lithium hexafluorophosphate according to claim 1, characterized in that Preparation of nano g-C3N4: Urea is placed in a crucible, calcined in a muffle furnace, and then cooled to room temperature. The obtained g-C3N4 powder is dispersed in water and ultrasonically treated to remove the unpeeled g-C3N4. The supernatant is dried to obtain nano g-C3N4.

3. The electrochemiluminescence analysis method for detecting fluoride ions in lithium hexafluorophosphate according to claim 1, characterized in that: The following steps are also included: (1) Preparation of fluoride ion standard solutions of different concentrations: Take a certain amount of 1000 ppm fluoride ion standard solution and add it to 0.1 mol / L PBS buffer solution with pH=7.5 containing 0.05 mol / L K2S2O8 to obtain a series of fluoride ion standard solutions with different concentrations ranging from 1.0x10 -11 ~5.0x10 -6 mol / L; (2) Drawing of standard curve: The three-electrode system is immersed in the above-mentioned 0.1 mol / L pH=7.5 PBS buffer solution containing a series of different concentrations of fluoride ions and 0.05 mol / L K2S2O8 for 10 minutes, and cyclic voltammetry scanning is performed in the electrochemical window range of -1.6~0V with a photomultiplier tube high voltage of 800V and a scan rate of 0.1V / s, and the potential-luminescence intensity curve (E-ECL) is recorded. A linear relationship between the difference in luminescence intensity before and after the addition of fluoride ions and the logarithm of the fluoride ion concentration is established to obtain the corresponding linear regression equation; (3) Actual sample testing: The test is carried out under the same electrochemiluminescence test conditions as step (2), the luminescence intensity is recorded, and the concentration of fluoride ions in the actual sample is calculated using the linear regression equation corresponding to the standard curve obtained in step (2).

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