Ammonium ion selective electrode, preparation method thereof and application of ammonium ion selective electrode in detection of ammonium ions in black and odorous water body

Abstract

The invention relates to an ammonium ion selective electrode, a preparation method thereof and application of the ammonium ion selective electrode in detection of ammonium ions in black and odorous water, and belongs to the field of electrochemical detection sensors. The method comprises the following steps: dispersing graphene oxide into water to obtain a dispersion liquid, and mixing the dispersion liquid with a Nafion solution to form a graphene oxide-Nafion mixed solution; coating on a substrate electrode, and drying to obtain a substrate electrode I; the substrate electrode I is placed in an electroplating solution for constant-current electrodeposition, and an ion selective electrode containing a solid contact layer is obtained; the electroplating solution contains 3, 4-ethylenedioxythiophene, a hydrophobic organic matter and lithium perchlorate; and dropwise adding an ammonium ion sensitive solution on the surface of the ion selective electrode containing the solid contact layer, and standing for 20-30 hours to obtain the ammonium ion selective electrode. The method is simple in preparation process, large-scale production can be achieved, the service life of the electrode is prolonged, the sensitivity of the electrode is improved, and meanwhile the stability of the electrode in fluid and the reliability of real-time monitoring are improved.

Description

Technical Field

[0001] The invention relates to an ammonium ion selective electrode and a preparation method thereof and application in detecting ammonium ions in black and smelly water bodies, belonging to the field of electrochemical detection sensors. Background Art

[0002] At present, the problem of black and smelly water bodies in cities after rain is becoming increasingly serious. According to existing tests, high concentrations of ammonia nitrogen after rain have a significant promoting effect on the black and smelly water bodies. Ammonia nitrogen in water bodies is mainly converted into ammonia nitrogen by microbial decomposition in water bodies, which converts nitrogen-containing organic matter into ammonia nitrogen. Ammonia nitrogen is usually present in water bodies with a pH value less than 7 as NH4 + The methods for determining the concentration of ammonia nitrogen in natural water and industrial wastewater mainly include colorimetry, fluorescence and electrochemical detection. Among them, the use of ion-selective electrodes for potential measurement is very promising for in-situ rapid detection because they are low-cost and highly sensitive.

[0003] Solid-state contact layer ion-selective electrodes have become a popular choice for real-time monitoring of NH4 due to their major advantages such as timeliness, cost-effectiveness, and ease of use. + The main means of detecting concentration. There are many materials used as solid contact layer materials to improve the stability of continuous monitoring of ion selective electrodes. Solid contact layer materials based on double-layer capacitors mainly involve carbon materials, such as fullerenes, carbon nanotubes, graphene, and precious metal nanoparticles. The most common solid contact layer material based on redox capacitors is conductive polymers. However, since the solid contact layer and the ion membrane are connected by drip coating, there is air strike, so a water layer will be formed, which will greatly affect the ion mass transfer efficiency, and due to the high sensitivity of ammonium ion selective electrodes, the voltage disturbance in the fluid is more obvious.

[0004] Most of the solid-state contact layer ion selective electrodes currently used are constructed based on the ion selective membrane of ammonium ion carrier and the all-solid-state electrode. The ion sensitive membrane identifies the target ion, and then the solid transfer layer converts the ion signal into an electronic signal. In this case, the electrode will face the following four disadvantages: 1) The bond between the ion sensitive membrane and the solid contact layer is not strong, which is easy to be damaged during use, resulting in the scrapping of the electrode; 2) The water layer inevitably formed at the interface between the ion sensitive membrane and the solid transfer layer will seriously affect the potential stability and reduce the reliability of the electrode; 3) The potential disturbance of the ion selective electrode in the flowing water is large, which affects the accuracy of monitoring.

[0005] Therefore, the development of a long-term and accurate monitoring system for NH4 + Solid-state contacts with high concentrations are crucial for ion-selective electrodes but remain a formidable challenge. Summary of the invention

[0006] In view of the problems existing in the above-mentioned prior art, one of the purposes of the present invention is to provide a method for preparing an ammonium ion selective electrode, which combines graphene oxide with 3,4-ethylenedioxythiophene to improve the stability of the ion selective electrode in the fluid. At the same time, the solid contact layer is modified by hydrophobic organic matter, which greatly reduces the presence of the water layer and reduces the response time. The method has a simple preparation process and can be mass-produced. While improving the life and sensitivity of the electrode, it also improves the stability of the electrode in the fluid and the reliability of real-time monitoring.

[0007] A second object of the present invention is to provide an ammonium ion selective electrode having good stability, short response time and low detection limit.

[0008] The third object of the present invention is to provide an application of an ammonium ion selective electrode, which is used as a sensor to detect the content of ammonium ions in black and smelly water, showing a low detection limit and a short response time.

[0009] In order to achieve the above object, the first aspect of the present invention is to provide a method for preparing an ammonium ion selective electrode, the method comprising: (1) dispersing graphene oxide in water to obtain a dispersion, and mixing the dispersion with a Nafion solution to form a graphene oxide-Nafion mixed solution; (2) drop-coating the graphene oxide-Nafion mixed solution onto the base electrode and drying to obtain a base electrode I; (3) placing the substrate electrode I in an electroplating solution for constant current electrodeposition to obtain an ion selective electrode containing a solid contact layer; the electroplating solution contains 3,4-ethylenedioxythiophene, a hydrophobic organic substance and lithium perchlorate; (4) Add an ammonium ion sensitive solution dropwise onto the surface of the ion selective electrode containing the solid contact layer, and allow to stand for 20 to 30 hours to obtain an ammonium ion selective electrode.

[0010] The innovation of the present invention is that after the graphene oxide solution is mixed with the Nafion solution, the graphene oxide-Nafion mixed solution is dripped onto the substrate electrode, and after drying, a constant current electrodeposition is performed using an electroplating solution containing 3,4-ethylenedioxythiophene and a hydrophobic organic substance. The method of drip coating and constant current electrodeposition can form a modified solid contact layer of spherical particles on the electrode surface, and the use of Nafion solution can further promote the formation of the structure. At the same time, the graphene oxide is combined with 3,4-ethylenedioxythiophene, and a CS bond is formed between the two, which improves the stability of the ion electrode, and its potential disturbance in the fluid can be ignored, therefore, greatly increasing the accuracy of the detection result. Further, the present invention also uses hydrophobic organic matter to modify the solid contact layer, reduces the presence of the water layer, and reduces the response time. In addition, both graphene oxide and 3,4-ethylenedioxythiophene have excellent chemical stability, mechanical strength and low cost, therefore, the method has great application potential and commercial prospects.

[0011] As a preferred solution, the substrate electrode is a screen-printed electrode. The screen-printed electrode has low cost and small size, can be widely used in on-site electrochemical analysis in the environmental, clinical or agricultural food fields, and has a simple structure, is easy to mass produce, and has flexible design. Therefore, it is an ideal tool for preparing ammonium ion selective electrodes, and the ammonium ion selective electrodes prepared by screen-printed electrodes have better stability and shorter response time.

[0012] As a preferred solution, the concentration of the graphene oxide in water is 1-1.5 mg / mL, and the volume ratio of the dispersion to the Nafion solution is 1:0.8-1.2.

[0013] As a preferred solution, the amount of the graphene oxide-Nafion mixed solution added is 10-15 μL.

[0014] As a preferred solution, the concentration of 3,4-ethylenedioxythiophene is 0.03-0.08 mol / L, and the concentration of hydrophobic organic matter is 0.008-0.015 mol / L. 3,4-ethylenedioxythiophene monomer is an active substance, and within this preferred range, a good electroplating effect can be guaranteed, so that it can be electroplated on the base electrode. If the content of 3,4-ethylenedioxythiophene is too low, it is difficult to electroplate on the base electrode. If the content is too high, it will not be completely dissolved. If there is undissolved 3,4-ethylenedioxythiophene in the plating solution, it will affect the electroplating effect. If the content of hydrophobic organic matter is too low, the hydrophobicity of the electrode will be reduced. If the content is too high, the conductive performance will be affected.

[0015] As a preferred solution, the method for preparing the electroplating solution comprises: mixing the 3,4-ethylenedioxythiophene, the hydrophobic organic matter and the lithium perchlorate and then uniformly mixing them by ultrasonication to obtain the electroplating solution.

[0016] As a preferred solution, the electroplating solution is prepared and used immediately, and is aerated with nitrogen for 6 to 8 hours before use.

[0017] As a preferred solution, the hydrophobic organic substance is perfluorooctanoic acid and / or perfluorooctane sulfonic acid.

[0018] As a preferred solution, the hydrophobic organic substance is perfluorooctanoic acid. Perfluorooctanoic acid is extremely hydrophobic, its chemical structure is more stable than other surfactants, and it is resistant to high temperatures and strong oxidants. Electroplating it onto the base electrode as a hydrophobic substance can increase the hydrophobicity and corrosion resistance of the electrode.

[0019] As a preferred solution, before adding the ammonium ion sensitive solution, the ion selective electrode containing the solid contact layer obtained by constant current electrodeposition is first washed with an alcohol solution and then dried at 40-80°C for 1-24h, and then the ammonium ion sensitive solution is added to obtain the ammonium ion selective electrode.

[0020] It should be noted that the present invention has no special requirements for the cleaning conditions, and any conditions known in the art may be used.

[0021] As a preferred solution, the constant current electrodeposition conditions are controlled so that the deposition charge is 0.8-0.15C.

[0022] As a preferred solution, the current density of the constant current electrodeposition is 0.15-0.25 mA / cm 2 .

[0023] As a preferred solution, the ammonium ion sensitive solution contains an organic solvent, an ammonium ion carrier, a plasticizer, polyvinyl chloride carboxylation and an ion exchanger; The concentration of the ammonium ion carrier in the organic solvent is 1-1.5 mg / mL, the concentration of the plasticizer in the organic solvent is 120-140 mg / mL, the concentration of the polyvinyl chloride carboxylation in the organic solvent is 60-75 mg / mL, and the concentration of the ion exchanger in the organic solvent is 0.2-0.4 mg / mL.

[0024] As a preferred solution, the organic solvent is tetrahydrofuran, the ammonium ion carrier is non-actin, the plasticizer is dioctyl sebacate and the ion exchanger is potassium tetrakis(4-chlorophenyl)borate.

[0025] As a preferred solution, the amount of the ammonium ion sensitive solution added is 8-12 μL.

[0026] The invention also provides an ammonium ion selective electrode, which has good stability, short response time and low detection limit.

[0027] The present invention also provides an application of an ammonium ion selective electrode, which is used as a sensor to detect the content of ammonium ions in black and smelly water.

[0028] As a preferred solution, the ammonium ion selective electrode is placed in a 0.8-1.2 mmol / L ammonium chloride solution for activation for at least 24 hours.

[0029] Compared with the prior art, the present invention has at least the following advantages: (1) The present invention combines graphene oxide with 3,4-ethylenedioxythiophene to prepare an ion-selective electrode containing a solid contact layer. Compared with the traditional ammonium ion-selective electrode, its potential disturbance in the fluid is almost negligible, which greatly increases the accuracy of the detection result. At the same time, the solid contact layer is modified by a hydrophobic substance, which increases the hydrophobicity of the electrode, reduces the presence of the water layer, and shortens the response time. In addition, both graphene oxide and 3,4-ethylenedioxythiophene have excellent chemical stability, mechanical strength and low cost. Therefore, this method has great application potential and commercial prospects.

[0030] (2) This method has a simple preparation process and can be mass-produced. It improves the stability of the electrode in the fluid and the reliability of real-time monitoring while improving the life and sensitivity of the electrode.

[0031] (3) The ammonium ion selective electrode provided by the present invention has a low detection limit and a short response time. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 The selectivity sensitivity and detection limit curve of the ammonium ion selective electrode prepared in Example 1 are as follows: Figure 1 a in the above electrode pair NH4 + The potential response curve of Figure 1 b in the figure is the corresponding potential-ammonium ion activity calibration curve; Figure 2 This is a schematic diagram of the selectivity coefficients of the ammonium ion selective electrode prepared in Example 1 for different cations; Figure 3 This is a diagram showing the results of the water layer experiment for preparing the ammonium ion selective electrode in Example 1; Figure 4 This is a schematic diagram of the long-term potential stability of the ammonium ion selective electrode prepared in Example 1; Figure 5 This is a schematic diagram of the anti-interference ability of the ammonium ion selective electrode prepared in Example 1. Figure 5 a in the figure is a schematic diagram of the ability to resist light interference. Figure 5 Figure b is a schematic diagram of the ability to resist gas interference. DETAILED DESCRIPTION

[0033] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0034] The present invention is further described below in conjunction with specific embodiments, but the protection scope of the present invention is not limited to the following specific embodiments. Obviously, the embodiments described below are only a part of the embodiments, and all other embodiments obtained by professionals in this field without creative work still belong to the protection scope of the present invention.

[0035] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or prepared by existing methods.

[0036] Example 1 (1) Weigh 2 mg of graphene oxide powder and mix it with 2 mL of deionized water, and ultrasonicate it for 30 min to obtain a graphene oxide dispersion. The dispersion was mixed with an equal volume of Nafion solution and ultrasonicate it for 30 min to obtain a graphene oxide-Nafion mixed solution. (2) 10uL of the graphene oxide-Nafion mixed solution was drop-coated on the base electrode and dried in air at room temperature to obtain a base electrode I; the base electrode was a screen-printed electrode; (3) The substrate electrode I is placed in the electroplating solution for constant current electrodeposition, using a constant current electrodeposition method with a current density of 0.2 mA / cm 2 , time is 500s, and an ion selective electrode containing a solid contact layer is obtained; The preparation method of the electroplating solution is as follows: 3,4-ethylenedioxythiophene (0.05 mol / L), perfluorooctanoic acid (0.01 mol / L) and lithium perchlorate are mixed by ultrasonication, and the obtained mixed solution is aerated in nitrogen for 7 hours to obtain the obtained solution; (4) The ion selective electrode containing the solid contact layer was washed with water and ethanol in sequence, dried (temperature: 60°C, time: 6 h), and then 10 uL of ammonium ion sensitive solution was added dropwise to obtain an ammonium ion selective electrode; Electrolyte for ammonium ion sensitive solution: Dissolve 1 mg of non-actin, 65.8 mg of polyvinyl chloride carboxyl, 131.6 mg of dioctyl sebacate and 0.3 mg of potassium tetrakis(4-chlorophenyl)borate in 1 mL of tetrahydrofuran.

[0037] (5) Activate the ammonium ion selective electrode in 1 mmol / L ammonium chloride solution for 24 h.

[0038] Performance test experiment: (1) The ammonium ion selective electrode prepared in this example was subjected to an electrochemical open circuit potential test. -8 ~10 -1 mol / L NH4 + The response potential in solution.

[0039] Figure 1 The selectivity sensitivity and detection limit curve of the ammonium ion selective electrode prepared in Example 1 of the present invention is as follows: Figure 1 a in the above electrode pair NH4 + The potential response curve of Figure 1 b in the figure is the corresponding potential-ammonium ion activity calibration curve. Figure 1 It can be seen that the electrode is + The sensitivity is 58.5mV / dec and the detection limit is 10 -5.3 mol / L. The sensitivity of the electrode is close to the Nernst slope, which meets the sensitivity and detection limit requirements of solid-state ammonium ion selective electrodes based on ammonium ion carriers.

[0040] (2) The ion selective electrode of this embodiment was tested using electrochemical open circuit potential for different interfering ions (Na + , Ca 2 + Mg 2+ and H + ) in the potential value, calculate the respective selectivity coefficients, as shown in Figure 2 , the calculation formula is: .

[0041] Combination Figure 1 and Figure 2 It can be seen that the electrode has a + , Ca 2+ Mg 2+ and H + The selectivity coefficients of NH4 + The selectivity coefficient.

[0042] (3) The open circuit potential of the ion selective electrode of this embodiment was tested in a 0.1 mol / L NH4Cl solution using an electrochemical open circuit potential, and the solution was replaced with 0.1 mol / L NaCl to perform a water layer experiment (after testing in NH4Cl for 30 min, the test solution was replaced with a NaCl solution to achieve the purpose of testing), as shown in FIG. Figure 3 .

[0043] from Figure 3 It can be seen that the point disturbance of the ion selective electrode in sodium chloride is very small, the potential drift is less than 1.2mv / h, and after the sodium chloride solution is replaced by ammonium chloride solution, the point does not decrease due to the increase in voltage, and the voltage is stable without sudden increase or decrease.

[0044] (4) The open circuit potential of the ion selective electrode of this embodiment was tested in 0.1 mol / L NH4Cl for 12 h using an electrochemical open circuit potential test. The specific results are shown in Figure 4 ,from Figure 4 It can be seen that the potential drift of the electrode is 1.43 mV / h, indicating that the electrode potential is stable and can be used for a long time.

[0045] (5) The ion selective electrode of this embodiment was subjected to light or gas interference experiment (the light was turned on and off or the gas was ventilated while the open circuit voltage was measured in 0.1 mol / L NH4Cl). The specific results are shown in Figure 5 ,from Figure 5 It can be seen that the electrode has a small potential fluctuation amplitude, the maximum potential fluctuation is less than 1mV, and has good resistance to gas and light interference.

[0046] (6) Contact angle test: After testing, the contact angle of the ion selective electrode prepared in this example is 101°, indicating that it has excellent hydrophobic properties.

[0047] Comparative Example 1 (1) The screen-printed electrode was placed in the electroplating solution for constant current electrodeposition. The constant current electrodeposition method was used with a current density of 0.2 mA / cm 2 , time is 500s, and an ion selective electrode containing a solid contact layer is obtained; Wherein, the preparation method of the electroplating solution is: The preparation method of the electroplating solution is as follows: 3,4-ethylenedioxythiophene (0.05 mol / L), perfluorooctanoic acid (0.01 mol / L) are mixed with lithium perchlorate, 2 mL of graphene oxide dispersion (1 mg / mL) and 2 mL of Nafion solution by ultrasonication, and the obtained mixed solution is aerated in nitrogen for 7 hours to obtain the obtained solution.

[0048] After constant current electrodeposition, the capacitance of the obtained ion-selective electrode was tested, and it was found that graphene oxide could not be electroplated onto the screen-printed electrode directly using the constant current electrodeposition method.

[0049] Comparative Example 2 This comparative example is carried out in a similar manner to the example, except that the perfluorooctanoic acid in step (3) is replaced with aniline hydrochloride of an equimolar concentration to prepare an ammonium ion selective electrode.

[0050] Contact angle test: After testing, the contact angle of the ion selective electrode prepared in this comparative example is 40°, indicating that it has hydrophilic properties.

[0051] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A method for preparing an ammonium ion selective electrode, characterized in that: The method includes: (1) dispersing graphene oxide in water to obtain a dispersion, and mixing the dispersion with a Nafion solution to form a graphene oxide-Nafion mixed solution; (2) drop-coating the graphene oxide-Nafion mixed solution onto the base electrode and drying to obtain a base electrode I; (3) placing the substrate electrode I in an electroplating solution for constant current electrodeposition to obtain an ion selective electrode containing a solid contact layer; the electroplating solution contains 3,4-ethylenedioxythiophene, a hydrophobic organic substance and lithium perchlorate; (4) Add an ammonium ion sensitive solution dropwise onto the surface of the ion selective electrode containing the solid contact layer, and allow to stand for 20 to 30 hours to obtain an ammonium ion selective electrode.

2. The method for preparing an ammonium ion selective electrode according to claim 1, characterized in that: The concentration of the 3,4-ethylenedioxythiophene is 0.03-0.08 mol / L, and the concentration of the hydrophobic organic matter is 0.008-0.015 mol / L.

3. The method for preparing an ammonium ion selective electrode according to claim 1 or 2, characterized in that: The hydrophobic organic substance is perfluorooctanoic acid and / or perfluorooctane sulfonic acid.

4. The method for preparing an ammonium ion selective electrode according to claim 1 or 2, characterized in that: The conditions of the constant current electrodeposition are controlled so that the deposition charge is 0.8-0.15C.

5. The method for preparing an ammonium ion selective electrode according to claim 4, characterized in that: The current density of the constant current electrodeposition is 0.15-0.25 mA / cm 2 .

6. The method for preparing an ammonium ion selective electrode according to claim 1 or 2, characterized in that: The ammonium ion sensitive solution contains an organic solvent, an ammonium ion carrier, a plasticizer, polyvinyl chloride carboxylation and an ion exchanger; The concentration of the ammonium ion carrier in the organic solvent is 1-1.5 mg / mL, the concentration of the plasticizer in the organic solvent is 120-140 mg / mL, the concentration of the polyvinyl chloride carboxylation in the organic solvent is 60-75 mg / mL, and the concentration of the ion exchanger in the organic solvent is 0.2-0.4 mg / mL.

7. The method for preparing an ammonium ion selective electrode according to claim 6, characterized in that: The organic solvent is tetrahydrofuran, the ammonium ion carrier is non-actin, the plasticizer is dioctyl sebacate and the ion exchanger is potassium tetrakis(4-chlorophenyl)borate.

8. The method for preparing an ammonium ion selective electrode according to claim 1 or 2, characterized in that: The concentration of the graphene oxide in water is 1-1.5 mg / mL, and the volume ratio of the dispersion to the Nafion solution is 1:0.8-1.

2.

9. An ammonium ion selective electrode prepared by the method for preparing an ammonium ion selective electrode according to any one of claims 1 to 8.

10. The ammonium ion selective electrode according to claim 9 is used as a sensor to detect the content of ammonium ions in black and smelly water.

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