A preparation process of an on-line monitoring nitrate nitrogen sensor based on three-dimensional electrospray film

Abstract

The application discloses a preparation process of an online monitoring nitrate nitrogen sensor based on a three-dimensional electro-spraying film, and comprises the following steps: S1, nitrate ion selective film liquid preparation; S2, assembly preparation; S3, film liquid charging atomization; and S4, three-dimensional electro-spraying film.The application realizes high-selectivity identification and response of nitrate nitrogen, realizes uniform film spreading through a drum-type three-dimensional electro-spraying film, realizes accurate control of the film thickness within dozens of nanometers by optimizing flow rate, spraying angle and other control process parameters, finally accurately controls the thickness of the selective film within 1 mu m, significantly reduces the ion diffusion coefficient in the film, and significantly reduces the detection limit and response time.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of sewage ammonia nitrogen monitoring, in particular to a preparation process of an online monitoring nitrate nitrogen sensor based on a three-dimensional electro-spray film. BACKGROUND

[0002] In the wastewater treatment process, monitoring of nitrate nitrogen has extremely important significance. Nitrate nitrogen is one of the important indicators of water pollution, and its high concentration can lead to water eutrophication, affecting the survival of aquatic organisms and water quality safety. As a key product in the nitrate nitrogen conversion process, the content of nitrate nitrogen is also a key factor for evaluating the effect of wastewater treatment. Traditional water quality monitoring methods usually rely on laboratory analysis, and after sample collection, complex pretreatment and instrument analysis are required, which makes the monitoring period longer and makes it difficult to realize online real-time monitoring. Therefore, it is urgent to provide a wastewater nitrate nitrogen sensor technology with lower detection limit and shorter response time.

[0003] Traditional nitrate nitrogen monitoring includes laboratory monitoring and wet chemical online analysis, and high-sensitivity quantification is realized through the existing gas-phase molecular absorption spectroscopy method to form nitrate nitrogen and nitrate. However, these methods generally have problems such as long analysis period, reagents and pretreatment, and large maintenance amount, and it is difficult to make feedback to the second-level working condition fluctuation. There are also studies on estimating nitrate nitrogen and nitrate nitrogen concentration through UV / Vis optical in-situ sensing. The UV / Vis sensor estimates through 200-400nm multi-wavelength / derivative spectrum, and has fast response time and does not require reagents. However, nitrite, dissolved organic matter (DOM), turbidity and other substrates can significantly interfere, and field multi-element calibration and frequent cleaning are often required to suppress pollution and drift, and the long-term quantitative accuracy is affected.

[0004] The solid-state potential type ion-selective membrane (S-ISM) sensor based on ionophore has the outstanding advantages of low detection limit, no external power supply, fast response speed and in-situ friendliness. However, the film thickness of the traditional solvent casting / drop coating film is usually 100-200µm, and the ion diffusion coefficient in the film phase is much lower than that in the water phase, which leads to slow diffusion / equilibrium process, limited response time, and easy drift due to temperature, matrix ion strength and biological pollution. In order to improve the response and consistency, thin layer / thin film schemes (such as spin-coated thin layer film, aerosol / atomization deposition and other controllable film formation) are used to reduce the film resistance and shorten the response time, but uniformity and film-substrate adhesion, long-term stability are still important challenges. Therefore, it is urgent to find a means to accurately control the inner film thickness, increase the uniformity of the inner film and reduce the ion diffusion coefficient in the film, so as to realize the online monitoring technology of the sensor with lower detection limit and faster response time for wastewater nitrate nitrogen. SUMMARY

[0005] Aiming at the problems of high detection limit and slow response time of existing sensors caused by the principle film thickness, a preparation process of an online monitoring nitrate nitrogen sensor based on a three-dimensional electro-spraying film is provided.

[0006] The technical scheme of the present application is:

[0007] The preparation process of the online monitoring nitrate nitrogen sensor based on the three-dimensional electro-spraying film comprises the following steps:

[0008] S1, nitrate ion selective membrane liquid preparation: 6.5-7 parts of tetraazatetraoxamacrocyclic compound C 28 H 60 N4O4, 92-93 parts of plasticizer dibutyl phthalate, 0.5-1 parts of tetraoctylammonium chloride are uniformly mixed to obtain a selective membrane mixture, then the selective membrane mixture is mixed with 49-51 parts of polyvinyl chloride, and is uniformly mixed in 148-152 parts of tetrahydrofuran under ultrasonic mixing to obtain a nitrate ion selective membrane liquid;

[0009] S2, assembly preparation: the sensor substrate is installed on a deposition film device, the deposition film device comprises a syringe, a needle, a cylindrical roller and a sliding table; the syringe is installed on the sliding table, then the needle is installed at the lower end of the syringe, and then the roller is installed below the needle and is driven to rotate by a motor; the sensor substrate is fixed on the rotating roller and located directly below the needle, a carbon-based electrode is installed on the middle of one side of the upper surface of the sensor substrate, and the film-coated surface of the carbon-based electrode faces outward, and the roller is set to rotate at a constant speed;

[0010] S3, membrane liquid electrified atomization: the nitrate ion selective membrane liquid is placed in the syringe, the syringe pump of the syringe is used to push at a constant flow rate, a positive high voltage is applied to the needle at the end of the syringe, so that the nitrate ion selective membrane liquid forms a stable conical jet at the needle and is atomized into fine droplets, which are uniformly sprayed along the direction of the electric field;

[0011] S4, three-dimensional electro-spraying film: the fine droplets sprayed by the needle are uniformly coated on the surface of the rotating roller and the carbon-based electrode, so that the surface of the carbon-based electrode obtains a circular deposition area and gradually spreads into a continuous film, at the same time, the needle is driven by the sliding table to make reciprocating motion scanning along the axial direction of the roller, so that the fine droplets sprayed by the needle cover the length section of the carbon-based electrode, and several times of reciprocating motion scanning are completed to obtain a nitrate ion selective membrane with a required thickness.

[0012] Further, the length of the sensor substrate is 35-40 mm, the width is 10-15 mm, and the thickness is 0.5-1 mm, and the material of the sensor substrate is glass carbon plate or dense graphite sheet.

[0013] Description: By reasonably controlling the size of the sensor substrate to improve the overall portability under the premise of ensuring monitoring effect, by selecting the appropriate material of the sensor substrate, the conductivity and excellent physical properties can be ensured.

[0014] Further, in S3, the pushing flow rate of the nitrate ion selective membrane solution is 3.0-5.0 mL / h, and the positive high voltage is 5-8 kV.

[0015] Description: By reasonably controlling the pushing flow rate and voltage of the nitrate ion selective membrane solution, a stable and uniform membrane solution conical jet flow mode spray is ensured.

[0016] Further, in S4, the rotating speed of the roller is 12-20 rpm, and 5-10 rotations are completed while depositing 5-10 times, and the needle rotates once through the position of the carbon-based electrode, corresponding to 2-3 times of axial reciprocating motion at the position of the carbon-based electrode.

[0017] Description: By reasonably controlling the rotating speed of the roller, a stable membrane solution collection surface is ensured.

[0018] Further, in S4, the height of the needle from the roller is 3-6 cm, a circular deposition area is reserved on the surface of the carbon-based electrode, and the remaining parts are shielded with a shield, and the shield is removed after the film is laid.

[0019] Description: By reasonably controlling the height of the needle from the roller, a stable membrane solution collection surface is ensured in the specified area.

[0020] Further, in S4, the axial reciprocating motion scanning speed of the needle is 300-400 μm / s, and the length section of the axial reciprocating motion is 10-20 cm.

[0021] Description: By reasonably controlling the axial reciprocating motion scanning speed, a stable membrane solution collection surface is ensured in the axial direction.

[0022] Further, it further includes S5, drying and curing: after the three-dimensional electro-sprayed film is completed, the sensor substrate laid with the film is placed in an inert gas atmosphere and light shielding condition, and is placed at room temperature for drying, to remove residual solvent and form a dense and uniform S-ISM film layer.

[0023] Description: After drying and curing, the S-ISM film layer can meet the actual water body use standard.

[0024] Further, the inert gas is nitrogen, the standing drying time is 24-72 h, and in S1-S4, it is carried out at room temperature, the room temperature is 20-25 ℃, and the relative humidity is 10-25%.

[0025] Description: By optimizing the external conditions of the whole process to ensure that the nitrate ion selective membrane formed is uniform and dense, and the ideal monitoring conditions are reached.

[0026] The beneficial effects of the present application are:

[0027] The present application introduces a four-nitrogen four-oxygen macrocyclic compound C 28 H 60 N4O4 as a nitrate ion carrier, realizes high selective recognition and response to target ions, realizes uniform film deposition through the drum type three-dimensional electro-spraying film, realizes precise control of film thickness within dozens of nanometers by optimizing flow rate, spraying angle and other control process parameters, and finally accurately controls the thickness of the selective membrane within 1 mu m, significantly reduces the ion diffusion coefficient in the membrane, and significantly reduces the detection limit and response time. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 is the left side structure schematic diagram of the deposition film laying device in the process of the present application when carrying out three-dimensional electro-spraying film laying;

[0029] Figure 2 is the right side structure schematic diagram of the deposition film laying device in the process of the present application when carrying out three-dimensional electro-spraying film laying;

[0030] Figure 3 is the front view of the deposition film laying device in the process of the present application when carrying out three-dimensional electro-spraying film laying;

[0031] Figure 4 is the top view of the deposition film laying device in the process of the present application when carrying out three-dimensional electro-spraying film laying;

[0032] Figure 5 is the structure schematic diagram of the online monitoring nitrate nitrogen sensor prepared by the process of the present application;

[0033] Figure 6 is the process flow diagram of the present application.

[0034] Among them, 1 is a sensor substrate, 11 is a carbon-based electrode, 2 is a syringe, 3 is a needle, 4 is a roller, and 5 is a sliding table. DETAILED DESCRIPTION

[0035] Example 1: An online monitoring nitrate nitrogen sensor preparation process based on three-dimensional electro-spraying film laying, comprising the following steps:

[0036] S1, nitrate ion selective membrane solution preparation: 7 parts of four-nitrogen four-oxygen macrocyclic compound C 28 H 60N4O4, 92 parts of plasticizer dibutyl phthalate, 1 part of tetraoctylammonium chloride are uniformly mixed to obtain a selective membrane mixture, then the selective membrane mixture is mixed with 50 parts of polyvinyl chloride, and is uniformly mixed in 150 parts of tetrahydrofuran under ultrasonic mixing to obtain a nitrate ion selective membrane solution;

[0037] S2, assembly preparation: install the sensor substrate 1 on the deposition coating device, the length of the sensor substrate 1 is 35 mm, the width is 15 mm, and the thickness is 1 mm, the material of the sensor substrate 1 is glassy carbon plate, the deposition coating device includes a syringe 2, a needle 3, a cylindrical roller 4, and a sliding table 5; install the syringe 2 on the sliding table 5, then install the needle 3 at the lower end of the syringe 2, and then install the roller 4 below the needle 3, the roller 4 is driven to rotate by a motor; fix the sensor substrate 1 on the rotating roller 4 and position it directly below the needle 3, install a carbon-based electrode 11 on the middle of one side of the upper surface of the sensor substrate 1, and make the film-covered surface of the carbon-based electrode 11 face outward, and set the roller 4 to rotate at a constant speed;

[0038] S3, membrane liquid electrified atomization: place the nitrate ion selective membrane solution in the syringe 2, push it at a constant flow rate by the injection pump of the syringe 2, the pushing flow rate of the nitrate ion selective membrane solution is 3.9 mL / h, at the same time, apply a positive high voltage to the needle 3 at the end of the syringe 2, the positive high voltage is 6.6 kV, so that the nitrate ion selective membrane solution forms a stable conical jet at the needle 3 and is atomized into fine droplets, which are uniformly sprayed along the direction of the electric field;

[0039] S4, three-dimensional electro-spraying coating: uniformly coat the fine droplets sprayed by the needle 3 to the surface of the rotating roller 4 and the carbon-based electrode 11, so that the surface of the carbon-based electrode 11 obtains a circular deposition area and gradually spreads into a continuous thin film, the rotating speed of the roller 4 is 14 rpm, 5 deposition times are completed while the roller 4 rotates 5 times, the height of the needle 3 from the roller 4 is 4.5 cm, at the same time, the needle 3 is driven by the sliding table 5 to make reciprocating motion along the axis of the roller 4 to scan, so that the fine droplets sprayed by the needle 3 cover the length section of the carbon-based electrode 11, the axial reciprocating scanning speed of the needle 3 is 350 μm / s, the length section of the axial reciprocating motion is 15 cm, the needle 3 rotates once through the position of the carbon-based electrode 11, which corresponds to 3 times of axial reciprocating motion at the position of the carbon-based electrode 11, a total of 15 times of reciprocating motion scanning is completed to obtain a nitrate ion selective membrane with a desired thickness, a circular deposition area is reserved on the surface of the carbon-based electrode 11, and the remaining parts are shielded with a shield, and the shield is removed after the coating is completed;

[0040] S5, drying and curing: after the completion of the three-dimensional electrospraying film, the sensor substrate 1 on which the film is formed is placed in an inert gas atmosphere and in the dark at room temperature and left to dry, the inert gas is nitrogen, and the left-to-dry time is 48 h, so as to remove the residual solvent and form a dense and uniform S-ISM film layer.

[0041] In S1-S5, the operations are all carried out at room temperature, the room temperature is 23°C, and the relative humidity is 16%.

[0042] Example 2: The difference between this example and Example 1 is that the length of the sensor substrate 1 is 37 mm, the width is 12 mm, and the thickness is 0.8 mm, and the material of the sensor substrate 1 is a dense graphite sheet.

[0043] Example 3: The difference between this example and Example 1 is that the length of the sensor substrate 1 is 35 mm, the width is 10 mm, and the thickness is 0.5 mm.

[0044] Example 4: The difference between this example and Example 1 is that in S1, 6.5 parts of the tetraazatetraoxamacrocyclic compound C 28 H 60 N4O4, 93 parts of the plasticizer dibutyl phthalate, and 0.5 parts of tetraoctylammonium chloride are uniformly mixed to obtain a selective film mixture, then the selective film mixture is mixed with 49 parts of polyvinyl chloride, and the mixture is placed in 148 parts of tetrahydrofuran and ultrasonically mixed uniformly to obtain a nitrate ion selective membrane solution.

[0045] Example 5: The difference between this example and Example 1 is that in S1, 7 parts of the tetraazatetraoxamacrocyclic compound C 28 H 60 N4O4, 92.5 parts of the plasticizer dibutyl phthalate, and 0.5 parts of tetraoctylammonium chloride are uniformly mixed to obtain a selective film mixture, then the selective film mixture is mixed with 51 parts of polyvinyl chloride, and the mixture is placed in 152 parts of tetrahydrofuran and ultrasonically mixed uniformly to obtain a nitrate ion selective membrane solution.

[0046] Example 6: The difference between this example and Example 1 is that in S3, the pushing flow rate of the nitrate ion selective membrane solution is 3.0 mL / h, and a positive high voltage of 5 kV is applied to the needle 3 provided at the end of the syringe 2.

[0047] Example 7: The difference between this example and Example 1 is that in S3, the pushing flow rate of the nitrate ion selective membrane solution is 5.0 mL / h, and a positive high voltage of 8 kV is applied to the needle 3 provided at the end of the syringe 2.

[0048] Example 8: The difference between this example and Example 1 is that in S4, the rotating speed of the roller 4 is 12 rpm, 5 depositions are completed while rotating 5 times, the height of the needle 3 from the roller 4 is 3 cm, the axial reciprocating motion scanning speed of the needle 3 is 300 pm / s, the length section of the axial reciprocating motion is 10 cm, and the needle 3 completes 2 axial reciprocating motions at the position of the carbon-based electrode 11 for each rotation, and a total of 10 reciprocating motions are completed to obtain a nitrate ion-selective membrane with a desired thickness.

[0049] Example 9: The difference between this example and Example 1 is that in S4, the rotating speed of the roller 4 is 20 rpm, 10 depositions are completed while rotating 10 times, the height of the needle 3 from the roller 4 is 6 cm, the axial reciprocating motion scanning speed of the needle 3 is 400 pm / s, the length section of the axial reciprocating motion is 20 cm, and the needle 3 completes 3 axial reciprocating motions at the position of the carbon-based electrode 11 for each rotation, and a total of 30 reciprocating motions are completed to obtain a nitrate ion-selective membrane with a desired thickness.

[0050] Example 10: The difference between this example and Example 1 is that in S5, the standing drying time is 24 h, and in S1-S4, all are carried out at room temperature, the room temperature is 20°C, and the relative humidity is 10%.

[0051] Example 11: The difference between this example and Example 1 is that in S5, the standing drying time is 72 h, and in S1-S4, all are carried out at room temperature, the room temperature is 25°C, and the relative humidity is 25%.

[0052] Experimental Example: The sensor prepared by the preparation process of Example 1 of the present application is applied to the monitoring of nitrate nitrogen in actual sewage, and it is verified that the sensor can accurately control the thickness of the selective membrane within the range of 1 pm, significantly reduces the ion diffusion coefficient in the membrane, and successfully reduces the detection limit of the sensor for nitrate nitrogen to 7.9 pg / L, and the detection limit of nitrate nitrogen is reduced to 55.7 pg / L. This technical index is significantly better than the current water quality detection standard requirement (nitrate nitrogen: 32 pg / L, HJ198-2024) in China. At the same time, compared with the current mainstream in-situ sensor technology, the detection limit is reduced by one order of magnitude. In addition, the response time of the sensor to nitrate nitrogen is significantly shortened from 22.5 seconds to 9.2 seconds, greatly improving the real-time monitoring capability of the sensor. The above technology makes it possible to collect real-time water quality data during sewage treatment, and provides a solid data foundation for intelligent sewage treatment systems.

Claims

1. A process for the preparation of an on-line monitoring nitrate sensor based on a three-dimensional electrospray film, characterized by, It comprises the following steps: S1, nitrate ion selective membrane liquid preparation: in mass fraction, 6.5~7 portions of tetraazatetraoxamacrocyclic compound C 28 H 60 N4O4, 92~93 portions of plasticizer dibutyl phthalate, 0.5~1 portions of tetraoctylammonium chloride are mixed uniformly to obtain a selective membrane mixture, then the selective membrane mixture is mixed with 49~51 portions of polyvinyl chloride, and is placed in 148~152 portions of tetrahydrofuran and is mixed uniformly by ultrasonic, to obtain a nitrate ion selective membrane liquid; S2, assembly preparation: install the sensor substrate (1) on the deposition coating device, which comprises a syringe (2), a needle (3), a cylindrical roller (4), a sliding table (5); install the syringe (2) on the sliding table (5), then install the needle (3) at the lower end of the syringe (2), and then install the roller (4) below the needle (3), which is driven to rotate by a motor; fix the sensor substrate (1) on the rotating roller (4) and locate it directly below the needle (3), install a carbon-based electrode (11) on the middle of the upper surface of the sensor substrate (1), and make the carbon-based electrode (11) face outward, and set the roller (4) to rotate at a constant speed; S3, film liquid electrified atomization: place the nitrate ion selective membrane liquid in the syringe (2), push it at a constant flow rate through the injection pump of the syringe (2), and apply a positive high voltage to the needle (3) at the end of the syringe (2) at the same time, so that the nitrate ion selective membrane liquid forms a stable conical jet at the needle (3) and is atomized into fine droplets, which are uniformly sprayed in the direction of the electric field; S4, three-dimensional electro-spraying coating: uniformly coat the fine droplets sprayed by the needle (3) to the surface of the rotating roller (4) and the carbon-based electrode (11), so that the surface of the carbon-based electrode (11) forms a circular deposition area and gradually spreads into a continuous film, at the same time, drive the needle (3) to move back and forth along the axis of the roller (4) by the sliding table (5) to scan, so that the fine droplets sprayed by the needle (3) cover the length section of the carbon-based electrode (11), and complete several times of back and forth scanning to obtain the nitrate ion selective membrane with the required thickness.

2. The preparation process of an on-line monitoring nitrate nitrogen sensor based on three-dimensional electrospray film according to claim 1, characterized in that, The length of the sensor substrate (1) is 35-40 mm, the width is 10-15 mm, and the thickness is 0.5-1 mm. The material of the sensor substrate (1) is glass carbon plate or dense graphite sheet.

3. The preparation process of an on-line monitoring nitrate nitrogen sensor based on three-dimensional electrospray film according to claim 1, characterized in that, In S3, the pushing flow rate of the nitrate ion selective membrane liquid is 3.0-5.0 mL / h, and the positive high voltage is 5-8 kV.

4. The preparation process of an on-line monitoring nitrate nitrogen sensor based on three-dimensional electrospray film according to claim 1, characterized in that, In S4, the rotating speed of the roller (4) is 12-20 rpm, and 5-10 rotations are completed at the same time with 5-10 depositions, and for each rotation of the needle (3) passing through the position of the carbon-based electrode (11), the corresponding axial reciprocating motion is completed 2-3 times at the position of the carbon-based electrode (11).

5. The preparation process of an on-line monitoring nitrate nitrogen sensor based on three-dimensional electrospray film according to claim 1, characterized in that, In S4, the height of the needle (3) from the roller (4) is 3-6 cm, a circular deposition area is reserved on the surface of the carbon-based electrode (11), and the remaining parts are shielded with a shield, and the shield is removed after the coating is completed.

6. The preparation process of an on-line monitoring nitrate nitrogen sensor based on three-dimensional electrospray film according to claim 1, characterized in that, In S4, the axial reciprocating scanning speed of the needle (3) is 300-400 μm / s, and the length section of the axial reciprocating motion is 10-20 cm.

7. The preparation process of an on-line monitoring nitrate nitrogen sensor based on three-dimensional electrospray film according to claim 1, characterized in that, It also comprises S5, drying and curing: after the three-dimensional electro-spraying coating is completed, place the coated sensor substrate (1) in an inert gas atmosphere and in the dark, and let it stand at room temperature to dry, remove the residual solvent and form a dense and uniform S-ISM film layer.

8. The preparation process of an on-line monitoring nitrate nitrogen sensor based on three-dimensional electrospray film according to claim 7, characterized in that, The inert gas is nitrogen, the standing dry time is 24-72h, in S1-S4, all at room temperature, the room temperature is 20-25℃, the relative humidity is 10-25%.

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