Preparation process of on-line monitoring nitrate nitrogen sensor based on three-dimensional electronic injection film laying

Abstract

The invention discloses a preparation process of an on-line monitoring nitrate nitrogen sensor based on three-dimensional electronic injection film laying. The preparation process comprises the following steps: S1, preparing nitrate ion selective membrane liquid; s2, assembling preparation; S3, electrified atomization of membrane liquid; and S4, performing three-dimensional electronic injection film laying. According to the method, high-selectivity recognition and response to nitrate nitrogen are achieved, uniform film laying is achieved through drum-type three-dimensional electronic spraying film laying, accurate control over the thickness of the inner film of dozens of nanometers is achieved by optimizing control process parameters such as the flow speed and the spraying angle, and finally the thickness of the selective film is accurately controlled within the range of 1 micrometer. The ion diffusion coefficient in the membrane is obviously reduced, and the detection limit and the response time are obviously reduced.

Description

Technical Field

[0001] This invention relates to the field of wastewater ammonia nitrogen monitoring technology, specifically to a fabrication process for an online nitrate nitrogen monitoring sensor based on three-dimensional electro-sprayed membrane laying. Background Technology

[0002] Monitoring nitrate nitrogen is of paramount importance in wastewater treatment. Nitrate nitrogen is a key indicator of water pollution; excessively high concentrations can lead to eutrophication, impacting aquatic life and water quality safety. As a crucial product in the nitrate nitrogen transformation process, nitrate nitrogen levels are also a critical factor in evaluating wastewater treatment effectiveness. Traditional water quality monitoring methods typically rely on laboratory analysis, requiring complex sample pretreatment and instrumental analysis, resulting in lengthy monitoring cycles and hindering real-time online monitoring. Therefore, there is an urgent need for a wastewater nitrate nitrogen sensor technology with lower detection limits and shorter response times.

[0003] Traditional nitrate nitrogen monitoring includes laboratory monitoring and wet chemical online analysis, achieving highly sensitive quantification using current gas-phase molecular absorption spectrometry to separate nitrate nitrogen and nitrate nitrogen according to national standards. However, these methods generally suffer from long analysis cycles, require reagents and pretreatment, and involve significant maintenance, making it difficult to respond to fluctuations in operating conditions down to the second. Some studies have also estimated nitrate nitrogen and its concentration using UV / Vis optical in-situ sensing. UV / Vis sensors estimate nitrate nitrogen and its concentration using multi-wavelength / derivative spectra from 200-400 nm, offering fast response times and requiring no reagents. However, matrices such as nitrite, dissolved organic matter (DOM), and turbidity can significantly interfere, often requiring on-site multivariate calibration and frequent cleaning to suppress contamination and drift, thus affecting long-term quantification accuracy.

[0004] Solid-state potentiometric ion-selective membrane (S-ISM) sensors based on ion carriers offer significant advantages such as low detection limits, no external power supply required, fast response speed, and in-situ compatibility. However, traditional solvent-cast / drop-coated membranes typically have thicknesses of 100-200 µm, resulting in an ion diffusion coefficient within the membrane phase that is much lower than that in the aqueous phase. This leads to slow diffusion / equilibrium processes, limited response time, and susceptibility to drift due to temperature, matrix ion strength, and biofouling. To improve response and consistency, thin-film / ultra-thin film methods (such as spin-coated thin films, aerosol / atom deposition, and other controllable film formation techniques) have been used to reduce membrane resistance and shorten response time. However, uniformity, membrane-substrate adhesion, and long-term stability remain significant challenges. Therefore, there is an urgent need to find a method that can precisely control the inner membrane thickness, increase inner membrane uniformity, and reduce the intramembrane ion diffusion coefficient to achieve online monitoring technology for nitrate nitrogen in wastewater with lower detection limits and faster response times. Summary of the Invention

[0005] To address the issues of high detection limits and slow response times of nitrate nitrogen in wastewater caused by the inherent membrane thickness of existing sensors, a fabrication process for an online nitrate nitrogen monitoring sensor based on three-dimensional electro-sprayed membrane laying is proposed.

[0006] The technical solution of this invention is: A fabrication process for an online nitrate nitrogen monitoring sensor based on three-dimensional electro-spray film deposition includes the following steps: S1. Preparation of nitrate ion-selective membrane solution: 6.5–7 parts by mass of tetranitrogen tetraoxane macrocyclic compound C... 28 H 60 N4O4, 92-93 parts of plasticizer dibutyl phthalate, and 0.5-1 parts of tetraoctyl ammonium chloride are mixed evenly to obtain a selective membrane mixture. Then, the selective membrane mixture is mixed with 49-51 parts of polyvinyl chloride and placed together in 148-152 parts of tetrahydrofuran and ultrasonically mixed evenly to obtain a nitrate ion selective membrane solution. S2. Assembly Preparation: Mount the sensor substrate onto the deposition film laying device, which includes a syringe, a needle, a cylindrical roller, and a slide table. Mount the syringe onto the slide table, then mount the needle onto the lower end of the syringe, and then mount the roller below the needle. The roller is driven to rotate by a motor. Fix the sensor substrate onto the rotating roller and position it directly below the needle. Install a carbon-based electrode on the middle of one side of the upper surface of the sensor substrate, with the carbon-based electrode facing outwards. Set the roller to rotate at a constant speed. S3. Electrostatic atomization of the membrane solution: The nitrate ion selective membrane solution is placed in a syringe and pushed at a constant flow rate by the syringe pump. At the same time, a positive high voltage is applied to the needle at the end of the syringe, so that the nitrate ion selective membrane solution forms a stable conical jet at the needle and atomizes into fine droplets, which are then sprayed out uniformly along the direction of the electric field. S4. Three-dimensional electrospray coating: The fine droplets sprayed from the needle are uniformly coated onto the rotating drum and the surface of the carbon-based electrode, so that the surface of the carbon-based electrode has a circular deposition area and gradually spreads into a continuous film. At the same time, the needle is driven by the slide to perform reciprocating motion scanning along the axis of the drum, so that the fine droplets sprayed from the needle cover the length section of the carbon-based electrode. After several reciprocating motion scans, a nitrate ion selective film of the required thickness is obtained.

[0007] Furthermore, the length of the sensor substrate is 35~40mm, the width is 10~15mm, and the thickness is 0.5~1mm. The material of the sensor substrate is glass carbon plate or dense graphite sheet.

[0008] Note: By properly controlling the size of the sensor substrate, overall portability can be improved while ensuring monitoring effectiveness. By selecting a suitable sensor substrate material, conductivity and excellent physical properties can be ensured.

[0009] Furthermore, in S3, the flow rate of the nitrate ion-selective membrane solution is 3.0~5.0 mL / h, and the positive voltage is 5~8 kV.

[0010] Explanation: By reasonably controlling the push flow rate and voltage of the nitrate ion selective membrane liquid, a stable and uniform membrane liquid cone jet spray pattern can be ensured.

[0011] Furthermore, in S4, the rotation speed of the roller is 12~20 rpm, and it completes 5~10 depositions in 5~10 rotations. Each time the needle rotates past the position of the carbon-based electrode, it completes 2~3 axial reciprocating movements at the position of the carbon-based electrode.

[0012] Note: By properly controlling the rotation speed of the roller, a stable membrane liquid collection surface can be formed.

[0013] Furthermore, in S4, the height of the needle from the roller is 3~6cm, a circular deposition area is reserved on the surface of the carbon-based electrode, and the remaining part is covered with a shielding material. After the film is laid, the shielding material is removed.

[0014] Note: By properly controlling the height of the needle from the roller, a stable membrane liquid collection surface can be formed in the designated area.

[0015] Furthermore, in S4, the axial reciprocating motion scanning speed of the needle is 300~400μm / s, and the length segment of the axial reciprocating motion is 10~20cm.

[0016] Explanation: By properly controlling the axial reciprocating motion scanning speed, a stable membrane liquid collection surface is ensured to be formed in the axial direction.

[0017] Furthermore, it also includes S5, drying and curing: After the three-dimensional electrospray film is laid, the film-laid sensor substrate is placed in an inert gas atmosphere and under light-proof conditions, and left to dry at room temperature to remove residual solvent and form a dense and uniform S-ISM film layer.

[0018] Note: After drying and curing, the S-ISM membrane can meet the actual water body's usage standards.

[0019] Furthermore, the inert gas is nitrogen, and the standing drying time is 24~72h. In S1~S4, the drying is carried out at room temperature, with a room temperature of 20~25℃ and a relative humidity of 10~25%.

[0020] Note: By optimizing the external conditions of the entire process, the final nitrate ion-selective membrane is made uniform and dense, achieving ideal monitoring conditions.

[0021] The beneficial effects of this invention are: This invention introduces a tetranitrogen tetraoxa macrocyclic compound C 28 H 60 N4O4, as a nitrate ion carrier, achieves highly selective recognition and response to target ions. Uniform film deposition is achieved through roller-type three-dimensional electrospraying. By optimizing process parameters such as flow rate and spray angle, the thickness of the inner film on the tens of nanometer scale is precisely controlled. Ultimately, the thickness of the selective film is precisely controlled within the range of 1 μm, which significantly reduces the ion diffusion coefficient within the film and significantly reduces the detection limit and response time. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the left side of the deposition and film laying apparatus in the process of the present invention during three-dimensional electrospray film laying; Figure 2 This is a schematic diagram of the right side of the deposition and film laying apparatus in the process of the present invention during three-dimensional electrospray film laying; Figure 3 This is a front view of the deposition and film laying apparatus in the process of the present invention when performing three-dimensional electrospray film laying; Figure 4 This is a top view of the deposition and film laying apparatus in the process of the present invention when performing three-dimensional electrospray film laying; Figure 5 This is a schematic diagram of the structure of the online monitoring nitrate nitrogen sensor prepared by the process of the present invention; Figure 6 This is a process flow diagram of the present invention.

[0023] Among them, 1-sensor substrate, 11-carbon-based electrode, 2-syringe, 3-needle, 4-roller, 5-slide table. Detailed Implementation

[0024] Example 1: A fabrication process for an online monitoring nitrate nitrogen sensor based on three-dimensional electro-spray film laying, comprising the following steps: S1. Preparation of nitrate ion-selective membrane solution: 7 parts by mass of tetranitrogen tetraoxane macrocyclic compound C 28 H 60 N4O4, 92 parts of plasticizer dibutyl phthalate, and 1 part of tetraoctyl ammonium chloride were mixed evenly to obtain a selective membrane mixture. Then, the selective membrane mixture was mixed with 50 parts of polyvinyl chloride and placed together in 150 parts of tetrahydrofuran. The mixture was then ultrasonically mixed evenly to obtain the nitrate ion selective membrane solution. S2. Assembly Preparation: Install the sensor substrate 1 on the deposition film laying device. The sensor substrate 1 is 35mm long, 15mm wide, and 1mm thick. The material of the sensor substrate 1 is glass carbon plate. The deposition film laying device includes a syringe 2, a needle 3, a cylindrical roller 4, and a slide table 5. Install the syringe 2 on the slide 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 in the middle of one side of the upper surface of the sensor substrate 1, with the carbon-based electrode 11 facing outwards. Set the roller 4 to rotate at a constant speed. S3. Electrostatic atomization of the membrane solution: The nitrate ion-selective membrane solution is placed in syringe 2 and pushed at a constant flow rate by the injection pump of syringe 2. The pushing flow rate of the nitrate ion-selective membrane solution is 3.9 mL / h. At the same time, a positive high voltage of 6.6 kV is applied to the needle 3 at the end of syringe 2, so that the nitrate ion-selective membrane solution forms a stable conical jet at the needle 3 and atomizes into fine droplets, which are uniformly sprayed out along the direction of the electric field. S4. Three-dimensional electrospray film deposition: The fine droplets sprayed from the needle 3 are uniformly coated onto the rotating roller 4 and the surface of the carbon-based electrode 11, so that a circular deposition area is obtained on the surface of the carbon-based electrode 11 and gradually spread into a continuous film. The rotation speed of the roller 4 is 14 rpm, and the deposition is completed 5 times in 5 rotations. The height of the needle 3 from the roller 4 is 4.5 cm. At the same time, the slide table 5 drives the needle 3 to perform reciprocating motion scanning along the axis of the roller 4, so that the fine droplets sprayed from the needle 3 cover the length section of the carbon-based electrode 11. The axial reciprocating motion scanning speed of the needle 3 is 350 μm / s, and the length section of the axial reciprocating motion is 15 cm. Every time the needle 3 rotates past the position of the carbon-based electrode 11, it completes 3 axial reciprocating motions at the position of the carbon-based electrode 11. A total of 15 reciprocating motion scans are completed to obtain a nitrate ion selective film of the required thickness. A circular deposition area is reserved on the surface of the carbon-based electrode 11, and the remaining part is covered with a masking material. After the film deposition is completed, the masking material is removed. S5. Drying and curing: After the three-dimensional electrospray film is laid, the sensor substrate 1 with the film is placed in an inert gas atmosphere and protected from light, and left to dry at room temperature. The inert gas is nitrogen, and the drying time is 48 hours to remove residual solvent and form a dense and uniform S-ISM film layer.

[0025] In S1 to S5, all experiments were conducted at room temperature, with a temperature of 23°C and a relative humidity of 16%.

[0026] Example 2: The difference between this example and Example 1 is that the length of the sensor substrate 1 is 37mm, the width is 12mm, the thickness is 0.8mm, and the material of the sensor substrate 1 is a dense graphite sheet.

[0027] Example 3: The difference between this example and Example 1 is that the length of the sensor substrate 1 is 35mm, the width is 10mm, and the thickness is 0.5mm.

[0028] Example 4: This example differs from Example 1 in that, in S1, 6.5 parts of tetranitrotetraoxa macrocyclic compound C are used. 28 H 60 N4O4, 93 parts of plasticizer dibutyl phthalate, and 0.5 parts of tetraoctyl ammonium chloride were mixed evenly to obtain a selective membrane mixture. The selective membrane mixture was then mixed with 49 parts of polyvinyl chloride and placed together in 148 parts of tetrahydrofuran. The mixture was then ultrasonically mixed evenly to obtain a nitrate ion selective membrane solution.

[0029] Example 5: This example differs from Example 1 in that, in S1, 7 parts of tetranitrotetraoxa macrocyclic compound C are used. 28 H 60 N4O4, 92.5 parts of plasticizer dibutyl phthalate, and 0.5 parts of tetraoctyl ammonium chloride were mixed evenly to obtain a selective membrane mixture. The selective membrane mixture was then mixed with 51 parts of polyvinyl chloride and placed together in 152 parts of tetrahydrofuran. The mixture was then ultrasonically mixed evenly to obtain a nitrate ion selective membrane solution.

[0030] Example 6: The difference between this example and Example 1 is that in S3, the 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 at the end of the syringe 2.

[0031] Example 7: The difference between this example and Example 1 is that in S3, the 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 at the end of the syringe 2.

[0032] Example 8: This example differs from Example 1 in that, in S4, the rotation speed of the roller 4 is 12 rpm, and it completes 5 depositions in 5 rotations. 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 μm / s, and the length of the axial reciprocating motion is 10 cm. Each time the needle 3 rotates past the position of the carbon-based electrode 11, it completes 2 axial reciprocating motions at the position of the carbon-based electrode 11. A total of 10 reciprocating motion scans are completed to obtain the nitrate ion selective film of the required thickness.

[0033] Example 9: This example differs from Example 1 in that, in S4, the rotation speed of the roller 4 is 20 rpm, and 10 rotations are completed to deposit 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 μm / s, and the length of the axial reciprocating motion is 20 cm. Each time the needle 3 rotates past the position of the carbon-based electrode 11, it completes 3 axial reciprocating motions at the position of the carbon-based electrode 11. A total of 30 reciprocating motion scans are completed to obtain the nitrate ion selective film of the required thickness.

[0034] Example 10: The difference between this example and Example 1 is that in S5, the static drying time is 24 hours, and in S1 to S4, the drying is carried out at room temperature, with a room temperature of 20°C and a relative humidity of 10%.

[0035] Example 11: The difference between this example and Example 1 is that in S5, the static drying time is 72 hours, and in S1 to S4, the drying is carried out at room temperature, with a room temperature of 25°C and a relative humidity of 25%.

[0036] Experimental Example: The sensor prepared using the process described in Example 1 of this invention was applied to the monitoring of nitrate nitrogen in actual wastewater. Verification showed that the sensor can precisely control the thickness of the selective membrane within a 1 μm range, significantly reducing the ion diffusion coefficient within the membrane. This successfully lowered the sensor's detection limit for nitrate nitrogen to 7.9 μg / L and the detection limit for nitrate nitrogen to 55.7 μg / L. This technical performance is significantly better than the requirements of my country's current water quality testing standards (nitrate nitrogen: 32 μg / L, HJ198-2024). Furthermore, compared to current mainstream in-situ sensor technologies, its detection limit is reduced by an order of magnitude. In addition, the sensor's response time to nitrate nitrogen is significantly shortened from 22.5 seconds to 9.2 seconds, greatly improving the sensor's real-time monitoring capability. These technologies enable real-time acquisition of water quality data during wastewater treatment, providing a solid data foundation for intelligent wastewater treatment systems.

Claims

1. A fabrication process for an online monitoring nitrate nitrogen sensor based on three-dimensional electro-spray film laying, characterized in that, Includes the following steps: S1. Preparation of nitrate ion-selective membrane solution: 6.5–7 parts by mass of tetranitrogen tetraoxane macrocyclic compound C... 28 H 60 N4O4, 92-93 parts of plasticizer dibutyl phthalate, and 0.5-1 parts of tetraoctyl ammonium chloride are mixed evenly to obtain a selective membrane mixture. Then, the selective membrane mixture is mixed with 49-51 parts of polyvinyl chloride and placed together in 148-152 parts of tetrahydrofuran and ultrasonically mixed evenly to obtain a nitrate ion selective membrane solution. S2, Assembly preparation: Install the sensor substrate (1) on the deposition film laying device, which includes a syringe (2), a needle (3), a cylindrical roller (4), and a slide (5); install the syringe (2) on the slide (5), then install the needle (3) on 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), and install a carbon-based electrode (11) in the middle of one side of the upper surface of the sensor substrate (1), with the carbon-based electrode (11) facing outwards. Set the roller (4) to rotate at a constant speed. S3, Electrostatic atomization of membrane solution: The nitrate ion selective membrane solution is placed in a syringe (2) and pushed at a constant flow rate by the injection pump of the syringe (2). At the same time, a positive high voltage is applied to the needle (3) at the end of the syringe (2) so that the nitrate ion selective membrane solution forms a stable conical jet at the needle (3) and atomizes into fine droplets, which are then sprayed out uniformly along the direction of the electric field. S4, Three-dimensional electrospraying film: The fine droplets sprayed from the needle (3) are uniformly coated onto the rotating roller (4) and the surface of the carbon-based electrode (11), so that the surface of the carbon-based electrode (11) has a circular deposition area and gradually spreads into a continuous film. At the same time, the needle (3) is driven by the slide (5) to perform reciprocating motion scanning along the axis of the roller (4), so that the fine droplets sprayed from the needle (3) cover the length section of the carbon-based electrode (11), and several reciprocating motion scans are completed to obtain a nitrate ion selective film of the required thickness.

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

3. The fabrication process of an online monitoring nitrate nitrogen sensor based on three-dimensional electro-spray film laying according to claim 1, characterized in that, In S3, the push flow rate of the nitrate ion selective membrane solution is 3.0~5.0 mL / h, and the positive voltage is 5~8 kV.

4. The fabrication process of an online monitoring nitrate nitrogen sensor based on three-dimensional electro-spraying film laying according to claim 1, characterized in that, In S4, the rotation speed of the roller (4) is 12~20 rpm, and it completes 5~10 depositions while rotating 5~10 times. Each time the needle (3) rotates past the position of the carbon-based electrode (11), it completes 2~3 axial reciprocating movements at the position of the carbon-based electrode (11).

5. The fabrication process of an online monitoring nitrate nitrogen sensor based on three-dimensional electro-spraying film laying according to claim 1, characterized in that, In S4, the height of the needle (3) from the roller (4) is 3~6cm. A circular deposition area is reserved on the surface of the carbon-based electrode (11), and the rest of the area is covered with a shielding material. After the film is laid, the shielding material is removed.

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

7. The fabrication process of an online monitoring nitrate nitrogen sensor based on three-dimensional electro-spraying film laying according to claim 1, characterized in that, It also includes S5, drying and curing: After the three-dimensional electrospraying film is completed, the film-coated sensor substrate (1) is placed in an inert gas atmosphere and under light-proof conditions, and left to dry at room temperature to remove residual solvent and form a dense and uniform S-ISM film layer.

8. The fabrication process of an online monitoring nitrate nitrogen sensor based on three-dimensional electro-spraying film laying according to claim 7, characterized in that, The inert gas is nitrogen, and the standing drying time is 24~72h. In S1~S4, the drying is carried out at room temperature, with a room temperature of 20~25℃ and a relative humidity of 10~25%.

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