A pure titanium material coating sensor for detecting low concentration ammonia gas and a preparation method and application thereof

Abstract

The application relates to the field of coating materials, and discloses a pure titanium material coating sensor for detecting low-concentration ammonia gas as well as a preparation method and application of the sensor. The sensor comprises a pure titanium material, a micro-arc oxidation coating and an electrode; the micro-arc oxidation coating is arranged on the surface of the pure titanium material through micro-arc oxidation of a sodium silicate, sodium stannate trihydrate and zinc acetate electrolyte; and the electrode is arranged on the micro-arc oxidation coating. The SnO2 / TiO2 coating capable of being applied to the detection of low-concentration ammonia gas under a high-humidity environment is formed on the surface of the pure titanium material through micro-arc oxidation of the composite electrolyte of sodium silicate, zinc acetate and sodium stannate trihydrate; the electrode is arranged, and the oxygen adsorption-desorption principle is utilized for detection; compared with conventional gases, the sensor exhibits excellent sensitivity and selectivity to ammonia gas, and therefore can effectively, timely and simply detect ammonia gas.

Description

Technical Field

[0001] This invention relates to the field of coating materials, specifically to a pure titanium material coated sensor for detecting low concentrations of ammonia, its preparation method, and its application. Background Technology

[0002] Ammonia (NH3) is a harmful gas, and its detection is of great significance in agriculture, industry, safety, and daily life. In particular, NH3, present in human exhaled breath, is becoming increasingly important as a potential diagnostic biomarker for various types of kidney disease and hepatitis. For example, the NH3 concentration exhaled by patients with end-stage renal disease (ESRD) (average 4.88 ppm, range 0.82-14.7 ppm) is several times higher than that of healthy individuals (average 0.96 ppm, range 0.425-1.8 ppm), while the ammonia concentration exhaled by patients with cirrhosis (0.745 ppm) is significantly higher than that of healthy individuals (0.278 ppm). However, effective detection of ammonia remains challenging, including detecting environmental conditions characterized by high water vapor levels and developing inexpensive, portable equipment.

[0003] Previous research in this invention provided a pure titanium material coating for detecting ammonia. However, further research revealed that this coating exhibits poor sensitivity in detecting low concentrations of NH3 in high-humidity environments, which is precisely one of the characteristics of NH3 in clinical respiratory testing. Therefore, there is an urgent need for stable and effective detection of low concentrations of NH3 in high-humidity environments. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide a pure titanium material coated sensor for detecting low concentrations of ammonia, which can have a high sensitivity response to low concentrations of NH3 in a high humidity environment and excellent selectivity for CO2 and other VOC gases.

[0005] Another object of the present invention is to provide a method for preparing the above-mentioned sensor and its application in detecting low concentrations of ammonia and in preparing products for detecting low concentrations of ammonia.

[0006] To solve the above-mentioned technical problems, or at least partially solve them, the present invention provides a method for solving the above-mentioned technical problems, or at least partially solves them. As a first aspect of the present invention, a pure titanium composite coating sensor for detecting low concentrations of ammonia is provided, comprising pure titanium material, a micro-arc oxidation coating, and an electrode; the micro-arc oxidation coating is disposed on the surface of the pure titanium material by micro-arc oxidation with sodium silicate, sodium stannate trihydrate, and zinc acetate electrolyte, and the electrode is disposed on the micro-arc oxidation coating.

[0007] Optionally, the pure titanium material includes TA1 to TA4 industrial pure titanium materials.

[0008] Optionally, the electrode is an interdigitated electrode.

[0009] Optionally, the electrolyte contains sodium silicate at a concentration of 5–8 g / L, zinc acetate at a concentration of 1.5–2.5 g / L, and sodium stannate trihydrate at a concentration of 0.5–1.5 g / L.

[0010] As a second aspect of the present invention, based on the superior performance of the sensor of the present invention in detecting low concentrations of ammonia, exhibiting high sensitivity and selectivity, the present invention provides the application of the sensor in detecting low concentrations of ammonia or in preparing products for detecting low concentrations of ammonia. The low concentration of ammonia includes ammonia in the range of 0.1 to 20 ppm.

[0011] As a third aspect of the present invention, a method for preparing the sensor is provided, comprising:

[0012] Step 1: Pre-treatment of pure titanium material, including grinding, degreasing, and cleaning;

[0013] Step 2: The pretreated pure titanium material is subjected to micro-arc oxidation in an electrolyte of sodium silicate, sodium stannate trihydrate and zinc acetate to form a micro-arc oxidation coating.

[0014] Step 3: Set electrodes on the micro-arc oxidation coating to obtain the sensor.

[0015] As a fourth aspect of the invention, a product for detecting low concentrations of ammonia is provided, comprising a device for recording changes in resistance and a sensor as described in the invention, wherein electrodes on the device and the sensor are connected by wires.

[0016] Optionally, the device for recording changes in resistance values ​​includes a multimeter and a data processor.

[0017] As a fifth aspect of the present invention, a method for detecting low concentrations of ammonia is provided, wherein the sensor of the present invention is placed in ammonia standard samples of different concentrations, and a standard curve of resistance change data and ammonia concentration is established by a device for recording resistance value changes; then the sensor is placed in the environment to be tested, resistance value change data is obtained, and the concentration of ammonia in the environment to be tested is obtained by the standard curve.

[0018] This invention utilizes a composite electrolyte of sodium silicate, zinc acetate, and sodium stannate trihydrate for micro-arc oxidation to form a SnO2 / TiO2 coating on the surface of pure titanium material. This coating is suitable for detecting low concentrations of ammonia in high humidity environments. By setting electrodes and utilizing the oxygen adsorption-desorption principle, the invention exhibits superior sensitivity and selectivity for ammonia compared to conventional gases. Therefore, it can effectively, in real-time, and conveniently detect ammonia. Attached image description:

[0019] Figure 1 The image shown is a SEM image of the sensor coating of this invention.

[0020] Figure 2 The image shown is an EDS diagram of the sensor coating of this invention;

[0021] Figure 3 The diagram shows the composition of the detection system for the gas selectivity test.

[0022] Figure 4 The figure shows the response of the sensors prepared by electrolyte groups (1) to (3) in Example 2 to high concentrations of ammonia (20-200 ppm); in the figure, zinc acetate (C4H6O4Zn) of 1.5 g / L, 2.0 g / L and 2.5 g / L represent electrolyte groups (1) to (3) respectively, and the broken lines from top to bottom are the corresponding results of electrolyte groups (2), (1) and (3);

[0023] Figure 5 The figure shows the response of the sensors prepared by electrolyte groups (2) and (4) to (6) in Example 2 to low concentrations of ammonia (0.1 to 20 ppm). In the figure, sodium stannate trihydrate (Na2[Sn(OH)6]) at concentrations of 0 g / L, 0.5 g / L, 1 g / L, and 1.5 g / L represents electrolyte groups (2) and (4) to (6), respectively. The broken lines from top to bottom represent the corresponding results of electrolyte groups (5), (6), (4), and (2).

[0024] Figure 6 The image shows the response of the sensor prepared by the electrolyte group of Example 2 (2) to low concentrations of ammonia (0.1-20 ppm) under different humidity conditions; the broken lines from top to bottom represent the results corresponding to 98% relative humidity, 57% relative humidity and 17% relative humidity;

[0025] Figure 7 The image shows the response of the sensor prepared by the electrolyte group of Example 2 (4) to low concentrations of ammonia (0.1-20 ppm) under different humidity conditions; the broken lines from top to bottom represent the results corresponding to 98% relative humidity, 57% relative humidity and 17% relative humidity;

[0026] Figure 8 The image shows the response of the sensor prepared by the electrolyte group of Example 2 (5) to low concentrations of ammonia (0.1-20 ppm) under different humidity conditions; the broken lines from top to bottom represent the results corresponding to 98% relative humidity, 57% relative humidity and 17% relative humidity;

[0027] Figure 9The image shows the response of the sensor prepared by the electrolyte group of Example 2 (6) to low concentrations of ammonia (0.1-20 ppm) under different humidity conditions; the broken lines from top to bottom represent the results corresponding to 98% relative humidity, 57% relative humidity and 17% relative humidity;

[0028] Figure 10 The chart shows the Ra / Rg values ​​for different test gases (results of gas selectivity test); in each group of results, the left bar represents the result at a relative humidity of 17%, and the right bar represents the result at a relative humidity of 98%.

[0029] Figure 11 The figure shows the fitting curves of the sensor of the present invention for detecting ammonia gas of different concentrations. Detailed implementation method:

[0030] This invention discloses a pure titanium material coated sensor for detecting low concentrations of ammonia, its preparation method, and its application. Those skilled in the art can refer to the content of this document and appropriately modify the process parameters to achieve the same result. It is particularly important to note that all similar substitutions and modifications are obvious to those skilled in the art and are considered to be included in this invention. The sensor, its preparation method, and its application have been described through preferred embodiments. Those skilled in the art can obviously make modifications or appropriate alterations and combinations to the sensor, its preparation method, and its application described herein without departing from the content, spirit, and scope of this invention to realize and apply the technology of this invention.

[0031] In a first aspect of the invention, a pure titanium composite coating sensor for detecting low concentrations of ammonia is provided, comprising pure titanium material, a micro-arc oxidation coating, and an electrode; the micro-arc oxidation coating is deposited on the surface of the pure titanium material via micro-arc oxidation using sodium silicate, sodium stannate trihydrate, and zinc acetate electrolyte; the electrode is disposed on the micro-arc oxidation coating; and a SEM image of the sensor coating is shown below. Figure 1 See EDS diagram Figure 2 .

[0032] In some embodiments of the present invention, the pure titanium material includes TA1 to TA4 industrial pure titanium materials, wherein Ti ≥ 99% is contained in the pure titanium material; in other embodiments of the present invention, the pure titanium material includes TA1 pure titanium material, and more specifically, the elemental composition (mass fraction) of the TA1 pure titanium material is: Fe: 0.2%, C: 0.08%, N: 0.03%, H: 0.015%, O: 0.18%, others: 0.4%, with the balance being Ti.

[0033] In some embodiments of the present invention, the electrode is an interdigital electrode.

[0034] In some embodiments of the present invention, the concentration of sodium silicate in the electrolyte is 5–8 g / L, the concentration of zinc acetate is 1.5–2.5 g / L, and the concentration of sodium stannate trihydrate is 0.5–1.5 g / L. In other embodiments of the present invention, the concentration of sodium silicate in the electrolyte is 5 g / L, 6 g / L, 7 g / L, or 8 g / L, the concentration of zinc acetate is 1.5 g / L, 2.0 g / L, or 2.5 g / L, and the concentration of sodium stannate trihydrate is 0.5 g / L, 1.0 g / L, or 1.5 g / L.

[0035] The sensor described in this invention detects ammonia gas based on the resistance change of a metal oxide formed by micro-arc oxidation and coating on its surface when exposed to air and ammonia gas, according to the principle of "oxygen adsorption-desorption" of metal oxides. When the pure titanium coating material is exposed to air, oxygen captures free electrons on the surface of the pure titanium coating material to form adsorbed oxygen, resulting in an increase in resistance. When ammonia gas is exposed to the surface of the pure titanium coating material, the ammonia gas and adsorbed oxygen undergo a redox reaction, releasing the captured electrons, and the resistance decreases, as shown in the following equation:

[0036]

[0037] In a comparison of different electrolytes, the ammonia responsiveness was tested using the prepared pure titanium material. The results showed that the electrolytes composed of sodium silicate, zinc acetate, and sodium stannate trihydrate exhibited excellent performance and high sensitivity in the detection of low concentrations of NH3 under high humidity conditions.

[0038] Compared with common gases produced during respiration such as CO2, N2, H2S, and acetone, the responsivity of each gas detected using the pure titanium material described in this invention was shown to be significantly higher for ammonia (K = Ra / Rg) than for other gases. This indicates that the tin-doped coating on the surface of the pure titanium material of this invention not only has high sensitivity for low-concentration ammonia but also good selectivity, reducing interference. In view of the beneficial effects of the sensor of this invention and its excellent performance in actual detection, a second aspect of this invention provides the application of the sensor in detecting low-concentration ammonia or in preparing products for detecting low-concentration ammonia. The low-concentration ammonia includes ammonia in the range of 0.1–20 ppm.

[0039] In a third aspect of the invention, a method for preparing the sensor is also provided, comprising:

[0040] Step 1: Pre-treatment of pure titanium material, including grinding, degreasing, and cleaning;

[0041] Step 2: The pretreated pure titanium material is subjected to micro-arc oxidation in an electrolyte of sodium silicate, sodium stannate trihydrate and zinc acetate to form a micro-arc oxidation coating.

[0042] Step 3: Set electrodes on the micro-arc oxidation coating to obtain the sensor.

[0043] In some embodiments of the present invention, step 1 is as follows:

[0044] The pure titanium material is polished in stages, followed by ultrasonic cleaning with anhydrous ethanol and water, and then degreasing and cleaning with an alkaline degreasing solution. The staged polishing uses silicon carbide sandpaper with progressively increasing grit, until the surface is smooth, free of obvious scratches, and has a uniform texture. The alkaline degreasing solution is sodium hydroxide, preferably a 10% sodium hydroxide solution.

[0045] To achieve a more uniform coating thickness, higher porosity, and submicron pores, which is beneficial for ammonia detection, in some embodiments of the present invention, the micro-arc oxidation is performed in a constant current mode. In other embodiments, the positive current in the constant current mode is preset to 2–8 A, and can be selected as 4 A; the negative current is preset to 1–5 A, and can be selected as 3 A; the pulse frequency is fixed at 0.1–0.3 Hz, and can be selected as 0.2 Hz; the duty cycle is set to 70%–90%, and can be selected as 80%. In other embodiments, in the constant current mode, the current ramp-up starts from 0 A and increases gradually in increments of 0.5 A until a preset value is reached, with both positive and negative currents occurring simultaneously. This allows for better quality of the prepared micro-arc oxidation coating and also protects the micro-arc oxidation power supply.

[0046] In some embodiments of the present invention, pure titanium is used as the positive electrode and other suitable metals such as stainless steel are used as the negative electrode, with the distance between the positive and negative electrodes controlled at 10 cm; the temperature of the electrolyte is controlled by an internal and external circulation cooling device and maintained at 20-35°C.

[0047] In some embodiments of the present invention, the micro-arc oxidation time can be selected according to the actual situation. In some embodiments of the present invention, the micro-arc oxidation time is 4 to 6 minutes, while in other embodiments, the micro-arc oxidation time is 4 minutes, 5 minutes or 6 minutes.

[0048] In some embodiments of the present invention, the electrode is fabricated as an interdigitated electrode by using a mask to cover the coating on the surface of the pure titanium material and then employing an ion sputtering process. In other embodiments of the present invention, the ion sputtering process uses a cyclic sputtering method, adjusting the sputtering duration and number of cycles according to the desired interdigitated electrode shape; in other embodiments of the present invention, the sputtering duration is 90 s and the number of cycles is 6.

[0049] In a fourth aspect of the invention, a product for detecting low concentrations of ammonia is provided, comprising a device for recording changes in resistance and a sensor as described in the invention, wherein electrodes on the device and the sensor are connected by wires.

[0050] In some embodiments of the present invention, the conductor is a conductive metal wire, such as a copper wire; in other embodiments of the present invention, the conductor is adhered to the electrode by conductive silver paste or other conductive materials to form a connection.

[0051] In some embodiments of the present invention, the device for recording changes in resistance value includes a multimeter and a data processor, wherein the multimeter may be a digital multimeter and the data processor may be a computer device.

[0052] In a fifth aspect of the present invention, a method for detecting low concentrations of ammonia is provided, wherein the sensor of the present invention is placed in ammonia standard samples of different concentrations, and a standard curve of resistance change data and ammonia concentration is established by a device for recording resistance value changes; then the sensor is placed in the environment to be tested, resistance value change data is obtained, and the concentration of ammonia in the environment to be tested is obtained by the standard curve.

[0053] Unless otherwise specified, the experimental environment and parameter conditions of each group in the specific implementation test are consistent, except for the differences that are explicitly pointed out.

[0054] The following is a further description of a pure titanium material coated sensor for detecting low concentrations of ammonia, its preparation method, and its application, provided by the present invention.

[0055] Example 1: Preparation of the sensor for ammonia detection according to the present invention

[0056] I. Preparation Method

[0057] 1. Pretreatment of pure titanium substrate

[0058] The pure titanium substrate is TA1 industrial pure titanium, with the following elemental composition (mass fraction): Fe: 0.2%, C: 0.08%, N: 0.03%, H: 0.015%, O: 0.18%, others: 0.4%, and the balance being Ti. The pure titanium substrate was wire-cut into 25mm × 25mm × 2mm pieces, and then polished with 400# → 800# → 1000# → 2000# silicon carbide sandpaper until the surface was smooth, without obvious scratches, and with a uniform texture. It was then ultrasonically cleaned for 10 minutes each in acetone, anhydrous ethanol, and deionized water, and finally air-dried with a hair dryer to obtain the pretreated pure titanium substrate.

[0059] Bright and clean pure titanium is immersed in a degreasing solution, which is a 10% sodium hydroxide solution at a temperature of 60°C, and then ultrasonically cleaned for 10 minutes. After removing the pure titanium, it is rinsed with water three times and then dried with a hair dryer to obtain a pure titanium substrate after ultrasonic treatment.

[0060] 2. Prepare the micro-arc oxidation electrolyte.

[0061] The micro-arc oxidation electrolyte formula consists of 6 g / L sodium silicate, 1.5 g / L, 2 g / L, or 2.5 g / L zinc acetate, and 0.5 g / L, 1.0 g / L, or 1.5 g / L sodium stannate trihydrate. To prepare, first add 3 L of deionized water to the electrolytic cell, then add appropriate amounts of sodium silicate, zinc acetate, and sodium stannate trihydrate, and dissolve thoroughly. The micro-arc oxidation electrolyte needs to be replaced after each micro-arc oxidation operation, and each batch of prepared electrolyte must be used within 24 hours to prevent deterioration.

[0062] 3. Micro-arc oxidation

[0063] Pretreated pure titanium was placed in a micro-arc oxidation electrolyte, with the pure titanium connected to the positive terminal of the power supply as the positive electrode, and the stainless steel electrolytic cell connected to the negative terminal as the cathode. The distance between the positive and negative electrodes was controlled at 10 cm. The cooling device was turned on, and the temperature was controlled at 30℃. A micro-arc oxidation AC pulse power supply was used to start the power supply. In constant current mode, the forward current was preset to 4A, and the negative current was preset to 3A. The current was increased from 0A in increments of 0.5A, with both positive and negative currents proceeding simultaneously until the preset values ​​were reached. The pulse frequency was fixed at 0.2Hz, the duty cycle was set to 80%, and the micro-arc oxidation time was 4 minutes. After this, pure titanium with a micro-arc oxidation coating on the surface was obtained.

[0064] 4. Ion sputtering

[0065] A mask was placed over the surface of the micro-arc oxidation coating and fixed in a vacuum ion sputtering instrument. The sputtering current was kept constant, and interdigitated electrodes were prepared by cyclic sputtering. Each sputtering lasted 90 seconds, and a total of 6 sputtering cycles were performed.

[0066] 5. Copper wire adhesion

[0067] After sputtering, the conductivity was tested using a multimeter to assess the processing quality of the interdigitated electrodes. Then, copper wires were adhered to the interdigitated electrodes using conductive silver paste and dried at 80°C for 2 hours to ensure good contact in the sensor circuitry.

[0068] SEM and EDS images of the sensor coating prepared in this invention are shown below. Figure 1 and Figure 2 ,Depend on Figure 1 SEM images show that the coating surface has uniformly distributed micron-sized pores, no visible defects, high porosity, and a large specific surface area, which is beneficial for ammonia detection. Figure 2 As shown in the EDS, Sn and Zn elements were successfully incorporated into the surface of the micro-arc TiO2 film.

[0069] Example 2: Effect of different tin doping concentrations on the performance of gas sensors with low ammonia concentrations

[0070] 1. Test Methods

[0071] Reference Figure 3 The detection system shown was tested by setting up a heating platform in a closed space and placing the sensor prepared in this invention on it. Copper wires were attached to the interdigital electrodes with conductive silver paste and connected to a multimeter. Data transmission was established between the multimeter and the computer.

[0072] A fixed amount of volatile gas solution is injected into a closed space. The gas is rapidly evaporated into gas by a heating platform. The gas reacts with the sensor to generate a signal. A thermometer is used to indicate the temperature of the closed space. A fan is used to quickly remove the measured volatile gas after the detection is completed.

[0073] 2. The Influence of Different Coatings on Ammonia Detection

[0074] The preparation method is the same as in Example 1, except that the composition of the electrolyte is adjusted.

[0075] (1) 6 g / L sodium silicate + 1.5 g / L zinc acetate;

[0076] (2) 6 g / L sodium silicate + 2 g / L zinc acetate;

[0077] (3) 6 g / L sodium silicate + 2.5 g / L zinc acetate;

[0078] (4) 6 g / L sodium silicate + 2 g / L zinc acetate + 0.5 g / L sodium stannate trihydrate;

[0079] (5) 6 g / L sodium silicate + 2 g / L zinc acetate + 1 g / L sodium stannate trihydrate;

[0080] (6) 6 g / L sodium silicate + 2 g / L zinc acetate + 1.5 g / L sodium stannate trihydrate;

[0081] The resistivity sensitivity (K = Ra / Rg) of the above 6 groups of electrolytes was measured, and the results are shown in the figure. Figure 4 and Figure 5 ;

[0082] Figure 4 The results showed that when sodium silicate and zinc acetate were used as electrolytes alone (electrolyte groups (1) to (3)), the prepared sensors had the highest sensitivity to high concentrations (20 to 200 ppm) of ammonia, with the addition of 2 g / L zinc acetate being the best.

[0083] Figure 5The results showed that, under low concentration (0.1–20 ppm) ammonia conditions, the prepared sensor had poorer sensitivity when using only sodium silicate and zinc acetate electrolyte (electrolyte group (2)) compared to the electrolyte group (electrolyte groups (4)–(6)) which also used sodium stannate trihydrate. The best result was achieved by adding an additional 1 g / L of sodium stannate trihydrate.

[0084] Example 3: Effect of different humidity levels on the sensitivity of ammonia detection

[0085] The detection system was performed according to Example 2, using electrolyte groups (2), (4) to (6) of Example 2. Before injecting ammonia, different saturated solutions (ammonium nitrate, potassium sulfate, hydrochloric acid, etc.) were injected to establish different humidity environments (17%, 57%, and 98%). The sensors prepared with the above four electrolyte groups were tested for resistivity sensitivity (K = Ra / Rg) of low-concentration (0.1–20 ppm) ammonia. The results are shown in […]. Figure 6-9 ;

[0086] according to Figure 6-9 It can be seen that electrolyte groups (4) to (6) exhibit excellent sensing performance under various humidity conditions, which is better than electrolyte group (2). They can respond with high sensitivity to low concentration of NH3 under high humidity conditions. At the same time, the effect is best when sodium stannate trihydrate is added at a concentration of 1 g / L.

[0087] Example 4: Gas Selectivity Test and Fitting Curve

[0088] 1. Gas selectivity test

[0089] The detection system was operated as described in Example 2. Once the sensor stabilized at the preset temperature, a solution of a preset gas (20 ppm of ammonia, nitrogen, carbon dioxide, hydrogen sulfide, and acetone) was added dropwise. Results are shown below. Figure 10 ; Figure 10 The results showed that at 180℃ and 20ppm, among the various volatile gases, the Ra / Rg value of the sensor for ammonia was significantly higher than that for the other volatile gases, indicating that it has extremely high sensitivity and strong selectivity for ammonia.

[0090] 2. Fitting curve experiment at different concentrations

[0091] The detection system in Example 2 is used as a reference. Once the sensor stabilizes at the preset temperature, ammonia solutions of different concentrations (0.1ppm, 0.5ppm, 1ppm, 5ppm, 10ppm, 20ppm) are added dropwise. Figure 11 The results show that the sensor of the present invention exhibits a good linear relationship (R0) for detecting ammonia. 2 =0.955).

[0092] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A pure titanium composite coating sensor for detecting low concentrations of ammonia, characterized in that, The device includes pure titanium material, a micro-arc oxidation coating, and an electrode. The micro-arc oxidation coating is applied to the surface of the pure titanium material via micro-arc oxidation using an electrolyte of sodium silicate, sodium stannate trihydrate, and zinc acetate. The electrode is disposed on the micro-arc oxidation coating. The electrolyte contains sodium silicate at a concentration of 5-8 g / L, zinc acetate at a concentration of 1.5-2.5 g / L, and sodium stannate trihydrate at a concentration of 0.5-1.5 g / L.

2. The sensor according to claim 1, characterized in that, The pure titanium material includes TA1~TA4 industrial pure titanium materials.

3. The sensor according to claim 1, characterized in that, The electrode is an interdigitated electrode.

4. The use of the sensor according to any one of claims 1-3 in detecting low concentrations of ammonia or in preparing products for detecting low concentrations of ammonia.

5. The application according to claim 4, characterized in that, The low-concentration ammonia gas includes ammonia gas at concentrations of 0.1 to 20 ppm.

6. The method for preparing the sensor according to claim 1, characterized in that, include: Step 1: Pre-treatment of pure titanium material, including grinding, degreasing, and cleaning; Step 2: The pretreated pure titanium material is subjected to micro-arc oxidation in an electrolyte of sodium silicate, sodium stannate trihydrate and zinc acetate to form a micro-arc oxidation coating. Step 3: Set electrodes on the micro-arc oxidation coating to obtain the sensor.

7. A product for detecting low concentrations of ammonia, characterized in that, The device includes a device for recording changes in resistance and a sensor as described in any one of claims 1-3, wherein the electrodes on the device and the sensor are connected by wires.

8. The product according to claim 7, characterized in that, The device for recording changes in resistance values ​​includes a multimeter and a data processor.

9. A method for detecting low concentrations of ammonia, characterized in that, The sensor described in any one of claims 1-3 is placed in ammonia standard samples of different concentrations, and a standard curve of resistance change data and ammonia concentration is established by a device that records the change of resistance value; then the sensor is placed in the environment to be tested, the resistance change data is obtained, and the concentration of ammonia in the environment to be tested is obtained by the standard curve.

Images