A high-performance TiO2@In2O3 / Pd sensitive film for a MEMS gas sensor, a synthesis method thereof and a MEMS gas sensor

Abstract

The application belongs to the technical field of sensitive materials, and discloses a high-performance TiO2@In2O3 / Pd sensitive film for a MEMS gas sensor, a synthesis method thereof and a MEMS gas sensor. The method comprises the following steps: synthesizing mesoporous TiO2 nanoparticle balls; mixing indium salt, an alkaline compound, a surfactant and the mesoporous TiO2 nanoparticle balls uniformly, and then performing hydrothermal reaction; centrifuging, washing and drying the product of the hydrothermal reaction, and then performing first annealing treatment in an air atmosphere to obtain In2O3-coated titanium dioxide nanoparticle balls TiO2@In2O3; modifying palladium nanoparticles to the nanoparticle balls TiO2@In2O3 by a solution method, centrifuging, washing and drying, and then performing second annealing treatment in a hydrogen atmosphere to obtain In2O3-coated titanium dioxide nanoparticle balls TiO2@In2O3 / Pd with Pd modification; and manufacturing the nanoparticle balls TiO2@In2O3 / Pd into a sensitive film. The sensitive film manufactured by the above method can improve the sensitivity of gas detection.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field related to sensitive materials, and more particularly relates to a high-performance TiO2@In2O3 / Pd sensitive film for a MEMS gas sensor, a synthesis method thereof and a MEMS gas sensor. BACKGROUND

[0002] A semiconductor gas sensor detects the composition or concentration of a gas by using a change in the resistance of a semiconductor sensitive material when the semiconductor sensitive material contacts the gas. The gas and the sensitive material undergo an oxidation-reduction reaction, which causes the resistance of the sensitive material to change. The change in the resistance is detected to achieve gas detection.

[0003] Titanium dioxide (TiO2) is an excellent photocatalytic material that exhibits excellent catalytic activity under light excitation. The excited titanium dioxide can undergo an oxidation reaction with volatile organic compounds (VOCs), which changes the resistance value. Therefore, titanium dioxide can be used to detect VOC gas, and has certain potential value in the detection of H2S. Therefore, titanium dioxide is commonly used as a semiconductor sensitive material for gas sensors, and is made into a titanium dioxide sensor.

[0004] However, using single titanium dioxide as a sensitive material has a high lower limit for detecting gas. When the gas concentration is low, it is difficult to trigger a response, or the response is weak, that is, the sensitivity of gas detection is low. SUMMARY

[0005] In view of the above defects or improvement needs of the prior art, the application provides a high-performance TiO2@In2O3 / Pd sensitive film for a MEMS gas sensor, a synthesis method thereof and a MEMS gas sensor, which aims to improve the sensitivity of gas detection.

[0006] To achieve the above-mentioned purpose, the application provides a synthesis method of a high-performance TiO2@In2O3 / Pd sensitive film for a MEMS gas sensor, which comprises the following steps:

[0007] Step S1: Synthesis of mesoporous TiO2 nanoparticle spheres;

[0008] Step S2: The indium salt, the basic compound, the surfactant and the mesoporous TiO2 nanoparticle spheres are uniformly mixed, and then subjected to a hydrothermal reaction. The product of the hydrothermal reaction is subjected to centrifugation, washing and drying, and then subjected to a first annealing treatment in an air atmosphere to obtain In2O3-coated titanium dioxide nanoparticle spheres TiO2@In2O3;

[0009] Step S3: modifying the palladium nanoparticle to the nanoparticle ball TiO2@In2O3 by solution method, centrifuging, washing and drying, and then performing second annealing treatment under hydrogen atmosphere to obtain the In2O3-coated and Pd-modified titanium dioxide nanoparticle ball TiO2@In2O3 / Pd;

[0010] Step S4: making the nanoparticle ball TiO2@In2O3 / Pd into the sensitive thin film.

[0011] In optional embodiments, in step S1, the synthesis of mesoporous TiO2 nanoparticle ball includes:

[0012] Step S11: dissolving the structure-directing agent alkylamine in ethanol and stirring to form a transparent solution;

[0013] Step S12: stirring the transparent solution and adding strong base strong acid salt during stirring, then adding titanium polyol and mixing uniformly, and standing to make the solution have stable precipitate;

[0014] Step S13: centrifuging, washing and drying the precipitate after standing to obtain powder;

[0015] Step S14: uniformly mixing the powder, ethanol and water and performing hydrothermal reaction;

[0016] Step S15: centrifuging, washing and drying the product of hydrothermal reaction to obtain the mesoporous TiO2 nanoparticle ball.

[0017] In optional embodiments, the structure-directing agent alkylamine contains one or more of methylamine, dodecylamine or hexadecylamine, the strong base strong acid salt contains one or more of KCl, NaCl or NaNO3, and the titanium polyol contains one or more of titanium isopropoxide, titanium ethylene glycol and titanium tetra-n-butyl alcohol;

[0018] In step S11 and step S12, the proportions of the structure-directing agent alkylamine, ethanol, strong base strong acid salt and titanium isopropoxide satisfy: (0.1-2.0) g structure-directing agent alkylamine: (18-22) ml ethanol: (0.3-0.5) ml 0.1M strong base strong acid salt: (4-6) ml titanium isopropoxide;

[0019] In step S14, the proportions of the powder, ethanol and water satisfy: (0.8-1.2) g powder: (18-22) ml ethanol: (8-12) ml water.

[0020] In optional embodiments, in step S2, the indium salt contains one or more of indium nitrate, indium chloride or indium acetate, the basic compound contains sodium citrate, and the surfactant contains urea.

[0021] In an optional embodiment, in step S3, the palladium nanoparticle is modified by the nanoparticle ball TiO2@In2O3 through a solution method, comprising:

[0022] The nanoparticle ball TiO2@In2O3, palladium salt, palladium salt reducing agent and deionized water are mixed uniformly, and the palladium salt reducing agent is used to reduce high-valence palladium ions in the palladium salt into palladium single element and embed in the nanoparticle ball TiO2@In2O3.

[0023] In an optional embodiment, in the nanoparticle ball TiO2@In2O3, the atomic number ratio of palladium to titanium ranges from 0.1% to 5%.

[0024] In an optional embodiment, the annealing temperature of the first annealing treatment is 450-550℃, and the annealing temperature of the second annealing treatment is 250-350℃.

[0025] In an optional embodiment, in step S4, the nanoparticle ball TiO2@In2O3 / Pd is made into the sensitive thin film, comprising:

[0026] The nanoparticle ball TiO2@In2O3 / Pd is made into the sensitive thin film through an air / water interface self-assembly method.

[0027] The application further provides a high-performance TiO2@In2O3 / Pd sensitive thin film for a MEMS gas sensor, wherein the sensitive thin film is made of a nanoparticle ball TiO2@In2O3 / Pd, and the nanoparticle ball TiO2@In2O3 / Pd is a titanium dioxide nanoparticle ball coated with In2O3 and modified with Pd.

[0028] The application further provides a MEMS gas sensor comprising the high-performance TiO2@In2O3 / Pd sensitive thin film as described above.

[0029] Overall, compared with the prior art, the above technical solutions conceived by the application mainly have the following beneficial effects:

[0030] The application provides a high-performance TiO2@In2O3 / Pd sensitive film synthesis method for a MEMS gas sensor. In the application, TiO2 nanoparticle balls are synthesized first, TiO2 is an excellent light excitation material and exhibits excellent photocatalytic activity under UV light, and the TiO2 nanoparticle balls can be used as the main structure of the sensitive film, so that the sensitive film can be activated by light activation, which can reduce the power consumption of the device and has higher safety performance. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 is a step flow chart of the high-performance TiO2@In2O3 / Pd sensitive film synthesis method for a MEMS gas sensor in an embodiment of the application;

[0032] Figure 2 is an SEM diagram of the mesoporous TiO2 nanoparticle balls in an embodiment of the application;

[0033] Figure 3 is a component mapping diagram of the nanoparticle ball TiO2@In2O3 / Pd in an embodiment of the application;

[0034] Figure 4are SEM images of different nanoparticle spheres, wherein (a) is an SEM image of TiO2 at different scales, (b) is an SEM image of TiO2@10In2O3 at different scales, (c) is an SEM image of TiO2@20In2O3 at different scales, and (d) is an SEM image of TiO2@30In2O3 at different scales;

[0035] Figure 5 are response curve diagrams of gas sensors corresponding to different nanoparticle spheres under UV light excitation to H2S gas, wherein (a) is a resistance change curve, and (b) is a response change curve;

[0036] Figure 6 are diagrams of the relationship between dynamic response and gas concentration of gas sensors corresponding to different nanoparticle spheres;

[0037] Figure 7 are SEM images of a MEMS sensor and a sensitive film thereof in an embodiment of the present application, wherein (a) is a MEMS sensor wafer structure, (b) is a set of interdigital structures in the MEMS sensor, (c) is a top view of the sensitive film, and (d) is a front view of the sensitive film. DETAILED DESCRIPTION

[0038] In order to make the objectives, technical solutions and advantages of the present application clearer, the present application is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and do not limit the present application. In addition, the technical features involved in each embodiment of the present application described below can be combined with each other as long as they do not conflict with each other.

[0039] The present application provides a high-performance TiO2@In2O3 / Pd sensitive film synthesis method for a MEMS gas sensor, as shown in Figure 1 As shown in the step flow chart of the high-performance TiO2@In2O3 / Pd sensitive film synthesis method for a MEMS gas sensor in an embodiment of the present application, the method comprises steps S1 to S4, and the steps are described below.

[0040] Step S1: Synthesis of mesoporous TiO2 nanoparticle spheres.

[0041] Specifically, mesoporous TiO2 nanoparticle spheres can be synthesized by a conventional method, for example, mesoporous TiO2 can be synthesized under the action of a structure-directing agent alkylamine and a strong base strong acid salt.

[0042] In an embodiment, mesoporous TiO2 nanoparticle spheres can be synthesized by the following five steps.

[0043] Step S11: Dissolve the structure-directing agent alkylamine in ethanol and stir to form a transparent solution.

[0044] Step S12: Stir the transparent solution and add the strong base-strong acid salt during stirring, then add the titanium polyol and mix well, and let stand to make the solution have stable precipitates.

[0045] In specific operation, the strong base-strong acid salt is added while stirring the transparent solution, so that the reaction can be more complete. After the addition of the strong base-strong acid salt is completed, the titanium polyol is added, and the reagents are mixed well under vigorous stirring at room temperature, and then stand for a period of time, so that the solution becomes stable precipitates, generally need to stand for 15h-20h, for example, stand for 18h.

[0046] In this process, the titanium polyol provides a titanium source, and the strong base-strong acid salt acts as a template for regulating the mesoporous structure.

[0047] Among them, the structure-directing agent alkylamine includes one or more of methylamine, dodecylamine or hexadecylamine, the strong base-strong acid salt includes one or more of KCl, NaCl or NaNO3, and the titanium polyol includes titanium isopropoxide, titanium ethylene glycol and titanium tetra-n-butyl alcohol, etc.

[0048] In the above steps, the ratio of the structure-directing agent alkylamine, ethanol, strong base-strong acid salt, and titanium polyol can be adjusted to control the pore structure and size of the mesoporous TiO2. In a preferred embodiment, the ratio of the structure-directing agent alkylamine, ethanol, strong base-strong acid salt, and titanium isopropoxide satisfies: (0.1-2.0) g structure-directing agent alkylamine: (18-22) ml ethanol: (0.3-0.5) ml 0.1M strong base-strong acid salt: (4-6) ml titanium isopropoxide. Under this ratio, the obtained precursor can subsequently synthesize TiO2 with uniform size and mesoporous structure.

[0049] Step S13: Centrifuge, wash and dry the precipitates after standing to obtain a powder.

[0050] At this time, the obtained powder is the precursor of mesoporous TiO2.

[0051] Step S14: Mix the powder, ethanol and water uniformly and perform a hydrothermal reaction.

[0052] At this time, mesoporous TiO2 nanoparticle spheres can be generated by hydrothermal reaction. In specific operation, the temperature range of the hydrothermal reaction can be 130℃-170℃, for example, it can be set to 150℃.

[0053] In specific operation, the ratio of the powder, ethanol and water satisfies: (0.8-1.2) g powder: (18-22) ml ethanol: (8-12) ml water.

[0054] Step S15: centrifuging, washing and drying the product of the hydrothermal reaction to obtain the mesoporous TiO2 nanoparticle spheres. It can be understood that, since no annealing treatment is performed, the sample obtained at this time may still contain residual organic matter, which is removed in the annealing operation in step S2, and no annealing is performed in step S1, which is also to facilitate the coating of In2O3 in step S2.

[0055] As shown in FIG. 2, the obtained TiO2 nanoparticle spheres have a mesoporous structure, and the pore size of the TiO2 nanoparticle spheres can be controlled in the range of 2-50 nm, and in this size range, the mesoporous structure is exhibited. In a preferred manner, by adjusting the ratio of the reagents, the size distribution of the TiO2 nanoparticle spheres is more uniform, which is conducive to improving the consistency of the dynamic response of the sensor to the gas. Figure 2

[0056] After the mesoporous TiO2 nanoparticle spheres are synthesized, step S2 is performed.

[0057] Step S2: first uniformly mixing the indium salt, the alkaline compound, the surfactant and the mesoporous TiO2 nanoparticle spheres, then performing a hydrothermal reaction, and then centrifuging, washing and drying the product of the hydrothermal reaction, and then performing a first annealing treatment in an air atmosphere to obtain the In2O3-coated titanium dioxide nanoparticle spheres TiO2@In2O3.

[0058] At this time, through the hydrothermal reaction, In2O3 nucleates and grows on the surface of TiO2 to form the In2O3-coated TiO2 nanoparticle spheres, and the surfactant functions to promote the rapid nucleation of In2O3. In specific operations, the temperature range of the hydrothermal reaction can be 110-150°C, for example, it can be set to 130°C.

[0059] In the formula, the indium salt contains one or more of indium nitrate, indium chloride or indium acetate, the alkaline compound contains sodium citrate, and the surfactant contains urea.

[0060] In this step, the ratio of the indium salt and the mesoporous TiO2 nanoparticle spheres can be adjusted to control the amount of In2O3 coating, and in a preferred embodiment, the ratio of the indium salt and the mesoporous TiO2 nanoparticle spheres satisfies (0.01-1.0) g:0.1 g, and within this range, the performance of the sensor is improved more obviously.

[0061] ​After the hydrothermal reaction, the resulting hydrothermal product is centrifuged, washed, and dried, and then subjected to a first annealing heat treatment in an air atmosphere. The annealing treatment in an air atmosphere stabilizes the structure of the mesoporous TiO2, thereby obtaining In2O3-coated titanium dioxide nanoparticle spheres TiO2@In2O3. In a specific embodiment, the annealing temperature of the first annealing heat treatment can be selected from 450°C to 550°C, and the annealing time can be selected from 1.5h to 2.5h. For example, annealing at 500°C for 2h can be selected to obtain nanoparticle spheres TiO2@In2O3.

[0062] Step S3: palladium nanoparticles are modified on the nanoparticle spheres TiO2@In2O3 by a solution method, and after centrifugation, washing and drying, a second annealing treatment is performed under a hydrogen atmosphere to obtain In2O3-coated and Pd-modified titanium dioxide nanoparticle spheres TiO2@In2O3 / Pd.

[0063] Specifically, the nanoparticles TiO2@In2O3, palladium salt, palladium salt reducing agent and deionized water can be evenly mixed. The palladium salt reducing agent can reduce the high-valent palladium ions in the palladium salt into a single palladium substance and embed it in the nanoparticles TiO2@In2O3. In actual operation, the content of palladium atoms can be flexibly adjusted to adjust the response characteristics of the sensor. For example, in the nanoparticles TiO2@In2O3, the ratio of the number of palladium and tin atoms ranges from 0.1% to 5%. Within this range, a good Pd particle modification effect can be achieved. In one embodiment, the palladium salt can be selected from one or more of dichlorotetramminepalladium, palladium nitrate and palladium chloride, and the palladium salt reducing agent is generally selected from sodium borohydride.

[0064] After the reaction, the product is centrifuged, washed, and dried, and then subjected to a second annealing treatment in a hydrogen atmosphere. The annealing treatment in a hydrogen atmosphere can reduce the well-oxidized Pd to zero-valent Pd, thereby obtaining In2O3-coated and Pd-modified titanium dioxide nanoparticles TiO2@In2O3 / Pd. In a specific embodiment, the second annealing heat treatment can be performed at a temperature of 250°C to 350°C and for a time of 1.5 hours to 2.5 hours. For example, annealing at 300°C for 2 hours can be performed to obtain the TiO2@In2O3 / Pd nanoparticles.

[0065] like Figure 3 The figure shows the composition mapping diagram of the nanoparticle sphere TiO2@In2O3 / Pd in ​​one embodiment. It can be seen from the figure that the nanoparticle sphere TiO2@In2O3 / Pd contains Ti, O, In, and Pd, indicating that In and Pd have been successfully added to the TiO2 nanoparticle sphere.

[0066] Step S4: The nanoparticle ball TiO2@In2O3 / Pd is made into a sensitive thin film.

[0067] In a preferred mode, the nanoparticle ball TiO2@In2O3 / Pd can be made into a sensitive thin film by an air / water interface self-assembly method, and the specific operation is as follows:

[0068] First, the nanoparticle ball is hydrophobized under dodecyl treatment, and then an ethanol dispersion solution of the TiO2@In2O3 / Pd nanoparticle ball is prepared. Finally, the dispersion solution is dropped drop by drop on the inner wall of a beaker containing deionized water, and a monolayer nanoparticle ball thin film is finally formed at the water / air interface. Finally, the thin film can be obtained by the method of MEMS device or wafer fishing.

[0069] In the specific operation, the composition ratio of indium salt can be adjusted to control the coating amount of In2O3, so as to control the sensitivity of the gas sensor.

[0070] The following selects In(NO3)3 as an example of indium salt, and gives the comparison of sensor performance under several different ratios of indium and titanium atoms.

[0071] Comparative Example

[0072] (1) 0.5 g of hexadecylamine was dissolved in 20 ml of ethanol and stirred to form a transparent solution. Then 0.4 ml of 0.1M KCl was added to the solution under constant stirring. 5 ml of titanium isopropoxide was added to the solution, which was stirred vigorously at room temperature and left to stand for 18 h. Then the powder was obtained by centrifugation, washing and drying. 1.0 g of dry powder was mixed with 20 ml of ethanol and 10 ml of H2O to form a mixed solution, and finally hydrothermal reaction was carried out at a temperature of 150℃ for 24 h.

[0073] (2) The hydrothermal product obtained in step (1) was subjected to centrifugation, washing and drying operations, and was subjected to 500℃ annealing heat treatment in air atmosphere for 2 h, and the obtained sample was marked as nanoparticle ball TiO2.

[0074] Example 1

[0075] (1) 0.5 g of hexadecylamine was dissolved in 20 ml of ethanol and stirred to form a transparent solution. Then 0.4 ml of 0.1M KCl was added to the solution under constant stirring. 5 ml of titanium isopropoxide was added to the solution, which was stirred vigorously at room temperature and left to stand for 18 h. Then the powder was obtained by centrifugation, washing and drying. 1.0 g of dry powder was mixed with 20 ml of ethanol and 10 ml of H2O to form a mixed solution, and finally hydrothermal reaction was carried out at a temperature of 150℃ for 24 h.

[0076] (2) 0.1 g of the sample obtained in (1) was mixed with 0.1 g of indium nitrate (In(N03)3-4.5H20), 0.1 g of sodium citrate (C6H5Na307), 0.025 g of urea and 40 ml of deionized water, and then transferred into a reaction kettle, followed by hydrothermal reaction at a temperature of 130 °C for 6 h;

[0077] (3) The hydrothermal product obtained in step (2) was subjected to centrifugation, washing and drying operations, and was subjected to annealing heat treatment at 500 °C for 2 h in an air atmosphere, and the sample obtained was marked as nanoparticle sphere Ti02@10In203.

[0078] Example 2

[0079] (1) 0.5 g of hexadecylamine was dissolved in 20 ml of ethanol and stirred to form a transparent solution. Then 0.4 ml of 0.1 M KCl was added to the solution under constant stirring. 5 ml of titanium isopropoxide was added to the solution, which was stirred vigorously at room temperature and left to stand for 18 h. Then the powder was obtained by centrifugation and drying, 1.0 g of the dry powder was mixed with 20 ml of ethanol and 10 ml of H20 to form a mixed solution, and finally hydrothermal reaction was carried out at a temperature of 150 °C for 24 h;

[0080] (2) 0.1 g of the sample obtained in (1) was mixed with 0.2 g of indium nitrate (In(N03)3-4.5H20), 0.2 g of sodium citrate (C6H5Na307), 0.030 g of urea and 40 ml of deionized water, and then transferred into a reaction kettle, followed by hydrothermal reaction at a temperature of 130 °C for 6 h;

[0081] (3) The hydrothermal product obtained in step (2) was subjected to centrifugation, washing and drying operations, and was subjected to annealing heat treatment at 500 °C for 2 h in an air atmosphere, and the sample obtained was marked as nanoparticle sphere Ti02@20In203.

[0082] Example 3

[0083] (1) 0.5 g of hexadecylamine was dissolved in 20 ml of ethanol and stirred to form a transparent solution. Then 0.4 ml of 0.1 M KCl was added to the solution under constant stirring. 5 ml of titanium isopropoxide was added to the solution, which was stirred vigorously at room temperature and left to stand for 18 h. Then the powder was obtained by centrifugation and drying, 1.0 g of the dry powder was mixed with 20 ml of ethanol and 10 ml of H20 to form a mixed solution, and finally hydrothermal reaction was carried out at a temperature of 150 °C for 24 h;

[0084] (2) 0.1 g of the sample obtained in (1) was mixed with 0.3 g of indium nitrate (In(NO3)3·4.5H2O), 0.3 g of sodium citrate (C6H5Na3O7), 0.045 g of urea, and 40 ml of deionized water, and then transferred to a reactor and subjected to a hydrothermal reaction at 130 °C for 6 h;

[0085] (3) The hydrothermal product obtained in step (2) is centrifuged, washed, and dried, and annealed at 500° C. for 2 h in an air atmosphere. The obtained sample is labeled as nanoparticle sphere TiO2@30In2O3.

[0086] Example 4

[0087] (1) Dissolve 0.5 g of hexadecylamine in 20 ml of ethanol and stir to form a transparent solution. Then, add 0.4 ml of 0.1 M KCl to the solution while stirring continuously. Add 5 ml of titanium isopropoxide to the solution, stir vigorously at room temperature, and let it stand for 18 hours. Then, centrifuge, wash, and dry to obtain a powder. Prepare a mixed solution of 1.0 g of the dry powder with 20 ml of ethanol and 10 ml of H2O. Finally, perform a hydrothermal reaction at 150°C for 24 hours.

[0088] (2) 0.1 g of the sample obtained in (1) was mixed with 0.2 g of indium nitrate (In(NO3)3·4.5H2O), 0.2 g of sodium citrate (C6H5Na3O7), 0.030 g of urea, and 40 ml of deionized water, and then transferred to a reactor and subjected to a hydrothermal reaction at 130 °C for 6 h;

[0089] (3) The hydrothermal product obtained in step (2) is centrifuged, washed, and dried, and then annealed at 500° C. for 2 h in an air atmosphere.

[0090] (4) 0.1 g of the sample obtained in step (3) was mixed evenly with 0.005 g of dichlorotetraamminepalladium, 0.1 g of sodium borohydride, and 10 ml of deionized water, and then centrifuged, washed, and dried.

[0091] (5) The sample obtained in step (4) was annealed at 300° C. in a hydrogen atmosphere, and the obtained sample was labeled as nanoparticle sphere TiO2@20In2O3 / Pd.

[0092] like Figure 4 Shown are SEM images of different nanoparticle spheres, where (a) is the SEM image of TiO2 at different scales, (b) is the SEM image of TiO2@10In2O3 at different scales, (c) is the SEM image of TiO2@20In2O3 at different scales, and (d) is the SEM image of TiO2@30In2O3 at different scales.

[0093] likeFigure 5 Fig. 2 shows the response curves of the gas sensors corresponding to different nanoparticle spheres under UV light excitation to H2S gas, wherein (a) is the resistance change curve, and (b) is the response change curve. As can be seen from the figure, compared with pure TiO2 nanoparticle spheres, whether only In2O3 coating is performed or In2O3 coating is performed on the basis of Pd modification, the response characteristics of the corresponding gas sensors are improved, and compared with only In2O3 coating, the effect of the material obtained by performing In2O3 coating on the basis of Pd modification is better.

[0094] As shown in Fig. 1, the TiO2@In2O3 / Pd nanoparticle spheres are prepared by the following steps: Figure 6 Fig. 3 shows the relationship diagram of the dynamic response of the gas sensors corresponding to different nanoparticle spheres and the gas concentration. By comparing the sensors corresponding to pure TiO2 nanoparticle spheres, TiO2@In2O3 nanoparticle spheres only coated with In2O3 and TiO2@In2O3 / Pd nanoparticle spheres coated with In2O3 on the basis of Pd modification, it is found that TiO2@In2O3 is better than TiO2, and TiO2@In2O3 / Pd is better than TiO2@In2O3, which indicates that the technical scheme of the present application can improve the sensitivity of the sensor to gas detection.

[0095] Correspondingly, the present application also relates to a high-performance TiO2@In2O3 / Pd sensitive film for a MEMS gas sensor. The sensitive film is made of TiO2@In2O3 / Pd nanoparticle spheres. The TiO2@In2O3 / Pd nanoparticle spheres are In2O3-coated and Pd-modified titanium dioxide nanoparticle spheres. Specifically, the sensitive film can be synthesized by the synthesis method introduced above.

[0096] Correspondingly, the present application also relates to a MEMS gas sensor comprising the sensitive film introduced above. Specifically, the gas sensor comprises a MEMS chip and a sensitive film covering the surface of the MEMS chip, as shown in Fig. 4. Figure 7 Fig. 5 shows the structure diagram of the MEMS sensor formed in an embodiment and the SEM diagram of the sensitive film thereof. The target gas in the environment will have an oxidation reaction with the sensitive film, causing the resistance of the sensitive film to change. The MEMS chip detects the resistance of the sensitive film to realize the detection of the target gas.

[0097] The technical features of the above-described embodiments can be combined in any manner. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described, however, as long as the combinations of the technical features do not exist contradictions, they should be considered as the scope of the present application. It should be noted that the “in an embodiment of the present application”, “for example”, “for instance” and the like in the present application are intended to illustrate the present application, rather than to limit the present application.

[0098] The above embodiments only express several implementation manners of the present application, which are described in a more specific and detailed manner, but should not be understood as a limitation to the scope of the application. It should be noted that, for those skilled in the art, several modifications and improvements can be made without departing from the concept of the present application, which are all within the protection scope of the present application.

Claims

1. A method for synthesizing high-performance TiO2@In2O3 / Pd sensitive thin films for MEMS gas sensors, characterized in that: include: Step S1: Synthesizing mesoporous TiO2 nanoparticles; Step S2: first, the indium salt, the alkaline compound, the surfactant and the mesoporous TiO2 nanoparticles are uniformly mixed and then subjected to a hydrothermal reaction. Then, the product of the hydrothermal reaction is centrifuged, washed and dried, and then subjected to a first annealing treatment in an air atmosphere to obtain In2O3-coated titanium dioxide nanoparticles TiO2@In2O3; Step S3: modifying the nanoparticle spheres TiO2@In2O3 with palladium nanoparticles by a solution method, centrifuging, washing, and drying, and then performing a second annealing treatment under a hydrogen atmosphere to obtain In2O3-coated and Pd-modified titanium dioxide nanoparticle spheres TiO2@In2O3 / Pd; Step S4: preparing the nanoparticle spheres TiO2@In2O3 / Pd into the sensitive film.

2. The method for synthesizing a high-performance TiO2@In2O3 / Pd sensitive thin film for a MEMS gas sensor according to claim 1, wherein: In step S1, the synthesis of mesoporous TiO2 nanoparticles comprises: Step S11: dissolving a structure-directing agent alkylamine in ethanol and stirring to form a transparent solution; Step S12: stirring the transparent solution and adding a strong base and a strong acid salt during the stirring period, then adding titanium polyol and mixing them evenly, and allowing the solution to stand until a stable precipitate appears; Step S13: centrifuging, washing and drying the precipitate after standing to obtain a powder; Step S14: uniformly mixing the powder, ethanol and water and performing a hydrothermal reaction; Step S15: centrifuging, washing and drying the product of the hydrothermal reaction to obtain the mesoporous TiO2 nanoparticle spheres.

3. The method for synthesizing a high-performance TiO2@In2O3 / Pd sensitive thin film for a MEMS gas sensor according to claim 2, wherein: The structure-directing agent alkylamine comprises one or more of methaneamine, dodecylamine or hexadecylamine, the strong base and strong acid salt comprises one or more of KCl, NaCl or NaNO3, and the polyol titanium comprises one or more of titanium isopropoxide, titanium ethylene glycol and titanium tetra-n-butoxide; In step S11 and step S12, the ratio of the structure-directing agent alkylamine, ethanol, strong base strong acid salt, and titanium isopropoxide is as follows: (0.1-2.0) g structure-directing agent alkylamine: (18-22) ml ethanol: (0.3-0.5) ml 0.1 M strong base strong acid salt: (4-6) ml titanium isopropoxide; In step S14, the mixing ratio of powder, ethanol and water satisfies: (0.8-1.2) g powder: (18-22) ml ethanol: (8-12) ml water.

4. The method for synthesizing a high-performance TiO2@In2O3 / Pd sensitive thin film for a MEMS gas sensor according to claim 1, wherein: In step S2, the indium salt includes one or more of indium nitrate, indium chloride, or indium acetate, the alkaline compound includes sodium citrate, and the surfactant includes urea.

5. The method for synthesizing a high-performance TiO2@In2O3 / Pd sensitive thin film for a MEMS gas sensor according to claim 1, wherein: In step S3, palladium nanoparticles are modified on the nanoparticle spheres TiO2@In2O3 by a solution method, comprising: The nanoparticle balls TiO2@In2O3, palladium salt, palladium salt reducing agent and deionized water are mixed evenly. The palladium salt reducing agent is used to reduce high-valent palladium ions in the palladium salt into palladium element and embed the palladium into the nanoparticle balls TiO2@In2O3.

6. The method for synthesizing a high-performance TiO2@In2O3 / Pd sensitive thin film for a MEMS gas sensor according to claim 1, wherein: In the nanoparticle spheres TiO2@In2O3, the ratio of the number of palladium atoms to that of titanium atoms ranges from 0.1% to 5%.

7. The method for synthesizing a high-performance TiO2@In2O3 / Pd sensitive thin film for a MEMS gas sensor according to claim 1, wherein: The annealing temperature of the first annealing treatment is 450°C to 550°C; the annealing temperature of the second annealing treatment is 250°C to 350°C.

8. The method for synthesizing a high-performance TiO2@In2O3 / Pd sensitive thin film for a MEMS gas sensor according to claim 1, wherein: In step S4, the step of preparing the nanoparticle spheres TiO2@In2O3 / Pd into the sensitive film comprises: The nanoparticle spheres TiO2@In2O3 / Pd are prepared into the sensitive film through an air / water interface self-assembly method.

9. A high-performance TiO2@In2O3 / Pd sensitive film for MEMS gas sensors, characterized in that: The sensitive film is made of nanoparticle balls TiO2@In2O3 / Pd, and the nanoparticle balls TiO2@In2O3 / Pd are titanium dioxide nanoparticle balls coated with In2O3 and modified with Pd.

10. A MEMS gas sensor, characterized in that: It comprises the high-performance TiO2@In2O3 / Pd sensitive film as claimed in claim 9.

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