Ultrafast response titanium dioxide quantum dot / silicon dioxide composite film humidity sensor, preparation method and multifunctional application

Abstract

The present invention belongs to the field of sensor technology, and specifically relates to an ultrafast response titanium dioxide quantum dot / silicon dioxide composite film humidity sensor, a preparation method, and multifunctional applications. The sensor includes a sensing layer and a substrate, wherein the sensing layer is a titanium dioxide quantum dot / silicon dioxide film (TiO2QDs / SiO2), and the substrate can be an interdigitated electrode. The superhydrophilicity of TiO2QDs facilitates the high-speed adsorption and desorption of water on the film surface. The addition of SiO2 microsphere structures can further increase the specific surface area of the humidity-sensitive film and improve the humidity-sensitive performance of TiO2QDs. The humidity sensor of the present invention has excellent humidity sensing performance, including ultrafast response and recovery time, high sensitivity, good repeatability, and long-term stability. The sensor has application value in humidity alarms and voice recognition.

Description

Technical Field

[0001] The present invention belongs to the field of sensor technology, and in particular relates to an ultrafast response titanium dioxide quantum dot / silicon dioxide composite film humidity sensor, a preparation method and multifunctional applications. Background Art

[0002] Humidity measurement and control have become a crucial component of industrial production processes. Many industrial sites, such as those in the petrochemical, energy, and mining industries, require continuous and accurate humidity monitoring. With the continuous development of these industries, the performance requirements for humidity sensors are becoming increasingly stringent. This is particularly true for humidity monitoring in complex working conditions, such as oil and gas exploration and industrial safety monitoring. These applications require fast-response humidity sensors. Therefore, fast-response humidity sensors have long been a research hotspot.

[0003] The response speed of humidity sensors is generally related to the material's microstructure. Selecting a novel humidity-sensitive material is crucial for achieving rapid humidity response. Quantum dots, due to their nanoscale size and wide, tunable band gap, have attracted attention and have been extensively studied in photocatalysis, quantum information, and sensing applications. Existing humidity sensors typically require several seconds of waiting time for the sensor to reach a stable water absorption state. Due to this long response time, these conventional sensors may not meet the requirements for instant, rapid humidity measurement.

[0004] Therefore, there is an urgent need to develop a humidity sensor with fast response speed that can meet the needs of instant humidity measurement. Summary of the Invention

[0005] The present invention aims to address at least one of the problems existing in the aforementioned prior art. To this end, it provides an ultrafast-response titanium dioxide quantum dot / silicon dioxide composite film humidity sensor, its preparation method, and its multifunctional applications. The sensor exhibits excellent humidity sensing performance, including ultrafast response and recovery times, high sensitivity, good repeatability, and long-term stability; it has applications in humidity alarms and voice recognition.

[0006] To achieve the above objectives, the first aspect of the present invention provides an ultrafast response titanium dioxide quantum dot / silicon dioxide composite film humidity sensor, comprising a sensing layer and a substrate, wherein the sensing layer is titanium dioxide quantum dots / silicon dioxide thin film (TiO2 QDs / SiO2), and the substrate can be an interdigitated electrode.

[0007] A second aspect of the present invention provides a method for preparing an ultrafast response titanium dioxide quantum dot / silicon dioxide composite film humidity sensor, comprising the following steps:

[0008] (1) dispersing butyl titanate in a solvent, adjusting the acidity of the solution and then reacting in a water bath to prepare titanium dioxide quantum dots;

[0009] (2) mixing ammonia water, anhydrous ethanol and deionized water, and then mixing the mixture with an ethanol solution of ethyl orthosilicate to react and obtain silicon dioxide;

[0010] (3) The substrate is sequentially immersed in a mixed suspension of polystyrene sulfonate-SiO2 and a TiO2 QDs solution, and after drying, the titanium dioxide quantum dot / silicon dioxide composite film humidity sensor is obtained.

[0011] Furthermore, the solvent in step (1) is a mixed solvent of cyclohexane and anhydrous ethanol, and the volume ratio of cyclohexane and anhydrous ethanol is (1.5-2.0): (1.5-2.0); the pH value is 2-4, and appropriate acidity conditions are very important for controlling the morphology and properties of titanium dioxide quantum dots. This acidic environment promotes the reaction and can affect the size and morphology of titanium dioxide quantum dots; the reaction temperature is 68-72°C, and the reaction time is 9.5-10.5h.

[0012] Furthermore, in step (2), the mixing volume ratio of ammonia water, anhydrous ethanol and deionized water is (0.9-1.1): (1.5-2.0): (2.4-3.2), and the mixing volume ratio of ethyl orthosilicate to ethanol in the ethanol solution of ethyl orthosilicate is (0.9-1.1): (8-12); the reaction temperature is 20-25° C., and the reaction time is 1.8-2.2 h;

[0013] Furthermore, the concentration of SiO2 in the suspension of step (3) is 0.08-0.12 mg / mL, the mass concentration of sulfonic acid polystyrene is 0.8-1.2 mg / mL, and the concentration of the TiO2 QDs solution is 0.12-0.18 mg / mL; and the immersion time in step (3) is 18-22 min.

[0014] A third aspect of the present invention provides multifunctional applications of an ultrafast response titanium dioxide quantum dot / silicon dioxide composite film humidity sensor, wherein the multifunctional applications include a humidity alarm application and a voice recognition application.

[0015] In some embodiments, the multifunctional application further includes a respiratory rate detection application, a diaper moisture monitoring application, and a soil moisture monitoring application.

[0016] In some embodiments, the humidity alarm application performs humidity monitoring and high humidity alarm through a humidity monitoring and alarm system, which includes a TiO2 QDs / SiO2 composite film humidity sensor, an amplification module, an overvoltage protection module, a control module, an alarm module, a display module, and a power supply module connected in sequence.

[0017] In some embodiments, the control module is used to control the TiO2 QDs / SiO2 composite film humidity sensor to collect humidity signals, control the amplification module to amplify the humidity signals, control the overvoltage protection module to protect the circuit, control the alarm module to sound an alarm, control the display module to display the humidity signal and alarm results, and control the power supply module to power the circuit.

[0018] In some embodiments, the TiO2 QDs / SiO2 composite film humidity sensor converts a humidity signal into an electrical signal, and the electrical signal contains humidity information.

[0019] In some embodiments, the control module includes an analysis unit, which generates an alarm signal in response to detecting that the humidity is greater than a humidity threshold, and controls the alarm module to sound an alarm.

[0020] In some embodiments, the amplification module includes an LMC8041 operational amplifier, the overvoltage protection module includes a BAT54S chip, the control module is an STM32F103C6T6, the display module is an OLED display, and the power supply module is a 5V DC power supply.

[0021] In some embodiments, the speech recognition application recognizes speech humidity signals through a speech recognition system, the speech recognition system has a Transformer structure, and the speech recognition system includes a position encoding module, a fully connected layer, two multi-head attention modules, four Add&Norm modules and two feedforward networks. The position encoding module is respectively connected to the multi-head attention module one and the Add&Norm module one, the multi-head attention module one is connected to the Add&Norm module one, the Add&Norm module two, the Add&Norm module one, and the feedforward network one are connected in pairs, the multi-head attention module two is connected to the Add&Norm module two and the Add&Norm module three, the Add&Norm module three is respectively connected to the Add&Norm module four and the feedforward network two, and the Add&Norm module four is connected to the fully connected layer.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] (1) The present invention utilizes titanium dioxide quantum dots and silicon dioxide microspheres to prepare a humidity sensor film with ultrafast response through electrostatic self-assembly. The super-hydrophilicity of TiO2 contributes to the high-speed adsorption and desorption of water on the film surface. The addition of SiO2 microsphere structure can further increase the specific surface area of the humidity-sensitive film and improve the humidity-sensitive performance of TiO2 QDs. The humidity sensor of the present invention has excellent humidity sensing performance, including ultrafast response and recovery time, high sensitivity, good repeatability and long-term stability.

[0024] (2) The TiO2 QDs / SiO2 composite film humidity sensor has application value in humidity alarm and voice recognition. The humidity monitoring and alarm system can accurately monitor humidity and issue high humidity alarms, and the voice recognition system can identify the voice humidity signals of different testers. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 a-1c are the contact angle test graphs of TiO2 QDs, SiO2 and TiO2 QDs / SiO2 respectively; Figure 1 d is the XRD patterns of TiO2 QDs and TiO2 QDs / SiO2 samples;

[0026] Figure 2 a is the SEM image of SiO2; Figure 2 b is the TEM image of TiO2 QDs / SiO2 composite material; Figure 2 c is the HRTEM image of TiO2 QDs / SiO2 composite material; Figure 2 d-2f are the element mappings of Ti, O, and Si in TiO2QDs / SiO2 composites, respectively;

[0027] Figure 3 a-3d are the XPS spectra of TiO2 QDs / SiO2 sample, Ti 2p, Si 2p and O1s, respectively;

[0028] Figure 4 Schematic diagram of the humidity sensor testing device of the present invention;

[0029] Figure 5 a is the resistance change of sensors prepared with different SiO2 and TiO2 QDs concentration ratios at 43% RH; Figure 5 b is the response comparison between TiO2 QDs / SiO2 composite film humidity sensor and pure TiO2 QDs thin film sensor; Figure 5 c is the resistance response of the TiO2 QDs / SiO2 composite film humidity sensor under different RH environments; Figure 5 d is the humidity hysteresis curve of the TiO2 QDs / SiO2 composite film humidity sensor;

[0030] Figure 6 a is the repeatability test graph of TiO2 QDs / SiO2 composite film humidity sensor under 33%, 52%, 97% and 11% RH environments; Figure 6 b is the response of the TiO2 QDs / SiO2 composite film humidity sensor as the relative humidity changes; Figure 6 c is the impedance change diagram of TiO2QDs / SiO2 composite film humidity sensor under different humidity environments; Figure 6d is the long-term stability test graph of TiO2 QDs / SiO2 composite film humidity sensor under different humidity environments;

[0031] Figure 7a Schematic diagram of the sensor response speed test device; Figure 7b This is the response speed test result; Figure 7c This is the response / recovery time test diagram; Figure 7d This is a simulation experiment diagram of formation water production; Figure 7e This is the response time diagram of the sensor when water comes out of the formation under simulated environment;

[0032] Figure 8 a is a schematic diagram of the humidity sensing principle of the TiO2 QDs / SiO2 composite film humidity sensor; Figure 8 b-8c are charge density diagrams of H2O adsorbed on TiO2 QDs and TiO2 QDs / SiO2, respectively; Figure 8 d is the total density of states diagram of TiO2 QDs and TiO2 QDs / SiO2 system; Figure 8 e is the projected density of states diagram of TiO2 QDs / SiO2 system; Figure 8 f is the total state density image of TiO2 QDs / SiO2 before and after H2O adsorption; Figure 8 g is the projected density of states after TiO2QDs / SiO2 adsorbs H2O;

[0033] Figure 9 a is the voice humidity response test at different distances; Figure 9 b is a test chart of different respiratory rates; Figure 9 c is a diagram of diaper humidity detection; Figure 9 d is the fast response test diagram of the diaper film sensor; Figure 9 e is the soil humidity value and sensor resistance value after the soil is dried every 10 minutes; Figure 9 f is the response time diagram of the TiO2 QDs / SiO2 composite film humidity sensor detecting different soil humidity;

[0034] Figure 10 a is a structural diagram of the speech recognition system; Figure 10 b is the waveform of 10 test subjects speaking “sensor”; Figure 10 c is the loss function and accuracy curve of the speech recognition system; Figure 10 d is the confusion matrix of the speech recognition system;

[0035] Figure 11 Schematic diagram of the structure of the multi-head attention module in the speech recognition system. DETAILED DESCRIPTION

[0036] The principles and features of the present invention are described below with reference to examples. The examples are only used to explain the present invention and are not used to limit the scope of the present invention.

[0037] An ultrafast response titanium dioxide quantum dot / silicon dioxide composite film humidity sensor comprises the following steps:

[0038] (1) Preparation of titanium dioxide quantum dots (TiO2 QDs): 30 mL of cyclohexane and 30 mL of anhydrous ethanol were mixed and stirred at 25 °C for 10 min. After uniform mixing, 18 mL of butyl titanate was added and the stirring was continued for 30 min. Then, 9 mL of dilute hydrochloric acid was added to adjust the pH of the solution to 3. The resulting mixture was transferred to a 250 mL three-necked flask and condensed under reflux in a water bath at 70 °C for 10 h. Then, an appropriate amount of anhydrous ethanol was added to the above solution to the mouth of the three-necked flask, and the solution was stirred in a water bath until it turned white and the temperature dropped to natural room temperature. The product was centrifuged at 10,000 r for 15 min, washed, and dried to obtain the product.

[0039] (2) Preparation of silicon dioxide (SiO2): Silica was synthesized using the Stober method. 9 mL of concentrated ammonia, 16.25 mL of anhydrous ethanol, and 24.75 mL of deionized water were placed in a beaker and magnetically stirred at 1100 rpm for 10 min to prepare solution A. 4.5 mL of ethyl orthosilicate and 45.5 mL of ethanol were mixed uniformly to prepare solution B. Solution B was quickly added to solution A and reacted at 25°C for 2 h. The resulting mixture was centrifuged, washed, and dried to obtain the product SiO2 powder.

[0040] (3) Repeatedly ultrasonically clean the interdigitated electrodes with deionized water to remove impurities on the electrode surface, and then dry them in a nitrogen stream for later use;

[0041] (4) Prepare a mixed suspension of polystyrene sulfonate (PSS) and SiO2, where the SiO2 concentration in the suspension is 0.1 mg / mL and the mass concentration of polystyrene sulfonate is 1 mg / mL; then immerse the dried interdigitated electrode in the suspension and place it at room temperature for 20 minutes to allow a layer of PSS and SiO2 mixture to adhere to the electrode surface; then place the interdigitated electrode in deionized water and gently rinse for 10 seconds to remove loosely attached materials, and then dry it in a dry nitrogen flow. After this step, a very thin layer of PSS@SiO2 film will adhere to the surface of the interdigitated electrode;

[0042] (5) The above-mentioned interdigital electrodes were placed in a TiO2 QDs solution with a concentration of 0.15 mg / mL for 20 min. A layer of TiO2 QDs was attached to the surface of the PSS@SiO2 film using the principle of electrostatic self-assembly. The interdigital electrodes were then gently rinsed in deionized water for 10 s to remove the loosely attached TiO2 QDs and make the sensor's humidity-sensitive film thin enough. At this time, a TiO2 QDs@SiO2 structure was formed on the surface of the interdigital electrodes, and the sensor was completed.

[0043] Figure 1 a-1c are the contact angle test diagrams of TiO2 QDs, SiO2 and TiO2 QDs / SiO2 respectively. The measurements were made using the fixed drop method using the SL200B contact angle analyzer. The surface hydrophilicity of the sample was determined by the water contact angle. When the contact angle is greater than 90°, it is hydrophobic, and when it is less than 90°, it is hydrophilic. Figure 1 As can be seen from a-1c, the water contact angles of TiO2QDs, SiO2 and TiO2 QDs / SiO2 are 30.08°, 26.02° and 20.21°, respectively. The smaller the water contact angle, the better the hydrophilicity of the film; therefore, the measurement results of the water contact angle confirm that the hydrophilicity of the TiO2QDs / SiO2 composite film is better than that of a single sample. Figure 1 d is the XRD spectra of TiO2 QDs and TiO2QDs / SiO2 samples, which were obtained using a Rigaku D / Max 2500PC diffractometer (radiation source: Cu Kα, ) were analyzed in the diffraction angle range of 20°-90°. The diffraction peaks of TiO2QDs were located at 2θ of (101), (004), (200), (211), (204), (116), (301) and (224) planes, which were 25.29°, 37.98°, 47.97°, 54.22°, 62.79°, 70.19°, 75.05° and 82.53°, respectively. No peaks of other substances were observed in the XRD spectrum, indicating that the synthesis purity of titanium dioxide quantum dots was good. The diffraction characteristic peaks of TiO2QDs were clearly observed in the XRD of TiO2QDs / SiO2 composite samples. Since SiO2 is amorphous, no related diffraction peaks were observed.

[0044] The microstructures of TiO2QDs, SiO2 and TiO2QDs / SiO2 composites were studied using field emission scanning electron microscopy (SEM; Hitachi S-4800) and high-resolution transmission electron microscopy (HRTEM). Figure 2 a is the SEM image of SiO2, which shows that SiO2 is a clear regular sphere. Figure 2b-2c is the TEM image of TiO2 QDs / SiO2 composite material. It can be seen that TiO2 quantum dots are evenly distributed on and around SiO2 microspheres, and the surface of TiO2QDs has a clear strip lattice. Figure 2 The lattice spacing of TiO2 QDs shown in c is and They correspond to the (101), (004) and (200) crystal planes, respectively, further confirming the crystallinity of TiO2 QDs. Figure 2 Figures d-2f show the regional distribution of TiO2 QDs / SiO2 elements. Ti, Si, and O are evenly distributed in this region. The distribution of Ti further verifies the uniform distribution of TiO2 QDs on the SiO2 microspheres. The characterization and analysis of the composite material above demonstrate the successful fabrication of the TiO2 QDs / SiO2 composite thin film sensor.

[0045] Figure 3 a-3d are the XPS spectra of TiO2 QDs / SiO2 sample, Ti 2p, Si 2p and O1s, respectively. Figure 3 The full width scan spectrum of a shows that the sample contains O, Ti and Si; Figure 3 b and 3c, where the peak with a binding energy of 457.48 eV corresponds to Ti 3+ , the peaks at binding energies of 458.03 eV and 463.83 eV correspond to Ti 4+ , Ti 4+ Corresponding to 2p 3 / 2 and 2p 1 / 2 The electron orbital verifies that Ti 4+ 、Ti 3+ and the presence of TiO2, the peak with a binding energy of 102.88eV is the Si 2p signal, proving that Si 4+ existence. Figure 3 d is the high-resolution spectrum of O1s of TiO2 QDs / SiO2, where the peaks of O1s are O L , O V and O C , usually, O L represents lattice oxygen, O V represents vacant oxygen, O C Represents adsorbed oxygen, O V and O C The proportion and interaction of the sensors have a great influence on the performance of the sensor.

[0046] Performance Testing

[0047] like Figure 4This is a schematic diagram of the humidity sensor testing apparatus of the present invention. Saturated salt solutions of LiCl, CH₃COOK, MgCl₂, K₂CO₃, Mg(NO₃)₂, CuCl₂, NaCl, KCl, and K₂SO₄ were placed in nine sealed tanks for over 48 hours, with relative humidity levels of 11%, 23%, 33%, 43%, 52%, 67%, 75%, 85%, and 97%, respectively. An Agilent Keysight 34470A data logger was then used to establish a humidity detection platform. The humidity sensor's resistance under different humidity conditions was measured to investigate its humidity response characteristics and sensing mechanism.

[0048] Figure 5 a is the resistance change of sensors prepared with different SiO2 and TiO2 QDs concentration ratios at 43% RH. Humidity sensor films with SiO2 and TiO2 QDs concentration ratios of 0:1, 1:6, 1:3, 1:2, 2:3, 5:6 and 1:1 were studied. Obviously, when the SiO2 and TiO2 QDs concentration ratio was 2:3, the resistance response was the largest among the 7 samples. Therefore, the TiO2 QDs / SiO2 sensor was selected in subsequent experiments, and its optimal concentration ratio was 2:3, that is, the titanium dioxide quantum dot concentration was 0.15 mg / mL and the silicon dioxide concentration was 0.1 mg / mL. Figure 5 b is the response comparison of TiO2 QDs / SiO2 composite film humidity sensor and pure TiO2 QDs thin film sensor. It can be seen from the figure that the response of TiO2 QDs / SiO2 humidity sensor is higher than that of pure TiO2QDs sensor. Figure 5 c shows the resistance response of the TiO2 QDs / SiO2 composite film humidity sensor under different RH environments. When the RH level increases from 11% to 97%, the resistance of the TiO2 QDs / SiO2 composite film humidity sensor decreases from 523.2959 MΩ to 265.2418 kΩ, indicating that the sensor is super sensitive to humidity. Figure 5 d The hysteresis characteristics of the TiO2 QDs / SiO2 composite film humidity sensor to humidity were studied. The sensor hysteresis is defined as H=(R a -R d ) / S(%RH), where R a and R d is the sensor resistance during the adsorption and desorption process of water molecules, S is the sensor sensitivity, Figure 5 d shows that the TiO2 QDs / SiO2 humidity sensor has the maximum hysteresis of about 3.29% at 43% RH.

[0049] Repeatability test of TiO2 QDs / SiO2 composite film humidity sensor at 33%, 52%, 97% and 11% RH is shown in Figure 2. Figure 6As shown in a, the test at each humidity was repeated three times. The test results showed that no obvious changes were found in the three repeated tests, and the sensor has excellent repeatability. Figure 6 b is the response of the TiO2QDs / SiO2 composite film humidity sensor as the relative humidity changes. It can be concluded that in the range of 11-97% RH, the response of the TiO2 QDs / SiO2 composite film humidity sensor increases significantly with the increase of relative humidity. Figure 6 Figure c shows the impedance change of the TiO2 QDs / SiO2 composite film humidity sensor under different humidity environments. The impedance of the TiO2 QDs / SiO2 composite film humidity sensor dropped from about 523MΩ at 11% RH to 265.2Ω at 97% RH, a decrease of 6 orders of magnitude. The long-term stability of the TiO2 QDs / SiO2 composite film humidity sensor under 23, 43, 67 and 97% RH conditions is shown in Figure 3. Figure 6 As shown in Figure d, the response of the sensor did not change significantly within 30 days, indicating that the humidity sensor has good stability.

[0050] In order to detect the response time of the sensor, dry compressed argon gas is used as the medium gas (the relative humidity of compressed argon gas is below 10%), a chopper that periodically interrupts the airflow and high and low humidity argon gas are used to build a response speed test device. The sensor is connected in series with a fixed resistor, and the speed of the voltage change at both ends of the sensor is measured to represent the sensor's response speed. The test results are tested using an oscilloscope (GDS-2102A). The device diagram is shown in the figure below. Figure 7a As shown in the figure, the ultrafast response of the humidity sensor was confirmed by time-resolved humidity response measurement. In the experiment, dry argon gas was passed into a warm water bottle to obtain a humid flow. The humid flow was cut by a chopper into high and low humidity flows with a frequency and duty cycle of 50%. The sensor was tested and the voltage response of each sensor was compared with the low humidity voltage value (U L , dry argon flow) and high humidity voltage value (U H , the measured value of the sample affected by the wet air flow) is normalized: S = (UU H ) / (U L -U H ). The test results are as follows Figure 7b 、 7c As shown in Figure 2, a square wave can be observed under the action of airflow. Signal detection under modulation shows that the response and recovery times of the TiO2 QDs / SiO2 composite film humidity sensor are 22.4ms and 40.8ms, respectively. Figure 7c As shown in the figure, the experiment proves that the TiO2 QDs / SiO2 composite film humidity sensor has ultra-fast response and recovery speed, which exceeds the response speed of the currently reported humidity sensors.

[0051] In order to verify the effectiveness of the humidity sensor in the actual gas drilling formation water production scenario, a Figure 7d In the simulation environment shown, rocks, sand, and mud are used in a transparent box to simulate bedrock, subsoil, and surface soil from bottom to top. Water generation occurs in the wellbore. An air pump combined with a faucet is used to simulate the wellbore, where water generation occurs. The left hose is connected to an electric pump for continuous air supply and serves as the dry argon gas inlet. The other end of the hose is placed at the bottom of the transparent box. The right hose port serves as the annulus return gas exhaust pipe and is also placed at the bottom of the box. A TiO2 QDs / SiO2 composite film humidity sensor is placed at the pipe outlet to form a detection node. Figure 7e This is the response time diagram when water is released from the formation under a simulated environment. Since the gas carrying water needs a certain length of path before humidity can be detected, the response time is 0.9s. This result shows that the TiO2QDs / SiO2 composite film humidity sensor has great potential in practical application environments.

[0052] Mechanistic explanation

[0053] The humidity sensor based on TiO2 QDs / SiO2 composite film has excellent humidity sensing performance, including ultrafast response and recovery time, high sensitivity, good repeatability and long-term stability. The main conductive mechanism of the sensor comes from the water molecules and active sites adsorbed by TiO2QDs. The high-speed adsorption and desorption of water on the surface of TiO2QDs is due to the super-hydrophilicity of the composite film. The addition of SiO2 microsphere structure further increases the specific surface area of the humidity-sensitive film and improves the humidity-sensitive performance of TiO2QDs. In order to further understand the sensitive mechanism of the TiO2QDs / SiO2 composite film humidity sensor, a graph was drawn. Figure 8 a Schematic diagram of the sensor humidity sensing principle.

[0054] TiO2 QDs adsorb free water in the air. The adsorbed water molecules form hydrogen bonds, making it difficult for them to move freely and their charges are restricted. During this adsorption process, the strong electrostatic field around the oxygen vacancies causes the water molecules to be adsorbed on the sensitive substances to be ionized. The reduction of electrons causes TiO2 QDs to 4+ Become Ti 3+ , air oxidizes surface oxygen to generate O 2- Oxygen atoms are excited to generate oxygen vacancies. Oxygen vacancy defects make the TiO2 surface very easy to adsorb water in the air or free water, so chemical adsorption water (OH - Group), chemically adsorbed water further adsorbs water in the air to form a physical adsorption layer, so on Ti 3+ Highly hydrophilic micro-regions are formed around the defects, while the remaining surface areas remain hydrophobic, so uniformly distributed nano-sized hydrophilic and hydrophobic micro-regions are formed on the TiO2 surface. Since the size of the water droplets is much larger than the size of the micro-regions, the surface appears hydrophilic on a macroscopic scale.

[0055] Modification of TiO2 QDs with SiO2 microspheres can play a synergistic role, such as Figure 8 As shown in a, the addition of silica introduces a microsphere structure to support TiO2 QDs and further increase the specific surface area of the humidity-sensitive film. In addition, studies have shown that in the TiO2QDs / SiO2 binary system, the addition of SiO2 can enhance the Lewis acid on the surface of TiO2 QDs, increase oxygen vacancy defects, form more surface adsorption sites, increase surface adsorbed water, and improve surface hydrophilicity. On the other hand, the surface stable chemical or physical adsorption water layer can effectively stabilize the TiO2 QDs formed on the surface. 3+ -OH structure, so that the TiO2 QDs surface can maintain a hydrophilic state for a long time. In addition, due to the interaction and mutual substitution of Ti and Si atoms in different coordination states, the surface Ti-O structure can be effectively stabilized, inhibiting grain growth. The refinement of grains is conducive to the improvement of surface hydrophilicity.

[0056] To verify the water absorption properties of the TiO2 QDs / SiO2 composite film humidity sensor, density functional theory calculations were performed on a single TiO2 QDs model and a TiO2 QDs / SiO2 composite model using Material Studio software. The structure and energy of the models were optimized using the Dmol3 module. All calculations were performed using Grimme empirical diffusion correction (DFT-D), and the generalized gradient approximation (GGA) and Perdew-Burke-Ernzerhof (PBE) function were used to calculate the electron exchange energy. The convergence value of the energy was 2.0×10 -5 Ha, the maximum force and maximum distance are set as and

[0057] The structural optimization parameters after DFT calculation are shown in Table 1. Distance is the minimum distance between water molecules and adsorption model, charge transfer is the amount of charge transfer between water molecules and adsorption model, and adsorption energy (E ad ) is the adsorption force of the adsorption model on water molecules, which is calculated as follows: E ad =E total -E system -E water In the above formula, E total is the total energy of the TiO2 QDs / SiO2 model after H2O adsorption, E system is the energy of the TiO2 QDs / SiO2 model, E wateris the energy of the H2O molecule. As can be seen from the table, the adsorption energy of the composite material after adsorption is greater than that of single TiO2 QDs, with the adsorption energy changing from -0.426eV to -1.008eV. In addition, the charge transfer of the composite material is greater than that of single TiO2 QDs. This result shows that the composite material has a better adsorption effect on H2O.

[0058] Table 1. Main parameters of TiO2 QDs / SiO2 and TiO2 QDs adsorption systems

[0059]

[0060] Figure 8 b and Figure 8 c are the charge density diagrams of H2O adsorbed by TiO2 QDs and TiO2 QDs / SiO2, respectively. Combined with the charge transfer amount in the table, it can be seen that the charge transfer amount of water molecules adsorbed by the composite model is greater than that of the single TiO2 QDs model, proving that more electrons are transferred between the material and the water molecules. Figure 8 d is the total state density diagram of TiO2 QDs and TiO2 QDs / SiO2 system, Figure 8 e is the projected state density diagram of the TiO2 QDs / SiO2 system. The single peak between -25eV and -17eV becomes a double peak, which is the result of the joint action of TiO2 QDs and SiO2. The peak in the range of -13eV to 5eV has been significantly increased, which is the result of the hybridization of Ti 3d, O 2p, Si 2p and O 2p orbitals. Among them, the Ti 3d orbital plays a major role at the Fermi level, while the SiO2 composite mainly plays a modification function. Figure 8 f is the total state density image of TiO2 QDs / SiO2 before and after adsorption of H2O, Figure 8 g is the projected state density after TiO2 QDs / SiO2 adsorbs H2O. It can be seen that after the composite model adsorbs water molecules, the DOS values at -5.2eV, -2.3eV and 0.7eV increase. It can be seen from the figure that the increase in DOS at -5.2eV is due to the effect of O2p in TiO2, and the increase in DOS at -2.3eV is due to the effect of O 2p in H2O after the adsorption of water molecules. The reason for the change at 0.7eV is the effect of Ti 3d orbital. The change between the two orbitals is the result of the joint hybridization of Ti 3d orbital, O 2p orbital, Si 2p orbital, O 2p orbital, H 1s orbital and O 2p orbital.

[0061] A third aspect of the present invention provides multifunctional applications of an ultrafast response titanium dioxide quantum dot / silicon dioxide composite film humidity sensor, wherein the multifunctional applications include a humidity alarm application and a voice recognition application.

[0062] In some embodiments, the multi-function application further includes a respiratory rate detection application, a diaper moisture monitoring application, and a soil moisture monitoring application.

[0063] In some embodiments, a humidity alarm application uses a humidity monitoring and alarm system to monitor humidity and provide high humidity alarms. The humidity monitoring and alarm system includes a TiO2 QDs / SiO2 composite film humidity sensor, an amplification module, an overvoltage protection module, a control module, an alarm module, a display module, and a power supply module, all connected in sequence. In some embodiments, the control module is used to control the TiO2 QDs / SiO2 composite film humidity sensor to collect humidity signals, the amplification module to amplify humidity signals, the overvoltage protection module to protect circuits, the alarm module to generate alarms, the display module to display humidity signals and alarm results, and the power supply module to power the circuits.

[0064] In some embodiments, the TiO2 QDs / SiO2 composite film humidity sensor can convert a humidity signal into an electrical signal, and the electrical signal contains humidity information.

[0065] In some embodiments, the control module includes an analysis unit. The analysis unit can generate an alarm signal in response to detecting that the humidity is greater than a humidity threshold, and control the alarm module to issue an alarm.

[0066] In some embodiments, the humidity threshold may be 50% RH.

[0067] In some embodiments, the amplification module may include an LMC8041 operational amplifier, the overvoltage protection module may include a BAT54S chip, the control module may be an STM32F103C6T6, the display module may be an OLED display, and the power supply module may be a 5V DC power supply.

[0068] In some embodiments, the alarm module may include a buzzer and an indicator light.

[0069] In some embodiments, the indicator light may include a green LED light and a plurality of red LED lights.

[0070] In some embodiments, when the humidity detected by the control module is less than or equal to 50% RH, the green LED light is controlled to light up, the buzzer is controlled not to sound, and the OLED display screen is controlled to display the humidity; when the humidity detected by the control module is greater than 50% RH and less than 70% RH, a red LED light is controlled to light up, the buzzer is controlled to sound, and the OLED display screen is controlled to display the humidity and alarm information; when the humidity detected by the control module is greater than or equal to 70% RH and less than 85% RH, two red LED lights are controlled to light up, the buzzer is controlled to sound, and the OLED display screen is controlled to display the humidity and alarm information; when the humidity detected by the control module is greater than or equal to 85% RH, three red LED lights are controlled to light up, the buzzer is controlled to sound, and the OLED display screen is controlled to display the humidity and alarm information.

[0071] like Figure 9 As shown in Figure a, the sensor's response when the word "sensor" is spoken at different distances. It can be seen that due to the rapid change in resistance, the TiO2 QDs / SiO2 composite film humidity sensor responds quickly, indicating that the sensor has extremely high sensitivity and has potential application value in speech recognition. Figure 9 b is the response curve of the TiO2QDs / SiO2 composite film humidity sensor at different respiratory rates, indicating that the sensor can meet the monitoring needs at different respiratory rates. Figure 9 c and Figure 9 Figure d represents the diaper humidity detection. It can be seen that when the sensor detects urine on the diaper, the resistance drops rapidly compared to dry diapers. The experimental results show that the combination of ultra-fast humidity detection and alarm functions has significant commercial value in embedded diapers. When the diaper is detected to be wet, the alarm can be used to remind parents to change it.

[0072] In addition, if Figure 9 As shown in Figures ef, the application of the TiO2 QDs / SiO2 composite film humidity sensor in soil moisture detection was verified. Five soil samples were prepared, and the same volume of deionized water was added to each. The samples were then dried at 180 degrees Celsius for 10 minutes, 20 minutes, 30 minutes, and 40 minutes, respectively, using a standard oven drying method. The TiO2 QDs / SiO2 composite film humidity sensor was then inserted into the samples continuously. The soil moisture was calibrated using a commercial sensor, and the resistance values at different humidity levels were recorded, as shown in Figure ef. Figure 9 As shown in e. Figure 9 It can be clearly seen in figure f that the TiO2 QDs / SiO2 composite film humidity sensor has good soil moisture perception performance and a fast response time, which shows that the TiO2 QDs / SiO2 composite film humidity sensor has broad application potential in agricultural soil moisture control and detection.

[0073] In some embodiments, a speech recognition application uses a speech recognition system to identify humidity signals emitted by a test subject. The test subject speaks the word "sensor" at a fixed distance from the TiO2 QDs / SiO2 composite film humidity sensor. The sensor then converts the acquired humidity signal into an electrical signal through a computer, generating a characteristic peak curve. Due to the sensor's ultrafast response, the waveform changes rapidly, and different test subjects' speaking habits and tone of voice can result in significant differences in the waveform.

[0074] In some embodiments, as Figure 10 As shown in Figure 1, the speech recognition system has a Transformer structure. The speech recognition system includes a position encoding module, a fully connected layer, two multi-head attention modules, four Add&Norm modules and two feedforward networks. The position encoding module is connected to the multi-head attention module 1 and the Add&Norm module 1 respectively, the multi-head attention module 1 is connected to the Add&Norm module 1, the Add&Norm module 2, the Add&Norm module 1 and the feedforward network 1 are connected in pairs, the multi-head attention module 2 is connected to the Add&Norm module 2 and the Add&Norm module 3, the Add&Norm module 3 is connected to the Add&Norm module 4 and the feedforward network 2 respectively, and the Add&Norm module 4 is connected to the fully connected layer.

[0075] In some embodiments, each Add&Norm module includes a residual layer and a layer normalization layer. The residual layer is used to retain information and prevent gradient disappearance, and the layer normalization layer is used to effectively improve the performance of the structure. Each feedforward network can perform nonlinear operations and extract nonlinear information. Figure 11 As shown, each multi-head attention module can extract attention information between information, including three linear layers, scaled dot product attention units connected to the three linear layers, and a merging unit connected to the scaled dot product attention unit.

[0076] The working process of the speech recognition system is as follows: the position encoding module is used to enable the speech recognition system to distinguish the position information of different features. First, the initial humidity signal and the position encoding result output by the position encoding module are input into the multi-head attention module 1 and the Add&Norm module 1. In the multi-head attention module 1, the three fixed values Q, K, and V are input and mapped through three linear layers respectively. Then, the scaled dot product attention unit is used to merge the output of each head together to obtain the output result. The output result is used by the Add&Norm module 1 to prevent the gradient from disappearing and normalize the samples to realize information transmission and gradient propagation. Secondly, the feedforward network 1 and the Add&Norm module 2 perform nonlinear operations to extract nonlinear information. The output result is then transmitted to the multi-head attention module 2 and the Add&Norm module 3. In the multi-head attention module 2, the three fixed values Q, K, and V are processed in parallel. The output result is then passed through the Add&Norm module 3 to prevent the gradient from disappearing and normalize the samples to improve the training stability of the model. Subsequently, the feedforward network 2 and the Add&Norm module 4 perform another nonlinear operation to extract nonlinear information. Finally, the fully connected network is used to implement classification and obtain the prediction result.

[0077] like Figure 10 As shown in b, there are 10 testers, each of whom collects 50 sets of data for training and verification through the speech recognition system. The training accuracy and loss function can prove the effectiveness of the speech recognition system, as shown in Figure 10 As shown in Figure c, after 20 training cycles, the speech detection and humidity recognition can achieve a high classification accuracy. Figure 10 d is the corresponding confusion matrix. The numbers 1 to 10 correspond to the voice signals collected from 10 testers. The average classification accuracy can reach 97.6%, which verifies the effectiveness and accuracy of the TiO2QDs / SiO2 composite film humidity sensor in speech recognition and classification.

[0078] In summary, the multifunctional applications presented in this application demonstrate the applicability of the TiO2 QDs / SiO2 composite film humidity sensor in humidity alarms, respiratory rate detection, diaper humidity monitoring, soil moisture monitoring, and voice recognition. The humidity monitoring and alarm system accurately monitors humidity and issues high humidity alarms, while the voice recognition system can identify the voice humidity signals of different test subjects.

[0079] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing an ultrafast response titanium dioxide quantum dot / silicon dioxide composite film humidity sensor, characterized in that: The preparation method comprises the following steps: (1) dispersing butyl titanate in a solvent, adjusting the acidity of the solution and then reacting in a water bath to prepare titanium dioxide quantum dots; the solvent in step (1) is a mixed solvent of cyclohexane and anhydrous ethanol, and the volume ratio of cyclohexane and anhydrous ethanol is (1.5-2.0): (1.5-2.0); the pH value of the solution is 2-4; the reaction temperature is 68-72 o C, reaction time is 9.5-10.5 h; (2) mixing ammonia water, anhydrous ethanol and deionized water, and then mixing the mixture with an ethanol solution of tetraethyl orthosilicate to react and obtain silicon dioxide; in step (2), the mixing volume ratio of ammonia water, anhydrous ethanol and deionized water is (0.9-1.1): (1.5-2.0): (2.4-3.2), and the mixing volume ratio of tetraethyl orthosilicate to ethanol in the ethanol solution of tetraethyl orthosilicate is (0.9-1.1): (8-12); the reaction temperature is 20-25 o C, reaction time is 1.8-2.2 h; (3) immersing the substrate in a mixed suspension of polystyrene sulfonate-SiO2 and a TiO2 QDs solution in sequence, and obtaining the titanium dioxide quantum dot / silicon dioxide composite film humidity sensor after drying; the concentration of SiO2 in the suspension in step (3) is 0.08-0.12 mg / mL, the mass concentration of polystyrene sulfonate is 0.8-1.2 mg / mL, and the concentration of the TiO2 QDs solution is 0.12-0.18 mg / mL; the immersion time in step (3) is 18-22 min respectively; The titanium dioxide quantum dot / silicon dioxide composite film humidity sensor includes a sensing layer and a substrate. The sensing layer is titanium dioxide quantum dots / silicon dioxide thin film TiO2 QDs / SiO2. The substrate is an interdigitated electrode. A layer of PSS@SiO2 film is attached to the surface of the interdigitated electrode. The principle of electrostatic self-assembly is used to attach a layer of TiO2 QDs to the surface of the PSS@SiO2 film. The SiO2 is in a clear and regular spherical shape, and the TiO2 quantum dots are evenly distributed on and around the SiO2 microspheres.

2. The multifunctional application of the ultrafast response titanium dioxide quantum dot / silicon dioxide composite film humidity sensor according to claim 1, characterized in that: The multi-functions include a humidity alarm application and a voice recognition application.

3. The multifunctional application of the ultrafast response titanium dioxide quantum dot / silicon dioxide composite film humidity sensor according to claim 2, characterized in that: The humidity alarm application performs humidity monitoring and high humidity alarm through a humidity monitoring and alarm system, which includes a TiO2 QDs / SiO2 composite film humidity sensor, an amplification module, an overvoltage protection module, a control module, an alarm module, a display module, and a power supply module connected in sequence; The control module is used to control the TiO2 QDs / SiO2 composite film humidity sensor to collect humidity signals, control the amplification module to amplify the humidity signals, control the overvoltage protection module to protect the circuit, control the alarm module to sound an alarm, control the display module to display the humidity signals and alarm results, and control the power supply module to power the circuit.

4. The multifunctional application of the ultrafast response titanium dioxide quantum dot / silicon dioxide composite film humidity sensor according to claim 2, characterized in that: The speech recognition application recognizes speech humidity signals through a speech recognition system. The speech recognition system has a Transformer structure. The speech recognition system includes a position encoding module, a fully connected layer, two multi-head attention modules, four Add&Norm modules and two feedforward networks. The position encoding module is respectively connected to the multi-head attention module one and the Add&Norm module one, the multi-head attention module one is connected to the Add&Norm module one, the Add&Norm module two, the Add&Norm module one and the feedforward network one are connected in pairs, the multi-head attention module two is connected to the Add&Norm module two and the Add&Norm module three, the Add&Norm module three is respectively connected to the Add&Norm module four and the feedforward network two, and the Add&Norm module four is connected to the fully connected layer.

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