A transition metal phosphide modified TiO2 gas sensor and its preparation method and application

Abstract

The present invention provides a transition metal phosphide modified TiO2 gas sensor, its preparation method and application, belonging to the technical field of gas detection. The transition metal phosphide modified TiO2 gas sensor provided by the present invention includes a conductive substrate, a TiO2 film layer attached to the surface of the conductive substrate, and transition metal phosphide nanoparticles distributed on the surface of the TiO2 film layer, and the transition metal phosphide is Ni2P and / or CoP. The present invention uses transition metal phosphide particles as a co-catalyst for TiO2. The modification effect of the transition metal phosphide can significantly improve the gas sensing performance of the TiO2 sensor, greatly reducing the preparation cost compared with the sensor modified by noble metals, which is conducive to large-scale popularization and use. The obtained gas sensor has the advantages of high sensitivity, high selectivity and long-term stability to H2 at room temperature.

Description

Technical Field

[0001] The present invention relates to the technical field of gas detection, and particularly relates to a transition metal phosphide modified TiO2 gas sensor and a preparation method and application thereof. Background Art

[0002] Hydrogen is widely used as an efficient clean energy source. However, due to the very small size of hydrogen molecules, it is very easy to leak and cause explosion accidents during the processes of production, storage, transportation and use. Therefore, reliable leak detection is of great importance.

[0003] In recent decades, gas sensors have been widely used in the detection of different gases in many aspects such as environmental protection, industrial safety, and medical diagnosis. Metal oxide semiconductors (SMOs) are an important type of gas-sensitive material with outstanding gas-sensitive properties. Chemoresistive gas sensors based on metal oxide semiconductors are widely used for the detection of gas components and concentrations.

[0004] However, due to the disadvantages of low sensitivity, long response and recovery times of the original metal oxide semiconductor gas sensors, modifying the surface of the gas sensor with a cocatalyst is an effective method to improve the gas-sensitive performance of the gas sensor. Among them, the method of surface noble metal modification has received a great deal of attention. Gas sensors based on SMO materials modified with noble metals such as Au, Ag, Pt, and Pd have been widely studied. For example, the sensitivity of the SnO2 thin film modified with Ag nanoparticles by Kim et al. to 1 ppm NO2 at 300 °C is 1000 (Kim, Sang, Sub, et al. “Optimization of metal nanoparticle amount on SnO2 nanowires to achieve superior gas sensing properties” [J]. Sensors & Actuators B: Chemical 2017, 238, 374 - 380). The sensitivity of the TiO2 modified with Au by Zhang et al. to 5 ppm formaldehyde at room temperature is 3 times that of pure TiO2 (Zhang S, Zhao L, Huang B, et al. “Enhanced Sensing Performance of Au-Decorated TiO2 Nanospheres with Hollow Structure for Formaldehyde Detection at Room Temperature” [J]. Social Science Electronic Publishing 2022).

[0005] Utilizing the excellent catalytic properties of noble metal nanoparticles, the adsorption and desorption reactions of target gases can be promoted, improving the performance of gas sensors. However, the main drawbacks of these noble metal cocatalysts are their low terrestrial abundance and high cost, making them unsuitable for large-scale applications. Summary of the Invention

[0006] In view of this, the object of the present invention is to provide a transition metal phosphide modified TiO2 gas sensor and its preparation method and application. The transition metal phosphide modified TiO2 gas sensor provided by the present invention has low cost and good detection sensitivity to H2.

[0007] To achieve the above object of the invention, the present invention provides the following technical solutions:

[0008] The present invention provides a transition metal phosphide modified TiO2 gas sensor, comprising a conductive substrate, a TiO2 film layer attached to the surface of the conductive substrate, and transition metal phosphide nanoparticles distributed on the surface of the TiO2 film layer, wherein the transition metal phosphide is Ni2P and / or CoP.

[0009] Preferably, the thickness of the TiO2 film layer is 1.5 - 4.0 μm.

[0010] Preferably, the particle size of the transition metal phosphide nanoparticles is 100 - 2000 nm.

[0011] The present invention provides a preparation method of the above transition metal phosphide modified TiO2 gas sensor, comprising the following steps:

[0012] Providing a precursor solution for preparing TiO2 by hydrothermal method;

[0013] Placing the conductive substrate in the precursor solution and performing hydrothermal reaction to obtain a conductive substrate with a TiO2 film layer attached thereto;

[0014] Loading an alcohol dispersion of transition metal phosphide on the surface of the TiO2 film layer of the conductive substrate with the TiO2 film layer attached thereto, and sequentially performing drying and annealing to obtain a transition metal phosphide modified TiO2 gas sensor.

[0015] Preferably, the precursor solution for preparing TiO2 by hydrothermal method comprises the following raw materials in parts by volume:

[0016] Water 20 - 35 parts;

[0017] Ethanol 0.05 - 5 parts;

[0018] Hydrochloric acid 20 - 40 parts

[0019] Tetrabutyl titanate 0.5 - 3 parts.

[0020] Preferably, the mass ratio of the transition metal phosphide to the volume of tetrabutyl titanate is 0.01 - 0.08 g: 0.5 - 3 mL.

[0021] Preferably, when the transition metal phosphide is Ni2P, the preparation method of the Ni2P includes the following steps:

[0022] Mix a soluble transition metal nickel source, red phosphorus, and an alcohol solvent, and carry out a solvothermal reaction to obtain Ni2P;

[0023] When the transition metal phosphide is CoP, the preparation method of the CoP includes the following steps:

[0024] Mix a soluble transition metal cobalt source, ammonium fluoride, urea, red phosphorus, and water, carry out a solvothermal reaction to obtain a precursor, and anneal the precursor to obtain CoP.

[0025] Preferably, the temperature of the hydrothermal reaction is 120 - 180 °C, and the time is 4 - 18 h.

[0026] Preferably, the temperature of the annealing is 300 - 550 °C, and the holding time is 10 - 60 min.

[0027] The present invention provides the application of the above-mentioned transition metal phosphide-modified TiO2 gas sensor in hydrogen detection.

[0028] The present invention provides a transition metal phosphide-modified TiO2 gas sensor, which includes a conductive substrate, a TiO2 film layer attached to the surface of the conductive substrate, and transition metal phosphide nanoparticles distributed on the surface of the TiO2 film layer. The transition metal phosphide is Ni2P and / or CoP. The present invention uses transition metal phosphide nanoparticles as a cocatalyst for TiO2. The transition metal phosphide nanoparticles have good electrical conductivity, good thermal stability and chemical stability, and extremely high catalytic activity similar to noble metals. The modification effect of the transition metal phosphide can significantly improve the gas-sensing performance of the TiO2 sensor, greatly reducing the preparation cost compared with the noble metal-modified sensor, which is conducive to large-scale popularization and use. The obtained gas sensor has the advantages of high sensitivity, high selectivity, and long-term stability to H2 at room temperature. The results of the examples show that the detection limit value of H2 concentration of the transition metal phosphide-modified TiO2 gas sensor provided by the present invention is less than 1 ppm, the sensitivity can reach 1826.18 when detecting H2 concentration of 8000 ppm, the response time is 12 s, and the recovery time is 148 s. Therefore, the gas sensor provided by the present invention has excellent sensitivity performance within the H2 concentration range of 1 - 8000 ppm, as well as extremely fast response and recovery times.

[0029] The present invention provides a method for preparing the above-mentioned transition metal phosphide modified TiO2 gas sensor, which has simple operation and is suitable for industrial mass production. Description of the Drawings

[0030] Figure 1 Schematic diagram of the transition metal phosphide modified TiO2 gas sensor for hydrogen detection;

[0031] Figure 2 SEM surface morphology diagrams of the Ni2P modified TiO2 gas sensors obtained in Examples 1 to 5;

[0032] Figure 3 X-ray diffraction patterns of the FTO substrate, Ni2P, TiO2 nanorods, and Ni2P modified TiO2 thin film samples in Example 1;

[0033] Figure 4 H2 sensing characteristic test diagram of the pure rutile TiO2 sample at room temperature;

[0034] Figure 5 H2 sensing characteristic test diagram of the sample 0.01Ni2P-TiO2 at room temperature;

[0035] Figure 6 H2 sensing characteristic test diagram of the sample 0.02Ni2P-TiO2 at room temperature;

[0036] Figure 7 H2 sensing characteristic test diagram of the sample 0.03Ni2P-TiO2 at room temperature;

[0037] Figure 8 H2 sensing characteristic test diagram of the sample 0.05Ni2P-TiO2 at room temperature;

[0038] Figure 9 H2 sensing characteristic test diagram of the sample 0.08Ni2P-TiO2 at room temperature;

[0039] Figure 10 Response time and recovery time diagrams of the sensors 0.01Ni2P-TiO2, 0.02Ni2P-TiO2, 0.03Ni2P-TiO2, 0.05Ni2P-TiO2, and 0.08Ni2P-TiO2 at room temperature in the H2 concentration range of 1 to 8000 ppm;

[0040] Figure 11 Surface coverage of the devices prepared by spin-coating different masses of nickel phosphide on the TiO2 surface and the response curve at an H2 concentration of 2000 ppm;

[0041] Figure 12 X-ray diffraction pattern of CoP;

[0042] Figure 13 It is a test chart of the H2 sensing characteristics of the 0.03CoP-TiO2 sample at room temperature;

[0043] Figure 14 It is a chart of the response time and recovery time of TiO2 and CoP-TiO2 with different spin-coating dosages (0.01g - 0.08g) of CoP at room temperature in the H2 concentration range of 1 - 4000 ppm. Specific implementation manners

[0044] The present invention provides a transition metal phosphide modified TiO2 gas sensor, which includes a conductive substrate, a TiO2 film layer attached to the surface of the conductive substrate, and transition metal phosphide nanoparticles distributed on the surface of the TiO2 film layer, and the transition metal phosphide is Ni2P and / or CoP.

[0045] In the present invention, the conductive substrate is preferably an FTO substrate or an ITO conductive substrate.

[0046] In the present invention, the thickness of the TiO2 film layer is 1.5 - 4.0 μm, more preferably 2 - 3.5 μm. In the present invention, the crystal phase of TiO2 in the TiO2 film layer is preferably rutile phase.

[0047] In the present invention, the particle size of the transition metal phosphide nanoparticles is preferably 100 - 2000 nm, more preferably 200 - 1500 nm, and further preferably 500 - 1000 nm.

[0048] The present invention provides a preparation method of the above-mentioned transition metal phosphide modified TiO2 gas sensor, which includes the following steps:

[0049] Provide a precursor solution for preparing TiO2 by hydrothermal method;

[0050] Place the conductive substrate in the precursor solution and carry out hydrothermal reaction to obtain a conductive substrate with a TiO2 film layer attached thereto;

[0051] Load an alcohol dispersion of transition metal phosphide on the surface of the TiO2 film layer of the conductive substrate with the TiO2 film layer attached thereto, and successively carry out drying and annealing to obtain a transition metal phosphide modified TiO2 gas sensor.

[0052] The present invention provides a precursor solution for preparing TiO2 by hydrothermal method. In the present invention, the precursor solution for preparing TiO2 by hydrothermal method preferably includes the following raw materials in volume parts:

[0053] Water 20 - 35 parts, more preferably 25 - 30 parts;

[0054] Ethanol: 0.05 - 5 parts, more preferably 1 - 3 parts;

[0055] Hydrochloric acid: 20 - 40 parts, more preferably 25 - 35 parts;

[0056] Tetrabutyl titanate: 0.5 - 3 parts, more preferably 1 - 2 parts.

[0057] In the present invention, the purity of the ethanol is preferably ≥99.7%, and the purity of the tetrabutyl titanate is preferably ≥99.0%. In the present invention, the concentration of the hydrochloric acid is preferably 36 - 38 wt%.

[0058] The present invention has no special requirements for the preparation method of the precursor for preparing TiO2 by the hydrothermal method, and the above raw materials can be mixed evenly.

[0059] In the present invention, the conductive substrate is placed in the precursor solution for hydrothermal reaction to obtain a conductive substrate with a TiO2 film layer attached. In the present invention, the conductive substrate is preferably inclined against the wall of the container containing the precursor solution, and the conductive surface of the conductive substrate faces downward.

[0060] In the present invention, the hydrothermal reaction is preferably carried out in a hydrothermal reaction kettle. The temperature of the hydrothermal reaction is preferably 120 - 180 °C, more preferably 130 - 150 °C; the time is preferably 4 - 18 h, more preferably 8 - 12 h.

[0061] In the present invention, after the hydrothermal reaction, the present invention preferably washes and dries the conductive substrate with a TiO2 film layer attached. The washing is preferably water washing; the drying is preferably natural air drying.

[0062] After obtaining the conductive substrate with a TiO2 film layer attached, in the present invention, an alcohol dispersion of transition metal phosphide is loaded on the surface of the TiO2 film layer of the conductive substrate with a TiO2 film layer attached, and drying and annealing are carried out in sequence to obtain a transition metal phosphide modified TiO2 gas sensor.

[0063] In the present invention, the mass ratio of the transition metal phosphide to the volume of tetrabutyl titanate is 0.01 - 0.08 g: 0.5 - 3 mL, preferably 0.02 - 0.03 g: 0.5 - 3 mL.

[0064] In the present invention, when the transition metal phosphide is nickel phosphide Ni2P, the preparation method of the Ni2P preferably includes the following steps:

[0065] Mix a soluble transition metal nickel source, red phosphorus and an alcohol solvent, and carry out a solvothermal reaction to obtain Ni2P.

[0066] In the present invention, the soluble transition metal nickel source is preferably nickel chloride; the alcohol solvent is preferably ethylene glycol.

[0067] In the present invention, the mass ratio of the soluble transition metal nickel source to red phosphorus is preferably 0.1-0.4:0.02-0.08, more preferably 0.2-0.3:0.04-0.06.

[0068] In the present invention, the mass ratio of the soluble transition metal nickel source to the volume of the alcohol solvent is preferably 0.1-0.4 g:20-80 mL.

[0069] In the present invention, the mixing method is preferably ultrasonic mixing. The power of the ultrasonic mixing is preferably 100-800 W, more preferably 200-600 W; the time is preferably 1-3 h, more preferably 2 h.

[0070] In the present invention, after the ultrasonic mixing, the present invention preferably allows the obtained mixed solution to stand, and the standing time is preferably 1 h.

[0071] In the present invention, the temperature of the solvothermal reaction is preferably 120-180 °C, more preferably 140-160 °C; the time is preferably 8-12 h, more preferably 10 h. In the present invention, during the solvothermal reaction, nickel chloride forms a stable complex with the ethylene glycol solvent. As the temperature rises, the complex slowly releases Ni 2+ , at high temperature, red phosphorus reacts with ethylene glycol to generate PH3, and PH3 reacts with Ni in the solution 2+ to generate Ni2P.

[0072] After the solvothermal reaction, the present invention preferably performs post-treatment on the obtained solvothermal reaction solution. The post-treatment includes:

[0073] Performing solid-liquid separation on the solvothermal reaction solution, washing and drying the obtained solid to obtain Ni2P solid.

[0074] In the present invention, the solid-liquid separation is preferably filtration; in the present invention, the detergent for washing is preferably water and ethanol, and the washing times for water and ethanol are each three times.

[0075] In the present invention, the drying method is preferably vacuum drying, and the vacuum drying time is preferably 1-6 h, more preferably 2-4 h.

[0076] In the present invention, when the transition metal phosphide is cobalt phosphide CoP, the preparation method of CoP preferably includes the following steps:

[0077] Mixing a soluble transition metal cobalt source, ammonium fluoride, urea, red phosphorus and water, performing a hydrothermal reaction to obtain a precursor, and annealing the precursor to obtain CoP.

[0078] In the present invention, the soluble transition metal cobalt source is preferably cobalt nitrate. In the present invention, the molar ratio of the soluble transition metal cobalt source, ammonium fluoride, urea, and red phosphorus is preferably 1:4:5:1.

[0079] In the present invention, the mass-to-volume ratio of the soluble transition metal cobalt phosphide source to water is preferably 0.1 - 0.3 g: 40 - 80 mL.

[0080] In the present invention, the mixing method is preferably ultrasonic mixing. The power of the ultrasonic mixing is preferably 100 - 800 W, more preferably 200 - 600 W; the time is preferably 0.5 - 2 h, more preferably 1 h.

[0081] In the present invention, the temperature of the solvothermal reaction is preferably 120 - 180 °C, more preferably 140 - 160 °C; the time is preferably 2 - 6 h, more preferably 4 h.

[0082] After the hydrothermal reaction, the present invention preferably performs post-treatment on the obtained hydrothermal reaction solution. The post-treatment includes:

[0083] Performing solid-liquid separation on the hydrothermal reaction solution, washing and drying the obtained solid to obtain a precursor.

[0084] In the present invention, the chemical composition of the precursor includes CoF 1.3 (OH) 0.7 and red phosphorus.

[0085] In the present invention, the annealing method is preferably annealing in an argon atmosphere. The annealing temperature is preferably 400 - 600 °C, more preferably 500 °C; the time is preferably 1 - 4 h, more preferably 2 - 3 h. In the present invention, during the annealing process, CoF 1.3 (OH) 0.7 reacts with red phosphorus to form cobalt phosphide.

[0086] In the present invention, the method for preparing the alcoholic dispersion of the transition metal phosphide preferably includes the following steps:

[0087] Ultrasonically mixing the transition metal phosphide with an alcoholic solvent to obtain an alcoholic dispersion of the transition metal phosphide.

[0088] In the present invention, the alcoholic solvent is preferably ethanol. In the present invention, the power of the ultrasonic mixing is preferably 100 - 800 W, more preferably 200 - 600 W; the time is preferably 1 - 3 h, more preferably 2 h. In the present invention, the mass-to-volume ratio of the transition metal phosphide to the alcoholic solvent is preferably 0.01 - 0.08 g: 2 mL.

[0089] In the present invention, an alcohol dispersion of a transition metal phosphide is loaded onto the surface of the TiO2 film layer of the conductive substrate with the TiO2 film layer, and drying and annealing are carried out in sequence to obtain a transition metal phosphide-modified TiO2 gas sensor. In the present invention, the method of loading the alcohol dispersion of the transition metal phosphide is preferably spin coating. In the present invention, the spin coating rate is preferably 500 - 3000 r / s, and preferably 2000 r / s. In the present invention, the spin coating amount of the transition metal phosphide is preferably 0.0016 - 0.0128 g / cm 2 .

[0090] In the present invention, the drying is preferably vacuum drying, and the time of the vacuum drying is preferably 0.5 - 1.5 h, more preferably 1 h.

[0091] In the present invention, the annealing is preferably carried out in a nitrogen atmosphere. In the present invention, the annealing temperature is preferably 300 - 550 °C, more preferably 400 °C; the heat preservation time is preferably 10 - 200 min, more preferably 20 - 120 min. By annealing in a nitrogen atmosphere in the present invention, the transition metal phosphide spin-coated on the surface of TiO2 can form a firm contact with the TiO2 film layer, and at the same time, the transition metal phosphide is prevented from being oxidized.

[0092] The present invention provides the application of the above-mentioned transition metal phosphide-modified TiO2 gas sensor in hydrogen detection. In the present invention, the method of the application includes the following steps:

[0093] A interdigital electrode is loaded onto the surface of the transition metal phosphide-modified TiO2 gas sensor, a voltage is applied between the interdigital electrodes, and the resistance value of the transition metal phosphide-modified TiO2 gas sensor is tested.

[0094] In the present invention, the interdigital electrode is preferably a Pt interdigital electrode. In the present invention, the preparation method of the Pt interdigital electrode preferably includes the following steps:

[0095] A high-purity Pt target is installed at the cathode target position of the magnetron sputtering system, magnetron sputtering is carried out, and a film is formed on the surface of the transition metal phosphide-modified TiO2 gas sensor to form a Pt interdigital electrode.

[0096] In the present invention, the power of the magnetron sputtering is preferably 40 W, and the time is preferably 5 min; the gas for the magnetron sputtering is preferably argon, and the working pressure is preferably 0.5 Pa.

[0097] In the present invention, the schematic diagram of the transition metal phosphide-modified TiO2 gas sensor for hydrogen detection is as Figure 1 shown.

[0098] The transition metal phosphide modified TiO2 gas sensor provided by the present invention, its preparation method and application will be described in detail below in conjunction with embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0099] Example 1

[0100] A preparation method of a Ni2P modified TiO2 gas sensor includes the following steps:

[0101] (1) Clean the FTO substrate ultrasonically with acetone, ethanol, and deionized water in sequence, and dry it in a drying oven.

[0102] (2) Prepare the precursor solution for hydrothermal preparation of TiO2:

[0103] Prepare the precursor solution according to the following volume percentages:

[0104] Deionized water: 28 ml (46%);

[0105] Ethanol: 2 ml (3.3%);

[0106] Hydrochloric acid: 30 ml (49%);

[0107] Tetrabutyl titanate 1 ml (1.6%).

[0108] Pour the precursor solution into a polytetrafluoroethylene-lined hydrothermal reaction kettle. Lean the FTO conductive side downwards against the inner wall of the reaction kettle containing the precursor solution. Immerse the FTO in the precursor solution. Tighten the reaction kettle and place it in a constant temperature oven for hydrothermal treatment at 150 °C for 8 h. After the reaction is completed, take out the reaction kettle cooled to room temperature, take out the FTO substrate, wash it with ultrapure water and air-dry it naturally to obtain a conductive substrate with a TiO2 film layer attached.

[0109] (3) Grind red phosphorus into extremely fine powder with a mortar. Add 0.1 g of nickel chloride hexahydrate to 50 mL of ethylene glycol, dissolve it ultrasonically, then dissolve 0.05 g of the ground extremely fine red phosphorus powder in the mixed solution, ultrasonically treat it at 500 W for 2 h, let it stand for 1 h, pour the standing solution into the reaction kettle, tighten the reaction kettle and place it in a constant temperature oven, heat it at 150 °C for 10 h. After the reaction is completed, take out the reaction kettle cooled to room temperature, filter off the supernatant, wash the obtained Ni2P powder with deionized water and ethanol by centrifugation three times each, and then dry it in a vacuum drying oven for 2 h.

[0110] (4) Disperse 0.01 g of Ni2P powder in 2 mL of ethanol and dissolve it by ultrasonic treatment. Then, spin-coat the suspension evenly on the surface of the conductive substrate with a TiO2 film layer. Place the sample after spin-coating in a vacuum drying oven and dry it for 1 h. Then, anneal it at 400 °C for 20 min in a nitrogen atmosphere to obtain a Ni2P-modified TiO2 gas sensor, denoted as 0.01Ni2P-TiO2.

[0111] Example 2

[0112] The difference from Example 1 is that the dosage of Ni2P powder is 0.02 g, denoted as 0.02Ni2P-TiO2.

[0113] Example 3

[0114] The difference from Example 1 is that the dosage of Ni2P powder is 0.03 g, denoted as 0.03Ni2P-TiO2.

[0115] Example 4

[0116] The difference from Example 1 is that the dosage of Ni2P powder is 0.05 g, denoted as 0.05Ni2P-TiO2.

[0117] Example 5

[0118] The difference from Example 1 is that the dosage of Ni2P powder is 0.08 g, denoted as 0.08Ni2P-TiO2.

[0119] Structure Characterization

[0120] The SEM surface morphology diagrams of the Ni2P-modified TiO2 gas sensors obtained in Examples 1-5 are as Figure 2 shown. It can be seen from Figure 2 that as the amount of nickel phosphide increases, the area covered on the surface of TiO2 gradually increases. When the amount of nickel phosphide increases to 0.05 g and 0.08 g, obvious agglomeration phenomena of nickel phosphide appear on the surface of TiO2.

[0121] The X-ray diffraction patterns of the FTO substrate, nickel phosphide, TiO2 nanorods, and nickel phosphide-modified TiO2 thin film sample in Example 1 are as Figure 3 shown. It can be seen from Figure 3 that for the TiO2 sample modified with nickel phosphide, no other impurity peaks appear except for the characteristic peaks of TiO2 and nickel phosphide.

[0122] Performance Test

[0123] 0.01Ni2P-TiO2, 0.02Ni2P-TiO2, 0.03Ni2P-TiO2, 0.05Ni2P-TiO2, 0.08Ni2P-TiO2, and pure rutile TiO2 samples (annealed in N2) were used as H2 gas sensors for detection. Pt interdigital electrodes were loaded on the surface of the gas sensors. When testing, a voltage of 1 V was applied between the interdigital electrodes to test their H2 sensing characteristics.

[0124] The test chart of the H2 sensing characteristics of the pure rutile TiO2 sample at room temperature is as Figure 4 shown. From Figure 4 it can be seen that the measured H2 concentration range is 1 - 6000 ppm. The device has good H2 sensing performance within the range of hydrogen concentration from 1 to 6000 ppm. However, when working at room temperature to detect H2 concentration in the range of 1 - 1200 ppm, the sensitivity is not high and the response discrimination is not significant. When working at room temperature to detect H2 concentration of 1 ppm, the sensitivity is 1.60 (R a / R g ). When detecting H2 concentration of 1200 ppm, the sensitivity can reach 8.02.

[0125] The test chart of the H2 sensing characteristics of the 0.01Ni2P-TiO2 sample at room temperature is as Figure 5 shown. From Figure 5 it can be seen that the measured H2 concentration range is 1 - 6000 ppm. The device has good H2 sensing performance within the range of hydrogen concentration from 1 to 6000 ppm. When working at room temperature to detect H2 concentration of 1 ppm, the sensitivity is 1.57 (R a / R g ). When detecting H2 concentration of 4000 ppm, the sensitivity can reach 32.08. After being modified with a small amount of nickel phosphide, both the H2 response sensitivity and the measured concentration range of the device are significantly improved.

[0126] The test chart of the H2 sensing characteristics of the 0.02Ni2P-TiO2 sample at room temperature is as Figure 6 shown. From Figure 6 it can be seen that the measured H2 concentration range is 1 - 8000 ppm. The device has good H2 sensing performance within the range of hydrogen concentration from 1 to 8000 ppm. When working at room temperature to detect H2 concentration of 1 ppm, the sensitivity is 2.85. When detecting H2 concentration of 4000 ppm, the sensitivity can reach 147.57, with extremely high detection sensitivity.

[0127] The test chart of the H2 sensing characteristics of the 0.03Ni2P-TiO2 sample at room temperature is as Figure 7 shown. From Figure 7It can be seen that the measured H2 concentration range is 1 - 8000 ppm. The device has good H2 sensing performance within the H2 concentration range of 1 - 8000 ppm. When operating at room temperature, the sensitivity is 3.30 when detecting an H2 concentration of 1 ppm, and the sensitivity can reach 1171.88 when detecting an H2 concentration of 4000 ppm, showing extremely high detection sensitivity.

[0128] The test diagram of the H2 sensing characteristics of sample 0.05Ni2P - TiO2 at room temperature is as Figure 8 shown. From Figure 8 It can be seen that the measured H2 concentration range is 1 - 8000 ppm. The device has good H2 sensing performance within the H2 concentration range of 1 - 8000 ppm. When operating at room temperature, the sensitivity is 1.44 when detecting an H2 concentration of 1 ppm, and the sensitivity is 10.00 when detecting an H2 concentration of 4000 ppm. The excessive amount of nickel phosphide leads to a decrease in the gas - sensing performance of the device.

[0129] The test diagram of the H2 sensing characteristics of sample 0.08Ni2P - TiO2 at room temperature is as Figure 9 shown. From Figure 9 It can be seen that the measured H2 concentration range is 1 - 8000 ppm. The device has good H2 sensing performance within the H2 concentration range of 1 - 8000 ppm. When operating at room temperature, the sensitivity is 1.15 when detecting an H2 concentration of 1 ppm, and the sensitivity is 2.20 when detecting an H2 concentration of 4000 ppm. The excessive amount of nickel phosphide leads to a decrease in the gas - sensing performance of the device.

[0130] The response time and recovery time diagrams of sensors 0.01Ni2P - TiO2, 0.02Ni2P - TiO2, 0.03Ni2P - TiO2, 0.05Ni2P - TiO2, and 0.08Ni2P - TiO2 at room temperature in the H2 concentration range of 1 - 8000 ppm are as Figure 10 shown. From Figure 10 It can be seen that 0.02Ni2P - TiO2 and 0.03Ni2P - TiO2 have faster response and recovery times. When the H2 concentration is in the range of 50 - 1200 ppm, their response time is shorter than 10 s and the recovery time is shorter than 20 s. After 1200 ppm, more time is required to absorb / desorb hydrogen, making their response and recovery times longer. Generally speaking, the nickel phosphide - modified titanium dioxide sensor has a faster response and recovery time compared with the pure rutile - phase titanium dioxide sensor.

[0131] The surface coverage of the devices prepared by spin - coating different masses of nickel phosphide on the TiO2 surface and the response curves at an H2 concentration of 2000 ppm are as Figure 11 shown. From Figure 11It can be seen that as the amount of nickel phosphide increases, the surface coverage rate of the device increases, and the response rate of the device to hydrogen first increases and then decreases. When the amount of nickel phosphide is 0.03 g, the gas-sensing performance of the device is the best. Continuing to increase the amount will cause nickel phosphide to agglomerate on the surface of TiO2, which is not conducive to the improvement of the H2 gas-sensing performance of the device.

[0132] Example 6

[0133] A preparation method of a CoP-modified TiO2 gas sensor includes the following steps:

[0134] Steps (1) and (2) are the same as those in Example 1.

[0135] (3) Grind red phosphorus into extremely fine powder in a mortar. Add 0.146 g of cobalt nitrate hexahydrate, 0.074 g of ammonium fluoride, 0.150 g of urea, and 0.016 g of red phosphorus to 60 mL of water, and ultrasonically dissolve it for 1 h at 500 W. Then pour the solution into a reaction kettle, tightly cover the reaction kettle, and place it in a constant-temperature oven. Heat it at 150 °C for 4 h. After the reaction is completed, take out the reaction kettle cooled to room temperature, filter off the supernatant, and centrifuge and wash the obtained precursor powder three times with deionized water and ethanol respectively. Then place it in a vacuum drying oven and dry it for 2 h. Place the dried precursor powder in a tube furnace and anneal it at 500 °C for 120 min in an argon atmosphere to obtain CoP powder.

[0136] (4) Disperse 0.03 g of CoP powder in 2 mL of ethanol and ultrasonically dissolve it. Then evenly spin-coat the suspension on the surface of the conductive substrate with a TiO2 film layer. Place the sample after spin-coating in a vacuum drying oven and dry it for 1 h. Then anneal it at 500 °C for 120 min in an argon atmosphere to obtain a CoP-modified TiO2 gas sensor, denoted as 0.03CoP-TiO2.

[0137] Example 7

[0138] The difference from Example 6 is that the amount of CoP powder used is 0.01 g, denoted as 0.01CoP-TiO2.

[0139] Example 8

[0140] The difference from Example 6 is that the amount of CoP powder used is 0.02 g, denoted as 0.02CoP-TiO2.

[0141] Example 9

[0142] The difference from Example 6 is that the amount of CoP powder used is 0.05 g, denoted as 0.05CoP-TiO2.

[0143] Example 10

[0144] The difference from Example 6 is that the dosage of CoP powder is 0.08 g, denoted as 0.08CoP-TiO2.

[0145] The X-ray diffraction pattern of CoP in Example 6 is as Figure 12 shown. It can be seen from Figure 12 that except for the characteristic peaks of cobalt phosphide, no other impurity peaks appear.

[0146] The H2 sensing characteristic test diagram of the sample 0.03CoP-TiO2 at room temperature is as Figure 13 shown. It can be seen from Figure 13 that the measured H2 concentration range is 1 - 4000 ppm, and the device has good H2 sensing performance within the range of hydrogen concentration from 1 to 4000 ppm. The sensitivity is 2.33 when detecting H2 concentration of 1 ppm at room temperature, and the sensitivity can reach 19696 when detecting H2 concentration of 4000 ppm, showing extremely high detection sensitivity.

[0147] The response time and recovery time diagrams of the sensors 0.01CoP-TiO2, 0.02CoP-TiO2, 0.03CoP-TiO2, 0.05CoP-TiO2 and 0.08CoP-TiO2 at room temperature within the H2 concentration range of 1 - 4000 ppm are as Figure 14 shown. It can be seen from Figure 14 that the sensor samples modified with a small amount of spin-coated cobalt phosphide have faster response and recovery times.

[0148] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A transition metal phosphide modified TiO2 gas sensor, comprising a conductive substrate, a TiO2 film layer attached to the surface of the conductive substrate, and transition metal phosphide nanoparticles distributed on the surface of the TiO2 film layer, wherein the transition metal phosphide is Ni2P and / or CoP.

2. The transition metal phosphide modified TiO2 gas sensor according to claim 1, wherein The thickness of the TiO2 film layer is 1.5 - 4.0 μm.

3. The transition metal phosphide modified TiO2 gas sensor according to claim 1 or 2, characterized in that, The particle size of the transition metal phosphide nanoparticles is 100 - 2000 nm.

4. The preparation method of the transition metal phosphide modified TiO2 gas sensor according to any one of claims 1 - 3, comprising the following steps: Providing a precursor solution for preparing TiO2 by a hydrothermal method; Placing the conductive substrate in the precursor solution and performing a hydrothermal reaction to obtain a conductive substrate with a TiO2 film layer attached thereto; Loading an alcohol dispersion of the transition metal phosphide on the surface of the TiO2 film layer of the conductive substrate with the TiO2 film layer attached thereto, and sequentially performing drying and annealing to obtain a transition metal phosphide modified TiO2 gas sensor.

5. The preparation method according to claim 4, characterized in that, The precursor solution for preparing TiO2 by the hydrothermal method comprises the following raw materials in parts by volume: Water 20 - 35 parts; Ethanol 0.05 - 5 parts; Hydrochloric acid 20 - 40 parts Tetrabutyl titanate 0.5 - 3 parts.

6. The preparation method according to claim 5, characterized in that, The mass ratio of the transition metal phosphide to the volume of tetrabutyl titanate is 0.01 - 0.08 g: 0.5 - 3 mL.

7. The preparation method according to claim 4, characterized in that, When the transition metal phosphide is Ni2P, the preparation method of the Ni2P comprises the following steps: Mixing a soluble transition metal nickel source, red phosphorus and an alcohol solvent, and performing a solvothermal reaction to obtain Ni2P; When the transition metal phosphide is CoP, the preparation method of the CoP comprises the following steps: Mixing a soluble transition metal cobalt source, ammonium fluoride, urea, red phosphorus and water, performing a solvothermal reaction to obtain a precursor, and annealing the precursor to obtain CoP.

8. The preparation method according to claim 4 or 7, characterized in that The temperature of the hydrothermal reaction is 120 - 180 °C, and the time is 4 - 18 h.

9. The preparation method according to claim 4 or 7, characterized in that, The temperature of the annealing is 300 - 550 °C, and the holding time is 10 - 200 min.

10. The application of the transition metal phosphide modified TiO2 gas sensor according to any one of claims 1 - 3 or the transition metal phosphide modified TiO2 gas sensor prepared by the preparation method according to any one of claims 4 - 9 in hydrogen detection.

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