Light-excited formaldehyde gas sensor and preparation process thereof

[0030] Example 1

[0031] A light-excited formaldehyde gas sensor, including a light source, a gas-sensitive material and a substrate, the gas-sensitive material is evenly coated on the surface of the substrate, and the gas-sensitive material is composed of a hollow microsphere zinc oxide tin dioxide double-layer heterojunction Composite nanomaterials, coated with a thickness of 1 μm to 100 μm. The hollow microsphere zinc oxide tin dioxide double-layer heterojunction composite nanomaterial is composed of a tin dioxide nano hollow sphere in the inner layer and a zinc oxide coating shell in the outer layer, and the zinc oxide coating shell accounts for 100% of the composite nanomaterial. 10%-30% of the mass. The diameter of the composite nanomaterial sphere is 100nm-300nm, the diameter of the inner tin dioxide hollow nanosphere is about 100nm-250nm, the thickness of the tin dioxide spherical shell is about 10nm-20nm, and the outer zinc oxide shell is about 20nm -40nm, the gap between the two layers of spherical shells is about 3nm-5nm, the overall thickness of the spherical shell is 30nm-50nm, and the mesoporous structure is evenly distributed on the surface of the sphere.

[0032] Step 1, preparing tin dioxide hollow nanospheres: mix carbon microspheres with a diameter of 500nm-1 μm and ethanol evenly to obtain suspension A with a material concentration of carbon microspheres of 0.25g/mL; dissolve tin tetrachloride pentahydrate In ethanol, the concentration of tin tetrachloride pentahydrate is 1mol/L to obtain a suspension B; the two suspensions are mixed in a volume ratio of 1:1, and the mixed solution is obtained after ultrasonic stirring; then the mixed solution is allowed to stand for 24 hours, wash and filter with ethanol, place the filtered solid in a drying oven to dry to obtain a carbon ball tin mixture, put the carbon ball tin mixture into a muffle furnace and calcined to 500 ° C to remove the carbon balls to obtain SnO2 nano hollow balls;

[0033]Step 2, prepare the zinc-tin precursor solution: dissolve the zinc acetate and the SnO2 hollow nanospheres prepared in step 1 into deionized water respectively to obtain a solution A with a concentration of zinc acetate of 0.08mol/L, and a concentration of SnO2 hollow nanospheres of 0.03 g/mL suspension B, mix the two liquids at a volume ratio of 1:1, adjust the pH to neutral with ammonia water after stirring evenly, and obtain the zinc-tin precursor solution;

[0034] Step 3, preparing a cetyltrimethylammonium bromide surfactant aqueous solution with a concentration of 0.042mol/L for connecting zinc ions and SnO2 hollow nanospheres;

[0035] Step 4, preparing hollow microsphere zinc oxide tin dioxide double-layer heterojunction composite nanomaterials: mixing the zinc-tin precursor solution prepared in step 2 with the surfactant solution prepared in step 3 in a volume ratio of 1:1, After stirring evenly, transfer the obtained liquid to a polytetrafluoroethylene stainless steel high-pressure reaction kettle, and heat it in a drying oven; take out the heated mixed liquid, wash the sample repeatedly with deionized water and ethanol, and place the sample after drying Calcined in a muffle furnace to 600°C to remove the surfactant to prepare a hollow microsphere zinc oxide tin dioxide double-layer heterojunction composite nanomaterial;

[0036] Step 5, prepare formaldehyde gas sensor: disperse the hollow microsphere zinc oxide tin dioxide double-layer heterojunction composite nanomaterial prepared in step 4 into ethanol to form a dispersion of 5 mg/mL~15 mg/mL, take 40 μL~ 60 μL of the dispersion was coated on the surface of the substrate and dried to obtain a formaldehyde gas sensor.

[0037] The hollow microsphere zinc oxide tin dioxide double-layer heterojunction composite nanomaterial sample obtained in this example is subjected to X-ray diffraction and electron microscope transmission, and the results obtained are shown in the accompanying drawings. figure 1 , figure 2.

[0038] Example 2

[0039] see image 3 As shown, a light-excited formaldehyde gas sensor testing system provided in this embodiment includes a multimeter, a fan, a sensor, an ultraviolet LED, and a heater. The gas sensor is a thick film resistive sensor, and the thickness of the sensitive material is about 1 μm to 100 μm.

[0040] Wherein, the gas sensor includes a semiconductor gas sensitive material and a substrate.

[0041] The semiconductor gas-sensing material is a hollow microsphere zinc oxide tin dioxide double-layer heterojunction composite nanomaterial, which is prepared by template method and high temperature calcination. The diameter of a single hollow nanosphere is about 100-300nm, and the thickness of the spherical shell is 30-50nm. An organic solvent is applied to the surface of the substrate.

[0042] The substrate is a Si substrate with Au electrodes.

[0043] Among them, the ultraviolet light LED is a bead-type LED light source with a light wavelength of 365nm and a power of 75mW.

[0044] Wherein, the necessary parameter setting of the multimeter is set by computer.

[0045] Wherein, the light source is placed on the vertical plane of the gas sensor, specifically the surface of the sensor is 5 cm.

[0046] The gas sensor of this embodiment is used to detect 1-100ppm formaldehyde gas.

[0047] see figure 1 As shown, the gas sensor operates at room temperature under air conditions. Set the necessary parameters of the multimeter through the PC, detect the resistance value of the sensor surface, and form a sensing signal. The gas sensor is excited by light for a certain period of time, and the resistance value tends to be stable. The resistance change of the gas sensor displayed on the PC in the air and in the environment of different concentrations of formaldehyde with air as the background is used as the response recovery signal of the sensor. Figure 4 It is the resistance change curve of the hollow microsphere zinc oxide tin dioxide double-layer heterojunction composite nanomaterial gas sensor to 1-100ppm formaldehyde under the excitation of 365nm light in the wavelength band of room temperature. It can be seen that the sensor shows a good response to low concentration formaldehyde. Formaldehyde gas can be detected accurately, with faster recovery and response times than similar sensors, and can work well at room temperature.

[0048] Example 3

[0049] A light-excited formaldehyde gas sensor, including a light source, a gas-sensitive material and a substrate, the gas-sensitive material is evenly coated on the surface of the substrate, and the gas-sensitive material is composed of a hollow microsphere zinc oxide tin dioxide double-layer heterojunction Composite nanomaterials, coated with a thickness of 1 μm to 100 μm. The hollow microsphere zinc oxide tin dioxide double-layer heterojunction composite nanomaterial is composed of a tin dioxide nano hollow sphere in the inner layer and a zinc oxide coating shell in the outer layer, and the zinc oxide coating shell accounts for 100% of the composite nanomaterial. 10%-30% of the mass. The diameter of the composite nanomaterial sphere is 100nm-300nm, the diameter of the inner tin dioxide hollow nanosphere is about 100nm-250nm, the thickness of the tin dioxide spherical shell is about 10nm-20nm, and the outer zinc oxide shell is about 20nm -40nm, the gap between the two layers of spherical shells is about 3nm-5nm, the overall thickness of the spherical shell is 30nm-50nm, and the mesoporous structure is evenly distributed on the surface of the sphere.

[0050] Step 1, preparing hollow tin dioxide nanospheres: mixing carbon microspheres with a diameter of 500nm-1 μm and ethanol evenly to obtain suspension A with a material concentration of carbon microspheres of 0.28g/mL; dissolving tin protochloride dihydrate In ethanol, a suspension B with a concentration of stannous chloride dihydrate of 1.2mol/L was obtained; the two suspensions were mixed at a volume ratio of 1:1, and the mixed solution was obtained after ultrasonic stirring and mixing; then the mixed solution was left to stand After 24 hours, wash and filter with ethanol, and dry the filtered solid in a drying oven to obtain a carbon ball tin mixture. Put the carbon ball tin mixture into a muffle furnace and calcinate to 500°C to remove the carbon balls to obtain SnO2 hollow nanospheres ;

[0051] Step 2, preparing zinc-tin precursor solution: dissolving zinc sulfate and the SnO2 hollow nanospheres prepared in step 1 into deionized water respectively to obtain solution A with a concentration of zinc sulfate of 0.06mol/L and a concentration of SnO2 hollow nanospheres of 0.04 g/mL suspension B, mix the two liquids at a volume ratio of 1:1, adjust the pH to neutral with ammonia water after stirring evenly, and obtain the zinc-tin precursor solution;

[0052] Step 3, preparing an aqueous solution of octadecyldimethylbenzyl ammonium bromide surfactant with a concentration of 0.038mol/L for connecting zinc ions and SnO2 hollow nanospheres;

[0053] Step 4, preparing hollow microsphere zinc oxide tin dioxide double-layer heterojunction composite nanomaterials: mixing the zinc-tin precursor solution prepared in step 2 with the surfactant solution prepared in step 3 in a volume ratio of 1:1, After stirring evenly, transfer the obtained liquid to a polytetrafluoroethylene stainless steel high-pressure reaction kettle, and heat it in a drying oven; take out the heated mixed liquid, wash the sample repeatedly with deionized water and ethanol, and place the sample after drying Calcined in a muffle furnace to 500°C to remove the surfactant to prepare a hollow microsphere zinc oxide tin dioxide double-layer heterojunction composite nanomaterial;

[0054] Step 5, preparing formaldehyde gas sensor: disperse the hollow microsphere zinc oxide tin dioxide double-layer heterojunction composite nanomaterial prepared in step 4 into acetone to form a dispersion of 5 mg/mL~15 mg/mL, take 40 μL~ 60 μL of the dispersion was coated on the surface of the substrate and dried to obtain a formaldehyde gas sensor.

[0055] The material of the semiconductor gas sensor selected in this embodiment is a hollow microsphere zinc oxide tin dioxide double-layer heterojunction composite nanomaterial, and the test gas is 100 ppm formaldehyde, ammonia water, ethanol, benzene, methanol, and acetone. Figure 5 It is a comparative response diagram of the formaldehyde sensor of the present invention to other volatile gases and formaldehyde under the excitation of 365nm light at room temperature. It can be seen that the response of the sensor to formaldehyde gas is several times that of other gases, indicating that the sensor has a high response sensitivity to formaldehyde gas.

[0056] As can be seen from the above examples, the present invention adopts the template method, realizes zinc oxide particles wrapping tin dioxide nano hollow spheres through two-step synthesis and calcining, and forms hollow microspheres zinc oxide tin dioxide double-layer heterojunction composite nanomaterials, double-layer hollow The microporous characteristics of the microsphere structure can greatly improve the gas adsorption capacity of the gas-sensing material, and the double-shell structure greatly increases the specific surface area of ​​the material and strengthens the gas-sensing performance of the material. A heterojunction is formed in the composite material wrapped with zinc oxide particles, which allows electrons to migrate and strengthens the characteristics of the material with superior gas-sensing performance. The use of 365nm band LED to excite the material greatly increases the electron concentration on the surface of the material, which strengthens the response strength of the material to volatile gases, so that the material can work at room temperature, and the electrons jump from the HOMO orbital on the surface of the material to the measured gas The phenomenon of molecular LOMO orbitals greatly enhances the selectivity of the material to different gases, and at the same time strengthens the recovery performance of the material in response to formaldehyde gas and accelerates the desorption of gas molecules.