Formaldehyde gas-sensitive material as well as preparation method and application thereof

Abstract

The invention discloses a formaldehyde gas-sensitive material as well as a preparation method and application thereof, and relates to the technical field of formaldehyde gas detection. According to the invention, samarium nitrate, lanthanum nitrate, ferric nitrate and palladium chloride are adopted as raw materials, citric acid is added as a complexing agent, and the formaldehyde gas-sensitive material can be synthesized by a one-step method through a hydrothermal reaction. The formaldehyde gas-sensitive material has excellent sensitivity to formaldehyde gas, and specifically, the response value of the formaldehyde gas-sensitive material at the working temperature of 140 DEG C for 1 ppm of formaldehyde gas is 6.83. Meanwhile, the SmFeO3 substrate material is modified through the combination of the La element and the Pd element, and a synergistic effect is achieved on improving the responsivity and the high selectivity of the formaldehyde gas sensitive material.

Description

Technical Field

[0001] The present invention relates to the technical field of formaldehyde gas detection, and in particular to a formaldehyde gas-sensitive material, a preparation method thereof, and an application thereof. Background Art

[0002] Formaldehyde (HCHO), also known as formic aldehyde, is a colorless and pungent gas. As a common indoor environmental pollutant, formaldehyde mainly comes from decoration materials, furniture, and industrial emissions, such as artificial boards, adhesives, etc. Formaldehyde can bind to proteins, and formaldehyde has been determined by the World Health Organization as a carcinogenic and teratogenic substance. Therefore, long-term exposure to a formaldehyde environment will not only cause symptoms such as respiratory irritation, skin irritation, and eye irritation, but there is even a certain carcinogenic risk. In addition, formaldehyde is not easily detectable at low concentrations and is easily masked by other odors. Therefore, it is of great significance to realize real-time monitoring of low-concentration formaldehyde in the environment.

[0003] ABO3 perovskite-type metal oxides are metal oxides with a composite structure. Compared with simple metal oxides, the composite metal oxides with a perovskite structure are more stable and reliable in terms of high-temperature chemical stability and crystal structure. Currently, LnFeO3 (Ln is a lanthanide element such as La, Sm, etc.) as a typical composite metal oxide with a perovskite structure has shown good potential as a gas-sensitive material in the field of gas sensing. In the prior art, the paper "Design and Performance Study of a Formaldehyde Gas Sensor Based on Lanthanum Ferrite Thin Films" (Xiangtan University, Chen Xiqi, June 2021) discloses the preparation of a LaFeO3 thin film gas sensor by the sol-gel spin coating method. Its detection limit for formaldehyde can be as low as 50 ppb at a working temperature of 120 °C, which can meet the lowest warning of the World Health Organization for indoor formaldehyde concentration. Although the LaFeO3 thin film gas sensor prepared in the above paper can detect formaldehyde gas at the ppb level, its response value (Rg / Ra) to 1 ppm of formaldehyde gas at the optimal working temperature of 120 °C is only 1.37. Thus, it can be seen that the above LaFeO3 thin film gas sensor has a very low sensitivity to 1 ppm of formaldehyde gas.

[0004] Therefore, it is necessary to develop a gas-sensitive material to improve its response value for detecting 1 ppm of formaldehyde gas, so as to achieve high-sensitivity detection of formaldehyde gas. Summary of the Invention

[0005] In view of the above-mentioned prior art, the object of the present invention is to provide a formaldehyde gas-sensitive material, a preparation method thereof, and an application thereof. The present invention uses samarium nitrate, lanthanum nitrate, iron nitrate, and palladium chloride as raw materials, adds citric acid as a complexing agent, and through a hydrothermal reaction, a formaldehyde gas-sensitive material can be synthesized by a one-step method. The formaldehyde gas-sensitive material has excellent sensitivity to formaldehyde gas. Specifically, the response value of the formaldehyde gas-sensitive material to 1 ppm of formaldehyde gas at a working temperature of 140 °C is 6.83. At the same time, the combination of La element and Pd element is used to modify the SmFeO3 substrate material, which has a synergistic effect in improving the response degree and high selectivity of the formaldehyde gas-sensitive material.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] In the first aspect of the present invention, a preparation method of a formaldehyde gas-sensitive material is provided, including the following steps:

[0008] (1) Using samarium nitrate, lanthanum nitrate, and iron nitrate as reaction raw materials, and citric acid as a complexing agent, after mixing the reaction raw materials and dissolving them in deionized water, then adding the complexing agent, adjusting the pH, a precursor solution is obtained;

[0009] (2) Adding a palladium chloride solution to the precursor solution, carrying out a hydrothermal reaction, after the reaction ends, cooling, centrifuging, collecting the solid after centrifugation, washing and drying, and thus obtaining the formaldehyde gas-sensitive material.

[0010] Preferably, the addition ratio of samarium nitrate, lanthanum nitrate, iron nitrate, palladium chloride, citric acid, and deionized water is (0.01 - 5) mol : (0.002 - 1) mol : (0.01 - 5) mol : (0.01 - 100) g : (10 - 50) g : (50 - 200) mL.

[0011] Preferably, in step (1), the pH is adjusted to 6.0 - 8.0.

[0012] Preferably, in step (1), ammonia water or sodium hydroxide solution is used to adjust the pH.

[0013] Preferably, in step (2), the hydrothermal reaction temperature is 150 - 200 °C, and the hydrothermal reaction time is 12 - 24 h.

[0014] Preferably, in step (2), it is washed 2 - 3 times with deionized water and ethanol.

[0015] Preferably, in step (2), the drying method is vacuum drying, the drying temperature is 70 - 90 °C, and the drying time is 6 - 12 h.

[0016] In the second aspect of the present invention, a formaldehyde gas-sensitive material prepared by the above preparation method is provided.

[0017] Preferably, the chemical formula of the formaldehyde gas-sensitive material is Xwt% Pd-Sm y La 1-y FeO3, where 0 < x ≤ 10 and 0 < y ≤ 0.5.

[0018] Preferably, the formaldehyde gas-sensitive material has a nanoparticle structure with an average particle size of 80-200 nm.

[0019] In a third aspect of the present invention, there is provided the use of the above gas-sensitive material in detecting formaldehyde gas.

[0020] Preferably, the concentration of the formaldehyde gas is 1-10 ppm.

[0021] In a fourth aspect of the present invention, there is provided the use of the above gas-sensitive material in preparing a formaldehyde gas sensor.

[0022] Preferably, the formaldehyde gas sensor is prepared by the following method:

[0023] The formaldehyde gas-sensitive material, deionized water and terpineol are mixed in a ratio of (1-5) g: (3-15) mL: (1-5) mL to obtain a slurry; the slurry is spin-coated on an alumina substrate to form a gas-sensitive film with a thickness of 100-300 μm, and the gas-sensitive film is aged at 180-220 °C for 10-24 hours to obtain the formaldehyde gas sensor.

[0024] Advantages of the present invention:

[0025] 1. The present invention uses samarium nitrate, lanthanum nitrate, iron nitrate and palladium chloride as raw materials, adds citric acid as a complexing agent, and through a hydrothermal reaction, the formaldehyde gas-sensitive material can be synthesized by a one-step method. The formaldehyde gas-sensitive material has excellent sensitivity to formaldehyde gas. Specifically, the response value of the formaldehyde gas-sensitive material to 1 ppm of formaldehyde gas at a working temperature of 140 °C is 6.83. In addition, the one-step hydrothermal synthesis of the formaldehyde gas-sensitive material in the present invention has a simple preparation process and is suitable for large-scale industrial promotion.

[0026] 2. The present invention uses SmFeO3 as the base material, dopes and modifies the A-site of the base material with La element while introducing Pd element for surface modification of the base material. The SmFeO3 base material is modified by the combination of La element and Pd element, which has a synergistic effect on improving the response degree and high selectivity of the formaldehyde gas-sensitive material. Among them, the A-site doping with La element increases the oxygen vacancy concentration, optimizes the surface charge distribution and electronic structure, and enhances the adsorption ability of the material to formaldehyde molecules; the surface modification with Pd element reduces the energy barrier of the formaldehyde oxidation reaction through its excellent catalytic performance, promotes the formation and regeneration of oxygen vacancies, accelerates the reaction kinetics of formaldehyde molecules with active sites, and thus promotes surface electron transfer and reaction activity. Description of the Drawings

[0027] Figure 1 : XRD pattern of the formaldehyde gas-sensitive material prepared in Example 1;

[0028] Figure 2 : SEM image of the formaldehyde gas-sensitive material prepared in Example 1;

[0029] Figure 3 : EDS Mapping images of Pd, La, and Sm elements in the formaldehyde gas-sensitive material prepared in Example 1;

[0030] Figure 4 : Relationship diagram between the gas-sensitive performance and temperature of the materials prepared in Example 1 and Comparative Examples 1-3 for 1 ppm formaldehyde gas;

[0031] Figure 5 : Relationship diagram between the gas-sensitive performance and humidity of the palladium-modified samarium lanthanum iron oxide prepared in Example 1 for 1 ppm formaldehyde gas;

[0032] Figure 6 : Schematic diagram of the long-term gas-sensitive stability of the palladium-modified samarium lanthanum iron oxide prepared in Example 1 for 1 ppm formaldehyde gas. Detailed Description of the Invention

[0033] It should be noted that the following detailed description is illustrative and is intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present application belongs.

[0034] In order to enable those skilled in the art to more clearly understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific examples.

[0035] The experimental materials used in the embodiments of the present invention are all conventional experimental materials in the art and can be obtained through commercial channels.

[0036] Example 1: Preparation of Formaldehyde Gas-Sensitive Material

[0037] (1) Using samarium nitrate (Sm(NO3)3·6H2O), lanthanum nitrate (La(NO3)3·6H2O) and iron nitrate (Fe(NO3)3·9H2O) as reaction raw materials, and citric acid as a complexing agent. After mixing the reaction raw materials, dissolve them in deionized water, then add the complexing agent, and add ammonia water to adjust the pH of the system to 7.0 to obtain a precursor solution;

[0038] (2) Add palladium chloride solution to the precursor solution so that the mass percentage of Pd is 5wt%. Carry out hydrothermal reaction at 180°C for 18h. After the reaction is completed, cool to room temperature, centrifuge the reaction product, collect the centrifuged solid, wash the precipitate 3 times with deionized water and ethanol, and then place the washed solid in a vacuum dryer at 80°C for 8h to obtain the formaldehyde gas-sensitive material 5wt% Pd-Sm 0.8 La 0.2 FeO3;

[0039] Among them, the addition amount ratio of samarium nitrate, lanthanum nitrate, iron nitrate, palladium chloride, citric acid and deionized water is 35.068g: 8.658g: 40.404g: 2.1g: 20g: 100mL.

[0040] Perform structural characterization on the formaldehyde gas-sensitive material prepared in this example, and the results are as Figures 1 - 3 shown.

[0041] From Figure 1 it can be seen that the crystallization peaks correspond to the crystal phases of (112), (202) and (200) of SmFeO3 (No. 74-1474). From Figure 2 it can be seen that the palladium-modified samarium lanthanum iron oxide presents a typical nanoparticle structure, with a relatively large specific surface area and porosity, and more reaction sites and transport channels for gas molecules. From Figure 3 it can be seen that there are Pd and La elements in the formaldehyde gas-sensitive material, and the three elements are evenly distributed. Thus, it can be seen that Pd and La elements are successfully doped into SmFeO3.

[0042] Example 2: Preparation of Formaldehyde Gas-Sensitive Material

[0043] (1) Using samarium nitrate (Sm(NO3)3·6H2O), lanthanum nitrate (La(NO3)3·6H2O) and iron nitrate (Fe(NO3)3·9H2O) as reaction raw materials, and citric acid as a complexing agent. After mixing the reaction raw materials, dissolve them in deionized water, then add the complexing agent, and add sodium hydroxide solution to adjust the pH of the system to 6.0 to obtain a precursor solution;

[0044] (2) Add palladium chloride solution to the precursor solution to make the mass percentage of Pd 8 wt%, and carry out hydrothermal reaction at 200 °C for 12 h. After the reaction is completed, cool it to room temperature, centrifuge the reaction product, collect the centrifuged solid, wash the precipitate 3 times with deionized water and ethanol, and then place the washed solid in a vacuum dryer at 80 °C for 10 h to obtain the formaldehyde gas-sensitive material 8 wt% Pd-Sm 0.8 La 0.2 FeO3;

[0045] Among them, the addition ratio of samarium nitrate, lanthanum nitrate, iron nitrate, palladium chloride, citric acid and deionized water is 35.068 g: 8.658 g: 40.404 g: 3.36 g: 30 g: 150 mL.

[0046] Example 3: Preparation of formaldehyde gas-sensitive material

[0047] (1) Use samarium nitrate (Sm(NO3)3·6H2O), lanthanum nitrate (La(NO3)3·6H2O) and iron nitrate (Fe(NO3)3·9H2O) as reaction raw materials, and citric acid as a complexing agent. After mixing the reaction raw materials, dissolve them in deionized water, then add the complexing agent, and add sodium hydroxide solution to adjust the pH of the system to 8.0 to obtain a precursor solution;

[0048] (2) Add palladium chloride solution to the precursor solution to make the mass percentage of Pd 2 wt%, and carry out hydrothermal reaction at 150 °C for 24 h. After the reaction is completed, cool it to room temperature, centrifuge the reaction product, collect the centrifuged solid, wash the precipitate 3 times with deionized water and ethanol, and then place the washed solid in a vacuum dryer at 80 °C for 6 h to obtain the formaldehyde gas-sensitive material 2 wt% Pd-Sm 0.8 La 0.2 FeO3;

[0049] Among them, the addition ratio of samarium nitrate, lanthanum nitrate, iron nitrate, palladium chloride, citric acid and deionized water is 35.068 g: 8.658 g: 40.404 g: 0.84 g: 10 g: 50 mL.

[0050] Comparative Example 1:

[0051] The difference between this comparative example and Example 1 is that lanthanum nitrate and palladium chloride were not added during the preparation process. Specifically as follows:

[0052] (1) Use samarium nitrate (Sm(NO3)3·6H2O) and iron nitrate (Fe(NO3)3·9H2O) as reaction raw materials, and citric acid as a complexing agent. After mixing the reaction raw materials, dissolve them in deionized water, then add the complexing agent, and add ammonia water to adjust the pH of the system to 7.0 to obtain a precursor solution;

[0053] (2) Place the precursor solution in a hydrothermal environment at 180 °C for 18 h. After the reaction is completed, cool it to room temperature. Centrifuge the reaction product, collect the centrifuged solid, wash the precipitate 3 times with deionized water and ethanol, and then place the washed solid in a vacuum dryer at 80 °C for 8 h to obtain the formaldehyde gas-sensing material SmFeO3.

[0054] Among them, the ratio of the addition amounts of samarium nitrate, iron nitrate, citric acid, and deionized water is 43.835 g: 40.404 g: 20 g: 100 mL.

[0055] Comparative Example 2:

[0056] The difference between this comparative example and Example 1 is that palladium chloride was not added during the preparation process. Specifically as follows:

[0057] (1) Use samarium nitrate (Sm(NO3)3·6H2O), lanthanum nitrate (La(NO3)3·6H2O), and iron nitrate (Fe(NO3)3·9H2O) as reaction raw materials, and citric acid as a complexing agent. After mixing the reaction raw materials, dissolve them in deionized water, then add the complexing agent, and add ammonia water to adjust the pH of the system to 7.0 to obtain a precursor solution;

[0058] (2) Hydrothermally treat the precursor solution at 180 °C for 18 h. After the reaction is completed, cool it to room temperature. Centrifuge the reaction product, collect the centrifuged solid, wash the precipitate 3 times with deionized water and ethanol, and then place the washed solid in a vacuum dryer at 80 °C for 8 h to obtain the formaldehyde gas-sensing material Sm 0.8 La 0.2 FeO3;

[0059] Among them, the ratio of the addition amounts of samarium nitrate, lanthanum nitrate, iron nitrate, palladium chloride, citric acid, and deionized water is 35.068 g: 8.658 g: 40.404 g: 2.1 g: 20 g: 100 mL.

[0060] Comparative Example 3:

[0061] The difference between this comparative example and Example 1 is that lanthanum nitrate was not added during the preparation process. Specifically as follows:

[0062] (1) Use samarium nitrate (Sm(NO3)3·6H2O) and iron nitrate (Fe(NO3)3·9H2O) as reaction raw materials, and citric acid as a complexing agent. After mixing the reaction raw materials, dissolve them in deionized water, then add the complexing agent, and add ammonia water to adjust the pH of the system to 7.0 to obtain a precursor solution;

[0063] (2) Add palladium chloride solution to the precursor solution so that the mass percentage of Pd is 5 wt%, carry out hydrothermal reaction at 180 °C for 18 h. After the reaction is completed, cool to room temperature, centrifuge the reaction product, collect the centrifuged solid, wash the precipitate 3 times with deionized water and ethanol, and then place the washed solid in a vacuum dryer at 80 °C for 8 h to obtain the formaldehyde gas-sensitive material 5 wt% Pd-Sm 0.8 La 0.2 FeO3;

[0064] Among them, the addition ratio of samarium nitrate, iron nitrate, palladium chloride, citric acid and deionized water is 35.068 g: 40.404 g: 2.1 g: 20 g: 100 mL.

[0065] Test example:

[0066] Coat the materials prepared in Example 1 and Comparative Examples 1-3 on the sensing film, and detect their gas-sensitive response (Rg / Ra) to formaldehyde gas. The results are as Figures 4 - 6 shown. Among them, Ra is the resistance of the sensor in air, and Rg is the resistance of the gas to be measured. The experimental environment is: RH is 20%, and the ambient temperature is 20 °C.

[0067] It can be seen from Figure 4 that the optimal working temperature of the formaldehyde gas-sensitive material prepared by the present invention is 140 °C. At the working temperature of 140 °C, the formaldehyde gas-sensitive material 5 wt% Pd-Sm 0.8 La 0.2 FeO3 has a response value of 6.83 to 1 ppm of formaldehyde gas. The response value of the SmFeO3 material prepared in Comparative Example 1 to 1 ppm of formaldehyde gas is 1.67. The response value of the Sm 0.8 La 0.2 FeO3 prepared in Comparative Example 2 to 1 ppm of formaldehyde gas is 2.93. The response value of the 5 wt% Pd-SmFeO3 prepared in Comparative Example 3 to 1 ppm of formaldehyde gas is 4.36. It can be seen that by loading and modifying the surface noble metal Pd of the SmFeO3 material and doping the La element at the B site, there is a synergistic effect in improving the response value of the material to formaldehyde gas.

[0068] Figure 5 shows the relationship diagram between the gas-sensitive performance of the formaldehyde gas-sensitive material 5 wt% Pd-Sm 0.8 La 0.2 FeO3 prepared by the present invention to 1 ppm of formaldehyde gas and humidity. It can be seen from Figure 5 that as the relative humidity increases, the gas-sensitive performance gradually decreases. When the relative humidity exceeds 40%, the gas-sensitive performance drops sharply, but within 40%, the change rate of the formaldehyde gas-sensitive performance of the formaldehyde gas-sensitive material is within 8%, indicating extremely high gas-sensitive relative humidity resistance.

[0069] Figure 6 shows the long-term stability of the formaldehyde gas-sensitive material 5wt% Pd-Sm 0.8 La 0.2 FeO3 to 1 ppm of formaldehyde gas. As can be seen from the figure, within one month, the response value change rate of the formaldehyde gas-sensitive material 5wt% Pd-Sm 0.8 La 0.2 FeO3 to 1 ppm of formaldehyde gas is within 3%. It can be seen that the formaldehyde gas-sensitive material prepared by the present invention has extremely high long-term gas-sensing stability.

[0070] The above are only the preferred embodiments of the present application and are not intended to limit the present application. For those skilled in the art, various changes and modifications can be made to the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A preparation method of a formaldehyde gas-sensitive material, characterized in that, It includes the following steps: (1) Using samarium nitrate, lanthanum nitrate and iron nitrate as reaction raw materials, and citric acid as a complexing agent. After mixing the reaction raw materials and dissolving them in deionized water, then adding the complexing agent, adjusting the pH, a precursor solution is obtained; (2) Adding a palladium chloride solution to the precursor solution, carrying out a hydrothermal reaction. After the reaction ends, cooling and centrifuging, collecting the solid after centrifugation, washing and drying, to obtain a formaldehyde gas-sensitive material; The addition amount ratio of samarium nitrate, lanthanum nitrate, iron nitrate, palladium chloride, citric acid and deionized water is (0.01 - 5) mol : (0.002 - 1) mol : (0.01 - 5) mol : (0.01 - 100) g : (10 - 50) g : (50 - 200) mL.

2. The preparation method of the formaldehyde gas-sensitive material according to claim 1, wherein, In step (1), ammonia water or sodium hydroxide solution is used to adjust the pH to 6.0 - 8.

0.

3. The preparation method of the formaldehyde gas-sensitive material according to claim 1, characterized in that, In step (2), the hydrothermal reaction temperature is 150 - 200 °C, and the hydrothermal reaction time is 12 - 24 h.

4. The preparation method of the formaldehyde gas-sensitive material according to claim 1, characterized in that, In step (2), the drying method is vacuum drying, the drying temperature is 70 - 90 °C, and the drying time is 6 - 12 h.

5. The formaldehyde gas-sensitive material prepared by the preparation method according to any one of claims 1-4, characterized in that, The chemical formula of the formaldehyde gas-sensing material is Xwt% Pd-Sm y La 1-y FeO3, where 0 < x ≤ 10 and 0 < y ≤ 0.

5.

6. Application of the formaldehyde gas-sensitive material according to claim 5 in detecting formaldehyde gas.

7. The application according to claim 6, characterized in that, The concentration of the formaldehyde gas is 1 - 10 ppm.

8. Application of the formaldehyde gas-sensitive material according to claim 5 in preparing a formaldehyde gas sensor.

9. The application according to claim 8, characterized in that, The formaldehyde gas sensor is prepared by the following method: Mixing the formaldehyde gas-sensitive material according to claim 5, deionized water and terpineol in a ratio of (1 - 5) g : (3 - 15) mL : (1 - 5) mL to obtain a slurry; spin-coating the slurry on an alumina substrate to form a gas-sensitive film with a thickness of 100 - 300 μm, and aging the gas-sensitive film at 180 - 220 °C for 10 - 24 hours to obtain a formaldehyde gas sensor.

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