CN113358710B - Olivine structure gas sensitive material for detecting formaldehyde and preparation method thereof - Google Patents
Olivine structure gas sensitive material for detecting formaldehyde and preparation method thereof Download PDFInfo
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Abstract
An olivine structure gas sensitive material with high sensitivity and excellent selectivity to formaldehyde and a preparation method thereof belong to the technical field of gas sensitive materials. The gas sensitive material with an olivine structure is prepared by taking a germanium source, a silicon source, a cadmium source and a surfactant as raw materials and adopting a hydrothermal synthesis method, and comprises cadmium germanate, cadmium silicon germanate, cadmium silicate and a compound thereof. The test result shows that: the material is composed of nano-sheets, the thickness of the nano-sheets is about 20nm, and the diameter of the nano-sheets is about 200 nm. At a lower working temperature (140 ℃), the material has high sensitivity to formaldehyde, extremely low detection lower limit and quick response recovery capability, and has small response to other volatile organic compounds (such as acetone, benzene, toluene, xylene, nitrobenzene and the like). The preparation method is a hydrothermal synthesis method, and the method has the advantages of simple required equipment, mild production conditions, simple process, stable structure of the target material and easy batch production and application.
Description
Technical Field
The invention belongs to the technical field of gas-sensitive materials, and particularly relates to an olivine structure gas-sensitive material with high sensitivity and excellent selectivity on formaldehyde and a preparation method thereof.
Background
Gas sensors are devices used to detect gas concentrations and components, and play an extremely important role in environmental protection and safety monitoring. Gas sensors are widely available, and among them, the most widely used is semiconductor gas sensors. This is because the semiconductor gas sensor has advantages of high sensitivity, fast response, long service life, low cost, and the like.
Formaldehyde is one of the main indoor gaseous pollutants and is extremely harmful to human bodies. The mild indoor excessive formaldehyde concentration can enhance the discomfort of people; the excessive concentration of formaldehyde in severe indoor environment can greatly increase the cancer probability of human bodies. Meanwhile, due to the lack of the ability of the human body to rapidly metabolize formaldehyde, formaldehyde can accumulate in the human body for a long time, causing continuous damage to the human body. According to the regulation of the indoor environmental pollution control code of civil building engineering (GB50325-2010) in China, the indoor formaldehyde concentration of the civil building is lower than 0.08mg/m3(about 60 ppb).
Currently, various nanostructured semiconductor oxides (e.g., In)2O3，SnO2ZnO, etc.) have been used in the detection of volatile organic compounds such as formaldehyde. However, these materials generally have more or less problems, and cannot fully meet the index requirements of indoor air detection such as sensitivity, selectivity, long-term stability, rapid response-recovery, and the like. Aiming at the problems, the development of a new formaldehyde sensitive material is significant.
In the present invention, we developed a novel gas sensitive material of olivine structure. The material reaches practical standards in the aspects of sensitivity, detection limit and other key indexes, and has potential of practical application.
Disclosure of Invention
The invention aims to provide a novel gas sensitive material with high sensitivity and excellent selectivity on formaldehyde, namely an olivine structure gas sensitive material and a preparation method thereof. Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) showed that: the material is composed of nano-sheets, the thickness of the nano-sheets is about 20nm, and the diameter of the nano-sheets is about 200 nm. At a lower working temperature (140 ℃), the material has high sensitivity to formaldehyde, and has extremely low detection limit and quick response recovery capability. The preparation method of the material is a hydrothermal synthesis method, the method needs simple equipment, the production condition is mild, the structure of the target material is stable, and the batch production and application are easy.
The invention relates to a preparation method of an olivine structure gas sensitive material with high sensitivity and excellent selectivity to formaldehyde, which takes cadmium germanate as an example and comprises the following steps:
(1) adding alkali into deionized water, and preparing an alkali solution with the concentration of 0.01-2 mol/L;
(2) Weighing a germanium source, adding the germanium source into the alkali solution obtained in the step (1) and stirring the solution, wherein the concentration of the germanium source is 0.01-1 mol/L;
(3) weighing a cadmium source, a silicon source or a cadmium source and a silicon source, adding the cadmium source and the silicon source into deionized water, and preparing a solution with the sum concentration of cadmium and silicon being 0.01-3 mol/L;
(4) mixing the solutions obtained in the step (2) and the step (3), adding a surfactant, and stirring for 10-30 minutes; transferring the stirred mixed solution into a reaction kettle, and carrying out hydrothermal reaction at 180-220 ℃ for 10-48 hours; the molar ratio of the germanium source to the cadmium source to the surfactant is 1: (1-4): (0.02-0.4);
(5) after the reaction kettle is cooled to room temperature, centrifugally separating reaction liquid, washing a centrifugal product with deionized water to be neutral, and drying at 60-90 ℃ for 10-20 hours to obtain the olivine structure gas-sensitive material with high sensitivity and excellent selectivity to formaldehyde, wherein the olivine structure gas-sensitive material is cadmium germanate (Cd)2GeO4) Cadmium silicate (Cd)2SiO4) Cadmium silicate (Cd)2Si(1-x)GexO4) Wherein 0 is<x<1。
The alkali in the step (1) is one or more of potassium hydroxide, sodium hydroxide, ammonia water, tetramethyl ammonium hydroxide, tetraethyl ammonium hydroxide and tetrapropyl ammonium hydroxide;
The germanium source in the step (2) is one or more of simple substance germanium, germanium oxide, sodium metagermanate and potassium metagermanate.
The silicon source in the step (2) is one or more of simple substance silicon, silicon oxide, sodium silicate, silica sol and potassium silicate.
In the step (3), the cadmium source is Cd (OH)2、CdI2、CdCO3、Cd(NO3)2、CdCl2、Cd(Ac)2One or more of;
the surfactant in the step (4) is one or more of polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer (P123), polyoxyethylene polyoxypropylene ether block copolymer (F127), Ethylene Diamine Tetraacetic Acid (EDTA), lauryl sulfosuccinate monoester Disodium (DLS) and fatty acid methyl ester sodium sulfonate (MES).
The olivine structure gas-sensitive material is prepared by the method.
The invention relates to a gas sensor with high sensitivity and excellent selectivity to formaldehyde, which consists of an alumina ceramic tube, a nickel-chromium alloy heating wire and a base; annular, mutually-separated and parallel gold electrodes are respectively distributed at two ends of the outer surface of the alumina ceramic tube, and each gold electrode is connected with two platinum wire leads; the olivine structure gas-sensitive material is coated on the outer surface of the alumina ceramic tube and the gold electrode; the nickel-chromium alloy heating wire penetrates through the inside of the alumina ceramic tube and has the function of providing stable working temperature for the gas sensitive element. The invention has the following advantages:
1. The olivine structure gas-sensitive material has low preparation cost and simple operation.
2. The olivine gas-sensitive material has high formaldehyde response value and low detection lower limit, and the detection lower limit is superior to the national specified standard, thus having practical application value.
3. The gas sensor prepared from the olivine structure gas-sensitive material has the advantages of simple preparation process, small volume, low working temperature, low energy consumption, good repeatability, good long-term stability and portability. The prepared sensor shows ultrahigh response to formaldehyde gas, and has very small response to other volatile organic compounds (such as acetone, benzene, toluene, xylene, nitrobenzene and the like), so that the material has excellent selectivity to formaldehyde, and has a wide application prospect in the field of gas sensing.
Drawings
FIG. 1: cadmium germanate (Cd) obtained in example 12GeO4) Scanning Electron Microscope (SEM) photographs of the nanoplatelets.
FIG. 2: (A) the response-recovery curve of a gas-sensitive device based on the cadmium germanate nanosheets obtained in example 1 to 10ppm formaldehyde. (B) The response-recovery curve of a gas-sensitive device based on the cadmium germanate nanosheets obtained in example 1 to 60ppb formaldehyde. The abscissa of fig. 2 is the resistance value of the gas sensitive device between two gold electrodes in air and formaldehyde atmosphere.
FIG. 3: a histogram of response values of gas-sensitive devices based on the cadmium germanate nanosheets obtained in example 1 for 10ppm of different gases. The response value is Ra/Rg, wherein Ra is the resistance value of the gas-sensitive device between two gold electrodes in the formaldehyde atmosphere, and Rg is the resistance value of the gas-sensitive device between two gold electrodes in the air atmosphere.
As shown in figure 1, the material is cadmium germanate with an olivine structure(Cd2GeO4) The thickness of the nanosheet layer is about 20nm, and the diameter of the nanosheet layer is about 200 nm.
As shown in FIG. 2A, from cadmium germanate (Cd)2GeO4) The gas-sensitive device prepared by the nanosheets has a response value of 1420% to 10ppm of formaldehyde, a response time of 5 seconds and a recovery time of less than 100 seconds. As shown in FIG. 2B, from cadmium germanate (Cd)2GeO4) The response value of the gas sensitive device prepared by the nano-sheets to 60ppb formaldehyde is 128%, which shows that the lower detection limit of the sensor reaches 60 ppb. Can meet the requirements of practical application.
As shown in FIG. 3, from cadmium germanate (Cd)2GeO4) The gas-sensitive device prepared by the nano-sheets basically does not respond to other gases except formaldehyde, and confirms that cadmium germanate (Cd)2GeO4) Excellent selectivity of the nanosheets to formaldehyde.
The present invention is further illustrated by the following examples, but the scope of the present invention is not limited to the following examples. It will be apparent to those skilled in the art that variations or modifications of the present invention can be made without departing from the spirit and scope of the invention, and these variations or modifications are also within the scope of the invention.
Detailed Description
Example 1: preparation of olivine structure gas-sensitive sensing material
(1) Adding 5mmol of sodium hydroxide (NaOH) into 5mL of deionized water to prepare an alkali solution with the concentration of 1 mol/L;
(2) 26.2mg germanium oxide (GeO) was weighed out2) Adding the mixture into the alkali solution obtained in the step (1), and stirring for dissolving; the molar concentration of the germanium solution is 0.05 mol/L;
(3) 114.2mg of cadmium chloride pentahydrate (CdCl) were weighed out2·2.5H2O), adding the cadmium solution into 5mL of deionized water to prepare a cadmium solution with the concentration of 0.1 mol/L;
(4) mixing the solutions obtained in the step (2) and the step (3), adding 50mg of surfactant polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer (P123), and stirring for 15 minutes; transferring the stirred mixed solution into a reaction kettle, and carrying out hydrothermal reaction for 12 hours at the temperature of 200 ℃;
(5) after the reaction kettle is cooled to room temperature, centrifugally separating reaction liquid, washing a centrifugal product with deionized water to be neutral, and then drying at 80 ℃ for 12 hours to obtain the olivine cadmium germanate nanosheet gas-sensitive material with high sensitivity and excellent selectivity to formaldehyde, wherein the mass of the product is about 50 mg.
Example 2: manufacturing and gas-sensitive property of gas-sensitive device based on cadmium germanate nanosheets
The gas sensitive element mainly comprises an alumina ceramic tube, a nickel-chromium alloy heating wire and a base. Wherein the length of the alumina ceramic tube is 4mm, and the diameter is 1 mm. Annular, mutually-separated and parallel gold electrodes are respectively distributed at two ends of the outer surface of the ceramic tube, the distance between the two gold electrodes is 1.15mm, the width of each gold electrode is 0.5mm, and each gold electrode is connected with two platinum wire leads. The heating part is a nickel-chromium alloy heating wire, penetrates through the inside of the alumina ceramic tube and is used for providing stable working temperature for the gas sensitive element.
The preparation steps of the gas sensor are as follows, (1) 50 mg of cadmium germanate nanosheet prepared in example 1 is placed in an agate mortar, 10mL of absolute ethyl alcohol with the mass fraction of 95% is added, and the mixture is fully ground for 10 minutes to obtain thick slurry. (2) The slurry was uniformly coated on the outer surface of the ceramic tube with a small clean brush and dried at room temperature. The gas-sensitive material forms a uniform film on the outer surface of the ceramic tube, and the film covers the gold electrode, and the thickness of the film is 0.1 mm. (3) And respectively welding platinum wire leads connected with the gold electrodes on the ceramic tubes with corresponding electrodes of the gas sensitive element base. And then the nickel-chromium alloy heating wire penetrates through the ceramic tube, and two ends of the nickel-chromium alloy heating wire are respectively welded on corresponding electrodes of the gas sensitive element base. (4) The gas sensor was aged at 140 ℃ for 24 hours. Thereby preparing the gas sensor.
Claims (6)
1. A preparation method of an olivine structure gas sensitive material with high sensitivity and excellent selectivity to formaldehyde comprises the following steps:
(1) adding alkali into deionized water, and preparing 0.01-2 mol/L alkali solution;
(2) weighing a germanium source, adding the germanium source into the alkali solution obtained in the step (1) and stirring the solution, wherein the concentration of the germanium source is 0.01-1 mol/L;
(3) weighing a cadmium source, adding the cadmium source into deionized water, and preparing a solution with the cadmium concentration of 0.01-3 mol/L;
(4) mixing the solutions obtained in the step (2) and the step (3), adding a surfactant, and stirring for 10-30 minutes; transferring the stirred mixed solution into a reaction kettle, and carrying out hydrothermal reaction at 180-220 ℃ for 10-48 hours; the molar ratio of the germanium source to the cadmium source to the surfactant is 1: 1-4: 0.02 to 0.4;
(5) after the reaction kettle is cooled to room temperature, centrifugally separating the reaction liquid, washing the centrifugal product with deionized water to be neutral, and then drying at 60-90 ℃ for 10-20 h to obtain the olivine structure gas-sensitive material cadmium germanate Cd with high sensitivity and excellent selectivity to formaldehyde2GeO4。
2. The method for preparing the olivine-structured gas-sensitive material having high sensitivity and excellent selectivity to formaldehyde according to claim 1, wherein: the alkali in the step (1) is one or more of potassium hydroxide, sodium hydroxide, ammonia water, tetramethyl ammonium hydroxide, tetraethyl ammonium hydroxide and tetrapropyl ammonium hydroxide.
3. The method for preparing the olivine-structured gas-sensitive material having high sensitivity and excellent selectivity for formaldehyde according to claim 1, wherein: the germanium source in the step (2) is one or more of simple substance germanium, germanium oxide, sodium metagermanate and potassium metagermanate.
4. The method for preparing the olivine-structured gas-sensitive material having high sensitivity and excellent selectivity to formaldehyde according to claim 1, wherein: in the step (3), the cadmium source is Cd (OH)2、CdI2、CdCO3、Cd(NO3)2、CdCl2And Cd (Ac)2One or more of them.
5. The method for preparing the olivine-structured gas-sensitive material having high sensitivity and excellent selectivity for formaldehyde according to claim 1, wherein: the surfactant in the step (4) is one or more of polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer, polyoxyethylene polyoxypropylene ether block copolymer, ethylene diamine tetraacetic acid, lauryl sulfonated succinic acid monoester disodium and fatty acid methyl ester sodium sulfonate.
6. An olivine structure gas sensitive material having high sensitivity and excellent selectivity to formaldehyde, characterized in that: is prepared by the method of any one of claims 1 to 5.
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