CN108398408A - A kind of composite air-sensitive material and preparation method thereof for formaldehyde gas detection - Google Patents

Abstract

The present invention provides a kind of composite air-sensitive materials for formaldehyde gas detection, it is combined with graphene quantum dot material by two-dimensional sheet metal oxide, the mass percentage that two-dimensional sheet metal oxide accounts for the composite material is 70% 99.99%, and the mass percentage that graphene quantum dot material accounts for the composite material is 0.01% 30%.The present invention also provides a kind of preparation methods of above-mentioned composite air-sensitive material for formaldehyde gas detection.The present invention also provides a kind of gas sensors, including a semiconductor element, in the above-mentioned composite air-sensitive material for formaldehyde gas detection of the surface even application of the semiconductor element.The present invention also provides the preparation methods of above-mentioned gas sensor.The advantages that gas sensor of the present invention has PARA FORMALDEHYDE PRILLS(91,95) gas sensitivity higher, and operating temperature is low, selectively preferable to interference gas, and stability is preferable and operating temperature is relatively low can be applied to the formaldehyde gas detection under different occasions.

Description

A composite gas sensitive material for formaldehyde gas detection and its preparation method

technical field

The invention belongs to the field of semiconductor materials, and relates to metal oxide semiconductor gas-sensitive materials, in particular to a composite gas-sensitive material for formaldehyde gas detection and a preparation method thereof.

Background technique

As one of the top ten chemicals with the highest output in the world, formaldehyde is a chemical substance in great demand. It is widely used in daily life. For example, adding formaldehyde-containing additives in the process of fabric processing can make Cloth has the advantages of anti-wrinkle, anti-shrinkage and flame-retardant; in addition, it also exists in various synthetic adhesives, among which urea-formaldehyde resin synthesized by formaldehyde and urea under certain reaction conditions has an irreplaceable role in the wood processing industry. status. However, along with the extensive use of formaldehyde in various fields, there are inevitably some troublesome side effects, that is, the indoor formaldehyde content exceeds the standard, which seriously affects people's health, especially for children, the elderly, pregnant women and others. People with weakened resistance are extremely harmful. At present, formaldehyde is listed as a primary carcinogen by the International Agency for Research on Cancer (IARC), and its harm to the human body is well known. There are many methods for determining the concentration of formaldehyde, such as phenol reagent method, gas chromatography, polarography, colorimetry, fluorescence measurement and spectrophotometry. Compared with these methods that need to be collected first and then analyzed, the formaldehyde sensor with real-time analysis function is undoubtedly the best choice. However, the price of high-sensitivity formaldehyde sensors currently on the market is generally too high, and the cheap ones have low sensitivity and poor anti-interference ability, which cannot meet the huge market demand of the household environmental protection industry.

Semiconductor oxide sensors are currently the most widely used type of gas sensors, which have the advantages of low cost, high sensitivity, easy maintenance, potential for miniaturization, and simple operation. However, for some sensors, their high operating temperature requirements require more cost and complex configurations compared with other sensors that work at room temperature, which limits their development.

Graphene/metal oxide semiconductor composite materials provide a new idea to solve this problem. First, graphene can enhance the electrical conductivity of the composite by facilitating charge transport, thereby lowering the operating temperatures normally required for metal oxides. Second, graphene and metal oxides can regulate or affect the charge transfer behavior in the gas sensing process by forming a heterojunction at the contact interface to generate strong electronic interactions.

With the development of nanotechnology, the preparation process of nanomaterials with two-dimensional structure has been continuously broken through. Various metal oxide semiconductor materials with sheet structure can be synthesized in large quantities by chemical vapor deposition, hydrothermal method, and template sacrificial method. Compared with metal oxide materials, these flake oxides have higher specific surface area and better electrical properties, and are more suitable for the synthesis of various gas sensors.

On the other hand, graphene quantum dots are single-layer or a small number of layered graphene, and the lateral size is usually less than 20nm. Compared with large sheets of graphene, graphene quantum dots with a zero-dimensional structure have more application potential in the field of gas sensing. First of all, graphene quantum dots have a larger specific surface area, a large number of suspensions on the surface and are easy to be functionalized, so the adsorption performance of target gas molecules can be greatly improved. Secondly, graphene quantum dots have an adjustable band gap, and their fluorescence properties and electron transport properties can be adjusted through their particle size, and their conductivity can be easily changed by doping. However, there are no relevant experimental reports on the gas-sensing properties of graphene quantum dots. This is mainly because it is difficult for pure graphene quantum dots to form a conductive network structure, and the device application is limited.

Combining the advantages of two-dimensional metal oxides and graphene quantum dots to prepare composite materials is a direction for the development of formaldehyde sensors and is of great significance.

Contents of the invention

Aiming at the above-mentioned technical problems in the prior art, the present invention provides a composite gas-sensitive material for formaldehyde gas detection and a preparation method thereof, the composite gas-sensitive material for formaldehyde gas detection and a preparation method thereof It is necessary to solve the technical problems of sensitivity, high working temperature, poor selectivity and stability of gas-sensitive materials for detecting formaldehyde gas in the prior art.

The invention provides a composite gas-sensitive material for formaldehyde gas detection, which is composed of a two-dimensional sheet metal oxide and a graphene quantum dot material, and the two-dimensional sheet metal oxide accounts for 1% of the composite material. The mass percentage is 70%-99.99%, and the mass percentage of the graphene quantum dot material in the composite material is 0.01%-30%.

Further, the two-dimensional sheet metal oxide is an oxide with semiconductor properties such as zinc oxide, tin oxide, and tungsten oxide; the graphene quantum dot material is intrinsic graphene quantum dot, doped graphene quantum dot Or surface-modified graphene quantum dots.

Further, the size of the two-dimensional flake metal oxide is 0.5-100 μm, and the thickness is 5-100 nm; the size of the graphene quantum dot material is 2-50 nm, and the thickness is 0.6-10 nm.

The present invention also provides the above-mentioned preparation method of a composite gas-sensitive material for formaldehyde gas detection, comprising the following steps:

1) A step for preparing two-dimensional metal oxide nanosheets;

2) a step for preparing graphene quantum dot material;

3) Weighing the two-dimensional sheet metal oxide and the graphene quantum dot material according to the mass percentage, and compounding the two-dimensional sheet metal oxide and the graphene quantum dot material in proportion, the compounding method It is a hydrothermal method or an ultrasonic method; and a composite gas-sensitive material for formaldehyde gas detection is obtained.

Further, the preparation method of the graphene quantum dots is a hydrothermal method or a chemical exfoliation method.

Further, the preparation method of the metal oxide is a chemical vapor deposition method, a hydrothermal method or a template sacrificial method.

Further, the above-mentioned method for preparing a composite gas-sensing material for formaldehyde gas detection, weighs the two-dimensional sheet metal oxide and the graphene quantum dot material according to the mass percentage, and mixes the metal oxide and the The graphene quantum dot material is mixed in the liquid phase and then stirred for 5-10 minutes; the control frequency is 300-400W and ultrasonic is carried out for 4-6 hours; finally, it is dried at a temperature of 60-80°C to obtain the composite compound for formaldehyde gas detection. gas sensitive material.

The present invention also provides the use of the above-mentioned composite gas-sensitive material for formaldehyde gas detection in preparing a gas-sensitive sensor.

Specifically, the preparation process of the above-mentioned composite gas-sensitive material for formaldehyde gas detection is as follows:

1) taking zinc chloride as raw material, the preparation concentration is the zinc chloride solution of 0.2mol/L;

2) Using hexamethylenetetramine as a raw material, prepare a hexamethylenetetramine solution with a concentration of 0.2mol/L;

3) Mix the zinc chloride solution in step 1) and the hexamethylenetetramine solution in step 2) uniformly at a volume ratio of 1:1, and place them in an oil bath at 60°C for 15-30 minutes;

4) Get zinc acetate and hexamethylenetetramine in equimolar amounts, and prepare a solution with zinc acetate concentration of 0.2-0.3mol/L;

5) uniformly mix the zinc chloride solution in step 3) and the zinc acetate solution in step 4), add an appropriate amount of ammonia water, and adjust the pH value of the solution to 6-8;

6) Transfer the solution in step 5) to a hydrothermal reaction kettle, place it in a high-temperature blast drying oven, react at 95°C for 2 hours, and cool naturally to room temperature;

7) The solid powder obtained in step 6) is centrifuged and washed 3-6 times, dried at 60-80° C. for 8-12 hours, and calcined at 400-600° C. for 1-2 hours to obtain zinc oxide nanosheets.

The present invention also provides a gas-sensing element, which includes a semiconductor element, and the above-mentioned composite gas-sensing material for formaldehyde gas detection is evenly coated on the surface of the semiconductor element.

Specifically, the semiconductor element is an alumina ceramic tube.

Specifically, the preparation method of the above-mentioned gas sensor includes the following steps:

1) taking zinc chloride as raw material, the preparation concentration is the zinc chloride solution of 0.2mol/L;

2) Using hexamethylenetetramine as a raw material, prepare a hexamethylenetetramine solution with a concentration of 0.2mol/L;

3) Mix the zinc chloride solution in step 1) and the hexamethylenetetramine solution in step 2) uniformly at a volume ratio of 1:1, and place them in an oil bath at 60°C for 15-30 minutes;

4) Get zinc acetate and hexamethylenetetramine in equimolar amounts, and prepare a solution with zinc acetate concentration of 0.2-0.3mol/L;

5) uniformly mix the zinc chloride solution in step 3) and the zinc acetate solution in step 4), add an appropriate amount of ammonia water, and adjust the pH value of the solution to 6-8;

6) Transfer the solution in step 5) to a hydrothermal reaction kettle, place it in a high-temperature blast drying oven, react at 95°C for 2 hours, and cool naturally to room temperature;

7) The solid powder obtained in step 6) is centrifuged and washed 3-6 times, dried at 60-80° C. for 8-12 hours, and calcined at 400-600° C. for 1-2 hours to obtain zinc oxide nanosheets.

8) Mix the zinc oxide nanosheets and graphene quantum dot materials in step 7) in the liquid phase according to the mass percentage of 79%-99.99%: 0.01%-30% and stir for 5-10min; the control frequency is 300-400W Perform ultrasonication for 4-6 hours; finally dry at a temperature of 60-80° C. to obtain a composite gas-sensing material.

9) Add ethanol to the composite gas-sensing material in step 8) to make a paste, and evenly apply it on the surface of the semiconductor element to obtain a gas-sensing element.

Further, the gas sensor is welded, aged and packaged to obtain a gas sensor for detecting formaldehyde.

The invention effectively improves the selectivity and sensitivity of metal oxides to formaldehyde gas by compounding the graphene quantum dot material.

The main technical indicators of the gas sensor of the present invention are as follows:

1. Detection of gas concentration: 1ppm-100ppm;

2. Component working temperature: 110-160°C;

3. Detection sensitivity (Ra/Rg): 100ppm formaldehyde sensitivity is 210;

4. Selectivity: the sensitivity to 100ppm ethanol, acetone, ammonia, and benzene is lower than that to formaldehyde;

5. Component response time: less than 45s;

6. Component recovery time: less than 5s.

Compared with the prior art, the technical progress of the present invention is remarkable. The gas sensor prepared by the invention has high sensitivity to formaldehyde gas, good selectivity to interfering gases, good stability, low working temperature, simple preparation process, economic benefits, etc., and can be applied Formaldehyde gas detection indoors and outdoors.

Description of drawings

Figure 1 is an X-ray diffraction pattern of the zinc oxide nanosheets of the present invention.

Fig. 2 is a scanning electron microscope image of the zinc oxide nanosheets of the present invention.

Fig. 3 is the response recovery curve to 100ppm formaldehyde of the zinc oxide nanosheet composite graphene quantum dot prepared by the method of the present invention and the gas sensor made without composite.

Fig. 4 is the selectivity comparison diagram of the gas sensor made of compounding 20% graphene quantum dots and non-compositing graphene quantum dots to 100ppm formaldehyde, as can be seen from the figure, the sensitivity and the selectivity of zinc oxide after compounding graphene quantum dots are both has seen an increase.

Figure 5 is a comparison chart of the response recovery curves of the gas sensor made after compounding different proportions of graphene quantum dots to 100ppm formaldehyde. It can be seen from the figure that the sensitivity of the gas sensor after compounding graphene quantum dots to formaldehyde has been improved. , 20% graphene quantum dots and zinc oxide nanosheet composite performance is the best.

Detailed ways

The present invention will be further described below with examples, but not limited thereto.

Example 1:

The composite gas-sensing material provided by the present invention is metal oxide and graphene quantum dot material calculated by mass percentage, that is, the graphene quantum dot material accounts for 5%, 10%, 20%, and 30% of the total mass percentage of the composite;

The metal oxide is zinc oxide;

The graphene quantum dots are nitrogen-doped graphene quantum dots;

The zinc oxide is a regular nanosheet structure with a size of 4-10 μm and a thickness of 50-100 nm;

The graphene quantum dot material is a circular nanosheet structure with a size of 5-20nm and a thickness of 0.6-5nm.

The preparation method of the above-mentioned composite gas-sensitive material specifically includes the following steps:

1. Preparation of ZnO nanosheets by hydrothermal method

a. Dissolve 4mmol of zinc chloride in 20ml of deionized water and stir for 10min to uniformly disperse zinc chloride in the solution; dissolve 4mmol of hexamethylenetetramine in 20ml of deionized water and stir for 10min to make the hexamethylene Tetramine dissolves completely. Mix the two solutions and place them in an oil bath at 60°C for 15 minutes;

b. Dissolve 8mmol of zinc acetate and 8mmol of hexamethylenetetramine in 30ml of deionized water, and stir for 15min to disperse the zinc acetate evenly in the solution and completely dissolve the hexamethylenetetramine;

c. Mix the two solutions of step a and step b, add an appropriate amount of ammonia water, and adjust the pH value of the solution to 7;

d. Transfer the solution in step c to a 100ml hydrothermal reaction kettle, place it in a high-temperature blast drying oven at 95°C for 2h, cool it down to room temperature naturally, wash the obtained precipitate with water and ethanol for 6 times, and dry it at 80°C for 12h , Calcined at 500°C for 1h to obtain ZnO nanosheets.

2. Using citric acid as carbon source and urea as nitrogen source to prepare nitrogen-doped graphene quantum dots.

3. Preparation of composite gas-sensing materials

The zinc oxide nanosheets of step 1 and the graphene quantum dots of step 2 are mixed into deionized water according to the ratio of graphene quantum dots accounting for 20% of the total mass percentage of the composite, stirred for 10min, controlled frequency is 400W, ultrasonic 6h, and then Control the temperature at 80° C. and dry for 2 hours to obtain a composite gas-sensing material, that is, a graphene quantum dot/zinc oxide composite gas-sensing material.

Further, the composite material is added with ethanol to make a slurry, and the slurry is evenly coated on the surface of the alumina ceramic tube to prepare a gas sensor.

Further, the gas sensor is welded, aged, packaged according to the manufacturing process of the side-heating semiconductor gas sensor, and the gas sensor is manufactured.

The zinc oxide nanosheets obtained above were characterized by X-ray diffraction, see FIG. 1 . It can be seen from FIG. 1 that the zinc oxide nanosheets have a wurtzite structure. Referring to Fig. 2 (a, b), it is a scanning electron microscope image of zinc oxide nanosheets. It can be seen from FIG. 2 that the zinc oxide nanosheets have a size of about 6 μm and a thickness of about 90 nm. Gas-sensing performance is tested on the CGS-8 gas-sensing element testing system through the static gas distribution method. Referring to Fig. 3, it is the response recovery curve of zinc oxide nanosheet composite graphene quantum dots and uncomposited gas sensor to 100ppm formaldehyde. It can be seen from Figure 3 that the gas sensor has a faster response recovery and higher sensitivity to 100ppm formaldehyde gas. Referring to FIG. 4 , it is a comparison diagram of selectivity of 100ppm formaldehyde for the gas sensor made by compounding 20% graphene quantum dots and non-compositing graphene quantum dots. It can be seen from Figure 4 that the sensitivity and selectivity of zinc oxide compounded with 20% graphene quantum dots to formaldehyde gas are improved. Referring to Figure 5, it is a comparison chart of the response recovery curves of the gas sensor made after compounding different proportions of graphene quantum dots to 100ppm formaldehyde, as can be seen from Figure 5, the zinc oxide after compounding graphene quantum dots has a certain The performance of zinc oxide nanosheets compounded with 20% graphene quantum dots is the best.

In summary, the resulting composite of zinc oxide nanosheets and graphene quantum dots has higher sensitivity to formaldehyde gas and better selectivity to interfering gases than pure zinc oxide materials. It has a good sensitization effect on the detection of formaldehyde gas.

The composite gas-sensing material of the present invention only takes the material obtained by compounding metal oxide zinc oxide and nitrogen-doped graphene quantum dots as an example, but does not limit the composite gas-sensing material obtained by other metal oxides and other graphene quantum dot materials .

Embodiment 2: This embodiment is basically the same as Embodiment 1, except that in step 3, graphene quantum dots account for 5% of the total mass of the composite.

Embodiment 3: This embodiment is basically the same as Example 1, except that in step 3, graphene quantum dots account for 10% of the total mass of the composite.

Embodiment 4: This embodiment is basically the same as Example 1, except that in step 3, graphene quantum dots account for 30% of the total mass of the composite.

Claims (10)

1. A composite gas sensitive material for formaldehyde gas detection, characterized in that: it is composed of a two-dimensional sheet metal oxide and a graphene quantum dot material, and the two-dimensional sheet metal oxide accounts for the composite The mass percentage of the material is 70%-99.99%, and the mass percentage of the graphene quantum dot material in the composite material is 0.01%-30%. 2. A composite gas-sensitive material for formaldehyde gas detection as claimed in claim 1, characterized in that: said two-dimensional flake metal oxide is an oxide with semiconductor properties such as zinc oxide, tin oxide, and tungsten oxide. The graphene quantum dot material is an intrinsic graphene quantum dot, a doped graphene quantum dot or a surface-modified graphene quantum dot. 3. A composite gas-sensitive material for formaldehyde gas detection as claimed in claim 1, characterized in that: the size of the two-dimensional sheet metal oxide is 0.5-100 μm, and the thickness is 5-100 nm; The size of the graphene quantum dot material is 2-50nm, and the thickness is 0.6-10nm. 4. a kind of preparation method of the composite gas-sensitive material that is used for formaldehyde gas detection as claimed in claim 1, is characterized in that comprising the steps: 1) A step for preparing two-dimensional metal oxide nanosheets; 2) a step for preparing graphene quantum dot material; 3) Weighing the two-dimensional sheet metal oxide and the graphene quantum dot material according to the mass percentage, and compounding the two-dimensional sheet metal oxide and the graphene quantum dot material in proportion, the compounding method It is a hydrothermal method or an ultrasonic method; and a composite gas-sensitive material for formaldehyde gas detection is obtained. 5. A method for preparing a composite gas-sensitive material for formaldehyde gas detection as claimed in claim 4, wherein the method for preparing the graphene quantum dots is a hydrothermal method or a chemical exfoliation method. 6. A kind of preparation method of the composite gas sensitive material that is used for formaldehyde gas detection as claimed in claim 4, it is characterized in that: the preparation method of described metal oxide is chemical vapor deposition method, hydrothermal method or template sacrificial method . 7. the purposes of a kind of composite gas sensitive material for formaldehyde gas detection described in claim 1 in the preparation gas sensor. 8. a kind of preparation method for the composite gas sensitive material that is used for formaldehyde gas detection as claimed in claim 4, is characterized in that comprising the steps: 1) taking zinc chloride as raw material, the preparation concentration is the zinc chloride solution of 0.2mol/L; 2) Using hexamethylenetetramine as a raw material, prepare a hexamethylenetetramine solution with a concentration of 0.2mol/L; 3) Mix the zinc chloride solution in step 1) and the hexamethylenetetramine solution in step 2) uniformly at a volume ratio of 1:1, and place them in an oil bath at 60°C for 15-30 minutes; 4) Get zinc acetate and hexamethylenetetramine in equimolar amounts, and prepare a solution with zinc acetate concentration of 0.2-0.3mol/L; 5) uniformly mix the zinc chloride solution in step 3) and the zinc acetate solution in step 4), add an appropriate amount of ammonia water, and adjust the pH value of the solution to 6-8; 6) Transfer the solution in step 5) to a hydrothermal reaction kettle, place it in a high-temperature blast drying oven, react at 95°C for 2 hours, and cool naturally to room temperature; 7) The solid powder obtained in step 6) is centrifuged and washed 3-6 times, dried at 60-80° C. for 8-12 hours, and calcined at 400-600° C. for 1-2 hours to obtain zinc oxide nanosheets. 9. A gas sensor, comprising a semiconductor element, uniform on the surface of the semiconductor element Coating the above composite gas sensitive material for formaldehyde gas detection. 10. The preparation method of a kind of gas sensor as claimed in claim 1, characterized in that: comprising the following steps Steps: 1) taking zinc chloride as raw material, the preparation concentration is the zinc chloride solution of 0.2mol/L; 2) Using hexamethylenetetramine as a raw material, prepare a hexamethylenetetramine solution with a concentration of 0.2mol/L; 3) Mix the zinc chloride solution in step 1) and the hexamethylenetetramine solution in step 2) uniformly at a volume ratio of 1:1, and place them in an oil bath at 60°C for 15-30 minutes; 4) Get zinc acetate and hexamethylenetetramine in equimolar amounts, and prepare a solution with zinc acetate concentration of 0.2-0.3mol/L; 5) uniformly mix the zinc chloride solution in step 3) and the zinc acetate solution in step 4), add ammonia water, and adjust the pH value of the solution to 6-8; 6) Transfer the solution in step 5) to a hydrothermal reaction kettle, place it in a high-temperature blast drying oven, react at 95°C for 2 hours, and cool naturally to room temperature; 7) The solid powder obtained in step 6) is centrifuged and washed 3-6 times, dried at 60-80° C. for 8-12 hours, and calcined at 400-600° C. for 1-2 hours to obtain zinc oxide nanosheets. 8) Mix the zinc oxide nanosheets and graphene quantum dot materials in step 7) in the liquid phase according to the mass percentage of 79%-99.99%: 0.01%-30% and stir for 5-10min; the control frequency is 300-400W Perform ultrasonication for 4-6 hours; finally dry at a temperature of 60-80° C. to obtain a composite gas-sensing material. 9) Add ethanol to the composite gas-sensing material in step 8) to make a paste, and evenly apply it on the surface of the semiconductor element to obtain a gas-sensing element.