CN106596652A - A kind of preparation method of high sensitivity NO2 gas sensor - Google Patents

Abstract

The invention discloses a preparation method of a high-sensitivity NO2 gas sensor. The preparation method comprises the following steps: (1) preparing WO3/graphene nanocomposites; taking graphene oxide, sulfate salt and tungstate as raw materials and preparing through a hydrothermal method to obtain the WO3/graphene nanocomposites; (2) preparing a NO2 gas sensor; weighing the WO3/graphene nanocomposites and adding the WO3/graphene nanocomposites into a beaker, carrying out ultrasound treatment for 10 minutes to be dissolved completely, absorbing suspension liquid by using a pipette to a plane electrode, and then preparing into a nano-composite based indirectly heated gas sensor. The gas sensor prepared by the method can show good selectivity and high sensitivity for NO2 at lower working temperature, and further has fast response and recovery characteristics, and potential application in the gas sensor with high performances and low power consumption.

Description

A kind of preparation method of high sensitivity NO2 gas sensor

technical field

The invention relates to the field of functional nanomaterial manufacturing, in particular to a preparation method of a high _- sensitivity NO2 gas sensor based _on WO3/graphene nanocomposite material.

Background technique

NO ₂ gas is a brown-red pungent poisonous gas, and the combustion of fossil fuels will produce a large amount of NO ₂ gas; inhalation of NO ₂ gas mainly damages the respiratory tract, and at the same time is harmful to the environment, prompting the formation of acid rain, causing water, soil and air pollution ; At present, methods for detecting NO ₂ gas include spectrophotometry and fluorescence photometry. However, the detection operation is complicated, the test time is long, the maintenance cost of the instrument is high, and on-site monitoring is not possible; therefore, the rapid and accurate test of NO ₂ gas is of great significance; the monitoring of NO ₂ gas by chemically synthesized nanomaterials is fast, easy to operate, and The advantages of high sensitivity have attracted widespread attention.

Graphene is a single-layer carbon structure in which carbon atoms are hybridized with sp ² , and has high mechanical force (>1060GPa), high thermal conductivity (-3000WM ^-1 K ^-1 ), and high electron mobility (15000cm ² v ^-1 s ^-1 ), high specific surface area (2600m ² /g); based on high electron mobility and large specific surface area, graphene is a promising P-type gas-sensing material; meanwhile WO ₃ as An n-type material, which is also widely used in gas-sensing testing; it has been reported that graphene is used in gas-sensing materials, although it can work at lower temperatures, but the gas selectivity is poor and the response is long Time and recovery time, and the sensitivity is low. At the same time, WO ₃ is used as a single gas-sensing material, which generally shows better selectivity and high sensitivity at higher working temperatures.

Contents of the invention

The technical problem to be solved by the present invention is to provide a kind of insufficiency in the existing single gas-sensitive material sensor, through _two kinds of system materials composite to achieve highly sensitive detection of NO gas, and excellent selectivity and stability based on Preparation method of WO ₃ /graphene nanocomposite material for highly sensitive NO ₂ gas sensor.

To achieve the above object, technical scheme of the present invention is as follows:

_A kind of preparation method based _on WO3/graphene nanocomposite high sensitivity NO2 gas sensor, described preparation method comprises:

(1) Preparation of WO ₃ /graphene nanocomposites

Using graphene oxide, sulfate radical salt, and tungstate as raw materials, WO ₃ /graphene nanocomposites were prepared by hydrothermal method;

(2) Preparation of gas sensor

Weigh the WO ₃ /graphene nanocomposite material into a beaker, ultrasonically dissolve it for 10 minutes, and use a pipette gun to draw the suspension onto the flat electrode to prepare a nanocomposite-based side-heating gas sensor.

In one embodiment of the present invention, the graphene oxide in the claim 1 is prepared by the following method:

Prepared by improved Hummers method, weigh 1.5g graphite powder, 9g KMnO ₄ , 180ml concentrated H ₂ SO ₄ , 20ml H ₃ PO ₄ (V _H2SO4 :V _H3PO4 = 9:1) into a 500ml round bottom flask, heat to 50 ℃, stirred and reacted for 12 hours, a brown solution was formed, cooled to room temperature, poured into 200ml ice water with 3ml 30% H ₂ O ₂ dropwise, and turned into a brownish yellow suspension; centrifuged, poured off the supernatant, and added concentrated HCl , after shaking evenly, centrifuge, and then wash with ethanol and deionized water several times. When the supernatant is close to neutral, the washing is completed, and put it in an oven at 80°C overnight.

In one embodiment of the present invention, the tungstate is H ₂ WO ₄ /oxalic acid transparent sol, and the preparation method of the H ₂ WO ₄ /oxalic acid transparent sol is as follows:

Stir and dissolve 8.15g Na ₂ WO ₄ in 20ml deionized water, add concentrated HCl, the solution becomes milky white, then add oxalic acid, after stirring, it becomes a transparent and stable H ₂ WO ₄ /oxalic acid transparent sol.

In one embodiment of the present invention, the specific preparation method _of WO3/graphene nanocomposite material is as follows:

Weigh 5-20 mg of graphene oxide and add it to a beaker, dissolve it completely by ultrasonication for 10 minutes, add sulfate radical salt and sonicate, add H ₂ WO ₄ /oxalic acid transparent sol dropwise, react for 8 hours, and prepare WO ₃ /graphene nanocomposite material.

In one embodiment of the present invention, the specific preparation method of the gas sensor is as follows:

Weld the planar electrode on the base of the base, weigh 10mg WO ₃ /graphene nanocomposite material into 10ml deionized water and ultrasonically vibrate for 30-60min to obtain a uniformly dispersed WO ₃ /graphene nanocomposite suspension, The suspension was added dropwise to the welded flat electrode with a pipette gun to make a side-heated gas sensor, dried at room temperature for 8 hours, and the prepared sensor electrode was heat-treated.

In one embodiment of the present invention, the amount of the concentrated HCl is any one of 4ml, 5ml, 6ml, 7ml or 8ml.

In one embodiment of the present invention, the sulfate salt is any one of K ₂ SO ₄ , ZnSO ₄ , (NH ₄ ) ₂ SO ₄ or CuSO ₄ .

In one embodiment of the present invention, the amount of the H ₂ WO ₄ /oxalic acid transparent sol is any one of 12ml, 14ml, 16ml, 18ml or 20ml.

In one embodiment of the present invention, the reaction temperature is any one of 120°C, 140°C, 160°C, 180°C or 200°C.

In one embodiment of the present invention, the temperature during the heat treatment is any one of 100°C, 120°C, 140°C, 160°C or 180°C, and the heat treatment time is 12h, 24h, 36h, 48h or Any one of 60h.

Through above-mentioned technical scheme, beneficial effect of the present invention is:

The present invention is based on WO ₃ /graphene nanocomposite high-sensitivity NO ₂ gas sensing material, which is characterized in that two different types of gas-sensing materials are used, and a gas-sensing material combining p-type and n-type semiconductor materials is prepared by hydrothermal method , used to improve the detection sensitivity, selectivity and response-recovery time of sensitive materials.

Its principle is:

(1) The n-type semiconductor material WO ₃ is compounded with the p-type material graphene. The two materials will form a pn heterojunction on the material contact surface due to the intermolecular Van der Waals force contact. Because the formed heterojunction has a lower energy level, Electrons can easily migrate from the n-type semiconductor material WO ₃ and be confined in the heterojunction. At this time, the movement of electrons will not be limited by the collision of impurities, and the mobility will increase.

(2) There will be a dynamic balance of carriers at the heterojunction of the n-type semiconductor material WO ₃ and the p-type material graphene composite surface, and the remaining positive and negative ions will form an internal electric field at the same time. Under the action of the electric field, the Carriers move in the opposite direction of diffusion to form a depletion layer, and the widening of the depletion layer can improve the sensitivity of the composite material.

(3) The composite material has a relatively large specific surface area, which can absorb more oxygen, which is conducive to the rapid diffusion of molecular O ^2- on the surface of WO _3. NO ₂ gas needs to obtain electrons on the surface of the composite material. This process can improve WO ₃ The surface hole concentration is conducive to the rapid response and recovery characteristics of the sensor at lower temperatures. In the present invention, the hydrothermal synthesis technology used mainly refers to pre-dispersing the H ₂ WO ₄ precursor in the oxalic acid solution, and then relying on the temperature of the reaction system, adding a template agent, etc. to remove the WO ₃ nanocrystals from the solution At the same time, graphene oxide is reduced to graphene; WO ₃ nanocrystals are deposited on the surface of graphene-sensitive materials in situ by using intermolecular van der Waals force; the dispersion density of WO ₃ nanocrystals on the graphene surface can be added by graphene oxide. The amount is controlled; by adding different amounts of graphene oxide and optimizing the reaction conditions, graphene oxide can be completely reduced, and WO ₃ can form uniform nanowires, and composite nanomaterials with controllable morphology and valence state can be prepared.

In the present invention, through the compounding of _two kinds of materials, the prepared NO2 gas sensor can have high sensitivity to NO2 gas at a relatively low temperature, reaching _65.623 to _20ppm NO2 at 100°C, and at the same time showing a very rapid response The time and recovery time are 10s and 126s respectively; by testing different concentrations of NO ₂ (5, 10, 15, 20, 25, 30ppm) gas, it can be found that the linearity of the sensor can reach 0.958, and the sensor can continuously test the absorption of 10ppm NO ₂ It can be found from the desorption experiment that the sensor shows good repeatability, and the long-term stability experiment on the sensor sensitivity shows that the sensor sensitivity has good stability.

Description of drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings that need to be used in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only These are some embodiments of the present invention. Those skilled in the art can also obtain other drawings based on these drawings without creative work.

Fig. ₁ is the sensitivity diagram of WO3/graphene nanocomposite material of the present invention to 20ppm NO2 at different working temperatures _;

Fig. ₂ is the scanning electron micrograph of the WO3/graphene nanocomposite material that the present invention adds different amounts of graphene oxide preparation;

Fig. ₃ is the response-recovery curve of WO3/graphene nanocomposite material of the present invention to 20ppm NO2 gas _;

Fig. ₄ is the selection diagram of WO3/graphene nanocomposite material of the present invention to different gases;

Fig. ₅ is the WO3/graphene nanocomposite material of the present invention to different concentrations (5, 10, 15, 20, ₂₅ , 30ppm) NO Gas response recovery diagram;

Fig. ₆ is the repeatability test graph of WO3/graphene nanocomposite material of the present invention to 10ppm NO2 gas _;

Fig. 7 is the long-term stability test of the WO ₃ /graphene nanocomposite material of the present invention to 20 ppm NO ₂ gas.

detailed description

In order to make the technical means, creative features, goals and effects achieved by the present invention easy to understand, the present invention will be further described below in conjunction with specific illustrations.

Example 1

The invention discloses a preparation method of a high _- sensitivity NO2 gas sensor based _on WO3/graphene nanocomposite material. The preparation method comprises:

(1) Preparation of graphene oxide

Prepared using the improved Hummers method, weigh 1.5g graphite powder, 9g KMnO4, 180ml concentrated H ₂ SO ₄ , 20ml H ₃ PO ₄ (VH ₂ SO ₄ :VH ₃ PO ₄ =9:1) and add to a 500ml round bottom flask , heated to 50°C and stirred for 12 hours to generate a brown solution, cooled to room temperature, poured into 200ml ice water with 3ml 30% H ₂ O ₂ added dropwise, turned into a brownish yellow suspension, centrifuged, poured off the supernatant, Add concentrated HCl, shake evenly, centrifuge, and then wash with ethanol and deionized water several times. When the supernatant is close to neutral, the washing is completed, and put it in an oven at 80°C overnight.

(2) Preparation of H ₂ WO ₄ /oxalic acid transparent sol

Stir and dissolve 8.15g Na ₂ WO ₄ in 20ml deionized water, add 6ml concentrated HCl, the solution is milky white, add 6.3g oxalic acid, and form a transparent and stable sol after stirring.

(3) Preparation of WO ₃ /graphene nanocomposites

Weigh 5 mg of graphene oxide and add it to a beaker, dissolve it completely by ultrasonication for 10 minutes, add 4 g of ammonium sulfate and ultrasonication, add dropwise 16 ml of H ₂ WO ₄ /oxalic acid transparent sol, and react at 180°C for 8 hours.

( ₄ ) Preparation of NO2 gas sensor

Weld the planar electrode on the base of the base, weigh 10 mg of the WO ₃ /graphene nanocomposite prepared in Example 1, add it to 10 ml of deionized water and oscillate ultrasonically for 30-60 minutes to obtain evenly dispersed WO ₃ /graphene ene nanocomposite material suspension, apply the suspension on the welded flat electrode with a pipette gun to make a side-heated gas sensor, dry it at room temperature for 8 hours, and heat-treat the prepared sensor electrode at 120°C for 24 hours, The sensitivity of the prepared WO ₃ /graphene nanocomposite to 20ppm NO ₂ gas at different working temperatures is shown in Figure 1L1.

Example 2

In the step (3) of embodiment 1, add 10mg graphene oxide, other steps and conditions are the same as in embodiment 1, specific conditions are changed and adjusted accordingly within the scope of the content of the invention, can obtain WO ₃ /graphite Graphene nanocomposite material; drop-coating graphene nanocomposite suspension on the welded flat electrode to make side-heating gas sensor, dry at room temperature for 8h, and heat-treat the prepared sensor electrode at 120°C for 24h; The sensitivity of the WO ₃ /graphene nanocomposite to 20ppm NO ₂ gas at different working temperatures is shown in Figure 1L2.

Example 3

In the step (3) of embodiment 1, add 15mg graphene oxide, other steps and conditions are the same as in embodiment 1, and specific conditions are changed and adjusted accordingly within the scope limited by the summary of the invention, can obtain WO ₃ /graphite Graphene nanocomposite material; drop-coating graphene nanocomposite suspension on the welded flat electrode to make side-heating gas sensor, dry at room temperature for 8h, and heat-treat the prepared sensor electrode at 120°C for 24h; The sensitivity of the WO ₃ /graphene nanocomposite material to 20ppm NO2 gas at different working temperatures, the test curve is shown in Figure 1L3.

Example 4

In the step (3) of embodiment 1, add 20mg graphene oxide, other steps and conditions are the same as in embodiment 1, specific conditions are changed and adjusted accordingly within the scope of the content of the invention, can obtain WO ₃ /graphite Graphene nanocomposite material, graphene nanocomposite material suspension was drip-coated on the welded flat electrode to make side heating gas sensor, dried at room temperature for 8h, and the prepared sensor electrode was heat treated at 120°C for 24h. The sensitivity of WO ₃ /graphene nanocomposites to 20ppm NO ₂ gas at different working temperatures is shown in Figure 1L4.

Example 5

On the basis of Example 2, the WO ₃ /graphene nanocomposite material was characterized by SEM, and its microstructure is shown in FIG. 2 .

Example 6

In the process of Example ₂ , the WO3/graphene nanocomposite material was obtained, and the response-recovery curve of the composite material to 20ppm NO2 gas at 100°C is shown in Figure ₃ .

Example 7

In the process of Example 2, the WO ₃ /graphene nanocomposite material was obtained, and the selectivity of the composite material was tested for 20 ppm of different gases at 100° C., as shown in Figure 4 .

Example 8

In the process of Example 2, the WO ₃ /graphene nanocomposite material was obtained, and the composite material was tested with different concentrations of NO ₂ to check the linearity of the composite material, as shown in Figure 5 .

Example 9

In the process of Example 2, the WO ₃ /graphene nanocomposite material was obtained, and the same concentration of NO ₂ was tested on the composite material to check the repeatability of the composite material. The response-recovery curve is shown in FIG. 6 .

Example 10

In the process of Example 2, the WO ₃ /graphene nanocomposite material was obtained, and the long-term stability test was carried out on the composite material to check the stability of the composite material. The sensitivity change is shown in FIG. 7 .

The basic principles and main features of the present invention and the advantages of the present invention have been shown and described above. Those skilled in the industry should understand that the present invention is not limited by the above-mentioned embodiments. What are described in the above-mentioned embodiments and the description only illustrate the principle of the present invention. Without departing from the spirit and scope of the present invention, the present invention will also have Variations and improvements are possible, which fall within the scope of the claimed invention. The protection scope of the present invention is defined by the appended claims and their equivalents.

Claims (10)

1. a kind of highly sensitive NO _The preparation method of gas sensor is characterized in that, described preparation method comprises: (1) Preparation of WO ₃ /graphene nanocomposites Using graphene oxide, sulfate radical salt, and tungstate as raw materials, WO ₃ /graphene nanocomposites were prepared by hydrothermal method; ( ₂ ) Preparation of NO2 gas sensor Weigh the WO ₃ /graphene nanocomposite material into a beaker, ultrasonically dissolve it for 10 minutes, and use a pipette gun to draw the suspension onto the flat electrode to prepare a nanocomposite-based side-heating gas sensor. 2. a kind of base high sensitivity NO according to claim ₁ The preparation method of gas sensor is characterized in that, the graphene oxide in the described claim 1 is prepared by the following method: Prepared using the improved Hummers method, weighed 1.5g graphite powder, 9g KMnO ₄ , 180ml concentrated H ₂ SO ₄ , 20ml H ₃ PO ₄ (V _H2SO4 :V _H3PO4 = 9:1) was added to a 500ml round bottom flask, heated to Stir and react at 50°C for 12 hours to form a brown solution, cool to room temperature, pour into 200ml ice water with 3ml 30% H ₂ O ₂ dropwise, and turn into a brownish yellow suspension; centrifuge, pour off the supernatant, add concentrated HCl, shake evenly, centrifuge, and then wash with ethanol and deionized water several times. When the supernatant is close to neutral, the washing is completed, and put it in an oven at 80°C overnight. 3. a kind of high sensitivity NO according to claim ₁ The preparation method of gas sensor is characterized in that, described tungstate is H ₂ WO ₄ / oxalic acid transparent sol, described H ₂ WO ₄ / oxalic acid transparent sol The preparation method is as follows: Stir and dissolve 8.15g Na ₂ WO ₄ in 20ml deionized water, add concentrated HCl, the solution becomes milky white, then add oxalic acid, after stirring, it becomes a transparent and stable H ₂ WO ₄ /oxalic acid transparent sol. 4. a kind of high sensitivity NO according to claim ₃ The preparation method of gas sensor is characterized in that, WO ₃ The concrete preparation method of/graphene nanocomposite material is as follows: Weigh 5-20 mg of graphene oxide and add it to a beaker, dissolve it completely by ultrasonication for 10 minutes, add sulfate radical salt and sonicate, add H ₂ WO ₄ /oxalic acid transparent sol dropwise, react for 8 hours, and prepare WO ₃ /graphene nanocomposite material. 5. a kind of high sensitivity NO according to claim ₁ The preparation method of gas sensor is characterized in that, described NO _The concrete preparation method of gas sensor is as follows: Weld the planar electrode on the base of the base, weigh 10mg WO ₃ /graphene nanocomposite material into 10ml deionized water and ultrasonically vibrate for 30-60min to obtain a uniformly dispersed WO ₃ /graphene nanocomposite suspension, The suspension was added dropwise to the welded flat electrode with a pipette gun to make a side-heated gas sensor, dried at room temperature for 8 hours, and the prepared sensor electrode was heat-treated. 6. A method for preparing a high-sensitivity NO2 gas sensor according to claim ₂ , wherein the amount of the concentrated HCl is any one of 4ml, 5ml, 6ml, 7ml or 8ml. 7. The preparation method of a high-sensitivity NO ₂ gas sensor according to claim 1 or 4, characterized in that, the sulfate radical salt is K ₂ SO ₄ , ZnSO ₄ , (NH ₄ ) ₂ SO ₄ or CuSO Any of ₄ . 8. A kind of high-sensitivity NO according to claim ₄ The preparation method of the gas sensor is characterized in that, the amount of the H ₂ WO ₄ /oxalic acid transparent sol is any one of 12ml, 14ml, 16ml, 18ml or 20ml A sort of. 9. A kind of high _- sensitivity NO gas sensor preparation method according to claim 4, is characterized in that, the temperature during described reaction is any one in 120 ℃, 140 ℃, 160 ℃, 180 ℃ or 200 ℃ kind. 10. The preparation method of a high-sensitivity NO gas sensor according to claim ₅ , characterized in that, the temperature during the heat treatment is any one of 100°C, 120°C, 140°C, 160°C or 180°C The time of the heat treatment is any one of 12h, 24h, 36h, 48h or 60h.