A gas sensor sensitive material and a preparation method thereof

Abstract

The application provides a kind of gas sensor sensitive material and its preparation method: after graphene is mixed with concentrated sulfuric acid and concentrated nitric acid, the product prepared is extracted, dialyzed in liquid, the solution outside dialysis bag is taken, dried to obtain graphene quantum dots, the graphene quantum dots and the tetracarboxy metal phthalocyanine are in the same order of magnitude;Take ethylenediamine, tetracarboxy metal phthalocyanine and the graphene quantum dots are dissolved in water and N, N-dimethylformamide mixed solution and reacted, and then dried to obtain a solid product.The gas sensor sensitive material of the application is used to solve the problem that single GR sheet is usually formed in the process of stacking to form a conductive network, which forms a dense structure, easily hinders and sticks to gas molecules, so that the GR sheet inside the conductive network cannot fully contact with gas molecules, affecting the gas sensing performance of the gas sensor.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of gas detection, in particular to a gas sensor sensitive material and a preparation method thereof. BACKGROUND

[0002] A gas sensor is a device that converts information such as the composition and concentration of a gas into information that can be used by personnel, instruments, computers, etc. The core component that reacts with the gas is the sensitive material. Currently, commercial gas sensors mainly use traditional metal oxide semiconductors and solid electrolytes as the sensitive material. The detection concentration of the gas sensor is in the order of one millionth (ppm), and there are problems such as the need to work at a high temperature, high power consumption, low sensitivity, poor anti-interference ability, etc.

[0003] With the rapid development of nanotechnology, in recent years, there have been a large number of research reports on gas sensors based on graphene (GR) nanomaterials. The excellent performance of graphene, such as a large specific surface area, high chemical stability, and excellent electrical conductivity, has made it one of the ideal materials for making nanometer gas sensors.

[0004] In 2007, Schedin et al. first used graphene as a gas-sensitive material and showed response performance to NO2 gas in the order of ppb at room temperature [Schedin, F., Geim, A. K., Morozov, S. V., et al. Detection of individual gas molecules adsorbed on graphene [J]. Nature Materials. 2007, 6(9): 652-655.]. The graphene sheets synthesized by Lv et al. can detect NO2 gas in the order of 1 ppb and NH3 gas in the order of 1 ppm [Lv, R., Chen, G., Li, Q., et al. Ultrasensitive gas detection of large-area boron-doped graphene [J]. Proceedings of the National Academy of Sciences. 2015, 112(47): 14527-14532.].

[0005] However, there are still some problems in the GR gas sensor that need to be solved through further research and exploration, for example, although the gas sensor based on a single GR sheet is feasible in experiments, its manufacturing process is complex, the cost is high, and the single nano structure is easily damaged and unreliable. During the process of stacking to form a conductive network, the single GR sheet usually forms a dense structure, which easily hinders and sticks to gas molecules, thereby not conducive to the full contact between the GR sheet inside the conductive network and the gas molecules. Therefore, it is very urgent and necessary to further improve the gas sensitive performance of the GR gas sensor. Considering that GQDs as carbon nanomaterials have the characteristics of large adsorption amount but slow desorption, how to realize the rapid response and recovery of the GQD gas sensor to gas molecules is the key to the research.

[0006] Generally, using the synergistic effect of composite materials is an effective method to solve such key problems. Metal phthalocyanine (MPc) has a unique macrocyclic conjugated structure and is an excellent organic semiconductor material, so it can be used as a sensitive material to prepare an organic gas sensor. Compared with traditional metal oxide semiconductor sensors and solid electrolyte sensors, MPc gas sensors have the advantages of rich raw material sources, low cost, simple film manufacturing process, easy compatibility with other technologies, and the ability to work at room temperature. The patent “Preparation method and use method of a gas sensor based on metal phthalocyanine” (application number: CN201810162282.3) dissolves metal phthalocyanine in a mixed solution of N,N-dimethylformamide and water, drops it on the electrode, and forms a metal phthalocyanine film covering the electrode after drying. When in use, the sensor is placed in a sealed cavity, a preset concentration of detection gas is filled in the sealed cavity, and a preset concentration of gas atmosphere is maintained. When recovering, dry air or nitrogen is filled in the sealed cavity, and a laser is used to irradiate the sensor to make the detection gas desorb. This method can effectively solve the problems of slow response and recovery speed and the inability to detect at room temperature in the prior art. However, metal phthalocyanine has poor conductivity (megaohm level), which requires high-precision semiconductor test instruments, and the response and recovery are slow (several tens of minutes), which affects the detection efficiency of the sensor in actual use. Moreover, metal phthalocyanine crystallizes into a granular shape, which cannot form a large-area conductive network structure. When the concentration is low, it is easy to form a breakpoint and cause the sensor to be unable to conduct. When the concentration is increased, it is easy to cause the film thickness to be too large, which increases the conductivity. These bring inconvenience to the actual production of the sensor. SUMMARY

[0007] In view of the above-mentioned disadvantages of the prior art, the purpose of the present application is to provide a gas sensor sensitive material and a preparation method thereof, which are used to solve the problem that the single GR sheet is usually formed into a dense structure in the process of stacking to form a conductive network, which is easy to hinder and stick gas molecules, thereby affecting the full contact between the GR sheet inside the conductive network and the gas molecules, and affecting the gas sensing performance of the gas sensor.

[0008] To achieve the above-mentioned purpose and other related purposes, the present application provides a preparation method of a gas sensor sensitive material, which comprises the following steps: a product prepared by mixing graphene with concentrated sulfuric acid and concentrated nitric acid is dissolved in a liquid after being extracted, dialysis is performed, the solution outside the dialysis bag is taken, and graphene quantum dots are obtained by drying; the size of the graphene quantum dots and the size of the metal phthalocyanine tetra-carboxylate are in the same order of magnitude; ethylenediamine, metal phthalocyanine tetra-carboxylate and the graphene quantum dots are dissolved in a mixed solution of water and N,N-dimethylformamide to perform a reaction, and a solid product is obtained by drying. The graphene quantum dots and the metal phthalocyanine are in the same order of magnitude, and are not easy to stack and interfere with the response performance of the metal phthalocyanine. The order of magnitude refers to a series of powers of 10, that is, the ratio between two adjacent orders of magnitude is 10.

[0009] Preferably, in step S1, the graphene is mixed with concentrated sulfuric acid and concentrated nitric acid for ultrasonic treatment for 6-12 hours, and the mass ratio of the three is 1:0.1-1:0.1-1; in step S2, the mixed solution in step S1 is diluted and extracted to obtain a solid product, the solid product is re-dissolved in deionized water and the pH is adjusted to 7-9 with sodium hydroxide, and then transferred to a reaction kettle for hydrothermal treatment at 180-220℃ for 8-12 hours; in step S3, the product in step S2 is cooled, extracted, dissolved in deionized water and dialyzed for 5-10 days, the solution outside the dialysis bag is taken, and graphene quantum dots are obtained by rotary evaporation; in step S4, ethylenediamine, metal phthalocyanine tetra-carboxylate and the graphene quantum dots in step S3 are taken, the mass ratio of the three is 0.05-0.5:1:0.1-1, dissolved in a mixed solution of water and N,N-dimethylformamide, and the ratio of the two is 1-9:1; in step S5, the solution in step S4 is ultrasonically dispersed for 15-60 minutes at an ultrasonic power of 100-600W, and then transferred to a high-pressure reaction kettle for reaction at 180-250℃ for 6-12 hours; in step S6, the product in step S5 is washed and freeze-dried for 12-24 hours, and the obtained solid is annealed in a vacuum environment at 200-500℃ for 2-8 hours.

[0010] Preferably, the gas sensor sensitive material has a micro-nano structure of a conductive network.

[0011] Preferably, the dialysis bag has a specification of 5000Da to 10000Da. In the present application, a dialysis bag with a suitable specification is selected to control the size of the graphene quantum dots to be less than 10nm, so that the size of the graphene quantum dots is in the same order of magnitude as that of the metal phthalocyanine.

[0012] Preferably, the metal phthalocyanine is cobalt phthalocyanine.

[0013] Preferably, the gas sensor sensitive material is used for detecting NO2 gas.

[0014] Preferably, the graphene quantum dots have carboxyl groups.

[0015] Preferably, the graphene quantum dots have a size of 4-6 nm.

[0016] The application also provides a gas sensor sensitive material having a micro-nano structure of a conductive network.

[0017] Preferably, the gas sensor sensitive material has a response to NO2, and the response value reaches 12.5-30.8 at 100 ppm; and the minimum response limit is 0.05 ppm, and the response value reaches 0.007-0.04 at 0.05 ppm.

[0018] As described above, the gas sensor sensitive material and the preparation method thereof have the following beneficial effects:

[0019] In the application, we select an organic semiconductor material, metal phthalocyanine (MPc-COOH), which has a good specific selection ability for gases. The metal phthalocyanine has rich peripheral functional groups, can be grafted with graphene quantum dots through a specific condensation reaction, and can make up for the defects of poor conductivity and slow electron transmission speed of the metal phthalocyanine by using the excellent conductivity of the graphene quantum dots, so as to improve the response speed and recovery speed of the metal phthalocyanine to gases.

[0020] The preparation method of the application is simple and easy to implement, and can be used for mass production. The graphene quantum dots prepared by the method have a large number of functional groups, including carboxyl groups, hydroxyl groups and epoxy groups, which are beneficial to the combination of the graphene quantum dots and the metal phthalocyanine, the formation of a new gas sensitive material, and the formation of good specificity for some gases through the adjustment of the functional groups. The application has good selectivity, good response and good stability for NO2 gas. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 is a NO2 gas concentration-response value test diagram in Example 1 of the application;

[0022] Figure 2 is a gas selectivity test diagram in Example 1 of the application;

[0023] Figure 3 is a long-term stability test diagram of NO2 gas in Example 1 of the application;

[0024] Figure 4is the NO2 gas concentration-response value test graph in the second embodiment of the present application;

[0025] Figure 5 is the gas selectivity test graph in the second embodiment of the present application;

[0026] Figure 6 is the NO2 gas long-term stability test graph in the second embodiment of the present application;

[0027] Figure 7 is the synthesis schematic diagram of the tetracarboxymetal phthalocyanine and graphene quantum dots in the second embodiment of the present application;

[0028] Figure 8 is the scanning electron microscope test graph of the graphene quantum dots in the second embodiment of the present application;

[0029] Figure 9 is the scanning electron microscope test graph of the gas sensor sensitive material in the second embodiment of the present application;

[0030] Figure 10 is the NO2 gas concentration-response value test graph in the third embodiment of the present application;

[0031] Figure 11 is the gas selectivity test graph in the third embodiment of the present application;

[0032] Figure 12 is the gas long-term stability test graph in the third embodiment of the present application. DETAILED DESCRIPTION

[0033] The present application is described herein with reference to specific and preferred embodiments thereof. Those skilled in the art will understand that other advantages and benefits can be achieved from other embodiments of the present application, and that matters set forth in the description below are merely exemplary and are not intended to limit the scope, applicability or configuration of the application in any way. Those skilled in the art will readily recognize various modifications and changes that can be made to the embodiments of the application without departing from the spirit and scope of the application.

[0034] Reference will now be made to the drawings, wherein: Figures 1-12 It should be noted that the diagrams provided in the present embodiment only schematically illustrate the basic concept of the present application, and thus only the components related to the present application are shown in the diagrams, rather than the number, shape and size of the components when actually implemented. The actual implementation of each component can be randomly changed in terms of shape, number and ratio, and the layout pattern of the components can be more complex.

[0035] The preparation method of the gas sensor sensitive material in the present application will be further described below in combination with the drawings:

[0036] Embodiment One

[0037] (1) Preparation of graphene quantum dots (GQDs): graphene as raw material was mixed with concentrated sulfuric acid (H2SO4, 98%) and concentrated nitric acid (HNO3, 68%) under ultrasonic for 8 h, and the mass ratio of the above three was 1:0.1:0.5. Deionized water was added for dilution and filtration to obtain a solid product. The product was dissolved in deionized water and the pH was adjusted to 7 with sodium hydroxide (NaOH), and then transferred to a reaction kettle for hydrothermal treatment at 180°C for 10 h. After cooling to room temperature, the product was filtered and dissolved in deionized water, and dialyzed (dialysis bag specification 10000 Da) for 7 days. The solution outside the dialysis bag was taken, and the final product was obtained by rotary evaporation.

[0038] (2) Synthesis steps: ethylenediamine (C2H8N2), metal phthalocyanine (MPc-COOH) and graphene quantum dots (GQDs) were taken in a mass ratio of 0.05:1:0.1 and dissolved in a mixed solution of water and N,N-dimethylformamide (DMF) in a ratio of 1:1. The solution was ultrasonically dispersed for 30 min at an ultrasonic power of 300 W, and then transferred to a high-pressure reaction kettle for reaction at 250°C for 6 hours. The product was washed with ethanol and deionized water alternately, and then freeze-dried for 18 h. Finally, the obtained solid was annealed at 200°C for 8 h in a vacuum environment. In this embodiment, the metal phthalocyanine is cobalt phthalocyanine.

[0039] Figure 1 is a gas concentration-response value test graph of the gas sensor sensitive material in this embodiment measured in a 100 ppm NO2 gas atmosphere. The response value R = Ra / Rg, where Ra is the initial resistance value and Rg is the resistance value after contacting the target gas. The working temperature is constant at 25°C, the humidity is 0 (dry gas is used as the background gas), and the ventilation time for each test is 100 seconds.

[0040] As can be seen from the graph, the response of the gas sensor sensitive material to NO2 changes basically linearly with the concentration, and the response value reaches 19.8 at 100 ppm. The minimum response limit reaches 0.05 ppm (50 ppb), and the response value is still 0.02 at 0.05 ppm.

[0041] Figure 2 is a gas selectivity test graph of the gas sensor sensitive material in this embodiment measured in a variety of different gas atmospheres. As can be seen from the graph, the selectivity to NO2 is excellent at the same concentration (100 ppm).

[0042] Figure 3 is a long-term stability test graph of the gas sensor sensitive material to NO2 gas in this embodiment. As can be seen from the graph, the long-term stability (10 weeks) of the sensor sensitive material is good, and the response capability attenuation is only 5.05% compared with the first week.

[0043] Example Two

[0044] (1) Preparation of graphene quantum dots (GQDs): graphene as raw material was mixed with concentrated sulfuric acid (H2SO4, 98%) and concentrated nitric acid (HNO3, 68%) for ultrasonic treatment for 12 h, and the mass ratio of the three was 1:0.2:1. Deionized water was added for dilution and filtration to obtain a solid product. The product was dissolved in deionized water and the pH was adjusted to 8 with sodium hydroxide (NaOH), and then transferred to a reaction kettle for hydrothermal treatment at 200°C for 8 h. After cooling to room temperature, the product was filtered and dissolved in deionized water, and dialyzed (dialysis bag specification 8000 Da) for 10 days. The solution outside the dialysis bag was taken, and the final product was obtained by rotary evaporation.

[0045] (2) Synthesis steps: ethylenediamine (C2H8N2), metal phthalocyanine (MPc-COOH) and graphene quantum dots (GQDs) were taken in a mass ratio of 0.2:1:0.25, dissolved in a mixed solution of water and DMF (N,N-dimethylformamide) in a ratio of 4:1. The solution was ultrasonically dispersed for 60 min at an ultrasonic power of 600 W, and then transferred to a high-pressure reaction kettle for reaction at 200°C for 12 hours. The product was washed with ethanol and deionized water alternately, and then freeze-dried for 24 h. Finally, the obtained solid was annealed at 300°C for 6 h in a vacuum environment. In this embodiment, the metal phthalocyanine is cobalt phthalocyanine.

[0046] Figure 4 is a gas concentration-response value test graph of the gas sensor sensitive material in this embodiment measured in a 100 ppm NO2 gas atmosphere. The response value R = Ra / Rg, where Ra is the initial resistance value and Rg is the resistance value after contacting the target gas. The working temperature is constant at 25°C, the humidity is 0 (dry gas is used as the background gas), and the ventilation time for each test is 100 seconds.

[0047] As can be seen from the results in the figure, the response of the gas sensor sensitive material to NO2 changes basically linearly with the concentration, and the response value reaches 30.8 at 100 ppm. The minimum response limit reaches 0.05 ppm (50 ppb), and the response value is still 0.04 at 0.05 ppm.

[0048] Figure 5 is a gas selectivity test graph of the gas sensor sensitive material in this embodiment measured in a variety of different gas atmospheres. As can be seen from the figure, the selectivity to NO2 is excellent at the same concentration (100 ppm).

[0049] Figure 6 is a long-term stability test graph of the gas sensor sensitive material to NO2 gas in this embodiment. As can be seen from the figure, the long-term stability (10 weeks) of the sensor sensitive material is good, and the response capability attenuation is only 7.47% compared with the first week

[0050] Figure 7 is a schematic diagram of the synthesis of the metal phthalocyanine and graphene quantum dots in this embodiment. As shown in the figure, the addition of the functional group carboxyl COOH causes the π bond on the carboxyl group to form a combination with the π bond on the phthalocyanine macromolecule, which promotes an increase in the electron density in the molecule and facilitates the smooth flow of electrons throughout the system.

[0051] Figure 8 is a scanning electron microscope test diagram of the graphene quantum dots in this embodiment. As shown in the figure, the size of the graphene quantum dots prepared in this embodiment is between 4-6 nm, with good uniformity of size, which is conducive to the performance stability of mass production; the small volume does not easily hinder the movement of gas molecules in the material. Figure 2

[0052] Figure 9 is a scanning electron microscope test diagram of the gas sensor sensitive material in this embodiment. As can be seen from the figure, the metal phthalocyanine preparation method of this embodiment forms a uniform film and forms a conductive network micro-nano structure.

[0053] Embodiment Three

[0054] (1) Preparation of graphene quantum dots (GQDs): Take graphene as raw material and mix with concentrated sulfuric acid (H2SO4, 98%) and concentrated nitric acid (HNO3, 68%) under ultrasonic for 6h, the mass ratio of the above three is 1:1:0.1. Dilute with deionized water and filter to obtain a solid product, re-dissolve the product in deionized water and adjust the pH to 9 with sodium hydroxide (NaOH), then transfer to a reaction kettle for hydrothermal treatment at 220℃ for 12h; after cooling to room temperature, the product is filtered and dissolved in deionized water, dialyzed (dialysis bag specification is 5000Da) for 5 days, take the solution outside the dialysis bag, and rotary evaporate to obtain the final product.

[0055] (2) Synthesis steps: Take ethylenediamine (C2H8N2), metal phthalocyanine with four carboxyl groups (MPc-COOH) and graphene quantum dots (GQDs), the mass ratio of the three is 0.5:1:1, dissolved in a mixed solution of water and DMF (N,N-dimethylformamide), the ratio of the two is 9:1. The solution is ultrasonically dispersed for 15min at an ultrasonic power of 100W, then transferred to a high-pressure reaction kettle for reaction at 180℃ for 10h. The product is washed with ethanol and deionized water alternately, and then freeze-dried for 12h. Finally, the obtained solid is annealed at 500℃ for 2h in a vacuum environment. In this embodiment, the metal phthalocyanine is cobalt phthalocyanine. In other embodiments, the metal phthalocyanine with four carboxyl groups can be one or more of cobalt phthalocyanine, nickel phthalocyanine, copper phthalocyanine and zinc phthalocyanine, etc.

[0056] Figure 10 ​is a gas concentration-response value test chart of the gas sensor sensitive material in the embodiment, which is measured when the gas sensor sensitive material is placed in 100 ppm NO2 gas. The response value R = Ra / Rg, wherein Ra is the initial resistance value and Rg is the resistance value after contacting the target gas. The working temperature is constant at 25°C, the humidity is 0 (dry gas is used as the background gas), and the ventilation time of each test is 100 seconds.

[0057] As can be seen from the results, the response of the gas sensor sensitive material to NO2 is basically linear with the concentration, and the response value reaches 12.5 at 100 ppm. The minimum response limit reaches 0.05 ppm (50 ppb), and the response value is still 0.007 at 0.05 ppm.

[0058] Figure 11 is a gas selectivity test chart of the gas sensor sensitive material in the embodiment, which is measured when the gas sensor sensitive material is placed in atmospheres of various different gases. As can be seen from the chart, the selectivity to NO2 is excellent at the same concentration (100 ppm).

[0059] Figure 12 is a long-term stability test chart of the gas sensor sensitive material to NO2 gas in the embodiment. As can be seen from the chart, the long-term stability (10 weeks) of the sensor sensitive material is good, and the response capacity attenuation is only 8% compared with the first week.

[0060] In summary, the new gas sensor sensitive material prepared in the embodiment effectively improves the gas sensitive performance of the gas sensor, effectively overcomes various shortcomings in the prior art, and has high industrial utilization value.

[0061] The above embodiments only exemplarily illustrate the principles and effects of the present application, and are not used to limit the present application. Any person skilled in the art can modify or change the above embodiments without departing from the spirit and scope of the present application. Therefore, all equivalent modifications or changes completed by those skilled in the art without departing from the spirit and technical thought disclosed in the present application should be covered by the claims of the present application.

Claims

1. A method for preparing a gas sensor sensitive material, characterized by, The method comprises the following steps: The product prepared by mixing graphene with concentrated sulfuric acid and concentrated nitric acid is dissolved in liquid by dialysis after being filtered, and the solution outside the dialysis bag is taken to obtain graphene quantum dots by drying, wherein the size of the graphene quantum dots and the size of the metal phthalocyanine are in the same order of magnitude. Step S1: graphene is mixed with concentrated sulfuric acid and concentrated nitric acid for ultrasonic treatment for 6-12 hours, and the mass ratio of the three is 1:0.1-1:0.1-1. Step S2: The mixed solution in step S1 is diluted and filtered to obtain a solid product, and the solid product is re-dissolved in deionized water and adjusted to a pH of 7-9 with sodium hydroxide, and then transferred to a reaction kettle for hydrothermal treatment at 180-220°C for 8-12 hours. Step S3: The product in step S2 is cooled, filtered, dissolved in deionized water, and dialyzed for 5-10 days, and the solution outside the dialysis bag is taken and rotary evaporated to obtain graphene quantum dots. The ethylenediamine, the metal phthalocyanine, and the graphene quantum dots are dissolved in a mixed solution of water and N,N-dimethylformamide to react, and then a solid product is obtained by drying, comprising the following steps: Step S4: The ethylenediamine, the metal phthalocyanine, and the graphene quantum dots in step S3 are dissolved in a mixed solution of water and N,N-dimethylformamide, and the mass ratio of the three is 0.05-0.5:1:0.1-1, and the ratio of the two is 1-9:

1. Step S5: The solution in step S4 is ultrasonically dispersed for 15-60 minutes at an ultrasonic power of 100-600 W, and then transferred to a high-pressure reaction kettle for reaction at 180-250°C for 6-12 hours. Step S6: The product in step S5 is washed and freeze-dried for 12-24 hours, and then the obtained solid is annealed at 200-500°C in a vacuum environment for 2-8 hours.

2. The method for preparing the gas sensor sensitive material according to claim 1, characterized in that: The gas sensor sensitive material has a conductive network micro-nano structure.

3. The method of producing a gas sensor sensitive material according to claim 1, characterized by: The dialysis bag has a specification of 5000 Da to 10000 Da.

4. The method for preparing the gas sensor sensitive material according to claim 1, characterized in that: The metal phthalocyanine is cobalt phthalocyanine.

5. The method of claim 1, wherein the gas sensor sensitive material is prepared by the steps of: The gas sensor sensitive material is used for detecting NO2 gas. ​ 6. The method for preparing the gas sensor sensitive material according to claim 1, characterized in that: The graphene quantum dots have carboxyl groups.

7. The method for preparing the gas sensor sensitive material according to claim 1, characterized in that: The size of the graphene quantum dots is 4-6 nm.

8. A gas sensor sensitive material, characterized by: The gas sensor sensitive material prepared by the preparation method of any one of claims 1-7 has a conductive network micro-nano structure.

9. The gas sensor sensitive material according to claim 8, characterized in that: The response of the gas sensor sensitive material to NO2 is that the response value reaches 12.5-30.8 at 100 ppm, and the minimum response limit is 0.05 ppm, and the response value reaches 0.007-0.04 at 0.05 ppm.

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