KR101156674B1 - Gas sensor using porous nano-fiber containing electrically conductive carbon material and manufacturing method thereof - Google Patents

Abstract

Disclosed are a method for manufacturing a gas sensor using a porous nanofiber containing a conductive carbon material, and a gas sensor manufactured according to the same.

Method for producing a gas sensor according to the invention comprises the steps of (1) mixing a polymer precursor and a solvent; (2) dispersing the conductive carbon material in the mixture obtained through the process of 'step (1)'; (3) preparing nanofibers by electrospinning the mixture obtained through the process of 'step (2); (4) oxidizing the nanofibers obtained through the process of 'step (3)'; (5) carbonizing the oxidized nanofibers through the process of 'step (4)'; (6) activating the carbonized nanofibers through the process of 'step (5)'; And (7) manufacturing a gas sensor by depositing the nanofibers activated through the process of 'step (6)' between the silicon wafer electrodes.

According to the present invention, it is possible to manufacture a reliable gas sensor having a very high sensitivity even at room temperature.

Gas sensor, conductive, carbon material, porous, nanofiber, gas, sensitive

Description

GAS SENSOR USING POROUS NANO-FIBER CONTAINING ELECTRICALLY CONDUCTIVE CARBON MATERIAL AND MANUFACTURING METHOD THEREOF}

The present invention relates to a gas sensor, and more particularly, to a method of manufacturing a reliable gas sensor having a very high sensitivity even at room temperature using porous nanofibers containing a conductive carbon material and to a gas sensor manufactured by the method. It is about.

In general, the gas sensor is operated by the principle of measuring the amount of harmful gas by using the characteristic that the electrical conductivity changes according to the adsorption of gas molecules. Materials that have been widely used as gas sensors include metal oxide semiconductors such as SnO ₂ , solid electrolyte materials, various organic materials, and carbon black and organic compounds. Gas sensors manufactured using the above materials have various problems, such as limited use. That is, in the case of a gas sensor manufactured using a metal oxide semiconductor or a solid electrolyte, the sensor operates normally at a temperature of 200 to 600 ° C. or higher, and when the organic material is used, the electrical conductivity is very low. In the case of using a composite of carbon black and an organic material, there is a problem of having very low sensitivity. In addition, the conventional gas sensor manufactured using the material has a slow response time, a very slow recovery speed, and an expensive price, which is not suitable for general use.

The present invention has been made to solve the above-mentioned problems, by forming a nanofiber containing a conductive carbon material through the electrospinning, and then oxidized, carbonized and activated, and then deposited between the silicon wafer electrode, even at room temperature It is an object of the present invention to provide a gas sensor having a very high sensitivity and a method of manufacturing the same.

In order to achieve the above object, the present invention provides a method for manufacturing a gas sensor using a nanofiber containing a conductive carbon material, the manufacturing method of a gas sensor according to the present invention,

(1) mixing a polymer precursor and a solvent;

(2) dispersing the conductive carbon material in the mixture obtained through the process of 'step (1)';

(3) preparing nanofibers by electrospinning the mixture obtained through the process of 'step (2)';

(4) oxidizing the nanofibers obtained through the process of 'step (3)';

(5) carbonizing the oxidized nanofibers through the process of 'step (4)';

(6) activating the carbonized nanofibers through the process of 'step (5)'; And

(7) preparing a gas sensor by depositing the nanofibers activated through the process of 'step (6)' between the silicon wafer electrodes.

In addition, the present invention may further include the step of heat-treating the gas sensor obtained through the process of the 'step (7)' after the 'step (7)'. The heat treatment is preferably made for 0.1 to 1 hour in the temperature range of 30 to 80 ℃.

The viscosity of the mixture obtained through the process of 'step (2)' is preferably 100 to 500 cP.

The mixing ratio of the mixture and the conductive carbon material in the step of dispersing the conductive carbon material in order to improve the electrical conductivity of the nanofibers in the mixture obtained through the step (1) of the step (2) is the mixture 100 It is preferably 0.5 to 5 parts by weight based on parts by weight. By adding the conductive carbon material as described above, the electrical conductivity of the nanofibers is improved, and thus a gas sensor having high sensitivity and quick response can be manufactured.

The process of oxidizing the 'step (4)' is heated at a rate of 1 to 5 ℃ / min, it is preferably made for 2 to 5 hours in the temperature range of 200 to 300 ℃.

The carbonization of the step (5) is preferably performed at a rate of 5 to 10 ° C./min and finally at 0.5 to 2 hours in a temperature range of 800 to 1,200 ° C.

The activation of the 'step (6)' is made by adding a potassium hydroxide solution, the concentration of the potassium hydroxide solution is preferably in the range of 5 to 10M.

The manufacturing of the gas sensor of 'step (7)' is performed by dispersing the nanofibers obtained through the process of 'step (6)' in a dispersion solution and depositing the same between the silicon wafer electrodes. Nanofibers dispersed in the amount is preferably 0.1 to 3 parts by weight based on 100 parts by weight of the dispersion solution.

The present invention also provides a gas sensor manufactured by the above method.

According to the present invention as described above, by forming the nanofibers containing the conductive carbon material through the electrospinning, and then oxidized, carbonized and activated again and deposited between the silicon wafer electrode, very high sensitivity even at room temperature It is possible to manufacture a reliable gas sensor.

The present invention provides a gas sensor manufactured using nanofibers containing a conductive carbon material and a method of manufacturing the same. Figure 1 shows a schematic diagram of a gas sensor manufactured according to an embodiment of the present invention. As shown, the gas sensor according to the present invention has a shape in which the porous nanofibers containing the conductive carbon material are evenly distributed between the silicon wafer electrodes.

Hereinafter, the present invention will be described in detail.

First, the present invention provides a method of manufacturing a gas sensor using a porous nanofiber containing a conductive carbon material, the manufacturing method of a gas sensor according to the present invention,

(1) mixing a polymer precursor and a solvent;

(2) dispersing the conductive carbon material in the mixture obtained through the process of 'step (1)';

(3) preparing nanofibers by electrospinning the mixture obtained through the process of 'step (2)';

(4) oxidizing the nanofibers obtained through the process of 'step (3)';

(5) carbonizing the oxidized nanofibers through the process of 'step (4)';

(6) activating the carbonized nanofibers through the process of 'step (5)'; And

(7) preparing a gas sensor by depositing the nanofibers activated through the process of 'step (6)' between the silicon wafer electrodes.

Any polymer precursor may be used as long as the polymer precursor used in step (1) 'is a material convertible to carbon. Specific examples include petroleum pitch, coal pitch, polyimide, polybenzimidazole, polyacrylonitrile, polyaramid, polyaniline, mesophase pitch, furpril alcohol, phenol, cellulose, sucrose, polyvinyl chloride and their It may be selected from the group consisting of a mixture.

The solvent used in the 'step (1)' may be used as long as it dissolves the polymer precursor. For example, dimethylformamide, chloroform, N-methylpyrrolidone tetrahydrofuran, Sulfuric acid, nitric acid, acetic acid, hydrochloric acid, ammonia, distilled water and mixtures thereof.

The conductive carbon material used in the 'step (2)' may be used as long as the conductive carbon material. Specific examples may be selected from the group consisting of single-walled carbon nanotubes, double-walled carbon nanotubes, multi-walled carbon nanotubes, graphite, activated carbon, carbon black, graphite and mixtures thereof.

The viscosity of the mixture obtained through the process of 'step (2)' is preferably 100 to 500 cP. The mixture obtained through the process of 'step (2)' is subjected to electrospinning using the electrospinning apparatus shown in FIG. 2 in the next step. The illustrated electrospinning apparatus is generally used, and the operation thereof is briefly described as follows. As shown in FIG. 2, the electrospinning apparatus includes a metering pump 1, a voltage generator 2, a concentrator 3 and a radiator 4. First, the solution is injected into the radiator 4 through the metering pump 1, and the solution radiated through the radiator 4 is focused by the rotating concentrator 3. The voltage generator 2 applies a necessary voltage. That is, the mixture obtained through the 'step (2)' is spun through the spinner, when the viscosity of the mixture exceeds 500 cP problem that the spinning nozzle is blocked by the cohesive force between the polymers does not have a smooth spinning It can happen. In addition, when the viscosity of the mixture is less than 100 cP there is a problem that does not have a constant shape due to too low viscosity is not preferred.

In the step of dispersing the conductive carbon material in the mixture obtained through the step (1) of the step (2), the mixing ratio of the mixture and the conductive carbon material is 0.5 to 5 based on 100 parts by weight of the mixture. It is preferable that it is a weight part. If the mixing ratio of the conductive carbon material is less than 0.5 parts by weight, the electrical conductivity of the prepared nanofibers is not different from the case where the conductive carbon material is not mixed. If the conductive carbon material exceeds 5 parts by weight, the above 'step ( It is difficult to uniformly disperse the conductive carbon material in the mixture obtained through the process of 1) ', which is not preferable.

Producing nanofibers by electrospinning the mixture made in step (3) is performed by a conventional electrospinning method using an apparatus as shown in FIG.

The process of oxidizing the 'step (4)' is heated at a rate of 1 to 5 ℃ / min, it is preferably made for 2 to 5 hours in the temperature range of 200 to 300 ℃. When the temperature increase rate is lower than 1 ° C./min in the oxidizing process, the cyclization reaction caused by the reaction of oxygen and carbon does not occur smoothly due to the slow reaction rate, and also lowers the fiber yield. If the temperature increase rate is faster than 5 ℃ / min due to the fast reaction rate is unstable fiber formation, when the next step of carbonization, the nanofiber melts or becomes glass transition and can not maintain the fiber form. When the final oxidizing temperature is less than 200 ℃ oxidation reaction is incomplete, the nanofibers melt or glass transition during the next carbonization can not maintain the fiber form, the condensation reaction between the carbon atoms is also not made smoothly. When the oxidation temperature exceeds 300 ° C., a high reaction temperature causes a rapid reaction, and thus, the cyclization reaction is not performed smoothly due to the carbon-oxygen coupling reaction in the peroxygen state. When the oxidation time is less than 2 hours, the same phenomenon occurs as when the final oxidation temperature is less than 200 ° C., and when the oxidation time is more than 5 hours, the oxidation time is not the same as that when 5 hours. Unnecessary reactions occur.

The carbonization of the step (5) is preferably performed at a rate of 5 to 10 ° C./min and finally at 0.5 to 2 hours in a temperature range of 800 to 1,200 ° C. When the carbonization process is carried out at a slower temperature than 5 ° C./min and at a high temperature exceeding 1,200 ° C., the reaction time increases and energy consumption increases. If the temperature increase rate is faster than 10 ℃ / min there is a problem that a lot of volatilization is reduced the yield of nanofibers. Moreover, when carbonizing at the temperature below 800 degreeC, carbonization may not be made completely and it is unpreferable. When the carbonization time is less than 0.5 hours, the carbonization is not sufficiently made, and when the carbonization time exceeds 5 hours, there is no difference from the case of 5 hours, it is not preferable because unnecessary reaction occurs.

The process of activating the 'step (6)' is made by adding a potassium hydroxide solution, the concentration of the potassium hydroxide solution is preferably in the range of 5 to 10M. When the concentration of the potassium hydroxide solution is less than 5M activation is not made sufficiently, if it exceeds 10M there is no significant difference from the case of 10M there is no benefit.

The manufacturing of the gas sensor of 'step (7)' is performed by dispersing the nanofibers obtained through the process of 'step (6)' in a dispersion solution and depositing the same between the silicon wafer electrodes. Various solutions may be selected as the dispersion solution, for example, ethanol, methanol, acetone, dimethylformamide and mixtures thereof. The proportion of the nanofibers dispersed in the dispersion solution is preferably 0.1 to 3 parts by weight based on 100 parts by weight of the dispersion solution. When the ratio of the nanofibers is less than 0.1 part by weight, there is a fear that the nanofibers may not be uniformly distributed between the silicon wafer electrodes, and when it exceeds 3 parts by weight, dispersion may be difficult, which is not preferable. A further example of this step of manufacturing a gas sensor is as follows. Grinding the nanofibers obtained through the process of 'step (6)' finely and evenly dispersed in the dispersion solution according to the intended ratio. Next, a solution in which the nanofibers are dispersed is deposited on a silicon wafer having a para film or the like attached to a wire connection part. The deposition may be performed by various methods such as vacuum deposition, spin coating, spray spraying, and the like.

In addition, the present invention may further include the step of heat-treating the gas sensor obtained through the process of the 'step (7)' after the 'step (7)'. The heat treatment is preferably made for 0.1 to 1 hour in the temperature range of 30 to 80 ℃. If the heat treatment temperature is less than 30 ℃, there is a fear that the dispersion solution is not easily evaporated, if it exceeds 80 ℃ it may cause problems such as melting the para film used to protect the wire connecting portion, etc. Not. In addition, when the heat treatment time is less than 0.1 hours, the dispersion solution may not easily evaporate. When the heat treatment time exceeds 1 hour, there is no significant difference from that of 1 hour.

The present invention also provides a gas sensor manufactured by the above method.

The present invention will be described in more detail with reference to the following examples.

Example 1 Preparation of Porous Nanofibers Containing a Conductive Carbon Material

Polyacrylonitrile was dissolved in dimethylformamide to prepare a mixed solution, and 1 part by weight of single-walled carbon nanotubes were dispersed in the mixed solution based on 100 parts by weight of the mixed solution. The viscosity of the mixed solution of the single-walled carbon nanotubes prepared by the above process was adjusted to 160 cP.

Nanofibers were prepared by electrospinning the mixed solution. Electrospinning conditions were a voltage of 17 kV, a distance between the collector and the syringe tip (TCD) of 12 cm, a pump flow rate of 2.0 ml / h, and a rotor speed of 200 rpm.

The nanofibers prepared by electrospinning as described above were heated up at a rate of 2 ° C./min and finally oxidized at 250 ° C. for 3 hours.

        The oxidized nanofibers were heated at a rate of 7 ° C./min and finally carbonized at 1,050 ° C. for 1 hour. Nitrogen gas was injected at a rate of 20 cc / min into the inert gas during carbonization.

        The carbonized nanofibers were immersed in 8M potassium hydroxide solution for 1 hour, and then activated. Activation was carried out at 750 ° C. for 3 hours.

Comparative Example 1: Preparation of Porous Nanofibers

Polyacrylonitrile was dissolved in dimethylformamide until the viscosity became 160 cP to prepare a mixed solution. The following procedure was performed in the same manner as in Example 1 to prepare a nanofiber.

Specific surface area analysis

The results of analyzing the specific surface area characteristics of the nanofibers according to Example 1 and Comparative Example 1 are shown in FIG. 3. The nanofibers according to Example 1 had a specific surface area of 1,317 m 2 / g, and the surface area due to the micropores was 64% of the total specific surface area. The nanofibers according to Comparative Example 1 had a specific surface area of 1,741 m 2 / g, and the surface area by double micropores was 64% of the total specific surface area. That is, the nanofibers according to the present example showed that the total specific surface area was reduced by about 24% compared with the comparative example.

Example 2 Fabrication of Gas Sensor Using Conductive Carbon Material-Containing Porous Nanofibers

        The nanofibers prepared in Example 1 were finely ground in a mortar and dispersed in dimethylformamide. Dispersion was performed at a ratio of 2 parts by weight of nanofibers based on 100 parts by weight of dimethylformamide.

The mixed solution formed through the above process was dropped on the silicon wafer, and spin-coated for 4 minutes at a rotational speed of 900 rpm to prepare a gas sensor.

Finally, a nanofiber-deposited gas sensor prepared through the above process was placed on a hot plate and heat-treated at 40 ° C. for 0.5 hour.

Comparative Example 2 Fabrication of Gas Sensor Using Nanofibers

The nanofibers prepared in Comparative Example 1 were finely ground in a mortar and dispersed in dimethylformamide. Dispersion was carried out in a ratio of 2 parts by weight of nanofibers based on 100 parts by weight of dimethylformamide, and the following procedure was carried out in the same manner as in Example 2 to prepare a gas sensor.

Surface characteristics

In order to determine the surface characteristics of the gas sensor manufactured according to Example 2, a scanning electron microscope (SEM) image was taken and shown in FIG. 4. As shown in the figure, it was confirmed that the porous nanofibers containing the conductive carbon material were evenly deposited on the silicon wafer.

Gas response characteristics

Next, the gas sensitivity characteristics of the gas sensors manufactured according to Example 2 and Comparative Example 2 were measured and evaluated. The schematic diagram of the apparatus for evaluating a gas sensitive characteristic is shown in FIG. Prior to evaluating the gas sensitive properties, pretreatment was performed to evaporate the water at 80 ° C. for 0.5 hours, respectively. The gas sensitivity was measured by injecting NO gas at a concentration of 50 ppm at a temperature of 25 ° C. (room temperature) using the apparatus shown in FIG. 5, and the measured results are shown in FIG. 6. As shown, the resistance change rate indicating the sensitivity of the gas sensor according to the sensitive characteristic of the NO gas according to Example 2 was about -15%, and the resistance indicating the sensitivity of the gas sensor according to the sensitive characteristic of the NO gas according to Comparative Example 2 The rate of change was about -9%.

The X axis of the graph shown in Figure 6 represents the measurement time, the Y axis represents the resistance change rate, as shown in the gas sensor according to Example 2 takes about 4.5 to 5 minutes to stabilize the resistance in the N ₂ gas atmosphere, For 50 ppm NO gas, it takes about 4.5 to 5 minutes for the resistance change rate to reach the limit. On the other hand, the gas sensor according to Comparative Example 2 takes about 5 to 6 minutes to stabilize the resistance in N ₂ gas atmosphere, and it takes about 6 to 7 minutes to reach the limit of resistance change rate for 50 ppm NO gas. have.

The gas sensor according to the embodiment of the present invention shows a higher resistance change rate and a shorter response time at room temperature, although the specific surface area is smaller than that of the gas sensor according to the comparative example. This is believed to be due to the improved electrical conductivity of the gas sensor by the conductive carbon material included in the gas sensor manufactured according to the embodiment of the present invention.

From this, the gas sensor according to the present invention was confirmed that the response time is short at room temperature and shows a high resistance change rate. That is, the gas sensor according to the present invention was confirmed to have a high sensitivity even at room temperature.

Although the present invention has been described with reference to the above-described embodiments and the accompanying drawings, other embodiments may be configured within the spirit and scope of the present invention. Therefore, the scope of the present invention is defined by the appended claims and equivalents thereof, and is not limited by the specific embodiments described herein.

1 is a schematic diagram of a gas sensor manufactured according to an embodiment of the present invention.

2 is a schematic diagram of an electrospinning apparatus for producing nanofibers.

3 is a nitrogen adsorption isotherm for confirming the porosity of the nanofibers prepared by Example 1 and Comparative Example 1 of the present invention.

4 is a scanning electron microscope (SEM) image photographed to determine the surface characteristics of a gas sensor manufactured according to an embodiment of the present invention.

5 is a schematic diagram of an apparatus for measuring gas sensitive characteristics.

Figure 6 is a graph showing the response characteristics for the NO gas of the gas sensor manufactured by Example 2 and Comparative Example 2 of the present invention.

Claims (14)

(1) mixing a polymer precursor and a solvent; (2) dispersing the conductive carbon material in the mixture obtained through the process of 'step (1)'; (3) preparing nanofibers by electrospinning the mixture obtained through the process of 'step (2)'; (4) oxidizing the nanofibers obtained through the process of 'step (3)'; (5) carbonizing the oxidized nanofibers through the process of 'step (4)'; (6) activating the carbonized nanofibers through the process of 'step (5)'; And (7) dispersing the activated nanofibers in the dispersion solution through the process of 'step (6)' and depositing them between the silicon wafer electrodes to manufacture a gas sensor; Manufacturing method. The method of claim 1, The method of manufacturing a gas sensor using nanofibers, further comprising the step of heat-treating the gas sensor obtained through the step (7) after the step (7). The method of claim 1, The conductive carbon material is a gas sensor using nanofibers, characterized in that selected from the group consisting of single-walled carbon nanotubes, double-walled carbon nanotubes, multi-walled carbon nanotubes, graphite, activated carbon, carbon black, graphite and mixtures thereof Manufacturing method. The method of claim 1, Method of producing a gas sensor using a nanofiber, characterized in that the viscosity of the mixture obtained through the process of 'step (2)' is in the range of 100 to 500 cP. The method of claim 1, In the step of dispersing the conductive carbon material in the mixture obtained through the step (1) of the step (2), the mixing ratio of the mixture and the conductive carbon material is 0.5 to 0.5 parts by weight based on 100 parts by weight of the mixture. Gas sensor manufacturing method using a nanofiber, characterized in that 5 parts by weight. The method of claim 1, Oxidation process of the 'step (4)' is a gas sensor using a nanofiber, characterized in that the temperature is raised at a rate of 1 to 5 ℃ / min, finally made for 2 to 5 hours in a temperature range of 200 to 300 ℃ Manufacturing method. The method of claim 1, Carbonization process of the 'step (5)' is a gas sensor using a nanofiber, characterized in that the temperature is raised at a rate of 5 to 10 ℃ / min, and finally made for 0.5 to 2 hours in the temperature range of 800 to 1,200 ℃ Manufacturing method. The method of claim 1, The process of activating the 'step (6)' is a method of manufacturing a gas sensor using nanofibers, characterized in that by adding a potassium hydroxide solution. The method of claim 8, The concentration of the potassium hydroxide solution is a method of manufacturing a gas sensor using nanofibers, characterized in that 5 to 10M range. delete The method of claim 1, The dispersion solution is a method of manufacturing a gas sensor using nanofibers, characterized in that selected from the group consisting of ethanol, methanol, acetone, dimethylformamide and mixtures thereof. The method of claim 1, The ratio of the nanofibers dispersed in the dispersion solution is a manufacturing method of a gas sensor using nanofibers, characterized in that 0.1 to 3 parts by weight based on 100 parts by weight of the dispersion solution. 3. The method of claim 2, The heat treatment is a method of manufacturing a gas sensor using nanofibers, characterized in that made for 0.1 to 1 hour in the temperature range of 30 to 80 ℃. delete

Images