阅读说明：本技术 气体吸附剂、气体吸附装置和气体传感器 (Gas adsorbent, gas adsorption device, and gas sensor ) 是由 守法笃 于 2020-03-26 设计创作，主要内容包括：本发明提供一种气体吸附剂,其包含有机材料和多个导电性颗粒,并且能够在暴露于气体的情况下使得电阻值响应性地发生变化。气体吸附剂(1)包括多个吸附颗粒(12)。多个吸附颗粒(12)聚集在一起形成多孔结构。吸附颗粒(12)包括：绝缘性颗粒(3)；以及全部附着于绝缘性颗粒(3)的表面的多个导电性颗粒(21)和有机材料(22)。(The present invention provides a gas adsorbent which comprises an organic material and a plurality of conductive particles and is capable of causing a responsive change in resistance value upon exposure to a gas. The gas adsorbent (1) comprises a plurality of adsorbent particles (12). A plurality of adsorbent particles (12) are aggregated together to form a porous structure. The adsorbent particles (12) comprise: insulating particles (3); and a plurality of conductive particles (21) and an organic material (22) all adhering to the surface of the insulating particles (3).)

1. A gas adsorbent comprising a plurality of adsorbent particles aggregated together to form a porous structure,

the plurality of adsorbent particles each comprise: insulating particles; and a plurality of conductive particles and an organic material all adhered to the surface of the insulating particles.

2. The gas adsorbent according to claim 1,

the insulating particles have an average particle diameter larger than that of the plurality of conductive particles.

3. The gas adsorbent according to claim 2,

the insulating particles have an average particle diameter 3 times or more larger than that of the plurality of conductive particles.

4. The gas adsorbent according to any one of claims 1 to 3,

the voids generated in the porous structure have a diameter larger than an average particle diameter of the plurality of conductive particles.

5. The gas adsorbent according to any one of claims 1 to 4,

the plurality of conductive particles and the organic material are attached to the surface of the insulating particles in a film shape.

6. The gas adsorbent according to any one of claims 1 to 5,

the organic material comprises a polymer.

7. The gas adsorbent according to any one of claims 1 to 6,

the plurality of conductive particles includes a carbon material.

8. The gas adsorbent according to any one of claims 1 to 7,

the plurality of conductive particles have an average particle diameter falling within a range of 10nm to 30 nm.

9. The gas adsorbent according to any one of claims 1 to 8,

the insulating particles have an average particle diameter falling within a range of 100nm to less than 1500 nm.

10. A gas adsorption device comprising: the gas sorbent according to any one of claims 1 to 9; and a base material member for supporting the substrate member,

the plurality of adsorbent particles of the gas adsorbent each comprise:

insulating particles;

a first coating layer formed of a plurality of conductive particles and continuously coating the surface of the insulating particles; and

a second coating layer formed of an organic material and continuously coating a surface of the first coating layer,

the porous structure is formed by continuously connecting the plurality of adsorbent particles to each other and creating voids surrounded by adjacent adsorbent particles of the plurality of adsorbent particles,

the gas sorbent is in contact with the substrate member on at least one of the first coating and the second coating.

11. A gas sensor, comprising:

the gas adsorbent according to any one of claims 1 to 9 or the gas adsorption device according to claim 10; and

an electrode electrically connected to the gas sorbent.

Technical Field

The present invention relates generally to a gas adsorbent, a gas adsorbing device, and a gas sensor, and more particularly to a gas adsorbent containing an organic material and conductive particles, a gas adsorbing device including the gas adsorbent, and a gas sensor including the gas adsorbent or the gas adsorbing device.

Background

A gas sensor is provided comprising a gas-adsorbing organic material and conductive particles dispersed in the organic material. For example, patent document 1 discloses a chemiresistor, which includes: an electrically insulating substrate member having a pair of electrodes arranged in a circular geometry parallel to each other; a chemically sensitive polymer in contact with the pair of electrodes; and carbon particles dispersed in the chemically sensitive polymer. In the chemiresistor, for example, when a chemically sensitive polymer adsorbs volatile organic compounds in a gas, its resistance value changes. The use of the chemiresistor enables the detection of volatile organic compounds in a gas based on a change in the resistance value of the chemiresistor.

CITATION LIST

Patent document

Patent document 1: US 7189360B 1

Disclosure of Invention

The problem to be solved by the present invention is to provide the following: a gas adsorbent comprising an organic material and a plurality of electrically conductive particles and capable of causing a responsive change in resistance value upon exposure to a gas; a gas adsorption unit comprising a gas adsorbent; and a gas sensor comprising a gas adsorbent or gas adsorption means.

A gas sorbent according to an aspect of the invention comprises a plurality of sorbent particles. A plurality of adsorbent particles are aggregated together to form a porous structure. Each of the plurality of adsorption particles includes an insulating particle, and a plurality of conductive particles and an organic material all adhering to the surface of the insulating particle.

A gas adsorption device according to another aspect of the present invention includes: the above-mentioned gas adsorbent; and a substrate member. The plurality of adsorbent particles of the gas adsorbent each comprise: insulating particles; a first coating layer formed of a plurality of conductive particles and continuously coating the surface of the insulating particles; and a second coating layer formed of an organic material and continuously coating a surface of the first coating layer. The porous structure is formed by continuously connecting a plurality of adsorbent particles to each other and creating voids surrounded by adjacent adsorbent particles in the plurality of adsorbent particles. The gas sorbent is in contact with the substrate member on at least one of the first coating and the second coating.

A gas sensor according to still another aspect of the present invention includes: the gas adsorbent or the gas adsorbing device; and an electrode electrically connected to the gas adsorbent.

Drawings

FIG. 1 is a schematic cross-sectional view of a pattern of a gas sorbent, a gas adsorption device, and a gas sensor in accordance with an exemplary embodiment of the present invention;

FIG. 2 is a schematic plan view of a pattern of gas sensors in an experiment used in the example;

fig. 3 is a graph showing the rate of change in resistance values measured in examples for samples #1, #2, and #3 in the case where nonanal is adsorbed to samples #1, #2, and # 3;

FIG. 4A is a Scanning Electron Microscope (SEM) micrograph showing a cross-section of an exemplary sample # 7;

FIG. 4B is an SEM micrograph showing a cross-section of an exemplary sample # 8;

FIG. 4C is an SEM micrograph showing a cross-section of an exemplary sample # 3;

FIG. 5A is an SEM micrograph showing the surface of an exemplary sample # 7;

FIG. 5B is an SEM micrograph showing the surface of an exemplary sample # 8;

FIG. 5C is an SEM micrograph showing the surface of an exemplary sample # 3;

fig. 6 is a graph showing how the rate of change in resistance value changes with time when measured against samples #3 to #8 having adsorbed benzaldehyde in the example; and

fig. 7 is a graph showing how the rate of change in the resistance value changes when measured for samples #3 to #8 having adsorbed benzaldehyde in the example.

Detailed Description

First, how the inventors conceived the idea of the present invention will be described accurately.

If a chemical substance in a gas is adsorbed into a gas adsorbent containing an organic material and conductive particles dispersed in the organic material by exposing the gas adsorbent to the gas, the resistance value of the gas adsorbent changes. The resistance value may partially vary because the organic material adsorbs the chemical substance and expands, whereby the separation distance between the conductive particles in the gas adsorbent changes. Based on such a change in the resistance value of the gas adsorbent, the chemical substance in the gas can be detected. That is, the chemical substance in the gas can be detected by using a gas sensor including such a gas adsorbent.

In the case where the gas adsorbent is exposed to a gas, the more significant and faster the resistance value of the gas adsorbent changes, the faster and more accurate the chemical substance can be detected.

However, the performance enhancement of the gas sorbent is limited, for example, by varying the combination of the selected organic material and the electrically conductive particles.

Accordingly, the present inventors have conducted extensive studies to develop a gas adsorbent in which the resistance value will responsively change upon exposure to a gas containing a chemical substance. As a result of extensive research and development, the present inventors conceived the idea of the present invention.

Next, an exemplary embodiment of the present invention will be described with reference to fig. 1.

The gas adsorbent 1 according to the present embodiment includes a plurality of adsorbent particles 12. The adsorbent particles 12 are particles having gas adsorbability. As used herein, "gas adsorption" refers to the property of adsorbing a chemical contained in a gas upon exposure to the gas. Examples of the chemical substance include volatile organic compounds and inorganic compounds. Examples of volatile organic compounds include ketones, amines, alcohols, aromatic hydrocarbons, aldehydes, esters, organic acids, methyl mercaptan, disulfides, and the like. Examples of the inorganic compound include hydrogen sulfide, sulfur dioxide, carbon disulfide, and the like. The adsorbent particles 12 preferably have the property of adsorbing at least one chemical species. Based on the knowledge of the known technique, it is possible to judge whether or not the adsorbent particles 12 have gas adsorbability. For example, in the case where a chemical substance derived from a gas is detected when the adsorbent particles 12 are exposed to the gas and then analyzed with a gas chromatography mass spectrometer, it can be judged that the adsorbent particles 12 should have gas adsorbability. The adsorbent particles 12 preferably have the property of adsorbing at least one volatile organic compound.

The adsorbent particles 12 aggregate together to form a porous structure. The adsorption particles 12 each include an insulating particle 3, and a conductive particle 21 and an organic material 22 attached to the surface of the insulating particle 3.

In other words, it can be said that the gas adsorbent 1 includes the insulating particles 3 and the adsorption part 2. In this case, the adsorption part 2 includes conductive particles 21 and an organic material 22. In the adsorption part 2, for example, the conductive particles 21 may be dispersed in the organic material 22. In the gas adsorbent 1, the insulating particles 3 each having a surface to which the adsorption part 2 is attached are aggregated to form a porous structure.

Specifically, for example, the adsorbent particles 12 may each include: insulating particles 3; a first coating layer 23 which is formed of the conductive particle(s) 21 and continuously coats the surface of the insulating particle 3; and a second coating layer 24 formed of the organic material 22 and continuously coating the surface of the first coating layer 23. The porous structure of the gas adsorbent 1 is formed by continuously connecting the adsorbent particles 12 to each other and creating voids 11 surrounded by adjacent ones of the adsorbent particles 12. That is, the voids 11 in the porous structure are each surrounded by the adsorbent particles 12. In this case, the adsorption part 2 is formed by gathering the adsorption particles 12 together so that the respective first coating layers 23 and second coating layers 24 of the adsorption particles 12 are integrated.

The gas adsorption device 20 according to the present embodiment includes a gas adsorbent 1 and a substrate member 6. For example, the gas adsorbent 1 is in contact with the substrate member 6 on at least one of the first coating layer 23 and the second coating layer 24.

Specifically, the conductive particle(s) 21 and the organic material 22 may be attached to the surface of the insulating particle 3 in a film shape, for example. In other words, it can also be said that the adsorption part 2 has a film shape for adhering to the surface of the insulating particles 3 and thereby covering the insulating particles 3. In this case, the conductive particle(s) 21 and the organic material 22 (i.e., the adsorption part 2) may completely cover the insulating particles 3 or only partially cover the insulating particles 3, whichever is appropriate. In the gas adsorbent 1, in the case where the interval between the adjacent insulating particles 3 is sufficiently narrow, or in the case where the insulating particles 3 are in contact with each other, the respective conductive particles 21 and the organic material 22 (i.e., the adsorption part 2) adhering to the insulating particles 3 tend to be joined and integrated. On the other hand, in the case where the interval between the adjacent insulating particles 3 is sufficiently wide, the voids 11 tend to be formed between the particles 3. Thereby, the insulating particles 3 each having the surface to which the conductive particle(s) 21 and the organic material 22 (i.e., the adsorption part 2) are attached are aggregated to form a porous structure. Note that this depends on the individual situation, and is difficult to define explicitly: how narrow the interval should be to increase the chance of the suction portions 2 joining together; and how wide the spacing should be to increase the chance of creating voids 11.

When the gas adsorbent 1 according to the present embodiment is exposed to a gas, the organic material 22 adsorbs a chemical substance in the gas, and therefore, the resistance value of the gas adsorbent 1 changes accordingly.

This embodiment increases the chance that the resistance value of gas adsorbent 1 changes rapidly when gas adsorbent 1 is exposed to a gas. That is, this embodiment promotes improvement in the responsiveness of the gas adsorbent 1. This should be due, in part, to the porosity of gas sorbent 1 being such that gas can more easily enter voids 11 in gas sorbent 1 (i.e., increase the gas permeability of gas sorbent 1) so that gas sorbent 1 can efficiently adsorb chemical species in the gas.

The organic material 22 preferably has gas adsorption properties. As used herein, "gas adsorption" refers to the property of adsorbing a chemical substance contained in a gas when exposed to the gas. Examples of the chemical substance include volatile organic compounds and inorganic compounds. Examples of volatile organic compounds include ketones, amines, alcohols, aromatic hydrocarbons, aldehydes, esters, organic acids, methyl mercaptan, disulfides, and the like. Examples of the inorganic compound include hydrogen sulfide, sulfur dioxide, carbon disulfide, and the like. The organic material 22 preferably has the property of adsorbing at least one chemical species. Based on the knowledge of the known art, it can be judged whether the organic material 22 has gas adsorbability. For example, in the case where the organic material 22 is exposed to a gas and then chemical substances derived from the gas are detected when analyzed with a gas chromatography mass spectrometer, it can be judged that the organic material 22 should have gas adsorbability. The organic material 22 preferably has the property of adsorbing at least one volatile organic compound.

For example, the organic material 22 is selected according to the kind of the chemical substance to be adsorbed by the gas adsorbent 1 and the kind of the conductive particles 21 in the gas adsorbent 1. The organic material 22 includes at least one type of material selected from the group consisting of a polymer and a low molecular weight compound. The organic material 22 preferably comprises a polymer or the like. If organic material 22 comprises a polymer, gas sorbent 1 can have heat resistance.

Examples of preferred organic materials 22 include materials commercially available as stationary phases for columns in gas chromatographs. More specifically, the organic material 22 includes at least one material selected from the group consisting of, for example, polyalkylene glycols, polyesters, silicones, glycerols, nitriles, dicarboxylic acid monoesters, and aliphatic amines. In this case, the organic material 22 can easily adsorb chemical substances in the gas, particularly volatile organic compounds.

Polyalkylene glycols include, for example, polyethylene glycol (heat resistant temperature 170 ℃). The polyester group includes, for example, at least one material selected from the group consisting of poly (diethylene glycol adipate) and poly (ethylene succinate). The silicone based, for example, includes at least one material selected from the group consisting of: dimethyl silicone, benzyl silicone, trifluoropropylmethyl silicone, and cyano silicone (heat resistant temperature 275 ℃). The glycerin includes, for example, diglycerin (heat resistant temperature 150 ℃). Nitriles include, for example, at least one material selected from the group consisting of: n, N-bis (2-cyanoethyl) formamide (heat resistance temperature: 125 ℃) and 1, 2, 3-tris (2-cyanoethoxy) propane (heat resistance temperature: 150 ℃). The dicarboxylic acid monoesters include, for example, at least one material selected from the group consisting of: nitroterephthalic acid-modified polyethylene glycol (heat resistant temperature 275 ℃ C.) and diethylene glycol succinate (heat resistant temperature 225 ℃ C.). The aliphatic amine includes, for example, tetrahydroxyethyl ethylenediamine (heat resistant temperature: 125 ℃ C.).

The conductive particles 21 include, for example, at least one material selected from the group consisting of: carbon materials, conductive polymers, metals, metal oxides, semiconductors, superconductors, and complexes. The carbon material includes, for example, at least one material selected from the group consisting of: carbon black, graphite, coke, carbon nanotubes, graphene, and fullerenes. The conductive polymer includes, for example, at least one material selected from the group consisting of: polyaniline, polythiophene, polypyrrole, and polyacetylene. The metal includes, for example, at least one material selected from the group consisting of: silver, gold, copper, platinum and aluminum. The metal oxide includes, for example, at least one material selected from the group consisting of: indium oxide, tin oxide, tungsten oxide, zinc oxide, and titanium oxide. The semiconductor, for example, includes at least one material selected from the group consisting of: silicon, gallium arsenide, indium phosphide, and molybdenum sulfide. The superconductor includes, for example, at least one material selected from the group consisting of: YBa (Yttrium barium sulfate)₂Cu₃O₇And Tl₂Ba₂Ca₂Cu₃O₁₀. The complex, for example, includes at least one material selected from the group consisting of: a complex of tetramethyl p-phenylenediamine and chloranil; a complex of tetracyano-p-quinodimethane and an alkali metal; a complex of tetrathiafulvalene and a halogen; complexes of iridium and halocarbonyl compounds; and tetracyanoplatins.

The conductive particles 21 preferably include a carbon material. The conductive particles 21 particularly preferably include carbon black or the like. In the case where the conductive particles 21 include a carbon material (such as carbon black, in particular), the resistance value of the gas adsorbent 1 may change particularly responsively upon exposure to a gas.

The average particle diameter of the conductive particles 21 is preferably less than 50nm, more preferably equal to or less than 44nm, and further preferably equal to or less than 30 nm. The average particle diameter is preferably equal to or less than 25nm, more preferably equal to or less than 20nm, and particularly preferably equal to or less than 15 nm. The smaller the average particle diameter of conductive particles 21 is, the more significantly the rate of change in the resistance value of gas adsorbent 1 increases in the case where gas adsorbent 1 adsorbs a chemical substance (i.e., the higher the sensitivity of gas adsorbent 1 becomes).

According to the present embodiment, even if the average particle diameter of the conductive particles 21 is small as described above, the gas adsorbent 1 can be made to have a porous structure by using the insulating particles 3. That is, even if the voids 11 are not easily generated because the average particle diameter of the conductive particles 21 is small, by adjusting the particle diameter of the insulating particles 3, the voids 11 can be generated and the porous structure can be formed.

The lower limit of the average particle diameter of the conductive particles 21 in the adsorption part 2 is not particularly limited. However, in order to improve the uniformity of the gas adsorbent 1 by reducing the chance of the conductive particles 21 aggregating together, the average particle diameter is preferably equal to or greater than 5nm, and more preferably equal to or greater than 10 nm.

Note that the average particle diameter of the conductive particles 21 is a number-based arithmetic average of the particle diameters of the conductive particles 21 obtained based on an electron microscope micrograph. Specifically, the electron microscope micrograph is subjected to image processing to find respective areas of the conductive particles 21 appearing on the electron microscope micrograph. Next, based on these areas of the conductive particles 21, the diameter of each conductive particle 21 when the particle is converted into a perfect circle is calculated. Then, the average of these diameters was calculated to obtain an average particle diameter.

Note that the shape of the conductive particles 21 is not limited in any way. Therefore, the conductive particles 21 may have a spherical shape, an elliptical shape, a crushed shape, or a flake shape, whichever is appropriate.

The insulating particles 3 include, for example, at least one of a resin material having an electrical insulating property and an inorganic material having an electrical insulating property. For example, the resin material having an electrical insulation property of the insulating particles 3 includes at least one material selected from the group consisting of: silicone, acrylic resin, melamine resin, epoxy resin, polylactic acid resin, ethylcellulose resin, and polyethersulfone resin. For example, the inorganic material having an electrical insulating property includes at least one material selected from the group consisting of: silica, alumina, zinc oxide, tin oxide, titanium oxide, copper oxide, tungsten oxide, iron oxide zirconia, magnesium oxide, yttrium oxide, barium titanate, hydroxyapatite, titanium carbide, and aluminum nitride.

Note that the shape of the insulating particles 3 is not limited at all. Therefore, the insulating particles 3 may have a spherical, elliptical, crushed, or flake shape, whichever is appropriate.

The average particle diameter of the insulating particles 3 preferably falls within a range of 50nm to 2000 nm. This increases the chance of generating voids 11 having an appropriate size for gas permeation in the gas adsorbent 1, and therefore the responsiveness of the gas adsorbent 1 is particularly significantly improved. The average particle diameter of the insulating particles 3 is more preferably 100nm or more and less than 1500 nm. This promotes an increase in the sensitivity of gas adsorbent 1. This is presumably because: if the average particle diameter is less than 1500nm, the size of the voids 11 does not become excessively large, thereby increasing the specific surface area of the voids 11.

Note that the average particle diameter of the insulating particles 3 is a numerical value calculated based on a particle diameter distribution obtained by a dynamic light scattering method. As a measuring device for measuring the average particle diameter, for example, Zetasizer Nano ZS90 manufactured by Malvern Panalytical can be used.

The average particle diameter of the insulating particles 3 is preferably larger than the average particle diameter of the conductive particles 21. This increases the chance of the conductive particles 21 adhering to the surface of the insulating particles 3, thereby facilitating the formation of the first coating layer 23. Therefore, a porous structure having the voids 11 is more easily formed.

In particular, the average particle diameter of the insulating particles 3 is preferably 3 times or more larger than the average particle diameter of the conductive particles 21. This increases the chances of creating voids 11 and enabling each void 11 to have an appropriate size for gas to pass through. The average particle diameter of the insulating particles 3 is more preferably 5 times or more larger than the average particle diameter of the conductive particles 21. The upper limit of the ratio of the average particle diameter of the insulating particles 3 to the average particle diameter of the conductive particles 21 is not particularly limited, and may be, for example, 100 or less.

The diameter of the voids 11 in the porous structure is preferably larger than the average particle diameter of the conductive particles 21. This increases the chance that gas adsorbent 1 has a porous structure and voids 11 having an appropriate size for gas to permeate therethrough are generated in gas adsorbent 1. The diameter of the void 11 can be determined by the following method. First, the gas adsorbent 1 is cut to expose its cross section. Next, the thus exposed cross section is polished, and then observed by an electron microscope to capture a micrograph. Then, circles inscribed in the respective contours of the voids 11 appearing on the micrograph are drawn, and the diameter of the largest one of these inscribed circles is measured. For example, diameter values of the inscribed circle are measured for 10 voids 11, and an average of 6 intermediate diameter values excluding two maximum diameter values and two minimum diameter values is selected from the 10 diameter values and is calculated as the diameter of the void 11.

For example, the respective contents of the organic compound forming the gas adsorbent 1, the conductive particles 21, and the insulating particles 3 are appropriately set according to the particle diameter of the conductive particles 21 and the particle diameter of the insulating particles 3, so that the gas adsorbent 1 according to the present embodiment can have a porous structure. In particular, the mass ratio of the insulating particles 3, the conductive particles 21, and the organic material 22 is preferably close to 1:1: 1. This increases the chance that gas adsorbent 1 has a porous structure and voids 11 having an appropriate size for gas to permeate therethrough are generated in gas adsorbent 1.

The gas adsorbent 1 preferably has a membrane shape. That is, the gas adsorbent 1 is preferably a porous membrane. This increases the specific surface area of gas adsorbent 1, thereby enabling gas adsorbent 1 to adsorb chemical substances in the gas more easily. The gas adsorbent 1 may, for example, have a thickness falling within a range of 0.1 μm to 10 μm.

Next, the gas sensor 10 including the gas adsorbent 1 or the gas adsorbing device 20 will be described. The gas sensor 10 includes: gas adsorbent 1 or gas adsorption device 20; and an electrode 5 electrically connected to the gas adsorbent 1. This gas sensor 10 is used such that, in the case where the gas adsorbent 1 is exposed to a gas containing a chemical substance, the gas adsorbent 1 adsorbs the chemical substance, thereby causing a change in the resistance value of the gas adsorbent 1. Based on the change in the resistance value, the chemical substance can be detected. As described above, this embodiment increases the chance of causing a change in resistance value in the case where gas adsorbent 1 is exposed to a gas. Therefore, the chemical substances in the gas can be accurately detected by using the gas sensor 10.

A specific example of the gas sensor 10 will be described with reference to fig. 1. The gas sensor 10 includes a gas adsorbent 1 and an electrode 5. The electrode 5 includes a first electrode 51 and a second electrode 52. The gas sensor 10 further includes a substrate member 6. That is, the gas sensor 10 according to the present specific example includes the gas adsorption device 20 and the substrate member 6.

The base member 6 has an electrical insulating property. The base member 6 has one face (hereinafter referred to as "support face 61"). On the support surface 61, a first electrode 51, a second electrode 52 and a gas adsorbent 1 are arranged. The base member 6 may have a plate shape having a thickness in a direction perpendicular to the supporting surface 61. The first electrode 51 and the second electrode 52 are disposed at an interval from each other in a direction perpendicular to a direction in which the support surface 61 faces.

The gas adsorbent 1 is disposed on the support surface 61 of the substrate member 6. As described above, the gas adsorbent 1 is in contact with the substrate member 6 on at least one of the first coating layer 23 and the second coating layer 24. The gas adsorbent 1 covers the first electrode 51 and the second electrode 52. This brings gas adsorbent 1 into contact with each of first electrode 51 and second electrode 52. Note that the electrical connection between gas adsorbent 1 and each of first electrode 51 and second electrode 52 may be established by any structure. For example, gas sorbent 1 may be in full or only partial contact with first electrode 51. Likewise, gas sorbent 1 may be in full or only partial contact with second electrode 52.

When a voltage is applied between the first electrode 51 and the second electrode 52 of the gas sensor 10, a current flows through the gas adsorbent 1 in an amount corresponding to the voltage and the resistance value of the gas adsorbent 1. This enables measurement of the resistance value of gas adsorbent 1. The chemical substance may be detected based on the resistance value. Alternatively, the chemical substance may also be detected based on the value of the current flowing between the first electrode 51 and the second electrode 52 in a state where a constant voltage is applied between the first electrode 51 and the second electrode 52. Alternatively, the chemical substance may also be detected based on the amount of voltage drop between the first electrode 51 and the second electrode 52 in a state where a constant current is allowed to flow through the gas adsorbent 1. That is, the chemical substance may be detected based on a change in some physical quantity (as an index) caused by a change in the resistance value of the gas adsorbent 1.

To manufacture this gas sensor 10, for example, the first electrode 51 and the second electrode 52 may be provided on the supporting surface 61 of the base member 6, and then the gas adsorbent 1 is formed on the supporting surface 61.

Next, a method of manufacturing the gas adsorbent 1 according to the present embodiment will be described.

The gas adsorbent 1 can be produced by: a mixed solution containing the organic material 22, the conductive particles 21, the insulating particles 3, and the solvent is prepared, a formed product is formed from the mixed solution, and then the solvent is volatilized from the formed product.

The method of manufacturing the gas adsorbent 1 will be described more specifically. First, a mixed solution containing the organic material 22, the conductive particles 21, the insulating particles 3, and a solvent is prepared.

The organic material 22, the conductive particles 21, and the insulating particles 3 are as described above.

Any solvent may be used without limitation as long as the solvent can dissolve or disperse the organic material 22, can disperse the conductive particles 21 and the insulating particles 3, and can be volatilized from the formed product. For example, the solvent includes at least one ingredient selected from the group consisting of: dimethyl sulfoxide, dimethylformamide, toluene, chloroform, acetone, acetonitrile, methanol, ethanol, isopropanol, tetrahydrofuran, ethyl acetate and butyl acetate.

Next, a formed product is formed from the mixed solution. The shaped product preferably has a film shape. In this case, gas adsorbent 1 in the form of a membrane can be obtained. Examples of film shapes include films, sheets, and layers. The shaped product may be formed by any method without limitation. For example, the mixed solution may be applied by an inkjet method, a dispensing (dispensing) method, or any other suitable method to form a shaped product. For example, the shaped product may have a thickness falling within a range of 0.1 μm to 10 μm.

Subsequently, the solvent is volatilized from the shaped product. The solvent may be volatilized by any method without limitation. For example, the solvent may be volatilized from the shaped product by subjecting the shaped product to a heat treatment. Alternatively, the solvent may be volatilized from the shaped product by placing the shaped product under reduced pressure. Alternatively, the solvent may be volatilized from the shaped product by subjecting the shaped product to heat treatment under reduced pressure. The temperature of the heat treatment may be appropriately set according to the type of the solvent to promote volatilization of the solvent. For example, the temperature of the heat treatment may fall within a range of 30 ℃ to 90 ℃. In addition, the temperature of the heat treatment is preferably set to prevent or at least delay pyrolysis of the organic material 22. Therefore, the temperature of the heat treatment is preferably less than a temperature 30 ℃ lower than the heat-resistant temperature of the organic material 22. The duration of the heat treatment is preferably designed such that all or most of the solvent in the shaped product is volatilized by the heat treatment. For example, the duration of the heat treatment may fall within the range of 10 minutes to 60 minutes.

Examples

Next, the methods and results of the experiments conducted by the present inventors with respect to the exemplary embodiments will be presented. Note that the method and results of the experiment described below should not be construed as limiting the configuration of the present embodiment.

1. Confirmation of influence of particle diameter of conductive particle

Carbon black particles having an average particle diameter of 50 μm are provided as the conductive particles 21. Dimethylformamide is provided as a solvent. Polyethylene glycol is provided as the organic material 22.

The conductive particles 21 and the organic material 22 were added to a solvent and stirred, thereby preparing a mixed solution including the conductive particles 21 having a concentration of 10mg/ml and the organic material 22 having a concentration of 10 mg/ml.

Next, the mixed solution is applied by an inkjet method to form a film-shaped formed product. The shaped product was subjected to a heat treatment at 50 ℃ for 20 minutes, thereby volatilizing the solvent from the shaped product.

In this way, sample #1 was obtained as the gas adsorbent 1 containing no insulating particles 3. In addition, sample #2 was obtained as another gas adsorbent 1 in the same manner as in the case of sample #1, except that the average particle diameter of carbon black was changed to 44 nm. Further, sample #3 was obtained as still another gas adsorbent 1 in the same manner as in the case of sample #1, except that the average particle diameter of carbon black was changed to 15 nm.

Each of these samples #1 to #3 was used to form a gas sensor 10 for testing. A schematic structure of the gas sensor 10 for testing is shown in fig. 2. In this gas sensor 10, a first electrode 51 and a second electrode 52 are arranged on a substrate member 6 having an electrical insulating property to form an interdigital (inter) electrode structure. A dimension L1 of the interdigital electrode structure measured along the comb teeth of the interdigital electrode structure is 520 μm, and a dimension L2 of the interdigital electrode structure measured perpendicularly to the comb teeth of the interdigital electrode structure is 500 μm. In addition, an electrically insulating film (insulating film 9) is also provided on the base member 6 so as to cover the first electrode 51 and the second electrode 52. As shown in fig. 2, through the insulating film 9, stripe-shaped openings 70 each having a width of 5 μm are provided so as to overlap with the first electrode 51 and the second electrode 52. The dimension L3 measured between the respective centerlines of the openings 70 shown in fig. 2 is 60 μm. Further, each sample of the gas adsorbent 1 was provided on the base member 6 so as to cover the insulating film 9 and to have a thickness of 1 μm. This brings gas adsorbent 1 into contact with first electrode 51 and second electrode 52 through opening 70. The diameter D1 of the gas adsorbent 1 shown in fig. 2 was 900 μm. In addition, the gas sensor 10 is also provided with a first terminal 81 and a second terminal 82, the first terminal 81 extending from one end of the first electrode 51 to the outside of the protruding gas adsorbent 1, and the second terminal 82 extending from one end of the second electrode 52 to the outside of the protruding gas adsorbent 1.

With a constant voltage applied between the first terminal 81 and the second terminal 82, the gas sensor 10 was placed in a nitrogen gas flow, and then nonanal was added to the gas flow to have a concentration of 1 ppm by volume. In this manner, each sample was exposed to a gas stream comprising nonanal until the resistance value of each sample substantially stopped changing. The resistance value of each sample is calculated based on the measurement result of the current flowing between the first terminal 81 and the second terminal 82.

Fig. 3 shows the rate of change in the resistance value of each sample with respect to the resistance value in the nitrogen gas flow. From these results, it can be easily seen that the rate of change in the resistance value increased more significantly in sample #2 having an average particle diameter of 44nm than in sample #1 having an average particle diameter of 50nm, and that the rate of change in the resistance value increased significantly in sample #3 having an average particle diameter of 15nm than in sample #1 having an average particle diameter of 50 nm.

In this way, the influence of the particle diameter of the conductive particles 21 on the sensitivity was confirmed.

2. Formation of samples

Silica particles having an average particle diameter of 10nm are provided as the insulating particles 3. Carbon black particles having an average particle diameter of 15nm are provided as the conductive particles 21. Dimethylformamide is provided as a solvent. Polyethylene glycol is provided as the organic material 22.

Insulating particles 3, conductive particles 21, and organic material 22 were added to a solvent and stirred, thereby preparing a mixed solution including insulating particles 3 having a concentration of 10mg/ml, conductive particles 21 having a concentration of 10mg/ml, and organic material 22 having a concentration of 10 mg/ml.

Next, the mixed solution is applied by an inkjet method to form a film-shaped formed product. The shaped product was subjected to a heat treatment at 50 ℃ for 20 minutes, thereby volatilizing the solvent from the shaped product.

In this way, sample #4 was obtained as gas adsorbent 1. In addition, sample #5 was obtained as another gas adsorbent 1 in the same manner as in the case of sample #4, except that the average particle diameter of the silica particles was changed to 30 nm. Further, sample #6 was obtained as still another gas adsorbent 1 in the same manner as in the case of sample #4, except that the average particle diameter of the silica particles was changed to 100 nm. Further, sample #7 was obtained as still another gas adsorbent 1 in the same manner as in the case of sample #4, except that the average particle diameter of the silica particles was changed to 500 nm. Further, sample #8 was obtained as still another gas adsorbent 1 in the same manner as in the case of sample #4, except that the average particle diameter of the silica particles was changed to 1500 nm.

3. Evaluation test

The following evaluation tests were performed on the above samples #4 to #8 and sample #3 prepared to confirm the influence of the particle diameter of the conductive particles 21.

3-1. microscopic examination

The respective surfaces of these samples and a cross section of these samples taken along a plane aligned with the thickness direction were observed by a Scanning Electron Microscope (SEM). As a result, no void 11 was recognized in sample #3 not containing the insulating particles 3 and samples #4 and #5 respectively containing the insulating particles 3 having an average particle diameter of 10nm and the insulating particles 3 having an average particle diameter of 30 nm. On the other hand, voids 11 were identified in all samples #6 to #8 each containing insulating particles 3 having an average particle diameter of 100nm or more.

For reference, cross-sectional micrographs of sample #7 (containing insulating particles 3 having an average particle diameter of 500 nm), sample #8 (containing insulating particles 3 having an average particle diameter of 1500 nm), and sample #3 (containing no insulating particles 3) are shown in fig. 4A, 4B, and 4C, respectively, and surface micrographs thereof are shown in fig. 5A, 5B, and 5C, respectively. As can be seen from these micrographs, the voids 11 were not recognized in sample #3, while in samples #7 and #8, it was observed how the adsorbed portions 2 and the voids 11 adhering to the insulating particles 3 were generated to form a porous structure. Note that in the cross-sectional micrograph of sample #7 shown in fig. 4A, since peeling occurred in the cross section, the presence of voids 11 was still recognizable even though the presence of voids was not as clear as shown in sample #8 shown in fig. 4B.

For samples #7 and #8, the diameter of the void 11 was measured in the following manner. Specifically, each of samples #7 and #8 was cut to expose their cross-sections. The thus exposed cross section was polished and then observed by an electron microscope to capture a micrograph. Then, circles inscribed in the respective contours of the voids 11 appearing on the micrograph are drawn, and the diameter of the largest one of these inscribed circles is measured. For example, diameter values of the inscribed circle are measured for 10 voids 11, and an average of 6 intermediate diameter values selected from the 10 diameter values excluding the two maximum diameter values and the two minimum diameter values is calculated and regarded as the diameter of the void 11. As a result, the diameter of the void 11 was 191nm in sample #7 and 684nm in sample # 8.

3-2 evaluation of sensor characteristics

The sensor characteristics of each sample were confirmed by the following method using the gas sensor 10 having the same configuration as described in "1. confirmation of influence of particle diameter of conductive particles" section.

The gas sensor 10 was placed in a nitrogen gas stream with a constant voltage applied between the first and second terminals 81 and 82 of the sensor, and then benzaldehyde was added to the gas stream for about 5 seconds to have a concentration of 1 ppm by volume. During this process, the amount of current flowing between the first terminal 81 and the second terminal 82 is measured. The resistance value of each sample as the gas adsorbent 1 was calculated based on the measurement result.

Fig. 6 shows how the resistance values of the respective samples change with time. In fig. 6, the horizontal axis indicates elapsed time. Benzaldehyde is added to the gas stream during a time period from a time point indicated as 30+ seconds to a time point indicated as 35+ seconds on a horizontal axis scale. On the other hand, the vertical axis indicates the normalized resistance value of each sample. Note that the normalized resistance value is defined by regarding the resistance value of each sample measured in advance in a nitrogen gas flow as a unit. Fig. 7 shows the average value of the normalized resistance values of the respective samples measured when 5 seconds have elapsed since the start of the addition of benzaldehyde to the gas stream in the case where the test was performed three times.

The results shown in fig. 6 reveal that in each of these samples, the resistance value began to increase at the point in time when benzaldehyde was added to the gas stream, and decreased when benzaldehyde was no longer added to the gas stream.

Of these samples, in samples #4 and #5 containing insulating particles 3 having an average particle diameter of 10nm and insulating particles 3 having an average particle diameter of 30nm, respectively, in which no voids 11 were recognized, the resistance value did not increase as rapidly as in sample #3 containing no insulating particles 3 (i.e., exhibited lower responsiveness than that of sample # 3).

On the other hand, in samples #6 to #8 each containing insulating particles 3 having an average particle diameter of 100nm or more, when benzaldehyde was added to the gas flow, their resistance values increased more rapidly than in sample # 3. Particularly, in sample #6 containing insulating particles 3 having an average particle diameter of 100nm and sample #7 containing insulating particles 3 having an average particle diameter of 500nm (among others, in sample # 7), the rate of change in the resistance value at the time point when 5 seconds elapsed was higher than that of any other sample. Therefore, it was confirmed that samples #6 and #7 exhibited high sensitivity.

As can be seen from the foregoing description of exemplary embodiments and examples, the gas adsorbent (1) according to the first aspect of the present invention includes insulating particles (3), a plurality of conductive particles (21), and an organic material (22). A plurality of conductive particles (21) and an organic material (22) are attached to the surface of the insulating particles (3) to form adsorption particles (12). A plurality of such adsorbent particles (12) are aggregated together to form a porous structure.

A first aspect provides a gas adsorbent (1) comprising an organic material (22) and a plurality of electrically conductive particles (21) and being such that it is capable of a responsive change in electrical resistance value on exposure to a gas.

In the gas adsorbent (1) according to the second aspect of the present invention that can be achieved in combination with the first aspect, the average particle diameter of the insulating particles (3) is larger than the average particle diameter of the plurality of conductive particles (21).

The second aspect increases the chance that the gas adsorbent (1) has a porous structure.

In the gas adsorbent (1) according to a third aspect of the present invention that can be achieved in combination with the first aspect or the second aspect, the average particle diameter of the insulating particles (3) is 3 times or more larger than the average particle diameter of the plurality of conductive particles (21).

The third aspect increases the chance that the gas adsorbent (1) has a porous structure.

In the gas adsorbent (1) according to a fourth aspect of the present invention that may be achieved in combination with any one of the first to third aspects, a diameter of a void (11) generated in the porous structure is larger than an average particle diameter of the plurality of conductive particles (21).

The fourth aspect increases the chance that the gas adsorbent (1) has a porous structure.

In the gas adsorbent (1) according to a fifth aspect of the present invention that can be achieved in combination with any one of the first to fourth aspects, the plurality of conductive particles (21) and the organic material (22) are attached in a film shape on the surface of the insulating particles (3).

The fifth aspect enables the gas adsorbent (1) to adsorb gas particularly easily.

In the gas adsorbent (1) according to a sixth aspect of the present invention that may be achieved in combination with any one of the first to fifth aspects, the organic material (22) includes a polymer.

The sixth aspect enables the gas adsorbent (1) to have heat resistance.

In a gas adsorbent (1) according to a seventh aspect of the present invention that may be realized in combination with any one of the first to sixth aspects, the plurality of electrically conductive particles (21) includes a carbon material.

The seventh aspect particularly significantly increases the chance that the gas adsorbent (1) will cause a change in its electrical resistance value when exposed to a gas.

In the gas adsorbent (1) according to an eighth aspect of the present invention that may be realized in combination with any one of the first to seventh aspects, an average particle diameter of the plurality of conductive particles (21) falls within a range of 10nm to 30 nm.

The eighth aspect increases the chance that the gas adsorbent (1) exhibits an increased sensitivity in the case of adsorbing a chemical substance.

In the gas adsorbent (1) according to a ninth aspect of the present invention that may be achieved in combination with any one of the first to eighth aspects, the insulating particles (3) have an average particle diameter falling within a range of 100nm or more and less than 1500 nm.

The ninth aspect increases the chance that the gas adsorbent (1) exhibits an increased responsiveness in adsorbing the chemical substance.

A gas adsorption device (20) according to a tenth aspect of the present invention includes: the gas adsorbent (1) according to any one of the first to ninth aspects; and a base material member (6). The plurality of adsorbent particles (12) of the gas adsorbent (1) each comprise: insulating particles (3); a first coating layer (23) that is formed from a plurality of conductive particles (21) and that continuously coats the surface of the insulating particles (3); and a second coating layer (24) which is formed of an organic material (22) and continuously coats the surface of the first coating layer (23). The porous structure is formed by continuously connecting a plurality of adsorbent particles (12) to each other and creating voids (11) surrounded by adjacent adsorbent particles in the plurality of adsorbent particles (12). The gas adsorbent (1) is in contact with the substrate member (6) on at least one of the first coating layer (23) and the second coating layer (24).

A tenth aspect provides a gas adsorption device (20) comprising a gas adsorbent (1), the gas adsorbent (1) comprising an organic material (22) and a plurality of conductive particles (21), and the resistance value of the gas adsorbent (1) being changed responsively upon exposure to a gas.

A gas sensor (10) according to an eleventh aspect of the present invention includes: the gas adsorbent (1) according to any one of the first to ninth aspects or the gas adsorption device (20) according to the tenth aspect; and an electrode (5) electrically connected to the gas adsorbent (1).

An eleventh aspect provides a gas sensor (10), the gas sensor (10) comprising a gas adsorbent (1), the gas adsorbent (1) comprising an organic material (22) and a plurality of conductive particles (21), and an electrical resistance value of the gas adsorbent (1) being changed responsively upon exposure to a gas.

A method for producing a gas adsorbent (1) according to a twelfth aspect of the present invention includes: preparing a mixed solution containing an organic material (22), a plurality of conductive particles (21), insulating particles (3), and a solvent; forming a shaped product from the mixed solution; and volatilizing the solvent from the shaped product.

The twelfth aspect enables production of a gas adsorbent (1) that contains an organic material (22) and a plurality of conductive particles (21), and in which the resistance value of the gas adsorbent (1) changes responsively upon exposure to a gas.

A method for producing a gas adsorbent (1) according to a thirteenth aspect of the present invention that can be implemented in combination with the twelfth aspect, includes: the gas adsorbent (1) is formed into a film shape by forming a film of the formed product.

The thirteenth aspect makes it possible to make the gas adsorbent (1) adsorb chemical substances in a gas more easily by increasing the specific surface area of the gas adsorbent (1).

Reference numerals

1 gas adsorbent

11 gap

12 adsorbent particles

2 adsorption part

21 conductive particle

22 organic material

23 first coating

24 second coating

3 insulating particles

5 electrodes

10 gas sensor

20 gas adsorption device