JPH0721476B2 - Organic semiconductor gas sensor-element - Google Patents

Description

TECHNICAL FIELD The present invention relates to an organic semiconductor gas sensor element, and more specifically to an aromatic system which is a condensate of an aromatic hydrocarbon compound having a phenolic hydroxyl group and an aldehyde. The present invention relates to an organic semiconductor gas sensor element that exerts a sensor function by a change in electric conductivity due to adsorption and desorption of a polar gas to which a heat-treated polymer product is applied.

[Conventional technology]

Polymer materials are excellent in moldability, light weight and mass productivity.
Therefore, by utilizing these characteristics of the polymer material, an organic polymer material having electrical semiconductivity is desired in many industrial fields including the electronics industry. Early organic semiconductors were difficult to form into a film or a plate, and their applications were limited.
In recent years, organic semiconductors having polyacetylene as a representative example and having relatively excellent moldability have been obtained. However, polyacetylene has a drawback that it is easily oxidized by oxygen. For this reason, it is difficult to handle in air and is not practical as an industrial material.

Japanese Patent Application Laid-Open No. 58-136649 filed by the same applicant as the present application
Japanese Patent Publication discloses an insoluble infusible substrate which is a heat-treated product of an aromatic condensation polymer composed of carbon, hydrogen and oxygen, and which contains a polyacene skeleton structure having an atomic ratio of hydrogen atoms / carbon atoms of 0.6 to 0.15. ing. The insoluble and infusible substrate has excellent heat resistance and oxidation resistance. However, nothing is described about the organic semiconductor gas sensor element using the insoluble and infusible substrate.

Further, Japanese Patent Application Laid-Open No. 60-152554 filed by the same applicant as the present application
Japanese Patent Laid-Open Publication No. 2003-242242 discloses a heat-treated product of an aromatic condensation polymer composed of carbon, hydrogen and oxygen, having an atomic ratio of hydrogen atoms / carbon atoms of 0.60 to 0.15 and having a specific surface area value of 6 according to the BET method.
An insoluble and infusible substrate containing a polyacene-based skeleton of 00 m ² / g or more is disclosed. However, the specification of this prior application does not describe anything about the organic semiconductor gas sensor element using the insoluble and infusible substrate.

In addition, Japanese Patent Application No. Sho 60-
No. 58603 has not been published yet, but in the prior application, it is a heat-treated product of an aromatic condensation polymer composed of carbon, hydrogen and oxygen, and has an atomic ratio of hydrogen atoms / carbon atoms of 0.6 to.
It has a polyacene-based skeleton structure of 0.05, a specific surface area value by BET method of at least 600 m ² / g or more, an average pore diameter of 1
A porous organic semiconductor having a communication hole of 0 μm or less has been proposed. The specification of this prior application also mentions a sensor material as one of the uses of the porous organic semiconductor, but does not describe any specific example of the organic semiconductor gas sensor element.

On the other hand, various sensors are becoming more important both socially and industrially as the high technology society deepens. Since the proposal of gas sensors using oxide semiconductor elements such as tin oxide and zinc oxide, gas sensor elements using various inorganic materials such as porous ceramics have been developed and used in many industrial fields and homes. There is. Further, a gas sensor using an organic substance has been developed, and a humidity sensor using a hygroscopic polymer has already been used, but there are many drawbacks. For example, it has been pointed out that the humidity sensor described above is apt to deteriorate due to moisture absorption and contraction due to dehumidification.

However, an organic semiconductor gas sensor element excellent in oxidation resistance and chemical resistance has not yet been developed in spite of great social needs in today's high technology era.

[Problems to be solved by the invention]

An object of the present invention is to provide an organic semiconductor gas sensor element.

Another object of the present invention is to provide an organic semiconductor gas sensor element having excellent oxidation resistance and chemical resistance.

Yet another object of the present invention is to provide an organic semiconductor gas sensor element that utilizes the change in electrical conductivity associated with adsorption and desorption of gas molecules.

Still another object of the present invention is to provide an organic semiconductor gas sensor element in the form of a film, a plate, a cylinder or the like.

Still another object of the present invention is to provide an organic semiconductor gas sensor element capable of repeatedly adsorbing and desorbing gas molecules and stable against repeated adsorption and desorption.

Further objects and advantages of the present invention will be apparent from the following description.

According to the present invention, the above objects and advantages of the present invention are a heat-treated product of an aromatic condensation polymer which is a condensate of an aromatic hydrocarbon compound having a phenolic hydroxyl group and an aldehyde, and which comprises hydrogen atoms / carbon atoms. It is achieved by an organic semiconductor gas sensor element characterized in that at least two electrodes are attached to a molded body made of an insoluble and infusible substrate having a polyacene skeleton structure having an atomic ratio of 0.6 to 0.15.

The aromatic condensation polymer in the present invention is a condensation product of an aromatic hydrocarbon compound having a phenolic hydroxyl group and an aldehyde. As such an aromatic hydrocarbon compound, for example, so-called phenols such as phenol, cresol and xylenol are preferable, but not limited to these, for example, the following formula Here, x and y are 0, 1, or 2 independently.

And methylene-bisphenols, hydroxy-biphenyls, and hydroxynaphthalenes. Of these, phenols, particularly phenol, are suitable for practical use.

The aromatic condensation polymer in the present invention further includes 1 of aromatic hydrocarbon compounds having a phenolic hydroxyl group.
It is also possible to use a modified aromatic polymer in which a part is substituted with an aromatic hydrocarbon compound having no phenolic hydroxyl group, such as xylene or toluene, for example, a modified aromatic polymer which is a condensate of phenol, xylene, and formaldehyde. it can.

Also, not only formaldehyde as aldehyde,
Other aldehydes such as acetaldehyde, furfural can be used, but formaldehyde is preferred. The phenol / formaldehyde condensate may be a novolac type, a resol type or a composite thereof.

The organic semiconductor gas sensor element of the present invention uses the heat-treated product of the aromatic condensation polymer as described above, and can be manufactured, for example, as follows.

Prepare an initial condensation product of an aromatic hydrocarbon compound having a phenolic hydroxyl group or an aromatic hydrocarbon compound having a phenolic hydroxyl group and an aromatic hydrocarbon compound not having a phenolic hydroxyl group and an aldehyde, and It is poured into a suitable mold and heated at a temperature of, for example, 50 to 200 ° C. to be cured and converted into a film-like or cylindrical form in the mold, and then the cured product is treated under a non-oxidizing atmosphere ( Heating to a temperature of 350 to 800 ° C, preferably 400 to 700 ° C (including vacuum).

The preferable heating rate at the time of heat treatment is somewhat different depending on the degree of the aromatic polymer used or its curing treatment or its shape, etc., but generally a relatively large heating rate from room temperature to about 300 ° C. It is also possible, for example, to set a rate of 100 ° C./hour. 300 ° C
At the above temperature, thermal decomposition of the aromatic condensation polymer starts, and gases such as steam (H ₂ O), hydrogen, methane, and carbon monoxide start to be generated, so the temperature can be raised at a sufficiently slow rate. Is advantageous.

The heating and heat treatment of the aromatic polymer are performed in a non-oxidizing atmosphere. The non-oxidizing atmosphere is, for example, nitrogen, argon, helium, neon, carbon dioxide or the like, and nitrogen is preferably used. The non-oxidizing atmosphere may be stationary or flowing.

Thus, by the above heating and heat treatment, a molded body composed of the insoluble and infusible substrate used for the organic semiconductor gas sensor element of the present invention can be obtained, but it can be further manufactured as follows.

An aqueous solution containing the above-mentioned initial condensate and an inorganic salt is prepared, and the aqueous solution is poured into an appropriate mold, and then the aqueous solution is formed into a form such as a film or a cylinder in the mold while suppressing evaporation of water. Cure and convert, then heat the cured body in a non-oxidizing atmosphere to a temperature of 350 ° C to 800 ° C,
Next, the obtained heat-treated body is washed to remove the inorganic salt contained in the heat-treated body.

The inorganic salt used together with the initial condensate is a pore-forming agent that is removed in a later step and is used for imparting communicating pores to the hardened material, such as zinc chloride, sodium phosphate, potassium hydroxide or potassium sulfide. is there. Of these, zinc chloride is preferably used. The inorganic salt can be used, for example, in an amount of 2.5 to 10 times the initial condensation product. Although the aqueous solution of the initial condensate and the inorganic salt varies depending on the type of the inorganic salt used, it can be prepared, for example, by using 0.1 to 1 times the weight of water of the inorganic salt. Thus, the aqueous solution is poured into a suitable mold and heated to a temperature of, for example, 50 to 200 ° C. At the time of this heating, it is important to suppress evaporation of water in the aqueous solution. That is, it is considered that the initial condensate is gradually hardened by being heated in the aqueous solution, and the communication holes are developed while separating zinc chloride and water, and grow into a three-dimensional network structure.

The cured product thus obtained is heated to a temperature of 350 to 700 ° C., preferably 400 to 600 ° C., in a non-oxidizing atmosphere (including a vacuum state) in the same manner as in the above-mentioned method to be heat treated. By thoroughly washing the obtained heat-treated body with water or dilute hydrochloric acid, the inorganic salts contained in the heat-treated body can be removed, and if this is then dried, it has porous pores with developed communication holes and a large specific surface area. An infusible substrate can be obtained.

Thus, it has a polyacene skeleton structure having an atomic ratio of hydrogen atoms / carbon atoms of 0.6 to 0.15 by the above-mentioned method or the method described below, or in addition to this, it has communicating holes with an average pore diameter of 10 μm or less, for example, 0.03 to 10 μm A molded product having an insoluble and infusible substrate used for the organic semiconductor gas sensor element of the present invention, which has a specific surface area ratio of 600 m ² / g or more by the BET method, is obtained.

The atomic ratio of hydrogen atoms / carbon atoms of the insoluble and infusible substrate is 0.6.
If it exceeds 0.1, the electric conductivity is low and it is not practical, and if it is less than 0.15, the increase in the electric conductivity due to adsorption of gas is small, which is not desirable.

The molded product is excellent in heat resistance, oxidation resistance and chemical resistance.
The atomic ratio of oxygen atoms / carbon atoms is usually 0.06 or less, preferably 0.03 or less. According to X-ray diffraction (CuK ₂ ), the position of the main peak is represented by 2θ and exists between 20.5 and 23.5 °, and in addition to the main peak, there is a broad peak between 41 and 46 °. To do.

That is, it is understood that the above-mentioned molded product has a polyacene-based benzene polycyclic structure uniformly and moderately developed among the polyacene-based molecules.

A molded body made of the insoluble and infusible substrate of the present invention is in the form of a film,
Although it is formed into a plate shape or a cylindrical shape, a film shape is preferable, and the thickness of this film is 0.01 to 500 μm, preferably 0.01 to 10 μm.
Is.

The organic semiconductor gas sensor element of the present invention is one in which at least two or more electrodes are attached to a molded body made of the insoluble and infusible substrate. This electrode is, for example, gold, platinum, copper, silver,
The conductive metal such as aluminum may be attached by a method such as vapor deposition, or may be attached by applying a conductive paste such as silver or carbon, but gold or platinum is vapor-deposited and attached. Is preferred. By attaching such an electrode, the electrical conductivity of the molded body can be directly measured.

The thus-obtained organic semiconductor gas sensor element of the present invention is sensitive to a polar gas by utilizing the fact that the electric conductivity increases due to the adsorption of the polar gas. The polar gas is a gas having a hyperbolic moment due to the structure of the molecule, and examples thereof include water vapor, alcohol gas such as methanol gas, acetone gas, carbon monoxide gas and the like. When the organic semiconductor gas sensor element of the present invention is placed under the polar gas atmosphere and the polar gas is adsorbed, the electric conductivity is, for example, 2 to 10,0.
When the polar gas is desorbed, the electrical conductivity decreases to the value before the adsorption of the polar gas. Further, the adsorption and desorption of the polar gas can be repeated, and the organic semiconductor gas sensor element of the present invention is very stable without deterioration against this repetition. Further, since the organic semiconductor gas sensor element of the present invention changes in electric conductivity according to the concentration of the polar gas, it is also possible to detect the concentration of the polar gas.

In particular, the organic semiconductor gas of the present invention using a molded body composed of an insoluble and infusible substrate having a large number of communicating holes by including an inorganic salt in the initial condensate and having a specific surface area value by the BET method of 600 m ² / g or more. The sensor element can adsorb a large amount of the polar gas, and can be sensitive to a small amount of gas.

As described above, the organic semiconductor gas sensor element of the present invention is excellent in heat resistance, oxidation resistance, and chemical resistance, and its electric conductivity changes depending on adsorption and desorption of polar gas, and further adsorption and desorption can be repeated. It is possible and is a good gas sensor element that does not deteriorate due to repetition thereof.

Example 1 (1) Methanol-soluble resol (about 60% concentration) was formed into a film on a glass plate with a film applicator, and heated at a temperature of about 150 ° C. for 1 hour to be cured.

The phenolic resin is cut into a size of 2 cm x 1 cm, then placed in a siliconit electric furnace, heated to a temperature of 40 ° C / hour under a nitrogen stream, and heat-treated to 600 ° C to form a film insoluble and infusible. A substrate was obtained. The thickness of the film is 10 μm
The electric conductivity was 10 ⁻⁸ (Ω · cm) ⁻¹ when measured by a direct current 4-terminal method at room temperature. Further, an elemental analysis showed that the atomic ratio of hydrogen atoms / carbon atoms was 0.35. The shape of the peak from X-ray diffraction is a pattern based on the polyacene-based skeleton structure, and a broad main peak was present near 20 to 22 ° at 2θ, and a small peak was confirmed near 41 to 46 °.

Gold was vapor-deposited on the film with a vacuum vapor-depositing machine, and a copper wire was adhered to the vapor-deposited surface with a silver conductive paste to obtain an electrode, and the organic semiconductor gas sensor element shown in FIGS. 1 and 2 was obtained.

(2) Next, the organic semiconductor gas sensor element was placed in the gas atmosphere shown in Table 1 and the electric conductivity was measured at room temperature.
The results are summarized in Table 1. After that, when the gas atmosphere containing the organic semiconductor gas sensor element was removed, the electric conductivity returned to the value before the adsorption. The above operation was repeated 10 times, but the same result was obtained from the 1st time to the 10th time.

Example 2 (1) An aqueous solution prepared by mixing water-soluble resol (about 60% concentration) / chlorite / water at a weight ratio of 10/25/4 was formed on a glass plate with a film applicator. Next, cover the aqueous solution with a glass plate to prevent water from evaporating.
It was cured by heating at a temperature of 0 ° C. for 1 hour.

The phenol resin film was cut into 2 cm x 1 cm and then placed in a silicon knit electric furnace, heated under a nitrogen stream at a rate of 40 ° C / hour, and heated to various predetermined temperatures shown in Table 2 for heat treatment. went. Next, the heat-treated product was washed with dilute hydrochloric acid, washed with water, and then dried to obtain a film-shaped porous body. The thickness of the film is 50 μm,
The specific surface area by the method is about 2000 m ² at any heat treatment temperature.
It was / g. The measurement results of elemental analysis are summarized in Table 2.

An electrode was attached in the same manner as in Example 1 to obtain a film-shaped organic semiconductor gas sensor element.

(2) Next, the organic semiconductor gas sensor element was placed in a water vapor atmosphere and the electrical conductivity was measured at room temperature. The results are summarized in Table 2. After that, when the water vapor atmosphere containing the organic semiconductor gas sensor element was removed, the electric conductivity returned to the value before the adsorption.

The above operation was repeated 10 times, but all gave the same results.

Example 3 The film-like organic semiconductor gas sensor element obtained in the same manner as in No. 1 of Example 2 was put in the gas atmosphere shown in Table 3 and the electric conductivity was measured at room temperature. Results are third
Shown in the table. After that, when the gas atmosphere containing the organic semiconductor gas sensor element was removed, the electric conductivity returned to the value before the adsorption.

The above operation was repeated 10 times, but all gave the same results.

[Brief description of drawings]

FIG. 1 is a side view of an organic semiconductor gas sensor element according to an embodiment of the present invention, FIG. 2 is a plan view thereof, (1) is a molded body made of an insoluble and infusible substrate, and (2) is Gold vapor deposition film, (3) copper wire, (4) silver conductive paste.

Claims (6)

[Claims] 1. A heat-treated product of an aromatic condensation polymer which is a condensation product of an aromatic hydrocarbon compound having a phenolic hydroxyl group and an aldehyde, the polyacene having an atomic ratio of hydrogen atoms / carbon atoms of 0.6 to 0.15. An organic semiconductor gas sensor element, characterized in that at least two electrodes are attached to a molded body made of an insoluble and infusible substrate having a system skeleton structure. 2. The organic semiconductor gas sensor element according to claim 1, wherein the aromatic polymer is a condensate of phenol and formaldehyde. 3. The organic semiconductor gas sensor element according to claim 1, wherein the insoluble and infusible substrate has communicating holes having an average pore diameter of 10 μm or less. 4. The organic semiconductor gas sensor element according to claim 1, wherein the insoluble and infusible substrate has a specific surface area value by the BET method of 600 to 3000 cm ² / g. 5. Oxygen atom (O) / carbon atom of an insoluble and infusible substrate
The organic semiconductor gas sensor element according to claim 1, which has a polyacene skeleton structure in which the atomic ratio of (C) is 0.06 or less. 6. An insoluble and infusible substrate is formed through a large number of communicating holes.
The organic semiconductor gas sensor element according to claim 1, which has a three-dimensional network structure.