JP2010054205A - Gas sensor, method of manufacturing sensor element, and gas detecting method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a gas sensor and gas detecting method for detecting phthalic acid dialkyl in gas in an easy method. <P>SOLUTION: This gas sensor comprises a sensor element 3 having a silica mask 2 with a predetermined pore 2a and a detector 4 for measuring the electric resistance value of the sensor element 3 on the surface of metal oxide 1 mainly made of SnO<SB>2</SB>. The gas to be detected is supplied to the sensor element 3, the electric resistance value of the sensor element 3 is measured, and phthalic acid dialkyl in the gas is detected. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a gas sensor for detecting dialkyl phthalate in gas, a method for producing a sensor element used in the gas sensor, and a method for detecting dialkyl phthalate in gas.

As one of gas sensors, a gas sensor using SnO ₂ as a sensor element is known. When the electric resistance of SnO ₂ is heated to 250 to 500 ° C. in the atmosphere, oxygen in the atmosphere is activated and adsorbed on the particle surface to increase the resistance. However, in reducing gas (organic substance), the adsorbed oxygen is increased. Is removed and the resistance value decreases. A gas sensor using SnO ₂ as a sensor element utilizing such properties is used for gas leak alarms such as LP gas and city gas.

  By the way, dialkyl phthalates such as dioctyl phthalate (DOP) and dibutyl phthalate (DBP) are widely used as plasticizers in the production process of chemical products and electronic parts. Mainly in the electronic device manufacturing process where the processing accuracy is on the order of several tens of nanometers, the presence of dialkyl phthalate in the clean room may cause product failure. Therefore, ventilate the clean room and phthalate in the clean room. Dialkyl is not mixed.

In clean rooms, there are many organic solvents such as toluene generated from building materials and the like, so dialkyl phthalate and organic solvents often coexist in the air in the clean room. However, since SnO ₂ responds to any reducing gas, it has been difficult to detect only a specific gas component from a gas in which various components are mixed. For this reason, the conventional gas sensor can detect the presence or absence of organic substances in the gas, but cannot selectively detect dialkyl phthalate.

On the other hand, in the following Patent Documents 1 and 2, a silica mask having specific pores is formed on the surface of a metal oxide such as SnO _{2 and} the size of the adsorption site on the surface of the metal oxide is controlled, It has been disclosed to selectively adsorb molecules to oxides.
Japanese Patent Laid-Open No. 7-218463 JP 2003-253426 A

  Patent Documents 1 and 2 disclose that the adsorption of molecules to the metal oxide is selectively performed by controlling the size of the adsorption site on the surface of the metal oxide. However, it is not disclosed that dialkyl phthalate is selectively detected in the presence of various substances such as toluene and acetone.

  Accordingly, an object of the present invention is to provide a gas sensor, a sensor element manufacturing method, and a gas detection method capable of selectively detecting dialkyl phthalate in a gas by a simple method.

In achieving the above object, the gas sensor of the present invention is a gas sensor for detecting dialkyl phthalate in a gas, and has predetermined pores on the surface of a metal oxide containing SnO ₂ as a main component. A sensor element on which a silica mask is formed, and a detector for measuring an electric resistance value of the sensor element.

According to the gas sensor of the present invention, the silica mask having the predetermined pores is formed on the surface of the metal oxide whose main component is SnO ₂ , so that the sensor device includes a dialkyl phthalate. When the detection gas is supplied, since the dialkyl phthalate has a relatively long side chain portion extending from the benzene ring, the side chain portion reaches the surface of SnO ₂ through the pores of the sensor element surface. . On the other hand, molecules that are bulkier than the side chain portion of dialkyl phthalate (for example, acetone) and short side chain molecules (for example, toluene) are blocked from contact with the surface of SnO ₂ by the silica mask. For this reason, according to the present invention, dialkyl phthalate can be selectively detected by an extremely simple operation of supplying a gas to be detected to the sensor element and measuring the electric resistance value of the sensor element. The presence or absence of dialkyl phthalate in the gas can be detected accurately in a short time.

The gas sensor of the present invention is another sensor element in which a silica mask having pores having a diameter different from that of the sensor element is formed on the surface of a metal oxide containing SnO ₂ as a main component, and / or SnO _2. It is preferable that a sensor element not having a silica mask is further provided on the surface of the metal oxide mainly composed of and the detector is configured to measure an electric resistance value of each sensor element. According to this aspect, by comparing the sensitivities of the respective sensor elements, it is possible to estimate the main component in the detection target gas, the presence or absence of dialkyl phthalate having a specific alkyl side chain, and the like.

The metal oxide gas sensor of the present invention is preferably one obtained by supporting a catalyst on SnO _2. The catalyst is preferably a noble metal, more preferably Pd. By supporting the catalyst on SnO ₂ , the oxidation activity of the organic matter is improved, so the sensitivity to dialkyl phthalate is improved, and a lower concentration of dialkyl phthalate can be detected with high sensitivity.

  The sensor element in which the silica mask of the gas sensor of the present invention is formed is a template forming compound selected from aliphatic aldehydes, aliphatic carboxylic acids, aromatic aldehydes and aromatic carboxylic acids on the surface of the metal oxide. It is preferable that a silica precursor molecule is deposited after being adsorbed at an adsorption density of less than a monomolecular layer, and this is decomposed into silica to form a silica mask. According to this aspect, a silica mask having predetermined pores on the surface of the metal oxide can be easily formed. In addition, since the size of the pore can be easily controlled by changing the type of the template forming compound, the detection sensitivity of dialkyl phthalate can be further improved.

  In the above aspect, the template-forming compound preferably has a maximum width of 0.5 to 1.2 nm in a direction parallel to the surface in the state of being adsorbed on the surface of the metal oxide. More preferred is 1-naphthaldehyde or 1-naphthalenecarboxylic acid. According to this aspect, dialkyl phthalate can be detected more selectively.

  The gas sensor of the present invention preferably concentrates the gas component to be detected and supplies it to the sensor element. In this embodiment, after a predetermined amount of gas is supplied to the collecting agent and the gas component to be detected is collected by the collecting agent, the temperature of the collecting agent is raised and detected from the collecting agent. It is preferable that the gas component to be diffused is diffused and the gas component is concentrated and supplied to the sensor element. By concentrating the gas component to be detected and supplying it to the sensor element, it is possible to detect dialkyl phthalate with high sensitivity even if the concentration of the dialkyl phthalate in the gas to be detected is extremely low.

  The method for producing a sensor element of the present invention is a method for producing a sensor element for use in a gas sensor for detecting dialkyl phthalate in a gas, wherein an aliphatic aldehyde, an aliphatic group is formed on the surface of the metal oxide. A silica mask is formed by adsorbing a compound for forming a template selected from carboxylic acids, aromatic aldehydes and aromatic carboxylic acids at an adsorption density less than a monomolecular layer, then depositing silica precursor molecules, and hydrolyzing them into silica. It is characterized by forming.

  According to the method for manufacturing a sensor element of the present invention, a silica mask having predetermined pores on the surface of a metal oxide can be easily formed. The pore size can be easily controlled by changing the type of the template forming compound.

  In the method for producing a sensor element of the present invention, the template-forming compound has a maximum width of 0.5 to 1.2 nm in a direction parallel to the surface when adsorbed on the surface of the metal oxide. 1-naphthaldehyde or 1-naphthalenecarboxylic acid is more preferable. According to this aspect, a silica mask having pores of a size that facilitates the selective passage of dialkyl phthalate can be formed on the surface of the metal oxide, and a sensor element with high detection sensitivity of dialkyl phthalate can be manufactured. .

In addition, the gas detection method of the present invention supplies a gas to be detected to a sensor element in which a silica mask having predetermined pores is formed on the surface of a metal oxide containing SnO ₂ as a main component, and the sensor element Is measured to detect dialkyl phthalate in the gas.

According to the gas detection method of the present invention, since a silica mask having predetermined pores is formed on the surface of a metal oxide whose main component is SnO ₂ as a sensor element, dialkyl phthalate is formed on the sensor element. When the gas to be detected is supplied, as described above, the dialkyl phthalate has a relatively long side chain portion extending from the benzene ring, so that the side chain portion passes through the pores on the surface of the sensor element. Molecules that can reach the surface of SnO ₂ and are bulkier than the side chain portion of dialkyl phthalate (for example, acetone) and short side chain molecules (for example, toluene) are brought into contact with the surface of SnO ₂ by the silica mask. Therefore, by supplying the gas to be detected to the sensor element and measuring the electric resistance value of the sensor element, the presence or absence of dialkyl phthalate in the gas to be detected can be determined in a short time, and Every time well can be detected.

In the gas detection method of the present invention, another sensor element in which a silica mask having pores having a diameter different from that of the sensor element is formed on the surface of a metal oxide containing SnO ₂ as a main component, and / or It is preferable to further use a sensor element not having a silica mask on the surface of a metal oxide containing SnO ₂ as a main component, supply a gas to be detected to each sensor element, and measure the electric resistance value of each sensor element. According to this aspect, by comparing the sensitivities of the respective sensor elements, it is possible to estimate the main component in the detection target gas, the presence or absence of dialkyl phthalate having a specific alkyl side chain, and the like.

According to the present invention, a gas to be detected is supplied to a sensor element in which a silica mask having predetermined pores is formed on the surface of a metal oxide containing SnO ₂ as a main component, and the electric resistance value of the sensor element is determined. The dialkyl phthalate in the gas can be selectively detected by an extremely simple operation of measuring.

A first embodiment of the gas sensor of the present invention will be described with reference to FIG. This gas sensor is a gas sensor for detecting dialkyl phthalate in a gas, and includes a sensor element 3 and a detector 4 for measuring an electric resistance value of the sensor element 3. This sensor element 3 is made by solidifying fine particles of metal oxide 1 mainly composed of SnO _2, and a silica mask 2 having predetermined pores 2 a is formed on the fine particle surface of each metal oxide 1. Is formed. The sensor element 3 is supported on the substrate 6 and surrounded by a housing 7 provided with a gas inlet 8. The sensor element 3 is connected to the detector 4 by a conducting wire 9.

The metal oxide 1 may be composed of SnO ₂ alone, or may be one in which a catalyst is supported on SnO ₂ . Examples of the catalyst include Pd, Pt, Ni, Co, Cu and the like, noble metals are preferable, and Pd is particularly preferable. By supporting the catalyst on SnO ₂ , the oxidation activity of the organic matter is improved and the sensitivity to dialkyl phthalate is improved, so that a lower concentration of dialkyl phthalate can be detected. Among them, the noble metal has a high effect of improving the oxidation activity, and particularly Pd has a high effect of improving the oxidation activity, so that the detection sensitivity is further improved.

  It is preferable that the pore 2a formed in the silica mask 2 has a dimension that allows a side chain portion extending from the benzene ring of the dialkyl phthalate to pass through. If the pore 2a is too small, the detection sensitivity of dialkyl phthalate may not be sufficient. If the pore 2a is too large, organic substances other than dialkyl phthalate may be detected, and dialkyl phthalate may not be selectively detected. The size of the pore 2a is preferably 0.25 to 1.5 nm, and more preferably 0.4 to 1.2 nm.

  The sensor element 3 can be manufactured as follows. As shown in FIGS. 5 and 6, first, a template forming compound selected from aliphatic aldehydes, aliphatic carboxylic acids, aromatic aldehydes and aromatic carboxylic acids (benzaldehyde, In FIG. 6, 1-naphthaldehyde is used) is adsorbed at an adsorption density less than a monolayer (see FIGS. 5A and 6A). Next, silica precursor molecules are vapor-deposited, and the vapor-deposited silica precursor molecules are hydrolyzed to silica (see FIGS. 5B and 6B). Thereafter, the template-forming compound is removed (see FIGS. 5C and 6C). In this way, it is possible to manufacture a sensor element in which a silica mask having predetermined pores is formed on the surface of a metal oxide. According to this method, since the template forming compound is removed from the surface of the metal oxide, pores corresponding to the size and shape of the template forming compound are formed in the silica mask. The pore size can be easily adjusted by simply changing the type.

  In the sensor element manufacturing method described above, the template forming compound preferably has a maximum width of 0.5 to 1.2 nm in a direction parallel to the surface of the compound when adsorbed on the surface of the metal oxide 1. Benzaldehyde, benzoic acid, 1-naphthaldehyde, 1-naphthalenecarboxylic acid and the like. Of these, 1-naphthaldehyde or 1-naphthalenecarboxylic acid is particularly preferable.

  As shown in the schematic diagram of FIG. 5, when benzaldehyde is used as a template-forming compound, the lateral width shown in FIG. 5A of the benzene ring portion of benzaldehyde is such that the CC bond distance in the benzene ring is 0.14 nm, When the C—H bond distance is 0.11 nm and the van der Waals radius of H atom is 0.12 nm, it is estimated to be approximately 0.71 nm. The thickness of the benzene ring is known to be 0.37 nm. Therefore, when benzaldehyde is used as a template forming compound, as shown in FIG. 5C, pores having a maximum width of about 0.71 nm in the direction parallel to the surface of the metal oxide 1 are formed in the silica mask. Expected to form. For example, in a clean room, toluene often exists in the air in the state of coexisting with dialkyl phthalate. However, for example, the pores of the silica mask formed when benzaldehyde is used as the template-forming compound is close to the size of the benzene ring, so that the benzene ring passes through the pore as shown in the schematic diagram of FIG. Can not. Moreover, since the side chain (methyl group) of toluene is short, toluene hardly reaches the surface of the metal oxide 1. On the other hand, the side chain portion of the dialkyl phthalate is relatively long and low in volume, and therefore, it can reach the surface of the metal oxide 1 more easily than toluene. In addition to toluene, for example, acetone may exist, but the acetone molecule has two methyl groups and oxygen branching in three directions from the central carbon atom, and is bulky compared to an alkyl group. For this reason, as shown in the schematic diagram of FIG. 14, acetone molecules cannot pass through the pores of the silica mask and hardly reach the surface of the metal oxide 1.

  In addition, in the case of dialkyl phthalates having branched alkyl side chains such as diisobutyl phthalate (DIBP), the use of benzaldehyde as a template-forming compound slows diffusion in the pores and reaches the surface. May be difficult. For this reason, the sensitivity may decrease at low concentrations, but the use of 1-naphthaldehyde or 1-naphthalenecarboxylic acid as a template-forming compound increases the pore size of the silica mask, and these phthalic acids. Since the diffusion rate in the pores of the dialkyl is improved, the sensitivity of the dialkyl phthalate is improved and the detection is easy even at a low concentration. For example, when 1-naphthaldehyde is used, pores having a maximum width of about 0.95 nm in the direction parallel to the surface of the metal oxide 1 are formed in the silica mask as shown in FIG. It is predicted.

  And if it is the silica mask formed using the compound for template formation whose said maximum width | variety will be 0.5-1.2 nm, even in the coexistence with organic solvents, such as toluene and acetone, dialkyl phthalate Reaches the surface of the metal oxide 1 preferentially, and dialkyl phthalate can be selectively detected by observing a change in the electric resistance value.

In the method for producing a sensor element described above, the silica precursor molecule is easy to form a bond with the surface of the metal oxide via an oxygen atom and is easily hydrolyzed to silica, and further decomposed to silica by firing. Easy one is preferred. Examples of such silica precursor molecules include alkoxysilane compounds and silane compounds. Typical examples include tetraalkoxysilane compounds represented by Si (OR) ₄ (R is an alkyl group), such as tetramethoxysilane, tetraethoxysilane, and tetrabutoxysilane. Other than this, for example, an alkylalkoxysilane compound represented by Si (R ¹ ) _n (OR ² ) _4-n (wherein R ¹ and R ² are alkyl groups, and n is a number of 1 to 3) is exemplified. . Moreover, if the vapor deposition is possible, the partial hydrolysis product of the above alkoxysilane compound and the alkyl alkoxysilane compound may be sufficient. These silica precursor molecules may be continuously supplied and vapor-deposited with respect to the metal oxide on which the template forming compound is adsorbed, or may be intermittently and pulse-wise supplied and vapor-deposited. Good. The temperature and pressure at that time can be appropriately determined as long as the silica precursor molecules are deposited in the gas phase. As a means for evaporation or gasification for vapor deposition in a gas phase, a means can be adopted as appropriate. For example, various means such as resistance heating or induction heating from a liquid material can be employed.

  Further, in the method for producing a sensor element described above, when hydrolyzing the silica precursor molecule, acetic acid, propionic acid, butyric acid, oxalic acid, chloroacetic acid, fluoroacetic acid, trifluoroacetic acid, citric acid, maleic acid, acetic anhydride. Preferably, a volatile acid such as maleic anhydride is supplied to the surface region of the metal oxide on which the silica precursor molecules are deposited. Volatile acids can accelerate the condensation rate of the silica precursor molecules and fill the gaps in the template-forming compound with a dense silica layer, so that the pore shape of the silica layer is adsorbed on the surface of the metal oxide. This makes it easier to match the shape of the template-forming compound and adjusts the pores of the silica mask to the shape of the template-forming compound.

  Next, the gas detection method of the present invention using the gas sensor will be described.

  In the gas detection method of the present invention, as shown in FIG. 1, the gas to be detected is supplied to the sensor element 3 through the gas inlet 8 of the housing 7, and the electric resistance value of the sensor element 3 is measured by the detector 4. Dialkyl phthalate in the test gas is detected from the change in electrical resistance.

  The dialkyl phthalate to be detected is not particularly limited. Dimethyl phthalate (DMP), diethyl phthalate (DEP), dibutyl phthalate (DBP), diisobutyl phthalate (DIBP), di-2-ethylhexyl phthalate ( Examples thereof include DEHP) and dioctyl phthalate (DOP).

When SnO ₂ comes into contact with the reducing gas, the electric resistance value changes. Since the dialkyl phthalate has a relatively long side chain portion extending from the benzene ring, the side chain portion reaches the surface of the metal oxide through the pores of the silica mask. On the other hand, molecules that are bulkier than the side chain portion of dialkyl phthalate (for example, acetone) and short side chain molecules (for example, toluene) are difficult to pass through the pores of the silica mask, and the surface of SnO ₂ by the silica mask. The contact with is easy to be blocked.

  Thus, since the gas components other than the dialkyl phthalate are prevented from contacting the surface of the metal oxide 1 by the silica mask 2, the electric resistance value of the sensor element 3 is compared with the gas components other than the alkyl phthalate. The dialkyl phthalate in the gas can be selectively detected even in the presence of toluene or acetone.

A second embodiment of the gas sensor of the present invention will be described with reference to FIG. In this embodiment, a first sensor element 13 in which a silica mask 12 having predetermined pores is formed on the surface of a metal oxide 11 containing SnO ₂ as a main component, and a metal oxide containing SnO ₂ as a main component. A second sensor element 22 having no silica mask is provided on the surface of the object 21. Each sensor element 13, 22 is supported on a respective substrate 6 and is surrounded by a housing 7 having a gas inlet 8. And the 1st sensor element 13 and the 2nd sensor element 22 are connected to the detector 30 which measures each electric resistance value by the conducting wire 9. FIG.

Since the sensitivity of the sensor varies depending on the type of substance and the measurement temperature, the ratio of the sensitivity of the first sensor element 13 and the sensitivity of the second sensor element 22 ([sensitivity of the first sensor element 13] / [second sensor element 22]. The main component in the detection target gas can be estimated by examining the ratio of the sensitivity to various substances in advance using the sensitivity]) as a guide. As the sensitivity of the sensor element, for example, a value represented by (R _a / R−1) is used, where R _{a is} the resistance before injection of the gas to be detected and R is the resistance after injection.

  The second sensor element 22 may be made of a metal oxide on which a silica mask having pores having a diameter different from that of the first sensor element 13 is formed. For example, since the alkyl side chain of diisobutyl phthalate (DIBP) is branched, the diffusion rate in the pores is lower than that of dioctyl phthalate (DOP), and the sensitivity tends to be low. For this reason, the presence or absence of dialkyl phthalate having a specific alkyl side chain, such as the presence or absence of diisobutyl phthalate (DIBP), can be estimated from the sensitivity ratio.

  A third embodiment of the gas sensor of the present invention will be described with reference to FIG. This embodiment is different from the first embodiment in that the gas concentrating device 5 is arranged on the upstream side of the gas inlet 8 of the housing 7 surrounding the sensor element 3.

  In this embodiment, the gas component to be detected by the gas concentrator 5 is concentrated, and the concentrated gas is supplied to the sensor element 3 in the housing 7. By concentrating the gas component to be detected and supplying it to the sensor element 3, it is possible to detect even if the concentration of the dialkyl phthalate of the detection target gas is very low, and the detection of the dialkyl phthalate on the ppb order is possible. It becomes possible.

  As the gas concentrator 5, after a predetermined amount of gas is supplied to the collecting agent and the gas component to be detected is collected in the collecting agent, the temperature of the collecting agent is raised and detected from the collecting agent. An example is a configuration in which a gas component to be emitted is diffused and the gas component is concentrated and supplied to the sensor element 3.

For example, by passing a gas of 300 cm ³ min ⁻¹ through a scavenger for 100 min and distilling the collected dialkyl phthalate into a gas of 100 cm ³ min ⁻¹ by rapid heating in 30 seconds, 600 times It will be concentrated. The concentration rate can be easily adjusted by changing the gas collection time in the collection agent, the gas flow rate to the collection agent, and the like.

  There is no limitation in particular as said collection agent, Activated carbon, glass wool, a solid adsorbent, etc. are mentioned. Examples of the solid adsorbent include trade name “TENAX-GR” and trade name “TENAX-TA” sold by GL Sciences Inc., as an example.

  When collecting the gas component to be detected by the collection agent, it is preferable to collect at a temperature of room temperature or lower from the viewpoint of collection efficiency.

  In diverging the gas component to be detected from the collecting agent, the collecting agent is preferably heated to 150 to 350 ° C, and more preferably 250 to 300 ° C.

  Hereinafter, the present invention will be described more specifically with reference to examples.

[Manufacture of sensor elements]
Example 1
Grade 28 wt% ammonia water (manufactured by Wako Pure Chemical Industries, Ltd.) 171cm ³ was prepared an aqueous ammonia solution diluted to 660 cm ³ with deionized water. Then mixed grade concentrated hydrochloric acid (manufactured by Wako Pure Chemical Industries) 1.85 cm ³ of ion-exchanged water 440 cm ^3, and dissolve in a special grade of tin chloride 100 g (II) dihydrate (manufactured by Wako Pure Chemical Industries) An aqueous tin chloride solution was prepared. While stirring this tin chloride aqueous solution, the aqueous ammonia solution was slowly dropped using a dropping funnel, and the resulting suspension was allowed to stand for 1 day, and the supernatant was discarded to obtain a tin hydroxide. Next, this tin hydroxide is mixed with 1000 cm ³ of ion-exchanged water, stirred, left to stand for one day, and the supernatant is discarded until white sediment is not observed even when the supernatant is mixed with an aqueous silver nitrate solution. Went and washed. Then, a tin hydroxide after cleaning was dried for 24 hours at 383K in a blast dryer to obtain a SnO ₂ powder was calcined for 2 hours at 773K in air with subsequent muffle furnace.
When the obtained SnO ₂ powder was subjected to a nitrogen adsorption experiment, the specific surface area calculated by the BET (Brunauer-Emmett-Teller) method was 20 m ² g ⁻¹ . The average mesopore diameter calculated by the BJH (Barrett-Joyner-Halenda) method was 21 nm. In the nitrogen adsorption experiment, about 50 mg of a sample was set in a sample tube of an adsorption experimental apparatus (product name “BELSorp Mini”) manufactured by Nippon Bell, vacuum degassed at 673 K for 1 hour, and then at 77 K at a pressure of 0 to 10 ⁵ Pa. The equilibrium adsorption amount of nitrogen was measured.
The SnO ₂ powder was fired at 773 K for 1 hour in an oxygen flow (atmospheric pressure, 50 cm ³ min ⁻¹ ) in a glass tube having an inner diameter of 18 mm. Next, helium (atmospheric pressure, 50 cm ³ min ⁻¹ ) dehydrated and purified using a liquid nitrogen trap is circulated, maintained at 423 K, and special grade benzaldehyde (heated to 473 K with a heater) from the upstream inlet (heated to 473 K with a heater). Liquid 1 mm ³ manufactured by Yakuhin Kogyo) was injected. Benzaldehyde was instantly vaporized to form vapor and contacted the SnO ₂ surface. After repeating the injection of benzaldehyde eight times, the vapor of helium was mixed with 360 Pa of vapor of tetramethoxysilane (manufactured by Tokyo Chemical Industry Co., Ltd.) at 473 K and supplied for 1 hour to deposit the Si component. A mixed solution of acetic acid (special grade, manufactured by Wako Pure Chemical Industries, Ltd.)-Ion exchange water at a molar ratio of 1: 1 was injected 8 times at 5 mm ³ times at 473 K, vaporized, and contacted with SnO ₂ . After injection of benzaldehyde three times at 473 K, tetramethoxysilane vapor 360 Pa was mixed into the helium flow at 473 K and supplied for 1 hour to deposit the Si component. Thereafter, the oxygen stream at 673 K (atmospheric ^pressure, 50 cm 3 ^{min -1)} and fired in 1.5 hours, to obtain a silica-modified SnO ₂ powder.
Silica modified SnO ₂ powder obtained, the surface of the SnO _2, pores benzaldehyde and mold, surface area per 1 nm ^2, were approximately 0.5 number generation. Further, the lateral width shown in FIG. 5 of the benzene ring portion of benzaldehyde is as follows: the C—C bond distance in the benzene ring is 0.14 nm, the C—H bond distance is 0.11 nm, and the van der Waals radius of the H atom is 0.12 nm. Is estimated to be approximately 0.71 nm. The thickness of the benzene ring is known to be 0.37 nm. Therefore, the maximum width in the direction parallel to the surface of benzaldehyde adsorbed on the surface of SnO ₂ is estimated to be approximately 0.71 nm. Therefore, this silica-modified SnO ₂ powder is predicted to have pores having a size of 0.71 nm in the horizontal direction and 0.37 nm in the depth direction of the paper surface. In addition, since it is known that the thickness of the silica layer is one set of Si and O atoms under these conditions, the thickness of the silica mask is 0.12 nm for the covalent bond radius of Si, and 0.2 mm for the covalent bond radius of O. It is estimated to be 0.38 nm, which is twice the sum of 07 nm. Therefore, this silica-modified SnO ₂ powder is presumed that a silica mask was formed with pores as shown in FIG.
Next, 30 mg of the silica-modified SnO ₂ powder was suspended in 0.1 cm ³ of special grade ethanol (manufactured by Wako Pure Chemical Industries, Ltd.) to form a slurry. Then, the suspension slurry is applied to a fixed base 31 made of an alumina plate shown in FIG. 4 so as to straddle two platinum wires 32 having a diameter of 0.1 mm wound through a hole 33, and an oxygen flow (atmospheric pressure) , 50 cm ³ min ⁻¹ ) at 773 K for 2 hours to obtain a sensor element of Example 1. The dimensions of each part of the fixed base 31 are as illustrated.

(Example 2)
Pd (NH ₃ ) ₄ Cl ₂ .H ₂ O (manufactured by Aldrich) 0.121 g was diluted with ion-exchanged water to 50 cm ^3, and 2 cm ³ of the resulting solution was 1 g of SnO ₂ powder prepared in Example 1. And heated in a beaker to evaporate water, and the dried solid was dried at 453 K for 4 hours to obtain Pd / SnO ₂ powder. In this Pd / SnO ₂ powder, approximately 0.3 Pd atoms were arranged per 1 nm ² .
The Pd / SnO ₂ powder was fired at 773 K for 1 hour in an oxygen flow (atmospheric pressure, 50 cm ³ min ⁻¹ ) in a glass tube having an inner diameter of 18 mm. Next, dehydrated and purified helium (atmospheric pressure, 50 cm ³ min ⁻¹ ) was circulated using a liquid nitrogen trap, maintained at 343 K, and primary 1-naphthaldehyde from an inlet (heated to 473 K with a heater) installed upstream. Liquid 1 mm ³ (manufactured by Wako Pure Chemical Industries, Ltd.) was injected. 1-Naphtoaldehyde was instantly vaporized into vapor and contacted the surface of Pd / SnO ₂ . After the injection of 1-naphthaldehyde was repeated 8 times, vapor of tetramethoxysilane (manufactured by Tokyo Kasei Kogyo Co., Ltd.) was mixed into the helium flow at 473 K and supplied for 1 hour to deposit the Si component. A mixed solution of acetic acid (special grade, manufactured by Wako Pure Chemical Industries, Ltd.)-Ion exchange water at a molar ratio of 1: 1 at 473 K was injected 8 times at a rate of 5 mm ³ from the injection port, vaporized, and contacted. After injection of 1-naphthaldehyde at 473 K three times, tetramethoxysilane vapor 360 Pa was mixed into the helium flow at 473 K and supplied for 1 hour to deposit the Si component. Thereafter, the oxygen stream at 673 K (atmospheric ^pressure, 50 cm 3 ^{min -1)} and fired in 1.5 hours to obtain a silica-modified Pd / SnO ₂ powder.
Silica modified Pd / SnO ₂ powder obtained, the surface of the metal oxide consisting of SnO _2, pores of 1-naphthaldehyde and mold, surface area per 1 nm ^2, were approximately 0.5 number generation. In addition, 1-naphthaldehyde is estimated to have a maximum width of about 0.95 nm in a direction parallel to the surface of SnO ₂ adsorbed on the surface. The thickness of the benzene ring is known to be 0.37 nm. Therefore, the silica-modified Pd / SnO ₂ powder is predicted to have pores having a size of 0.95 nm in the horizontal direction and 0.37 nm in the depth direction of the paper surface. In addition, since it is known that the thickness of the silica layer is one set of Si and O atoms under these conditions, the thickness of the silica mask is 0.12 nm for the covalent bond radius of Si, and 0.2 mm for the covalent bond radius of O. It is estimated to be 0.38 nm, which is twice the sum of 07 nm. Therefore, it is assumed that the silica-modified Pd / SnO ₂ powder has pores as shown in FIG. 6C formed in the silica mask.
Next, 30 mg of the silica-modified Pd / SnO ₂ powder was suspended in 0.1 cm ³ of special grade ethanol (manufactured by Wako Pure Chemical Industries, Ltd.) to form a slurry. And the said suspension slurry is apply | coated so that the two platinum wires 32 wound around the fixing stand 31 shown in FIG. 4 may be straddled, and it baked at 773K for 2 hours in oxygen flow (atmospheric pressure, 50 cm < ³ > min < ^-1 >). Thus, a sensor element of Example 2 was obtained.

(Example 3)
The Pd / SnO ₂ powder prepared in Example 2 was calcined at 773 K in an oxygen flow (atmospheric pressure, 50 cm ³ min ⁻¹ ) for 1 hour in a glass tube having an inner diameter of 18 mm. Next, helium (atmospheric pressure, 50 cm ³ min ⁻¹ ) dehydrated and purified using a liquid nitrogen trap was circulated, maintained at 423 K, and from a high-grade inlet (heated to 473 K with a heater), special grade benzaldehyde (Wako Pure) Liquid 1 mm ³ manufactured by Yakuhin Kogyo) was injected. Benzaldehyde was instantly vaporized to form vapor and contacted the SnO ₂ surface. After repeating the injection of benzaldehyde eight times, the vapor of helium was mixed with 360 Pa of vapor of tetramethoxysilane (manufactured by Tokyo Chemical Industry Co., Ltd.) at 473 K and supplied for 1 hour to deposit the Si component. A mixed solution of acetic acid (special grade, manufactured by Wako Pure Chemical Industries, Ltd.)-Ion exchange water at a molar ratio of 1: 1 was injected 8 times at 5 mm ³ times at 473 K, vaporized, and contacted with SnO ₂ . After injection of benzaldehyde three times at 473 K, tetramethoxysilane vapor 360 Pa was mixed into the helium flow at 473 K and supplied for 1 hour to deposit the Si component. Thereafter, the oxygen stream at 673 K (atmospheric ^pressure, 50 cm 3 ^{min -1)} and fired in 1.5 hours to obtain a silica-modified Pd / SnO ₂ powder.
Silica modified SnO ₂ powder obtained, the surface of the SnO _2, pores benzaldehyde and mold, surface area per 1 nm ^2, were approximately 0.5 number generation.
Next, 30 mg of the silica-modified Pd / SnO ₂ powder was suspended in 0.1 cm ³ of special grade ethanol (manufactured by Wako Pure Chemical Industries, Ltd.) to form a slurry. Then, coating the suspension slurry so as to straddle the two platinum wires 32 wound around the fixing stand 31 shown in FIG. 4, 2 h calcination at 773K oxygen stream (atmospheric ^pressure, 50 cm 3 ^{min -1)} in Thus, a sensor element of Example 3 was obtained.

(Comparative Example 1)
30 mg of SnO ₂ powder prepared in Example 1 was suspended in 0.1 cm ³ of special grade ethanol (manufactured by Wako Pure Chemical Industries, Ltd.) to form a slurry. And the said suspension slurry is apply | coated so that two platinum wires 32 wound around the fixing stand 31 shown in FIG. 4 may be straddled, and it baked at 773K for 2 hours in oxygen flow (atmospheric pressure, 50 cm < ³ > min < ^-1 >). Thus, a sensor element of Comparative Example 1 was obtained.

(Comparative Example 2)
30 mg of Pd / SnO ₂ powder prepared in Example 2 was suspended in 0.1 cm ³ of special grade ethanol (manufactured by Wako Pure Chemical Industries, Ltd.) to form a slurry. And the said suspension slurry is apply | coated so that the two platinum wires 32 wound around the fixing stand 31 shown in FIG. 4 may be straddled, and it baked at 773K for 2 hours in oxygen flow (atmospheric pressure, 50 cm < ³ > min < ^-1 >). Thus, a sensor element of Comparative Example 2 was obtained.

<< Test Example 1 >>
The sensor elements 3 of Example 1 and Comparative Example 1 were placed in the glass tube 41 of the pulse experiment apparatus 40 shown in FIG. 7, and the sensitivity of each sensor element 3 with respect to various substances was compared by the pulse method. In this experimental apparatus, the inner diameter of the glass tube 41 is 18 mm, and the installation portion of the sensor element 3 can be heated by the electric furnace 42. Further, an inlet 43 is provided upstream of the glass tube 41, and a liquid sample can be injected into the inlet 43 and a nitrogen-oxygen mixed gas A can be introduced through the silica gel 44. Further, the vicinity of the inlet 43 is surrounded by a ribbon heater 45, and the liquid sample is vaporized by the heater 45. Further, the platinum wire 32 of the sensor element 3 is connected to an ohmmeter 47 through a nickel conducting wire 9 inserted through a rubber plug 46 that closes one end of the glass tube 41. When a liquid sample is injected into the injection port 43, the liquid sample is heated and vaporized by the heater 45, and is supplied so as to come into contact with the sensor element 3 together with the nitrogen-oxygen mixed gas A. And it is comprised so that direct-current electrical resistance may be recorded by the ohmmeter 47 through the platinum wire 32 and the conducting wire 9 of the sensor element 3.

The sensor element 3 is set in the glass tube 41 of the pulse experiment apparatus of FIG. 7, and after pretreatment at 673 K for 1 hour in an oxygen flow (atmospheric pressure, 40 cm ³ min ⁻¹ ), a nitrogen-oxygen mixed gas A (nitrogen: A liquid sample of 0.5 mm ³ at 543 K in an oxygen molar ratio of 4: 1, atmospheric pressure, 100 cm ³ min ⁻¹ ) was injected from the injection port 43 as a test substance, and the change in electrical resistance of the sensor element 3 was recorded. As the liquid sample, toluene and dioctyl phthalate were used. The resistance before injection was R _a , the resistance after injection was R, and the response was expressed as R _a / R−1.

  FIG. 8 shows a response example of toluene (broken line) and dioctyl phthalate (solid line) of the sensor element of Example 1, and FIG. 9 shows a response example of the sensor element of Comparative Example 1, respectively. As shown in FIG. 9, the sensor element of Comparative Example 1 showed a large response to toluene and dioctyl phthalate. However, as shown in FIG. 8, the sensor element of Example 1 was selective to dioctyl phthalate. Responds and hardly responds to toluene.

The sensitivity of the sensor element of Example 1 to toluene is low, as shown in the schematic diagram of FIG. 10, because the benzene ring cannot pass through narrow pores formed using benzaldehyde as a template, and toluene has side chains. This is probably because the side chain portion cannot reach the SnO ₂ surface because it is short. Although the pores of this sensor element are thought to be approximately the size of a benzene ring, the diffusion of molecules of the same size as the pores is slow in the pores, and only molecules slightly smaller than the pores are substantially Since it can react, it is estimated that it hardly responded to toluene.
On the other hand, as shown in the schematic diagram of FIG. 11, dioctyl phthalate has a long side chain extending from the benzene ring, and it is assumed that this side chain portion reached the SnO ₂ surface and showed a response. Is done.

Next, using the acetone, toluene, dibutyl phthalate, and dioctyl phthalate as the liquid sample, the sensitivity of the sensor elements of Example 1 and Comparative Example 1 at the measurement temperatures of 493K to 643K (R _a / R-1) was compared.

  FIG. 12 shows a response example of the sensor element of Example 1 to acetone, toluene, dibutyl phthalate and dioctyl phthalate at measurement temperatures of 493K to 643K, and FIG. 13 shows a response example of the sensor element of Comparative Example 1 respectively. Show.

  As shown in FIG. 13, the sensor element of Comparative Example 1 responded to any of acetone, toluene, dibutyl phthalate, and dioctyl phthalate. In contrast, as shown in FIG. 12, the sensor element of Example 1 had high sensitivity to dibutyl phthalate and dioctyl phthalate, but low sensitivity to acetone and toluene. In particular, in the range of 543 to 643 K, the sensor element of Example 1 had high sensitivity to dibutyl phthalate and dioctyl phthalate, while having low sensitivity to acetone and toluene. For this reason, the sensor element of Example 1 was able to selectively detect dibutyl phthalate and dioctyl phthalate without being affected by the coexistence of acetone or toluene.

  As described above, the sensitivity of the sensor element of Example 1 to toluene is low because the benzene ring cannot pass through narrow pores formed using benzaldehyde as a template, and toluene has a short side chain. Guessed. Moreover, the sensitivity to acetone is low, as shown in the schematic diagram of FIG. 14, the acetone molecule has two methyl groups and oxygen branches in three directions from the central carbon atom, which is bulky compared to the alkyl group. Therefore, it is difficult to pass through the pores, and the sensitivity is considered low.

  Next, the measurement temperature is set to 543 K and 643 K, and acetone, toluene, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, 2-methyl-2-propanol, 1-pentanol, 1 are used as liquid samples. Sensitivity of the sensor elements of Example 1 and Comparative Example 1 to various substances was determined by a pulse method using hexanol, 1-octanol, dibutyl phthalate, and dioctyl phthalate. The sensitivity ratio between the sensor element of Example 1 and the sensor element of Comparative Example 1 at 543 K for each test substance ([Sensitivity of sensor B of Example 1] / [Sensitivity of sensor A of Comparative Example 1]) 15 shows the sensitivity ratio at 643 K. FIG.

  As shown in FIG. 15, at 543K, the sensitivity ratio of toluene was zero. The sensitivity ratio to ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, 2-methyl-2-propanol, 1-pentanol, 1-hexanol, and 1-octanol was 0.04 or less. It was. On the other hand, dioctyl phthalate, dibutyl phthalate, and acetone showed high sensitivity ratios.

  Since 2-propanol, 2-butanol, and 2-methyl-2-propanol have a branched molecular structure, it is difficult to pass through the pores, and it is assumed that the sensitivity to the sensor element of Example 1 was low.

  On the other hand, ethanol, 1-propanol, 1-butanol, 1-pentanol, 1-hexanol, and 1-octanol were linear alcohols, but the sensitivity ratio was low. That is, as shown in Table 1 below, the linear alcohol showed high sensitivity (RaK / R-1 of 40 to 400 at 543 K) for the sensor element of Comparative Example 1. The sensitivity of the sensor element was low (Ra / R-1 was 0.8 to 3). As the cause, the following is estimated.

Linear alcohols, linear alkane _(R a / _R-1 hexane under the same conditions about 11) the sensitivity on SnO ₂ tends to be higher than, this is OH group of the alcohol is SnO ₂ surface It is presumed that this is because it is easily adsorbed on the surface.
However, in the tin oxide sensor, an electrical response is generated by depriving oxygen in the tin oxide by the reducing substance. Therefore, when the OH is simply adsorbed on the SnO ₂ surface, it does not respond, and the CH adjacent to the strongly adsorbed OH. High sensitivity appears when the part reacts with the SnO ₂ surface. That is, for high sensitivity to occur, it is presumed that the OH group and the alkyl group need to contact the SnO ₂ surface simultaneously. As shown in the schematic diagram of FIG. 17A, in the sensor element of Comparative Example 1, the CH group adjacent to the OH group can simultaneously contact the SnO ₂ surface. On the other hand, as shown in the schematic diagram of FIG. 17 (b), the sensor element of Example 1 is a linear alcohol and passes through the pores of the silica mask from the alkyl group side or the OH group side. Can reach tin oxide. For this reason, although a certain amount of response is shown when the alkyl group side reaches the SnO ₂ surface, as shown in the schematic diagram of FIG. 17A, the CH group adjacent to OH cannot simultaneously contact the SnO ₂ surface. . For this reason, it is presumed that the sensitivity of the sensor element of Example 1 with respect to the linear alcohol is lower than that of the sensor element of Comparative Example 1, and the sensitivity ratio is lowered.

  As shown in FIG. 16, at 643K, dibutyl phthalate and dioctyl phthalate showed a higher sensitivity ratio than acetone and toluene.

  Therefore, for example, when the constituent substance group of an unknown sample is known, it can be estimated whether or not dioctyl phthalate or dibutyl phthalate is contained in the gas component to be measured according to the criteria shown in Table 2 below. . Furthermore, it can be estimated whether more dibutyl phthalate or dioctyl phthalate is contained.

  Next, the measurement temperature was set to 543 K, the liquid sample was dimethyl phthalate, diethyl phthalate, diisobutyl phthalate, dibutyl phthalate, and dioctyl phthalate. Sensitivity was determined. As shown in FIG. 18, high sensitivity was shown for any dialkyl phthalate, but the sensitivity of dimethyl phthalate and diisobutyl phthalate was low. As shown in the schematic diagram of FIG. 19, this is presumed to be caused by the fact that dimethyl phthalate has a short side chain, so that the side chain hardly passes through the pores. Further, diisobutyl phthalate has a branched side chain, and since the tip of the branch is short, it is presumed that the side chain hardly passes through the pores as shown in the schematic diagram of FIG.

<< Test Example 2 >>
The sensitivity of the sensor elements of Example 3 and Comparative Examples 1 and 2 to low concentrations of dioctyl phthalate was examined.
First, a dioctyl phthalate liquid was placed in a glass container, heated at 383 K for 11 hours while flowing a helium stream, and helium was circulated for 12 hours or more at room temperature. Thereafter, dry air was circulated at room temperature to obtain an air stream containing approximately 300 ppb of dioctyl phthalate.
Next, in the glass tube 41 of the pulse experiment apparatus shown in FIG. 7, the sensor element of Example 3 (SilO ₂ with a silica mask / Pd), the sensor element of Comparative Example 1 (SnO ₂ without a silica mask), and a comparative example 2 sensor elements (silica maskless SnO ₂ / Pd) were placed, and the sensor elements were pretreated at 673 K in an oxygen stream (atmospheric pressure, 40 cm ³ min ⁻¹ ) for 1 hour, and then dried air (atmospheric pressure, 50 cm ^The electrical resistance _Ra was recorded at 543 K in ³ min ⁻¹ ). Thereafter, air containing the dioctyl phthalate vapor was supplied, and changes in electrical resistance were recorded.

The results are shown in FIG. The thin line in the figure is the response of the sensor element of Example 3, the thin broken line is the response of the sensor element of Comparative Example 1, and the thick line is the response of the sensor element of Comparative Example 2. As shown in FIG. 21, the response of the sensor element of Comparative Example 1 consisting only of SnO ₂ was indistinguishable from noise, but the sensitivity was improved by supporting Pd on SnO ₂ and a silica mask was formed. Even with this, it was detected with sufficient sensitivity.

<< Test Example 3 >>
The sensor elements of Example 2 and Comparative Example 2 were set in the apparatus shown in FIG.
In the experimental apparatus 50, the installation portion of the sensor element 3 of the glass tube 51 can be heated by the electric furnace 52. An inlet 53 is provided upstream of the glass tube 51, and a concentrating device 60 is connected to the inlet 53 so that the test gas can be concentrated and supplied to the sensor element 3.
The concentrator 60 is provided with a dry air supply valve V1 and a helium gas supply valve V2. By opening and closing the respective valves, the dry air or helium gas can be introduced into the flow path in the concentrator 60. ing. Since helium gas is circulated for the purpose of cleaning the flow path in the apparatus, the helium gas supply valve V2 is closed during the test (while the dry air valve V1 is open).
The flow path in which the dry air supply valve V1 and the helium gas supply valve V2 are arranged is branched into flow paths L1 to L4, and flow rate adjustment valves V3 to V7 are arranged in the respective flow paths. .
The flow paths L1 and L2 merge in the middle, and a silica gel drying tube 61, a trap C, and a steam saturator 62 are disposed on the downstream side. The steam saturator 62 is filled with a dioctyl phthalate liquid, and a flow path L5 in which a switching valve V8 is disposed extends downstream thereof. By switching this switching valve V8, the flow path L5 and the flow path L7 described later can be connected / disconnected.
Further, a steam saturator 63 is disposed downstream of the flow path L3. The steam saturator 63 is filled with a liquid of toluene, and on the downstream side thereof, a flow path L6 in which the switching valve V9 is disposed extends. By switching the switching valve V9, the flow path L5 and the flow path L7 described later can be connected / disconnected.
Further, a trap B is disposed downstream of the flow path L4, and the flow path L7 extends from the downstream of the trap B so that the above-described flow paths L5 and L6 can be connected. And the hexagonal cock V10 is arrange | positioned at the downstream end part of this flow path L7.
In the hexagonal cock V10, the flow path L7, the trap A, the trap D, and the trap E are arranged. Then, by switching the flow path with the hexagonal cock V10, the flow path L7 and the trap A are connected, and the test gas passing through the flow path L7 is captured by the adsorbent filled in the trap A, and the trap D and trap E is connected to the inlet 53, and O ₂ and N ₂ are introduced into the sensor element 3 (the embodiment of FIG. 22), or the flow path L7 is separated from the trap A, and the trap A, trap D, and inlet 53 And the gas component trapped in the trap A together with N ₂ supplied to the trap D is introduced into the sensor element 3, the trap E is connected to the inlet 53, and O ₂ is introduced into the sensor element 3. (Aspect of FIG. 23)
The trap A is filled with a column filler (trade name “TENAX-GR” manufactured by GL Sciences). In addition, traps B, C, D, and E are packed with a column filler (trade name “TENAX-GR” manufactured by GL Science) and activated carbon for chemical filters (manufactured by Nippon Puretech) to adsorb and remove organic substances. And kept at 273K during the experiment.

The sensor element 3 was set in the glass tube 51 of such an experimental apparatus 50 and pretreated at 673 K for 1 hour in an oxygen flow (atmospheric pressure, 40 cm ³ min ⁻¹ ).
Then, the steam saturation is performed through the dry air (N ₂ + O ₂ ) supplied through the trap C to the steam saturator 62 while opening the dry air supply valve V1 and adjusting the opening degree of the flow rate adjusting valves V3 and V4. The vessel 62 was kept at room temperature and a gas having a dioctyl phthalate concentration of approximately 300 ppb was supplied.
Further, air containing nothing is circulated through the trap B, the total flow rate is made constant at 300 cm ³ min ⁻¹ together with the gas supplied from the steam saturator 62, and the flow rate ratio is adjusted to adjust any concentration. The dioctyl phthalate vapor was supplied to the trap A via the hexagonal cock V10, and the dioctyl phthalate was collected by keeping the trap A at 273K. After trapping for 100 min in trap A, the hexagonal cock V10 was switched to the state shown in FIG. Then, nitrogen (atmospheric pressure, 71 cm ³ min ⁻¹ ) is supplied to the trap A through the trap D, and oxygen (atmospheric pressure, 29 cm ³ min ⁻¹ ) is merged into the downstream of the trap E to enter the sensor element 3. The glass tube was supplied. During the measurement, the temperature of the sensor element 3 was kept at 673K, the trap A was rapidly heated to 523K, and the change of the electric signal was recorded. Further, the electrical resistance before heating of the trap A was R _a. In addition, the piping drawn with the thick line in the figure is heated to about 473K.

  FIG. 24 shows the response of the sensor element of Example 2, and FIG. 25 shows the response of the sensor element of Comparative Example 2. The thin line in the figure is the response when only air is flowed, the broken line is the response when 0.3 ppb dioctyl phthalate is flowed, and the thick line is when 0.5 ppb dioctyl phthalate is flowed Is the response. As shown in FIGS. 24 and 25, when dioctyl phthalate was allowed to flow through 0.3 to 0.5 ppb, a peak was clearly observed and could be detected even in a region of 1 ppb or less.

Next, we looked at the response in the presence of toluene and dioctyl phthalate. When toluene is circulated, dry air (N ₂ + O ₂ ) is circulated through the steam saturator 63 while adjusting the degree of opening of the flow rate adjusting valve V5 through the steam saturator 63 of the experimental apparatus 50 shown in FIG. I let you. By maintaining the temperature in the steam saturator 63 at 273 K, a gas having a toluene concentration of approximately 9000 ppm was obtained. Further, a gas containing 300 ppb of dioctyl phthalate supplied to the steam saturator 62 through dry air (N ₂ + O ₂ ) supplied via the trap C, a gas supplied from the steam saturator 63, and a trap B The gas containing any concentration was obtained by combining the air containing nothing and the flow rate ratio by changing the flow rate ratio while keeping the total flow rate constant at 300 cm ³ min ⁻¹ . And this gas was supplied to the trap A, and the concentration process was performed like the above.

  FIG. 26 shows the response of the sensor element of Example 2, and FIG. 27 shows the response of the sensor element of Comparative Example 2. In addition, the thin line in a figure is a response with respect to the gas of dioctyl phthalate 0ppb and toluene 30ppm. The broken line is the response to a gas of 0.3 ppb dioctyl phthalate and 30 ppm toluene. The thick line is the response to a gas of 0.5 ppb and 30 ppm toluene.

The sensor element of Comparative Example 2 showed R _a / R-1 = 2 under the conditions of dioctyl phthalate 0 ppb and toluene 30 ppm, and showed high sensitivity to toluene (thin line in FIG. 27). When the toluene concentration was kept at 30 ppm and the dioctyl phthalate concentration was increased to 0.3 ppb (broken line in FIG. 27) and 0.5 ppb (thick line in FIG. 27), the response increased. However, since the sensor element of Comparative Example 2 has a large response to toluene, the concentration of dioctyl phthalate contained therein cannot be estimated from the response to an unknown sample.

  In contrast, the sensor element of Example 2 showed almost no response under the conditions of dioctyl phthalate 0 ppb and 30 ppm toluene (thin line in FIG. 26), while maintaining the toluene concentration at 30 ppm and the dioctyl phthalate concentration at 0.3 ppb ( The response increased when the value was raised to 0.5 ppb (the thick line in FIG. 26). That is, the sensor element of Example 2 did not react with toluene on the order of ppm, and was able to detect ppb order dioctyl phthalate stably regardless of the presence or absence of toluene.

  And when the sensitivity was plotted with respect to the concentration of dioctyl phthalate of the sensor element of Example 2, it was as shown in FIG. 28, and the relational expression of the following expression (1) was obtained.

  Considering this equation as a calibration curve, calculating the dioctyl phthalate concentration from the actual measurement value in the sensor element of Example 2 is as shown in Table 3. The difference between the experimental value and the calculated value is 0.14 ppb at the maximum. Therefore, dioctyl phthalate could be detected on the order of 1 ppb regardless of the presence or absence of toluene.

It is the schematic which shows 1st embodiment of the gas sensor of this invention. It is the schematic which shows 2nd embodiment of the gas sensor of this invention. It is the schematic which shows 3rd embodiment of the gas sensor of this invention. It is the schematic of a sensor fixed base. It is the schematic which forms a silica mask on the surface of a metal oxide using benzaldehyde as a compound for template formation. It is the schematic which forms a silica mask on the surface of a metal oxide using 1-naphthaldehyde as a compound for template formation. It is the schematic of a pulse experiment apparatus. It is a graph which shows the example of a response by the pulse method of toluene (broken line) and dioctyl phthalate (solid line) of the sensor element of Example 1. It is a chart which shows the example of a response by the pulse method of toluene (dashed line) and dioctyl phthalate (solid line) of the sensor element of comparative example 1. FIG. 4 is a schematic diagram of a reaction with toluene on the surface of the sensor element of Example 1. FIG. 3 is a schematic diagram of a reaction with dioctyl phthalate on the surface of the sensor element of Example 1. It is a graph which shows the example of a response by the pulse method with respect to acetone, toluene, dibutyl phthalate, and dioctyl phthalate in measurement temperature 493K-643K of the sensor element of Example 1. It is a graph which shows the example of a response by the pulse method with respect to acetone, toluene, dibutyl phthalate, and dioctyl phthalate in the measurement temperature of 493K-643K of the sensor element of the comparative example 1. FIG. 3 is a schematic diagram of a reaction with acetone on the surface of the sensor element of Example 1. 5 is a chart showing a sensitivity ratio ([sensor sensitivity of Example 1] / [sensor sensitivity of Comparative Example 1]) between the sensor element of Example 1 and the sensor element of Comparative Example 1 at 543K. 10 is a chart showing a sensitivity ratio ([sensor sensitivity of Example 1] / [sensor sensitivity of Comparative Example 1]) between the sensor element of Example 1 and the sensor element of Comparative Example 1 at 643K. It is a reaction schematic diagram with alcohol on the sensor element surface. 2 is a chart showing an example of response of the sensor element of Example 1 to a dimethyl phthalate, diethyl phthalate, diisobutyl phthalate, dibutyl phthalate, and dioctyl phthalate by a pulse method. FIG. 3 is a schematic diagram of a reaction with dimethyl phthalate on the surface of the sensor element of Example 1. FIG. 3 is a schematic diagram of a reaction with diisobutyl phthalate on the surface of the sensor element of Example 1. It is a graph which shows the example of a response with respect to 300 ppb of dioctyl phthalates of the sensor element of Example 3 and Comparative Examples 1 and 2. It is the schematic of the measuring device using a trap, Comprising: It is the state figure which is collecting the vapor | steam of predetermined concentration with the trap A. FIG. It is the schematic of the measuring apparatus using a trap, Comprising: It is the state figure which desorbs the collected gas by heating and distribute | circulates to the reaction tube containing a sensor element. It is a graph which shows the example of a response of the sensor element of Example 2 when the dioctyl phthalate density | concentration in gas is set to 0 ppb (thin line), 0.3 ppb (dashed line), and 0.5 ppb (thick line). It is a graph which shows the example of a response of the sensor element of the comparative example 2 when the dioctyl phthalate density | concentration in gas is 0 ppb (thin line), 0.3 ppb (dashed line), and 0.5 ppb (thick line). The chart which shows the example of a response of the sensor element of Example 2 when dioctyl phthalate density | concentration in gas is set to 0 ppb (thin line), 0.3 ppb (dashed line), and 0.5 ppb (thick line), supplying 30 ppm of toluene. is there. The chart which shows the example of a response of the sensor element of the comparative example 2 when supplying 30 ppm of toluene and setting the dioctyl phthalate concentration in the gas to 0 ppb (thin line), 0.3 ppb (dashed line), and 0.5 ppb (thick line). is there. It is a relationship figure which shows the dioctyl phthalate density | concentration dependence of the sensitivity of the sensor element of the comparative example 1 and the sensor element of Example 2 in toluene 0ppm and 30 ppm coexistence.

Explanation of symbols

1, 11, 21: Metal oxide 2, 12: Silica mask 2a: Fine pore 3: Sensor element 4, 30: Detector 5: Gas concentrator 13: First sensor element 22: Second sensor element

Claims (15)

A gas sensor for detecting dialkyl phthalate in gas,
A sensor element in which a silica mask having predetermined pores is formed on the surface of a metal oxide containing SnO ₂ as a main component;
A detector for measuring an electrical resistance value of the sensor element;
A gas sensor comprising: Another sensor element in which a silica mask having pores having a diameter different from that of the sensor element is formed on the surface of a metal oxide mainly composed of SnO ₂ and / or a metal mainly composed of SnO ₂ A sensor element not having a silica mask on the surface of the oxide;
The gas sensor according to claim 1, wherein the detector is configured to measure an electric resistance value of each sensor element. The gas sensor according to claim 1, wherein the metal oxide is a catalyst in which SnO ₂ is supported.   The gas sensor according to claim 3, wherein the catalyst is a noble metal.   The gas sensor according to claim 3, wherein the catalyst is Pd.   The sensor element in which the silica mask is formed has a template forming compound selected from aliphatic aldehydes, aliphatic carboxylic acids, aromatic aldehydes and aromatic carboxylic acids on the surface of the metal oxide, less than a monomolecular layer. The gas sensor according to any one of claims 1 to 5, which is formed by vapor-depositing silica precursor molecules after being adsorbed at an adsorption density of, and hydrolyzing the silica precursor molecules to form a silica mask.   The gas sensor according to claim 6, wherein the template forming compound has a maximum width in a direction parallel to the surface in a state of being adsorbed on the surface of the metal oxide of 0.5 to 1.2 nm. .   The gas sensor according to claim 6, wherein the template forming compound is 1-naphthaldehyde or 1-naphthalenecarboxylic acid.   2. A gas concentrating device is disposed upstream of the sensor element in a gas flow direction, and is configured to introduce gas into which the gas component to be detected by the gas concentrating device is concentrated to the sensor element. The gas sensor of any one of -8.   The gas concentrator includes a means for supplying a predetermined amount of gas to a collecting agent to collect a gas component to be detected, and a gas component to be detected from the collecting agent while raising the temperature of the collecting agent. The gas sensor according to claim 9, further comprising: means for diverging gas to supply gas containing the gas component concentrated. A method for producing a sensor element used in a gas sensor for detecting a dialkyl phthalate in a gas,
Silica precursor molecules after adsorbing a template forming compound selected from aliphatic aldehydes, aliphatic carboxylic acids, aromatic aldehydes and aromatic carboxylic acids to the surface of the metal oxide with an adsorption density less than a monolayer. Is vapor-deposited and hydrolyzed into silica to form a silica mask.   The sensor according to claim 11, wherein the template-forming compound has a maximum width of 0.5 to 1.2 nm in a direction parallel to the surface of the template when adsorbed on the surface of the metal oxide. Device manufacturing method.   The method for producing a sensor element according to claim 12, wherein the template forming compound is 1-naphthaldehyde or 1-naphthalenecarboxylic acid. A gas to be detected is supplied to a sensor element in which a silica mask having predetermined pores is formed on the surface of a metal oxide containing SnO ₂ as a main component, and an electric resistance value of the sensor element is measured. A gas detection method comprising detecting dialkyl phthalate in a gas. Another sensor element in which a silica mask having pores having a diameter different from that of the sensor element is formed on the surface of a metal oxide mainly composed of SnO ₂ and / or a metal mainly composed of SnO ₂ Further using a sensor element having no silica mask on the surface of the oxide,
The gas detection method according to claim 14, wherein a gas to be detected is supplied to each sensor element, and an electric resistance value of each sensor element is measured.