JP5358838B2 - Gas sensor and gas detection method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a gas sensor and a gas detection method capable of detecting a dialkyl phthalate in a gas by a convenient way. <P>SOLUTION: A dialkyl phthalate in a gas is detected by using a gas sensor comprising a collection column 1 filled with mesoporous silica, a heating apparatus 2 for heating the collection column 1, a sensor element 4 in which a silica mask having predetermined pores is formed on a surface of a metal oxide mainly composed of SnO<SB POS="POST">2</SB>, a detector 5 for measuring an electric resistance value of the sensor 4 and air distribution means which distributes the air collected from a space to be measured to the collection column 1 as a sample gas and distributes the same gas to the collection column 1 and the sensor element 4 as a gas for desorption. <P>COPYRIGHT: (C)2012,JPO&amp;INPIT

Description

  The present invention relates to a gas sensor for detecting dialkyl phthalate in gas 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 electrical resistance of SnO ₂ is heated to 250 to 500 ° C. in an oxygen atmosphere, oxygen is activated and adsorbed on the particle surface of SnO ₂ to increase the resistance. However, in a reducing gas (organic substance), adsorbed oxygen 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.

However, not only in clean rooms, dialkyl phthalates often coexist with other volatile organic compounds such as toluene. Since SnO ₂ responds to all reducing gases, it has been difficult to detect only a specific gas component, for example, dialkyl phthalate, from a gas in which various components are mixed.

  For this reason, in detecting the presence or absence of a specific component from a gas in which various components are mixed, conventionally, the sample gas is brought into contact with a collection agent to collect and concentrate the gas component to be detected. The collection agent was heated while circulating an inert gas such as gas, and the collected gas components were desorbed from the collection agent, and the components and concentrations were analyzed using an analytical instrument such as a gas chromatograph. .

  However, in the method using an analytical instrument such as a gas chromatograph, the analysis takes time, so that real-time detection is difficult.

For example, in Patent Document 1 described below, after a gas component to be detected is adsorbed to a collection agent, the gas component to be detected is diffused by heating the collection agent to divert the gas component to be detected. Sample gas 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 measured. Thus, a gas detection method for detecting dialkyl phthalate in a gas is disclosed.

JP 2010-54205 A (claims, paragraph numbers 0040 to 0046)

  Conventionally, polymer particles such as “TENAX-TA” (trade name, 2,6-diphenyl-p-phenylene oxide, manufactured by GL Sciences Inc.) as a scavenger for volatile organic compounds such as dialkyl phthalates. Activated carbon, glass wool, etc. are used. Also in the said patent document 1, this scavenger is used.

  However, polymer particles such as “TENAX-TA” and activated carbon have low heat resistance, and when heated in the presence of oxygen, the trapping agent itself thermally decomposes or burns. For this reason, when heating the collection agent, it is necessary to switch the flow path and let the inert gas flow, and there is a mechanism for supplying the inert gas (cylinder, mass flow valve, etc.) and switching of the flow path. For this reason, there is a problem that the device configuration is complicated. Furthermore, it was necessary to prepare an inert gas source such as a nitrogen gas cylinder.

  Although glass wool has heat resistance, it has a low adsorptive power for dialkyl phthalates and the like, and dialkyl phthalates may not be sufficiently concentrated.

  Accordingly, an object of the present invention is to provide a gas sensor and a gas detection method capable of selectively detecting a low concentration dialkyl phthalate with a simple apparatus configuration.

  As a result of various studies, the present inventors have found that mesoporous silica is heat resistant, has excellent adsorptivity of dialkyl phthalate, and can further desorb the adsorbed dialkyl phthalate at a relatively low temperature. Invented.

That is, the gas sensor of the present invention is a gas sensor for detecting dialkyl phthalate in a gas, and is a collection column packed with mesoporous silica having a specific surface area of 300 m ² / g or more and an average pore diameter of 1.5 nm or more. A heating device for heating the collection column; a sensor element in which a silica mask having predetermined pores is formed on the surface of a metal oxide mainly composed of SnO _2; and an electric resistance of the sensor element A detector for measuring the value and the air collected from the space to be measured are circulated through the collection column as a sample gas, and the air is circulated as a desorption gas through the collection column and the sensor element. And an air circulation means.

The mesoporous silica is excellent in adsorbing dialkyl phthalate, and further, the adsorbed dialkyl phthalate can be eliminated at a relatively low temperature, so that the dialkyl phthalate adsorbed by the mesoporous silica without oxidative decomposition of the dialkyl phthalate. Almost all of this can be eliminated. For this reason, dialkyl phthalate can be efficiently concentrated and supplied to the sensor element.
Moreover, since this mesoporous silica is excellent in heat resistance, it is not necessary to use an inert gas such as nitrogen gas as a desorption gas when desorbing the gas component adsorbed by the mesoporous silica from the mesoporous silica. That is, air collected from the space to be measured can be used as the desorption gas. For this reason, it is not necessary to separately prepare a nitrogen cylinder or the like, and further, a piping route or the like can be further simplified.
And since the sensor element used for this gas sensor is formed by forming a silica mask having predetermined pores on the surface of a metal oxide containing SnO ₂ as a main component, the sensor element contains dialkyl phthalate. When the sample 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, dialkyl phthalate can be selectively detected by supplying sample gas to a sensor element and measuring the electrical resistance value of the sensor element.
As described above, according to the gas sensor of the present invention, since dialkyl phthalate in the sample gas is concentrated and supplied to the sensor element, even if the dialkyl phthalate in the sample gas is extremely small, the presence or absence of dialkyl phthalate Can be detected accurately in a short time.

  In the gas sensor of the present invention, after the air is circulated through the collection column at a predetermined flow rate for a predetermined time, the heating means is operated to adjust the atmospheric temperature in the collection column to 250 to 450 ° C., It is preferable that the flow rate of the air is made lower than the flow rate so as to flow through the collection column to the detector. By adjusting the atmospheric temperature in the collection column to 250 to 450 ° C., the dialkyl phthalate adsorbed on the mesoporous silica can be almost completely eliminated. And since the concentration rate of dialkyl phthalate can be further increased by slowing the flow rate of air when detaching dialkyl phthalate from mesoporous silica, the detection accuracy of dialkyl phthalate is improved.

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. 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 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. After adsorbing at an adsorption density less than a monomolecular layer, a silica precursor molecule is vapor-deposited, and this is hydrolyzed to 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.

Further, the gas detection method of the present invention is a gas detection method for detecting dialkyl phthalate in the air, wherein mesoporous silica having a specific surface area of 300 m ² / g or more and an average pore diameter of 1.5 nm or more is used. A packed collection column, a heating device for heating the collection column, 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 the electrical resistance value of the sensor element, air collected from the space to be measured as a sample gas, and after flowing through the collection column at a predetermined flow rate for a predetermined time, And adjusting the ambient temperature to 250 to 450 ° C., lowering the flow rate of the air below the flow rate, allowing the sensor element to flow through the collection column, and the electric resistance value of the sensor element And detecting the dialkyl phthalate of the sample gas measured by.

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 sample gas to each sensor element, and measure the electric resistance value of each sensor element.

  According to the present invention, even if the amount of dialkyl phthalate in the sample gas is extremely small, the presence / absence of dialkyl phthalate can be accurately detected in a short time with a simple apparatus configuration.

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 of a sensor fixed base.

  The gas sensor of the present invention is a gas sensor for detecting dialkyl phthalate in gas. A first embodiment of the gas sensor of the present invention will be described with reference to FIG.

  The gas sensor shown in FIG. 1 mainly includes a collection column 1, a heating device 2 that heats the collection column 1, and a sensor body 3. That is, the pipe L1 extending from the sample gas supply source is connected to the gas inlet of the collection column 1. A heating device 2 is disposed in the collection column 1. A sensor main body 3 is disposed downstream of the collection column 1 and is connected to each other via a pipe L2. A pipe L3 in which an intake pump P1 is interposed is connected to the gas exhaust port of the sensor body 3.

The collection column 1 is filled with mesoporous silica. Mesoporous silica is porous silica made of SiO ₂ and having substantially uniform and regular pores (mesopores). Mesoporous silica is made of SiO ₂ and has excellent heat resistance, and is hardly thermally decomposed even when heated in oxygen. However, when inorganic impurities, organic impurities, and the like are included, the heat resistance tends to be impaired by these impurities. For this reason, in the present invention, mesoporous silica having a composition substantially consisting only of SiO _{2 and} having an impurity content other than moisture of 1% or less is preferably used.

The specific surface area of the mesoporous silica is at 300 meters ² / g or more, preferably 800 m ² / g or more, more preferably from 950~1300m ² / g. Moreover, an average pore diameter is 1.5 nm or more, Preferably it is 2 nm or more, More preferably, it is 2.5-10 nm. In order to adsorb volatile organic compounds efficiently, it is preferable that the specific surface area is large and the average pore diameter is large, but in general, the average pore diameter of materials other than mesoporous silica decreases as the specific surface area increases. Therefore, it is preferable to use mesoporous silica. If the specific surface area of mesoporous silica is 300 m ² / g or more and the average pore diameter is 1.5 nm or more, volatile organic compounds such as dialkyl phthalate can be efficiently adsorbed.

  In the present invention, the specific surface area of mesoporous silica means a value calculated by a BET (Brunauer-Emmett-Teller) method from a nitrogen adsorption isotherm at 77K. The average pore diameter of mesoporous silica means a value calculated by the BJH (Barrett-Joyner-Halenda) method from a nitrogen adsorption isotherm at 77K.

  Such a method for producing mesoporous silica is publicly known, and for example, those shown in the following documents can be preferably used. For example, “MCM-41” (C. K. Kresge, M. E. Leonowicz, W. J. Roth, J. C. Vartuli, J. S. Beck, Nature, Vol. 359, 710 (1992)), “MCM-48” (US Pat. No. 6,096,288), “FSM-16” (S. Inagaki, A. Koiwai, N. Suzuki, Y. Fukushima, K. Kuroda, Bull. Chem. Soc. Jpn., Vol. 69, 1449 (1996)), “SBA-15” (D. Zhao, J. Feng, Q. Huo, N. Melosh, GH Fredrickson, BF Chmelka, GD Stucky, G. H .; D. Science, vol. 279, 548 (1998)).

_{Incidentally,} such _{Al 2 O 3, TiO 2,} ZrO 2, in the case of the metal oxide other than SiO _2, because it tends to strongly adsorb the volatile organic compound, these metal oxides than 450 ° C. Even when heated, the volatile organic compound adsorbed on the metal oxide was not completely desorbed and easily remained in the metal oxide. Further, since it is necessary to increase the desorption temperature, the dialkyl phthalate may be oxidatively decomposed by heating during desorption. For this reason, metal oxides other than SiO ₂ could not concentrate dialkyl phthalate efficiently. On the other hand, in the case of mesoporous silica, since the adsorption power of dialkyl phthalate is moderate, it is excellent in absorption and release of dialkyl phthalate, and dialkyl phthalate adsorbed at a relatively low temperature can be almost completely eliminated. Dialkyl can be concentrated efficiently.

  The heating device 2 provided in the collection column 1 is activated when the gas component to be detected such as dialkyl phthalate adsorbed on the mesoporous silica in the collection column 1 is desorbed from the mesoporous silica. . The heating device 2 is not particularly limited as long as it can heat the collection column 1. For example, a hot air heater, an electric heater, etc. are mentioned.

  The sensor main body 3 in this embodiment includes a sensor element 4, a detector 5 that measures the electric resistance value of the sensor element 4, and a heater 6 that heats the sensor element 4.

The sensor element 4 is obtained by solidifying fine particles of a metal oxide 11 mainly composed of SnO _2, and a silica mask 12 having predetermined pores 12 a is formed on the fine particle surface of each metal oxide 11. Is formed.

The metal oxide 11 may be composed of SnO ₂ alone or may be formed by supporting a catalyst 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 pores 12a formed in the silica mask 12 have dimensions that allow a side chain portion extending from the benzene ring of the dialkyl phthalate to pass through. If the pores 12a are too small, the detection sensitivity of dialkyl phthalate may not be sufficient. Moreover, when the pore 12a is too large, organic substances other than dialkyl phthalate may be detected, and dialkyl phthalate may not be selectively detected. The size of the pores 12a is preferably 0.25 to 1.5 nm, and more preferably 0.4 to 1.2 nm.

  The sensor element 4 can be manufactured based on, for example, the method described in paragraph numbers 0025 to 0031 of JP2010-54205A. That is, first, a template-forming compound selected from aliphatic aldehydes, aliphatic carboxylic acids, aromatic aldehydes and aromatic carboxylic acids is adsorbed onto the surface of the metal oxide with an adsorption density less than a monomolecular layer. Next, silica precursor molecules are vapor-deposited, and the vapor-deposited silica precursor molecules are hydrolyzed to silica. Thereafter, the template forming compound is removed. 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.

  As the template-forming compound, those having a maximum width in the direction parallel to the surface of the metal oxide 11 in the state of being adsorbed on the surface are preferably 0.5 to 1.2 nm. Benzaldehyde, benzoic acid, 1- Examples thereof include naphthaldehyde and 1-naphthalenecarboxylic acid. Of these, 1-naphthaldehyde or 1-naphthalenecarboxylic acid is particularly preferable.

  When benzaldehyde is used as a template forming compound, the lateral width of the benzene ring portion of benzaldehyde is as follows: the CC bond distance in the benzene ring is 0.14 nm, the CH bond distance is 0.11 nm, and the van der Waals radius of the 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, it is predicted that pores having a maximum width of approximately 0.71 nm in the direction parallel to the surface of the metal oxide 11 are formed in the silica mask. 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 the benzene ring cannot pass through the pore. Moreover, since the side chain (methyl group) of toluene is short, toluene hardly reaches the surface of the metal oxide 11. On the other hand, since the side chain portion of dialkyl phthalate is relatively long and low in volume, it reaches the surface of the metal oxide 11 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, acetone molecules cannot pass through the pores of the silica mask and hardly reach the surface of the metal oxide 11.

  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 the 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 11 are expected to be formed in the silica mask.

  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 11 preferentially, and dialkyl phthalate can be selectively detected by observing a change in the electric resistance value.

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

  First, air sampled from the space to be measured is introduced into the collection column 1 as a sample gas, and volatile organic compounds such as dialkyl phthalate in the sample gas are adsorbed to the mesoporous silica filled in the collection column 1. (Adsorption process).

  In this adsorption step, the sample gas is introduced into the collection column 1 at an atmospheric temperature in the collection column 1 of preferably 200 ° C. or lower, more preferably 20 to 100 ° C. When the ambient temperature in the collection column 1 is within the above temperature range, almost the entire amount of volatile organic compounds such as dialkyl phthalate contained in the sample gas is adsorbed on the mesoporous silica. During the adsorption process, the gas discharged from the collection column 1 passes through the sensor body 3 and is exhausted out of the system through the pipe L3. However, a flow path switching valve or the like may be provided in the pipe L2, and the exhausted air may be exhausted outside the system without passing through the sensor body 3.

In the adsorption process, it is preferable to flow the sample gas as much as possible. Even if the dialkyl phthalate concentration in the sample gas is low, by flowing a large amount of the sample gas, the dialkyl phthalate in the sample gas is adsorbed by the scavenger, so that the substantial sensitivity can be increased. it can. To explain with a specific example, it is preferable to flow the sample gas at a flow rate of 20 to 50 cm ³ / min per 1 mg of the collecting agent. When the flow rate of the sample gas exceeds 50 cm ³ / min per 1 mg of the collecting agent, the dialkyl phthalate in the sample gas may pass through without being adsorbed by the collecting agent.

  Thus, after adsorbing volatile organic compounds such as dialkyl phthalate in the sample gas to mesoporous silica, the heating device 2 is operated to heat the collection column 1 (desorption step), and the sample The gas is introduced into the collection column 1, passes through the sensor body 3, and is exhausted out of the system from the pipe L <b> 3. That is, in the present invention, the sample gas, that is, air can be used as the desorption gas. In this case, air particles may be passed through a filter or the like to remove floating particles and the like and used as a desorption gas.

  In the desorption step, the collection column 1 is heated so that the ambient temperature is 250 to 450 ° C., preferably 300 to 400 ° C., more preferably 325 to 375 ° C. When the atmospheric temperature of the collection column 1 in the desorption step is less than 250 ° C., the volatile organic compound adsorbed by the mesoporous silica may not be completely desorbed. If it exceeds 450 ° C, the dialkyl phthalate may be oxidatively decomposed.

In the desorption process, the flow rate of the sample gas is preferably small. By reducing the flow rate of the sample gas during the desorption step, the concentration of the dialkyl phthalate that is the target substance can be further increased. To explain with a specific example, it is preferable to flow the sample gas at a flow rate of 1 to 20 cm ³ / min per 1 mg of the collecting agent. When the flow rate of the sample gas is less than 1 cm ³ / min per 1 mg of the trapping agent, the dialkyl phthalate detached from the trapping agent may not be supplied to the sensor body 3.

  The gas component desorbed from the mesoporous silica is introduced into the sensor body 3 together with the desorbed gas (sample gas), the electric resistance value of the sensor element 4 is measured by the detector 5, and the change in the electric resistance value causes the sample gas. Detects dialkyl phthalates in it.

  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 detecting dialkyl phthalate, the temperature of the sensor element 4 is preferably 250 to 450 ° C, more preferably 300 to 400 ° C. If the temperature of the sensor element 4 is within the above range, good sensitivity can be obtained.

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. For this reason, since the gas components other than the dialkyl phthalate are prevented from contacting the surface of the metal oxide 11 by the silica mask 12, the electric resistance value of the sensor element 4 is less than the gas components other than the alkyl phthalate. There is almost no response, and even in the presence of toluene, acetone, etc., dialkyl phthalate in the gas can be selectively detected.

  In the present invention, since the gas component (dialkyl phthalate) to be detected is concentrated in the collection column 1 and supplied to the sensor body 3, the dialkyl phthalate concentration in the sample gas is very low. Therefore, it is possible to detect with high sensitivity, and it is possible to detect dialkyl phthalate on the order of ppb.

  Moreover, since the mesoporous silica packed in the collection column 1 is excellent in heat resistance, it is difficult to burn even when heated in the presence of oxygen. Therefore, in the desorption process, it is not necessary to use an inert gas as a desorption gas as in the prior art, and air as a sample gas can be used as a desorption gas. Therefore, it is necessary to prepare an inert gas cylinder separately. The operating cost can be reduced. In addition, when switching between the adsorption process and the desorption process, it is not always necessary to switch the flow path, and it is only necessary to control the operation of the heating device 2, so that the apparatus configuration is simplified.

A second embodiment of the gas sensor of the present invention will be described with reference to FIG. In this embodiment, as the sensor body 3 ', the surface of the metal oxide 11 comprising a SnO ₂ as a main component, a first sensor element 4a silica mask 12 having a predetermined pores, a SnO ₂ A second sensor element 4b having no silica mask is provided on the surface of the metal oxide 21 as a main component. Each sensor element 4a, 4b is supported on a respective substrate. And as for the 1st sensor element 4a and the 2nd sensor element 4b, detector 5a, 5b which measures each electric resistance value is connected by the conducting wire.

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 4a and the sensitivity of the second sensor element 4b ([sensitivity of the first sensor element 4a] / [second sensor element 4b). 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), where R _{a is} the resistance before injection of the sample gas and R is the resistance after injection, is used.

  The second sensor element 4b 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 4a 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.

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

[Manufacture of sensor elements]
(Production Example 1-1)
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.
3 mg of the 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. 3 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 material. The dimensions of each part of the fixed base 31 are as illustrated.
The sensor element material was fired 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 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 Co., Ltd. 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. Then, it baked in oxygen stream (atmospheric pressure, 50 cm < ³ > min <^-1> ) for 1.5 hours at 673K, and the sensor element of manufacture example 1-1 was obtained.
Silica modified SnO ₂ powder on the obtained sensor element, the surface of the SnO _2, pores benzaldehyde and mold, surface area per 1 nm ^2, were approximately 0.5 number generation. The lateral width of the benzene ring portion of benzaldehyde 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.

(Production Example 1-2)
Pd (NH ₃ ) ₄ Cl ₂ .H ₂ O (Aldrich) 0.121 g was diluted with ion-exchanged water to 50 cm ^3, and 2 cm ³ of the obtained solution was SnO ₂ prepared in Production Example 1-1. It was mixed with 1 g of powder, 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 .
3 mg of the 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, the suspension slurry is applied to a fixed base 31 made of an alumina plate shown in FIG. 3 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 material. The dimensions of each part of the fixed base 31 are as illustrated.
The sensor element material was fired 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, 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. Then, it baked for 1.5 hours in oxygen flow (atmospheric pressure, 50 cm < ³ > min <^-1> ) at 673K, and the sensor element of manufacture example 1-2 was obtained.
The resulting silica-modified Pd / SnO ₂ powder on the sensor element produced approximately 0.5 pores with a surface area of 1-naphthaldehyde per 1 nm ^{2 on} the surface of a metal oxide composed of SnO _2. It had been. 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.

(Production Example 1-3)
The sensor element material prepared in Production Example 1-2 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 Co., Ltd. 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. Then, it baked for 1.5 hours in oxygen flow (atmospheric pressure, 50 cm < ³ > min <^-1> ) at 673K, and the sensor element of manufacture example 1-3 was obtained.
Silica modified SnO ₂ powder on the obtained sensor element, the surface of the SnO _2, pores benzaldehyde and mold, surface area per 1 nm ^2, were approximately 0.5 number generation.

[Production of mesoporous silica]
(Production Example 2)
Mesoporous silica was prepared based on the method described in “K. Okumura, K. Nishigaki, M. Niwa, Microporous and Mesoporous Materials vol. 44-45 (2001) 509”.
That is, 34.8 g of colloidal silica HS-40 (manufactured and sold by Sigma-Aldrich) was dissolved in 169.6 g of water, 0.669 g of 28% aqueous ammonia, 4.68 g of sodium hydroxide, 13.12 g of Tetradecyltrimethylammonium bromide was sequentially added and stirred. The mixture was heated in a sealed container at 100 ° C. for 1 day. While cooling, the pH of the mixture was measured while stirring, and a 30 wt% aqueous acetic acid solution was added dropwise until a pH of 11 was reached. This operation of heating at 100 ° C. for 1 day and adding an aqueous acetic acid solution to keep the pH at 11 was repeated 5 times. The solid produced in the mixture was filtered, washed with ion exchange water, and calcined at 540 ° C. for 4 h in a flow of oxygen-nitrogen (molar ratio 1: 1, total flow rate 60 cm ³ / min) to obtain mesoporous silica.
The specific surface area and average pore diameter of the mesoporous silica thus obtained were measured by a BET method from a nitrogen adsorption isotherm at 77 K. The specific surface area was 1100 m ² / g and the average pore diameter was 3 nm.

[Detection test for dioctyl phthalate]
Example 1
Dioctyl phthalate was detected using the gas sensor shown in FIG. In addition, as the sensor element 4, the sensor element of Production Example 1-2 was used. As the collection column 1, a stainless steel tube having an inner diameter of 4 mm and a length of 4 cm and 5 mg of the mesoporous silica (specific surface area 1100 m ² / g, average pore diameter 3 nm) of Production Example 2 was used. Moreover, air containing 0.09 to 7.5 ppb of dioctyl phthalate was used as the sample gas.
The sample gas was introduced from the pipe L1 and circulated for 40 minutes at a flow rate of 250 cm ³ / min. During this period, the ambient temperature in the collection column 1 was about 75 ° C.
Next, the flow rate of the sample gas was set to 100 cm ³ / min, the heating device 2 was operated, the collection column 1 was heated to 420 ° C., and the response of the sensor element 4 was examined. The results are shown in Table 1. As shown in Table 1 below, it was possible to detect dioctyl phthalate at the ppb level.

(Comparative Example 1)
In the same manner as in Example 1, except that Al ₂ O ₃ (average particle size 0.1 μm, specific surface area 150 m ² / g, average pore size 35 nm) was used instead of mesoporous silica, When dioctyl acid was detected, no response of the sensor element was observed, and dioctyl phthalate could not be detected. Since dioctyl phthalate has been firmly adsorbed on Al ₂ O _3, during the desorption process, it can be inferred that dioctyl phthalate is because it could not desorbed from the Al ₂ O _3.

(Comparative Example 2)
In Example 1, dioctyl phthalate was detected in the same manner as in Example 1 except that ZrO ₂ (average particle size 0.2 μm, specific surface area 30 m ² / g) was used instead of mesoporous silica. However, no response of the sensor element was observed, and dioctyl phthalate could not be detected. Since dioctyl phthalate has been firmly adsorbed on ZrO _2, at the time of desorption process, dioctyl phthalate can be inferred that this is because that could not be eliminated from the ZrO _2.

(Comparative Example 3)
In Example 1, dioctyl phthalate was detected in the same manner as in Example 1 except that TiO ₂ (average particle size 0.2 μm, specific surface area 40 m ² / g) was used instead of mesoporous silica. However, no response of the sensor element was observed, and dioctyl phthalate could not be detected. Since dioctyl phthalate has been firmly adsorbed on TiO _2, during the desorption step, dioctyl phthalate can be inferred that this is because that could not be desorbed from the TiO _2.

1: Collection column 2: Heating device 3: Sensor body 4: Sensor element 4a: First sensor element 4b: Second sensor elements 5, 5a, 5b: Detector 6: Heater 11, 21: Metal oxide 12: Silica mask 12a: Fine pores L1 to L3: Piping P1: Intake pump

Claims (7)

A gas sensor for detecting dialkyl phthalates in air,
A collection column packed with mesoporous silica having a specific surface area of 300 m ² / g or more and an average pore diameter of 1.5 nm or more;
A heating device for heating the collection column;
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;
Air sampled from the space to be measured as sample gas, and circulated through the collection column, and air flow means for circulating the air as desorption gas through the collection column and the sensor element. A gas sensor characterized by comprising:   After circulating the air through the collection column at a predetermined flow rate for a predetermined time, the heating means is operated to adjust the atmospheric temperature in the collection column to 250 to 450 ° C., and the flow rate of the air is The gas sensor according to claim 1, wherein the gas sensor is configured to flow through the collection column through the collection column at a lower flow rate. 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 metal oxide is one obtained by supporting a catalyst on SnO _2, gas sensor according to any one of claims 1 to 3.   The sensor element on which the silica mask is formed has a monomolecular layer formed on the surface of the metal oxide with a template forming compound selected from aliphatic aldehydes, aliphatic carboxylic acids, aromatic aldehydes and aromatic carboxylic acids. The silica precursor molecule according to any one of claims 1 to 4, wherein the silica precursor molecules are vapor-deposited after being adsorbed at an adsorption density of less than 1, and hydrolyzed to silica to form a silica mask. Gas sensor. A gas detection method for detecting dialkyl phthalates in air,
A collection column packed with mesoporous silica having a specific surface area of 300 m ² / g or more and an average pore diameter of 1.5 nm or more;
A heating device for heating the collection column;
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;
Using a detector that measures the electrical resistance value of the sensor element,
The air collected from the space to be measured is used as a sample gas, and after flowing through the collection column at a predetermined flow rate for a predetermined time, the atmospheric temperature in the collection column is adjusted to 250 to 450 ° C., and the air The flow rate of the sample gas is reduced to be lower than the flow rate, and is passed through the collection column through the sensor element, and the electric resistance value of the sensor element is measured to detect dialkyl phthalate in the sample gas. Gas detection method. 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 6, wherein a sample gas is supplied to each sensor element, and an electric resistance value of each sensor element is measured.

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