WO2007010617A1

WO2007010617A1 - Adsorption sensor, and instrument and method for measuring gas concentration

Info

Publication number: WO2007010617A1
Application number: PCT/JP2005/013470
Authority: WO
Inventors: Yasuo Yamagishi; Ryozo Takasu
Original assignee: Fujitsu Limited
Priority date: 2005-07-22
Filing date: 2005-07-22
Publication date: 2007-01-25
Also published as: JP4567735B2; JPWO2007010617A1

Abstract

A pair of electrodes are formed on the surface of an oscillation body which oscillates when applied with an AC voltage. The electrodes apply a voltage to the oscillation body. An adsorbent is fixed to the oscillation body. The adsorbent has a photocatalytic function and adsorbs an object to be measured when it comes into contact with the object

Description

Specification

Adsorption type sensor, gas concentration measuring device and measuring method

Technical field

TECHNICAL FIELD [0001] The present invention relates to an adsorption type sensor, a gas concentration measuring apparatus using the same, and a measurement method, and more particularly, a substance to be measured is adsorbed on an adsorbent formed on the surface of the vibrator. The present invention relates to an adsorption-type sensor that utilizes a change in natural frequency of gas, a gas concentration measuring device and a measuring method using the same.

Background art

[0002] As a technique for measuring the concentration of volatile organic compounds and odor molecules in the atmosphere, the change in resonance frequency due to the adsorption of organic matter on a piezoelectric body such as a quartz crystal resonator. An estimation method has been proposed.

[0003] In the method disclosed in Patent Document 1 below, the resonance frequency changing force can be directly read by measuring the relationship between the concentration of the odor substance and the resonance frequency in advance. . The resonance frequency varies depending on the temperature of the piezoelectric body. The temperature of the environment where the piezoelectric body is arranged is measured with a temperature sensor, and the change in the resonance frequency due to the temperature change is corrected.

[0004] In the method disclosed in Patent Document 2, a gas containing a substance to be measured is circulated through a temperature adjusting device to adjust the temperature, and then brought into contact with an adsorption sensor to adjust the concentration of the substance to be measured. taking measurement.

[0005] In addition to drift due to temperature changes that are relatively easy to correct, drift due to humidity and drift due to accumulation-type adsorbate occur in the resonance frequency of the adsorption sensor.

[0006] First, a conventional technique relating to humidity drift will be described. The atmosphere contains a large amount of moisture compared to a trace amount of the substance to be measured. Furthermore, the moisture concentration varies greatly with time and place. Since moisture is adsorbed by most adsorption sensors, it has a significant effect on its resonance frequency. A humidity sensor that positively utilizes the fluctuation of the resonance frequency is disclosed in Patent Document 3 below. This also indicates the magnitude of the effect of humidity on the adsorption sensor.

[0007] Patent Document 4 listed below discloses a volatile organic compound in a clean room for a semiconductor process. An adsorption type sensor for measuring the concentration of is disclosed. In a clean room, the humidity is controlled with high precision, so there is little need to consider the effects of humidity changes. However, in the general atmosphere, fluctuations in the resonance frequency due to changes in the concentration of a small amount of substance to be measured are concealed by large fluctuations due to changes in humidity. Patent Document 5 below discloses an adsorption type sensor that is affected by changes in humidity by making the adsorbent hydrophobic. However, in measuring the concentration of a very small amount of the substance to be measured, the effect of excluding the influence of humidity change is sufficient if the adsorbent is made hydrophobic.

[0008] Next, a conventional technique for reducing the effect of drift due to the storage-type adsorbate will be described. There are a small amount of various molecules in the atmosphere. The mode of adsorption of these molecules is classified into the following three types.

[0009] The first is a mode of reversibly adsorbing and desorbing. For example, the first mode includes adsorption in which the relationship between the concentration and the amount of adsorption is almost 1: 1, such as a low molecular weight organic compound captured in a lipid bilayer membrane.

[0010] Second, the adsorbent force is not easily desorbed even if the concentration of the substance to be adsorbed in the surrounding gas is reduced when adsorbed firmly on the surface of the adsorbent. is there. The second mode is when a highly polar molecule adheres to the metal surface and forms a hydrogen bond with a hydroxyl group on the metal surface.

[0011] The third is an embodiment in which the adsorbent is fixed by a chemical reaction. When gases such as S02, H2S, and HC1 are adsorbed on the metal surface, some of them react with the metal (the metal corrodes) and are fixed semi-permanently. In addition, the silicone molecule becomes non-volatile by polymerization reaction on the adsorption surface. Such an aspect of adsorption is an example of the third aspect.

[0012] In the atmosphere, there are molecules that are irreversibly adsorbed to the adsorbent in the second and third modes. Further, although the degree of irreversible adsorption differs depending on the combination of the adsorbent and the molecule to be adsorbed, the adsorption of the second and third aspects occurs to a greater or lesser extent. For this reason, when the adsorption type sensor is used for a long period of time, the resonance frequency drifts due to the adsorption of the second and third modes. In addition, if adsorption of the substance to be measured proceeds to some extent, further adsorption occurs. In order to avoid these effects, it is necessary to replace the adsorption sensor with a new LV at a specified frequency. [0013] In the invention disclosed in Patent Document 6 below, a photocatalyst is disposed in the vicinity of the adsorption sensor. The adsorbed substance adsorbed on the adsorption sensor is decomposed and removed by radical groups or ozone generated by irradiating the photocatalyst with light. By removing the substance to be adsorbed, the adsorption sensor can be reused. However, the lifetime of oxygen radicals with strong oxidizing power is extremely short. For this reason, many oxygen radicals disappear before reaching the surface of the adsorption sensor. The lifetime of ozone is longer than that of oxygen radicals, but its decomposing ability is extremely small compared to oxygen radicals. For this reason, the ability to decompose an adsorbed substance is small and not practical.

Patent Document 1: Japanese Patent Laid-Open No. 10-90152

Patent Document 2: JP 2000-304672 A

Patent Document 3: Japanese Patent Application Laid-Open No. 2004-226177

Patent Document 4: JP 2002-333394 A

Patent Document 5: Japanese Unexamined Patent Application Publication No. 2004-61391

Patent Document 6: JP 2001-343315 A

Disclosure of the invention

Problems to be solved by the invention

An object of the present invention is to provide an adsorption-type sensor that is not easily affected by humidity or a resonance frequency drift due to irreversible adsorption. Another object of the present invention is to provide a gas concentration measuring apparatus and measuring method using this adsorption type sensor.

Means for solving the problem

According to one aspect of the present invention, a vibrating body that vibrates by application of an alternating voltage, a pair of electrodes that are formed on the surface of the vibrating body and applies a voltage to the vibrating body, and a gas molecule of a substance to be measured When the is touched, an adsorption-type sensor having an adsorbent that adsorbs the substance to be measured and has a photocatalytic function is provided.

According to another aspect of the present invention, a vibrating body that vibrates by application of an alternating voltage, a pair of electrodes that are formed on a surface of the vibrating body and applies a voltage to the vibrating body, and a gas to be measured When the molecule touches, an adsorbent that adsorbs the substance to be measured and has a photocatalytic function, an oscillator that forms a resonance circuit together with the vibrator and the pair of electrodes, and the resonance There is provided a gas concentration measuring device having a frequency counter for measuring a resonance frequency of a circuit, and light irradiation means for irradiating the adsorbent with light having a wavelength at which the adsorbent exhibits a catalytic function.

[0018] According to still another aspect of the present invention, (a) the gas concentration is measured using an adsorption sensor whose resonance frequency changes depending on the amount of the adsorbent adsorbed on the adsorbent having a photocatalytic function. (B) irradiating the adsorbent with light after the resonance frequency of the adsorption sensor reaches a steady state; and (c) irradiating the adsorbent with light. And a step of calculating the gas concentration in the space where the adsorption sensor is arranged based on the change in the resonance frequency of the adsorption sensor.

The invention's effect

[0019] Due to the photocatalytic function of the adsorbent, the adsorbed substance adsorbed on the adsorbent can be decomposed and the adsorbent force desorbed. By calculating the gas concentration based on the change in the resonance frequency when the adsorbent is desorbed, the influence of the resonance frequency drift due to humidity and the resonance frequency drift due to the accumulated adsorbent is avoided or reduced. be able to. Brief Description of Drawings

FIG. 1 is a front view of an adsorption type sensor according to an embodiment.

FIG. 2 is a cross-sectional view of the adsorption sensor according to the example.

FIG. 3 is a schematic view of a gas concentration measuring apparatus according to an embodiment.

FIG. 4 is a schematic diagram of an experimental chamber and a gas introduction system used in an evaluation experiment.

[FIG. 5] FIG. 5A is a graph showing the change over time of the relative humidity of the simulated atmosphere introduced into the experimental chamber, and FIG. 5B is a graph showing the resonance frequency of the adsorption sensor arranged in the experimental chamber. FIG. 5C is a graph showing the time change of the resonance frequency when ultraviolet irradiation is performed from time tl to t4, and FIG. 5D is the time of the resonance frequency at the time of ultraviolet irradiation. It is a diagram which shows the waveform which expanded the change.

[Fig. 6] Fig. 6A is a graph showing an example of the relationship between the resonance frequency increase Δ ίΐ and the concentration of acetonitrile, and Fig. 6Β shows the relationship between the change in the resonance frequency and the concentration of the gas to be measured. It is a graph which shows an example.

[Figure 7] Figure 7 shows the resonance frequency when the adsorption sensor is left in a clean room. Fig. 7B is a graph showing the relationship between the amount of displacement and the number of days elapsed. Fig. 7B shows an evaluation experiment in which an adsorption sensor that has been allowed to stand in a clean room for one week and whose resonance frequency has been recovered by ultraviolet irradiation is placed in an experimental chamber. It is a graph which shows the time change of the resonant frequency when performing this. BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1 is a front view of the adsorption sensor according to the embodiment, and FIG. 2 is a cross-sectional view taken along one-dot chain line A2-A2 in FIG. Electrodes 2A and 2B are formed on both surfaces of a disk-shaped vibrating body 1 made of a piezoelectric material, respectively. As the vibrator 1, for example, an AT-cut crystal is used. The electrodes 2A and 2B are made of, for example, gold, and each has a thickness of, for example, 0.2 μm. The electrodes 2A and 2B can be formed by sputtering, for example.

Adsorbent 3A and 3B forces are formed so as to cover electrodes 2A and 2B, respectively, and are fixed to vibrating body 1. The adsorbents 3A and 3B are made of, for example, titanium apatite, and each has a thickness of 0.2 m. The adsorbents 3A and 3B can be formed, for example, by sputtering using a target obtained by sintering titanium apatite powder. Titanium apatite is one in which one of the calcium atoms of calcium hydroxyapatite (CalO (P04) 6 (OH) 2) is replaced by a titanium atom. The adsorbents 3A and 3B made of titanium apatite have both a function of adsorbing an adsorbed substance such as a volatile organic compound and a photocatalytic function.

[0023] The outer peripheries of the adsorbers 3A and 3B are located between the outer peripheries of the electrodes 2A and 2B and the outer perimeter of the vibrator 1, respectively. Thus, the electrodes 2A and 2B are completely covered with the adsorbents 3A and 3B, respectively. Lead extraction part 2C force The outer side of the electrode 2A extends outward from the outer periphery of the adsorber 3A. The lead extraction part 2C is formed simultaneously with the electrode 2A. Lead wire 4A is connected to the tip of lead outlet 2C. A similar lead extraction portion extends from the other electrode 2B, and the other lead wire 4B is connected to the tip thereof.

When an AC voltage is applied to the electrodes 2 A and 2 B, the vibrating body 1 vibrates due to the piezoelectric phenomenon of the vibrating body 1. When the frequency of the applied AC voltage matches the natural frequency of vibrating body 1, a resonance phenomenon occurs. For example, the thickness of the vibrating body 1 is set so that the resonance frequency is about 25 MHz. Is set.

When this adsorption type sensor is arranged in a gas to be measured, an adsorbed substance such as a volatile organic compound contained in the gas is adsorbed on the adsorbents 3A and 3B. This reduces the resonant frequency.

FIG. 3 shows a schematic diagram of a gas concentration measuring apparatus according to the embodiment. The adsorption type sensor 10 shown in FIGS. 1 and 2 is housed in the sensor holder 11. The sensor holder 11 includes a cylindrical member l ib and a base 11a that closes one end thereof. A number of through holes are formed in the cylindrical member l ib, and gas freely flows between the inside and the outside of the cylindrical member l ib. The adsorption sensor 10 is supported in the sensor holder 11 by fixing the two lead wires 4A and 4B to the base 11a.

[0027] The light irradiation device 12 is configured by the light emitting diode 15, the lens 16, and the optical fibers 17A and 17B. The light emitting diode 15 emits light in the ultraviolet region having a peak wavelength of 380 nm, for example. The output is 85 mW, for example. The light force emitted from the light emitting diode 15 is converged by the lens 16, and the incident end force is also incident on the optical fibers 17A and 17B. The optical fibers 17A and 17B are made of, for example, quartz fiber.

The emission ends of the optical fibers 17A and 17B are supported so as to face the adsorbing bodies 3A and 3B of the adsorption type sensor 10 accommodated in the sensor holder 11, respectively. The ultraviolet rays that are also emitted from the output end forces of the optical fibers 17A and 17B are irradiated to the adsorbents 3A and 3B, respectively. When the adsorbents 3A and 3B are irradiated with ultraviolet rays, the adsorbed substances adsorbed by the adsorbents 3A and 3B are decomposed and desorbed from the adsorbents 3A and 3B by the photocatalytic function. Instead of the light emitting diode 15, a light source that emits light having a wavelength such that the adsorbents 3A and 3B exhibit a photocatalytic function may be employed.

The oscillator 20 is connected to the adsorption sensor 10 and constitutes a resonance circuit together with the adsorption sensor 10. The frequency counter 21 measures the resonance frequency of this resonance circuit and transmits the measurement result to the control device 30. The control device 30 is composed of, for example, a personal computer or a dedicated control device. The control device 30 controls the light emission timing of the light emitting diode 15.

[0030] The characteristics of the gas concentration measuring apparatus according to the above example were evaluated. The following The value result will be described.

FIG. 4 shows a schematic diagram of the experimental chamber and gas introduction system used in the evaluation experiment. Nitrogen gas generated from liquid nitrogen and oxygen gas generated from liquid oxygen oxygen are introduced into branch point 45 through valves VI and V2, respectively, with the flow rate adjusted. By adjusting the flow ratio of nitrogen gas and oxygen gas to 4: 1, a simulated atmosphere can be generated.

[0032] From the branch point 45, the gas flows into three gas flow paths of the first system 51, the second system 52, and the third system 53. The gas flow paths of the first to third systems 51 to 53 are connected to the experimental chamber 40 after merging at the merging point 46. In the first system 51, a bubbling tank 41 filled with a liquid of a volatile organic compound and a valve V3 are inserted. The simulated atmosphere flowing through the first system 51 contains volatile organic compounds and is introduced into the experimental chamber 40. In this evaluation experiment, acetaldehyde was used as a volatile organic compound.

[0033] In the second system 52, a publishing tank 42 filled with pure water and a valve V4 are inserted. The simulated atmosphere flowing through the third system is humidified in the publishing tank 42 to a relative humidity of 90% RH.

[0034] A valve V5 is inserted into the third system 53. The simulated atmosphere flowing through the third system 53 is introduced into the experimental chamber 40 through the valve V5 as it is. The humidity of the simulated atmosphere introduced into the experimental chamber 40 and the concentration of the volatile organic compound are adjusted by adjusting the flow rate of the gas flowing through the first to third systems 51 to 53 by the valves V3 to V5. be able to. The temperature of the simulated atmosphere was 25 ° C.

The sensor holder 11 shown in FIG. 3 is inserted into the experimental chamber 40. In the sensor holder 11, the adsorption type sensor 10 is accommodated. The simulated atmosphere introduced into the experimental chamber 40 flows out through the insertion port for inserting the sensor holder 11.

Next, the procedure of the evaluation experiment will be described. A new adsorption sensor 10 was inserted into the experimental chamber 40.

As shown in FIG. 5A, a simulated atmosphere having a relative humidity of 80% and a cetaldehyde concentration of 1 ppm was introduced into the experimental chamber 40. After 1 hour, the relative humidity of the simulated atmosphere was 20%. The concentration of cetaldehyde remains at lppm.

FIG. 5B shows the resonance frequency of the resonance circuit including the adsorption sensor 10 (hereinafter simply referred to as “resonance frequency”). Call it "number". ) Fluctuations. The resonance frequency fo at the start of measurement depends on the humidity just before that. When a simulated atmosphere with a relative humidity of 80% and a cetaldehyde concentration of 1 ppm is introduced, the resonance frequency decreases because moisture and acetoaldehyde are adsorbed on the adsorbents 3A and 3B of the adsorption sensor 10. After a certain time, the steady state is reached and the resonance frequency becomes constant. When the relative humidity is lowered to 20% after 1 hour has elapsed, a part of the water adsorbed on the adsorbents 3A and 3B is desorbed, and the resonance frequency increases. After a certain time, the resonance frequency becomes constant.

As described above, since the resonance frequency greatly varies depending on the humidity, it is impossible to measure the concentration of acetonitrile.

[0040] Fig. 5C shows the adsorbent when 20 minutes have elapsed (time tl), 40 minutes have elapsed (time t2), 80 minutes have elapsed (time t3), and 100 minutes have elapsed (time t4). This shows the change in resonance frequency when 3A and 3B are irradiated with ultraviolet rays for 3 minutes. Figure 5D shows an enlarged view of the resonance frequency waveform during UV irradiation.

[0041] It can be seen that when the ultraviolet ray is irradiated, the resonance frequency temporarily rises. When UV irradiation is stopped, the resonance frequency returns to the value just before UV irradiation in about 10 minutes.

[0042] The water adsorbed on the adsorbents 3A and 3B is originally an acid oxide and therefore is not decomposed by the photocatalyst. The adsorbed acetaldehyde is probably decomposed into water and carbon dioxide by the photocatalyst and desorbed from the adsorbents 3A and 3B. For this reason, the increase in resonance frequency is thought to be due to the decomposition and elimination of acetoaldehyde.

[0043] The increase in resonance frequency Δ ίΐ was almost the same when the relative humidity of the simulated atmosphere was 80% and 20%. This increase width Δ ίΐ depends on the amount of acetate aldehyde adsorbed on the adsorbents 3 and 3, that is, the concentration of acetate aldehyde.

FIG. 6 (b) shows an example of the relationship between the resonance frequency increase Δ Δ and the concentration of acetoaldehyde. The horizontal axis represents the concentration of acetonitrile, and the vertical axis represents the increase in resonance frequency Δ 共振. When the concentration of cetaldehyde increases, the amount of separation from the adsorbents 3Α and 3Β upon irradiation with ultraviolet light increases, so that the resonance frequency increase Δ ίΐ increases. The graph shown in Fig. 6 (b) can be created by measuring the resonance frequency rise Δ for a gas with a known concentration of cetaldehyde. Resonance frequency rise Δ ίΐ and acetoaldehyde Is stored in the control device 30 shown in FIG.

Next, a method for measuring the concentration of acetate aldehyde according to the example will be described. It is assumed that the relationship between the increase width Δίΐ shown in FIG. 6A and the concentration of acetoaldehyde is known and stored in the control device 30. First, the sensor holder 11 in which the adsorption type sensor 10 shown in FIG. 3 is accommodated is placed in the space where the gas concentration is to be measured. After the resonance frequency reaches a steady state, the adsorption bodies 3 and 3 of the adsorption sensor 10 are irradiated with ultraviolet rays.

[0046] The resonance frequency is measured even during irradiation with ultraviolet rays. When it is detected that the resonance frequency is almost constant, the ultraviolet irradiation is stopped. For example, it can be determined that the resonance frequency has become constant when the rate of change of the resonance frequency (the time derivative of the resonance frequency) is below a certain reference value. If you know the time until the resonance frequency becomes almost constant, set the UV irradiation time to a fixed value.

[0047] The difference Δί between the resonance frequency immediately before the ultraviolet irradiation and the resonance frequency at the end of the ultraviolet irradiation is measured. Based on the measured difference Δίΐ and the relationship shown in Fig. 6Α, the concentration of acetonitrile can be obtained.

[0048] In the above embodiment, the case where the gas to be measured is acetaldehyde has been described, but it is also possible to measure the concentration of other gases that are adsorbed on the adsorbent and decomposed by the photocatalyst. .

[0049] When the substance to be adsorbed is acetaldehyde, the substance produced by the decomposition of the substance to be adsorbed is almost entirely desorbed from the adsorbents 3Α and 3Β. When UV irradiation is stopped, almost the same amount of acetaldehyde as the desorbed acetaldehyde is re-adsorbed on the adsorbents 3Α and 3 吸着. For this reason, the increase width Δί of the resonance frequency at the time of ultraviolet irradiation is equal to the decrease width Δ f 2 of the resonance frequency after the ultraviolet irradiation is stopped. Therefore, the gas concentration can also be obtained by measuring the decrease width Δ f 2 of the resonance frequency.

[0050] When a non-volatile substance such as S02 is generated after the substance to be adsorbed is decomposed by the action of the photocatalyst, the non-volatile substance remains on the surfaces of the adsorbents 3A and 3B even after ultraviolet irradiation. Remains. Since the adsorption conditions are different before and after UV irradiation, the increase width Δί Δ of the resonance frequency is not equal to the decrease width Δ f 2. In this case, instead of the graph of FIG. 6A, it is necessary to obtain in advance the relationship between the resonance frequency drop Δf 2 and the concentration of the adsorbed substance. There is a point.

[0051] It is also possible to obtain the concentration of the gas to be measured based on the slope of the change in the resonance frequency after the ultraviolet irradiation is stopped. In this case, instead of the graph of FIG. 6A, as shown in FIG. 6B, the relationship between the gradient of the change in the resonance frequency and the concentration of the measurement target gas may be measured in advance. In the method of measuring the slope of the change in resonance frequency, there is no need to wait for the measurement until the resonance frequency reaches a steady state. For this reason, the concentration of the gas to be measured can be calculated more quickly.

[0052] In measuring the resonance frequency, a moving average of about several seconds to several minutes is generally measured in order to remove extremely short and periodic noise components. In the above embodiment, when the inclination of the change in the resonance frequency is obtained, if the moving average is made too long, the change cannot be detected. In order to detect a sudden change in resonance frequency, it is preferable to set the moving average time width to several seconds.

Next, with reference to FIG. 7A and FIG. 7B, the influence of the resonance frequency drift due to the storage-type adsorbent will be described.

FIG. 7A shows a change in resonance frequency when the adsorption sensor according to the above example is left in a clean room with a humidity of 50% for one week. The initial resonant frequency fO is about 25 MHz. It can be seen that the resonant frequency decreases as the number of days elapses, and decreases by about 1200 Hz in one week. This is because a small amount of contaminants present in the clean room are adsorbed by the adsorption sensor.

[0055] When the adsorbents 3A and 3B of the adsorptive sensor left in a clean room for 1 week were irradiated with ultraviolet light for 20 minutes, the resonance frequency was recovered to a frequency f0 that was approximately 300 Hz lower than the initial resonance frequency. This decrease in resonance frequency of 300 Hz is considered to be because non-volatile oxides derived from inorganic gas remain on the surfaces of the adsorbents 3A and 3B.

[0056] FIG. 7B shows the result of the same experiment as the evaluation experiment shown in FIG. 5C, using the adsorption sensor whose resonance frequency is recovered to fO ′. Comparing the graph in Fig. 7B with the graph in Fig. 5C, the initial resonant frequency is reduced from fO to fO ', and it is shifted downward by fO – fO' as a whole. The increase in resonance frequency Δ ί1 during UV irradiation, the decrease in resonance frequency Δ F 2 after UV irradiation is stopped, and the slope of the change in resonance frequency are shown in Fig. 5C and Fig. 7B. The case was almost the same. In other words, the resonance frequency rise ΔΔ1, the resonance frequency fall ΔΔ2, and the gradient of the change in the resonance frequency, which are directly measured in the above-described embodiment, are not affected by the resonance frequency drift due to the storage adsorbed substance.

[0057] Therefore, it is possible to eliminate the influence of the resonance frequency drift due to the storage substance to be adsorbed and to measure the concentration of the measurement target gas.

[0058] Although the present invention has been described with reference to the embodiments, the present invention is not limited thereto. It will be apparent to those skilled in the art that various modifications, improvements, combinations, and the like can be made.

Claims

The scope of the claims

[1] a vibrating body that vibrates by application of an alternating voltage;

A pair of electrodes formed on the surface of the vibrating body, for applying a voltage to the vibrating body; and an adsorbing body that adsorbs the measured substance when the gas molecule of the measured substance is touched and has a photocatalytic function;

An adsorption type sensor.

[2] The adsorption sensor according to [1], wherein the adsorbent contains titanium apatite.

[3] The adsorption sensor according to [1], wherein the vibrator is an AT-cut quartz crystal unit

[4] a vibrating body that vibrates by application of an alternating voltage;

A pair of electrodes that are formed on the surface of the vibrating body and apply a voltage to the vibrating body; and an adsorbing body that adsorbs the measured substance and has a photocatalytic function when a gas molecule of the measured substance is touched;

An oscillator constituting a resonance circuit together with the vibrating body and the pair of electrodes; a frequency counter for measuring a resonance frequency of the resonance circuit;

A light irradiation means for irradiating the adsorbent with light having a wavelength at which the adsorbent exhibits a catalytic function;

A gas concentration measuring device.

[5] The light irradiation device is controlled to irradiate the adsorbent with light, and has a control device that reads the resonance frequency measured by the frequency counter, and the control device applies to the adsorbent. 5. The gas concentration measuring apparatus according to claim 4, wherein a gas concentration in an environment where the adsorbent is disposed is calculated based on a change in the resonance frequency due to light irradiation.

[6] The control device may be configured such that a difference between the resonance frequency at the end of light irradiation on the adsorbent and the resonance frequency immediately before the light irradiation, or the resonance frequency at the end of light irradiation on the adsorbent. 6. The gas concentration measuring device according to claim 5, wherein the gas concentration is calculated based on a difference between the resonance frequency at the time when the resonance frequency reaches a steady state after light irradiation.

[7] The control device may change the resonance frequency of the force immediately after the light irradiation to the adsorbent is completed. 6. The gas concentration measuring apparatus according to claim 5, wherein the gas concentration is calculated based on a rate.

[8] The control device may stop the light irradiation to the adsorbent when it detects that the rate of change of the resonance frequency is equal to or lower than a reference value after the light irradiation to the adsorbent is started. The gas concentration measuring device described in 1.

[9] (a) a step of arranging an adsorption type sensor whose resonance frequency changes depending on the amount of the adsorbent adsorbed on the adsorbent having a photocatalytic function in a space where the gas concentration is to be measured;

(b) irradiating the adsorbent with light after the resonance frequency of the adsorption sensor has reached a steady state;

(c) calculating a gas concentration in a space in which the adsorption type sensor is arranged based on a change in a resonance frequency of the adsorption type sensor due to light irradiation on the adsorbent.

[10] In the step c, the difference between the resonance frequency at the time when the light irradiation to the adsorbent ends and the resonance frequency immediately before the light irradiation, or the resonance frequency at the time when the light irradiation to the adsorbent ends 10. The gas concentration measuring method according to claim 9, wherein the gas concentration is calculated based on a difference from the resonance frequency when the resonance frequency reaches a steady state after light irradiation.

11. The gas concentration measuring method according to claim 9, wherein, in the step c, the gas concentration is calculated based on a change rate of the resonance frequency immediately after completion of light irradiation to the adsorbent.

[12] The request includes a step of stopping the light irradiation to the adsorbent when detecting that the change rate of the resonance frequency has become a reference value or less after the light irradiation to the adsorbent is started. Item 10. The gas concentration measurement method according to Item 9.