JPH01116446A - Sensor for reducing substance - Google Patents

Abstract

PURPOSE:To realize a sensor for a reducing organic substance usable for a long time repeatedly at a normal temperature by using a titania-carrying porous substance. CONSTITUTION:A sensor for a reducing organic substance is used having titania (TiO2) supported on a porous body. When irradiated with light, TiO2 changes to TiO with oxygen being deprived thereof and turn to black from white. In this case, with the presence of a reducing substance, active oxygen generated by this reaction is bonded to the reducing substance to promote the reaction. As a result, the degree of coloring varies according to the density of the reducing substance to allow measurement of the amount of the reducing substance depending on the degree of the coloring. When the causative reducing substance is gone after the coloring, TiO changes to TiO2 being bonded to oxygen or the like in the air and the color returns to original white, thereby enabling the use of the titania for the subsequent measurement again.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a sensor that can detect the amount of reducing substances in gas or liquid, especially reducing organic substances with relatively low molecular weight, even at room temperature. Regarding.

[Prior Art] Conventionally, semiconductor sensors, especially S n02, have been used as sensors for detecting gases such as alcohol, hydrogen gas, and hydrocarbons.
Sensors are known. With these sensors,
This method utilizes the fact that the electrical chamber conductivity of the semiconductor changes when a gas comes into contact with the surface of the semiconductor. These sensors are normally kept at a high temperature of 300 to 500° C. in order to increase detection sensitivity. For this reason, a heater is placed near the detection part.

[Problems to be solved by the invention] However, such conventional semiconductor sensors have disadvantages in that they must be used at high temperatures, which increases heating costs and requires safety measures such as fire prevention. . Furthermore, as sintering of the semiconductor particles progresses during use, the detection sensitivity decreases significantly over time, resulting in the inconvenience of having to be replaced every few years.

The present invention solves the above conventional problems and provides a sensor for reducing organic substances that can be used repeatedly at room temperature for a long period of time.

[Means for solving the problems] The reducing substance sensor of the present invention includes titania (
It supports titanium dioxide (Ti02).

In general, when TiO2 is irradiated with light of about 420 nm or less, a reaction such as (white) (black) occurs, whereby oxygen is absorbed from TiO2 and becomes TiO, turning it black.

In this case, the presence of a reducing substance, particularly a relatively low-molecular-weight luminescent organic substance, promotes the reaction because the active oxygen generated by the reaction combines with the reducing substance.

Therefore, the degree of coloring changes depending on the concentration of the reducing substance, so the amount of reducing substance can be measured by quantifying the degree of coloring by the change in light intensity when a reference light is irradiated. .

After coloring, when the reducing substance that causes it disappears,
By recombining with oxygen in the air or dissolved oxygen in the liquid, Ti
O becomes TiO2, quickly fades, and becomes usable again for the next measurement.

By the way, the above-mentioned coloring is very weak in a single-layer TiO2 thin film, and for example, in a glass plate coated with a TiO2 thin film with a thickness of 500 people, the coloring is not visible to the naked eye. However, as in the present invention, by supporting TiO2 on a porous body, the contact area between TiO2 and a reducing substance, especially a reducing organic substance in the gas phase or liquid phase, increases, and as a result, the visual appearance degree increases. Furthermore, since the optical path length of the TiO2 layer through which visible light passes becomes large, the coloring of TiO2 becomes clear.

The configuration of the present invention will be explained in more detail below.

The reducing substance sensor of the present invention has titania supported on a porous body, and specific examples of the supported form of titania include the following.

■ Impregnate the porous body with titania fine particles.

■ Form a coating film of titania thin film on the surface of the porous body.

etc.

The particle size and impregnation amount of the titania fine particles to be impregnated in (1) above, and the thickness of the titania thin film in (2) are determining factors such as the sensitivity of the sensor, so they are determined as appropriate depending on the purpose of use, required sensitivity, etc., but in general The particle size of the titania fine particles is about 1ooA to 0.5 μm, the amount of impregnation is about 0.005 to 5% by volume of the pore volume of the porous body, and the thickness of the titania thin film is appropriately thin in the range of about 300 to 2000A. It is windowed.

On the other hand, the porous body supporting titania is (1) a woven or non-woven fabric made of inorganic fibers, especially glass fibers. (Woven or non-woven fabrics made of organic 1M fibers or filter paper can also be used, but inorganic fibers are preferred because they are highly stable and have a long life.) ■ Sintering of glass particles with a particle size of 1 to 200 μm. body. In this case, for example, a glass sintered body commercially available as a glass filter can be used.

(2) Porous glass having pores of 0.5 to 10 μm in diameter.

etc.

In the present invention, in order to obtain sufficient coloring, especially when used as a sensor in the measurement method described below,
The pore diameter of the porous body is about 0.5 to 200 μm, especially 1 to
It is desirable that the thickness be in the range of 100 μm. Moreover, it is preferable that the porosity of the porous body is about 10 to 80%.

As a method for impregnating these porous bodies with titania fine particles, titania (anatase) sol (-sized particle diameter:
There is a method in which a porous body is immersed in tooA, 26% TiO, Tamoto Kagaku@), the pressure is reduced to impregnate the sol into the pores of the porous body, and then the sol is dried. Instead of titania sol, an isopropyl alcohol suspension of titania (anatase) fine particles (diameter 300A, Sumitomo Cement ■) may be used. The above impregnation operation may be repeated several times.

In addition, as a method for forming a titania thin film on the surface of a porous body, tetraisopropyl orthotitanate (Ti[(
CH3)2 CHO4) or titanium tetrachloride (T i
C20) alcohol solution or acetylacetone titanium (T i 0(CH2COCH2COCH3)
2) of N,N dimethylformamide (HCON (C
H3) 2) After immersing the porous body in the solution and adhering the titanium compound inside the porous body, after drying the porous body at 400 to 600°C
There is a method in which a TiO2 thin film is produced by firing in air at a low temperature.

In the present invention, titania preferably has an anatase crystal structure, but titania having other crystal structures such as rutile or titanite may also be used.

Next, a method for detecting and measuring reducing substances using the sensor of the present invention will be described.

First, the sensor of the present invention is placed in a gaseous or liquid phase to be measured in which a reducing substance is present, and the sensor in the phase to be measured is irradiated with light having a wavelength of about 420 nm or less from an appropriate position. Since the TiO2 supported on the sensor becomes black TiO when irradiated with light of the above wavelength in the presence of a reducing substance, the presence or absence of the reducing substance can be detected by the color change of the sensor.

In order to quantify reducing substances, a discolored sensor is taken out from within the phase to be measured, irradiated with reference light of a wavelength of approximately 450 nm or more, and changes in the amount of reflected or transmitted light relative to the amount of incident light at the reference target are measured. By measuring, the degree of coloring, that is, the amount of reducing substances can be determined. especially,
In this case, by creating a calibration curve in advance, it becomes possible to extremely easily determine the amount of reducing substance with respect to a change in the amount of light using this calibration curve as a reference. Note that the S/N ratio may be increased by modulating the reference destination with a chopper or the like and detecting it with a lock-in amplifier.

When the sensor of the present invention is placed in an oxidizing state after being used for measurement, TiO combines with oxygen in the gas or liquid phase again and returns to TiO2, quickly fading and being reused for the next measurement. It becomes possible.

Such a sensor of the present invention can be used to detect reducing substances in the gas phase or liquid phase, particularly reducing liquids such as alcohols such as methanol and ethanol, and reducing gases such as carbon oxide, methane, and propane. It is extremely effective in detecting various low molecular weight reducing organic substances.

[Example] Examples will be described below.

Example 1 Glass filter No. 3 (opening 20 to 30 μm, diameter 3
0 mm) and tetraisopropyl orthotitanate (Ti
It was immersed in a 10% ethyl alcohol solution of [(CH3)2CHO]4), dried, and then heated at 450°C in an electric furnace.
, baked for 30 minutes.

The glass filter plate used for measuring reducing substances was placed in a Pyrex glass beaker containing an aqueous methanol solution, and an ultra-high pressure mercury lamp (
400 W) at a distance of 10 cm for 5 minutes, and then taken out into the air to measure the degree of coloration. This operation was performed on methanol aqueous solutions of various concentrations. Note that the measurement light used was radiation from a 12V, 20W halogen lamp. A luminometer was used as a measuring device, and the degree of coloring was expressed as optical density.

The results are shown in Figure 1, No. 1. In addition, the horizontal axis of FIG. 1 shows the methanol concentration (volume %), and the vertical axis shows the optical density of coloring.

Example 2 Similar measurements were carried out in Example 1 using an ethanol aqueous solution as the phase to be measured. The results are shown in Figure 1, No. 2.

No. 1 in Figure 1. From No. 2, it is clear that the optical density increases as the methanol or ethanol concentration increases.

Example 3 1 ヱ 2 ± 11 Glass filter No. 4 (opening 5-10 μm.

Ti [(CHs) 2CH
O] 4 was immersed in a 10% ethyl alcohol solution, dried, and then baked at 450° C. for 30 minutes in an electric furnace.

lii raw! The glass filter plates described above were placed in aqueous ethanol solutions of various concentrations, and the same measurements as in Example 1 were performed.

The results are shown in FIG. 1, No. 003.

In this case, it is clear that a linear proportional relationship between concentration and optical density is obtained in the range from ethanol concentration o,ooot% (ippm) to 100%.

In this example, the sensor used to measure 100% ethyl alcohol was left in the air, and the fading change over time was investigated by measuring optical density. The results are shown in Figure 2.

From FIG. 2, it is clear that the sensor of the present invention loses its coloring over time and can be reused repeatedly.

Examples 4-6 The sensor manufactured in Example 3 was treated with CO (Example 4), methane (Example 5), or propane (Example 6) at f! The sample was placed in a closed container containing the same concentration, and measurements were carried out in the same manner as in Example 3.

The results are shown in FIG. 3, Nos. 1 to 3.

From FIG. 3, it is recognized that the sensor of the present invention is also effective for measuring reducing substances in the gas phase.

[Effects of the Invention] As detailed above, the reducing substance sensor of the present invention: (1) Operates repeatedly at room temperature without causing fatigue or deterioration of sensitivity over time;

■ The degree of coloration of the sensor can be detected optically, so
Favorable from safety and environmental standpoints.

■ Stable measurements can be made in any location without interference from electrical noise.

With these effects, it is possible to industrially advantageously detect and quantify reducing substances, especially low molecular weight organic substances, in the gas or liquid phase.

In particular, the sensor of the present invention can continuously monitor the concentration of a reducing substance in a liquid, and is useful in various fields, such as when attached to industrial equipment and the like to manage products. The sensor of the present invention is particularly effective in detecting ethyl alcohol, and is capable of detecting even trace amounts of ippm, so its industrial value is extremely high.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the measurement results in Examples 1 to 3;
FIG. 2 is a graph showing the fading of the sensor in Example 3, and FIG. 3 is a graph showing the measurement results in Examples 4 to 6. Agent Patent Attorney Go Pei Shigeno 01-Tsuchimepe 0+-Nippon

Claims (9)

[Claims] (1) A reducing substance sensor made of a porous material supporting titania. (2) The sensor according to claim 1, wherein titania is supported by impregnating a porous body with titania fine particles. (3) The sensor according to claim 1, wherein titania is supported by forming a titania coating film on the surface of the porous body. (4) The sensor according to any one of claims 1 to 3, wherein the porous body is a woven or nonwoven fabric of inorganic fibers. (5) Claim 4 in which the inorganic fiber is glass fiber
Sensors listed in section. (6) The sensor according to any one of claims 1 to 3, wherein the porous body is a sintered body of glass particles. (7) The sensor according to claim 6, wherein the glass particles have a particle size of 1 to 200 μm. (8) Claim 1 in which the porous body is porous glass
The sensor according to any one of Items 1 to 3. (9) The sensor according to claim 8, wherein the porous glass has a pore diameter of 0.5 to 10 μm.