JPH02304340A - Ammonia sensor - Google Patents

Abstract

PURPOSE:To enable actuation at the ordinary temp. and to miniaturize the sensor and to make it lightweighted by forming the sensing part of gaseous ammonia of polyaniline. CONSTITUTION:Polyaniline is dissolved in a polar organic solvent such as N, N'-dimethylformamide, N,N'-dimethylacetamide, dimethylsulfoxide and N- methylpyrolidone. This soln. is applied to an insulating base plate 2 provided with the comb-type electrodes 3. Thereby since the electric resistance of polyaniline is sharply changed even at the ordinary temp. by the concn. of gaseous ammonia, the concn. of ammonia can be detected at high sensitivity by measuring the electric resistance thereof. Further the sensor is miniaturized, made lightweighted and thin because coating is only applied to the base plate 2 provided with the comb-type electrodes 3.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an ammonia sensor, and more particularly to an ammonia sensor using polyaniline as a gas sensing portion.

Conventionally, as a sensor for detecting ammonia gas,
■Ammonia gas electrode using an ammonia permeable membrane, ■Semiconductor sensor using resistance change of inorganic oxide semiconductor,
■Ammonia detectors using conductive polypyrrole have been proposed, but the ammonia gas electrode described in ■ above is large and the mounting plate is inconvenient, making it impossible to use in microscopic spaces. Maintenance is troublesome, and semiconductor sensors described in (1) above generally have low selectivity for ammonia gas, and they must be used in heated conditions, which can lead to explosions if used in an atmosphere containing flammable gas or powder. There is a danger, and the above ■
Detectors using polypyrrole have the disadvantage that their properties change significantly over time.

The inventors of the present invention have conducted intensive research to provide an ammonia sensor that is small, lightweight, highly reliable, and highly sensitive and can operate at room temperature without having the above-mentioned drawbacks or difficulties. They found that it is extremely suitable as a sensing section for ammonia gas, and have completed the present invention.

Thus, according to the present invention, an ammonia sensor characterized by being made of polyaniline is provided.

Polyaniline used as a sensor in the present invention is a polymer substance known per se as a conductive organic polymer, and can be produced by chemical or electrochemical polymerization of aniline [for example, A, G, MacDiarmi
D, J., C. Chiang and M. Halp.
er, n+Polym.

Prepr, (1984) 248; B., Wang, J.
Tang and F, Wang, 5ynth
etic Metals, 13 (1986) 329
For example, polyaniline can be produced by electrolyzing a polymerization bath containing aniline and a suitable electrolyte in a conventional electrolytic cell using platinum as an anode and palladium as a cathode. The electrolytic voltage at that time is usually 0.3 to 2 V (can be compared to standard calomel/alumel voltage, and the current density is 1 to 100 mA/
A value within the range of am' is appropriate. Examples of electrolytes that can be used include mineral acids such as hydrochloric acid and sulfuric acid; HCi'O, Na
Perchloric acid (salt) such as C104, K C10, etc.; Phosphate buffer, tetraethylammonium fluoroborate;
Examples include organic sulfonic acids such as toluenesulfonic acid and naphthalenesulfonic acid, which are generally used in a polymerization bath at a concentration of 0.
It can be used at concentrations within the range of 0.01-5M, preferably 0.03-4M.

Aniline can also be used in the polymerization bath generally at a concentration of 0.0601 to 5M, preferably 0.03 to 4M. Furthermore, examples of solvents that can be used in the polymerization bath include water, ethanol, acetonitrile, propylene carbonate,
Examples include nitrobenzene or mixtures thereof.

Polyaniline produced by electrolysis is separated from the polymerization bath,
After sufficiently washing with water until it is completely neutralized, it can be dried until the residual water content is 5% by weight or less, preferably 2% by weight or less.

The polyaniline thus obtained is preferably one that is soluble in common polar organic solvents.

The present inventors discovered that the electrical resistance of polyaniline obtained by electrolytic polymerization as described above changes depending on the ammonia concentration in air or other gas atmospheres, and that by measuring the electrical resistance, an extremely sensitive They discovered a scale that can detect ammonia concentration and found that polyaniline is extremely effective as an element for an ammonia sensor.

Thus, when this polyaniline is actually used as an ammonia sensor, for example, polyaniline can be dissolved in a polar organic solvent such as N,N'-dimethylformamide, N,N'-dimethylacetamide, dimethylsulfoxide, N-methylpyrrolidone, etc. Dissolve the solution in the first
It can be applied onto an insulating substrate provided with comb-shaped electrodes as shown in the figure.

The concentration of polyaniline in the above solution is not particularly limited, but is usually 1 to 30%, preferably 3 to 20%.
%. Further, the material for the comb-shaped electrode is preferably a conductive metal with excellent corrosion resistance such as platinum, gold, or palladium, and the insulating substrate is usually made of ceramic such as glass or alumina.

Examples of methods for applying the polyaniline include conventional coating methods such as spin coating and dipping, and by removing the solvent after application, the ammonia sensor of the present invention can be obtained.

The thickness of the coating film is generally from 0.01 to 100 microns, preferably from 0.1 to 10 microns.

In the ammonia sensor made of polyaniline provided by the present invention, the electrical resistance of polyaniline changes depending on the ammonia gas concentration, and the change is sensitive even at room temperature.
It has the excellent effect of operating at room temperature without heating part of the sensor. In addition, as shown in Figure 1, the ammonia sensor of the present invention is simply coated on a substrate provided with electrodes, so it is easy to manufacture and can be made small, lightweight, and thin, making it convenient to handle and manage. is also easy. Moreover, the ammonia sensor of the present invention has excellent linearity with respect to changes in ammonia gas concentration and is highly sensitive.
It has various advantages such as ease of design when incorporated into electronic circuits and the like.

Thus, the ammonia sensor of the present invention can be used to control ammonia concentration in various plants, automate leak detection, alarms, and shutdown measures, and can be used in combination with enzymes and microorganisms that metabolize proteins and amino acids to produce ammonia gas. It can be effectively used in the detection of white matter and amino acids, and in various other reactions (detection of generated ammonia gas and reaction control based on this).

Next, the present invention will be explained in more detail with reference to Examples.

Example 1 Electrolytic cell in which both the anode and cathode are platinum (size = 2 cm)
+
As a result of electrolytic polymerization for 10 minutes using an alumel electrode, a blue-black precipitate was produced. This precipitate was separated, washed with water until the pH of the washing water became approximately 7, and dried under reduced pressure at room temperature.

The obtained dried polyaniline was dissolved in N,N'-dimethylformamide to prepare a 10% by weight solution, which was spray coated with platinum onto an alumina substrate provided with comb-shaped electrodes and dried to form a polyaniline film with a thickness of 10 μm. Formed.

The obtained ammonia sensor was set in a glass tube with a diameter of 24 volumes, air was flowed from one end of the glass tube at a flow rate of 11/min, and a certain amount of ammonia was intermittently injected into the air flow. The electrical resistance of the sensor was measured. The results are shown in FIG.

Example 2 An ammonia sensor was manufactured in exactly the same manner as in Example 1 except that 30 g of propylene carbonate in the electrolytic bath composition was replaced with Log of water.

Set the obtained ammonia sensor in a sealed container,
10 ppm ammonia gas was injected at 4 minute intervals and the electrical resistance of the sensor was measured. The results are shown in FIG.

Example 3 Example 1 except that 15 g of tetraethylammonium fluoroborate is used instead of 12 g of perchloric acid in the electrolytic bath composition, water Log is used instead of 30 g of propylene carbonate, and palladium is used instead of platinum as the cathode.
I created an ammonia sensor using exactly the same procedure as above.

Set the obtained ammonia sensor in a sealed container,
Air only or! -(2, Co, No or 02 to 10
．． 1 at 4 minute intervals after filling with air containing OOOppm
Inject 0 ppm ammonia, measure the electrical resistance of the sensor, and calculate the ammonia concentration (ppm) and the electrical resistance difference (R
Draw 10 points on a graph to show the relationship with Re>. Here R is air only, H2, CO, No or 0. This is the measured value of electrical resistance when ammonia is injected into air containing
R.

is the measured value of electrical resistance when only air is used. The results are shown in Figure 4. As is clear from FIG. 4, the sensor of the invention is not affected by the coexistence of other gases.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of an example of the ammonia sensor of the present invention, in which 1 is a polyaniline film, 2 is an insulating substrate, 3 is a comb-shaped electrode, and 4 is a lead wire. 2 to 4 are graphs showing the relationship between ammonia concentration and electrical resistance of the ammonia sensor of the present invention.

Claims (1)

[Claims] 1. An ammonia sensor characterized by being made of polyaniline.