RU2308712C2 - Nitrogen oxide concentration sensor and a method for formation its light-sensitive layer - Google Patents

Abstract

FIELD: analytical instrumentation engineering.

SUBSTANCE: invention is designed for use in environmental monitoring systems and provides nitrogen oxide concentration sensor comprising support carrying electrodes, iron polyphthalocyanine-based sensitive layer with continuous conjugation system, and resistive heater. Method of forming sensitive layer comprises preparation of iron polyphthalocyanine with continuous conjugation chain followed by de[positing it onto support with electrode system formed on the surface thereof. Above preparation is accomplished via synthesis of iron polyphthalocyanine under an inert atmosphere from reaction mixture of 2.0 g pyromellitic acid tetranitile, 0.035 g urea, and 0.95 g anhydrous ferrous chloride in 70 mL nitrobenzene heated for 5 h at 210^°C, after which reaction medium is filtered, nitrobenzene-insoluble precipitate is washed with boiling ethanol and dried. Deposition of iron polyphthalocyanine with continuous conjugation chain on support is performed using vacuum thermal spraying technique for 4-7 min at 1000-1200^°C.

EFFECT: increased sensitivity and selectivity of sensor toward nitrogen oxide in mixture with other gases.

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Description

This invention relates to the field of analytical instrumentation, namely to gas composition sensors and methods for forming their sensitive layers.

The proposed sensor is designed to determine the concentration of nitric oxide in gas-vapor mixtures, including in exhaled air for the diagnosis of early stages of bronchial asthma and cardiovascular diseases.

A known sensor for monitoring the composition of gases, a gas sensitive layer of which is made of tin dioxide containing silver as an activating additive [1].

The disadvantages of such a sensor include its low selectivity and insufficient gas sensitivity with respect to nitric oxide, as well as the high power consumption for heating.

A ceramic gas sensor is known, the gas sensitive layer of which is α-Fe ₂ O ₃ doped with Nb [2].

The disadvantages of such a sensor include its low gas sensitivity and selectivity with respect to nitric oxide and poor readability.

A gas sensor is known, the gas-sensitive layer of which is made of a thin WO ₃ film [3], obtained by the method of high-frequency magnetron deposition on a sapphire substrate under conditions leading to the formation of epitaxially oriented (polycrystalline) WO ₃ films.

The disadvantages of such a sensor also include its lack of sensitivity and selectivity with respect to nitric oxide.

As a prototype, a gas sensor was chosen, the gas-sensitive layer of which is made of a film of copper phthalocyanine [4], deposited by evaporation in plasma on two electrodes located on a glass substrate.

The technical effect of the invention is to increase the sensitivity and selectivity of the sensor with respect to nitric oxide in its mixture with other gases.

This is achieved by the fact that in a nitric oxide concentration sensor including a substrate on which electrodes and a sensitive layer based on metal polyphthalocyanine are located, as well as a resistive heater, iron polyphthalocyanine with a continuous conjugation chain was used as the sensitive layer, and the iron content in the polyphthalocyanine macromolecule with the continuous coupling circuit is 10.9% by weight. A method of forming a sensitive layer of a nitric oxide concentration sensor, including the production of iron polyphthalocyanine with a continuous conjugation chain, followed by applying it to a substrate with a system of electrodes formed on its surface, is the production of iron polyphthalocyanine with a continuous conjugation chain by the synthesis of an iron polyphthalocyanine from an inert atmosphere 2.0 g of pyromellitic acid tetranitrile, 0.035 g of urea, 0.95 g of anhydrous iron chloride in 70 ml of nitrobenzene by heating the reaction mixture for 5 hours at a temperature of 210 ° C, followed by filtering the reaction mass, washing the precipitate insoluble in nitrobenzene with boiling alcohol and drying, followed by applying polyphthalocyanine iron with a continuous conjugation chain to the substrate by vacuum thermal spraying for 4-7 minutes at a temperature of 1000-1200 ° C.

In the proposed nitric oxide concentration sensor, the sensitive layer is made of iron polyphthalocyanine with a continuous conjugation chain. This iron polyphthalocyanine is a continuous conjugation polymer whose macromolecule consists of repeating phthalocyanine macrocycles. Sensors based on polyphthalocyanines of various metals are used to monitor the composition of liquid and gas media. However, it is unknown to use sensors with a sensitive layer made of iron polyphthalocyanine with a continuous conjugation chain, the iron content in the macromolecule of which is 10.9 wt.% And the method of formation of which involves the production of iron polyphthalocyanine with a continuous conjugation chain, followed by applying it to a substrate with a formed on its surface, a system of electrodes, which is the production of iron polyphthalocyanine with a continuous conjugation chain by polyphthal synthesis in an inert atmosphere iron cyanine from the reaction mixture 2.0 g of pyromellitic acid tetranitrile, 0.035 g of urea, 0.95 g of anhydrous iron chloride in 70 ml of nitrobenzene by heating the reaction mixture for 5 hours at a temperature of 210 ° C, followed by filtering the reaction mass, washing the precipitate insoluble in nitrobenzene with boiling alcohol and drying, followed by the application of iron polyphthalocyanine with a continuous conjugation chain on the substrate by vacuum thermal spraying for 4-7 minutes at a temperature of 1000-1200 ° C.

Figure 1 presents one of the design variants of the sorption-impedance sensor of the concentration of nitric oxide.

Figure 2 presents typical kinetic dependences of the response of a nitric oxide concentration sensor with a sensitive layer based on iron polyphthalocyanine with a continuous conjugation circuit in the mode of pulsed supply of 50.0 ppb nitric oxide (curve 1) and 50.0 ppb of hydrogen sulfide (curve 2) in air .

Figure 3 shows a typical kinetic dependence of the response of a nitric oxide concentration sensor with a sensitive layer based on polyphthalocyanine iron with a continuous conjugation circuit in the pulse supply mode of 50.0 ppb (curve 1) and 100.0 ppb (curve 2) of nitric oxide in air.

The nitric oxide concentration sensor, one of the design options of which is shown in Fig. 1, consists of a dielectric substrate 1 made, for example, of ceramic, sapphire or oxidized silicon, on the surface of which there are metal (nickel, gold, chromium) comb-like electrodes 2, on top of which a gas-sensitive layer is applied 3. A thin-film resistive (nickel or platinum) heater 4 is formed on the reverse side of the substrate to maintain the sensor’s operating temperature.

The principle of operation of the sensor is based on a change in the electrophysical characteristics (resistance) of the sensitive layer during its interaction with nitric oxide. The gas sensitivity value was estimated by the formula (SS _o ) / S _o , where S _o is the initial, S is the measured electrophysical quantity (in particular, resistance). The selectivity coefficient was determined as the ratio of the gas sensitivity of the sensor to nitric oxide to gas sensitivity to other gases. All measurements were carried out at a working temperature of the sensor of 100 ° С; air was used as a carrier gas.

The manufacturing process of the nitric oxide concentration sensor is implemented as follows. A metal layer (metal, which can be used as nickel, gold or chromium) is sprayed onto a substrate made of glass, sapphire or oxidized silicon, washed in a standard process (for example, peroxide-ammonia). After this, the configuration of the electrodes, heater and thermistor is formed by photolithography and subsequent chemical or plasma chemical etching. Then, a layer of iron polyphthalocyanine with a continuous conjugation chain obtained by synthesis in an inert atmosphere of iron polyphthalocyanine from the reaction mixture of 2.0 g of pyromellitic acid tetranitrile, 0.035 g of urea is applied to the substrate for 4-7 minutes at a temperature of 1000-1200 ° C for 4-7 minutes 0.95 g of anhydrous ferric chloride in 70 ml of nitrobenzene by heating the reaction mixture for 5 hours at a temperature of 210 ° C, followed by filtering the reaction mass, washing the wasp insoluble in nitrobenzene boiling alcohol and drying. At temperatures below 1000 ° C during the vacuum thermal spraying, formation of an iron polyphthalocyanine film with a continuous conjugation chain is not observed on the substrate, since at these temperatures the activation energy of the process is insufficient to form a film of a gas-sensitive polyphthalocyanine layer. At temperatures exceeding 1200 ° C, in the process of vacuum thermal spraying, the formation of films of simple iron oxide is observed on the substrate, while the formation of a film of iron polyphthalocyanine with a continuous conjugation chain does not occur. If the time of the vacuum thermal spraying process is less than 4 minutes, the formation of a defective polyphthalocyanine film is observed, in which there are no individual fragments of a continuous polymer conjugation chain. If the time of the vacuum thermal spraying process exceeds 7 minutes, a thick polyphthalocyanine film is formed with poor adhesion to the substrate and low gas sensitivity. When deviating from the weight ratio of tetranitrile pyromethylic acid, anhydrous iron chloride and urea in the reaction mass, the formation of a different amount of metal-containing phthalocyanine macrocycles is observed, which leads to a change in the characteristics of the formed polyphthalocyanine with a continuous conjugation chain, in particular, to a significant decrease in its gas sensitivity and selectivity with respect to oxide nitrogen.

EXAMPLE 1

Using sensors, the design of which is shown in Fig. 1, made on 16.0 × 4.0 mm ceramic glass substrates, on the surface of which gold comb-shaped electrodes 0.25 μm thick are applied, with a sensitive layer based on iron polyphthalocyanine with a continuous pairing chain , resistance measurements were carried out in the feed mode of 50.0 ppb nitric oxide and 50.0 ppb of hydrogen sulfide in air. A method of forming a sensitive layer of a nitric oxide concentration sensor is the production of iron polyphthalocyanine with a continuous conjugation method by synthesis in an inert atmosphere of iron polyphthalocyanine from the reaction mixture 2.0 g of pyromellitic acid tetranitrile, 0.035 g of urea, 0.95 g of anhydrous iron chloride in 70 ml of nitrobenzene by heating the reaction mixture for 5 hours at a temperature of 210 ° C, followed by filtering the reaction mass, washing the precipitate insoluble in nitrobenzene with boiling alcohol m and dried, followed by coating with a continuous poliftalotsianiana iron interface circuit on a substrate by vacuum thermal spraying for 4-7 minutes at a temperature of 1000-1200 ° C. The distance between adjacent teeth and the width of the electrodes was 40 μm. The required level of active gas concentration in the gas mixture was set using a special experimental bench implemented according to the dynamic mixer scheme and allowing to set a specific concentration of active gas components in the measuring chamber and the Environics 4000 series gas mixture generator. The electrophysical characteristics of the sensors in the mode of determining the concentration of nitric oxide and hydrogen sulfide were measured in direct current using a specially designed measuring stand, the measurement circuit of which provides measurement of the resistance of the gas-sensitive layer of sensors with an error of no more than 2% in the range of resistance measurement from 200.0 Ohms to 1.5 GOhm.

Typical kinetic dependences of the sensor response on the concentration of nitric oxide in a pulsed feed mode of 50.0 ppb (curve 1) of nitric oxide and 50.0 ppb (curve 2) of hydrogen sulfide are shown in FIG.

In the presence of nitric oxide in the analyzed mixture, a noticeable change in the resistance of the sensitive layer occurred. In the presence of hydrogen sulfide in the analyzed gas mixture, no resistance changes were observed.

EXAMPLE 2

Sensors with a design, the composition of the gas-sensitive layer and the method of its formation, similar to those described in example 1, measured the concentration of nitric oxide, carbon monoxide and ammonia in the air. The measurements of the characteristics of the sensors, as well as the preparation of the gas mixture were carried out analogously to example 1. Table 1 shows the selectivity coefficients of the sensors of nitric oxide in the mode of measuring the concentration of nitric oxide, carbon monoxide and ammonia in the air.

Table 1 Coefficients of selectivity of sensors based on iron polyphthalocyanine with a continuous conjugation chain Detectable substance Selectivity factors for gas concentration, ppb 50,0 100.0 400,0 Nitrogen oxide 1,0 1,0 1,0 Carbon monoxide 35.5 47.8 60.0 Ammonia 30.5 39,4 56.3

EXAMPLE 3

Sensors with a design, the composition of the gas-sensitive layer and the method of its formation, similar to those described in example 1, measured the concentration of nitric oxide in the air. The measurements of the characteristics of the sensors, as well as the preparation of the gas mixture were carried out analogously to example 1. A typical kinetic dependence of the response of the sensor of the concentration of nitric oxide in the pulse supply mode of 50.0 ppb (curve 1) and 100.0 ppb (curve 2) of nitric oxide is shown in figure 3 .

EXAMPLE 4

Sensors with a design, the composition of the gas-sensitive layer and the method of its formation, similar to those described in example 1, measured the concentration of nitric oxide in the air. Measurement of the characteristics of the sensors, as well as the preparation of the gas mixture was carried out analogously to example 1. Table 2 shows the gas sensitivity coefficients of the concentration sensors of nitric oxide in the mode of measuring the concentration of nitric oxide in the air. For comparison, the gas sensitivity coefficients of the prototype — sensors based on copper phthalocyanine — are also given there.

table 2 Gas sensitivity coefficients of sensors based on iron polyphthalocyanine with a continuous pairing chain and based on copper phthalocyanine (prototype) Gas sensitive layer Gas sensitivity coefficients at nitric oxide concentration in air, ppb 50,0 100.0 10,000.0 Continuous Polyphthalocyanine Iron 0.104 0.212 0.642 Copper phthalocyanine - - 0.2

Thus, in comparison with the prototype, the proposed nitric oxide concentration sensor and the method of forming its sensitive layer have the following advantages:

- higher sensitivity to nitric oxide;

- higher selectivity with respect to nitric oxide.

Literature

1. Mizsei J., Lantto V., Air pollution monitoring with a semiconductor gas sensor array system. - Sensors and Actuators B, 1992, V.B6, N.1-3, pp.223-227.

2. Cantalini C., Sun HT, Faccio M., Ferri G., Pelino., Niobium-doped α-Fe ₂ O ₃ semiconductor ceramic sensors for the measurement of nitric oxide gas. - Sensors and Actuators B, 1995, V.B24-25, pp. 673-677.

3. Fruhberger B., Stirling N. .. Grillo F.G., Ma S., Ruthven D., Lad R.J., Frederick B.G., Detection and quantification of nitric oxide in human breath using a semiconducting oxide based chemiresistive microsensor. - Sensors and Actuators B, 2001, V.B76, pp. 226-234.

4. Chang-Gu Choi, Soonchil Lee, Won-Jong Lee, NO gas-sensing characteristics of copper phthalocyanine film prepared by plasma-activated evaporation. - Sensors and Actuators B, 1996, V.B32, pp. 77-82.

Claims (3)

1. A nitric oxide concentration sensor comprising a substrate on which electrodes and a sensitive layer based on metal phthalocyanine are located, as well as a resistive heater, characterized in that iron polyphthalocyanine with a continuous conjugation chain is used as a sensitive layer. 2. The concentration sensor of nitric oxide according to claim 1, characterized in that the iron content in the polyphthalocyanine molecule with a continuous conjugation chain is 10.9 wt.%. 3. A method of forming a sensitive layer of a nitric oxide concentration sensor, including producing polyphthalocyanine iron with a continuous conjugation chain, followed by applying it to a substrate with a system of electrodes formed on its surface, characterized in that the polyphthalocyanine iron with a continuous conjugation chain was obtained by synthesis in an inert atmosphere polyphthalocyanine iron from the reaction mixture 2.0 g of pyromellitic acid tetranitrile, 0.035 g of urea, 0.95 g of anhydrous iron chloride in 70 ml of nitrobenzene by heating the reaction mixture for 5 hours at a temperature of 210 ° C, followed by filtering the reaction mass, washing the precipitate insoluble in nitrobenzene with boiling alcohol and drying, followed by the application of iron polyphthalocyanine with a continuous conjugation chain on the substrate by vacuum thermal spraying for 4-7 minutes at a temperature of 1000-1200 ° C.

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