WO2018158692A1

WO2018158692A1 - Formaldehyde gas sensor and method for producing the same

Info

Publication number: WO2018158692A1
Application number: PCT/IB2018/051257
Authority: WO
Inventors: Chickmaglur NAVEEN SHIVAPPA; Ayalasomayajula RATNA PHANI; Baijayanti GHOSH; Varun Gupta
Original assignee: Inm Technologies Pvt Ltd
Priority date: 2017-03-03
Filing date: 2018-02-28
Publication date: 2018-09-07

Abstract

A gas sensor is used for detecting gas in the air, especially formaldehyde. The sensor comprises gas-sensitive zone which is preferably a layer on a substrate and which contains the nanocomposite material of Polyaniline-MnO₂ as the gas-sensitive material. In order to produce the gas-sensitive zone, facile casting is carried out, organometallic compounds of polyanilinc and manganese being used as reactants. The gas sensor is especially suitable for the online gas detection.

Description

FORMALDEHYDE GAS SENSOR AND METHOD FOR PRODUCING THE SAME

FIELD OF INVENTION The present invention relates to a gas sensor for detecting gases in the air, in particular formaldehyde, as well as a method for producing said sensor.

BACKGROUND OF THE INVENTION Formaldehyde is a chemical compound industrially used in a versatile manner. It is used in the production of plastics, in the processing of wood adhesive in plywood boards and chip boards, in the construction industry as heat insulation, in the textile industry for crease-resistant and easy-care finishing as well as in agriculture and in the food industry as a preserving agent. Formaldehyde is also used in the fishery industry as a preservative to maintain its freshness and prevent microbial spoilage. Formaldehyde is used as a disinfectant and is furthermore contained in cosmetics, body and mouth care products as well as sometimes in paints, varnishes and carpets.

Moreover, Formaldehyde develops from incomplete combustion processes. For example, it is found in combustion engines of motor vehicles, in foundries, in the production of plastic articles or in the burning of woods in small firing systems. In the same manner, formaldehyde is a by-product formed during smoking, contributing to the contamination of the air.

Formaldehyde is a gaseous substance which can cause health problems such as eye and/or mucous membrane irritations. Short-term exposure leads to irritation of the eyes and the respiratory tract even at low concentration levels: irritation of the eyes as from 0.01 ppm, irritation of the eyes and the nose as from 0.08 ppm and irritation of the throat as from 0.5 ppm. Concentrated vapors of more than 10 ppm can lead to severe irritation of the mucous membranes including lacrimation, coughing and burning in the nose and throat. Concentrations of more than 30 ppm cause toxic edema of the lungs and pneumonia with a life-threatening situation.

Chronic effects of formaldehyde are malaises such as insomnia, lassitude, loss of drive, lack of appetite or nervousness, eye irritations and conjunctivitis, skin irritations, chronic cough, colds and bronchitis, head ache, depressions and others. Furthermore, formaldehyde can also elicit hypersensitivities and has for some time been suspected to be able to cause cancer or to act mutagenic or teratogenic in humans. For that reason, the German Health Authority has introduced a maximum work place concentration (Maximum Allowable Concentration MAC) of 0.3 ppm (0.375 mg/m³). The indoor reference value is even as low as 0.1 ppm (0.125mg/m³) since permanent exposure is to be assumed in this case.

Further in the fish industry, formaldehyde is harmful for human consumption when used in excess as the residues retained in the fish muscles although it has been cooked, roasted or boiled. Besides it can induce cancer and has been classified "as carcinogenic to humans" by international Agency for Research on Cancer (IARC) in Group 1 (Bianchi et al., 2007). As established by Food Regulation 1985, formaldehyde content should not be more than 5mg/kg and this level must be monitored strictly. For this reason, an effective and rapid detection and measurement of formaldehyde in the air is to be attached great importance.

Several methods for detecting formaldehyde in the air are known from the prior art (an overview of the known methods is given for example in the publication of H. Nishikawa and T. Sakai (Journal of chromatography A, Vol. 710, pp.159-165,1995).

For example, gas chromatography (GC) analysis and High-performance liquid chromatography (HPLC) analysis are analytical standard methods. For assessing occupational risks, the NIOSH (National Institute for Occupational Safety and Health) has standardized several analytical methods for detecting formaldehyde in the air.

In case of the NIOSH method 2016, for example, test air is passed through a medium composed of a silica gel that is coated with dinitrophenylhydrazine (DNPH). The chemical reaction leads to formation of hydrazones that can be identified and quantified as stable derivatives by use of HPLC, GC/FID, GC/ECD or diode array detectors.

The NIOSH method 2541 is based on GC/FID-analysis. Here, test air is passed through a tube coated with 2-hydroxymethylpiperidine (2-HMP). Formaldehyde of the sample reacts with 2- HMP to yield a derivative of oxazolidine which is subsequently desorbed and analyzed in a gas chromatograph.

The NIOSH method 3500 is based on spectrometric measurements. There is condensation of formaldehyde in the presence of sulfuric acid with 2 molecules of chromotropic acid and a red carbenium cation is formed. After that, the spectroscopic verification is effected by means of a measurement at 580 nm.

A substantial disadvantage of the analytical methods is that the air sample needs elaborate preparation for derivatization of formaldehyde and that the actual measurement is to be effected in a special laboratory. An online detection is not feasible using these methods.

Besides the analytical methods, a number of instrumental methods is known from the prior art. Formaldehyde can be detected due to its ionization potential of 10.87 eV by means of a photo ionization detector after ionization with an argon lamp. The main disadvantage of said method lies with the great effort thereof as well.

Another method for formaldehyde detection is based on an electro-chemical cell. Said method has the drawback that the equipment required for the measurement is very expensive. Moreover, regular recalibration is required for the measuring instruments, and the life cycle of an electric cell is limited to less than one year.

Furthermore, fluorescence-based methods for detecting formaldehyde are known from the prior art, for example a detection method based on a Hanzsch reaction. Indeed, the method provides a comparatively high selectivity, but the corresponding measuring device is very expensive. Another disadvantage is the elaborate preparation of the air sample where the formaldehyde is correspondingly derivatized for the measuring.

The above-mentioned methods for detecting formaldehyde require high effort in equipment for derivatization and subsequent analysis of formaldehyde. Thus these methods can only be used in large laboratories and the results are available only after periods of long preparation times.

A MOX-based method is known from the prior art to allow even an online determination of the formaldehyde concentration. In this case, formaldehyde from the sample reacts with the sensing film of the metal oxide sensor which thereupon changes its conductivity. A sensitive layer of differently combined oxides of Zn, Ni, Sn, Cd, In and other metals is used as a sensor. The following list of references provides an overview of the thus far known metal oxides used for detection of formaldehyde.

1. James A. Dirksen, Kristin Duval, Terry A. Ring, NiO thin-film formaldehyde gas sensor, Sensors and Actuators B: Chemical, Volume 80, Issue 2, 20 Nov. 2001 , Pages 106-1 15, ISSN 0925-4005, DOI: 10.1016/S0925-4005(01)00898-X

2. Xingjiu Huang, Fanli Meng, Zongxin Pi, Weihong Xu, Jinhuai Liu, Gas sensing behavior of a single tin dioxide sensor under dynamic temperature modulation, Sensors and Actuators B: Chemical, Volume 99, Issues 2-3, 1 May 2004, Pages 444-450, ISSN 0925-4005, DOI: 10.1016/j.snb .2003.12.013

3. Liqin Shi, Wei Gao, Yuki Hasegawa, Teruaki Katsube, Mamoru Nakano, Kiyozumi Nakamura, High Sensitive Formaldehyde Gas Sensor Prepared by R.F. Induction Plasma Deposition Method. 1EEJ Transactions on Sensors and Micromachines, 2005. 125(12): p.485-489.

4. Ling Zhang, Jifan Hu, Peng Song, Hongwei Qin, Xiangdong Liu, Minhua Jiang, Formaldehyde-sensing characteristics of perovskite La0.68Pb0.32FeO3 nano- materials, Physica B: Condensed Matter, Volume 370, Issues 1 -4, 15 Dec. 2005, Pages 259-263.

5. Chia-Yen Lee, Che-Ming Chiang, Yu-Hsiang Wang, Rong-Hua Ma, A self-heating gas sensor with integrated NiO thin film for formaldehyde detection, Sensors and Actuators B: Chemical, Volume 122, Issue 2, 26 Mar. 2007, Pages 503-510, ISSN 0925-4005, DOI: 10.1016/j.snb.2006.03.033.

6. Jiaqiang Xu, Xiaohua Jia, Xiangdong Luo, Guaxi Xi, Jianjun Han, Qiaohuan Gao, Selective detection of HCHO gas using mixed oxides of ZnO/ZnSn03, Sensors and Actuators B: Chemical, Volume 120, Issue 2, 10 Jan. 2007, Pages 694-699, ISSN 0925- 4005, DOI: 10.1016/j.snb.2006.03.033.

7. T, Chen, Q. J. Liu, Z. L. Zhou, Y. D. Wang, The fabrication and gas-sensing characteristics of the formaldehyde gas sensor with high sensitivity, Sensors and Actuators B: Chemical, Volume 131 , Issue, Special Issue: Selected Papers from the 12th International Symposium on Olfaction and Electronic Noses— ISOEN 2007, International Symposium on Olfaction and Electronic Noses, 14 Apr. 2008, Pages 301 - 305, ISSN 0925-4005, DOI: 10.1016/j.snb.2007.1 1.025 8. Shanxing Huang, Hongwei Qin, Peng Song, Xing Liu, Lun Li, Rui Zhang, ifan Hu, Hongdan Yan, Minhzua Jiang, The formaldehyde sensitivity of LaFel-x Zn x 03-based gas sensor. Journal of Materials Science, 2007. 42(24): p. 9973-9977.

9. Pin Lv, Zhenan Tang, Guangfen Wei, Jun Yu, Zhengxing Huang, Recognizing indoor formaldehyde in binary gas mixtures with a micro gas sensor array and a neural network. Measurement Science and Technology, 2007. 18(9): p. 2997.

10. Zikui Bai, Changsheng Xie, Mulin Hu, Shunping Zhang, Formaldehyde sensor based on Ni-doped tetrapod-shaped ZnO nanopowder induced by external magnetic field. Physica E: Low-dimensional Systems and Nanostructures, 2008. 41 (2): p. 235-239. 1 1. T. Chen, Q. J. Liu, Z. L. Zhou, Y. D. Wang, A high sensitivity gas sensor for formaldehyde based on CdO and In 2 O 3 doped nanocrystalline Sn02. Nanotechnology, 2008. 19(9): p. 095506.

12. Jinyun Liu, Zheng Guo, Fanli Meng, Yong Jia, Jinhuai Liu, A novel Antimony-Carbon Nanotube-Tin Oxide Thin Film: Carbon Nanotubes as Growth Guider and Energy Buffer. Application for Indoor Air Pollutants Gas Sensor. The Journal of Physical

Chemistry C, 2008. 1 12(15): p. 61 19-6125.

13. Pin Lv, Zhen A. Tang, Jun Yu, Feng T. Zhang, Guang F. Wie, Zheng X. Huang, Yann Hu, Study on a micro-gas sensor with Sn02-Nio sensitive film for indoor formaldehyde detection. Sensors and Actuators B: Chemical, 2008. 132(1): p. 74-80.

14. Jing Wang, Li Liu, Song-Ying Cong, Jin-Qing Qi, Bao-Kun Xu, An enrichment method to detect low concentration formaldehyde. Sensors and Actuators B: Chemical, 2008. 134(2): p. 1010-1015.

15. Xiangfeng Chu, Tongyun Chen, Wangbing Zhang, Banqiao Zheng, Hengfu Shui, Investigation on formaldehyde gas sensor with ZnO thick film prepared through microwave heating method. Sensors and Actuators B: Chemical, 2009. 142(1): p. 49-

54.

16. Ning Han, Yajun Tian, Xiaofeng Wu, Yunfa Chen, improving humidity selectivity in formaldehyde gas sensing by a two-sensor array made of Ga-doped ZnO. Sensors and Actuators B: Chemical, 2009. 138(1): p. 228-235.

17. Yude Wang, Ting Chen, Quiying Mu, Guofeng Wangm. A nonaqueous sol-gel route to synthesize Cdln₂0₄ nanoparticles for the improvement of formaldehyde-sensing performance, Scripta Material ia, Volume 61 , Issue 10, November 2009, Pages 935-938, ISSN 1359-6462, DOI: 10.1016/j.scriptamat.2009.07.029. 18. Jing Wang, Peng Zhang, Jin-Qing Qi, Peng-Jun Yao, Silicon-based micro-gas sensors for detecting formaldehyde, Sensors and Actuators B: Chemical, Volume 136, Issue 2, 2 Mar. 2009, Pages 399-404, ISSN 0925-4005, DOI: 10.1 016/j.snb.2008.12.056.

19. Zeng W., Liu T., Wang Z., Tsukimoto S., Saito M, Ikuhara Y. Selective Detection of Formaldehyde Gas Using a Cd-Doped Ti02— Sn02 Sensor. Sensors. 2009;

9(l l ):9029-9038

20. M. A. Aronova, K. S. Chang, I. Takeuchi, H. Jabs, D. westerheim, A. Gonzalez-Martin, J. Kim, B-Lewis, Combinatorial libraries of semiconductor gas sensors as inorganic electronic noses— Appl. Phys. Lett. 83, 6, 1255-1257.

The above references 1 to 20 shows that all gas sensors that are known thus far and whose functioning is based on metal oxides (except for ZnO nanowires), work at very high concentration levels that are far above the maximum reference value permitted by law, or have a low sensor signal (sensor signals that cover a concentration range of 3 orders of magnitude and that merely lie in the range of 1 to 1 .6 do not allow relevant concentration grading). The operating temperature of these sensors is also significantly above room temperature, which reduces operational life of the sensor. With reference to the nanowires, problems in the long term stability of the sensors are reported in the publication of Chu. US200201 18027A1 discloses a nano-structured anodic aluminium oxide substrate for gas sensors that has parallel pores with electrodes. The sensitive material is deposited within the pores to considerably increase the surface of the sensitive layer as compared to the planarly applied layer and thus should increase the sensitivity of the sensor. The material used for the sensitive layer plays a less important role in said document. The cost for the production of such a substrate may be comparatively high.

WO201201 1798 A2 discloses a method for detecting formaldehyde by contacting the sample with an amperomctric sensor, wherein the sensor comprising an electrode coated with an immobilized enzyme; and measuring the current changes as the output signal at a constant voltage which indicates the presence of formaldehyde in the sample. The cost for the production of such electrode coated with an immobilized enzyme is comparatively high.

US Patent No. 9091669 discloses a sensor for detecting gases comprising at least one gas- sensitive zone applied on a substrate, characterized in that the gas-sensitive zone comprises a metastable mixed oxide phase of ln₄Sn30i_ applied using flame spray pyrolysis (FSP). The cost for the production of such sensor is comparatively high and works at high temperature.

Therefore, the need exists to provide a novel gas sensor that has a high sensitivity that allows online detection and that can be produced at competitive cost, which operates at room temperature with longer life, and exhibits high response and good recovery times at such temperatures.

OBJECTS OF THE INVENTION

The object of the present invention is to provide a novel gas sensor that has a high sensitivity that allows online detection at room temperature and that can be produced at competitive cost.

A further object of the invention is to provide a novel gas sensor that is simple, rapid, sensitive and selective in determining the presence of formaldehyde.

SUMMARY OF THE INVENTION

In accordance with one embodiment of the present invention, a method for detecting the formaldehyde gas is provided.

In another embodiment, the formaldehyde gas is detected by a gas sensor that contains the nanocomposite material Polyaniline-Mn02 in its gas sensitive zone. The gas sensor according to the invention comprises at least one gas sensitive zone, consisting of nanocomposite material Polyaniline-Mn02 which is preferably in the form of a thin layer. In the case of gas detection, using the sensor according to the invention, its sensitive layer is contacted with a gas sample (e.g. formaldehyde). After reaction, the electrical properties of the sensitive layer changes, a fact that can be measured as a change in the electrical impedance, the work function and/or capacity change. It is preferred to measure the change of the resistance.

It is an advantage of the present invention to provide a simple, rapid and sensitive method and device for the determination of formaldehyde. It is another advantage of the present invention to provide a method and device that does not require materials which may possess toxic effects. BRIEF DESCRIPTION OF DRAWINGS

Figure 1 : schematic sketch view of a sensor is shown to comprise a sensor element layer 4 (Polyaniline-Mn02 gas sensitive zone) in the form of a thin film, which can allow a sensing gas to reach the surface of the sensing element, and an electrode 1 that is the platinum electrode covered on gold electrodes 3. The base substrate for the entire setup is the ceramic substrate 2.

Figure 2: shows as a function of time the curve of the resistance for measurements of formaldehyde concentration of 1 ppm with the sensor (sensor element prepared with 0.2wt% of manganese chloride with respect to aniline) according to the invention. The sensor changes its resistance value when the gas is purged into the chamber which represents the ON state. The OFF state represents when the fresh air is purged into the gas chamber so that the sensor resistance value comes to its normal base line state. The figure also represents the repeatability of the sensor performance up to four cycles. Figure 3: shows the sensor signal of the sensor according to the invention depending on manganese concentration. A maximum sensor signal is achieved in the range from about 0.2wt% of manganese chloride source material to about 0.4wt% of manganese chloride source material with respect to aniline source material. Figure 4: shows the sensor response for formaldehyde gas compared with other two different gases i.e. Methanol and Ethanol. It is clearly represents that the response for the other gases is relatively low when compared with the formaldehyde gas.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a method and gas sensor for detecting the formaldehyde gas.

According to the preferred embodiment of the invention the formaldehyde gas is detected by a gas sensor that contains the nanocomposite material Polyaniline-Mn0₂ in its gas sensitive zone. The term "nanocomposite" is used to stress that the main feature of this class of materials, distinguishable, for example, by electron microscopy, is the existence of regions of one or more of the constituents (substances like Mn0₂) dispersed randomly in the matrix such as polyaniline, wherein the constituents range from sizes of about 1 to about lOOnm.

The nanocomposite material Polyaniline-Mn0₂ has not been described in the prior art with regard to the production of gas sensors. In the scope of present invention, it surprisingly turned out that the nanocomposite material Polyaniline-Mn0₂ possesses properties of an effective gas sensor.

The gas sensor according to the invention comprises at least one gas sensitive zone, consisting of nanocomposite material Polyaniline-Mn0₂ which is preferably in the form of a layer. In the case of gas detection, using the sensor according to the invention, its sensitive layer is contacted with a gas sample (e.g. air). After a reaction, the electrical properties of the sensitive layer changes, a fact that can be measured as a change in the electrical impedance, the work function and/or capacity change. It is preferred to measure the change of the resistance. According to the another preferred embodiment of the invention, the sensor according to the invention is used for detection of formaldehyde. By use of the sensor according to the invention, sensor signal ranges from 1 .2ΜΩ to 1 .4ΜΩ, which can be obtained for the concentration range of formaldehyde between 0.6 ppm and 1.5 ppm. Another advantage of the sensor according to the invention lies in its low sensitivity towards alcohols especially methanol and ethanol, which are predominantly present in industrial environment. In other words, the sensor according to the invention has high selectivity to detect formaldehyde gas against alcohols.

Further advantages of the sensor according to the invention is that it operates at room temperature with longer life, and exhibits high response and good recovery times at room temperatures, wherein the power requirement is very low, whereas the commercially available sensors are equipped with heating coils as the materials sense at temperature above 200°C, which require high power consumption. The method for producing the sensor according to the invention is also a subject of the present invention. At least one gas-sensitive zone is effected by means of the facile casting method. To that end, a gas-sensitive nanocomposite material Polyaniline-MnCh layer is applied on a substrate by means of facile casting method as disclosed in Mir Reza Majidi etal, Polymers; Volume 37, Issue 2, 1996, Pages 359-362.

Furthermore, it turned out that the concentration of the source substances plays an important role in the method for producing the gas-sensitive layer of the sensor according to the invention. The best results were achieved when the source substance Manganese Chloride (MnCl₂) concentration is used in each case at the weight percentage with respect to aniline of about 0.2% to about 0.4%.

Another subject of the present invention is the use of the above described gas sensor for detecting gas in home environments in order to allow online analysis of the corresponding contamination of the air. Furthermore, the sensor is adapted to allow and air analysis in business establishments where formaldehyde is handled.

In the embodiments of the present invention the process for preparation of nanocomposite material layer Polyaniline-MnC is prepared by the following steps

1. Encapsulation of aniline molecules with a surfactant in purified water,

2. Addition of manganese chloride as a dopant to contents of step 1

3. Polymerizing the contents of step 2 by addition of oxidizing agent ammonium peroxydisulfate to form manganese doped polyaniline (Emeraldinc) salt

4. Inorganic acid or organic acid was added onto step 3 product, to obtain Emeraldine salt dispersion.

In the embodiments of the invention the oxidizing agents used in the polymerizing step for the preparation of manganese doped polyaniline Emeraldine salt is ammonium peroxydisulfate. The inorganic acids used are selected from the group of HC1, HBr, H2SO4 and H3PO₄. The most preferred inorganic acid is H3PO4. The organic acid preferably used is acetic acid. The surfactant used are selected from camphor- 10-sulfonic acid (CSA), dinonylnapthalene sulfonic acid (DNSA), dinonylnapthalene sulfonic acid (DNDSA) and dodecyl benzene sulfonic acid (DBSA). The most preferred surfactant is dodecyl benzene sulfonic acid (DBSA). In the specific embodiment of the present invention nanocomposites of Polyaniline-MnC is prepared by the following steps

1 . Encapsulation of aniline molecules with a surfactant dodecyl benzene sulfonic acid (DBS A) in purified water,

2. Addition of manganese chloride as a dopant to the contents of step 1 ,

3. Polymerizing the contents of step 2 by addition of oxidizing agent ammonium peroxydisulfate to form manganese doped polyaniline Emeraldine salt,

4. H3PO4 was added onto step 3 product, to obtain manganese doped polyaniline Emeraldine salt dispersion.

In one embodiment the method for producing the sensor according to the invention is also a subject of the present invention. The nanocomposite material Polyaniline-MnCh is applied onto the substrate by facile casting method. The facile casting method comprises the steps of facile casting nanocomposite material of polyaniline-MnC (manganese doped polyaniline Emeraldine salt dispersion) onto the substrate. The substrate used in the present invention is ceramic.

In another embodiment the dispersion of nanocomposite material Polyaniline-MnCh (manganese doped polyaniline Emeraldine salt dispersion) is applied on to the substrate by dip coating method.

Since to date there has not been a possibility for detecting formaldehyde by online application at room temperature, the sensor according to the invention is a novel milestone with regard to the prior art.

Further advantages, features and application possibilities of the sensor and the method of producing the same are subsequently described not limited by the following examples. Examples:

Example: 1

1. Encapsulation of aniline molecules with a surfactant dodecyl benzene sulfonic acid (DBSA) in purified water, 2. Addition of manganese chloride as a dopant to the contents of step 1 ,

3. Polymerizing the contents of step 2 by addition of oxidizing agent ammoni um peroxydisulfate to form manganese doped polyaniline Emeraldine salt,

4. Part of step 3 product was treated with Ammonia solution to convert it to Emerald ine base. Product was coated onto substrate,

5. Acetic Acid was added onto step 4 product, to obtain coating of Emeraldine salt.

Example: 2

1. Encapsulation of aniline molecules with a surfactant dodecyl benzene sulfonic acid (DBSA) in the purified water.

2. Addition of manganese chloride as a dopant to the contents of step 1 ,

3. Polymerizing the contents of step 2 by addition of oxidizing agent ammonium peroxydisulfate to form manganese doped polyaniline Emeraldine salt.

4. Part of step 3 product was treated with Ammonia solution to convert it to Emeraldine base. Product was coated onto substrate.

5. HC1 was added onto step 4 product, to obtain coating of Emeraldine salt.

Example: 3

1 . Encapsulation of aniline molecules with a surfactant camphor- 10-sulfonic acid (CSA) in purified water.

2. Addition of manganese chloride as a dopant to the contents of step 1 ,

5. H3PO4 was added onto step 4 product, to obtain coating of Emeraldine salt.

Example: 4

Preparation of manganese doped polyaniline Emeraldine salt dispersion and facile casting on to the ceramic sensor substrate

1. Preparation of manganese doped polyaniline Emeraldine salt dispersion a. Encapsulation of aniline molecules with a surfactant dodecyl benzene sulfonic acid (DBSA) in purified water.

b. Addition of manganese chloride as a dopant to the contents of step 1 , c. Polymerizing the contents of step 2 by addition of oxidizing agent ammonium peroxydisulfate to form manganese doped polyaniline Emeraldine salt.

d. H3PO4 was added onto step 3 product, to obtain manganese doped polyaniline Emeraldine salt dispersion.

2. The above manganese doped polyaniline Emeraldine Salt dispersion is coated on to the substrate by facile casting method.

Example: 5

Preparation of manganese doped polyaniline Emeraldine salt dispersion and facile casting on to the ceramic sensor substrate (0.2wt% manganese chloride concentration)

1 . Preparation of manganese doped polyaniline Emeraldine salt dispersion

a. l mL of aniline and 0.348g of dodecyl benzene sulfonic acid (DBSA) is dispersed in 20mL purified water.

b. 0.002g of manganese chloride as a dopant is added to the contents of step c. The contents of step 2 are polymerized by 2.28g of oxidizing agent ammonium peroxydisulfate to form manganese doped polyaniline Emeraldine salt.

d. lmL of H3PO4 was added onto step 3 product, to obtain manganese doped polyaniline Emeraldine salt dispersion.

Example: 6

Preparation of manganese doped polyaniline Emeraldine salt dispersion and facile casting on to the ceramic sensor substrate (0.3wt% manganese chloride concentration)

1. Preparation of manganese doped polyaniline Emeraldine salt dispersion

a. lmL of aniline and 0.348g of dodecyl benzene sulfonic acid (DBSA) is dispersed in 20mL purified water.

b. 0.003g of manganese chloride as a dopant is added to the contents of step c. The contents of step 2 are polymerized by 2.28g of oxidizing agent ammonium peroxydisulfate to form manganese doped polyaniline Emeraldine salt.

d. lmL of H₃PO4 was added onto step 3 product, to obtain manganese doped polyaniline Emeraldine salt dispersion.

Example: 7 Preparation of manganese doped polyaniline Emeraldine salt dispersion and facile casting on to the ceramic sensor substrate (0.4wt% manganese chloride concentration)

1 . Preparation of manganese doped polyaniline Emeraldine salt dispersion

a. lmL of aniline and 0.348g of dodecyl benzene sulfonic acid (DBS A) is dispersed in 20mL purified water.

b. 0.004g of manganese chloride as a dopant is added to the contents of step c. The contents of step 2 are polymerized by 2.28g of oxidizing agent ammonium peroxydisulfate to form manganese doped polyaniline Emeraldine salt.

Example 8: Measurement of Resistance The sensors are entered in corresponding measuring chamber lhat has been developed especially for the working with small concentrations of formaldehyde. The resistance of the sensitive layer is read out by a multimeter (RISH multi 12S) which ensures the collection of measuring data in combination with a computer. Figure 2 shows a function of time the curve of a resistance measurement (Sensor element prepared with 0.2wt% of manganese chloride with respect to aniline for lppm of formaldehyde in four has cycles). Said data can be transformed by mathematical operations into the terms sensor signal and sensitivity, in order to get the rough indication about the quality of sensor for a certain application. In Figure 3, the sensor signals of different compositions of sensitive layers are indicated.

Claims

1. A sensor for detecting gases, comprising at least one gas-sensitive zone applied on a substrate, characterized in that the gas-sensitive zone comprises a nanocomposite material of polyaniline and manganese oxide (Mn0₂).

2. The sensor according to claim 1 , characterized in that at least one gas-sensitive zone is in the form of a layer.

3. A method for producing a sensor according to claim 1 , wherein the production of the gas-sensitive zone is effected by means of facile casting method.

4. The method according to claim 3, characterized in that organometallic compound of manganese is dissolved in purified water and polyaniline polymer used as source materials.

5. The method according to claim 3, characterized in that the source materials are manganese chloride and aniline.

6. The method according to claim 5, characterized in that the source material manganese chloride in each case is used in concentrations of about 0.2wt% to 0.4wt% with respect to aniline.

7. Use of the sensor according to claim 1 , for online gas detection.

8. Use of the sensor according to claim 1 , for detecting formaldehyde.

9. Use of the sensors according to claim 1 , for detecting gas in home environment or in the business establishments