Optical ammonia gas sensor based on nanostructure dye-doped polypyrrole
Introduction
Among many different substances used in the production of explosives, fertilizers, and as an industrial coolant, ammonia is very dangerous for human health even at very low concentration. Thus, it is necessary to detect such substance with sensitive and selective devices. Moreover, these devices must be simple, small, with the possibility of mass production leading then to low cost [1]. In the past decade, many kinds of ammonia sensors have been developed based on different sensing mechanisms. These include electrical, mass, or optical-based methods [2], [3], [4], [5], [6], [7], [8], [9], [10], [11], [12]. Among all the sensors developed, optical devices have proved their ability to meet drastic requirements such as strong immunity to electromagnetic noise, high stability, low power consumption, and compatibility with explosive environments [13]. Various optical methods to measure ammonia based on dye incorporated into polymer layers have been developed in the last two decades [5].
Conducting polymers (CPs) are of great interest for a large number of applications due to their easy processing and relatively low cost compared to other materials such as inorganic ones [14], [15], [16]. The incorporation of a chromophore into a CPs chain offers a route to combine a polymer with electrical conductivity with optical properties (e.g. high extension coefficient and fluorescence quantum yields) of the dye. The presence of dye in the polymer chain has no effect in polymerization mechanism and the electrochemical properties of the polymer. These polymers after incorporation of functional dyes show large changes in optical spectra when exposed to distinctive gases, humidity, acid–base active gases, etc. which can be effectively used for optical gas sensors having very fast response time [17].
The eriochrome cyanine R (ECR) molecule (Fig. 1), frequently used in chemical analysis as an indicator for complexometry, has two carboxylic groups, one hydroxyl, one carbonyl and one sulfonic group which ensure compatibility with polar solvents that are commonly used in chemical polymerization [18].
In this paper, we report the use of absorption spectroscopy method for ammonia sensing with a dye-doped polypyrrole (PPy–ECR) film. We prepared the PPy–ECR with nanostructure layer by simple and straightforward in situ chemical polymerization of pyrrole on the surfaces of commercial polystyrene. Designed sensor with relatively high sensitivity and fast response time was developed for detection of ammonia in gas phase. According to our knowledge, this is the first study reported on a dye-doped polypyrrole (PPy–ECR) film as optical transducer of ammonia for determination of ammonia in the gas phase.
Section snippets
Reagents
Pyrrole (Fluka, Switzerland) was distillated and stored in a refrigerator in dark prior to use. Ferric chloride (FeCl3), eriochrome cyanine R (ECR), methanol, ethanol, acetonitrile, hexane, sodium hydroxide and hydrochloric acid were purchased from Merck (Darmstadt, Germany). All amines were analytical grade products and used without further purification. Ammonia solutions were prepared from a stock ammonia solution (from Aldrich) by proper dilution methods using double distilled water and
Optical properties of PPy–ECR film
Dye sensitization of conducting polymer (DCPs) has resulted in the development of new materials having excellent properties for applications in sensor devices. Two synthetic routes are usually adopted in production of DCPs; electro-polymerization [19], [20] or chemical oxidation [20] of numerous resonance stabilized aromatic molecules in acid dye solutions. Chemical synthesis entails the oxidative polymerization of the monomer in an acidic medium using an oxidant in the presence of a dye. For
Conclusion
A sensitive and selective optical ammonia gas sensor has been developed using dye-doped polypyrrole film. The sensor presents significant absorbance variations upon exposure to different ammonia gas concentrations at room temperature and exhibits fast response time (50 s) and a low detection limit (5 μg L−1), which is well under IDLH (immediate danger to life and health) limit of 210 mg m−3 and PEL (permissible exposure) limit of 35 mg m−3 (∼25 ppm) regulated by NIOSH (National Institute for
Acknowledgements
The financial support of the Research Council of Tarbiat Modares University and the Iranian Nanotechnology Initiative Office (INSF) is gratefully acknowledged.
Naader Alizadeh received his PhD degree in analytical chemistry at the Tarbiat Modares University in 1996. He is currently a professor of analytical chemistry in Tarbiat Modares University, Tehran, Iran. His research interests cover chemical and electrochemical synthesis of nano-structure conducting polymers and its applications in chemical sensors and microextraction methods, exchange kinetics and complexation of macrocyclic ligands.
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Naader Alizadeh received his PhD degree in analytical chemistry at the Tarbiat Modares University in 1996. He is currently a professor of analytical chemistry in Tarbiat Modares University, Tehran, Iran. His research interests cover chemical and electrochemical synthesis of nano-structure conducting polymers and its applications in chemical sensors and microextraction methods, exchange kinetics and complexation of macrocyclic ligands.
Farnaz Tavoli was born on 9 July 1985 and received her BSc in chemistry from Shahid Beheshti University in 2008, MSc degree in analytical chemistry from Tarbiat Modares University in 2011. She is currently a PhD student of Tarbiat Modares University in analytical chemistry. Her research interests cover synthesis and application of conducting polymers and its application in optical sensors.