Humidity effect on ammonia sensing properties of substituted and unsubstituted cobalt phthalocyanines Thibaut Sizun, Marcel Bouvet n , Jean-Moı¨se Suisse Institut de Chimie Mole ´culaire de l’Universite ´ de Bourgogne, CNRS UMR 6302, Universite´ de Bourgogne, 21078 Dijon, France article info Article history: Received 3 February 2012 Received in revised form 10 April 2012 Accepted 19 April 2012 Available online 28 April 2012 Keywords: Humidity Ammonia Gas sensor Organic electronics Molecular material Phthalocyanine Environment abstract In this paper, we studied the effect of humidity on the response of cobalt phthalocyanine—containing resistors to ammonia, in the ppm range. We pointed out the fact that, when alternating exposure periods with recovery periods, the humidity effect had to be carefully studied, in correlation with the flow variation. Thus, for a sulfonated cobalt phthalocyanine, the effect of NH 3 was totally screened as soon as the relative humidity (RH) was above 10%. On the contrary, when using unsubstituted cobalt phthalocyanine (CoPc) as sensing material, the sensors’ response to NH 3 appears to be quite stable in a wide RH range, allowing a discrimination between 12, 25 and 50 ppm of NH 3 over the 10–70% RH range. Finally, CoPc offers a promising perspective as sensing material for air quality control applications, even at relatively high humidity levels. & 2012 Elsevier B.V. All rights reserved. 1. Introduction Most people know of the dangers CO 2 poses for the environ- ment, being a green house gas and of the negative role played by ozone in our cities, being responsible for pollution peaks. But, for a full air quality awareness, the impact of many other gases on environment and/or health has to be considered. Air quality should be monitored outdoors as well as indoors and compounds such as BTEX (benzene, toluene, ethylbenzene and xylene), VOC (Volatile Organic Compounds) and also NH 3 [1,2] must be kept in check. This latter gas is encountered most of the time in industry because of its use as refrigerant gas and in raw materials as fertilizer. As a result, it is important to monitor NH 3 concentra- tions in air as a safety measure to protect industrial employees. In order to do so, European air quality labor legislation for NH 3 sets a daily exposure limit at 20 ppm. Many detectors that cover this range are available for sale. However, those sensors, which are often used as alarm or leakage detectors, could be improved to be much more compact, more simple and less sensitive to other gaseous species. The main drawback of such devices is indeed their lack of selectivity towards NH 3 , which makes them prone to the influence of other species. Moreover, within an industrial environment the effect of humidity is not very well known. In literature, many solutions for NH 3 sensing are available. Those are based on various kinds of transducers, namely electrochemi- cal, acoustic, optical or conductimetric [3–9]. However, articles which deal specifically with cross sensitivity between NH 3 and humidity are quite rare [10–15]. Most of the time, when neces- sary, humidity sensors are combined with NH 3 sensors. This kind of setup using multiple sensing devices is rather expensive because of the supplementary sensors and electronics, and because of computer generally added for in situ data processing, especially for principal component analysis or neural network [5,8,10]. Moreover, many sensors such as catalytic sensors, are equipped with a heating component that consumes a lot of power. This is the reason why new materials must be studied to address these issues. Materials with a simple processability are needed, associated with a transduction principle suitable for simple electronic design and data processing. They should also be able to work at room temperature. All these conditions must be fulfilled to allow a cost effective device for this application. In this study, we decided to use molecular materials commonly found in organic electronics [16,17]. Phthalocyanines are inter- esting candidates for the development of conductimetric sensors [18–21]. These compounds offer a large variation of molecular properties, which can be tuned by introducing various chemical moieties. Thus, it is possible to introduce hydrophilic and/or hydrophobic substituents, which opens the door to low cost deposition methods like aqueous solution processing, Langmuir– Blodgett [22,23], Langmuir–Sch ¨ afer [24] and related deposition Contents lists available at SciVerse ScienceDirect journal homepage: www.elsevier.com/locate/talanta Talanta 0039-9140/$ - see front matter & 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.talanta.2012.04.037 n Corresponding author. Tel.: þ33 380396086; fax: þ33 380396098. E-mail address: marcel.bouvet@u-bourgogne.fr (M. Bouvet). Talanta 97 (2012) 318–324