Synthetic Metals 159 (2009) 1019–1023 Contents lists available at ScienceDirect Synthetic Metals journal homepage: www.elsevier.com/locate/synmet CO sensor based on polypyrrole functionalized with iron porphyrin Santhosh Paul ∗ , Francis Amalraj, S. Radhakrishnan Polymer Science and Engineering, National Chemical Laboratory, Dr. Homibhaba Road, Pune 411008, India article info Article history: Received 13 November 2008 Received in revised form 18 December 2008 Accepted 12 January 2009 Available online 8 February 2009 Keywords: Chemical sensor Fe(III) porphyrin Polypyrrole Carbon monoxide abstract Polypyrrole (PPy) was chemically functionalized with 5,10,15,20-tetraphenyl-21H,23H-porphyrin iron(III) chloride (FeTPPCl) with special interest on noxious carbon monoxide (CO) gas in ppm level. Controlled functionalization of PPy was achieved with incorporation of various concentrations of porphyrin. The resulted semiconducting material was well characterized by different techniques such as UV–vis spec- troscopy, FTIR, GFAAS, XRD, and EDAX. The functionalized polypyrrole material on interdigitated electrode was experienced an immediate increase in resistance when exposed to carbon monoxide gas at very low concentration. The CO gas interacted very fast with the FeTPPCl functionalized PPy at room temperature (RT) and then slowly saturated. The response of these materials was not unidirectional, but reverses to the original resistance level when CO was removed from the test chamber. The highest response factor (R/R 0 × 100) and lowest response time (t 50 ) obtained are 12 and 169s, respectively. An optimum level of doping (1 mol% of FeTPPCl) was established for the highest sensitivity and the detection level is as low as 100 ppm. © 2009 Elsevier B.V. All rights reserved. 1. Introduction It is well understood that redox properties of the polypyrrole matrix can be modified strongly by the linkage of electroactive species, especially with coordination compounds. Thus, pyrrole- based polymers containing redox sites of adequately designed transition metal complexes like porphyrin, phthalocyanine, etc. have been prepared by chemical as well as electrochemical meth- ods. The polymerization of these pyrrole substituted complexes has produced interesting polymers aimed at catalyzing redox and organic reactions, but not mainly for gas sensor applications [1–6]. Bedioui et al. have shown that pyrrole-based polymers contain- ing porphyrin complexes appeared among one of the candidates for NO gas sensor [7,8] applications. Metal porphyrins dispersed in polyurethane have been used in ion selective electrodes since the selectivity of these detectors was controlled by the central metal atom. For example, with the In(III) as central metal atom gives good response to chloride, Ga(III) for fluoride and Co(III) for nitrate was obtained [9]. It is well known that carbon monoxide interacts with hemoglobin/heme and causes deterioration of their oxygen uptake/transfer activity [10]. Hence, those groups are poten- tial candidates for functionalization of conducting polymer used for detection of carbon monoxide. ∗ Corresponding author. Tel.: +91 20 2590 3002; fax: +91 20 2590 2615. E-mail address: santhosh538@yahoo.com (S. Paul). In this work, we described the synthesis of polypyrrole modi- fied with porphyrin (PPy–FeTPPCl) moieties during in situ chemical polymerization reaction. Carbon monoxide sensitivity of the func- tionalized material was studied in detail. 2. Experimental 2.1. Chemical functionalization of PPy with iron porphyrin A typical reaction as follows: 10mg iron porphyrin (Sigma– Aldrich) was dissolved in 50 mL methanol in a stoppered flask and stirred well with 1.62 g (0.1 M) anhydrous ferric chloride. 1 mL pyr- role (silica column purified) was added into the reaction system with continued stirring, followed by slow addition of 50 mL dis- tilled water. The initial brown colour of the solution became darker with the addition of water. The stirring continued for another two more hours at room temperature to ensure complete oxidation of pyrrole monomer into polypyrrole and the insertion of FeTPPCl into the polymer, which eventually precipitated as a dark residue at the bottom of the flask. The PPy–FeTPPCl material was filtered, washed with distilled water and finally with methanol. It was dried at 60 ◦ C in a vacuum oven. The polymerization process was also monitored continuously while the reaction being carried out in the 10-mm path length dis- posable cell using spectro-electrochemical unit (model USB 2000, Ocean Optics, USA) provided with fiber optic cable, which in turn is interfaced with a computer. The spectra were scanned from 300 to 1000 nm and recorded every minute. 0379-6779/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.synthmet.2009.01.018