The Interaction of CO to the Co(salen) Complex Bull. Korean Chem. Soc. 2012, Vol. 33, No. 4 1297 http://dx.doi.org/10.5012/bkcs.2012.33.4.1297 The Interaction of CO to the Co(salen) Complex in to PEDOT:PSS Film and Sensor Application Raheleh Memarzadeh, Farhad Panahi, † Sirus Javadpour, * Ali Khalafi-Nezhad, † Hui-Bog Noh, ‡ and Yoon-Bo Shim ‡,* Department of Materials Science & Engineering, Shiraz University, Shiraz, Iran. * E-mail: Javadpor@sirazu.ac.ir † Department of Chemistry, College of Sciences, Shiraz University, Shiraz, Iran ‡ Department of Chemistry and Institute of BioPhysio Sensor Technology, Pusan National University, Busan 609-735, Korea * E-mail: ybshim@pusan.ac.kr Received January 20, 2012, Accepted January 27, 2012 The interaction between carbon monoxide (CO) and a cobalt-salen complex (Co(salen)) was studied and applied to detect CO. The metal complex doped PEDOT:PSS film exhibited good sensitivity to CO and differentiate CO from other gases. The response of the composite to CO was reversible (RSD < 5%) change in resistance upon removal of CO gas from the test chamber. The effects of adding Co(salen) in the probe film on the response of the sensor were investigated using AFM, XPS, and FT-IR spectroscopy. The sensitivity of the sensor increased as the Co(salen) concentration enhanced as it increased from 0.0 to 1.5 wt. %, where the highest sensitivity (%ΔR/R o ) of -25.0 ± 0.05% was achieved with 1.0 wt. % Co(salen). The sensor containing probe exhibited a linear response (R 2 = 0.983) in the range of 0.5 to 10.0% CO (v/v) N 2 , and the detection limit was 1.74% CO (v/v) in N 2 . Key Words : Chemical sensor, PEDOT:PSS, Co(salen), Carbon monoxide Introduction A reliable carbon monoxide (CO) sensor must be able to qualitatively and quantitatively detect of the toxic CO gas. 1 There are two main classes of gas-sensing materials; organic and inorganic compounds. Inorganic gas-sensing materials are sensitive to gases at high operating temperatures. 2,3 Organic materials such as conductive polymers have received considerable attention in recent years because they can operate at room temperature. 4 The electrical conductivity of a conductive polymer changes when it is exposed to a particular gas; thus, conductive polymers can be used as gas- sensing probes. Among conductive polymers, poly(thiophene) is an important class of gas-sensing polymers due to its many applications in sensing. 5,6 It has been used in many different kinds of chemical and electrochemical sensors such as gas sensors and biosensors. 4,7-12 In recent, poly(3,4-ethyl- enedioxy) thiophene-poly(styrenesulfonate) (PEDOT:PSS) has been used in recent studies and is an important con- ductive polymer (its conductivity is approximately 10 S/ cm). 13,14 PEDOT:PSS has been used as a base substrate for gas sensors because it has several advantages in comparison with other conductive polymers, namely, high conductivity, high stability, abundance, and low cost. 15-18 PEDOT:PSS has a polar structure where PEDOT is positively charged and PSS is negatively charged. Therefore, PEDOT:PSS is more sensitive to polar species such as water vapor, NO and CO. 19 There are some reports on the incorporation of metals, metal oxides, and organometallic complexes into intrinsically conductive polymers to enhance the electron or ion mobility and improve conductivity and stability. 20 For example, an Fe-Al doped polyaniline film exhibited a fast response and excellent sensitivity to CO in a previous study. 21 The re- sponse of ultra thin films of polyaniline-SnO 2 and poly- aniline-TiO 2 nanocomposites to CO have also been studied. 22 Several metal organic complexes have also been added to conductive polymer sensors to enhance sensor selectivity and sensitivity. 23 PEDOT:PSS has been doped separately with materials such as Fe, Al, Kryptofix-21 (Kr 21), Kryptofix- 22 (Kr 22), 1,4-dioxane, and piperazine and in some cases with mixtures of these materials. 16 Among doped PEDOT:PSS polymers, a morpholine doped PEDOT:PSS film behaves as a sensor for CO sensor. Cobalt compounds have also been added to PEDOT:PSS as selective CO gas adsorbents to improve selectivity of the resulting sensor. 24-26 Therefore, in this study, we enhanced the performance of a PEDOT:PSS CO sensor by adding a Co(salen) complex to a PEDOT:PSS film. In the present study, the CO sensor probe was fabricated by doping PEDOT:PSS with a Co(salen) complex. A PEDOT: PSS film containing Co(salen) complex was characterized using atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and fourier transform infrared (FT-IR) spectroscopy. Experimental parameters such as the gas flow rate and Co(salen) concentration were controlled to optimize the sensitivity of the CO sensor. In addition, the performance of sensors with and without the Co(salen) complex were compared. Experimental Materials and Instruments. Chemical reagents were purchased from Fluka and Aldrich Co. (U.S.A.) and were used without further purification. The solid content, maximum