pH Electrodes Constructed From Polyaniline/zeolite and Polypyrrole/zeolite Conductive Blends P. Malkaj, 1 E. Dalas, 2 E. Vitoratos, 3 S. Sakkopoulos 3 1 Department of Physics, Polytechnic University of Tirana, Tirana, Albania 2 Department of Chemistry, University of Patras, GR-26504 Patras, Greece 3 Department of Physics, University of Patras, GR-26500 Patras, Greece Received 4 July 2005; accepted 24 October 2005 DOI 10.1002/app.23590 Published online in Wiley InterScience (www.interscience.wiley.com). ABSTRACT: A new type of solid state electrodes sensitive to pH changes is described, in which the chemical-sensitive layer consists of Pt microparticles deposited on a conducting polymer (polyaniline, polypyrrole) blend containing 22.7% w/w zeolite. These sensors are stable in aqueous electrolyte solutions of low pH value at temperatures up to 45°C with response time in seconds. At 25°C, sensor sensitivity was -310  40 mV/pH and -1300  100 mV/pH for polyani- line and polypyrrole blends, respectively. Interferences ap- pear to be acceptably small. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1853–1856, 2006 Key words: conducting polymers; electrochemistry; charge transport; blends; surfaces INTRODUCTION Electrochemical cells containing conducting polymers as electrodes permit the construction of miniature, compact detectors that cannot be damaged in highly corrosive environments. 1–3 A major impediment to the application of the conducting polymers for the con- struction of electrochemical devices has always been their processibility, as well as their mechanical prop- erties. The development of polymer blends resulted in the improvement of their mechanical properties, 4–7 and the application of polyaniline (PA) and polypyr- role (PPy) in electrochemical devices has been re- ported. 8 –10 In the present work, the behavior of a new type of solid state pH electrodes based on an electro- chemical cell constructed of a Pt microparticles layer on a conducting polyanilne/zeolite and PPy/zeolite blend with 22.7% w/w in zeolite is studied. Zeolite with its pores, channels, and cages provides great effective surface for cations to be arranged by adsorp- tion, intercalation, or cation exchange reaction. As a result, this has the minimization of the cell volume. Moreover, the acidity of the zeolite surface ensures the good adhesion with the conducting polymer and so the easy charge carrier transport through the cell, min- imizing the internal resistance and maximizing its ef- ficiency. Besides, the intercalation of a conducting polymer into a porous and leafy material, like zeolite, protects the former from degradation, reducing its aging rate. EXPERIMENTAL Clay mineral must be purified according to the follow- ing procedure 11,12 : first, it is dispersed in distilled water and the emulsion is stirred for 24 h. If the solution becomes viscous like a gel, water is added until the gel is dispersed. The suspension is then pu- rified by sedimentation to collect 2m, in diameter, fraction, washing with 1M CH 3 COONa and CH 3 COOH (pH = 5) to remove carbonate. Then wash- ing with 0.3M sodium citrate, 1M NaHCO 3, and Na 2 S 2 O 4 to remove free iron sulfide takes place. The precipitate is dispersed in 100 mL 1N NaCl and is stirred for 30 min. The emulsion is repeatedly centri- fuged to obtain the same type of exchange cations. Polyaniline and PPy blends were prepared by chemical polymerization at room temperature in 0.2N HCl aqueous solution (monomer: oxidant = 1:1 mol %) and in the presence of pure zeolite added prior of the monomer and oxidant addition. 13,14 The oxidant was FeCl 3 (Ferrak, Analar). The precipitates were washed with 1N HCl and dried overnight under ni- trogen atmosphere. From these precipitates, PA/zeolite and PPy/zeo- lite blends disc-shaped specimens 13 mm in diameter and 1.5 mm thick were made in an infra red press with 22.7 and 22 w/w content in zeolite, respectively. The selection of the above concentrations is due to the best mechanical properties of the disc-shaped specimens in further handling and chemical deposition of Pt micro- Correspondence to: E. Vitoratos (vitorato@pelops.physics. upatras.gr). Journal of Applied Polymer Science, Vol. 101, 1853–1856 (2006) © 2006 Wiley Periodicals, Inc.