Application of polypyrrole coated on wood sawdust for removal of Cr(VI) ion from aqueous solutions R. Ansari * , N. Khoshbakht Fahim Chemistry Department, Faculty of Science, Guilan University, Rasht, Iran Received 9 May 2006; received in revised form 8 November 2006; accepted 3 February 2007 Available online 12 February 2007 Abstract In this study polypyrrole (PPy) was synthesised chemically on the surface of sawdust that has already been soaked with monomer solution (pyrrole). FeCl 3 were used as chemical oxidants for oxidation of pyrrole into polymer (PPy/Cl). The sawdust coated by PPy (PPy/SD) was used as an efficient sorbent for removal of Cr(VI) ion from aqueous solutions. It was found that PPy/SD is very easy and simple to prepare and can be used as an effective sorbent for removal of Cr(VI) from water and wastewater solutions. The Cr(VI) removal is assumed to be mainly due to the anion exchange properties of the polymer which is formed as PPy + /Cl  . The introduced sorbent in this paper shows that PPy/SD can be used to elim- inate or separate anionic contaminations from aqueous solutions under open circuit conditions. Ó 2007 Elsevier Ltd. All rights reserved. Keywords: Removal; Cr(VI); Polypyrrole; Chemical polymerisation; Sawdust; pH 1. Introduction Chromium is one of the heavy metals that its compounds are extensively used in chemical indus- tries. Its widespread use is in electroplating, textile, leather tanning, metal finishing, wood preservation, and electroplating and chromate preparation indus- tries. It is also used as oxidizing agents in the man- ufacturing many organic chemicals. Environmental pollution problem by heavy metal ions is generally considered to be a global environmental issue because the impacts and damages affect not only the countries origin, but go beyond their national boundaries and can reach a global scale. Among the heavy metal ions, Cr(VI) is highly poisonous and endangers public health and the environment. It has been considered as a powerful carcinogenic agent. The threshold value for hexavalent chro- mium is 0.1 mgl 1 [1]. Therefore, removal of this ion from water and wastewater is considered to be obligatory. Chromium is most commonly found in two oxidation states, Cr(III) and Cr(VI), and all other oxidation states are not stable in aerated aqueous media. The chemistry of Cr(VI) is greatly dependent on pH of the solution. At pH value below 1, the predominant species is H 2 CrO 4 Cr(VI) normally exists in the anionic form, as Cr 2 O 2 7 , HCrO  4 or CrO 2 4 forms depending on pH and con- centration (Eqs. (1)–(3) and Table 1). In acidic 1381-5148/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.reactfunctpolym.2007.02.001 * Corresponding author. Tel.: +98 0131 3233262; fax: +98 0131 3233510. E-mail address: ransari@guilan.ac.ir (R. Ansari). Reactive & Functional Polymers 67 (2007) 367–374 www.elsevier.com/locate/react REACTIVE & FUNCTIONAL POLYMERS