The Open Process Chemistry Journal, 2009, 2, 1-5 1 1875-1806/09 2009 Bentham Open Open Access Removal of Nitrite Ions from Aqueous Solutions Using Conducting Electroactive Polymers R. Ansari * , N. Khoshbakht Fahim and A. Fallah Delavar Chemistry Department, University of Guilan, Rasht, Iran Abstract: This paper deals with a new application of polypyrrole (PPy) and polyaniline (PAni) electroactive polymers synthesized chemically, coated on sawdust and then used for removal of NO 2 - ions from aqueous solutions. Adsorption studies were performed using both batch and column systems at room temperature. The effects of some important parame- ters such as initial concentration, adsorbent dosage, and contact time on the uptake of NO 2 - ions were also investigated. PPy and PAni conducting electroactive polymers were found to be effective adsorbents for the uptake of nitrite ions from aqueous solutions. Adsorption studies have shown that pH of the nitrite solution has an important influence on the nitrite ion uptake. In order to find out the possibility of the frequent use of the adsorbent, desorption study was also carried out in this investigation. Key Words: Nitrite ion, polypyrrole, polyaniline, sorption, desorption. 1. INTRODUCTION Nitrite ion is one of the most important wide-spread con- taminants of aqueous environment and serves as a significant indicator of natural water quality. The increasing level of nitrite in surface or ground waters results mainly from agri- cultural application of fertilizers as well as from many indus- trial processes [1]. Removal of nitrite ions from waters has received increas- ing attention in recent years because of their potential harm- ful impact on human health. NO 2 - is highly toxic to certain species of fish. Nitrite ions enter the bloodstream through gills by a mechanism that normally transports chloride [2]. After entering the bloodstream, NO 2 - oxidizes iron in the hemoglobin molecule from ferrous state (Fe 2+ ) to the ferric state (Fe 3+ ). The resultant product, called methemoglobin, is incapable of reversibly binding with oxygen, so exposure to NO 2 - causes respiratory distress because of the loss in oxy- gen- carrying capacity of blood. Nitrite is one of the major components of wastewater from nuclear power production and involved in the corrosion and bacterial process known as the nitrogen cycle. Nitrite and its salts have many industrial and commercial applica- tions. Sodium nitrite is a food additive that has been used for decades to preserve meat, poultry and fish. When used alone or in conjunction with sodium nitrate, nitrite gives cured meats their characteristic reddish-pink color, flavor and tex- ture. The allowed concentration of nitrite in drinking water and food reported by the public health service is 0.06 mg L -1 [3]. Elevated concentrations of nitrite can be found in water receiving nitrogenous effluents, in various hypoxic environ- ments or in effluents from agricultural application of fertili- *Address correspondence to this author at the Chemistry Department, Uni- versity of Guilan, Rasht, POB 41335-1914, Iran; Fax: 0098-0131-3233262; E mail: ransari@guilan.ac.ir zers and industries producing metals, dyes and celluloid [4]. Ion exchange, reverse osmosis, electrodialysis, distillation and activated carbon adsorption are processes that have been employed for uptake of nitrite from drinking water supplies [4], but these processes are expensive and a brine of difficult management is generated. Recently, we have found that polypyrrole and polyaniline conducting electroactive polymers (CEPs) can be employed for removal of some toxic metal ions from aqueous solutions [5, 6]. Synthesis of these reactive and functional polymers have been carried out by either electropolymerization at a conductive substrate (electrode) through the application of an external potential, or chemical polymerization in solution by the use of a chemical oxidant [7-10]. The overall polymeri- zation reaction of pyrrole can be shown as the following (Fig. 1). H N n Oxidize A - Pyrrole H N N H H N + n A - Polypyrrole Fig. (1). Overall polymerisation reaction of polypyrrole. Where, the A - (termed as dopant or counterion) is the anion of oxidant in monomer solution or reduced product of oxidant. The value of n has been determined to be between 2.2 and 2.4. The level of oxidation of ppy is 0.25-0.32 per pyrrole unit, depending on the type and the charge of the incorporated anion, corresponding to one anion for every 3-4 pyrrole units in order to achieve electroneutrality, and this makes up 30-40% of the final weight of the polymer [10]. However, chemical polymerization remains of interest for processing purposes, because it may be easier to scale up this batch process for bulk production.