Influence of pH on the specific surface area of polyaniline matrices

We report the successful measurement of the specific surface area of chemically synthesized and treated polyaniline (PANI) and its composite PANI/silica (SiO2). PANI was synthesized chemically from an aqueous solution of aniline and hydrochloric acid (HCl) in the presence of an oxidant, ammonium peroxydisulfate [(NH4)(2)S2O8]. In the synthesis of PANI/SiO2, SiO2 was incorporated from its colloidal solution contained in the solution for the polymerization of PANI. PANI and PANI/SiO2 thus synthesized were pretreated with double-distilled water (pH = 6.95), aqueous HCl (pH = 1.09), and aqueous ammonia (pH = 10.15) solutions to control their pH levels. Surface morphologies of the treated PANI and PANI/SiO2 matrices were investigated with scanning electron microscopy. The successful incorporation of SiO2 into the PANI/SiO2 composite was confirmed by the characteristic infrared absorption band at 1096 cm(-1). The adsorption of methylene blue, which was found to follow the Langmuir isotherm, onto the prepared materials was probed to estimate the real surface area. The base-treated PANI matrix showed a higher surface area than the acidic and neutral ones. The incorporation of SiO2 into the PANI matrix yielded a larger surface area. However, the treated PANI/SiO2 showed the same trend as the treated PANI matrices. (C) 2008 Wiley Periodicals, Inc.