Estudo teórico e experimental do processo de formação da polianilina e da adsorção do azul de metileno em pani(adbs)

Abstract

In this work, theoretical models were developed with the purpose of contributing with the formation mechanism of polyaniline (PAni), its doping with dodecylbenzenesulfonic acid (DBSA) and the adsorption properties using methylene blue (AM) as reference. Experimentally, were performed: the chemical synthesis of PAni(ADBS); the dedoping of PAni; the adsorption of methylene blue in aqueous solution by PAni and PAni (ADBS); and the characterization by vibrational spectroscopy in the infrared region, UV-Vis electronic spectroscopy and determination of electrical conductivity using the four-point method. The quantum mechanical methods applied to the molecular modeling were semi-empirical (PM7) and ab-initio (DFT-B3LYP with base functions 3-21G, 6-311 + G *). The modeling suggested that: the ADBS and the aniline are soluble in water forming the anilinium salt (DBS), which was confirmed by infrared vibrational spectroscopy; the ammonium persulphate (PSA) oxidizing agent is water soluble and the most stable product of its reduction, in acid medium, is bisulfate. The results indicated that the anilinium cation is preferably oxidized than aniline. The formation of aniline and anilinium dimers, trimers and tetramers is energetically favorable, indicating that PAni (ADBS) is formed by both aniline/anilinium polymerization and protonation of emeraldine base (BE), in agreement with the experimental results. The modeling showed that AM is water soluble and is better adsorbed by PAni (ADBS) than by BE. This result is also in agreement with the experimental data and shows that there is an "anion rule" in the processes of adsorption with polyaniline.