Preparação e caracterização de híbridos de óxido de ferro magnético com PAni dopada com ácido cítrico e sua avaliação em adsorção/fotodegradação

Abstract

Recently, the materials with combined of organic-inorganic properties have been an alternative as adsorbent materials in carbon dioxide and dyes absorption. Polyaniline (PAni) with its electrical properties and iron oxide with its magnetic properties can form hybrid materials with the ability to adsorb organic dyes present in waste water. The objective of this work is to prepare polyaniline doped with citric acid PAni(AC), to prepare its hybrids with OM and to evaluate the adsorption and photodegradation of the methylene blue dye. The synthesis of magnetic iron oxide was made by the co-precipitation method with iron salts in aqueous and alkaline medium. The preparation of PAni(AC) was carried out by chemical polymerization of anilinium citrate salt using ammonium persulfate (PSA) as an oxidizing agent. The OM/PAni(AC) hybrids were obtained from the in situ chemical polymerization of aniline and citric acid in the presence of iron oxides, in the proportions by weight of aniline: iron oxide of 1:1 (H–1), 1:2 (H–2) and 2:1 (H–3). The samples were characterized by vibration absorption spectroscopy in the infrared region, X-ray diffraction, thermogravimetric analysis, scanning electron microscopy with dispersive energy spectroscopy and transmission electron microscopy, Mössbauer spectroscopy, vibrating sample magnetometry and electrical conductivity measurements by the four-point method. The characterization results showed the formation of magnetic iron oxide in maghemite and magnetite phase, PAni(AC) and OM/PAni(AC) hybrids. The PAni(AC) and hybrids samples showed electrical conductivity in the order of 10-2 S cm-1. In the adsorption and photodegradation test the UV–Vis spectrophotometer was used to monitoring the methylene blue concentration after the contact time. In the adsorption, the H–1, H–2 and H–3 hybrids showed a decrease of the concentration of the methylene blue dye in 64 %, 38 % and 77 %, respectively, in 9 h of contact. In the photodegradation test, the hybrids H–1, H–2 and H–3 obtained, respectively, 87 %, 84 % and 86 % reduction of the concentration of the dye during the same time of the adsorption. After 24 h contact of the H–1, H–2 and H–3 hybrids in dye solution under ultraviolet radiation, the reduction of the dye concentration was observed in 99 %, 99 % and 97 %. Samples of the OM/PAni(AC) hybrids demonstrated that they are materials with adsorbent properties of the methylene blue dye and that the adsorption process prevails over the photodegradation.