Akaganeíta Sintética [?-FeO(OH)] Obtida por Termohidrólise e na Superfície de Argilas Esmectitas: Caracterização e Aplicação

Abstract

In this work, new clay-iron oxide materials were synthesized through the forced hydrolysis of a ferric chloride (0.1 M) at 90ºC for 48 hours in different concentrations of a clay suspension. Another synthesis was performed using only the ferric chloride (0.1M) solution as a control material, from which aliquots were removed at intervals of 4, 8, 12, 24, 36, and 48 hours for analysis by scanning electron microscopy (SEM). The X-ray diffractometry (XRD) revealed the presence of hematite (10%) and akaganèite (90%), which were quantified using the Rietvield method. The SEM images revealed the presence of crystals measuring approximately 200 nm after the first 4 hours of the reaction. The rodlike morphology was predominant, with some small spheres interspersed. In the mixed materials (MM_FeClays) after Rietvield refinement, the presence of small amounts of another iron oxide (FeO(OH)) was revealed, in the proportion of 2.8% to 3.7% for the MM_FeClay Volclay and 1.5% to 2.7% for MM_FeClay Argel. SEM images revealed the presence of only acicular morphology, with no change in the size of the crystals observed. Simultaneous thermal analysis (TG/DTA) of the MM_FeClays showed no significant differences when compared with one another, and a slight difference in the stability of the starting materials was noted. Akaganèite seemed to gain a bit of thermal stability, while the clay lost some of its thermal stability, showing synergy among its parts. The electrochemical behavior of the clays was studied using a carbon paste modified electrode (CPME) for the MM_FeClays. The CPMEs showed electrochemical response in saline and acidic media, and the electrochemical response was faster in the CPME_FeClay electrodes. Of these, the best results were obtained for the MM_FeClay containing 0.5% clay. The electrode response was directly related to the electrolyte used, and different phases of iron oxides can be generated in this way , including metallic iron. The CPME can also serve as a reagent in the manufacture of new electrodes, possibly hexacyanoferrates and ferrites. The CPMEs exhibited satisfactory electrochemical response to glucose (at 0.53V), especially the MM_FeClay Volclay (VFe05).