A Precursor Approach for the Development of Lace-like Fe2O3 Nanocrystallites Triggered by Pressure Dependent Nucleation and Growth of Akaganeite over Clay Based Composites for Toluene Combustion

Embedded catalysts for toluene combustion, featuring iron oxide (FeOx) moieties on the surface of clay derived porous heterostructural supports (PCH) were developed. The nucleation and growth of Fe4Cl0.44O3.56(OH)(4.44)(H2O)(0.2) (akaganeite) in the function of Fe precursor interaction with the support entailed creation of nanostructured Fe oxides on the PCH surface. The hydrothermal forcing of ions migration and thermal transformation of as-synthesized Fe-PCH altered the surface composition and crystallinity of the formed nanostructured Fe oxides, thereby affecting the advantageous effects of donation gauged by electronic transfer. The polymorphism of Fe oxides created on PCH supports resulted in diverse catalytic activity of toluene combustion. Analysis of XPS Fe 2p core excitations showed that elongation of crystallization time of iron moieties on as synthesized Fe-PCH, as well as shortening of the annealing time, led to highly oxidized Fe species, mainly in the form of an alpha-Fe2O3 phase. Pressure dependent functionalization induced morphology changes with consequent uncommon lace-like morphology of alpha-Fe2O3 nanocrystals. The octahedral coordination of Fe3+ species was found to be beneficial in toluene decomposition, while the presence of Fe3O4 diminished the catalysts activity. The distinction of the alpha-Fe2O3 and Fe3O4 based on DFT calculations and experimental assignments at the far-infrared (FIR) region is proposed.