Alteration of the structure and surface composition of crystalline-amorphous porous clay heterostructures upon iron doping from metal-organic source

摘要

Porous clay heterostructures (PCH) have been prepared through the surfactant directed assembly of organosilica in the galleries of synthetic layered clay mineral Laponite. Fe-containing PCH nanostructures with nominal (Si+Mg)/Fe=10 were prepared by post-synthesis impregnation of porous clay hybrid composites with metal-organic C6H5FeO. After impregnation, the as-synthesized Fe-PCH samples were either directly calcined at 550 degrees C or, prior to calcination, hydrothermally treated in the high pressure reactor. The impact of the PCH composite doping by the trivalent (Fe3+) cations on the physicochemical properties was investigated with the use of spectroscopic methods. Detailed information on the character and lattice positions occupied by iron, the extent of its incorporation, its local structure and symmetry within samples were provided by comparing the FTIR analysis with the Fe-57 Mossbauer spectroscopy and Si-29 MAS NMR data. The nature of different Fe species formed after post-synthesis treatments was determined by Mossbauer spectroscopy and HRTEM. High pressure treatment resulted in the alteration of sample morphology and better, more homogenous dispersion of the Fe species in the composite lattice. FTIR indicated slight impairment of the clay structure in the PCH network followed by surface enrichment with Mg species because of Mg cations leaching from the octahedral sheets as confirmed by XPS study. Copyright (c) 2016 John Wiley & Sons, Ltd.