Synthesis and characterization of iron-rich highly ordered mesoporous Fe-MCM-41

Abstract

Iron-rich and highly ordered 2D-hexagonal mesoporous ferrisilicates containing predominantly tetrahedrally coordinated Fe3+ in the silica network have been prepared using cetyltrimethylammonium bromide (CTAB) as the structure-directing agent (SDA) under mild alkaline hydrothermal conditions (initial pH = 8-8.5 in the synthesis gel). The optimum limit of iron loading for the ordered mesophase in the present study was 8.2 wt %; beyond this limit, disordered iron oxide/silica phase was observed in the same pH range. These mesoporous ferrisilicate samples were characterized using XRD, N2 sorption, EPR, SEM-EDX, TEM, FT-IR and UV-visible spectroscopies, and Mössbauer measurements. The average pore diameters were 2.2-2.8 nm, and the mesopore volumes were 0.39-0.5 cm3g-1. Moderately high Brønsted acidity was observed in the temperature-programmed desorption (TPD) pattern of ammonia over these mesoporous ferrisilicate materials. Wet chemical analysis, EPR, and Mössbauer spectroscopic data suggested that most of the iron species are tetrahedrally coordinated Fe3+ attached to the silica framework.