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 Fe 3+ 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, N 2 sorption, EPR, SEM-EDX, TEM, FT-IR and UV-visible spectroscopies, and Mo ¨ssbauer measurements. The average pore diameters were 2.2-2.8 nm, and the mesopore volumes were 0.39-0.5 cm 3 g -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 Mo ¨ssbauer spectroscopic data suggested that most of the iron species are tetrahedrally coordinated Fe 3+ attached to the silica framework.

Direct synthesis of highly ordered Fe-SBA-15 mesoporous materials under weak acidic conditions

“…The spectrum of the Fe-SBA-15 sample prepared with pH value of 3.0 shows an obvious absorption centered at 320 nm in addition to the band centered at 210-250 nm, which is assigned to the presence of octahedral extra framework iron oligomer. The spectra of the Fe-SBA-15 samples prepared with pH value of 4.0 or higher show another obvious absorption band centered at %500 nm in addition to the band at 210-250 nm and the band at 320 nm, indicating that aggregated iron oxide clusters are also formed [20]. From above results, formation of the different iron species are very sensitive to the pH values of the solutions and different iron species could be controlled through tuning the pH values of the synthesis solutions.…”

“…Nonionic triblock copolymer surfactant EO 20 PO 70 EO 20 (P123, Aldrich) was used as the structure-directing agent. Concentrated HCl aqueous solution was used as acid source.…”

“…Notably, many efforts have been devoted to the incorporation of Al, Ti and V into SBA-15 [11][12][13][14][15][16][17], including the two-steps pH adjusting methods [14,15], the hydrolysis-controlled methods [15,16], and microwave-hydrothermal procedures [17]. However, the incorporation of Fe into the framework of SBA-15 by simple direct hydrothermal methods prepared in acidic media has rarely been reported [18], although Fe-zeolites and Fe-MCM-41 prepared in basic media have been widely investigated [6,[19][20][21][22][23][24][25]. It has been reported that Fe species in the framework of mesoporous materials such as MCM-41 [23], MCM-48 [24], and HMS [25] are tetrahedral coordinated but easily escape from the framework and turn to iron oxide when these materials are calcined at high temperature to remove the organic template.…”

Selective catalytic oxidation of H2S over iron oxide supported on alumina-intercalated Laponite clay catalysts

“…In any case, the adsorption bands can be divided into three charge transfer (CT) bands around 220 nm, 350 nm, 500 nm, respectively. The band under 300 nm corresponds to isolated iron species (Fe 3+ ) in an oxidic environment, while the band in range of 300-370 nm can be assigned to the existence of oligonuclear Fe 3+ x O y complexes and the band around 500 nm can be ascribed to larger Fe 2 O 3 nanoparticles [21][22][23]. Moreover, the spectra are dominated by the band around 220 nm, attributed to isolated iron species, indicating that iron oxide are well dispersed on the support.…”

Removal of citric acid from aqueous solution by catalytic wet peroxidation using effective mesoporous Fe‐MCM‐41 molecular sieves

“…15 Fe-MCM-41 can be prepared by isomorphic substitution of Si by Fe in MCM-41. 16,17 Fe-MCM-41, which has redox properties, 18 is expected to enhance intraparticle diffusion when compared to microporous zeolite materials, owing to its special characteristics such as higher surface area together with large pore size. In this study Fe-MCM-41 with various Si/Al ratios (25, 50, 75 and 100) were synthesized, characterized and evaluated for removal of citric acid by oxidation with H 2 O 2 .…”