Direct formation of iron oxide/MCM-41 nanocomposites via single or mixed n-alkyltrimethylammonium bromide surfactants.

Iron oxide/MCM-41 nanocomposites, Fe(2)O(3)/MCM-41, containing 5%, 10%, and 20% (w/w) iron oxide, were prepared via a direct nonhydrothermal method at room temperature. The preparations were preformed by using iron(III) nitrate, tetra-ethoxysilane (TEOS), and cetyltrimethylammonium bromide (CTAB) mixed or unmixed with dodecyltrimethylammonium bromide (DTAB). The produced materials were dried and calcined at 550 °C for 3 h. Test materials were characterized by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), N(2) gas adsorption/desorption isotherms, small angle and wide angle X-ray diffraction (XRD). Results indicate that mixing of CTAB with DTAB does not harm the formation of blank MCM-41 structure. For the composite Fe(2)O(3)/MCM-41 materials, results showed formation of more stable MCM-41 structure with higher surface area and improved porosity in the presence of mixed (CTAB+DTAB) than in the presence of single (CTAB) surfactants for up to 10% Fe(2)O(3)/MCM-41 (w/w). This was explained in terms of the effect DTAB on contraction of the template micellar size to compensate for the expected size expansion upon the addition of ionic iron(III) nitrate precursor. Highly dispersed Fe(2)O(3) nanoparticles were formed in all cases even with the highest iron oxide percentage. Formation of the nanocomposites was postulated to be determined by fast nucleation and slow growth of iron oxide species, which facilitated formation of well dispersed iron oxide nanoparticles inside and on the wall of the MCM-41 material.