An acid-free route for the facile synthesis of iron-functionalized mesoporous silicas: Transformation between hollow nanospheres and cage-like mesostructures

Iron-substituted silicas with hollow nanospherical morphology and cage-like mesostructure have been synthesized using triblock copolymer F127 as surfactant and tetramethoxysilane (TMOS) as silica source with no necessary addition of mineral acids. Iron-functionalized hollow nanospheres were obtained using Fe(acac)(3) as iron source. When Fe(NO3)(3) was employed as iron source, iron-containing cage-like FDU-12 mesostructure and hollow nanospheres were formed with Fe/Si molar ratio lower than 0.008 and higher than 0.015, respectively. The formation of hollow spheres at high Fe/Si ratio can be regarded as gradually dissociation of nanocages from Fe-FDU-12. The structure of the iron centers was determined by spectroscopic methods (UV-vis and UV-Raman measurements) and by elemental analyses. The facile structural evolution between cage-like and nanospherical structures may be helpful for further understanding the formation mechanism of mesoporous silicas. (C) 2014 Elsevier Inc. All rights reserved.