P123-PMMA Dual-Templating Generation and Unique Physicochemical Properties of Three-Dimensionally Ordered Macroporous Iron Oxides with Nanovoids in the Crystalline Walls

Three-dimensionally (3D) ordered macroporous (3DOM) iron oxides with nanovoids in the rhombohedrally crystallized macroporous walls were fabricated by adopting the dual-templating [Pluronic P123 and poly(methyl methacrylate) (PMMA) colloidal microspheres] strategy with ferric nitrate as the metal precursor in an ethanol or ethylene glycol and methanol mixed solution and after calcination at 550 °C. The possible formation mechanisms of such architectured materials were discussed. The physicochemical properties of the materials were characterized by means of techniques such as XRD, TGA/DSC, FT-IR, BET, HRSEM, HRTEM/SAED, UV−vis, XPS, and H2-TPR. The catalytic properties of the materials were also examined using toluene oxidation as a probe reaction. It is shown that 3DOM-structured α-Fe2O3 without nanovoids in the macroporous walls was formed in the absence of P123 during the fabrication process, whereas the dual-templating strategy gave rise to α-Fe2O3 materials that possessed high-quality 3DOM structures with the presence of nanovoids in the polycrystalline macropore walls and higher surface areas (32−46 m2/g). The surfactant P123 played a key role in the generation of nanovoids within the walls of the 3DOM-architectured iron oxides. There was the presence of multivalent iron ions and adsorbed oxygen species on the surface of each sample, with the trivalent iron ion and oxygen adspecies concentrations being different from sample to sample. The dual-templating fabricated iron oxide samples exhibited much better low-temperature reducibility than the bulk counterpart. The copresence of a 3DOM-structured skeleton and nanovoids in the macropore walls gave rise to a drop in the band-gap energy of iron oxide. The higher oxygen adspecies amounts, larger surface areas, better low-temperature reducibility, and unique nanovoid-containing 3DOM structures of the iron oxide materials accounted for their excellent catalytic performance in the oxidation of toluene.