Abstract
In this work, we prepared oriented mesoporous thin films of silica on various solid substrates using the pluronic block copolymer P123 as a template. We attempted to insert guest iron oxide (FexOy) nanoparticles into these films by two different methods: (a) by co-precipitation—where iron precursors are introduced in the synthesis sol before deposition of the silica film—and subsequent oxide production during the film calcination step; (b) by preparing and calcining the silica films first then impregnating them with the iron precursor, obtaining the iron oxide nanoparticles by a second calcination step. We have examined the structural effects of the guest nanoparticles on the silica film structures using grazing incidence X-ray scattering (GISAXS), high-resolution transmission electron spectroscopy (HRTEM), spectroscopic ellipsometry, X-ray photoelectron spectroscopy (XPS), and Raman microscopy. Formation of nanoparticles by co-precipitation may induce substantial changes in the film structure leading, in our adopted process, to the appearance of lamellar ordering in the calcination stage. On the contrary, impregnation-based approaches perturb the film structures much more weakly, but are also less efficient in filling the pores with nanoparticles.
Highlights
Ordered inorganic mesoporous films are a promising category of functional materials for many applications due to their high specific surface area, pore sizes that can be tailored in the nanometer range, and the possibility to incorporate functional groups, or to immobilize active molecules in the mesopores or in the inorganic network [1,2,3,4,5,6,7,8]
Mesoporous silica films were synthesized by dip-coating via evaporation-induced self-assembly (EISA) using, for the most part, a previously described procedure [50], which is a modification of the method originally described by Alberius et al [15]
Depending on the synthesis conditions, SiO2 films templated by P123 may have a lamellar, hexagonal, or cubic crystalline structure [15,16,17,18]
Summary
Ordered inorganic mesoporous films are a promising category of functional materials for many applications (e.g., in catalysis, drug delivery, sensing, and photonics) due to their high specific surface area, pore sizes that can be tailored in the nanometer range, and the possibility to incorporate functional groups, or to immobilize active molecules in the mesopores or in the inorganic network [1,2,3,4,5,6,7,8]. In this work we have examined two ways of inserting iron oxide (FexOy) semiconductor nanoparticles in P123-templated oriented mesoporous silica films. The second method is to prepare the silica film, remove the template by calcination, impregnate the film with precursors of the guest, and make a further calcination step to create oxide nanoparticles on the surface and in the pores of the film. Raman microscopy may give useful information about the presence of nanoparticle species on the surface and in the pores of the films [37,38] It discriminates between different crystalline forms (e.g., hematite and maghemite, or magnetite in the case of iron oxides) [39,40,41,42] and sometimes even the size of the particles, through measured broadenings and shifts of the Raman bands [43].
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