Three-dimensionally ordered macroporous (3DOM) LiMn 2 O 4 spinel was prepared by a colloidal templating process. An opal structure consisting of monodispersed poly[styrene-co-methacrilic acid] beads (380 nm in diameter) was used as a template. After infiltration of Li and Mn nitrates, the assembly was calcined in air at temperatures between 500 and 700 °C. Chemical processes were studied by means of thermal analysis, X-ray diffraction (XRD), and solid-state nuclear magnetic resonance (NMR). Morphological and microstructural characterizations were carried out by scanning and transmission electron microscopy (SEM, TEM) and by gas adsorption volumetry. Despite the simple preparation procedure, several steps are detected, which prove to be critical for the successful formation of high-quality 3DOM materials. Optimization of the preparation conditions gave extended macroporous networks with relatively smooth nanocrystalline spinel walls and a surface area of 24 m 2 /g. Porosity results from three ranges of pores: (1) the macroporous sublattice (replica of the opal lattice), (2) the pores formed after mineralization of the tetrahedral and octahedral holes of the template, and (3) the porosity from the nanocrystallites forming roughened macroporous walls. Films of 3DOM LiMn 2 O 4 were prepared on conductive substrates and used as electrodes, showing fast and reversible lithium deinsertion over a large number of cycles without suffering significant morphological or electrochemical degradation.

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SiO 2 -aerogel inverse opals were produced for the first time in supercritical carbon dioxide (scCO 2 ) with three-dimensional (3D) latex arrays as templates. The polymeric templates were reacted with tetraethyl orthosilicate in humidified scCO 2 at 40 °C and 85 bar. After calcination of the template, highly porous materials replicating the structure of the original template were obtained. Polystyrene latex particles decorated with different hydrophilic groups were organized in 3D ordered arrays and used as templates. Particles were impregnated with benzenesulfonic acid, which activates the condensation process of silica precursors. Scanning and transmission electron microscopy (SEM and TEM) images showed that the reaction in scCO 2 takes place only on the particle surface and that the octahedral and tetrahedral holes in the original fcc packing of latex spheres are empty. N 2 adsorption isotherms showed broad adsorptiondesorption loops characteristic of mesopores. Brunauer-Emmett-Teller (BET) surface areas are large and range from 270 to 594 m 2 /g, since these materials are structured aerogels produced directly in scCO 2 . Analysis of the desorption branch revealed the presence of an extremely large mesoporosity that is located in the macropore walls. The porosity of the materials obtained for each template is different. Furthermore, shrinkage of the network upon condensation in scCO 2 was small. The synthesis of inverse opals in scCO 2 overcomes some of the limitations of the liquid-phase techniques, being a faster method of synthesis and, at the same time, rendering materials of unique properties.