Gema González

Study of the mechano-chemical transformation of goethite to hematite by TEM and XRD

A study of the mechano-chemical transformation of goethite to hematite was carried out using transmission electron microscopy (TEM) and X-ray diffraction (XRD). Synthetic goethite was dry-ground in air for different times up to 104 h and characterized with the aim of understanding the mechanisms taking part in the transformation, the phases formed, and particle distribution, morphology and size. It was found that the transformation is topotactic, without the formation of intermediate phases, and takes place by fragmentation of crystals, creation of twins, dehydration of goethite particles, and formation of voids. The voids are arranged in almost parallel striations, and are associated with the loss of hydroxyl groups and formation of hematite in small domains of equiaxial crystallites. The hematite crystal size is about 10 nm at the initial stages and after prolonged periods of grinding remains constant at about 19 nm.

Infuence of Microstructure in Drug Release Behavior of Silica Nanocapsules

Meso- and nanoporous structures are adequate matrices for controlled drug delivery systems, due to their large surface areas and to their bioactive and biocompatibility properties. Mesoporous materials of type SBA-15, synthesized under different pH conditions, and zeolite beta were studied in order to compare the different intrinsic morphological characteristics as pore size, pore connectivity, and pore geometry on the drug loading and release process. These materials were characterized by X-ray diffraction, nitrogen adsorption, scanning and transmission electron microscopy, and calorimetric measurements. Ibuprofen (IBU) was chosen as a model drug for the formulation of controlled-release dosage forms; it was impregnated into these two types of materials by a soaking procedure during different periods. Drug loading and release studies were followed by UV-Vis spectrophotometry. All nano- and mesostructured materials showed a similar loading behavior. It was found that the pore size and Al content strongly influenced the release process. These results suggest that the framework structure and architecture affect the drug adsorption and release properties of these materials. Both materials offer a good potential for a controlled delivery system of ibuprofen.