A good correlation was obtained between the electronic properties of Cu-doped anatase TiO₂ by virtue of both physical chemistry characterization and theoretical calculations. Pure and Cu-doped TiO₂ were synthesized. The composition, structural and electronic properties, and the band gap energy were obtained using several techniques. The method of synthesis used produces Cu-doped anatase TiO₂, and XRD, XPS and Raman spectroscopy indicate that Cu atoms are incorporated in the structure by substitution of Ti atoms, generating a distortion of the structure and oxygen vacancies. In turn, the band gap energy of the synthesized samples decrease drastically with the Cu doping. Moreover, periodic density functional theory (DFT-periodic) calculations were carried out both to model the experimentally observed doped structures and to understand theoretically the experimental structures obtained, the formation of oxygen vacancies and the values of the band gap energy. From the analysis of density of states (DOS), projected density of states (PDOS) and the electron localization function (ELF) a decrease in the band gap is predicted upon increasing the Cu doping. Thus, the inclusion of Cu in the anatase structure implies a covalent character in the Cu–O interaction, which involves the appearance of new states in the valence band maximum with a narrowing in the band gap.

This study introduces a new synthesis route for obtaining homogeneous chitosan (CS)-silica hybrid aerogels with CS contents up to 10 wt%, using 3-glycidoxypropyl trimethoxysilane (GPTMS) as coupling agent, for tissue engineering applications. Aerogels were obtained using the sol-gel process followed by CO₂ supercritical drying, resulting in samples with bulk densities ranging from 0.17 g/cm³ to 0.38 g/cm³. The textural analysis by N₂-physisorption revealed an interconnected mesopore network with decreasing specific surface areas (1230–700 m²/g) and pore sizes (11.1–8.7 nm) by increasing GPTMS content (2–4 molar ratio GPTMS:CS monomer). In addition, samples exhibited extremely fast swelling by spontaneous capillary imbibition in PBS solution, presenting swelling capacities from 1.75 to 3.75. The formation of a covalent crosslinked hybrid structure was suggested by FTIR and confirmed by an increase of four hundred fold or more in the compressive strength up to 96 MPa. Instead, samples synthesized without GPTMS fractured at only 0.10–0.26 MPa, revealing a week structure consisted in interpenetrated polymer networks. The aerogels presented bioactivity in simulated body fluid (SBF), as confirmed by the in vitro formation of hydroxyapatite (HAp) layer with crystal size of approximately 2 µm size in diameter. In vitro studies revealed also non cytotoxic effect on HOB^® osteoblasts and also a mechanosensitive response. Additionally, control cells grown on glass developed scarce or no stress fibers, while cells grown on hybrid samples showed a significant (p < 0.05) increase in well-developed stress fibers and mature focal adhesion complexes.

The sol-gel process has been found to be successful in applications for the conservation and restoration of stone. However, a well-known drawback of the materials obtained by this process is their tendency to crack during drying inside the pores of the treated stone. In this article, we present an overview of our current research centred on producing crack-free sol-gel materials for consolidating and protecting building stone. A novel synthesis, in which a surfactant acts as a template to make the pore size of the gel network coarser and more uniform, is shown to provide an effective alternative for preventing the cracking of consolidants. We also highlight an alternative pathway, in which we add an organic component to the silica precursor in the presence of the surfactant. The hybrid organic-inorganic gel prepared in our laboratory provides excellent waterproofing to the stones under study.