RESUMEN
Special attention has recently been paid to surface-defective titanium dioxide and black TiO2 with advanced optical, electrical, and photocatalytic properties. Synthesis of these materials for photodegradation and mineralization of persistent organic pollutants in water, especially under visible radiation, presents interest from scientific and application points of view. Chemical reduction by heating a TiO2 and NaBH4 mixture at 350 °C successfully introduced Ti3+ defects and oxygen vacancies at the surface of TiO2, with an increase in the photocatalytic degradation of amoxicillin-an antibiotic that is present in wastewater due to its intense use in human and animal medicine. Three TiO2 samples were prepared at different annealing temperatures to control the ratio between anatase and rutile and were subjected to chemical reduction. Electron paramagnetic resonance investigations showed that the formation of surface Ti3+ defects in a high concentration occurred mainly in the anatase sample annealed at 400 °C, contributing to the bandgap reduction from 3.32 eV to 2.92 eV. The reduced band gap enhances visible light absorption and the efficiency of photocatalysis. The nanoparticles of ~90 m2/g specific surface area and 12 nm average size exhibit ~100% efficiency in the degradation of amoxicillin under simulated solar irradiation compared with pristine TiO2. Mineralization of amoxicillin and by-products was over 75% after 48 h irradiation for the anatase sample, where the Ti3+ defects were present in a higher concentration at the catalyst's surface.
RESUMEN
Cation-substituted hydroxyapatite (HA), standalone or as a composite (blended with polymers or metals), is currently regarded as a noteworthy candidate material for bone repair/regeneration either in the form of powders, porous scaffolds or coatings for endo-osseous dental and orthopaedic implants. As a response to the numerous contradictions reported in literature, this work presents, in one study, the physico-chemical properties and the cytocompatibility response of single cation-doped (Ce, Mg, Sr or Zn) HA nanopowders in a wide concentration range (0.5-5 at.%). The modification of composition, morphology, and structure was multiparametrically monitored via energy dispersive X-ray, X-ray photoelectron, Fourier-transform infrared and micro-Raman spectroscopy methods, as well as by transmission electron microscopy and X-ray diffraction. From a compositional point of view, Ce and Sr were well-incorporated in HA, while slight and pronounced deviations were observed for Mg and Zn, respectively. The change of the lattice parameters, crystallite size, and substituting cation occupation factors either in the Ca(I) or Ca(II) sites were further determined. Sr produced the most important HA structural changes. The in vitro biological performance was evaluated by the (i) determination of leached therapeutic cations (by inductively coupled plasma mass spectrometry) and (ii) assessment of cell behaviour by both conventional assays (e.g., proliferation-3-(4,5-dimethyl thiazol-2-yl) 5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium assay; cytotoxicity-lactate dehydrogenase release assay) and, for the first time, real-time cell analysis (RTCA). Three cell lines were employed: fibroblast, osteoblast, and endothelial. When monophasic, the substituted HA supported the cells' viability and proliferation without signs of toxicity. The RTCA results indicate the excellent adherence of cells. The study strived to offer a perspective on the behaviour of Ce-, Mg-, Sr-, or Zn-substituted HAs and to deliver a well-encompassing viewpoint on their effects. This can be highly important for the future development of such bioceramics, paving the road toward the identification of candidates with highly promising therapeutic effects.