Obtenção de um híbrido luminescente derivado de nanotubos de titanato e európio com promissora atividade antibacteriana

Abstract

Considering the role of agents in inhibiting the development of bacteria, it is necessary to develop materials with antibacterial properties, since strains of bacteria have proved resistant to antibiotics, representing a real threat to the success of treatments in hospitals, and infections caused by gram-positive and gram-negative bacteria. In this context, nanohybrid systems, which are materials made up of combinations of materials on the nanometric scale, can be considered as powerful antibacterial materials. These include metal oxide derivatives, such as titanate nanotubes (NtsTi), a low-cost, oxidizing, chemically stable and non-toxic semiconductor. Although this material exhibits absorption in the UV region, other applications can still be envisioned when considering modifications that increase absorption in the visible region. Thus, incorporation with lanthanides, such as the europium ion, could be an interesting strategy, especially when NtsTi and absorbing chromophores are coordinated/adsorbed to the metal center, ensuring greater absorption of the electromagnetic spectrum and thus reducing electron-lacuna recombination. Also to be considered is the increase in the lifetime of the charge carriers and the formation of reactive oxygen species, which results in the oxidation of bacterial membranes. In view of these considerations, this work aimed to synthesize photoluminescent nanohybrids derived from: (i) titanate nanotubes obtained via the alkaline hydrothermal method, (ii) europium ion and (iii) the ligands tenyltrifluoracetone (tta) and 1-10-phenanthroline (phen) to study their potential antibacterial properties. The NtsTi synthesized had a nanotube structure with a diameter of 10 nm and the molecular formula Na2- xHxTi3O7·nH2O. Spectroscopic techniques identified absorption in the 200 to 313 nm region, a band gap of 3.22 eV, and deformations þTi-O and þO-H at 460 and 3360 cm- 1, respectively. The NtsTiEu nanohybrids, synthesized from the functionalization of NtsTi using sodium dodecyl sulphate (SDS), show a tube-shaped morphology, but are agglomerated. In terms of optical properties, the hybrid shows emission in the red region, a characteristic that indicates a suitable absorption/emission mechanism for the europium ion (Eu3+). The spectroscopic techniques confirm a widening of the absorption band to regions between 200 and 400 nm, and a band gap of 3.07 eV, as well as the disappearance of the þTi-O-Na deformation at 896 cm-1. The luminescent nanohybrids (NtsTi[Eu(tta)3phen]) were obtained by adding the ligands tenyltrifluoracetone (tta) and 1-10-phenanthroline (phen) to NtsTiEu. The material had a tubular morphology with an additional layer around the NtsTi due to the incorporation of the ligands (tta and phen). Spectroscopic techniques identified the presence of the tta and phen chromophores at 1624 and 1601cm-1, respectively. The absorptions remained between 200 and 400 nm, with an increase in the band gap to 3.30 eV. Confocal microscopy and photoluminescence spectroscopy showed the presence of europium ion (Eu3+) in the nanohybrids, since there was emission in the red region of the electromagnetic spectrum. Potential antibacterial activity was observed for the luminescent nanohybrid (NtsTi[Eu(tta)3phen]) at concentrations of 12.5 mg L-1, against the bacteria S. aureus and E. coli, identifying inhibition halos of 25 and 31 mm, respectively.