Perovskita livre de chumbo para tratamento de efluentes e combate a patógenos: NaNbO3 com propriedades fotocatalítica e antibacteriana

Abstract

Heterogeneous photocatalysis has been established as an effective technology for addressing environmental challenges, particularly in the treatment of wastewater containing recalcitrant pollutants. Among the materials investigated as photocatalysts, sodium niobate (NaNbO3), a semiconductor with a perovskite-type crystalline structure, has attracted interest due to its physicochemical properties favorable for this purpose. Although antibacterial properties represent an important advantage in materials due to the rise of resistant strains, the use of NaNbO3 in antimicrobial applications remains underexplored. In this context, the aim of this thesis, structured in five papers, was to investigate the photocatalytic and antibacterial properties of NaNbO3 and its structural and compositional modifications, aiming at its application in the removal of emerging pollutants from aqueous media and in the combat against pathogenic bacteria. In the first paper, NaNbO3 was synthesized using the microwave-assisted hydrothermal method (MAHM), followed by thermal treatment, resulting in nanowires and nanograins with high photocatalytic activity. Increasing the calcination temperature promoted the transformation of nanowires into nanograins, which exhibited superior performance in the degradation of Rhodamine B (RhB) under UV light. The high photocatalytic efficiency was attributed to the combination of high crystallinity and favorable morphology. In the second paper, a heterostructured photocatalyst was developed from the previously obtained NaNbO3 nanograins and eumelanin (a pigment extracted from human hair waste). The broad optical absorption of eumelanin, combined with the efficient charge separation promoted by the junction of the materials, enabled the degradation of RhB under visible light. In the following three papers, NaNbO3 was synthesized also synthesized via the MAHM, and the influence of doping with Cu(II), Al(III), and Zn(II) on its photocatalytic activity was investigated. The insertion of these dopants promoted changes in the crystal symmetry and significantly influenced the optical properties of NaNbO3. At optimized concentrations, doping reduced the band gap and the recombination rate of the photogenerated charges, resulting in greater efficiency in the degradation of RhB. In the studies with Cu(II) and Zn(II), antibacterial activity was also evaluated. Doping with Cu(II) resulted in the inhibition of Escherichia coli (E. coli) growth. In the study involving Zn(II), pure NaNbO3 exhibited significant antibacterial activity against E. coli, Staphylococcus aureus (S. aureus), and Klebsiella pneumoniae (K. pneumoniae), while the doped sample also inhibited bacterial growth, although its effectiveness was dependent on the sample concentration. Thus, the results obtained highlight the great potential of NaNbO3 as a photocatalyst for wastewater purification and as an antimicrobial agent. Additionally, the papers produced within the scope of this thesis were the first to report the antibacterial activity of pure NaNbO3, without additional stimulation, against E. coli, as well as to demonstrate its effectiveness against K. pneumoniae and S. aureus.