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    Síntese, caracterização e aplicação de semicondutores nanoescalares compostos por óxidos de Ti e Cu para a redução fotoeletrocatalítica de CO2
    (Universidade Federal de São Paulo (UNIFESP), 2021) Almeida, Juliana de [UNIFESP]; Rodrigues, Christiane de Arruda [UNIFESP]; Universidade Federal de São Paulo
    Copper species exhibit favorable positions in the conduction band and high potential for reducing compounds adsorbed on its surface, being widely studied on the CO2 conversion towards in multicarbon oxygenated products. However, when applied in photoelectrocatalytic processes, they are easily oxidized and susceptible to photocorrosion, so their stability is a challenge. Copper species can be coupled with other materials, such as TiO2, a n-type semiconductor with excellent charge transfer properties and chemical stability. In addition, it nanostructured morphology has their properties are enhanced, obtaining better photocatalytic efficiency. Therefore, this work evaluated the synthesis of semiconductors obtained from substrates of the Ti-xat.% Cu (x = 0.5 / 5.5 / 10 / 20 / 30 and 50) system after annealing and annealing / quenching heat treatment. The substrates phases were identified by optical microscopy, diffraction and X-ray dispersion and quantified using Rietveld method. These data revealed that the solid solution was absent only in the equiatomic alloy and that phases, such as Ti3Cu and Cu3Ti were detected. The nanostructured films of Ti– O - Cu were growth by anodic process from the manufactured alloys, it showed nantubular morphology, but the equiatomic composition was exception, which showed only formation of porous layer on its surface. This indicates, that Ti-α or Ti-β phases even doped with copper were essential for the formation of the nanotubes. The matrices were investigated by scanning electron microscopy and X-ray diffraction and revealed that the presence of intermetallic and Ti3Cu, when present in the substrates, leads to the formation of matrices with ternary oxides. The photoelectrochemical and impedance spectroscopy characterizations showed that the films of the Ti-O-Cu system have n-type behavior, but obtained an anodic shift in the potential for increasing the current density, characterizing the formation of a pn heterojunction. Therefore, these were used as a photocathode in the photoelectrocatalytic reduction of CO2 under 100 mW / cm2 illumination. The reduction reactions led, after 60 min, the formation of 0.10 mmol L-1 of methanol for the matrices composed only of binary oxides and a significant concentration of ethanol around 2.20 mmol L-1 for those rich in presence of ternary oxides. Therefore, the presence of Cu2Ti4O and Cu3TiO5 oxides promote significant concentrations of ethanol and high selectivity of the final products, as well as the stability of copper species.