HYDROTHERMAL SYNTHESIS OF COPPER II-DOPED TITANATES FROM DOPED PRECURSORS

• DOI: 10.22533/at.ed.3172242226101

• Palavras-chave: Photocatalysis, Nanostructures, Doped precursors, Titanates.

• Keywords: Photocatalysis, Nanostructures, Doped precursors, Titanates.

• Abstract:

  TiO₂ is an interesting material for wide application such as photovoltaic cells, photonic crystals and photocatalysts. The Polymeric Precursor Method is suitable for synthesizing reactive materials, however, during the polymer decomposition, the process can increase the temperature of the sample, in the case of the TiO₂ semiconductor, leading to a phase transition (anatase-rutile). In this work, two ways to control the phase transition were used: a pre-calcination step and the insertion of a dopant (Cu²⁺). Citric acid was dissolved in isopropyl alcohol, then titanium isoproxide was added and the solution was stirred, ethylene glycol was added and the temperature was increased for polymer formation. Copper ions were inserted in this step. This resin was subjected to heat treatment at 350 °C for 4 hours and then at 500 °C for 2 hours (TiO₂-350-500; TiO₂-Cu-350-500). For XRD about 42% rutile was observed which is due to the fact that organic firing leads to phase transition. For TiO₂-350-500 about 11% rutile was observed. The TiO₂-Cu-350-500 sample showed 100% anatase phase. Using the Scherrer equation it was found that the pre-calcination step leads to an increase in crystallite size from 26.02 nm to 31.74 nm (TiO₂-350-500). The same effect was observed after the insertion of copper ions (37.81 nm), caused mainly by the differences in the ionic radius: Ti⁴⁺= 0.60 Å and Cu²⁺ = 0.72 Å. With Raman spectroscopy it is possible to observe the presence of the main active modes related to the anatase phase, for the TiO₂-350-500 sample, located at 146, 195, 396, 514 and 637 cm^-1. For the copper sample (TiO₂-Cu-350-500) the 146 cm^-1 peak, related to the titanium atom at the center of the octahedron, was shifted to 151 cm^-1, indicating that during doping the titanium was efficiently replaced by copper.