Structural, dielectric properties and electrical conductivity of highly efficient photocatalytic TiO2@ZrO2 system

In this work, binary TiO₂@ZrO₂ hybrid nanotubes was prepared using a fast efficient solvothermal procedure. The solvent used in this reaction is 1.3-propandiol reacted as both solvent, oxidant and surfactant agent. The obtained binary TiO₂@ZrO₂ hybrid nanotubes was then fully characterized to evaluate the microstructure, size and shape using XRD diffraction technique, TEM microscopy and XPS spectrometry. The photocatalytic activity, evaluated via methyl orange degradation under UV irradiation, showed a remarkable 94.6 % efficiency and excellent recyclability. In addition to their photocatalytic performance, the materials exhibit interesting electrical properties. After that, the microwave dielectric properties of binary TiO₂@ZrO₂ hybrid nanotubes were investigated over the range of frequency between 100 Hz and 1 MHz and in the temperature range of 20 °C-300 °C. The AC conductivity is insured by a process defined as a hopping transport mechanism. The Nyquist plots show the dominance of the bulk effect in the compound. Electrical phenomena in the material can appropriately be modeled in terms of an equivalent circuit with R and CPE in parallel. The fitting procedure used here allows us to determine the value of R and parameters of CPE with good precision. At temperatures above 100 °C the equivalent circuit model shows the appearance of an additional Constant Phase Element (CPE2) in equivalent circuit which can be related to the dielectric relaxation processes associated with the migration of oxygen vacancies or ions such as Ti⁴⁺ and/or Zr⁴⁺. This ionic migration could be responsible for the dielectric relaxation observed at low frequencies and could also explain the large decrease in permittivity in this frequency range.