Photocatalytic activity of ZnO-TiO₂ hierarchical nanostructure prepared by combined electrospinning and hydrothermal techniques

In this study, a new hierarchical nanostructure consisting of zinc oxide (ZnO) and titanium dioxide (TiO₂) was prepared by an electrospinning process followed by a hydrothermal technique for use as a photocatalyst for dye degradation. First, the electrospinning of a colloidal solution consisting of titanium isopropoxide/poly(vinyl acetate)/zinc nanoparticles was performed to produce polymeric nanofibers embedded in solid nanoparticles. Calcination of the obtained electrospun nanofiber mats in air at 600 °C produced TiO ₂ nanofibers containing ZnO nanoparticles (i.e., ZnO-doped TiO ₂ nanofibers). The ZnO nanoparticles formed were then exploited as seeds to produce the outgrowth ZnO branches around the TiO₂ nanofibers using the hydrothermal technique. Photodegradation of methyl red and rhodamine B (RB) dyes was examined individually using four photocatalysts: ZnO nanoparticles prepared by the same hydrothermal technique, pristine TiO ₂ nanofibers, ZnO-doped TiO₂ nanofibers and the produced nanostructure. The results showed that the introduced ZnO-TiO₂ hierarchical nanostructure can eliminate all the methyl red dye within 90 min and the rhodamine B dye within 105 min. However, the other three nanostructures could not totally remove any of the dyes, even after 3 h. Therefore, the introduced nanostructure has higher photocatalytic activity than any of its ingredients individually, which highlights the advantages of synthesizing this novel structure.