Abstract
A comparative study on the structure and photocatalytic activity of halo-aggregated and differently connected ZrO_2@TiO_2 and TiO_2@ZrO_2 nanocomposites was investigated here towards photodegradation of Alizarin yellow GG model azo dye. The nanocomposites were synthesized by two-step sol-gel method with predominant monoclinic phase for ZrO_2, anatase phase for TiO_2, and characterized through different structural and spectroscopy tools. The photocatalysts with high adsorption capability were however differing in their photodegradation efficiency attributed to varying preferential binding at their interfaces and Zr~(4+) substitution in the TiO_2 lattice. Between the two nanocomposites, superior photocatalytic property was shown by ZrO_2@TiO_2 exhibiting 90-93% degradation efficiency with reproducibility. The growth of titania over zirconia in ZrO_2@TiO_2 reduced the surface states and defects of the core nanocrystal (NC) through strong Zr-O-Ti binding, besides providing shallow traps in smaller TiO_2 NCs that enhanced the separation of photogenerated carriers. The process was also assisted through trapping of holes by surface OH groups on ZrO_2 reducing the carrier migration to TiO_2. The type I heterojunction had favorable positive and negative potentials for valence and conduction bands in ZrO_2 and TiO_2 compared to intermediate superoxide anion and hydroxyl radical generation potentials that catapulted the dye degradation. The interfacial contact in TiO_2@ZrO_2 nanocomposite on the other hand, has been very weak as understood from their absorption and photoluminescence spectra resulting in poorer degradation efficiency. Alizarin yellow GG being a prominent textile azo dye and there are not many reports on its photodegradation, the study also assumes significance in the context of sunlight driven photocatalysis and environmental remediation.
NSTL
Elsevier