Tunable TiO2-Heterophase Junctions for Studying and Enhancing Photocatalytic H2 Production Under Visible Light

Abstract

Photocatalytic performance of titanium dioxide under visible light was optimized by preparing heterophase compounds (containing two or more phases) by hydrolysis method using TiCl₄ as a precursor with different concentrations (0.5, 0.7, 1, and 2) to adjust condensation modes of Ti⁴⁺. The structural and textural properties of the synthesized TiO₂ multiphase were fully characterized by XRD, Raman scattering, FTIR, BET, MEB-EDX, XPS, diffuse UV–vis, and EIS spectroscopy. The increase of TiCl₄ amount precursor has a significant effect on the heterophase junctions of TiO₂ structure and more especially on textural and structural properties. The best specific surface area (131 m²/g) is observed for the sample at high Ti-content (2 in Ti⁴⁺). The anatase phase (79%) is detected only for 0.5 in Ti⁴⁺ sample. However, both rutile (R) and brookite (B) phases are present in 0.7, 1, and 2 Ti-contents. On the one hand, the band gap of 2.9 eV allows titanium dioxide to be active under visible light. In addition, the presence of rutile/brookite heterophase junction contributes significantly to the improvement of active sites for photocatalytic reaction. The separation efficiency of photogenerated electrons and holes contributes to photocatalytic evolution performance under visible light for hydrogen production. The optimal sample (0.7 content in Ti⁺⁴ species) which presents in its structure 52% of rutile and 46% of brookite phases presented the highest photocatalytic activity with a 230 µmol/h of hydrogen generation, attributed to the heterophase junctions R52/B46, highly pore size 20.60 nm, and relatively small bandgap energy 2.974 eV. This work opens new horizons on the creation and study of a multiphase TiO₂ that works under visible light in the fields of renewable energies and various other fields.