Hierarchical (ZnO/ZnFe₂O₄/α-Fe₂O₃)–TiO₂ heterostructures with Strain-Tunable Photoluminescence

TiO₂ nanoparticles decorated hierarchical ZnO/ZnFe₂O₄/α-Fe₂O₃ nanospheres have been prepared using a two-step hydrothermal synthesis method. Microstructural studies such as FESEM and HRTEM reveal the formation of hierarchical heterostructure between ZnO/ZnFe₂O₄/α-Fe₂O₃ and TiO ₂ systems. This heterostructure system exhibits a higher surface area (66.19 m² g⁻¹) than the hierarchical core (53.54 m² g⁻¹), while increasing in average pore sizes from 5 nm to 9 nm. At an optimum concentration (0.082 M) of TiO₂ precursor, Titanium Isopropoxide (TTIP), the developed heterostructure facilitates effective heterojunction formation between anatase TiO₂ and ZnO/ZnFe₂O₄/α-Fe₂O₃. This results increase in tensile strain in coupled TiO₂ nanoparticles by more than 100% than the bare TiO ₂ nanoparticles prepared in the same reaction condition. Formation of the heterojunction is further correlated with reduced photoluminescence for this system. A higher concentration of TTIP (0.122 M), the strain generated in TiO ₂ is found less and so developed system shows enhanced photoluminescence. A very high concentration of TTIP (0.236 M) leads to the formation of a significant fraction of fine-sized TiO₂ nanoparticles, along with weakly coupled TiO₂ on the hierarchical core, resulting in a blue shift of the photoluminescence peaks and enhanced emission across the entire spectral range. The results of the photocatalytic experiments support the findings from the photoluminescence analysis.