Hierarchical Ti1−xZrxO2−y nanocrystals with exposed high energy facets showing co-catalyst free solar light driven water splitting and improved light to energy conversion efficiency

Abstract

Zr substitution in the anatase TiO₂ lattice with exposed high energy facets has been accomplished by a solvothermal process and characterized in detail. We observed that the selection of the solvent (n-propanol, nP or iso-propanol, iP) in the presence of titanium tetrachloride–zirconium n-propoxide mixture and structure directors played a crucial role in tuning the morphology, crystal structure and exposed facets of the resulting nanocrystals. Rietveld refinement of the PXRD data revealed the formation of Ti_0.665Zr_0.335O_1.955 (TZ_nP) and Ti_0.912Zr_0.088O_1.963 (TZ_iP) nanocrystals. TEM confirmed the presence of low index high energy {100} and {001} facets in cube-like TZ_nP and hollow spherical TZ_iP decorated with truncated crystallites, respectively. XPS revealed the presence of Ti³⁺ (13–16%) defect states in both the systems. These nanocrystalline materials were explored as co-catalyst free photocatalysts in solar water splitting for H₂ generation. Interestingly, Zr modified photocatalysts (TZ_nP and TZ_iP) showed H₂ evolution rates of 90 and 356 μmol g⁻¹ after 6 h, respectively without any support of a Pt co-catalyst. Further, the overall solar light to energy conversion efficiencies of TZ_nP and TZ_iP as photoanodes in dye sensitized solar cell (DSSCs) have been investigated and their efficiencies were found to be 5.40 and 7.52%, respectively. Therefore, these Zr modified TiO₂ nanocrystals could be very promising as cost-effective photocatalysts for future fuel generation and DSSC materials.