Morphological control of 1D and 3D TiO2 nanostructures with ammonium hydroxide and TiO2 compact layer on FTO coated glass in hydrothermal synthesis

The effects of ammonium hydroxide (AH) concentration in the hydrothermal reaction precursors and time on growth, morphological, optical and spectroscopic properties of TiO2 nanostructures have been investigated in detail. The dandelion nanostructures were also observed on the top surface of vertically aligned nanorods whose density increases with increase in AH concentration and reaction time. Dandelion nanostructures were also observed on top of vertically aligned nanorods surface whose density increases with increase in AH concentration and reaction time. The average nanorod length increases with an enhancement in the second generation of nanorods with AH addition. In the case where C-layer was deposited on FPO, the dandelion structures grown via hydrothermal technique were denser exhibiting transformation to flower like morphology. Hence, with AH addition, the formation of 1D/3D (aligned nanorods/dandelion structures) structure has been observed. AH plays crucial role by facilitating second generation crystallite growth and significantly effects resultant morphology. Specifically, the structures grown with AH addition; i.e. primary, first generation and second generation crystals have been observed to be different. Both Raman and XRD studies revealed that nanorods were crystalline (rutile phase) while the C-layer exhibited anatase phase and no extra phase appeared in the spectra. The reflectance increase has been observed with increasing concentration of AH and temperature which is attributed to the increased scattering by dandelion-like structures. (C) 2018 Elsevier B.V. All rights reserved.