This review article provides an exhaustive overview of efficient synthesis, growth mechanism and research activities of multiphase TiO2 nanostructures to provide their structural, morphological, optical and biological properties co-relations.

In this review, we discuss new developments and recent trends in both amorphous and crystalline Al2O3 oxide nanofluids related to their phase dependent characteristics in detail. Nowadays, nanofluids have gained significant attention with the enhanced energy/heat efficiency, which is highly desirable to improve the performance of any energy based devices and technology. This review article systematically describes the various chemical synthesis routes followed by bottom-up approaches, surface morphologies, and detailed microstructure characteristics, and phase dependent thermal as well as optical properties for potential use of such materials in various applications.

Herein, we have demonstrated the high yield facile growth of Al2O3 nanowires of uniform morphology with different polymorph phases (e.g. γ, δ and θ) via a hydrothermal method with varying calcination temperatures. The synthesized θ-Al2O3 nanowires were well characterized by XRD, FTIR, SEM/EDAX, AFM and HRTEM techniques. Microstructural analysis confirmed that the dimensions of the individual θ-Al2O3 nanowires are approximately in the ranges 5-20 nm in width and 40-150 nm in length, and the aspect ratio is up to 20. AFM results evidenced the uniform distribution of the nanowires with controlled morphology. Furthermore, UV-vis spectroscopic data reveal that the estimated optical band gap of the θ-Al2O3 nanowires was ~5.16 eV. The photoluminescence spectrum exhibits blue emission upon excitation at a wavelength of 252 nm. Time-resolved spectroscopy demonstrates that these nanowires illustrate a decay time of ~2.23 nanoseconds. The obtained photoluminescence results with a decay time of nanoseconds suggest that the θ-Al2O3 phase could be an exceptional choice for next generation fast optical sensors.