Formation and crystallization of TiO2 nanostructures on various surfaces

A comparative study of the synthesis of TiO₂ nanorods on fluorine-doped tin oxide (FTO) glass, Si, SiO₂, Si/Ta, Si/TiN, Si/TiN/Ti and Si/HFO₂ substrates by hydrothermal reaction is presented. Detailed analysis on the growth of TiO₂ on pre-annealed Si/TiN/Ti and HfO₂ (HFO) surfaces is also given. For Si/TiN/Ti, a pre-annealing procedure led to the transformation of Ti to a TiO₂ layer which acts as a seed for aligned growth of TiO₂ nanorods. In contrast, Si/HFO does not provide a nucleation site for the formation of aligned nanorods. Various samples were prepared by varying the synthesis conditions, i.e. pre- and post-annealing temperatures and hydrothermal reaction time to figure out the optimum conditions which lead to unidirectional and highly aligned nanorods. X-ray diffraction, scanning electron microscopy, ultraviolet-visible spectroscopy and Raman spectroscopy were used to study structural, morphological and optical properties of synthesized samples. It is found that TiO₂ nanorods exhibit a rutile phase on the Si/Ti/TiN and Si/HFO substrates, but highly oriented vertical growth of nanorods has been observed only on pre-annealed Si/TiN/Ti substrates. On the other hand, TiO₂ nanorods form dandelion-like structures on Si/HFO substrates. Growth of vertically oriented TiO₂ nanorods on Si/TiN/Ti is attributed to the TiO₂ seed layer which forms after the process of pre-annealing of substrates at a suitable temperature. Variation in hydrothermal reaction time and post-annealing temperature brings further improvement in crystallinity and morphology of nanorods. This work shows that the pre-annealed Si/TiN/Ti substrate is the optimal choice to achieve vertically oriented, highly aligned TiO₂ nanorods.

Designing TiO2 nanostructures through hydrothermal growth: influence of process parameters and substrate position

Synthesis conditions and processing parameters profoundly affect the growth and morphology of nanostructures. In particular, when nanostructures are fabricated through a chemical technique such as hydrothermal, the process parameters such as reaction time, temperature, precursor concentration, and substrate orientation play a crucial role in determining the structure-property relationships. In this work, we report the hydrothermal growth of Titanium dioxide (TiO2) nanostructures as a function of these parameters and show that specific morphologies can be obtained by a variation of these parameters. A systematic study is carried out to understand the influence of reaction time (from 0.5 h to 3.0 h), reaction temperature (180 °C–200 °C), titanium precursor concentration (0.25 ml and 0.50 ml in 20 ml solution of HCl and deionized water) and substrate orientation (horizontal and tilted at an angle), and we show that significant variation in morphology- from nanowires to nanorods and then dandelions can be achieved. In particular, we demonstrate that high surface area multidirectional growth of nanorods leading to flower-like nanostructures or dandelions resulting from precipitation during the hydrothermal process. This is in contrast with previous reports on similar structures, where the role of precipitations was not analyzed. The work shows a possibility to control such growth by manipulating substrate position inside the autoclave during the hydrothermal process and will be useful for surface-dependent applications.

Quantum dot-sensitized solar cells

A comprehensive overview of the development of quantum dot-sensitized solar cells (QDSCs) is presented.

A fast chemical approach towards Sb2S3 film with a large grain size for high-performance planar heterojunction solar cells

A facile chemical method is developed for the fabrication of Sb₂S₃ film with a lateral grain size as large as ∼12 μm. A solar cell based on this Sb₂S₃ film achieves a power conversion efficiency of 4.3%, which is the highest value in solution processed planar heterojunction solar cells based on Sb₂S₃ film.

In Situ Grown TiO2 Nanospindles Facilitate the Formation of Holey Reduced Graphene Oxide by Photodegradation

Titanium dioxide (TiO2) nanostructures and TiO2/graphene nanocomposites are intensively studied materials for energy conversion, energy storage, and organic contaminant photodegradation. However, for TiO2/graphene composites, impermeability across the graphitic basal plane for electrolytes, metal ions, and gas molecules hinders their practical applications. Herein we report a simple, environmentally friendly synthetic route for mesoporous anatase TiO2 nanospindles, and successfully apply this method to obtain in situ grown TiO2 nanospindles/graphene oxide composite. After a thermal reduction at 400 °C, holes are created in the reduced graphene oxide (RGO) sheets through a photocatalytic oxidation mechanism. The formation of holes in RGO is promoted by photogenerated hydroxyl radicals that oxidize and subsequently decarboxylate the graphitic surface of RGO. The proposed mechanism was supported by photocatalytic electrochemical properties of the nanomaterials. The resulting TiO2/holey RGO composites may overcome the original impermeability of graphene sheets and find applications in catalysis, energy conversion/storage devices, and sensors.

Improving the anode performances of TiO2–carbon–rGO composites in lithium ion batteries by UV irradiation

A three-dimensional TiO₂–carbon–rGO (TCG) composite was fabricated and post-treated with UV irradiation (254 nm) for 0.5 h to improve the anode performances in LIBs.