Successful Growth of TiO Nanocrystals with {001} Facets for Solar Cells.

The growth of nanocrystals (NCs) from metal oxide-based substrates with exposed high-energy facets is of particular importance for many important applications, such as solar cells as photoanodes due to the high reactivity of these facets. The hydrothermal method remains a current trend for the synthesis of metal oxide nanostructures in general and titanium dioxide (TiO) in particular since the calcination of the resulting powder after the completion of the hydrothermal method no longer requires a high temperature. This work aims to use a rapid hydrothermal method to synthesize numerous TiO-NCs, namely, TiO nanosheets (TiO-NSs), TiO nanorods (TiO-NRs), and nanoparticles (TiO-NPs). In these ideas, a simple non-aqueous one-pot solvothermal method was employed to prepare TiO-NSs using tetrabutyl titanate Ti(OBu) as a precursor and hydrofluoric acid (HF) as a morphology control agent. Ti(OBu) alone was subjected to alcoholysis in ethanol, yielding only pure nanoparticles (TiO-NPs). Subsequently, in this work, the hazardous chemical HF was replaced by sodium fluoride (NaF) as a means of controlling morphology to produce TiO-NRs. The latter method was required for the growth of high purity brookite TiO NRs structure, the most difficult TiO polymorph to synthesize. The fabricated components are then morphologically evaluated using equipment, such as transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), electron diffraction (SAED), and X-ray diffraction (XRD). In the results, the TEM image of the developed NCs shows the presence of TiO-NSs with an average side length of about 20-30 nm and a thickness of 5-7 nm. In addition, the image TEM shows TiO-NRs with diameters between 10 and 20 nm and lengths between 80 and 100 nm, together with crystals of smaller size. The phase of the crystals is good, confirmed by XRD. The anatase structure, typical of TiO-NS and TiO-NPs, and the high-purity brookite-TiO-NRs structure, were evident in the produced nanocrystals, according to XRD. SAED patterns confirm that the synthesis of high quality single crystalline TiO-NSs and TiO-NRs with the exposed {001} facets are the exposed facets, which have the upper and lower dominant facets, high reactivity, high surface energy, and high surface area. TiO-NSs and TiO-NRs could be grown, corresponding to about 80% and 85% of the {001} outer surface area in the nanocrystal, respectively.