Phase controlled synthesis of bifunctional TiO 2 nanocrystallites via d-mannitol for dye-sensitized solar cells and heterogeneous catalysis.

The crystal architecture of TiO 2 was successfully tailored via a low-temperature (≤200 °C) hydrothermal process in the presence of d-mannitol for feasible applications in dye-sensitized solar cells (DSSCs) and heterogeneous catalysis. In the development of anatase-TiO 2 (A-TiO 2 ), d-mannitol does not merely acts as a complexing agent to manage the zigzag chains of octahedral TiO 6 2- with dominant edge sharing but also performs as a capping agent by influencing the hydrolysis process during nucleation, as confirmed by Fourier-transform infrared spectroscopy and dynamic light scattering studies. After physical measurements, the as-synthesized nanocrystallites (NCs) of A-TiO 2 were used in DSSCs, where a fascinating power conversion efficiency (PCE) of 6.0% was obtained, which showed excellent performance compared with commercial anatase-TiO 2 (CA-TiO 2 : 5.7%) and rutile-TiO 2 (R-TiO 2 ) obtained without d-mannitol (3.7%). Moreover, a smart approach was developed via the A-TiO 2 catalyst to synthesize pharmaceutically important C-3 alkylated 4-hydroxycoumarins through different activated secondary alcohols under solvent-free, and heat/visible light conditions. In addition, the catalytic activity of the so-produced A-TiO 2 catalyst under solvent-free conditions exhibited remarkable recyclability with up to five consecutive runs with negligible reduction, which is superior to existing reports, and clearly reveals the novelty, and green, sustainable nature of the as-synthesized A-TiO 2 catalyst. A plausible reaction mechanism of both coupling partners was activated through the interaction with the A-TiO 2 catalyst to produce valuable C-3 alkylated 4-hydroxycoumarins with 95% yield and high selectivity.