Simultaneous phase- and size-controlled synthesis of TiO2 nanorods via non-hydrolytic sol-gel reaction of syringe pump delivered precursors

The simultaneous phase- and size-controlled synthesis of TiO2 nanorods was achieved via the non-hydrolytic sol-gel reaction of continuously delivered two titanium precursors using two separate syringe pumps. As the injection rate was decreased, the length of the TiO2 nanorods was increased and their crystalline phase was simultaneously transformed from anatase to rutile. When the reaction was performed by injecting titanium precursors contained in two separate syringes into a hot oleylamine surfactant solution with an injection rate of 30 mL/h, anatase TiO2 nanorods with dimensions of 6 nm (thickness) x 50 nm (length) were produced. When the injection rate was decreased to 2.5 mL/h, star-shaped rutile TiO2 nanorods with dimensions of 25 nm x 200 nm and a small fraction of rod-shaped anatase TiO2 nanorods with dimensions of 9 nm x 100 nm were synthesized. Pure star-shaped rutile TiO2 nanorods with dimensions of 25 nm x 450 nm were synthesized when the injection rate was further decreased to 1.25 mL/h. The simultaneous phase transformation and length elongation of the TiO2 nanorods were achieved. Under optimized reaction conditions, as much as 3.5 g of TiO2 nanorods were produced. The TiO2 nanorods were used to produce dye-sensitized solar cells, and the photoconversion efficiency of the mixture composed of star-shaped rutile TiO2 nanorods and a small fraction of anatase nanorods were comparable to that of Degussa P-25.