Controlled Growth of Pt-Containing SiO2 Nanotubes with High Aspect Ratios

Rectangular prisms of [Pt(NH3)4](HCO3)2 were grown from its aqueous solution by solvent modification with ethanol. The polydispersity of the prisms, being influenced by temperature, the rate of ethanol addition, and the Pt concentration in the aqueous solution, actually results from the iso-oriented aggregation of primary nanofibers into bundles. The employment of prehydrolyzed tetraethyl orthosilicate (TEOS) as a capping agent can effectively stabilize the primary nanofibers. With this stabilized nanofiber as a structure-directing agent, about 100−200 nm thick and up to 40 μm long SiO2 nanotubes, which contain up to 40 wt % of Pt, could be synthesized by further addition of TEOS. The capping mechanism of hydrolyzed TEOS can be reasonably explained through the selective adsorption of silanol species on specific surfaces of primary nanofibers. In our method, the ingenious employment of TEOS as the reactant for the nanotube formation and also as a capping agent avoids the introduction of additional substances to the reaction system.