Synthesis of Well-Defined Silica and Pd/Silica Nanotubes through a Surface Sol−Gel Process on a Self-Assembled Chelate Block Copolymer

The synthesis of well-defined silica nanotubes and Pd nanoparticle-decorated silica nanotubes is reported. The synthesis of silica nanotubes involves (1) formation of a 1-D template of the core−corona threadlike micelles through self-assembly of poly(ethylene glycol)-<i>block</i>-poly(4-vinylpyridine) in water, (2) a directed surface sol−gel process of tetraethylorthosilicate (TEOS) on the template of the threadlike micelles, and (3) calcination to remove the template. Because of the inherently pendent catalyst sites of the poly(4-vinylpyridine) block on the threadlike micelles, the surface sol−gel process is directed onto the template, and therefore, formation of irregular silica aggregates is avoided. Following the proposed method, well-defined silica nanotubes with thicknesses ranging from 3 to 17 nm are produced by changing the weight ratio of TEOS/micelles. Also benefiting from the chelate poly(4-vinylpyridine) block, Pd nanoparticles are introduced into the cavum of silica nanotubes initially through coordination between the poly(4-vinylpyridine) block with the Pd precursor, followed by reduction with NaBH<sub>4</sub> aqueous solution.