Synthesis of nanocomposite Pd balls and wires by chemical vapor infiltration

Abstract
Our study presents the preparation of well-defined Pd nanoballs and nanowires using the different pore size of cubic and hexagonal shaped MCM type mesoporous silicate materials as matrix templates. The synthesis involves loading the organometallic precursor into template matrix via chemical vapor infiltration (CVI), followed by mild thermal decomposition to generate Pd metals self-organized inside the template. For Pd@MCM-48, the Pd metal forms spherical domains (~38 nm) consisting of three dimensionally interconnected into Pd arrays; for Pd@SBA-15 and Pd@MCM-41, the Pd metal forms of one-dimensional wires. Etching out the matrix produces porous Pd nanoballs (pore sizes of ~1.5 - 2.0 nm) with retaining original domain sizes of ~38 nm; similarly Pd@SBA-15 and Pd@MCM-41 afford freestanding Pd nanowires. In addition, phase transition behavior and melting point depression of the Pd nanowires is studied.