Matrix-Assisted Synthesis of Palladium Nanocage and Nanowires
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Matrix-Assisted Synthesis of Palladium Nanocage and Nanowires Jinwoo Cheon*, Kyung-Bok Lee, Hongkyu Kang, S. J. Oh1 and H.-C. Ri1 Department of Chemistry and School of Molecular Science-BK21, Korea Advanced Institute of Science and Technology (KAIST), Taejon, 305-701, Korea. 1 Korea Basic Science Institute (KBSI), Taejon, 305-333, Korea. ABSTRACT Our study describes the synthesis of novel nanoscale Pd cage and wires whose sizes and shapes are templated by mesoporous matrices. The templates used are cubic phase MCM-48 and hexagonal phase CnMCM-41 (n = 16, and 22), SBA-15, which have pore diameters of ~3, ~3.8, ~4.7, and ~9 nm, respectively. 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 cages (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. All the materials are examined by TEM, XRD, BET, and EDAX analysis. Furthermore, the thermal behavior of Pd nanowire is briefly described.
INTRODUCTION G
Recently, interest has grown in the synthesis of nanosized materials due to their novel electronic, optical, and catalytic properties [1]. Of the various methods available to prepare these materials, one is the templated synthesis where the desired nanomaterial is encapsulated into the channels and pores of a host [2]. Mesoporous solids with pore size tunability ranging from ~2 to ~30 nm have been the focus of special attention as hosts for quantum dots and wires [3]. One of the studies used the two step nanocasting process where mesoporous organic networks were grown by polymerization of monomers and subsequent removal of silicate matrix [4]. Excellent carbon-based mesoporous materials were also obtained from a MCM-48 template [5]. The fabrication of stable metallic structures with ordered nanopores of less than 10 nm are rare and have recently been reported for Ag, Pt, and Sn [6]. Using the mesoporous silica template, it is potentially feasible to have various 1 to 3 dimensional shapes of nanostructured materials depending on the architecture of the silicate host. For example, recently, Stucky and coworkers reported the preparation of Au, Ag, and Pt nanowires using hexagonal mesoporous silica (SBAC3.3.1
15) via a solution phase infiltration process [7]. Ordered porous gold nanostructures with larger pore dimensions (~150 nm – 1 µm) have been synthesized by using latex spherical templates [8]. We present in this report matrix free palladium based porous nanoballs and nanowires as well as palladium superlattices and wires inside of cubic MCM-48 and hexagonal MCM-41 and SBA-15 matrices. Pd was chosen as the case study material because of its catalytic activity and its potential applications in H2 storage and advanced electronics [9].
EXPERIMENTAL DETAILS G
Matrix materials such as MCM-48 (pore size of ~3 nm), C16MCM-41, C22MCM-41, and SBA
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