Functional helical silica nanofibers with coaxial mixed mesostructures for the fabrication of PtCo nanowires that display unique geometry-dependent magnetism

Abstract

Helical mesoporous silicas are notable from a self-assembly and applications points of view. We report a novel confinement-free synthesis of chloropropyl-functionalized helical mesoporous silica nanofibers (CP-HMSNFs) possessing straight channels at the fiber center surrounded by concentric short-pitch helical channels. The chloropropyl groups are found mainly distributed at the central cylindrical portion of the fibers, allowing the selective inclusion of guest species to fabricate novel nanocomposite fibers. Moreover, the chloropropyl-functionalized nanofibers were applied as a hard template to fabricate helical platinum–cobalt (PtCo) alloy nanowires with small and narrowly distributed radii of gyration. The helical metal nanowires exhibited distinct ferromagnetic properties as compared with their straight counterpart. Platinum–cobalt nanowires can be constructed into twisted, magnetically active helical shapes using a novel silica template. Mesoporous silica is a sieve-like material, ideal for directing the growth of metal nanowires. Previously, researchers have developed helical mesoporous silicas to grow spiral metal nanowires. Now, Chia-Min Yang from National Tsing Hua University in Taiwan and co-workers have made these templates more versatile. By introducing silanes bearing chloropropyl groups into the synthesis mixture, the materials self-assembled into nanofibres having a straight central core surrounded by concentric short-pitch helical channels. Because the hydrophobic chloropropyl groups localized near the nanofibre core, the team used them to selectively deposit various materials into the helical templates — iron oxide, pure platinum metal and ferromagnetic platinum–cobalt nanocomposites with possible high-density storage applications. A novel confinement-free synthesis of CP-HMNSFs possessing straight channels at fiber center surrounded by concentric short-pitch helical channels is discovered. The chloropropyl groups are found mainly located at central cylindrical part of the nanofibers. Helical PtCo nanowires with small and narrowly distributed radii of gyration are also fabricated, showing distinct ferromagnetic properties as compared with the straight counterparts.