Nanonecklaces of Platinum and Gold with High Aspect Ratios Synthesized in Mesoporous Organosilica Templates by Wet Hydrogen Reduction

Nanowires of platinum and gold with high aspect ratios are synthesized in one-dimensional channels of ordered mesoporous organosilica HMM. Water-saturated hydrogen reduction (wet H 2 -reduction) is significantly effective for large-scale synthesis of long nanowires, while dry H 2 -reduction gives monodispersed metal nanoparticles. The nanowires are characterized by TEM, XRD, UV−vis, STM, and XAFS. The Pt and Au wires are 3 nm in diameter and several hundred nanometers to micrometers in length. The metal wires extracted from HMM with HF have a nanonecklace structure, while the wires from siliceous FSM-16 have a nanorod structure. The results indicate that the hydrophobicity or hydrophilicity of the internal pore gives a significant influence on the morphology of nanowires. The nanonecklace structure is also affected by the organic groups in HMM. The mechanism for formation of Pt nanowires in wet H 2 -reduction was studied. In the impregnation process, the [PtCl 6 ] 2 - ion is physically adsorbed on HMM, and the Pt(IV) ion is reduced to Pt(0) via Pt(II). Tiny Pt nanoparticles are formed in the mesoporous channels, and the water vapor in the H 2 flow enhances the migration of Pt ions, leading to the growth of long nanowires.