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

Abstract

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 ] 2ion 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.

Mesoporous silica nanoparticles: structural design and applications

“…For example, the production of nanowires with specific aspect ratios by using 65 mesoporous silica as templates could be facilitated if the particle size of MSN is monodisperse. 66 So does the production of carbon or metal replicas of MSN if they are intended for applications in confined spaces. 67 Small particle size and controlled morphology can be relevant also for 70 catalysis and sensing because of the uniform and increased diffusion rates that can occur within short pores, and because small and regular sized particles give more homogeneous dispersion of catalysts, unfortunately these properties have not been systematically studied yet.…”

Shape- and Orientation-Controlled Gold Nanoparticles Formed within Mesoporous Silica Nanofibers

“…It is reported in a recent experiment that the reduction of NaAu(OH) 4 with dry H 2 in mesoporous silica particles produces gold nanoparticles and that the reduction with water-saturated H 2 gives gold nanowires with large aspect ratios. [24] In that experiment, the reduction temperature was 120°C, and mesoporous organosilica with either a CH 2 CH 2 or a C 6 H 4 bridging group was used. The diameters of the resulting gold nanoparticles and nanowires are close to the pore sizes, suggesting that the growth of gold nanoparticles is confined by the stable pore walls of the mesoporous organosilica.…”

Gold Nanoparticles Embedded in a Mesoporous Carbon Nitride Stabilizer for Highly Efficient Three‐Component Coupling Reaction

“…[17] The ordered mesopores dictate the size and shape of the nanoparticles as they are formed in the confined matrix, and the high surface area and large pore volume help the formation of a high degree of homogeneously dispersed nanoparticles on the surface of the support. Although the size of the nanoparticle can be controlled by a mesoporous support strategy, stabilization and reduction of the particles on the porous surface after their formation is quite challenging.…”