Permeable Silica Shell through Surface-Protected Etching

• Published in: Nano letters Vol. 8; no. 9; pp. 2867 - 2871
• Main Authors: Zhang, Qiao, Zhang, Tierui, Ge, Jianping, Yin, Yadong
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 01.09.2008
• Subjects: Cross-disciplinary physics: materials science; rheology; Exact sciences and technology; Materials science; Methods of nanofabrication; Nanocrystalline materials; Nanolithography; Nanoscale materials and structures: fabrication and characterization; Physics; Aggregation; Hollow sphere; Core shell structure; Porous materials; Silica gel; Etching; Nanostructured materials; Sol-gel process; Silica
• ISSN: 1530-6984; 1530-6992
• DOI: 10.1021/nl8016187

We describe a “surface-protected etching” strategy that allows convenient conversion of sol−gel derived silica into porous structures. Poly(vinyl pyrrolidone) is used to protect the near surface layer, and NaOH is used to selectively etch the interior of the silica spheres. Etching initially yields porous structures and eventually removes the core to leave behind hollow silica spheres with porous shells. This strategy is useful for constructing core−shell systems where active nanomaterials are embedded in silica shell for enhanced stability against aggregation. We experimentally demonstrate use of the surface-protected etching approach to create openings on silica shells; these openings allow dissolved chemical species to reach embedded catalytic particles to be chemically transformed while the porous shells continue to act as effective barriers against aggregation and loss of activity of the core particles. We also show that, by controlling the extent of etching, it is possible to control the permeation rate of the chemical species through the shells.