Manipulating colloids and surfactants as co-templates for porous nanostructures and nanocomposites.

Abstract

Templating is a general and efficient strategy for creating nanostructured, particularly nanoporous materials. Two commonly employed classes of templates are colloidal crystals and surfactants. Colloidal crystals typically have an opal-like structure and have been used to produce macroporous (>50 nm pores) solids; surfactants generate various mesoporous structures (2−50 nm pores) as a result of their versatile phase behavior. One aim of this study is to combine colloidal crystals and surfactants to realize simultaneous templating at two length scales. A series of hierarchically structured porous silica samples were synthesized under different synthetic conditions, comprehensive TEM characterization was conducted to reveal the detailed hierarchical porous structures, and simulation was performed to correlate the structures to the surfactant phase behavior within the colloidal crystal confinement. The dual templating approach was further extended to synthesize functional materials with composite porous architectures, in which functional cores were embedded in a hierarchically porous framework for optical ionsensing application. A second aim of this study is to develop a template-based strategy for sculpting nanoparticles of desired shapes and sizes. Owing to the ordered structure and symmetry of the template, a templating-disassembly process was found to produce uniform, nanometer-level, multipodal particles. This method is applicable to a variety of compositions, including oxides, phosphates and carbon, and it could further lead in-situ organization of particles following a self-reassembly process. In addition, through a coupled passivation-disassembly process, site-specific functionalization was achieved to modify only the tips of the multipods with a range of functional groups, and therefore to enable their directional bonding to other colloidal particles. (256 words)