DOI
https://doi.org/10.25772/MR9K-K220
Defense Date
2012
Document Type
Dissertation
Degree Name
Doctor of Philosophy
Department
Chemistry
First Advisor
Maryanne Collinson
Abstract
Hierarchical materials offer great promise for high-performance sensors and catalysis carriers. Well-defined hierarchically porous materials are promising candidates for a wide range of applications relating to biosensors, separations, drug delivery, surface-enhanced Raman scattering (SERS), etc. Research on synthetic methodologies is expanding. However, fabrication of hierarchical porous structures with tunable pore dimension and shape, controllable pore distribution and interconnectivity is still a challenging task in materials science. One of the main tasks of this work is to establish a facile and reliable approach of making well-defined hierarchically porous materials. Then, based on those multimodal porous structures, different functions and applications can be realized. This work utilizes a direct hard templating method to obtain hierarchical porous structures with a well-defined bimodal distribution of the pores based on hierarchical templates. The hierarchical templates were prepared by synthetically joining appropriately functionalized commercially available polystyrene (PS) latex spheres together. Two different coupling reactions were used to form the hierarchical templates: carbodiimide-assisted coupling of COOH groups with NH2 groups and base-assisted coupling of epoxy groups with NH2 groups. Two different morphologies of templates, "raspberry-like" and "strawberry-like" were made. The template can be defined by the sizes of both the "core" and the "satellite" spheres, and altering the coverage of "satellites" on the "core". The main advantage of this strategy is the tailorability of the size and shape of the hierarchical templates, which allows an easy and independent adjustment to the multiporosity of the material structure design. Also, the monodispersed hierarchical templates are constructed of only one material, can be isolated, and can be assembled using standard template packing procedures that have been used for unimodal porous material fabrication described in published literature. Based on the predefined monodispersed hierarchical templates, multimodal porous silica, bimodal porous gold film and porous capsules were fabricated in this work as representative 3D, 2D, and 0D hierarchical porous structures, respectively. Because the template was predefined as one whole body, the connectivity between the big pores and small pores is guaranteed. The way the templates are packed together on a surface also ensures connections between each "template-shaped pore cluster". The uniform interconnectivity and ordered arrangement among the pores allows the different modals of pores to communicate with each other. The different hierarchical porous materials made in this work were characterized with SEM, TEM, AFM, XPS, STEM, gas adsorption, and mercury intrusion porosity. The results indicate that the multimodal porous materials can be successfully fabricated using predefined hierarchical templates. The different arrangement (3D, 2D, 0D) of those templates and the independent tailorability of the pore sizes provide more flexibility and control on the hierarchical porous material fabrication. The main parts of this work are as follows: (1) Fabrication and characterization of morphology controllable hierarchical templates (2) Fabrication and characterization of various multimodal porous structures of different materials based on the obtained templates (3) Study of the application of hierarchical porous gold electrode obtained and (4) The comparison between conventional porous structures and hierarchical porous structures.
Rights
© The Author
Is Part Of
VCU University Archives
Is Part Of
VCU Theses and Dissertations
Date of Submission
April 2012