Date

2015

Document Type

Dissertation

Degree

Doctor of Philosophy

Department

Chemical Engineering

First Adviser

Snyder, Mark A.

Other advisers/committee members

Gilchrist, James F.; Mittal, Jeetain; Ou-Yang, Daniel H.

Abstract

Nanoporous materials have attracted extensive research interest owing to their potential for applications spanning arenas as diverse as energy (e.g., catalysts, separations), the environment (e.g., sorbents), and health (e.g., drug delivery). The ability to achieve tunable control over pore size, dimensionality, and specific pore topology is a persistent challenge when it comes to rational synthesis of micro-, meso-, and/or hierarchically-porous materials. In this thesis, we develop a multiscale synthetic strategy and its fundamental physicochemical underpinnings for realizing nanoporous and hierarchically porous materials with three-dimensionally ordered pores spanning classes of nanoporous materials as diverse as amorphous mesoporous silicas, micro-mesoporous carbons, and crystalline microporous zeolites. We also demonstrate the versatility of this approach in terms of material morphology from porous particles/powders to thin films.We establish strategies for bottom-up assembly of binary silica nanoparticles for realizing template-free ordered mesoporous silicas (OMSs). We first study the phase behavior of evaporation-induced convective assembly of binary silica nanoparticles, and show that even without specific solvent index matching or stabilization beyond intrinsic properties of the amino acid nanoparticle synthesis solution, symmetry of the binary assemblies is governed solely by particle size ratio, consistent with binary hard-sphere predictions. The demonstrated robustness of the binary nanoparticle assembly and the control over silica particle size translate to a facile, template-free approach to OMSs with independently tunable pore topology associated with the interstices of AB, AB2 , AB13, and AB interstitial nanoparticle crystals that are isostructural with NaCl, AlB2, and NaZn13. Moreover, we elucidate the role of the amino acid, L-lysine, employed in the nanoparticle synthesis, the structural evolution of the silica network upon aging of dialyzed nanoparticle sols, and substrate character in tuning particle stability and thereby the yield of ordered binary assemblies achievable in both bulk and thin film morphologies.We subsequently employ these novel multi-modal OMSs as sacrificial hard templates in realizing a facile method to synthesize a new class of bimodal three-dimensionally ordered mesoporous (b-3DOm) carbons with tunable bimodal mesoporosity. Continuously adjustable bimodal mesoporosity in the range of 15-23 nm for small pores and 40-50 nm for large pores with controlled pore topology is confirmed. Attractive textural properties result, including high surface areas (>1000 m2/g), narrow pore size distributions, and large pore volumes (2-5 cm3/g). The structural stability of these large-pore volume materials is underscored by the pore robustness upon removal of the hard sacrificial silica template and even in the face of carbon loss during subsequent activation of microporosity in the carbon walls. We conclude the thesis by demonstrating a top-down strategy to scaffold the growth of ultra-thin crystalline microporous (zeolite) films. Here, we combine nanoparticle crystal-templated carbon thin films to force in-plane crystal growth. Through tuning of nucleation and growth within the carbon film scaffolds, the strategy developed in this thesis enables realization of large silicalite-1 crystal regions formed by intergrowth of separately nucleated crystal domains. The thickness of the silicalite-1 domains can be tuned and scaled down to the order of 10 nm by controlling the carbon scaffold thickness, with remarkable flexibility of the inorganic films observed.

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