Understanding the Growth of Porous Carbons Templated by FAU zeolite

Abstract

In Chapter 1, we begin by introduction of carbon allotropes, followed by presenting the structure and fundamental aspects of zeolites. Specifically, we define zeolites and describe their general characteristics, framework composition, building units, and the role of the Si/Al ratio in determining their properties. We then focus on Zeolite Y and its functional modifications. Following this, we introduce the topic of zeolite-templated carbons (ZTCs), discussing what they are, how they are synthesized, the influence of the template, and the applications of ZTCs. Finally, we outline the objectives of our research and provide a review of the relevant literature. In Chapter 2, we describe how we achieved the synthesis of an ordered 3D microporous graphene architecture via chemical vapor deposition using the faujasite type zeolite as the template, i.e., “zeolite templated carbon” (ZTC). We found that implanting Ca2+ in this zeolite effectively catalyzed the growth of ZTC and greatly lowered the growth temperature. To further improve the ZTC, we investigated the influence of various synthetic parameters on its growth: Ca2+ amount, growth temperature, growth time, growth pressure, stabilization temperature and stabilization time, and describe these in detail. High-quality ZTC samples having regions of what are likely continuous single-layer carbon structures composed of trivalently bonded carbon were grown and characterized. This effective and practical synthetic method should benefit the synthesis of other ZTCs and the evaluation and exploration of the structural characterization and application of ZTCs. In Chapter 3, our study provides insights into the structural evolution from the early to later stages, and finally, the completed stages of growth (i.e., carbon deposition inside the zeolite pores) of Ca-exchanged FAU zeolite-templated carbon using acetylene as a carbon source, through integrated differential phase contrast (iDPC) STEM. We observed that the carbon contrast in the different Ca-FAU channels varies over a wide range at the beginning of the growth (growth times of 10- and 20-minutes), indicating that different channels have a different number of carbon atoms in this early stage, and that a complete network has not yet been formed. As the time exposure to acetylene is extended (to 60- and 180-minutes), samples are made that show a high contrast in all channels and carbon atoms are more uniformly distributed (and more uniformly at 180 min than 60 min). Furthermore, the combination of CO₂ and Ar adsorption techniques provides a full pore size distribution and provides values for the inner and outer surface areas and volumes of the hollow carbon structure. These findings can help to better understand the structure of ZTCs at the atomic and near-atomic levels, which can be leveraged to enhance ZTC performance in existing applications and potentially enable their use in new applications. In Chapter 4, we briefly present preliminary studies conducted on 13C-labeled ZTC samples. In Chapter 5, we provide future plans and summary.