(652f) Investigation of Amine Silane Film Formation Via Particle Molecular Layer Deposition for CO2 Capture

Particle Molecular Layer Deposition (MLD), closely related to Atomic Layer Deposition (ALD), involves a series of alternating gas phase reactions on a particle surface. Our work studies particle MLD as a method of generating aminosilane films on a variety of solid supports to create CO­₂ capture materials. In addition, we describe the construction and validation the custom particle ALD/MLD system used in this work.

In the past few decades, solid adsorbent materials have been a focus of research as an alternative to traditional liquid amine absorbent systems which require substantial regeneration energy and cost. Supported amine adsorbents have gained much interest as it maintains the traditional acid-base chemistry, operates under ambient conditions, and is tolerant of humidity. However, the current liquid-based functionalization techniques have limitations; grafted materials tend to have lower adsorption capacities and impregnated materials tend to have poorer regeneration abilities. (Unveren, 2017) In addition, liquid phase grafting is heavily dependent on numerous process conditions and produces amorphous 3-dimensional films. (Yadav 2013) Vapor deposition of aminosilanes has been demonstrated to produce reliable mono- and sub-monolayer films, which provide greater surface control but has not been studied in depth for CO₂ capture applications. (Yadav 2013, Rozyyev 2021) Vapor deposition also differs from MLD, as vapor deposition only exposes the surface to one reactant whereas MLD regenerates reactive groups on the surface through a series of reactions in each cycle.

Here, we use MLD to deposit a covalently bonded aminopropylsiloxane network on particle supports. A custom vibrating fluidized bed particle ALD reactor was constructed in house and validated through fluidization experiments and deposition of aluminum oxide as a benchmark chemistry. Following validation, the system was employed to investigate the MLD chemistry of (3-aminopropyl)triethoxysilane (mono-amine) and water. Sorbent materials were generated according to design of experiments that focused on factors related to film formation such as the number of cycles and deposition temperature. For comparison, materials were also generated through traditional liquid phase grafting and vapor phase deposition. Characterization of the sorbents included BET surface area analysis, LECO elemental analysis, X-ray photoelectron spectroscopy (XPS), and thermogravimetric analysis (TGA). The adsorption capacity was shown to be affected by both the number of MLD cycles and the temperature of deposition. It was previously found by Rozyyev et al. that for vapor deposition, lower deposition temperature led to greater amine content. Interestingly, MLD materials produced at higher temperatures lead to higher adsorption capacity.

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