Particle Molecular Layer Deposition Enhances Adsorption Capacity for CO2 Capture Materials through Amine Film Deposition

Amine adsorbent materials retain traditional acid-base chemistry, operate under ambient conditions, and benefit from the presence of humidity. Current liquid-based functionalization techniques face limitations: grafted materials tend to have lower adsorption capacities, while impregnated materials suffer from poor regeneration due to the lack of covalent tethering. Vapor-phase grafting (VPG) of aminosilanes demonstrate reliable monolayer and sub-monolayer film formation, offering enhanced surface control, but this has not been extensively studied for CO2 capture applications. We propose that VPG, which exposes the substrates surface to a single reactant, can be extended to deposit larger quantities of amines by regenerating active groups on the particles surface through particle molecular layer deposition (MLD). Particle MLD utilizes a series of alternating gas-solid phase reactions to deposit a thin uniform coating. In our research, we focus on applying particle MLD to generate aminosilane films onto various powder substrates for the evaluation of CO2 capture materials.

The reactions occur in a custom-built vibrating fluidized bed particle MLD reactor system, which was validated through fluidization experiments and benchmark Al2O3 atomic layer deposition. We investigated the MLD chemistry of (3-aminopropyl)triethoxysilane and water, which deposited amine functional groups anchored by Si-O linkages. A design of experiments was implemented to optimize the number of cycles and deposition temperatures for generating sorbent materials. For comparison, we also generated materials using liquid phase solvent grafting and VPG. We employed BET surface area analysis, LECO elemental analysis, X-ray photoelectron spectroscopy (XPS), and thermogravimetric analysis (TGA) for film characterization. Research has demonstrated, in VPG processes, lower deposition temperature results in a higher amine content. However, for particle MLD materials, higher deposition temperature leads to increased adsorption capacity. Our results indicate that both the number of cycles and reaction temperature significantly affect the amine film’s adsorption capacity. This observation provides a clear distinction from the traditional VPG processes, where the amine content decreases at higher deposition temperatures. Across the different supports used, particle MLD led to consistent densities of coating and consistent adsorption capacities on a surface-area basis. Our work demonstrates that particle MLD is a promising route to prepare solid adsorbent materials for CO2 capture applications.