(70d) Molecular Layer Deposition of Amine-Functional Groups on Fumed Silica Nanoparticles for CO2 Capture
Traditional liquid CO2 capture techniques have relied on the chemical reaction between the acidic CO2 and a basic absorbent, usually liquid amines such as monoethanolamine. However, more recently, solid adsorbent materials have received much attention due to the high regenerative energy requirements and physical limitations of liquid systems. Popular materials have included zeolites, metal organic frameworks (MOFs), microporous organic polymers (MOPs), and supported amines. Polymers and porous silica have served as common support materials for amines due to their high surface area and low production cost. Current processes of loading the amines have focused on impregnation (physical mixture of support material and amine-containing compound) and grafting (bonding amine-containing compounds to the surface, usually through wet reactions). However, sorbents made through impregnation face poor regeneration stability and transport limitations; while grafted sorbents tend to have low adsorption capacities. Here, Particle Molecular Layer Deposition (MLD) is used as a loading method to improve the regeneration stability and adsorption capacity of supported amine sorbents. Two MLD chemistries have been confirmed: (3-aminopropyl)triethoxysilane (mono-amine) and N1-(3-trimethoxysilylpropyl)diethylene triamine (tri-amine). Both precursors were deposited at 150oC. Adsorption capacity and regeneration stability were investigated using a thermogravimetric analyzer (TGA). Adsorption capacity of the amine functional groups increased to ~2mmol/g as the number of MLD cycles increased, prompting further investigation for optimal loading. Regeneration temperatures are known to be low for supported amines and were demonstrated by both the mono-amine and tri-amine. The mono-amine and tri-amine particles with 10 cycles of MLD underwent 25 regeneration cycles with adsorption at 30oC and desorption at 80oC. Both materials appear stable and robust over these cycling conditions, although the tri-amine may need a longer desorption time due to transport limitations. These materials will be stable for adsorption/desorption cycling temperatures below the deposition temperature of 150oC.