Enhanced CO₂ Capture Performance of Mesoporous Silica Materials with TEPA Amine-Based Deep Eutectic Solvent: Kinetics and Mechanism

Abstract

Conventional amine-based sorbents exhibit two major drawbacks: progressive structural deterioration under repetitive CO2 adsorption-desorption cycling and diminished gas capture efficiency with extended cycle iterations. To mitigate these issues, a new amine-based deep eutectic solvent (DES) containing tromethamine (TrMA) salt as a sterically hindered amine and tetraethylenepentamine (TEPA) was prepared and incorporated on several mesoporous silica materials for CO2 capture, including SBA-15, SBA-16, MCM-41, and KIT-6. In comparison to SBA-16 and MCM-41 materials, SBA-15 and KIT-6 could maintain their mesoporous structure after incorporation of 50% DES, as revealed by the N2 sorption analysis. According to the findings, (50%) TrMA-TEAP (1:2)/SBA-15 had higher CO2 adsorption of 120.8 (mg g-1) than (50%) pure TEAP (1:2)/SBA-15 and higher than other hybrid amine-based DES/mesoporous silica materials at 75 °C under 15% CO2 balanced N2. Furthermore, the adsorption index values for (50%) TrMA-TEAP (1:2)/SBA-15 and (50%) pure TEAP (1:2)/SBA-15 were 94.9% and 92.5%, respectively, demonstrating that amine-based DES had superior cycle performance, albeit (50%) TrMA-TEAP (1:2)/KIT-6 had an excellent cyclic performance by maintaining the original CO2 adsorption capacity of 97.3%, amongst other sorbents. Pseudo-first order, pseudo-second order, Vermeulen, Avrami, and fractal-like exponential kinetic models were used to investigate the kinetic adsorption of hybrid sorbents, with the last kinetic model offering the best fitting. The DFT analysis demonstrated that the primary amine site on hydrogen bond donor acceptor is a more active site in DES, while the hydrogen bond donor plays a dominant role in CO2 adsorption due to possessing more amine active sites, particularly primary amine sites.