Synergistic Enhancement of CO₂ Adsorption Capacity and Kinetics in Triethylenetetrammonium Nitrate Protic Ionic Liquid Functionalized SBA-15

A series of triethylenetetrammonium nitrate protic ionic liquid (TNPIL) functionalized, highly ordered mesoporous SBA-15 molecular sieves with different loadings have been synthesized via impregnation. The CO₂ capture performance of the hybrid sorbents was evaluated under conditions mimicking a combustion flue gas (15% CO₂) over the temperature range of 298-348 K. The breakthrough experiments revealed that the sieves with 66% mass loadings of TNPIL (S15-66TNPIL) exhibited the highest CO₂ adsorption capacity of 2.12 mmol g^-1 at 333 K, representing a dramatic enhancement compared to the bare support (883%). The intraparticle diffusion model analysis of the hybrid sorbents demonstrated that S15-66TNPIL had the fastest CO₂ uptake rate of 131 × 10^-3 mmol g^-1 s^-0.5 in the rate-controlling stage. This was almost 5 times higher than that of the bare support alone and is a significant improvement over other IL-functionalized and amine-modified support systems. This can be attributed to the synergistic effects of the high affinity between the TNPIL and CO₂ and the fast diffusion rate from the distribution of TNPIL across the support with a large surface area. In addition, S15-66TNPIL exhibited a great regeneration capacity. The Fourier transform-infrared spectroscopy analysis coupled with isosteric heat and density functional theory simulations revealed that the adsorption state is dominated by chemisorption, and the CO₂ preferentially interacts with the primary amine-N(3)H₂ to form carbamate based on the high binding energy. Therefore, this novel TNPIL-supported system represents a promising candidate for CO₂ capture and recovery applications.