(180ab) Silica-Based Aerogels Catalyst Impregnated with Tepa and [Emim]Br: A Recyclable Platform for CO2 Capture and Metal-, Co-Catalyst, and Solvent-Free Cycloaddition Reaction

Industrialization and urbanization have driven surging carbon dioxide (CO₂) emissions, intensifying global warming and climate change. Excessive atmospheric CO₂ accelerates temperature rises, sea level increases, and ecosystem disruptions. To counter these effects, extensive research focuses on reducing CO₂ emissions and developing capture and conversion technologies. Notably, simultaneous capture and conversion of CO₂ into value-added products garners attention for its dual environmental and resource benefits.

A critical component of CO₂ capture and conversion technologies is the development of advanced adsorbent materials capable of selectively capturing CO₂ and enabling its efficient transformation. Conventional adsorbents such as activated carbon, metal-organic frameworks (MOFs), and zeolites have been extensively studied for CO₂ capture, each of them offering unique advantages and limitations. Activated carbon is widely used due to its high surface area and cost-effectiveness, but it suffers from low CO₂ selectivity and moderate adsorption capacity. MOFs, with their tunable structures and customizable adsorption properties, offer promising performance but are limited by their high cost and reduced stability during recycling. Similarly, zeolites provide high thermal stability and ion-exchange properties but have less adaptable porous structures, which restrict their capacity for optimizing adsorption characteristics.

In contrast, silica-based aerogels have emerged as a highly promising alternative for CO₂ capture and conversion. Their ultrafine porous structure and high surface area allow for superior CO₂ adsorption capacity. Additionally, silica-based aerogels are lightweight, thermally stable, and chemically resistant, making them suitable for demanding industrial environments. These properties also ensure structural integrity and consistent performance even after repeated use, addressing the limitations of other conventional materials. Furthermore, silica-based aerogels provide remarkable flexibility for functionalization, enabling the introduction of specific chemical properties or catalytic functionalities by incorporating various active components. Recent studies have demonstrated the potential of silica aerogel-based systems for efficient CO₂ capture. For instance, Linneen et al. developed TEPA-impregnated silica aerogels, achieving a CO₂ adsorption capacity of 3.5 mmol g^–1 at 348 K due to strong interactions between large surface area of the aerogel and amine groups of TEPA. Similarly, Feng et al. developed amine-modified silica aerogels (AMSAs) via grafting with 3-(aminopropyl) triethoxysilane (APTES), achieving a CO₂ adsorption capacity of 3.37 mmol g^–1 at 70°C. These AMSAs demonstrated excellent cycle stability, retaining 87.6% of their capacity after 10 cycles, highlighting their potential for efficient CO₂ capture. In another study, Zhou et al. prepared a cellulose-silica composite impregnated with TEPA, achieving a CO₂ adsorption capacity of 2.25 mmol g^–1, combining the mechanical stability of cellulose with the high porosity of silica aerogel.

In recent years, integrated approaches for both capturing and transforming CO₂ into value-added products have gained increasing attention. Among various reaction pathways, the cycloaddition of CO₂ with epoxides stands out for delivering cyclic carbonates with a 100% atom economy and favorable thermodynamics, while also offering a wide range of commercial applications. These carbonates find use as aprotic polar solvents, electrolytes in lithium-ion batteries, and intermediates in polymer synthesis, thereby providing notable environmental and economic advantages. Nonetheless, conventional cycloaddition methods often demand substantial energy input, elevated CO₂ pressure, or reliance on metal-based catalysts and solvents factors that can restrict both scalability and sustainability. Consequently, the pursuit of efficient, metal-free catalytic systems operating under mild conditions has become crucial to lowering energy requirements and enhancing the feasibility of CO₂ conversion.

In this study, silica-based aerogel catalysts were synthesized via a sol-gel process where polyvinylpyrrolidone (PVP) underwent tautomerization, contributing to enhanced solvent stability by reinforcing the aerogel framework. The aerogels were functionalized with tetraethylenepentamine (TEPA) and [EMIm]Br for efficient CO₂ capture and conversion. Their adsorption performance showed efficient mass transfer behavior and excellent CO₂ selectivity over nitrogen. The captured CO₂ was converted into cyclic carbonates through a metal-, co-catalyst, and solvent-free cycloaddition reaction, offering an eco-friendly process. These functionalized aerogel catalysts maintained high stability and recyclability, retaining structure and performance even after repeated impregnation and reuse.