Template-free and one-pot synthesis of nano-SiO2 via CO2-induced gelation for efficient and stable solid amine CO2 adsorbents

The widespread application of solid amine adsorbents is hindered by the cost and complexity of synthesizing porous supports, which typically require templating agents and energy-intensive calcination. Herein, we report a facile and mild method to fabricate nanoporous silica, involving CO 2 -induced gelation of low-cost sodium metasilicate, followed by freeze-drying. The obtained silica support exhibits a pore volume of 1.22 cm 3 /g and a specific surface area of 378.5 m 2 /g, which is suitable for amine loading. After impregnation with tetraethylenepentamine, the optimal adsorbent with 50% tetraethylenepentamine loading delivers a competitive CO 2 adsorption capacity of 3.48 mmol/g at 70 °C. More importantly, it demonstrates exceptional cycling stability, maintaining 3.37 mmol/g of CO 2 adsorption capacity after 10 cycles, with a minimal capacity loss of only 0.3% per cycle. This work demonstrates that high-performance adsorbents can be fabricated via a drastically simplified process, offering an amenable to scale-up and economically attractive strategy for practical CO 2 capture. Graphical abstract This paper presents an innovative and template-free synthesis of a high-performance solid amine adsorbent for CO 2 capture. The method innovatively utilizes CO 2 as both a reactant and an in-situ porogen to fabricate nanoporous silica from sodium silicate via a simple one-pot gelation process, entirely bypassing the need for templating agents and energy-intensive calcination. After freeze-drying and tetraethylenepentamine (TEPA) impregnation, the optimal adsorbent with 50% TEPA loading achieves a high CO 2 capacity of 3.48 mmol/g at 70 °C and demonstrates exceptional cyclic stability with 96.8% capacity retention after 10 cycles. This study provides a simplified, cost-effective, and scalable pathway for practical carbon capture applications.