Upcycling rice husk waste into a tetraethylenepentamine (TEPA)-modified dendritic hierarchical silica adsorbent for selective CO2 capture

Abstract

Addressing the dual challenges of CO₂ emissions and waste management requires innovative approaches to develop efficient and sustainable adsorbent materials. In this work, dendritic hierarchically structured silica (DHS) with a BET specific surface area of 692.7 m² g⁻¹ and a total pore volume of 0.85 cm³ g⁻¹ was synthesized from renewable and inexpensive rice husk waste and functionalized with tetraethylenepentamine (TEPA) for selective CO₂ adsorption. At 298 K, the optimized adsorbent, with a TEPA impregnation level of 60% (DHS-T-60), achieved CO₂ uptake capacities of 0.65 and 1.02 mmol g⁻¹ at 50 mbar and 1 bar, respectively, representing 9.3-fold and 1.6-fold increases compared to the parent DHS. Notably, DHS-T-60 also exhibited excellent CO₂/N₂ selectivities of 573 and 34 under the same conditions, which are 38-fold and 7-fold higher than those of the parent DHS. Furthermore, the CO₂ uptake performance of DHS-T-60 increased with temperature, reaching 1.33 mmol g⁻¹ at 333 K, which is 3.3-fold higher than that of the parent DHS. At 333 K, N₂ adsorption was negligible, indicating exceptional CO₂/N₂ selectivity and confirming its capability for high-purity CO₂ adsorption. Moreover, at 298 K, DHS-T-60 showed improved hydrophobicity, reducing water vapor sorption by 41.3% and 45.8% at 25% and 75% relative humidity, respectively, compared to the parent DHS. Additionally, DHS-T-60 retained over 95% of its initial CO₂ uptake capacity after five adsorption–desorption cycles, indicating excellent cyclic stability. Overall, this study demonstrates a combined strategy to develop a sustainable adsorbent for efficient CO₂ emission mitigation while upcycling rice husk waste, simultaneously addressing two global challenges.