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Carbon nanotubes (CNTs), granular activated carbon (GAC), and zeolites were modified by 3-aminopropyltriethoxysilane (APTS) and were selected as adsorbents to study their physicochemical properties and adsorption behaviors of CO 2 from gas streams. The surface nature of these adsorbents was changed after the modification, which make them adsorb more CO 2 gases. Under the same conditions, the modified CNTs possess the greatest adsorption capacity of CO 2 , followed by the modified zeolites and then the modified GAC. The mechanism of CO 2 adsorption on these adsorbents appears mainly attributable to physical force, which makes regeneration of spent adsorbents at a relatively low temperature become feasible. The APTS-modified CNTs show good performance of CO 2 adsorption as compared to many types of modified carbon and silica adsorbents reported in the literature. This suggests that the APTS-modified CNTs are efficient CO 2 adsorbents and that they possess potential applications for CO 2 capture from gas streams.

Commercially available Y-type zeolite with a Si/Al molar ratio of 60 (abbreviated as Y60) was modified by tetraethylenepentamine (TEPA) to study their characterizations and adsorption/desorption properties of CO 2 from gas streams. The surface nature of Y60 was changed after TEPA modification, which causes a significant enhancement in CO 2 adsorption capacity. The CO 2 adsorption capacity of Y60(TEPA) increased with the temperature at 30-60 °C but decreased with the temperature at 60-70 °C. The mechanism of CO 2 adsorption on Y60 is entirely a physical interaction but becomes mainly attributable to a chemical interaction after TEPA modification. The CO 2 adsorption capacity of Y60(TEPA) was influenced by the presence of water vapor and reached as high as 4.27 mmol of CO 2 /g of sorbent at a water vapor of 7%. The cyclic CO 2 adsorption showed that the adsorbed CO 2 could be desorbed from the surface of Y60(TEPA) at 75 °C for 4 h. The adsorption capacities and the physicochemical properties of Y60(TEPA) were preserved after 20 cycles of adsorption and regeneration, suggesting that the Y60(TEPA) can be stably employed in the prolonged cyclic operation and that they are possibly cost-effective sorbents for CO 2 capture from flue gas.