Application of halloysite nanotubes for carbon dioxide capture

Halloysite is a naturally occurring clay, with physical structure represented by halloysite nanotubes (HNTs). We investigated the potential applicability of HNTs for carbon dioxide (CO2) capture, using two amine-functionalized HNTs: (3-aminopropyl) triethoxysilane (APTES)-grafted HNTs and polyethylenimine (PEI)-impregnated HNTs. APTES-HNTs and PEI-HNTs resulted in 5.6 and 30 wt.% (in sorbent) in functionalization onto HNTs, respectively. Capture efficiency was higher in APTES-HNTs at lower temperatures, while it was maximum in PEI-HNTs at 70 degrees C-75 degrees C. At 75 degrees C, adsorption/desorption tests showed that 95% of the two reactions occurred within 30 min, and exhibited 0.15 and 0.21 millimole of CO2 adsorption capacity per millimole of amine group for APTES-HNTs and PEI-HNTs, respectively. During 10 cycles of CO2 adsorption/desorption, there was no significant decrease in sorbent weight and adsorption capacity in both HNTs. These results show that inherent structural features of HNTs can be easily tailored for the development of operational condition-specific CO2 capture system.