Free Radical Scavenging Activity of Ultrashort Single-Walled Carbon Nanotubes with Different Structures through Electron Transfer Reactions

The scavenging activity of ultrashort single-walled carbon nanotubes (US-SWCNTs) is analyzed in this work considering the electron transfer mechanism. Such processes have been modeled using density functional theory for a wide variety of US-SWCNTs and free radicals. Different structures with diverse diameters and helicities (armchair and zigzag) have been considered. In addition, US-SWCNTs with three different kinds of defects and carboxylic functionalized US-SWCNTs have been taken into account. It stands out that ultrashort zigzag nanotubes are better electron acceptors and also slightly better electron donors than their corresponding armchair partners. Pristine zigzag nanotubes were found to be better electron donors and worse electron acceptors than carboxylated US-SWCNTs. The electron donor capability of carboxylated armchair nanotubes is equivalent to that of the pristine US-SWCNT, while they are better electron acceptors than the nonfunctionalized tubes. Our results indicate that neither the length nor the defects have a significant effect on the free radical scavenger capacity of the US-SWCNTs, when reacting through the electron transfer mechanism. The electron transfer reaction mechanism depends on the characteristics of the free radical and on the nature of the nanotubes.