Application of Chemical Force Microscopy for Finding Selective Functional Groups for Discriminating Different Electronic Type Single-Walled Carbon Nanotubes.

We recently reported a noncovalent chemistry bead-based method that can sort single-walled carbon nanotubes (SWNTs) to ultrahigh purity. The method is based on the higher affinity of functionalized agarose beads for M(etallic) carbon nanotubes in acidic pH versus S(emiconducting) SWNTs based on the selective charge reversal of metallic carbon nanotubes. However, fundamental understanding of the relative selective affinity of various functional groups for certain electronic type nanotubes remains somewhat lacking. We show that the chemical force microscopy (CFM) technique can measure the subtle differences between various common functional groups (such as −NH2, −OH, −SO3H/–SO3–Na+, −NO2, etc.) and the different electronic types of SWNTs. We show that the amine-functionalized alkane has significantly higher interaction forces with S SWNTs. On the other hand, SO3–Na+- and NO2-functionalized naphthalene show significantly higher interaction forces with M SWNTs compared with S SWNTs; the −SO3H substitution on ...