(Invited, Digital Presentation) Application of Polyacid Clusters in Modifying Single-Walled Carbon Nanotubes

Abstract

Phosphotungstic acids (PTAs) are a typical family of polyacids with tunable composition, structure and morphology. Relying on their super strong acidity and moderate oxidizability, they may take different roles when interacting with single walled carbon nanotubes (SWCNTs).We found that PTA could be used as stable dopants for SWCNT films to reduce the resistance without damaging the transparency. By simply dipping the SWCNT films in the solution of PTAs and drying afterwards, the sheet resistance was cut in half with long term stability. The doped films showed excellent flexibility. Both Raman spectroscopic studies and Kelvin probe force microscopy measurements revealed that the strong acidity of PTAs plays a key role in the doping effect by increasing the redox potential of the ambient O2 and thus the Fermi level of the SWCNTs is brought down.The PTA clusters can be encapsulated into the inner cavity of SWCNTs when their diameters are compatible. Such a host-guest molecular interaction between SWCNTs and inner clusters with designed size was applied to separate large-diameter s-SWCNTs. When a kind of PTA of ~1 nm in size were filled within SWCNT cavities, s-SWCNTs with diameters concentrated at ~1.3–1.4 nm were selectively extracted with the purity of ~98% by a commercially available polyfluorene derivative. The sorting mechanisms associate with oxidation effect of PTA and the size-dependent electron transfer from nanotubes to inner PTA clusters. The flexible regulation of interaction between the nanotube and clusters, thus tuning the diameter of sorted s-SWCNTs.PTAs have shown great power in tuning the properties of SWCNTs, presenting amazing potentials in the applications of SWCNTs.