Ionic peapods from carbon nanotubes and phosphotungstic acid

Using a mild wet-chemical route, cage-like phosphotungstic acid (HPW) molecules of 1.2 nm diameter were successfully filled into opened carbon nanotubes (CNTs) with cavity diameter of 2 nm. High resolution transmission electron microscope revealed that HPW molecules arrayed in a chain in the tube cavity, forming a new kind of peapod structure. In aqueous solution these unusual peapods showed higher ionic property than the opened nanotubes, with a ζ-potential of −47.5 ± 1.3 mV, and dissolved finely as a stable solution. Raman spectra confirmed the strong interaction between HPW molecules and CNT graphite wall. It could substantially tune the electronic properties of CNTs and thus promote their applications in novel electronic devices.