Controlled synthesis of N-type single-walled carbon nanotubes with 100% of quaternary nitrogen

Despite significant improvements in the synthesis of nitrogen (N)-doped carbon nanotubes (CNTs) and their versatile applications, there has always been a large difficulty in controlling the bonding configuration of N atoms within CNTs. In the current work, we report an effective chemical strategy to synthesize single-walled carbon nanotubes (SWNTs) with 100% of quaternary N via a chlorosulfonic acid(CSA) treatment. In this process, the pyridinic and pyrrolic groups were selectively and completely removed while retaining the quaternary N atoms. The presence of 2.04 at. % of quaternary N atoms within SWNTs was directly identified from a single sharp peak in the N 1s spectra of XPS, and indirectly supported by the downshift of C 1s peak in XPS, the upshift of G'-band in Raman spectroscopy, and the decrease of the work function from 5.46 to 4.59 eV. The doping effect of the quaternary N atoms on the macroscopic properties of SWNT fibers was verified by a large increase in the electrical conductivity from 0.63 to 2.17 MS/m. In perspective, our chemical approach can now be applied to synthesize carbon materials with controlled N functionalities for different applications.