Assembly of ring-shaped phosphorus within carbon nanotube nanoreactors

January 2017

by Jinying Zhang, Dan Zhao, Dingbin Xiao, Chuansheng Ma, Hongchu Du, Xin Li, Lihui Zhang, Jialiang Huang, Hongyang Huang, Chun-Lin Jia, David Tománek and Chunming Niu

A phosphorus allotrope that has not been observed so far, ring-shaped phosphorus consisting of alternate P8 and P2 structural units, has been assembled inside multi-walled carbon nanotube nanoreactors with inner diameters of 5 - 8 nm by a chemical vapour transport and reaction of red phosphorus at 500 °C.

The ring-shaped nanostructures with surrounding graphene walls are stable under ambient conditions. The nanostructures were characterised by high-resolution transmission electron microscopy, scanning transmission electron microscopy, energy-dispersive X-ray spectroscopy, Raman scattering, attenuated total reflectance Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy.

HRTEM image and structural simulation suggested that the observed nanostructure is r-P, which has been theoretically predicted to be stable but never experimentally observed. The r-P consists of alternate P8 and P2 structural units with variable ring diameters, observed inside the MWCNTs with inner diameters of 5–8 nm.

A ring with a diameter of 5.30 nm, consisting of 23 P8 and 23 P2 units with a total of 230 P atoms, was observed inside a MWCNT with an inner diameter of 5.90 nm. The distance between neighboring rings is 6.4 Å. The surrounding graphitic walls of MWCNTs establish a nanoreactor for r-P structure formation and its protection against oxidation in air. A blue-shift of the G-band was observed from the sample containing both external and internal phosphorus, whereas a small red-shift was observed after removing most of the external phosphorus.

The depth profile of P 2p XPS spectra of r-P@MWCNT shows that phosphorus oxides were distributed on the surfaces of the sample and could be etched away with an Ar ion beam. Observed P 2p core-level binding energies of r-P inside MWCNTs are smaller than external phosphorus.

Further reading:

Jinying Zhang, Dan Zhao, Dingbin Xiao, Chuansheng Ma, Hongchu Du, Xin Li, Lihui Zhang, Jialiang Huang, Hongyang Huang, Chun-Lin Jia, David Tománek and Chunming Niu:
Tungsten bronze barium neodymium titanate (Ba6–3nNd8+2nTi18O54): Assembly of ring-shaped phosphorus within carbon nanotube nanoreactors,
Angew Chem Int Ed 56 (2017) 1 – 6.