Effects of activation on the properties of electrospun carbon nanofibers and their adsorption performance for carbon dioxide

Abstract

Microporous carbon nanofibers were prepared by stabilization, carbonization, and activation of electrospun polyacrylonitrile-based nanofibers. The average fiber diameters of activated electrospun carbon nanofibers (AECNF) samples, ranging from 280 to 500 nm, generally decreased with increasing activation degree. The evolution of nitrogen was observed during the fabricated processes, and the predominant nitrogen functionalities were shifted to those at higher binding energies when the activation degree increased. The N/C ratios on the surface of the samples were affected significantly by the activation temperature and activation time. The AECNF samples were featured with microporosity and the ultramicropores were also newly formed with increasing activation degree. It was expected that the activation process involved a three-step predominant reaction: the transformation from ultramicropores to submicropores, the micropore enlargement reaction followed by the micropore formation reaction. The equilibrium CO2 adsorption capacities could achieve 1.2 mmole/g (0.15 atm) and 3.2 mmole/g (1 atm) at 298 K. The CO2 uptake at low partial pressure and ultramicroporosity of the adsorbents were related to the isosteric heat of adsorption. The AECNF samples for CO2 adsorption had an energetically heterogeneous surface and Freundlich equation provided a satisfactory fit. Synergetic effects of microporosity and nitrogen content of AECNF on CO2 uptakes at low pressure were observed.