Templated synthesis of nitrogen-doped graphene-like carbon materials using spent montmorillonite

Abstract

Montmorillonite (Mt) as an environmentally-friendly, low-cost, and highly-efficient adsorbent for cationic dyes has a promising application in dye wastewater treatment. However, proper disposal of the spent Mt is still a challenge holding back the wide application of Mt. This article reports a simple method which can synthesize N-doped graphene-like carbon materials using the spent Mt after the adsorption of crystal violet (CV). The spent Mt was pyrolyzed under the protection of N₂ to carbonize the adsorbed CV within the interlayer space of Mt, and the interlayer spacing of Mt decreased from 11.0 Å to approximately 3.6 Å, close to the thickness of a single graphene layer (3.4 Å). After demineralization (i.e., washing with a mixture of HF and HCl), the carbon material was released from the interlayer space of Mt. Raman spectra showed the presence of both the D-band and G-band on the obtained carbon materials, and transmission electron microscopy observed the thin layers of carbon material. X-ray photoelectron spectroscopy results indicated the simultaneous presence of pyridinic, pyrrolic, and quaternary N on the carbon materials. In addition, the percentage of pyridinic N increases with increasing pyrolysis temperature; whereas that of quaternary N decreases and of pyrrolic N remains relatively constant. The above results suggested the successful synthesis of N-doped graphene-like carbon material. Finally, the obtained materials show interesting electrocatalytic activity for the oxygen reduction reaction and show potential to be used as efficient metal-free electrocatalysts in fuel cells.