Chemical transformation during the carbonisation in air and the pyrolysis under argon of a vinylpyridine–divinylbenzene copolymer by X-ray photoelectron spectroscopy

Abstract

X-ray photoelectron spectroscopy was used to identify and characterise the nitrogen functional forms present in a vinylpyridine–divinylbenzene copolymer, its chars, obtained by heating in air at different temperatures and the pyrolysates, obtained by heating the different chars at 950°C under argon. By fitting the N1s envelope, six component peaks were individualised corresponding to a last six different forms of pyridinic nitrogen. The C1s and O1s envelopes were also `decomposed' which permits to follow the fixation of oxygen by the polymer during the carbonisation in air as a function of the temperature and the subsequent depletion of oxygen during the pyrolysis. It is shown that during the condensation process at high temperature, nitrogen atoms were incorporated in the graphene layers replacing carbon atoms in different positions; at the edge of graphene layers as pyridinic N or in the inside as `quaternary' heterocyclic N. Upon exposure to the ambient pyridone-type N and pyridine oxide can be formed by post-oxidation of the pyrolysate. The nitrogen content and the distribution of the different forms of pyridinic nitrogen are identical in the different pyrolysates whatever the char from which they are derived.