Pore structure modification of pitch-based activated carbon by NaOCl and air oxidation/pyrolysis cycles

Two complementary wearing off cycling methods based on an initial wet oxidation in a sodium hypochlorite solution or an initial dry oxidation under air, both followed by a thermal pyrolysis under nitrogen, have been applied to a same carbon molecular sieve to study its gradual pore structure modifications. The changes in microporous properties resulting from these cycles were studied by N₂ physisorption at 77 K and analyzed by using the Dubinin–Radushkevich equation. The observed textural behaviour is different from those usually observed using conventional activation processes. The surface complexes created on the surface of carbon by each NaOCl oxidation were characterized by temperature-programmed desorption (TG-TPD-MS), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR). Corresponding surface functional species have been identified and quantified.

Each of the two methods leads to the formation of two distinct microporous domains developed on the obtained modified CMS series. The gradual mean pore size values of one of those domains are common to the two series while the others are much more enlarged by the oxygen than by the NaOCl treatments. Therefore, the two methods lead to complementary data allowing experimental differentiation of the different porosities encountered in activated carbons. Such series of materials of common origin and surface chemistry but different gradual textural properties are of great interest for activated carbons structural studies as well as for characterization technique improvements.