Preparation of hollow carbon nanospheres from oxidation of spent tyre oil-derived carbon black in air

Hollow carbon nanospheres (HCNS) were prepared from carbon black (CB) derived from spent tyre pyrolysis oil. The pristine CB produced by partial oxidation of the pyrolysis oil in a drop tube furnace was subsequently oxidised in air in a fixed bed reactor to yield HCNS. The effect of oxidation temperature (300 to 700°C) and time (1 to 8 h) on the burn-off (B_t) of the sample over the duration (t) of oxidation and average reaction rate (R_t) was assessed. The BET surface area and pore volume and the nanostructure of the HCNS samples obtained were characterised using N₂ adsorption–desorption and high-resolution transmission electron microscope (HRTEM) techniques, respectively. Higher temperature and longer oxidation time led to higher B_t. As B_t increased, the BET surface area and pore volume initially increased linearly due to the removal of the amorphous core and then decreased because of the collapse of the shell of the carbon nanostructure. At B_t of ~56%, the maximum BET surface area and pore volume of the HCNS were 383.2 m² g⁻¹ and 0.39 cm³ g⁻¹, respectively, compared to ~19.5 m² g⁻¹ and 0.033 cm³ g⁻¹ of the pristine CB. The HRTEM images indicate that the change in BET surface area corresponds to the formation of the HCNS, as the core of the CB particle was preferentially consumed to create a hollow structure. The formation of HCNS follows an internal oxidation model, which is characterised by rapid core consumption and relatively slow shell consumption.