Carbonization and activation of leather buffing dust to a biocarbon and its conductivity

Abstract

Buffing dust, one of the collagenous wastes produced in the footwear industry, was carbonized at 400–1200 °C in an inert atmosphere to microfibrous nitrogen-containing biocarbons enriched with chromium. The evolution of molecular microstructure with increasing carbonization temperature or exposure time was followed with FTIR and Raman spectra. The resistivity of the powdered products was determined by van der Pauw four-point method and recorded as a function of applied pressure in the 0.1–10 MPa range. The highest conductivity 13.9 S cm⁻¹ at 10 MPa was found after the carbonization at 1200 °C. The mechanical properties, such as the change of sample volume with applied pressure, are also discussed. The specific surface area was low, ca 5–7 m²g⁻¹, independent of the carbonization temperature. This parameter was enhanced by the chemical activation with ammonium peroxydisulfate or potassium hydroxide by two orders of magnitude, while the conductivity decreased at the same time by less than one order of magnitude.