Conductivity of carbonized and activated leather waste

The conductivity of chromium-tanned pigskin leather waste carbonized in various manner to nitrogen-containing carbons is reported. Four protocols have been tested: (1) The simple carbonization at 800 °C in inert atmosphere, (2) the carbonization at 500 °C followed by the activation with potassium hydroxide at 800 °C, (3) direct activation with the alkali at 800 °C and (4) the similar activation with potassium hydroxide excess. The fibrous collagen morphology was preserved after the carbonization except for some shrinkage. The yield in the simple carbonization, 26.9 wt%, was reduced to 23.9 wt% for the activated products. Elemental analysis indicated reduced content of organic elements after carbonization, and X-ray fluorescence the composition of growing inorganic part. The chromium content in biochar was close to 12 wt% and the X-ray diffraction revealed also the presence of metallic chromium in addition to expected chromium(III) oxide and sulfide. FTIR and Raman spectroscopies demonstrated the typical pattern of carbonized materials. The specific surface area and pore volume increased after the activation. The resistivity of the powdered carbonized leather was determined in four-point van der Pauw setup. It decreased by more than one order of magnitude as applied pressure increased from 0.1 to 10 MPa. The sample conductivity depended only a little on the way of carbonization and was of the order of tenths to units S cm−1 at 10 MPa. The precarbonization followed by the activation provided the best result with respect to the yield, nitrogen-content, specific surface area and conductivity of the carbonized material.