Comparative study on one-step pyrolysis activation of walnut shells to biochar at different heating rates

Pyrolysis of walnut shells to biochar at 700 degrees C using N-2 gas was compared to one-step activation using steam/KOH under four different heating rates (10-40 degrees C/min). Steam biochars developed better surface area property of 342-556 m(2)/g compared to others (19-135 m(2)/g) over the same heating rates; meanwhile, increasing heating rate caused functional groups alteration and was distinct on the surface area property as about six-fold and two-fold difference from the lower to higher rates were recorded in neutral char and the steam/KOH activated biochars respectively. Increasing heating rate affected the neutral and steam biochars' Raman intensity ratio whereas trivial influence was recorded on KOH-biochars. (C) 2021 The Author(s). Published by Elsevier Ltd.