Characteristics of activated carbon from peanut hulls in relation to conditions of preparation

Powdered dried peanut hulls were treated by one-step procedures to get activated carbon using chemical activation by H3PO4, ZnCl2, KOH and thermal activation by steam pyrolysis. Products were characterized by adsorption of N2 at 77 K and methylene blue (MB) from aqueous solution. Simple carbonization at 700–900 °C yields low adsorbing microporous carbons. Steam pyrolysis at 600 °C generates porosity in the mesopore range. KOH activation results in carbons of low surface area similar to steam pyrolysis, but with much developed mesoporosity, whereas ZnCl2 activation yields a moderate adsorbing carbon, essentially microporous. Treatment with H3PO4 at increasing impregnation ratios creates abundant microporosity with extended surface area attaining a maximum at a ratio of 1.0. Considerable loss in porosity accompanies additional activating acid indicating the governing action of the amount of activant. A 50% diluted H3PO4 acid results in a carbon with considerable reduction in the internal porosity. Highest removal capacity of MB appears with H3PO4-activated carbons, whereas KOH-activated carbons show the weakest uptake for the dye.