Walnut shells: food processing waste from western Himalayan state of Himachal Pradesh as an excellent source for production of activated carbon with highly acidic surface

Abstract

Activated carbon one of the best adsorbent for various organic and inorganic pollutants can be made from various raw materials and by different methods of processing. The activated carbon was produced at different temperature, i.e., 300°C, 350°C, 400°C and 500°C respectively. The properties of the activated carbon were further modified and enhanced by treating it with H2SO4, H3PO4 and ZnCl2. Development of porous structure as a consequence of chemical activation is clearly visible from the SEM micrographs of these carbons. Out of the three different chemically activated carbon produced, i.e., sulphuric acid activated walnut shell carbon (SAAWSC), zinc chloride activated walnut shell carbon (ZCAWSC) and phosphoric acid activated walnut shell carbon (PAAWSC), the sulphuric acid activated carbon has been found having the highest surface area of 745 m2/g. The surface of these activated carbons is highly acidic with a maximum phenol group (5.72 meq/g) in the case of phosphoric acid activation. The pHzpc ranges between 4-4.5 for these activated carbons from waste walnut shells.