Philippine Journal of Science
150 (1): 291-305, February 2021
ISSN 0031 – 7683
Date Received: 02 Jul 2020

Adsorption of Cadmium (II) onto Oxidized
Activated Carbon Derived from Mahogany
(Swietenia macrophylla King) Pericarp: Equilibrium,
Thermodynamics, and Kinetics

John Rafael N. Granada^1,2, Allan Christopher C. Yago^1,3*, and Jose S. Solis^1,3

¹Institute of Chemistry, College of Science, University of the Philippines
Diliman, Quezon City1101 Philippines
²Physical Science Department, College of Science,
University of the City of Manila, Intramuros, Manila 1002 Philippines
³Natural Sciences Research Institute, University of the Philippines
Diliman, Quezon City 1101, Philippines

*Corresponding author: acyago@up.edu.ph

ABSTRACT

The thermodynamics and kinetics of the adsorption of Cd(II) ions onto oxidized activated carbon derived from mahogany pericarp were studied. The activated carbon was prepared via initial carbonization and activation by phosphoric acid, followed by oxidization using different concentrations of nitric acid (HNO3; 2.5 M, 5.0 M, and 10.0 M). With increasing concentration of HNO3, the number of carboxylic acid groups increased while the number of phenolic groups decreased. Adsorption equilibrium studies revealed that the maximum adsorption capacity for Cd(II) increased with the increasing degree of oxidation of carbon material. The adsorption of Cd2+ ions onto the oxidized carbon was best described by the Freundlich model. Results of kinetic studies showed that the adsorption of Cd(II) ions onto the oxidized activated carbon is limited by film diffusion; for the unmodified carbon, Cd(II) adsorption was limited by intraparticle diffusion. The adsorption process onto the oxidized activated carbon materials was determined to be spontaneous, at the temperature range studied (25–50 °C).