Spectroscopic and computational evaluation of cadmium adsorption using activated carbon produced from rubber tires

The aim of this work was to investigate the utilization of waste tire carbons as a low cost adsorbent for removal of cadmium (II) ion from aqueous solution with density functional theory calculations to shed more light on the adsorption process. Thus, activated carbon was prepared from waste rubber tires and characterized by means of field emission scanning electron microscopy, energy-dispersive X-ray and Fourier transform infrared spectroscopies. Effect of various operating parameters like contact time, dosage, agitation speed and pH on the removal of Cd(II) from aqueous solution by the batch adsorption technique was investigated. The adsorption process was relatively fast and the equilibrium was reached after about 60 min of contact. Characterization of activated carbon after adsorption was also conducted. Density functional theory (DFT) calculations were performed to estimate the binding energy of Cd ^{2 +} ions towards carboxylic acid, carbonyl and hydroxyl groups. The calculated binding energy of the adsorption process was predicted to be in the range of 190-212 kcal/mol, and the Cd^{2 +} ion tends to approach more conveniently towards the carbonyl's oxygen atom in the carboxylic acid and carbonyl groups. The developed sorbent exhibited the advantages of being inexpensive and of double benefit to the environment.