Adsorption of Cationic Dyes on Dacryodes edulis Seeds Activated Carbon Modified Using Phosphoric Acid and Sodium Chloride

Abstract

The aim of this study was to investigate the adsorption of Congo red (CR) and Vat yellow 4 (VY4) cationic dyes from aqueous media using adsorbents developed from Dacryodes edulis (African pear) seeds (DES) activated using phosphoric acid (H3PO4) and sodium chloride (NaCl). The adsorbents were characterised using X-ray Fluorescence (XRF), Fourier Transforms Infrared Spectrophotometry (FTIR) and Scanning Electron Microscopy (SEM). Maximum uptake of CR and VY4 was observed at an initial pH of 2. H3PO4 activated Dacryodes edulis carbon (ADES) performed better than the NaCl activated Dacryodes edulis carbon (SDES) which implied that the H3PO4 increased the porosity and surface area of DES compared to NaCl use. Maximum dye removal of 99.59%, 96.88%, 99.70% and 98.99% were obtained for the VY4/ADES, VY4/SDES, CR/ADES and CR/SDES, respectively. The Langmuir-Freundlich isotherm showed best fitting when using ADES as adsorbent and the Freundlich isotherm when using SDES. The pseudo-second-order kinetic model was found to best correlate with the experimental data and the adsorption process was controlled by film diffusion. Thermodynamics revealed that adsorption was favourable, spontaneous, and endothermic.