Dacryodes edulis leaf derived biochar for methylene blue biosorption

Abstract

Carbonized Dacryodes edulis leaf (CDEL) which was obtained at 250 ◦C, was used for the biosorption of methylene blue (MB) dye from aqueous solutions. The biosorbent was characterised using Boehm titration, pH of zero point charge (pHzpc), FTIR, SEM, XRD and ED-XRF. Mineral compositions of CDEL revealed good amounts of Fe, Ca and K which are of nutritional importance. The pH at zero point of charge (pHzpc) and specific surface area (SSA) of CDEL were found to be 7.5 and 0.983 m2/g respectively. Freundlich isotherm gave good fit to equilibrium biosorption data. Elovich kinetic model gave the best fit to kinetic data which is consistent with chemisorption. Scanning electron microscopy (SEM) and infrared spectroscopy (FTIR) revealed effective biosorption processes. Calculated thermodynamic parameters revealed spontaneous and exothermic biosorption of MB onto CDEL. Highest amount of MB was removed at pH 4 and the percentage removal was about 93%; hence, CDEL is a good biosorbent for MB from aqueous solutions. Generally, CDEL exhibited > 70% MB removal after three adsorption- desorption cycles, showing that it is re-usable and a promising biosorbent for the treatment of MB dye contaminated water.