Kinetics and mechanisms of congo-red dye removal from aqueous solution using activated Moringa oleifera seed coat as adsorbent

Moringa oleifera (MO) seed coat, a postharvest waste of MO seed, was mercerized and used as eco-friendly adsorbent for removal of Congo red (CR) dye from aqueous solution at different time and temperature. Mercerized M. oleifera seed coat (MSC) was characterized through scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) before and after adsorption process. Data obtained from effect of contact time on CR dye-uptake were applied on Elovich, pseudo-first- and second-order kinetic models, as well as on intraparticle diffusion and Boyd models. SEM and FTIR showed adsorption of CR dye on MSC through filled holes (SEM), appearance of new and shifting existing of functional groups (FTIR) on the surface of MSC after adsorption process. Adsorption kinetics was seen to be best fitted with pseudo-second-order model with the highest value of correlation coefficient at all temperatures. Film diffusion mechanism controlled the adsorption process, where external mass transfer was higher than internal mass transfer. Adsorption kinetics parameters confirmed removal of CR dye from aqueous solution through chemical and physical adsorption on MSC.