Comparative study of kinetics of adsorption of methylene blue from aqueous solutions using cinnamon plant (Cinnamonum zeylanicum) leaf powder and pineapple (Ananas comosus) peel powder

Batch adsorption of methylene blue (MB) onto Cinnamon plant (Cinnamonum Zeylanicum) leaf powder (CPLP) and Pineapple (Ananas Comosus) peel powder (PPP) was investigated. Different parameters such as initial sorbate concentration, adsorbent dosage, pH, contact time, agitation speed, temperature and particle size. All isotherm models were found to be best fitting with high values of regression coefficient i.e. for Langmuir (R2 = 0.989 to 0.994 for CPLP and 0.993 to 0.995 for PPP), for Freundlich (R2 = 0.996 to 0.998 for CPLP and 0.995 for PPP) and for Temkin (R2 = 0.983 to 0.995 for CPLP and 0.984 to 0.989 for PPP). The monolayer (maximum) adsorption capacities (qm) were found to be 250 and 333.333 mg/g for CPLP and PPP respectively. Lagergen pseudo -second order model best fits the kinetics of adsorption (R2 = 0.999 for CPLP and 1 for PPP). The amount of dye adsorbed at equilibrium qe(the) obtained from Lagergen pseudo -second order model were found to be nearly same with the experimental data. Intra particle diffusion plot showed boundary layer effect and larger intercepts indicates greater contribution of surface sorption in rate determining step. Adsorption was found to be directly proportional to pH and temperature but inversely proportional to particle size. Thermodynamic analysis ( G, H and S values) showed adsorption was favourable, spontaneous, endothermic physisorption and increased disorder and randomness at the solid- solution interface of MB with the adsorbents. The forward rate constant was much higher than reverse rate constant suggesting dominance of rate of adsorption. PPP was found to be better adsorbent than CPLP.