Adsorption of methylene blue onto citric acid treated carbonized bamboo leaves powder: Equilibrium, kinetics, thermodynamics analyses

In this article, the adsorption of methylene blue (MB) from its aqueous solution onto citric acid treated carbonized bamboo leaves powder as an adsorbent is reported. The adsorbent was characterized by determining the density, pH(pzc) (6.6), particle size (32.53 mu m), and was analyzed by SEM, BET (surface area 393.3 m(2)/g) and FTIR. Batch experiments were performed as a function of various operating parameters - initial concentration (100 to 400 mg/L), contact time (10 to 100 min), adsorbent dose (0.2 to 1.4 g/L), shaker speed (50 to 350 rpm) and temperature (290 to 305 K) at natural pH of 7.5. The batch data followed Temkin isotherm amongst seven isotherms and pseudo-second order kinetic model. Further, analysis of batch data upon various diffusion models indicated that film diffusion was controlling the rate though intra-particle diffusion was taking place. Thermodynamic parameters (Delta G(0): - 33.70 to - 25.43 kJ/mol; Delta H-0: 134.97 kJ/mol; Delta S-0: 554.51 J/molK) revealed spontaneity of adsorption and the nature was chemisorption which also followed the activation energy (84.07 to 98.90 kJ/mol) estimated from pseudo-second order rate constant as a function of temperature. Novelties achieved were - higher removal of MB (99.97%), higher adsorption capacity (725 mg/g), final solution pH well within the safe discharge limit. Besides, the seasonal variation was used to investigate the temperature effect in a novel manner. (C) 2017 Elsevier B.V. All rights reserved.