Adsorption characteristics of cytochrome C onto cationic Langmuir monolayers of sulfonated poly(glycidylmethacrylate)-grafted cellulose: Mass transfer analysis, isotherm modeling and thermodynamics

An investigation was conducted regarding the adsorption and desorption of cytochrome C (Cyt C) from aqueous solutions with a new cellulose adsorbent, poly(glycidylmethacrylate)-grafted cellulose having sulfonate functional group (PGMA-g-Cell-SO3H), synthesized by graft copolymerization of glycidylmethacrylate (GMA) onto cellulose in the presence of ethyleneglycoldimethacrylate as crosslinker using alpha,alpha'-azobisisobutryronitrile as initiator. The epoxy groups of the poly(glycidylmethacrylate) polymer were converted into sulfonic acid groups (as proton exchange groups) with reaction of sodium sulfite. Synthesized PGMA-g-Cell-SO3H was characterized by FTIR, XRD, SEM and BET analysis. The maximum value of Cyt C adsorption was found to be 99.7 and 119.6 mg g(-1) for an initial concentration of 200 and 250 mg L-1, respectively, at pH 9.0 and equilibrium was attained in 3 h. Experimentally obtained isotherms were evaluated with reference to Langmuir, Freundlich and Sips equations and found the adsorption process followed the Langmuir adsorption isotherm with a maximum adsorption capacity of 157.13 mg g(-1) at 30 degrees C. The pseudo-first-order equation fitted well with the experimental data. The intraparticle mass transfer diffusion model gave a better fit to the experimental data. Thermodynamic study revealed the sorption process to be feasible, spontaneous and endothermic in nature. Almost 100% Cyt C adsorbed on the adsorbent could be recovered with 0.2 M CH3COOH solution. After 4 cycles of adsorption and desorption, the decrease in adsorption capacity reached to 4.9%. Results obtained from repeated adsorption/desorption process showed that PGMA-g-Cell-SO3H can be used for the separation of Cyt C from various aqueous solutions. (C) 2011 Elsevier B.V. All rights reserved.