Kinetic, Isothermal, and Thermodynamic Studies of Cr(VI) Adsorption on L-Tryptophan-Containing Microspheres.

Poly(ethylene glycol dimethacrylate-N-methacryloyl-(L)-tryptophan) [poly(EGDMA-MATrp)] microspheres containing L-tryptophan (average diameter=106-300 μm) were synthesized and characterized; their use as adsorbents in removal of Cr(VI) from aqueous solutions was investigated. The poly(EGDMA-MATRP) microspheres were prepared by copolymerizing of ethylene glycol dimethacrylate (EGDMA) with N-methacryloyl-(L)-tryptophan methyl ester (MATrp). The poly(EGDMA-MATrp) microspheres were characterized by N2 adsorption-desorption isotherms, elemental analysis, scanning electron microscope, and swelling studies. At fixed solid/solution ratio, various factors affecting the adsorption of Cr(VI) ions from aqueous solutions, such as pH, initial concentration, contact time, and temperature, were analyzed. Cr(VI) adsroption kinetic data followed pseudo-second-order kinetics. Experimental isotherms of Cr(VI) ions were successfully fit to both the Langmuir and the Dubinin-Radushkevich isotherm models. Thermodynamic aspects of the adsorption process, such as Gibbs free energy, enthalpy, and entropy changes, were investigated. [ABSTRACT FROM AUTHOR]