Synthesis and characterization of polyamide powders for sorption of reactive dyes from aqueous solutions

Polyamide (PA) fine powders or granules, obtained by anionic solution/ suspension polymerization of lactams, were used for the sorption of reactive dye Brilliant Red HE-3B from aqueous solutions. They provided a relatively large surface area and porosity that allowed an increased sorption rate. The visible molecular absorption spectroscopy was used to evaluate the performance of the investigated systems. Under the same conditions, the sorption capacity of polyamide particles decreases in the following manner: PA6-powders > PA12-powders > PA4-granules. The effect of pH, initial dye concentration, temperature, and sorption duration on dye removal was studied for the PA6-powder/reactive dye system. The equilibrium sorption isotherms have been analyzed by the linear, Freundlich, and Langmuir models. The data conform to a Langmuir isotherm and a pseudosecond order kinetic model, respectively. In addition, the apparent thermodynamic parameters were calculated and the obtained values support the conclusion that the reactive dye molecules are adsorbed onto PA-powders by an entropy-driven, endothermic process. (c) 2007 Wiley Periodicals, Inc.