Adsorption of FD&C Red 40 by chitosan: isotherm analysis

Abstract

The adsorption of azobenzene FD&C Red No. 40 (C.I. 16035) from aqueous solutions by chitosan was studied through adsorption isotherms. The effects of pH (5.7, 6.6 and 7.5), particle size ranges (0.10 ± 0.02, 0.18 ± 0.02 and 0.26 ± 0.02 mm), deacetylation degree (42 ± 5%, 64 ± 3% and 84 ± 3%) and temperature (25, 35 and 45 °C) were investigated. Langmuir, Freundlich and Redlich–Peterson (R–P) adsorption models were applied in order to describe the experimental isotherms and isotherm constants. Coefficients of determination (R2 > 0.95) and mean relative error (MRE < 0.10) values showed that Langmuir and R–P models presented better fit with the experimental data. The maximum monolayer adsorption value has been found to be 529 mg g−1, at pH 6.6, temperature 35 °C, particle size range 0.10 ± 0.02 mm, and deacetylation degree 84 ± 3%.