New physicochemical interpretations for the adsorption of food dyes on chitosan films using statistical physics treatment

In this work, statistical physics treatment was employed to study the adsorption of food dyes onto chitosan films, in order to obtain new physicochemical interpretations at molecular level. Experimental equilibrium curves were obtained for the adsorption of four dyes (FD&C red 2, FD&C yellow 5, FD&C blue 2, Acid Red 51) at different temperatures (298, 313 and 328 K). A statistical physics formula was used to interpret these curves, and the parameters such as, number of adsorbed dye molecules per site (n), anchorage number (n′), receptor sites density (NM), adsorbed quantity at saturation (Nasat), steric hindrance (τ), concentration at half saturation (c1/2) and molar adsorption energy (ΔEa) were estimated. The relation of the above mentioned parameters with the chemical structure of the dyes and temperature was evaluated and interpreted.