Donnan Approach to Equilibrium Sorption: Interactions of Cationic Dyes with Acrylic Fibers

Abstract

The equilibrium sorption of ten cationic dyes by porous and regular acrylic fibers has been investigated. The data have been interpreted by a simple Donnan approach, based on the assumption that there are two different types of acidic groups in these fibers. The ionic distribution coefficients KD for the dyes and the fibers were calculated. These coefficients provide an indirect measure of the “affinity” of the dyes for the fibers. The values of KD have been discussed in relation to the structures of the dyes and fibers, and in relation to the effects of salts, pH, and temperature.

Donnan Approach to Equilibrium Sorption: Influence of Electrolytes on Dyeing of Dralon X-100 with CI Basic Blue 3

“…In aqueous solution at 0-2.5 X 10-' mol/ 1 range, Lambert-Beer's law was obeyed at 655 nm; at a dyebath concentration of 5.86 X 10 -s mol / 1, a decrease lower than 2% in the absorbance occurred at room temperature in a 0-1 mol / salt concentration range-T h e commercial fiber Dralon X-100 was supplied by Bayer Akfiengewllschai Dormangen, West Germany, and pretreated as previously described [ 21 ] . The strongly (Si) and weakly ( S2 ) acidic group content used for the calculation was obtained after cation exchange ' [3]:…”

“…With increasing salt concentration, the dye sorption decreases, but with sodium and ammonium sulphate, an unusual increase of dye sorption occurs at salt concentrations up to 0.5 mol/l. The equilibrium sorption of cationic dyes by acrylic fibers can be described on the basis of a generalized macroscopic Donnan model [ 3,[17][18][19] , assuming that each ionic concentration of the species i in the fiber C;f is related at equilibrium with the corresponding concentration in the external solution C;s, through the electrical charge z;, the Donnan distribution coefficient a, and the individual ionic distribution coefficient K;: At equilibrium, the fiber, containing acidic groups of j types at concentration Sj mol / kg of dry fiber and with apparent dissociation constants K., has to be electrically neutral, and then we can write Equation 2:The only unknown of Equation 2 is ~: the equation can be solved for X by the iterative process and the equilibrium concentrations C;f calculated using Equation 1.In the absence of detailed measurements of the inorganic ion distributions between the solution and the fiber, McGregor assumed that all the inorganic ions behave in the same way and have the same average ionic distribution coefficient K, [ 16 ] :. The convention that for NaCI, ' provides an operational definition of KI, which has been calculated [10] ] by measurements of the concentrations involved in Equation 4.…”

“…The convention that for NaCI, ' provides an operational definition of KI, which has been calculated [10] ] by measurements of the concentrations involved in Equation 4. There is no way, however, of solving K, into unique contributions clearly attributable separately to KN, or Ko [ 15 ].By means of Equations 1 and 2, we have analyzed data from the literature [I] and investigated the sorption of some cationic dyes by porous and regular acrylic fibers [ 3 ] .The ionic distribution coefficients KD for the cationic dyes are calculated and discussed in relation to the structures of the dyes and the fibers. More recently we have studied dye sorption isotherms at different pH and NaCI concentrations on Dralon X-100 and Dralon U-100 [ 2 ] .…”

“…With increasing salt concentration, the dye sorption decreases, but with sodium and ammonium sulphate, an unusual increase of dye sorption occurs at salt concentrations up to 0.5 mol/l. The equilibrium sorption of cationic dyes by acrylic fibers can be described on the basis of a generalized macroscopic Donnan model [ 3,[17][18][19] , assuming that each ionic concentration of the species i in the fiber C;f is related at equilibrium with the corresponding concentration in the external solution C;s, through the electrical charge z;, the Donnan distribution coefficient a, and the individual ionic distribution coefficient K;: At equilibrium, the fiber, containing acidic groups of j types at concentration Sj mol / kg of dry fiber and with apparent dissociation constants K., has to be electrically neutral, and then we can write Equation 2:…”

“…By means of Equations 1 and 2, we have analyzed data from the literature [I] and investigated the sorption of some cationic dyes by porous and regular acrylic fibers [ 3 ] .…”