Acid dyes adsorption isotherms

Adsorption. Adsorption (qv) is an effective means of lowering the concentration of dissolved organics in effluent. Activated carbon is the most widely used and effective adsorbent for dyes (4) and, it has been extensively studied in the waste treatment of the different classes of dyes, ie, acid, direct, basic, reactive, disperse, etc (5—22). Commercial activated carbon can be prepared from lignite and bituminous coal, wood, pulp mill residue, coconut shell, and blood and have a surface area ranging from 500—1400 m /g (23). The feasibiUty of adsorption on carbon for the removal of dissolved organic pollutants has been demonstrated by adsorption isotherms (24) (see Carbon, activated carbon). Several pilot-plant and commercial-scale systems using activated carbon adsorption columns have been developed (25—27). 

The basicity of OLOA 1200 has been evidenced by its interaction with the oil-soluble acidic indicator dye, Brom Phenol Magenta E (EK 6810) which is normally yellow but turns blue and then magenta with increasing bacicity. The acidic form has an adsorption peak at 390 nm, the basic at 610 nm, and the isobestic point is at 460 nm. These spectra have be used to determine the concentration of OLOA 1200 in solution for adsorption isotherms. 

The adsorption isotherms of acid azo dyes onto water soluble and insoluble polymers containing cyclodextrin were measured in aqueous solution. The adsorption of dyes on both types of polymers increased with increase in the ratio of hydrophobic components in the dyes [38], Dyes derivative of dialkylaminobenzene were used for the dyeing of nylon 6 and 6,6 in the presence of interacting / -CD [39], / -CD showed good levelling properties in the dyeing of polyamide fibers. The observed effect can be due to the formation of complexes between /Acyclodcxtri n and dyes. 

In order to test the adsorption behaviors of this kind of macroporous materials, three colored materials Rhodamine B, indophenol, and methyl violet were chosen. The changes of concentrations of the solutions of dyes in a period were detected by UV-VIS spectrometer. The adsorption isotherms are shown in Figure 6. From the adsorption isotherms we can see that the adsorption behaviors of macroporous materials are not good. The reason may be (I) that the surface areas of macroporous materials are low ca. lOOmVg) and the active sites are few (II) the solvent ethanol was adsorbed by the hybrid materials. The adsorption isotherms of three colored materials were different. Methyl violet was an alkaline indicator and the adsorption of methyl violet and hybrid materials may correspond to a chemisorption. Acid indicator Rhodamine B was not adsorbed by the adsorbent and the solvent ethanol was adsorbed instead. Therefore, after reaction the concentration of the solution increased and the adsorption capacity appeared negative. Compared with the former two, indophenol molecule is smaller and is easy to be absorbed. Therefore, its adsorption behavior is stronger relatively. 

Because amino groups act autocatalytically (15-17) in the presence of water, for acid catalysis an excess of HC1 was used to overcompensate the formation of -NH3+C1 . In these cases, the gels were washed with methanol and water until no Cl" could be detected in the filtrate. How far the incorporation of amino groups into silica could affect the adsorption of acid components was of interest. Lactic acid and a sulfonic acid (a commercially available dye named Telon Light Yellow) were chosen as test components (18). In Figure 7 the adsorption isotherm of lactic acid is shown. Unmodified Si02 does not have remarkable adsorption in aqueous solution under these circumstances. The result shows the effect of the amino modification quite clearly, because the lactic acid load of the adsorbent is remarkable, and it is difficult to adsorb small water-soluble molecules in an aqueous environment. 

Wong, Y.C., Szeto, Y.S., Cheung, W.H., and McKay, G. 2004. Adsorption of acid dye on chitosan-equihhrium isotherm analyses. Proc. Biochem. 39 693-702. 

The Langmuir isotherm applies to adsorption on specific sites in the solid, of which there are often only a limited number. Such a situation exists in the dyeing of nylon, wool and silk with simple acid dyes by an ion exchange mechanism. The Langmuir adsorption isotherm is easily derived. The rate of desorption depends only on the fraction of occupied sites The rate of adsorption of... 

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