Various approaches for the estimation of thermodynamic functions of adsorption for a number of azo dyes on activated carbon

Author(s): Emad A.S.Al-Hyali, Aiman S.M.T.Shndala

This study is concerned with testing the adsorption efficiency of a new type of activated carbon for removal of azo dyes from their aqueous solutions. Three azo dyes are synthesized from the reaction of para substituted anilines with â-naphthol via diazonium salts are used as adsorbate for achieving this study. The optimal conditions of the considered adsorption systems are determined by studying factors affecting adsorption efficiency such as adsorbent dose, contact time, initial concentration of dye, pH of the adsorptionmediumand temperature. The amount of adsorbed dye is estimated spectrophotometrically by constructing a calibration curve for each dye at its maximumwave length (ëmax). The adsorption processes are carried out as batch methods and by employing single component systems. Three models of adsorption isotherms namely; Freundlich, Langmuir, and Tempkin are applied to fit the experimental data of adsorption at equilibrium at certain range of concentrations (1*10-4 – 9*10-4M) and at various temperatures. The results indicated that, the Freundlich isothermis better fitted to the experimental data of the studied systems, although, the other isotherms exhibited good fit. For sets of thermodynamic functions of adsorption (ÄH, ÄGo, and ÄSo) are estimated depending on the values of the equilibrium constants of adsorption which are represented by four different ways; First, the distribution coefficient calculated from the ratio between the concentrations of the adsorbed and free dye in solution at equilibrium. Its then represented by Freundlich constant (KF), Langmuir constant (KL), and finally is described by Tempkin constant (TK). The results obtained showed good consistency among the four set of functions in terms of their values and physical meaning.

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