Adsorption of dyes acid red 1 and acid green 25 on grafted clay: Modeling and statistical physics interpretation

A grafted clay with 3-aminopropyl-triethoxysilane was employed to study the adsorption of two textile dyes acid red 1 (AR-1) and acid green 25 (AG-25). Adsorption isotherms were analyzed at six temperatures (298-323 K) to characterize the behavior of the adsorption capacity of AR-1 and AG-25. A generalized adsorption model based on statistical physics was selected to understand the removal of these textile dyes from aqueous solution. Modeling results showed that both dyes were adsorbed with a parallel position on clay surface at all tested temperatures and, consequently, this adsorption was a multi-docking (multi-interactions) process. Steric interpretations were discussed to explain the dyes adsorption mechanism via the investigation of the number of linked dyes per main active site of the grafted clay, the estimated number of dyes formed layers, the density of receptor sites and the adsorption capacity. This generalized model provided two adsorption energies characterizing the possible interactions between dye-grafted clay and dye-dye, which ranged from 27.149 to 32.991 and from 20.139 to 24.968 kJ/mol, respectively. These energies were estimated and interpreted to understand the thermodynamic behavior of the adsorption mechanism. Results showed that only physical interactions were possible for these adsorption systems. (C) 2019 Elsevier B.V. All rights reserved.