Synthesis of silica gel modified with 2,2′-(hexane-1,6-diylbis(oxy)) dibenzaldehyde as a new adsorbent for the removal of Reactive Yellow 84 and Reactive Blue 19 dyes from aqueous solutions: Equilibrium and thermodynamic studies

In this study, a new sorbent was prepared by the chemical modification of silica gel with 2,2'-(hexane-1,6-diylbis(oxy))dibenzaldehyde (SiO2-NH2-BH) through a Schiff base bond formation by a normal method and a vice versa method. The structure and morphology of the synthesized materials were characterized by Fourier Transform Infrared (FT-IR), Scanning Electron Microscopy (SEM), Thermogravimetric Analyzes (TGA) and Ultraviolet Visible (UV-vis). The produced modified silica gel with normal method was used as an efficient adsorbent for the removal of two anionic reactive dyes, namely Reactive Yellow 84 (RY84) and Reactive Blue 19 (RB19) from their aqueous solutions by batch adsorption procedure. The effect of various operation parameters such as adsorbent dose, solution pH, solution temperature, initial dye concentration and contact time on the adsorption behavior of both the anionic dyes was investigated. The experimental data were analyzed by the Langmuir and Freundlich adsorption models. Based on the correlation coefficient values, it is observed that Langmuir isotherm is appropriate model to explain the adsorption isotherm of both the anionic dyes on SiO2-NH2-BH. The maximum adsorption capacities for Reactive Yellow 84 (RY84) and Reactive Blue 19 (RB19) dyes under room temperature were found to be 68.02 and 72.99 mg/g, respectively. The optimized pH for the effective removal of Reactive Yellow 84 (RY84) and Reactive Blue 19 (RB19) dyes were obtained at 6 and 4, respectively. Meanwhile, different thermodynamic parameters such as the Gibbs free energy (AG), enthalpy (AH) and entropy (AS) were evaluated and the results indicated that the adsorption of both investigated dyes was a spontaneous and endothermic process in nature. Therefore, the silica modified with 2,2'-(hexane-1,6-diylbis(oxy))dibenzaldehyde can be employed as an effective and inexpensive adsorbent for the removal of anionic reactive dyes from aqueous solutions. (C) 2017 Elsevier B.V. All rights reserved.