Removal and selective separation of synthetic dyes from water using a polyacrylic acid-based hydrogel: Characterization, isotherm, kinetic, and thermodynamic data

The aim of the present study was to perform the removal and selective separation of synthetic dyes from water using a polyacrylic acid-based hydrogel. Dye removal experiments were performed with pH from 3.0 to 10.0, an initial dye concentration from 150 to 1500 mg L-1, contact time from 1 to 4500 min, and temperature from 4.85 to 39.85 degrees C. The best isotherm fits at temperatures from 4.85 to 19.85 degrees C were found using the Redlich-Peterson and Sips models, whereas the best isotherm fit at temperatures from 19.85 to 39.85 degrees C was found using the Langmuir model. The best kinetic fit was found using the pseudo-first order model. Thermodynamic results demonstrated that cationic dye adsorption to the hydrogel chain is spontaneous, favorable, and endothermic. Fourier-transform infrared (FT-IR) spectra confirmed the efficient formation of the hydrogel chain and scanning electron microscopy (SEM) revealed a porous structure on the hydrogel surface, which is fundamental to the occurrence of intermolecular interaction and solute diffusion. Thermogravimetric analysis and differential scanning calorimetry confirmed that the polymer matrix is stable at low temperatures and starts to degrade at temperatures above 200 degrees C. The best cationic dye removal efficiency was determined at 3500 min, pH 8.0, and 39.85 degrees C, whereas the anionic dye concentration was not reduced. Hence, cationic and anionic dyes were selectively separated at pH from 8.0 to 10.0. The hydrogel synthesized in this work proved to be a potential solid matrix for reducing and separating mixtures of cationic and anionic synthetic dyes from aqueous solutions.