Equilibrium isotherm, kinetic, and thermodynamic studies of Safranin O adsorption on pomegranate (Punica granatum) peels as a low-cost adsorbent

The present study considered the adsorption capacity of Safranin O (SO) dye onto pomegranate peel powder (PP). The effect of operating parameters such as contact time, adsorbent dosage, initial concentration, pH and temperature on the performance of the dye adsorption process was also investigated. The PP was characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Thermogravimetric analysis (TGA), point of zero charge (pH <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mrow/> <mml:mi mathvariant="normal">pzc</mml:mi> </mml:msub> </mml:math> ), and Boehm titration. According to the results, the dye removal rate increased proportionally to the amount of adsorbent used. Langmuir, Freundlich, Temkin, and Dubinin–Radushkevich isotherms in their linear and non-linear forms were tested to determine the most appropriate model. The results showed an adsorption capacity by PP of 44 mg/g at natural pH, room temperature, in 30 min, and with an adsorbent dosage of 10 g/L. From the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mi>R</mml:mi> <mml:mn>2</mml:mn> </mml:msup> </mml:math> , SSE, and RMSE values, it was found that the pseudo-second-order model best fitted the kinetic data and intraparticular diffusion was one of the rate-limiting steps. Thermodynamic analysis revealed that SO adsorption on PP is endothermic and favored. The results demonstrate that PP is a promising adsorbent for removing cationic dyes, such as SO, from aqueous solutions.