Preparation and Characterization of a Novel Chemically Modified PVC Adsorbent for Methyl Orange Removal: Optimization, and Study of Isotherm, Kinetics, and Thermodynamics of Adsorption Process

An iron(III)-polyvinyl chloride (PVC)-Schiff base adsorbent was prepared for removal of methyl orange (MO) as an anionic dye from the aqueous samples. PVC was reacted with ethylenediamine to prepare aminated PVC. Salicylaldehyde was then added to the aminated PVC to incorporate the Schiff base group into the polymer structure. This product was further reacted with iron (III) nitrate to form an iron complex as the modified PVC adsorbent (PVC-[Fe(EDA)(Sald)]). The prepared adsorbent was characterized by Fourier transform-infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), Brunauer-Emmett-Teller (BET) surface area analysis, and thermogravimetric analysis (TGA). The special parameters influencing the adsorption process such as the solution pH, contact time, initial dye concentration, and the solution temperature were investigated. Removal percentage (%R) and adsorption capacity (qₜ) greater than 50% and 140 mg g⁻¹, respectively, were obtained under the following conditions: pH, 7;contact time, 150 min; dye concentration, 100 mg.L⁻¹; and solution temperature, 25 °C. The adsorption isotherm and kinetic data were well fitted by the Freundlich isotherm model and the pseudo-second-order kinetic model, respectively. The thermodynamic data revealed that the adsorption process was endothermic and spontaneous. The changes in entropy (ΔS°) and enthalpy (ΔH°) were calculated to be 0.110 kJ mol⁻¹ K⁻¹ and 31.011 kJ mol⁻¹, respectively. In this work, we developed for the first time the synthesis of an iron(III)-polyvinyl chloride (PVC)-Schiff base adsorbent that can be successfully used for removal of methyl orange from the aqueous sample. Furthermore, these findings showed that modified PVC was more efficient than neat PVC on MO removal for adsorption process.