Comprehensive characterization and RSM-based optimization of crystal violet adsorption using SnCl2–FeCl3 and SnCl2–ZnCl2 activated pomegranate peel biosorbents

Abstract

This study investigates the potential of modified pomegranate peel biosorbents, specifically those activated with SnCl₂–FeCl₃ and SnCl₂–ZnCl₂, for the efficient removal of crystal violet (CV) dye from synthetic wastewater. The physicochemical properties of the prepared materials were examined using FTIR, SEM-EDX, XRD, TGA/DTG, BET, and pH_pzc analyses. Process optimization and modeling were performed using Response Surface Methodology (RSM) based on Central Composite Design (CCD), with statistical validation conducted through ANOVA. The modified pomegranate peel powders (PPP/Sn–Fe and PPP/Sn–Zn) exhibited enhanced adsorption efficiency, achieving maximum capacities of 675.47 mg g⁻¹ and 357.18 mg g⁻¹, respectively. The adsorption behavior was best fitted by both the Langmuir and Freundlich isotherms, and followed a pseudo-second-order kinetic model. Thermodynamic evaluation confirmed that the process is spontaneous and endothermic. Additionally, the biosorbents demonstrated strong reusability, retaining high performance through up to seven adsorption/desorption cycles.