A novel biosorbent from raw pomegranate peel modified with SnCl₂/FeCl₂ for the adsorption of crystal violet cationic dye: response surface methodology process optimization, thermodynamic, kinetic, isotherm, and recyclability studies

This study investigates the utilization of biosorbents derived from both raw and modified pomegranate peel treated with SnCl₂/FeCl₂ for the adsorptive removal of crystal violet (CV) dye from synthetic wastewater. The obtained biosorbents were analyzed using various analytical methods, including Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), energy dispersive X-ray (EDX), X-ray diffraction (XRD), thermogravimetric analysis (TGA), X-ray fluorescence (XRF), Brunauer–Emmett–Teller (BET), and point of zero charge analysis. The adsorption process was modeled using the central composite design model, and its suitability was assessed through ANOVA analysis. The results indicate that treated pomegranate peel (PP/SnCl₂-FeCl₂) exhibits a higher adsorption capacity for CV dye removal compared to raw pomegranate peel (RPP). The maximum adsorption capacities for CV by RPP and PP/SnCl₂-FeCl₂ were found to be 172.40 mg/g and 389.88 mg/g, respectively. This novel biosorbent, PP/SnCl₂-FeCl₂, showed a larger maximum adsorption capacity compared to similar studies, confirming its superior CV removal effectiveness. The adsorption process conforms to Langmuir and Freundlich isotherms, and the kinetics follow a pseudo-second-order model, as indicated by isotherm and kinetic analysis. Thermodynamic data suggest a spontaneous and endothermic process. Furthermore, the prepared biosorbents exhibit good reusability, maintaining efficacy for up to seven consecutive cycles.