Use of pomegranate peels for the effective removal of the hazardous dye Solophenyl Blue GL (CI Direct Blue 71) from aqueous solution

This study focuses on the valorization of agro-industrial waste for water treatment applications. Pomegranate peels were employed as a biosorbent for the removal of the anionic textile dye Solophenyl Blue GL (SB) from aqueous solutions. The materials were characterized using scanning electron microscopy (SEM), thermogravimetric analysis (TGA), Fourier-transform infrared spectroscopy (FTIR), and determination of the point of zero charge (pHₚzc). The results showed that SB dye undergoes denaturation under highly acidic conditions, leading to its decomposition into toxic amine compounds that pose environmental risks. Batch adsorption experiments were conducted to investigate the effects of various parameters, including moisture, ash and volatile matter contents, specific surface area, solution pH, adsorbent dosage, initial dye concentration, salt effect, and contact time. Biomaterial optimization was achieved through chemical and physical modifications. Chemically activated materials (PEGa) were prepared by NaOH impregnation (1 M), while activated carbon (PEGc) was produced by pyrolysis of pomegranate peel powder (PEGb) at 500°C. A comparative adsorption study of the native, chemically activated, and calcined materials under identical conditions demonstrated that dye biosorption was enhanced at pH values below the pHₚzc due to electrostatic attraction, whereas it was inhibited at pH values above the pHₚzc because of electrostatic repulsion. The adsorption affinity followed the order: calcined (PEGc) > activated (PEGa) > native (PEGb). Overall, calcined pomegranate peel biochar (PEGc) appears to be a promising, low-cost adsorbent for the removal of persistent anionic dyes from water.