Biosorption of Solophenyl Red 7BE Dye onto Raw Sunflower Seed Hulls: Characterisation, Ionic Strength Effects, Kinetics and Isotherm Modelling

Anionic textile dyes released into wastewater streams pose a significant environmental challenge because of their chemical stability, poor biodegradability, and adverse effects on aquatic ecosystems. This study investigates, for the first time, the removal of the anionic dye Solophenyl red 7BE using the low cost biosorbent Sunflower seed hulls. The adsorption process was conducted in batch mode at room temperature under neutral conditions. The biosorbent was used in its raw form. The adsorbent was characterized using several characterization techniques such as the Fourier-transform infrared spectroscopy, thermogravimetry, X-ray diffraction and scanning electron microscopy coupled with Energy Dispersive X-ray spectroscopy. The adsorption mechanisms were discussed using equilibrium isotherms and kinetic models. Results demonstrated that Sunflower seed hulls is a highly effective and sustainable biosorbent for removing the Solophenyl red 7BE textile dye. At an adsorbent dose of 2.5 g / L and in presence of 5.84 g / L of sodium chloride, the Solophenyl red 7BE dye with 20 mg/L initial concentration has been removed with an efficiency above 97%. The addition of sodium chloride improves adsorption about 20% with less biosorbent. The kinetic study and characterization analyses revealed that the adsorption of Solophenyl red 7BE dye is a combination of physisorption and chemisorption mechanisms. The pseudo-first-order kinetic model describes the adsorption dynamic, while Freundlich isotherm provides the best fit for biosorption process. Strong and specific interactions between the dye and the matrix were observed.