Gundelia, a genus of flowering plants native to the Mediterranean region, particularly in Iraq, holds promise as a sustainable adsorbent for the treatment of dye-polluted water. This study explores the potential of Gundelia seeds (GS) waste as a biobased adsorbent for removing methylene blue dye from synthesized wastewater. Utilizing various analytical techniques, including scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, and X-ray diffraction analysis (XRD), we assessed GS as an active adsorbent with performance comparable to fabricated and expensive composites. Key parameters such as pH (3-11), pH at the point of zero charge, temperature (298-328 K), dose (0.02-0.1 g), dye concentration (10-50 ppm), and contact time (10-40 min) were systematically investigated. The point of zero charge was determined to be at pH 8, with the highest removal efficiency observed at pH 11. A contact time of 30 minutes yielded a removal rate of approximately 90 %, with an adsorption capacity of 11.07 mg/g. The highest adsorption capacity, 30.57 mg/g, was attained under conditions of 50 ppm dye concentration, 0.02 g dose, and a 40-minute contact time. The study examined three isotherm models, namely Langmuir, Freundlich, and Temkin; all demonstrating a high fit, with Langmuir exhibiting preferability. On the other hand, five kinetic models were explored; the Pseudo second-order model provided the most accurate description of the adsorption process. Prog. Color Colorants Coat. 18 (2025), 53-71© Institute for Color Science and Technology.
