Abstract
Used fennel seeds (Foeniculum vulgaris) are a waste product of various industries, including laboratories producing traditional medicine. The biodegradable nature of this agricultural product makes it eco-friendly and offers applications for green technology. Adsorption of zinc(II) on fennel seeds has been investigated after optimizing the pH, contact time, adsorbent and zinc(II) concentrations, and temperature. The characterization was performed by infrared spectroscopy to identify the functional groups involved in the interactions with the metal ions. The hydrogen ion capacity, water-regain capacity, and chemical stability were also determined. The Langmuir, Freundlich, and Dubinin-Radushkevich isotherm models were studied. Pseudo-first-order, pseudo-second-order, and intraparticle diffusion kinetic models were evaluated to characterize the adsorption process. The observed thermodynamic parameters suggest spontaneous adsorption. The adsorption process was found to follow a pseudo-first-order kinetic model with intraparticle diffusion for up to 60 min of contact time. Regeneration studies indicated the retention of 98% of the sorption capacity for up to three cycles.