Ion-exchanged zeolite as a hybrid system: Fluoxetine removal and antibacterial activity

Abstract

The increasing consumption of antidepressants, aggravated by the coronavirus disease 2019 (COVID-19) pandemic, has resulted in the detection of compounds such as fluoxetine in drinking water. This substance is highly toxic to aquatic organisms and has the potential for bioaccumulation in aquatic environments. This study evaluated the effects of modifying natural zeolites through ion exchange to enhance their adsorption capacity and assess their multifunctional potential. Natural zeolites were modified by immersion in 0.1 mol L⁻¹ solutions of AgNO₃, MgCl₂, FeSO₄, and FeCl₃, and their performance in fluoxetine removal was systematically compared. The samples were characterized by Fourier-transform infrared spectroscopy, X-ray diffraction, X-ray fluorescence spectroscopy, thermogravimetric analysis, point of zero charge, scanning electron microscopy, and transmission electron microscopy. Adsorption experiments were conducted with an adsorbent concentration of 1 g L⁻¹ and an initial fluoxetine concentration of 20 mg L⁻¹. The silver-modified zeolite (ZN-AgNO₃), which achieved the best performance among the tested materials, was selected for further testing. The pseudo-second-order and Langmuir models provided the best kinetic and isotherm fits, respectively, with a maximum adsorption capacity of 36.36 mg g⁻¹, achieved at 308 K and an equilibrium time of 21 h. Desorption experiments showed that the adsorbent maintained recovery rates above 50 % over four cycles of reuse. The main adsorption mechanisms involved ion exchange, electrostatic interactions, and hydrogen bonding, in addition to the affinity of silver with the functional groups of fluoxetine. The adsorbent also inhibited the growth of Escherichia coli. Overall, ZN-AgNO₃ demonstrated potential for fluoxetine removal and antibacterial activity.