Imobilização e caracterização de ZnO em esferas de alginato aplicada para remoção fotocatalítica da cafeína

Abstract

The presence of emerging contaminants in water bodies has raised increasing concern due to their persistence and the limited efficiency of conventional treatment processes for their removal. Among these compounds, caffeine stands out because of its widespread consumption and frequent detection in surface water and wastewater, being widely used as a model contaminant and an indicator of anthropogenic pollution. In this context, heterogeneous photocatalysis using zinc oxide (ZnO) has emerged as a promising alternative for the degradation of this contaminant. However, the difficulty of recovering the catalyst after the reaction limits its practical application, highlighting the need for strategies that facilitate catalyst recovery and reuse. Therefore, this study aimed to immobilize ZnO in sodium alginate beads to facilitate the recovery and reuse of the photocatalyst, as well as to evaluate its efficiency in the photocatalytic degradation of caffeine. The beads were prepared by incorporating ZnO into a sodium alginate solution followed by gelation in a calcium chloride solution. The obtained materials were characterized according to their physical properties and applied in photocatalytic degradation experiments. The results showed a progressive reduction in caffeine concentration throughout the reaction time under all evaluated conditions. Hydrated beads exhibited superior performance compared to dry beads, achieving a removal efficiency of up to 90.4% after 120 minutes of reaction. In addition, reuse experiments demonstrated that the immobilized photocatalyst maintained its photocatalytic activity after an additional cycle, confirming the stability of the developed system. The results indicate that the immobilization of ZnO in sodium alginate beads is a promising strategy for photocatalytic processes, combining high efficiency in caffeine degradation with easy catalyst recovery and reuse. Since caffeine is widely employed as a model contaminant, the developed methodology also shows potential for future applications in the degradation of other emerging organic contaminants.