Photocatalytic Degradation of Caffeine Using Biogenic Silver Doped Zinc Oxide Nanoparticles

Abstract

This study explores the degradation of caffeine using biogenic silver-doped zinc oxide (Ag/ZnO) nanoparticles (NPs) as a heterogeneous photocatalyst. Zinc nitrate (Zn(NO<inf>3</inf>)<inf>2</inf>) and silver nitrate (AgNO<inf>3</inf>) were utilized as precursors in the biogenic synthesis of Ag/ZnO NPs. The synthesis involved incubating the mixtures for 72 h at pH 11 and a temperature of 28 °C ± 1 °C. The incorporation of silver resulted in a reduction of the bandgap energy of ZnO from 3.33 to 2.29 eV, confirming the successful synthesis of Ag/ZnO NPs. Key parameters were optimized to enhance caffeine degradation efficiency, including catalyst loading (5, 10, 15, and 20 mg), initial pollutant concentration (20, 40, 60, 80, 100, 120, and 140 ppm), hydrogen peroxide (H<inf>2</inf>O<inf>2</inf>) concentration (1, 3, 5, and 7 mM), and radiation exposure duration (20 to 200 min). The optimal conditions achieved a maximum degradation efficiency of 85.78% with a pollutant concentration of 60 ppm, catalyst loading of 15 mg/100 mL at pH 8, 5 mM H<inf>2</inf>O<inf>2</inf> as an electron acceptor, and a radiation exposure duration of 160 min. The kinetics of caffeine degradation were found to follow a pseudo-first-order reaction. After 160 min of irradiation, the removal rates of chemical oxygen demand (COD) and total organic carbon (TOC) were 71.23% and 67.87%, respectively, indicating significant mineralization of caffeine. Additionally, the photocatalyst demonstrates impressive reusability and stability, maintaining 81.3% of its degradation capacity for caffeine even after five cycles. This highlights the excellent reusability of Ag/ZnO, making it a sustainable and environmentally friendly choice for treating industrial wastewater. Notably, the method is environmentally friendly and does not involve toxic chemicals.; To synthesize Ag@ZnO NPs using an endophytic fungal isolate from medicinal plant. Nothapodytes foetida. To study the morphological, structural, optical, and stability properties of biogenic Ag@ZnO NPs. To investigate the caffeine degradation and its underlying kinetic analysis. To characterize caffeine degradation using total organic carbon (TOC) and chemical oxygen demand (COD) analysis. © University of Tehran 2025.; © University of Tehran 2025.