Enhanced photocatalytic degradation of penicillin G using magnetic silica doped ZnAl- layered double hydroxides

In this study, a magnetic photocatalyst, Fe₃O₄-SiO₂-EN (FSE) doped with Zn-Al-LDH nanocomposites (FSEZAL), was successfully synthesized via the sol-gel method. The catalyst was then applied for the removal of penicillin G (PNG) under solar, visible, and UV irradiation. The optimal conditions for achieving 100% PNG removal were determined to be an initial PNG concentration of 25 mg/L, a solution pH of 3-5, an FSEZAL dose of 0.4 g/L, and a reaction time of 60 min. The study also examined the degradation mechanism and oxidation pathway. The experimental observations highlighted that the catalyst had high reusability, with only a slight decrease in PNG degradation ratios after five consecutive cycles (from 100 to 94.3%). Under UV and visible radiation, PNG (25 mg/L) was completely degraded, while sunlight exposure achieved 90.1% removal and required 100 min for full degradation. At the beginning of the process, the BOD₅/COD (five-day biochemical oxygen demand to total organic carbon) and BOD₅/TOC (total organic carbon) ratios were 0.22 and 0.73, respectively, indicating non-biodegradable wastewater. By the end of the process, these ratios increased to 0.73 and 1.37, reflecting complete mineralization of the wastewater. Toxicity assays performed with Daphnia magna confirmed complete detoxification of the PNG solution, in contrast to the adsorption process, which lowered toxicity by only 30%. According to scavenger tests, the degradation of the studied pollutant involved hydroxyl radical (^·OH), superoxide radical (^·O₂^-), electron (e^-), and hole (h⁺), among which ^·OH was the most influential. In conclusion, it can be stated that the evaluated process has the potential to effectively eliminate a range of antibiotics from water-based solutions.