Green synthesis of graphitic carbon nitride-based metal oxide photocatalysts and their application in the removal of antibiotics from aqueous solutions

Environmental problems arising from pharmaceutical pollution in water sources are increasing and demand creative and sustainable solution approaches. In this study, ZnO/g-C3N4, NiO/g-C3N4, and NiO nanoparticles were synthesized using a green synthesis method with Salix Aegyptiaca extract for the degradation of tetracycline (TC), a model antibiotic. This method not only offers an environmentally friendly and low-cost approach, but also holds significance due to the potential applications of the synthesized nanoparticles in photocatalytic degradation processes. The structural characterizations of the photocatalysts were carried out using FTIR, XRD, SEM-EDS, TEM, XPS, zeta potential, and UV-DRS analyses. The experimental design was optimized using Design Expert v8 software. The photocatalytic degradation of TC with ZnO/g-C3N4 was examined under parameters such as pH (4–10), adsorbent dosage (0.2–0.8 mg/mL), initial TC concentration (10–60 mg/L), and catalyst type (synthesized with extract or distilled water). The highest degradation efficiency of 70.21% was achieved using the catalyst synthesized with plant extract, while the one synthesized with distilled water resulted in 72.30% degradation. Additionally, the photocatalytic performance of NiO nanoparticles was investigated. NiO was classified as a suitable semiconductor for use in the photocatalytic degradation of tetracycline. Adsorption experiments showed that NiO nanoparticles had a high adsorption capacity (93.46 mg/g) and a good adsorption rate (0.0033 g/mg.min). Finally, the study emphasizes that photocatalytic degradation methods present a promising solution for eliminating antibiotic contamination from water resources and combating antibiotic resistance. For NiO/g-C3N4, an optimal degradation efficiency of 27.94% under visible light within 60 minutes was achieved. This optimum value was obtained with an adsorbent dosage of 0,8 mg/mL, a solution pH of 4, and an initial TC concentration of 59,62 mg/L. The reusability of ZnO/g-C3N4 (synthesized using extract and water) and NiO nanoparticles was evaluated over three consecutive photocatalytic cycles under optimal conditions. Only a slight decrease in degradation efficiency was observed, indicating good structural and functional stability. For ZnO/g-C3N4, energy and cost analysis revealed a total energy consumption of 0.693 kWh and an estimated treatment cost of 1.162 USD/L. These results highlight the environmental sustainability and economic feasibility of the developed photocatalysts.