Microwave-synthesised graphitic carbon nitride for photocatalytic 5-fluorouracil removal

The widespread use of cytostatic drugs like 5-fluorouracil (5-FU) has unavoidably led to their concerning presence in hospital wastewaters and aquatic environments, demanding efficient and sustainable removal technologies. In this study, highly efficient graphitic carbon nitride (g-C 3 N 4 ) photocatalysts were synthesised via an eco-friendly, time-saving, and cost-effective microwave-assisted method. Various single and mixed nitrogen-rich precursors (urea, thiourea, and dicyanamide) were evaluated. The catalyst prepared from a 50% mass mixture of urea and thiourea (U-TU) exhibited superior physicochemical properties, including a large specific surface area (47 m 2 g −1 ), enhanced crystallinity, a narrow bandgap (2.65 eV), and abundant sp 2 nitrogen vacancies that discourage charge carrier recombination. Under UV-A LED irradiation, the optimised U-TU catalyst achieved a remarkable 98.6% degradation of 5-FU (1 mg L −1 ) within 90 min in ultrapure water. Scavenger experiments and band structure analysis revealed that direct oxidation by photogenerated positive holes (h + ) was the primary mechanism driving the degradation process. The proposed system demonstrated high energy efficiency with an Electrical Energy per Order (EEO) of 4.3 kWh m −3 order −1 , representing a more viable alternative than other advanced oxidation processes. Furthermore, the U-TU photocatalyst demonstrated excellent stability and reusability over four successive cycles, and phytotoxicity tests using Lepidium sativum and Sorghum saccharate seeds confirmed that the treated solution and its resulting transformation products exhibit lower toxicity in comparison to the parent 5-FU contaminant.