Graphitic carbon nitride photocatalyst for the degradation of oxytetracycline hydrochloride in water

A common antibiotic, oxytetracycline hydrochloride (OTC) is hardly biodegradable due to its complex structure, hence is harmful to the environment. Photocatalysis is often performed using metallic photocatalysts and causes secondary pollution. The novelty of this study is that in this paper, graphitic carbon nitride (GCN), a metal-free photocatalyst was employed to degrade OTC via photocatalysis. Three low-cost carbon and nitrogen-rich precursors namely urea, thiourea and melamine were employed to synthesize the GCN (GCN-Urea, GCN-Thiourea, GCN-Melamine) and their abilities to degrade OTC were investigated. This is a prior study in investigating the effect of GCN synthesizing using precursors in degrading antibiotics OTC. FTIR and XRD analysis depicted that GCN photocatalysts were successfully synthesized using the three different precursors. SEM micrographs showed that GCN-Urea particles are ultrathin while GCN-Thiourea and GCN-Melamine are bulky, contributing to high surface area of GCN-Urea at 73.62 m2/g, while GCN-Thiourea and GCN-Melamine have surface area merely at 5.82 and 3.99 m2/g. Meanwhile, GCN-Urea has the highest band gap at 2.7 eV, followed by GCN-Melamine and GCN-Thiourea and are 2.3 and 2.2 eV respectively. GCN-Urea demonstrated the highest capability to absorb light and to induce effective transmission of photoinduced electron-hole, proven by UV–Vis spectra, EIS, Cyclic voltammetry and photocurrent analysis. The best OTC degradation performance was achieved by GCN-Urea at ∼60%, which was 2.5 times higher than GCN-Thiourea and GCN-Melamine. e− and ⸳OH are the main photocatalytic radical species, and GCN-Urea exhibited good stability after being recycled in four cycles.