A comparative study on tetracycline photodegradation over ZnO/BiOBr and ZnO/BiOI nanoarchitectures: The relationships between synthesis parameters and photocatalytic activity

The presence of antibiotics in surface waters and wastewater leaked from different sources causes risks to humans and animals. Today, the photocatalytic decomposition of antibiotics-contaminated wastewater is an effective and promising method. This research synthesized ZnO nanorods/BiOBr nanosheets and ZnO nanorods/BiOI nanosheets photocatalysts on a stainless-steel mesh substrate. ZnO/BiOX (X = Br and I) samples were prepared at different pHs, and the pH-dependent morphology evolution was studied to tune the synthesis conditions. Adjusting the synthesis pH amounts changed the photocatalytic activity for tetracycline (TC) photodegradation under both UV and visible LED lights. The order of photodegradation rates was ZnO/BiOI, pH = 7> ZnO/BiOBr, pH = 9> ZnO/BiOI, pH = 9> ZnO/BiOI, pH = 4> ZnO/BiOBr, pH = 4> ZnO > ZnO/BiOBr, pH = 7> photolysis. Based on the results, ZnO/BiOI prepared at the neutral condition, and ZnO/BiOBr synthesized at the basic condition demonstrated higher photocatalytic activity under UV light. Accordingly, the photodegradation rate constants (k) ZnO/BiOI, pH = 7, and ZnO/BiOBr, pH = 9, were about 7.4 and 7.1 min−1, respectively, which was more significant than pure ZnO nanorods (4.3 min−1). The mechanistic study for the photodegradation pathway under UV light revealed that the Z-scheme heterojunction between ZnO nanorods and BiOX (X = Br and I) nanosheets governs the role of enhanced photodegradation. Also, under white LED light as a visible source, efficient charge separation and transfer of photogenerated electrons of BiOX act as crucial photodegradation pathways. This study shows that ZnO/BiOI, pH = 7, has a slightly higher TC photodegradation under both UV and visible light than ZnO/BiOBr, pH = 9. Also, The flexibility and accessible synthesis of our photocatalysts and the fast recovery from the treated wastewater are promising for this photocatalyst's practical applications.