Reducing the adverse effects of emerging pollutants, especially antibiotic contamination in water, is one of the major challenges of the 21st century. Photocatalysis, as a promising technology for removing stubborn pollutants, has attracted attention from researchers worldwide. Graphitic carbon nitride (g-C3N4, CN) is known as a photocatalytic material with unique properties and can be applied under visible light. However, due to the rapid recombination of charge carriers, bulk CN exhibits poor photocatalytic performance. Therefore, the aim of this study is to develop delaminated CN photocatalysts for enhancing visible light-driven and increasing the degradation of various antibiotics.

To achieve this goal, two strategies were employed. Firstly, morphological engineering was used to prepare high-surface-area delaminated CN. Then, another semiconductor material with an appropriate bandgap position was selected, and heterostructures of zinc ferrite (ZnFe₂O₄, ZFO) modified on the surface of delaminated CN (ZFO@CN) were successfully prepared using different synthesis methods: one using calcination-assisted method (c-ZFO@CN), and the other using hydrothermal-assisted method (h-ZFO@CN). Subsequently, the h-ZFO@CN nanocomposite was evaluated for the photocatalytic degradation of ciprofloxacin (CIP) as a model contaminant in the presence of persulfate (PMS).

In this study, two different precursors, urea and dicyandiamide, were used to synthesize delaminated CN through a simple calcination method. The microstructure, morphology, surface area, atomic bonding, optical, and thermal properties were analyzed. Furthermore, the photocatalytic performance of ZFO@CN nanocomposite materials was evaluated under 465 nm visible light irradiation using CIP as the target antibiotic pollutant. The results showed that, compared to pristine delaminated CN, the c-ZFO@CN nanocomposite enhanced visible light response and photocatalytic efficiency in CIP degradation, with a 5-fold increase in photocatalytic performance compared to pristine delaminated CN. To understand the photocatalytic degradation mechanism of c-ZFO@CN nanocomposite, experiments were conducted to capture free radical species during CIP photocatalytic degradation. The results indicated that the main active species of c-ZFO@CN were ●O₂− and h+, and the Z-type c-ZFO@CN heterostructure enhanced the main free radicals of CIP photocatalytic degradation. On the other hand, h-ZFO@CN exhibited different photocatalytic performance. Although the Eg between c-ZFO@CN-2 and h-ZFO@CN-2 was almost similar, the photocatalytic performance of c-ZFO@CN-2 in CIP photocatalytic degradation was 3.4 times higher than that of h-ZFO@CN-2 within 30 minutes. Specifically, the kobs of c-ZFO@CN-2 reached 0.043 min^-1, while that of h-ZFO@CN-2 was only 0.013 min^-1. Since the SBET of c-ZFO@CN-2 was 1.7 times higher than that of h-ZFO@CN-2, SBET played an important role in CIP removal. To enhance the photocatalytic activity of h-ZFO@CN-2, PMS was used as an oxidant. The h-ZFO@CN-2/PMS system exhibited high photocatalytic degradation efficiency (>99%) for CIP within 30 minutes, with a kobs of 0.156 min^-1. The results showed that the h-ZFO@CN-2/PMS system was 12 times and 4 times higher in CIP photocatalytic degradation than the h-ZFO@CN-2 and c-ZFO@CN-2 systems without PMS, respectively. The main ROS of CIP photocatalytic degradation in the h-ZFO@CN-2/PMS system were h+, SO₄●−, and ●OH, while ●O²⁻ and 1O₂ were secondary ROS. The h-ZFO@CN-2/PMS system exhibited excellent photocatalytic performance under various environmental parameters, applicable to a wide pH range. Additionally, the h-ZFO@CN-2/PMS system successfully prevented metal leaching, providing environmentally friendly applications. This study proposes a new insight into the activation of PMS by the type II heterostructure of h-ZFO@CN under visible light irradiation. The synergistic effect between h-ZFO@CN and PMS showed good repeatability and stability after 10 continuous cycles, exhibiting over 90% photocatalytic degradation ability for various emerging pollutants. Furthermore, the possible photocatalytic degradation pathways of CIP on h-ZFO@CN-2/PMS were proposed. The results of this study confirm that the photocatalytic performance of ZFO@CN nanocomposite materials can be effectively enhanced by forming heterointerfaces between ZFO.