Synergistic effect of the heterojunction g-C3N4/Bi2MoO6/clinoptilolite to enhance the photocatalytic degradation of antibiotics in water in the presence of persulfate†

Abstract

A novel and highly efficient photocatalyst, g-C₃N₄/Bi₂MoO₆/clinoptilolite nanocomposite (CNBC), was synthesized by a hydrothermal method and acted as a Z-scheme heterojunction for efficient activation of peroxydisulfate (PDS) to degrade oxytetracycline (OTC) under visible light (vis) irradiation. The morphology and structure of the photocatalyst were determined by XRD, FT-IR, FE-SEM, EDX, BET, TGA, UV-vis DRS, PL, and XPS. The results showed that CNBC-30 had the best photocatalytic performance with an OTC removal efficiency of more than 87% within 120 min under the conditions of [OTC] = 20 mg L⁻¹, [catalyst] = 500 mg L⁻¹, [Na₂S₂O₈] = 1.26 mM, and pH = 4 at room temperature, which was much better than those of pure g-C₃N₄, Bi₂MoO₆, and CNB composites. This superiority is due to the excellent adsorption ability of clinoptilolite that effectively forms the g-C₃N₄/Bi₂MoO₆ heterojunctions, thus improving the ability to separate charge carriers while decreasing the recombination rate of electron–hole pairs. Furthermore, the effect of catalyst dosage, oxidant concentration, initial pollutant concentration, solution pH, and coexisting anions on the OTC degradation was comprehensively studied. The results showed that the CNBC-30/PDS system had high reusability and adaptability at different pH levels (3.0–11.0). Quenching tests showed that ¹O₂, O₂˙⁻, and h⁺ played the main roles in OTC degradation. In addition, OTC intermediates were identified and degradation pathways were proposed based on the results of MS analysis. DFT calculations successfully predicted the positions on the OTC molecule with high Fukui numbers that are suitable for attack by oxidants. CNBC-30 was stable for OTC degradation after four cycles with a degradation efficiency of above 78%, demonstrating its durability and potential for practical applications. This study provides insight into PDS activation in the visible light region by a clinoptilolite-based Z-scheme heterojunction for organic pollutant degradation.