Bandgap-Engineered In2S3 Quantum Dots Anchored on Oxygen-Doped g-C3N4: Forging a Dynamic n-n Heterojunction for Enhanced Persulfate Activation and Degradation of Metronidazole

Herein, an ultrasonication approach was used to anchor In2S3 quantum dots (QDs) onto oxygen-doped graphitic carbon nitride (O@g-C3N4), resulting in a novel heterojunction catalyst. Characterization techniques validated the successful incorporation of In2S3 into the O@g-C3N4 matrix, with transmission electron microscopy (TEM) indicating the existence of In2S3 QDs measuring 6.62 nm. The photocatalyst (0.24 g/L) effectively degraded 15 mg/L of Metronidazole (MDZ) via persulfate (PS) activation under visible light irradiation, with a degradation efficiency of 98.17 ± 1.53% in 25 min. This improved performance was due to the creation of an n-n heterojunction, in which the Fermi energy levels of O@g-C3N4 and In2S3 reached equilibrium, resulting in an internal electrostatic field at their interface that enabled efficient carrier transfer. Combining trapping tests with a well-established S-scheme charge transfer mechanism indicated an excellent photocatalytic process for the In2S3/O@g-C3N4 heterojunction. Chemical oxygen demand (COD) and total organic carbon (TOC) studies were used to measure the photocatalyst's efficacy in degrading MDZ, while its capacity to degrade other pollutants was also tested. Furthermore, after seven cycles, the catalyst displayed remarkable reusability and maintained efficiency in various water conditions with coexisting species such as cations, anions, and organic compounds. As a result, the discovered In2S3/O@g-C3N4 heterojunction catalyst shows significant promise for the effective and long-term removal of MDZ and other toxic pollutants from water, paving the door for enhanced water treatment technologies.