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

Abstract

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⁻¹) effectively degraded 15 mg L⁻¹ 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 way for enhanced water treatment technologies.