One-step calcination synthesis of 2D/2D g-C3N4/WS2 van der Waals heterojunction for visible light-induced photocatalytic degradation of pharmaceutical pollutants.

Abstract

It is well-documented that accumulation of pharmaceutically active compounds (PhACs), such as antibiotics, in aquatic ecosystems is a prominent environmental hazard. Herein, a series of 2D materials-based heterojunctions, conceptualized based on the integration of graphitic carbon nitride (g-C3N4) with tungsten disulfide (WS2), was fabricated through a facile one-step calcination process, and systematically evaluated for eliminating tetracycline (TC) and sulfamethoxazole (SMX) from aqueous matrices. The microstructure, optical properties, and surface chemistry of the as-prepared composites were examined with a range of microscopy and spectroscopy techniques. In comparison with pristine g-C3N4 or bare WS2, the g-C3N4/WS2 material, with optimal WS2 loading, showed significantly improved photocatalytic activity, towards degradation of TC (84%) and SMX (96%), under visible light. Free radical scavenging experiments revealed that superoxide anions and hydroxyl radicals were predominantly responsible for the rapid breakdown of the PhACs. In addition, the dissociation intermediates and residues were identified and the plausible photocatalytic degradation pathways of TC and SMX over the as-constructed 2D/2D heterojunction were discussed. Further, the photocatalysis end products were non-toxic, as inferred via the resazurin cell viability assay, employing Escherichia coli as a model organism. Most importantly, the 2D/2D g-C3N4/WS2 architecture was structurally resilient and exhibited a fairly stable cycling performance for persistent usage in wastewater treatment. The outcomes of this study testify that 2D/2D heterojunction of g-C3N4 fragments and WS2 nanosheets holds great promise for destroying antibiotics or their metabolites, usually present in wastewaters.