Visible light-activated NGQD/nsC3N4/Bi2WO6 microsphere composite for effluent organic matter treatment

The diminishing availability of clean water resources has led to a high demand for advanced, effective waste-water effluent reclamation techniques. In this study, a new microsphere composite of nitrogen-doped graphene oxide quantum dots, nanosheet C3N4, and Bi2WO6 was synthesized and characterized to examine its feasibility as a visible light-activated photocatalyst for wastewater reclamation. At the optimal dose of 1 g.L-1 under 6 h of illumination, the composite exhibited a high removal capability for effluent organic matter (82.8 +/- 1.6%). Its high performance and stability over multiple cycles are attributed to two factors: (1) its harvesting ability over a wide range of the visible light region and (2) its ability to separate photoinduced charge carriers effectively, which is driven by the efficient interfacial contact of the hosts and inclusion of the photosensitized nitrogen-doped graphene oxide quantum dots in the structural network. The complex effluent organic matter removal process of the compound was further examined by fluorescence spectroscopy and size exclusion chromatography. Fluorescence spectroscopy showed that humic-like components with a higher degree of aromatic condensation and greater molecular size were preferentially removed by photocatalysis. Protein-like components were removed more rapidly than the humic-like components due to the synergetic effects of OH and O-1(2) on the rapid decomposition of low-molecular-weight compounds. Size exclusion chromatography revealed that the photocatalytic system preferentially removed larger molecules via adsorption and oxidation; however, smaller size fractions might be produced via the breakdown of biopolymer and humic substance fractions in effluent organic matter.