Origin of the enhanced photocatalytic activity of graphitic carbon nitride nanocomposites and the effects of water constituents

A metal-free heterostructure system composed of graphitic carbon nitride (g-C3N4), reduced graphene oxide (rGO), and cyclooctasulfur (alpha-S) is developed as a facile route for establishing efficient photo catalysts. We aim to identify the governing factors that contributed to the photochemical performance of g-C3N4/rGO/alpha-S nanocomposites, which are important to advance potential applications but remain unexplored. The results indicate that the constituent ratio of each component in g-C3N4/rGO/alpha-S composites leads to varying surface microstructure, band alignment, and photochemical properties. The enhanced visible-light photocatalytic activity originates from an upward shift of the conduction bands toward higher energies, higher content of sp(2)-hybridized pyridine nitrogen in triazine rings (C=N-C), and a lower amount of hydrogen bonds. The established structural integration informs a guiding framework for the design of emerging g-C3N4-based nanocomposites. Additionally, the influence of humic acid (HA) on photocatalytic decontamination was studied and shows an overall detrimental effect on the photocatalytic activity of g-C3N4 nanocomposites. Although HA advanced the photoexcited electrons, and therefore the reactive oxygen species, as well as enhanced the adsorption of the pollutants onto g-C3N4, especially at lower pH, attenuation of oxygen transfer as a result of active site competition between oxygen and target pollutants was found. (C) 2020 Elsevier Ltd. All rights reserved.