Effective removal of organic compounds by g-C₃N₄-AQ/Fe(III) via photocatalytic oxidation and photochemical cycling of iron

Anthraquinone-anchored graphitic carbon nitride (denoted as g-C₃N₄-AQ), which has been reported in the photochemical production of H₂O₂, demonstrated significant visible light photocatalytic activity with Fe(III) for the degradation of organic compounds. The synthesized g-C₃N₄-AQ exhibited a light absorption spectrum and crystallinity comparable to that of pristine g-C₃N₄. FT-IR and XPS analyses confirmed the covalent bonding between AQ and g-C₃N₄. The synthesized g-C₃N₄-AQ generated 12 μM of H₂O₂ within 2 h under visible light illumination, a quantity negligible for the degradation of organic compounds. However, in the combination with Fe(III), the system successfully degraded organic compounds, achieving degradation of 88 – 99 % in the presence of dissolved oxygen. It was also observed that the photochemical activity of g-C₃N₄-AQ/Fe(III) was non-selective towards the target organic compounds. Intriguingly, the visible light-illuminated g-C₃N₄-AQ/Fe(III) selectively degraded target organic compounds in the absence of dissolved oxygen. Experimental work employing reactive oxidant scavengers and oxidant probes revealed that ^•OH is the main reactive species responsible for the degradation of organic compounds in the presence of dissolved oxygen, whereas in its absence, the hole acts as the primary oxidant in the selective degradation of organic compounds. This finding provides important insights into the application of the g-C₃N₄-AQ/Fe(III) system for effective micropollutant removal.