Oxygen functionalized g-C3N4 strengthen Fe(III)/H2O2 system by accelerating Fe(III)/Fe(II) cycles under natural solar light: A mutual-promoting configuration

In response to the inherent restriction of low Fe(II) regeneration in the Fenton process, this study demonstrated a mutual-promoting configuration, where oxygen functionalized g-C3N4 (OCN) was applied in Fe(III)/H2O2 system to utilize mild natural solar light (SL) for persistent Fe(II) generation. The constructed OCN/Fe(III)/H2O2/SL system exhibited strong adaptability to various pollutants, and it well outperformed the g-C3N4 (GCN) modified system and the traditional Fenton system in pollutants degradation efficiency. Compared with GCN, OCN could significantly promote the Fe(II) generation under solar light (SL), leading to more efficient H2O2 activation. The characterization analyses revealed the larger surface area and enhanced charge separation of OCN, which were considered to take main responsibility for its enhanced photoactivity. The complexation of Fe(III) with the carboxyl groups of OCN also benefited the Fe(II) generation. ·OH was detected as the dominant radical responsible for metronidazole (MNZ) degradation, and its production in the OCN modified system was about twice that in the GCN modified system and the Fenton system. Moreover, the precipitation of FeOx on the OCN surface benefited the charge separation of the OCN, so that the improved OCN enabled a slight enhancement of MNZ degradation in the reuse experiments. The intermediates of MNZ degradation were analyzed based on the results of LC-MS, which provided insight into MNZ degradation pathways. This work highlighted the concept of self-improving photocatalyst, the ingenious combination of photocatalysis and Fenton-like system formed a mutual-promoting situation where the OCN and the Fenton-like system could both be improved, which endowed the configuration great potential for green and economical oxidation in environmental remediation.