Rapid degradation of organics by peroxymonosulfate activated with ferric ions embedded in graphitic carbon nitride

Abstract

In this study, Fe3+ was embedded in graphitic carbon nitride (g-C3N4) and used as a catalyst for acid orange 7 (AO7) removal via peroxymonosulfate (PMS) activation. The w/w% Fe3+ dopant was varied (0–2.5) and the changes in the physical and chemical characteristics of g-C3N4 after Fe3+ doping were studied. The results indicated that, while there was no distinct change in the g-C3N4 morphology, Fe3+ doping increases the specific surface area and catalytic active sites for enhanced PMS activation. However, increasing the Fe3+ doping decreased the structural stability of the g-C3N4. It was found that the g-C3N4 with 2.5 w/w% Fe3+ dopant (denoted as gCN-Fe3) gave the highest AO7 removal rate (initial rate constant, ki = 0.096 min−1) with at least 5.6 higher than that of g-C3N4. The effects of PMS dosage, gCN-Fe3 loading and pH on AO7 removal were investigated. The results showed that increasing the gCN-Fe3 loading provided ~3.7 times better performance enhancement compared to increasing the PMS dosage while pH 5 (ki = 0.151 min−1) was the optimum pH. The chemical scavengers were employed to identify the dominant reactive species. Based on the results, it is proposed that higher valent Fe species generated from the interaction between PMS and Fe3+ is the dominant reactive species. The results also indicated that gCN-Fe3 can still retain its catalytic activity after three cycles and AO7 mineralization was achieved. Besides AO7, the gCN-Fe3/PMS system can be employed to degrade various other organics including antibiotics and endocrine disruptors. This indicates that the catalyst has promising application as PMS activator for organics removal.