g-C3N4-triggered super synergy between photocatalysis and ozonation attributed to promoted OH generation

• Lower redox potential of the conduction band of g-C3N4 benefitted electron trapping.
• (Cl/) g-C3N4 triggered a super synergy between photocatalysis and ozonation.
• Promoted surface-charge separation and ozone self-decomposition were achieved.
• Synergistically generated OH accounted for enhanced photocatalytic ozonation.

We coupled g-C3N4 or chlorine modified g-C3N4 (Cl/g-C3N4) photocatalysis with ozonation for mineralization of oxalic acid (OA) under visible light. g-C3N4 and Cl/g-C3N4 could trigger a super synergy between photocatalysis and ozonation, with a coupling coefficient at 17.8 and 9.9, respectively. The great gap of redox potential between the conduction band of g-C3N4 and ozone greatly benefitted electrons captured by ozone molecules, and thus promoted charge separation and ozone self-decomposition into a growing number of hydroxyl radicals in a photocatalytic ozonation process. Besides, the influence of chlorine modification on g-C3N4 to photocatalysis and photocatalytic ozonation was also clearly stated.

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