Enhanced decomplexation of Cu(II)-EDTA: The role of acetylacetone in Cu-mediated photo-Fenton reactions

Cu(II)-EDTA is a stable metal-organic complex in electroplating wastewater and is hard to be removed by the conventional precipitation method. UV decomplexation is a useful strategy for its removal. Here, we report that acetylacetone (AA) can enhance the decomplexation of Cu(II)-EDTA by facilitating the photo-Fenton reactions. Under UV irradiation, the pseudo-first-order decomplexation rate constant (k1) of Cu(II)-EDTA (0.3 mM) was enhanced 2-3 times by AA at a [AA]: [Cu(II)-EDTA] molar ratio of 1, whereas the photochemical consumption of AA was reduced 2-3 times by the presence of Cu(II)-EDTA. Based on intermediate species and product analyses, the first step in decomplexation was confirmed as direct photo-decarboxylation of Cu(II)-EDTA via the ligand to metal charge transfer (LMCT) process. Once Cu+ was formed, there would be Fenton-like reactions. AA facilitated the photo-Fenton reactions in two ways: (1) reducing Cu2+ to Cu+ and (2) providing more H2O2 via the redox cycle of AA. Besides, the degradation products of AA could also involve in the decomplexation of Cu(II)-EDTA through LMCT. The work here might provide a promising solution for the decomplexation of metal-organic complexes in industrial wastewater.