Highly effective photocatalytic decomplexation of Cu-EDTA by MIL-53(Fe): Highlight the important roles of Fe

Heavy metal–organic complexes are difficult to remove by classic precipitation methods. In this study, MIL-53(Fe) photocatalyst was successfully synthesized and its photocatalytic activity for the decomplexation of heavy metal–organic complex was explored. Ethylenediaminetetraacetic acid complexed copper (Cu-EDTA) was chosen as the target. Experimental results showed that approximately 91% of Cu-EDTA was decomposed within 60 min under ultraviolet irradiation (UV), and 64% was mineralized within 120 min. Cu-EDTA decomplexation was mainly driven by the production of h+, HO• and 1O2 from the MIL-53(Fe). Fe(III) released from the MIL-53(Fe) was reduced by the photogenerated electrons and Cu(I) to form Fe(Ⅱ), which inhibited the recombination of photogenerated electrons and h+. More importantly, Fenton-like reactions and coprecipitation derived from the released Fe(III) promoted the decomplexation of Cu-EDTA. As a result, some small molecular compounds, including glycine, acetic acid, nitrilotriacetic acid, oxalic acid, oxamic acid, and NO3–, were generated. The possible decomplexation pathways of Cu-EDTA by MIL-53(Fe) photocatalysis were proposed. Effects of coexisting inorganic ions and organic matter on Cu-EDTA decomplexation were evaluated. Furthermore, the photocatalytic degradation potentials for other heavy metal complexes were also explored.