Photoinduced transformation of γ-HCH in the presence of dissolved organic matter and enhanced photoreactive activity of humate-coated α-Fe₂O₃

This study examined phototransformation of γ-hexachlorocyclohexane (γ-HCH) in different solutions. The presence of dissolved organic matter (DOM) inhibited the phototransformation of γ-HCH. This phenomenon could be correlated to the binding interaction between γ-HCH and DOM. α-Fe₂O₃ promoted the transformation of γ-HCH. The humate-coated α-Fe₂O₃ revealed a slight, however significant, favorable effect compared to the bare one. Fourier transform infrared spectroscopy (FTIR) offered the direct evidence that humate-coated α-Fe₂O₃ could form surface Fe(III)-carboxylate complexes by ligand exchange. Additional experiments demonstrated that the photocorrosion of α-Fe₂O³ coated by DOM was much more acute than that of the bare one. These combined results suggested that the transformation of γ-HCH on humate-coated α-Fe₂O ₃ is more related to a surface complex and not to a semiconductor-assisted photoreaction. In the humate-coated α-Fe ₂O₃, absorption of a photon results in an excited ligand-to-metal charge-transfer state of the complexes, and a rich variety of free radical reactions ensue, which is concurrently accompanied by the dissolution of the iron oxide. Such reactions may generate reactive transients such as Superoxide and hydroxyl radicals, which may be expected to transform γ-HCH.