Characterization Of The Fe(Ⅲ)-humate Complexes And Its Photocatalytic Function On γ-HCH Photodegradation In Water

α-Fe2O3 (hematite), α-FeOOH (goethite) and (3-FeOOH (akaganeite) samples were obtained by direct precipitation from the ferric solutions under different conditions.Three marked morphologically different crystallites, grainy-like particles for α-Fe2O3, needle-like ones for a-FeOOH and rod-like ones for p-FeOOH were observed by Transmission electron micrograph (TEM). X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) of the products were found to be identical with the target oxidesThe complexes formed between humic substances (HSs) and the iron oxides were characterized by FTIR. When the humic substances interacted with the iron oxides. the intensity of the peak near 1700cm-1 became lower or disappear, and synchronously, a new strong and pointed band at 1384 cm-1 appeared, which indicated that a part of carboxylic acid were deprotonated by the ligand exchange with the surface species of both a-Fe2O3 and a-FeOOH (◇-FeOH2+;◇-FeOH) and ultimately transformed to the carboxylate. However, no complexation occurred in the case of [3-FeOOH, only surface adsorption. In general, the binding affinities of iron oxides with the HSs was in the order of α-Fe2O3 >α-FeOOH >β-FeOOH.This study was also to examine photodegradation of y-hexachlorocyclohexane (γ-HCH) by α-Fe2O3 and the influence of the HSs in this photochemical process. A 300 W high-pressure mercury vapor lamp was employed as the light source. The results showed that the UV light alone could play an important role in the degradation of y-HCH. The presence of α-Fe2O3 was found to promote the photodegradation of y-HCH. Furthermore. the photodegradation of y-HCH by α-Fe2O3 follows pseudo-first-order reaction kinetics. The effect of the HSs on the photodegradation of y-HCH in the presence and at the absence of α-Fe2O3 was also performed. The results revealed that the HSs adversely affected the photodegradatopm of y-HCH. This phenomenon could be correlated to the bindinginteraction between y-HCH and the HSs.α-Fe2O3 complexed by the HSs revealed a slight, however significant, favorable effect compared to the bare one. FTIR offered the direct evidence that α-Fe2O3 complexed by the HSs could form surface Fe(III)-carboxylate complexes by ligand-exchange. Additional experiments demonstrated that the photocorrosion of α-Fe2O3 complexed by the FA was much more acute than that of the bare one. These combined results suggested that the photodegradation of γ-HCH on α-Fe2O3 complexed by the HSs is more related to a surface complex and not to a semiconductor-assisted photoreaction. In the case of α-Fe2O3 complexed by the HSs, 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 y-HCH.In the aquatic system that both HSs and iron oxides coexist, the balance between the positive effect and the negative effect of HSs on the photodegradation of the pollutant can be principally due to the amount of HSs. When the amount of HSs greatly exceeded surface site saturation of the iron oxide, HSs will mask the valuable function of the surface complexes and even show an adverse effect as a radical scavenger, an absorber for available light or via interaction with the pollutant molecular. If, on the other hand. abundant reactive iron is available but little reactive organic matter. HSs will play a positive role by the surface complexes formed on the oxide surface.