Photocatalytic Degradation Of Dye And Reduction Of Heavy Metal Chromium By Iron-Bearing Clay Minerals

Cr(Ⅵ) species are known acutely toxic, carcinogenic, mobile and are of environmental concern. Dyes are one of the most notorious contaminants in aquatic environments because of their huge volume of production from industries, slow biodegradation and toxicity. The simultaneous reduction of Chromium (VI)(Cr (VI)) and oxidation of cationic dyes in dispersions of Montmorillonite K10(MK10) were examined under visible irradiation (λ>420nm). The iron species (i.e. iron oxides, structural iron and exchangeable interlayer iron) in layered clays are active for catalytically reducing Cr(VI) by using Malachite green (MG) and Rhodamine B (RhB) as the electron donors. Especially, the exchangeable interlayer iron ions in the clay exhibit much better ability to catalyze reduction of Cr(VI) and the decrease of malachite green (MG) than the Fe(Ⅲ) oxides on the clay surface and structural iron at the centers of octahedrons that are sandwiched by two layers of SiO4tetrahedrons. The efficiencies of the three tested clays towards the simultaneous conversion of dye and Cr(VI) followed this order:Fe3+-MMT> MK10> C-MK10. Molecular oxygen does not have a significant effect on clay-catalyzed Cr(VI) reduction, but is important for oxidative degradation of dye pollutants. MK10catalysts are stable and reusable, and are therefore considered as a promising naturally-abundant material for decontamination of dye and heavy metals.The conventional photo-Fenton reaction often suffers from the constraints of operation pH, low iron loading, ultraviolet availability in solar light and instability of iron-based catalysts. Here we report a novel heterogeneous Fenton catalyst-nontronite (NAU) which works with a dye-photosensitized structural Fe(Ⅲ)/Fe(Ⅱ) redox cycling mechanism. The synthesized catalyst was characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared spectra (FTIR), X-ray photoelectron spectroscopy (XPS) analysis, and thermal gravimetric analysis (TG). NAU exhibited excellent catalytic activity over a wide pH range (3.0-8.0) for highly efficient degradation of Rhodamine B by hydrogen peroxide (H2O2) under visible light irradiation(λ,>420nm). This iron-rich clay mineral (total Fe,24.4wt%) is chemically and mechanically stable. There are no measurable iron leaching, not any noticeable loss of activity and damage of the clay structure observed after6recycles. Therefore, NAU clay has outstanding merits for the practical treatment of organic dye pollutants at large scale.