A composite photocatalyst (La/TiO2/Fe3O4) with a lanthanum doped TiO2 (La/TiO2) shell and a magnetite core was prepared by coating photoactive La/TiO2 onto a magnetic Fe3O4 core. The morphological, structural, and optical properties of as-prepared samples were charac-terized by transmission electron microscopy (TEM), X-ray diffraction (XRD) and UV-vis absorption spectroscopy. The effect of lanthanum content on the photocatalytic properties was studied, and the result revealed that 0.15 mol% La/TiO2/Fe3O4 exhibited the highest photoactiv-ity. The photocatalytic properties of the prepared photocatalyst under UV and visible light were investigated in aqueous solution using methyl orange (MO) as a target pollutant. The results showed that the prepared photocatalyst was activated by visible light and used as an ef-fective catalyst in photooxidation reactions. In addition, the possibility of cyclic usage of the prepared photocatalyst was also confirmed. Moreover, La/TiO2 was tightly bound to Fe3O4 and could be easily recovered from the medium by a simple magnetic process.
Mobilization of arsenic under anaerobic conditions is of great concern in arsenic contaminated soils and sediments. Bacterial reduction of As(V) and Fe(III) influences the cycling and partitioning of arsenic between solid and aqueous phase. We investigated the impact of bacterially mediated reductions of Fe(III)/Al hydroxides-bound arsenic(V) and iron(III) oxides on arsenic release. Our results suggested that As(V) reduction occurred prior to Fe(III) reduction, and Fe(III) reduction did not enhance the release of arsenic. Instead, Fe(III) hydroxides retained their dissolved concentrations during the experimental process, even though the new iron mineral-magnetite formed. In contrast, the release of reduced As(III) was promoted greatly when aluminum hydroxides was incorporated. Thus, the substitution of aluminum hydroxides may be responsible for the release of arsenic in the contaminated soils and sediments, since aluminum substitution of Fe(III) hydroxides universally occurs under natural conditions.
