Efficient photocatalytic removal of RhB using magnetic Fe 3 O 4 –SnO 2 nanocomposites containing Sn 2+ interstitial impurities

Fe3O4–SnO2 nanocomposites with SnO2 in the reduced form (without post-annealing) were prepared. X-ray diffraction, high resolution TEM microscopy, X-Ray photoelectron spectroscopy (XPS), photoluminescence spectroscopy and magnetization measurements were used for sample characterizations. Additionally, nitrogen adsorption–desorption isotherms and surface area measurements (BET) were made for porosity and surface area determination. Depending on the amount of SnCl2 used in preparation, tetragonal tin oxide hydroxide Sn6O4(OH)4 or SnO secondary phases were also formed in various samples. XPS analysis shows the presence of surface Sn2+ states and as well as lack, or non-detectable, interstitial tin inside SnO2 nanocrystallites. The presence of Sn2+ surface states determines important changes of both magnetic and photocatalytic properties of samples. Thus Sn2+ surface states determine, on the one hand, an increased efficiency of photocatalytic processes and, on the other hand, a significant decrease of the saturation magnetization of Fe3O4 cores. Moreover, by using ESR spin trapping technique, the generation of reactive oxygen species (·OH, O2·−) resulted by light irradiation of samples was evidenced.