Indium-Iron Oxide Nanosized Solid Solutions as Photocatalysts for the Degradation of Pollutants under Visible Radiation.

A series of solid solutions of indium and iron oxides with different In/Fe ratios (InFeO, with x + y = 2) were synthesized in the form of nanoparticles (diameter of ca. 30-40 nm) with the purpose of generating enhanced photocatalysts with an intermediate band gap compared to those of the monometallic oxides, InO and FeO. The materials were prepared by co-precipitation from an aqueous solution of iron and indium nitrates and extensively characterized with a combination of techniques. XRD analysis proved the formation of the desired InFeO solid solutions for Fe content in the range 5-25 mol%. UV-Vis absorption analysis showed that the substitution of In with Fe in the crystalline structure led to the anticipated gradual decrease of the band gap values compared to InO. The obtained semiconductors were tested as photocatalysts for the degradation of model organic pollutants (phenol and methylene blue) in water. Among the InFeO solid solutions, InFeO displayed the highest photocatalytic activity in the degradation of the selected probe molecules under UV and visible radiation. Remarkably, InFeO showed a significantly enhanced activity under visible light compared to monometallic indium oxide and iron oxide, and to the benchmark TiO P25. This demonstrates that our strategy consisting in engineering the band gap by tuning the composition of InFeO solid solutions was successful in improving the photocatalytic performance under visible light. Additionally, InFeO fully retained its photocatalytic activity upon reuse in four consecutive cycles.