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 (In_xFe_yO₃, 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, In₂O₃ and Fe₂O₃. 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 In_xFe_yO₃ 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 In₂O₃. The obtained semiconductors were tested as photocatalysts for the degradation of model organic pollutants (phenol and methylene blue) in water. Among the In_xFe_yO₃ solid solutions, In_1.7Fe_0.3O₃ displayed the highest photocatalytic activity in the degradation of the selected probe molecules under UV and visible radiation. Remarkably, In_1.7Fe_0.3O₃ showed a significantly enhanced activity under visible light compared to monometallic indium oxide and iron oxide, and to the benchmark TiO₂ P25. This demonstrates that our strategy consisting in engineering the band gap by tuning the composition of In_xFe_yO₃ solid solutions was successful in improving the photocatalytic performance under visible light. Additionally, In_1.7Fe_0.3O₃ fully retained its photocatalytic activity upon reuse in four consecutive cycles.