TiO₂/Fe₂O₃ and Fe₂O₃/TiO₂ heterojunction nanocomposites applied to As(III) decontamination

Arsenic contamination in water, particularly in its toxic form As(III), is a significant environmental issue in Brazil and globally. To address this, simple oxides of Fe₂O₃ and TiO₂, along with heterojunction structures TiO₂/Fe₂O₃ and Fe₂O₃/TiO₂, were synthesized using an adapted Pechini method for the decontamination of As(III) via heterogeneous photocatalysis. TiO₂ exhibited only the anatase phase, while Fe₂O₃ showed only the hematite phase (α-Fe₂O₃). The Fe₂O₃/TiO₂ structure displayed both the hematite and anatase phases, whereas the TiO₂/Fe₂O₃ heterojunction exhibited the anatase, rutile, hematite, and maghemite (γ-Fe₂O₃) phases. The materials displayed micro/mesoporous characteristics, with surface areas ranging from 20 to 45 m² g^-1, and band gap energies in the range of 2.1 to 3 eV. Hematite was the most effective adsorbent for arsenic. Under UV light irradiation, photolysis achieved 87% oxidation of As(III) in 20 min. The decontamination efficiencies achieved were 63%, 88%, 88%, and 99% for Fe₂O₃, TiO₂, Fe₂O₃/TiO₂, and TiO₂/Fe₂O₃, respectively. Catalyst reuse tests demonstrated excellent stability, with all catalysts maintaining over 80% decontamination efficiency after four cycles. These results highlight the promising potential of TiO₂/Fe₂O₃ heterojunctions for efficient and sustainable As(III) decontamination from contaminated water.