P25-inspired α/γ-Fe2O3 isoelement heterostructures for visible-light photocatalysis: Optimization of crystalline ratios and mechanism investigation

Abstract

Heterojunction with same elements but different types of semiconductors is a special material which is convenient for fabrication and industrialization. In this work, a series of α/γ-Fe2O3 isoelement heterostructures with different crystal contents (γ-Fe2O3, 10 % α-Fe2O3/90 % γ-Fe2O3, 33 % α-Fe2O3/67 % γ-Fe2O3, 55 % α-Fe2O3/45 % γ-Fe2O3, 78 % α-Fe2O3/22 % γ-Fe2O3 and α-Fe2O3) were constructed by hydrothermal method combined with controlled partial annealing process. Physicochemical analyses including XRD, TEM, XPS, BET, UV-Vis, PL spectra and ESR analyses were applied to investigate the advantages of isoelement α/γ-Fe2O3 compared with the pure single-crystalline Fe2O3. Benefiting from the enlarged specific surface area and staggered band structure, the fabricated heterostructure with 78 wt% α-Fe2O3 content exhibited more efficient separation of charge carriers and thus superior photodegradation efficiency than pure Fe2O3 under visible-light irradiation. Different from TiO2-based P25 heterostructures, Fe2O3 system possesses narrower bandgap and cannot efficiently consumed the excited holes. As a result, the accumulated h+ would inhibit the further separation of excitons with photocatalysis proceeding and thus induce insufficient driving force for the increment of photocatalytic ability like P25. The results presented in this work would be conducive to the rational design of staggered heterostructures.