Photocatalytic Properties of Porous Films Based on α-Fe2O3 Hollow Microspheres

• Published in: Inorganic materials Vol. 59; no. 3; pp. 272 - 283
• Main Authors: Demirov, A. P., Blinkov, I. V., Belov, D. S., Kozlova, N. S., Zabelina, E. V., Kasimova, V. M., Kostishin, V. G.
• Format: Journal Article
• Language: English
• Published: Moscow Pleiades Publishing 01.03.2023; Springer Nature B.V
• Subjects: Absorptivity; Chemistry; Chemistry and Materials Science; Ferric oxide; Heat treatment; Industrial Chemistry/Chemical Engineering; Inorganic Chemistry; Materials Science; Methylene blue; Microspheres; Nanoparticles; Optical properties; Photocatalysis; Polyethylene glycol; Porous materials; Thickness; Thin films; films; photoanode; hollow microspheres; photocatalysis; α-Fe; O
• ISSN: 0020-1685; 1608-3172
• DOI: 10.1134/S0020168523030032

— We have studied photoelectrochemical and photocatalytic properties of porous materials based on hollow α-Fe 2 O 3 microspheres, characterized by the presence of dangling magnetic Fe–O–Fe bonds due to an increased oxygen vacancy concentration on the wall/closed pore interface. Using such powder and firing slips at an isothermal holding temperature of 400°C, we obtained two series of thin-film samples on glass with a conductive layer from suspensions of two compositions: aqueous Fe(NO 3 ) 3 solution + hollow α-Fe 2 O 3 microspheres (series 1 ) and aqueous Fe(NO 3 ) 3 solution + polyethylene glycol + hollow α-Fe 2 O 3 microspheres (series 2 ). The films of series 2 were shown to have a structure with spatially separated particles differing in size: α-Fe 2 O 3 nanoparticles and hollow α-Fe 2 O 3 microspheres. The films of series 1 consisted predominantly of hollow microspheres connected by “necks” formed during heat treatment. The thickness of the films of series 2 was of order 2 μm and that of the films of series 1 was of order 4 μm. The structural distinctions between the films of the two series had a significant effect on the optical properties of the material. In the wavelength range 350–1500 nm, the absorption coefficient of the films of series 2 (3.50 × 10 5 m –1 ) was about twice that of the films of series 1 (1.75 × 10 5 m –1 ). Photoelectrochemical characterization in an aqueous 0.1 M KOH solution showed that the onset potential for the anodic reaction was 0.87 V vs. Ag/AgCl in the case of the films of series 2 and 0.97 V vs. Ag/AgCl in the case of series 1 . The films of both series showed an unusual increase in current density during prolonged illumination at a potential of 1 V vs. Ag/AgCl, due to Fe(IV) formation on the photoanode surface. Photocatalytic properties of the materials were assessed from the rate of methylene blue degradation. The reaction rate constant ( k ) was determined to be 0.015 and 0.018 min –1 for the films of series 1 and 2 , respectively, whereas the k of the photocatalyst-free reaction was 2.8 × 10 –4 min –1 .