Scavenger-Supported Photocatalytic Evidence of an Extended Type I Electronic Structure of the TiO2@Fe2O3 Interface

Anita Trenczek-Zajac; Milena Synowiec; Katarzyna Zakrzewska; Karolina Zazakowny; Kazimierz Kowalski; Andrzej Dziedzic; Marta Radecka

doi:10.1021/acsami.2c06404

Scavenger-Supported Photocatalytic Evidence of an Extended Type I Electronic Structure of the TiO₂@Fe₂O₃ Interface

ACS Appl Mater Interfaces. 2022 Aug 24;14(33):38255-38269. doi: 10.1021/acsami.2c06404. Epub 2022 Aug 15.

Authors

Anita Trenczek-Zajac¹, Milena Synowiec¹, Katarzyna Zakrzewska², Karolina Zazakowny¹, Kazimierz Kowalski³, Andrzej Dziedzic⁴, Marta Radecka¹

Affiliations

¹ Faculty of Materials Science and Ceramics, AGH University of Science and Technology, Krakow 30-059, Poland.
² Faculty of Computer Science, Electronics and Telecommunications, AGH University of Science and Technology, Krakow 30-059, Poland.
³ Faculty of Metals Engineering and Industrial Computer Science, AGH University of Science and Technology, Krakow 30-059, Poland.
⁴ Institute of Physics, College of Natural Sciences, University of Rzeszow, Rzeszow 35-310, Poland.

Abstract

Heterostructures of TiO₂@Fe₂O₃ with a specific electronic structure and morphology enable us to control the interfacial charge transport necessary for their efficient photocatalytic performance. In spite of the extensive research, there still remains a profound ambiguity as far as the band alignment at the interface of TiO₂@Fe₂O₃ is concerned. In this work, the extended type I heterojunction between anatase TiO₂ nanocrystals and α-Fe₂O₃ hematite nanograins is proposed. Experimental evidence supporting this conclusion is based on direct measurements such as optical spectroscopy, X-ray photoemission spectroscopy, scanning electron microscopy, high-resolution transmission electron microscopy (HRTEM), and the results of indirect studies of photocatalytic decomposition of rhodamine B (RhB) with selected scavengers of various active species of OH^•, h^•, e^-, and ^•O₂^-. The presence of small 6-8 nm Fe₂O₃ crystallites at the surface of TiO₂ has been confirmed in HRTEM images. Irregular 15-50 nm needle-like hematite grains could be observed in scanning electron micrographs. Substitutional incorporation of Fe³⁺ ions into the TiO₂ crystal lattice is predicted by a 0.16% decrease in lattice parameter a and a 0.08% change of c, as well as by a shift of the Raman E_g(1) peak from 143 cm^-1 in pure TiO₂ to 149 cm^-1 in Fe₂O₃-modified TiO₂. Analysis of O 1s XPS spectra corroborates this conclusion, indicating the formation of oxygen vacancies at the surface of titanium(IV) oxide. The presence of the Fe³⁺ impurity level in the forbidden band gap of TiO₂ is revealed by the 2.80 eV optical transition. The size effect is responsible for the absorption feature appearing at 2.48 eV. Increased photocatalytic activity within the visible range suggests that the electron transfer involves high energy levels of Fe₂O₃. Well-programed experiments with scavengers allow us to eliminate the less probable mechanisms of RhB photodecomposition and propose a band diagram of the TiO₂@Fe₂O₃ heterojunction.

Keywords: Fe2O3; TiO2; band diagram; electron transfer; heterostructures; interface; photocatalysis.