Effect of the Degree of Inversion on the Photocatalytic Activity of Spinel ZnFe2O4

Luis I. Granone^a^,^b, Ralf Dillert^a^,^b, Detlef W. Bahnemann^a^,^b^,^c

^aInstitute of Technical Chemistry, Gottfried Wilhelm Leibniz University Hannover, DE, Callinstraße, 3, Hannover, Germany

^bLaboratory of Nano- and Quantum-Engineering (LNQE), Wilhelm Leibniz University Hannover, DE, Schneiderberg, 39, Hannover, Germany

^cLaboratory “Photoactive Nanocomposite Materials”, Saint-Petersburg State University, Ulyanovskaya str. 1, 198504 Peterhof, Saint-Petersburg, Russia

Materials for Sustainable Development Conference (MATSUS)
Proceedings of nanoGe Fall Meeting 2018 (NFM18)

S2 Light Driven Water Splitting

Torremolinos, Spain, 2018 October 22nd - 26th

Organizers: Wolfram Jaegermann and Bernhard Kaiser

Oral, Luis I. Granone, presentation 091
DOI: https://doi.org/10.29363/nanoge.nfm.2018.091
Publication date: 6th July 2018

Recently, due to promising results in the fields of photocatalysis and photoelectrocatalysis, the attention has been focused on ferrites as new visible light-active materials [1,2]. Properties such as narrow band gap energies (≈ 2 eV), high stability, abundance, and low cost make ferrites promising for solar energy production and solar remediation. Zinc ferrite (ZnFe₂O₄) is one of the most widely studied compounds belonging to the spinel ferrite family. However, various and even contradictory results regarding the photocatalytic activity of ZnFe₂O₄ have been reported in the scientific literature [3]. ZnFe₂O₄ crystallize in a phase-centered cubic spinel structure with Fe³⁺ and Zn²⁺ ions occupying tetrahedral or octahedral sites[1]. When the Fe³⁺ and Zn²⁺ ions are arranged in octahedral and tetrahedral sites, respectively, the ferrite exhibits a so-called normal spinel structure (^T[Zn]^O[Fe₂]O₄). However, when all the Zn²⁺ ions at the tetrahedral sites are exchanged by Fe³⁺ ions from octahedral sites, the compound adopts a so-called inverse spinel structure (^T[Fe]^O[ZnFe]O₄). The degree of inversion, x, defined as the fraction of Zn²⁺ ions occupying octahedral sites, can consequently adopt values from 0 (normal structure) to 1 (inverse structure) according to ^T[Zn_1-xFe_x]^O[Zn_xFe_2-x]O₄ with 0 ≤ x ≤ 1. The degree of inversion closely depends on the synthetic route.

For the first time, the effect of the degree of inversion on the physicochemical properties affecting the photocatalytic behavior of ZnFe₂O₄ has been investigated. Interestingly, as the degree of inversion increases, the conductivity of the material increases exponentially and an influence on the photocatalytic activity is observed. Thus, the degree of inversion plays a fundamental role and is a parameter of utmost importance to be investigated in order to get a meaningful approach regarding the photocatalytic performance of spinel ferrites.

[1] R. Dillert, D. H. Taffa, M. Wark, T. Bredow and D. W. Bahnemann, APL Materials, 2015, 3, 104001.

[2] D. H. Taffa, R. Dillert, A. C. Ulpe, K. C. Bauerfeind, T. Bredow, D. W. Bahnemann and M. Wark, Journal of Photonics for Energy, 2016, 7, 012009.

[3] A. Arimi, L. Megatif, L. I. Granone, R. Dillert and D. W. Bahnemann, Journal of Photochemistry and Photobiology A: Chemistry, 2018, DOI: 10.1016/j.jphotochem.2018.03.014.

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