Extrinsic Point Defects in TiO2-Acetylacetone Charge-Transfer Complex and Their Effects on Optical and Photochemical Properties

Jessica Gil-Londoño; Klaus Krambrock; Raphaela de Oliveira; Marco Cremona; Marcelo E H Maia da Costa; Bojan A Marinkovic

doi:10.1021/acs.inorgchem.2c04016

Extrinsic Point Defects in TiO₂-Acetylacetone Charge-Transfer Complex and Their Effects on Optical and Photochemical Properties

Inorg Chem. 2023 Feb 6;62(5):2273-2288. doi: 10.1021/acs.inorgchem.2c04016. Epub 2023 Jan 26.

Authors

Jessica Gil-Londoño¹, Klaus Krambrock², Raphaela de Oliveira², Marco Cremona³, Marcelo E H Maia da Costa³, Bojan A Marinkovic¹

Affiliations

¹ Department of Chemical and Materials Engineering, Pontifical Catholic University of Rio de Janeiro (PUC-Rio), Rio de Janeiro22453-900, Brazil.
² Department of Physics, Federal University of Minas Gerais, Belo Horizonte31270-901, Brazil.
³ Department of Physics, Pontifical Catholic University of Rio de Janeiro (PUC-Rio), Rio de Janeiro22453-900, Brazil.

PMID: 36700852
DOI: 10.1021/acs.inorgchem.2c04016

Abstract

TiO₂-based visible-light-sensitive nanomaterials are widely studied for photocatalytic applications under UV-Vis radiation. Among the mechanisms of visible-light sensitization, extrinsic oxygen vacancies have been introduced into TiO₂ and charge-transfer complexes (CTCs) have been formed between chelating ligands, such as acetylacetone, and nanocrystalline TiO₂ (TiO₂-ACAC). However, the influence of extrinsic oxygen vacancies on the photocatalytic performance of TiO₂-based CTCs is unknown. In this work, surface/bulk extrinsic oxygen vacancies were introduced into TiO₂-ACAC through calcination at 270 °C under static air, argon, and hydrogen atmospheres. TiO₂-ACAC CTCs were characterized by X-ray powder diffraction, thermogravimetric analysis, diffuse-reflectance spectroscopy, photoluminescence, electron paramagnetic resonance (EPR), and X-ray photoelectron spectroscopy techniques. The correlation between EPR-spin trapping and tetracycline (TC) photodegradation, using scavengers, highlighted the key role of the superoxide radical in TC degradation by TiO₂-ACAC CTCs under low-power visible-light radiation. The increased extrinsic oxygen vacancies concentration was not beneficial for the photocatalytic performance of TiO₂ CTCs, since bulk extrinsic oxygen vacancies additionally act as recombination centers. In fact, the TiO₂-ACAC CTC with the lowest extrinsic oxygen vacancies concentration exhibited the highest photocatalytic performance for TC degradation due to an adequate distribution of extrinsic bulk oxygen vacancies, which led to the trapped electrons undergoing repeated hopping, reducing the recombination rates and improving the efficiency in superoxide radicals production. Our findings indicated that TiO₂-ACAC CTCs are able to degrade pollutants via interactions with electronic holes and principally superoxide radicals and also, provided fundamental information about the influence of surface/bulk extrinsic oxygen vacancies on the photocatalytic performance, lattice parameters, and optical and photochemical properties of TiO₂-based CTCs.