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21 pages, 2923 KiB

Open AccessArticle

A Combination of EPR, Microscopy, Electrophoresis and Theory to Elucidate the Chemistry of W- and N-Doped TiO₂ Nanoparticle/Water Interfaces

by Sam Gorman, Kirstie Rickaby, Li Lu, Christopher J. Kiely, Donald E. Macphee and Andrea Folli

Catalysts 2021, 11(11), 1305; https://0-doi-org.brum.beds.ac.uk/10.3390/catal11111305 - 28 Oct 2021

Viewed by 1569

Abstract

The doping of

T i O_{2}

-based nanomaterials for semiconductor-sensitised photoreactions has been a practice extensively studied and applied for many years. The main goal remains the improvement of light harvesting capabilities under passive solar irradiation, that in the case of undoped [...] Read more.

The doping of

T i O_{2}

-based nanomaterials for semiconductor-sensitised photoreactions has been a practice extensively studied and applied for many years. The main goal remains the improvement of light harvesting capabilities under passive solar irradiation, that in the case of undoped

T i O_{2}

is limited and restricted to relatively low latitudes. The activity and selectivity of doped

T i O_{2}

photocatalysts are generally discussed on the basis of the modified band structure; energetics of intrinsic or extrinsic band gaps including trapping states; redox potentials of band edges, including band bending at solid/fluid interfaces; and charge carriers scavenging/transfer by/to adsorbed species. Electron (and hole) transfer to adsorbates is often invoked to justify the formation of highly reactive species (e.g.,

H O^{.}

from water); however, a complete description of the nanoparticle surface chemistry dictating adsorption/desorption events is often missing or overlooked. Here, we show that by employing a surface electrochemical triple-layer (TLM) approach for the nanoparticles/water interface, in combination with electron paramagnetic resonance spectroscopy (EPR), transmission electron microscopy and electrophoretic measurements, we can elucidate the surface chemistry of doped

T i O_{2}

nanoparticles and link it to the nature of the dopants. Exemplifying it for the cases of undoped, as well as W- and N-doped and codoped

T i O_{2}

nanoparticles, we show how surface charge density; surface, Stern and

ζ

potentials; surface acidity constants; and speciation of surface sites are influenced by the nature of the dopants and their loading. Full article

(This article belongs to the Special Issue Electron Paramagnetic Resonance in Photocatalysis)

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Review

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21 pages, 3057 KiB

Open AccessReview

Electron Paramagnetic Resonance Spin Trapping (EPR–ST) Technique in Photopolymerization Processes

by Fabienne Peyrot, Sonia Lajnef and Davy-Louis Versace

Catalysts 2022, 12(7), 772; https://0-doi-org.brum.beds.ac.uk/10.3390/catal12070772 - 12 Jul 2022

Cited by 9 | Viewed by 4564

Abstract

To face economic issues of the last ten years, free-radical photopolymerization (FRP) has known an impressive enlightenment. Multiple performing photoinitiating systems have been designed to perform photopolymerizations in the visible or near infrared (NIR) range. To fully understand the photochemical mechanisms involved upon [...] Read more.

To face economic issues of the last ten years, free-radical photopolymerization (FRP) has known an impressive enlightenment. Multiple performing photoinitiating systems have been designed to perform photopolymerizations in the visible or near infrared (NIR) range. To fully understand the photochemical mechanisms involved upon light activation and characterize the nature of radicals implied in FRP, electron paramagnetic resonance coupled to the spin trapping (EPR–ST) method represents one of the most valuable techniques. In this context, the principle of EPR–ST and its uses in free-radical photopolymerization are entirely described. Full article

(This article belongs to the Special Issue Electron Paramagnetic Resonance in Photocatalysis)

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37 pages, 10272 KiB

Open AccessFeature PaperReview

Application of EPR Spectroscopy in TiO₂ and Nb₂O₅ Photocatalysis

by Osama Al-Madanat, Barbara Nascimento Nunes, Yamen AlSalka, Amer Hakki, Mariano Curti, Antonio Otavio T. Patrocinio and Detlef W. Bahnemann

Catalysts 2021, 11(12), 1514; https://0-doi-org.brum.beds.ac.uk/10.3390/catal11121514 - 13 Dec 2021

Cited by 28 | Viewed by 6112

Abstract

The interaction of light with semiconducting materials becomes the center of a wide range of technologies, such as photocatalysis. This technology has recently attracted increasing attention due to its prospective uses in green energy and environmental remediation. The characterization of the electronic structure [...] Read more.

The interaction of light with semiconducting materials becomes the center of a wide range of technologies, such as photocatalysis. This technology has recently attracted increasing attention due to its prospective uses in green energy and environmental remediation. The characterization of the electronic structure of the semiconductors is essential to a deep understanding of the photocatalytic process since they influence and govern the photocatalytic activity by the formation of reactive radical species. Electron paramagnetic resonance (EPR) spectroscopy is a unique analytical tool that can be employed to monitor the photoinduced phenomena occurring in the solid and liquid phases and provides precise insights into the dynamic and reactivity of the photocatalyst under different experimental conditions. This review focus on the application of EPR in the observation of paramagnetic centers formed upon irradiation of titanium dioxide and niobium oxide photocatalysts. TiO₂ and Nb₂O₅ are very well-known semiconductors that have been widely used for photocatalytic applications. A large number of experimental results on both materials offer a reliable platform to illustrate the contribution of the EPR studies on heterogeneous photocatalysis, particularly in monitoring the photogenerated charge carriers, trap states, and surface charge transfer steps. A detailed overview of EPR-spin trapping techniques in mechanistic studies to follow the nature of the photogenerated species in suspension during the photocatalytic process is presented. The role of the electron donors or the electron acceptors and their effect on the photocatalytic process in the solid or the liquid phase are highlighted. Full article

(This article belongs to the Special Issue Electron Paramagnetic Resonance in Photocatalysis)

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