UVA-Induced Processes in the Aqueous Titanium Dioxide Suspensions Containing Nitrite (An EPR Spin Trapping Study)

Brezová, Vlasta; Barbieriková, Zuzana; Dvoranová, Dana; Staško, Andrej

doi:10.1515/jaots-2016-0213

Cited by 6 publications

(3 citation statements)

References 23 publications

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“…Our previous EPR and UV/VIS experiments evidenced that photoinduced one-electron reduction of 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS) •+ radical cation to diamagnetic ABTS (standard electrode potential for ABTS •+ /ABTS is +0.68 V vs. NHE [56]) represents an efficient tool to measure the photoinduced activity of the photocatalysts in the dispersed systems, as ABTS •+ radical cation can be reduced by photogenerated electrons as well as O2 •- [26,51]. This process can be followed by EPR spectroscopy, monitoring the changes in the intensity of an overmodulated EPR signal of ABTS •+ (g = 2.0036; inset in Figure 7b).…”

Section: Resultsmentioning

confidence: 99%

EPR Investigations of G-C3N4/TiO2 Nanocomposites

et al. 2018

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Abstract:The g-C 3 N 4 /TiO 2 nanopowders prepared by the annealing of melamine and TiO 2 P25 at 550 • C were investigated under dark and upon UV or visible-light photoactivation using X-and Q-band electron paramagnetic resonance (EPR) spectroscopy. The EPR spectra of powders monitored at room temperature and 100 K showed the impact of the initial loading ratio of melamine/TiO 2 on the character of paramagnetic centers observed. For the photocatalysts synthesized using a lower titania content, the paramagnetic signals characteristic for the g-C 3 N 4 /TiO 2 nanocomposites were already found before exposure. The samples annealed using the higher TiO 2 loading revealed the photoinduced generation of paramagnetic nitrogen bulk centers (g-tensor components g 1 = 2.005, g 2 = 2.004, g 3 = 2.003 and hyperfine couplings from the nitrogen A 1 = 0.23 mT, A 2 = 0.44 mT, A 3 = 3.23 mT) typical for N-doped TiO 2 . The ability of photocatalysts to generate reactive oxygen species (ROS) upon in situ UV or visible-light photoexcitation was tested in water or dimethyl sulfoxide by EPR spin trapping using 5,5-dimethyl 1-pyrroline N-oxide. The results obtained reflect the differences in photocatalyst nanostructures caused by the differing initial ratio of melamine/TiO 2 ; the photocatalyst prepared by the high-temperature treatment of melamine/TiO 2 wt. ratio of 1:3 revealed an adequate photoactivity in both spectral regions.

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Section: Resultsmentioning

confidence: 99%

EPR Investigations of G-C3N4/TiO2 Nanocomposites

et al. 2018

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“…Moreover, the spin trapping technique was not only used to detect and monitor the formed reactive species such as the oxygen and nitrogen reactive radicals [94,99] during the photocatalytic degradation process, but also is employed within the mechanistic pathway to monitor and/or to be involved in controlling the experimental conditions during the photocatalysis organic synthesis [82,[100][101][102]. The involvement of TEMPO derivative radical within a mechanistic pathway of the synthesis reaction is assumed to act as a selective redox mediator involved in reactions of the generated reactive oxygen species.…”

Section: Spin Trapping In the Liquid Phasementioning

confidence: 99%

Application of EPR Spectroscopy in TiO2 and Nb2O5 Photocatalysis

et al. 2021

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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.

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“…Without light irradiation, no signal is observed in the EPR spectra, indicating the absence of reactive species production. However, when the reaction solution is irradiated with light and contains formic acid as a scavenger, sextet characteristic peaks are observed with hyperfine coupling constants of aN = 15.8 G and aH = 19.1 G, along with a nuclear magnetic factor g = 2.0058. , These peaks are indicative of the presence of the DMPO • -CO 2 – spin adduct, confirming the formation of CO 2 •– during light irradiation. However, in methanol, an EPR signal consisting of four characteristic peaks with standard intensity ratios of 1:2:2:1, ascribed to the • DMPO–OH adduct, is formed .…”

Section: Resultsmentioning

confidence: 74%

Advancing the Understanding of Photocatalytic Nitrate Reduction for Ammonia Synthesis: Copper Catalysts and Formic Acid Synergy

Varghese,

T. P.,

Neppolian

et al. 2024

ACS Appl. Energy Mater.

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In recent years, photo-and electrocatalytic nitrate reductions have emerged as promising methods for sustainable ammonia production. Among the catalysts studied, copper-based systems have shown superior efficiency and selectivity in nitrate conversion, especially in the presence of sacrificial formic acid. However, the catalytic activity of copper is often hindered by its unstable oxidation state, primarily due to surface oxidation, and the underlying reaction mechanism remains poorly understood. This study reports that the scavenger formic acid plays a versatile role in the CuO x :TiO 2 catalytic system: first, it stabilizes the Cu 2 O phase on the TiO 2 surface. Second, it acts as a hole scavenger, reducing electron−hole recombination. Third, as formic acid undergoes oxidation, it produces CO 2•− radicals with significant reduction potential. These radicals effectively facilitate the reduction of nitrate ions, resulting in ammonia production. Moreover, copper's unique ability to degrade formic acid contributes to the creation of bound atomic hydrogen on its surface. This, in turn, promotes selective nitrate hydrogenation and subsequent formation of ammonia within the catalytic system. The CuO x :TiO 2 produced 1.639 mmol/g/h ammonia with an 82% nitrate-to-ammonia conversion rate. These findings not only deepen our comprehension of photocatalytic nitrate reduction processes but also highlight the potential of Cu:TiO 2 /Cu 2 O catalysts for sustainable ammonia production and environmental remediation applications.

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UVA-Induced Processes in the Aqueous Titanium Dioxide Suspensions Containing Nitrite (An EPR Spin Trapping Study)

Cited by 6 publications

References 23 publications

EPR Investigations of G-C3N4/TiO2 Nanocomposites

EPR Investigations of G-C3N4/TiO2 Nanocomposites

Application of EPR Spectroscopy in TiO2 and Nb2O5 Photocatalysis

Advancing the Understanding of Photocatalytic Nitrate Reduction for Ammonia Synthesis: Copper Catalysts and Formic Acid Synergy

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