Browsing by Author "Wegstein, Deborah"

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    The Importance of Precise Reaction Condition Control for the Comparison of Photocatalyst Materials on the Example of Hydrogen Peroxide Formation over Polymeric Carbon Nitrides
    (Weinheim : Wiley-VCH, 2023-08-02) Wegstein, Deborah; Zaim, Abdelkarim; Burek, Bastien O.; Bloh, Jonathan Z.
    In our study, we aimed to show how different reaction parameters can affect production rates using photocatalytic hydrogen peroxide formation by different polymeric carbon nitrides (PCN). For this purpose, selected materials were first compared under the same reaction conditions and compared with TiO2 (P25). We also show that different light intensities can have a different influence on seemingly similar materials. Since hydrogen peroxide production in the presence of an electron donor proceeds mainly by reduction of oxygen, we also show an influence of the oxygen flow on the formation rates. Thus, with high oxygen fluxes and high intensities of irradiated light, we were able to achieve an H2O2 concentration of 125 mM after about 25 h. Finally, the two best PCN materials were selected to measure light intensity dependence at different wavelengths up to visible light. It was found that they behaved differently at the different wavelengths and thus it could be shown that an exact specification of the reaction parameters is indispensable for comparisons in the literature.
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    Photocatalytic Synthesis of Hydrogen Peroxide from Molecular Oxygen and Water
    ([Cham] : Springer International Publishing, 2023-05-09) Garcia‑Munoz, Patricia; Valenzuela, Laura; Wegstein, Deborah; Schanz, Tobias; Lopez, Girlie Eunice; Ruppert, Agnieszka M.; Remita, Hynd; Bloh, Jonathan Z.; Keller, Nicolas
    Hydrogen peroxide is a powerful and green oxidant that allows for the oxidation of a wide span of organic and inorganic substrates in liquid media under mild reaction conditions, and forms only molecular water and oxygen as end products. Hydrogen peroxide is therefore used in a wide range of applications, for which the well-documented and established anthraquinone autoxidation process is by far the dominating production method at the industrial scale. As this method is highly energy consuming and environmentally costly, the search for more sustainable synthesis methods is of high interest. To this end, the article reviews the basis and the recent development of the photocatalytic synthesis of hydrogen peroxide. Different oxygen reduction and water oxidation mechanisms are discussed, as well as several kinetic models, and the influence of the main key reaction parameters is itemized. A large range of photocatalytic materials is reviewed, with emphasis on titania-based photocatalysts and on high-prospect graphitic carbon nitride-based systems that take advantage of advanced bulk and surface synthetic approaches. Strategies for enhancing the performances of solar-driven photocatalysts are reported, and the search for new, alternative, photocatalytic materials is detailed. Finally, the promise of in situ photocatalytic synthesis of hydrogen peroxide for water treatment and organic synthesis is described, as well as its coupling with enzymes and the direct in situ synthesis of other technical peroxides.
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    Robust Light Driven Enzymatic Oxyfunctionalization via Immobilization of Unspecific Peroxygenase
    (Weinheim : Wiley-VCH, 2023-06-25) De Santis, Piera; Wegstein, Deborah; Burek, Bastien O.; Patzsch, Jacqueline; Alcalde, Miguel; Kroutil, Wolfgang; Bloh, Jonathan Z.; Kara, Selin
    Unspecific peroxygenases have attracted interest in synthetic chemistry, especially for the oxidative activation of C−H bonds, as they only require hydrogen peroxide (H2O2) instead of a cofactor. Due to their instability in even small amounts of H2O2, different strategies like enzyme immobilization or in situ H2O2 production have been developed to improve the stability of these enzymes. While most strategies have been studied separately, a combination of photocatalysis with immobilized enzymes was only recently reported. To show the advantages and limiting factors of immobilized enzyme in a photobiocatalytic reaction, a comparison is made between free and immobilized enzymes. Adjustment of critical parameters such as (i) enzyme and substrate concentration, (ii) illumination wavelength and (iii) light intensity results in significantly increased enzyme stabilities of the immobilized variant. Moreover, under optimized conditions a turnover number of 334,500 was reached.