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- ItemRole of SrCO3 on Photocatalytic Performance of SrTiO3-SrCO3 Composites(Basel : MDPI, 2022) Boga, Bíborka; Steinfeldt, Norbert; Moustakas, Nikolaos G.; Peppel, Tim; Lund, Henrik; Rabeah, Jabor; Pap, Zsolt; Cristea, Vasile-Mircea; Strunk, JenniferPerovskites such as SrTiO3 are interesting for photocatalytic applications due to their structure-related and electronic properties. These properties are influenced by the presence of SrCO3 which is often formed simultaneously during the hydrothermal synthesis of SrTiO3. In this study, SrTiO3-SrCO3 composites with different contents of SrCO3 (5–24 wt%) were synthesized. Their morphological, structural, and optical properties were investigated using complementary methods such as scanning electron microscopy (SEM), X-ray diffraction (XRD), nitrogen sorption, and diffuse reflectance spectroscopy (DRS). Their photocatalytic activity was assessed during the degradation of diclofenac (DCFNa) in aqueous solution and CO2 photoreduction under Xe lamp irradiation. Improved photocatalytic efficiency in DCFNa degradation was observed for all the studied composites in comparison with SrTiO3, and the highest mineralization efficiency was obtained for the sample with 21 wt% SrCO3 content. The presence of SrCO3 led to an increased concentration of active species, such as •OH radicals. Otherwise, its presence inhibits CH4 and C2H6 production during CO2 photoreduction compared with pure SrTiO3.
- ItemSupported Vanadium Oxide as a Photocatalyst in the Liquid Phase: Dissolution Studies and Selective Laser Excitation(2021) Kortewille, Bianca; Pfingsten, Oliver; Bacher, Gerd; Strunk, JenniferSupported vanadium oxide species are tested for their capability to perform photocatalytic methyl orange degradation in the aqueous phase. Excitation is performed with a frequency-tripled (λ=270 nm) or frequency-doubled (λ=405 nm) Ti:sapphire laser in a newly designed 15 ml photoreactor. Photocatalytic activity in dye degradation is only observed at 270 nm excitation, indicating that larger vanadium oxide structures (V2O5 nanoparticles, decavanadates) are either not present in sufficient quantities, or not active in the reaction. Reference experiments exclude pure photodegradation of the dye. It is found that a major part of the supported vanadium oxide species becomes detached from the silica support, and a very small fraction detaches from alumina. Considerations of the aqueous phase chemistry of dissolved vanadate ions allow to identify the formed dissolved species to be predominantly H2VO4− ions. These doubly protonated monovanadates are the main active species in the photocatalytic reaction, together with small anchored species on alumina.
- ItemVerification of impurity-related photocatalytic activity of insulating oxide supports(Amsterdam : Elsevier, 2021) Kortewille, Bianca; Springer, Armin; Strunk, JenniferPhotocatalysts composed of vanadium oxide species supported on commercial MgO and ZrO2 are investigated in selective methanol oxidation. Both support oxides are insulators, so the vanadium oxide species are expected as sole active component in photocatalysis. However, the pure supports showed considerable activity: Bare MgO was more active than MgO-supported vanadia catalysts, and ZrO2 showed intermediate activity. By various characterization methods, the presence of TiO2 (anatase) in the MgO support, and the presence of Zn, possibly as ZnO, in ZrO2 is demonstrated. The present study highlights that photocatalysts containing commercial supports must be carefully checked for impurity-related photocatalytic performance. © 2021 The Authors
- ItemPhotocatalytic nitrogen reduction to ammonia: Insights into the role of defect engineering in photocatalysts(New York, NY [u.a.] : Springer, 2021) Shen, Huidong; Yang, Mengmeng; Hao, Leiduan; Wang, Jinrui; Strunk, Jennifer; Sun, ZhenyuEngineering of defects in semiconductors provides an effective protocol for improving photocatalytic N2 conversion efficiency. This review focuses on the state-of-the-art progress in defect engineering of photocatalysts for the N2 reduction toward ammonia. The basic principles and mechanisms of thermal catalyzed and photon-induced N2 reduction are first concisely recapped, including relevant properties of the N2 molecule, reaction pathways, and NH3 quantification methods. Subsequently, defect classification, synthesis strategies, and identification techniques are compendiously summarized. Advances of in situ characterization techniques for monitoring defect state during the N2 reduction process are also described. Especially, various surface defect strategies and their critical roles in improving the N2 photoreduction performance are highlighted, including surface vacancies (i.e., anionic vacancies and cationic vacancies), heteroatom doping (i.e., metal element doping and nonmetal element doping), and atomically defined surface sites. Finally, future opportunities and challenges as well as perspectives on further development of defect-engineered photocatalysts for the nitrogen reduction to ammonia are presented. It is expected that this review can provide a profound guidance for more specialized design of defect-engineered catalysts with high activity and stability for nitrogen photochemical fixation.