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2. Role of Magnetic Coupling in Photoluminescence Kinetics of Mn2+-doped ZnS Nanoplatelets

Author

Dai, Liwei, Torche, Abderrezak, Strelow, Christian, Kipp, Tobias, Vuong, Thanh Huyen, Rabeah, Jabor, Oldenburg, Kevin, Bester, Gabriel, Mews, Alf, Klinke, Christian, and Lesyuk, Rostyslav

Subjects
Condensed Matter - Materials Science
Abstract

Mn2+-doped semiconductor nanocrystals with tuned location and concentration of Mn2+ ions can yield diverse coupling regimes, which can highly influence their optical properties such as emission wavelength and photoluminescence (PL) lifetime. However, investigation on the relationship between the Mn2+ concentration and the optical properties is still challenging because of the complex interactions of Mn2+ ions and the host and between the Mn2+ ions. Here, atomically flat ZnS nanoplatelets (NPLs) with uniform thickness were chosen as matrixes for Mn2+ doping. Using time-resolved (TR) PL spectroscopy and density functional theory (DFT) calculations, a connection between coupling and PL kinetics of Mn2+ ions was established. Moreover, it was found that the Mn2+ ions residing on the surface of a nanostructure produce emissive states and interfere with the change of properties by Mn2+/Mn2+ coupling. In a configuration with suppressed surface contribution to the optical response we show the underlying physical reasons for double and triple exponential decay by DFT methods. We believe that the presented doping strategy and simulation methodology of the Mn2+-doped ZnS system is a universal platform to study dopant location- and concentration-dependent properties also in other semiconductors.

Published
2022
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5. Colloidal manganese doped ZnS nanoplatelets and their optical properties

Author

Dai, Liwei, Strelow, Christian, Kipp, Tobias, Mews, Alf, Benkenstein, Iris, Eifler, Dirk, Vuong, Thanh Huyen, Rabeah, Jabor, McGettrick, James, Lesyuk, Rostyslav, and Klinke, Christian

Subjects
Condensed Matter - Materials Science
Abstract

Manganese (Mn)-doped ZnS nanocrystals (NCs) have been extensively explored for optical applications with the advantages of low toxicity, large Stokes shifts, and enhanced thermal and environmental stability. Although numerous studies on Mn-doped ZnS dots, rods, and wires have been reported, the literature related to Mn-doped ZnS nanoplatelets (ZnS:Mn NPLs) is scarce. Here, we present the first example of direct doping of Mn2+ ions into ZnS NPLs via the nucleation-doping strategy. The resulting ZnS:Mn NPLs exhibit Mn luminescence, indicative for successful doping of the host ZnS NPLs with Mn2+ ions. The energy transfer from the ZnS NPLs to the Mn2+ ions was observed by employing spectroscopic methods. Furthermore, the impact of the Mn concentration on the optical properties of ZnS:Mn NPLs was systematically investigated. As a result of Mn-Mn interaction, tunable Mn emission and shortened photoluminescence (PL) lifetime decay were observed and rationalized by means of electron paramagnetic resonance (EPR) and X-ray photoelectron spectroscopy (XPS). Finally, we show that the initially low dopant PL quantum yield (QY) of ZnS:Mn NPLs can be dramatically enhanced by passivating the surface trap states of the samples. The presented synthetic strategy of ZnS:Mn NPLs opens a new way to synthesize further doped systems of two-dimensional (2D) NPLs., Comment: 19 pages, 6 figures

Published
2021
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13. A Protocol for Unveiling the Nature of Photocatalytic Hydrogen Evolution Reactions: True Water Splitting or Sacrificial Reagent Acceptorless Dehydrogenation?

Author

Peng, Yong, Rabeah, Jabor, Junge, Henrik, and Beller, Matthias

Subjects
*HYDROGEN evolution reactions, *SUSTAINABILITY, *COUPLING reactions (Chemistry), *REDUCTION potential, *DEHYDROGENATION
Abstract

Photocatalytic water splitting for hydrogen evolution is a highly topical subject in academic research and a promising approach for sustainable fuel production from solar energy. Due to the mismatched energy diagram of the photosensitizer (especially semiconductor‐based materials where band‐edge engineering is not trivial) and the redox potential of the half‐reactions of water splitting, photocatalytic H2 generation from water splitting is usually accelerated by the addition of hole scavengers, i.e. sacrificial reagents such as alcohols, amines, and thiols. However, the source of the protons of the evolved H2 is often neglected, and it is questionable whether such systems are really water splitting. Here, we discuss recent reports on sacrificial reagent‐assisted photocatalytic water splitting and present our recent findings, which showcase that the sacrificial reagent in the investigated photocatalytic water splitting systems inherently undergoes acceptorless dehydrogenation, with H2O serving as the proton shuttle, the amount of which doesn't change during the course of the reaction. [ABSTRACT FROM AUTHOR]

Published
2024
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14. A Covalent Triazine Framework for Photocatalytic Anti‐Markovnikov Hydrofunctionalizations.

Author

Maiti, Rakesh, Chakraborty, Jeet, Kumar Sahoo, Prakash, Nath, Ipsita, Dai, Xingchao, Rabeah, Jabor, De Geyter, Nathalie, Morent, Rino, Van Der Voort, Pascal, and Das, Shoubhik

Subjects
CHARGE transfer, MASS transfer, HYDROAMINATION, PROTON transfer reactions, WASTE recycling
Abstract

Porous materials‐based heterogeneous photocatalysts, performing selective organic transformations, are increasing the applicability of photocatalytic reactions due to their ability to merge traditional photocatalysis with structured pores densely decorated with catalytic moiety for efficient mass and charge transfer, as well as added recyclability. We herein disclose a porous crystalline covalent triazine framework (CTF)‐based heterogeneous photocatalyst that exhibits excellent photoredox properties for different hydrofunctionalization reactions such as hydrocarboxylations, hydroamination and hydroazidations. The high oxidizing property of this CTF enables the activation of styrenes, followed by regioselective C−N and C−O bond formation at ambient conditions. A change in the physicochemical and optoelectronic properties of the CTF, upon protonation during catalysis, lies at the basis of its photocatalytic properties. This allows us to obtain hydrocarboxylations, hydroamination, and hydroazidations from a myriad of electron‐donating and ‐withdrawing aromatic and aliphatic substrates. This catalytic approach is further extended to late‐stage functionalization of bio‐active molecules. Finally, detailed characterizations of the CTF and further mechanistic investigations provide mechanistic insights into these reactions. [ABSTRACT FROM AUTHOR]

Published
2024
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15. Unraveling the NH3‐SCR‐DeNOx Mechanism of Cu‐SSZ‐13 Variants by Spectroscopic and Transient Techniques.

Author

Jabłońska, Magdalena, Mollá Robles, Alejandro, Rotko, Marek, Vuong, Thanh Huyen, Lei, Huarong, Lavrič, Žan, Grilc, Miha, Lukman, Muhammad Fernadi, Valiullin, Rustem, Bertmer, Marko, Möllmer, Jens, Rabeah, Jabor, Pöppl, Andreas, Simon, Ulrich, and Gläser, Roger

Subjects
NUCLEAR magnetic resonance, ACTIVATION energy, COPPER ions, CATALYTIC reduction, COPPER
Abstract

Commercial SSZ‐13 zeolite with different n(Si)/n(Al) ratios and from different suppliers were subjected to a post‐synthetic treatment in order to create mesopores of up to 15 nm. Furthermore, the materials were modified with copper ions and thoroughly physico‐chemically characterized. The modified textural properties varied the nature of copper species, and thus, activity in the selective catalytic reduction of NOx with ammonia (NH3‐SCR‐DeNOx). Pulsed‐field gradient nuclear magnetic resonance (PFG‐NMR) studies with hexane as probe liquid revealed improved intracrystalline diffusion for some Cu‐containing SSZ‐13 materials. The NH3‐SCR‐DeNOx pathways are verified via in situ DR UV‐Vis, in situ FT‐IR and EPR, temperature‐programmed studies as well as SSITKA studies that provide a mechanistic understanding of the reaction. Kinetic modelling results demonstrate the highest NH3‐SCR‐DeNOx reaction rates and up to 20 % lower energy barriers with n(Si)/n(Al) ratio of 6.5 for all modified forms (i. e., (NH4)Cu‐SSZ‐13_6.5 and Cu‐SSZ‐13_6.5_NaOH/0.1) and cause only negligible parasitic ammonia oxidation. The modelling of the stop‐flow experiments further demonstrates that the SCR pathway via the HONO surface intermediate is present but barely contributes to the overall NO conversion compared to the dominant path between adsorbed NH3 and NO from the gas phase. [ABSTRACT FROM AUTHOR]

Published
2024
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22. An Atomically Dispersed Photocatalyst for para-Selective C-H bond Functionalization of Electron-Poor Arenes

Author

Pradhan, Suman, primary, Hu, Jun, additional, Ren, Peng, additional, Qin, Yuman, additional, Jain, Noopur, additional, Monti, Susanna, additional, Barcaro, Giovanni, additional, Jaworski, Aleksander, additional, Dai, Xingchao, additional, Rabeah, Jabor, additional, Silvestre-Albero, Joaquin, additional, Celorrio, Veronica, additional, Rokicińska, Anna, additional, Kuśtrowski, Piotr, additional, Van Aert, Sandra, additional, Bals, Sara, additional, and Das, Shoubhik, additional

Published
2024
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23. In situ formation of ZnO.sub.x species for efficient propane dehydrogenation

Author

Zhao, Dan, Tian, Xinxin, Doronkin, Dmitry E., Han, Shanlei, Kondratenko, Vita A., Grunwaldt, Jan-Dierk, Perechodjuk, Anna, Vuong, Thanh Huyen, Rabeah, Jabor, Eckelt, Reinhard, Rodemerck, Uwe, Linke, David, Jiang, Guiyuan, Jiao, Haijun, and Kondratenko, Evgenii V.

Subjects
Propane -- Chemical properties, Dehydrogenation -- Methods, Zinc oxide -- Chemical properties, Environmental issues, Science and technology, Zoology and wildlife conservation
Abstract

Propane dehydrogenation (PDH) to propene is an important alternative to oil-based cracking processes, to produce this industrially important platform chemical.sup.1,2. The commercial PDH technologies utilizing Cr-containing (refs. .sup.3,4) or Pt-containing (refs. .sup.5-8) catalysts suffer from the toxicity of Cr(vi) compounds or the need to use ecologically harmful chlorine for catalyst regeneration.sup.9. Here, we introduce a method for preparation of environmentally compatible supported catalysts based on commercial ZnO. This metal oxide and a support (zeolite or common metal oxide) are used as a physical mixture or in the form of two layers with ZnO as the upstream layer. Supported ZnO.sub.x species are in situ formed through a reaction of support OH groups with Zn atoms generated from ZnO upon reductive treatment above 550 °C. Using different complementary characterization methods, we identify the decisive role of defective OH groups for the formation of active ZnO.sub.x species. For benchmarking purposes, the developed ZnO-silicalite-1 and an analogue of commercial K-CrO.sub.x/Al.sub.2O.sub.3 were tested in the same setup under industrially relevant conditions at close propane conversion over about 400 h on propane stream. The developed catalyst reveals about three times higher propene productivity at similar propene selectivity. Propene is obtained through propane dehydrogenation using catalysts that are toxic, expensive or demanding to regenerate with ecologically harmful compounds, but the ZnO-based alternative reported here is cheap, clean and scalable., Author(s): Dan Zhao [sup.1] [sup.2] , Xinxin Tian [sup.2] [sup.3] , Dmitry E. Doronkin [sup.4] , Shanlei Han [sup.1] [sup.2] , Vita A. Kondratenko [sup.2] , Jan-Dierk Grunwaldt [sup.4] , [...]

Published
2021
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32. Exfoliated Polymeric Carbon Nitride Nanosheets for Photocatalytic Applications

Author

Huang, Junhao, primary, Klahn, Marcus, additional, Tian, Xinxin, additional, Dai, Xingchao, additional, Rabeah, Jabor, additional, Aladin, Victoria, additional, Corzilius, Björn, additional, Bartling, Stephan, additional, Lund, Henrik, additional, Steinfeldt, Norbert, additional, Peppel, Tim, additional, Logsdail, Andrew J., additional, Jiao, Haijun, additional, and Strunk, Jennifer, additional

Published
2024
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39. Hierarchical Porous Covalent Organic Frameworks: The Influence of Additional Macropores on Photocatalytic Hydrogen Evolution and Hydrogen Peroxide Production

Author

Khalil, Islam E., Das, Prasenjit, Küçükkeçeci, Hüseyin, Dippold, Veit, Rabeah, Jabor, Tahir, Warisha, Roeser, Jérôme, Schmidt, Johannes, and Thomas, Arne

Abstract

Covalent organic frameworks (COFs), an emerging class of crystalline porous materials, have garnered significant interest due to their low density, tunable chemical and physical properties, porous structure, and high surface area. COFs typically exhibit microporosity, i.e., pores below 2 nm influenced by their specific linkers and binding patterns. In addition, some COFs are reported to exhibit small mesopores, especially when extended linkers are used. In applications such as catalysis, where rapid mass transport is a crucial factor, hierarchical pore structures of catalysts are beneficial. This involves the presence of small micropores to generate a large surface area and additional macropores to facilitate the transport of reactants to catalytic sites and to promote product diffusion. This study describes the application of such a hierarchical porous COF (macro-TpBpy) for photocatalysis. The macro-TpBpy architecture seamlessly integrates intrinsic microporosity with additional macropores, thereby yielding a substantial increase in the surface area. The hierarchical porous material demonstrates a promising performance in photocatalytic hydrogen evolution reaction, exhibiting a rate of 4.88 mmol g–1h–1. Notably, this is a fourfold improvement compared to the COF analogue featuring micropores only. Furthermore, the introduction of macropores proved to be beneficial for the photocatalytic production of hydrogen peroxide (H2O2). Specifically, macro-TpBpy exhibited a production rate of 2716 μmol g–1h–1, in water without sacrificial hole scavengers, whereas pristine TpBpy had a rate of 2134 μmol g–1h–1. This work thus contributes to the further development of COFs in photocatalysis and shows that, in addition to suitable band structure and surface functionality, the pore size and substrate transport influenced by it must also be considered as important factors.

Published
2024
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49. Mechanismus der CO Oxidation an einem molekular‐definierten Kupfer‐Einzelatom‐Katalysator auf einer metallorganischen Gerüstverbindung

Author

Abdel‐Mageed, Ali M., primary, Rungtaweevoranit, Bunyarat, additional, Impeng, Sarawoot, additional, Bansmann, Joachim, additional, Rabeah, Jabor, additional, Chen, Shilong, additional, Häring, Thomas, additional, Namuangrak, Supawadee, additional, Faungnawakij, Kajornsak, additional, Brückner, Angelika, additional, and Behm, R. Jürgen, additional

Published
2023
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