TY - GEN A1 - Grönke, Martin A1 - Arrozi, Ubed S. F. A1 - Bronkalla, Nadine A1 - Schmidt, Peer A1 - Valldor, Martin A1 - Oswald, Steffen A1 - Woodcock, Thomas G. A1 - Eckert, Victoria A1 - Hao, Qi A1 - Plüschke, Laura A1 - Lederer, Albena A1 - Nielsch, Kornelius A1 - Büchner, Bernd A1 - Kaskel, Stefan A1 - Hampel, Silke T1 - Layered α-TiCl₃: Microsheets on YSZ Substrates for Ethylene Polymerization with Enhanced Activity T2 - Chemistry of Materials N2 - The transition metal halide α-titanium(III) chloride (α-TiCl₃) is a layered two-dimensional compound and a well-established Ziegler–Natta catalyst for the polymerization of ethylene. A new synthesis technique is used to obtain thin sheets of α-TiCl₃ that show exceptional physical properties in contrast to their bulk counterparts, due to an enlarged surface-to-volume ratio. Chemical vapor transport (CVT) of α-titanium(III) chloride directly on substrates results in microsheets that exhibit an improved catalytic effect. For rational planning of synthesis conditions, thermodynamic simulations of occurring gas-phase equilibria were performed. Based on these calculation results, crystal growth was achieved by adding GaCl₃via pure short term CVT in a temperature gradient of 700–600 K on yttrium-stabilized zirconia (YSZ) substrates. Phase pure, as-grown, single crystal sheets with high crystallinity and a thickness of around 4 μm were obtained. These thin sheets of α-TiCl₃ on YSZ substrates were implemented as catalysts for the ethylene polymerization reaction. A significant improvement of catalytic activity of 16% was achieved, probably due to an increased surface-to-volume ratio. As a highlight, the as-grown microsheets were exfoliated subsequently to a thickness lower than 200 nm and an even higher catalytic activity of up to 24% was confirmed experimentally due to delamination effects. This is the first time that an improved catalytic effect of α-TiCl₃ is observed as a result of downscaling from bulk to microsheets by CVT. KW - Crystal growth KW - Chemical vapor transport KW - Thermodynamic modeling KW - 2D layered compounds KW - Halides KW - Nanocrystals (1) Y1 - 2019 UR - https://pubs.acs.org/doi/10.1021/acs.chemmater.9b01818 U6 - https://doi.org/10.1021/acs.chemmater.9b01818 VL - 31 IS - 14 SP - 5305 EP - 5313 ER - TY - GEN A1 - Garai, Bikash A1 - Bon, Volodymyr A1 - Efimova, Anastasia A1 - Gerlach, Martin A1 - Senkovska, Irena A1 - Kaskel, Stefan T1 - Reversible switching between positive and negative thermal expansion in a metal–organic framework DUT-49 T2 - Journal of Materials Chemistry A N2 - Three-dimensional architectures constructed via coordination of organic ligands to metal ions (broadly termed metal–organic frameworks, MOFs), are highly interesting for many demanding applications such as gas adsorption, molecular separation, heterogeneous catalysis, molecular sensing, etc. Being constructed from heterogeneous components, such framework solids show characteristic features from both the individual components and framework-specific features. One such interesting physicochemical property is thermal expansion, which arises from thermal vibration from the organic linker and metal ions. Herein, we show a very unique example of thermal responsiveness for the DUT-49 framework, a MOF well-known for its distinctive negative gas adsorption (NGA) properties. In the guest-free form, the framework shows another counter-intuitive phenomenon of negative thermal expansion (NTE), i.e. the lattice size increases with decrease of temperature. However, in the solvated state, it shows both NTE and positive thermal expansion (i.e. lattice size decreases with lowering of temperature, PTE) based on a specific temperature range. When the solvent exists in the liquid form inside the MOF pore, it retains the pristine NTE nature of the bare framework. But freezing of the solvent inside the pores induces the strain, which causes a structural transformation through in-plane bending of the linker and this squeezes the framework by ∼10% of the unit cell volume. This effect has been verified using 3 different solvents where the structural contraction occurs immediately at the freezing point of the individual solvent. Furthermore, studies on a series of DUT-49(M) frameworks with varying metals confirm the general applicability of this mechanism. KW - Metal organic framework (MOF) KW - Thermal analysis KW - Crystal structure Y1 - 2020 UR - https://pubs.rsc.org/en/content/articlehtml/2020/ta/d0ta06830f U6 - https://doi.org/10.1039/D0TA06830F SN - 2050-7496 VL - 39 IS - 8 SP - 20420 EP - 20428 ER - TY - GEN A1 - Ehrling, Sebastian A1 - Senkovska, Irena A1 - Efimova, Anastasia A1 - Bon, Volodymyr A1 - Abylgazina, Leila A1 - Petkov, Petko A1 - Evans, Jack D. A1 - Attallah, Ahmed Gamal A1 - Wharmby, Michael Thomas A1 - Roslova, Maria A1 - Huang, Zhehao A1 - Tanaka, Hideki A1 - Wagner, Andreas A1 - Schmidt, Peer A1 - Kaskel, Stefan T1 - Temperature Driven Transformation of the Flexible Metal-Organic Framework DUT-8(Ni) T2 - Chemistry - a European journal N2 - DUT-8(Ni) metal-organic framework belongs to the family of flexible pillared layer materials. The desolvated framework can be obtained in the open pore form (op) or in the closed pore form (cp), depending on the crystal size regime. In the present work, we report on the behaviour of desolvated DUT-8(Ni) at elevated temperatures. For both, op and cp variants, heating causes a structural transition, leading to an new, crystalline compound, containing two interpenetrated networks. The state of the framework before transition (op vs. cp) influences the transition temperature: the small particles of the op phase transform at significantly lower temperature in comparison to the macroparticles of the cp phase, transforming close to the decomposition temperature. The new compound, confined closed pore phase (ccp), was characterized by powder X-ray diffraction and spectroscopic techniques, such as IR, EXAFS, and positron annihilation lifetime spectroscopy (PALS). Thermal effects of structural cp to ccp transitions were studied using differential scanning calorimetry (DSC), showing an overall exothermic effect of the process, involving bond breaking and reformation. Theoretical calculations reveal the energetics, driving the observed temperature induced phase transition. KW - Metal organic framework (MOF) KW - Thermal analysis KW - Crystal structure KW - Phase transition Y1 - 2022 UR - https://chemistry-europe.onlinelibrary.wiley.com/doi/10.1002/chem.202201281 U6 - https://doi.org/10.1002/chem.202201281 SN - 1521-3765 VL - 28 IS - 55 SP - 1 EP - 10 ER -