Winfried Böhlmann

New element organic frameworks viaSuzuki coupling with high adsorption capacity for hydrophobic molecules

We present new highly microporous element organic frameworks synthesized by the Pd catalyzed Suzuki coupling reaction. They show specific surface areas of up to 1380 m2 g−1 with a strong hydrophobic character. Thus, they are interesting for the adsorption of non-polar substances. By variation of the organic linkers, the modular concept of the materials in analogy to the metal–organic frameworks is demonstrated. The polymeric materials have thermal stability up to 573 K and show no decomposition in aqueous environment, allowing excellent handling and processing. They are accessible by a basic synthetic approach, and by their chemical and thermal stabilities they may provide adequate properties for applications in many fields, especially in adsorptive separation processes and storage of non-polar gases.

Platinum induced crosslinking of polycarbosilanes for the formation of highly porous CeO2/silicon oxycarbide catalysts

A new synthesis scheme for the formation of porous CeO2/Pt-polycarbosilane composites using inverse microemulsions is presented. Aqueous hexachloroplatinic acid was used as a hydrosilylation catalyst causing crosslinking of allyl groups in a liquid polycarbosilane (PCS). The resulting polymers are temperature stable and highly porous. The Pt catalyst content and post-treatment of the polymer can be used to adjust the porosity. For the first time hydrophobic polymers with specific surface areas up to 896 m2/g were obtained by catalytic crosslinking of polycarbosilanes. Ceria nanoparticles 2–3 nm in diameter are well dispersed in the PCS matrix as proven using high resolution electron microscopy. Porosity of the hydrophobic materials could be increased up to 992 m2/g by adding divinylbenzene in the oil phase. Pyrolyses at 1200–1500 °C and post-oxidative treatment at various temperatures produce porous ceramic structures with surface areas up to 423 m2/g. X-Ray diffration investigations show that the crystallinity of the SiC matrix can be controlled by the pyrolysis temperature. Post-oxidative treatments cause silicon oxycarbide formation. Structure and morphology of the polymeric and ceramic composites were investigated using 29Si MAS NMR, FESEM, FT-IR and EDX techniques. The temperature programmed oxidation (TPO) of methane shows a high catalytic activity of CeO2/Pt-SiC(O) composites lowering the onset in the TPO to 400–500 °C.

Can Doping Graphite Trigger Room Temperature Superconductivity? Evidence for Granular High‐Temperature Superconductivity in Water‐Treated Graphite Powder

Granular superconductivity in powders of small graphite grains (several tens of micrometers) is demonstrated after treatment with pure water. The temperature, magnetic field and time dependence of the magnetic moment of the treated graphite powder provides evidence for the existence of superconducting vortices with some similarities to high-temperature granular superconducting oxides but even at temperatures above 300 K. Room temperature superconductivity in doped graphite or at its interfaces appears to be possible.

A new route to porous monolithic organic frameworks via cyclotrimerization

Cyclotrimerization of bifunctional acetyl compounds is used to obtain highly porous organic frameworks. Syntheses in solution induced by silicon tetrachloride result in highly disperse powders while syntheses in molten 4-toluene sulfonic acid result in polymeric monoliths with a hierarchical pore structure containing micro- and macropores allowing for direct impregnation of textiles with a porous polymer. The materials show specific BET surface areas up to 895 m2 g−1 and large pore volume (1.99 cm3 g−1) combined with a highly hydrophobic character. The amorphous materials are thermally stable below 300 °C in air and show no decomposition effects in aqueous environment. These outstanding properties in combination with the opportunity to generate shapes of any kind desired for an application render the materials as highly promising for application in air filtration systems and individual protection, as well as gas storage and separation.

Broadband dielectric spectroscopy of water confined in MCM-41 molecular sieve materials : low-temperature freezing phenomena

Dielectric properties of water adsorbed in pure siliceous and aluminium containing mesoporous MCM-41 materials have been investigated in the frequency range from 20 Hz to 1 MHz. The dielectric spectra revealed three dispersion regions, liquid-like free water in the centre of the mesopores, an intermediate water layer with reduced mobility, and an interfacial water layer at the inner surface of the mesopores. The analysis of the relaxation time distribution by means of a double-well potential indicates a strong dependence of the barrier height of reorienting water molecules dipoles in the interfacial layer on the Si/Al ratio in the framework.

On the diffusion of water in silicalite-1: MD simulations using ab initio fitted potential and PFG NMR measurements

Abstract Molecular dynamics simulations of water diffusion in silicalite-1 are reported. The simulations are carried out using an ab initio fitted silicalite-1–water potential based on quantum chemical calculations. In addition, preliminary results of pulsed field gradient (PFG) NMR diffusion measurements of water and small alkane molecules in silicalite-1 samples are presented. Pre-adsorption of water in silicalite-1 samples was found to change the intra-crystalline diffusivities of small alkane molecules in silicalite-1. This is interpreted as an indirect evidence that under our experimental conditions water molecules occupy a significant part of the silicalite-1 channel system. The preliminary results of the PFG NMR diffusion measurements of water in silicalite-1 samples are discussed in terms of the contributions of extra- and intra-crystalline water to the measured signals. An-order-of magnitude agreement between the measured and the simulated intra-crystalline diffusivities of water in silicalite-1 is obtained.

Dielectric and NMR Studies of Nanoporous Matrices Loaded with Sodium Nitrite

NMR and dielectric studies have been performed on NaNO2 loaded in mesoporous matrices of MCM-41 and SBA-15 with pore sizes of 20, 37, and 52 Å. The spin-lattice relaxation rate and 23Na NMR line shape, as well as the complex impedance, were measured within a broad temperature interval including the ferroelectric phase transition in bulk NaNO2. Two different phases of sodium nitrite, the crystalline and melt phases, are shown to coexist under conditions of a restricted geometry. The crystalline phase undergoes a ferroelectric phase transition. The melt fraction increases with temperature. The existence of two phases accounts for all experimental data on NaNO2 under conditions of a restricted geometry.

NMR studies of structure and ferroelectricity for Rochelle salt nanoparticles embedded in mesoporous sieves

NMR studies were carried out for Rochelle salt embedded in molecular sieves. 23 Na magic angle spinning (MAS) and multiple quantum (MQ) MAS NMR spectra revealed a complex structure of the confined crystalline material. The major part of particles within nanopores had a structure similar to that of bulk Rochelle salt. The 23 Na spin‐lattice relaxation times at various temperatures associated with this modification were also similar to those for bulk Rochelle salt and showed broad minima that corresponded to the ferroelectric and re-entrant phase transitions under nanoconfinement at temperatures just below the relevant transitions in bulk. This result suggests that the bulk-like modification within pores is ferroelectric in between. Fast spin relaxation in the rest of the confined material reflected high molecular mobility.

Intrinsically Microporous Polyesters From Betulin - Toward Renewable Materials for Gas Separation Made From Birch Bark

Betulin, an abundant triterpene, can be extracted from birch bark and can be used as a renewable monomer in the synthesis of microporous polyesters. Cross-linked networks and hyperbranched polymers are accessible by an A(2) + B(3) reaction, with betulin being the A(2) monomer and B(3) being a trifunctional acid chloride. Reaction of betulin with a diacid dichloride results in linear, soluble polyesters. The present communication proves that the polyreaction follows the classic schemes of polycondensation reactions. The resulting polymers are analyzed with regard to their micro-porosity by gas sorption, NMR spectroscopy, and X-ray scattering methods. The polymers feature intrinsic microporosity, having ultrasmall pores, which makes them candidates for gas separation membranes, e.g., for the separation of CO(2) from N(2) .

Titanium terephthalate (TT-1) hybrid materials with high specific surface area

A porous inorganic–organic titanium terephthalate (TT-1) based hybrid material is prepared using a solvothermal synthesis without templates. The nitrogen physisorption measurements show a combination of type IV and type I isotherms with a broad pore size distribution and a high specific BET surface area of Sg = 534 m2 g−1. The material has predominately mesopores (BJH pore volume = 0.54 cm3 g−1), with a small amount of micropores (specific micropore volume Vg = 0.11 cm3 g−1). The IR and solid state 13C MAS NMR spectra indicate coordination of the terephthalate ligand to Ti4+ ions and the ligand is a building block of the TT-1 hybrid material. The energy difference of 189 and 160 cm−1 between νasym(COO−) and νsym(COO−) indicates monodentate and bridging coordination of the terephthalate group, respectively. According to X-ray powder diffraction patterns TT-1 is amorphous. Upon heat treatment at 400 °C crystallisation of anatase and a significant loss of the specific surface area is detected.