Institut für Nichtklassische Chemie

Infrared dielectric function spectra and phonon modes of high-quality, single crystalline, and highly resistive wurtzite ZnO films were obtained from infrared (300–1200 cm−1) spectroscopic ellipsometry and Raman scattering studies. The ZnO films were deposited by pulsed-laser deposition on c-plane sapphire substrates and investigated by high-resolution x-ray diffraction, high-resolution transmission electron microscopy, and Rutherford backscattering experiments. The crystal structure, phonon modes, and dielectric functions are compared to those obtained from a single-crystal ZnO bulk sample. The film ZnO phonon mode frequencies are highly consistent with those of the bulk material. A small redshift of the longitudinal optical phonon mode frequencies of the ZnO films with respect to the bulk material is observed. This is tentatively assigned to the existence of vacancy point defects within the films. Accurate long-wavelength dielectric constant limits of ZnO are obtained from the infrared ellipsometry analysis and compared with previously measured near-band-gap index-of-refraction data using the Lyddane–Sachs–Teller relation. The ZnO model dielectric function spectra will become useful for future infrared ellipsometry analysis of free-carrier parameters in complex ZnO-based heterostructures.

Sulfur dioxide (SO2) is an acidic and toxic gas and its emission from utilizing energy from fossil fuels or in industrial processes harms human health and environment. Therefore, it is of great interest to find new materials for SO2 sorption to improve classic flue gas desulfurization. In this work, we present SO2 sorption studies for the three different metal–organic frameworks MOF-177, NH2-MIL-125(Ti), and MIL-160. MOF-177 revealed a new record high SO2 uptake (25.7 mmol·g–1 at 293 K and 1 bar). Both NH2-MIL-125(Ti) and MIL-160 show particular high SO2 uptakes at low pressures (p < 0.01 bar) and thus are interesting candidates for the removal of remaining SO2 traces below 500 ppm from flue gas mixtures. The aluminum furandicarboxylate MOF MIL-160 is the most promising material, especially under application-orientated conditions, and features excellent ideal adsorbed solution theory selectivities (124–128 at 293 K, 1 bar; 79–95 at 353 K, 1 bar) and breakthrough performance with high onset time, combined with high stability under both humid and dry SO2 exposure. The outstanding sorption capability of MIL-160 could be explained by DFT simulation calculations and matching heat of adsorption for the binding sites Ofuran···SSO2 and OHAl-chain···OSO2 (both ∼40 kJ·mol–1) and Ofuran/carboxylate···SSO2 (∼55–60 kJ·mol–1).

Adamantane substituted with two to four 4-cyanophenyl groups was used for preparation of a new series of robust Porous Covalent Triazine-based Framework (PCTF) materials. Novel adamantane PCTFs were synthesized in good yields (>80%) by the trimerization reaction of 1,3-bis-, 1,3,5-tris- and 1,3,5,7-tetrakis(4-cyanophenyl)adamantane, respectively, in the presence of ZnCl2 (Lewis acid condition) and CF3SO3H (strong Brønsted acid condition). From N2 adsorption isotherms, the Lewis acid condition gives higher surface areas than the strong Brønsted acid condition. The amorphous nano- to microporous frameworks (>50% micropore fraction) exhibit excellent thermal stabilities (>450 °C) with BET surface areas up to 1180 m2 g−1. A very similar ultramicropore size distribution between 4 and 10 Å was derived from CO2 adsorption isotherms with a “CO2 on carbon based slit-pore model”. At 1 bar the gases H2 (at 77 K), CO2 (at 273 and 293 K) and CH4 (at 273 K) are adsorbed up to 1.24 wt%, 58 cm3 g−1 and 20 cm3 g−1, respectively. Gas uptake increases with BET surface area and micropore volume which in turn increase with the number of cyano groups in the monomer. From single component adsorption isotherms, IAST-derived ideal CO2:N2, CO2:CH4 and CH4:N2 selectivity values of up to 41 : 1, 7 : 1 and 6 : 1, respectively, are calculated for p → 0 at 273 K. The adamantane PCTFs have isosteric heats of adsorption for CO2 of 25–28 kJ mol−1 at zero loading and most of them also >25 kJ mol−1 over the entire adsorption range which is well above the heat of liquefaction of bulk CO2 or the isosteric enthalpy of adsorption for CO2 on activated carbons.

Abstract Herein, we report a pre‐synthetic pore environment design strategy to achieve stable methyl‐functionalized metal–organic frameworks (MOFs) for preferential SO 2 binding and thus enhanced low (partial) pressure SO 2 adsorption and SO 2 /CO 2 separation. The enhanced sorption performance is for the first time attributed to an optimal pore size by increasing methyl group densities at the benzenedicarboxylate linker in [Ni 2 (BDC‐X) 2 DABCO] (BDC‐X=mono‐, di‐, and tetramethyl‐1,4‐benzenedicarboxylate/terephthalate; DABCO=1,4‐diazabicyclo[2,2,2]octane). Monte Carlo simulations and first‐principles density functional theory (DFT) calculations demonstrate the key role of methyl groups within the pore surface on the preferential SO 2 affinity over the parent MOF. The SO 2 separation potential by methyl‐functionalized MOFs has been validated by gas sorption isotherms, ideal adsorbed solution theory calculations, simulated and experimental breakthrough curves, and DFT calculations.

Crystal structures of two metal-organic frameworks (MFU-1 and MFU-2) are presented, both of which contain redox-active Co(II) centres coordinated by linear 1,4-bis[(3,5-dimethyl)pyrazol-4-yl] ligands. In contrast to many MOFs reported previously, these compounds show excellent stability against hydrolytic decomposition. Catalytic turnover is achieved in oxidation reactions by employing tert-butyl hydroperoxide and the solid catalysts are easily recovered from the reaction mixture. Whereas heterogeneous catalysis is unambiguously demonstrated for MFU-1, MFU-2 shows catalytic activity due to slow metal leaching, emphasising the need for a deeper understanding of structure-reactivity relationships in the future design of redox-active metal-organic frameworks. Mechanistic details for oxidation reactions employing tert-butyl hydroperoxide are studied by UV/Vis and IR spectroscopy and XRPD measurements. The catalytic process accompanying changes of redox states and structural changes were investigated by means of cobalt K-edge X-ray absorption spectroscopy. To probe the putative binding modes of molecular oxygen, the isosteric heats of adsorption of O(2) were determined and compared with models from DFT calculations. The stabilities of the frameworks in an oxygen atmosphere as a reactive gas were examined by temperature-programmed oxidation (TPO). Solution impregnation of MFU-1 with a co-catalyst (N-hydroxyphthalimide) led to NHPI@MFU-1, which oxidised a range of organic substrates under ambient conditions by employing molecular oxygen from air. The catalytic reaction involved a biomimetic reaction cascade based on free radicals. The concept of an entatic state of the cobalt centres is proposed and its relevance for sustained catalytic activity is briefly discussed.

Pure gas adsorption isotherms of CH4 and N2 and their binary mixtures were measured at 273 K, 298 K and 323 K and up to 2 MPa on two different microporous metal–organic frameworks (MOFs), i.e. the commercially available Basolite® A100 and the recently reported copper-based triazolyl benzoate MOF 3∞[Cu(Me-4py-trz-ia)] (1). The Tòth isotherm model and the vacancy solution model were used to describe the experimentally determined isotherms and proved to be well suited for this purpose. While 1 shows a more homogeneous surface with a nearly constant isosteric heat of adsorption of 18–18.5 kJ mol−1 for CH4 and 12–15 kJ mol−1 for N2, the isosteric heat of adsorption at zero coverage for Basolite® A100 is 19 kJ mol−1 for CH4 and 16.2 kJ mol−1 for N2, decreasing significantly with increasing loading. Binary adsorption isotherms were measured gravimetrically to determine the total adsorbed mass of CH4 and N2. The van Ness method was successfully applied to calculate partial loadings from gravimetrically measured binary adsorption isotherms. Further studies by volumetric–chromatographic experiments support the good correlation between experimental data and predictions by the vacancy solution model (VSM-Wilson) and the ideal adsorbed solution theory (IAST) from pure gas isotherms. The experimental selectivities were determined to be αCH4/N2 = 4.0–5.0 for 1, slightly higher than for Basolite® A100 with αCH4/N2 = 3.4–4.5. These values are in good agreement with predictions for ideal selectivities based on Henry's law constants. From the experimental selectivities the potential of both MOFs in gas separation of CH4 from N2 can be derived.

Fully accessible: Uptakes of 9.2 mmol g−1 (40.5 wt %) for CO2 at 273 K/0.1 MPa and 15.23 mmol g−1 (3.07 wt %) for H2 at 77 K/0.1 MPa are among the highest reported for metal–organic frameworks (MOFs) and are found for a novel, highly microporous copper-based MOF (see picture; Cu turquoise, O red, N blue). Thermal analyses show a stability of the flexible framework up to 250 °C.

As a basis for the evaluation of hydrogen storage by physisorption, adsorption isotherms of H2 were experimentally determined for several porous materials at 77 K and 298 K at pressures up to 15 MPa. Activated carbons and MOFs were studied as the most promising materials for this purpose. A noble focus was given on how to determine whether a material is feasible for hydrogen storage or not, dealing with an assessment method and the pitfalls and problems of determining the viability. For a quantitative evaluation of the feasibility of sorptive hydrogen storage in a general analysis, it is suggested to compare the stored amount in a theoretical tank filled with adsorbents to the amount of hydrogen stored in the same tank without adsorbents. According to our results, an “ideal” sorbent for hydrogen storage at 77 K is calculated to exhibit a specific surface area of >2580 m2 g−1 and a micropore volume of >1.58 cm3 g−1.

A new, efficient method for the isolation of (2R,3S)-isocitric acid (ICA) from its fermentation solution was developed. It is noteworthy that this method is based on selective adsorption directly from the fermentation solution on activated carbon, followed by the release of both ICA and citric acid by means of elution with methanol and their final separation by known methods. Thereby, several disadvantages were overcome: Electrodialysis is no longer necessary to remove cations such as Na+ from the fermentation solution. Also, several hitherto accompanying dyestuffs were not observed with this method. Furthermore, removal of water by distillation is expendable. Eventually, the new crude product is of a quality that also avoids the use of a tedious slide vane rotary vacuum pump distillation of the trimethyl esters of both acids, which hitherto was the basis for the separation of ICA. In summary, the new method distinctly spares energy as well as time.

Phosphate-based inorganic-organic hybrid nanoparticles (IOH-NPs) with the general composition [M](2+)[Rfunction(O)PO3](2-) (M = ZrO, Mg2O; R = functional organic group) show multipurpose and multifunctional properties. If [Rfunction(O)PO3](2-) is a fluorescent dye anion ([RdyeOPO3](2-)), the IOH-NPs show blue, green, red, and near-infrared fluorescence. This is shown for [ZrO](2+)[PUP](2-), [ZrO](2+)[MFP](2-), [ZrO](2+)[RRP](2-), and [ZrO](2+)[DUT](2-) (PUP = phenylumbelliferon phosphate, MFP = methylfluorescein phosphate, RRP = resorufin phosphate, DUT = Dyomics-647 uridine triphosphate). With pharmaceutical agents as functional anions ([RdrugOPO3](2-)), drug transport and release of anti-inflammatory ([ZrO](2+)[BMP](2-)) and antitumor agents ([ZrO](2+)[FdUMP](2-)) with an up to 80% load of active drug is possible (BMP = betamethason phosphate, FdUMP = 5'-fluoro-2'-deoxyuridine 5'-monophosphate). A combination of fluorescent dye and drug anions is possible as well and shown for [ZrO](2+)[BMP](2-)0.996[DUT](2-)0.004. Merging of functional anions, in general, results in [ZrO](2+)([RdrugOPO3]1-x[RdyeOPO3]x)(2-) nanoparticles and is highly relevant for theranostics. Amine-based functional anions in [MgO](2+)[RaminePO3](2-) IOH-NPs, finally, show CO2 sorption (up to 180 mg g(-1)) and can be used for CO2/N2 separation (selectivity up to α = 23). This includes aminomethyl phosphonate [AMP](2-), 1-aminoethyl phosphonate [1AEP](2-), 2-aminoethyl phosphonate [2AEP](2-), aminopropyl phosphonate [APP](2-), and aminobutyl phosphonate [ABP](2-). All [M](2+)[Rfunction(O)PO3](2-) IOH-NPs are prepared via noncomplex synthesis in water, which facilitates practical handling and which is optimal for biomedical application. In sum, all IOH-NPs have very similar chemical compositions but can address a variety of different functions, including fluorescence, drug delivery, and CO2 sorption.

Aluminium dihydroxyterephthalate [Al(8)(OH)(4)(OCH(3))(8)(BDC(OH)(2))(6)]⋅x H(2)O (denoted CAU-1-(OH)(2)) was synthesized under solvothermal conditions and characterized by X-ray powder diffraction, IR spectroscopy, sorption measurements, as well as thermogravimetric and elemental analysis. CAU-1-(OH)(2) is isoreticular to CAU-1 and its pores are lined with OH groups. It is stable under ambient conditions and in water, and it exhibits permanent porosity and two types of cavities with effective diameters of approximately 1 and 0.45 nm. The crystallization of CAU-1-(OH)(2) was studied by in situ energy-dispersive X-ray diffraction (EDXRD) experiments in the 120-145 °C temperature range. Two heating methods-conventional and microwave-were investigated. The latter leads to shorter induction periods as well as shorter reaction times. Whereas CAU-1-(OH)(2) is formed at all investigated temperatures using conventional heating, it is only observed below 130 °C using microwave heating. The calculation of the activation energy of the crystallization of CAU-1-(OH)(2) exhibits similar values for microwave and conventional synthesis.

In this study, the adsorption of CO2 and H2S has been investigated on commercial activated carbon Desorex K43 impregnated with K2CO3, NaOH, or Fe2O3 in order to assess their potential for “upgrading” and desulfurization of biogas or contaminated natural gas. Different chemical [Fourier transformed infrared spectra (FTIR), X-ray fluorescence (XRF) and pH measurements] and textural characterization techniques (N2 adsorption/desorption isotherms) were used to study the material surface and confirm the presence of K, Na, and Fe. Gravimetric experiments of single and binary gas sorption isotherms were used to evaluate CO2 uptake and selectivity with respect to CH4. Breakthrough curves under dry and humid conditions were performed to assess the adsorption of H2S. The materials studied showed high adsorption capacities for both gases: in the range from 0.85 to 4.58 mmol g–1 for H2S and from 1.61 to 1.88 mmol g–1 CO2, under dry conditions and 1 bar. Furthermore, the selectivity of the activated carbons for CO2 in relation to CH4 was in the range of 1.2–2.4, Desorex K43-BG being the material with higher adsorption capacity for gases under study. The data obtained by the adsorption experiments were correlated with the textural characteristics and the chemical properties of the materials, which allowed one to identify how promising an adsorbent is for the removal of acidic gases from biogas to obtain biomethane. The best compromise between H2S adsorption and CO2/CH4 selectivity was found for the sample containing Na (Desorex K43-Na), which benefited from both a basic surface chemistry and pore size distribution restricted to the micropore range.

Abstract The degradation of organic compounds in water is the subject of a number of fundamental and applied investigations. Aquasonolysis of organic compounds is an advanced technology for the purification of contaminated water. The process is based on the phenomenon of acoustic cavitation. Dominant reactions of volatile compounds are: cavitative high‐temperature gas‐phase reactions and thermal‐oxidative decay in bubbles. Nonvolatile compounds are mainly decomposed by OH radicals in the aqueous solution (sonolytical cleavage of water). This article reviews mechanisms and kinetics of pollutant decomposition in water and discusses the influence of different experimental parameters. An overview of the application spectrum of aquasonolysis is provided, analyzing results gathered in experiments completed in our group as well as results reported in the literature.

Abstract Organogold compounds having at least one Au–C δ or π bond and gold‐carborane complexes have recently received rapidly increasing attention, from the point of view of valence theory and structure as well as on practical grounds. Interesting possibilities are offered particularly in connection with the use of gold and its derivatives as heterogeneous or homogeneous catalysts for organic reactions, and new problems also arise.

Infrared dielectric function spectra and phonon modes with polarization parallel and perpendicular to the c axis of high quality, highly relaxed, and single crystalline wurtzite MgxZn1−xO films with 0⩽x⩽0.2 prepared by pulsed-laser deposition on c-plane sapphire substrates were obtained from infrared spectroscopic ellipsometry (380–1200 cm−1) and Raman scattering studies. A two-mode behavior is found for the modes with E1 symmetry, a lattice mode and an impurity-type mode are obtained for the A1 symmetry phonons. Model dielectric function spectra will become useful for future infrared ellipsometry analysis of complex MgxZn1−xO-based heterostructures.

Prototype of a new aromatization reaction: thermal rearrangement of 1,3-hexadiene-5-yne (1) to benzene (3) via isobenzene 2, a highly reactive benezene isomer. Trapping experiments with styrene and the behavior of arenes containing 1 as a subunit indicate that this isomerization is also suitable for preparing condensed arenes and fullerene fragments.

Temperature-dependent dielectric and electro-optic properties of a ZnO-BaTiO3-ZnO heterostructure grown by pulsed-laser deposition on (0001) sapphire are reported. The wurtzite-structure ZnO layers serve as transparent conducting electrodes. Previously observed coupling effects within the wurtzite-perovskite heterostructure by spectroscopic electro-optic ellipsometry birefringence measurements manifest themselves as a “pinning” of the ferroelectric polarization in the BaTiO3 layer by the cladding ZnO layers. Temperature-controlled electro-optic Raman measurements assign the electro-optic birefringence results to a temperature-driven phase transition resulting from the leakage current within the sample. High-temperature small-signal capacitance measurements exploiting the conductive electrode properties of the cladding layers reveal occurrence of the Curie temperature of the BaTiO3 layer at 384 K.

The Ca isotopic composition of modern seawater has been determined using a 43 Ca‐ 48 Ca double spike, which was calibrated using a 42 Ca/ 44 Ca seawater ratio of 0.30587 ± 0.00026. This ratio was determined from a total evaporation experiment in which the ion beam was measured from the beginning to the end of the emission. With integration of the peak intensities, the fractionation effects can be minimised, since total evaporation of the reservoir cancels out the effect of vapour enrichment in the light isotopes. This experiment avoids the gravimetric uncertainty inherent in the double spike calibration. This calibration allows the precise redetermination of the seawater isotopic composition of Ca. A mean 40 Ca/ 44 Ca ratio for two Atlantic water samples of 45.143 (2s mean = 0.003) was found. The good reproducibility of the Ca isotope ratios in present seawater and the very strong isotopic homogeneity of Ca in the oceans illustrate the advantage of using seawater as the common standard, with the advantage of decreasing interlaboratory bias.

In this paper within a field-theoretical approach taking into account explicitly a co-solvent with a nonzero dipole and a polarizability tensor, we derive a modified Poisson-Boltzmann equation. Applying the modified Poisson-Boltzmann equation, we formulate a generalized Gouy-Chapman theory for the case when an electrolyte solution is mixed with a polar co-solvent having a large polarizability. We show that an increase of the co-solvent concentration as well as the co-solvent polarizability lead to a significant increase of differential capacitance at sufficiently high surface potentials of the electrode, whereas the profile of the electrostatic potential becomes considerably more long-ranged. On the contrary, an increase in the permanent dipole of the co-solvent only weakly affects the differential capacitance.

Porous adsorbents with hierarchical structured macropores ranging from 1 to 100 μm are prepared using a combination of freeze casting and additional sacrificial templating of polyurethane foams, with a zeolite 13X powder serving as adsorbent. The pore system of the prepared monoliths features micropores assigned to the zeolite 13X particle framework, interparticular pores of ∼1-2 μm, lamellar pores derived from freeze casting of ∼10 μm, and an interconnected pore network obtained from the sacrificial templates ranging from around 100 to 200 μm with a total porosity of 71%. Gas permeation measurements show an increase in intrinsic permeability by a factor of 14 for monoliths prepared with an additional sacrificial templated foam compared to monoliths solely providing freeze casting pores. Cyclic CO2 adsorption and desorption tests where pressure swings between 8 and 140 kPa reveal constant working capacities over multiple cycles. Furthermore, the monoliths feature a high volumetric working capacity of ∼1.34 mmol/cm(3) which is competitive to packed beds made of commercially available zeolite 13X beads (∼1.28 mmol/cm(3)). Combined with the faster CO2 uptake showing an adsorption of 50% within 5-8 s (beads ∼10 s), the monoliths show great potential for pressure swing adsorption applications, where high volumetric working capacities, fast uptakes, and low pressure drops are needed for a high system performance.