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Organisationseinheit der BAM
A series of Ca-based coordination polymers were prepared mechanochemically by milling Ca(OH)2 with phthalic acid (H2oBDC), isophthalic acid (H2mBDC), and terephthalic acid (H2pBDC). The hydrated compounds [Ca(oBDC)(H2O)], [Ca(mBDC)(H2O)3.4], and [Ca(pBDC)(H2O)3] were prepared for the first time via mechanochemical routes. The refined structures were validated by extended X-ray absorption data. The new dehydrated compound [Ca(oBDC)] (1-H2O), obtained after the thermal post-treatment of 1 in a reversible phase transition process, was determined ab initio based on the powder X-ray diffraction (PXRD) data. The materials were thoroughly characterized using elemental analysis, thermal analysis, and spectroscopic methods: magic-angle spinning NMR and attenuated total reflection-infrared spectroscopy. The specific surface areas and sorption properties of the hydrated and dehydrated samples were determined using the isotherms of gas sorption and dynamic vapor sorption measurements.
Mechanochemical synthesis of [Zn3(C2O4)3(4,4'-bipy)4] and its reorganization at high temperatures
(2014)
The metal organic layered structure catena-(bis(µ2-4,4'-bipyridine)-tris(µ2-oxalato)-bis(4,4'-bipyridine)-tri-zinc(ii)) ([Zn3(C2O4)3(4,4'-bipy)4]) was synthesized mechanochemically applying three different routes. The synthesis succeeded by i) simultaneously neat grinding the three starting materials zinc acetate dihydrate, oxalic acid dihydrate and 4,4'bipyridine, ii) grinding two compounds and adding the third afterwards, independent of the sequence. The products were characterized using powder X-ray diffraction, Raman spectroscopy, gas adsorption measurements, and scanning electron microscopy. Temperature-dependent synchrotron XRD measurements revealed that the monoclinic structure of [Zn3(C2O4)3(4,4'-bipy)4] rearranges reversibly to a higher ordered orthorhombic structure [Zn(C2O4)(4,4'-bipy)] at high temperatures.
Zeolitic Imidazolate Frameworks (ZIFs) are crystalline materials
that comprise of metal nodes and Imidazole derivatives as
linkers. ZIF-67 is often used in polymer composite materials
e. g. for gas separation membranes. Post-synthesis treatment of
ZIF-67 crystals with ultrasound leads to unforeseen plasticity
that resulted in sintered ZIF-67 and ZIF-67 nano-flakes.
Consequently, ultrasound increases the external surface area of
ZIF-67 which might improve e.g. blending with polymers in
composite materials. These new morphologies of ZIF-67 were
characterized by transmission electron, scanning electron, and
atomic force microscopy. The ultrasound treatment of ZIF-67
did not result in the formation of an amorphous framework or
a meta-stable crystal structure as indicated by powder x-ray
diffraction. In addition, ultra-sonicated ZIF-67 retained the high
gas adsorption capacity and pore size compared to synthesized
ZIF-67. The morphological changes are hard to detect with
standard analytical methods that are usually utilized for MOF
characterization. These findings also suggest that sonochemical
treatment of ZIFs leads to structural effects beyond increasing
the amount of nucleation clusters during sono-chemical synthesis,
which is currently not addressed in the field.
Established maximum levels for the mycotoxin zearalenone (ZEN) in edible oil require monitoring by reliable analytical methods. Therefore, an automated SPE-HPLC online system based on dynamic covalent hydrazine chemistry has been developed. The SPE step comprises a reversible hydrazone formation by ZEN and a hydrazine moiety covalently attached to a solid phase. Seven hydrazine materials with different properties regarding the resin backbone, pore size, particle size, specific surface area, and loading have been evaluated. As a result, a hydrazine-functionalized silica gel was chosen. The final automated online method was validated and applied to the analysis of three maize germ oil samples including a provisionally certified reference material. Important performance criteria for the recovery (70–120 %) and precision (RSDr <25 %) as set by the Commission Regulation EC 401/2006 were fulfilled: The mean recovery was 78 % and RSDr did not exceed 8 %. The results of the SPE-HPLC online method were further compared to results obtained by liquid&–liquid extraction with stable isotope dilution analysis LC-MS/MS and found to be in good agreement. The developed SPE-HPLC online system with fluorescence detection allows a reliable, accurate, and sensitive quantification (limit of quantification, 30 µg/kg) of ZEN in edible oils while significantly reducing the workload. To our knowledge, this is the first report on an automated SPE-HPLC method based on a covalent SPE approach.
Pectin-water interactions: comparison of different analytical methods and influence of storage
(2015)
Interactions of pectin with water are essential for nearly all pectin applications. It was assumed that these interactions strongly depend not only on chemical molecular parameters but also on physical powder material properties and that they might be affected by storage. This was examined with nine different pectin samples from three suppliers. Storage at 60 °C and 80% humidity for two weeks was used in order to simulate long term storage at moderate conditions. Material properties were tested by measuring solid density and BET surface and by mercury porosimetry and X-ray analysis. Pectin-water interactions were examined with two different methods, a modified sorption method at αw around 1.0 and the capillary sucking method (Baumann method). After storage, the BET surface of the pectin samples was reduced, solid density was altered differently and crystalline structures became amorphous. It is assumed that storage at high heat and humidity caused particle surfaces softening, swelling and partly dissolution. The particle surfaces smoothed, small inter-particle voids were reduced or sealed and particles agglomerated. These alterations caused a reduced water uptake of stored pectins. In general, the accessibility of hydrophilic groups in pectin was more important for pectin-water interactions than their number. All applied methods for testing pectin-water interactions detected special sample properties and their combination allowed an extensive evaluation of the water binding properties.
Aim of the present study was to investigate the effect of the method of demethoxylation on the particle structure and techno-functional properties of pectins with different degree of methoxylation and distribution of free carboxyl groups. Two groups of model pectins, one with 57% and one with 42% degree of methoxylation have been prepared from one single commercial pectin. Modifications were performed by an acidic and two enzymatic methods using fungal and plant-derived pectin methyl esterases. Thermal stability was investigated by thermal analysis and water uptake was determined by a sorption and a capillary sucking method.
The enzyme-treated pectins were thermally less stable than the acid-treated. The water uptake of enzyme-treated pectins was higher than in acid-treated samples in the sorption method and lower in the capillary sucking tests. The different behaviour is explained by differences in pH during demethoxylation and a co-occurring variation in sodium content. Both parameters affected intermolecular interactions of the pectin macromolecules in solution, which resulted in differences in the particle morphology. The effect of the distribution of free carboxyl groups (statistical or block-wise) on the techno-functional properties was more pronounced in high-methoxylated pectins than in low-methoxylated pectins.
Zeolite synthesis was studied using two silica rich filtration residues (FR 1 and FR 2) as Si-source
and sodium aluminate in a direct synthesis at 60°C at strong alkaline conditions (8 M - 16 M NaOH).
In addition to these one-pot syntheses, a two-step process was investigated. Here, an alkaline digestion
of FR at 60°C was followed by gel precipitation with sodium aluminate and gel crystallization
under usual conditions of 80°C - 90°C. The results show that the substitution of chemical
reagent sodium silicate by a waste material like FR as Si-source is possible but requires fine tuning
of the reaction conditions as zeolite crystallization is a process under kinetic control. The
solubility behaviour and impurities of the inserted filtration residues strongly influenced the
course of reaction. Thus zeolites like hydrosodalite or intermediate zeolite between cancrinite
and sodalite, or zeolite NaA or Z-21 in cocrystallization with hydrosodalite could be observed in
the one pot syntheses already in a short time interval between 1 - 4 h depending on the alkalinity.
The two step process yield to zeolites NaA and NaX in very good quality. The reaction process of FR
in both reaction methods was characterized by chemical analyses, X-ray powder diffraction,
Fourier transform infrared spectroscopy as well as scanning electron microscopy. Surface area
and water content of selected products were further characterized by the BET-method and by
thermogravimetry. Summing up the results, we can show that zeolite formation from filtration residues
is possible by several reaction procedures as model cases for a re-use of industrial waste
materials. Beside the importance for environmental protection, the reactions are of interest for
zeolite chemistry as the re-use of FR is possible under economically conditions of low energy consumption
at 60°C and short reaction periods.
There is currently a debate within the SIP community about the characteristic textural length scale controlling relaxation time of consolidated porousmedia.One idea is that the relaxation time is dominated by the pore throat size distribution or more specifically the modal pore throat size as determined in mercury intrusion capillary pressure tests. Recently new studies on inverting pore size distributions from SIP data were published implying that the relaxation mechanisms and controlling length scale are well understood. In contrast new analytical model studies based on the Marshall-Madden membrane polarization theory suggested that two relaxation processes might compete: the one along the short narrow pore (the throat) with one across the wider pore in case the narrow pores become relatively long.
This paper presents a first systematically focused study into the relationship of pore throat sizes and SIP relaxation times. The generality of predicted trends is investigated across a wide range of materials differing considerably in chemical composition, specific surface and pore space characteristics. Three different groups of relaxation behaviors can be clearly distinguished. The different behaviors are related to clay content and type, carbonate content, size of the grains and the wide pores in the samples.
A two-component core-shell UiO-68 type metal-organic framework (MOF) with a nonfunctionalized interior for efficient guest uptake and storage and a thin light-responsive outer shell was prepared by initial solvothermal MOF synthesis followed by solvent-assisted linker exchange. The bulky shell linker features two tetra-ortho-fluorinated azobenzene moieties to exploit their advantageous photoisomerization properties. The obtained perfect octahedral MOF single crystals can be switched repeatedly and with an unprecedented efficiency between E- and Z-rich states using visible light only. Due to the high photoswitch density per pore of the shell layer, its steric demand and thus molecular uptake (and release) can be conveniently modulated upon green and blue light irradiation. Therefore, the "smart" shell acts as a light-controlled kinetic barrier or "gate" for the diffusion of cargo molecules in and out of the MOF crystals.
A series of new epoxide-based monoliths is synthesized by self-polymerization of polyglycerol polyglycidyl ether as porous support for affinity chromatography. Porosity and mean pore sizes are investigated as a function of the porogen ratio and analyzed by mercury porosimetry. The morphologies are visualized by environmental scanning electron microscope. With a particularly rigid monolith prepared with 75 vol% porogen (66% porosity and 12 µm mean pore size), a capillary column (0.5 mm ID) is prepared and directly functionalized with recombinant protein A to extract immunoglobulin G from rabbit serum.