Spherical particles of phenylene-bridged periodic mesoporous organosilica for high-performance liquid chromatography.
Explore the source record for details and available documents.
Journal Article↗
Biomedical subjects
Michael Fröba
Publications and source records attributed to Michael Fröba.
Silica-based mesoporous organic-inorganic hybrid materials.
Mesoporous organic-inorganic hybrid materials, a new class of materials characterized by large specific surface areas and pore sizes between 2 and 15 nm, have been obtained through the coupling of inorganic and organic components by template synthesis. The incorporation of functionalities can be achieved in three ways: by subsequent attachment of organic components onto a pure silica matrix (grafting), by simultaneous reaction of condensable inorganic silica species and silylated organic compounds (co-condensation, one-pot synthesis), and by the use of bissilylated organic precursors that lead to periodic mesoporous organosilicas (PMOs). This Review gives an overview of the preparation, properties, and potential applications of these materials in the areas of catalysis, sorption, chromatography, and the construction of systems for controlled release of active compounds, as well as molecular switches, with the main focus being on PMOs.
Journal Article↗
Temperature-resolved in situ X-ray absorption spectroscopic study on the reduction of nanostructured Fe(2)O(3) within the pore system of mesoporous carbon CMK-1.
Results of in situ X-ray absorption spectroscopy experiments on the reduction of thin-layered nanostructured X-ray amorphous iron(III) oxides inside the pore system of mesoporous carbon CMK-1 are presented. These in situ measurements were carried out using 4% hydrogen in nitrogen as reduction gas over a 300-1000 K temperature range. The thermochemical behaviour of the nanostructured materials was compared with that of the bulk phases. The spectra series examined by factor analysis gave a good insight into the reduction products of iron oxide nanoparticles occurring in mesoporous carbon CMK-1.
Journal Article↗
Multiple-scattering extended X-ray absorption fine structure analysis of nanostructured iron(III) oxide in the pore system of mesoporous carbon CMK-1.
This work is devoted to the EXAFS analysis of nanostructured iron(III) oxide synthesized inside the pore system of mesoporous carbon CMK-1. A detailed study of the recording, preparation and evaluation of data recorded in fluorescence mode at the iron K-edge with and without multiple scattering is shown. The results obtained show that the local structure of Fe3+ inside nanostructured iron(III) oxide is different to that of the bulk material. Due to the small particle size, data analysis is much more difficult and data preparation more complex. Incorporating multiple scattering paths in the Fourier transforms and back-transforms during data evaluation gives structural insights that cannot be obtained using other spectroscopic methods, and this technique was used to draw conclusions about the first four coordination spheres of the nanostructured iron(III) oxide.
Carbon↗
Periodic mesoporous organosilicas (PMOs): past, present, and future.
Periodic mesoporous organosilicas (PMOs) represent a new class of organic-inorganic hybrid materials suitable for a broad range of applications such as chromatography, catalysis, sensing and microelectronics. Unlike in organic functionalized mesoporous silica phases obtained via grafting or co-condensation procedures the organic groups in PMOs are direct parts of the 3D framework structure, thus giving raise to enormous possibilities to tune their chemical and physical properties in designated ways by varying the structure of the precursors. In this review the distinctive features of PMOs are discussed, the latest developments concerning compositions, structures, morphologies and potential applications are figured out and finally a brief outlook of future aspects is given.
Microscopy, Electron, Scanning↗
Stabilization of the thermodynamically favored polymorph of cadmium chalcogenide nanoparticles CdX (X = S, Se, Te) in the polar mesopores of SBA-15 silica.
A versatile synthetic approach to cadmium chalcogenide nanoparticles in the mesopores of SBA-15 silica as a host matrix was developed. The use of cadmium organochalcogenolates of the type Cd(XPh)(2).TMEDA (X = S, Se, Te) allowed the preparation of nanoparticles of all three cadmium chalcogenides following the same experimental protocol. Particles of CdS, CdSe, and CdTe with a particle size of 7 nm were prepared from this class of single-source precursors. The incorporation of the precursor molecules into the pores was achieved by melt infiltration at a temperature of 140 degrees C. Subsequent pyrolysis of the precursors in the mesopores yielded the semiconductor particles. Owing to the high polarity of the silanol-covered pore walls, which lower the surface energy of the particles to a large extent, the dimorphic cadmium chalcogenides are obtained in their thermodynamically favored modifications; e.g., CdS particles crystallize in the wurtzite type, CdTe particles are obtained in the zinc blende structure, and CdSe (where no unambiguous preference exists) crystallizes as a "mixture" of both structures with a rather random stacking sequence.
Journal Article↗
A new X-ray spectrometer with large focusing crystal analyzer.
A new focusing spectrometer employing Johann geometry has been built and permanently installed at the wiggler beamline W1 at the Hamburger Synchrotron Strahlungslabor (HASYLAB) am Deutschen Elektronen Synchrotron (DESY). It is now available for user operation. The design of the spectrometer is optimized for the use of a large source spot size at the DORIS storage ring as well as for simple operation and robustness under user-mode conditions. Nevertheless, the ideal source for enlarging the number of possible applications in the future would be an undulator at one of the PETRA III beamlines. In the following the spectrometer design is described and boundary conditions such as the available energy range for future experiments are discussed. Two benchmark experiments, resonant inelastic X-ray scattering (RIXS) and X-ray absorption fluorescence spectroscopy (XAFS), on samples with complicated matrices demonstrate the performance of the new instrument.
Calibration↗
Enantioselective semipreparative HPLC separation of PCB metabolites and their absolute structure elucidation using electronic and vibrational circular dichroism.
Polychlorinated biphenyls (PCBs) remain one of the most important groups of environmental contaminants. The fate (transformation) as well as the toxicological implications of the different metabolism steps are subject to considerable debate. The aim of this study is to start a comprehensive investigation of atropisomeric PCB metabolites, i.e., hydroxy, methoxy, methylthionyl, and methylsulfonyl PCBs in different biota. For this purpose, enantioselective semipreparative liquid chromatography is used to obtain pure enantiomers of PCB metabolites. Electronic circular dichroism (UV-CD) and vibrational circular dichroism (VCD) in combination with computational techniques were applied to determine their absolute structures. Approximately 18-25 mg of each enantiomer of the following metabolites were obtained using semipreparative HPLC on beta-cyclodextrin-based columns: 4-MeO-CB149, 4-MeS-CB149, 4-MeSO2-CB149, 3-MeS-CB149, and 3-MeSO2-CB149. The enantiomeric purity of the separated enantiomers was in the range of 95.0-99.9%. Rotational angles and absolute configurations were also determined. This study establishes a sound method for future preparation and absolute structure determination of compounds belonging to the same class.
Chromatography↗
A new in situ cell for XAFS investigations.
A new in situ cell for X-ray absorption spectroscopic investigations has been designed and tested. In contrast to existing cells, it is able to reach temperatures as high as 1250 K and can record X-ray absorption spectra in transmission and fluorescence modes. Furthermore, the cell is equipped with a new sample-holder system which allows an easy sample changing. All components are commercial and are simple to build. The cell is light and easy to handle, and can be used under reducing or oxidizing conditions which makes it suitable for performing reduction and oxidation investigations as demanded, e.g. in heterogeneous catalysis experiments. The cell was tested on the reduction of haematite.
Journal Article↗
Formation of Zn(1-x)MnxS nanowires within mesoporous silica of different pore sizes.
Arrays of highly ordered Zn(1-x)MnxS quantum wires with x ranging from 0.01 to 0.3 and with lateral dimensions of 3, 6, and 9 nm were synthesized within mesoporous SiO2 host structures of the MCM-41 and SBA-15 type. The hexagonal symmetry of these arrays (space group p6m) and the high degree of order was confirmed by X-ray diffraction and transmission electron microscopy (TEM) studies. Physisorption measurements show the progressive filling of the pores of the SiO2 host structures, while TEM and Raman studies reveal the wire-like character of the incorporated Zn(1-x)MnxS nanostructures. X-ray absorption near-edge structure, extended X-ray absorption fine structure, photoluminescence excitation (PLE), and electron paramagnetic resonance studies confirm the good crystalline quality of the incorporated Zn(1-x)MnxS guest species and, in particular, that the Mn2+ ions are randomly distributed and are situated on tetrahedrally coordinated cation sites of the Zn(1-x)MnxS wires for all x up to 0.3. The amount of Mn2+ ions loosely bound to the surface of the Zn(1-x)MnxS nanowires is less than 4% of the total Mn content even for the 3 nm nanostructures up to the highest Mn content of x = 0.3. The effects of the reduction of the lateral dimensions on electronic properties of the diluted magnetic semiconductor were studied by PLE spectroscopy. Due to the quantum confinement of the excitons in the wires an increase of the direct band gap with decreasing particle size is observed.
Journal Article↗
Mesoporous aluminophosphates from a single-source precursor.
Mesoporous aluminophosphates with a strict ratio of A1:P = 1:1 have been synthesized from a single-source molecular precursor.
Journal Article↗
Ordered arrays of II/VI diluted magnetic semiconductor quantum wires: formation within mesoporous MCM-41 silica.
We present a novel way of synthesising highly ordered arrays of hollow Cd(1-x)Mn(x)S quantum wires with lateral dimensions of 3-4 nm separated by 1-2 nm SiO2 barriers by forming Cd(1-x)Mn(x)S (0 < or = x < or = 1) semiconductors inside the pore system of mesoporous MCM-41 SiO2 host structures. X-ray diffraction and transmission electron microscopy (TEM) studies reveal the hexagonal symmetry of these arrays (space group p6m) and confirm the high degree of order. Physisorption measurements show the filling of the pores of the MCM-41 SiO2. The X-ray absorption near-edge structure (XANES), extended X-ray absorption fine structure (EXAFS), electron paramagentic resonance (EPR), and Raman studies confirm the good crystalline quality of the incorporated (Cd,Mn)S guest. The effects of reducing the lateral dimensions on the magnetic and electronic properties of the diluted magnetic semiconductor were studied by photoluminescence (PL) and PL excitation spectroscopy and by SQUID and EPR measurements in the temperature range 2-400 K. Due to the quantum confinement of the excitons in the wires, an increase of about 200 meV in the direct band gap was observed. In addition, the p-d hybridisation-related bowing of the band gap as a function of Mn concentration in the wires is much stronger than in the bulk. This effect is related to the increase in the band gap due to quantum confinement, which shifts the p-like valence band edge closer to the 3d-related states of Mn in the valence band. Thus, the p-d hybridisation and the strength of the band gap bowing are increased. Compared to bulk (II,Mn)VI compounds, antiferromagnetic coupling between the magnetic moments of the Mn2+ ions is weaker. For the samples with high Mn concentrations (x > 0.8) this leads to a suppression of the phase transition of the Mn system from paramagnetic to antiferromagnetic. This effect can be explained by the fact that the lateral dimensions of the wires are smaller than the magnetic length scale of the antiferromagnetic ordering.
Journal Article↗