@inbook{25973, abstract = {{Chemical sensors are integral to the automation of myriad industrial processes, as well as everyday monitoring of such activities as public safety, engine performance, medical therapeutics, and many more...}}, author = {{Tiemann, Michael}}, booktitle = {{Nanostructured Materials}}, editor = {{Korotcenkov, Ghenadii}}, pages = {{291 -- 310}}, publisher = {{Momentum Press}}, title = {{{Ordered Mesoporous Films and Membranes: Synthesis, Properties and Applications in Gas Sensors}}}, volume = {{2}}, year = {{2010}}, } @article{25975, abstract = {{The synthesis and characterization of ordered mesoporous In2O3 materials by structure replication from hexagonal mesoporous SBA-15 silica and cubic KIT-6 silica is presented. Variation of the synthesis parameters allows for different pore sizes and pore wall thicknesses in the products. The In2O3 samples turn out to be stable up to temperatures between 450 °C and 650 °C; such high thermal stability is necessary for their application as gas sensors. Test measurements show a high sensitivity to methane gas in concentrations relevant for explosion prevention. The sensitivity is shown to be correlated not only with the surface-to-volume ratio, but also with the nanoscopic structural properties of the materials.}}, author = {{Waitz, Thomas and Wagner, Thorsten and Sauerwald, Tilman and Kohl, Claus-Dieter and Tiemann, Michael}}, issn = {{1616-301X}}, journal = {{Advanced Functional Materials}}, pages = {{653--661}}, title = {{{Ordered Mesoporous In2O3: Synthesis by Structure Replication and Application as a Methane Gas Sensor}}}, doi = {{10.1002/adfm.200801458}}, year = {{2009}}, } @article{25977, abstract = {{We report a systematic study of the photoluminescence properties of ZnO nanostructures. In particular, mesoporous ZnO powders of varying surface-to-mass ratio are investigated and compared to a bulk reference. At low temperatures the emission from higher-energy states is very pronounced and even dominant for samples with high surface-to-mass ratio.}}, author = {{Schwalm, Michael and Horst, Swantje and Chernikov, Alexej and Rühle, Wolfgang W. and Lautenschläger, Stephan and Klar, Peter J. and Meyer, Bruno K. and Waitz, Thomas and Tiemann, Michael and Chatterjee, Sangam}}, issn = {{1610-1634}}, journal = {{physica status solidi (c)}}, pages = {{542--545}}, title = {{{Time-resolved photoluminescence study of mesoporous ZnO nanostructures}}}, doi = {{10.1002/pssc.200880315}}, year = {{2009}}, } @article{25974, abstract = {{We present the preparation of a semiconductor gas sensor based on ordered mesoporous In2O3. The In2O3 was synthesized by structure replication procedure from cubic KIT-6 silica. A detailed analysis of the morphology of the mesoporous powders as well as of the prepared sensing layer will be shown. Unique properties arise from the synthesis method of structure replication such as well defined porosity in the mesoporous regime and nanocrystallites with high thermal stability up to 450 °C. These properties are useful for the application in semiconducting gas sensors. Test measurements show sensitivity to methane gas in concentrations relevant for explosion prevention.}}, author = {{Wagner, T. and Sauerwald, T. and Kohl, C.-D. and Waitz, T. and Weidmann, C. and Tiemann, Michael}}, issn = {{0040-6090}}, journal = {{Thin Solid Films}}, pages = {{6170--6175}}, title = {{{Gas sensor based on ordered mesoporous In2O3}}}, doi = {{10.1016/j.tsf.2009.04.013}}, year = {{2009}}, } @article{25976, abstract = {{Halbleitende Metalloxid-Gassensoren werden sowohl im industriellen Bereich als auch im Haushalt zur Luftüberwachung verwendet. Die Funktionsweise basiert auf einer reversiblen Änderung des Sensorwiderstandes in Anwesenheit sowohl oxidierender als auch reduzierender Gase, die mit einfachen Mitteln gemessen werden kann. In diesem Artikel wird vorgestellt, wie sich die bei der Gasdetektion ablaufenden Vorgänge mit Hilfe des Ionosorptionsmodells in Kombination mit einem einfachen Festkörperbändermodell deuten lassen. Abschließend werden einfache, im Chemieunterricht zu realisierende Experimente mit Gassensoren präsentiert.}}, author = {{Waitz, Thomas and Tiemann, Michael}}, issn = {{0944-5846}}, journal = {{CHEMKON}}, pages = {{183--186}}, title = {{{Halbleitende Metalloxide als Gassensoren im Chemieunterricht}}}, doi = {{10.1002/ckon.200910099}}, year = {{2009}}, } @article{25980, abstract = {{Mesoporous SBA-15 (space group p6mm), KIT-6 (Ia3d) and KIT-5 (Fm3m) silicas, exhibiting different 2-D and 3-D channel- or cage-like pore structure and pore dimensions have been used as supports for iron oxide nanoparticles. The iron modification of the silica was performed according to a frequently used impregnation technique from aqueous iron nitrate solution. The materials were characterized by nitrogen physisorption, X-ray diffraction, TEM–EDX, Moessbauer spectroscopy, and temperature-programmed reduction (TPR) and tested in the catalytic decomposition of methanol. It is established that the location and dispersion of iron oxide nanoparticles are affected by the pore topology of the support. The most homogeneously dispersed iron oxide nanoparticles are observed using silica host matrix exhibiting a 3-D channel-like structure and pore diameters about 7 nm, and the thus-obtained composites exhibit high catalytic activity and selectivity in methanol decomposition to CO and hydrogen. For all the samples, characterized with a low mesopore volume and small pore diameters/pore entrances, the formation of larger iron oxide particles, mainly located on the outer surface, is observed. Inhomogeneously dispersed iron oxide particles with a large fraction of isolated, strongly interacting with the support, iron species, and possessing low catalytic activity and usually high selectivity to methane, are found for the silicas with relatively larger pores/pore entrances.}}, author = {{Tsoncheva, Tanya and Rosenholm, Jessica and Linden, Mika and Kleitz, Freddy and Tiemann, Michael and Ivanova, Ljubomira and Dimitrov, Momtchil and Paneva, Daniela and Mitov, Ivan and Minchev, Christo}}, issn = {{1387-1811}}, journal = {{Microporous and Mesoporous Materials}}, pages = {{327--337}}, title = {{{Critical evaluation of the state of iron oxide nanoparticles on different mesoporous silicas prepared by an impregnation method}}}, doi = {{10.1016/j.micromeso.2007.10.005}}, year = {{2008}}, } @article{25979, abstract = {{Various measures to optimise the impregnation of mesoporous CMK-3 carbon and SBA-15 silica matrices with metal nitrates for the synthesis of mesoporous metal oxides by structure replication are investigated. The effect of surface modification of the matrix pores, the choice of a solvent with suitable polarity, and the concentration of the metal nitrate solution are studied in detail. The efficiency of pore loading is monitored by nitrogen physisorption measurements. The creation of polar functions at the pore surface of CMK-3 carbon is shown to increase the impregnation efficiency substantially while maximizing the pore wall polarity of SBA-15 silica by increasing the amount of free silanol groups does not have any significant impact. The choice of a less polar solvent (THF instead of water) has a positive effect on the wettability of CMK-3 carbon in the first impregnation cycle but turns out to be disadvantageous in the second cycle; a similar trend is observed for variation of the metal salt concentration.}}, author = {{Roggenbuck, Jan and Waitz, Thomas and Tiemann, Michael}}, issn = {{1387-1811}}, journal = {{Microporous and Mesoporous Materials}}, pages = {{575--582}}, title = {{{Synthesis of mesoporous metal oxides by structure replication: Strategies of impregnating porous matrices with metal salts}}}, doi = {{10.1016/j.micromeso.2007.12.018}}, year = {{2008}}, } @article{25982, abstract = {{Iron (III) containing nanoparticles with superparamagnetic behaviour are prepared via deposition on various mesoporous supports (MgO, CeO2 and SBA-15). XRD, TEM-EDX, N2 physisorption, FTIR, and Moessbauer spectroscopy are used for their characterization. The reductive properties and catalytic behaviour in methanol decomposition of the materials are also studied. Depending on the chemical nature of the support, the predominant formation of: isolated iron species, strongly interacting with the support (for SBA-15), mixture of hematite and binary MgFe2O4 nanoparticles (for MgO) or almost homogeneously dispersed hematite particles (for CeO2) are observed. The state of iron species strongly affects their catalytic properties. The favorable effect of the support mesoporosity on the catalytic activity is most pronounced for the iron modified CeO2.}}, author = {{Tsoncheva, Tanya and Roggenbuck, Jan and Tiemann, Michael and Ivanova, Lyubomira and Paneva, Daniela and Mitov, Ivan and Minchev, Christo}}, issn = {{1387-1811}}, journal = {{Microporous and Mesoporous Materials}}, pages = {{339--346}}, title = {{{Iron oxide nanoparticles supported on mesoporous MgO and CeO2: A comparative physicochemical and catalytic study}}}, doi = {{10.1016/j.micromeso.2007.06.021}}, year = {{2008}}, } @inbook{25983, abstract = {{Nanoporous semiconducting metal oxide materials (In2O3, WO3) with uniform pore systems, large specific surface areas (80 m2 g−1), and pore-wall crystallinity were prepared by structure replication, using KIT-6 silica as a template. The products show improved properties as gas sensors (for methane or butanone) as compared to non-porous samples. In addition, porous WO3 samples with comparable porosity (prepared by conventional ‘soft templating’, using pluronic P123), which are amorphous on the atomic length scale show poorer gas sensitivity, indicating that crystallinity is a crucial factor in the sensing process.}}, author = {{Waitz, Thomas and Wagner, Thorsten and Kohl, Claus-Dieter and Tiemann, Michael}}, booktitle = {{Zeolites and related materials: Trends, targets and challenges, Proceedings of the 4th International FEZA Conference}}, issn = {{0167-2991}}, title = {{{New mesoporous metal oxides as gas sensors}}}, doi = {{10.1016/s0167-2991(08)80227-3}}, year = {{2008}}, } @article{25981, abstract = {{The growth of ZnS nanoparticles during precipitation from aqueous solution is studied by in situ stopped-flow UV absorption spectroscopy at temperatures between 283 and 323 K. Particle growth is marked by substantial ripening during the first 60 ms. Kinetic data suggest that a ripening mechanism by coalescence (oriented attachment) is predominant over Ostwald ripening, although the latter seems to coexist to a significant degree at early temporal stages, predominantly at low temperatures.}}, author = {{Tiemann, Michael and Marlow, Frank and Hartikainen, Juha and Weiss, Özlem and Lindén, Mika}}, issn = {{1932-7447}}, journal = {{The Journal of Physical Chemistry C}}, pages = {{1463--1467}}, title = {{{Ripening Effects in ZnS Nanoparticle Growth}}}, doi = {{10.1021/jp077729f}}, year = {{2008}}, } @article{25978, abstract = {{In recent years, a lot of research activity has focused on the synthesis of new ordered porous materials by utilization of porous matrices as templates. Since the matrices are themselves created by templating procedures, the entire process can be envisaged as “repeated templating”. This review describes recent conceptual developments in the field of structure replication and summarizes the large number of publications on new functional materials prepared by this method.}}, author = {{Tiemann, Michael}}, issn = {{0897-4756}}, journal = {{Chemistry of Materials}}, pages = {{961--971}}, title = {{{Repeated Templating}}}, doi = {{10.1021/cm702050s}}, year = {{2008}}, } @inbook{25984, abstract = {{Mesoporous ceria was synthesized by using both CMK-3 carbon and SBA-15 silica as structure matrices. All products exhibit uniform mesopores with diameters of 5-6 nm in a two-dimensional periodic arrangement in addition to varying amounts of interparticle porosity. The gas sensing properties (methane detection) of ordered mesoporous ceria was compared to a non-porous sample.}}, author = {{ROGGENBUCK, JAN and Tiemann, Michael}}, booktitle = {{Nanoporous Materials}}, title = {{{Mesoporous Ceria by Structure Replication from Various Porous Matrices}}}, doi = {{10.1142/9789812779168_0019}}, year = {{2008}}, } @article{25987, abstract = {{Mesoporous CeO2 was synthesised by using CMK-3 carbon as a structure matrix. Nitrogen physisorption, powder X-ray diffraction, transmission electron microscopy (TEM), selected-area electron diffraction (SAED), energy-dispersive X-ray (EDX), X-ray absorption near-edge structure (XANES), and thermal (TG/MS) analysis were used for their characterisation. Methanol decomposition to hydrogen, CO, and methane was used as a catalytic test reaction. The obtained products exhibit uniform pores with a diameter of ca. 5 nm in a two-dimensional hexagonal periodic arrangement, as well as interparticle porosity, broadly distributed around ca. 35 nm; the specific surface area is 148 m2 g−1. The pore walls are polycrystalline. The polycrystalline nature and high surface-to-volume ratio of the products is reflected in an increased signal intensity in X-ray absorption spectroscopy. The synthesis of CeO2 from Ce(NO3)3 within the pores of the carbon matrix and the subsequent thermal combustion of the carbon is monitored by thermal analysis. Catalytic tests reveal that the activity of the mesoporous products in methanol decomposition are substantially higher than for a non-porous sample.}}, author = {{Roggenbuck, Jan and Schäfer, Hanno and Tsoncheva, Tanya and Minchev, Christo and Hanss, Jan and Tiemann, Michael}}, issn = {{1387-1811}}, journal = {{Microporous and Mesoporous Materials}}, pages = {{335--341}}, title = {{{Mesoporous CeO2: Synthesis by nanocasting, characterisation and catalytic properties}}}, doi = {{10.1016/j.micromeso.2006.11.029}}, year = {{2007}}, } @article{25986, abstract = {{The authors report the synthesis of nanoporous ZnO, which exhibits a periodically ordered, uniform pore system with crystalline pore walls. The crystalline structure is investigated by x-ray diffraction, transmission electron microscopy, and selected area electron diffraction. The large specific surface area and the uniformity of the pore system are confirmed by nitrogen physisorption. Raman spectroscopy along with low-temperature photoluminescence measurements confirms the high degree of crystallinity and gives insight into defects participating in the radiative recombination processes. The authors thank Günter Koch for recording the TEM images and Marie-Luise Wolff for valuable help in the laboratory one of the authors (M.T.) thanks Michael Fröba for the continuous support.}}, author = {{Waitz, T. and Tiemann, Michael and Klar, P. J. and Sann, J. and Stehr, J. and Meyer, B. K.}}, issn = {{0003-6951}}, journal = {{Applied Physics Letters}}, title = {{{Crystalline ZnO with an enhanced surface area obtained by nanocasting}}}, doi = {{10.1063/1.2713872}}, year = {{2007}}, } @inbook{25990, abstract = {{In-situ X-ray diffraction study on the formation of a periodic mesoporous organosilica material...}}, author = {{Tiemann, Michael and Teixeira, Cilâine V. and Cornelius, Maximilian and Morell, Jürgen and Amenitsch, Heinz and Lindén, Mika and Fröba, Michael}}, booktitle = {{Recent Progress in Mesostructured Materials - Proceedings of the 5th International Mesostructured Materials Symposium (IMMS2006), Shanghai, P.R. China, August 5-7, 2006}}, issn = {{0167-2991}}, title = {{{In-situ X-ray diffraction study on the formation of a periodic mesoporous organosilica material}}}, doi = {{10.1016/s0167-2991(07)80253-9}}, year = {{2007}}, } @article{25988, abstract = {{We report on the synthesis and the gas-sensing properties (CO and NO2 detection) of mesoporous zinc oxide. A two-step structure replication method for the synthesis is employed. In the first step mesoporous SBA-15 silica is prepared by the utilization of self-organization of amphiphilic organic agents. This mesoporous silica is used as the structure matrix for synthesizing mesoporous carbon CMK-3, which, in turn, is employed for yet another replication step, using zinc nitrate as the precursor. The resulting material is characterized by X-ray diffraction and nitrogen physisorption and its gas-sensing properties are compared with a non-porous ZnO sample.}}, author = {{Wagner, T. and Waitz, T. and Roggenbuck, J. and Fröba, M. and Kohl, C.-D. and Tiemann, Michael}}, issn = {{0040-6090}}, journal = {{Thin Solid Films}}, pages = {{8360--8363}}, title = {{{Ordered mesoporous ZnO for gas sensing}}}, doi = {{10.1016/j.tsf.2007.03.021}}, year = {{2007}}, } @article{25985, abstract = {{Semiconducting metal oxides are frequently used as gas-sensing materials. Apart from large surface-to-volume ratios, well-defined and uniform pore structures are particularly desired for improved sensing performance. This article addresses the role of some key structural aspects in porous gas sensors, such as grain size and agglomeration, pore size or crack-free film morphology. New synthesis concepts, for example, the utilisation of rigid matrices for structure replication, allow to control these parameters independently, providing the opportunity to create self-diagnostic sensors with enhanced sensitivity and reproducible selectivity.}}, author = {{Tiemann, Michael}}, issn = {{0947-6539}}, journal = {{Chemistry - A European Journal}}, pages = {{8376--8388}}, title = {{{Porous Metal Oxides as Gas Sensors}}}, doi = {{10.1002/chem.200700927}}, year = {{2007}}, } @inbook{25989, abstract = {{Gas-sensing properties of ordered mesoporous Co3O4 synthesized by replication of SBA-15 silica...}}, author = {{Wagner, Thorsten and Roggenbuck, Jan and Kohl, Claus-Dieter and Fröba, Michael and Tiemann, Michael}}, booktitle = {{Recent Progress in Mesostructured Materials - Proceedings of the 5th International Mesostructured Materials Symposium (IMMS2006), Shanghai, P.R. China, August 5-7, 2006}}, issn = {{0167-2991}}, title = {{{Gas-sensing properties of ordered mesoporous Co3O4 synthesized by replication of SBA-15 silica}}}, doi = {{10.1016/s0167-2991(07)80332-6}}, year = {{2007}}, } @article{25993, abstract = {{The growth of ZnS nanoparticles by precipitation from supersaturated aqueous solution is studied by stopped-flow UV absorption spectroscopy. The average size, size distribution, and concentration of the particles are monitored within the sub-second time regime with a resolution of 1.28 ms. Particle growth at these early stages is governed by pronounced ripening. The UV absorption data strongly suggest that growth occurs by preferential adsorption of HS- anions relative to Zn2+ or ZnOH+ cations. Correspondingly, the initial sulfide concentration has a much more pronounced influence on the growth kinetics than the initial zinc concentration. These findings are verified by ζ-potential measurements which confirm that the particle surfaces are negatively charged under near-neutral pH conditions.}}, author = {{Tiemann, Michael and Marlow, Frank and Brieler, Felix and Lindén, Mika}}, issn = {{1520-6106}}, journal = {{The Journal of Physical Chemistry B}}, pages = {{23142--23147}}, title = {{{Early Stages of ZnS Growth Studied by Stopped-Flow UV Absorption Spectroscopy:  Effects of Educt Concentrations on the Nanoparticle Formation}}}, doi = {{10.1021/jp0638383}}, year = {{2006}}, } @article{25992, abstract = {{We report on the synthesis and CO gas-sensing properties of mesoporous tin(IV) oxides (SnO2). For the synthesis cetyltrimethylammonium bromide (CTABr) was used as a structure-directing agent; the resulting SnO2 powders were applied as films to commercially available sensor substrates by drop coating. Nitrogen physisorption shows specific surface areas up to 160 m2·g-1 and mean pore diameters of about 4 nm, as verified by TEM. The film conductance was measured in dependence on the CO concentration in humid synthetic air at a constant temperature of 300 °C. The sensors show a high sensitivity at low CO concentrations and turn out to be largely insensitive towards changes in the relative humidity. We compare the materials with commercially available SnO2-based sensors.}}, author = {{Wagner, Thorsten and Kohl, Claus-Dieter and Fröba, Michael and Tiemann, Michael}}, issn = {{1424-8220}}, journal = {{Sensors}}, pages = {{318--323}}, title = {{{Gas Sensing Properties of Ordered Mesoporous SnO2}}}, doi = {{10.3390/s6040318}}, year = {{2006}}, }